The influence of stress and temperature on the residual strain generated during pseudoelastic cycling of NiTi SMA wires

Abstract

The focus of the present work is to study the effect of stress and temperature on the accumulated residual strain during the thermomechanical cycling of Shape Memory Alloys (SMAs). NiTi wires were pseudoelastically trained at different temperature above the austenitic finish temperature, up to different maximum applied stress levels. The total residual strain recorded during each training experiment was decomposed into the contributing plastic strain and retained martensite. The quantity of retained martensite in the trained wire was determined by a flash heating the trained SMA and recording the recovered strain. Preliminary observations from the thermomechanical test results suggest that the retained martensite formation is dependent on the maximum applied stress level during the thermomechanical test and is not dependent on the transformation plateau stress level of the SMA. On the contrary the transformation plateau stress level or consequently the test temperature is a critical parameter in dictating the irrecoverable plastic strain generated during the thermomechanical cycling of SMAs.