The changing role of physical testing in vehicle development programmes

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hypilknde 2dued eocito ed pformance can be achieved within shorter times and with reduced development and manufacturing costs. The approach was illustrated byusing computer aided engineering (CAE) tools has devel-2. Role of testing with a new product developmentprogrammeEssentially, testing has just one objective: to ensure theproduct will deliver a protable return to the manufac-meeting or exceeding the customers expectations in termsthe particular new product development programme. Amassive test programme may be justied for a high volumecar, based on the warranty costs associated with any fail-ures and the number of units across which the costs of test-ing can be spread. For smaller volume programmes, suchas are more typical in the o-road sector, the size of the testE-mail address: 4Journaloped to the point where virtual product developmentcan be considered a realistic proposition. Many car manu-facturers, for example, are already usingCAE tools to enablethem to go straight to producing prototype vehicles fromproduction tooling, eliminating one stage in the traditionalproduct development process and improving the quality ofdesign. So, what is the future for physical testing is it stillnecessary or is physical testing becoming a thing of the past?of functionality, reliability and durability and achieveall of these whilst maintaining a sucient gap betweenwhat a customer is willing to pay and what the productcosts to manufacture if it is to deliver prots to the organi-sation. Testing has traditionally played a major role in nd-ing and resolving weaknesses in a design before it goes intoproduction and through to the customers. However, testingis a cost to the organisation and the amount of testing thatcan be contemplated depends on the economic equation ofa process of reducing in-cab noise during the design of a new truck. 2006 Published by Elsevier Ltd on behalf of ISTVS.Keywords: Testing; CAE; FMEA; QFD; Noise; Vibration; Virtual1. IntroductionIn the past, testing has been seen as an essential part ofproduct development. Only by testing could weaknesses ina design be discovered before the product got into the handsof customers.However, over the last 20 years the capacity forcompleting detailed analysis of many aspects of a designturer. It is a kind of insurance policy and the more paid,the better the cover. Do no testing and there is a high riskthat the product will fail in some way, leading to eitherexcessive warranty costs, poor sales or even costly legalaction. Complete an extensive test and development planand the risks reduce.A product must meet the legislative requirements, whilstThe changing role of pdevelopmentPaul WLTC Ltd., Aston Way, LeylaAvailable onlinAbstractThe role of physical testing in product development is changingtolerance of failures in the eld and the emergence of computer aidemust be seen as an integral part of the process for reducing risks ass(QFD) and failure modes and eects analysis (FMEA) can be usedof virtual and physical testing. By eectively integrating virtual anJournal of Terramechan0022-4898/$20.00 2006 Published by Elsevier Ltd on behalf of ISTVS.doi:10.1016/j.jterra.2006.01.004sical testing in vehiclerogrammesinsonPR26 7TZ, United Kingdom9 March 2006to the requirements for faster new product development, reducedngineering (CAE) technologies. To be used most eectively, testingated with new product introductions. Quality function deploymentstablish eective test and development plans that integrate the usehysical test technologies signicant improvements in product (2007) 1522ofTerramechanicsprogramme needs to be very carefully tailored to the eco-nomic realities. Whilst probabilistic approaches exist tohelp identify the appropriate level of testing [1], mostorganisations use a knowledge based approach to decideon what is necessary based on the scale of change andthe projected sales volumes.It is very helpful to think of testing in relation to riskin this way. Too often testing is seen as something that isbolted on at the end. In reality the best approach is toconsider the test programme as an integral part of theprocess. Many companies are now doing this and usingtools such as quality function deployment (QFD) [2]and failure modes and eects analysis (FMEA) [3] tofocus attention on meeting or exceeding customerrequirements whilst minimising risk, and hence testrequirements.3. Tools for risk reductionIf we consider that many new products are actuallydevelopments of existing products then we could denethe requirement for the new product design as being toestablish which systems within the existing product need:the customers and relate these customer requirements toengineering quantities that can be identied. Fig. 1 givesan example of this matrix for the comfort of a drivers seat.Once the attributes are understood and the method ofmeasuring them