Download - 2. Introduction to Durability Testing
Introduction to Durability Testingy g
What is Durability?
• Ability of a vehicle to survive an expected service life– Reliability is the probability of a product’sReliability is the probability of a product s
successful performance of an intended function up to a pre-determined life.Q lit i th i t ith hi h l ti– Quality is the consistency with which a population of products perform throughout their life.
– Durability is a subjective term relating to the useful life of a product and is the term given to the type of testing used to determine the objective measures mentioned above.
• What are the major durability issues:Oft l t t li bilit i ith t– Often relate to reliability issues with components
– Less often are structural
What is Durability?
• DurabilityDurability– How long will it last ?– What is the fatigue life?– Repetitive loading emphasis
• Performance• Performance– Does it behave as expected ?– What are the characteristics ?– Measurement emphasis
Durability Specifications
• Durability is the ability to survive an expected service life– Warranty period such as 3 years or 50,000 miles– 150,000 miles, 6000 hours of targeted customer
usageusage– Safety Critical parts 3-4 targeted customer lifetimes
Why Do We Need To Test?
Test Topics
• Next we will go on to discuss the:h–why,
–who,when–when,
–what,where–where,
–& howof testingof testing.
Why Do We Test?
• Confirm physical performance meets predicted design targetsg g
• Ensure correct operation throughout the service life of d tour products
• Identify and correct manufacturing and assembly y g yincidents prior to final vehicle release
Provide “complete” durability coverage• Provide complete” durability coverage
• Significant recall and customer perception costs g p passociated with field failure
Why Do We Test?
• The variability of end-users, manufacturing processes materials etc can severely impactprocesses, materials, etc. can severely impact durability
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• To efficiently address durability issues we must first understand and replicate the durability phenomenonp y p
Why Do We Test?
• Consider the impact of a component failure:– Ignition switch failure ($15 part)Ignition switch failure ($15 part)– $15 (part) + $35 (labor) * 8M (vehicles) = $400M
• Recall Notice– $0.39 Postage stamp * 8M (vehicles) =
• $3 1 Million• $3.1 Million… Just for the Stamps!
Who Tests?
• Vehicle Manufacturers (OEMs)
• Tier 1 suppliers (suppliers to OEMs)
• Tier 2 suppliers (suppliers to Tier 1)
• Independent test houses
• Government agencies
Who Tests?
• Vehicle manufacturers (OEMs) passing test responsibility to Suppliersp y pp
– Testing required to confirm manufactured t d b bli t OEMcomponents and sub-assemblies meet OEM
performance goals
– Suppliers increasingly have to accept consequential liability for non-performance of products in serviceproducts in service
– More testing on components and sub-systems, l t ti f ll hi lless testing on full vehicles.
Who Tests?
• Suppliers need to test both for validation of product performance and to protect against warranty liabilityp p g y y
– Testing to OEM requirements will show ifi ti fspecification conformance
– Testing is necessary to support quality g y pp q yimprovements and cost reduction activities
Component reliability evaluated through testing– Component reliability evaluated through testing
When Do We Need To Test?
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Where Do We test?
Where Do We Test?
• Proving Ground Testing
– Full vehicle testing on the Proving G dGround
• ~$3/mile• 3 months• Functional
running vehicle requiredrequired
Where Do We Test?
• Proving Ground Activity (Customer Correlation)– Pave or Belgian BlockPave or Belgian Block– Washboard– Pot Holes– Curb Strikes– Rough Road
Cross Country– Cross Country– Ride & Handling– Other Special Events
Where Do We Test?
• Laboratory Testing
– Full vehicle testing in the Laboratory• ~$0.70/mile• 3 weeks• Functional running vehicle NOT required
Where Do We Test?
• Laboratory testing moves into the Computer– Laboratory and Proving Ground Testing is testingLaboratory and Proving Ground Testing is testing
of physical prototypes, sub-systems and components
– Computer methods are performance evaluation of virtual prototypes using analytical testing
Where Do We Test?
• Virtual Tools commonly employed today:– Finite Element AnalysisFinite Element Analysis– Life Predication– Multi Body Dynamics
• Analytical = PredictionAnalytical Prediction• Physical = Confirmation
What Do We Test?
• Durability is not the only Vehicle attribute, testing is also conducted for:
– Crash– Powertrain– NVH– Ride and Handling
• Testing occurs at the component, sub-system, and full vehicle levels
What Do We Test?
Full Vehicle
System
or Component
What Do We Expect From Test?
