Bio-inspired, helically oriented tubular structures with tunable deformability and energy absorption performance under compression

This study designs a series of helically oriented tubular structures inspired by Bouligand-type natural materials to optimize their mechanical performance. Thermoplastic polyurethane-based helically oriented tubular specimens are fabricated by 3D printing and their mechanical properties and energy absorption efficiency under compression are investigated. An auxetic behavior with a negative Poison’s ratio is observed for specimens with low helix angles (0°–12°), while specimens with higher helix angles (30°–90°) exhibit a typical buckling behavior and those with intermediate helix angles (13.85°, 16.36°) demonstrate a hybrid helical-like buckling mechanism. Finite-element simulations are performed to elucidate the deformation behaviors and stress distributions under compression. Experimental results show that the helically oriented tubular samples with 90° helix angles yield maximum energy efficiency and compressive strength of 440% and 124%, respectively, higher than for the helically oriented tubular samples with 0° angles. Cyclic tests further show that the 0° sample can almost recover to its original shape, while cracks and delamination are observed for the 30° sample after 200 cycles. The bio-inspired helically oriented tubular structures designed in this study can be applied in engineering, requiring lightweight and energy absorption performance.