COMPARATIVE ANALYSIS OF FRONTAL ZONE OF DEFORMATION IN VEHICLES WITH SELF-SUPPORTING AND FRAMED BODIES

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1 Journal of KONES Powertran and Transport, Vol. 18, No COMPARATIVE ANALYSIS OF FRONTAL ZONE OF DEFORMATION IN VEHICLES WITH SELF-SUPPORTING AND FRAMED BODIES Leon Prochowsk, Andrzej uchowsk Mltary Unversty of Technology, Faculty of Mechancal Engneerng Insttute of Motor Vehcles and Transportaton Gen. S. Kalskego Street 2, 00-8 Warsaw, Poland tel.: , fax: e-mal: lprochowsk@wat.edu.pl; azuchowsk@wat.edu.pl Abstract The work consders changes occurred n the features of the supportng structure n three categores of cars, namely: wth the self-supportng body, framed body an ntermedate structures between these two solutons. The area of analyss ncludes the length of deformaton (crush) of the front al part of the car after collson wth a rgd obstacle (barrer). The range of deformaton s a sgnfcant factor of the passve car safety and ndcates the effcency of fulfllng the protectve functon for the passengers. The work shows absolute and relatve (percentage and unt) varatons of the car deformaton, dependng on the year of manufacture, ncludng the perod of Marked trend lnes ndcated general nature of the deformaton range varatons together wth the mprovement of the car supportng system structures. The course of the trend lne has been calculated on the bass of average deformaton length values, calculated n defned perods of vehcle manufacture. Selected sectons of tme result from the dvson of the perod of analyss nto sx parts. The analyss of the deformaton length of the frontal part of passenger cars, SUVs and pckups has been combned wth smultaneous evaluaton of total car length varatons and ther weght values. The car weght drectly affects the knetc energy of the mpact so t has a sgnfcant nfluence on the range of deformaton of the car front durng collson wth an obstacle. Keywords: transport, road safety, vehcle safety, crash tests, body deformaton range 1. Introducton The passenger car body s a developed spatal structure whch conssts of the supportng structure (framework), elements ntegrated wth the supportng structure or removable ones (bonnet and platng) and equpment tems. Apart from sgnfcant dfferentaton of structure of ndvdual components and the whole bodes, they can be dvded not only accordng to ther form (shape) but frst of all n respect of the supportng structure type. In that aspect, there are usually two types of the structures: framed and self-supportng ones. Self-supportng bodes make a domnant soluton but the framed structured can stll be found n the SUV and sport vehcles. The shell bodes make an example of the self-supportng structure (fg.1a), made of properly shaped spatal elements, pressed from thn sheets and wth numerous renforcements (thresholds, pllars, frames etc.). Off-road vehcles are usually equpped wth durable framed chasss (fg.1b). The most often solutons nclude stff longtudnal frames where longtudnal ones are parallel or almost parallel to the vehcle symmetry axs. Sometmes, the sem self-supportng bodes are used supportng frame welded wth the body. The floor plate and ts renforcements make the basc supportng structure n the self-supportng bodes. The ncreasng popularty of off-road vehcles affects ther ncreasng share n the road traffc, resultng n hgher share n the road accdents. In that type of accdents, the results of sgnfcant structural ncompatblty wth the passenger cars can be observed [1, 5].

