2015 STLE Tribology Frontiers Conference

Including Pre-Conference Workshop Advances & Opportunities in Lubrication: Wind Turbine

October 25 - 27, 2015

Grand Hyatt Denver Denver, Colorado

2015 Preliminary Technical Program

as of 8/29/15

2015 STLE Tribology Frontiers: Pre-Conference Workshop

Advances & Opportunities in Lubrication: Wind Turbines

Sunday, October 25, 2015 8:30am – 12:30pm

Grand Hyatt, Denver, Colorado This pre-conference workshop will holistically address the technical drivers for high performance lubricants in extreme environments ranging from formulation, testing, applications and failure diagnosis. It is intended to complement the 2015 STLE Tribology Frontiers Conference by providing current information on new and emerging advances in lubrication for extreme environments with a focus on wind turbines. It is the ideal preconference workshop to attend because of its coverage of practical considerations to state-of-the-art information on wind turbine lubrication from an application and mechanistic perspective.

Time Topic Speaker 8:30 – 8:45 Welcome and opening remarks Dr. Kathleen O. Havelka, Fuchs Lubricants

Dr. Ali Erdemir, Argonne National Lab

8:45 – 9:15 Wind Turbine Lubricants: Selection, challenges, applications and opportunities

Don Brazen, Fuchs Lubricants

9:15– 9:45 High performance wind turbine formulations

Dr. Abhi Patil, ExxonMobil Dr. Jessie Prince, ExxonMobil

9:45 – 10:15 Pushing boundaries with new components Dr. Selim Erhan, Elevance Renewable Sciences

10:15 – 10:30 Break

10:30 – 11:00 Additive and bench test development Dr. Jeffrey Guevremont, Afton

11:00 – 11:30 Oil filtration and condition monitoring Dr. Shawn Sheng, National Renewable Energy Lab (NREL)

11:30 – 12:00 Failure modes and testing methods Dr. Aaron Greco, Argonne National Lab

12:00 – 12:30 Panel Discussion Dr. Kathleen O. Havelka, Fuchs Lubricants

Organizing Committee Dr. Kathleen O’Leary Havelka, Fuchs Lubricants, Chair

Dr. Ali Erdemir, Argonne National Lab Dr. Selim Erhan, Elevance Renewable Sciences

Dr. Abhi Patil, ExxonMobil Dr. Aaron Greco, Argonne National Lab

Preliminary

TABLE OF CONTENTS Program-at-a-Glance ............................................................................................ 4 Presentation from Invited Speakers .................................................................... 5 Planning Committee ............................................................................................. 6 Program with Abstracts

Sunday ....................................................................................................... 7 Monday ....................................................................................................... 21 Tuesday ...................................................................................................... 48

Author Index .......................................................................................................... 69

4

2015 STLE Tribology Frontiers October 25-27, 2015 Grand Hyatt Denver

Denver, Colorado Preliminary Program-at-a-Glance

As of 8/21/15 – Subject to Change

Saturday, October 24, 2015

Registration – 2nd Floor Foyer 12:00 pm – 6:00 pm

Sunday, October 25, 2015 Registration – 2nd Floor Foyer 7:00 am – 6:00 pm Speakers Lunch – Maroon Peak 12 noon - 12:45 pm Keynote Session - 1:30 – 2:40 pm – Mt. Elbert A “Elastic Coupling Between Layers in 2D Films” – Elisa Riedo, PhD, Associate Professor, Georgia Institute of Technology in Atlanta Technical Sessions - 3:20 pm - 5:20 pm 1A Lubricants I – Mt. Elbert A 1B Surface Science I – Mt. Elbert B 1C Testing/Instrumentation – Pikes Peak 1D Materials Tribology I – Gray’s Peak A 1E Materials Tribology Ia – Gray’s Peak B Sunday Afternoon Career Mentoring Session: Ken Pelczarski, Pelichem Associates – Mt. Elbert A – 5:20pm – 6:20 pm Offsite Student Function - 6:30 pm – 8:00 pm Break is in Mt. Evans Room at 2:40 pm – 3:20 pm.

Monday, October 26, 2015 Registration – 2nd Floor Foyer 7:30 am – 5:00 pm Speakers and Attendee Breakfast 8:00 am – 8:45 am Keynote Session - 9:00 – 9:40 am – Mt. Elbert A “Bioinspired Lubrication: How Far We Can Go and Beyond” – Professor Feng Zhou, State Key Laboratory of Solid Lubrication’s Lanzhou Institute of Chemical Physics, China Technical Sessions – 10:20 am – 12:00 pm 2A Lubricants II – Mt. Elbert A 2B Surface Science – Mt. Elbert B 2C Boundary Lubrication and EHL I – Pikes Peak 2D Materials Tribology II – Gray’s Peak A 2E Materials Tribology IIa – Gray’s Peak B Lunch on your own 12 noon – 1:40 pm

Technical Session – 1:40 pm – 4:40 pm 3A Lubricants III – Mt. Elbert A 3B Surface Science III – Mt. Elbert B 3C Boundary Lubrication and EHL II – Pikes Peak 3D Materials Tribology III – Gray’s Peak A 3E Materials Tribology IIIa – Gray’s Peak B Keynote Session – 4:40 pm – 5:20 pm - Mt. Elbert A “Probing Constitutive Laws and Dissipative Processes with Atomistic Simulations” – Anne Tanguy, PhD, HDR, Institut Lumiere Matiere – Theory Group at the University of Lyon in France Networking and Poster Reception – Mt. Evans 5:20 pm – 7:00 pm Breakfast and Breaks are in Mt. Evans Room. Scheduled at 9:40 am – 10:20 am and 3:00 pm – 3:40 pm. Visit Exhibits and Posters.

Tuesday, October 27, 2015

Registration – 2nd Floor Foyer 7:30 am – 3:00 pm Speaker and Attendee Breakfast 8:00 am – 8:45 am Keynote Session - 9:00 – 9:40 am – Mt. Elbert A “Exploring Mars: Designing the Rovers “Spirit” and “Opportunity” - Kobie Boykins, NASA Engineer-Mechanism & Mobility Groups for the Jet Propulsion Laboratory in Pasadena, California Technical Sessions – 10:20 am – 5:00 pm 4A Fluid Film Lubrication – Mt. Elbert A 4B Surface Science IV – Mt. Elbert B 4C Biotribology I – Pikes Peak 4D Energy/Environment/Manufacturing – Gray’s Peak A 4E Beyond the Cutting Edge: Featuring Highlights from Tribology Letters – Gray’s Peak B Technical Session – 1:40 pm – 3:20 pm 5A Machine Components – Mt. Elbert A 5B Special Tribute to Dr. Frederick F. Ling: Organized by the Journal of Tribology – Mt. Elbert B 5C Biotribology II – Pikes Peak 5D Energy/Environment/Manufacturing II – Gray’s Peak A 5E Beyond the Cutting Edge II – Gray’s Peak B Breakfast and Breaks are in Mt. Evans Room. Scheduled at 9:40 am – 10:20 am. Visit Exhibits and Posters.

5

Presentations from Invited Speakers

Sunday, October 25, 2015 Keynote Session - 1:30 – 2:40 pm – Mt. Elbert A “Elastic Coupling Between Layers in 2D Films” Elisa Riedo, PhD, Associate Professor, Georgia Institute of Technology in Atlanta Monday, October 26, 2015 Keynote Session - 9:00 – 9:40 am – Mt. Elbert A “Bioinspired Lubrication: How Far We Can Go and Beyond” Professor Feng Zhou State Key Laboratory of Solid Lubrication’s Lanzhou Institute of Chemical Physics, China Keynote Session – 4:40 pm – 5:20 pm – Mt. Elbert A “Probing Constitutive Laws and Dissipative Processes with Atomistic Simulations” Anne Tanguy, PhD, HDR Institut Lumiere Matiere – Theory Group at the University of Lyon in France Tuesday, October 27, 2015 Keynote Session - 9:00 – 9:40 am – Mt. Elbert A “Exploring Mars: Designing the Rovers “Spirit” and “Opportunity” Kobie Boykins, NASA Engineer-Mechanism & Mobility Groups for the Jet Propulsion Laboratory in Pasadena, California

Dr. Elisa Riedo

Dr. Feng Zhou

Dr. Anne Tanguy

Kobie Boykins

6

STLE Tribology Frontiers 2015 Planning Committee

Daniel Nelias INSA-LaMCoS LaMCoS (UMR 5259 CNRS) Bat. J. Jacquard (302) Villeurbanne, CEDEX 69621 France Ashlie Martini Assistant Professor School of Engineering University of California Merced Merced, CA David L. Burris University of Delaware Newark, DE Daejong Kim Mechanical and Aerospace Engineering University of Texas at Arlington Arlington, TX Aaron Greco Argonne National Laboratory Argonne, IL Daniele Dini Mechanical Engineering Imperial College London London, SW7 2AZ United Kingdom Bart Raeymaekers University of Utah Salt Lake City, UT Yemi Oyerinde Chevron Phillips Chemical Co. 1862 Kingwood Drive Kingwood, TX

7

Sunday

Session 1A – Sunday, October 25, 2015 Mt. Elbert A

Lubricants I

Session Chair: S. Bair, Georgia Tech, School of Mechanical Engineering, Atlanta, GA Session Vice Chair: D. White, Mechanical Engineering, Iowa State University, Ankeny, IA 3:20 pm - 3:40 pm Study on Anti-wear and Extreme Pressure Properties of Metal-working Lubricants with Nanoparticle Additives L. Peña-Parás, J. Taha-Tijerina, J. Gutiérrez, M. Irigoyen, M. Lozano, M. Velarde, D. Maldonado, Universidad de Monterrey, Garza Garcia, Mexico Lubrication is essential for protecting moving surfaces against friction and wear in metal-working applications. In this work two metal-working nanolubricants containing Triethanolamine (TEA) and TEA/Hexylene glycol with viscosities of 42 and 80 Cst, respectively, were treated with varying rates of CuO and TiO2 nanoparticle additives. Anti-wear properties of wear scar diameter (WSD) and coefficient of friction (COF) were characterized with a four-ball T-02 tribotester according to ASTM 5183 and with a ball-on-disk apparatus. Extreme pressure properties, namely load carrying capacity poz, was determined according to the ITeEPib Polish method for testing lubricants under scuffing conditions. Nanoparticle additives showed an overall improvement of the tribological properties of polymeric lubricants. The load carrying-capacity increased up to 25% and 34% for the TEA and TEA/Hexylene glycol based lubricant, respectively, with the addition of 0.1 TiO2 wt%, demonstrating the potential of nanolubricants for improving the efficiency of mechanical components. 3:40 pm - 4:00 pm Self-Assembly and Response to Pressure, Temperature and Water of Calcium Carbonate Nanoparticles in Hydrophobic Solvents and in the Presence of Co-Surfactants D. Dini, M. Bodnarchuk, D. Heyes, Imperial College London, London, United Kingdom Surfactant-stabilized calcium carbonate, CaCO3, nanoparticles are included in commercial engine oils to neutralize the acidic byproducts of combustion. These so-called overbased detergents (ODs) are synthesized in vivo by carbonation of lime in the presence of the surfactant. The structural properties of the OD have been extensively characterized by experiment and simulation under ambient laboratory conditions. While the basic features of the OD particles are now well-characterized, their responsiveness to other components in the engine oil and changes in external conditions during operation are less well established. Their reaction to temperature and pressure changes is of interest, as engine temperatures can be ∼150°C and the pressure can be ∼150 bar under operating conditions. Very little is known about how temperature and pressure affect the OD particles and their influence on the OD neutralization reactivity. In this study we show the recent progress we have made using molecular dynamics (MD) simulations to study the self-assembly and the effects of surfactant-type on the size and shape of the OD particle in hydrophobic solvent. We then explore their response to the environmental

8

conditions of temperature, pressure, and trace water and water droplets (likely to be the acid carrieirs) that mimic some of the external conditions experienced by the OD nanoparticles during the operation of the engine. 4:00 pm - 4:20 pm The Effect of Nanoparticle Geometry on Friction and Antiwear Properties of Cu and Mo Nanolubricants D. White, Iowa State University, Ankeny, IA, S. Sundararajan, Iowa State University, Ames, IA, A. Martini, University of California-Merced, Merced, CA The tribological performance of Cu and Mo nanoparticles dispersed in mineral oil was experimentally investigated. Nanoparticles of varying geometries were dispersed in an isoparaffinic API Group III base oil using an ultrasonicator. Friction and antiwear properties were then tested using an in-house ball-on-flat microtribometer. A 5mm diameter 440C stainless steel probe was loaded onto a 8620 carburized steel substrate to a maximum Hertzian contact pressure of 0.44 GPa. Both ramped load and reciprocating tests were conducted to quantify friction coefficients and wear resistance, respectively. Surface roughness analysis was performed before and after the tests. 4:20 pm - 4:40 pm Effect of Concentration on Tribological Performance of IF-MoS2 Nanoparticles Additives M. Lorenzo Martin, D. Dandurand, B. Good, O. Ajayi, J. Bansal, Argonne National Laboratory, Lemont, IL, F. Dassenoy, Ecole Centrale de Lyon, Écully, France, P. Afanasiev, CNRS, Lyon, France Inorganic fullerene (IF) MoS2 and WS2 nano-particulate additives are being developed and evaluated as a means of enhancing tribological performance of lubricated contacts. In general, the concentration of chemical-based lubricant performance additives, such as ZDDP and MoDTC do affect their effectiveness and tribological performance. The current paper presents an experimental evaluation of the effect of IF-MoS2 nano-particulate additives in synthetic PAO basestock fluid. Using a ball-on-flat contact configuration in both unidirectional and reciprocating sliding, friction and wear tests were conducted with PAO-4 fluid containing 0.01-2.5% wt. IF-MoS2. Friction and wear results (ball & flat) showed that a minimum concentration of 0.05% wt. is required to reduce friction and wear. At the concentration, friction coefficient was reduced from 0.14 to about 0.05, and wear was eliminated through the formation of a protective surface layer from the particulate additives. Load carrying capacity of the additives was also evaluated using a step load increase in reciprocating sliding contact. A cyclical friction behavior was observed coinciding with the formation and removal of surface tribofilm from the additives. The frequency of frictional variation cycle is dependent on the concentration of the additives. 4:40 pm - 5:00 pm Tribological Behavior of CuO and TiO2 Nanolubricants Under Extreme Pressure Conditions L. Peña-Parás, J. Taha-Tijerina, D. Maldonado, G. Garza, P. García, Universidad de Monterrey,

9

Garza Garcia, Mexico Lubrication under extreme pressure (EP) conditions relies on additives in order to provide protection to working components. In this study, the effect of the addition of nanoparticle additives of CuO and TiO2 on the load carrying capacity of a water-based metal-working fluid containing Triethanolamine (TEA) used for deep-drawing was investigated. Concentrations of 0.01, 0.05, and 0.10 wt% were homogeneously dispersed in the fluid by extensive bath sonication. Extreme pressure measurements were performed with a T-02 tribotester with a four-ball configuration according to the ITeEPib Polish method for testing lubricants under scuffing conditions. Tests were ran at temperatures varying from 25 to 750C in order to further decrease the lubricant film thickness and simulate a boundary lubrication regime. Nanoparticle additives significantly increased load-carrying capacity of the base lubricant; the highest improvement was found at 750C showing the effectiveness of nanoparticle additive under boundary lubrication conditions. 5:00 pm - 5:20 pm Effects of Nanoparticles Additives on the Lubricity and Rheological Properties of Water-Based Drilling Fluids J. Abdo, Sultan Qaboos University, Alkhoud, Oman, H. Al-Sharji, Petroleum Development Oman, Muscat, Oman The lubricity and rheological properties of water-based drilling fluids containing two different nano-clays, nano-sepiolite (NSP) and nano-attaplgite (NATT), under high-temperature high- pressure, HTHP (up to 200 °C, 17 ksi) conditions are investigated. NSP and NATT were purified, synthesized, characterized, functionalized, and tested in nano-form (25-50 nm diameter) for its effectiveness on reducing friction between the drill pipes and the borehole wall. An in-house laboratory drilling rig was specifically designed for this purpose. The rheological properties stability of the drilling fluids were also investigated using the API standards and the Grace Instrument M7500 Ultra HPHT Rheometer. The investigations reveal that the level of friction reduction and the improvement in the axial force transfer depend on the size and the additive type (NSP or NATT). In this study the NSP modified drilling fluids improved the friction force by 26% and the axial force transfer by 52% while the NATT modified drilling fluids improved the friction force by 19% and the axial force transfer by 40%. The rheological properties of both NSP and NATT modified drilling fluids were stable up to 200 °C, 17 ksi.

Session 1B - Sunday, October 25, 2015 Mt. Elbert B

Surface Science I

Session Chair: TBD Session Vice Chair: TBD

10

3:20 pm - 3:40 pm Thermal and Shear-induced Effects in Boundary Film Formation W. Tysoe, H. Adams, M. Garvey, UW-Milwaukee, Milwaukee, WI, A. Martini, University of California-Merced, Merced, CA Boundary film form in several steps involving the initial adsorption and reaction on the surface, followed by shear-induced decomposition and formation of the boundary film. Systems are studied for which the interface is at thermodynamic equilibrium to allow kinetic models, such as transition-state theory to be applied. The first regime occurs when the interfacial temperatures are high (~1000 K), so-called extreme-pressure (EP) lubrication. Here, the film formation pathways are dominated by thermal reactions at the surface. This chemistry is illustrated using the example of small chlorinated hydrocarbons reacting with iron surfaces. The second regime occurs under mild sliding conditions for which the interfacial temperature rise is small. The tribochemistry is investigated by carrying out friction measurements in ultrahigh vacuum, by analyzing the elemental composition in the wear track region using Auger spectroscopy and by detecting gas-phase products evolved during sliding and is illustrated for copper lubrication by dialkyl disulfides and trisulfides. They initially react to form thiolate species on the surface and shear at the interface causes sulfur and some carbon to penetrate the substrate to form a boundary film that reduces friction. The variation in the amount of methane desorbing from the surface per pass during sliding allows the shear-induced rate of thiolate reaction to be measured, allowing models for the shear-induced decomposition to be tested experimentally. 3:40 pm - 4:00 pm Heat Resistance Improvement of Perfluoropolyether Lubricant Film on Magnetic Disks by UV Irradiation with Bias Voltage to Disk Surface H. Tani, Kansai University, Suita-shi, Japan, Y. Sakane, Western Digital Technologies, San Jose, CA, S. Koganezawa, Kansai University, Suita-shi, Japan, N. Tagawa, Kansai University, Suita, Japan It was confirmed in our previous study that the ultraviolet (UV) irradiation with the bias voltage between the magnetic disk and the counter electrode above disk surface increased the bonded ratio of the perfluoropolyether (PFPE) lubricant film on disk surface. In this study, two types of lubricant materials (Fomblin Z-tetraol and Moresco ADOH) were prepared and were coated on disks. After coating of lubricant film, the UV irradiation treatment with the bias voltage to lubricated disk surface was performed and the depletion of these lubricant films was compared by the pin-on-disk test with the laser heating mechanism. As the results, the lubricant film treated by UV irradiation without the bias voltage showed the deeper depletion of lubricant film than that with the bias voltage, and the ADOH showed the shallower depletion than Z-tetraol. On the other hand, the molecular weight distributions of ADOH film on disk surface treated by UV irradiation with and without the bias voltage were compared using the time of flight secondary ion mass spectroscopy (TOF-SIMS) and that with the bias voltage did not change by the dissociation of UV irradiation. Therefore, the UV irradiation with the bias voltage to ADOH lubricant film on magnetic disks improves the heat resistance of lubricant film because of the high bonded ratio of lubricant film without the main-chain dissociation by the UV irradiation with the bias voltage.

11

4:00 pm - 4:20 pm A Study of Abrasive Wear on the High Speed Steel Surface in Hot Rolling H. Phan, University of Wollongong, Wollongong, NSW, Australia In hot rolling mills, the asperities of the oxidised high speed steel (HSS) roll surface comprise of hard carbides within an iron matrix will contact the oxidised surface of the strip. The initial mating surfaces of the work-roll and strip are rough and covered with hard oxide layers. Abrasive wear will occur and material will be removed from the HSS surface. This work applied the Discrete Element Method (DEM) to simulate this abrasive wear phenomenon. DEM is a well-known method and has been widely used in the problems involving a significant deformation and material removal that are difficult to handle by the finite element method (FEM). The mechanical properties of these thin oxide layers and their thickness values have been determined from nanoindentation, TEM and SEM images. The ductile DEM wear model has been validated and used successfully to simulate the compression and tensile behavior. The nanoindentation test was also simulated and compared well with the experiment of nanoindentation on the oxide layer. Moreover, a scratching test has also been implemented to study the abrasive wear removal on the HSS surface due to broken bonds among particles during sliding contact. The model has demonstrated that it can provide a physically based abrasive roll wear model of HSS work roll with the consideration of carbides and oxide layers. This has not been reported anywhere and is the main focus of this research. 4:20 pm - 4:40 pm Toward More Efficient Utilization of Microgeometric Parameters in Engineering Problems. Review of the Composite Roughness Models Used for Estimating Lubricant Film Parameter › V. Dunaevsky, VVD Engineering, LLC, Michigan City, IN An equation for the lubricant film parameter lambda (› ), which was presented in the ASME engineering design guide for life adjustment factors for ball and roller bearings, was reviewed. The study demonstrated that the equation is suitable exclusively for interacting surfaces that have Gaussian roughness distribution and plastic asperity contact. However, not all surfaces fit this definition. Moreover, the film thickness calculated with this equation is substantially smaller than the combined surface roughness height. The listed factors do not render this equation a reliable engineering tool. An alternative formula for the parameter lambda was recommended, which does not depend on contact specifics (elastic or plastic) and statistical distribution of surface roughness heights, and which obviates other shortcomings of the previous equation. Thus, the proposed equation is a more viable tool for estimating the effectiveness of the lubricant film. In addition, a modified equation for › , associated with Gaussian surfaces, was proposed. 4:40 pm - 5:00 pm Experimental Investigation of Sliding Friction and Contact Area on the Microscale A. Alazemi, F. Sadeghi, Purdue University, West Lafayette, IN Friction phenomena is observed in every mechanical system. Yet there is a lack of complete understanding of friction nature and behavior. The difference between static friction and dynamic friction can be related to the presence of adhesion forces before sliding initiation. A Micro Friction Test Rig (MFTR) was designed and developed to investigate the onset of friction

12

and allows in situ optical observation of contact area during sliding for a ball-on-flat configuration. A steel ball sliding between two fixed sapphire windows with submicron steps size is used in this investigation. Tests are carried at low operating frequencies (0.1 - 1 Hz) and low applied normal loads (50 - 1000 mN) with dry, oil, and grease lubricated conditions. Experiment is performed at low frequency in order to carefully study the transition from static to dynamic friction and investigate sliding friction force behavior. A friction model that fully describe both static and dynamic friction regions is presented. 5:00 pm - 5:20 pm Effect of Surface Texturing on Friction of Elastomeric Seals in Pneumatic Applications M. Zimmermann, M. Wangenheim, Leibniz University of Hannover, Hannover, Germany In recent years surface texturing was established as a technique to enhance the performance of tribological systems; e.g. friction, lubrication and load capacity could be influenced positively. The new technique was applied to components like mechanical face seals and piston rings. However, only limited knowledge exists about the influence of surface texturing on elastomeric seals. We investigate how different textures influence the friction of dynamic elastomeric seals with simulation tools and experiments. Surface texturing affects the adhesion friction as well as the viscous friction component of the dynamic seal friction. Adhesion friction is dependent on the real area of contact between seal and counter surface, which as a matter of course is influenced significantly by surface texturing. Furthermore, surface textures can influence the formation of a lubrication film positively by altering its fluid flow and by providing lubricant storage. We developed simulation tools to predict the influence of a textured seal surface on the adhesion as well as the viscous component of the dynamic friction for different operation conditions; i.e. sliding velocities and contact pressures. In addition, we experimentally measured friction forces of rod and piston seals with different textures for pneumatic drives. A reduction of friction could be obtained by texturing. Simulation and experimental results are compared and limitations of surface texturing are discussed.

