Phase Field Simulation on the Crack Propagation and its Gran Size Dependence of Niti Shape Memory Alloy Under Cyclic Loading

Abstract

Based on crystal plasticity theory, a three-dimensional non-isothermal fracture phase field model was proposed, considering various inelastic deformation mechanisms presented in NiTi shape memory alloys (SMAs). The crack propagation of NiTi SMA under cyclic loading was simulated by addressing, respectively, its one-way shape memory effect (OWSME) and super-elasticity (SE). The effects of stress-induced martensite transformation (MT, involved in the SE NiTi system), temperature-induced MT (occurred in the OWSME system) and plastic deformation on the crack propagation of NiTi SMA were examined. The simulated results indicate that the dissipation caused by MT, martensite reorientation (MR) and plastic deformation effectively reduces the crack propagation rate. Differences in elastic energy between grain interior and grain boundary affect the crack initiation and propagation at grain boundary, thereby influencing the fracture mode of the system. As the grain size increases, the crack propagation rate in the SE NiTi system rises, and the fracture mode changes from the transgranular fracture to the intergranular one gradually. However, the crack growth in the OWSME NiTi system does not exhibit a significant dependence on the grain size. The crack propagation rate within the OWSME system is slightly lower than that in the SE system.

Keywords: NiTi shape memory alloy, Martensite transformation, Plastic deformation, Crack propagation, Phase field simulation, Grain size