Experimental and computational evaluation of tensile properties of additively manufactured hexa- and tetrachiral auxetic cellular structures

The auxetic cellular structures with two different chiral geometries (tetrachiral and hexachiral) were fabricated using laser powder bed fusion (LPBF) technology from two different materials (aluminium alloy AlSi10Mg and stainless steel AISI 316L). The specimen's microstructure, porosity and surface texture were observed by X-ray diffraction, optical and electron microscopy and micro-computed tomography. The mechanical properties of all specimens were determined experimentally with a simple tensile test. The results show that hexachiral and tetrachiral auxetic structures have similar initial stiffness, whereas the former provides a more ductile response with more than four times larger failure strain. The AISI316L steel provides for a much more ductile response than AlSi10Mg at comparable normalised load-carrying capability. The samples' deformation behaviour was analysed with the digital image correlation and tracking method, where it was shown that hexachiral samples exhibit a lower Poisson's ratio. The experimental results were used to validate the corresponding computational models, providing a more detailed analysis of deformation behaviour. They allow for cost-effective parametric studies and the development of new optimised chiral geometries.