Structural Bifurcation of Side Members in Vehicle Frontal Impact

The impact behavior of a vehicle frame is studied in this research. We focus on frontal impact in which the vehicle with an initial velocity is set in full contact with a rigid barrier at zero inclination angle. It is generally agreed and widely noted that in both physical crash tests and crash simulation analyses, there tend to exist significant variations in the final deformation shape for crash tests under what appear to be the same conditions. The purpose of this paper is to demonstrate that structural bifurcation could be the potential cause of the apparent randomness in frontal impact deformation. Advanced finite element analysis is used to study the impact behavior. A simple thin-walled beam element with box cross section is used to model the side rails of the vehicle frontal frame. Comparisons are made between impact of the perfect structure and the structure with a slight initial geometric imperfection. The magnitude of the imperfection is very small so that the imperfect structure and the perfect structure can not be distinguished by the naked eye. It is demonstrated that with this very small initial geometric imperfection on the side rails, the final deformation can adopt a dramatically different mode shape.