Development Of A Human Thoracic FE Model And Applied Research On Thorax Injury Biomechanics In Vehicle Impact

Human thoracic injury could be observed frequently in vehicle traffic accidents. It was reported that about30%of all the reported deaths in road traffic accidents were related with thoracic injuries. Thoracic injuries of the occupants ranked second in number of fatalities and serious injuries recorded in passenger vehicle collisions, only secondary to head injuries. Traffic accident data have also indicated that thoracic and upper abdominal injuries are frequently occurred in Minicar-pedestrian collisions, which was only lower than those of head and lower extremity injuries, especially in high speed accidents the incidence of the pedestrian thorax injuries is rather high. It is therefore necessary to have a good understanding of the thoracic injury mechanisms in order to reduce the injury risk in automobile accidents. The human thorax has an extremely complex structure that includes the most vital chest internal organs:the heart, lung, liver, spleen and kidney. The thorax rib-cage plays a key role of protect the organs from external attack. During the past several decades, many studies have been presented on human thoracic injury in vehicle collisions, but there is still long to get better understanding of thoracic injury biomechanics, such as rib fracture failure and injury criteria.In this study, an FE thorax model was developed and validated based on the human anatomical data. The thorax FE model was then used for analysis of rib fracture in different loading conditions and it was also used to analyze the effectiveness of the rib failure models and the thoracic injury assessment criteria, according to the three selected rib fracture failure models. Finally thoracic injury prevention in Minicar-to-pedestrian impacts was analyzed by using the FE model in combination with the selected failure models and injury assessment criteria.A new3D finite element thoracic model was developed based on the anatomical structure of a real Chinese human body of average size. The main structures of the model include thoracic and lumbar vertebrae and intervertebral discs, ribs, a sternum, costal cartilages, internal organs and other soft tissues. The entire model consisted of more than87,000elements and63,000nodes. The material properties of the thoracic model were defined based on the biomechanical data from literature. For the purpose of the model validation, the force-displacement responses of rib from simulations were compared with the test results of three-point bending tests; The isolated rib anterior-posterior loading structural tests were reconstructed by the FE model, and the calculated results were compared with experimental data in terms of the rib force-displacement responses, rib fracture locations, rib fracture timing and the resultant forces under static and dynamic loading conditions. In addition, using the volunteer tests and cadaver tests, the entire thorax force-displacement responses were simulated in frontal impactor loading, and the thorax model was also validated against the human thorax impactor loading tests in both pure lateral and oblique impacts by comparing the impact force, chest deformation mode, and the force-displacement responses.Three selected rib failure models of T1, T2, and T3based on either von Mises stress and/or plastic failure strain were utilized in the current study, in order to simulate and analyze the rib fractures under various loading conditions by using the thorax FE model. According to the failure models and the loading conditions, the simulated injury data were compared and analyzed. The results from simulations indicated that the rib fracture responses obtained using failure model T3exhibit the best agreement with the three-point bending experimental data; the rib fracture responses using failure model T2demonstrate the best agreement between the simulations and the isolated rib anterior-posterior loading structural tests in terms of both force magnitude and time of rib fracture occurrence. The cross sectional stress&strain at the fracture location were analyzed as well and the relationship between the Number of Rib Fracture (NRF) and impact speed obtained from the simulations using failure model T1exhibited the best agreement with the observations in the thorax frontal impactor loading tests.The current thorax model was used to analyze human thorax injury responses in side impact. For this purpose, the thorax impacts were simulated in pure lateral and oblique impactor loading conditions at a range of different impact angles. The calculated NRF and the injury parameters related to the thoracic injury assessment criteria were obtained from simulations, including the impact force, chest deflection, compression, deflection rate and spine acceleration. A correlation evaluation function between NRF and the injury criteria was built up for a comparative analysis of effectiveness in prediction and assessment of thorax injuries.Finally the FE model was used to study the human thorax dynamic and injury responses in pedestrian impacting by Minicars with different frontal structures at different impact velocities. The influences of Minicar frontal structures and vehicle impact velocities on pedestrian dynamic response were analyzed in terms of the chest impact velocity, chest deflection, both chest AIS3+(Abbreviated Injury Scale-AIS) and AIS4+injury risks based on injury criterion of Thorax Trauma Index (TTI), and the NRF.Based on the present study the conclusions can be drawn as follows. The results of validation simulations fit well with those of previous tests recorded in literature. Rib fracture failure model T1is the most appropriate for the thoracic responses analysis in impactor loading. The TTI criterion has the best effectiveness in prediction and assessment of thorax injuries according to the evaluation analysis. The pedestrian would suffer high AIS3+and AIS4+thoracic injury risk when impacting a Minicar. The frontal structure of Minicar and the vehicle impact velocity has significant influence on pedestrian dynamic responses and thoracic injury, and the frontal structure of Minicar has a greater effect on pedestrian thoracic injury risk than vehicle impact velocity.