book of abstracts - cas · 2019-06-03 · institute of theoretical and applied mechanics, v.v.i.,...

Institute of Theoretical and Applied Mechanics, v.v.i.Czech Academy of Sciences

Book of AbstractsXVII th Youth Symposium on Experimental Solid Mechanics

Faculty of Transportation SciencesCzech Technical University in Prague

University Centre Telč, Telč, Czech Republic

June 6 th June 8th, 2019

Institute of Theoretical and Applied Mechanics, v.v.i., Czech Academy of Sciences

Faculty of Transportation Sciences, Czech Technical University in Prague

Book of Abstracts

XVIIth Youth Symposium on Experimental Solid Mechanics

University Centre Telc, Telc, Czech Republic

June, 6th - June, 8th 2019

supported by:

Czech Academy of Sciences

Czech Technical University in Prague

under auspices of:

International Measurement Confederation (IMEKO)

Editors: Daniel Kytyr, Tomas Doktor, Petr Zlamal

YSESM 2019, June 6th – June 8th, Telc, Czech Republic

Book of Abstract

Youth Symposium on Experimental Solid Mechanics 2019

Editors: Daniel Kytyr, Tomas Doktor, Petr Zlamal

Publisher:

Institute of Theoretical and Applied Mechanics

Prosecka 809/76

190 00 Prague 9

Acknowledgment:

The conference was supported by Grant Agency of the Czech Technical University in Prague (grant no.

SVK 44/19/F6) and by Czech Academy of Sciences in program “Support for research and educational

activities for youth researchers from abroad” (project no. VVAM-19-04). All the financial support is

gratefully acknowledged.

Sponsored by:

VUZ a.s.

40 pages, issue No. 1

ISBN: 978-80-86246-45-1

DOI: 10.21495/45-1

3


About YSESM 2019

The YSESM symposium provides a forum for young researchers and engineers, PhD students and students

dealing with subjects of experimental mechanics. The Symposium concentrates on current work in all areas

of experimental research and its application in solid and fluid mechanics. The topic will particularly concern

to:

• Conventional and Advanced Experimental Methods in Solid and Fluid Mechanics

• Non-Destructive Testing and Inspection

• Measurements in Material Science

• Computer Assisted Testing and Simulation

• Engineering Design Simulation

• Hybrid Methods, Experimental Techniques Numerical Simulation

• Optical Methods and Image Processing

• Measurements in Biomechanics

• Sensor Techniques for Micro- and Nano-Applications

YSESM 2019 - Local Organizing Committee:Tomas Doktor, Jan Falta, Ivana Kumpova, Daniel Kytyr, Michaela Neuhauserova, Petr Zlamal

YSESM 2019- Scientific Committee:Lajos Borbas, Matej Borovinsek, Tomas Doktor, Marc Gutermann, Stephen Hall, Daniel Kytyr, Dagnija

Loca, Zoltan Major, Giangiacomo Minak, Martin Reiter, Sascha Senck, Jacek Tarasiuk, Petr Zlamal

4


Symposium Programme

5


Schedule of Lectures

6


Contents

EVALUATION OF HOPKINSON BAR EXPERIMENTS USING SEVERAL DIGITAL IMAGE

CORRELATION TOOLS 9

M. Adorna, J. Falta, P. Zlamal, T. Fıla

A TEST BENCH FOR THE EXPERIMENTAL CHARACTERIZATION OF SOLID TRUCK

WHEELS: DESIGN, PROTOTYPE, AND VALIDATION 10

C. Barone, D. Castagnetti, A. Spaggiari, E. Dragoni, F. Ascari, F. Monica, A. Perrone

MECHANICAL AND OPTICAL INVESTIGATION OF LASER WELDED STRUCTURAL STEEL

PMMA HYBRID JOINT STRUCTURES 11

T. Csiszer, T. Temesi, L. Molnar

MULTIAXIAL INVESTIGATION OF PVC FOAMS AND ANALYSIS OF THE DEFORMATION

MECHANISM BY 3D-DIC 12

F. Concas, S. Diebels, A. Jung

HIGH STRAIN-RATE COMPRESSIVE TESTING OF FILLING MATERIALS FOR INTER-

PENETRATING PHASE COMPOSITES 13

T. Doktor, T. Fıla, P. Zlamal, P. Koudelka, D. Kytyr, O. Jirousek

IMPACT RESISTANCE OF COMPOSITES WITH DIFFERENT TYPES OF INCLUSIONS 14

K. K. Dudek

NUMERICAL MODELLING OF WAVE SHAPES DURING SHPB MEASUREMENT 15

R. Dvorak, P. Koudelka, T. Fıla

DIRECT MEASUREMENT OF REACTION FORCES DURING FAST DYNAMIC LOADING -

APPLICATIONS FOR SHPB AND ITS MODIFICATION 16

J. Falta, M. Adorna, T. Fıla, P. Zlamal

CUSTOM-MADE RHEOMETER FOR THE EXPERIMENTAL STUDY OF POLYURETHANE

RESIN PU9010 17

L. Fissore, S. Diebels

ADDITIVE MANUFACTURING PROCESS PARAMETER INFLUENCE ON MECHANICAL

STRENGTH OF ADHESIVE JOINTS, PRELIMINARY ACTIVITIES 18

M. Frascio, L. Bergonzi, F. Moroni, A. Pirondi, M. Avalle, M. Monti, M. Vettori

IN-SITU COMPRESSION TEST OF ARTIFICIAL BONE FOAMS IN CONTROLLED ENVI-

RONMENT USING X-RAY MICRO-COMPUTED TOMOGRAPHY 20

J. Glinz, D. Kytyr, T. Fıla, J. Sleichrt, A. Schrempf, D. Furst, J. Kastner, S. Senck

REFRACTIVE-INDEX-CORRECTED 3D SUPER RESOLUTION MICROSCOPY OF CELLS 21

F. Hauser, J. Jacak

EXPERIMENTAL INVESTIGATION AND SIMULATION OF 3D-PRINTED LATTICE STRUC-

TURES 22

E. Heiml, A. Kalteis, Z. Major

7


COMBINED APPROACH OF TOPOLOGY AND PARAMETER OPTIMIZATION FOR THE

DESIGN OF LIGHTWEIGHT MULTICOPTER DRONES 23

F. Kiehas, M. Reiter

MECHANO-BIOLOGICAL DEFORMATION RESPONSE OF MESENCHYMAL STEM CELLS

ADHERED TO POLYDIMETHYL-SILICONE MEMBRANES 24

B. Kronsteiner, M. Pasztorek, E. Rossmanith, M.B. Fischer, W. Baumgartner

STRAIN MEASUREMENT ON 2124-T851 ALUMINUM NOTCHED BAR SPECIMENS BY DIG-

ITAL IMAGE CORRELATION METHOD 25

M. Lutovinov, J. Papuga, J. Kuzelka

DEFORMATION RESPONSE OF POLYDIMETHYLSILOXANE SUBSTRATES SUBJECTED

TO UNIAXIAL QUASI-STATIC LOADING 26

F. Martino, V. Vinarsky, J. Sleichrt, D. Kytyr

INVERSE COMPUTATIONAL DETERMINATION OF JOHNSON-COOK PARAMETERS US-

ING THE SHPB TEST APPARATUS 27

A. Mauko, B. Necemer, Z. Ren

A PENDULUM ELECTROMAGNETIC ENERGY HARVESTER 28

M. Mistrulli, D. Castagnetti

LIGHTWEIGHT AUXETIC METAMATERIALS DESIGNED THROUGH TRUSS NETWORKS 29

L. Mizzi, A. Spaggiari

STRAIN RATE DEPENDENCY OF COMPRESSIVE BEHAVIOUR OF 3D PRINTED SS316L

BULK SPECIMENS WITH RESPECT TO PRINTING DIRECTION 30

M. Neuhauserova, P. Koudelka, J. Falta, M. Adorna, T. Fıla, P. Zlamal

MECHANICAL AND STRUCTURAL PROPERTIES OF COLLAGEN NANOFRIBROUS LAY-

ERS UNDER SIMULATED BODY CONDITIONS 31

J. Rıhova, T. Suchy, L. Vistejnova, L. Horny, M. Supova

DESIGN AND VALIDATION OF A MINIMALLY INVASIVE ADJUSTABLE TITANIUM PROS-

THESIS AS A VERTEBRAL BODY REPLACEMENT 32

A. Sorrentino, D. Castagnetti, F. Taddei, E. Schileo

DEVELOPMENT OF AN INJECTION MOULDING SIMULATION ALGORITHM TO CON-

SIDER THE EFFECT OF SEGREGATION DURING INJECTION MOULDING 33

T. Temesi, L. Szabo

WIND TUNNEL TESTS FOR LIFETIME ESTIMATION OF BRIDGE AND MAST CABLES

EXPOSED TO VORTEX INDUCED VIBRATIONS 35

A.Trush, S.Pospısil, S. Kuznetsov

FEASIBILITY STUDY: MULTIPHOTONLITHOGRAPHY 36

M. Wimmer

SIMULATION AND OPTIMIZATION OF POROUS BONE-LIKE MICROSTRUCTURES WITH

SPECIFIC MECHANICAL PROPERTIES 37

A. Wit, S. Wronski, J. Tarasiuk

8


EVALUATION OF HOPKINSON BAR EXPERIMENTS USING SEVERAL DIGITAL

IMAGE CORRELATION TOOLS

M. Adorna 1 , S. Bronder 2 J. Falta, P. Zlamal, T. Fıla

Keywords: Digital Image Correlation, Hopkinson Bar, impact loading, high-speed imaging

Abstract

In this paper, several different tools for Digital Image Correlation (DIC) were used for evaluation of dynamic

experiments performed using custom Open Hopkinson Pressure Bar (OHPB) apparatus. High strain-rate

measurements were performed on specimens of advanced cellular materials with predefined structure and

negative Poissons ratio (so called auxetic structures). These specimens were manufactured by electrodepo-

sition of a nickel coating on a base structure produced by 3D printing of polymer (coating layer thickness

of approx. 60µm and 120µm). Low impedance polymethyl methacrylate (PMMA) bars instrumented with

both foil and semiconductor strain-gauges were used for dynamic loading of the specimens. Experimets were

observed using a pair of high-speed cameras (frame rate set to 270 kfps) for imaging of loading process in suf-

ficient quality. Precise synchronisation of the high-speed cameras and the strain-gauge record was achieved

using a through-beam photoelectric sensor. Custom developed evaluation DIC tool [1] implemented in Mat-

lab, open-source Matlab tool [2] and commercial DIC software (ISTRA 4D) were all used for evaluation of

image sequences recorded by high-speed cameras. Coprarison of results obtained using all three different

DIC tools and results of complementary strain-gauge measurement are shown in this paper. Verification of

prescision and reliability of custom made DIC software tool is presented.

