NUMERICAL FLEET OPTIMIZATION STUDIES FOR IMPROVED COMPATIBILITY Paul Lemmen Cor van der Zweep Flors Leneman TNO Automotve The Netherlands Paul Altamore TNO-MADYMO North Amerca Unted States Paper No. 445 ABSTRACT On behalf of NHTSA and the Dutch Mnstry of Traffc and Transport the Safety department of TNO Automotve s performng numercal fleet studes usng mult-body models. Am s to develop strateges for optmzaton of front-end structures mnmzng the total harm n car-to-car crashes on a fleet-wde bass. For these studes mult-body models are beng constructed from exstng fnte element models. Front-end structure and passenger cell are modeled n detal to provde realstc deformaton modes. Furthermore dummes, arbags, belts and man nteror parts lke dashboard and steerng wheel are ncluded. Currently four models are avalable, each of a dfferent vehcle class. To ndcate the performance of the mult-body vehcle models for crashworthness optmzaton of a fleet a study on offset frontal mpacts s performed. Usng the multbody models a seres of parameter sweeps over relevant accdent and desgn parameters were performed. The accdent parameters ncluded vehcle type, belt usage and occupant sze. The desgn parameters relate to the frontend geometry of the two smaller vehcles and the frontend stffness of all vehcles. A total set of 25 scenaros was smulated. INTRODUCTION Compatblty s an mportant subject n road traffc safety research, because n many accdents more than one road user s nvolved. In that case the passve safety of the dfferent road users s often n unbalance. Ths leads to an ncompatble stuaton n whch one of the partes suffers from the relatve aggressveness of the other. A soluton to ths problem may be found n mproved vehcle compatblty whch combnes self and partner protecton characterstcs. Durng the last decades extensve research was done on the statstcs of car-to-car crashes gvng a/o nterestng rates of aggressveness [1,2]. Although the occupant safety has mproved sgnfcantly car-to-car crashes form an ncreasngly mportant class of accdents to be examned makng t one of the most mportant safety ssues for the car ndustry and governmental bodes [1,3, 4, 5, 9]. There are two man njury-causng aspects to car collsons n general but also wth respect to compatblty: excessve deceleraton and ntrusons [8]. The deceleraton aspects relate to the phenomenon that lghter cars undergo larger deceleratons than heaver cars n a collson between both. So, n the lghter car the occupants can get njured more easly, due to these large deceleratons and contacts drectly resultng from these deceleratons. On the other hand, ntrusons relate to enterng of structural car parts nto the passenger cabn that should be avoded as much as possble. A frst mportant step to avod ntrusons s the avodance of geometrcal msmatch. Shearlaw and Thomas [6] show that t s very dffcult to tackle the queston whether or not cars are compatble wth respect to these ntruson effects. Furthermore, the passenger compartment ntegrty should be preserved as much as possble: collapse of the compartment should be avoded. For ths purpose, the global strength of the passenger compartment should be larger than the strength of the front and of course large enough to wthstand the forces durng the whole crash. Ths also means that the strength of two cars n a crash should be optmzed such, that the collson energy s dsspated wthout compartment collapse of any of the cars [3]. Of course, the strengths of the cars are closely related to the deceleraton of the cars. When assessng compatblty the overall safety of a fleet should be consdered. For the evaluaton of the overall safety of an automotve fleet systems modelng approaches have been developed. In the nneteenseventes Ford Motor Company developed a method for maxmzng a sngle vehcle s safety performance n frontal crashes [1]. Ths program was updated by the Unversty of Vrgna to nclude new bomechancal transforms and updated accdent data as well as multvarable analyss capablty [11]. Other car manufacturers also developed programs, manly for optmzng sngle vehcle desgn. On behalf of NHTSA Volpe developed a model that predcts the total harm over a range of vehcle types rather than a sngle subject vehcle [12]. The model estmates njures over a gven set of crashes consderng ar bags, seat belts and occupants of varyng sze. It ncorporates updated accdent data for the statstcal accdent envronment model and njury rsk functons that convert njury measures nto the AIS scale [14]. Injury values are obtaned from MADYMO occupant knematc models of a car and LTV loaded by crash pulses obtaned from one-dmensonal lumped parameter models. Fgure 1 summarzes the methodology.