established it is then possible to measurethe out-going product against the competition and identifywhich aspects require enhancement.Opportunities for cost reduction can be highlighted bydetailed cost analysis of the design and also the manufac-turing process. The results of such analysis are the identi-cation of components, systems or processes that requirechange.Warranty cost information is normally very well knownand often the root causes of any weaknesses in the currentdesign will be known before the new product developmentprocess even begins. But again, this information needs tobe fed into the process as it implies change to components,systems or processes.Whilst looking at these demands for change, it isalways important to try and quantify the benets of mod-ication in nancial terms to dene an economic equa-tion for the project [4]. This economic equation wouldinclude the eects of component costs, manufacturingcosts, test and development costs and potential warranty16 P. Wilkinson / Journal of Terramechanics 44 (2007) 1522(a) enhancement to satisfy or delight the customer;(b) modication to reduce costs (either directly or inmanufacture);(c) modication to reduce warranty costs.QFD can be used very eectively to identify the charac-teristics of the product that are perceived as important toFig. 1. QFD relationship matrix house for drivers seat comfort, showingtogether with details of the importance of what the customer wants and the ecosts in relation to the date of introduction into the mar-ket, expected sales volumes and selling price. This toolcan be used throughout the programme, but used earlyit can quickly establish the priorities for developing thedesign, taking into account the things that will deliverbest value in terms of perceived improvement (by the cus-tomer) and nancial return.the relationship between customer wants and engineering characteristics,ngineering characteristics.rra4. Physical testing versus virtual testing?Over the last 20 years the capability of computer aidedsimulation has grown out of all recognition. Simulationsthat used to require mainframe computers can now berun on a desk-top PC. Equally, more complex processescan now be simulated, expanding the range of attributesthat can be investigated in the virtual domain. However,there are still limitations and whilst the completely digitalproduct development process remains a valid goal, todaysreality is that simulation can be more expensive, more timeconsuming and less reliable than physical testing in certaincircumstances.When designing any test it is essential to start out byunderstanding what output is required. Is it a validation thatthe fatigue limit of a material is never exceeded in a particu-lar component? Or a thorough understanding of the sensi-tivity of ride comfort to suspension set-up is required?There are some simple rules to deciding when it is appropri-ate to use CAE and when it is more appropriate to use phys-ical testing [5]. In essence, the use of CAE supports a systemsapproach and enables multi-attribute optimisation that is atbest cumbersome in the physical test domain. Whenever adetailed understanding of a system is required and especiallywhen CAD data is available, then a CAE approach is likelyto be more ecient and more eective.However, some systems with which we are very familiarare extremely dicult to model because of the physicsinvolved. For example, analysing the fatigue behaviour ofa hot exhaust system is currently an extremely dicultthing to do in simulation (because of uncertainty aboutmaterial properties, crack propagation at elevated temper-atures, the eect of weld geometry and material propertychanges at elevated temperature), but it is relatively easyto t an exhaust to an engine and run a test to nd out ifthe exhaust cracks. Such systems are often better developedusing traditional physical testing. Equally, if the serviceconditions are not quantied then it is very dicult to havecondence in the results of CAE simulation. In such casesthe service conditions can be measured by test, but it maybe more ecient to complete the whole exercise as a phys-ical test and keep the data for future use with CAE models.Whilst it is often presented as a straight choice betweenphysical testing and CAE testing, the reality is that edgescan be rather blurred. Computer aided testing (CAT) is anew term that has begun to be used to describe activitiesin which data from physical tests is manipulated andenhanced within a computer to yield far greater value. Aperfect example of this is experimental modal analysis,where a mathematical model is tted to a set of measuredtransfer functions to yield a modal model of a structure.This model can then be used to present results in the formof animated displays showing how the structure vibrates ata particular frequency. Extending the application even fur-ther, the model can be modied in software to investigateP. Wilkinson / Journal of Tethe eects of adding mass, or