Experimental studies of phase transformation in shape memory alloys

Abstract

This research incorporates an experimental study of stress-induced martensitic phase transformation in the shape memory alloy Nickel-Titanium. The rich local thermo-mechanical interactions that underlie the solid-to-solid state phase transformation between the cubic austenite phase and the monoclinic martensite phase are examined via Digital Image Correlation (to obtain local strain fields) and infrared imaging (to obtain corresponding local thermal fields). Although other methods have been used to explore phase transformation in shape memory alloys, this methodology is unique in providing a quantitative estimate of the strain inside the area of martensitic transformation, as well as direct correlations of local strain and temperature fields. Using this combined methodology, we are able to quantify the complex local interactions between released/absorbed latent heat and the extent of transformation, and explore the characteristics of the phase fronts (velocity, width, etc) and the evolution of martensitic volume fraction. There is also evidence of a remarkable cyclic strain memory on the microscale. ©2010 Society for Experimental Mechanics Inc.