This article was downloaded by: [Yong Peng] On: 03 July 2012, At: 11:32 Publisher: Taylor & Francis Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK International Journal of Crashworthiness Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/tcrs20 Effects of pedestrian gait, vehicle-front geometry and impact velocity on kinematics of adult and child pedestrian head Yong Peng a b d, Caroline Deck b, Jikuang Yang a c & Remy Willinger b a Research Center of Vehicle and Traffic Safety, State Key Laboratory of Advanced Design and Manufacture for Vehicle Body, Hunan University, Changsha, China b Institute of Fluid and Solid Mechanics, Strasbourg University, Strasbourg, Alsace, France c Department of Applied Mechanics, Chalmers University of Technology, Gothenburg, Sweden d State Key Laboratory of Vehicle NVH and Safety Technology, Chongqing, China Version of record first published: 03 Jul 2012 To cite this article: Yong Peng, Caroline Deck, Jikuang Yang & Remy Willinger (2012): Effects of pedestrian gait, vehicle-front geometry and impact velocity on kinematics of adult and child pedestrian head, International Journal of Crashworthiness, DOI:10.1080/13588265.2012.698578 To link to this article: http://dx.doi.org/10.1080/13588265.2012.698578 PLEASE SCROLL DOWN FOR ARTICLE Full terms and conditions of use: http://www.tandfonline.com/page/terms-and-conditions This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. The publisher does not give any warranty express or implied or make any representation that the contents will be complete or accurate or up to date. The accuracy of any instructions, formulae, and drug doses should be independently verified with primary sources. The publisher shall not be liable for any loss, actions, claims, proceedings, demand, or costs or damages whatsoever or howsoever caused arising directly or indirectly in connection with or arising out of the use of this material.
International Journal of Crashworthiness ifirst 2012, 1 9 Effects of pedestrian gait, vehicle-front geometry and impact velocity on kinematics of adult and child pedestrian head Yong Peng a,b,d, Caroline Deck b, Jikuang Yang a,c and Remy Willinger b a Research Center of Vehicle and Traffic Safety, State Key Laboratory of Advanced Design and Manufacture for Vehicle Body, Hunan University, Changsha, China; b Institute of Fluid and Solid Mechanics, Strasbourg University, Strasbourg, Alsace, France; c Department of Applied Mechanics, Chalmers University of Technology, Gothenburg, Sweden; d State Key Laboratory of Vehicle NVH and Safety Technology, Chongqing, China (Received 31 January 2012; final version received 28 May 2012) The objective of the study is to investigate the effects of pedestrian gait, vehicle-front geometry and impact velocity on the dynamic responses of the head. The multi-body dynamic (MBD) models were used to simulate the head responses in vehicle to pedestrian collisions with different vehicle types in terms of head-impact point measured with Wrap Around Distance (WAD), head relative velocity and impact angle. Furthermore, the distribution of the head contact point on the vehicle fronts is analysed for a comparison of the contact point with the testing areas in the EEVC headform impactor test procedures. A simulation matrix is established using five vehicle types, two mathematical models of the pedestrians represented a 50th male adult and a 6-year-old child as well as seven pedestrian gaits based on typical postures in pedestrian accidents. In order to simulate a large range of impact conditions, four vehicle velocities (30 km/h, 40 km/h, 50 km/h and 60 km/h) are considered for each pedestrian position and vehicle type. The results indicated that the pedestrian gait and vehicle-impact velocity strongly influence head-impact condition. It is obvious that due to different vehicle-front geometry, the head-impact velocity, impact angle and head-impact point could be varied as well. This study provides suggestions for different head-impact conditions of subsystem test to the front part of different passenger vehicles. Keywords: crash simulation; pedestrian gait; vehicle-front geometry; impact velocity; head-impact conditions 1. Introduction Pedestrians are considered to be an extremely vulnerable group of road users. Furthermore, head injury is one of the most common injuries in car-to-pedestrian accidents. International Harmonized Research Activities (IHRA) investigated and analysed 1605 pedestrian accidents from Australia, Germany, Japan and the USA and the results show that head injuries accounted for 31.4% of 3305 AIS2+ (Abbreviated Injury Scale) injuries [10]. Neal-Sturgess et al. [12] reviewed APROSYS European In-Depth Pedestrian Database from 1997 to 2004 and found that the most frequently injured body regions were the head and lower limbs. A statistical analysis was undertaken by Fildes et