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Technical Paper

Investigation of a Simplified Vehicle Model that Can Reproduce Car-Pedestrian Collisions

Japanese accident statistics show that despite the decreasing trend of the overall traffic fatalities, more than 1,000 pedestrians are still killed annually in Japan. One way to develop further understanding of real-world pedestrian accidents is to reconstruct a variety of accident scenarios dynamically using computational models. Some of the past studies done by the authors' group have used a simplified vehicle model to investigate pedestrian lower limb injuries. However, loadings to the upper body also need to be reproduced to predict damage to the full body of a pedestrian. As a step toward this goal, this study aimed to develop a simplified vehicle model capable of reproducing pedestrian full-body kinematics and pelvis and lower limb injury measures. The simplified vehicle model was comprised of four parts: windshield, hood, bumper and lower part of the bumper. Several different models were developed using different combinations of geometric and stiffness representation.
Journal Article

Development of Injury Probability Functions for the Flexible Pedestrian Legform Impactor

The goal of this study was to develop injury probability functions for the leg bending moment and MCL (Medial Collateral Ligament) elongation of the Flexible Pedestrian Legform Impactor (Flex-PLI) based on human response data available from the literature. Data for the leg bending moment at fracture in dynamic 3-point bending were geometrically scaled to an average male using the standard lengths obtained from the anthropometric study, based on which the dimensions of the Flex-PLI were determined. Both male and female data were included since there was no statistically significant difference in bone material property. Since the data included both right censored and uncensored data, the Weibull Survival Model was used to develop a human leg fracture probability function.
Journal Article

Investigation on Pelvis Injury Indices Using a Human Finite Element Model

For accurately predicting different fracture patterns of the pelvis frequently observed in pedestrian accidents with SUV/Mini-van, human finite element (FE) models have been developed. Although those models with failure representation can predict occurrence or nonoccurrence of fractures, quantitative estimation of probability of fractures is not possible. For human models without failure representation, typically stress or strain of elements is used for fracture prediction. However, numerous elements must be evaluated when fracture location is not predetermined. This study investigated methodology for accurately predicting probability of pelvic fractures using a minimal number of output parameters. The hood edge and upper and lower parts of the bumper were chosen for representing vehicle fronts. These components were modeled using rigid surfaces with the stiffness of them represented by springs, to constitute 3-component models.
Technical Paper

Development of a Finite Element Model for a Pedestrian Pelvis and Lower Limb

A finite element (FE) model that can predict impact response and injuries to a human pelvis and lower limb was developed in PAM-CRASH™ by accurately representing human anatomical structures. In our previous study, three-dimensional (3D) geometry of the thigh, leg and knee joint was developed based on MRI scans from a human volunteer. 3D geometry of a bony pelvis created in this study was based on CT scans from a Post Mortem Human Subject (PMHS). The model was validated using published quasi-static and dynamic test results with human pelves and lower limbs. The thigh and leg models were validated against recently published dynamic 3-point bending test results with off-center loading. The validation results showed that this model can reproduce force-deflection and moment-deflection responses of a human thigh and leg in various loading conditions along with average force and moment at fracture.
Technical Paper

Development and Validation of a Finite Element Model for the Polar-II Upper Body

The goal of this study was to develop and validate a finite element (FE) model of the Polar-II pedestrian dummy. An upper body model consisting of the head, neck, shoulder, thorax, and abdomen was coupled with a previously validated model of the lower limb The viscoelastic material properties of the dummy components were determined from dynamic compression tests of shoulder urethane, shoulder rubber and abdominal foam. For validation of the entire upper body, the model was compared with NHTSA response requirements for their advanced frontal dummy (Thor) including head and neck pendulum tests as well as ribcage and abdominal impact tests. In addition, the Polar-II full body FE model was subjected to simulated vehicle-pedestrian impacts that recreated published experiments. Simulated head and pelvis accelerations as well as upper body trajectories reasonably reproduced the experiment.
Technical Paper

Biofidelity Improvements to the Polar-II Pedestrian Dummy Lower Extremity

Experimental tests were performed on the modified Polar-II pedestrian dummy lower extremity components to evaluate their biofidelity in lateral impact loading corresponding to a 40 km/h pedestrian-car collision. The bending moment-angle response from a newly developed knee joint, dynamically loaded in four-point valgus bending, was compared against previously published postmortem human subject (PMHS) response corridors. In addition to the stiffness characteristics of the knee joint, individual ligament forces were also recorded during the bending tests. The evaluated force-relative elongation response of the medial collateral ligament (MCL) in the new knee was compared against PMHS data on MCL tensile stiffness. Lower extremity long bones developed for improved anthropometrical accuracy and deformability were dynamically loaded in latero-medial three-point bending.
Technical Paper

