International Journal of Automotive Technology, Vol. 16, No. 5, pp. 791−797 (2015) DOI 10.1007/s12239−015−0080−8
Copyright © 2015 KSAE/ 086−08 pISSN 1229−9138/ eISSN 1976−3832
METHOD FOR INVESTIGATION OF CHILD OCCUPANT IMPACT DYNAMICS BASED ON REAL-WORLD ACCIDENT Y. PENG1), R. LI1), G. B. LI2), X. M. YANG2) and D. ZHOU1)* 1)
Key Laboratory of Traffic Safety on Track of Ministry of Education, School of Traffic & Transportation Engineering, Central South University, Changsha 410075, China 2) Research Center of Vehicle and Traffic Safety, State Key Lab of Advanced Design and Manufacture for Vehicle Body, Hunan University, Changsha 410082, China (Received 23 May 2014; Revised 26 October 2014; Accepted 15 January 2015)
ABSTRACT−The objective of the study is to propose a method to investigate child occupant impact dynamics based on realworld accident reconstruction. A real-world child occupant accident was reconstructed by using PC-Crash and finite element (FE) modeling software, with the aim of comparing simulation output with injuries sustained. Firstly, PC-Crash reconstruction was carried out to calculate vehicle impact conditions of vehicle impact velocity, vehicle position and vehicle orientation. The dynamics responses at the head, neck, thorax and pelvis of the child occupant were simulated. Hybird III 6-year-old FE model was employed in FE simulation. The results of two vehicles’ positions agreed well with that in real-world accident case, the dynamics responses at the head, neck and thorax of the child occupant well indicate the injury status of the child occupant. The simulation results showed that booster seat headrest and intrusive door mainly causes head injuries and seat belt mainly causes abdominal bruise of children. This study provides a useful method to investigate the impact dynamic and injury risk of child occupantre. KEY WORDS : Child occupant, Accident reconstruction, Dynamic response, Injuries analysis
1. INTRODUCTION
safety, researches have been carried out using accident data, mathematical models, sled tests and intelligent control. Bohman et al. (2011) identified the AIS2+ head injury causation scenarios for rear-seated, belt-restrained children in frontal impacts based on 27 children occupant real-world accidents. Macy et al. (2013) provided the assessment of the seating positions occupied by child passengers and the relationship between Child restraint systems (CRS) and other second-row passengers based on the accident data from the 2007 ~ 2009 National Survey of the Use of Booster Seats. Peng et al. (2011) reported child occupant safety in passenger vehicle using accident data from Changsha, China. Nilson and Haland (1995) analyzed the relationship between lap belt load and belt-to-pelvis angle and found that when the belt force exceeds 3 kN, the maximum pelvis-to-belt angle corresponds to the submarining risk window. Lap belt load and maximum pelvis rotation were also defined as assessment criteria combined with visual analysis of videos by (Couturier et al., 2007). Garcia-Espana and Durbin (2008) found that shoulder belts routed too far outward will be ineffective in restraining the torso when child put the shoulder belt behind the back or under the arm. In order to evaluate the performance of various restraint systems and countermeasures for child occupants in different crash scenarios, sled tests were carried out with a Hybrid III 6 year old anthropomorphic test device in frontal, oblique and side impact configurations
Children are considered to be a vulnerable group in road traffic and child safety is a worldwide concern (NHTSA, 2005; MPSTA, 2005; ERSO, 2007). The traffic accident is the key factor in the deaths of children (up to 14 years old). The Centers for Disease Control and Prevention (CDC) Web-based Injury Statistics Query and Reporting System reported that in 2003 and 2004, motor vehicle accidents were the leading cause of death for children age 1 ~ 9 (Beaudoin et al., 2008). In the United States, motor vehicle crashes (MVCs) were the major cause of death in children aged 5 ~ 15 years (NVSS, 2009) and more than 150,000 children were injured in MVCs in 2006 (NHTSA, 2008). Furthermore, data from the fatality analysis reporting system (FARS) from 1991 ~ 2000 showed that frontal and side crashes consist the majority of child occupant fatalities (Kapoor et al., 2008). Side impact crashes are still related to severe child’ injuries (Arbogast et al., 2010; Nance et al., 2010) despite significant improvements in passenger safety (CDCP, 2009) through vehicle engineering, increased use of child passenger restraints, and enhanced child restraint systems. Lately, child occupant safety has become an increasing concern in the world. In order to improve child occupant *Corresponding author. e-mail:
