Martensitic inelasticity of TiNi-shape memory alloy under pulsed loading

Some inelastic properties of TiNi shape memory alloy in martensitic state under pulsed loading were investigated. Two millimeter-diameter TiNi wire specimens were subjected to deformation by a magneto-pulsing installation under three-point bending conditions. The dependencies of residual strain on the force amplitude applied to the strikers during eight test series using different mechanical pulse durations from 400 to 1300 μs, were obtained. For each test series the threshold (minimal) value of force impulse amplitude which causes appearance of residual strain was found. Also, the threshold value of stress in each case was calculated using the elastic beam method, the value found to be within the range of 300–900 MPa. In order to describe dynamic mechanical behavior of TiNi shape memory alloy in martensitic state an attempt was made to apply the principles of yielding based on the concept of the so called incubation time. For inelastic deformation the incubation time was calculated based on the data resulting from the above-mentioned experiments. Its value of about 2 ms characterizes the range of occurrence of dynamic properties.