Influence of stress softening on energy-absorption capability of polymeric foams

The energy-absorption capability of the polymeric foam used in vehicle bumpers is investigated through cyclic loading tests in different loading types, including uniaxial compression, biaxial compression and three-point bending. The test results indicate, due to significant stress softening, the energy-absorption capability of the bumper foam is greatly reduced after it is repeatedly loaded from the raw state. It is also revealed that both the softening effect and the reduction of energy-absorption are dependent on the deformation history. To account for the softening effect as well as its dependence on deformation history in simulation of the bumper foam, appropriate material models are identified and a modeling approach is developed. Using consecutive low-speed impact tests on a bumper system, the influence of the stress softening on the structural performance is studied. Both the experimental and modeling results indicate that the stress softening of the foam cushion compromises to a certain extent the bumper impact performance in subsequent impacts.