Design flow for the crash box in a vehicle to maximize energy absorption

Vehicle collisions frequently happen at a low speed. Insurance companies and the Research Council for Automobile Repairs both require reduction of repair costs and improvement in occupant safety in a low-speed crash. In order to reduce repair costs, an energy absorbing device such as the crash box is usually installed. The crash box is a thin-walled structure attached between the vehicle bumper structure and the side rail. The determination of the crash box geometry is quite important to absorb the impact energy, since the installation space of the crash box is not very large. In this research, a design procedure to determine the cross-sectional dimensions is proposed to enhance the energy absorption capability of the crash box. The proposed process has two steps. In the first step, the cross-sectional dimensions for the conceptual design are determined in two ways. One is a parameter study using discrete design with an orthogonal array. The cross-sectional dimensions of the crash box are selected among the available cross-sections, such as a circle or a polygon. The cross-sectional dimensions are determined by the analysis of the mean from the discrete design with an orthogonal array. The other is topology optimization, which is performed to determine the cross-section of the crash box to maximize the absorbed strain energy based on the Research Council for Automobile Repairs test conditions. The equivalent static loads method for non linear static response structural optimization is employed to solve the formulated topology optimization problems. The cross sections of the crash box are determined from the results of the conceptual design. In the second step, the detailed design processes are performed by using discrete design with an orthogonal array for the models that are selected in the first step. The detailed shapes of the new crash boxes are determined from the detailed design. The optimization problem for the crash box is formulated considering the geometric constraints of fitting into the given space for the crash box. Three new types of crash box are suggested, with detailed shapes from the proposed design procedure.