al. [2] using real world crash data and the results showed that head and face regions accounted for a sizeable proportion of serious injuries comprising 29% to children and 28% to adults as per the University of Hannover data and head injuries alone of AIS 4+ severity accounted for 20% of fatal injuries as per Australian fatal file. In order to minimise the risk of head injuries to pedestrians in traffic accidents, the subsystem test procedures with headform impactors have been used to assess the passenger vehicle-front performance for pedestrian protection since 1996 in EuroNCAP tested passenger vehicles. The child headform impacts on the vehicle area are from Wrap Around Distance (WAD) 1000 mm to WAD 1500 mm, with an impact angle of 65 to the ground, while the adult headform impacts on the vehicle area are from WAD 1500 mm to 2100 mm, with an impact angle of 50 to the ground. Both headforms are launched against the impact zones at a speed of 40 km/h. Recently, in order to harmonise with impactor specifications used in the draft of Global Technical Regulation on pedestrian protection, the EuroNCAP pedestrian test protocols were modified by the European Enhanced Safety of Vehicles Committee. Furthermore, the IHRA specifies three groups of vehicle shape: Sedan, SUV and 1-box, and defines different impact test speeds and different impact angles. The child headform impacts on the vehicle area determined by WAD between 1000 mm and 1700 mm and the impact angle for Sedan, SUV and 1- box are, respectively, 65,60 and 25. While the adult headform impacts on the vehicle are determined by WAD between 1700 mm and 2100 mm and the impact angle for Sedan, SUV and 1-box is 65,90 and 50, respectively. The impact test speed is 32 km/h both for child and adult headform. The Japanese legislation was developed based Corresponding author. Email: pengyong20080708@163.com ISSN: 1358-8265 print / ISSN: 1754-2111 online C 2012 Taylor & Francis http://dx.doi.org/10.1080/13588265.2012.698578 http://www.tandfonline.com
2 Y. Peng et al. on the IHRA recommended method. In the draft of Global Technical Regulation on pedestrian protection, the test protocols are carried out at a speed of 35 km/h. However, these subsystem tests cannot evaluate the integrated safety performance of a vehicle design in terms of the overall responses of pedestrian. The pedestrian protection testing protocols did not take into account the influence of different vehicle types and pedestrian gait on pedestrian head-impact conditions, but specified the identical head-impact conditions for all types of vehicle. The researches on the effects of vehicle-front parameters and impact speed on pedestrian dynamic responses have been widely studied by using mathematical models [3, 7, 8, 17, 18], pedestrian dummy crash tests [4, 11, 13] and in-depth accident data [5, 6, 12, 19]. For instance, the influences of impact speed, vehicle-front structure and the stiffness properties on the pedestrian dynamic responses have been investigated using the validated pedestrian multibody model [7, 8, 18]. These studies found that compared to the bumper lead length and bumper height, the hood edge height will have a great effect on the resultant head velocity and the resulted injury severity of head is strongly controlled by the local stiffness of head contact area. Han et al. [3] investigated the effect of vehicle types on the pedestrian kinematic by using finite element models. They found that the frontal shape of the vehicle had a large effect on the pedestrian kinematic behaviour, including the impact velocity of the pelvis, chest and head against the vehicle. Okamoto et al. [13] also reported that the headimpact conditions are influenced by the front construction of the vehicle and the pedestrian size. Kerrigan et al. [4] assessed pedestrian head-impact dynamics in small sedan and large SUV collisions using post-mortem human surrogates (PMHS) and the Polar-II pedestrian crash dummy. The results indicated that HIC 15 values and angular accelerations were higher in windshield impacts in the sedan tests than in hood impacts in the SUV tests and the head impacts to the sedan windshield were potentially more injurious than the head impacts to the SUV hood. In Moradi and Lankarani s study [11], different sizes of pedestrians were impacted by a utility vehicle with a frontal guard to evaluate the pedestrian kinematics and injury potential and the results showed that the mid-body region is more vulnerable for the vehicle with a frontal guard. Li and Yang [6] investigated the pedestrian dynamic responses and head brain injuries in car-to-pedestrian collisions with reconstructions using in-depth accident data in China. In their study, the results illustrated that the head-impact relative velocity to the car was proportional to the vehicle speed and head-impact angle was influenced by pedestrian