2 L. Prochowsk, A. uchowsk a) b) Fg.1. Shell structure of the self-supportng body (a) and the frame of the off-road vehcle Mercedes Benz G (b) 2. Objectve and scope of the work The objectve of ths work s to analyze the nfluence of changes that have been made to the structures of the self-supportng systems n recent years on the vehcle crashworthness. The analyss ncluded the range of deformaton of the frontal part of cars wth framed structure of the supportng system and the self-supportng body. The analyss ncluded the cars wth the followng body types: - self-supportng (sedan, hatchback, coupe), - sem self-supportng and framed (SUV); - framed (pckup). The objectve of the work s to show general trends of deformaton range varatons n those bodes durng frontal collson wth a rgd obstacle and to evaluate the safety of the car passengers on that bass. The work made use of results of many frontal car collsons wth a rgd obstacle [6]. A global nature of car manufacture and automotve market results n the same car structure on all contnents. The followng ponts of the work consder the car models popular n Europe, USA and Poland. 3. Characterstcs of cars selected for analyss Car desgn decdes about ts structure and equpment and t affects the car weght and dmensons. The work pays attenton to the cars of weght between 1500kg and 3000 kg. The weght term refers to a car prepared for a crash test and results from a sum of the complete car kerb weght and the weght of 1-3 test dummes. Fgure 2 presents the ponts that show consdered weght values of over 650 cars n three aforementoned categores: - passenger wth self-supportng body, n=347 (number of consdered vehcles); - SUV (sem self-supportng and framed bodes), n=213; - pckup (framed bodes), n=109. Collected data was systematzed and dvded nto groups, accordng to the year of manufacture. Perods of tme and ther markng s as follows: 2 years of ; 3 years of ; 4 years of ; 5 years of ; 6 years of ; 7- years of ; 8 years after That dvson makes further calculatons easer. Usng the data compared on fgure 2, collected on the bass of [6], the course of the lnes characterzng the weght varaton trend n the consdered perod of tme was marked. The course of the trend lne ndcates the ncreasng kerb weght f the pckup type vehcles, when the passenger car weght undergoes only mnor changes. The weght of consdered passenger cars wth the self-supportng bodes (sedan, hatchback, coupe) usually does not exceed 2200 kg and no sgnfcant change was observed durng last 30 years. 398

3 Comparatve Analyss of Frontal Zone of Deformaton n Vehcles Wth Self-Supportng and Framed Bodes 1 Mass [kg] Mass Mass - STD Mass + STD Appr. (Mass) Appr. (Mass + STD) Appr. (Mass - STD) 1500 Year nterval Mass [kg] Mass Mass - STD Mass + STD Appr. (Mass) Appr. (Mass + STD) Appr.( Mass - STD) Year nterval Mass [kg] Mass Mass - STD Mass + STD Appr. (Mass) Appr. (Mass - STD) Appr. (Mass + STD) Year nterval Fg.2. Varatons of the average value and standard devaton of the car weght for three vehcle categores (, and ) The weght ncrease trend n the SUV group does not have unambguous nature. However, the pckups are manufactured as the more heavy vehcles, from 10 kg durng the s to 20 kg nowadays. Such condton probably results from constant mprovement of the vehcle standard. They were often transformed from the operatng vehcles nto luxury SUVs. Analyzed weght value varatons have a sgnfcant nfluence on the mpact energy durng the car collson wth an obstacle and n that way they affect the range of deformaton. 4. Car body deformaton 4.1. Range of car body deformaton n three car categores Protectve role of the car body s fulflled by a proper assocaton of a rgd supportng structure of the cabn and specal shaped energy-consumng zones (that undergo sgnfcant deformatons), that surround the cabn from each sde. It should be underlned that the supportng structure of the car body conssts of basc energy-consumng elements and provdes hgh dsperson of mpact energy or transfers them to the supportng structure areas outsde the vehcle crash zone. The authors have already ndcated [2, 3, 4, 7], that the course of car deformaton durng the frontal collson depends on the arrangement of drve unts, ther fttngs and the volume of the space n the engne chamber. 399

