A study on the crashworthiness and rollover characteristics of low-floor bus made of sandwich composites

Transcription

1 Journal of Mchanical Scinc and Tchnology 3 (009) 686~693 Journal of Mchanical Scinc and Tchnology DOI /s A study on th crashworthinss and rollovr charactristics of low-floor bus mad of sandwich composits H-Young Ko 1, Kwang-Bok Shin,*, Kwang-Woo Jon 1 and So-Hyun Cho 3 1 Graduat School of Mchanical Enginring, Hanbat National Univrsity, Dajon, , Kora Division of Mchanical Enginring, Hanbat National Univrsity, Dajon, , Kora 3 Transit Division, HanKuk Fibr Glass Co., LTD., , Kora. (Manuscript Rcivd Dcmbr 6, 008; Rvisd Jun 9, 009; Accptd July, 009) Abstract This papr dscribs th rsults of th numrical valuation on crashworthinss and rollovr charactristics of a lowfloor bus vhicl mad of sandwich composits. Th sandwich composit usd for th vhicl structurs was composd of aluminum honycomb cor and WR580/NF4000 glass-fabric/poxy laminat facshts. Matrial tsts wr conductd to dtrmin th input paramtrs of th composit laminat facsht modl and th ffctiv quivalnt damag modl for th orthotropic honycomb cor matrial. Crashworthinss and rollovr analysis of th low-floor bus was conductd using th xplicit finit lmnt mthod (FEM) analysis cod LS-DYNA3D with th laps of tim. Th crash condition of th low-floor bus was a frontal accidnt with a spd of 60 km/h. Rollovr analysis was don according to th safty ruls of th Europan standards (ECE-R66). Th angular and translation vlocity and its angl with th ground just bfor impact for rollovr wr calculatd using th dynamic analysis program. Th rsults showd that th survival spacs for th drivr and passngrs wr scurd against frontal crashworthinss and rollovr of th low-floor bus. In addition, th modifid Chang-Chang failur critrion is rcommndd to prdict th failur mods of th composit structurs for crashworthinss and rollovr analysis. Kywords: Honycomb sandwich composit; Crashworthinss analysis; Rollovr analysis; Effct quivalnt damag modl Introduction Th currnt havy traffic of ground transportation is aggravatd du to th incras in th numbr of privat cars. With rgard to th nvironmntal impact, th incras in th volum of numbr of xhaust fums in accordanc with th incrasing numbr of cars svrly causs nvironmntal pollution and global warming. To solv ths problms, svral countris hav dvlopd advancd thrmoplastic composit matrials and manufacturing tchnologis to rduc th wight of th bus and tram vhicl [1]. This papr was rcommndd for publication in rvisd form by Associat Editor Jong Sam Han * Corrsponding author. Tl.: , Fax.: addrss: shin955@hanbat.ac.kr KSME & Springr 009 Composit sandwich panls ar widly usd in lightwight structurs bcaus of thir high spcific strngth and stiffnss []. Rcntly, th us of sandwich composit structurs has bn dvlopd in Kora for ground transportation applications such as th tilting train, low-floor bus, and tram vhicl [3-4]. Th safty of th drivr and passngrs according to frontal crashworthinss and rollovr accidnt has bcom an important issu for bus manufacturs and customrs. Thrfor, th structural stability of th vhicl should b valuatd according to th rgulation of frontal crashworthinss and rollovr bfor th manufacturing of buss. This rgulation has bn continud to covr buss mad of convntional matrials such as stainlss stl or aluminum. Howvr, thr is no rgulation standard for bus structurs mad

