Passenger muscle responses in emergency braking events with reclined seating.

Emergency braking can generate forward displacement that may influence the effectiveness of protection in collisions, especially for passengers. The development of automated vehicles has enabled the diversification and rationalization of sitting positions, including reclined seating. However, the passenger response in pre-crash scenarios in reclined seating differs from that in standard seating, which poses different requirements for biofidelic human body models (HBMs) to evaluate passenger injuries in collisions. This study conducted emergency braking trials in vehicles at an initial velocity of 80 km/h. Five volunteers were exposed to approximately 1 g manual emergency braking (MEB), and the muscle responses at the front passenger seat with backrest angles of 25°, 45°, and 65° were recorded. The electromyography obtained from 14 muscles of the neck, torso, and lower extremity were normalized using maximum voluntary contractions (MVCs). In the quiet sitting phase, the activity levels were low (< 5% MVC) in all muscles for the three sitting positions. During emergency braking, the muscles are activated to restrict the body motion. There were differences in muscle amplitude and onset time in different backrest angles, with higher muscle activity levels in most muscles in a reclined sitting position. In particular, the sternocleidomastoid, rectus abdominis, and vastus medialis showed different patterns in the peak and steady-state phases. We found that the tibialis anterior was consistently activated at a lower level in all sitting postures (< 8% MVC), which indicates limited support of the shank for the body. The data provided in the paper are presented in corridors and intended for use in the development and validation of HBMs with active muscle models to simulate evasive maneuvers that potentially occur before a crash in the reclined sitting position.

Influence of Skull Fracture on Traumatic Brain Injury Risk Induced by Blunt Impact.

This study is aimed at investigating the influence of skull fractures on traumatic brain injury induced by blunt impact via numerous studies of head-ground impacts. First, finite element (FE) damage modeling was implemented in the skull of the Total HUman Model for Safety (THUMS), and the skull fracture prediction performance was validated against a head-ground impact experiment. Then, the original head model of the THUMS was assigned as the control model without skull element damage modeling. Eighteen (18) head-ground impact models were established using these two FE head models, with three head impact locations (frontal, parietal, and occipital regions) and three impact velocities (25, 35, and 45 km/h). The predicted maximum principal strain and cumulative strain damage measure of the brain tissue were employed to evaluate the effect of skull fracture on the cerebral contusion and diffuse brain injury risks, respectively. Simulation results showed that the skull fracture could reduce the risk of diffuse brain injury risk under medium and high velocities significantly, while it could increase the risk of brain contusion under high-impact velocity.

Numerical reconstruction of injuries in a real world minivan-to-pedestrian collision.

PURPOSE: The purpose of this study was to evaluate the capability of the Total Human Model for Safety (THUMS) - pedestrian model in predicting pedestrian injuries, and to investigate pedestrian injury mechanisms in minivan collisions via numerical reconstruction of a real world minivan-to-pedestrian impact case. METHODS: A typical minivan-to-pedestrian collision case was selected from the In-depth Investigation of car Accidents in Changsha (IVAC) database. The THUMS middle-size adult male FE model and a minivan front FE model were then employed to represent the case participants and injuries to the pedestrian's lower limb, thorax and head were reconstructed. Finally, the capability of the THUMS model in predicting pedestrian injuries and pedestrian injury mechanisms in minivan collisions were analyzed through comparisons between predictions and the accident data. RESULTS: The results show that the THUMS has a good capability in predicting pedestrian thorax injuries, but a lower prediction of leg bending moment and brain strain. The extra bull bar concentrates crash load to pedestrian's leg and raises tibia/fibula fracture risk, thorax injuries in the struck side are mainly from direct contact at the lower chest level, lung injury in the non-struck side could be caused by inertia force from the heart. Rotational acceleration shows good match with brain strain and could be the key mechanism for concussion. CONCLUSIONS: The results suggest that further improvement in biofidelity of the THUMS model is still needed. The findings also offer basic understanding on pedestrian injury mechanisms in minivan collisions.

A Computationally Efficient Finite Element Pedestrian Model for Head Safety: Development and Validation.

Head injuries are often fatal or of sufficient severity to pedestrians in vehicle crashes. Finite element (FE) simulation provides an effective approach to understand pedestrian head injury mechanisms in vehicle crashes. However, studies of pedestrian head safety considering full human body response and a broad range of impact scenarios are still scarce due to the long computing time of the current FE human body models in expensive simulations. Therefore, the purpose of this study is to develop and validate a computationally efficient FE pedestrian model for future studies of pedestrian head safety. Firstly, a FE pedestrian model with a relatively small number of elements (432,694 elements) was developed in the current study. This pedestrian model was then validated at both segment and full body levels against cadaver test data. The simulation results suggest that the responses of the knee, pelvis, thorax, and shoulder in the pedestrian model are generally within the boundaries of cadaver test corridors under lateral impact loading. The upper body (head, T1, and T8) trajectories show good agreements with the cadaver data in vehicle-to-pedestrian impact configuration. Overall, the FE pedestrian model developed in the current study could be useful as a valuable tool for a pedestrian head safety study.

[Determination of a visco-hyperelastic material law based on dynamic tension test data].

The objective of this study was to determine the visco-hyperelastic constitutive law of brain tissue under dynamic impacts. A method combined by finite element simulations and optimization algorithm was employed for the determination of material variables. Firstly, finite element simulations of brain tissue dynamic uniaxial tension, with a maximum stretch rate of 1.3 and strain rates of 30 s -1 and 90 s -1, were developed referring to experimental data. Then, fitting errors between the engineering stress-strain curves predicted by simulations and experimental average curves were assigned as objective functions, and the multi-objective genetic algorithm was employed for the optimation solution. The results demonstrate that the brain tissue finite element models assigned with the novel obtained visco-hyperelastic material law could predict the brain tissue's dynamic mechanical characteristic well at different loading rates. Meanwhile, the novel material law could also be applied in the human head finite element models for the improvement of the biofidelity under dynamic impact loadings.

A Review on Injury Mechanism of Intracerebral Hemorrhage in Vehicle Accidents.

BACKGROUND: Intracerebral hemorrhage is one of the most common injuries in vehicle accidents. The aim of this paper is to survey the injury mechanism of intracerebral hemorrhage in vehicle accidents, including contusion, subarachnoid hemorrhage (SAH), subdural hematoma (SDH) and diffuse axonal injury (DAI). METHODS: A condensed overview is given based on the published studies in biomechanical studies on intracerebral hemorrhage. Animal tests, cadaver tests, accident investigations and numerical simulation are the main method used for the mechanism studies. RESULTS: Angular velocity and acceleration can be used to predict these injuries and they are the main causation of DAI. Intracranial pressure is the main causation of coup/contrecoup contusion. Shear stress and strain contribute to the rupture of bridging veins that result in SDH, SAH. CONCLUSION: Injury mechanism of intracerebral hemorrhage in vehicle accidents is complicated that with multiple causations. In-depth works need to be carried out in mechanism studies especially for child head injuries.