Session 1C- Sunday, October 25, 2015 Pikes Peak

Testing/Instrumentation

Session Chair: A. Greco, Argonne National Laboratory, Argonne, IL Session Vice Chair: B. Gould, Mechanical Engineering, University of Delaware, Wilmington, DE 3:20 pm - 3:40 pm In-situ Measurement of the Viscosity of a Fuel Lubricant Mixture J. Dench, Imperial College London, London, United Kingdom, N. Morgan, Shell Global Solutions, Manchester, United Kingdom, J. Wong, Imperial College London, London, United Kingdom A technique to measure the viscosity of various fuel lubricant mixtures in-situ, in a parallel plate contact, has been developed. This simulates a piston ring liner contact and enables the effects of

13

fuel dilution on the lubricating properties of the oil to be studied. The shear rate can be varied to study these mixtures at conditions similar to at the pistons top ring reversal point. The measured viscosity combined with film thickness measurements enables the frictional force to be estimated. This provides useful insight into the effect of fuel dilution on engine friction and film thickness generation. It is known that the levels of fuel dilution are high at the top ring reversal point, an area where the film thickness is already low due to the entrainment speeds tending towards zero. These correlations will be compared to Mini Traction Machine studies, of the frictional properties of the fuel lubricant mixtures, to enable the lubricating properties to be analysed. This has potential not only to provide insight into the lubricating properties of the fluid, but also the propensity for of the lubricating film to instigate a Low Speed Pre Ignition event, due to fuel dilution. Which is a major obstacle in current engine development. The development of such a technique provides many opportunities for in-situ measurement of the viscosity in lubricated engineering contacts. 3:40 pm - 4:00 pm Characterization of Wear Debris Generated in Steel-Steel and Steel-DLC Contacts Lubricated by an Ionic Liquid Additized Oil Y. Zhou, D. Leonard, H. Luo, J. Qu, Oak Ridge National Laboratory, Oak Ridge, TN A newly developed phosphorous-containing ionic liquid (IL) was added into a SAE 0W-30 base oil at 1 wt% treat rate to lubricate a-C:H diamond-like carbon (DLC) coating and A2 steel flats against AISI 52100 steel balls. Linearly reciprocating ball-on-flat sliding wear tests were performed at 100 °C. Significantly increased wear was observed on the ball that rubbed against a-C:H when IL was present. Wear debris was collected and characterized using scanning transmission electron microscopy (STEM), combined with electron energy loss spectroscopy (EELS) and energy-dispersive X-ray spectroscopy (EDS). Within the aggregates of wear debris, iron oxide nanoparticles were observed. In steel-DLC contacts, carbon flakes were detected in the debris and both sp2 C and sp3 C contents were determined. The morphology and chemistry of wear debris were correlated to tribological behavior and wear mechanism. 4:00 pm - 4:20 pm Nanosensors for Pressure and Temperature Mapping in Confined Lubricant Films D. Philippon, S. Albahrani, M. Querry, J. Bluet, INSA de Lyon, Villeurbanne, France, P. Reiss, CEA, Grenoble, France, P. Vergne, INSA de Lyon, Villeurbanne, France Pressure and temperature are two relevant parameters in the elastohydrodynamic lubrication (EHL) regime. For instance, the pressure may reach values up to 1-2 GPa inducing an important elevation of the lubricant viscosity. In addition, the temperature can rise up to 100°C due to sliding conditions. A new in situ experimental technique allowing local and simultaneous measurement of pressure and temperature in lubricated contacts is under development. This technique is based on the sensitivity of some photoluminescent nanoparticles (NP) to temperature and pressure variations. In this paper, the calibration of different semiconductor-based NP dispersed in lubricant is detailed and their potential use as nanosensors is discussed. Their respective temperature and pressure sensitivities (variations of the fluorescence wavelength) were calibrated using a high pressure diamond cell in which temperature can be controlled precisely.

14

4:20 pm - 4:40 pm The Grease EHL Film Measurement of Needle Roller Contacts under Oscillating X. Chen, L. Shi, X. Shen, Shanghai University, Shanghai, China Needle roller bearings are usually used for applications requiring exceptionally large load-supporting capability, in which the radial space is at a premium. There are many oscillatory applications for the needle roller bearing with grease lubrication, such as in the Hooke's universal joints. It is well known that the needle roller contacts are separated by a viscous oil film during oscillating, which results in the EHL state. The load-bearing capacity, working velocity and service life of roller contacts is deeply influenced by the film thickness, film shape and pressure distribution of the film. The EHL oil film thickness and shape between a needle roller and a flat rectangular glass in pure rolling oscillated working conditions had been measured based on optical interferometry in this paper. The EHL behavior affected by the applied load, oscillating frequency and different grease lubricants was investigated. And a developed image processing method was used to analyze the interference pictures of EHL film thickness. The typical film shape varies of interference pictures on non-steady state motion, such as acceleration and deceleration, stop and start rapidly, was obtained. It is found the side constrictions are always the most severe and they are strongly speeds and loads dependence. 4:40 pm - 5:00 pm Experimental Research on the Dynamic Oil Film Pressure of Tilting-pad Journal Bearings J. Shen, X. Xiong, X. Wang, M. Li, Shanghai University, Shanghai, China With the development of large rotating machinery, higher requirements are put forward for tilting-pad journal bearings. Oil film pressure is an important parameter of journal bearing concerning load-bearing capacity. Researchers and engineers have been carried out in-depth research on the oil film pressure of the journal bearings. However, these researches were mainly focused on the oil film pressure as a steady state coefficient. Considering that oil film pressure is a transient variable coefficient, in this paper, the experimental research of the dynamic oil film pressure in tilting-pad journal bearings is carried out. At the different excitation frequency and dynamic excitation loads, the data of dynamic oil film pressure were measured under the static and dynamic loads conditions in the inverted tilting-pad bearing test rig. Meanwhile, accelerations of the stator in the x (unloaded) and y (loaded) directions were obtained, and the relative motions between the rotor and the stator in the x,y directions were tested. To illustrate the sensitivity of the dynamic oil film pressure data on additional load, the unsteady spectrum of dynamic oil film pressure, acceleration and displacement are analyzed under the different vibration frequency. The testing results indicated that comparing that with the displacement signals, the dynamic oil film pressure signals and acceleration signals could directly response the change of the excitation loads. 5:00 pm - 5:20 pm Tapping Torque Technology System: Visualize the Effectiveness and Lubricity of Lubricant Formulations

15

K. Mueller, microtap GmbH, Taufkirchen / Munich, Germany Lubricant Efficiency: Based on a torque-controlled and process secured thread tapping machine (process security avoids tool breakage and pressure differences in the ground hole), complemented with a specialized evaluation and analysis software, the Tapping Torque Technology visualizes the effectiveness of lubricating media. The system depicts decisive process-parameters (*) during forming and machining and allows for a reliable prediction about the performance capability of metal working fluids (coolants) and optimized tool geometries and tool coatings. (*) Torque as a coefficient for the factually generated work performance (Torque Mz Ncm), Mean Value as a coefficient for the generated work performance in average (arithmetic mean). Standard Deviation as a coefficient for the mean deviation of torque around the Mean Value. Gaussian Curvature shows the frequency distribution of the number of the various torques during process Integral as a coefficient for the total stress (wear) on the measurement tool. Temperature • T as an indicator for the tribological mechanisms of action.

Session 1D - Sunday, October 25, 2015 Gray's Peak A

Materials Tribology I

Session Chair: S. Berkebile, US Army Research Laboratory, Aberdeen Proving Ground, MD Session Vice Chair: TBD 3:20 pm - 3:40 pm Wear of Alumina-PTFE Nanocomposites: Environmental Influences on Polymer Tribochemistry D. Haidar, D. Burris, University of Delaware, Newark, DE A particular alumina-PTFE nanocomposite has distinguished itself with unusually significant wear reductions at trace filler loadings. Recent studies have shown that the formation of carboxyl end groups in humid environments is a critical part of the wear reduction mechanism. This finding has important implications for the utility of the material in space and other extreme environments. In this paper, wear rates, surface morphology and composition were characterized as a function of environmental composition and surface temperature to better understand the environmental limitations of this solid lubricating system. The results showed: (1) decreased humidity increased steady-state wear rates; (2) trace oxygen and elevated surface temperature from 25°C to 100°C had no effect on steady-state wear rates; (3) filler only accumulated on the pin in cases of high wear; (4) low wear was characterized by a decreased fluorine and increased oxygen content in both the transfer film and pin. The results provide evidence against two previous hypotheses: (1) that filler accumulation is an important wear resistance mechanism of this system and (2) that the primary role of polymer degradation is to anchor the transfer films. Although carboxyl end groups almost certainly help anchor the transfer film, the results suggest that the tribochemical changes of the pin are what ultimately drive the wear reduction mechanism. 3:40 pm - 4:00 pm

16

Tenacity of Alumina-PTFE Nanocomposite Transfer Films D. Burris, J. Ye, University of Delaware, Newark, DE, A. Moore, University of Delaware, Millsboro, DE In most cases, transfer films are removed and replenished throughout sliding. However, one particularly low wear rate solid lubricant has been shown to produce persistent transfer films that thicken and homogenize throughout sliding. Based on a mass balance, the transfer film can only persist and grow if it is more wear resistant than the parent polymer. However, recent transfer film wear rate measurements show that these films are orders of magnitude less wear resistant than the polymer against steel. This paper uses HDPE to study the wear properties of the transfer films under contact conditions that are more comparable to the native three-body situation. During run-in, transfer films were poorly adhered and immediately removed (k~100 mm3/Nm). During steady-state, however, transfer films exhibited ultra-low wear rates in the range from 10-

8-10-10 mm3/Nm; to our knowledge, this is the first direct observation of ultra-low wear transfer films. The wear rate was strongly dependent on the surface energy of the probe used for wear testing; probes with g < ~40mJ/mm2 consistently produced ultra-low wear rates (k~10-9

mm3/Nm) while probes of g > ~40mJ/mm2 produced wear rates that were many orders of magnitude higher in the vicinity of those observed in prior studies. The results suggest that low wear is only possible when a weak pin-film interface promotes interfacial slip; higher surface energy pins caused subsurface film failures and increased wear rates. 4:00 pm - 4:20 pm Mechanochemistry in Ultralow Wear PTFE composites K. Harris, A. Pitenis, University of Florida, Gainesville, FL, B. Krick, LeHigh University, Bethlehem, PA, W. Sawyer, University of Florida, Gainesville, FL Over the last decade composite materials based on Teflon* PTFE 7C (a granular molding resin) and certain alumina "nanoparticles" have been heavily studied. These materials are exceptional because small amounts of alumina additive (often less than 5 wt.%) improve the wear performance of the PTFE composite by over four orders of magnitude. Mechanochemistry at the sliding interface allows generation of a robust thin transfer film and thus ultra-low wear. This unique chemistry and the role it plays during fluoropolymer sliding wear against a metal countersurface will be described and discussed. 4:20 pm - 4:40 pm Effect of In-situ Processing Parameters on the Mechanical and Tribological Properties of Hybrid Aluminum Nanocomposites A. Dorri Moghadam, E. Omrani, P. Menezes, P. Rohatgi, UW-Milwaukee, Milwaukee, WI Aluminum alloys possess a number of superior physical and mechanical properties that make them attractive materials for several automotive and aerospace applications. However, they exhibit extremely poor tribological properties, such as wear resistance. Reinforcement to aluminum alloys results in development of advanced hybrid metal matrix micro- and nano-composites with precise balances of physical, mechanical and tribological properties. The present research focuses on the investigation of mechanical and tribological properties of aluminum metal matrix nano-composites reinforced with in situ prepared nano-sized TiB2 and Al2O3 particle by stir casting method. Investigations of the mechanical and tribological

17

properties were undertaken by utilizing microhardness test and pin-on-disk test in dry sliding conditions against 440 stainless steel at varying normal loads. The wear mechanism was studied by examining the worn surfaces of the contacting materials using scanning electron microscope. Results showed that the hardness and the wear resistance of Al/TiB2/Al2O3 nano-composites were improved significantly when compared to aluminum alloys. The improved mechanical and tribological properties are due to the fact of high hardness of the ceramics particles and strong particle-matrix bonding. The mechanisms governing the improved mechanical and tribological properties will be discussed. 4:40 pm - 5:00 pm Friction Behavior of Grease Lubricated C/C Composite under Low Speed High Load Conditions Y. Jiao, X. Wang, School of mechanical Engineering and Automation, Shanghai University, Shanghai, China, B. Ruicheng, Materials Science and Engineering, Shanghai, China, B. Yang, H. Diann Y, 2. Henan University of Science and Technology, Luoyang, Henan, China, Z. Hua, School of mechanical Engineering and Automation, Shanghai University, Shanghai, China Carbon fiber reinforced carbon matrix composites (C/C composites) are engineering materials with special properties for industrial applications. Researchers and engineers have been carried out in-depth research on the friction and wear properties of C/C composites. However, the research was mainly focused on the friction properties of C/C composite under dry testing condition. For the widely used lubricated conditions of rotary friction, the friction and wear research for C/C composite material is extremely lacking. In this paper, a special designed rig with shaft-sleeve configuration was used to measure the friction. The testing was focused on low speed and heavily loaded conditions. At different temperatures, the influence of load and speed on the friction properties of C/C composites was tested. The same experimental conditions were tested for bearing steel as comparison baseline. The testing results indicated that the friction behavior of grease lubricated C/C composite material has a general trend that it increases as sliding speed increases, and it decreases as applied load increases. The friction of C/C composites is less sensitive to the speed but more influenced by the load. The operating temperature has pronounced effect on the friction behavior as expected. It has demonstrated that C/C composite material exhibited lower friction in comparison to steel material under ultra low speed and moderate loading condition. 5:00 pm - 5:20 pm Tribological Behaviors of Self-lubricating Composites with Continues Lubricating Property in Wide Temperature Ranges J. Jia, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou, China Lubrication and wear at high temperature is one of the key technical problems of advanced engine, aerospace crafts, nuclear technology, etc. With the fast development of the of advanced engines, there emerges a urgent demand of self-lubricating composites with continues lubricating properties in wide temperature range (RT~1000℃), which require the tribo-materials with a stable lubricating performance adapt to different temperature changes. In present talk, I will discuss the selection of the matrix and lubricants for the high temperature lubricating and anti-wear materials as well as propose the material formulation with excellent mechanical and

18

tribological properties at high temperature. Thereinto, understanding the mechanism responsible for the materials with continues lubricating properties and clarify the synergistic effect of multi-lubricants phases and tribochemical interaction. The results show that the different compositions of friction layer and the transfer film are obtained with the change of temperature,in order to maintain lubrication performance under different temperatures. The research results provide encouraging prospects for high temperature lubricating materials in aerospace field to solve the continuous lubricating problem in wide temperature range.

Session 1E - Sunday, October 25, 2015 Gray's Peak B

Materials Tribology Ia

Session Chair: M. Eriten, University of Wisconsin-Madison, Madison, WI Session Vice Chair: TBD 3:20 pm - 3:40 pm The Mechanical and Tribological Properties of Cr-N Coatings Prepared by Modulated Pulsed Power Magnetron Sputtering for High Pressure Die Casting Applications B. Wang, G. Bourne, S. Midson, A. Korenyi-Both, M. Kaufman, Colorado School of Mines, Golden, CO H13 tool steel is widely used as a die material for high pressure aluminum die casting. During die casting, soldering can occur between the Al alloy and the H-13 steel dies. Thin film ceramic protective coatings are routinely used to mitigate detrimental soldering. We deposited an experimental matrix of PVD chromium nitride (Cr-N) coatings on H13 tool steel coupons by modulated pulsed power (MPP) magnetron sputtering from a Cr target in an Ar+N2 mixture. The mechanical and tribological properties of the various Cr-N coatings are reported and discussed. Additionally, a novel test method was developed to provide a quantitative assessment of the adhesive behavior of aluminum A380 alloy to these coatings. 3:40 pm - 4:00 pm 60NiTi Intermetallic Material Evaluation for Lightweight and Corrosion Resistant Spherical Sliding Bearings for Aerospace Applications C. DellaCorte, NASA, Cleveland, OH Spherical sliding bearings made with 60NiTi inner races were evaluated to assess the feasibility of manufacturing lightweight, corrosion resistant bearings for aerospace and industrial applications. The fabricated bearing assemblies utilized standard reinforced polymer liners and 60NiTi balls. Testing included oscillatory motion at a load of 4.54kN (10,000 lb), according to the requirements of the plain bearing specification SAE AS81820. Several test bearings were exposed to hydraulic fluid or aircraft deicing prior to and during testing. Tribological performance was comparable to conventional stainless steel (440C) bearings. Further, exposure of 60NiTi bearings to the contaminant fluids had no apparent performance effect. It is concluded that 60NiTi is a feasible bearing material for aerospace and industrial spherical bearing applications.

19

4:00 pm - 4:20 pm Nanostructured Composite Ni-P Electrodeposits as Alternative to Hard Chrome Coatings E. Georgiou, D. Drees, Falex Tribology NV, Rotselaar, Belgium, A. Zoikis-Karathanasis, T. Kosanovic Milickovic, Centre for Research & Technology Hellas, Volos, Greece, I. Deligkiozi, Center for Technology Research and Innovation, Limassol, Cyprus, J. Celis, KU Leuven, Leuven, Belgium Ni-P nanocomposites have attracted the scientific and industrial interest mainly due to their mechanical and chemical characteristics. Nowadays Ni-P nanocomposites are applied in various applications, such as components for pumps and valves, butter-fly pumps for the oil and gas industry, fasteners, precision instrument parts, aluminum air cylinders, in foundries to reduce wear, and on yarn brakes, variable gears and friction clutches in the textile industry. Another potential application, could be the replacement of hard chrome coatings, as chromium plating poses serious environmental and hazard issues. In view of that, electrolytic Ni-P nanocomposite electrodeposited coatings were developed to replace chromium plating. This study presents the synthesis, characterization and tribological properties of nanostructured electrodeposited Ni-P coatings containing dispersed SiC and CNT nanoparticles. The microstructure-property relationship for these nanocomposites, as well as their tribological performance are compared to existing industrially applied hard chrome coatings and state-of-the-art benchmark materials. The results clearly illustrate that Ni-P nanocomposite coatings can be used to replace hard chrome coatings. Furthermore, it should be pointed out, that electrodeposition is a very flexible technique that can be easily implemented on the industrial scale. 4:20 pm - 4:40 pm Chemical and Microstructural Investigation of Third Body Material Formed from Cold Sprayed Al and Al-Al2O3 Coatings S. Descartes, INSA-Lyon / Université de Lyon, Villeurbanne, France, J. Schockley, R. Chromik, McGill University, Montreal, QC, Canada Particle-reinforced aluminum matrix composites generally exhibit lower wear rates and more stable friction than those un-reinforced. Cold spray is a popular consolidation route for Al-Al2O3, allowing for its application as a coating for corrosion and tribological protection. Previous work by the authors has found that 22 wt.% of angular Al2O3 particles (ANG22) leads to significantly lower wear rates and greater friction stability during dry sliding against sapphire compared to unreinforced pure Al cold sprayed coatings (CS0). The differing behavior was attributed to the formation of a smooth, coherent, hardened third body film for sample ANG22, which did not form for sample CS0. The near-surface third body layers were analysed by scanning and transmission electron microscopy (SEM and TEM), scanning TEM and Energy-Dispersive X-ray spectroscopy. Focused ion beam cross-sectioning was used to prepare thin foils, in order to target the fine surface layers (2-10 µm thick) of the wear track. For sample ANG22, the TEM images revealed a complex third body microstructure: it was largely amorphous with occasional nanocrystalline phases 5 - 20 nm in diameter. Oxygen levels in the third body were elevated, yet below that associated with crystalline Al2O3. A full discussion of these results, in context with TEM images of the CS0 third body layer, will be used to describe the transformations occurring

20

at the sliding interface and the influence of the presence of Al2O3 particles thereof. 4:40 pm - 5:00 pm Quantifying Wear Volume Uncertainty Based on Interrupted Topography Measurements N. Garabedian, University of Delaware, Newark, DE, H. Khare, University of Pennsylvania, Philadelphia, PA, D. Burris, University of Delaware, Newark, DE Tribological coatings are typically insufficiently thick to produce measurable mass losses before failure. As a result, coating wear volumes are typically assessed using profilometry. Most measurements use a single post-test scan, which can introduce uncertainties from surface extrapolation and the inability to isolate transient wear from steady-state wear. Interrupted measurements can solve both problems, while providing insights into the evolution of wear and its influence on friction. However, perfect reposition is impossible and these repositioning errors cause wear rate measurement errors. This paper quantifies the wear volume error as a function of repositioning error using controlled wear surfaces. We quantify the statistics of these errors to establish recommended error bars for wear rate reporting of such measurements. The results are applied to the interrupted measurements of low wear coatings to illustrate the potential sensitivity of such measurements to wear events. 5:00 pm - 5:20 pm Assessment of Surface Modifications From Interactions of Alumina-nanofluids on Heat-exchanger Materials G. Molina, F. Aktaruzzaman, V. Soloiu, M. Rahman, Georgia Southern University, Statesboro, GA Nanofluids are suspensions of nano-size-powders in ordinary fluids. While nanoparticles seem to enhance cooling properties, nanofluid-led surface modifications from their interactions with heat-exchanger materials are largely unknown. The authors have developed ad-hoc test rigs and assessment tools to study these tribological interactions. Experimental research is presented on typical nanofluids (2%-volume alumina-nanopowder in water, and in 50/50 ethylene glycol/water) which are jet-impinged on aluminium and copper during accelerated tests with varied jet speeds (ranging from 3.5 m/s to 15.5 m/s). The studied surface modifications (which were assessed by roughness measurements, weighing of removed-material, and optical-microscopy) suggest that addition of nanopowders can lead to patterns of material removal that are substantially different than those typically obtained from the base-fluid impact. This study sets baseline test methodologies for further systematic research and development in this new field of tribology.

