Heat Source Processing for Localized Deformation with Non-Constant Thermal Conductivity. Application to Superelastic Tensile Tests of NiTi Shape Memory Alloys

This paper presents a methodology for heat source estimation when thermal conductivity is not constant. Both thermal and kinematic field measurements are necessary. The method requires spatiotemporal synchronization of these fields and a possible method to achieve this is presented. Temperature and heat source fields can then be properly estimated at every material points in the reference or deformed configurations of the tested sample. The proposed method also highlights the importance of precise determination of thermophysical properties in heat estimations. The method is applied for heat source estimation during a superelastic tensile test of a NiTi shape memory alloy displaying both stress-induced phase transformation and deformation localization. Spatiotemporal change in thermal conductivity occurs during deformation of this material. Typical heat source distribution results observed during mechanical tests are given. Heat sources are integrated over time, at each material point, for local estimation of heat energy associated with stress-induced phase transformation. Such a measurement can be qualified as a first step towards an in situ local DSC during a mechanical test. It is shown that the spatiotemporal distributions of these energy fields correlate well with strain field distributions during superelastic localized deformation.