2 H.-Y. Ko t al. / Journal of Mchanical Scinc and Tchnology 3 (009) 686~ of composits. For som rason, th nforcmnt proposal for th crashworthinss and rollovr tst of buss in Europ and Japan has bn suggstd basd on th statistics of bus accidnts [5]. Th Europan rgulation ECE-R66 is applid to prvnt catastrophic rollovr accidnts. In this study, ths rgulations ar suggstd as standards for th valuation of scuring th survival spacs of th passngrs and th drivr. Th objctiv of this study is to valuat th structural dynamic intgritis of a low-floor bus mad of composits through th frontal crashworthinss and rollovr analysis. Crashworthinss and rollovr analysis of a bus is carrid out using th xplicit finit lmnt mthod (FEM) analysis cod LS-DYNA3D, confirming th dformation of th vhicl structur and th failur mods of th sandwich composit structurs. Th failur mods of th sandwich composit structurs ar xamind using th modifid Chang-Chang failur critrion. Th mchanical proprtis of th laminat composits and aluminum honycomb cor ar obtaind by coupon tsts according to th ASTM standard. Tabl 1. Th construction of th sandwich panls of a lowfloor bus. Nam Facsht matrial Cor matrial GE/AH Glass fabric/ Epoxy (WR580/NF4000) Aluminum 505 Honycomb (Cll siz : 3/8" / thicknss : 0.005") t O : outr facsht, t C : cor, t I : innr facsht Thicknss (t O /t C /t I ) 3.0/5.4/1.5. Manufacturing concpt and finit lmnt modl of th low-floor bus.1 Dscription of th low-floor bus Th low-floor bus is dvlopd using a hybrid dsign concpt combind with honycomb sandwich and laminatd composit structurs. Th sandwich construction is considrd for application to primary structurs such as th body shll, roof, and floor, whil laminatd composits ar applid only for componnts with a rlativly high curvatur and complx gomtry, which ar mor troublsom to manufactur using th sandwich panls. Fig. 1 shows th manufacturing concpt of th low-floor bus mad of composits. Tabl 1 shows th constructions of th sandwich panl usd in th body shll, floor, and roof structurs of a low-floor bus. Sandwich panls ar composd of a wovn glass fabric/poxy laminat facsht and aluminum 505 honycomb cor. Th outr facsht of th sandwich panl has a thicknss that is twic thicknss of th innr facsht to sav on additional cost and wight. Th facshts of th sandwich panl ar laminatd with wovn glass fabric/poxy prprg. This glass fabric has fiv-hardnss satin wavs, with th sam tow count in th warp and fill-dirction. Th Fig. 1. Dsign concpt of a low-floor bus. wovn glass fabric/poxy laminats hav th dimnsions of th sandwich with facshts of unqual thicknss. Th cor usd in th sandwich panls is aluminum honycomb with a thicknss of 5.4 mm.. Finit lmnt modl Th vhicl structur is modld as a combination of shll, solid, bam, and spring lmnts. A fournod Blytschko-Tsai shll lmnt is usd for modling th composit facsht and rinforcd bam, whil ight-nod solid lmnts ar mployd to modl th ffctiv quivalnt honycomb cor. Prvious rsarch shows that th ffctiv quivalnt damag modl of a honycomb cor has confirmd th small rror rang of xprimntal and numrical simulations [6]. Th finit lmnt modl with 149,510 lmnts has 8 dfind proprty sts and 13 matrial modls. Th solid modls of th CNG tank, ngin, and air conditionr apply wight on ach part. All parts ar connctd using diffrnt multi-point constraints and