21

Monday

Session 2A - Monday, October 26, 2015 Mt. Elbert A

Lubricants II

Session Chair: B. Raeymaekers, University of Utah, Salt Lake City, UT Session Vice Chair: J. Ewen, Mechanical Engineering, Imperial College London, London, United Kingdom 10:20 am - 10:40 am Oxidation Effects on Physical and Chemical Properties of a Base Oil Both Untreated and Oxidation-Inhibited J. Evans, T. Selby, Savant Group, Midland, MI, W. VanBergen, M. Manning, Savant Lab, Midland, MI One of the primary causes of degradation of a lubricant is oxidation. Antioxidants are incorporated into base stocks to increase their oxidative resistance and extend operating life. This paper will explore the physical and chemical property changes associated with progressive oxidation of a particular base stock and antioxidant. The oil blend was exposed to ASTM Test Method D2272 (Rotating Pressure Vessel Oxidation Test [RPVOT]) oxidation conditions utilizing a versatile isothermal, high pressure, high temperature bench test instrument equipped with a specialized sampling mechanism. Oil samples were taken at select intervals and analyzed for changes in physical and chemical behavior as the degree of oxidation increased. 10:40 am - 11:00 am Terraced Spreading of Nanometer-thin Lubricant Using Molecular Dynamics B. Noble, University of Utah, Salt Lake City, UT, A. Ovcharenko, Western Digital, San Jose, CA, B. Raeymaekers, University of Utah, Salt Lake City, UT Ultra-thin lubricant films are of concern in the design of nanoscale systems and devices, as surface effects become increasingly important on the nanoscale. We have used molecular dynamics simulations to quantify terraced spreading of perfluoropolyether lubricant on a flat substrate as a function of polymer chain length, lubricant thickness, and functional end groups of the lubricant and the substrate. In addition, we have investigated the physical mechanisms that drive terraced lubricant spreading on a flat substrate. The results show that terraced lubricant spreading follows a process of diffusion and instability, where functional lubricant end groups are attracted to other functional end groups to form clusters that organize into layers. These distinct layers of functional end groups cause the lubricant thickness profile to take on a terraced shape, where layers correspond to the locations at which terraced formations occur. The presence of functional end groups determines the locations of both layer and terrace formations, and greatly affects lubricant spreading. 11:00 am - 11:20 am Quantitative Elastohydrodynamic Film Forming for a Gear Oil with Complex Shear-

22

Thinning S. Bair, Georgia Tech, Atlanta, GA, W. Habchi, Lebanese American University, Byblos, Lebanon, P. Sperka, M. Hartl, Brno University of Technology, Brno, Czech Republic Perhaps the most thorough characterization of the elevated pressure properties of any EHL lubricant is presented here for a commercial gear oil. Compressibility, thermal conductivity and low-shear viscosity were measured. Of particular interest is the shear dependence of viscosity, measured across four decades of stress, which shows two transitions each with a specific value of power-law exponent. An attempt to capture a suspected third transition at very high stress resulted in mechanical degradation of the liquid in the viscometer. Numerical simulations of a point contact between a steel ball and a glass disc showed good agreement over a range of slide-to-roll ratio for the measured central thickness. The agreement for the minimum thickness was excellent. A surprising result is that shear-thinning of a higher molecular weight component that occurs from 3 to 200 kPa had little effect on the film thickness and could therefore be neglected in a film thickness calculation. 11:20 am - 11:40 am Viscosity and Structure of Model Viscosity Index Improvers U. Ramasamy, University of California-Merced, Merced, CA, L. Cosimbescu, Pacific Northwest National Laboratory, Richland, WA, A. Martini, University of California-Merced, Merced, CA Viscosity index (VI) improvers are a class of additives that reduce the decline of fluid viscosity with temperature, enabling optimum lubricant performance over a wider range of operating temperatures. The additives' ability to increase their molar volume and improve the temperature-viscosity dependence of lubricants indicates a strong correlation between molecular structure and blend viscosity. The objective of this work is to understand the relationship between additive molecular structure and the viscosity-temperature behavior of base oil-additive blends. Here, Molecular Dynamics (MD) simulation is used to predict viscous behavior of base oil-additive blends for several model additive molecules. MD, which provides explicit representation of molecular structure, is also used to characterize conformational changes that the additives experience during shear and at different temperatures. Specifically, we aim to evaluate changes in additive conformation and correlate these trends to viscous properties of the blends. A fundamental understanding of the contribution of additive molecular structure to changes in viscosity can enable the design of VI improving polymers. 11:40 am - 12:00 pm "Thixotropy" of Greases B. Zhang, Saga University, Saga-shi, Japan Abstract. The time dependent stress of greases at constant shear rate is analyzed on the basis of the Maxwell viscoelastic model by using the complex analysis. It is first found that the Maxwell viscoelastic fluid will give a stress overshoot when the angular velocity of the fluid in simple shear flow is greater than the characteristic angular velocity of the fluid which is defined as the ratio of the shear elastic modulus to the viscosity. The stress overshoot occurs without any requirement of changes in the rheological properties of both the viscosity and the elastic modulus. Numerical analysis is given for the experimental examples from the literature, and good agreement between the analysis and the experimental results is obtained. The stress

23

overshoot of greases is generally considered to be the consequence of the change in viscosity during shearing, which is commonly known as thixotropy. The analysis of the paper shows that the thixotropy of greases is possibly pseudo.

Session 2B - Monday, October 26, 2015 Mt. Elbert B

Surface Science II

Session Chair: TBD Session Vice Chair: TBD 10:20 am - 10:40 am Aluminum Stain/Corrosion Inhibitors for MWFs: Chemistry-structure-Performance Relationship H. Kim, P. Konopi, A. Tomaszewska, Chemetall, New Providence, NJ For metalworking fluids (MWFs), the anti-staining performance, especially on aluminum alloys, mostly relies on various carboxylate, phosphate and silicate chemistry. The choice of those stain inhibitors depends on the type of alloys, composition of the alloy, metalworking fluid composition, pH and temperature, etc. Efficiency of the inhibitor is based on the ability to adsorb on metal surface through electrostatic attraction ultimately to form protective film. And the adsorption is dominated by chemistry/structure of the inhibitor, charge of the metal surface and composition of MWFs. Along this line, in this presentation we present our recent investigation on chemistry-structure-performance relationship of various aluminum stain inhibitor systems including amine carboxylates, phosphates and silicates. 10:40 am - 11:00 am In-situ Observation of Crystalline Orientation During Scuffing of Steel by Synchrotron X-ray Diffraction K. Yagi, Kyushu University, Fukuoka, Japan, T. Izumi, Toyota Central R&D Labs., Inc., Aichi, Japan, J. Koyamachi, Kyushu University, Fukuoka, Japan, S. Sanda, S. Yamaguchi, Toyota Central R&D Labs., Inc., Aichi, Japan, K. Saito, Toyota Motor Corporation, Aichi, Japan, J. Sugimura, Kyushu University, Fukuoka, Japan In the current study, in-situ observation of X-ray diffraction was conducted during scuffing of steel. A frictional area was created between a rotating sapphire ring and a fixed steel pin. The current in-situ X-ray diffraction analysis was conducted during tests by synchrotron, which captured X-ray diffraction patterns by a two-dimensional detector. A visible digital camera and a near-infrared camera were used to simultaneously capture visible and near-infrared images of the frictional area. All data such as X-ray diffraction pattern, visible image, near-infrared image, surface temperature measured by embedded thermocouple and friction were simultaneously obtained during the tests. Crystalline orientation of the steel surface was estimated from several peaks of the XRD spectrum and variations in Debye ring. It was found that the crystalline of the steel surface was orientated along the sliding direction when plastic flow occurred in the frictional area. The relationship between the crystalline orientation of the surface and

24

catastrophic scuffing process is discussed. 11:00 am - 11:20 am Surface Structure of Hydrogenated Diamond-like Carbon - Origin of Run-in Behavior Prior to Super-lubricious Interfacial Shear A. Alazizi, S. Kim, The Pennsylvania State University, State college, PA The oxidized layers at the surface of hydrogenated diamond-like carbon (H-DLC) were studied with x-ray photoelectron spectroscopy, near-edge x-ray absorption fine structure, and Raman spectroscopy. The structure of these layers was correlated with the friction and wear behavior observed on H-DLC. H-DLC is well known for its ultra-low friction in inert environments, but the steady super-lubricious state is always preceded by a run-in period with a high friction. It was hypothesized that the run-in period is related to the surface oxide layer formed naturally upon exposure of the sample to air. To test this hypothesis, thermal oxide layers were grown and their structures were analyzed and compared with the native oxide layer on a pristine sample. It was found that the Raman spectra of the surface oxide layers of H-DLC have higher D/G band ratio than the bulk, indicating a larger amount of aromatic clusters compared to the bulk film. Thick oxide layers grown at 300 oC showed a run-in friction behavior that resembled the friction of graphite. The run-in periods were found to become longer when the thickness of the oxide layers increased, indicating that the run-in behavior of H-DLC is attributed to the removal of the surface oxide layers. 11:20 am - 11:40 am Cupronickel-based Nanostructured Coatings with Exceptional Tribological Properties G. Ramirez, O. Eryilmaz, A. Erdemir, Argonne National Laboratory, Argonne, IL Nanocomposite coatings based on the segregation of two crystalline phases were prepared by a dual magnetron sputtering system, using a transition metal nitride as the primary phase and cupronickel alloy as a secondary phase. Cupronickel alloy is expected to provide high catalytic activity and higher toughness and oxidation resistance in comparison to pure copper and nickel. Bench-top tribological testing of the coated 52100 steel samples were carried out in different gaseous and liquid environments in order to study the wear and friction behaviors for different applications. Pin-on-Disk experiments were performed under 900 mBar of methane gas pressure to evaluate the performance of the coatings in natural gas applications. Other sets of experiments were done in the presence of polyalphaolefin (PAO) base oil and fully formulated synthetic oil to see the potential of these coatings under lubricated conditions, mainly for automotive applications. The results of the mentioned experiments show that the cupronickel-based nanocomposite coatings have exceptional resistance to wear; essentially showing almost no wear on rubbing surfaces, and reduction in friction is at least 20% in comparison with uncoated steel samples. Confocal Raman was used to evaluate the tribofilms formed during rubbing and to understand the mechanisms involved in the excellent tribological behavior of this new type of nanostructured coatings. 11:40 am - 11:40 am Tuning Iterfacial Damping in Built-up Structures by Dynamic Preloading

25

M. Eriten, S. Shinde, University of Wisconsin-Madison, Madison, WI, D. Patil, Molex Electronic Solutions, Auburn Hills, MI Accurate prediction of interfacial (slip) damping is critical for safe, reliable and energy efficient operation of built-up structures. Stochastic and non stationary events occurring across these interfaces introduce nonlinearity to interfacial damping, and hence inhibits predictive dynamic response. The current state of the art in estimating nonlinear interfacial damping is through phenomenological models, which cannot ensure predictive results for untested conditions. Physics based models cannot account for all possible events and changes occurring at multiple spatial and temporal scales. A simpler alternative to complicated modeling processes is to control and if possible eliminate the degree of nonlinearity in interfacial damping. This talk features such a tuning property that could be achieved by proper selection of dynamic preloading. In particular, phase difference and frequency ratio between normal and tangential loading over the interfaces are utilized as tuning parameters. Certain combinations of external loading conditions are shown to enable linear interfacial damping, and thus fully predictable dynamic response. In addition, proper choice of tuning parameters would provide wider ranges of damping values to be effective in broadband and transient responses. With this approach, the interfacial damping magnitude can be tuned approximately several orders of magnitude as opposed to 4-5 times in semi-active interfaces.

Session 2C - Monday, October 26, 2015 Pikes Peak

Boundary Lubrication and EHL I

Session Chair: I. Kudish, Kettering University, Flint, MI Session Vice Chair: TBD 10:20 am - 10:40 am Experimental Study of Capillary-Driven Flow between Contacting Rough Surfaces A. Rostami, J. Streator, Georgia Institute of Technology, Atlanta, GA The liquid flow between narrow spaces such as in the capillary tubes and porous media (wetting of soils or drainage through rocks) is of interest to researchers. In this work, we are interested in how liquids flow within the confined regions defined by the interface between contacting rough surfaces due to capillary effects. An experimental setup is designed to compare some of the characteristics of the capillary flow between contacting rough surfaces with the previous numerical works. These experiments are employed to visualize and quantify the flow of liquid films within the interface between two rough surfaces as well as to determine the level of adhesive forces generated in such a process. Additionally, we investigate the possibility that the capillary forces are sufficiently strong to initiate collapse of the interface as predicted theoretically. Results are presented for several common liquids interposed between different types of solid materials. 10:40 am - 11:00 am Ultimate Behavior of Confined Fluids Under Very High Pressure and Shear Stress

26

S. Ndiaye, Lamcos de Mécanique des Contacts et des Strucutures (LAMCOS), Villeurbanne, France, L. Martinie, LaMCoS, Villeurbanne, France, D. Philippon, INSA de Lyon, Villeurbanne, France, P. Vergne, Lamcos de Mécanique des Contacts et des Strucutures (LAMCOS), Villeurbanne, France Lubricants in the EHL regime are submitted to severe conditions, namely very high pressures, slide-to-roll ratios (SRR) and confinement, which can lead to a peculiar behavior of the lubricant itself. Indeed, at a given high pressure, the shear stress experienced by a lubricant can reach a maximum value, the so-called Limiting Shear Stress (LSS). The LSS origin is still not clear, which limits the proper modeling of EHD contacts. Previous researches attribute this LSS to either a modification of the lubricant state (liquid/glassy/solid) or a specific velocity field in the contact (wall slip and shear localization). However, these scenarios most of time assumed under extreme experimental conditions make very difficult to validate one of them. Our approach aims to explore the origins and consequences of the LSS by measuring in situ the evolution of the microstructural state of a lubricant when the LSS initiates. Lubricants that exhibit both a strong Raman response and a LSS behavior are a prerequesite for this study. After being calibrated, friction experiments are performed in a lubricated contact submitted to high contact pressures and low SRR. Next step is to make a correlation between the lubricants microstructure and friction measurements. Finally, these measurements are compared to pressure-velocity mapping of the lubricants behavior from the literature. 11:00 am - 11:20 am The Lbrication of DLC Coated Point Contacts Under Infinite Sliding Conditions J. Raisin, Total Marketing & Services, Research Center of Solaize, Solaize, France, N. Fillot, P. Vergne, D. Dureisseix, LaMCoS, INSA, Villeurbanne, France In recent years, Diamond-like carbon (DLC) coatings have been increasingly used in tribological applications thanks to their ability to mitigate friction. Among other factors, the low thermal conductivity of these coatings was shown to play a significant part, especially in the EHL regime. By disrupting the heat removal, the presence of DLCs or other low thermal inertia coatings induces higher temperatures in the central region of the contact than for steel-steel configurations. These higher temperatures in turn lead to a reduction in viscous friction without notable consequences on the film thickness. While valid for low to moderate sliding conditions, this statement seems questionable for infinite sliding conditions where the temperature balance strongly affects the film thickness through the so-called "thermal viscosity wedge mechanism". The present work therefore investigated the influence of low thermal inertia coatings on the lubrication of contacts operating under infinite sliding conditions. Thermal Elastohydrodynamic (TEHD) simulations of circular steel-steel contacts with and without low thermal inertia coatings were performed. Pressure and film thickness profiles as well as temperature distributions obtained in both configurations with a Newtonian lubricant were compared and analyzed. Results show that the use of low thermal inertia coatings significantly affects the film thickness in infinite sliding conditions. 11:20 am - 11:40 am Nonlinear Mechanics of Wear at Boundary Lubricated Interfaces E. Wornyoh, D. Patel, E. Asante-Asamani, J. Laate, S. Iyiola, University of Wisconsin-

27

Milwaukee, Milwaukee, WI Boundary lubrication is encountered in most lubrication schemes especially at the running-in where the severest forms of wear occur. And since uncontrolled wear adversely affects machine and engine components, tribologists strive to predict its occurrence in order to device novel lubrication schemes that limit or eliminate its impact. We demonstrate a fundamental mechanics model of wear that includes the simultaneous occurrence of friction and lubrication. Our model captures wear as a predictable nonlinear phenomenon and offers several schemes for evaluating wear under different stringent operational conditions of speed and load. The robust computational scheme adopted is based on a backward Euler Newton approach and may be used for other similarly complex nonlinear models.

Session 2D - Monday, October 26, 2015 Gray's Peak A

Materials Tribology II

Session Chair: B. Raeymaekers, University of Utah, Salt Lake City, UT Session Vice Chair: D. Haidar, University of Delaware, Newark, DE 10:20 am - 10:40 am Strucutral and Chemical Characterization of Diamondlike Carbon Boundary Films Extracted from Lubricating Oils A. Erdemir, O. Eryilmaz, G. Ramirez, Y. Liao, Argonne National Laboratory, Argonne, IL Systematic surface and structural studies have been carrried out to determine the chemical nature of diamondlike carbon (DLC) boundary films resulting from unformulated base oils, such as PAO. These boundary films form on rubbing surfaces of strategically designed nanocomposite coatings made of hard nitride phases (such as MoNx, NbNx, or VNx, etc.) and catalytically active metals (such as Co, Cu, Ag, Ni, Pd, etc.). When tested under severe boundary lubricated conditions, such composite films derive a carbon-rich boundary film that in every respect ressembles DLC which is typically produced by plasma-based CVD and PVD methods. DLC boundary film reduces friction by as much as 50% under severe boundary conditions and virtually eliminates wear in base oil. Raman, TEM, and EELS clearly confirm the formation of such DLC boundary films on rubbing surfaces and thus elucidate their fundamental lubrication mechanisms. 10:40 am - 11:00 am Quantifying the Deformation of Ultra-thin Multi-layer Diamond-like Carbon Coatings Under Combined Normal and Tangential Loading M. Price, University of Utah, Salt Lake City, UT, A. Ovcharenko, Western Digital, San Jose, CA, B. Raeymaekers, University of Utah, Salt Lake City, UT The ultra-thin diamond-like carbon (DLC) coating on the recording heads in a hard disk drive (HDD) protects the intricate magnetic read/write structures from wear and corrosion. This multi-layer coating consist of a tetrahedral amorphous carbon (ta-C) layer and a Si or SiN layer that strengthens adhesion between the DLC layer and the substrate material of the recording head.

28

Damage or wear of the DLC coating, even in part, can expose the substrate material to corrosion, which may decrease the reliability of the HDD. We have implemented a molecular dynamics (MD) model to simulate accidental contact between the recording head and the magnetic disk and evaluate the deformation of the multi-layer coating under combined normal and tangential loading. We investigate the effect of ta-C layer thickness, Si layer thickness, and operating temperature on coating deformation during multiple loading/unloading cycles. The results indicate that deformation occurs primarily within the Si layer and at the Ni-Si and Si-C interfaces, and increases with increasing number of loading cycles and increasing temperature. Coating deformation increases with decreasing ta-C layer thickness and decreasing Si layer thickness. 11:00 am - 11:20 am Molecular Dynamics Study of Thermal Transportation in Heat-Assisted Magnetic Recording Q. Liu, L. Li, W. Song, G. Zhang, Harbin Institute of Technology, Harbin, China Heat-assisted magnetic recording (HAMR) is a promising way to enable the magnetic recording area density to reach 1 T/in2. In HAMR, the magnetic material with high anisotropy and coercivity is used. A laser with a spot size on the order of nanometers can decrease the coercivity of magnetic media during the writing process. The heating time is in a few nano seconds during the heating process. For such a rapid heating time and small heating spot size, the temperature profile and thermal transportation inside the disk need to be revealed before its application in HAMR. In this work, a molecular dynamics (MD) model is developed to investigate the temperature profile and thermal conductivity between a DLC film and a magnetic recording layer in a media used in HAMR. The two-temperature model is used to investigate the thermal transport inside the DLC film and magnetic recording media caused by an ultra fast laser heating. The effect of laser spot size, laser power and thermal conductivity of DLC film on the temperature profile of the disk is analyzed. The heat transport between the nanometer thick DLC film and the magnetic recording layer are identified. 11:20 am - 11:40 am Thermomechanical Properties and Contact Performance of Oxidized Diamond-like Carbon Film J. Song, C. Yeo, Texas Tech University, Lubbock, TX Diamond like carbon (DLC) is widely used in hard disk drive (HDD) industry, biomedical devices, and micro-electro-mechanical systems (MEMS) due to its mechanical strength, optical transparency, and chemical inertness. When DLC films experience dynamic surface contact especially at hot/wet condition, oxygen atoms can be diffused through the layer changing its contact performance thereafter. Therefore, it is of great importance to investigate the scientific relationship between DLC material properties and its oxidation process. In this study, the thermal and mechanical properties of DLC film are quantitatively measured with atomic percentage of oxygen atoms through molecular dynamics (MD) simulations. Using a single asperity contact model, the thermomechanical contact performance of oxidized DLC films is examined with respect to contact velocity and surface interference. Lastly, nanoscratch experiments are performed on oxidized DLC film, whose results are compared to MD simulations.

