Improved Assessment Methods of Lower Extremity Injuries in Vehicle-To- Pedestrian Accidents Using Impactor Tests and Full-Scale Dummy Tests
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IMPROVED ASSESSMENT METHODS OF LOWER EXTREMITY INJURIES IN VEHICLE-TO- PEDESTRIAN ACCIDENTS USING IMPACTOR TESTS AND FULL-SCALE DUMMY TESTS Oliver Zander Federal Highway Research Institute (BASt) Germany Dirk-Uwe Gehring Peter Leßmann BGS Böhme & Gehring GmbH Germany Paper Number 11-0079 ABSTRACT vehicles still needs to be evaluated in detail. A first clue is given by the application of an additional A flexible pedestrian legform impactor (FlexPLI) accelerometer to the legform. has been evaluated by a Technical Evaluation Group (Flex-TEG) of the Working Party on Passive INTRODUCTION Safety (GRSP) of the United Nations Economic Commission for Europe (UN-ECE). It will be The preamble of the Global Technical Regulation implemented within phase 2 of the global technical on Pedestrian Safety (GTR No. 9), published in regulation (GTR 9) as well as within a new ECE January 2009, considers the flexible pedestrian regulation on pedestrian safety as a test tool for the legform impactor (FlexPLI) to replace the EEVC assessment of lower extremity injuries in lateral WG 17 pedestrian legform impactor which is vehicle-to-pedestrian accidents (UN-ECE 2010-1, currently used for type approval tests according to 2010-2 and 2010-3). European Regulation (EC) 78/2009 in the near Due to its biofidelic properties in the knee and tibia future. Therefore, a Technical Evaluation Group section, the FlexPLI is found to having an (Flex-TEG) of UNECE-GRSP has evaluated the improved knee and tibia injury assessment ability FlexPLI within 12 meetings and has given final when being compared to the current legislative test recommendations for the introduction within tool, the lower legform impactor developed by the world-wide legislation. The introduction of the Pedestrian Safety Working Group of the European FlexPLI is also one of the main mid term activities Enhanced Vehicle-safety Committee (EEVC WG on the agenda of the Pedestrian Subgroup of the 17). However, due to a lack of biofidelity in terms European New Car Assessment Programme (Euro of kinematics and loadings in the femur part of the NCAP). FlexPLI, an appropriate assessment of femur injuries is still outstanding. A study of the German In Depth Accident Database The study described in this paper is aimed to close GIDAS in 2009 was aimed at examining the this gap. Impactor tests with the FlexPLI at distribution of lower extremity injuries in lateral different impact heights on three vehicle frontends vehicle-to-pedestrian accidents focusing on the with Sedan, SUV and FFV shape are performed particular injury locations at 3 or 9 o’ clock related and compared to tests with a modified FlexPLI to the pedestrian. All accidents with pedestrians with upper body mass. Full scale validation tests crossing (from the left or the right only) and with using a modified crash test dummy with attached the vehicle front, bonnet leading edge or bumper as FlexPLI that are carried out for the first time prove injury causing part were taken into account. The the more humanlike responses of the femur section described selection criteria resulted in a total of with applied upper body mass. Apart from that they 6330 pedestrian injuries, thereof 1921 lower also show that the impact conditions described in extremity injuries. Figure 1 shows the distribution the current technical provisions for tests with the in terms of injury location. 818 of the described FlexPLI don’t necessarily compensate the missing injuries are located in the lower leg area, followed torso mass in terms of knee and tibia loadings by 460 knee injuries and 226 femur injuries. 417 either. injuries are not clearly specified or occurred in Therefore it can be concluded that an applied upper other areas. Though the femur injuries represent the body mass will contribute to a more biofidelic smallest group in this statistical analysis, they are overall behavior of the legform and subsequently of a high relevance in the actual accident scenario an improved injury assessment ability of all lower and thus cannot be neglected. extremity injuries addressed by the FlexPLI. Nevertheless, the validity of the original as well as the modified legform for tests against vehicles with extraordinary high bumpers as well as flat front Zander 1 from Nyquist et al. (1985) and Kerrigan et al. (2004) under modification of the standard tibia length and standard tibia plateau height, making the assumption that the height scale factor and length scale factor should correlate to each other. TheWeibull Survival Model was used to develop the injury probability function. The proposed final threshold value resulted in 380 Nm (JAMA, 2009-1 and 2009-2). BASt derived the Flex-GTR tibia bending moment threshold also using the corresponding transition equation between human and Flex-GTR FE models. The average human tibia bending moment threshold value was taken from an injury risk curve th