3 688 H.-Y. Ko t al. / Journal of Mchanical Scinc and Tchnology 3 (009) 686~693 Tabl. Th modifid Chang-Chang failur critrion in LS- DYNA3D. Mod Following conditions Tnsil, σ x > 0 σ τ x xy ft = + 1 Xt S whr, f 0 : faild & Fibr f < 0 : lastic brakag Comprssiv, σ x < 0 σ x fc = 1 X c whr, m 0 : faild & c Tnsil, σ x > 0 τxy < 0 σ y mt = + 1 Yt S : lastic whr, m 0 : faild & Matrix m < 0 : lastic cracking Comprssiv, σ x < 0 σ y Yc σ y τxy mc = S S Yc S whr, d 0 : faild & d < 0 : lastic Tnsil and Comprssiv Fibr and σ y τxy ( Yc Yt) σ y Matrix md = YY c t S YY c t sharing whr, md 0 : faild & md < 0 : lastic σ x, σ y, τ xy : strss of principal matrial dirction,; X t, Y t : Tnsil strngth of fibr and matrix dirction; Y c, Y c : Comprssiv strngth of fibr and matrix dirction; S : In-plan shar strngth; : failur indx; ft : fibr tnsil; fc : fibr comprssiv; mt : matrix tnsil; mc : matrix comprssiv; md : sharing mod of fibr & matrix spcial links to th actual typs of structural connctions such as bolts and spot wlds. Contact rprsnts th intraction btwn th adjoining parts..3 Dfinition of th matrial attributs Th LS-DYNA3D matrial modl #4 (*MAT_ PIECEWISE_LINEAR_PLASTICTIY) is usd for th stainlss stl matrial of th shll lmnt, whil th LS-DYNA3D matrial modl #54 (*MAT_ ENHANCED_COMPOSITE_DAMAGE) is usd for th WR580/NF4000 glass fabric/poxy facsht of th shll lmnt. Ths constitutiv modls ar basd on th thory of continuum damag mchanic. It is assumd that th dformation of th matrials introducs micro-cracks and cavitis, which rduc th matrial stiffnss. This is xprssd through th intrnal damag paramtrs that dscrib th volution of th damag stat undr loading, hnc th stiffnss dgradation [7]. Th basis of th modl is th modification mad by Matznmillr [8] to th wll-known Chang and Chang composit damag modl [9]. Th Chang and Chang failur critrion is utilizd by th modl to (a) Comprssion (b) Shar (c) Tnsion Fig.. Various typs of aluminum honycomb cor tst. prdict matrix cracking, comprssiv failur, and fibr brakag of th laminat. Th modifid Chang and Chang failur critrion is shown in Tabl. Th LS-DYNA3D matrial modl #16 (*MAT_ MODIFIED_HONEYCOMB) is usd for th honycomb cor matrial of th solid lmnt. In this orthotropic matrial modl, th nonlinar lastoplastic constitutiv bhavior is usd basd on th xprimntally dtrmind strss-strain curv..4 Th ffctiv quivalnt damag modl of th aluminum honycomb cor Th application of th honycomb cor matrials proprtis on th ffctiv quivalnt damag modl brings about tim rduction, which in turn is subjctd to analysis. Th honycomb cor tsts ar conductd according to th ASTM standards. Th honycomb cor tst is comprisd of comprssion (ASTM C365), tnsion (ASTM C363), and shar (ASTM C73). Fig. shows th various componnts of th of honycomb cor tst [10-1]. Th two main componnts of th honycomb cor tst ar th comprssiv and flatwis shar tsts [13]. In th comprssiv tst, th cor comprssiv strngth and modulus ar dtrmind. Th comprssiv tst spcimn siz is 75 mm x 75 mm, and th thicknss of th aluminum honycomb cor is 0mm with a laminat composit facsht of 1 mm. Th flatwis shar tst is probably th most important honycomb tst. Through this tst, th strngth and modulus of th honycomb cor shar ar dtrmind. Th tst spcimns of th flatwis shar tst ar bondd to 1.7 mm thick stl plats at th dg of th cor matrial. Th tnsil tst of th honycomb cor is also calld th cor dlamination tst. Th tst spcimn consists of putting pins on th top and bottom rows, with a width of 130 mm and lngths of 60 mm, of honycomb cor and thn pulling th cor apart. In this tst, th failur mod manifst from th pling of th nods.