stiness. So is such a test aphysical test or a virtual test?Often themost eective use of technology is when the twodisciplines are brought together [6]. CAE models are best atdelivering an understanding of system behaviour, interac-tions and sensitivity, whilst physical tests are good at identi-fying absolute levels of performance and the response ofcomplex systems. These characteristics lead quite naturallyto a hybrid approach whereby high quality legacy data fromprevious tests on carry-over systems can be included in a sys-temmodel in which new elements of the design are modelledin the CAE environment. These hybrid models can deliverhigh levels of accuracy within shortened model creationtimes and with increased condence.The form in which a hybrid approach is used dependsvery strongly on the availability of information. Is therea CAD geometry or existing FE model available? Is therelegacy test data from a previous product development pro-ject? Does hardware exist that could be tested? Is a modelrequired for analysis of some other attributes and can theoptimisation of all attributes be brought together?5. Purposes of physical testingIn this new context of physical and virtual testing work-ing together, physical testing is conducted for a variety ofreasons, which can be classied as: Benchmarking and Target Setting to determine thestatus of the current product in comparison with thecompetition and set targets for the new product. Thiscan be completed at various levels, starting from a sim-ple comparison of performance as perceived by the cus-tomer through to a complete strip down and componentlevel characterisation. At one level this type of testingprovides information about the areas in which improve-ments are required. At another level information abouthow competitors products achieve their levels of perfor-mance can be generated. Identication of inputs for CAE models to establishthe forces, displacements, accelerations, pressures, tem-peratures, etc., encountered either in real-world use orduring existing physical tests. This data is used by theCAE teams to provide output from simulation thatcan be related directly to target levels of performance. Identication of transfer functions of output/input forcomplex systems which can be used either to developanalytical models for subsequent use within a CAEmodel or which are to provide a look-up table of valuesthat can be called directly from the simulation. CAE model validation to provide information thatestablishes not only that the model predicts responsesto the required level of accuracy but that the modelachieves such a result by accurately simulating the pro-cesses that deliver the overall characteristic. Product validation to conrm that the product meetsthe applicable legal standard of performance and alsomechanics 44 (2007) 1522 17achieves the companys objectives in terms of function-ality, reliability and durability.ctivrra Problem solving to provide information required toidentify and validate a solution to any problems encoun-tered during the validation phase or even once the prod-uct has entered service.Each of these functions has a place in the developmentprocess as described in Fig. 2. By applying the correct func-tion at the right time in the process the overall developmentcycle time can be reduced, as can the total test cost and thecost of modications.6. Example development of the in-cab noise of a new truckFig. 2. Description of where physical testing a18 P. Wilkinson / Journal of TeTo illustrate the process an example will be given thatshows when and how physical and virtual techniques wereused in conjunction with each other to deliver an extremelysuccessful programme.6.1. BackgroundA new small truck range was being developed to replacea product that was highly successful in the UK market. Amajor target for the new vehicle was to win a greater shareof the European market whilst maintaining its UK marketshare. It was established that one area where improvementwas required was the in-cab noise.6.2. Use of risk reduction toolsThe customer descriptions of noise were related to engi-neering measurements as shown in the QFD matrix ofFig. 3. This helped identify the need to measure subjectiveevaluation of normal driving using a standard rating sys-tem and overall noise level during constant speed driving,supplemented by noise measured during full loadacceleration.Engineering tests were completed on the out-goingmodel and several competitor models to establish the scaleof improvement required in relation to the competition.From this work it was also possible to identify a targetvehicle for the noise attributes. Interestingly, it was foundthat there were two aspects to the requirement for aquiet vehicle. One was that low frequency componentsrelating to engine ring needed to be controlled (but noteliminated) whilst mid-frequency noise also needed to besignicantly improved. Getting the right balance betweenring frequency related noise and general engine