A new methodology for the optimal design of crash-boxes

Crash-boxes are thin-walled structural elements able to absorb a great amount of energy during the impact of a transportation vehicle. In this paper a new procedure to optimize the performances of a crash-box, in terms of energy absorption or acceleration peak, is presented. The new developed methodology allows, after choosing the size of the crash-box (longitudinal and transversal dimensions) and the function to optimize, to identify the best number of edges of the transversal section and the best value of the thickness of the wall tube. The main innovative aspect of the here proposed tool is that, thanks to it, designers can easily choose the best crash-box depending on the considered working condition. A full parametric CAD model has been created to easily update the main geometric characteristics of crash-boxes. Explicit dynamics FEM models have been setup to simulate crash-tests and to evaluate the amounts of the wasted energy and the acceleration peaks during the impact of the crash-box against a rigid wall. A zero-order optimization method has been used to identify the best design variables set. The obtained results show that the optimal number of edges of the transversal section and the optimal crash-box thickness strongly depend on its main dimensions and on the considered objective function.