Acknowledgment

The research was supported by the Czech Science Foundation (project no. 19-23675S) and the internal grants

of the Czech Technical University in Prague (projects no. SGS18/153/OHK2/2T/16 and

SGS18/154/OHK2/2T/16). All the financial support is gratefully acknowledged.

References

[1] Jandejsek, I. et al. Optimization and Calibration of Digital Image Correlation Method. Experimentalni

analyza napeti 2010, 121-126, 2010.

[2] Blaber, J. et al. Ncorr: Open-Source 2D Digital Image Correlation Matlab Software. Experimental

Mechanics 2015, 55(6), DOI: 10.1007/s11340-015-0009-1. ISSN 0014-4851.

1Ing. Marcel Adorna, CTU in Prague, Faculty of Transportation Sciences, Department of Mechanics and Materials, Konviktska

20, 120 00 Prague 1, Czech Republic, email: [email protected] des Saarlandes, Institute of Applied Mechanics, Campus A4.2, Saarbrucken, 66123, Germany

9


A TEST BENCH FOR THE EXPERIMENTAL CHARACTERIZATION OF SOLID

TRUCK WHEELS: DESIGN, PROTOTYPE, AND VALIDATION

C. Barone, D. Castagnetti, A. Spaggiari, E. Dragoni 1 F. Ascari, F. Monica, A. Perrone 2

Keywords: solid truck wheels, experimental characterization, operating conditions test

bench, design, prototype, predictive model

Abstract

Solid wheels are extensively used in automated and manual industrial trucks for goods movimentation, thanks

to their versatility. They have a composite structure: a metal body, which provides structural support, coated

with elastomeric polyurethane o rubber, giving grip and resilience. Elastomeric polyurethane, being ex-

tremely versatile, abrasion resistant and available in a wide range of hardnesses, is preferred over rubber in

applications that require a more durable coating, and a stiffer wheel for an accurate motion control. The

aim of this work is to design, develop and validate a test bench for the experimental characterization of solid

wheels, simulating the real behaviour in exercise, and consequently diagnose and reproduce the causes of

failure. The test bench must be able to manage and reproduce the typical operating conditions of the wheel,

for example: the load carried by the wheel, the speed, the type of pavement, the ambient temperature, and the

contaminants. The design of the test bench was performed according to the Quality Function Deployment

procedure, and organized in the following steps: identification of the customer needs and technical specifica-

tions, concepts generation and design implementation. The test bench features a rotating circular plate, 5 m in

diameter, on which four different pavements can be installed: steel, concrete, ceramic, asphalt. Four simple

frame structures, angularly equispaced, support the wheels close to the outer radius of the circular plate. On

each frame, an actuator loads the wheel against a plane pavement, as in real conditions, with a maximum

load on the wheel equal to 100 kN, either static or dynamic. The maximum speed of the wheel is 5 m/s and

both idle wheels or drive wheels can be tested: in case of idle wheels, an external drive acts the circular plate

which consequently drive the wheels; in case of drive wheels, the actuation of the wheels causes the rotation

of the circular plate. The test bench, able to accommodate wheels ranging from 200 mm up to 600 mm in

diameter, will allow to develop a predictive model of the wheel response in typical operating conditions and

to describe either the abrasion, the mechanical fatigue or the thermomechanical fatigue of the wheels.

1Department of Sciences and Methods for Engineering - University of Modena and Reggio Emilia Via G. Amendola, 2 - 42122

Reggio Emilia - Corresponding Author Calogero Barone, Univ. of Modena and Reggio Emilia, Via G. Amendola 2, 42122 Reggio

Emilia, Italy. E-mail:[email protected] Via G. Marconi, 23 42030 Viano (RE) Italy

10


MECHANICAL AND OPTICAL INVESTIGATION OF LASER WELDED STRUCTURAL

STEEL PMMA HYBRID JOINT STRUCTURES

T. Csiszer 1 T. Temesi 2 L. Molnar 3

Keywords: laser welding, metal-polymer hybrid structures, poly(methyl-methacrylate)

Abstract

The reduction of costs, both in the manufacturing processes and throughout the lifespan of a vehicle is an

important aim of the vehicle industry. One possible method to achieve this is to use materials with lower den-

sity, such as using aluminum, or even polymers and polymer composites instead of steel. Modern, productive

welding processes that can easily be automated (such as friction stir welding, laser welding and ultrasonic

welding) are gaining popularity in joining metal-polymer hybrid structures [1]. In all of these processes, the

polymer material is heated until it is able to bond to the metal surface, however the procedure and cause of the

bonding process itself is not yet well-discussed in scientific publications. This field of science is intensively

studied around the globe, as a dependable, productive joining method that directly produces structurally sound

joints between a metal and a polymer structure could unleash unforeseen potential and possibilities in the ve-

hicle industry [2, 3]. In our experiments, we manufactured hybrid steel-poly(methyl-methacrylate) (PMMA)

joints with laser welding, using the 2p design of experiment method. We measured the shear strength of the

joints, the effect of welding parameters and cellulose fibres (in varying weight percentages) on the mechani-

cal properties of the joint and the degradation of the PMMA material and examined the seam with scanning

electron microscopy.

Acknowledgment

This research was supported by the grant No. EFOP-3.6.1-16-2016-00009.

References

[1] Amancio-Filho S. T., Blaga L.: Joining of polymer-metal hybrid structures - principles and applications.

John Wiley and Sons, Inc., Hoboken, New Jersey, USA, 2018.

[2] Amend P., Pfindel S., Schmidt, M.: Thermal joining of thermoplastic metal hybrids by means of mono-

and polychromatic radiation. Physics Procedia, 41, p. 98-105, 2013.

[3] Chen, Y.J., Yue, T.M., Guo, Z.N.: A new laser joining technology for direct-bonding of metals and

plastics. Materials and Design, 110, p. 775-781, 2016.

1Tamas Csiszer PhD, Engineering Institute, Edutus University, Studium ter 1., Tatabanya, H-2800, Hungary and Rejto Sndor

Faculty of Light Industry and Environmental Protection Engineering, buda University, Doberdo ut 6, H-1034, Budapest, Hungary,

email: [email protected] Temesi, PhD student, Department of Polymer Engineering, Faculty of Mechanical Engineering, Budapest University of

Technology and Economics, Muegyetem rakpart 3, Budapest, H-1111, Hungary, email: [email protected] Molnar, Engineering Institute, Edutus University, Studium ter 1., Tatabanya,, H-2800, Hungary,

email: [email protected]

11


MULTIAXIAL INVESTIGATION OF PVC FOAMS AND ANALYSIS OF THE

DEFORMATION MECHANISM BY 3D-DIC

F. Concas 1 , S. Diebels 2 , A. Jung 3

Keywords: polymeric foams, multiaxial testing, three-dimensional digital image correla-

tion

Abstract

Closed-cell polyvinychloride (PVC) foams are widely used as core for sandwich composites, especially for

the construction of marine vessels and wind turbine blades. In the above-mentioned applications, the foam

core undergoes multiaxial loading conditions. The investigation of the multiaxial mechanical properties

of PVC foams has been the main topic of several works. Nevertheless, there is a lack of analysis on the

multiaxial response of high performance PVC foams, particularly in the case of simultaneous tensile and

torsional loading. The present work gives a contribution in this field through the application of a wide range

of uniaxial and multiaxial experiments on a high performance PVC foam with the trade name of Divinycell

HP100 (DIAB AB, Sweden). The conducted experiments included: pure tension, pure compression and pure

torsion, simultaneous tension-torsion as well as simultaneous compression-torsion. All experiments were

performed on the same cylindrical geometry. Failure data for each experiment were collected and depicted in

the invariants plane. The yield function proposed by Bier et al. [1, 2] was successfully adapted to failure data

of the foam. The occurrence and the evolution of deformation bands of PVC foams during multiaxial loading

were also analysed by three-dimensional digital image correlation (3D-DIC) with an 8-camera system, which

allows the monitoring of 360◦ of the specimen surface. Despite of the simple specimen geometry. The usage

of an 8-camera system was essential for the observation of the deformation mechanism, especially for pure

compression, pure torsion and combined axial-torsional loading cases. In the aforeseen experiments, the

arising of deformation bands is affected by buckling and by the orthotropy of the foam, respectively.