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by Malott et al. (2004). Lee et al. (2011) proposed a stereovision-based real-time occupant classification system and intelligent algorithm installed within an embedded system. Hannan et al. (2010) investigated the decision fusion strategies of a multi-sensing embedded system to achieve significant enhancement in the reliability of occupant safety through the fused decisions. Kuk et al. (2008) analyzed the operational principle of a buckle that prevents the inertial release during the explosion of the pretensioner. In order to improve child occupant safety combining accidents, it is necessary to carry out reconstruction of real-world child occupant accident to understand child occupant dynamic responses, investigate child injury mechanism and causes and evaluate the protection performance of Child Restraint System. In this study, a side-impact collision accident case of child occupant was selected from German In-Depth Accident Study (GIDAS) database. Then the real-world child occupant accident was reconstructed by using a combination of PC-Crash and finite element (FE) simulation methods. Hybrid III 6-year-old FE model was employed to investigate child dynamic responses and output injuries parameters.
2. METHODOLOGY 2.1. Description of Accident Accident case was selected from Germany GIDAS database. The GIDAS database has on-scene accident cases in the areas of Hannover and Dresden, Germany, since 1999 (Otte et al., 2003). Accident scene photo and sketch is shown in Figure 1. The front-end of vehicle 2 (Mercedes190 E2.0) impacted with the right side of vehicle 1 (Opel OMEGA GL). As shown in Figure 1 (b), vehicle 2 was going straight, and vehicle 1 was taking a left turn in the adjacent lane. The weather was fine and the ground was dry. The limited speed of the road is 100 km/h. Targeted child occupant was 7 years old, sitting in child booster seats on the right side of backseat in vehicle 1. Injuries were described as follows: intracranial hematoma, cerebral edema, Abbreviated Injury Scale (AIS 5); abdominal soft tissue bruising, AIS 9; Maximum Abbreviated Injury Score (MAIS) was 9 and Injury Severity Score (ISS) was 75, the child was died.
Figure 1. Photo and sketch of accident scene (GIDAS database): (a) Photo of accident scene; (b) Sketch of accident scene.
2.2. Accident Reconstruction Reconstructions include two parts: PC-Crash simulation and FE simulation. PC-Crash is a three-dimensional collision and trajectory simulation tool that enables a quick analysis of a wide variety of motor vehicle collisions and other incidents. FE simulation used LS-DYNA. LS-DYNA is a general-purpose finite element program capable of simulating complex real world problems. A scaled, on-site sketch of the accident scene is important for PC-Crash simulation. From the sketch of the accident, we used estimated initial impact location, rest positions of vehicles, skidding marks and certain other marks. Vehicle information contains car type, model and manufacturer, and so on. The PC-Crash simulation results were used for the initial setup of car velocity and dynamics in FE reconstructions. The final configuration that reproduced the same impact points on the vehicles and the same injuries to the real accident was retained. 2.2.1. Development of PC-crash reconstruction model Based on the information of the real-world accident, a twodimensional collision model was built according to the vehicle model geometry and quality parameters. According to the stop position of the two vehicles and wheel brake marks in the scene, adjusting the collision position of the two vehicles, brakes, steering and other relevant parameters to make stop position and the wheel trajectory of twovehicle collision accident simulation to meet the stop position and the wheel trajectory in actual accident. The friction coefficients are 0.7 for wheels/ground and 0.2 for the contacts between vehicle 1 and vehicle 2. The obtained impact conditions included linear vehicle velocity, angular velocity and the relative position at the point of contact in collision can be applied to FE model of collided vehicles as the initial boundary conditions. 2.2.2. Development of FE reconstruction model Vehicle FE models Vehicle finite element models used in the process of reconstruction are the similar finite element models of two accident vehicles, as shown in Figure 3. The vehicle 1 and vehicle 2 were simulated by Dodge Neon and Geely King Kong respectively. The FE model of Dodge Neon was developed by the National Highway Traffic Safety Administration (NHTSA, 1996). The FE model developed mainly for frontal impacts and the material data derived from coupon testing. The total FE model includes 283859 nodes and 270768 elements. The FE model was validated against Euro-NCAP impact test results. The FE model of Geely King Kong was developed by Lu (2005). The total FE model includes 332278 nodes and 330591 elements. The FE model was validated by comparing with the experimental results of front impact, rear impact and side impact respectively. Child FE model
METHOD FOR INVESTIGATION OF CHILD OCCUPANT IMPACT DYNAMICS BASED
Figure 2. Hybrid III Six-Year-Old FE model.