Figure 1. Distribution of lower extremity of the 50 percentile male for tibia fracture, taking injuries (n=1921) in selected vehicle-to- into account scaled male PMHS data from Nyquist pedestrian accidents within GIDAS (2009). et al. (1985) using the standard tibia plateau height provided by DIN 33402-2 German However, up to now the pedestrian protection anthropometrical database. The cumulative potential of modern vehicle frontends is limited to Gaussian distribution was used to develop the the assessment using the FlexPLI, only taking into injury probability function. The calculated account the tibia bending moments acquired by threshold value under consideration of possible four strain gauges as well as the elongation of scatter of test results and of a reproducibility medial collateral and cruciate ligaments measured corridor derived from inverse certification test by three string potentiometers. As the biofidelity of results was 302 Nm (Zander, 2009). the FlexPLI is limited by the absence of a A comparison of both approaches revealed that the pedestrian torso or equivalent mass, femur injuries calculated threshold values mainly depend on cannot be assessed appropriately. • the underlying set of PMHS data The application of an additional upper body mass is • the consideration of female and / or male data meant to close this gap. Component tests with a • the use of scaled or unscaled data modified FlexPLI against three different vehicles • the particular anthropometrical database based front shapes are validated by full scale dummy on which human data are scaled tests. • the injury risk to be covered • the statistical procedure to develop an injury DERIVATION OF INJURY CRITERIA AND probability function THRESHOLD VALUES As consensus for both approaches BASt proposed a rounded average value of 340 Nm for the In one of its latest status reports to GRSP, the maximum tibia bending moment threshold. Technical Evaluation Group recommended In parallel to BASt proposing a rounded average threshold values for the FlexPLI tibia bending value, JAMA conducted a correlation study on the moments and ligament elongations that previously EEVC WG 17 PLI tibia acceleration and FlexPLI had been controversially discussed. tibia bending moment. As a result, they found that the 170 g EEVC WG 17 PLI tibia acceleration in Threshold value for tibia bending moment GTR 9 was correlated to 343 Nm Flex-GTR tibia bending moment At the 8th GRSP Flex-TEG meeting in May 2009, As this was almost the value proposed by BASt as two proposals for the tibia threshold value of the average value between the BASt and former JAMA FlexPLI version GTR (also called Flex-GTR) were proposals, the group agreed at the 9th TEG meeting made by the Japan Automobile Manufacturers in September 2009 on a consensus of the rounded Association (JAMA) and the German Federal value of 340 Nm. Highway Research Institute (BASt), coming to different conclusions. Threshold value for MCL elongation JAMA derived the Flex-GTR tibia bending moment threshold using a linear transition equation JAMA developed an MCL injury risk function as between human and Flex-GTR finite element (FE) average function between the risk functions from models derived from computer simulation results. Ivarsson et al. (2004) and Konosu et al. (2001), The average human tibia bending moment latter one revised using the Weibull Survival threshold value was taken from an injury risk curve Model. In this function, a 50% risk of knee injury th of the 50 percentile male for tibia fracture, taking in terms of MCL rupture corresponded to a human into account scaled male and female PMHS data knee bending angle of 19 degrees. This value was Zander 2 converted to 19.2 mm MCL elongation, using a The European Automobile Manufacturers corresponding transition equation from computer Association (ACEA) was, for the time being, in simulation. After incorporating the effect of muscle favour of not considering an ACL/PCL injury tone the threshold value was calculated at 21.1 mm assessment at all. (JAMA, 2009-2). As this value was converted to 16.9 degrees of EEVC WG 17 PLI knee bending Current status within GRSP angle by using a corresponding transition equation which would be approx. 11 % more conservative During its 48 th session in December 2010, GRSP than the GTR threshold value of 19 deg, a 5% more discussed the phase of introduction of the FlexPLI conservative approach, equal to 18 deg EEVC WG within GTR No. 9 as well as the new ECE 17 PLI knee bending angle was proposed and Regulation on Pedestrian Safety. The introduction transformed to 22 mm MCL elongation, using the will be based on the threshold values for the tibia same transition equation as before. bending moments and MCL elongation agreed by As BASt was not in the position to validate or Flex-TEG, amended by a relaxation zone for double-check those results, they investigated a bumper test widths of a maximum of 264 mm direct correlation between the EEVC WG 17 PLI where the maximum tibia bending moment shall knee bending angle and the FlexPLI MCL not exceed 380 Nm.