4 L. Prochowsk, A. uchowsk In the consdered tests, the car ht a rgd barrer at the speed of about 56 km/h, placed at the angle of o aganst the drecton of the moton. Obtaned results were used n the calculatons ther results are shown on fgure 3. Crush [mm] Crush Crush - STD Crush + STD Appr.(Crush) Appr.(Crush - STD) Appr.(Crush + STD) Year nterval Crush [mm] Crush Crush - STD Crush + STD Appr.(Crush) Appr.(Crush - STD) Appr.(Crush + STD) 200 Year nterval Crush [mm] Crush Crush - STD Crush + STD Appr.(Crush) Appr.(Crush+STD) Appr.(Crush - STD) Year nterval Fg.3. Varatons of average car deformaton value and standard devaton (STD) n the followng year ntervals The lnes on fgure 3 show the course of varatons of the average deformaton value and the standard devaton from the average value n partcular perods of car manufacture. Compared results refer to three car body categores, and, and t has a drect nfluence on shapng the supportng structure of ther front part. The course of the trend lne ndcates that deformaton decreases n each analyzed car category as the car structure was mproved n the followng years of manufacture. That mprovement s proven by ncreasng energy dsspaton capactes at decreasng deformaton. However, the paste of deformaton declne, obtaned n the followng year ntervals s gettng lower. It ndcates that the car structure mprovement process wthn that scope s gettng more and more dffcult. Table 1 shows an approxmate analytcal descrpton of the functon approxmatng the dependence of the average car front deformaton on the perod of years of manufacture, namely: b D a x, (1) where D s an average car deformaton value n [mm], manufactured n x year nterval and a and b make the approxmaton coeffcents. 400

5 Comparatve Analyss of Frontal Zone of Deformaton n Vehcles Wth Self-Supportng and Framed Bodes 1 Table 1. Approxmaton of deformaton dependence on the years of car manufacture durng the perod of (x s a number ndcatng the year nterval of car manufacture) Deformaton Approxmaton of average car deformaton dependence on the nterval of years of manufacture D = x -0,122 D = x 0,005 D = 695.4x -0,098 Table 2. Characterstcs of the car structure mprovement on the bass of the crash test results. Years: Years: Car group Average Range of deformaton Average Range of deformaton HIC36 weght [kg] depth [mm] weght [kg] depth [mm] HIC The courses of approxmatng functon (gven n table 1) confrm the values of domnatng range of deformaton varatons shown n table 2. Crash zone structure mprovement s proven by the reducton of the HIC (Head Performance Crteron) ndex value n the followng years of car manufacture wth smultaneous decrease of the deformaton range apart from the ncreasng mpact energy (car weght ncrease). The HIC ndex values refer to a 50-centle male dummy (drver) Percentage deformaton varatons Usng the data from fgure 3, the followng fgure 4 shows relatve (percentage) varatons that refer to average values from the perod of n all car categores. Courses of relatve deformaton varatons make the progress evaluaton easer. In order to do that, fgure 4 shows, apart from a lne characterzng the course of deformaton (dc), the course of car length varatons (dl) and knetc mpact energy (de), whch was changng (mantanng almost constant barrer mpact velocty) as the tested car weght was changed. The deformaton approxmaton functon shown n table 3. Table 3. Functons approxmatng the car deformaton length varatons D n %, as a dependence on the year nterval of the car manufacture; x as n table 1 Deformaton Deformaton approxmaton functon D = 0.346x x D = x x D = x x Durng , over 20% reducton of front car body deformaton at lttle decrease of car body length and weght was obtaned n the car category. It ndcates the ncrease of the passenger safety zone length by app. mm n front of the car. In the car category,.e. SUV, the reducton of deformaton by app. 5% was obtaned at the ncrease of general car length by over 10% and the car weght by over 20% (fg. 4). So n that category the front passenger safety zone was ncreased by app. 60 mm. The category cars ncreased ther length by app. 8% and ther weght by 30%, obtanng a sgnfcant mprovement of usable features at the same tme durng the analyzed perod. 401

6 L. Prochowsk, A. uchowsk Reducton of deformaton by 15% ndcates sgnfcant structural modfcatons n the supportng elements n the front of the car body. In total, those modfcatons allowed for the ncrease of the passenger safe zone length by almost 150 mm. Percentages de dc dl Appr.(dE) Appr.(dC) Appr.(dL) Year nterval Percentages de dc dl Appr.(dE) Appr.(dC) Appr.(dL) Year nterval Percentages de dc dl Appr.(dE) Appr.(dC) Appr.(dL) Year nterval Fg.4. Percentage varatons of deformaton (dc), length (dl) and mpact energy (de) n three car categores (,, ) 4.3. Unt deformaton Synthetc specfcaton of calculaton results presented on fgure 4 refers to the average values n ndvdual perods of years of manufacture. At present, the results of ndvdual car measurements were used for calculaton of the unt deformaton of the front part of the car body (fg.5), namely: WDD W1( ) %, (2) WDD where WDD s an average unt deformaton of the of the front part of the car body, calculated n each year nterval of car manufacture, that s: k n 1 Dk WDD, (3) n L 2 k 1 Nk n s a data quantty n nterval, and of k car n that nterval. (D LN ) k are the car body deformaton and length values 402

