Strain, Temperature and Heat Source Fields During Shear Tests of Superelastic and Ferroelastic Thin NiTi Plates

NiTi Shape Memory Alloys are being increasingly used in the fields of aeronautical, structural engineering and biomedical applications. To design such products, knowledge of thermomechanical properties of the material is of great importance. Most of the experimental characterizations have been achieved in tension using wires, strips or bone-shaped samples. It is now well known that NiTi tensile tests may exhibit strong deformation localization phenomena, both in superelastic and ferroelastic deformation modes.

In this paper, we report results obtained by performing shear tests on two thin NiTi plates, in martensitic and austenitic state at room temperature. Strain and temperature fields are recorded during the experiments. The kinematical measurement allows full-field detection of strain heterogeneity. Heat source fields are estimated from the temperature fields and from their time evolution, by using at any point of the sample the local heat diffusion equation. Dependency of the heat source on local shear strain and stress is studied for the two plates, during loading and unloading. These results are used to analyse the deformation mechanisms during the different deformation stages. The heat energy is estimated by a time integration of the heat sources for each point of the plate. This energy is compared to the heat energy measured by means of DSC experiments performed during thermal induced transformations.