Abstract: The crashworthiness of an automotive thinwall structure with functionally graded strength (FGS) is simulated by finite element method in this paper. Firstly taking the peak crash force F and the specific energy absorption E of the structure during crash as evaluation indicators to analyze the effects of thickness t, the strength s of impacting end and gradient index m on the crashworthiness of the structure. An approximate relationship between performance parameters （F andＥ）and design variables (m, t and s) is established by response surface method, and a multiobjective optimization is conducted on the structure to obtain the optimal Pareto frontier. Then with consideration of the instability of technological factors, three characteristic points on Pareto frontier are chosen to analyze the robustness of optimal designs and it is found that the robustness is the best when m<05 (in this case s and t should take minimum value). Finally a frontal crash simulation on the front longitudinal beam of a pickup truck is performed with three materials, i.e. original material with lowstrength homogeneous property, highstrength homogeneous material and FGS material. The results show that FGS thinwall structure has better performance than the traditional design with original material in respects of cab deceleration, front bulkhead intrusion and specific energy absorption with less mass, so has the best overall performance.

Key words:  automotive crashworthiness, graded strength, multi objective optimization, robustness design