• Functional Evaluation– Confirmation of the basic kinematics of theConfirmation of the basic kinematics of the
specimen (e.g. suspension, window winding mechanism)
• Parameter Evaluation– Measurement of the characteristics of the
specimen (e.g. roll steer, modal survey)
Durability Evaluation• Durability Evaluation– Confirmation that the wear and fatigue properties
of the specimen meet design goals
What Do We Test – What Are The Objectives?
• Target mismatch– Design Engineer TargetsDesign Engineer Targets
• Determine “average” service load then– keep all stresses below 2/3 of Yield– keep maximum identified stress using
Finite Element analysis below “fatigue limit”
– Test Engineer Targets• “With 99% confidence assure that less than 5
parts in 100 will fail in service”parts in 100 will fail in service”• “Service” is defined as “95th percentile
customer, 160,000km usage…”• Does meeting the design targets necessarily mean
meeting the test targets?
What Do We Test – What Are The Objectives?For each durability test we must define “failure”.
• A few possible definitions of failure:- Fracture of the specimen into two or more pieces.- Development of visible cracks of a certain size.- Large-scale yielding of the specimen.
Ch i tiff f th i- Change in stiffness of the specimen.- Excessive deflection of the specimen.- Excessive wear of the specimen- Excessive wear of the specimen.
• Design tests so that failure is detectable.g
What Do We Need to Achieve?
P(x)“Safety Factor”
Service loading Strength
What Do We Need to Achieve?
P(x)“Safety Factor”
Service loading Strength
Over-design
What Do We Need to Achieve?
P(x)“Safety Factor”
Service loading Strength
Under-design
What Do We Include in Test – What Are The Environmental Considerations?• Mechanical Loading
– Forces applied to the specimen and reacted eitherForces applied to the specimen and reacted either inertially or though a fixed load path
• Thermal Load and Humidity– Thermal environment, ambient, under-hood, sun load
and humidity may need to be applied if specimen durability is sensitive to these effects (e.g. thermoplastics)
• Corrosion and Abrasion– Salt spray may be needed to correctly evaluate– Salt spray may be needed to correctly evaluate
durability for ferrous materials– Dust may need to be introduced to correctly evaluate
wear
What is Fatigue?
• Fatigue of a metal is a process in which the metal pexperiences progressive structural damage from repeated cyclic loading.repeated cyclic loading.
• Fatigue results in the f ti d th fformation and growth of cracks. The cracks may propagate to cause complete fracture of the component.
What is Fatigue?
• Fatigue life is a measure of the duration of cyclic loading required to form and grow cracks to a g q gpredetermined size.
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• Fatigue life consists of two principle stages:Life to Failure
(Cycles)
103 104 105 106 107 108
Fatigue life consists of two principle stages:– Crack initiation– Crack propagation
Test Loading Methodologies
• Descending order of realism and time– Customer UsageCustomer Usage– Proving Ground
– Road Simulation– Shaped Random Noise
End Level Sequence– End-Level Sequence– Block Cycle– Constant Amplitude
• The challenge to test engineering is to achieve an acceptable level of realism in the time allotted to be economically competitive!economically competitive!
How Do We Test?
Durability TestingDurability TestingApproaches
Success Testing Failure TestingSuccess Testing(no failures occur)
Failure Testing
L l i • Smaller sample size (more• Large sample size required to achieve confidence
• Little understanding of d t b h i
Smaller sample size (more practical).
• Understand product weaknesses (make continual improvements).
• Ensure that lab tests duplicateproduct behavior Ensure that lab tests duplicate field failure modes.
How Do We Test? Success Testing
Example – Field Testing:– Assess reliability by testing numerous parts up to y y g p p
one design life, with no failures.
Downfalls:Downfalls:1. Sample size:
• How many samples must be tested without failure to have 90% confidence of 98% reliability?have 90% confidence of 98% reliability?
)boss!thetell(YOU!!parts!113)90.01(98.0 1
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)boss!the tell(YOU !!parts!113n
failure modes.1
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R = Estimate of reliability of population.C = Confidence (I.e., probability that the population reliability is at
least as high as the estimate, R).n = Number of specimens tested.
How Do We Test? Failure TestingIf failures occur, can estimate life distribution using Weibull distribution.
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• Now, reliability for any time, t, can be estimated.