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Figure 4. PC-Crash simulation results.
Figure 5. Draft of SAE J224. Figure 3. Finite element models of collided vehicles.
The Hybrid III Six-Year-Old FE model was employed in this study. The FE model was jointly developed by Livermore Software Technology Corporation (LSTC) and National Crash Analysis Center (NCAC). The total Hybrid III Six-Year-Old FE model includes 201,084 nodes, 127,621 solid elements, 48,566 shell elements and 137 beam elements and the effective mass is 24.2 kg (Figure 2). It has been validated to the certification tests described in the Code of Federal Regulations (LSTC, 2011). The certification tests include head drop test, neck pendulum tests, thorax impact test, and knee impact test. Setup of FE reconstruction The set up of FE reconstruction is configured based on the output of PC-Crash simulation impact conditions before vehicle 2 contact with vehicle 1. The impact conditions include linear velocity and angular velocity of each vehicle, and the relative position and orientation between two vehicles, as shown in Figure 3.
3. RESULTS 3.1. Results of PC-Crash Reconstruction It can be seen from Figure 4 that the stop position of two collided vehicles and the actual stop position as well as trajectories of wheels of the accident are basically consistent. Thus, the simulation model is valid. The precrash velocity of two collided vehicles and the collision contact position obtained at this time can be used as initial boundary conditions in FE reconstruction. The angle between two vehicles was about 66o and ΔV was about 26±5 km/h.
Nagabhushana et al. (2007) analyzed the side collision accident involving children occupant aged 1 ~ 8 in NASS/ CDS database during 1991 ~ 2005 and found that 90 percent of the incident angle in side collision were between 30o ~ 90o, 56% of the injury occurred in the main direction of impact force (PDOF) is 60o, 61% of the children were on the right side of the vehicle, 66% of children were in the second row of seats, 84% of children were located in the impact side, 50% or more injuries occurred in ΔV > 29 km/ h, 83% of the injuries occurred in the head and face and 80% of collision involved ‘Y’ or ‘Z’ zone damage (see Figure 5). In this study, the accident case was selected from GIDAS database based on the above principles. According to the actual situation of the accident scene, the accident scene sketch was drawn using a scale of 1:200. Collided region of targeted vehicle 1 was located in ‘Z’ area divided in Figure 5 and the angle between two vehicles was about 66o, the target child occupant was on the right of vehicle 1 (being hit side) in the second row, ΔV was about 26±5 km/ h. Thus the accident is a universal and typical case. In an actual two vehicle collision accident, the collision of the vehicle includes translation on z and rotation around x and y-axis in addition to translation on x and y and rotation about the axis of z. However, considering the occupant in this accident mainly got damage from impact on x-y plane, therefore only considers the motion on the xy plane. 3.2. Results of FE Reconstruction As finite element model calculation is time-consuming, select 150 ms from two vehicles contact to separate, during when the main occupant injury occurs. Figure 7 and Figure 8 show deformation of inside and outside door of the
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Figure 6. Comparison of external deformation of door between accident photo (left) and simulation (right).
