Influence of Auxetic Structure Parameters on the Dynamic Impact Energy Absorption

The present work focuses on the dynamic crushing response of 2D re-entrant auxetic honeycomb by extending previous published models in order to include more design parameters (specific geometric ratios and/or material properties). If the crushing velocity is constant, the energy absorption occurs at the constant plateau stage upto densification of the structure.

An analytical equation based on the shock wave propagation analogy in a rigid, perfectly plastic, locking material model is deduced from the study of periodic collapse of the structure. Our analysis enables us to theoretically predict the dynamic crushing strength. The formulation not only depends on the geometric and material characteristics of the auxetic but also on the impact velocity.

Two series of Finite Element simulations of quasi-static and dynamic compressive test of the auxetic structure were carried out using the RADIOSS^TM explicit solver. The first simulation series consists of a crushing plate loading the structure at a constant imposed velocity (0.5 m/s up to 100 m/s). Results show good accordance between analytical and Finite Element results. The time history of the cell-strain (ratio of deformed cell height to initial cell height) in the crushing direction shows that the peaks observed in the stress–strain curve of the entire structure are linked to complete crushing of each unit cell within a row. The second simulation series replicates the impact of the plate on the structure (initial plate velocities 50 m/s up to 100 m/s).

The numerical simulations presented in this study, make it possible to relate the cell-strain, energy absorption and geometrical/material parameters of the auxetic structure.