References

[1] Bier, W. et al. A finite strain constitutive model for metal powder compaction using a unique and convex

single surface yield function. European Journal of Mechanics-A/Solids 25 (6), p. 1009-1030 (2006).

[2] Bier, W. et al. Die compaction of copper powder designed for material parameter identification. Inter-

national Journal of Mechanical Sciences 49 (6), p. 766-777 (2007)

1Dr. Francesca Concas, Chair of Applied Mechanics, Saarland University, Campus A4.2, 66123 Saarbrucken, Germany,

email: [email protected]. Dr.-Ing. Stefan Diebels, Chair of Applied Mechanics, Saarland University, Campus A4.2, 66123 Saarbrucken, Germany,

email: [email protected] Dr.-Ing. Dr. rer. nat. Anne Jung, Chair of Applied Mechanics, Saarland University, Campus A4.2, 66123 Saarbrucken,

Germany, email: [email protected]

12


HIGH STRAIN-RATE COMPRESSIVE TESTING OF FILLING MATERIALS FOR

INTER-PENETRATING PHASE COMPOSITES

T. Doktor, T. Fıla, P. Zlamal, P. Koudelka, D. Kytyr, O. Jirousek 1

Keywords: interpenetration phase composite, SHPB, strain energy density

Abstract

Cellular materials or open cell metal foams pose favourable impact energy absorption properties [1] which

may be enhanced when their porous structure is equipped with a suitable filling material to form inter-

penetrating phase composite (IPC). The filling has to provide a good strain energy absorption with acceptable

increase of the overall density of such IPC. In this study behavior of selected types of filling material were

tested in compressive loading mode at low and high strain rates.

Three types of filling material were tested, (i) ordnance gelatin, (ii) low expansion polyurethane foam, and

(iii) thixotropic polyurethane putty. To evaluate their impact energy absorption bulk samples of the selected

materials were tested in compression loading mode at strain rates 1000 s−1 to 4000 s−1.

The high strain rate compressive loading was provided by Split Hopkinson Pressure Bar (SHPB) [2]

which was equipped with PMMA bars to enable testing of cellular materials with low mechanical impedance.

From the records of strain-gages signal stress-strain diagrams of tested materials were obtained and subse-

quently, their plateau stress, plateau strain and strain energy density was evaluated and compared with results

of quasi-static tests.

Based on the comparative measurement response to compressive loading at both low and high strain rates

in three types of materials were analysed. The obtained results show a significant strain rate sensitivity in

ordnance gelatin and in polyurethane putty. Strain rate effect in polyurethane foam was not observed in the

investigation.

Acknowledgment

The financial support of the Czech Science Foundation (project No. 19-23675S).

References

[1] Qiao, P., Yang, M., Bobaru, F. Impact Mechanics and High-Energy Absorbing Materials: Review.

Aerospace Engineering 21, 235248 (2008).

[2] Hopkinson, B. A Method of Measuring the Pressure Produced in the Detonation of High Explosives or

by the Impact of Bullets. Phil. Trans. R. Soc. Lond. A 213, 437-456 (1914).

1Ing. Tom Doktor, Ing. Tom Fıla, Ing. Petr Zlamal, Ph.D., Ing. Petr Koudelka, doc. Ing. Daniel Kytyr, Ph.D., prof. Ing. Ondej

Jirousek , Ph.D., Czech Technical University in Prague, Faculty of Transportation Sciences, Department of Mechanics and Materials,

Konviktska 20, 120 00 Prague 1, Czech Republic, email: [email protected]

13


IMPACT RESISTANCE OF COMPOSITES WITH DIFFERENT TYPES OF INCLUSIONS

K. K. Dudek 1

Keywords: composites, impact resistance, mechanical metamaterials

Abstract

In this work, through numerical studies, I investigate the effect that the use of different types of inclusions

has on protective properties of a particular type of an elastic composite. As a result of my studies, I show

that the use of a certain class of inclusions may significantly enhance impact resistance of a given material.

I also show that depending on the properties of the implemented inclusions, the response of the material to a

collision with an external body may be very different which allows to choose a specific type of inclusions for

a given type of an application. Finally, it is shown that the use of the concept proposed in this work may be

used in order to increase the efficiency of the conventional protective devices.

Acknowledgment

K.K.D. acknowledges the financial support from the program of the Polish Minister of Science and Higher

Education under the name Regional Initiative of Excellence in 2019 - 2022, project no. 003/RID/2018/19,

funding amount 11 936 596.10 PLN.

1Institute of Physics, University of Zielona Gora, ul. Szafrana 4a, 65-069 Zielona Gora, Poland, email: [email protected]

14


NUMERICAL MODELLING OF WAVE SHAPES DURING SHPB MEASUREMENT

R. Dvorak 1 , P. Koudelka 2 , T. Fıla 3

Keywords: SHPB, pulse shaping, FE simulation

Abstract

The paper aims at the theory and a numerical simulation of the wave propagation through one-dimensional

continuum represented by the SHPB apparatus. The work focus mainly on SHPB principles, optimisation of

a numerical model and techniques of pulse shaping [1]. The parametric model of the typical SHPB configu-

ration developed for LS-DYNA environment is introduced and optimised (distribution and refinement of the

mesh) using the sensitivity study. Then, a parametric analysis of a geometric properties of the pulse shaper

is carried out to reveal of their influence on a shape of the incident pulse [2]. The analysis is algorithmized

together with the processes involved, and thus, automated processing of results and a comparison with the

experimental data is enabled. Results of the parametric analysis and the amount of the influence of geometric

properties of the pulse shaper on the incident wave are demonstrated as well as automation procedure for

creating models, rendering the simulations, and evaluation of outcomes.

Acknowledgment

The research has been supported by Czech Science Foundation (research project No. 19-23675S).

References

[1] Chen, W.W.: Split Hopkinson (Kolsky) bar: design, testing and applications. Springer, New York, 2011.

Mechanical engineering series. ISBN 978-1-4419-7981-0.

[2] Naghdabadi et al. Experimental and numerical investigation of pulse-shaped split Hopkinson pressure

bar test. Material Science and Engineering A.(539), p.285-293 (2012).

1Bc. Radim Dvorak, Czech Technical University in Prague, Faculty of Transporation Sciences, Konviktska 20 Prague 1, 110 00,

email: [email protected]. Petr Koudelka, Czech Technical University in Prague, Faculty of Transporation Sciences, Konviktska 20 Prague 1, 110 00,

email: [email protected]. Tomas Fıla, Czech Technical University in Prague, Faculty of Transporation Sciences, Konviktska 20 Prague 1, 110 00,


15


DIRECT MEASUREMENT OF REACTION FORCES DURING FAST DYNAMIC

LOADING - APPLICATIONS FOR SHPB AND ITS MODIFICATION

J. Falta, M Adorna, T. Fıla, P. Zlamal 1

Keywords: force transducer, SHPB, dynamic loading, instrumentation

Abstract

The presented paper is focused on embedding of the serially manufactured piezo-electric impact load-cell into

Split Hopkinson Pressure Bar (SHPB) for a direct force measurement during dynamic loading. Convention-

ally, during the SHPB test dynamic force equilibrium is investigated by a comparison of the transmitted signal

wave and the difference between the incident and reflected signals waves to the incident bar, measured by

strain gauges [1]. However, in the experiments with specimens with low

mechanical impedance, a major portion of the incident wave is reflected back on the boundary between the bar

and the specimen. Comparison between two-large amplitude incident and reflected pulse and

a small-amplitude transmitted pulse can be influenced by large error and resulting force equilibrium can

be inaccurate. Therefore, a piezo-electric quartz impact force transducer was used to directly measure the

axial forces in the vicinity of the specimen end surfaces, allowing to analyze the force equilibrium which

is an essential characteristic for reliable measurement. Measured values from strain gauges were compared

with values obtained from force transducer, to verify the validity of the acquired signals which will increase

the reliability of the measured data. The presented solution will help to determine the mechanical properties

of advanced materials which is necessary for investigation of complex modern material structures behaviour.

Acknowledgment

The research was supported by the Czech Science Foundation (project no. 19-23675S) and the internal grants

of the Czech Technical University in Prague (project no. SGS18/153/OHK2/2T/16 and

SGS18/154/OHK2/2T/16). All the financial support is gratefully acknowledged.

References

[1] Fıla, T. et al. Testing of Auxetic Materials Using Hopkinson Bar and Digital Image Correlation. DYMAT

2018 - 12th International Conference on the Mechanical and Physical Behaviour of Materials under

Dynamic Loading, EPJ Web Conf. Volume 183, 2018.

1Ing. Jan Falta, Czech Technical University in Prague, Faculty of Transportation Sciences, Department of Mechanics and Mate-

rials, Konviktska 20, 120 00 Prague 1, Czech Republic, email: [email protected]

16


CUSTOM-MADE RHEOMETER FOR THE EXPERIMENTAL STUDY OF

POLYURETHANE RESIN PU9010

L. Fissore 1 , S. Diebels 2

Keywords: rheology, curing, dynamics

Abstract

Polymers are extensively studied and used due to their high versatility, high specific properties and wide-range

applications. Polyurethane resins are well-known examples in aerospace industry, electronics and automo-

tive as an adhesive or coating because of their broad spectrum of properties. The polymeric system PU9010

is obtained by mixing diisocyanate (Desmodur VP.PU 1806), a diol (Baygal K55) and a triol (Desmophen

3600Z). They are obtained by a process called curing, where in the initial uncured state the mixture exhibits

a viscous behavior and at the end of the polymeric reaction, a solid with viscoelastic properties is formed.

