Experimental investigation of auxetic lattice structures under quasi-static and dynamic loading : with a focus on additively manufactured re-entrant auxetic honeycombs

Abstract

Re-entrant auxetic honeycombs – porous lattice structures that are characterised by a negative Poisson’s ratio – have attracted growing interest for use in vibration damping and energy absorption applications. The aim of this thesis was to investigate their behaviour experimentally under both quasi-static and dynamic loading. Based on a screening of the literature, several modified re-entrant topologies were selected for testing alongside the conventional re-entrant topology. These topologies were then fabricated from 316L stainless steel via laser-based powder bed fusion. Under quasi-static compression combined with digital image correlation, the specimens were evaluated in terms of Young’s modulus, energy absorption and Poisson’s ratio, and their deformation modes were characterised. One modified topology demonstrated improvements over the conventional re-entrant topology across the investigated properties. Under dynamic loading, the loss factor was determined using two test setups: a universal testing machine, evaluated via the phase-shift and hysteresis methods, and an excitation shaker, evaluated via the half-power bandwidth method. Only the latter proved suitable for determining the damping properties of the metallic auxetic specimens. However, not all topologies could be evaluated using the shaker setup, so that the influence of topology on damping cannot yet be conclusively established. The results nonetheless indicate that the loss factor depends more on the microstructure than on the macrostructure, with no direct correlation observed between improved energy absorption and damping. Future work should resolve these limitations and explore alternative modifications to enhance damping.