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1 Transactions of KSAE, Vol. 14, No. 3, pp (2006) Copyright C 2006 KSAE /2006/ 고강도강판 ULSAB-AVC 모델과일반강판모델의충돌성능비교평가 윤종헌 1) 허훈 *1) 김세호 2) 김홍기 3) 박성호 3) 한국과학기술원기계공학과 1) 대구대학교자동차산업기계공학부 2) POSCO 기술연구소 3) Comparative Crashworthiness Assessment of the ULSAB-AVC Model with Advance High Strength Steel and with Low Strength Steel Jongheon Yoon 1) Hoon Huh *1) Seho Kim 2) Hongkee Kim 3) Seungho Park 3) 1) Department of Mechanical Engineering, Korea Advanced Institute of Science and Technology, Daejeon , Korea 2) School of Automotive, Industrial and Mechanical Engineering, Daegu University, Gyeongbuk , Korea 3) POSCO Technical Research Laboratories, 699 Cumho-dong, Gwangyang-si, Jeonnam , Korea (Received 15 June 2005 / Accepted 10 February 2006) Abstract : As the regulation and assessment program for safety of passengers become stringent, automakers are required to develop lighter and safer vehicles. In order to fulfill both requirements which conflict with each other, automobile and steel companies have proposed the application of AHSS(Advance High Strength Steel) such as DP, TRIP and martensite steel. ULSAB-AVC model is one of the most remarkable reactions to offer solutions with the use of steel for the challenge to improve simultaneously the fuel efficiency, passenger safety, vehicle performance and affordability. This paper is concerned with the crash analysis of ULSAB-AVC model according to the US-SINCAP in order to compare the effectiveness between the model with AHSS and that with conventional steels. The crashworthiness is investigated by comparing the deformed shape of the cabin room, the energy absorption characteristics and the intrusion velocity of a car. Key words : Crashworthiness( 충돌성능 ), Side impact analysis( 충돌해석 ), ULSAB-AVC(Ultralight Steel Auto Body Advanced Vehicle Concepts), AHSS( 고강도강판 ), US-SINCAP( 북미측면충돌상품성시험 ) 1. 서론 1) 차량경량화는에너지절감의필요성과세계적으로강화되고있는배기가스규제등에대응하기위하여절실히요구되는과제이다. 대표적인예로 ULSAB-AVC(Ultra Light Steel Auto Body - Advanced Vehicle Concepts) 는국제철강협회 (IISI) 주도하에차량경량화및에너지절감의요구를실현시키기위하여차체용강판의 85% 이상을고강도강판으로 * Corresponding author. hhuh@kaist.ac.kr 대체하는시도를하였으며하이드로포밍과테일러용접블랭크등의신성형기법을이용하여부재의강도확보및부품수를최소화하는경량화를달성하였다. 이러한추세와더불어차량의안전성확보에대한관심이늘어나고있으며엄격한법규의제정이이루어지고있는실정이다. 실제로자동차업계의경우개발된차량을국외로수출하기위해서는각국의충돌안전규제를통과하여야만해당국가로의수출이가능할뿐아니라상품가치를높이기위하여충돌상품성시험에서도좋은점수를얻어 22

고강도강판 ULSAB-AVC 모델과일반강판모델의충돌성능비교평가 야하는상황이다. 이렇게상반되는경량화및충돌성능향상을동시에얻기위한대안으로는구조적인최적설계부분과고강도강판의적용및 TWB, 하이드로포밍, 프레스경화등의기술을이용한신성형기법의적용을통하여가능하다.