7 Comparatve Analyss of Frontal Zone of Deformaton n Vehcles Wth Self-Supportng and Framed Bodes 1 The WDD ndex values of the cars manufactured durng fall between 0,10-0,13 (table 4). Table 4. Index value of relatve car deformaton and weght varaton Car category WDD ndex WMD ndex The WMD ndex values gven n table 4 were calculated n the followng way WMD 1 n k n k 1 M L k Nk, [kg/mm], (4) where M k s the k car weght value n year nterval of car manufacture. W1, % 60 Appr.() Appr.() Appr.() Year nterval Fg.5. Percentage varatons of the W1 unt deformaton n three car categores (,, ) Trend lnes on fgure 6 show the average course of unt deformaton dependence W1() on the weght unt ndex,.e. W2() WMD W 2( ) %, (5) WMD 2 Calculaton results presented on fgure 6 allow for the followng conclusons: - a sgnfcant decrease of deformaton of the front part of the car body was obtaned at a lttle car weght ncrease n the category cars; - a sgnfcant dsperson of values of the analyzed ndexes n the whole set of the SUV cars can be observed, so t s dffcult to defne a stable trend of deformaton varatons; - a sgnfcant decrease of the unt deformaton was also obtaned at a dstnct car weght ncrease n the category. 5. Summary Dependences gven n ths work have been obtaned on the bass of the analyss of the test results ncludng 650 cars. They show dfferent car body features n the aspect of transferrng the dynamc loads n the cars wth framed and self-supportng bodes durng collson wth a rgd barrer. The trends of the car structure modfcatons n the analyzed car categores observed n recent years can be defned n the followng way: 403

8 L. Prochowsk, A. uchowsk W1, % Appr.() Appr.() Appr.() W2, % Fg.6. Trend lnes of the unt deformaton varaton dependng on the car weght modfcatons - range of deformaton, tested n comparable crash test condtons, does not ncrease n any consdered category; - unt car body deformaton n the and car categores s gettng lower and lower and t was reduced by app. 20% n the analyzed perod. Durng the perod of 30 years, the ncrease of the passenger safe zone length by app. 60mm n category to almost 150mm n category were obtaned n all cars of the analyzed categores (by reducng the range of deformaton). The work was done under Project No 5596/B/T02/2011/40, funded by the Natonal Scence Centre References [1] Mzuno, K., Tatesh, K., Ara, Y., Research on vehcle compatblty n Japan. 18 th Internatonal Techncal Conference on the Enhanced Safety of Vehcles, Nagoya, Japona [2] Prochowsk, L., uchowsk, A., Zelonka, K., Analza wp ywu pr dko c uderzena w przeszkod na obc ena dynamczne osób w samochodze z ramow konstrukcj no n, Archwum Motoryzacj, 3/2011, Warszawa [3] Prochowsk, L., uchowsk A., Obc ena dynamczne bloku nap dowego podczas zderzena samochodu, Journal of KONES Powertran and Transport, Vol.13, No.2, Warszawa [4] Prochowsk, L., uchowsk, A., W a cwo c nadwoza w zakrese poch anana energ podczas uderzena samochodu w sztywn przeszkod, Zeszyty Naukowe Poltechnk w tokrzyskej, Mechanka Nr 84, Kelce [5] Wcher, J., Kompatyblno agresywno nowoczesnych rodków transportu drogowego. Matera y M dzynarodowej Konferencj Naukowej Transport XXI weku, Poltechnka Warszawska, PAN, Warszawa [6] [7] uchowsk, A., Prochowsk, L., Sztywno nadwoza analza s dza aj cych na przeszkod podczas zderzena, Zeszyty Naukowe Poltechnk w tokrzyskej, Nr 8/2008, Kelce