On instabilities and autocatalytic effects associated with the nucleation of martensite bands in polycrystalline SMA flat tensile specimens

The mechanical response in the pseudoelastic range of polycrystalline NiTi SMA specimens in displacement controlled tensile tests exhibits a load drop associated with the nucleation of martensitic bands, a phenomenon which is similar to the formation of Lüders bands in mild steel. A continuum mechanical energy approach allows to calculate the nominal stress-strain curve incorporating the characteristic load drop. The influence of the geometrical aspect ratio, i.e., thickness-to-width ratio of the flat tensile test specimens on the load drop is discussed and compared to the experimental data.