Influence of phase transformation on stress wave propagation in thin-walled tubes

Phase transformation can change the properties of a material and significantly affect the stress wave propagation features. This study presents an analytical model of coupled stress wave propagation in pseudo-elastic shape memory alloy thin-walled tubes subjected to combined longitudinal and torsional impact loading. An incremental constitutive model considering the effect of the hydrostatic pressure and deviatoric stress was employed to describe the mechanical behavior of SMA. The phase transformation ellipses shift along the sigma-axis in the sigma - tau plane due to the asymmetry of tension and compression induced by the hydrostatic pressure. The generalized characteristic theory was used to obtain the characteristic wave speed,simple wave solution, and the differential equation determining the stress path. The numerical results showed that the wave structure in the thin-walled tube is affected by the initial stress state and the final loading state. For the initially static and unstressed thin-walled tube, there is a special region on the sigma-tau plane. When the combined longitudinal and torsion impact load lies in this region, an elastic compression wave, elastic shear wave and coupled phase transformation fast waves appear in the thin-walled tube in turn. The abnormal phenomenon is not observed in the conventional elastoplastic tubes.