2 고강도강판 ULSAB-AVC 모델과일반강판모델의충돌성능비교평가 야하는상황이다. 이렇게상반되는경량화및충돌성능향상을동시에얻기위한대안으로는구조적인최적설계부분과고강도강판의적용및 TWB, 하이드로포밍, 프레스경화등의기술을이용한신성형기법의적용을통하여가능하다. 본논문에서는 ULSAB-AVC 연구과제에사용된실차해석모델을이용하여기존일반강판이적용된차체와고강도강판이적용된차체의측면충돌해석을수행하고고강도강판을적용하였을경우의충돌성능및효용성을일반강판을적용하였을경우와비교하여정량적으로확인하였다. 2. 측면충돌시험법해석에적용된시험법은미교통부 (US DOT) 산하의도로교통안전청 (NHTSA) 의 FMVSS 214D에기초한측면충돌신차평가프로그램인 SINCAP(Side Impact test for New Car Assessment Program) 을이용하였다. 이시험법은 Fig. 1과같이규정된이동대차 (MDB: Moving Deformable Barrier) 가 27 의경사를유지하여 61.96(km/h) 의속도로차체와충돌하게된다. 대차의총중량은 1,361(kg) 이며, 차체와의충돌시 Fig. 2와같이규정화된수직, 수평충돌선상에정렬시킨후충돌시험을수행하게된다. 해석에사용된 ULSAB-AVC 차체모델의경우윤거 (Wheelbase) 가 3,041(mm) 인 PNGV-Class(Partnership New Generation Vehicle) 이므로 Fig. 2의그림에서전방차축을기준으로후방으로 508(mm) 인지점에충돌선이있어야한다. 시험차량의총중량은유체만체상태의중량과최대적재중량, 운전석과뒷자석에놓이게되는더미 (SID) 2개의중량을더한값으로표현한다. Fig. 1 Facility and equipment for SINCAP test procedure : vehicle simulator; side impactor- moving deformable barrier 3. 차체의측면충돌해석 3.1 측면충돌모델측면충돌해석은 ULSAB-AVC 모델을사용하여수행하였으며구성된유한요소모델은 Fig. 3과같이약 205,000개의쉘과솔리드요소를사용하였다. 해석은외연적유한요소프로그램인 LS-DYNA3D v.970을사용하였으며조각선형 (piecewise linear) 물성모델을사용하였다. 또한고속충돌시발생하는 Fig. 2 Schematic diagram of impact line for SINCAP test procedure Transactions of the Korean Society of Automotive Engineers, Vol. 14, No. 3,

또한기존의 ULSAB-AVC 모델과비교하여충돌성능향상및해석의안정성을위하여루프보강재 2개를추가하고해석하였다. Fig.

3 Jongheon Yoon Hoon Huh Seho Kim Hongkee Kim Seungho Park Table 1 Mechanical properties of high strength steels used in ULSAB-AVC model 7) Fig. 3 Finite element model for the side impact analysis of ULSAB-AVC vehicle 형률선도를나타내었다. 해석의단순화를위하여승객상해치를고려하기위한더미모델은사용하지않았으며, 시트크로스멤버부분에더미에해당하는질량을집중질량으로부과하였다. 또한기존의 ULSAB-AVC 모델과비교하여충돌성능향상및해석의안정성을위하여루프보강재 2개를추가하고해석하였다. Fig. 4 Dynamic stress-strain curves of the high strength steels with various strain rate level used in the simulation: DP400/700; Mart950/1200 변형률효과를고려하기위하여준정적변형률부터중고속변형률속도조건까지의인장시험을통하여얻은유동응력값을대입하여변형률경화를고려하였다. ULSAB-AVC 모델에적용된강판의경우 85% 이상이 Table 1 에제시된바와같이인장강도 60kg급이상의고강도강판으로이루어져있다. Fig. 4는대표적인고강도강판의변형률에따른응력-변 3.2 측면충돌해석 ULSAB-AVC모델의경우부재의대부분이고강도강판으로이루어져있기때문에본논문에서는현재적용되고있는일반강판과비교하여이러한고강도강판의적용이충돌성능에어떠한영향을미치는지고찰하여보았다. 충돌성능비교를위하여 ULSAB-AVC모델에적용되어있는고강도강판을일반강판으로대체하였으며적용된일반강판의변형률에따른물성데이터는자체개발한중고속인장시험기 2) 를이용하여실험으로부터구하였다. 대체된일반강판종류및인장물성을 Table 2에도시하였으며, 대표적인강판의응력-변형률선도는 Fig. 5에나타내었다. 해석은 60(msec) 동안수행하였으며변형후에주요부재가흡수하는내부에너지는 Fig. 6에도시하였다. 사이드아우터패널 (Side Outer Panel), 라커이너멤버 (Rocker Inner Member), 사이드이너패널 (Side Inner Panel) 등에서에너지흡수율이가장높게측정되며에너지흡수율이지배적인 9개부재를 Fig. 7에나타내었다. 측면충돌의특성상대차가충돌하게되는부위인 B- 필라와사이드시일 (Side Sill), 도어부를비롯하여플로어부까지환형 ( 環形 ) 을이루는부재들이대부 24 한국자동차공학회논문집제 14 권제 3 호, 2006