The method does not nclude an optmzaton strategy to mnmze the overall Harm n a fleet envronment. Fgure 1. Fleet Systems Model Methodology [12] Ideally njury values are to be computed usng detaled vehcle FE models. However, whle potentally very accurate these are computatonally too expensve to execute for fleet systems models that a substantal amount of smulatons [15]. Alternatvely smpler but faster runnng lumped mass models n MADYMO may be used. Although less accurate these models requre substantally less computer tme makng t easer to conduct the necessary smulatons. The models were successfully appled n numercal optmzaton studes brngng all njury levels n a small fleet (lmted number of scenaros) below crtcal values by adjustment of the frontal stffness [9, 16]. The result was obtaned by optmzng the stffnesses of man load carryng members n the frontends. Geometrcal nteracton was not consdered, as t could not be translated nto a contnuous parameter for numercal optmzaton usng drect methods. However, whle the front-end stffness does affect compatblty, geometrcal nteracton s regarded as the prme factor for good compatblty. Therefore structural varants should be consdered n the optmzaton process whch may be stated as [15] Mnmze Inj (x,u) = p I s I (x,u) subject to: Wgt(x) < Wgtmax Cost(x,w(x)) < Costmax x mn < x < x max where: x = Vector of desgn varables u = Belt usage rate Inj(x,u) = Total njures Wgt(x) = Incremental weght for wth desgn x Cost = Incremental cost for x and Wgt(x) Wgtmax = Upper constrant on ncremental weght Costmax= Upper constrant on ncremental costs p s Statstcal Model of Accdent Envronment Accdent Characterstcs Vehcle Impact Models Occupant Knematc Models Injury Harm = p s = Probablty of event = Injures resultng from event The restrants on the desgn varables x are ncluded to lmt weght as well as costs of the proposed desgn modfcatons and to ensure that modfcatons reman wthn realstc ranges. Each crash event may be characterzed by sx accdent varables namely vehcle p s Injury Rsk Functons types, mpact mode, mpact speed, seat poston, occupant sze and belt usage [12, 15]. In vew of the large number of scenaros to be consdered n fleet studes optmzaton by consderng structural varants can only be acheved usng desgn of experments (DOE) or dentcal methods that scan the desgn space by varaton of relevant desgn parameters. Correct nterpretaton of results requres an adequate formulaton of the object or target functon. Statstcal Model of Accdent Envronment Accdent Characterstcs Lumped mass vehcle models and desgn varants k w.r.t. stffness and geometry Fgure 2. Fleet Systems Model Methodology usng multbody vehcle models wth occupants Fgure 2 depcts the fleet systems model usng multbody vehcle models to predct njures. In ths paper the vehcle models, the njury rsk functons that form the bass of the object functon and results of a fleet study consderng desgn varants wll be dscussed. VEHICLE MODEL DEVELOPMENT AND VALIDATION Based on exstng FE models four lumped mass models representatve for the US fleet were developed. The vehcles are lsted n table 1. Table 1. Avalable vehcle models Model Class Mass p Injury for each varant k mn(inj (k))= mn p s ( k ) [kg] Test Mass [kg] Geo Metro Subcompact 8 1191 Chrysler Compact pass. 185 1371 Ford Taurus Mdsze pass. 1488 1728 Ford Explorer SUV 1971 225 s (k) Injury Rsk Functons The front-ends and the sde structures were modeled n detal to descrbe the actual nteracton for frontal and sde mpacts. The rgd bodes are connected by non-lnear sprng and damper elements, whch represent the stffness behavor. Characterstcs of these elements were derved usng FE models and component test data. Attenton was focussed on the man load carryng components lke longtudnals and shotguns. The occupant compartment ntruson s descrbed usng contact surfaces. The nteror of the car s modeled ncludng a dashboard, steerng wheel, belts, arbag and Hybrd III dummy at the drver sde. Fgure 3 shows the models of the Ford Taurus and the Chrysler n the undeformed confguraton. Lemmen, 2
