Jaeho Shin

A Finite Element Model of the Foot and Ankle for Automotive Impact Applications

A finite element (FE) model of the foot and leg was developed to improve understanding of injury mechanisms of the ankle and subtalar joints during vehicle collisions and to aid in the design of injury countermeasures. The FE model was developed based on the reconstructed geometry of a male volunteer close to the anthropometry of a 50th percentile male and a commercial anatomical database. While the forefoot bones were defined as rigid bodies connected by ligament models, the surrounding bones of the ankle and subtalar joints and the leg bones were modeled as deformable structures. The material and structural properties were selected based on a synthesis of current knowledge of the constitutive models for each tissue. The whole foot and leg model was validated in different loading conditions including forefoot impact, axial rotation, dorsiflexion, and combined loadings. Overall results obtained in the model validation indicated improved biofidelity relative to previous FE models. The developed model was used to investigate the injury tolerance of the ankle joint under brake pedal loading for internally and externally rotated feet. Ligament failures were predicted as the main source of injury in this loading condition. A 12% variation of failure moment was observed in the range of axial foot rotations (±15°). The most vulnerable position was the internally rotated (15°) posture among three different foot positions. Furthermore, the present foot and ankle model will be coupled together with other body region FE models into the state-of-art human FE model to be used in the field of automotive safety.

A Finite Element Model of the Lower Limb for Simulating Automotive Impacts

A finite element (FE) model of a vehicle occupant’s lower limb was developed in this study to improve understanding of injury mechanisms during traffic crashes. The reconstructed geometry of a male volunteer close to the anthropometry of a 50th percentile male was meshed using mostly hexahedral and quadrilateral elements to enhance the computational efficiency of the model. The material and structural properties were selected based on a synthesis of current knowledge of the constitutive models for each tissue. The models of the femur, tibia, and leg were validated against Post-Mortem Human Surrogate (PMHS) data in various loading conditions which generates the bone fractures observed in traffic accidents. The model was then used to investigate the tolerances of femur and tibia under axial compression and bending. It was shown that the bending moment induced by the axial force reduced the bone tolerance significantly more under posterior-anterior (PA) loading than under anterior-posterior (AP) loading. It is believed that the current lower limb models could be used in defining advanced injury criteria of the lower limb and in various applications as an alternative to physical testing, which may require complex setups and high cost.

Biomechanical and Injury Response of Human Foot and Ankle Under Complex Loading

Ankle and subtalar joint injuries of vehicle front seat occupants are frequently recorded during frontal and offset vehicle crashes. A few injury criteria for foot and ankle were proposed in the past; however, they addressed only certain injury mechanisms or impact loadings. The main goal of this study was to investigate numerically the tolerance of foot and ankle under complex loading which may appear during automotive crashes. A previously developed and preliminarily validated foot and leg finite element (FE) model of a 50th percentile male was employed in this study. The model was further validated against postmortem human subjects (PMHS) data in various loading conditions that generates the bony fractures and ligament failures in ankle and subtalar regions observed in traffic accidents. Then, the foot and leg model were subjected to complex loading simulated as combinations of axial, dorsiflexion, and inversion loadings. An injury surface was fitted through the points corresponding to the parameters recorded at the time of failure in the FE simulations. The compelling injury predictions of the injury surface in two crash simulations may recommend its application for interpreting the test data recorded by anthropometric test devices (ATD) during crash tests. It is believed that the methodology presented in this study may be appropriate for the development of injury criteria under complex loadings corresponding to other body regions as well.

Potential of Pedestrian Protection Systems—A Parameter Study Using Finite Element Models of Pedestrian Dummy and Generic Passenger Vehicles

Objective: To study the potential of active, passive, and integrated (combined active and passive) safety systems in reducing pedestrian upper body loading in typical impact configurations. Methods: Finite element simulations using models of generic sedan car fronts and the Polar II pedestrian dummy were performed for 3 impact configurations at 2 impact speeds. Chest contact force, head injury criterion (HIC15), head angular acceleration, and the cumulative strain damage measure (CSDM0.25) were employed as injury parameters. Further, 3 countermeasures were modeled: an active autonomous braking system, a passive deployable countermeasure, and an integrated system combining the active and passive systems. The auto-brake system was modeled by reducing impact speed by 10 km/h (equivalent to ideal full braking over 0.3 s) and introducing a pitch of 1 degree and in-crash deceleration of 1 g. The deployable system consisted of a deployable hood, lifting 100 mm in the rear, and a lower windshield air bag. Results: All 3 countermeasures showed benefit in a majority of impact configurations in terms of injury prevention. The auto-brake system reduced chest force in a majority of the configurations and decreased HIC15, head angular acceleration, and CSDM in all configurations. Averaging all impact configurations, the auto-brake system showed reductions of injury predictors from 20 percent (chest force) to 82 percent (HIC). The passive deployable countermeasure reduced chest force and HIC15 in a majority of configurations and head angular acceleration and CSDM in all configurations, although the CSDM decrease in 2 configurations was minimal. On average a reduction from 20 percent (CSDM) to 58 percent (HIC) was recorded in the passive deployable countermeasures. Finally, the integrated system evaluated in this study reduced all injury assessment parameters in all configurations compared to the reference situations. The average reductions achieved by the integrated system ranged from 56 percent (CSDM) to 85 percent (HIC). Conclusions: Both the active (autonomous braking) and passive deployable system studied had a potential to decrease pedestrian upper body loading. An integrated pedestrian safety system combining the active and passive systems increased the potential of the individual systems in reducing pedestrian head and chest loading.

