Abstract: Aiming at the light-weight modification design of the bumper assembly of a B-class car, its energy absorption target is determined based on crash energy management method and the detailed dimension design is conducted with forward design scheme. The energy-absorbing box adopts a two-layer twelve-right-angle-section thin-walled beam structure with an outer layer of carbon fiber reinforced polymer and an inner layer of low-carbon steel sheet, and its theoretical thickness values of both layers are determined based on the collapse theory for thin-walled beam. The bumper beam uses the same twelve-right-angle-section thin-walled beam structure but with single layer and its theoretical thickness value is determined by using equivalent stiffness substitution method. A series of comparison schemes are designed based on theoretical thickness values and a reasonable scheme is finally selected through high-speed and low-speed crash verifications, achieving a mass reduction rate of 41.5% for bumper assembly while meeting the requirements of energy absorption

Key words: bumper, crash energy absorption, lightweighting, CFRP, twelve right-angle section thin-walled beam