Phenomenological analysis of plateaus on stress-strain hysteresis in TiNi shape memory alloy wires

Abstract

Abstract The formation of the steps, the plateaus, on the stress-strain curves in TiNi shape memory alloy wires is discussed from the continuum mechanical point of view. The two metallurgical processes are considered to be essential: The phases, the parent phase and the martensite phase, are separated by a phase interface which propagates along the wire when the wire is subjected to straining. The stress-strain hysteresis loop shifts both to the higher strain side and the lower stress side during strain controlled cyclic loading. The latter process is, following the metallurgical observation, characterized by introducing three internal variables; the residual stress and strain which are accumulated during cycling and the martensite phase which is also accumulated and takes no part in the subsequent transformations. The numerical simulation well explains the formation of the plateaus in the stress-strain loops during cycling.