Interacton between the vehcles s realzed wth contact facets at the front and the sde. Except for the Chrysler all vehcle models show a good correlaton wth test results. Based on NCAP test data NHTSA has dentfed AHoBF ranges for dfferent vehcle classes [17]. Results for all vehcle models except the are wthn the specfed class range. Fndngs for the are currently beng nvestgated n more detal usng FE models. Table 2. Comparson of Average Heght Of Barrer Force. Car Fgure 3. Undeformed frame model of Chrysler (left) and Ford Taurus (Rght) The frame models were valdated aganst Full Wdth barrer NCAP test data. In addton, the vehcle sgnals are valdated aganst FE smulatons under dfferent angels and dfferent crash scenaros. Fgure 4 shows typcal results for vehcle sgnals (left) and dummy response (rght). Results correlate well. MADYMO (98429) Test (V232) acceleraton (m/s2) AHoBF AHoBF Class range [m] (NCAP) [m] 1) Geo Metro.44.42.41.47 Chrysler.51.45.43.48 1) Ford Taurus.49.5.43.5 Ford Explorer.58.63.5.62 1) Data somewhat dfferent than values ndcated by NHTSA n ref. [2] The Average Heght of Barrer Force s known as a relevant measure, however, for compatblty the force dstrbuton on the barrer s even more mportant. Fgure 5 therefore compares load cell data at two tme frames for the Ford Taurus. velocty (m/s) dsplacement (m/s) tme (s) Fgure 4. Valdaton frontal Chrysler model: frontal car structure (left) and resultant head acceleraton of a 5th percentle Hybrd-III (rght) In addton to the vehcle and dummy sgnals the proposed compatblty measurables were compared. Table 2 compares the Average Heght of Barrer Force (AHoBF) whch s calculated as follows [17] (F (t )h ) AHoF(t) = F (t ) AHoBF = t AHoF (t ) F (t ) F (t ) t where: - F = Force on cell - h = heght of cell (1) Fgure 5. Comparson of smulated (left) and expermental (rght) load cell wall data for the Ford Taurus at t = 25 ms (top) and t = 6 ms (bottom). Note that the dmensons of the grd szes n the smulaton are somewhat dfferent from the test (smulaton: 8*8; test: 4*9). At 25 ms hgh loads are located at longtudnal locatons. Note that the dmensons of the cells and therefore the grd szes are somewhat dfferent, whch may affect the results to some extend. At 6 ms the sub-frame and engne of the smulaton model partake n the load transfer whch s not the case n the actual test. Despte ths dscrepancy the smulated results generally correlate very well wth expermental data and the models may be regarded adequate for usage n fleet studes. INJURY RISK FUNCTIONS For frontal mpacts the most commonly used njury measures nclude Head Injury Crteron (HIC), Vscous Crteron (VC), 3 mllsecond acceleraton (3 MS), Combned Thoractc Index (CTI), Femur Force Compresson (FFC), Nj, FNIC, Tbea Index (TI) and TCFC. See also fgure 6. All of these njury measures used as regulatory crtera except for the CTI. CTI though s recommended by NHTSA for research use [13]. Lemmen, 3