height, car front structure and impact speed. In-depth accident data indicated that the range of impact velocity is from 10 km/h to 60 km/h in about 95% real world pedestrian accidents [5, 12, 19]. In this study, the influences of pedestrian gait, vehicle type and impact speed on pedestrian dynamic responses are evaluated by using fully validated human-body mathematical models. The final objective of this study is to define relative head-impact condition as a function of vehicle-frontend geometry, if it is necessary to specify head-impact test condition for different types of cars. 2. Methods and materials The multi-body dynamic (MBD) models were used to simulate responses of vehicle to pedestrian collisions with different vehicle types in terms of head-impact point (Wrap Around Distance: WAD), head relative velocity and impact angle. Furthermore, the distribution of the head contact points on the vehicle fronts is analysed for comparison with current testing areas used in the EEVC impactor procedures. In order to simulate a large range of impact conditions, a simulation matrix is established using five vehicle types, two mathematical models of the pedestrians, seven pedestrian gaits defined based on walking postures in typical pedestrian accidents, as well as four impact speeds are considered for each pedestrian position and vehicle type. 2.1. Pedestrian models Two mathematical models of the pedestrians which represented a 50th male adult and a 6-year-old child are used in this study. The Pedestrian Models (PM) were developed by TNO in the MADYMO environment. The TNO PM consists of 52 rigid bodies and includes six frangible joints in each leg. This model can be scaled to any required body size using GEBOD program. The 50th male PM was validated against blunt impact tests and car pedestrian crash tests [14, 16]. Both of the 50th percentile male model and the 6-year-old child model are shown in Figure 1. 2.2. Vehicle models As shown in Figure 2, five vehicle models are constructed according to the shapes and sizes of the main existing vehicles [1, 10]. In this study, five vehicles including Super Mini Car (SMC), Small Family Car (SFC), Large Family Car (LFC), Multi Purpose Vehicle (MPV) and Sport Utility Vehicle (SUV) are selected and constructed based on the vehicle geometry corridors. Vehicle-front model consists of bumper, hood edge, hood top, windscreen and four wheels ellipsoids to approximate the exterior profile of a vehicle. The contact stiffnesses of vehicle-front components are obtained according to Martinez et al. s work [9]. 2.3. Set-up of configurations and simulation matrix The configurations for simulations of vehicle-to-pedestrian collisions are developed using four different impact speeds
International Journal of Crashworthiness 3 Figure 3. Pedestrian stances for different gait parameters (%) vehicle-front geometry and vehicle-impact speed. Simulation outputs concern pedestrian impact conditions such as head-impact velocity, head-impact angle and head-impact location (Wrap Around Distance: WAD). A simulation matrix was designed with a total of 280 simulations. Figure 1. Pedestrian models. of 30, 40, 50 and 60 km/h. Seven pedestrian gaits (0%, 20%, 40%, 60%, 80%, front and rear) are used in the simulations for each child and adult PM as shown in Figure 3. The stances of the PM are obtained using functions of joint angles and H-point according to literature [15]. The pedestrian contact position is selected at the vehicle central line of the model in all of simulations. The friction coefficients are 0.6 for foot/ground and wheels/ground, and 0.5 for the contacts between body segments and vehicle-front structures [8]. A parametric study is conducted using four variables to understand the influence of pedestrian size and gait, 3. Results 3.1. Wrap around distance (WAD) A pedestrian hit by a car is wrapped around the front of the vehicle. Therefore, head-impact location is estimated by the WAD, which is the length measured along the vehicle s front profile from the ground to the head-impact location. The WAD values for five vehicle types are compared at different pedestrian gaits and impact velocity in Figure 4. For the adult pedestrian, the WAD values exceed 2.1 m above collision velocity of 40 km/h for the SFC and LFC, while the WAD values are closer to 1.8 m for the SMC, MPV and SUV. However, the effect of vehicle velocity on the WAD is not significant over collision velocity of 40 km/h. In the case of the child, the WAD values are below 1.35 m except the LFC, and there is a slight increase with increase in vehicle velocity. It can be seen in Figure 4 that the effects of pedestrian gait on WAD are larger for the adult than for the child, and that the WAD values are larger for the SFC and the LFC than other vehicle types in the adult simulations. Figure 2. Vehicle types used in this study.
