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

D bilitL d G tDurabilityLoads Geometry

lsM

ater

ial

• 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?

Toolingd

$C

PPd $

Com

mitt

ed

Manufacture

Design

n

e

Co

c

roduct

roduct

Com

mitt

edSub-system Manufacture

DesignVehicle

Manufacture

pt

ion

ion

Vehicle

1. Design Confirmation

2. Sub-system Validation

3. Product Validation

4 Q lit4. Quality

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




Over-design




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.

ng S

tress

) a)σ

Log

(Alte

rnat

iLo

g ( σ

• 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

1

=−= +

n

n

2. No information on product behavior, weaknesses, failure modes

)boss!the tell(YOU !!parts!113n

failure modes.1

1

)1( +−= nCR

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.

lity

Sca

le)

• Now, reliability for any time, t, can be estimated.

ibul

l Pro

babi

l

• Ideally, want 6-10 samples tested to failure, but can estimate Weibull

t ith f l (l

elia

bilit

y (W

eiparameters with fewer samples (lower confidence)

Time to Failure (log scale)U

nre

γ

α⎟⎠⎞

⎜⎝⎛−

−=t

etF )1()(

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

t

Am

plitu

de

• 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

de

tplitu

de

Am

plitu

d

t

Am

f

• 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

t t

Simulation Loads

tyn

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


• Broad Testing Solutions


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 Simulation Test Consultants– Instrumentation and Data AcquisitionInstrumentation and Data Acquisition– Analysis and Editing– Fatigue Correlation– Test Development– Fixture Design

Global Support– Global Support– Training

mm

Engineering a better world for ground vehiclesEngineering a better world for ground vehicles

2. introduction to durability testing

Documents