noisewas seen as key to achieving a pleasing sound quality thatgave the right aural cues to re-assure the driver.ities support the product development cycle.mechanics 44 (2007) 1522Completing an FMEA, as shown in Fig. 4, on the causesof high in-cab noise enabled a test programme to bedesigned which would develop an understanding of the dif-ferences between the target vehicle and the out-goingmodel in terms of noise transmission. Because the behav-iour of the out-going vehicle had not previously been char-acterised in detail the FMEA showed a high level of riskassociated with almost all potential transmission paths.However, the contributions from each were relatively easyto measure experimentally so it was possible to achieve agood level of understanding of where the real risks wereto be found and what would need to be done to reduce thatrisk. One of the key ndings was the need for a mulevehicle on which many of the at risk systems could be pro-ven before going to full prototype build. Introducing thismule vehicle into the programme reduced all the risk prior-ity numbers calculated in the FMEA to below 100 (seeTable 1).Interestingly, at the start of the project there was a gen-eral belief that the target vehicle must simply have a quieterengine. By completing the detailed benchmarking exerciseit was found that the target vehicle actually had a noisierengine, but that the chassis and cab design were sucientlyrraP. Wilkinson / Journal of Tesuperior so that the handicap of the noisier engine wasovercome. Analysing how the chassis and cab diered fromthe out-going production model gave signicant insightinto changes that could be introduced to help the newmodel achieve its global target of being quiet.Targets for the new vehicle were derived from the bench-marking exercise in terms of overall vehicle targets and sys-tem level targets for: engine radiated noise and vibration; chassis mount stinesses;Fig. 3. QFD relationship matriFig. 4. (a) Prototype vehicle on test in LTCs semi-anechoic chassis dynamomnew vehicle).mechanics 44 (2007) 1522 19 chassis vibration transfer between the engine mountsand the cab mounts; cab mount stinesses; cab acoustic attenuation between the engine bay,intake orice and exhaust orice and the interior ofthe cab; cab noise transfer functions (noise response in the cab inresponse to a dynamic force applied at the cab mounts); exhaust orice noise; intake orice noise; in-cab noise level and quality.x house for in-cab noise.eter and (b) noise levels (out-going vehicle, target vehicle and prototype ofPotfailInacabHotheEnCaExcExc7 HigInacabHotherraNoise duringnormal drivingSubjectivelyunacceptableProgramme delayand overspend77Table 1Simple FMEA table for in-cab noisePotentialfailure modePotential failureeects (KPOVs)SEV CLASSConstant speednoise levelNoise levelsabove targetProgramme delayand overspend77777720 P. Wilkinson / Journal of TeThese targets were then assessed in terms of the likelycost to achieve them, the conicts with other design criteriasuch as package and other attribute requirements, such asride and handling.6.3. Test and development programmeBy the end of the FMEA, benchmarking and target set-ting exercises there was a clear set of requirements fordesign modications. These requirements were fed intothe design process and concepts developed to support therequired modications.The main elements of the proposed modications were: softer front engine mounts; softer front cab mounts; improved stability of the chassis; improved sealing of the cab oor.Areas that were identied at risk due to changesrequired for other reasons included:7 En7 Ca7 Exc7 Exc7 Hig7 CluKey: SEV severity; CLASS highlight if severity is rated 9 or 10 (health andnumber.ential causes ofure (KPIVs)OCC Current process controls DET RPNdequate isolation onoor4 Laboratory test 1 28les or poor sealing ofcab4 Laboratory test 1 28gine mounts too sti 6 Dynamic stinessmeasurement3 126b mounts too sti 5 Dynamic stinessmeasurement3 105essive frame response 7 FE analysis 4 196essive cab response 6 Experimentalmodal analysis andnoise transfer functionmeasurement4 168h wind noise 4 Validation teston mule vehicle3 84dequate isolation onoor4 Laboratory test 1 28les or poor sealing ofcab4 Laboratory test 1 28mechanics 44 (2007) 1522 engine noise emission; exhaust noise emission; cab structural response.Considering these features, a combination of physicaland virtual testing was planned to make best use of avail-able carry-over hardware and CAE tools.Analysis of the system was broken down into severalsubsets: engine mount system rigid body dynamics and vibra-tion transmission; chassis response mode shapes and forced response; cab mount system rigid body dynamics and vibrationforce transmission into the cab; cab response acoustic attenuation and conversion offorce inputs into noise within the cab.The split between physical and virtual testing is identi-ed in Table 2. As can be seen, the majority of investigativework was