The shrinkage due to cross-linking and the temperature applied to the system cause the generation of residual

stresses which often result in broken adhesive layers. Therefore, the reduction of such problems is of utmost

importance. Hence, studying changes in mechanical properties during curing is important. The mentioned

phase transition can be studied applying an oscillatory strain or stress during the chemical reaction.

In this study, a rheometer capable to conduct such oscillatory-strain-controlled experiments was built in order

to apply large deformations not only to the sample at the beginning of the reaction but also to the cured, solid,

adhesive without changing the device. The design of the machine makes this possible using a Crank - Slider

- mechanism attached to a lever in order to reduce the needed force and therefore be able to apply high torque

at high frequency. Given the fact that the chemical reaction is highly sensitive to moisture in air and fast,

the polymeric system also influences the design of the machine. For this reason, the rheometer as well as the

working place must fit inside a box with controlled atmosphere.

The effect of using Slider - Crank mechanism increases the dynamic forces on the sample but they were

reduced to low values using a lever arm capable of changing the distance of force application. As a conse-

quence, a same deformation can be applied but with smaller amplitude. The testing device works as expected

and the design allows to use small motors to generate big torques.

1Ing. Luciano Fissore, Chair of Applied Mechanics, Universitat des Saarlandes, Campus A4.2 66123, Saarbrucken, Germany,

email: [email protected]. Dr.-Ing. Stefan Diebels, Chair of Applied Mechanics, Universitat des Saarlandes, Campus A4.2 66123, Saarbrucken,

Germany, email: [email protected]

17


ADDITIVE MANUFACTURING PROCESS PARAMETER INFLUENCE ON

MECHANICAL STRENGTH OF ADHESIVE JOINTS, PRELIMINARY ACTIVITIES

M. Frascio 1 , L. Bergonzi 2 , F. Moroni 3 , A. Pirondi 4 , M. Avalle 5 , M. Monti 6 , M. Vettori 7

Keywords: additive manufacturing, FFF, bonded joints, surface characterization

Abstract

The work illustrates how building parameters of the Additive Manufacturing (AM) process fused filament

fabrication can affect not only the mechanical properties [1] but also the surface wettability and morphology.

Wettability and morphology are relevant factors in bonded joints performance [2]. Advantages of polymeric

AM are to allow a re-design of components with locally controlled properties [3] and integrated functions.

Major limitations are related to the lack of material testing standardization and constraints due to the build

volume and to the object orientation for printability: the latter problem can be addressed with the use of

bonded joints that allow to create bigger assemblies from smaller parts optimally designed to take advantage

of the anisotropy of the material and without the structural drawbacks due to other joining method, such as

stress concentration in bolted joints. As for the Mechanical properties, they are obtained with uniaxial tensile

tests using MaCh3D [4], an innovative cost effective solution for materials testing. The as built surface

properties are investigated quantitatively and qualitatively using a plate specimen of 15 × 15 × 1.2mm.

Roughness parameters are measured by surface scanning with a CCI Taylor-Hobson 3D optical profilometer

while contact angle values between specimens and a drop of Milli-Q water are measured in order to evaluate

wettability. Different materials, such as ABS and PLA, are characterized at different combinations of nozzle

temperature, print speed and layer thickness. The analysis of the collected data provide information on how

building parameters can modify two fundamental aspects in adhesive joints such as surface roughness and

wettability in order to maximize joint performance.

Acknowledgment

This research was supported by Universit degli studi di Genova, Universit degli studi di Parma, MaCh3D srl.

References

[1] Frascio, M. et al. Fatigue strength of plastics components made in additive manufacturing: first experi-

mental results. Procedia Structural Integrity 12, S32-S43, (2018).

1Ing. Mattia Frascio, Universit degli studi di Genova, Via Opera Pia 15a, email: [email protected]. Lorenzo Bergonzi, Universit degli studi di Parma, MaCh3D srl, email: [email protected]. Fabrizio Moroni, PhD, Universit degli studi di Parma, email: [email protected]. Ing. Alessandro Pirondi, PhD, Universit degli studi di Parma, email: alessandro.pirondi@unipr5Prof. Ing. Massimiliano Avalle, PhD, Universit degli studi di Genova, Via Opera Pia 15a ,email: [email protected]. Margherita Monti, PhD, Universit degli studi di Genova, Via Opera Pia 15a, email: [email protected]. Matteo Vettori, PhD, MaCh3D srl, email: [email protected]

18


[2] Arenas Reina, J.M. et al. Influence of the Surface Finish on the Shear Strength of Structural Adhesive

Joints and Application Criteria in Manufacturing Processes. The Journal of Adhesion 6, S324-S340

(2008).

[3] Li, L. et al. Composite Modeling and Analysis for Fabrication of FDM Prototypes with Locally Con-

trolled Properties. Journal of Manufacturing Processes 4, S129-S141 (2002).

[4] Bergonzi, L. et al. Numerical and experimental validation of a non-standard specimen for uniaxial

tensile test. Procedia Structural Integrity 12, S392-S403, (2018).

19


IN-SITU COMPRESSION TEST OF ARTIFICIAL BONE FOAMS IN CONTROLLED

ENVIRONMENT USING X-RAY MICRO-COMPUTED TOMOGRAPHY

J. Glinz 1 , D. Kytyr 2 , T. Fıla2, J. Sleichrt2, A. Schrempf 3 , D. Furst3, J. Kastner1, S. Senck1

Keywords: x-ray micro-computed tomography, artificial bone foams, in-situ testing

Abstract

X-Ray Micro-computed tomography (XCT) has already become a standard method for investigations of bone

and bone replacement materials in medical research. For an in-depth characterization of histomorphometric

features, digital volume data acquired by XCT can be processed and visualized three dimensionally to deter-

mine parameters such as bone volume fraction, cortical thickness and porosity. In this study, we investigated

specimens of artificial bone foams, developed by the research group for surgical simulators at the UAS Linz,

which are used to mimic the haptic feedback of physiologic and pathologic bone for more realistic surgery

training. Similar specimen of artificial bone foam in a dry state have already been characterized precisely

in [1]. However, since physiological bone typically is in a wet state, the main purpose of this study was the

investigation of the influence of environmental conditions on artificial bone foams of varying composition.

Thus, specimens with two kinds of mineral filler material as well as different amounts of foaming agent were

prepared and tested in an in-situ loading stage developed by the ITAM CAS. In this stage, specimens can

be immersed in liquid and tested under temperature-controlled conditions. Consequently, a total amount of

12 specimens was subjected to compression loading; half of them immersed in water at 36.5◦C and half in

dry condition. Results showed that there is no significant influence of liquid immersion to the compression

outcome. However, foams with less amount of foaming agent appeared to have smaller pores resulting in

higher compression strength. Different types of mineral filler material also showed no significant influence

on compression strength. Furthermore, a time-lapse in-situ investigation with XCT scans in-between the load

steps was performed for one specimen immersed in water to investigate behavior during load. Despite of the

open porous morphology of the foam, water immersed only partially into the foam, leaving pores closer to the

center unfilled. Concluding, the usage of the artificial bone foams investigated is despite their physiologically

wet condition also valid in a dry state since environmental differences are nonessential for their mechanical

properties.

Acknowledgment

This work is supported by the project Competence Center for High-Resolution 3D X-ray Imaging (Com3d-

XCT) and the European Regional Development Fund (EFRE) in the framework of the Interreg V program

’Austria-Czech Republic’.

References

[1] D. Furst, S. Senck, M. Hollensteiner, B. Esterer, P. Augat, F. Eckstein, A. Schrempf, Characterization

of synthetic foam structures used to manufacture artificial vertebral trabecular bone, Materials Science

and Engineering C 76, p1103-p1111 (2017).

1University of Applied Sciences Upper Austria, Stelzhamerstrae 23, 4600 Wels, Austria, email: [email protected] of Theoretical and Applied Mechanics of the Czech Academy of Sciences, Proseck 76, Prague 9, Czech Republic3University of Applied Sciences Upper Austria, Garnsionstrasse 21, 4020 Linz, Austria

20


REFRACTIVE-INDEX-CORRECTED 3D SUPER RESOLUTION MICROSCOPY OF

CELLS

F. Hauser 1, J. Jacak2

Keywords: 3D super resolution microscopy, phase retrieval, tomography

Abstract

Conventional microscopy allows robust imaging of cells used in many laboratories. Relatively large cell

features such as the nucleus and some organelles are observable, but not clearly distinguishable. Best contrast

is possible via fluorescence microscopy by labeling of individual proteins with fluorescent dyes. However,

only a resolution of about 250 nm is possible due to the diffraction limit and details like the actin cytoskeleton

cannot be resolved. Single Molecule Localization Microscopy (SMLM) based on direct Stochastic Optical

Reconstruction Microscopy (dSTORM) overcomes this limitation and allows a resolutions down to 15 nm

[1]. By mounting a cylindrical lens in the optical detection pathway, dSTORM can be extended to the third

dimension. Nevertheless, for imaging of the whole cell or even cell clusters the astigmatic point spread

function (PSF) is insufficient in the axial direction and the sample has to be scanned axially at defined steps.

Thereby, the sample is divided in multiples slices consisting of 10 000 - 20 000 frames of stochastically

blinking single molecules at a defined axial step. However, due to the refractive index mismatch between

sample medium and objective, the PSF is asymmetrically axially distorted due to spherical aberration. These

aberrations cause large gaps between observed and real axial positions, especially for large image depths.