Investigating Pedestrian Kinematics with the Polar-II Finite Element Model

This paper is from the SAE World Congress & Exhibition, held in April 2007 in Detroit, Michigan, USA. Part of the Pedestrian Safety session, this paper reports on a study of pedestrian kinematics with the Polar-II Finite Element Model. The authors describe how earlier studies on pedestrian-vehicle impact kinematics used post-mortem human surrogates (PMHS) and determined that vehicle shape may influence pedestrian kinematics and injury mechanisms. The authors describe finite element (FE) modeling as a more feasible approach, since numerous experiments can be conducted with a significantly lower cost. The authors report on their study which used an FE model of the Polar-II pedestrian dummy to evaluate the influence of shifting body contact points with respect to vehicle geometry on impact kinematics. Multiple simulations were performed by moving the pedestrian vertically with respect to the vehicle reference frame. Another component of the study was undertaken to evaluate the contribution of the mass distribution with respect to vehicle geometry. In this part, simulations were performed where the center of gravity of the dummy was shifted around the baseline location. The authors discuss the results of this study which suggest a nonlinear sensitivity of response to changes in the body contact points with respect to vehicle structures, as well as a linear variation of upper body trajectories when the dummy center of gravity height was adjusted.

Development and validation of pedestrian sedan bucks using finite-element simulations: a numerical investigation of the influence of vehicle automatic braking on the kinematics of the pedestrian involved in vehicle collisions

Previous vehicle-to-pedestrian impact simulations and experiments using pedestrian dummies and cadavers have shown that factors such as vehicle shape, pedestrian anthropometry and pre-impact conditions influence pedestrian kinematics and injury mechanisms. Generic pedestrian bucks, which approximate the geometrical and stiffness properties of current vehicles, would be useful in studying the influence of vehicle front-end structures on pedestrian kinematics and loading. This study explores the design of pedestrian bucks, intended to represent the basic vehicle front-end structures, consisting of five components: lower stiffener, bumper, hood leading edge and grille, hood and windshield. The deformable parts of the bucks were designed using types of currently manufactured materials, which allow fabricating the bucks in the future. The geometry of pedestrian bucks was approximated according to the contour cross-sections of two sedan vehicles used in previous pedestrian dummy and cadaver impact tests. Other cross-sectional dimensions and the stiffness of the buck components were determined by parameter identification using finite-element (FE) simulations of each sedan model. In the absence of a validated FE model of human, the FE model of the POLAR II pedestrian dummy was used to validate a mid-size sedan (MS) pedestrian buck. A good correlation of the pedestrian dummy kinematics and contact forces obtained in dummy–MS pedestrian buck with the corresponding data from dummy–MS vehicle simulation was achieved. A parametric study using the POLAR II FE model and different buck models – an MS buck and a large-size sedan (LS) buck – were run to study the influence of an automatic braking system for reducing the pedestrian injuries. The vehicle braking conditions showed reductions in the relative velocity of the head to the vehicle and increases in the time of head impact and in the wrap-around-distances (WAD) to primary head contact. The head impact velocity showed a greater sensitivity to the different buck shapes (e.g. LS buck versus MS buck) than to the braking deceleration. The buck FE models developed in this study are expected to be used in sensitivity and optimisation studies for the development of new pedestrian protection systems.

A Finite Element Model of the Occupant Lower Extremity for Automotive Impact Applications

Although not life-threatening, lower limb injuries are the most frequent injury of moderate severity (AIS 2), sustained in a vehicle crash (Pattimore et al., 1991). To better understand the injury mechanisms, several lower extremity (LEX) finite element (FE) models were developed to investigate traffic accidents involving occupants in vehicles (Yang et al., 2006). The main limitations of existing lower limb FE models are due to their geometries, the modeling approaches used to represent their components, and limited test data used for the model validation.Copyright