Predcton of the lower leg njures requres accurate representaton of ntrusons, whch can only be acheved by use of detaled fnte element models wth correct geometry and materal modelng. The mult-body models have nsuffcent detal to represent ntrusons correctly and therefore TTI and TCFC are not consdered here. Alternatvely an approach based on the Abbrevated Injury Scale (AIS) may be used, see e.g. [19]. Injury rsk functons are used to convert njury values nto AIS levels, whch subsequently may be transformed nto an overall njury rsk usng the Injury Severty Scale (ISS). Fgure 7 and fgure 8 show mathematcal models to transfer CTI and HIC values nto the AIS probabltes. Identcal models have been derved for 3ms, CD, FFC, and Nj. The models, generally known as the njury rsk functons, have been proposed by NHTSA on the bass of expermental data and prevous research [14]. The experments were performed wthn the regulatory range of nterest up to crtcal values. For hgher njury values the plotted approxmatons are therefore more heurstc. Fgure 6. Hybrd III 5 th percentle frontal mpact dummy wth njury crtera. Except for the lower leg njures all ndcated mechansms are consdered n ths study. Each MADYMO smulaton results n a set of njury values for the drvers n both vehcles. To compare rsks n the dfferent scenaros results need to be converted nto a measure that gves an ndcaton for the overall njury rsk (AIR). In prevous studes nto the optmzaton of the front-end stffness ths was acheved by summng squared normalzed njury values for head, upper leg and chest [16] obj = HIC( ) HICcrt ( ) 2 2 2 FFC( ) 3MS( ) + + FFC crt ( ) 3MScrt ( ) (2) Fgure 7. Injury rsk functon for CTI [14] The njury values used n eq. (2) were selected based on results of parametrc studes [16]. Ths functon was found to be qute effectve as t s very dscrmnatve for crtcal or near crtcal njures. Man dsadvantage tough s that all njures have dentcal weghts, whch s not realstc when consderng the harm. Therefore njury sgnfcance ratngs should be ntroduced: 2 2 2 HIC( ) FFC( ) 3MS( ) obj = α + β + γ HICcrt ( ) FFCcrt ( ) 3MScrt ( ) (3) where α, β and γ are the weght factors for the respectve njury types. Estmates for the weght factors are provded n table 3. These numbers, based on feld studes, were derved n the early nnetes to evaluate the performance of restrant systems [18]. Table 3. Injury sgnfcance factors [18] Body regon Sgnfcance Weghts Head 6% α =,6 Chest 35% β =,35 Extremtes 5% γ =,5 Fgure 8. Injury rsk functon for HIC [14] Mathematcal expressons for the njury rsk functons can be found on the NHTSA webste (http://www.nhtsa.dot.gov/cars/rules/rulngs/aarbagsnp RM/PEA/pea-III.n.html). Usng these cumulatve functons a vector of AIS probabltes (AIS=,1,2,3,4,5,6) s obtaned by subtractng each AIS probablty at the computed njury level from the next AIS probablty. For each njury type a vector of AIS probabltes s computed whch s converted nto an expected AIS value accordng to Lemmen, 4
6 E( X ) = w P ( X ) = 1 where X = Injury value E = Expected AIS value P w = Probablty of AIS level w w = AIS level,1,2,3,4,5,6 w (4) depcted modfcatons are easly mplemented n the mult-body models. The expected AIS values for each njury mechansm may be converted nto an overall body crteron usng normalzed cost functons to obtan communal costs (HARM) or usng the Injury Severty Scale (ISS) [19]. In ths paper the ISS wll be used. FLEET SETUP AND ACCIDENTS SCENARIOS To explore the potental of the mult-body models for usage n optmzng the crashworthness behavor of a fleet a study wth four vehcles was performed. Frontal offset mpacts at a closure speed of 5 km/h were analyzed n a fleet consstng of the Geo Metro, Chrysler, Ford Taurus and Ford Explorer. Fgure 8 shows the accdent scenaros. Crashes between the Explorer and the Geo Metro are not consdered, as ths scenaro s strongly ncompatble, even when applyng the desgn modfcatons suggested below. The accdent varables occupant sze (5 th percentle female, 5 th percentle male and 