We developed software tools for correction of these aberrations which allows the application of standard

software for astigmatic 3D Super Resolution Microscopy analysis (e. g. RapidSTORM, ThunderSTORM, 3D

STORM Tools). The calibration needed for z-position determination based on the elliptical distortion of the

PSF is recalculated using an enhanced modeling of the PSF which accounts for the refractive index mismatch.

The PSF model is determined by phase retrieval of the original calibration stack of single molecules using

algorithms based on ZOLA-3D [2]. The calibration PSF for each slice is simulated using the information

from the phase retrieval and applied to create refractive-index-corrected calibrations at the specific axial

height. Therefore, a reconstruction of the whole sample with less artifacts is yielded.

Acknowledgment

This work was done within the FFG founded project Tomo3d (project number 845419).

References

[1] Sandra Mayr et al. Localization microscopy of actin cytoskeleton in human platelets. International Jour-

nal of Molecular Sciences 19.4 (2018).

[2] Andrey Aristov et al. ZOLA-3D allows flexible 3D localization microscopy over an adjustable axial

range. Nature Communications 9.1 (2018), p. 2409.

1Dipl. Ing. Fabian Hauser, University of Applied Sciences Upper Austria, School of Applied Health and Social Sciences,

Garnisonstr. 21, 4020 Linz, Austria, email: [email protected]. Ing. Dr. Jaroslaw Jacak, University of Applied Sciences Upper Austria, School of Applied Health and Social Sciences,

Garnisonstr. 21, 4020 Linz, Austria, email: [email protected]

21


EXPERIMENTAL INVESTIGATION AND SIMULATION OF 3D-PRINTED LATTICE

STRUCTURES

E. Heiml 1, A. Kalteis 2, Z. Major 3

Keywords: lattice structures, additive manufacturing, mechanical testing, finite element

analysis

Abstract

Lattice structures are currently of high interest especially for lightweight design. They generally have bet-

ter structural performance per weight than parts made of bulk material. With conventional manufacturing

techniques they are difficult to produce, but with additive manufacturing fabrication is quite easy. To better

understand their behaviour under various loading conditions two lattice structures in different configurations

were observed. For each structure three different test specimens were designed and manufactured using se-

lective laser sintering. To investigate the mechanical performance under large deformations the specimens

were made of a thermoplastic polyurethane, which shows a hyperelastic material behaviour. The diameter

of the trusses and the overall dimension of each structure were adapted, so that the volume fraction stayed

the same for each specimen. Beside the experimental observations also finite element simulations were con-

ducted. Therefore, the deformation behaviour of the structures could be investigated in more detail and the

results of the experiments and simulations could be compared.

1Eva Heiml, Institute of Polymer Product Engineering, Altenberger Straße 69, 4040 Linz, email: [email protected] Anna Kalteis, Institute of Polymer Product Engineering, Altenberger Straße 69, 4040 Linz, email: [email protected]. Dr. Zoltan Major, Institute of Polymer Product Engineering, Altenberger Straße 69, 4040 Linz,


22


COMBINED APPROACH OF TOPOLOGY AND PARAMETER OPTIMIZATION FOR

THE DESIGN OF LIGHTWEIGHT MULTICOPTER DRONES

F. Kiehas 1 , M. Reiter 2

Keywords: FEM-Simulation, parameter optimization, topology optimization, drone, multi-

copter, 3D-printing, injection moulding

Abstract

Due to the possibility of being completely electric driven, the ability for vertical take offs and simple rotor

mechanics for flight control, the most advantageous design for small-scale unmaned aircraft transportation is

the so called multicopter, a rotorcraft featuring more than two rotors.

To maximize the payload capacity and flight endurance, the vehicle has to be as light as possible while

still fullfilling the necessary strength and stiffness requirements. The optimization of the frame weight is im-

perative. A large potential for weight reduction is offered by utilization of modern materials like composites,

as well as modern manufacturing techniques such as 3D-printing.

Two seperate design studies for Quad- and Octocopters have been conducted. Based on preparatory topology

optimizations, general baseline design layouts for the frame structures have been developed. Various design

parameters have been defined to enable further parametric optimization of the geometry, with the objective of

minimizing part weight while being constrained to maintain sufficient strength levels. Correlations between

these parameters have been explored in a large number of finite element method simulations to get a better

understanding of which features offer the most potential for weight reduction.

1Dipl. Ing. Florian Kiehas, Institut fur Polymer Product Engineering, Johannes Kepler Universitat, Altenbergerstraße 69, 4040

Linz, email: [email protected]. Martin Reiter, Institut fur Polymer Product Engineering, Johannes Kepler Universitat, Altenbergerstraße 69, 4040 Linz,


23


MECHANO-BIOLOGICAL DEFORMATION RESPONSE OF MESENCHYMAL STEM

CELLS ADHERED TO POLYDIMETHYL-SILICONE MEMBRANES

B. Kronsteiner 1 , M. Pasztorek, E. Rossmanith, M.B. Fischer 2 , W. Baumgartner 3

Keywords: MSCs, PDMS functionalization, polydopamine, mechanical stretch

Abstract

To investigate the mechanobiological signaling of human amnion-derived mesenchymal stromal cells (hAM-

SCs) in response to tensile strength, cells were cultured on elastic polydimethylsiloxane (PDMS) surfaces.

Because of the inherent high hydrophobicity of PDMS surfaces, causing cells to dislodge from the surface,

chemical functionalization of PDMS surfaces with polydopamine (PD) was performed. PD proved to immo-

bilize collagen type 1 on PDMS membranes and thus, to stabilize the adherence of MSCs on the membrane

surface [1, 2]. In detail, in-house produced PDMS membranes were functionalized with polydopamine solu-

tion in different PD concentrations (0.01%w/v and 0.10%w/v) using different durations of functionalization

(1 h and 24 h). Additional coating of 20µg/ml collagen type1 (Diamed, Austria) was performed to investi-

gate the combinatorial effect of PD- and collagen-treated PDMS membrane surfaces on hAMSC adhesion [1].

hAMSC were cultured for 16 h on the PD-treated and collagen-coated PDMS surfaces; one group was me-

chanically stretched for 1 h and the other group remained un-stretched. To analyze the effect of stretching

to the MSC culture, carbon particles that served as orientation points for distance measurements before vs.

after stretching procedure were molded into the fluid PDMS membranes. After stretching procedure, both

groups were stained for actin, Live/Dead assessment and MSC surface marker CD90. hAMSC cultures were

then detached from the membranes enzymatically with accutase. Cell number, viability and actin stress fiber

formation were analyzed in both groups using flow cytometry and confocal microscopy.

Acknowledgment

The research has been supported by the European Regional Development Fund in frame of the projects

Kompetenzzentrum MechanoBiologie (ATCZ133) in the Interreg V-A Austria - Czech Republic programme.

References

[1] Kuddannaya, S. et al. Surface Chemical Modification of Poly(dimethylsiloxane) for the Enhanced Ad-

hesion and Proliferation of MSCs. ACS Appl. Mater. Interfaces 2013, 5: 9777–9784

[2] Chuah, Y. et al. Simple surface engineering of polydimethylsiloxane with polydopamine for stabilized

mesenchymal stem cell adhesion and multipotency. Sci. Rep. 2013, 5: 18162

1Bettina Kronsteiner, Faculty of Health Science and Biomedicine, Department for Biomedical Research, Danube University

Krems, Austria, email: [email protected] for Biomedical Research, Danube University Krems, Austria3Institute of Biomedical Mechatronics, Johannes Kepler University, Linz, Austria

24


STRAIN MEASUREMENT ON 2124-T851 ALUMINUM NOTCHED BAR SPECIMENS

BY DIGITAL IMAGE CORRELATION METHOD

M. Lutovinov 1 , J. Papuga 2 , J. Kuzelka 3

Keywords: DIC, load controlled, multiaxial loading, notch specimens, strain

Abstract

The strain response was measured by the Digital Image Correlation method on three types of notched spec-

imens made of 2124-T851 aluminum alloy. The types of the specimens were round bars with the U-notch,

V-notch and fillet notch. The experiments were load-controlled in tension-compression and torsion. Tested

loading paths include both proportional and non-proportional multiaxial paths.

The aim of the experimental program was to obtain the local strain response for verifying various notch

stress-strain approximate methods [1, 3]. Samples were loaded so that the yield strength in the notch was

exceeded. This ensured that the plasticization has occurred and the data include plastic strains. At least one

hundred cycles were measured by the Digital Image Correlation method in order to capture the potential

plastic softening effect.

Measured shear and axial strains are presented in the form of graphs. The differences in responses of the

three tested types of specimens are evaluated and the experimental measurement process is described.

Acknowledgment

This work was supported by the Grant Agency of the Czech Technical University in Prague, grant No.

SGS17/175/OHK2/3T/12.

References

[1] Lutovinov, M. et al. A comparison of methods for calculating notch tip strains and stresses under mul-

tiaxial loading. Frattura ed Integrita Strutturale 38, pp.237-243 (2016).

[2] Barkey, M.E.: Calculation of Notch Strains Under Multiaxial Nominal Loading. PhD Thesis, University

of Illinois at Urbana-Champaign, USA, 1993.

[3] Firat, M. A notch strain calculation of a notched specimen under axial-torsion loadings. Materials and

Design 32, pp.3876-3882 (2011).

