The changing role of physical testing in vehicle development programmes

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    formance can be achieved within shorter times and with reduced development and manufacturing costs. The approach was illustrated by

    using computer aided engineering (CAE) tools has devel-

    2. Role of testing with a new product development

    programme

    Essentially, testing has just one objective: to ensure theproduct will deliver a protable return to the manufac-

    meeting or exceeding the customers expectations in terms

    the 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: pwilkinson@ltc.ltd.uk.

    ics 4

    Journaloped 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; Virtual

    1. Introduction

    In 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 design

    turer. 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 pdevelopment

    Paul W

    LTC Ltd., Aston Way, Leyla

    Available onlin

    Abstract

    The 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 an

    Journal of Terramechan0022-4898/$20.00 2006 Published by Elsevier Ltd on behalf of ISTVS.doi:10.1016/j.jterra.2006.01.004sical testing in vehiclerogrammes

    inson

    PR26 7TZ, United Kingdom

    9 March 2006

    to 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 per-

    www.elsevier.com/locate/jterra

    4 (2007) 1522

    ofTerramechanics

  • programme 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 reduction

    If 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 warranty

    16 P. Wilkinson / Journal of Terramechanics 44 (2007) 1522(a) enhancement to satisfy or delight the customer;(b) modication to reduce costs (either directly or in

    manufacture);(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.T