Comparative Crashworthiness Assessment of the ULSAB-AVC Model with Advance High Strength Steel

6 Energy absorption characteristics of important panels and members in the side impact crash Fig.

5 Dynamic stress-strain curves of the conventional steels with various strain rate level used in

전체적인변형량이일반강판을적용하였을때급격히증가하는것을확인할수있으며 B-필라부및이에연결된루프와플로어의변형이상대적으로많은것을볼수있다.

4 Comparative Crashworthiness Assessment of the ULSAB-AVC Model with Advance High Strength Steel and with Low Strength Steel Table 2 Mechanical properties of conventional steels Fig. 6 Energy absorption characteristics of important panels and members in the side impact crash Fig. 7 Important parts for energy absorption Fig. 5 Dynamic stress-strain curves of the conventional steels with various strain rate level used in the simulation: SPRC45E; SPCC 분의에너지를흡수하고있다. 변형후의차체형상은 Fig. 8에비교하였다. 전체적인변형량이일반강판을적용하였을때급격히증가하는것을확인할수있으며 B-필라부및이에연결된루프와플로어의변형이상대적으로많은것을볼수있다. 일반강판을적용한경우에루프와플로어의변형량이 Fig. 8 Deformed shapes of the vehicle for the crash analysis at time 0.06sec: AHSS; conventional steel Transactions of the Korean Society of Automotive Engineers, Vol. 14, No. 3,

5 윤종헌 허훈 김세호 김홍기 박성호 Fig. 9 Amount of intrusion distance of the B-pillar with respect to the time Fig. 10 Points of time at which the local minimum and local maximum velocity occurs: AHSS; conventional Steel 매우큰것을확인할수있으며 B-필라내부보강재가하중을지지하지못하고붕괴되어승객탑승공간으로차체의침입량이증가하였다. 이는실제충돌시운전석의공간을확보할수없으며결과적으로머리부나기타신체부위의상해치가증가하여 낮은충돌성능을보이게됨을의미한다. 보다정량적인비교를위하여 Fig. 9와같이차체의충돌부와반대편 B-필라중심부의폭방향침입량과침입속도를비교하였다. 고강도강판을적용하였을때 B-필라부위의침입량은 133(mm) 였으며일반강판을적용하였을때는 282.5(mm) 로침입량이두배이상증가하였다. 침입속도를측정한결과를 Fig. 10에도시하였으며, 초기피크속도를비롯하여최고침입속도모두일반강판을적용한결과가일반강판을적용한경우가급격히높게나오는것을확인할수있다. 또한고강도강판을적용한차량의침입속도가초기피크이후에상승하지않는반면일반강판을적용한차량의침입속도는초기피크이후에상승하는곡선을그리게된다. 이러한현상을분석하기위하여충돌중침입속도의기울기가변하는극대, 극소값시점을추출하여해당되는시점의차량의변형모드를 Fig. 11와 Fig. 12에도시하였다. 대차가충돌하는순간부터도어부가변형하는시점까지초기피크를이루게되며도어부가완전히붕괴되어임팩트빔이하중을지지하면서속도는감소하게된다. 도어부가붕괴된후 B-필라에대차가접촉하는순간까지속도는다시증가하게되지만고강도강판을적용한차체의경우는루프가붕괴되지않고지지하는효과로인하여일반강판을적용한차체에비해서침입속도가높아지지않는다. 형상이차체바깥쪽으로곡률이있는 B-필라를포함한포함한사이드아우터패널부는대차가밀려들어옴에의하여수직화된이후붕괴되기시작하며침입속도가영이되는시점이후로는차체의대차충돌부와반대편측정부에서상대운동이일어나지않고강체운동을하게되어차체가전체적으로이동하는효과만을보이게된다. 4. 결론본논문에서는차량경량화및충돌성능향상을위하여시도되고있는고강도강판적용의효용성을살펴보기위하여 ULSAB-AVC 모델을이용하여측면충돌해석을수행하였다. 또한고강도강판의성능을정량화하기위하여실험을통하여얻어진기존일반강판의물성치를대입하여추가로측면 26 한국자동차공학회논문집제 14 권제 3 호, 2006