1Dipl. Ing. Maxim Lutovinov, Czech Technical University in Prague, Technicka 4, 166 07 Prague 6,

email: [email protected]. Jan Papuga, Ph.D., Czech Technical University in Prague, Technicka 4, 166 07 Prague 6, email: [email protected]. Jirı Kuzelka, Ph.D., Czech Technical University in Prague, Technicka 4, 166 07 Prague 6, email: [email protected]

25


DEFORMATION RESPONSE OF POLYDIMETHYLSILOXANE SUBSTRATES

SUBJECTED TO UNIAXIAL QUASI-STATIC LOADING

F. Martino, V. Vinarsky 1 , J. Sleichrt, D. Kytyr 2

Keywords: compression loading, hyperelasticity, polydimethylsiloxane substrates

Abstract

To investigate cellular response of cardiomyocytes to substrate mechanics, biocompatible material with stiff-

ness in physiological range is needed. Polydimethylsiloxane (PDMS) based material Sylgard 184 is used for

construction of microfluidic organ on chip devices for cell culture due to ease of device preparation, bonding,

and possibility of surface functionalization. However it has stiffness orders of magnitude out of physiolog-

ical range. Therefore we adapted recently published protocol [1] aiming to prepare substrates which offer

stiffness in physiological range 5−100 kPa using various mixtures of Sylgard 527 and Sylagard 184. The in-

house developed loading device with the loading capacity of 3 kN with 1µm position tracking accuracy and

sub-micron position sensitivity was employed for this experimental campaign. The experiments were con-

trolled by the proprietary LinuxCNC software running on the real-time kernel [2]. All batches of the samples

were subjected to monotonic compression loading. During the displacement driven experiment with loading

rate 10µm · s−1 the samples with diameter 12.00 ± 0.05mm and height 14 − 16mm were compressed to

minimally 50% deformation. Because of high differences in the samples stiffness various load cells with

nominal capacity 50N, 10N, and 1N was used for the most reliable force logging. Material properties for

all batches were derived from a set of tests under dry and simulated physiological conditions. The results are

represented in the form of stress-strain curves calculated from the acquired force and displacement data and

elastic moduli are estimated as secant up to 10% deformation.

Acknowledgment

The research has been supported by the European Regional Development Fund in frame of the projects

Kompetenzzentrum MechanoBiologie (ATCZ133) in the Interreg V-A Austria - Czech Republic programme.

References

[1] Palchesko R.N. et al. Development of Polydimethylsiloxane Substrates with Tunable Elastic Modulus to

Study Cell Mechanobiology in Muscle and Nerve, PLoS ONE 2012, 7(12): e51499.

[2] Rada, V. et al. Multi-channel control system for in-situ laboratory loading devices, Acta Polytechnica

Proceedings CTU Proceedings 2018, 18: 15–19

1Fabiana Martino, Vladimır Vinarsky, International Clinical Research Center of St. Annes University Hospital Brno, Pekarka 53,

656 91 Brno, Czech Republic, email:{fabiana.martino,vladimir.vinarsky}@fnusa.cz2Jan Sleichrt, Daniel Kytyr, Institute of Theoretical and Applied Mechanics AS CR, v.v.i., Prosecka 76, 190 00 Prague 9, Czech

Republic, email: {sleichrt,kytyr}@itam.cas.cz

26


INVERSE COMPUTATIONAL DETERMINATION OF JOHNSON-COOK

PARAMETERS USING THE SHPB TEST APPARATUS

A. Mauko, B. Necemer, Z. Ren 1

Keywords: SHPB test apparatus, Johnson-Cook constitutive model, inverse determination,

Nelder-Mead optimization, computer simulations

Abstract

The Split Hopkinson Pressure Bar (hereinafter SHPB) test apparatus is used to determine the constitutive

material response at higher deformation rates between 102 s−1 and 8·104 s−1. The Johnson-Cook constitutive

model (hereinafter JC) is one of the most popular empirical material models that can be used for calculation of

the stress-strain relationship during high strain rate deformation also at elevated temperatures. The JC model

contains 5 material parameters that can be determined experimentally quite easily. The temperature material

softening was neglected in our study and the remaining 4 material constants were determined by the inverse

computational method [1]. First, a classic quasi-static tensile test of selected steel material was conducted,

followed by dynamic tests at two strain rates using the SHPB apparatus. A numerical model was built in the

LS-Dyna system to carry out the necessary simulations of the SHPB test [2]. The inverse determination of JC

parameters was done by comparing the measured and computed stress signals on input and output bars and

minimising their discrepancy by searching for appropriate parameters by applying the Nelder-Mead simplex

method [3]. The obtained JC material parameters much better describe the material behaviour at very high

strain rates in computational simulations if compared to the parameters derived by the classic procedure.

Acknowledgment

The authors acknowledge the financial support from the Slovenian Research Agency (research core funding

No. P2- 0063).

References

[1] Mauko, A.: Inverse computational determination of Johnson-Cook constitutive model parameters for

steel by using SHPB test apparatus, Master thesis, University of Maribor, Faculty of Mechanical Engi-

neering, 2018.

[2] Neemer, B.: Numerical modelling and validation of SHPB test apparatus, Master thesis, University of

Maribor, Faculty of Mechanical Engineering, 2017

[3] Nelder, J.A., Mead, R.: A Simplex Method for Function Minimization, The Computer Journal 7(4), pp.

308–313, 1965

1MSc. Anja Mauko, MSc. Branko Necemer, prof. Zoran Ren, University of Maribor, Faculty of Mechanical Engineering,

Smetanova ul. 17, 2000 Maribor, Slovenia, email: [email protected]

27


A PENDULUM ELECTROMAGNETIC ENERGY HARVESTER

M. Mistrulli 1 , D. Castagnetti 2

Keywords: energy harvesting, pendulum, T-structure, magnetic spring, electromagnetic

Abstract

Energy harvesters able to efficiently convert ambient energy into electrical energy allow the development of

self-sustainable electronic systems and remote sensors. Both piezoelectric or electromagnetic converters are

promising solutions and many examples can be found in the literature. This paper presents the design and

validation of an innovative double pendulum electromagnetic energy harvester including a magnetic spring.

Thanks to the magnetic spring, which stabilizes the pendulum with respect to its frame, the system can work

on whichever orientation, and, in addition, by calibrating the magnetic spring we easily obtain frequency

tuning of the converter. The system consists of a continuous T-structure, hinged in the intersection of the

arms: a coil is fixed on each end of the horizontal arms, while the magnetic spring is on the vertical arm.

The T-structure oscillates around the hinge as it receives an external dynamic excitation, consequently the

coils cross the magnetic field originated by a couple of permanent magnets fixed to the support frame. The

prototype, with a volume of about one cubic decimeter, was built and validated in two steps, using a dynamic

testing machine. First, we investigated the frequency response for different stiffness of the magnetic spring.

Second, we measured the output voltage and calculated the power output of the converter for three different

stiffness levels of the magnetic spring. The first results show that the resonant frequency of the system is in

the range between 2 Hz and 10 Hz and a power output up to about 2.5 mW, thus proving the validity of this

solution.

1Ing. Mistrulli Michele, Modena and Reggio Emilia University via Amendola 2, Reggio Emilia, email: [email protected]. Ing. Davide Castagnetti, Modena and Reggio Emilia University via Amendola 2, Reggio Emilia, email: da-

[email protected]

28


LIGHTWEIGHT AUXETIC METAMATERIALS DESIGNED THROUGH TRUSS

NETWORKS

L. Mizzi 1 , A. Spaggiari 2

Keywords: auxetics, metamaterials, Finite Element Analysis, 3D printing

Abstract

Auxetic metamaterials are a class of systems which exhibit the anomalous property of having a negative

Poissons ratio. This behaviour is primarily dependent on the geometry of the system rather than its inherent

material properties. One particularly well-known class of auxetic metamaterials is that of rotating unit sys-

tems which involve large rigid or semi-rigid blocks of material rotating relative to each other. In this work,

an attempt was made to design auxetic systems based on rotating unit mechanisms where the rotating unit

component of the system is made up of trusses rather than bulk material as is normally the case. Six well

known 2D auxetic geometries were studied, namely: rotating triangles, rotating quadrilaterals (squares, rect-

angles and parallelograms), anti-tetrachiral and hexachiral systems, and for each of these systems three forms

of truss configurations were investigated. The mechanical properties of these systems were compared with

those of the corresponding filled rotating unit structures using Finite Element Analysis and experimental tests

on 3D printed prototypes. The results obtained show that in cases where a triangular truss network is used to

build the rotating unit, the rigidity of the unit is retained and thus these systems possess similar mechanical

properties to their full rotating unit geometry equivalents, despite possessing a much lower overall material

volume.

