Analysis of a thermally induced phase transformation strain state for the TiNi shape memory alloy under a complex stress state

In the paper an analysis of isostatic testing results for the Ti-51.0 at. % Ni shape memory alloy are presented. Tests were performed in a complex stress state, the tubular specimen being loaded by a combination of axial load and torque. After achieving a specified level of the load under complex and various stress states, a thermal cycle was started. During the test, the temperature-induced phase transformations were observed as variations in the transformation strain tensor components. These strain components were measured with the use of resistive strain gauges, digitally recorded and processed to extract pure phase transformation strains. For selected complex stress states, the transformation strain tensor components, principal transformation strains and characteristic temperatures of the phase transformations were found. On the basis of the experimental data, basic relations between characteristic parameters of an imposed stress state and the temperature-induced phase transformation strain state were determined.