Experimental and computational study of the NiTi thin wires mechanical behavior

NiTi wires used for biological implants demonstrated ductile fracture. NiTi 40, 60, and 90 mu m thick wires were tested in uniaxial tension to fracture and loading-unloading. Uniaxial stress-strain curves demonstrate superelastic behavior. The inelastic martensite transformation strain is completely recovered upon unloading, forming thermo-mechanical hysteresis. A mathematical model was developed to describe superelasticity effects in NiTi wires. Modeling results are qualitatively and quantitatively similar to experimental data, and capture elastic deformation of austenite, forward martensite phase transformation stress plateau before the onset of martensite elastic deformation and the entire unloading range. The elastic limit and strength increase with the wire thickness.