4 H.-Y. Ko t al. / Journal of Mchanical Scinc and Tchnology 3 (009) 686~ Tabl 3. Th ffctiv quivalnt mchanical proprtis of th honycomb cor. Cas Strngth (MPa) Elastic modulus (MPa) Comprssion Shar Fig. 4. Th initial condition of th crashworthinss analysis. (a) Comprssiv tst Fig. 5. Th squnc of dformation for a frontal crashworthinss vnt. (b) Shar tst Fig. 3. Th strss-strain curv for th aluminum honycomb cor. Fig. 3 shows th strss-strain curvs for th aluminum honycomb cor as obtaind by th tsts. Th matrial proprtis of th honycomb cor ar listd in Tabl Frontal crashworthinss analysis of th lowfloor bus 3.1 Crashworthinss condition In th frontal crashworthinss analysis, rigid boundaris wr usd to simulat a ston wall and roads. A st of nods on th bus modl was spcifid so that it could not pntrat th rigid wall. Whn contact occurrd, th componnts of th vlocity of th contacting nods in th normal dirction wr zro, whil it was subjct to th friction cofficint in th tangntial dirction. Each nod in th modl had th sam translational initial vlocity of 60 km/h, with zro rotational vlocitis as shown in Fig. 4. Th distanc from th rigid wall to th sat of th drivr was 465 mm, and th lngth of th safty rgion of th drivr was 1100 mm. As th rgulations on th drivr s safty spac to th frontal crashworthinss of th bus was not spcifid, th spac of 1100 mm from th location of th drivr s sat was slctd as th safty spac. This confirmd th possibility of pntration du to th car body s dformation. 3. Rsults of th crashworthinss analysis Th dformation of th vhicl and th failur mod of th composit structur wr obtaind from th frontal crashworthinss analysis. Fig. 5 shows th squnc of dformation of th vhicl in rlation to th laps of tim. Th maximum dformation of this crashworthinss analysis was 316 mm, which occurrd btwn th ston wall and safty rgion of th drivr. Fig. 6 shows th history curvs of th kintic nrgy and intrnal nrgy, as wll as th total nrgy

5 690 H.-Y. Ko t al. / Journal of Mchanical Scinc and Tchnology 3 (009) 686~693 Fig. 6. Enrgy history curv of th frontal crashworthinss simulation. ovr tim. Th kintic nrgy of th carbody structur was 1.9 MJ bfor contact with th rigid wall. In addition, th incras of intrnal nrgy and dcras of kintic nrgy crossd at 30 msc. Fig. 7 shows th tnsil failur mod of th matrix and fibr for th composit structurs of th vhicl. In this procss, th failurs of composits ar considrd to rsult to a damagd stat whn th damag indx turns out to b mor than 1 in accordanc with th modifid Chang-Chang failur critrion. Furthrmor, although th damag indx turns out to b lss than 1, it cannot b considrd as a prfctly saf situation bcaus th failurs of th composits drastically incras with non-linarity. 4. Rollovr analysis of th low-floor bus 4.1 Rollovr condition (a) Th tnsil failur mod of matrix ( mt) (b) Th tnsil failur mod of fibr ( ft) Fig. 7. Failur indx contours of composit carbody structur using modifid Chang-Chang failur critrion for th crashworthinss vnt. Th rollovr analysis of th bus was xamind using th Europan rgulation ECE-R66 [14]. According to this rgulation, a passngr s survival spac is scurd against th dformation of th vhicl structur during or aftr th rollovr. This nsurs that th bus structur has sufficint strngth to avoid th pntration of th dformation into th survival spac. In ordr to simulat th situation of th rollovr of th bus, th bus modl was placd on th tilting platform and was tiltd slowly from its position. Th tir stoppr of th tilting platform prvntd th sliding motion of th bus tirs. Th bus platform, according to ECE-R66, was pulld up by a cran rotational spd of on dgr pr scond to lt th bus roll ovr. Th hight diffrnc btwn th horizontal lowr plan of th ditch and th plan of th tilting platform on which th bus was standing was 800 mm. Th axis of its rotation was 100 mm maximum from th vrti- Fig. 8. Spcifications of th rollovr tst. Fig. 9. Th dynamic simulation modl for th rollovr tst.