29

11:40 am - 12:00 pm Sliding Wear Behavior of Uncoated and DLC-coated Surfaces in Oil and Ethanol R. Souza, M. Ara, S. Hellmeister, N. Fukumasu, A. Sinatora, University of Sao Paulo, Sao Paulo, Brazil In this work, sliding tests were conducted with a fixed specimen made of gray cast iron and a sliding specimen made of nitrided stainless steel. Specimens were tested in the uncoated condition as well as with diamond-like carbon (DLC) coatings. Two DLC coatings were evaluated, being provided by different research institutions. Tests were run in an Optimol SRV-4 tribometer, in reciprocating mode. Different test environments were considered, including dry, lubrication with poly-alpha-olefin (PAO) oil and anhydrous ethanol. The surfaces in contact were characterized prior to the tests by means of optical profilometry. Tribological results were compared in terms of mass loss, variation of friction coefficient as a function of time, as well by means of the test-induced modifications in surface topography. Results have confirmed that significant changes in terms of steady state friction coefficient and running-in time may be obtained depending on the materials tested. These differences are a result of not only the differences in mechanical properties, but also chemical differences associated with surface evolution and formation of a tribo layer.

Session 2E - Monday, October 26, 2015 Gray's Peak B

Materials Tribology IIa

Session Chair: D. Van Citters, Thayer School of Engineering, Dartmouth College, Hanover, NH Session Vice Chair: N. Gosvami, Philadelphia, PA 10:20 am - 10:40 am Two Roads to Improve Tribological Performances of a Ring-on-Ring Sliding Contact : DLC Coating or Carbon-Graphite Ring K. Delbé, S. Lafon-Placette, J. Denape, Université de Toulouse - ENIT, Tarbes, France, M. Ferrato, BOOSTEC, Bazet, France To design new mechanical seal applications, we study silicon carbide in dry sliding contact with a ring-on-ring configuration. This material presents a favorable behavior in lubricated conditions with pin-on-disc configuration, but damage can be catastrophic in dry friction. A SiC/SiC pair is used as reference. To improve the tribological performance of this pair of ring, we proposed two ways. First, a SiC ring is coated with Diamond-like Carbon (DLC). Second, a SiC ring is replace with a carbon-graphite ring. The tribological study takes in account their accommodation mechanisms in the contact, the chemical evolution of the interface and their thermal diffusion properties. Tribological tests were run at 3 different temperatures (ambient, 120°C and 300°C), 3 speeds (0.5, 1 and 2 m/s) and different contact pressure (0.5, 0.75 and 1 MPa) with an environmental tribometer. During tests, the thermal evolution is recorded via thermocouple and interface temperature is modeling. Results are presented in term of friction coefficients and wear.

30

Characterization of the tribofilm is obtained by using analytical microscopy and Raman spectroscopy. This vibrational spectroscopy is also used to investigate the evolution of mechanical stress at the surface of the 2 rings and for every pairs. A mechanism based on the third body model and flow of debris in the interface is proposed. The energy balance is also discussed. 10:40 am - 11:00 am Effect of Stroke Length on Wear Response of Aluminum A356 and A390 Alloy Under Reciprocating Sliding T. Harish, Goverment Engineering College, Bartonhill, Thiruvananthapuram, India, P. Varghese, V. Rajeev College of Engineering, Trivandrum, Kerala, India, College of Engineering, Trivandrum (CET), Thiruvananthapuram, India Wear mechanism in aluminium alloys are classified into mild wear, severe wear and seizure wear. Dry sliding wear depends on normal load, sliding velocity, frictional temperature and material properties like hardness and yield and fatigue strength. Studies on wear response variation with wear test parameters had constant stroke length (SL). Wear under reciprocating condition is by fatigue fracture. Frequency of loading alters fatigue crack initiation, propagation and fracture. Varying SL varies loading frequency. In this study wear response of aluminum alloys A319, A356 and A390 at various SL is reported. The pins of alloys were allowed to reciprocate against counter surface of En 31 steel. The wear loss of alloys for different SL under same load and linear velocity was found out for each alloy. Experiment was repeated for different loads and speeds of sliding. It was found that the wear rate reduces with stroke length when load and speed are same. Wear rate variation with SL was non linear at larger loads and higher velocity. This is due to earlier transformation to severe wear mechanism at larger loads. Trend in wear response variation with SL at higher velocity was similar to increasing load. Silicon percentage and its form changes wear response with changes in SL. A390 alloy had higher wear resistance at larger SL. Higher percentage of Si gives this wear resistance. Increasing fatigue strength and percentage globular silicon reduces reciprocating wear at larger SL. 11:00 am - 11:20 am Wear in Silicon Nitride/Steel Contacts Under High Speed Conditions S. Berkebile, N. Murthy, M. Riggs, US Army Research Laboratory, Aberdeen Proving Ground, MD Hybrid bearings with ceramic rolling elements and steel races have found increasing use in aerospace applications due to their higher speed capabilities and increased lifetime. Under starved lubrication conditions, the limiting factor for extended operation is degradation of the steel surface through heat-activated plastic deformation, adhesion to the ceramic element, and oxidative wear. The degradation of the steel over the ceramic is due to the lower hardness and cohesion of steel at higher temperatures. Although studies of wear behaviour in hybrid bearing contacts with different steel hardnesses have been published, these have typically been conducted at low sliding speeds and with no rolling motion component. Since higher contact velocities with varying slide-to-roll ratios affect the wear behaviour and rate, a study of wear and degradation behaviour at various velocities and slide-to-roll ratios has been conducted for silicon

31

nitride/steel contacts at high entrainment velocities. The differences between standard and new high hot hardness steel alloys will be presented and discussed. 11:20 am - 11:40 am High Temperature Wear Evaluation of Materials: Challenges and Industrial Case Studies E. Georgiou, D. Drees, Falex Tribology NV, Rotselaar, Belgium, J. Celis, KU Leuven, Leuven, Belgium High temperature materials testing often requires the development of complex and demanding mechanical setups. Especially in the field of tribology, there is a lack of experimental equipment for testing accurately and efficiently the wear behaviour of materials at high temperatures. Nowadays, the need for the development of such equipment has become even greater if we take into consideration the large number and diverse applications that require the use of materials under demanding conditions, combining high temperature oxidation and wear phenomena. Some typical examples are commonly met in the aeronautical, transportation, energy field. In this study, the development of a state-of-the-art experimental setup to study the reciprocating sliding behaviour of various bulk and coated materials at temperatures that can reach up to 1000 °C is presented. The aim of this work is twofold: First some of the main challenges relating to the mechanical design, safety issues, sample geometry, and material selection are highlighted. Furthermore, the advantages, limitations and design novelties of this apparatus are analysed. Secondly, examples of existing industrial case studies are presented to illustrate the need for using such advanced equipment. In particular, three different industrial examples are shown from the: (a) aerospace industry - nanostructured bearings, (b) transportation industry - brake materials, and (c) energy field - multi-layered solar cell coatings. 11:40 am - 12:00 pm Fretting Wear Analysis of Ti-6Al-4V with A Duplex Surface Treatment G. Doll, The University of Akron, Akron, OH, B. McMillen, Akron Research Technologies, Inc., Akron, OH Titanium alloys are known to experience high wear rates and friction when they are in contact and in relative motion with themselves or most other materials. In this study, a duplex surface treatment consisting of solution nitriding and a titanium-containing diamondlike carbon coating have been applied to Ti-6Al-4V discs. Friction and wear of the duplex treated discs have been examined in mixed fretting and gross slip regimes against hardened steel and ceramic counter faces and compared to untreated discs, and discs treated with either nitriding or the titanium-containing diamondlike carbon coating. Experiments have been carried out at different temperatures and wear coefficients were obtained for the various materials pairs. It is observed that the duplex treated Ti-6Al-4V discs display considerably less wear against the counter faces than any other materials pair tested in this study.

Session 3A - Monday, October 26, 2015 Mt. Elbert A

Lubricants III

32

Session Chair: Y. Oyerinde, Chevron Phillips Chemical Co., Kingwood, TX Session Vice Chair: TBD 1:40 pm - 2:00 pm Lubricant--Chemistry Kinetic Model of Antiwear Film Formation by Oil Additives Based on Structure Oriented Lumping, Part I: Theoretical and Numerical Framework C. Zhang, Shanghai University, Shanghai, China, V. Wong, Massachusetts Institute Of Technology, Cambridge, MA Structure Oriented Lumping (SOL) is an analytical technique that describes the reactions of multi-species mixtures. A kinetic model for antiwear film formation by oil additives is presented. The model considers representing reactant molecules and constructing reaction networks by the structure oriented lumping method, calculating the pre-exponential constant and the activation energy of the reactions in the form of the Arrhenius equation, and solving the resultant kinetic differential equations. Structure vectors (as in the SOL method) in this tribochemical system consist of molecular composition of lubricants, additives, intermediates, wear debris, and surface materials, illustrating the process of surface protection from antiwear additives. 2:00 pm - 2:20 pm Tribological Properties of Micro- and Nano-sized Solid Lubricant (Graphite and Graphene) as Lubricant Oil Additives E. Omrani, C. Reeves, P. Menezes, P. Rohatgi, UW-Milwaukee, Milwaukee, WI Inadequate or inefficient lubrication often gives rise to high friction and wear losses in machine components, which adversely affect lubrication performance, efficiency, and durability. Many approaches have been explored to enhance the antifriction and antiwear properties of machine components during sliding. The size of particulate additives in a lubricant influences their friction and wear performance during sliding contact. In the present investigation, a pin-on-disk apparatus was employed to investigate the influence of graphite and graphene solid lubricant additives on the tribological behavior of lubricants containing particulate additives. In the experiments, aluminum pins were slid against 440 stainless steel disk in the presence of lubricant containing micro-sized and nano-sized graphite and graphene additives. Scanning electron microscope and optical profilometer were used to evaluate the influence of particle size on wear damage and surface roughness. When graphite and graphene additives were dispersed at 1 wt% concentration in a lubricant, the friction and wear performance were significantly enhanced under boundary-lubricated sliding conditions. The improved friction and wear performance is due to the formation of carbon-rich boundary film, the formation of which is attributed to tribochemical interactions between the carbon particles and contact surfaces. 2:20 pm - 2:40 pm A Synergistic Hybrid Anti-Wear Additive by Combining a Phosphonium-Alkylphosphate Ionic Liquid and a ZDDP J. Qu, W. Barnhill, H. Luo, H. Meyer, D. Leonard, Oak Ridge National Laboratory, Oak Ridge, TN, B. Kheireddin, H. Gao, B. Papke, Shell Global Solutions (US), Houston, TX, S. Dai, Oak Ridge National Laboratory, Oak Ridge, TN

33

Synergistic effects have been observed between a group of phosphonium-alkylphosphate ILs and a conventional secondary ZDDP when used as lubricant additives, resulting in ~30% friction and >70% wear reductions. The ZDDP+IL tribofilm distinguishes itself from ZDDP or IL tribofilms by substantially increased zinc and iron phosphates but reduced metal oxides and sulfur compounds. Notably, concentrations of the IL and ZDDP reactive elements on the lubricant surface were revealed to be 30-70 times higher than the nominal values, which may explain the superior tribological performance and the phosphates dominance in the tribofilm. Based on the chemical hardness principle, anion exchange is hypothesized to occur between the IL and ZDDP to produce a new compound ZOTP, whose atomic ratio of O:Zn:S:P matches well with what was detected on the oil surface. FTIR analysis confirmed new compounds in the ZDDP+IL mixture. It remains to be fully understood why the concentration of ZOTP on the oil surface is 1-2 orders of magnitude higher than nominal. No such synergy with ZDDP, however, was observed for phosphonium-alkylphosphinate or ammonium-alkylphosphate ILs, even though they share either the same cation or the same anion with phosphonium-alkylphosphate ILs. This research was sponsored by the Vehicle Technologies Office, Office of Energy Efficiency and Renewable Energy, US Department of Energy (DOE). ). 2:40 pm - 3:00 pm Lubricant--Chemistry Kinetic Model of Antiwear Film Formation by Oil Additives Based on Structure Oriented Lumping, Part II: Model Testing and Validation C. Zhang, Shanghai University, Shanghai, China, V. Wong, Massachusetts Institute Of Technology, Cambridge, MA Structure Oriented Lumping (SOL) is an analytical technique that describes the reactions of multi-species hydrocarbon mixtures. The technique involves solving parallel molecular kinetic differential equations in time, applied to the complex and combined system of lubricant-additive-antiwear-film and surface during the tribochemical wear process in this case. Lubricant chemistry kinetic model of antiwear film formation by oil additives based on structure oriented lumping is described in a companion paper, and the modeling is validated experimentally in the current article. Predicted and in situ measured effects of various factors, including operating temperature, antiwear additive type and concentration, and the presence of dispersant, on film formation are used for validation. It is shown that predictive analysis is possible and useful as a design tool. The sensitivity of the antiwear film formation to the considered sub-processes including the decomposition process, adsorption process and oxidation process in addition to input parameters are analyzed and demonstrated. 3:00 pm - 3:40 pm - Break 3:40 pm - 4:00 pm Molecular Dynamics Simulations of the Atomic-Scale Behaviour of Organic Friction Modifiers in Base-Oil Solution and at Surfaces J. Ewen, D. Dini, Imperial College London, London, United Kingdom, C. Gattinoni, University College London, London, United Kingdom, H. Spikes, Imperial College London, London, United Kingdom

34

Organic Friction Modifiers (OFMs) are becoming increasingly important automotive lubricant additives, not least because of progressively more stringent limits for elements found in traditional friction modifiers in specifications. Whilst monolayer formation is well known to be the route to low friction in the boundary regime in OFM containing formulations, there is still much uncertainty with regards to the action of certain OFM molecules. Much of this ambiguity stems from the fact that most simulation and experimental studies use fatty (carboxylic) acids, which are generally not included in commercial additive packages, because they are corrosive and can neutralise detergent additives. Commercially utilised OFMs include fatty amides and glycerol esters, which have been less extensively studied. The friction reduction mechanism of commercial OFMs is also expected to be through monolayer formation, however, specific details regarding how well they adsorb, and form monolayers, as well as why certain molecules outperform others in friction tests remain uncertain. Molecular Dynamic simulations are a useful tool with which to give atomic-level insight into the behaviour of OFM additives. Through comparative simulations, with carefully chosen potential models, information such as the relative efficacy of different polar head groups and fatty tail groups in terms of adsorption strength, monolayer strength and friction reduction can be extracted. 4:00 pm - 4:20 pm MD Simulation on Novel Friction Modifiers in Boundary Lubrication J. Lu, P. Liu, X. He, M. Desanker, T. Marks, Y. Chung, Q. Wang, Northwestern University, Evanston, IL Friction reduction is one of the key concerns in designing novel lubricants for better performance. In particular, friction in the boundary lubrication (BL) regime greatly affects fuel efficiency and service time of the components. Thus, BL friction modifiers containing organic, inorganic, ring or line structures have been developed and implemented in engine oils. In order to further reduce friction in the BL regime, novel friction modifiers with different functional groups have been designed and synthesized. Experimental result (Pin-on-disk) showed that one of the synthesized friction modifier (C12CYC) was the best in reducing 70% friction in the BL regime. In order to explain the experiment results, the structure and adsorption properties of several friction modifiers on a hydrated silica surface are studied using the molecular dynamics (MD) simulations. The hydrated silica surface is modified by artificially grafting hydroxyl group (-OH) group, and the structural parameter and partial charge of such surface are determined by the ab initio quantum mechanics (QM) computation. The adsorption process of these friction modifiers are then studied with an all-atom MD simulation using the LAMMPS code; and the adsorption energies of those friction modifiers are calculated during the adsorption simulations. Comparison between the MD results and tribological experiment data are made, and a good trend between the adsorption energies and nano-scratch friction coefficients is observed. 4:20 pm - 4:40 pm Balancing Friction and Wear in Next Generation Engine Oils with New Formulation Constraints Introduced with Low Speed Preignition K. Fletcher, A. gupta, K. Garelick, G. Pollard, J. guevremont, Afton Chemical Corporation, Richmond, VA Turbocharged, gasoline direct injection (TGDI) engines are the future of engine technology and

35

will assist auto manufacturers in achieving target fuel economy gains without the consumer experiencing a loss of performance or power. Low speed preignition (LSPI), or stochastic preignition, is a type of abnormal combustion that can cause catastrophic engine damage in TGDI engines. Because of the potential damage that can result from even one LSPI event there has been intense interest in understanding the cause of LSPI as well as potential options to reduce its frequency. Many researchers have demonstrated that a reduction in calcium-based detergent loading and a boost in phosphorus can reduce the likelihood that LSPI will occur. It is well known that detergent type and treat rate as well as ZDDP play a significant role in tribofilm formation on a steel surface, and film properties can have a dramatic effect on friction and wear. In this study we explore the relationship between tribofilm properties in prototype oils that will impart LSPI protection and discuss the trade-offs between friction, wear and LSPI control that need to be understood.

Session 3B - Monday, October 26, 2015 Mt. Elbert B

Surface Science III

Session Chair: TBD Session Vice Chair: TBD 1:40 pm - 2:00 pm Influence of Potential Shape on Constant-Force Atomic-Scale Sliding Friction Models W. Tysoe, UW-Milwaukee, Milwaukee, WI, O. Furlong, S. Manzi, National University of San Luis, San Luis, Argentina, A. Martini, University of California-Merced, Merced, CA The majority of atomic-scale friction models in which sliding is proposed to occur over the atomic-scale energy corrugation at the sliding interface assume a simple sinusoidal potential. An analysis of these models shows that the energy barrier is reduced by the imposition of an external force F, becoming zero at a critical force defined as F*. It was first suggested by Prandtl that the energy barrier approaches a limiting value with a force dependence that is proportional to . In order to explore the effects of the shape of the energy potential on the sliding behavior, this model is analyzed for constant-force sliding with a non-sinusoidal potential of the form , where n is an even integer e2. The same asymptotic dependence is found as suggested by Prandl, where the proportionality constant depends on the shape of the potential. These results are used to calculate the velocity and temperature dependences of sliding friction for constant-force sliding over non-sinusoidal surface potentials. 2:00 pm - 2:20 pm Periodic Normal Contact Problems in Plane Elasticity - the Fracture Mechanics Approach Y. Xu, R. Jackson, Auburn University, Auburn, AL The periodic contact problems in plane elasticity has been extensively studied for almost 80 years since the seminal work of Westergaard. The main analytical approaches include: (1) complex variable method, (2) Fourier transform (series) method, (3) Green's function and (4) stress (potential) function method. Due to the nature of the mixed boundary-value problem, the

36

unknown interfacial state of stress needs to be solved from the integral equations or sets of dual series equations. When the contacting materials are dissimilar and slip and adhesion are introduced, a complete closed-form solution is often impossible due to the mathematical complexity. In this study, a more straight-forward method is introduced. We only consider the purely normal contact case between an elastic half-plane with a periodic profile and a rigid flat under a uniform compressive normal stress acting at the far end. Adhesion and interfacial friction are neglected. Through the fracture mechanics approach, we are able to directly obtain the real area of contact by setting the corresponding stress intensity factor to zero. Then, the interfacial state of stress (within the contact area) and interfacial gap (outside the contact area) can be determined through the Green's function. In order to show the validity of this method, we resolve the classic periodic plane contact problem of an elastic sinusoidal waviness in contact with a rigid flat (Westergaard solution). 2:20 pm - 2:40 pm A Novel Approach to Model Effects of Surface Roughness Parameters on Wear A. Ghosh, F. Sadeghi, Purdue University, West Lafayette, IN Engineering surfaces with similar average or RMS roughness exhibit different values of skewness and kurtosis due to different machining processes. As the surfaces evolve during operation and the wear process, the roughness parameters undergo significant changes. To investigate the change in the roughness parameters and their effect on wear rate, it is of significant importance to investigate and simulate deep wear scars. In this study, a novel method to simulate wear on rough surfaces is proposed. The surface is treated as a collection of asperities of different radii at different heights. The method is applied to an elastic-plastic material model and material removal is simulated by a simple truncation model. Surfaces with various values of RMS roughness, skewness and kurtosis are investigated and two distinct wear rates are obtained for each surface, running-in (severe) wear and steady state (mild) wear. It is also predicted that surfaces with high roughness, kurtosis and positive skewness exhibit higher wear rates. This investigation highlights the importance of studying the effects of surface parameters on wear rate and demonstrates that although a linear wear law is assumed at each asperity, a non-linear wear rate of rough surfaces can be obtained computationally, which are similar to trends observed in experiments. 2:40 pm - 3:00 pm Friction, Contact Area and Stiffness Dependence on Surface Fractality in Rough Contacts D. Dini, C. Putignano, Imperial College London, London, United Kingdom We employ a recently developed numerical methodology to investigate the role played by the fractal parameters used to describe rough surfaces in determining quantities of prominent practical interest. The paper will show results aimed at highlight the effect that fractality has on viscoelastic friction, contact area and contact stiffness. In particular, the importance of the cut-off wavelength, crucially related to the acquisition of the instrument employed during experiments, is pointed out. Furthermore, a simple definition of a speed dependent modulus is provided in order to reduce the rough viscoelastic contact to an equivalent elastic description. Advantages and limitations of such an approach, in comparison with exact numerical calculations, are discussed. Finally, results are also shown for layered viscoelastic contacts in the presence of