95 th percentle male) and seat belt usage (belted an unbelted) were vared. Geo Fgure 9. Modfed front-end Geo Metro. To mprove the nteracton wth other vehcles cross members have been renforced (Green bodes) and two vertcal members lnkng shotguns and longtudnals (red bodes) have been added. Fgure 1. Modfed front-end Chrysler. To mprove the geometrcal nteracton a sub-frame was added (red bodes) and the lower cross-beam was renforced (yellow bodes) SIMULATION RESULTS Taurus Explorer Fgure 8. Crash scenaros between vehcles. The Explorer Geo scenaro s not consdered, as t s hghly ncompatble. For the optmzaton two desgn varables were ntroduced namely front-end stffness and front-end geometry. For the stffness structural components relevant for the crash behavor were dentfed n each vehcle and related bodes grouped such that ther connectng sprngs and damper characterstcs can be changed smultaneously. The scalng of the characterstcs corresponds to overall changes n elastc and plastc stffness of the component. The allowable range of the stffness was set between 75 and 15% of the orgnal values to be wthn physcally realstc bounds. Weght and cost restrants were not consdered here but are largely covered by the above-mentoned restrant. For the frontend geometry desgn varants of the Geo Metro and the Chrysler were created, see fgures 9 and 1. The Parametrc smulaton of all scenaros for relevant desgn varables yelds a total of 25 ndvdual cases. Here the stffness for each vehcle s vared n fve dscrete steps rangng between 75% and 15% of the orgnal stffness. Each case requres approxmately 2 mnutes of CPU tme on a PC server system. The total requred CPU was about 83 hours. For each case a vector of njures s obtaned whch s processed nto an overall body value usng eq. (2) or the alternatve method based on AIS and ISS. Results of the smulatons are analyzed wth the SPSS statstcal program [21]. The computed dstrbutons for the entre subset are shown n fgures 1 (ISS) and 11 (weghted squared njures usng eq. (2)). Both fgures show dentcal trends but results based on eq. 2 appear to have larger relatve dfferences whch s manly due to use of squared relatve values rather then relatve values, see also [16]. Ths fndng may be mportant for optmzaton studes as t focuses the search towards crtcal or near crtcal cases. However, as t s based on a lmted set of accdent varants care should be taken when generalzng Lemmen, 5
ths fndng. Therefore ISS wll stll be used n the sequel of ths paper. To obtan an ndcaton for the contrbuton of dfferent njures to these results 3MS, HIC and FFC are plotted n Fgure 12 through 14 for the entre subset. FFC values for the smaller vehcles are near or over crtcal (FFC crt = 1). Chest values are relatvely hgh especally for the smaller cars (3MS crt = 6 g). HIC values are generally low at values up to 4 (HIC crt = 1). Fgure 15 shows ISS values sorted by belt usage. Only lmted nfluence of the belt usage s observed, whch s unrealstc. Fgure 16 and 17 show FFC and 3MS values. From these fgures t s observed that the upper leg load levels for belted drvers are sgnfcantly lower as to be as expected. However, 3MS values for the belted drvers are hgher than for the unbelted. Ths s explaned by the fact that the belt systems n the vehcle models do not have a load lmter resultng n hgh chest loads. For a more realstc representaton of the fleet behavor a load lmter should be ncluded. Fgure 13. 3MS dstrbuton (mean values) of entre subset plotted as functon for vctm and opponent car. Fgure 13. HIC dstrbuton (mean values) of entre subset plotted as functon of vctm and opponent car. Fgure 11. ISS dstrbuton (mean values) for entre subset plotted as functon of vctm and opponent car. Fgure 14. FFC dstrbuton (mean values) of entre subset plotted as functon of vctm and opponent car. Fgure 12. Weghted squared njury dstrbuton (mean values) for entre subset plotted as functon of vctm and opponent car. Fgure 15. ISS dstrbuton (mean values) of entre subset plotted as functon of vctm car and belt usage. Lemmen, 6
