ELASTOCALORIC PERFORMANCE OF SHAPE MEMORY ALLOY THIN PLATES WITH HOLES: EXPERIMENTAL OBSERVATION AND THEORETICAL MODELING

NiTi shape memory alloy has a wide application prospect in the emerging field of solid-state refrigeration due to its excellent elastocaloric performance. However, the high critical stress of martensite transformation requires a high driving force to trigger the elastocaloric effect. It brings a challenge to the miniaturization and large-scale application of the solid-state refrigeration devices made by NiTi shape memory alloy. To overcome this shortcoming, NiTi shape memory alloy thin plates with holes are employed in this work. The effects of hole volume fraction and hole distribution form on the elastocaloric effect of the thin plates are revealed. Experimental results indicate that the stress concentration effect caused by the holes can significantly reduce the driving force of martensite transformation, and effectively increase the overall cooling temperature of the thin plates. During deformation, the overall force-displacement response and temperature evolution of the thin plates depend on the hole volume fraction strongly. However, the distribution form of the holes only affects the local stress, strain and temperature fields, but plays a minor role in the overall thermo-mechanical responses. Based on the logarithmic stress rate, a finite deformation thermo-mechanically coupled constitutive model of shape memory alloys is established within the framework of irreversible thermodynamics. The proposed model is further implemented into the finite element program. By comparing the predicted results with the experimental ones, it can be found that the proposed model can effectively predict the effect of holes on the deformation behavior and elastocaloric performance of NiTi shape memory alloy thin plates. This work provides a theoretical guidance to design and assess the refrigeration device manufactured by shape memory alloy thin plates.