Compression and shear behaviour of graded chiral auxetic structures

Abstract

Graded chiral auxetic cellular metal structures were produced from copper alloy powder using Selective Electron Beam Melting (SEBM) technique and tested under compressive and shear loading conditions. The predesigned geometry of chiral structures has a variable chiral amplitude through the length of the specimens, which results in graded porosity of the analyzed auxetic structures. The deformation mechanisms and mechanical response were evaluated with compression and shear testing at two loading velocities. The infrared thermography has been used to track the evolution of plastic deformation in the specimens. The deformation process under compression loading starts in the area with the largest chiral amplitude and then continues through the whole height of the specimen. The shear loading shows two significantly different groups of responses, which are affected by local defects causing the start of failure in different parts of structure. The results of experimental testing were further used for validation of developed finite element models of chiral structures. The influence of graded porosity on the mechanical response of chiral structures was evaluated with parametric computational simulations and compared to the non-graded structure with constant chiral amplitude and same weight. The non-graded auxetic structure offers a stiffer response due to deformation uniformly distributed through the height of the specimens but fails abruptly at lower strains.