In-plane impact failure behavior and energy absorption of gradient bimaterial honeycomb structures with negative Poisson's ratio cells

This work proposes a negative Poisson's ratio honeycomb gradient structures with curved concave bimaterial unit cells. By tailoring the material distribution of horizontal and vertical curved ligaments, four gradient configurations are designed: positive, negative, symmetric positive and symmetric negative Poisson's ratio gradients. The in-plane impact performances of these gradient structures are studied using the ABAQUS software explicit dynamic system. The investigation focuses on analyzing the effects of different gradient patterns and impact velocities on the deformation modes, dynamic response characteristics, energy absorption efficiency, and plateau stress. The main findings include: The deformation modes transition from layer-by-layer crushing at low velocities to more uniform collapse at higher speeds, with reduced auxetic effects. Energy absorption differences among configurations become significant only at higher velocities, where the negative gradient outperforms others. Plateau stress increases substantially with impact velocity but shows minimal dependance on gradient pattern. The findings provide guidance for designing impact-resistant negative Poisson's ratio structures with programable mechanical responses.