6 H.-Y. Ko t al. / Journal of Mchanical Scinc and Tchnology 3 (009) 686~ Tabl 4. Angular and translation vlocity during rollovr of th bus. Typs Angular vlocity in X-axis Angular vlocity in Y-axis Angular vlocity in Z-axis Translation vlocity in X-axis Translation vlocity in Y-axis Translation vlocity in Z-axis Valu rad/sc rad/sc rad/sc.407 mm/sc mm/sc mm/sc Fig. 11. Failur indx contours of th composit carbody structur using th modifid Chang-Chang failur critrion for th rollovr vnt. th rollovr analysis. Fig. 10. Th squnc of dformation for th rollovr tst. 4. Rsults of th rollovr analysis Th dformation of th vhicl and th failur mod of th composit structur wr obtaind from th rollovr analysis. Th rollovr analysis was conductd until th vhicl and ground touchd ach othr compltly. Fig. 10 shows th squnc of th dformation of th vhicl with th laps of tim. In th rollovr analysis, th maximum dformation of 100 mm occurrd on th sid fram. Fig. 11 shows th tnsil matrix failur mod of th composits laminat applid to th vhicl structur. Th failur of th fibr did not occur in th rollovr analysis. cal wall of th ditch and 100 mm maximum blow th plan of th horizontal tilting platform. Whn contact of th vhicl with th ground occurrd, th sliding motion was rstrictd by th friction cofficint. Th passngrs wight applid to th vhicl structur was,800 kg. Th tilting tabl gomtry is shown in Fig. 8. Th initial vlocity was applid to th bus for th rduction of analysis tim. Th initial vlocity was calculatd using th ADAMS program whn th vhicl structur startd to hit th ground. Furthrmor, th cntr of gravity of th vhicl was calculatd using th CATIA program. Fig. 9 shows th dynamic simulation modl applid to th cntr of gravity of th vhicl using th ADAMS program to calculat th angular vlocity and paralll moving vlocity of th vhicl. All angular and translational vlocitis of th bus block from its first contact point with th ground wr notd down, as listd in Tabl 4. At this tim, th y and z dirction angular vlocity was not considrd in 5. Conclusion Th low-floor bus was th first dvlopmnt projct subjctd to th wight limit rgulations for intrcity buss in Kora. Th low-floor bus was dvlopd using a composit structur with high stiffnss towards wight and strngth to wight ratios for th rduction of th wight of th vhicl. Th sandwich composit usd for th vhicl structurs was composd of aluminum honycomb cor and WR580/ NF4000 glass-fabric/poxy laminat facshts. This papr discussd th rsults of th numrical simulation on crashworthinss and rollovr charactristics of th low-floor bus. Th crash condition of th low-floor bus was a frontal accidnt with a spd of 60 km/h. Rollovr analysis was don according to th ECE-R66. To prform th FEM analysis on th crash and ovrturn of th low-floor bus whr th aluminum honycomb sandwich panl was applid, as shown in Fig. 3, th basic proprty tst of th spcimn was conductd. Ths xprimntal data wr

7 69 H.-Y. Ko t al. / Journal of Mchanical Scinc and Tchnology 3 (009) 686~693 usd as an input for th FEM analysis. Likwis, th rsult of th low vlocity crash tst on th sandwich panl spcimn in convntional rsarch and th rsult of th FEM analysis using our modl wr wllcorrspondd. Th frontal crashworthinss and rollovr analysis ld to th following conclusions: (1) Th frontal crashworthinss analysis of a bus mad of honycomb sandwich composit showd that th safty rgion of drivr was scurd. In addition, th rollovr analysis of th bus showd that th survival spac of passngrs was scurd. It should b notd that passngrs wight was considrd. () In this study, th ffctiv quivalnt damag modl was usd to simulat ffctivly th orthotropic matrial proprtis of th ral honycomb cor. Th ffctiv quivalnt damag modl for th honycomb cor was obtaind by coupon tsts such as tnsion, comprssion, and shar. As a rsult, th us of th ffctiv quivalnt damag modl for honycomb cor could rduc th tim of calculation and modling work without th rror btwn th ral and ffctiv