Figure 7. Comparison of internal deformation of door between accident photo (left) and simulation (right). vehicle 1 between real-world accident and simulation. From Figure 6 and 7, it could be observed that the simulation results agree well with the real-world accident. As can be seen from Figure 6, the largest damage area outside of the door in simulation and actual accident is basically consistent. Maximum intrusion amount of door in simulation is similar with actual deformation as shown in Figure 7. Child dummy kinematics is shown in Figure 8. At about 30 ms, contact started; about 62 ms head hit the headrests
Figure 8. Kinematics response of child dummy.
Figure 9. Child occupant head kinetic response curves: (a) Head linear acceleration time history; (b) Head angular acceleration time history; (c) Head angular velocity time history.
of child booster seat and hit the bottom edge of the window in intrusion door at about 79 ms. Figure 9 to Figure 13 show the child occupant dummy response during collision. As can be seen from Figure 9 (a), the head linear acceleration reaches a maximum value 128 g at 62 ms. The peak value is mainly due to collision impact force of dummy’s head by hitting on headrest of child booster seat. As a result, the maximum HIC36 value is 1979, and the initial and final times of the interval during which the HIC36 attains maximum value are 59.3 ms and 88.5ms respectively. The second peak value is a 99 g occurred at 79 ms; this peak is mainly due to the hit of dummy's head on crashed door. From Figure 9 (b) and Figure 9 (c), it can be observed that the maximum angular acceleration and maximum angular velocity are 12927 rad/ s2 and 69 rad/s respectively and occurred at 48 ms and 66 ms respectively. The neck moment y and neck fore Z are shown in Figure 10. From Figure 10, it can be seen that neck moment y reached a maximum value 51 Nm at 86 ms and the maximum neck force Z is 2.7 kN occurred 59 ms. For the load of neck,
Figure 10. Child occupant neck kinetic response curves: (a) Neck moment y time history; (b) Neck force Z time history.
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4. DISCUSSIONS
Figure 11. Child occupant chest kinetic response curves: (a) Chest acceleration time history; (b) Chest deflection time history.
they were generated mainly because of asynchrony of dynamic between dummy head and upper torso when the dummy upper torso was restrained by safety belt. Figure 11 shows the child occupant chest kinetic responses. It can be seen that the chest acceleration reach a maximum value of 118 g at 53 ms and then decrease rapidly, and the biggest chest deflection is found at 58 ms and the value is 55 mm. As shown in Figure 12, the maximum value of pelvis acceleration appeared at 39 ms and the value is 163 g. Because the first deformation area of impacted vehicle was directly facing the part of pelvis, the occurrence time of peak value is early. Figure 13 is contact force curves of seat belt and child dummy. As can be seen from Figure 14 (a), contact force curve of shoulder belt and dummy has two peaks, which are maximum 3.76 kN at approximately 40 ms, and 2.57 kN at 56 ms respectively. As shown in Figure 14 (b), the contact force of lap belt and dummy reached a maximum of 1.89 kN at 51 ms.
Figure 12. Pelvis acceleration time history.
Figure 13. Contact force curves of belts: (a) Shoulder belt force time history; (b) Lap belt force time history.