2. 15. ISS Geo (Vctm) 1. 5. Fgure 16. FFC dstrbuton (mean values) of entre subset plotted as functon of vctm car and belt usage.. n=67 n=53 n=53 n=57 n=58.75.87 1. 1.25 1.5 Stffness Geo (Vctm) Fgure 18. ISS of Geo drver as functon of frontal stffness 1 75 HIC Geo (Vctm) 5 Fgure 17. 3MS dstrbuton (mean values) of entre subset plotted as functon of vctm car and belt usage. Fgure 18 shows ISS values of the Geo drver for stffness varatons n the front-end of the Geo. The columns ndcate the 25% to 75% range of samples. The vertcal lnes related to each column ndcate ultmate and merdan values. Mnmum ISS values occur at the orgnal stffness. However, when consderng separate njures, fgures 19 through 21, dfferent trends are observed. HIC n fgure 19 shows an dentcal behavor as the overall measure. 3MS n fgure 2 s farly nsenstve to the front-end stffness. FFC-left n fgure 21 shows a clear reducton wth front-end stffness brngng the 95% range below crtcal. Ths trend s not observed n the ISS result due to the relatvely low weght factor for FFC. The fndng s n agreement wth prevous studes usng drect optmzaton [9, 16]. Fgure 22 and 23 show results of the Geo drver for stffness varaton n the Taurus front-end. The nfluence on ISS s farly low but the FFC shows a trend wth reduced njury for reduced stffness of the Taurus frontend, as to be expected. 25 n=67 n=53 n=53 n=57 n=58.75.87 1. 1.25 1.5 Stffness Geo (Vctm) Fgure 19. HIC of Geo drver as functon of frontal stffness 6 4 2 Chest acc. (3ms) Geo (Vctm) n=67 n=53 n=53 n=57 n=58.75.87 1. 1.25 1.5 Stffness Geo (Vctm) Fgure 2. 3MS of Geo drver as functon of frontal stffness Lemmen, 7
FFC Geo (Vctm) 25 2 15 1 5 n=67 n=53 n=53 n=57 n=58.75.87 1. 1.25 1.5 Stffness Geo (Vctm) Fgure 21. 3MS of Geo drver as functon of frontal stffness Fgures 24 through 26 compare njury values between the updated and the orgnal Chrysler. The fgures show results for the reference confguratons (orgnal stffness and a belted 5-percentle dummy) only as smulatons for the complete statstcal study were stll n progress at 4 the tme of wrtng. The modfcaton of the front-end depcted n fgure 1 was meant to mprove the structural nteracton and as such reduce ntrusons. 3 Knowng the lmtatons for the lower extremtes, results related to upper legs, chest and head are plotted. The results ndcate that acceleraton compat related 2 njures for head orgnal and chest reman nearly unaffected whereas ntruson related njures for the upper legs reduce sgnfcantly. The 1 reducton of ntruson becomes clear from fgure 27 that shows deformed confguratons for the -Geo scenaros. Identcal results where found for the adjusted Geo. 3ms upper thorso 2 HIC value 4 3 2 1 14 Ne E 12 2. 15. FFC left 15 1 compat orgnal FFC rght 1 8 6 5 4 1. 2 ISS Geo (Vctm) 5. Ne E. n=18 n=11 n=19 n=19 n=8.75.87 1. 1.25 1.5 Fgure 24. FFC values for orgnal and updated for crashes aganst other cars. Stffness Taurus (Opponent) Fgure 22. ISS of Geo 4 drver as functon of frontal stffness Ford Taurus 4 2. 15. 3ms upper thorso 3 2 1 compat orgnal HIC value 3 2 1 compat orgnal ISS Geo (Vctm) 1. 5.. 2 n=18 n=11 15 n=19 n=19 n=8 compat.75.87 1. orgnal 1.25 1.5 FFC left Stffness 1 Taurus (Opponent) Fgure 23. FFC of Geo drver as functon of frontal stffness Ford Taurus 5 Fgure 14 25. HIC values for orgnal and updated for crashes aganst other cars. 12 FFC rght 1 8 6 4 2 compat orgnal Lemmen, 8