4 Y. Peng et al. Figure 4. Comparison of the WAD value on different vehicles for different pedestrian gaits and vehicle-impact velocity. (a) at vehicleimpact velocity 30 km/h, (b) at vehicle-impact velocity 40 km/h, (c) at vehicle-impact velocity 50 km/h, (d) at vehicle-impact velocity 60 km/h. The results show that at a vehicle-impact velocity of 40 km/h, the mean values of WAD for the SMC, SFC, LFC, MPV and SUV are 1.78 m, 2.11 m, 2.14 m, 1.82 m and 1.74 m, respectively. However, for the 6-year-old child, the mean values of WAD for the SMC, SFC, LFC, MPV and SUV are 1.20 m, 1.16 m, 1.29 m, 1.14 m and 1.17 m, respectively. 3.2. Head-impact velocity relative to the vehicle The head relative impact velocities for five vehicle types and seven pedestrian gaits obtained at velocities of 30 60 km/h for adult and child are plotted in Figure 5. The head-impact velocity is gradually increasing with the increase of vehicletravel velocity both for adult and child. It was found that the head-impact velocity is higher for the adult impacted with all of the vehicles than for the child. For the adult, the mean values of the head-impact velocity are larger for the SFC and the LFC than for the other vehicles and the head-impact velocities are below vehicle velocities in all cases except for the SFC, while the mean value of child head-impact velocity is the smallest for the SUV, and the value is lower than the vehicle velocity and the adult headimpact velocity. It can be also observed that the effects of pedestrian gait on head-impact velocity are larger for the adult than for the child. When the vehicle-travel velocity is set to 40 km/h, the mean value of head-impact velocity of the 50th percentile adult is 36 km/h for SMC, 42 km/h for SFC, 40 km/h for LFC, 36 km/h for MPV and 37 km/h for SUV, while the child head-impact velocity is 29 km/h for SMC, 35 km/h for SFC, 33 km/h for LFC, 31 km/h for MPV and 23 km/h for SUV. The maximum value of adult head-impact velocity for SMC, SFC, LFC, MPV and SUV is, respectively, 49 km/h, 50 km/h, 53 km/h, 47 km/h and 51 km/h. For the 6-year-old child, the maximum value of WAD for SMC, SFC, LFC, MPV and SUV is 34 km/h, 43 km/h, 36 km/h, 38 km/h and 42 km/h, respectively. 3.3. Head-impact angle The head-impact angle refers to the angle between the direction of the head-impact speed and the ground reference level in a downward and rearward direction. As shown in Figure 6, a comparison is made between the head-impact angle for different pedestrian gaits, vehicle types and vehicle-impact velocities. Figure 6 shows that a specific trend cannot be observed about the influence of vehicle types both for adult and child. However, in case of the child impact, the headimpact angle is observed to be highly dependent on the geometry of the vehicle. It also can be found that the headimpact angle is influenced by gait both for the adult and child and the fluctuation of head-impact angle is about 10. When the vehicle-travel velocity was set to 40 km/h, the mean value of adult head-impact angle is 63 for SMC, 55 for SFC, 66 for LFC, 55 for MPV and 63 for SUV, while the mean value of child head-impact angle is 63 for SMC, 55 for SFC, 66 for LFC, 48 for MPV and 29 for SUV.
