Three-point bending performance of sandwich beam with novel gradient re-entrant-chiral-triangular honeycomb core

The negative Poisson's ratio sandwich structure has excellent energy absorption characteristics and is widely used in aerospace and protective applications. The design of gradient negative Poisson's ratio (NPR) core can greatly enhance bending energy absorbing ability of the sandwich structure. The dependence and sensitivity related to the gradient distribution of NPR cores deserve further exploration. In this study, the sandwich structure with a new NPR core is proposed by combining re-entrant chiral cells with re-entrant triangular cells. Through the density gradient design and angle gradient design of NPR core, thirteen kinds of gradient sandwich structures including uniform, horizontal and vertical changes are proposed. To analyze influence of the gradient distribution on bending resistance of the proposed sandwich structure, the quasi-static three-point bending experiments and numerical simulation are carried out. Effects of panel debonding, panel thickness, and cell's angle on the bending characteristics are evaluated. At the same relative density, increasing the cell's wall thickness around the indenter can enhance the three-point bending performance of the sandwich structure. By appropriately increasing angle of honeycomb cells locating at the I-shaped position of the sandwich beam, the bending performance can also be improved. Panel debonding and reduced panel thickness will weaken bending resistance of the structure. The design and research results of the gradient negative Poisson 's ratio honeycomb core can propose a new structural design scheme for the bending protection system.