3ms upper thorso FFC left 4 3 2 1 5 compat orgnal Fgure 27. Deformed confguratons at 8 ms for - Geo scenaros: orgnal (top) and updated (bottom). s blue, Geo s green. CONCLUSIONS AND RECOMMENDATIONS To ndcate the performance of the mult-body vehcle models for crashworthness optmzaton of a fleet a study on offset frontal mpacts was presented. Usng models of four dfferent vehcles, that represent the US car fleet, parameter sweeps over relevant accdent and desgn varants were performed. The vehcle models are 3-D rgd mass models derved from FE models. The rgd bodes are connected by nonlnear sprng and damper elements representng the stffness behavor. Man nteror parts and dummes are ncluded. Comparson wth test results shows that the models provde realstc crash and occupant behavor. The models ntegrate vehcle and occupant models that were HIC value FFC rght separated n prevous fleet studes. Front-end stffness and 4 geometry can be adjusted easly by scalng the stffness of man members and addng new bodes and jonts. 3 Although less accurate than fnte element models the mult-body models requre substantally less CPU makng them sutable for compat the large amount of smulatons requred 2 n fleet studes. orgnal In the fleet study frontal offset mpacts between the 1 four vehcles (Geo Metro, Chrysler, Ford Taurus and Ford Explorer) were consdered. Crashes between the dfferent vehcles were smulated wth belted an unbelted drvers Ne Ex of Ne Ne dfferent Ne Ta sze Ne Ge (5 th percentle female, 5 th percentle male and 95 th percentle male dummes). The front-end stffness of each vehcle was vared between 75 Fgure 26. 2 3MS values for orgnal and updated for and 15% of ther orgnal value. For the two smallest 14 crashes aganst other cars. vehcles desgn varants that provde mproved structural 12 nteracton were consdered. A full factoral parameter 15 compat 1 sweep over these compat accdent and desgn varables resulted n orgnal 25 scenaros orgnal where the stffness of each vehcle was 8 1 6 vared n fve steps. Smulatng these scenaros requred an acceptable 83 hours of CPU on a PC server system. Statstcal analyss of results showed that njury levels for these consdered accdent scenaro can be reduced below crtcal values. Evaluaton of results for belt usage showed that the modelng Ne Ex of Ne Ne restrants Ne Ta needs Ne Ge mprovements. Despte ths the study showed that the models have hgh potental for 4 2 ths type of fleet studes snce they provde realstc vehcle behavor at lmted CPU costs. Also structural modfcatons are easly ntroduced. In future work the modelng of the restrant systems should be mproved. Comparson of belted and unbelted results showed that the belt models should nclude load lmters to provde more realstc chest loads. Also the trggerng of the arbags should be made dependent on the accdent scenaro n terms of mpact speed and other relevant factors. Ths allows the smulaton of scenaros at dfferent mpact speeds. Wth these mprovements fleet studes usng scenaro weght factors from a statstcal accdent envronment model can be made. Resultng njury dstrbutons can be compared wth real world data for valdaton purposes. In these studes the accdent scenaros can be extended, e.g. wth sde mpacts for whch valdated models are avalable. Apart from the fleet modelng work the mult-body models and ther mproved varants wll be employed to mprove proposals for compatblty test procedures. Car to barrer smulatons wth orgnal and mproved vehcles wll be performed to evaluate proposed barrer desgn and assessment crtera. Ths actvty wll be performed n the European 5 th framework project VC Compat. ACKNOWLEDGEMENTS The authors wsh to thank Jos Hubers from TNO Automotve as well as Gjs Kellendonk and Francos Bronkers from the Unversty of Endhoven for support n the development of use of the mult-body frame models. They also thank Stephen Summers and Thomas Hollowell of NHTSA as well as Leo Schlosser and Jan Busstra from Lemmen, 9