1Luke Mizzi, Department of Sciences and Methods for Engineering, University of Modena and Reggio Emilia, Italy

email: [email protected] Spaggiari, Department of Sciences and Methods for Engineering, University of Modena and Reggio Emilia, Italy,


29


STRAIN RATE DEPENDENCY OF COMPRESSIVE BEHAVIOUR OF 3D PRINTED

SS316L BULK SPECIMENS WITH RESPECT TO PRINTING DIRECTION

M. Neuhauserova 1 , P. Koudelka, J. Falta, M. Adorna, T. Fıla, P. Zlamal

Keywords: 3D printing, stainless steel 316L, bulk, dynamic compression, quasi-static com-

pression

Abstract

The paper is focused on evaluation of the relation between mechanical properties of 3D printed material

(particularly stainless steel 316L) and printing direction (i.e. the orientation of the part which is being printed)

with respect to various strain rates during a compressive loading. The knowledge of these dependencies is

essential for calibration of material model used in numerical simulations, and thus for reliable prediction

of mechanical behaviour of 3D printed parts. In order to evaluate the strain rate dependency of the 3D

printed material’s compressive characteristics, dynamic and quasi-static experiments are performed. The

Split Hopkinson Pressure Bar (SHPB) is used for high strain rate experiments, which are performed at two

different strain rates. Quasi-static loading is performed using the Instron 3382 measuring device. Three

series of bulk specimens are produced using Renishaw AM250 printing device. Specimens from each of the

series have different printing orientation (vertical, horizontal and tilted - at an angle of 45 ◦ - with respect to

the powder bed). The specimens for high strain-rate experiments are dogbone-shaped and the specimens for

quasi-static loading have cylindrical shape. During both types of experiments the deformation of specimens

is observed using an optical setup. Custom developed Digital Image Correlation (DIC) tool [1] is used to

evaluate deformation of the specimens from the images captured during loading. Based on the measurements,

mechanical properties such as Young’s modulus, Poisson’s ratio, yield strength and compressive strength of

the 3D printed material are evaluated with respect to different printing orientations and strain rates.

Acknowledgment

The research was supported by the Czech Science Foundation (project no. 19-23675S) and the internal

grants of the Czech Technical University in Prague (projects no. SGS19/123/OHK2/2T/16). All the financial

support is gratefully acknowledged.

References

[1] Jandejsek, I. et al. Optimization and Calibration of Digital Image Correlation method. Experimentalni

analyza napeti 2010, 121-126, 2010

1Ing. Michaela Neuhauserova, Department of Mechanics and Materials, Faculty of Transportation Sciences, Czech Technical

University in Prague, Konviktskaa 20, 110 00 Prague 1, email: [email protected]

30


MECHANICAL AND STRUCTURAL PROPERTIES OF COLLAGEN NANOFRIBROUS

LAYERS UNDER SIMULATED BODY CONDITIONS

J. Rıhova 1 T. Suchy 2 L. Vistejnova 3 L. Horny 4 M. Supova 5

Keywords: collagen, fibroblasts, osteoblasts, mechanical properties, structural properties

Abstract

The main aim of this paper is the analysis of mechanical and structural properties of nanofibrous collagen

layers under conditions that simulate the body environment and in the presence of osteoblasts (bone cells) and

dermal fibroblasts (cells of connective tissues). Collagen layers were prepared by electrostatic spinning of

8wt.% collagen type I dispersion with 8wt.% (to collagen) of polyethylene oxide in phosphate buffer/ethanol

solution (1/1 vol) [1]. The stability of collagen nanolayers was enhanced by means of cross-linking with EDC

and NHS at a molar ratio of 1 : 4 . Prepared layers were exposed in cell culture medium containing 10% fetal

bovine serum for up to 21 days without or with human SAOS-2 human dermal fibroblasts or osteoblasts which

were cultured therein for up to 21 days. Cells were cultured in a standard culture medium that was used to

expose separate cell-free layers at 37 ◦C and 5% CO2. The proper seeding by both cell types was evaluated.

First, the cell culture on collagen nanolayers was assessed by fluorescence microscopy and determination

of metabolic activity. Second, the metabolic activity of both cell types grown on collagen nanolayers and

control (polystyrene surface) were measured after 1, 7, 14 and 21 days after the start of the experiment using

the Alamar Blue assay method. Mechanical properties (Young modulus and tensile strength) were determined

using the uniaxial tensile test. The influence of the cell activity on secondary structure of collagen nanofibrous

layers was verified by infrared spectroscopy. Furthermore, the influence of cells on given layers was evaluated

by electron spectroscopy.

References

[1] Suchy T. et al.: The release kinetics, antimicrobial activity and cytocompatibility of differently prepared

collagen/hydroxyapatite/vancomycin layers: Microstructure vs. Nanostructure, Eur. Pharma. Sci. 100

(2017).

1Ing. Jitka Rıhova Czech Technical University in Prague, Technicka 4, 166 07 Prague 6, email: [email protected]. Tomas Suchy, Ph.D.Institute of Rock Structure and Mechanics, Academy of Sciences of the Czech Republic, Prague,

email: [email protected]. Lucie Vistejnova Biomedical Center, Medical Faculty in Pilsen, Charles University, Prague email: lu-

[email protected]. Ing. Lukas Horny, Ph.D.Czech Technical University in Prague, Technicka 4, 166 07 Prague 6,

email: [email protected]. Monika Supova, Ph.D. Institute of Rock Structure and Mechanics, Academy of Sciences of the Czech Republic, Prague,


31


DESIGN AND VALIDATION OF A MINIMALLY INVASIVE ADJUSTABLE TITANIUM

PROSTHESIS AS A VERTEBRAL BODY REPLACEMENT

A. Sorrentino 1 , D. Castagnetti 2 , F. Taddei 3 , E. Schileo 4

Keywords: VBR, lumbar spinal recostruction, 3D printed implant, titanium structures

Abstract

Unstable vertebral body compression fractures, spinal tumors and post-traumatic deformities require a ver-

tebral body replacement (VBR). Usually, the reconstruction of the lumbar spinal column requires metallic

implants, also called cages, which are inserted after a total corpectomy in combination with an internal spinal

fixation device. These implants show several complications, including a low bone fusion rate, localized con-

tact between prosthetic endplates and vertebral endplate, and eventually overload the vertebral body due to

the excessive insertional force. Creation of a misalignment between prosthetic and bone endplate sometimes

causes the subsidence and collapse of the VBR [1]. Then, the ability of the prosthesis/bone interface to sup-

port vertebral loading is crucial to the successful implantation of these devices. Recently developed additive

manufacturing techniques (i.e. EBM) allow the production of trabecular titanium structures which provides

better biomechanics and customized solutions. Furthermore, most of vertebral body implants are currently

designed and produced in batches with standard dimensions, that are not able to meet the patient peculiar

features. This work aims to design, optimize and validate a new 3D printed trabecular titanium prosthesis

with adjustable height for lumbar VBR. The work focused on the durability of the implant considering the

lumbar spinal fatigue loadings acting on the porous cage, with the aims to improve bone ingrowth and, at the

same time, to minimize the effects of the surgical treatment on the sagittal alignment of the patient. In order

to achieve better performances in terms of spinal stabilization and fatigue life resistance, the design of this

new customized prosthesis takes into account the most critical factors of the vertebral body resection, with

the aim to ensure minimally invasive surgical procedure.

References

[1] A. Viswanathann et al, Initial experience with the use of an expandable titanium cage as a vertebral

body replacement in patients with tumors of the spinal column: a report of 95 patients, Eur. Spine J.,

vol. 21, n. 1, pagg. 8492, gen. 2012.

1M.Sc. Andrea Sorrentino, Department of Science and Methods for Engineering, University of Modena and Reggio Emilia, Via

Amendola 2, 42122, Reggio Emilia, Italy, email: [email protected]. Ph.D. Davide Castagnetti, Department of Science and Methods for Engineering, University of Modena and Reggio Emilia,

Via Amendola 2, 42122, Reggio Emilia, Italy, email: [email protected]. Ph.D. Fulvia Taddei, Bioengineering and Computing Laboratory, IRCCS Istituto Ortopedico Rizzoli, Via di Barbiano 1/10,

40126, Bologna, Italy, email: [email protected]. Ph.D. Enrico Schileo, Bioengineering and Computing Laboratory, IRCCS Istituto Ortopedico Rizzoli, Via di Barbiano

1/10, 40126, Bologna, Italy, email: [email protected]

32


DEVELOPMENT OF AN INJECTION MOULDING SIMULATION ALGORITHM TO

CONSIDER THE EFFECT OF SEGREGATION DURING INJECTION MOULDING

T. Temesi 1 F. Szabo 2

Keywords: numerical simulation, injection moulding, additives

Abstract

Injection moulding is one of the most versatile and dynamically evolving polymer forming processes. With

injection moulding, three-dimensional polymer parts with complex geometry can be manufactured with vir-

tually zero waste output. As a result of the inherent properties of the injection moulding technology, every

part needs its unique mould, and a careful optimization of the process and technological parameters is also

necessary. Numerical simulation methods are increasingly used to support and ease the design of the moulds

and the manufacturing process itself. The amount of time, energy and cost that can be saved using these

methods depend on the algorithms precision in approximating certain properties of the material and the poly-

mer part during the injection moulding process. Todays algorithms apply numerous simplifying conditions

in the simulation because the behaviour of the polymer material is quite complex during the manufacturing

process. One of the most basic simplification is that no irreversible change happens in the materials structure

during the simulation. However, during the injection moulding of polymers filled with additives, a so-called

segregation effect occurs, depending on the size of the additives and technological parameters. This means

that the distribution of the additive is uneven in the injection moulded part: certain areas are enriched, while

in other areas, the concentration of the additive is decreased. This effect leads to different amounts of shrink-

age in the moulded part, which can not be predicted with current simulation algorithms [1, 2].

Our aim is to develop models and methods, in which the effect of inhomogeneities in the polymer mate-

rial is considered, leading to a better approximation of real-world processes in the numerical modelling and

simulation of the injection moulding process [3].

Acknowledgment

This paper was supported by the Jnos Bolyai Research Scholarship of the Hungarian Academy of Sciences

and by the NKP-18-4 New National Excellence Program of the Ministry of Human Capacities.

The authors wish to thank Arburg Hungaria Kft. for the Arburg Allrounder 370S 700-290 injection molding

machine, Lenzkes GmbH for the clamping tool system, and Piovan Hungary Kft. for their support.

