Dynamic crashing behavior of new extrudable multi-cell tubes with a functionally graded thickness

•A new multi-cell tube with functionally graded thickness was presented.•Establish the finite element model of multi-cell tube.•The finite element model of multi-cell tube was experimentally verified.•Multiobjective optimization design for multi-cell tube was performed.

Multi-cell structures have been extensively studied for their outstanding performance as potential energy absorbers. Unlike existing multi-cell tubes with a uniform thickness (UT), this paper introduces a functionally graded thickness (FGT) to multi-cell tubes under dynamic impact, which can be fabricated by an extrusion process. A numerical model is first established using the nonlinear finite element analysis code LS-DYNA and validated with experimental data. Based on a numerical study, the thickness gradient parameters in different regions have considerable effects on the crashworthiness of the FGT multi-cell tubes. Moreover, the FGT multi-cell tubes are able to absorb more energy while yielding a similar level of peak impact force to the UT multi-cell tubes. Finally, multiobjective optimizations of the UT and FGT multi-cell tubes are then performed to determine the optimal gradient parameters that simultaneously improve the specific energy absorption (SEA) and reduce the maximum impact force. In these optimizations, the multiobjective particle optimization (MOPSO) algorithm and response surface (RS) surrogate modeling technique are adopted. The optimization results demonstrate that the FGT multi-cell tubes produce more competent Pareto solutions than the conventional UT counterparts; similar gradients in the outer walls and stronger internal ribs are recommended for the FGT multi-cell tubes because of their improved interactions.