Crushing and parametric studies of polygonal substructures based hierarchical cellular honeycombs with non-uniform wall thickness

Abstract

Hierarchical honeycomb topology is one of the most promising bio-inspired ultralight materials with superior specific strength and stiffness. The existing investigations mainly focus on the hierarchical structures composed of conventional triangular or hexagonal unit cells; however, the influences of other types of polygonal unit cells and non-uniform wall thickness were less studied. This paper gives an insight into the out-of-plane crushing of vertex based hierarchical honeycombs with polygonal substructures and non-uniform wall thickness. The experimental results report that the deformation mode of hierarchical honeycomb varies from progressive folding to irregular folding at a relative density of 0.0386. With the increase of relative density, the failure mechanism changes from elastic wall bulking to plastic wall buckling. The theoretical solutions suggested that the wall thickness ratio affects the half wavelength and plateau crushing stress more considerably than the edge length ratio. Though the substructures with less edge number decrease the overall plateau crushing stress level of hierarchical honeycombs, they increase the maximum plateau crushing stress due to the raise of the wall thickness ratio achieved. The specific peak values of the maximum plateau crushing stress are increased by 27.7–51.8% compared to those of the uniform wall thickness hierarchical honeycombs.