completed in the virtual world, taking advantageof the ease with which parameter variations could be stud-gine mounts too sti 6 Dynamic stinessmeasurement3 126b mounts too sti 5 Dynamic stinessmeasurement3 105essive frame response 7 FE analysis 4 196essive cab response 6 Experimentalmodal analysis andNTF measurement4 168h wind noise 4 Validation teston mule vehicle3 84nks due to clashes 4 ADAMS analysisof cab and enginemovement5 140safety risk); OCC occurrence; DET detectability; RPN risk priorityginicdatinalyd wicdatiababrraTable 2Breakdown of the division of activities between physical and virtual testinPhysical testEngine mount system rigidbody dynamicsNot required sucient condenceresultsEngine mount system vibrationtransmissionConrmed through testing of dynamthe components and full vehicle valimule vehicleChassis response Conrmed by experimental modal atesting of a chassis system. Validatevehicle testing using a mule vehicleCab mount system rigid bodydynamicsCab mount system vibrationforce transmissionConrmed through testing of dynamthe components and full vehicle valimule vehicleCab response acousticattenuationInvestigated using a rig test of the cCab response conversion of Investigated using a rig test of the cP. Wilkinson / Journal of Teied. This environment also provided the ideal opportunityto run evaluation of noise and vibration in parallel withevaluation of ride and handling performance, allowingtrade-os and opportunities to be established very earlyin the programme. Physical testing was used primarily toconrm the ndings of CAE work.An important element of the testing was the use of amule vehicle to validate much of the work completedusing CAE tools. Such a mule vehicle was relatively easyto create by re-using elements of the out-going vehicleand introducing prototypes of modied systems that werecritical to noise and vibration. This was initially dictatedby the fact that several CAE technologies were being usedtogether for the rst time on this programme with anassociated risk. However, the availability of the mulevehicle meant that much simpler models could be usedwith the aim of establishing mechanisms and direction,whilst relying on the physical results to provide therequired evidence that absolute target levels of perfor-mance were being achieved. This helped to reduce thetime needed to complete the CAE work and allowedforce into noise including modal analysis and measuremnoise transfer functionsEngine noise and vibration Validated performance on prototype enExhaust noise Validated during full vehicle testing onvehicleCab structural response Validated by experimental modal analyprototype cabIn-cab noise level and quality Investigated using legacy data and validthrough measurement on mule vehicleVirtual (CAE) testCAE Investigated using ADAMS softwarestiness ofon using aInvestigated using ADAMS softwaresis and rigith fullInvestigated using NASTRAN and using ADAMS fullvehicle model with imported exible chassis element anddamper model identied from physical testingInvestigated using ADAMS softwarestiness ofon using aInvestigated using ADAMS full vehicle model withimported exible chassis element and damper modelidentied from physical testingsystem Not required easier and quicker to test physical partsthat existed at the right timesystem, Not required easier and quicker to test physical partsmechanics 44 (2007) 1522 21results to be generated in time to inuence the designdirection very early in the programme.6.4. ResultsThere were several important results of thisprogramme. The risk of failure to meet the noise targets had beenmoved from very high to very low by the time manufac-ture of the prototype vehicles was started. When the rst vehicles emerged from the prototype shopthey all met the targets for in-cab noise with no furtherdevelopment required. The targets for noise level reduction of some 5 dB andimproved noise quality were met with fewer noise andvibration specic components than the out-going model,as shown in Fig. 4. Sucient understanding of the vehicle was gained thatfurther mid-life improvement of noise could be achievedwith condence at very low cost.ent of that existed at the right timegines Completed by supplier of the enginea mule Completed by suppliersis on a Investigated using NASTRAN to evaluate modal responseand forced response using forcing functions measuredfrom vehicle testing on a mule vehicleated Low frequency initial predictions based on ADAMSbased prediction of force at the cab mounts combined withmeasured noise transfer functionsMid/high frequency not completed due to insucientcondence in available predictive techniquesThe questions that should be asked before commencing22 P. Wilkinson / Journal of Terramechanics 44 (2007) 1522 The overall spend on noise development was signicantlylower than that of the out-going models development. A process had been established and proven that could beused and developed on future programmes with the scaleof activity matched to the