International Journal of Crashworthiness 5 Figure 5. Effects of pedestrian gait and vehicle type on head-impact angle at different vehicle-impact velocity. (a) at vehicle-impact velocity 30 km/h, (b) at vehicle-impact velocity 40 km/h, (c) at vehicle-impact velocity 50 km/h, (d) at vehicle-impact velocity 60 km/h. Figure 6. Effects of pedestrian gait and vehicle type on head-impact velocity at different vehicle-impact velocity. (a) at vehicle-impact velocity 30 km/h, (b) at vehicle-impact velocity 40 km/h, (c) at vehicle-impact velocity 50 km/h, (d) at vehicle-impact velocity 60 km/h. 4. Discussions 4.1. Distribution of head-impact location by WAD values The WAD value is influenced by the front construction of the vehicle. The bumper centre height, hood edge height, hood slope angle and hood length all have significant effects on the pedestrian kinematics. For the adult, the WAD values are bigger for the SFC and the LFC than other vehicle types, and for the child, the WAD value is biggest for the LFC. As shown in Figure 7, for the SMC, the adult head-impact points are distributed on the lower end of the
6 Y. Peng et al. Figure 7. Comparison of the distribution of head contact point on different vehicle for different vehicle velocity and pedestrian gait. windscreen and the child head hits the middle of bonnet. Results from the simulations with the SFC show that the distribution of adult and child head-impact points is on the middle of the windscreen and bonnet areas, respectively. In the case of the LFC, the adult head hits the bonnet rear area and the low windscreen, and the child head-impact points are located on the bonnet middle area. From the simulation results of the MPV, it can be found that the adult and child heads are expected to hit the low windscreen area and the bonnet front, respectively. For the SUV, the adult head hits the lower end of the windscreen and rear bonnet, while the child head-impact points are concentrated on the bonnet front edge. At a vehicle-impact velocity of 40 km/h, for the SFC and the LFC, the adult head contact points are more rearward than the 2.1 m WAD position, while most of the pedestrian head-impact points are closer to the 1.7 m WAD position for other vehicle types. In the case of the child, most of head-impact points are closer to the 1.2 m WAD position located on the bonnet front edge for the MPV and SUV and the bonnet middle area for the SMC, SFC and LFC. Vehicle-impact velocity and pedestrian gait also have critical effects on the WAD. The WAD gradually increases with the increase of vehicle-travel velocity. The dynamic responses of the legs have a great influence for the adult pedestrian dynamic responses, but the growth trends are not remarkable at a collision velocity of 40 km/h and higher for the adult. In the case of the child, at the time of impact, the child s upper body came in contact with the vehicle, so the effect of vehicle-front structure and child gait on the WAD is not remarkable. 4.2. Head-impact velocity relative to the vehicle The average impact velocity of the adult pedestrian head is below the vehicle velocity except in the case of the SFC, while the child head-impact velocity is lower than the vehicle velocity and the adult head-impact velocity. When a vehicle impacts a pedestrian, the leg of the pedestrian first contacts with vehicle-front end and then the pedestrian is rotated around the impact position. So, the different bumper centre height, bumper lead length and hood slope angles of various vehicle types lead to different kinematics of the pedestrians. At a vehicle-impact velocity of 40 km/h, the head-impact velocity for the SMC, MPV and SUV is about 36 km/h which is 10% lower than 40 km/h for adult, while the child head-impact velocity is about 25% lower than the 40 km/h specified by EEVC. 4.3. Head-impact angle The differences in head-impact angle can be mainly attributed to the different vehicle-front geometries and pedestrian gaits (Figures 8 and 9), which lead to different kinematics of the pedestrian after impact. For the adult, the initial contacted position of the SFC and MPV is higher than other vehicle types, so the vertical component of the