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• Ideally, want 6-10 samples tested to failure, but can estimate Weibull
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Time to Failure (log scale)U
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F(t) = fraction that fails by time t (“Unreliability”)γ = shape parameterα = characteristic life
Test Types
• Laboratory Durability Test Acceleration
– The goal of t ti i ttesting is to induce fatigue damage faster th i ithan in service (or on the proving ground)
Test Types
• Accelerating accumulation of damage achieved by:– Increasing amplitudeIncreasing amplitude– Increasing frequency– Removing “non-damaging” content
• Main approachesCyclic– Cyclic
– Block Cycle– Shaped Random Noise– End Level Sequence– Simulation
Accelerated Durability Testing – Simple Cyclic
Range-Mean Material PropertiesMeasured
Service Strainεm
gRainflow Matrix ε
Material Properties
εrN
Calculate fraction of fatigue life usedCalculate fraction of fatigue life used
Sε
Adjust applied load to achieveselected strain level t
Cyclic Test N
Select strain level d l Loadand cycle count
Accelerated Durability Testing – Simple Cyclic
• Advantages– Test Acceleration (1000 x real time) due toTest Acceleration (1000 x real time) due to
increased average amplitude of applied load and increased rate of strain cycle application
• Disadvantages– Multi-axial loading not possibleg p– Dynamic load amplification (frequency effects)
due to specimen resonance not replicatedTest results may be a poor indicator of service life– Test results may be a poor indicator of service life if the material properties, manufacturing process or design of the specimen changes
– Not suitable for inertially-reacted systems.
Accelerated Durability Testing – Block Cycle
Range-Mean Material PropertiesMeasured
Service Strainεm
gRainflow Matrix ε
Material Properties
ε0εrN
ε0
εεm
εr
ε0
St
ε
Adjust applied loads to achieve
Remove strain rangesbelow fatigue limit
t
Block cycle
Develop equivalent block cycle strain history
Adjust applied loads to achieveselected strain levels test load
Accelerated Durability Testing – Block Cycle
• Advantages– Test Acceleration (100 x real time) due to removalTest Acceleration (100 x real time) due to removal
of “non-damaging” cycles and increased rate of strain cycle applicationR l ti l i iti t t i l d– Relatively insensitive to material and manufacturing process changes
– Multi-axial loading possible
• DisadvantagesTrue multi axial loading not possible– True multi-axial loading not possible
– Dynamic load amplification (frequency effects) due to specimen resonance not replicated
– Not suitable for inertially-reacted systems.
Accelerated Durability Testing –End-Level Sequence Loadingq g• Description
– Sequence of end-levelsSequence of end levels
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• ApplicationsApplications– Specimens subjected to variable amplitude loading
(uniaxial and multiaxial).When sequence effects are important– When sequence effects are important.
– When phase relationship between channels must be maintained.Fi d i i– Fixed-reaction component testing.
Accelerated Durability Testing –End-Level Sequence Loadingq g• Advantages
– Reproduces realistic sequence of amplitudesReproduces realistic sequence of amplitudes.– Allows simulation of sequence effects.– Maintains approximately correct phasing between
channels.– Allows frequency acceleration (fixed-reaction
tests).)
• Disadvantages– Some errors in phase simulation in multi-axial
tests.– Not as easy to accelerate as block cycle tests.y y– Not suitable for inertially-reacted systems.
Accelerated Durability Testing –Shaped Random Noise Loadingp g
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• Description– Random signal with specified spectral shape.
• Applications– Specimens subjected to variable amplitude loading
(uniaxial or uncorrelated multiaxial).– Single axis vibration tests– Single axis vibration tests.– Squeak and rattle
Accelerated Durability Testing –Shaped Random Noise Loadingp g• Advantages
– Easy to specifyEasy to specify.– Minimal specification and storage.– Replicates a wide variety of natural vibrations.
• DisadvantagesNo control of end levels– No control of end levels.
– Uncorrelated multi-channel tests may not induce realistic fatigue damage.
– Does not well-represent “periodic overload” conditions and their associated sequence effects.
