Structural optimization of the automobile frontal structure for pedestrian protection and the low-speed impact test

Abstract

A variety of regulations are involved in the design of an automobile frontal structure. The regulations are pedestrian protection, the Federal Motor Vehicle Safety Standard (FMVSS) part 581 bumper test, and the Research Council for Automobile Repairs (RCAR) test. The frontal structure consists of the bumper system and a crash box that connects the bumper system and the main body. The detailed design of the bumper system is performed to meet two conditions: first, regulation for pedestrian protection (lower-legform impact test); second, FMVSS part 581. In the two regulations, the stiffness requirements of the bumper system conflict with each other. In order to meet lower leg protection, a relatively soft bumper system is required, while a relatively stiff system is typically needed to manage the pendulum impact. A new bumper system is proposed by adding new components and is analysed by using the non-linear finite element method. An optimization problem is formulated to incorporate the analysis results. Each regulation is considered as a constraint from a loading condition, and two loading conditions are used. Response surface approximation optimization is utilized to solve the formulated problem. RCAR requires reduction in the repair cost when an accident happens. The repair cost in a low-speed crash could be reduced by using an energy-absorbing structure such as the crash box. The crash box is analysed by using the non-linear finite element method. An optimization problem for the crash box is formulated to incorporate the analysis results. Discrete design using orthogonal arrays is utilized to solve the formulated problem in a discrete space.