Theoretical study and numerical simulations on the stress-induced twin interface nucleation in single-crystalline NiMnGa alloys

In this paper, the stress-induced twin interface nucleation in single-crystalline NiMnGa alloys is studied through theoretical analyses and numerical simulations. First, the mechanical governing system for a single-crystalline NiMnGa sample is formulated, which contains the mechanical field equation and the twin interface movement criteria. To complete the governing system, the nucleations of twin interfaces in the NiMnGa sample under general mechanical loads are investigated. By considering the connection conditions of some physical quantities across a “fictitious” twin interface, the explicit expression of the configurational force on the twin interface is derived. Then, based on the twin interface movement criteria, a practical scheme for predicting the twin interface nucleation is proposed. This scheme can be integrated into the iterative numerical algorithm for solving the mechanical governing system. To demonstrate the efficiency of this scheme, some simulation results are presented for two typical deformations of a NiMnGa sample (i.e., the axial compression and the bending deformation), which show good consistency with the experimental results. By analyzing the evolution properties of the configurational forces on the possible nucleation interfaces, the mechanism responsible for twin interface nucleations under different loading conditions can be revealed. The results obtained in the current work would be helpful for the design of smart devices by utilizing NiMnGa alloys.In this paper, the stress-induced twin interface nucleation in single-crystalline NiMnGa alloys is studied through theoretical analyses and numerical simulations. First, the mechanical governing system for a single-crystalline NiMnGa sample is formulated, which contains the mechanical field equation and the twin interface movement criteria. To complete the governing system, the nucleations of twin interfaces in the NiMnGa sample under general mechanical loads are investigated. By considering the connection conditions of some physical quantities across a “fictitious” twin interface, the explicit expression of the configurational force on the twin interface is derived. Then, based on the twin interface movement criteria, a practical scheme for predicting the twin interface nucleation is proposed. This scheme can be integrated into the iterative numerical algorithm for solving the mechanical governing system. To demonstrate the efficiency of this scheme, some simulation results are presented for two typical ...