Accelerated Durability Testing –Road Simulation
ε Measure rig transferfunction Hxy
tyn
Measured Service Strains and Loads (yn)
xybetween drives xnand responses yn
R P C lRemote Parameter Control(RPC) process compensates
for multi-axial dynamictest system response
ε Material Properties
xn
Nε0 ε
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Simulation Loads
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Desired ResponsesDesired Responses
Accelerated Durability Testing –Response Simulationp• Advantages
– Test Acceleration (10 x real time) due to removalTest Acceleration (10 x real time) due to removal of “non-damaging” events
– Multi-axial loading effects correctly replicated – Dynamic loading effects correctly replicated– Minimal modification of real road data– Correct sequence of loading reproducedCorrect sequence of loading reproduced– Accurate replication of failure mode and failure
location
• Disadvantages– Currently requires instrumentation and measuredCurrently requires instrumentation and measured
loads data for different test specimens (e.g. different vehicles)
Challenges with Durability Assessment
• Validation of durability targets occurs late in the development programp p g
• The inherent lack of confidence in current predictive t l it t h i l t ttools necessitates physical test
• Most automotive components under go multi-axial p gvariable amplitude loading
Global Durability Trends
• Testing is expensive but testing is necessary
• Lack of experience can result in expensive mistakes
• Increased focus on CAE generates greater demand for component data and validation tests
• Increased reuse of existing test data requires test focused data management
MTS Systems Corporation
• Global Market leader in testing systems and software in Durability and Ride & Handling.y g
6DOF Long Stroke Road SimulatorHigh Frequency MAST
SWIFT Wheel Force Transducer
MTS Systems Corporation
• Broad Testing Solutions
MTS Systems Corporation
Full Vehicle System Component
Durability Test Type
MTS Product Line
4-Poster / Spindle Coupled Simulator
Drivetrain
MAST
D / Sh k &Damper / Shock &Elastomer
Ball Joint, Exhaust &,Steer
TestStand & Testline
RPC & MPT Software
4-Poster / Spindle Coupled SimulatorsFull VehicleSystemComponent
MTS Model 320 Tire Coupled Road Simulator (Four Poster)• Fast setup time• Able to produce results quickly. • Actuators can be mounted below floor level• Actuators can be mounted below floor level
- Drive-on simulators- Able to interface with environmental chambers
MTS Model 329 Spindle-Coupled Road Simulator U t 6 DOF C t l t h h l• Up to 6 DOF Control at each wheel
• Highest degree of simulation accuracy available• Configurations available to reproduce
- Body roll (slalom events)- Body pitch (brake events)y p ( )
MAST SystemsFull VehicleSystemComponent
MTS MAST (Multi-Axial Simulation Table) Systems• Accelerated replication of service data for- Body components and assemblies
Seats- Seats- Fuel Tanks- Radiators- Engine mounts- Exhaust systems- and more!
Model 353.20 High Frequency MAST• Controlled frequency exceeding 100 HzControlled frequency exceeding 100 Hz• 2 meter table• Compact design• Applications include- Seats
R di t- Radiators- Instrument Panels- HVAC Systems
Drivetrain SystemsFull VehicleSystemComponent
MTS Model 814 Spinning Torsion System• Designed for torsional dampers in
- Manual clutches- Torque converters
• Durability testing of the damper under - Rotation and - Torsional solicitationTorsional solicitation
• Hysteresis measurements at multiple speeds
MTS Shaft Test SystemsD bilit T ti• Durability Testing on- Driveshafts - Halfshafts- Joints
• Proven tools for simulation
Shock, Damper & Elastomer SystemsFull VehicleSystemComponent
MTS Model 835, 849, 850 and 851 systems• Performance characterization & durability testing for- Shock absorbers
Dampers- Dampers- Struts
MTS Models 831 and 833 SystemsCh t i ti d d bilit t ti• Characterization and durability testing
• 100 to 400 Hz typical• High Frequency system .01 to 1000 Hz
Ball Joint, Exhaust and Steer SystemsFull VehicleSystemComponent
MTS Model 324 Exhaust Test Systems• Valves to tailpipe• Full Simulation Testing
B d MTS MAST T h l• Based on proven MTS MAST Technology
MTS Steering Test SystemsS l t t h f i l di• Several systems to choose from including- Model 335 & 337 Rack & Pinion Systems
• Lateral, Vertical and Steering Loads• Block cycle or Time History Reproduction
TestStand & Testline SystemsFull VehicleSystemComponent
TestLine• For the “Do It Yourselfer• Versatile and reliable array of test components
C t Eff ti• Cost Effective
TestStand SolutionsT t t d i d lti i• Test system design and consulting services
• Acquire leading-edge technology - In a cost-effective manner
• Collaborative process to augments in-house skills.
RPC & MPT SoftwareFull VehicleSystemComponent
RPC Pro Software (Remote Parameter Control)• Full-featured Road Simulation• Advances signal processing and editing
F ti A l i• Fatigue Analysis• State of the art simulation technologies
MPT (Multi-Purpose TestWare) SoftwareE t• Easy to use
• For creating and automating many test types• Test Procedures can be built that include- Function Generation- Data Acquisitionq- Event Action- Triggers
MTS Systems Corporation
• MTS Simulation Test Consultants– Instrumentation and Data AcquisitionInstrumentation and Data Acquisition– Analysis and Editing– Fatigue Correlation– Test Development– Fixture Design
Global Support– Global Support– Training
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Engineering a better world for ground vehiclesEngineering a better world for ground vehicles