Quasi-static and dynamic responses of bio-inspired auxetic structures

At present, most structures with negative Poisson’s ratio (NPR) exhibit stress-strain behaviour with only a single plateau and disordered deformation patterns when subjected to large compressive load. Therefore, new NPR structures, inspired by such natural curving shapes noticed in crabs and peacock mantis shrimp, were introduced. The rotational petal circle structure (RPCS) and rotational moon circle structure (RMCS) were constructed based on a common rotational structure and their load bearing capacities were then studied in details. FE simulations of these structures under compression were performed using rate-dependent hardening model and effects of design geometries including angle and radius parameters were examined. Predicted stress-strain responses were firstly validated by comparing with results from experiments. It was found that the proposed geometrical shapes significantly affected deformation modes and mechanical behaviors of the structures. The changes in angle showed more substantial impacts on the critical speed of structures than the radius, while variations of radius primarily governed their specific energy absorptions (SEA). For the RPCS and RMCS models at 30◦, SEA values were increased about 97 % and 83.7 %, respectively, due to occurred three-stage deformation. The highest SEA was achieved at the angle of 30◦ and radius of 2.5 mm, whereas the largest critical velocity was noticed at 45◦ and 2.25 mm for both structures. A trade-off between energy absorption and critical speed of different configurations were described. Finally, the design guideline using equal arc segmentation for generating structures with multi-stage plateau responses was provided.