Full-Scale Validation of a Human FE Model for the Pelvis and Lower Limb of a Pedestrian

In order to investigate injury mechanisms to the pedestrian pelvis and lower limb, the authors have developed a finite element (FE) human model for the pedestrian pelvis and lower limb in their previous studies. Quasi-static and dynamic responses of the pelvis and lower limb components were individually validated against recently published experiments. However, the pelvis and lower limb models have not been validated at the assembly level under impact conditions that better represent an actual car-pedestrian impact situation. In this study, the pelvis and lower limb models were assembled in a standing position, and an upper body model with rigid body segments connected by mechanical joints was integrated into the FE pelvis and lower limb model assembly to create a full-body pedestrian model. The model was subjected to car impacts at 40 km/h to represent published car-to-pedestrian impact experiments using human subjects.
Journal Article

Estimation of Knee Ligament Injury Measures for a Pedestrian Dummy

In order to enhance understanding of pedestrian injury mechanisms, full-body pedestrian dummies have been developed in past studies. The goal of this study was to estimate knee ligament injury measures for a pedestrian dummy based on the correlation between dummy and human responses. For estimating knee ligament force of the dummy approximating the average ligament failure, finite element (FE) human and dummy knee joint models were subjected to dynamic 4-point bending. The estimated measures for the modified dummy knee ligaments were 3.0, 0.5 and 1.1 kN for the MCL, PCL and ACL, respectively. A full-body FE dummy model was subjected to impacts from a small sedan and a Sport Utility Vehicle (SUV) for validating the estimated force levels. The results showed that the estimated dummy knee ligament force levels predicted failure of human knee ligaments that is likely to take place first when leg fractures are not present in impacts from a small sedan and a SUV.
Technical Paper

Pedestrian Dummy Pelvis Impact Responses

In order to investigate pedestrian injury mechanism by representing whole body kinematics of a pedestrian, a pedestrian dummy (POLAR II) has been developed. Previous studies indicated that the original pelvis design needed to be modified from the comparison of POLAR II and PMHS (Post Mortem Human Subject) responses in a pedestrian impact test with a SUV (Sports Utility Vehicle). In addition, according to the results of an in-depth investigation of pedestrian versus SUV or mini-van accidents in the US, pelvis fracture was found to be most frequent in AIS 2+ pelvis and lower limb injuries. Based on these findings, the POLAR II pelvis was modified for improved biofidelity. The modified pelvis design incorporated the flexible ilium (polyacetal resin) and pubic symphysis (rubber material) as opposed to the original pelvis cast in aluminum. The modified pelvis responses were verified against published isolated pelvic PMHS test results in lateral compression of the pelvis.
Technical Paper

Development of Omni-directional Injury Criteria for a Pedestrian Dummy for Evaluating Rib Fracture

Pedestrian - motor vehicle collisions account for approximately 15% of all traffic fatalities in Europe and the US, and 35% or more in Japan and Asian countries. Several studies have addressed this issue, such as the EEVC study. In the development of the test methods, body region priorities are mainly based on studies of pedestrian collisions with passenger vehicles. However recently, the populations of SUVs and LTVs are increasing in many countries. Pedestrian collision data indicate that thoracic and upper abdominal injuries are also frequent in pedestrian collisions where these kinds of vehicles are involved. However, evaluation methods for pedestrian torso injuries are not currently available. This paper describes a study for the evaluation of pedestrian thoracic and upper abdominal injuries using the POLAR II pedestrian dummy.
Technical Paper

A Multi-Body Computational Study of the Kinematic and Injury Response of a Pedestrian with Variable Stance upon Impact with a Vehicle

This research investigates the variation of pedestrian stance in pedestrian-automobile impact using a validated multi-body vehicle and human model. Detailed vehicle models of a small family car and a sport utility vehicle (SUV) are developed and validated for impact with a 50th percentile human male anthropometric ellipsoid model, and different pedestrian stances (struck limb forward, feet together, and struck limb backward) are investigated. The models calculate the physical trajectory of the multi-body models including head and torso accelerations, as well as pelvic force loads. This study shows that lower limb orientation during a pedestrian-automobile impact plays a dominant role in upper body kinematics of the pedestrian. Specifically, stance has a substantial effect on the subsequent impacts of the head and thorax with the vehicle. The variation in stance can change the severity of an injury incurred during an impact by changing the impact region.
Technical Paper

A Comparative Evaluation of Pedestrian Kinematics and Injury Prediction for Adults and Children upon Impact with a Passenger Car

