A Magnetization- and Strain-Dependent Free Energy Model for FEM Simulation of Magnetic Shape Memory Alloys

Berthold Krevet 1Manfred Kohl 1Phillip D. Morrison 2Stefan Seelecke 2

1. Forschungszentrum Karlsruhe, IMT, Postfach 3640, Karlsruhe 76021, Germany
2. North Carolina State University (NCSU), 3211 Broughton Hall, Raleigh, NC 27695, United States

Abstract

Ferromagnetic shape memory alloys (FSMAs) allow the development of novel kinds of actuators, which can be controlled by a combination of applied stress, temperature, and magnetic field. For simulation and optimization of such actuators having an arbitrary shape, it is important to develop a validated model and an appropriate tool for field simulation such as the finite element method (FEM). The main goal of the present study is to develop a free energy model, which captures the main effects of variant reorientation on the strain and magnetization, and to implement the model in a FEM routine, which takes into account both the actuator geometry and the complex thermo-magneto-mechanical coupling of the material. A free energy function is constructed, which couples strain and magnetic moments in the FSMA material. The associated Gibbs function is used to calculate time-dependent transition probabilities between martensite variants in a magnetic field under applied stress. By keeping track of the variant fractions, the evolution of strain and magnetization is determined. The simulation model is applied to a beam actuator to verify magnetic field-dependent strain and magnetization characteristics. The influence of a coupling term between strain and magnetic anisotropy on these characteristics is discussed.

 

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Presentation: Oral at E-MRS Fall Meeting 2007, Symposium E, by Berthold Krevet
See On-line Journal of E-MRS Fall Meeting 2007

Submitted: 2007-05-14 14:57
Revised:   2009-06-07 00:44