Thoracic injuries in frontal car crashes: risk assessment using a finite element human body model

Doktorsavhandling, 2014

Accident data show that there is a clear need to improve the protection to occupants’ thorax in frontal car crashes. For this purpose, models that can predict the risk of injuries and assess the occupant protection offered by different restraint systems are needed. Two types of models are usually applied to accomplish this, mechanical models, also known as anthropomorphic test devices (ATDs), and numerical models, of ATDs and of the human body. Numerical models of the human body based on the finite element method (FE-HBM) offer a more detailed representation of humans than ATDs. On the other hand, there is no clear consensus on the injury criteria and thresholds to predict thoracic injuries using FE-HBMs. The general aim of this thesis is to contribute to the reduction in number and severity of thoracic injuries in frontal car crashes by utilising an FE-HBM. To reach this aim, the FE-HBM Total HUman Model for Safety version 3.0 (THUMS v3.0) was improved by comparing its kinematic and thoracic stiffness responses to tests with Post Mortem Human Subjects (PMHSs). Thoracic injury criteria at the global, structural and material levels were calculated with the modified THUMS in simulations of PMHS tests. Injury risk curves, with and without age adjustment, were constructed by applying the survival analysis method to matched pairs of injury criteria calculated with the modified THUMS and the injury outcome of the PMHS test. The injury risk curves that best approximated the test data were selected. Then, the risks predicted by the modified THUMS and the selected curves were compared to the risks predicted by an injury risk curve constructed based on real-world crash data. Different configurations of the modified THUMS were simulated and the results of the changes in the thoracic stiffness and coupling were applied to support the design update of the thorax of an existing ATD. The contributions of this thesis include: modified THUMS, with an enhanced biofidelity in frontal car crashes compared to THUMS v3.0; injury risk curves for the modified THUMS to predict the risk of two or more fractured ribs in frontal car crashes; and recommendations to improve the design of an existing ATD thorax.