Studies show that the pedestrian population at high risk of injury consists of both young children and adults. The goal of this study is to gain understanding in the mechanisms that lead to injuries for children and adults. Multi-body pedestrian human models of two specific anthropometries, a 6year-old child and a 50th percentile adult male, are applied. A vehicle model is developed that consists of a detailed rigid finite element mesh, validated stiffness regions, stiff structures underlying the hood and a suspension model. Simulations are performed in a test matrix where anthropometry, impact speed and impact location are variables. Bumper impact occurs with the tibia of the 50th percentile adult male and with the thigh of the 6-year-old child. The head of a 50th percentile male impacts the lower windshield, while the 6-year-old child's head impacts the front part of the hood.
Technical Paper


In the current test procedure proposed by the European Enhanced Vehicle-safety Committee (EEVC)/WG17 for evaluating leg injuries to pedestrians, a legform impactor with a rigid bony structure is used. The risk of damages to knee ligaments is evaluated with the shearing displacement and the bending angle at the knee joint. A recent study has focused on evaluating biofidelity of the legform. However, it was not possible to obtain a local deformation at the knee joint from published experiments with Post Mortem Human Subjects (PMHSs). In addition, past PMHS experiments have suggested that the height of a bumper significantly affects the risk of ligamentous damages.
Technical Paper

Development and Validation of the Finite Element Model for the Human Lower Limb of Pedestrians

An impact test procedure with a legform addressing lower limb injuries in car-pedestrian accidents has been proposed by EEVC/WG17. Although a high frequency of lower limb fractures is observed in recent accident data, this test procedure assesses knee injuries with a focus on trauma to the ligamentous structures. The goal of this study is to establish a methodology to understand injury mechanisms of both ligamentous damages and bone fractures in car-pedestrian accidents. A finite element (FE) model of the human lower limb was developed using PAM-CRASH™. The commercially available H-Dummy™ lower limb model developed by Nihon ESI for a seated position was modified to represent the standing posture of pedestrians. Mechanical properties for both bony structures and knee ligaments were determined from our extensive literature survey, and were carefully implemented in the model considering their strain rate dependency in order to simulate the dynamic response of the lower limb accurately.
Technical Paper

Improvement and Validation of the Lower Limb and the Pelvis for a Pedestrian Dummy

The evaluation of pedestrian safety performance of vehicles required by regulations and new car assessment programs (NCAPs) have been conducted. However, the behavior of a pedestrian in an actual car-pedestrian accident is complex. In order to investigate injuries to the pedestrian lower body, the biofidelity of the lower limb and the pelvis of a pedestrian dummy called the POLAR II had been improved in past studies to develop a prototype of the next generation dummy called the POLAR III. The biofidelity of the thigh and the leg of the POLAR III prototype has been evaluated by means of 3-point bending. However, the inertial properties of these parts still needed to be adjusted to match those of a human. The biofidelity of the pelvis of the POLAR III prototype has been evaluated in lateral compression. Although the experiment using PMHSs (Post Mortem Human Subjects) was conducted in dynamic condition, the dummy tests were performed only in quasi-static condition.
Technical Paper

Simplifying the Structural Design of the Advanced Pedestrian Legform Impactor for Use in Standardized Testing

The advanced Pedestrian Legform Impactor (aPLI) incorporates a number of enhancements for improved lower limb injury prediction capability with respect to its predecessor, the FlexPLI. The aPLI also incorporates a simplified upper body part (SUBP), connected to the lower limb via a mechanical hip joint, that expands the impactor’s applicability to evaluate pedestrian’s lower limb injury risk also in high-bumper cars.As the aPLI has been developed to be used in standardized testing, further considerations on the impactor’s manufacturability, robustness, durability, usability, and repeatability need to be accounted for.. The aim of this study is to define and verify, by means of numerical analysis, a battery of design modifications that may simplify the manufacturing and use of physical aPLIs, without reducing the impactors’ biofidelity. Eight candidate parameters were investigated in a two-step numerical analysis.
Technical Paper

Investigation on an Injury Criterion Related to Traumatic Brain Injury Primarily Induced by Head Rotation

The high frequency of fatal head injuries is one of the important issues in traffic safety, and Traumatic Brain Injuries (TBIs) without skull fracture account for approximately half of them in both occupant and pedestrian crashes. In order to evaluate vehicle safety performance for TBIs in these crashes using anthropomorphic test dummies (ATDs), a comprehensive injury criterion calculated from the rotational rigid motion of the head is required. While many studies have been conducted to investigate such an injury criterion with a focus on diffuse brain injuries in occupant crashes, there have been only a limited number of studies focusing on pedestrian impacts. The objective of this study is to develop a comprehensive injury criterion based on the rotational rigid body motion of the head suitable for both occupant and pedestrian crashes.