Due to magnetic field diffusion and structural dynamics, the relationship between magnetic field and strain in Ni-Mn-Ga changes significantly as the frequency of applied field is increased. In order to describe this behavior, which is critical for actuator applications, we present a strain model for Ni-Mn-Ga driven with dynamic magnetic fields. The magnitude and phase of the magnetic field inside the sample are modeled as a 1-D magnetic diffusion problem, from where an averaged or effective field is calculated. A continuum thermodynamics constitutive model is used to quantify the hysteretic response of the martensite volume fraction due to this effective magnetic field. The evolution of volume fractions with effective field is proposed to behave as a zero order system. To quantify the dynamic strain output, the actuator is represented as a lumped-parameter 1-DOF resonator with force input dictated by the twin-variant volume fraction. This results in a second order, linear ODE whose periodic force input is expressed as a summation of Fourier series terms. The total dynamic strain output is obtained by superposition of strain solutions due to each harmonic force input. The model accurately describes experimental measurements at frequencies of up to 250 Hz.

Date Published: 2 April 2008
PDF: 12 pages
Proc. SPIE 6929, Behavior and Mechanics of Multifunctional and Composite Materials 2008, 69291R (2 April 2008); doi: 10.1117/12.776486

Published in SPIE Proceedings Vol. 6929:
Behavior and Mechanics of Multifunctional and Composite Materials 2008
Marcelo J. Dapino; Zoubeida Ounaies, Editor(s)