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

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.