Martensite and Reverse Transformation during Complete Cycle of Simple Shear of NiTi Shape Memory Alloy

Investigation into the quasi‐static simple shear of shape memory alloy (SMA) was carried out. A special grip was designed which allowed replacing compression into the shear process on testing machine. At the same time the shear zone temperature was observed by an infrared camera. The mechanical and thermal characteristics of sheet specimens of NiTi subjected to superelastic shear deformation due to reversible stress‐induced phase transformation were clarified. By comparison of the data, the processes of martensite and reverse transformations during the shear deformation were analysed. The investigation shows that stages of the phase transformations during the simple shear process are similar like those observed during tension test. Moreover, during the simple shear deformation no uniform temperature distributions were noticed, especially at higher shear rate, manifesting that the stress‐induced phase transformation during the shear process is also inhomogeneous. The thermomechanical properties of the NiTi SMA for various shear rates were investigated. It was found that an increase in the strain rate results in an increase in temperature variation, the shear stresses and the magnitude of hysteresis loops between the forward and reverse transformations.