the Dutch Mnstry of Transport for ther support of the compatblty research at TNO. REFERENCES [1] Hollowell, W.T., and Gabler, H.C., NHTSA s Vehcle Aggressvty and Compatblty Research program, 15th Int. Techncal Conf. on the Enhanced Safety of Vehcles, Melbourne, Australa, May 13-17, 1996. [2] Evans, L., and Frck, M.C., Drver fatalty rsk n twocar crashes -- dependence on masses of drven and strkng cars, n Proc. of the 13th ESV Conf., paper no. 91-S1-O- 1, Pars, France, 1991. [3] Zobel, R., 1997, 'Barrer mpact tests and demands for compatblty of passenger vehcles', n: VDI Tagungsbercht 1354, Innovatver Insassenschutz m PKW, pp. 29-225, Düsseldorf, Germany, 1997. [4] Faerber, E., 'Improvement of crash compatblty between cars', (project summary), Conference on road nfrastructure and safety research n Europe, Rsc '97, Brussels, 1997. [5] Wykes, N.J., et al., 1998, Accdent analyses for the revew of the frontal and sde mpact drectves, Report to the European Commsson DGIII, TRL, UK. [6] Shearlaw, A., and Thomas, P., Vehcle to vehcle compatblty n real world accdents, Proc. of the 15th ESV conference, paper no. 96-S4-O-4, 1996. [7] H. G. Moo, J. H. A. M. Hubers (1998). Smple and effectve lumped mass model for determnng knetcs and dynamcs of car-to-car crashes. n:proc. of Int. Crashworthness Conf. IJCrash 98, 9-11 September 1998, Delft, The Netherlands. [8] H. G. Moo, T. Nastc., J. H. A. M. Hubers (1999). Modellng and Optmzaton of Car-to-Car compatblty. VDI berchte NR 1471 (ISBN 3-18-91471-8), pages 239-255, delft, The Netherlands. [9] A.W.J. Gelen, H.G. Moo, J.H.A.M. Hubers (2). An optmzaton methodology for mprovng car-to-car compatblty, ImechE transactons C567/47/2, Delft, The Netherlands [1] Ford Motor Co. (1978). Safety Systems Optmzaton Model, Fnal Report, DOT Report Number DOT HS 6-1446, USA [11] K.P. Whte, H.C. Gabler, W.D. Plkey and W.T. Hollowell (1985). Smulaton Optmzaton of the Crash Worthness of a Passnger Vehcle n Frontal Collsons usng Response Surface Methodology, SAE Paper 85512. [12] A.C. Kuchar, R. Gref, G.W. Neat (21). A Systems Methodology For Evaluaton of Vehcle Aggressvty In The Automotve Accdent Envronment, SAE Paper 21-1-1172 [13] M. Klenberger, E. Sun, R. Eppnger, et al. (1998). Defelopment of Improved Injury Crtera for the Assessment of Advanced Automotve Restrant system, NHTSA Docket No. 1998-445-9 [14] R. Eppnger, E. Sun, et al. (1985). Development of Improved Injury Crtera for the Assessment of Advanced Automotve Restrant Systems II, Supplement to NHTSA Docket No. 1998-445-9 [15] S.M. Summers, W.T. Hollowell (21). NHTSA s Crashworthness Modelng Actvtes, ESV Paper No. 251 [16] C.D. van der Zweep, P.L. Lemmen (22). Improvement of Crash Compatblty between Passenger Cars by Numercal Optmsaton of Front-end Stffness, JSAE Paper No. 22-5353 [17] S.M. Summers, A. Prasad, W.T. Hollowell (21). NHTSA s Compatblty Research Program Update, SAE Paper No. 21-1-1167 [18] D.C. Vano, S. Arepally (199). Assessng the Safety Performance of Occupant Restrant Systems, SAE Paper No. 92328 [19] J.S.H.M. Wsmans, et al. (1994), Injury Bomechancs, Course Notes Endhoven Unversty of Technology No. PRO 1411 TUE [2] http://www-nrd.nhtsa.dot.gov/ NHTSA s web-page [21] SPSS Base 1. Applcatons Gude, SPSS Inc., Chcago, IL, USA, 1999 Lemmen, 1