Impact response of metallic stacked origami cellular materials

Abstract

Cellular materials are attractive for applications in structural protection and impact energy absorption. Progressive buckling of cell walls during compression delivers good specific strength and energy absorption. In a cellular solid, the arrangement of the cell wall material with respect to the direction of loading has a key influence on its mechanical response. This is especially true for cellular materials loaded in dynamic compression, where dynamic buckling and inertial stabilisation effects can also be sensitive to the alignment of cell walls with the loading direction. Origami-based geometries provide one route to designing cellular materials to achieve controllable collapse modes and, in some cases, auxeticity. The stacked Miura-ori geometry has been proposed recently as a strategy for constructing a volume of periodic cellular solid from an origami-inspired unit cell. However, these have been previously difficult to manufacture. Using selective laser melting, an additive manufacturing process, stainless steel stacked origami materials were produced in a periodic cellular arrangement for the first impact tests on such a cellular material. The origami specimens were tested with a gas gun and direct impact Hopkinson bar apparatus, at impact speeds of 50 m/s and 100 m/s. The auxetic behaviour of the origami fold was observed to diminish at the higher impact speeds, due to the localisation of deformation to individual fold layers. Different fold configurations were studied through simulations, with clear trends observed between fold angle and specific energy absorption and strength. Lastly, the influence of material strain rate sensitivity was investigated numerically.