Design Study of Shape Memory Alloy Honeycombs for Energy Absorption

Shape memory alloys (SMA), which exhibit the shape memory effect and superelasticity, utilize a reversible solid-solid state phase transformation to recover large strains. Likewise, honeycomb structures under in-plane loading take advantage of deformation kinematics to amplify the structure’s macroscopic strain. The combination of a sparse honeycomb structure made of an SMA material can recover larger deformations than would be possible with either conventional metal honeycombs or monolithic SMAs. NiTi honeycombs and corrugations of about 5% relative density with robust properties were demonstrated recently [1]. Potential future applications include high performance energy absorbers, light-weight deployable devices, and high stroke actuators. This numerical study focuses on the design of superelastic SMA hexagonal honeycombs under in-plane compression for application to reusable energy absorbers. A design study with respect to honeycomb geometric parameters was performed to gain a better understanding of the geometric effects on energy absorption characteristics. A nonlinear finite element method was used to simulate their mechanical response using a hysteretic, trilinear, constitutive law to model the superelastic behavior of SMAs. Bloch wave analysis was used to evaluate the stability characteristics of the honeycomb structure. The corresponding energy absorption characteristics, under constraints of local strain limits, structural stability and allowable force levels, were evaluated to determine the optimum honeycomb geometries. It was found that diamond-like honeycombs, with greater height than width, had the best energy absorption properties.