Energy absorption characteristics of three-layered sandwich panels with graded re-entrant hierarchical honeycombs cores

Two innovative re-entrant hierarchical sandwich panels constructed by substituting the cell walls of re-entrant honeycombs with isotropic regular hexagon substructure (RHH) and equilateral triangle substructure (RHT) are proposed in this paper, and their crashworthiness performance has been investigated systematically. Based on the Euler beam theory, the Young's moduli of units of re-entrant hierarchical sandwich panels are derived. A comparison between the re-entrant hierarchical sandwich panels and re-entrant sandwich panel has been conducted to study their energy absorption ability. Furthermore, the parametric analysis based on numerical analysis has been carried out to discuss the effects of the gradient, arranged orientation of hierarchical sandwich cores and the impact velocities. Results show that both the two proposed sandwich panels can greatly improve the in-plane stiffness and the energy absorption capacity, and the energy absorption mechanisms are discussed. In addition, the graded sandwich panels can effectively reduce initial peak force under quasi-static compression, and the configuration of large- medium -small (LMS) performs the best under high impact velocity. The cross-arranged cores can significantly improve the impact resistance ability of RHT sandwich panels. This work provides a new solution for designing lightweight sandwich structures.