On the Folding Mechanics of Square Columns with Double-Surfaced Gradients

The implementation of graded thicknesses in structural designs is an efficient strategy for improving the energy absorption performance of thin-walled columns. In this study, the mechanical responses of square columns with double-surfaced gradients under axial crushing forces were analytically and numerically investigated. A mathematical expression for the mean crushing force on a novel tube design is derived according to the super folding element method by introducing two novel parameters: the average thickness of the efficient energy absorbing region (EEAR) and global average thickness. The analytical predictions show good agreement with the simulation results that were obtained using the nonlinear finite element program ANSYS/LS-DYNA. The results demonstrate that a greater coefficient of average thickness of the EEAR versus global average thickness improves the energy absorption efficiency. However, increasing this coefficient largely depends on the sectional material distribution law. To explore the effects of this law on crushing responses, three different material distribution types were investigated. A significant improvement in specific energy absorption (approximately 30%) was obtained for a double-surfaced column with an optimized material distribution type compared to that of a square column with a uniform thickness.