Thermomechanical analysis of strain recovery in shape memory alloys under variable non-isothermal conditions

The present work focuses on size dependencies in thermo-mechanical testing of shape memory alloys and a phenomenon occurring for direction-dependent activation. Emphasis is on strain recovery which is enabled by a martensiteto-austenite transformation, modeled using a phenomenological evolution equation. In transient numerical studies performed with the finite element method for a non-isothermal tension testing case, the influence of the Fourier and Stefan number is investigated. The results indicate that, in experiments, the Fourier number should ideally be much greater than ten to prevent falsification by the current Stefan number. An additional study is carried out for the activation of a beam in its thickness direction. It shows that the gradient in transformation causes bending, which can only be considered in simulations by adequate spatial resolution.