고강도강판 ULSAB-AVC 모델과일반강판모델의충돌성능비교평가 (c) (d) (e) Fig. 11 Subsequent deformation mechanism with AHSS: 0.007sec; 0.011 sec; (c) 0.016 sec; (d) 0.03 sec; (e) 0.047 sec (c) (d) (e) Fig.

일반강판을적용한차체와비교하여고강도강판을적용한차체의경우충돌시측면부재침입량의급감과침입속도의감소로인하여운전석의공간을확보할수있었으며, 신체부위에전달되는상해치의감소를예측할수있었다. 따라서고강도강판을적용한차체의충돌성능이향상되었음을확인할수있다. References 1) H. Huh, J. H. Lim, J. H. Song, K. S. Lee, Y. W.

6 고강도강판 ULSAB-AVC 모델과일반강판모델의충돌성능비교평가 (c) (d) (e) Fig. 11 Subsequent deformation mechanism with AHSS: 0.007sec; sec; (c) sec; (d) 0.03 sec; (e) sec (c) (d) (e) Fig. 12 Subsequent deformation mechanism with conventional steel: sec; sec; (c) 0.02 sec; (d) 0.04 sec; (e) 0.06 sec 충돌해석하고결과를비교하였다. 일반강판을적용한차체와비교하여고강도강판을적용한차체의경우충돌시측면부재침입량의급감과침입속도의감소로인하여운전석의공간을확보할수있었으며, 신체부위에전달되는상해치의감소를예측할수있었다. 따라서고강도강판을적용한차체의충돌성능이향상되었음을확인할수있다. References 1) H. Huh, J. H. Lim, J. H. Song, K. S. Lee, Y. W. Lee and S. S. Han, Crashworthiness Assessment of Side Impact of an Auto-Body with 60TRIP Steel for Side Members, Int. J. Automotive Technology, Vol.4, No.3, pp , ) H. Huh, J. H. Lim, S. B. Kim, S. S. Han and S. H. Park, Formability of the Steel Sheet at the Intermediate Strain Rate, Key Engineering Materials, Vol , pp , ) J. Cafolla, R. W. Hall and D. P. Norman, Forming to Crash Simulation in Full Vehicle Models, 4th European LS-DYNA Users Conf., Metal Forming II, E-II-17-26, ) S. Simunovic, J. Shaw and G. A. Aramayo, Steel Processing Effects on Impact Deformation of UltraLight Steel Auto Body, SAE , ) H. Huh, K. P. Kim, S. H. Kim, J. H. Song, H. S. Kim and S. K. Hong, Crashworthiness Assessment of Front Side Members in an Auto-Body Considering the Fabrication Histories, Int. J. Mech. Sci., Vol.45, pp , ) ULSAB-AVC ProgramTechnical Transfer Dispatch#1-6, Porsche Engineering Services, Inc., ) ULSAB-AVC Engineering Report, Porsche Engineering Services, ) LSTC, LS-DYNA970 Keyword User s Manual, Transactions of the Korean Society of Automotive Engineers, Vol. 14, No. 3,

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