37

rough surfaces. 3:00 pm - 3:40 pm - Break 3:40 pm - 4:00 pm The Influence of Single Asperity Models on Predicting Contact Between Elastic and Elastic-plastic Rough Surfaces Using Statistical Methods R. Jackson, Y. Xu, H. Ghaednia, S. Saha, Auburn University, Auburn, AL Many single asperity models have been developed since the original statistical rough surface contact model was created by Greenwood and Williamson. Some models have sought to include plasticity, while others have changed the shape of the asperity such as to a wavy or sinusoidal peak. These models might improve the effectiveness of the statistical methods to predict the real contact area, contact force and surface separation. The magnitude of their effect is uncertain though and this work seeks to characterize it. The usage of the one dimensional surface stiffness method (I.e. the winkler or voxel method) is also investigated. 4:00 pm - 4:20 pm Contact Between Heterogeneous Elastic-plastic Bodies - Application to Roller Bearings and Indentation of Materials T. Chaise, K. Amuzuga, LaMCoS - INSA Lyon - University of Lyon, Villeurbanne, France, D. Nelias, INSA-LaMCoS, Villeurbanne, France The semi analytical methods are a class of numerical methods that can be considered as an interesting alternative to the finite element method for their rapid computation time and robustness in the resolution of contacts. Furthermore, the recent developments made in the field allow to consider contact between bodies containing both heterogeneities and plastic properties, opening the field to a wide new range of applications. In particular the presence of heterogeneities being model, roughly, as the superposition of Eshelby's based solutions on the elastic contact problem, the meshing of bodies with multiple, complex shaped heterogeneities becomes relatively simple. Two fields of application will be presented. First the rolling contact behavior of bearings that may contain carbides involving plastic flow around inclusions. The influence of the bodies' behavior on the contact pressure, plastic strain level and residual stresses is observed. Second, the normal contact, i.e. indentation, on a heterogeneous (either porous or containing carbides) elastic body. For this contact type, the influence of heterogeneities on the macroscopic indentation response will be studied. 4:20 pm - 4:40 pm The Stress Analysis of Roller Contact Modeled in the Quarter-Space X. Shen, Z. Wang, X. Chen, Shanghai University, Shanghai, China The rigorous mathematical and numerical methods of the contact problem have been developed to calculate the distribution and magnitude of surface stresses in finite line contact situation. By using these methods, the effect of crowning of rollers and raceways is discussed. But all these

38

simulations are established on a half-space model. Simply to say, the relationship between stress and strain is based on the assumption of the half space. This assumption ignores the effect of the free surface at the ends of contact bodies. At the free ends, the compressive stress is relaxed, permitting the solids to expand slightly in the axial direction and thereby reducing the contact pressure at the end. So the effect of the end free surface in real rollers and raceways cannot be ignored. Due to the fact that the end faces are usually perpendicular to the length direction, the roller contact problem can be approximately modeled as a quarter-space problem. The authors will present an efficient algorithm for the solution of the finite line contact problem in a quarter-space to accurately evaluate the contact stress and guide profile designing. Discrete convolution-fast Fourier transforms (DC-FFT) and Hetenyi's correction processes are combined to calculate the elastic displacement and subsurface stresses in a quarter-space.

Session 3C - Monday, October 26, 2015 Pikes Peak

Boundary Lubrication and EHL II

Session Chair: D. Kim, University of Texas at Arlington, Arlington, TX Session Vice Chair: TBD 1:40 pm - 2:00 pm Dynamic Experimental Research in PTFE-Faced Pad Thrust Bearings Y. Jiao, X. Wang, J. Shen, M. Li, J. Jin, Z. Hua, School of mechanical Engineering and Automation, Shanghai University, Shanghai, China With an increasing capacity of large turbine engines, the axial vibration becomes a new problem. Then the experimental study of the dynamic characteristics of thrust bearings is necessary. The dynamic properties of PTFE-faced pad thrust bearings are tested with the thrust bearing test rig, which is inverted structure, namely the shaft to rotate only, the test bearing in the axial direction can float up and down.The test rig includes stepper motor, spindle, static loading system, electromagnetic vibration exciter and test bearings. In order to realize dynamic loading, we adjust the size of the vibrator output power, frequency, and phase by adjusting the signal generator connected to the vibrator.We test the influence of different loads, speed and excitation force on dynamic characteristics of PTFE-faced pad. The experiments compare the stiffness and damping coefficients of the PTFE-faced and Babbitt-faced pad. The results indicate that the influence of load on stiffness coefficient is noteworthy. The increase of load lead to increase stiffness coefficients, but it has little impact on the damping coefficients. Under the other condition is constant, the oil film stiffness decrease with the increase of rotating speed. The experimental results show that the trends of oil film stiffness damping coefficients corresponding to Babbitt and PTFE pad bearing with the change of load are similar, but the stiffness and damping of PTFE-faced pad is less than Babbitt-faced one. 2:00 pm - 2:20 pm Transient EHL Point Contact Analysis during Impact Load Conditions Y. Kang, R. Evans, The Timken Company, North Canton, OH Machine components such as bearings and gears experience transient and steady-state loading

39

conditions within highly localized EHL contacts. Rapid impact loads with high sliding conditions may occur at the EHL contacts during transient operating conditions, including shock loading or erratic load zone scenarios. In the present study, a transient EHL point contact model was used to determine the pressure and film thickness distributions within the contact during rapid impact load conditions. Influences of impact loads on the film collapse and reformation were studied. Results show that impact load conditions significantly influence the pressure and film thickness distributions at the rolling and sliding EHL contacts. Also, the transient EHL model was used to simulate experimental smearing test conditions to evaluate the usefulness of a simple smearing criterion factor. 2:20 pm - 2:40 pm Some Criteria for Coating Effectiveness in Heavily Loaded Line EHL Contacts. Part 1. Dry Contacts I. Kudish, Kettering University, Flint, MI, A. Vasiliev, S. Volkov, S. Aizikovich, Don State Technical University, Rostov-on-Don, Russian Federation Contacts of indentors with functionally graded elastic solids may produce pressures significantly different from the results obtained for homogeneous elastic materials (Hertzian results). It is even more so for heavily loaded line elastohydrodynamically lubricated (EHL) contacts. The goal of the paper is to indicate two distinct ways the functionally graded elastic materials may alter the classic results for the heavily loaded line EHL contacts. Namely, besides pressure the other two main characteristics which are influenced by the non-uniformity of the elastic properties of the contact materials are lubrication film thickness and frictional stress/friction force produced by lubricant flow. The approach used for analyzing the influence of functionally graded elastic materials on parameters of heavily loaded line EHL contacts is based on the asymptotic and kernel approximation methods earlier developed by authors \cite{C1} - \cite{C3}. More specifically, it is based on the analysis of contact problems for dry contacts of functionally graded elastic solids and the lubrication mechanisms in the inlet and exit zones as well as in the central region of heavily lubricated contacts. Dry contacts with free and fixed boundaries involving coatings which are "softer" or "harder" than the substrate are considered. The pressure distributions, contact size as well as the asymptotic behavior of the pressure in the vicinity of the contact boundary are determined. 2:40 pm - 3:00 pm Some Criteria for Coating Effectiveness in Heavily Loaded Line EHL Contacts. Part 2. Lubricated Contacts I. Kudish, Kettering University, Flint, MI, A. Vasiliev, S. Volkov, S. Aizikovich, Don State Technical University, Rostov-on-Don, Russian Federation Contacts of indentors with functionally graded elastic solids may produce pressures significantly different from the results obtained for homogeneous elastic materials. It is even more so for heavily loaded line EHL contacts. The goal of the paper is to indicate two distinct ways the functionally graded elastic materials may alter the classic results for the heavily loaded line EHL contacts. The main focus of the paper is the influence of the non-uniformity of the elastic properties of the contact materials on lubrication film thickness and frictional stress/friction force. The approach used for analyzing the influence of functionally graded elastic materials on

40

parameters of heavily loaded line EHL contacts is based on the asymptotic and kernel approximation methods earlier developed by the authors. It is based on the analysis of contact problems for dry contacts of functionally graded elastic solids and the lubrication mechanisms in the inlet and exit zones as well as in the central region of heavily lubricated contacts. The way the solution of the EHL problem for coated materials is obtained provides a very clear structure of the solution involving in the Hertzian region the solution of dry contact problem while in the inlet and exit zones the solution of the EHL problem with the right asymptotes coming from the solution of the dry contact problem. The effects of functionally graded elastic materials on the lubrication film thickness and friction force are analyzed. 3:00 pm - 3:40 pm - Break 3:40 pm - 4:00 pm Revision of a Fundamental Assumption in the EHL Theory and Friction in Heavily Loaded Line Contacts with Notable Sliding I. Kudish, Kettering University, Flint, MI An analysis of the classic friction modeling in lubricated contacts is conducted. Its major deficiency \emph{for "soft" materials (low elastic modules)} leading to significant overstating of friction in heavily loaded isothermal and thermal lubricated contacts is revealed. An improved model of friction in a heavily loaded lubricated contact is proposed. The model is based on incorporating the tangential displacements of the solid surfaces in contact leading to significant reduction of the frictional stress due to the decrease of the actual sliding of lubricated surfaces. Generally, this frictional stress reduction increases with the slide-to-roll ratio and it is extremely important for high slide-to-roll ratios for which classic approaches lead to unrealistically overestimated values of frictional stresses. The high slide-to-roll ratio values can be founded in many practical applications such as, for example, clutches. Several examples of the friction stress calculated based on this model as well as the comparison with the classical results are given for the case of smooth solid surfaces and lubricants with Newtonian rheology. Also, the results allow to take a look at the role and the necessity of considering thermal and lubricant non-Newtonian effects on solution of various EHL problems for such heavily loaded contacts. 4:00 pm - 4:20 pm What Is Regularization, Its Role and Place in Solution of Isothermal Problems for Heavily Loaded EHL Contacts? I. Kudish, Kettering University, Flint, MI A typical defect of numerical solutions obtained for isothermal heavily loaded EHL contacts such as solution instability is considered. Some analysis and numerical examples of solutions for dry and lubricated contact with instability are presented. The main roots of numerical instability are discussed and a regularization process, i.e. the process which makes the numerical solution stable, is revealed. A regularization of EHL problems slightly modifies the problem equations to make their numerical solution stable. The level of this problem modification is controlled by just one parameter. The effect of the level of regularization on parameters of EHL contacts is considered. The idea of such a regularization comes from the solution of a thermal EHL problem

41

with low generation of energy in the contact. Some examples of regularized numerical solutions for classic EHL problem and an EHL problem which takes into account tangential surface displacements caused by frictional stresses are presented. The approach showed its effectiveness for very high values of pressure viscosity coefficients.

Session 3D - Monday, October 26, 2015 Gray's Peak A

Materials Tribology III

Session Chair: D. Burris, University of Delaware, Newark, DE Session Vice Chair: TBD 1:40 pm - 2:00 pm In Situ Observation of PEEK Transfer Film Formation at the Sliding Interface with Fluorescent Microscopy Y. Sawae, T. Morita, T. Yamaguchi, Kyushu University, Fukuoka, Japan A new experimental system in combination with fluorescent microscopy has been developed to explore the basic friction and wear mechanism of polymeric materials. Sliding tests were conducted upon an inverted fluorescent microscope and dynamic behavior of the polymer transfer to the sliding counter face was observed during sliding by capturing autofluorescence from transferred polymer. By using this setup, effects of surface roughness of a sliding counterface on material transfer from polyethelethelketone (PEEK) and resultant frictional behavior were examined. Two glass plates with different roughness parameters were prepared and used as a sliding counterface in the experiment. Although both plates have similar Ra value around 3 mm, they have different skewness and kurtosis. As a result, the friction behavior was closely related to the dynamics of PEEK transfer, which was highly depended on the roughness parameters of the glass surface. PEEK could adhered stably on the glass surface with positive skew and large kurtosis and the transfer film formation was gradually proceeded and reached to the equilibrium state. In this case, the friction coefficient also increased gradually and reached to the steady state. However, PEEK adhesion was unstable on the surface with negative skew and small kurtosis and amount of transferred PEEK increased continuously. Consequently, the excessive PEEK transfer induced unstable frictional behavior and continuous increase in the friction coefficient. 2:00 pm - 2:20 pm A Lubricant Additive for In Situ Formation of Lubricious Graphitic and Diamond-like Carbon Tribofilms B. Johnson, Q. Wang, Y. Chung, Northwestern University, Evanston, IL We report on the use of a class of cycloalkanes as lubricant additives that readily dissociate into lubricious carbon tribo-films due to flash heating at asperity contacts. Both friction and wear were markedly reduced upon the formation of these carbon tribo-films. No special surface modification was required to effect such dissociation. Therefore, these surface-active additives

42

provide in situ on-demand lubrication of surfaces operating in the boundary lubrication regime. 2:20 pm - 2:40 pm In-Situ Study of ZDDP Antiwear Tribofilm Growth in Nanoscale Single-Asperity Sliding Contacts: The Role of Temperature and Stress N. Gosvami, J. Bares, F. Mangolini, University of Pennsylvania, Philadelphia, PA, A. Konicek, D. Yablon, ExxonMobil Research and Engineering, Annandale, NJ, R. Carpick, University of Pennsylvania, Philadelphia, PA Zinc dialkyldithiophosphate (ZDDPs) have been used as antioxidants and antiwear agents in engine oils since the 1940s. The generally accepted view of ZDDP's antiwear mechanism is that the additive reacts at sliding interfaces to form protective tribofilms. However, the high amount of P, S, and Zn in these additives can degrade the efficiency of the catalytic converters. The replacement of ZDDPs is thus highly desired, and this requires a thorough understanding of the tribofilm growth mechanisms and antiwear properties. I will present a novel approach based on atomic force microscopy for visualizing and quantifying ZDDP tribofilm formation in-situ in single asperity contacts with controlled loading and nanometer-scale resolution [1]. Experiments reveal that sliding leads to nucleation and growth of robust films with a pad-like lateral structure, similar to macroscopic observations. The growth rate increases exponentially with temperature and contact pressure, in agreement with reaction rate theory. This is the first direct confirmation and quantification of asperity-level formation of such films, enabling us to directly compare with atomistic predictions and other possible proposed mechanisms. [1] Gosvami, N.N., Bares, J. A., Mangolini, F., Konicek, A.R., Yablon D.G., and R. W. Carpick. "Mechanisms of Antiwear Tribofilm Growth Revealed in situ by Single Asperity Sliding Contacts," Science, 348, 102 (2015). 2:40 pm - 3:00 pm The Antiwear Performance of Molybdenum Disulfide Greases Using 4 Balls Wear Tests Under Extreme Pressure and Optimized Loading at Different Rotational Speeds G. Nehme, University of Balamand, Koura, Lebanon The use of Molybdenum Disulfide (MoS2) greases in extreme pressure applications is increasingly important. Research described here is aimed at providing good friction and wear performance while optimizing different loading conditions. Technical grade molybdenum disulfide is used since it is very effective in extreme pressure situations. Two scheduled loads programmed directly in Plint machine software were used to investigate and examine the lithium base grease wear behaviour with and without molybdenum disulfide (Schedule or variable load # 1: 392 N-785N-392N-785N, and schedule or variable load # 2: 785N-392N-785N-392N). These variable loads are used at two different speeds of 600 and 1200 rpm and are compared to steady state loads of 392N and 785N for the same time duration and test conditions. The 4 ball wear tests were conducted using chrome-plated steel balls ( Aircraft Grade E52100) and following ASTM 2266, the wear behaviour under different loading conditions for a total of 36000 revolutions was examined. The grease was heated to 75°C and different Design of Experiment (DOE) conditions were followed. The goal of this study was to examine the variable load conditions and their influences on the wear properties of lithium base grease under different MoS2 concentrations. Results indicated that wear was largely dependent on the loading and

43

speed conditions. It is believed that a reduced amount of MoS2 greases perform better under schedule load # 2. 3:00 pm - 3:40 pm - Break 3:40 pm - 4:00 pm Structural and Nanomechanical Characterizations of Antiwear Films Fabricated From a Novel Nano-additive in Nanoscale Sliding Contact I. Lahouij, H. Khare, N. Gosvami, A. Jackson, University of Pennsylvania, Philadelphia, PA, Z. Chen, G. Cooper, Pixelligent Technologies LLC, Baltimore, MD, R. Carpick, University of Pennsylvania, Philadelphia, PA Integration of nanoscale materials into tribological systems has been driven over the last two decades by the wide range of potential benefits. In lubricants, several types of nanoparticles have been considered as a potential candidates for the reduction or replacement of ZDDPs, which are used for their anti-wear benefits in spite of their drawbacks related to emissions. Alternatives under consideration are nanoparticle additives, whose anti-wear performance will depend on the properties of the tribofilms formed in the contact. Thus, a comprehensive understanding of tribofilm properties is essential to elucidate the formation process and to optimize the anti-wear performance. The present work examines the structural and mechanical properties of tribofilms formed from zirconia nanoparticles (ZrO2) dispersed in oil. Tribofilms are generated in an oil-immersed nano-scale contact using an AFM. Structural characterization of the tribofilms are performed using cross-sectional TEM imaging, electron diffraction, and EDS analysis, which together enable the identification of the structure and chemical composition of the tribofilm. This elucidates the tribofilm formation process, which is crucial for understanding, predicting, and optimizing the anti-wear properties of the nanoparticles. Further, mechanical property characterization is performed using nano-indentation and indicates a much higher modulus and hardness than values reported in literature for tribofilms formed from ZDDP. 4:00 pm - 4:20 pm Modeling Nanoscale Wear of an Atomic Force Microscope Tip during Run-in X. Hu, University of California Merced, Merced, CA, V. Altoe, Lawrence Berkeley National Laboratory, Berkeley, CA, A. Martini, University of California-Merced, Merced, CA Nanoscale wear between a scanning probe tip and substrate is of fundamental importance in nanoscale measurement and manufacturing. In this work, molecular dynamics (MD) simulation is employed to study the nanoscale wear of a silicon atomic force microscope (AFM) tip with a native oxide scanning against on a sapphire substrate at room temperature. In MD simulations, the size and shape of the tip apex and the crystallographic planes in contact are defined to be comparable to those observed from transmission electron microscopy. Model wear is then compared directly to that measured in AFM experiments after tens of nanometers of sliding. Such comparisons provide insight into the mechanisms of nanoscale wear during the initial sliding period.

44

4:20 pm - 4:40 pm Friction at the Nanoscale: Dislocations and In-Situ Studies L. Marks, Northwestern University, Evanston, IL Friction, wear and chemical reactions during sliding are pervasive phenomena, and while many details have been known and understood empirically at the macroscale for centuries, the details at the nanoscale remain obscure. Most approaches have employed constitutive models for macroscopic mechanics at the nanoscale, but this has problems; the constitutive models are generalizations for the collective behavior of nanoscale defects such as dislocations, and as the size is reduced there will be a transition from collective to single defect behavior. Rather than this traditional top-down approach, an alternative is to consider the problem from the bottom-up, i.e. reformulate friction and wear processes based upon the nanoscale behavior. This work will focus upon progress in this approach, ranging from early work on describing friction via the sliding of interfaces involving misfit dislocations to more recent work where in-situ observations of these processes show that at the nanoscale sometimes the continuum approaches are valid, but in some cases there are completely new processes taking place which require a rethinking of what friction and wear are.

Session 3E - Monday, October 26, 2015 Gray's Peak B

Materials Tribology IIIa

Session Chair: C. Yeo, Mechanical Engineering, Texas Tech University, Lubbock, TX Session Vice Chair: TBD 1:40 pm - 2:00 pm Modelling and Simulation of Micropitting A. Oila, C. Lung, Newcastle University, Newcastle upon Tyne, United Kingdom We have seen in recent years valuable contributions to a better understanding of micropitting but a solution to prevent this form of surface contact fatigue has not yet been found. Preventive solutions might be difficult to identify unless a mechanism capable to describe the initiation and propagation of the observed cracks was firstly developed. A significant amount of experimental results is available in the published literature regarding the conditions under which micropitting occurs and progresses. A number of simplified models have also been proposed but generally they do not consider the changes in material properties caused by microstructural changes. We developed a micropitting model which takes into account the evolution of steel microstructure under lubricated conditions. The microstructure has been investigated by electron microscopy such as Scanning Electron Microscopy (SEM), Electron Backscattered Diffraction (EBSD) and Transmission Electron Microscopy (TEM) and mechanical properties have been determined by nanoindentation. The contact surface was investigated by optical profilometry, SEM and X-Ray Photoelectron Spectroscopy (XPS). The proposed mechanism is based on the results from the above investigations and first principle calculations of material properties combined with Finite Element Analysis of the contact region. The model shows agreement with the experimentally observed features of micropitting.