International Journal of Crashworthiness 7 Figure 8. Comparison of child pedestrian kinematics for different vehicle type (at 40 km/h and 60% gait). Figure 9. Comparison of adult pedestrian kinematics for different vehicle type (at 40 km/h and 60% gait). head-impact velocity is lower and the impact angle is lower. The child head-impact angles are larger for the SMC, SFC and LFC than for the MPV and SUV, and it is the smallest for the SUV. For the SUV, the head impacted directly with the hood edge before there is big neck bending (Figure 8), so the child head contact angle is the smallest. At a vehicle-impact velocity of 40 km/h, the average of headimpact angles for the SFC and MPV are 55, which is 16% lower than the 65 specified by EEVC for an adult. The average head-impact angles for the SMC and LFC are 63 and 66, respectively, which are about 28% higher than the 50 specified by EEVC for a child, while for the SUV, the headimpact angle is 29 which is 42% lower than 50 specified by EEVC for a child. The kinematic of the pedestrian head is determined by the first contact between the vehicle and the pedestrian s legs. Therefore, the head-impact orientation at the time of contact with vehicle is influenced by pedestrian gaits, which can be observed from Figures 10 and 11. The head orientations at the time of impact simulated from different gaits are different which can result in different injuries. Due to change in gaits percentage the centre of gravity of the pedestrian changes, thus resulting in different stress points on pedestrian head, leading to different linear and angular accelerations. This analysis demonstrates that further investigation is needed in order to assess the pedestrian head injury risk in more details. There are several limitations of the current study and they are to be mentioned. In case of all the simulations, the pedestrian hitting position is restricted at the central line of vehicle model, whereas other impact situations should also be considered to be more realistic. The stiffness properties of each part of the vehicle models are selected from the data available in the literature and not from actual experimental data of the individual vehicle. Different brands of vehicle have different stiffiness properties in the real world situation. Also, the same friction coefficients are defined in all the simulations, which can also change the response of pedestrian. Finally, the validation of PM needs some detailed evaluations, especially for the child PM.
8 Y. Peng et al. Figure 10. SFC). Comparison of child pedestrian head-impact orientation at time of contact with vehicle for different gaits (at 40 km/h for Figure 11. SFC). Comparison of adult pedestrian head-impact orientation at time of contact with vehicle for different gaits (at 40 km/h for 5. Conclusions This study presents an extensive analysis of pedestrian head motion based on multi-body simulation and focusing on the head-impact conditions at the time before impact. The results contribute to an in-deep understanding of the headimpact conditions in regulation test procedures to the front part of different passenger vehicles. The WAD is influenced by the vehicle-front geometry and pedestrian gait, especially for the adult pedestrian. The WAD gradually increases with the increase of vehicle-travel velocity, but this trend will slow down while the velocity is above 40 km/h both for the adult and child. For the SFC, LFC and MPV, the adult head-impact points focus on the windscreen. The simulation results indicated that the adult headform impacts on the vehicle between 1700 mm and 2100 mm or more. The head-impact velocity is determined by vehiclefront geometry, vehicle-impact velocity and pedestrian gait. Most of the simulations, the head-impact velocities, are lower than the initial vehicle velocities, especially for the child, the head-impact velocity is about 25% lower than the vehicle velocity. The head-impact velocity is higher for the SFC and LFC than for SMC, MPV and SUV. The study recommends that the subsystem test procedures should define different impact speeds for different vehicle types. Furthermore, the child headform impact speed should be lower than the adult headform impact speed. The head-impact angle depends on the vehicle-front geometry and pedestrian gait. The head-impact orientation at the time of contact with vehicle is mainly influenced by the pedestrian gait. For the adult, the angles for the SFC and MPV are lower than for the other vehicle types, while the child head contact angles are larger for the SMC, SFC and LFC than for the MPV and SUV, and it is the smallest for the SUV. The simulation results also suggest that the subsystem test procedures should define different impact test angles for different vehicle types. The head-impact angles for the SFC and MPV should be lower than the 65 specified by EEVC for an adult. The head-impact angles for the SMC and LFC should be higher than the 50 specified by EEVC for a child, while for SUV, the head-impact angle should be lower than the 50 specified by EEVC for a child. Acknowledgements This study was sponsored by the State Key Laboratory of Vehicle NVH and Safety Technology No. NVHSKL-201003, the Ministry of Education of P.R. China 111 program No. 111-2-11. The authors like to thank Fondation Securite Routiere-France and the MAIF foundation for their supports. In addition, thanks for the financial support of the China Scholarship Council (CSC).
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