According to the reconstruction results, the maximum child dummy head linear acceleration is 128 g, far higher than the regulatory standard 80 g (NHTSA, 2002). The second peak value of 99 g is also bigger than 80 g. In addition, the HIC36 value is 1979, far higher than 1000. HIC36 value equals to 1000 means that 20% of AIS3+ head injury risk (NHTSA, 1998). The maximum angular acceleration and maximum angular velocity are 12, 927 rad/s2 and 69 rad/s respectively. A threshold for brain injury was suggested (LoÈ, 1974; Marguiles and Thibault, 1992; Ryan et al., 1989; Ryan and Vilenius, 1995) by using a critical strain curve expressed in terms of the peak angular acceleration and angular velocity. It was suggested that the bridging vein could be ruptured when the head angular acceleration exceeds 4500 rad/s2 and the angular velocity is above 50 rad/s. It can be concluded the simulation meets the target child occupant's head injury record (intracranial hematoma, cerebral edema, AIS5) in actual accident. Also, head injury is usually related to angular acceleration of the head in addition to quantitative relationship with linear acceleration of head. In terms of neck injury, the simulation results shown that the maximum neck moment y and the maximum neck force Z are 51 Nm and 2.7 kN respectively. According to Eppinger et al. (1999) study, the flexion limit for the HybridIII 6 dummy is 93 Nm and the extension limit is 37 Nm, and the moment limits of compression and tension are both 2.8 kN. So, the calculated value of Nij is associated with approximately a 45% risk of an AIS3 injury. In this study, the simulation results showed that the maximum chest acceleration is 118 g and the biggest chest deflection is 55 mm. According to the FMVSS 208 regulation, the limit for child chest acceleration is 60 g, chest deflection is 40 mm and duration is 3 ms. And the ECER44 (UNECE, 1998) also suggested that the duration is no more than 3 ms when the value of child dummy chest acceleration is higher than 55 g. The report of National Highway Traffic Safety Administration showed that the limited value of child chest deflection is 58 mm to 61 mm for side impact collision. The 28% to 35% of chest deflection corresponds to a 25% probability of an AIS3 thoracic injury for child. For abdominal injuries, there are no child abdominal protection standards or injury evaluation techniques and HybridIII 6-year-old dummy cannot output abdomen force or other abdominal injury indicators, thus this study only output contact forces between shoulder belt/Lap belt and dummy. Simulation results shows that the maximum contact force of seat belt and dummy is 3.76 kN, and seat belt is the only part that contacts with child dummy abdomen directly. At the same time, it can be found that the maximum value of pelvis acceleration is 163g. Thus, it can be inferred that the belt is the main reason for abdominal abrasions.
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According to analysis of the reconstruction results, the main reason for the peak in head synthesis acceleration was hit on the seat headrests and door from dummy's head. The chest and abdomen injuries were mainly caused by seat belts.
5. CONCLUSION In this study, a real-world child occupant accident was selected from German In-Depth Accident Study (GIDAS) database and reconstructed in order to investigate the child occupant impact dynamic and injury risk. The accident reconstruction was carried out using a combination of multi-body dynamics and finite element (FE) methods using PC-Crash software and LS-DYNA software, which are used to reconstruct two vehicle impact conditions and vehicle deformation and child impact kinetics in collision respectively. The preliminary results prove the effectiveness of the models and methods. The simulation results showed the main reason and major cause of the child’s death in this accident case. Seat belt is the main cause of abdominal bruise of the target children. ACKNOWLEDGEMENT−The authors thank the Accident Research Unit (ARU) of the Medical University of Hannover for the valuable accident data. The authors are grateful for the financial support of the China Scholarship Council (CSC) and scientific research start-up capital of Central South University.
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Tannous, R., Zhang, A. and Saul, R. (1999). Development of Improved Injury Criteria for the Assessment of Advanced Automotive Restraint SystemsII. National Highway and Traffic Safety Administration. European Experimental Vehicles Committee (EEVC). (2002). Improved Test Methods to Evaluate Pedestrian Protection Affordable by Passenger Cars, Technical Report, European Enhanced Vehicle-Safety Committee, Working Group 17 Report, December 1998 with September 2002 updates. Please ensure refer in the text. Ex) (European Experimental Vehicles Committee (EEVC), 2002) European Road Safety Observatory (ERSO). (2007). Traffic Safety Facts 2006-Children (Age