scale of the programme.7. ConclusionsNew technologies are increasing the eectiveness ofCAE and as organisations gain experience with these toolsthe role and requirements for physical testing are changing.In simple terms, physical testing now has a young andaggressive competitor that is providing new opportunitiesto develop and validate designs without the encumbranceof physical hardware.However, to view the issue as a straightforward competi-tion between virtual and physical is to miss an enor-mous opportunity. Each approach should be deployed onmerit and integrated to deliver the most eective productdevelopment process. Often it is reasonably easy to createa model that gives information about how a systemresponds to its inputs and boundary conditions but muchmore dicult to achieve a faithful reproduction of everynuance of the physical system. Equally, the results from amodel will only ever be as good as the assumptions maderegarding load cases and boundary conditions. On the otherhand, obtaining detailed information about why a systemresponds the way it does, or how sensitive it is to changesin design can be very time consuming and expensive toachieve through physical testing.The best product development processes take intoaccount the capabilities of both physical and virtualapproaches and uses both together to generate better infor-mation more quickly and with least cost. Typically, physi-cal testing may be used to: establish inputs to a model; provide information about the response of parts of asystem that are easy to test but would be extremely dif-cult to model accurately, enabling black box model-ling of such parts; conrm performance where there is a subjective elementto assessment of the characteristic and the humanresponse cannot easily be simulated; validate the CAE predictions.Is physical testing becoming a thing of the past? No but the role of testing is changing away from being the pri-mary means of identifying and resolving problems with adesign. Now testing is very much concerned with support-ing CAE by providing those elements that are dicult tosimulate and resolving problems that slip through theproduct development process undetected.The questions that should always be asked before creat-ing a CAE model are:physical testing are: Is this test necessary, or do a combination of experienceand CAE prediction give sucient condence? Is the test intended to simply record the output responseof a system to a given set of input conditions, or is it nec-essary to gain an understanding of how the system deliv-ers that response? Is it better to use a simple CAE model to gain under-standing of the system and use the physical test simplyas a validation? Does the physical test correspond to both the real-worlduse situation and the CAE model conditions?Signicant improvements in product performance canbe achieved with reduced development time and coststogether with reduced unit manufacturing costs by eec-tively combining the best of physical testing with the bestof CAE simulation technologies.AcknowledgementsThe author thanks Leyland Trucks and the ADAU ofISVR for their work and support in relation to the examplegiven in this paper.References[1] Seksaria D, Baker J. A Probabilistic Approach to Evaluating FinancialRisk and Determining Testing Requirements for Low Volume NewProducts. SAE Paper 861280; 1986.[2] Day RG. Quality function deployment: linking a company with itscustomers. American Society for Quality; 1993.[3] Stamatis DH. Failure mode and eect analysis: FMEA from theory toexecution. American Society for Quality; 1995.[4] Reinerstein DG. Managing the design factory a product developerstoolkit. New York, NY: The Free Press; 1997.[5] Campbell RM. Analysis When and When Not. SAE Paper 982011;1998.[6] Vandeurzan U. Empowering a real breakthrough in functionalperformance engineering. In: LMS conference for physical and virtualprototyping, Paris; 2001. Is there sucient knowledge from previous designs todecide there is no need to test the design either in the vir-tual or physical domains? Is it quicker and cheaper to create a virtual model of thissystem than to build a physical prototype and is therecondence that the results will be suciently accurateto support the decisions that will be based on them? Are the real-world operating conditions understood andcan they be replicated in the model? Could a better model be developed if data from somelimited physical testing were incorporated? Does the model need to be validated and if so, how willthis be done?The changing role of physical testing in vehicle development programmesIntroductionRole of testing with a new product development programmeTools for risk reductionPhysical testing versus virtual testing?Purposes of physical testingExample - development of the in-cab noise of a new truckBackgroundUse of risk reduction toolsTest and development programmeResultsConclusionsAcknowledgementsReferences


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