Investigation of Shape Memory Alloy Spring Elastic Coefficient Based on Varying Applied Currents in a Cardiac Assist Device

Abstract

This paper analyses the mechanical properties of shape memory alloy (SMA) springs based on different electric currents applied in a cardiac assist device (CAD). Experimental results show that when the input drive current is constant, the SMA spring is equivalent to a tension spring with determined elastic coefficient that increases with the current. Based on our experiments, the theoretical maximum recovery force produced by SMA can be obtained through this input current. The phase transformation of SMA from austenite to martensite is able to be controlled by the drive current instead of the surface temperature of SMA. In addition, this experiment designed a cardiac supporting device composed of eight SMA springs, and used a saline bag to simulate human heart. The peak pressure inside the saline bag produced by this device was 17.4% of the normal heart systolic pressure. Our results can provide further support for the research of advanced CAD.