Computer Study of Material and Prestrain Effects on Bumper Damageability

An analytical procedure has been developed to evaluate the relative damageability of a bumper with respect to the geometrical and material properties by means of a nonlinear thin shell computer program as reported at the last VSM conference. The analysis has been extended to determine the effects of various high strength steels with different prestrains on bumper damageability since the fabrication procedure will induce varying degrees of prestrain in the finished bumper. The effect of prestrain is particularly important for dual phase steels because of the lower initial yield to tensile strength ratio of these materials. The analysis was carried out for three types of steels of potential use for bumpers, namely SAE 950X, SAE 980X and DP 980. The relative damageability of bumpers in these steels was evaluated analytically for various levels of prestrains. These computer results can furnish some guidelines to designers selecting high strength steels for bumper material where weight reduction is an important criterion.