Experimental study on the response of additively-manufactured polymeric lattices to impact along different directions

Abstract

Diverse lattice architectures have been proposed with the aim of enhancing their mechanical response, particularly in relation to compression along their three principal geometrical axes. Most lattice cell topologies have been designed to display cubic symmetry, with the goal of achieving quasi-isotropic behaviour. Even if this is achieved in practice, it does not ensure similarly favourable responses for impact along other directions, and this aspect has received little attention or been reported. Nevertheless, it deserves examination, because in actual applications, lattices are likely to sustain loads or required to mitigate impact from any or multiple directions. Furthermore, cell components such as struts can display significant angle-dependent properties associated with additive manufacturing processes employed to fabricate them, and this exacerbates anisotropy in the lattice global response. Consequently, in addition to the vertical build direction, it is instructive to examine the compressive responses of lattices loaded along oblique directions, especially under impact, to elicit the degree of mechanical anisotropy under gross deformation. In this study, samples of Octet and Rhombic Dodecahedron lattices, as well as a hybrid descendant lattice (HS), are additively manufactured, and subjected to dynamic uniaxial compression along two oblique directions, i.e., the face diagonal and body diagonal directions with respect to the lattice cubes. Compared to the responses for compression along the geometrical principal axes defining the cube, significantly dissimilar stress-strain responses and crushing modes are observed, indicating sensitivity to impact direction, and this is associated with cell geometry. The influence of angle-dependent strut material properties in inducing anisotropy is highlighted, and the smaller degree of anisotropy observed with the novel HS lattice, demonstrates its advantage in yielding more consistent, direction-independent behaviour.