On austenite-martensite interface evolution in pseudoelastic NiTi ribbonsThursday (29.09.2016) 09:45 - 10:00 Part of:
Localization of the stress-induced martensitic transformation in pseudoelastic NiTi under uniaxial tensile loading is well-known. Martensite bands nucleate and propagate within the austenitic specimen under continuous loading. Differences in martensite band orientation and evolution have been observed as a function of specimen geometry and clamping conditions. In numerous experiments it was shown that in tensile specimens with circular cross sections the austenite/martensite interface is oriented perpendicular to the loading direction, and that the orientation of the interface is hardly changed during the tensile test. For ribbon specimens or microtubes, on the other hand, different band morphologies have been reported. We use an analytical beam model to show that mainly the clamping conditions and the cross-section aspect ratio affect the interface angle especially for ribbons. We study a case where, due to a skew clamping, the tensile loading is superimposed with a bending moment. By minimizing the elastic deformation energy of the model that consists of two beam parts (one austenitic, one martensitic), the current martensite volume fraction and the corresponding interface angle can be calculated as a function of the macroscopic tensile deformation and of clamping imperfections. Our results show that the austenite/martensite interface angle in a ribbon specimen depends on its geometry, the clamping conditions and the amount of tensile elongation (Fig. 1). An increasing clamping imperfection and/ or an increasing area moment of inertia leads to an increase of the interface angle. The calculated angles are in good agreement with experimental data. Our study contributes to a more detailed understanding of martensite/austenite interface evolution during tensile loading of NiTi ribbons.