References

[1] Huamin, Z.: Computer Modeling for Injection Molding: Simulation, Optimization, and Control. John

Wiley and Sons, Inc., Hoboken, New Jersey, USA, 2013.

1Tamas Temesi, PhD student, Department of Polymer Engineering, Faculty of Mechanical Engineering, Budapest University of

Technology and Economics, Muegyetem rakpart 3, Budapest, H-1111, Hungary, email: [email protected] Szabo, PhD, Assistant Professor, Department of Polymer Engineering, Faculty of Mechanical Engineering, Budapest

University of Technology and Economics, Muegyetem rakpart 3, Budapest, H-1111, Hungary, email: [email protected]

33


[2] Rhodes, M.: Introduction to Particle Technology. John Wiley and Sons, Ltd., London, UK, 2008.

[3] Kovcs, J.G.: Shrinkage Alteration Induced by Segregation of Glass Beads in Injection Molded PA6:

Experimental Analysis and Modeling. Polymer Engineering and Science, 51(12), p. 2517-2525, 2011.

34


WIND TUNNEL TESTS FOR LIFETIME ESTIMATION OF BRIDGE AND MAST

CABLES EXPOSED TO VORTEX INDUCED VIBRATIONS

A.Trush 1 , S.Pospısil 2 , S. Kuznetsov 3

Keywords: bridge cable, wind tunnel, vortex shedding

Abstract

A significant number of TV and radio broadcasting masts in the Czech Republic was built in the 70-80s of

the last century. At the moment is an actual issue is the reconstruction and determination of residual life

of these structures. Guyed masts and particularly guy ropes have significant dimensions and comparatively

low mass and damping with high flexibility. Therefore, aerodynamic and aeroelastic loads, such as vortex

induced vibrations, galloping, wind gusts, etc., see [1], are key for them. As a tensile construction elements

(guy ropes) for guyed masts the traditional open wire spiral strand cables are used. This type of cable has

a characteristic helical surface roughness pattern that can act as vortex suppressor, high fatigue endurance,

although somewhat lower corrosion resistance comparing to modern locked coil cables with non-circular

shaped wires of outer layer and cables with protective polymer coatings. At the same time, on numerous

bridges with the above-mentioned modern cable types the fatigue damage to wires in anchorage zones and

destruction of protective coatings was detected, see [2]. Present paper provides results of wind tunnel test-

ing of three models of helical strake cable in order to evaluate separately impact of lay angle and surface

roughness factors and reference smooth cylinder model in flow with grid generated turbulence of different

intensities. The reduction of the lock-in range of helical strand cables comparing to reference smooth model

was observed whereby the greatest impact was an increase of lay angle.

Acknowledgment

The activity presented in the paper is part of the research grant No. 19-04695S of the Czech Science Foun-

dation (GAR).

References

[1] Zdravkovich, M.M.: Flow around circular cylinders. Vol. 1: Fundamentals. Oxford University Press,

USA, 1997.

[2] Siegert, D. and Brevet, P. Fatigue of stay cables inside end fittings high frequencies of wind induced

vibrations. OIPEEC Bulletin 89, S43-S51 (2005).

1Mgr. Arsenii Trush, Institute of Theoretical and Applied Mechanics AS CR, v.v.i., Prosecka 76, 190 00 Prague and Czech

Technical University, Thakurova 7, 160 00 Prague, Czech Republic, email: [email protected]. Ing. S.Pospısil, Ph.D., Institute of Theoretical and Applied Mechanics AS CR, v.v.i., Prosecka 76, 190 00 Prague, Czech

Republic, email: [email protected]. Ing. S. Kuznetsov, Dr.Sc., Institute of Theoretical and Applied Mechanics AS CR, v.v.i., Prosecka 76, 190 00 Prague,

Czech Republic, email: [email protected]

35


FEASIBILITY STUDY: MULTIPHOTONLITHOGRAPHY

M. Wimmer 1

Keywords: multiphoton lithography, additive manufacturing

Abstract

The thesis describes the possibilities of additive manufacturing with multiphoton lithography.

The basis of this technology is, that a mixture of a liquid monomer and photo-initiator can be forced to

start a polymerization by emitting a laser of a certain wave length into the fluid. The power of the laser cracks

the photo-initiator and starts a radical polymerisation.

This study focuses on the influences during the manufacturing process. One of the important aspects is

the choice of the solvent for the post processing. In sequence to the solvent problem, the influence of the

layer height is examined. With the data gathered from those experiments the main objectives of the study

was, to build a cube with the maximum possible side length in 12 hours. Furthermore the limits and possibil-

ities of the setup in use were investigated. As an example the differences in fabrication with the laser firing

with constant frequency and constant density were subject of this investigation.

The second goal of the study was to compare three different structures consisting of periodically repeating

elements, scaled in size and number of elements per side.

1Markus Wimmer, Institute of Polymer Product Engineering, Altenbergerstraße 69, 4040 Linz,

email:[email protected]

36


SIMULATION AND OPTIMIZATION OF POROUS BONE-LIKE MICROSTRUCTURES

WITH SPECIFIC MECHANICAL PROPERTIES

A. Wit, S. Wronski, J. Tarasiuk 1

Keywords: Bone modeling, Voronoi tessellation, porous structure

Abstract

Bone is a complex structure made of stiff mineral scaffold and soft tissue filling their internal pores. The

various geometry and heterogeneity of bone beams give the bone special mechanical properties. Bone can be

characterized as a connected network of bars or plates with specific organization depending on where they

are in the bones. However, the geometry of the bone beams and their spatial arrangement are not random.

The structure of the trabecular bone (meso scale) is adapted to the values of stresses and strains affecting

the skeletal system. In order to build a correct numerical model of bone tissue, it is necessary to know what

is the structure and function of the bones in the human body. Many studies discuss the problem of porous

structures but only a few connect their geometric properties with mechanical characteristics [1]. To simulate

bone structure we propose stochastic structure based on hyperuniform spatial points distribution connected

by the combination of Voronoi tessellation and Delaunay triangulation. The synergy of this two method

allow us to create more natural and smooth scaffold configurations. We are specially aware of features

that mostly influence mechanical stiffness: porosity, connectivity and anisotropy. Numerical methods of

analyzing, generating, and optimizing structure seems to be promising method to obtain the structure with

most similar values to the real bone. Additionally the generator is characterized by good repability in the

satisfactory minimal size of structures. Results of simulations strongly depend on initial model parameters

and the type of simulations. Developed methods of simulation and optimization lead to better bone substitutes

which will enable correct adaptation when using as bone implants.

Acknowledgment

This work was financed by the Polish National Centre for Science (NCN) under decision number:

2017/26/E/ST5/00043. Adrian Wit has been partly supported by the EU Project POWR.03.02.00-00-I004/16.

References

[1] S. Munoz S. et al. Different models for simulation of mechanical behaviour of porous materials, Journal

of the Mechanical Behavior of Biomedical Materials 2018, 80, 88–96.

1B.Eng. Adrian Wit, Dr hab. Sebastian Wronski, Dr hab. Jacek Tarasiuk, Faculty of Physics and Applied Computer Science,

AGH, al. Mickiewicza 30, 30-059 Krakow, Poland, email: {adrian.wit,wronski,tarasiuk}@fis.agh.edu.pl

37

Index

Adorna, M., 8, 15, 29

Ascari, F., 9

Avalle, M., 17

Barone, C., 9

Baumgartner, W., 23

Bergonzi, L., 17

Castagnetti, D., 9, 27, 31

Concas, F., 11

Csiszer, T., 10

Diebels, S., 11, 16

Doktor, T., 12

Dragoni, E., 9

Dudek, K. K., 13

Dvorak, R., 14

Furst, D., 19

Fıla, T., 8, 12, 14, 15, 19, 29

Falta, J., 8, 15, 29

Fischer, M. B., 23

Fissore, L., 16

Frascio, M., 17

Glinz, J., 19

Hauser, F., 20

Heiml, E., 21

Horny, L., 30

Jacak, J., 20

Jirousek, O., 12

Jung, A., 11

Kalteis, A., 21

Kastner, J., 19

Kiehas, F., 22

Koudelka, P., 12, 14, 29

Kronsteiner, B., 23

Kuzelka, J., 24

Kuznetsov, S., 34

Kytyr, D., 12, 19, 25

Lutovinov, M., 24

Major, Z., 21

Martino, F., 25

Mauko, A., 26

Mistrulli, M., 27

Mizzi, L., 28

Molnar, L., 10

Monica, F., 9

Monti, M., 17

Moroni, F., 17

Necemer, B., 26

Neuhauserova, M., 29

Papuga, J., 24

Pasztorek, M., 23

Perrone, A., 9

Pirondi, A., 17

Pospısil, S., 34

Reiter, M., 22

Ren, Z., 26

Rossmanith, E., 23

Rıhova, J., 30

Schileo, E., 31

Schrempf, A., 19

Senck, S., 19

Sorrentino, A., 31

Spaggiari, A., 9, 28

Suchy, T., 30

Szabo, L., 32

Sleichrt, J., 19, 25

Supova, M., 30

Taddei, F., 31

Tarasiuk, J., 36

Temesi, T., 10, 32, 34

Vettori, M., 17

Vistejnova, L., 30

Vinarsky, V., 25

Wimmer, M., 35

Wit, A., 36

Wronski, S., 36

Zlamal, P., 8, 12, 15, 29

38


39


40

book of abstracts - cas · 2019-06-03 · institute of theoretical and applied mechanics, v.v.i.,...

Documents