Effect of Stress Softening in Bumper Foams on the Low Speed Impact Performance of Vehicles 2008-01-1126

The experimental findings have revealed that there is a significant stress softening phenomenon for the polymer foams used in vehicle bumpers after they are loaded repeatedly from the raw undeformed state. With a series of loading-unloading test data under different maximum strains, dependence of the stress softening on the deformation history is analyzed. The corresponding material models in ABAQUS are chosen to characterize such special features of the polymer foams in FEA. The low speed impact models of a subsystem consisting of a bumper assembly and front-rails are established, and a process for transferring the deformation history of the bumper foams between the consecutive impact-loading cases is set up in the environment of ABAQUS. Based on the FE simulations, it can be seen that the stress softening of the polymer foams compromises the low speed impact performance of bumpers in subsequent impacts. Therefore the stress softening effect of polymer foams should be taken into account during safety designs of vehicle bumpers.