45

2:00 pm - 2:20 pm The Synergistic Antiwear - Frictional Properties and Tribological Mechanisms of Organic Tungstate Compound with Zinc Dialkyldithiophosphate J. Hu, S. Yang, X. Zhang, oil institute, Xuzhou, China The synergistic antiwear and friction reducing properties of oils containing sulfur- and phosphorus-free tungstate compound (SPFTC) with zinc dialkyldithiophosphate (ZDDP) were evaluated by four ball tester. The results show that the combination of organic tungstate compound and ZDDP exhibits good synergistic antiwear and friction reducing properties. Moreover, at the same concentration of ZDDP with different alkyl groups, there was an different optimum SPFTC concentration for better antiwear and friction reducing properties. when mc concentration exceed this optimum valves, the antiwear and friction reducing properties of lubricants were not improved obviously. However, these properties were affected significantly by ZDDP type, while the effect of ZDDP type on these properties became small at higher MC/ ZDDP ratios. Especially, the combination of mc with ZDDP containg primary C8 alkyl groups is very effective on tribological behaviours under lower dosage of SPFTC added to oils. Finally, the surface analysis indicated that tungstate, s atoms are distributed evenly on the wear scar, which contribute to improve the tribological properties of lubricants. 2:20 pm - 2:40 pm Surprisingly Low Wear Behavior of Gallium Nitride B.A. Krick, G. Zeng, Mechanical Engineering & Mechanics, Lehigh University, Bethlehem, PA C. Tan, N. Tansu, Lehigh University, Bethlehem, PA In recent years, gallium nitride (GaN) coatings have been of paramount interest to several research communities because of their remarkable semiconducting properties. One major unexplored aspect of GaN is the tribological performance of the crystalline material. Our studies on the wear of metal organic chemical vapor deposited (MOCVD) GaN coatings have revealed several surprising results: 1) The wear rate of gallium nitride is remarkably low (less than 10-8 mm3/Nm) under contact pressures as high 1.94 GPa. 2) Wear of GaN shows strong crystalline dependence that can be explained by simple energetic modeling of the crystalline structure. 3) Wear of GaN is a strong function of many other factors, including humidity, coating quality, doping levels and alloy composition. 2:40 pm - 3:00 pm Investigations into Seizure Behaviour of Pb-free Engine Bearing Materials Under Dry Condition D. Gebretsadik, J. Hardell, B. Prakash, Luleå University of Technology, Luleå, Sweden Due to new environmental regulations, Pb-free engine bearing materials are becoming more common and there is a need for studying their tribological performance. Under severe and non-ideal operating conditions, failure due to seizure can occur in engine bearings. In this work, seizure behaviour of different multi-layered engine bearing materials has been studied by using a block-on-ring test set up. These materials included Al-Sn based lining with no overlay, bronze lining with Polyamide-imide (PAI) based overlay containing MoS2 and graphite, bronze lining with two overlays of Al-Sn based and PAI based overlay, bronze based lining with Sn-based

46

overlay and bismuth (Bi) containing bronze with Sn-based overlay. Tests were performed by progressively increasing the load in a stepwise manner at a constant speed under unidirectional dry sliding conditions. Bronze based lining with a PAI based overlay containing MoS2 and graphite did not exhibit seizure up to a load of 475 N. For Al-Sn based lining without overlay, seizure occurs at relatively lower load of 125 N. In most cases, there is material transfer onto the counter surface test ring. The test materials, counter surfaces and the wear debris were analysed using SEM incorporating EDS with a view to explain the seizure mechanisms. 3:00 pm - 3:40 pm - Break 3:40 pm - 4:00 pm Scuffing Factor and Scuffing Failure Mapping C. ZHANG, Shanghai University, Shanghai, China This article defines a scuffing factor, the ratio of the temperature-dependent shear strength of the material to the surface tangential traction corresponding to the initial scuffing, and describes industrial applications of its contour plot for scuffing failure mapping. The scuffing factor reflects interaction among the related distinct mechanisms of wear and the inaccuracy in modeling, and involves material properties, geometry, roughness, contact degree, and operating conditions. The surface tangential traction is taken by the product of the frictional coefficient and the average contact pressure from the relationship between the average contact pressure and the average gap based on the contact model. The calculated flash temperature is used to determine near-surface material temperature. A set of the contour plots of the scuffing factors in the mapping show scuffing failure regions, the variation ranges of the combinations of the frictional coefficients, material properties, geometrical characteristics, and roughness. 4:00 pm - 4:20 pm Experimental Investigations on the Tribological Effects of Alumina-nanofluids in a Flow-through Test-rig G. Molina, F. Aktaruzzaman, V. Soloiu, M. Rahman, Georgia Southern University, Statesboro, GA Nanofluids (colloidal suspension of nano-size-powders in a base liquid) are being considered as alternative fluids in heat-exchangers because of their enhanced thermal properties. The authors previously investigated nanofluid-led surface-effects on heat-exchanger materials with accelerated jet-impingement tests. But the interactions on same solid-fluid systems are unknown when lower-speed flows are parallel to surfaces (as in typical heat-exchangers conduits). Therefore, experimental research was conducted to assess nanofluid tribological interactions by employing the author's developed ad-hoc flow-through test-rig and several evaluation tools. In this research, wear and erosion effects has been studied for aluminum and copper in this pipe-flow system with distilled water and its alumina-nanofluid (of 2%-volume of alumina nanopowder in distilled water) and low-speed fluid flows (of 1 m/s). The results are presented on the observed substantially different surface modifications when same tests are conducted on the two materials, and by both the base fluid and its alumina-nanofluid. Measured roughness, removed-material by weighing, and optical-microscopy are employed to obtain insights on the

47

possible processes of surface-change.

48

Session 4A - Tuesday, October 27, 2015 Mt. Elbert A

Fluid Film Lubrication

Session Chair: Bart Raeymaekers, University of Utah, Salt Lake City, UT Session Vice Chair: TBD 10:20 am - 10:40 am Effects of Inertia Forces of Air Flow on Bearing Characteristics of Small-Sized Aerostatic Circular Thrust Bearings with Single Feed Hole K. Ishibashi, S. Yoshimoto, M. Miyatake, Tokyo University of Science, Katsushika-ku, Japan Many researchers investigated aerostatic bearings for small-sized machines with the outer diameter of less than 10 mm such as micro gas turbines and micro cutting machines. In these small-sized aerostatic bearings, the distance between feed holes and bearing edges usually becomes very short and less than 5 mm. This means that the velocity of air flow in the bearing clearance becomes very fast and easily exceeds supersonic velocity. Accordingly, it is expected that the inertia forces of air flow largely affect the bearing characteristics of small-sized aerostatic bearings. In this paper, the static and dynamic characteristics of small-sized aerostatic circular thrust bearings with single feed hole and 10 mm outer diameter were investigated numerically and experimentally. In numerical calculations, the Navier-Stokes equations, equation of continuity and equation of energy were simultaneously solved by using the finite element method(ANSYS), taking into account the inertia forces of air flow in the bearing clearance. It was confirmed that the inertial effect had the influence of raising the damping coefficient of aerostatic bearings, and that the numerical results showed good agreement with experimental results. 10:40 am - 11:00 am Challenges in Hybrid Hydrodynamic Theory of Lubrication: Theory and Experiment A. Kornaev, L. Savin, State University ESPC, Oryol, Russian Federation, E. Kornaeva, State University — Education-Science-Production Complex, Oryol, Russian Federation The duality of the nature of the hydrodynamic lubrication is in the fact that its function is to lower the friction, and its cause is the presence of friction. The friction force is connected with the lifting force, so the idea of the lubricant modification is in the search for the means of lowering the friction force to a greater extent than the lifting force. It is theoretically obtained that the lubricant, viscosity of which in the area of the flow is inhomogeneous in a specific way, can lower the friction without a significant change in a load capacity. On the basis of variational principles of continious media mechanics a mathematical model and a simulation program of the basic characteristics of the fluid-film bearings were developed in case of complex rheology media lubrication. The comparative results are presented for the basic known rheological models and the developed hybrid models. By means of calculation the rheological model was determined for such media which combines a number of known rheological models of the fluids and hard bodies in a new hybrid form. A new method and a device were developed to measure the viscosity of the media with complex rheology. Presently, the experimental research is carried out

49

on the lubricants with various types and concentration of the superdispersed additives, the size of which is significantly smaller than the thickness of the lubricant film. Some positive effects were obtained when using the oil with the fullerene additives. 11:00 am - 11:20 am Active Hybrid Bearings as Mean of Rotor Motion Control in Complexly Loaded Systems D. Shutin, L. Savin, A. Babin, R. Polyakov, State University - ESPC, Oryol, Russian Federation Some rotor systems operate under complex loads, e.g. when the value of imbalance or other external forces changes over time during the operation. Under such conditions the fluid-film bearings can often not provide the necessary quality level. It is possible to eliminate the early wear of bearings in such cases by means of active bearings where the targeted change in some operational parameters allows to adjust the position of the rotor in the bearing. In the hybrid bearings such scheme can be implemented by controlling the lubricant supply pressure in each feeding chamber by using the electrohydraulic devices. The developed and numerically solved mathematical model of an active hybrid bearing is based on a joint solution of Reynolds equation, flow balance equation, the motion equations for a single mass system and the equations of a control system. The implemented complex of calculational and physical experiments allowed to produce the verification of the mathematical model, which showed a fine compliance with the modeling results, and to justify its further application in research on the systems in question. The evaluation of the effect of the system and operational parameters on the displacement of the rotor under different load modes allows to make a conclusion on the feasibility of the principles, which the active hybrid bearings are based on. They can be applied in complexly loaded rotor systems decreasing the negative effect of the previously mentioned factors.

Session 4B - Tuesday, October 27, 2015 Mt. Elbert B

Surface Science IV

Session Chair: TBD Session Vice Chair: TBD 10:20 am - 10:40 am The Effect of Lamination and Composition on the Mechanical Properties of Tin-based Metallic Coatings for the Tribological Applications of Engine Bearing Y. Zhang, I. Tudela, R. Verbickas, M. Anand, I. Kerr, Daido Metal European Headquarters, Ilminster, United Kingdom In this study a laminated tin multilayer coating and a composite tin-TiO2 coating manufactured by electrodeposition were proposed aiming at improved mechanical properties for the tribological application of internal combustion engine plain bearings. The compositional and microstructural properties of the coatings produced under various conditions have been investigated using Wavelength X-ray Fluorescence Spectrometry (W-XRF), Scanning Electron

50

Microscopy (SEM) and Focus Ion Beam Scanning Electron Microscopy (FIB-SEM). The mechanical and tribological performances of the coatings were assessed on various tribometers and simulated engine testers and then compared with an existing tin alloy coating. The results showed the performances of tin multilayer coating and tin-TiO2 composite coating have been substantially increased. The coatings after test were characterized using microscopic methods to understand the mechanism behind the performance improvements. 10:40 am - 11:00 am Effects of Lubricant Materials on Light Contact Between Dynamic Fly-height Control Sliders and Disk Surfaces in Hard-disk Drives N. Tagawa, Kansai University, Suita, Japan We investigated the effects of ultra-thin liquid lubricant film materials on light contact between sliders and disk surfaces using dynamic fly-height (DFH) control sliders. Three different lubricants (Ztetraol2000, D-4OH, and QA-40) were used to evaluate the lubricant pickup by the slider, lubricant wear, and slider wear. QA-40 exhibited the largest pickup volume; the pickup volumes for Ztetraol2000 and D-4OH were smaller but almost the same. Regarding the lubricant wear, QA-40 also exhibited the largest lubricant depletion depth. The depletion depths for Ztetraol2000 and D-4OH were smaller but not by a significant margin. In addition, QA-40 exhibited the largest slider wear, and Ztetraol2000 exhibited the smallest. It was found that lubricant pickup, lubricant wear, and slider wear under light contact conditions depended on the lubricant materials and were affected by the conformation of the lubricant molecules. The mechanism underlying this dependency was investigated. The experimental results obtained under light contact conditions for QA-40 when the lubricant was approximately one monolayer thick were attributed to the lack of robustness of the bonded fraction of the QA-40 lubricant molecules under a shear force. Therefore, it is clearly important to reduce the lubricant wear—particularly the bonded lubricant wear—to achieve a head-disk interface with high reliability under light contact conditions. 11:00 am - 11:20 am Determining the Effect of Retained Austenite Levels in Carburized AISI 8620 Steel on its Wear Behavior Under Dry Sliding Conditions S. ROY, S. Sundararajan, Iowa State University, Ames, IA Retained austenite (RA) is one of the crucial factors that affect the wear and fatigue behavior of steel. RA can be transformed to martensite or bainite depending on loading condition, contact pressure and other factors. Although several studies have been conducted to investigate the effect of RA on wear under specific materials & conditions, there is still a lack of clarity in observed trends and mechanisms involved. The objective of this study is to investigate the effect of RA on the sliding wear behavior of carburized AISI 8620 steel. This particular material is commonly used in drivetrain components and can undergo sliding or rolling under high contact conditions. In particular RA was varied by varying carbon potential (0.45% to 1.05%) during carburizing as well as by employing different end-quenching routes to maximize our anticipated range of RA. RA of the samples was measured using X-ray diffraction. Wear tests were carried out using a ball on flat reciprocating micro-tribometer designed to produce hertzian pressures between 5.2-7.9 GPa between a diamond probe and samples. Samples were analyzed using scanning electron

51

microscopy and non-contact profilometry to observe wear behavior and mechanisms. It was observed that beyond a particular hertz pressure, an increase in RA helps to increase the abrasive wear resistance of the steel. Ploughing of material induces work hardening on surface which results positive environment for transformation of austenite to martensite. 11:20 am - 11:40 am Mechanical Durability and Frictional Behaviour of Layer-by-Layer Superhydrophobic Coatings T. Young, S. Sundararajan, H. Ceylan, S. Kim, J. Jackson, A. Locurto, P. Barthiban, Iowa State University, Ames, IA The self-cleaning and anti-wetting properties of superhydrophobic surfaces can increase the operational lives of weather-exposed infrastructure such as oil platforms and fishing vessels. More recent studies have focused on superhydrophobic surfaces that reduce or completely stop the accretion of ice and snow on power lines and aircraft that operate in cold regions. Concrete pavements that experience extreme icing conditions and numerous freeze-thaw cycles are perfect candidates for superhydrophobic coatings. This study evaluated the mechanical durability and tribological behavior of candidate coatings for superhydrophobic concrete pavement applications. Layer-by-layer coatings composed of selected micro/nanoparticles (polytetrafluoroethylene (PTFE), polyetheretherketone (PEEK) diatomaceous earth (DE), and zinc oxide (ZnO)), and epoxy were spray-deposited on aluminum substrates. The extent of superhydrophobicity was assessed by measuring the static water contact angle on coated concrete specimens. A ball-on-flat micro tribometer was used to evaluate the fiction and wear resistance of the coatings under dry siding conditions. Ramp load tests were used to assess the friction coefficient on coated and uncoated substrates while reciprocating wear tests were conducted using a steel probe. A contact profilometer was used to measure the roughness, thickness and wear track depths of the coatings. The viability of using the materials in this study as coatings on pavement is discussed. 11:40 am - 12:00 pm Identification of the Mechanical Properties Gradient in the Tribologically Transformed Surfaces S. Descartes, INSA-Lyon / Université de Lyon, Villeurbanne, France, D. Tumbajoy Spinel, G. kermouche, Mines Saint Etienne, Saint Etienne, France, J. Bergheau, Université de Lyon / ENISE, Saint Etienne, France To improve the engineering systems performances, the wear of surfaces of parts in relative motion could be reduced by improving the functional properties of surface. Taking the reasoning one step further, the control of wear will go through the "design" of surfaces, especially of near-surface layers, of the spare parts. Wear processes are the results of physical-mechanical phenomena distributed into three phases: conception (material transformation), birth (detachment of particles) and life (flow, ejection) of wear particles. The objective is to focus on the conception phase, i.e. on the formation of Tribological Transformed Surfaces (TTS). In these near-surface layers (over a maximum thickness of a few tens of µm), tribological stresses induce extremely deformed microstructures. A critical issue is to measure the constitutive laws of TTS, which are required as input parameters for tribological contact models. To assess locally to the

52

mechanical properties of TTS, appropriate nanomechanical testing, such as nanoindentation and micropillars compression, has been used. Focus Ion Beam microscopy was used to locate precisely the micropillars and to machine them. Moreover when reaching the surface from the bulk, the TTS microstructure becomes finer, leading to a variation of mechanical properties. Therefore special attention has been paid to the identification of the mechanical properties gradient by nano-indentation.

Session 4C - Tuesday, October 27, 2015 Pikes Peak

Biotribology I

Session Chair: A. Pitenis, Mechanical and Aerospace Engineering, University of Florida, Gainesville, FL Session Vice Chair: D. Burris, University of Delaware, Newark, DE 10:20 am - 10:40 am Effect of Immobilized Proteoglycan 4 on Contact Lens Hydrogel Surface Properties and Lubrication M. Samsom, University of Calgary, Calgary, AB, Canada, M. Korogiannaki, McMaster University, Hamilton, ON, Canada, L. Subbaraman, University of Waterloo, Waterloo, ON, Canada, H. Sheardown, McMaster University, Hamilton, ON, Canada, T. Schmidt, University of Calgary, Calgary, AB, Canada Purpose: High friction may contribute to contact lens (CL) discomfort. Proteoglycan 4 (PRG4), a mucin-like glycoprotein, is a natural boundary lubricant found in the eye. PRG4 can be immobilized on a CL surface to produce bio-mimetic self-lubricating hydrogels. The objective of this study was to determine friction reducing ability, wettability and protein sorption of surface immobilized PRG4 on CL hydrogels. Methods: A model CL hydrogelolyhydroxyethylmethacrylate [pHEMA] and silicone hydrogel HEMA,Methacryloxypropyltris(trimethylsiloxy)silane [pHEMA TRIS] were prepared. Recombinant human PRG4 (Lubris) was immobilized on hydrogels using carbonyldiimidazole. Water contact angle (WCA) was measured using the sessile drop technique. Human serum albumin (HSA) and lysozyme sorption was measured using I125 radiolabeling. Friction was measured by sliding hydrogels against a human cornea (Lions Eye Bank) in a saline bath on a BOSE ELF3200 tester. Results: PRG4 reduced lysozyme and HSA sorption by 50-68% for both hydrogels. PRG4 reduced the WCA by 7% for pHEMA and 32% for pHEMA TRIS. PRG4 did not significantly reduce friction for pHEMA, but did so for pHEMA TRIS by 20%. Conclusion: PRG4 is an effective boundary lubricant on pHEMA TRIS, but not pHEMA, which may be due to different PRG4 surface adsorption confirmation. Conversely, PRG4 an effective anti-adhesive and WCA modifier for both CL hydrogels tested here. PRG4 is a promising CL additive/coating for improved material performance. 10:40 am - 11:00 am Tribological Rehydration: A New Lubrication Mechanism for Biphasic Materials

53

A. Moore, D. Burris, University of Delaware, Newark, DE Cartilage achieves its unusual tribological functionalities through a unique mechanism known as interstitial lubrication. Interstitial fluid pressure develops in response to tribological contacts to lower matrix stresses, friction, and wear by at least an order of magnitude. It has been shown that if the contact moves faster than the exudation rate of the interstitial fluid the loss of fluid from the contact can be prevented, unfortunately there are invariably periods of static loading and rest that occur throughout a person's daily routine. The question of how fluid is transported back into the cartilage remains unanswered. The goal of this study is to demonstrate that under physiological speeds cartilage can pump fluid back into the interface and rehydrate the contact. The mechanism, which we term tribological rehydration, is able to rapidly decrease friction and re-pressurize interstitial fluid. These findings suggest that conditions of high friction and wear in cartilage are short lived transient events. 11:00 am - 11:20 am Polymer Fluctuation Lubrication in Gemini Hydrogels A. Pitenis, J. Urueña, K. Schulze, R. Nixon, T. Angelini, W. Sawyer, University of Florida, Gainesville, FL Soft, permeable hydrogels are excellent synthetic materials for fundamental biotribology studies. Recent experiments with polyacrylamide (PAAm) hydrogels in a Gemini sliding contact has shown friction behavior at low speeds that is contrary to the classic Stribeck curve. The friction coefficients at these interfaces are minimum at low speeds and appear speed-independent. Here we explore the role of mesh size, ¾, on the low friction regime, termed thermal fluctuation lubrication and we also investigate the origins of a transition from this behavior at higher speeds to polymer relaxation lubrication. Mesh size was controlled by synthesizing PAAm hydrogels with varying polymer concentrations and crosslink density. Hydrogel samples were slid in a Gemini configuration submerged in ultrapure water using a custom-built pin-on-disk microtribometer over four orders of magnitude in sliding speeds. We discovered that increasing hydrogel mesh size or decreasing polymer concentration promotes lower friction coefficients. We observed that many hydrogel samples experienced a transition in friction behavior with increasing sliding speed, and the transition speed was found to correlate with the mesh size and relaxation time of the polymer network. 11:20 am - 11:40 am Tribological and Mechanical Characterization of Poroelastic Materials and its Correlation with Structural Composition Revealed by MRI A. Usta, M. Eriten, University of Wisconsin-Madison, Madison, WI Poroelastic materials are found in tissue scaffolds, water purification systems, fuel cells and cartilage. Poroelastic material properties define the load carrying, relaxation, damping and adaptation capacity of cartilage. Composition of solid fiber matrix, fluids and ions influence overall mechanical response of the cartilage. Quantitative magnetic resonance imaging (MRI) and spectroscopy provide in-vivo characterization of tissue composition. Therefore, these techniques are promising in early detection of weakening and lack of adaptation of the tissue. In this study, we first use mechanical and tribological characterization tools to retrieve local properties of model soft materials (hydrogels). We then apply those techniques to compare

54

quantitative MRI parameters to local poroelastic properties of porcine and human articular cartilage. Our results show unprecedented correlation between fiber-bound water quantities and indentation modulus of the cartilage. In addition, free water content in the tissue correlates well with the localized time-dependent response. 11:40 am - 12:00 pm A Model for Cartilage Tribomechanics: Validation and Application D. Burris, University of Delaware, Newark, DE, A. Moore, University of Delaware, Millsboro, DE The unique biphasic mechanics of cartilage are unlike those of any other material studied to date. As a result, standard tools like Hertz's contact theory provide little to no quantitative insight into the contact areas, pressures, or even friction forces involved during sliding. We recently developed an analytical contact mechanics model specifically for cartilage; however, until recently there was no way to validate the solution. This paper uses FEBio, a new open source finite elements package designed specifically for complex biological materials, for validation. We performed standard creep indentation experiments on cartilage. We fit the experimental response with our analytical solution and FEBio to obtain independent sets of predicted material properties. We find that the predicted compressive moduli, tensile moduli, and permeability values agree well, especially considering the differences in the details of the models used. To our knowledge, this is the first direct comparison of any two cartilage mechanics models; the agreement observed serves to validate both models. More importantly, the results indicate that our analytical solution, which can be used almost as easily as Hertz's solutions, provides reliable predictions of the contact response of cartilage to dynamic tribological conditions.

