Quasi-Static Modeling of NiMnGa Magnetic Shape Memory Alloy

摘要

A quasi-static model for NiMnGa magnetic shape memory alloy (MSMA) is formulated in parallel to the Brinson and Tanaka thermal SMA constitutive models. Since the shape memory effect (SME) and pseudoelasticity exist in both NiTi and NiMnGa, constitutive models for SMAs can serve as a basis for MSMA behavioral modeling. The quasi-static model for NiMnGa was characterized by nine material parameters identified by conducting a series of uniaxial compression tests in a constant field environment. These model parameters include free strain, Young's modulus, fundamental critical stresses, fundamental threshold fields, and stress-influence coefficients. The Young's moduli of the material in both its field and stress preferred configurations were determined to be 450 MPa and 820 MPa respectively, while the free strain was measured to be 5.8%. These test data were used to assemble a critical stress profile that is useful for determining model parameters and for understanding the dependence of critical stresses on magnetic fields. Once implemented, the analytical model shows good correlation with test data for all modes of NiMnGa quasi-static behavior, capturing both the magnetic shape memory effect and pseudoelasticity. Furthermore, the model is also capable of predicting partial pseudoelasticity, minor hysteretic loops and stress-strain behaviors. To correct for the effects of magnetic saturation, a series of stress influence functions were developed from the critical stress profile. Although requiring further refinement, the model's results are encouraging, indicating that the model is a useful analytical tool for predicting NiMnGa actuator behavior.