Mechanical behavior and energy absorption of expansion circular tube with negative Poisson's ratio

The expansion tube plays a crucial role in the field of train collision safety protection. In this study, we combine the expansion characteristics of negative Poisson's ratio (NPR) with the deformation mechanism of the expansion tube to propose a novel design for material reconstruction: embedding NPR structures into the conventional expansion tube wall. The typical specimens of NPR tube were fabricated using additive manufacturing technology, and the experiments and numerical simulations were conducted to investigate its expansion behavior by two expansion cones with different sizes. By employing a validated numerical simulation model, the effects of cone size, expansion angle, wall thickness, and material gradient design on the mechanical response of NPR tubes were investigated. It is demonstrated that the expansion behavior and energy absorption mechanism of NPR tubes differ from that of conventional circular tube. The material of wall generates radial expansion rather than compression due to a special auxeticity characteristics subjected to circumferential tensile load. The increased normal pressure on the inner surface from the expansion cone results in the resistance reinforcement of NPR tube. The proposed expansion tube achieves higher load capacity while utilizing less material, which provides a promising approach for designing lightweight and efficient expandable tubes.