Variant reorientation in a single-crystalline Ni-Mn-Ga sample induced by a quasi-static rotating magnetic field: Mechanism analyses based on configurational forces

In this paper, we introduce a modeling work on the variant reorientation in a single-crystalline Ni-Mn-Ga sample induced by a quasi-static rotating magnetic field. First, some constitutive assumptions are proposed for the variant state distribution, the effective magnetization and the elastic energy density of Ni-Mn-Ga alloys. Then, the total energy functional for a Ni-Mn-Ga sample subject to coupled magneto-mechanical loads is formulated. Through a variational approach, the governing equation system of the model can be formulated, which is composed of the magnetic and mechanical field equations, the evolution laws of some internal variables and the twin interface movement criteria. An efficient numerical scheme is adopted to solve the governing system. With the obtained numerical solutions, we first analyze the evolution properties of the configurational force on the twin interfaces. Especially, the effects of the application directions of magnetic fields on the configurational force are investigated. The influences of the different energy terms on the configurational force are also analyzed. Based on these results, we further conduct numerical simulations on the magneto-mechanical behavior of the Ni-Mn-Ga sample subject to a quasi-static rotating magnetic field. The predicted global responses of the Ni-Mn-Ga sample show good consistency with the experimental result. The configurations of the sample and the distributions of some important physical quantities in the sample during the different loading stages can also be described. Furthermore, by considering the properties of the configurational forces, the underlying mechanisms responsible for the rotating field-induced variant reorientations can be revealed. (C) 2020 Elsevier B.V. All rights reserved.