Numerical study of a re-entrant diamond structure under dynamic compression

Abstract

Auxetic materials, due to its negative Poisson’s ratio, shrink laterally when compressed axially and expand laterally when pulled axially. A re-entrant diamond structure was developed by replacing the vertical walls in a conventional re-entrant structure with diamond cells, which featured cross-linking members to make them rigid. The incorporation of the rigid diamond unit cells increased the stiffness, strength, and energy absorption of the structure. A validated finite element (FE) model was adopted from previous work, and the structures were compressed at a speed of 5 m/s in the FE model. The independent geometrical parameters of the re-entrant diamond unit cell were re-entrant wall length (L1 ), diamond angle (θ2 ), and diamond wall length (L2 ). The FE model based on these values was thus used to investigate the influence of geometrical parameters (θ2 & L2/L1 ) on the deformation mode, stiffness, strength, and specific energy absorption (SEA) of the structure. The value of diamond angle (θ2 ) varied from 40° to 90° at intervals of 10°, while the length ratio (L2/L1 ) varied from 0.7 to 1.2 in increments of 0.1. The specific strength was used in the discussion to account for differences in the relative density of re-entrant diamond structures.