Session 4D - Tuesday, October 27, 2015 Gray's Peak A

Energy/Environment/Manufacturing I

Session Chair: Y. Oyerinde, Chevron Phillips Chemical Co., Kingwood, TX Session Vice Chair: TBD 10:20 am - 10:40 am Highlights of Research Sponsored by the Department of Energy, Vehicle Technologies Lubricants' Program K. Stork, E. Bardasz, Vehicle Technologies Office, U.S. Department of Energy, Washington, DC Over last decade the DOE Vehicle Technologies Program had created multiple research thrusts aimed at understanding improvements in light duty vehicle/ heavy duty truck overall fuel consumption efficiency, reducing exhaust emissions and at developing sources of various gaseous, liquid and electricity based alternate fuels to reduce the consumption of petroleum derived fuels. Since lubricants' technologies can provide a vital role in reducing friction losses, prolonging vehicle and engine life, and preserving exhaust emissions systems performance, 2015 DOE lubricants' technologies program supports multidiscipline research in new base fluids, additives, performance testing, modeling fundamental rheology/lubrication knowledge and

55

creating correlation methods. Colaborative projects are conducted at national laboratories, universities, and private industry through direct funding and through competitive solicitations. This talk will describe the overall research portfolio and discuss data from selected the research projects. These results cover progress made in developing novel polymers for VI improvements, understanding the relationship between the results of bench screen tests and engine performance in the areas of friction and wear reduction, lubricant effects on combustion, and developing/optimizing tribochemical films to reduce friction, reduce wear, and improve fuel economy. 10:40 am - 11:00 am Recreation of Surface Initiated White-Etching Cracks, on a Benchtop Test Rig, by Varying Contact Severity B. Gould, University of Delaware, Wilmington, DE, A. Greco, Argonne National Laboratory, Argonne, IL White-Etching Cracks (WECs) are the leading cause of failure in bearings within wind turbine gearboxes. These failures incur large costs on turbine operators through component replacement, as well as extended downtime. WECs are thought to initiate in both the surface and the subsurface of wind turbine bearings, and form do to various drivers such as slip, impacts, lubricant chemistry, electrical current, and water contamination. Since the exact conditions which wind turbine gearboxes experience during steady and transient operation is highly debated, the formation mechanism of WECs in turbine gearboxes remains unknown. Previous work has shown that WECs can be reproduced in full- scale bearing test rigs through various drivers. However, in this paper, the authors will present the first work ever done which has led to the formation of WECs in a benchtop test rig, where postulated drivers such as slip can be varied, and their impact on the formation of WECs can be quantified. 11:00 am - 11:20 am Analysis of Bearing Under-loading as a Cause of Planetary Bearing Failure in Wind Turbines N. Garabedian, B. Gould, D. Burris, University of Delaware, Newark, DE It is reasonable to assume that planetary bearings in wind turbines fail prematurely due to uncharacterized load sources that overload the bearings. Recent studies showing correlation between fault-rates and wind shear conditions seem to support this conventional wisdom. We tested this hypothesis in a recent paper and showed that overloading and premature rolling contact fatigue are unlikely for a machine the Gearbox Reliability Collaborative has adopted as the analysis standard. In this paper, we analyze the loads on the planetary bearings of the same turbine under more typical operating conditions rather than extreme conditions. Quite surprisingly, we find that planet bearings are underloaded under the most typical operating conditions. This happens in a wind turbine because the design allows non-torque loads to be passed into the gearbox; these loads subtract from the torque loads causing underloading once per rotation under certain conditions. Interestingly, the conclusion that underloading and wear are more likely to contribute to premature bearing failure than overloading and fatigue is consistent with field observations, which indicate wear related failures in this particular application.

56

11:20 am - 11:40 am Effects of Lubricant Additives on Hydrogen Permeation Under Rolling Contact H. Tanaka, Kyushu University, Fukuoka, Japan This study describes effects of additives on hydrogen permeation into bearing steel under rolling contact. Rolling contact tests were conducted under oil lubrication in hydrogen. TOP, DBDS, ZDDP and MoDTC were used as lubricant additives. Thermal Desorption Spectrometry, TDS, was performed to measure the amount of permeated hydrogen just after rolling contact test. TDS analysis suggested that ZDDP was effective to prevent the hydrogen permeation. A protective film containing oxygen, phosphorus and sulfur was observed in test with ZDDP by Auger Electron Spectroscopy. The protective film may prevent the permeation of hydrogen into bearing steel. 11:40 am - 12:00 pm The Hypothesis and the Numerical Model of Electromagnetic Impact on White Etching Cracks in Bearing Steel M. Scepanskis, A. Jakovics, University of Latvia, Riga, Latvia, W. Holweger, Schaeffler AG & Co. KG, Herzogenaurach, Germany, B. Nacke, Leibniz University of Hanover, Hannover, Germany Despite the ongoing debates on influence of hydrogen uptake and penetration in the steel, pulsed and extraordinary fatigue on white etching cracks (WEC) formation in bearing steel SAE52100, the present work advocates an alternative hypothesis on electrothermal initiation of the WEC. Electrical current in bearings is generally associated with a breakdown through a lubricant film and circulation of a changed layer of polar molecules of additives attached on the race. A numerical model qualitatively shows penetration of the current into the subsurface of the inner ring due to induction effects. The hypothesis pointed out difference between electrical and thermal properties of elements of steel microstructure that lead sequentially to redistribution of current, resistivity heating, thermal expansion and deformations of the carbide particle. Appearance of a nano-void is also predicted by the model in the cases of the martensite and the bainite structures. The model also predicts higher probability of the WEC formation for the bainitic steel.

Session 4E - Tuesday, October 27, 2015 Gray's Peak B

Beyond the Cutting Edge I

Session Chair: N. Spencer, Laboratory for Surface Science and Technology, Zurich, Switzerland Session Vice Chair: W. Tysoe, University of Wisconsin-Milwaukee, Milwaukee, WI

Special Session

57

10:20 am - 10:40 am Beyond the Cutting Edge: Highlights from Tribology Letters W. Tysoe, University of Wisconsin-Milwaukee, Milwaukee, WI, N. Spencer, Laboratory for Surface Science and Technology, Zurich, Switzerland This symposium includes presentations by authors whose work has been the subject of "Cutting Edge" articles in the STLE magazine "Tribology and Lubrication Technology" that were co-written by Nicholas Spencer and Wilfred Tysoe. The authors will summarize the work from the Cutting Edge articles and present recent advances in the area. 10:40 am - 11:00 am Lessons from the Lollipop: Tribocorrosion, Biotribology, and Irregular Surfaces W. Sawyer, Research Institute of Industrial Science and Technology, Gainesville, FL Biotribology and tribocorrosion are often not included in wear predicting numerical or computational modeling efforts due to complexity in geometry, material removal rate variability, and the difficulties incurred with combining time-dependent removal processes like corrosion with cyclic volume loss from wear. The lollipop presents a well-known, accessible, but scientifically underexplored bio-tribocorrosion problem. Stress-assisted dissolution was discovered to be the dominating tribocorrosion process. A model of material removal was described and approached by coupling the intrinsically time-dependent process with a mechanically-driven process into a single cyclic volumetric material removal rate. This effort required the collection of self-reported wear data from 58 participants that was used in conjunction with statistical analyses of actual lollipop cross-sectional areas. Thousands of repeated numerical simulations of material removal and lollipop shape evolution were performed using a Monte Carlo process. The resulting computations were analyzed to calculate the average number of licks required to reach the Tootsie Roll ® center of a Tootsie Roll ® pop. 11:00 am - 11:20 am Mechanisms of Organic Friction Modifiers S. Campen , H. Spikes, Imperial College London, London, United Kingdom Friction modifier additives are becoming increasingly important in modern lubricants due to the need to reduce friction and thus increase the efficiency of machine components. The oldest but still most important class of friction modifiers are the organic friction modifiers. These are based on surfactant-like molecules comprising a long alkyl chain and a polar head group and they are generally believed to adsorb from solution in oil on to polar surfaces to provide a very thin, low shear strength film. Despite their longevity there is still considerable uncertainty about the nature of the surface films formed by organic friction modifiers and thus how they act to reduce friction. Recent work has suggested that the films formed by saturated alkyl chain additives may be quite different from those formed by unsaturated ones. This talk presents recent work aimed as understanding the nature and properties of the films formed by organic friction modifier additives. 11:20 am - 11:40 am Chemical and Mechanical Properties of the Uppermost Layer on Articular Cartilage

58

R. Crockett, Empa, Duebendorf, Switzerland Natural Articular cartilage is well know for its remarkable tribological properties and although large numbers of investigations have been carried out there are still a large number of conflicting theories concerning the mechanism of lubrication at the surface. In an attempt to shed some light on this subject we investigated the chemistry of the uppermost layer as well as the mechanical properties of this layer and the one below it. Much of the confusion surrounding varying results from tribological experiments results from the lack of a clear definition of where and what the surface is. As the uppermost layer could easily be removed with phosphate buffered saline, this was not considered to be an integral part of the cartilage and the layer below that was described as the surface. The uppermost layer was found to be gel-like with a very low elastic modulus. Chemical analysis showed a similar chemical composition to that of synovial fluid but with very different concentrations of each component. Proteins were present in much lower concentrations in the gel-like layer whereas the polysaccharide hyaluronan was present in much larger concentrations. It could not be determined whether this layer was formed at the end of loading and destroyed when reloading occurred. In order to determine the feasibility of such a mechanism, gel-like layers where formed using amphiphilic polymers, which were then studied in lab experiments as well as in computer simulations. 11:40 am - 12:00 pm Interfacial Properties of Soft Mateirals S. Perry, University of Florida, Gainesville, FL Soft surfaces, such as many natural tissues or synthetic polymeric hydrogels, present a number of challenges with respect to the characterization of interfacial properties. Predominantly, many of these surfaces rely upon the presence of water as a vital component of their structure. In addition, such surfaces are known to exhibit complex dynamics with respect to their composition and their interaction with the environment and contacting surfaces. Using a combination of atomic force microscopy and X-ray photoelectron spectroscopy we have investigated a range of soft interfaces regarding tribologically relevant properties. These include surface composition, compression modulus, and interfacial friction. Results will be presented highlighting the nature of approaches required to understand these important materials.

Session 5A - Tuesday, October 27, 2015 Mt. Elbert A

Machine Components

Session Chair: J. Streator, Georgia Institute of Technology, Atlanta, GA Session Vice Chair: TBD 1:40 pm - 2:00 pm Load Profiling of A Rolling Element Bearing Contact with Ultrasound W. CHEN, T. Howard, R. Dwyer-Joyce, University of Sheffield, Sheffield, United Kingdom To properly predict bearing fatigue life, accurate load data is needed since load applied by each

59

rolling element on a bearing raceway controls friction, wear and thus seizure. This study develops a novel technique to directly measure load transmitted by a rolling element to the raceway by using the time of flight (ToF) of ultrasonic reflections, after the success in using ultrasonic technique to measure film thickness in bearings [1-3]. The time of flight of ultrasound from the sensor to the raceway-roller contact depends on the ultrasound speed and the thickness of the raceway. Both of them are load dependent, acoustoelastic effect and deformation respectively, therefore, ultrasonic ToF is load dependent. In practical ultrasonic measurement for a rolling contact, the phase of the reflected wave changes with contact stiffness and in simple peak to peak measurement, this phase change appears as a ToF change which is of the same order of ToF change caused by deflection and speed change. In this work the Hilbert transform was used to remove this contact dependent phase shift. Experiments have been performed on a single row cylindrical roller bearing for a wind turbine epicyclic gearbox. ToF change under different load was recorded and used to determine the raceway deflection, which was then related to the bearing load using a simple elastic contact model. Measured load from ultrasonic ToF was compared with the applied bearing load with good agreement. 2:00 pm - 2:20 pm Optimizing Friction to Improve Fatigue J. Guevremont, G. Pollard, Afton Chemical Corporation, Richmond, VA Ball and rolling element bearings are widely used in industrial machinery and have received considerable attention and research focus recently due to premature failure of wind turbine bearings which has been associated with white etching cracks. The root cause of WEC is under debate, but there is some consensus that high stresses are involved. High load does not necessarily lead to high stresses in the material because the tribological properties of surfaces are related to their response to surface loading and their deformation behavior. To influence the deformation behavior, and in turn the surface and subsurface stress, one can change the material of the contact. But the lubricant can also impact the deformation in the contact by impacting friction or by coating the surface with a tribofilm. In this study, by careful additive selection, a set of fluids were designed to vary friction in the various ranges of the friction curve (namely boundary, mixed, and elastohydrodynamic regimes) for testing. By probing the frictional characteristics of the fluids by mini-traction machine (MTM) and the ability of the fluids to protect from fatigue by examination of a micropitting rig (MPR) end of test roller, a relationship between fatigue and friction regimes will be presented. 2:20 pm - 2:40 pm Analysis of Rough surface Spur Gear under Thermal Elastohydrodynamic Lubrication with Liquid-Solid Lubricants M. Mongkolwongrojn, King Mongkut' Institute of Technology Ladkrabang, Bangkok, Thailand This paper presents the characteristics of rough surface spur gear under thermal elastohydrodynamic lubrication with SAE 90 blended with Al2O3 nano-particles and with SAE 90 blended with MoS2 micro-particles. The time dependent modified Reynolds equation, elasticity equation,powder load carrying capacity and energy equation with initial conditions were formulated and solved numerically using a multigrid multilevel with full approximation

60

technique for an involute spur gear. In this analysis, the transitions from two pairs to one pair and vice versa are modeled as a step variation of load. The effects of particle concentration and surface roughness were examined in the region along the line of action of the meshing gear. The results show that particle concentration and surface roughness have significantly affected the film thickness, film temperature and friction coefficient. For SAE 90 blended with Al2O3 nano-particles, at approach point and at the point of load transition from two pairs to one pair, the film thickness increases due to the thermal enhancement of nano-fluid. Maximum film temperature and friction coefficient increase only slightly but minimum film thickness decreasess lightly with the increase of Al2O3 nanoparticle concentration. For SAE 90 mixed with MoS2 micro-particle, minimum film thickness increases but maximum film temperature and friction coefficient decrease with particle concentration.

Session 5B - Tuesday, October 27, 2015 Mt. Elbert B

Special Tribute to Fred Ling I

Session Chair: TBD Session Vice Chair: TBD 1:40 pm - 2:00 pm Optimized design of a Large Reversible Thrust Bearing C. Ettles, Bearing Sciences, Inc, Glenmont, NY The thrust bearing duty in a pump-turbine generator can be quite arduous, since the pad support system must be symmetrical about the center of the pad, yet the oil-film must converge adequately for either direction of rotation. Special care must be taken with large machines since the thermal and elastic deformation of the pads will increase non-linearly with size. Poorly shaped films can develop when a design standard is scaled-up to larger sizes. In this instance an upper limit of thrust bearing temperature was specified. Penalties would incur if this were exceeded. It is shown using a design code (GENMAT) that the best performance is achieved with a spring support arranged to give a convex film shape in the direction of sliding, and a slightly concave film in the radial direction. This is achieved by limiting the extent of the spring pack in the circumferential direction so that there are unsupported ‘overhangs' at the lead and trail edges. The radial concavity is arranged by having the spring pack extend edge-to-edge in the radial direction. The bearing has performed very well since commissioning. The original machining patterns are untouched after thousands of reversals under load. The pads appear as new. 2:00 pm - 2:20 pm Maximum von Mises Stress and its Location in Trilayer Materials in Contact C. Yu, Northwestern University, Evanston, IL, Z. Wang, Chongqing University, Chongqing, China, G. Liu, Northwestern Polytechnical University, Xi'an, China, L. Keer, Q. Wang, Northwestern University, Evanston, IL Trilayer materials consisting of a functional outer layer on a substrate containing one

61

intermediate layer are widely used in data processing devices, biomedical components, and mechanical elements. The recent analytical frequency response functions derived by the authors' group for the contact of multilayer materials stimulate novel deterministic modeling of frictionless and frictional contact involving a trilayer material system designed with various thickness and elastic property combinations. Displacements and stresses for point contacts are calculated effectively by employing the discrete-convolution and fast Fourier transform method based on the influence coefficients obtained from the analytical frequency response functions. The maximum von Mises stress and its location, which are critical information for understanding the material contact status, are thoroughly investigated for a wide range of trilayer materials. The results provide an informative guideline for the design of bilayer coatings without contact failure. 2:20 pm - 2:40 pm Experimental and Computational Thermal Modeling of In Vitro Pin on Disk Tests of Ultra High Molecular Weight Polyethylene K. Lewicki, D. Van Citters, Dartmouth College, Hanover, NH Background: Pin on disk tribometer testing of ultra-high molecular weight polyethylene (UHMWPE) is used as an initial standard for predicting in vivo wear rates. Bovine serum used as a lubricant in these tests is sensitive to changes in temperature and could be affected by frictional heating. It is important to understand how changing test parameters can affect the frictional heating of the system. Methods: A six-station multidirectional pin on disk tribometer was instrumented with needle type thermocouples to determine differences in temperature in the bovine serum for two size pins (6.35 and 9.5 mm) and two sliding velocities (0.04 and 0.08 mm/s) at a constant load (445 N). Changes in temperature and coefficient of friction were determined at each station. A computational model was created to predict temperature responses of the system. Results: Experimental results showed that significant differences existed between pin sizes and sliding speeds. The computational model was able to predict with practical significance the temperature change based on the sliding speed and pin size so researchers can determine appropriate testing parameters. Discussion: Frictional work is defined by the coefficient of friction, sliding speed, and the load of the system. Differences in temperature rise for pin size could be attributed to a statistically significant (p<0.001) difference in coefficient of friction while sliding speed directly affected the temperature rise of the system. 2:40 pm - 3:00 pm Constitutive Relations for Friction from Thermodynamic Laws and Consequences M. Bryant, University of Texas at Austin, Austin, TX Constitutive relations for friction force, normal force and friction coefficient are presented. A first thrust combines the laws of thermodynamics for a tribological control volume under non equilibrium conditions, to relate heat, energy, matter, entropy, and work of friction and normal forces. The equation sums multiple terms---each with a differential multiplied by a coefficient term---to zero. Thermodynamic considerations suggest that two of the variables of the differentials, internal energy and entropy production, must depend on the variables of the other independent differentials. Linear independence of differentials then renders equations that yield thermodynamic quantities, properties, and normal and friction forces as functions of the internal energy and entropy production, which in turn depend on the independent variables. Coefficient

62

of friction is then derived and nuances explored. A second thrust formulates dynamics of sliding, with friction coefficient and slip velocity as state variables. Differential equations were derived using newton's law for velocity and the Degradation Entropy Generation Theorem for friction coefficient to model changes to the sliding interface induced by friction dissipation. The solution reveals that the well known transition from static to kinetic coefficient of friction with respect to slip velocity, for dry and boundary lubricated sliding, is a property and consequence of system dynamics, and not a true constitutive relation. 3:00 pm - 3:20 pm Surface Temperature Modeling of Accelerating Heat Sources T. Blanchet, S. Lenihan, Rensselaer Polytechnic Institute, Troy, NY While compact temperature expressions are readily available for cases of heat sources moving across a surface at constant speed under steady-state conditions, it is uncertain whether such expressions may also pertain at a speed that only exists instantaneously under a heat source whose motion is accelerating. In response, surface temperatures were modeled in the case of a uniform band source with constant acceleration from rest, both in the case of a source whose strength is proportional to instantaneous speed (Coulomb friction) as well as in the case where the strength is constant, for example electrical contacts of relatively negligible friction. In both cases temperature distributions are eventually developed which may indeed be well-approximated using instantaneous speed in high-Peclet steady-state constant speed expressions, with surface temperature varying with the square root of distance from the leading edge of the band with maximum temperature therefore at the band's trailing edge. However at earlier stages of motion a broad ‘flat-top' region of uniform temperature instead exists, with this region having increased temperature over a region that becomes less broad and moves towards the trailing edge of the band with increasing time. The magnitude of this flat-top temperature may be well-described by a one-dimensional conduction model, which persists only until surface positions within the band when it started at rest are no longer overlapped by the displaced band.

3:20 pm – 3:40 pm Starved Hydrodynamic Gas Foil Bearings -- Experiment, Micromechanical Phenomenon and Hypotheses H. Heshmat, Mohawk Innovative Technology, Inc., Albany, NY In this paper, a hypothesis for the operating tribological mechanisms and phenomena occurring in compliant surface gas foil bearings subjected to low ambient pressure conditions, such as occur at high altitude or in soft vacuum, will be presented and discussed. Both theoretical and experimental evidence supporting the proposed hypothesis will be presented to show that, under low ambient pressure conditions (i.e., something akin to starved fluid film lubrication), the shaft is supported by a combination of hydrodynamic and morphological elements. The theoretical treatment of the compressible fluid film in a simple gas bearing is highly non-linear inand- of-itself, and especially more so when combined with a compliant surface supported on a frictionalelastic foil foundation. Adding a "molecularly starved gas film" to this highly nonlinear system, one encounters a very interesting and complex system that, heretofore, has not been considered. When operating compliant foil gas bearings in a near or soft vacuum, the term hydrodynamic may be considered oxymoronic in that there is little or no apparent fluid/gas to provide "a full hydrodynamic” action. However, theoretical and experimental evidence of

63

compliant surface foil gas bearings operating at low ambient pressures shows that they do continue to work and, in fact, can do so quite well given the appropriate compliancy and other factors, as yet to be discussed.

