Infrared imaging of TiNi shape memory alloy subjected to deformation at various temperatures

Abstract

The infrared imaging of stress-induced martensitic transformation occurring in TiNi shape memory alloy subjected to deformation in various conditions has been presented. During the loading and unloading processes the mechanical parameters and the infrared radiation from the specimen surface have been continuously recorded by infrared camera. Basing on the obtained stress-strain curves and the elaborated temperature changes it was found that onset of the martensitic transformation appears at the end of the elastic part of the stress-strain curve, since a temperature increase was noticed there. The uniform temperature distribution observed there means that the initial transformation started at this stage is macroscopically homogeneous. It is followed by the martensitic intense transformation, related to the significant temperature increase. The more advanced transformation, the higher temperature changes. For the shape memory alloy pseudoelastic behavior the narrow bands of higher temperature are observed, manifesting localized Lüders-like deformation. For the shape memory effect behavior the process of transformation is much more homogeneous and characterized by uniform temperature distribution. Using a modern, sensitive and fast dynamic infrared camera enables to obtain new results of the start and development of the martensite forward and reverse transformation.