Finite element analysis of magnetostrictive energy harvesting concept device utilizing thermodynamic magneto-mechanical model

This paper utilizes a thermodynamic approach based on Helmholtz free energy density and a finite element model to analyze a galfenol-based magnetostrictive energy harvesting prototype device. An analytical energy density function is first presented assuming an isotropic material for the identification of a magneto-mechanical constitutive law. Contrary to earlier approaches, the constitutive model utilizes magnetic flux density and strain as state variables. This serves as a convenient option when the model is applied in finite element (FE) analysis using formulations with magnetic vector potential and mechanical displacement. The Maxwell and mechanical balance equations are then solved utilizing the constitutive law in an axisymmetric FE model. A prototype device is developed and tested under uniaxial cyclic compressive loading of 100 Hz at different preload and dynamic loading case. Finally, the results from the simulations are compared with the experimental results for validation. The comparison shows that the analytical constitutive model fits well to the magnetization curves measured under static loading. Furthermore, the FE model closely predicts the measured power with some discrepancies in absolute value, but is able to predict the behavior of the device with respect to preload, load resistance and magnetization of the sample, proving to be an effective tool in the design of such devices.