Image processing to estimate the heat sources related to phase transformations during tensile tests of NiTi tubes

Temperature and strain fields have been observed during superelastic tensile tests on NiTi tubes. They show strong localisations that take the shape of helical bands with characteristics that depend on global tensile strain and strain rate. To obtain quantitative energy information, allowing a better recognition of the deformation mechanisms involved inside and outside the helical bands, an estimation of the local heat sources based on image processing of the temperature fields is proposed in the present paper. This processing method is first calibrated and validated on numerically simulated temperature fields calculated using theoretical heat sources close to those associated with martensitic phase transformation. It is then applied to experimentally observed temperature fields during a typical superelastic tensile test of an NiTi tube.