Session 5C - Tuesday, October 27, 2015 Pikes Peak

Biotribology II

Session Chair: D. Van Citters, Thayer School of Engineering, Dartmouth College, Hanover, NH Session Vice Chair: D. Burris, University of Delaware, Newark, DE 1:40 pm - 2:00 pm Examining the Relationship between Wear Rates and Testing Parameters for Pin on Disk Tests of UHMWPE K. Lewicki, D. Van Citters, Dartmouth College, Hanover, NH Background: Pin on disk tests of ultra-high molecular weight polyethylene (UHMWPE) are used as initial benchmarks for predicting the wear response in vivo. Many combinations of load, pin size, and sliding velocity have been reported for pin on disk tests of UHMWPE. However, due to the complex wear mechanisms of UHMWPE, varying these test parameters may affect the apparent wear rate. Methods: A 6-station multidirectional pin on disk tribometer was used to examine 2 average sliding speeds (0.08 and 0.04 m/s) and 2 pin sizes (6.35 and 9.5 mm) at a constant load (445 N) of clinically relevant UHMWPE. Mass lost was determined gravimetrically. Results: If all data for each pin size are combined, a significant difference is noted between small and large pins (p<0.001). Testing speed had less impact on the results, as there were no significant differences between the 2 tested speeds within the small or large pins. Variability in wear rates was at least 3 times less in the small fast pins, demonstrating this difference in variability was repeatable. Discussion: It is important to understand how testing parameters affect resulting wear data so that the optimal testing parameters are used. Additionally, when comparing values in literature, there may be discrepancies in wear rates due to testing parameters. This work supports the literature-based theory that contact area is the driving factor for wear in UHMWPE. Testing speeds are not shown to cause significant differences in wear rate. 2:00 pm - 2:20 pm Estimation of Tactile Feedback From Surface Properties Including Tribological Test M. Kim, Y. Lee, J. Park, Sungkyunkwan Univ., Republic of Korea, Swon-Si, Gyeong Gi-Do, Korea (the Republic of) Touch feeling is closely related with several of mechanical and chemical properties of human skin and material surfaces. For example, the surface topography, such as roughness, fineness affects to tactile sensibility of people, and also the compatibility between skin and surfaces are important factor to determine the frictional characteristics and emotional perception. In this paper, experiments were carried about twenty types of sample surface on which experimenter sliding his finger. From these, roughness, frictional and normal force, and also

64

vibration frequency were acquired. During the experiments, the atmosphere condition of room was maintained to not vary. In addition, this paper includes emotional feedbacks with quantitative form from 100 people who have various age, gender, and skin conditions. The relation between the surface properties and tactile sensitivity from survey are studied with numerical and statistical method and this paper suggested that experimental results can explain how people recognize many different signatures of material surfaces, and also when the experimental result are given, touch feedback of people can be expected. 2:20 pm - 2:40 pm Analysis of the Friction Induced Squeaking of Ceramic-on-ceramic Hip Prostheses Using a Pelvic Bone Finite Element Model Z. Hua, X. Yan, D. Liu, Shanghai University, Shanghai, China, Z. Jin, University of Leeds, Leeds, United Kingdom, X. Wang, Shanghai University, Shanghai, China Total joint arthroplasty is regarded as a significant advance in the treatment of painful and disabling joint pathologies. Ceramic-on-ceramic (COC) artificial joints have been shown to produce substantially less wear debris than traditional metal-on-polyethylene bearings. However, with the recent increase in popularity of COC bearing, postoperative audible squeaking has become a recognized clinical complication. Although the nature of squeaking is a multifactorial combination of interaction among patient, surgical, and implant, it is generally agreed that friction is the driving force inducing the vibration and sound emission. Thus, biotribologically induced acoustic issues have become the new problems for CoC artificial joints. In this study, a finite element model containing human pelvis, ceramic hip endoprosthesis and femur is established to analyze the mechanism of clinical squeaking phenomenon in ceramic-on-ceramic artificial joints. Complex eigenvalue method is used to study frictional induced dynamic response of the whole recon-pelvis. By comparing the vibration characteristics of all the components, the generation mechanism of squeaking is discussed. Results show that the main cause of the squeaking is the bending and torsional resonance of the femoral stem, while pelvis is involved in the noise emitting as well.

Session 5D - Tuesday, October 27, 2015 Gray's Peak A

Energy/Environment/Manufacturing II

Session Chair: Y. Oyerinde, Chevron Phillips Chemical Co., Kingwood, TX Session Vice Chair: TBD 1:40 pm - 2:00 pm Effect of Al2O3 Coating on Fretting Wear Performance of Zr Alloy K. Hartman, Argonne National Laboratory, Lemont, IL, S. Bhattacharya, Northwestern University, Evasnton, IL, M. Lorenzo Martin, O. Ajayi, A. Yacout, Argonne National Laboratory, Lemont, IL Fretting wear caused by flow-induced vibration (FIV) is one of the predominant tribological failure modes in nuclear power plants and industry. Examples of components in which fretting

65

can occur include steam generator tubes, fuel channel tubes; etc. Because of the safety and cost consequences of such failure, considerably effort is devoted to the mitigation of fretting problem. The bulk of the efforts have been devoted to analytical prediction of the failure. The current paper presents experimental evaluation of the effect of alumina (Al2O3) coatings produced by atomic layer deposition (ALD) process onto Zr-alloy (ZIRLO); a common nuclear fuel cladding alloy; on its fretting performance. Using a pin-on-flat contact configuration in a low-amplitude reciprocating contact, fretting performance of uncoated, Al2O3 coated and Al2O3 coated and heat treated samples were evaluated. Results of the study showed that Al2O3 coated alone provided slightly improvement in fretting wear resistance. However, coating combined with heat treatment produced two order of magnitude reduction in fretting wear of the Zr-alloy. Differences were also observed in the wear mechanism for coated and uncoated surfaces. 2:00 pm - 2:20 pm A Study of the Efficiency of Spur Gears Made of Powder Metallurgy Materials - Ground Versus Super-finished Surfaces X. Li, Royal Institute of Technologu, Stockholm, Sweden Power loss is one of the main concerns in gear transmission systems. In this study a recirculating power back-to-back FZG test rig was used to make an efficiency investigation of spur gears made of powder metallurgy gear material using two different surface manufacturing methods (ground and super-finished). The results were compared with previously presented results with standard gear material from the same test rig. The influence of material combination, surface roughness, rotational speed and transmitted torque on gear mesh efficiency and total efficiency of gearbox were analyzed in details. Higher surface energy combined with smoother surface lead to lower transmission efficiency of super-finished powder metallurgy gear combination in contrast to the results from the standard gear material. 2:20 pm - 2:40 pm Wear Properties of Pulsed Laser Micropolished Ti6Al4V and S7 Tool Steel Samples S. Chen, A. Usta, M. Eriten, University of Wisconsin-Madison, Madison, WI Ti6Al4V and S7 tool steel are widely used in structural, manufacturing and biomedical systems. Wear properties are critical in safe, reliable and cost-efficient use of those materials in many engineering systems. Pulsed laser micropolishing (PLuP) has a potential to emerge as a surface finishing process that could improve wear-resistance. In this process, pulses of microscale laser spots are used to melt small volume of material in the vicinity of free surface. Molten material will then experience high cooling rates leading to various microstructural changes such as hardening, which could further improve wear-resistance. In this study, we investigate the wear resistance of Ti6Al4V and S7 tool steel samples processed by pulsed laser micro polishing. We utilize an advanced nanoindenter/scratch system to obtain wear maps over areas comparable to single laser spots. By this, we are able to study the influence of heterogeneity in heating/cooling rates within a laser spot, and identify the influence of laser processing parameters on the wear properties. 2:40 pm - 3:00 pm

66

A Deterministic Friction-Based Efficiency Formalism for Engine Modeling E. Wornyoh, M. Rahman, F. Akresi, S. Iyiola, E. Asante-Asamani, University of Wisconsin-Milwaukee, Milwaukee, WI From the time of Leonardo da Vinci in the sixteenth century and even before then, the adverse effects of friction on the performance of labor-intensive tasks has been well known by humankind. Also, since tribology became a recognized scientific entity in the twentieth century, the study of friction, lubrication, and wear has gained and continues to gain more in depth and concerted approaches to query, understand, and mitigate the detrimental impact of friction on engine efficiency technologies. Undoubtedly, a sustainable, viable, and environmentally friendly engine efficiency technology will bolster engine innovations. Yet, an efficiency model that fundamentally incorporates the effect of friction is uncommon. Applying first principles techniques, we unveil a universal friction-based efficiency formalism that determines the thermomechanical efficiency during irreversible sliding in a power-stroke event. This efficiency protocol harnesses insights from fundamental conservation laws and will greatly enhance the efforts of engine efficiency innovators. We illustrate our approach with a prototype piston-cylinder engine.

3:00 pm - 3:20 pm Research on Friction Torque Analysis of Planetary Roller Screw Mechanism Considering Load Distribution F. Gan, X. Qi, D. Wang, Y. Fu, School of Mechanical and Automation Engineering , Beihang University, Beijing, China Based on the Hertzian contact theory, frictional moment of planetary roller screw mechanism (RSM) caused by elastic hysteresis, roller’s spinning sliding and differential sliding was analyzed, which were considering load distribution of roller threads. The relationship between friction torque of screw-roller pairs, nut-roller pairs and its input axial load were obtained respectively. Finally, the frictional moment of the screw pairs under the situation overstress will created at some localized contact surfaces were discussed. Results shows that the frictional moment caused by elastic hysteresis gives the greatest rise to the total frictional moment and that due to differential sliding can be ignored. The stress uniformity has great influence on the frictional moment.

Session 5E - Tuesday, October 27, 2015 Gray's Peak B

Beyond the Cutting Edge II

Session Chair: W. Tysoe, University of Wisconsin-Milwaukee, Milwaukee, WI Session Vice Chair: N. Spencer, Laboratory for Surface Science and Technology, Zurich, Switzerland 1:40 pm - 2:00 pm The Dirt on Da Vinci: Celebrating Friction Experiments Roughly 500 Years Later W. Sawyer, Research Institute of Industrial Science and Technology, Gainesville, FL

67

Leonardo da Vinci (1452-1519) is widely regarded as a visionary engineer of the Renaissance era. However, due to the delayed discovery of his notebook pages, his immense contribution to the field of tribology has only recently surfaced. From his notebooks, da Vinci's three observations that preceded the development of the laws of friction were uncovered: (1) the resistance of friction is proportional to applied load, (2) friction is independent of contact area, and (3) friction has a value of µ = 0.25. In this work, we put forth our best effort to reconstruct da Vinci's friction measuring apparatus, and based on his notebook illustrations we attempted to reproduce da Vinci's findings. For friction on wood, da Vinci's finding of µ = 0.25 was revealed, but only under specific conditions. 2:00 pm - 2:20 pm Elimination of Stick-Slip Motion in Sliding of Split or Rough Surface M. Varenberg, Georgia Institute of Technology, Atlanta, GA, Y. Kligerman, Technion - Israel Institute of Technology, Haifa, Israel Here, we present a mass-less quasi-static model of stick-slip phenomenon built exclusively on the difference between higher static and lower kinetic friction force. The model allows explaining the disappearance of stickslip motion when elastic surface slid in contact with rigid counter-face bears large amount of small outgrowths. Adjusting the model parameters, it is also possible simulating systems with different transient responses. The results obtained may also be helpful in understanding the variety of sliding behavior of different materials. 2:20 pm - 2:40 pm Recent Discoveries in Soft Water-lubricated Gemini Interfaces A. Dunn, University of Illinois at Urbana-Champaign, Urbana, IL, J. Urueña, A. Pitenis, R. Nixon, K. Schulze, University of Florida, Gainesville, FL, B. Krick, Lehigh University, Bethlehem, PA, T. Angelini, W. Sawyer, University of Florida, Gainesville, FL Tribological contacts in the human body such as the blinking eye or the articulating cartilage tend to be twinned pairs, or Gemini interfaces. Polyacrylamide hydrogels of over 90% water by mass were used in a self-mated ball-on-flat configuration to emulate this condition, and we found that at a low applied pressure, the measured friction coefficient was consistent and low, mu<0.06, over 1.5 orders of sliding speed. In contrast, a stiff impermeable surface introduced as either side of the sliding pair resulted in a return to more common lubrication behavior of higher friction at lower sliding speeds. When the contact was migrating across the hydrogel, a strong dependence on speed was identified; when contact area sat stationary on the hydrogel, a strong contact area dependence resulted. Recent work has focused on the Gemini aspect of friction between soft hydrated surfaces, but swept a much larger range of sliding speeds under a consistent applied normal load. This uncovered an eventual increase in friction coefficient at higher sliding speeds, with the lowest friction at the lowest speed. Most recently, friction between polyacrylamide hydrogels with controlled mesh sizes displayed a speed dependence, but the friction at lowest speeds depended upon the mesh size, with the largest mesh providing the least resistance to sliding. Thus, soft hydrated materials forming a Gemini interface exhibit lubrication behavior controlled by sliding speed and the size of the polymer mesh.

68

2:40 pm - 3:00 pm Beyond Simple Vapor Phase Lubrication -- Chemistry of Molecules Compressed and Sheared at Tribological Interfaces of Nano to Macro Scales S. Kim, Pennsylvania State University, State College, PA Tribology involves not only two-body contacts of two sliding solids, but it also involves third bodies where are sometimes intentionally introduced or inevitably created during the sliding or rubbing. The intentionally added third body could be lubricant oils or engineered additives designed to mitigate the friction and wear of the sliding contact. The inevitably added third body could be wear debris (solid particles) created during sliding. Even in the absence of any solid third-body between the sliding surfaces, moleculed adsorbed from the surrounding gas-phase environment can drastically alter the friction and wear behavior of solid interfaces tested in the absence of lubricant oils. This talk will address the last case: the effects of molecular adsorption on sliding solid surfaces both inevitably occurring due to the ambient test condition or intentionally introduced as a vapor phase lubricant. The talk will review how adsorbed molecules can change the course of wear and friction, as well as the mechanical and chemical behavior, of a wide range of materials over multiple scales (from nano to macro).

Author Index As of 8/21/15 – Subject to Change

69

A Abdo, J, 1A Adams, H, 1B Afanasiev, P, 1A Aizikovich, S, 3C, 3C Ajayi, O, 1A, 4D Akresi, F, 5D Aktaruzzaman, F, 1E Alazemi, A A., 1B Alazizi, A, 2B Albahrani, S, 1C Al-Sharji, H, 1A Altoe, V, 3D Amuzuga, K, 3B Anand, M, 4B Angelini, T, 4C, 5E Asante-Asamani, E, 2C, 5D B Babin, A, 4A Bair, S, 2A Bansal, J, 1A Bardasz, E A., 5D Bares, J A., 3D Barnhill, W, 3A Barthiban, P, 4B Bergheau, J, 4B Berkebile, S, 2E Bhattacharya, S, 4D Blanchet, T.A, Bluet, J, 1C Bodnarchuk, M, 1A Braun, M J., 4A Bryant, M D., 5B Burris, D, 1D, 1D, 1E, 4C, 4C, 4D C Campen, S, 4E Carpick, R W., 3D Celis, J, 2E Ceylan, H, 4B Chaise, T, 3B Chen, S, 5D Chen, X, 1C, 3B Chen, W, 5A Chromik, R, 1E Chung, Y, 3A, 3D Cosimbescu, L, 2A Crockett, R, 4E D

Dai, S, 3A Dandurand, D, 1A Dassenoy, F, 1A Delbé, K, 2E DellaCorte, C, 1E Denape, J, 2E Dench, J S., 1C Desanker, M, 3A Descartes, S, 1E, 4B Diann Y, H, 1D Dini, D, 1A, 3A, 3B Dorri Moghadam, A, 1D Drees, D, 2E Dunaevsky, V, 1B Dunn, A C., 5E Dureisseix, D, 2C Dwyer-Joyce, R, 5A E Erdemir, A, 2B, 2D Eriten, M, 4C, 5D Eryilmaz, O, 2B, 2D Ettles, C M., 5B Evans, J C., 2A Evans, R, 3C Ewen, J, 3A F Ferrato, M, 2E Fillot, N, 2C Fletcher, K A., 3A Furlong, O, 3B G Gao, H, 3A Gan, F.J., 5D Garabedian, N T., 1E, 4D García, P, 1A Garelick, K, 3A Garvey, M, 1B Garza, G T., 1A Gattinoni, C, 3A Georgiou, E, 2E Ghaednia, H, 3B Ghosh, A J., 3B Good, B, 1A Gosvami, N, 3D Gould, B J., 4D, 4D Greco, A, 4D Guevremont, J, 3A, 5A Gupta, a, 3A Gutiérrez, J, 1A

H

Author Index As of 8/21/15 – Subject to Change

70

Habchi, W, 2A Haidar, D, 1D Harish, T V., 2E Harris, K, 1D Hartl, M, 2A Hartman, K, 4D He, X, 3A Heyes, D, 1A Holweger, W, 4D Howard, T, 5A Hu, J, 3E Hu, X, 3D Hua, Z, 1D, 3C, 5C I Irigoyen, M, 1A Ishibashi, K, 4A Iyiola, S, 2C, 5D Izumi, T, 2B J Jackson, J, 4B Jackson, R L., 3B, 3B Jakovics, A, 4D Jeng, Y, 4A Jia, J, 1D Jiao, Y, 1D, 3C Jin, J, 3C Jin, Z, 5C Johnson, B, 3D K Kang, Y, 3C Keer, L M., 5B Kermouche, G, 4B Kerr, I, 4B Khare, H, 1E Kheireddin, B, 3A Kim, H, 2B Kim, M, 5C Kim, S H., 2B, 5E Kim, S, 4B Kligerman, Y, 5E Koganezawa, S, 1B Konicek, A, 3D Konopi, P, 2B Kornaev, A V., 4A Kornaeva, E, 4A Korogiannaki, M, 4C Kosasih, B, 3C Koyamachi, J, 2B Krick, B A., 1D, 3E, 5E Kudish, I I., 3C, 3C, 3C, 3C

L Laate, J, 2C Lafon-Placette, S, 2E Lee, Y, 5C Lenihan, S.P, 5B Leonard, D, 1C, 3A Lewicki, K, 5B, 5C Li, x, 5D Li, L, 2D Li, M, 1C, 3C Liao, Y, 2D Liu, D, 5C Liu, G, 5B Liu, P, 3A Liu, Q, 2D Locurto, A, 4B Lorenzo Martin, M, 1A, 4D Lozano, M, 1A Lu, J, 3A Lung, C, 3E Luo, H, 1C, 3A M Maldonado, D, 1A, 1A Mangolini, F, 3D Manning, M, 2A Manzi, S, 3B Marks, L, 3D Marks, T, 3A Martini, A, 1A, 1B, 2A, 3B, 3D Martinie, L, 2C Menezes, P, 1D, 3A Meyer, H M., 3A Miyatake, M, 4A Molina, G J., 1E Mongkolwongrojn, M, 5A Moore, A C., 1D, 4C, 4C Morgan, N M., 1C Morita, T, 3D Mosey, N, 3E Mueller, K M., 1C Murthy, N, 2E N Nacke, B, 4D Ndiaye, S N., 2C Nehme, G N., 3D Nelias, D, 3B Nixon, R, 4C, 5E Noble, B, 2A

O Oila, A, 3E

Author Index As of 8/21/15 – Subject to Change

71

Omrani, E, 1D, 3A Ovcharenko, A, 2A, 2D

P Papke, B L., 3A Park, J, 5C Patel, D, 2C Peña-Parás, L, 1A, 1A Perry, S, 4E Phan, H T., 1B Philippon, D, 1C, 2C Pitenis, A A., 1D, 4C, 5E Pollard, G, 3A, 5A Polyakov, R, 4A Price, M, 2D Putignano, C, 3B Q Qu, J, 1C, 3A Querry, M, 1C R Raeymaekers, B, 2A, 2D Rahman, M, 5D Rahman, M, 1E Raisin, J, 2C Rajeev, V R., 2E Ramasamy, U, 2A Ramirez, G, 2B, 2D Reeves, C, 3A Reiss, P, 1C Riggs, M, 2E Rohatgi, P, 1D, 3A Rostami, A, 2C ROY, S, 4B Ruicheng , B, 1D S Sadeghi, F, 1B, 3B Saha, S, 3B Saito, K, 2B Sakane, Y, 1B Samsom, M, 4C Sanda, S, 2B Savin, L, 4A, 4A Sawae, Y, 3D Sawyer, W, 1D, 4C, 4E, 5E, 5E Scepanskis, M, 4D Schmidt, T, 4C Schockley, J M., 1E Schulze, K, 4C, 5E Selby, T W., 2A Sheardown, H, 4C Shen, J, 1C, 3C

Shen, X, 1C, 3B Shi, L, 1C Shutin, D, 4A Soloiu, V, 1E Song, J, 2D Spencer, N, 4E Sperka, P, 2A Spikes, H, 4E Spikes, H, 3A Stork, K, 5D Streator, J, 2C Subbaraman, L, 4C Sugimura, J, 2B Sundararajan, S, 1A, 4B, 4B Song, W, 2D T Tagawa, N, 1B, 4B Taha-Tijerina, J, 1A, 1A Tanaka, H, 4D Tani, H, 1B Tieu, K A., 3C Tomaszewska, A, 2B Tudela, I, 4B Tumbajoy Spinel, D, 4B Tysoe, W, 1B, 3B, 4E U Urueña, J, 4C, 5E Usta, A D., 4C, 5D V VanBergen, W, 2A Van Citters, D W., 5B, 5C Varenberg, M, 5E Varghese, P, 2E Vasiliev, A, 3C, 3C Velarde, M, 1A Verbickas, R, 4B Vergne, P, 1C, 2C, 2C Volkov, S, 3C, 3C W Wang, Q J., 3A, 3D, 5B Wang, X, 1C, 1D, 3C, 5C Wang, Z, 5B Wang, Z, 3B White, D, 1A Wong, J S., 1C Wong, V, 3A, 3A Wornyoh, E, 2C, 5D

Author Index As of 8/21/15 – Subject to Change

72

X Xiong, X, 1C Xu, Y, 3B, 3B Y Yablon, D, 3D Yacout, A, 4D Yagi, K, 2B Yamaguchi, S, 2B Yamaguchi, T, 3D Yan, X, 5C Yang, B, 1D Yang, S, 3E Ye, J, 1D Yeo, C, 2D Yoshimoto, S, 4A Young, T J., 4B Yu, C, 5B Z Zhang, B, 2A Zhang, G, 2D Zhang, X, 3E Zhang, Y, 4B Zhang, C, 3A, 3A, 3E Zhou, Y, 1C Zhu, H, 3C