Crushing performances and crashworthiness optimization of polygonal double tubes under multiple angle loadings

A finite element model of a thin-walled square tube is developed for evaluating its crushing performance. The axial crushing behavior of the square tube is experimentally evaluated, and the obtained force-displacement responses are applied to estimate the accuracy of the model. The validated model is subsequently used to study the crushing performances of the polygonal single and double tubes under different angle loadings. It is shown that the double tube has higher specific energy absorption and energy absorption capacity under axial and small-angle oblique loadings. However, the energy absorption characteristics of the double tube are more sensitive to the loading angle, and it is more prone to occur global bending deformation under loadings at large angles. The energy absorption characteristics of the polygonal double tubes with different cross-sectional forms are calculated and ranked. The results show that the B9 double tube has the best comprehensive performance. The B9 double tube is constructed with a gradient thickness instead of a uniform thickness to improve its crushing performance under large-angle loadings and raise its critical angle of occurring global bending deformation. A multiobjective optimization procedure is proposed to find the optimal design of the FGT double tube for enhanced crashworthiness performance.