modls. In this procss, th proprtis of th ffctiv quivalnt damag modl wr rducd from 8,904 to 3,080 or 65% in comparison with th ral modl. Thus, th tim of analysis convrgnc was shortnd, and th modling tim was rducd compard with th ral honycomb configuration. (3) In ordr to chck th failur mods of th matrix and fibr for th composit structur of th bus vhicl, th modifid Chang-Chang failur critrion was usd in th frontal crashworthinss and rollovr analysis. Th modifid Chang-Chang failur critrion is rcommndd to prdict th failur mods of th composit structurs bfor th crashworthinss and rollovr tst of a ral vhicl. Acknowldgmnt Th authors would lik to thank th Ministry of Land, Transport and Maritim Affairs(MLTM) for thir financial support and assistanc. Rfrncs [1] Martc Limitd Prvost Car, Intrcity Bus Wight Rduction Profram Phas, (000). [] C. C. Foo, G. B. Chai and L. K. Sah, A Modl to Prdict Low-Vlocity Impact Rspons and Damag in Sandwich Composit, Composits Scinc and Tchnology, Vol. 68 (008), [3] J. S. Kim, S. J. L and K. B. Shin, Manufacturing and Structural Safty Evaluation of a Composit Train Carbody, Composit Structurs, Vol. 0, No. 9 (007), [4] J. Y. L, K. B. Shin and S. J. L, A Study on Failur Evaluation if Koran Floor Bus Structur mad of Hybrid Sandwich Composit, Koran Socity of Automotiv Enginrs, Vol. 15, No. 6 (007), [5] Pankaj S. Dshmukh, Rollovr and Roof Crush Analysis of Low-Floor Mass Transit Bus, Ambdkar Marathwada Univrsity (00). [6] J. Y. L, K. B. Shin and J. C. Jong, Simulation of Low Vlocity Impact of Honycomb Sandwich Composit Panls for th BIMODAL Tram Application, Koran Socity for Composit Matrials, Vol. 0, No. 4 (007), [7] M. Q. Nguyn, S. S. Jacombs, R. S. Thomson, D Hachnbrg and M. L. Scott, Simulation on Impact on Sandwich Structurs, Composit Structurs, 67 (005), [8] A. Matznmillr, J. Luvlinr and R. L. Taylor, A Constitutiv Modl for Anisotropic Damag in Fibr-Composits, Journal of Mchanical of Matrials, 1 (1995), [9] F. K. Chang and K. Y. Chang, A Progrssiv Damag Modl For Laminatd Composit containing Strss Concntrations, Journal of Composit Matrials, 1 (1987), [10] ASTM C 365, Flatwis Comprssiv Proprtis of Sandwich Cors. [11] ASTM C 73, Shar Proprtis of Sandwich Cor Matrials. [1] ASTM C 97, Flatwis Tnsil Strngth of Sandwich Constructions. [13] Tom Bitzr, Honycomb Tchnology, Hxcl Corporation, (1997). [14] Unitd Nations, Addndum 65: Rgulation No. 66, Uniform Provisions Concrning th Approval of Larg Passngr Vhicl with Rgard to th Strngth of thir Suprstructur (1986).

8 H.-Y. Ko t al. / Journal of Mchanical Scinc and Tchnology 3 (009) 686~693 Kwang-Bok Shin rcivd his Ph.D. dgr in Mchanical Enginring from th Kora Advancd Institut of Scinc and Tchnology (KAIST), Kora, in 000. Dr. Shin is a Profssor at th Dpartmnt of Mchanical Enginring at Hanbat National Univrsity in Dajon, Kora. H is a rgular mmbr of th Koran Socity for Aronautical and Spac Scincs, th Koran Socity for Composit Matrials, th Koran Socity for Mchanical Enginrs, th Koran Socity for Prcision Enginring, th Koran Socity for Railway, and th Koran Socity for Automotiv Enginrs. H-Young Ko rcivd his B.S dgr in Mchanical Dsign Enginring from th Hanbat National Univrsity, in 009. Now h is in a graduat school at Mchanical Dsign Enginring at Hanbat National Univrsity. Also, H is working as a rsarch nginr at th LS-CAE lab in Hanbat National Univrsity. His rsarch intrsts ar optimization dsign & CAE. 693 Kwang-Woo Jon is in a Mchanical Dsign Enginring at Hanbat National Univrsity. Alos, H is working as a rsarch nginr at th LS-CAE lab in Hanbat National Univrsity. His rsarch intrsts includ impact bhavior of composit matrials and structural analysis. So-Hyun Cho rcivd his B.S dgr in Mchanical Dsign Enginring from th Kyungnam Univrsity, in H thn rsivd his M.S dgr form th Hanbat National Univrsity, Kora, in 008. Now h is working as a managing dirctor at th transit division at Hankuk Fibr Glass, in Miryang, Kora.