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 (FE) model to analyze a galfenol-based magnetostrictive energy harvesting concept device. An analytical energy density function is first presented assuming an isotropic material for the identification of a magneto-mechanical constitutive law. The model utilizes the magnetic flux density and mechanical strain as state variables. Compared to some earlier approaches, this simplifies the implementation of FE models based on magnetic vector potential and mechanical displacement, since time-consuming inversion of the constitutive law is not required. 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 cases. 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 under different preload values. The model 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.