Computational Study of Stretching Rate Effects on Pattern Formation in NiTi Thin Strips

Different macroscopic domain patterns have been observed in thin strips of nano-gained polycrystalline NiTi under different stretching rates. To study the formation and evolution of the domain patterns, 2D finite element method (FEM) and non-local strain gradient model with non-convex free energy function are used for simulation of the patterns. It is shown that the average spacing between neighboring domains is governed by a power-law scaling with exponent −1/2 to stretching rates in the stretching rate range of 10⁻⁴–3×10⁻²/s, while the scaling exponent is −1/6 in the range of 3 × 10⁻²–3/s. With further increase of stretching rate (>3/s), the pattern formation is suppressed and the transformation becomes spatially homogenous. The above 2D non-local FEM simulation results are supported by experimental observations.