Nonlinear Modeling Of Multi-Field Coupling Effects On Mechanical Behavior Of Magnetostrictive Materials

Magnetostrictive materials have an immeasurable applied prospect in smart devices and systems owing to many unique benefits in performance like large displacement, fast response and simple driving. A considerable coupling effect among mechanical field, magnetic field, thermal field, electrical field is therefore being a relevant concern in the applications of magnetostrictive devices. Motivated by the need to promote a more efficient design process and higher performance achievement of development of materials, devices and system designs, this dissertation presents nonlinear modeling of multi-field coupling effects on mechanical behavior of magnetostrictive materials.A thermodynamic framework is constructed to describe the bidirectionally coupled magnetization, and the movement of the domain walls is incorporated to describe hysteresis based on Jiles-Atherton's model. Furthermore, the temperature dependence of irreversible and reversible magnetization is discussed. The predictions show good correlation with experimental data.It is shown that demagnetization field makes the magnetization hard and increases energy losses, as well as decreases the unsaturation magnetostriction. The coercive field varies with temperature and prestress can be also well described by this work. It is revealed that enhancing temperature and reducing prestress is an effective way to lessen hysteretic losses.A constitutive model which can describe the magneto-thermal-elastic coupling and hysteresis inherent to magnetostrictive materials is proposed. Comparing this model with other existing models in this field, the quantitative results show that the relationships obtained here are more effective to describe the effects of the prestress or in-plane residual stress and ambient temperature on the magnetization or the magnetostriction hysteresis loops for magnetostrictive rods or films.A magnetocrystalline anisotropy model is presented with incorporating the effects of stress, thermal, demagnetization field. The model is validated against experiment measurements made on Terfenol-D alloys. It is shown that magnetocrystalline anisotropy shows a remarkable effect on the magnetization and magnetostriction. With the anisotropy constant increasing, the nonlinear regions of magnetization curves and magnetostrictive curves are enlarged, and magnetization becomes hard. It is also shown that different forms of anisotropy (axially anisotropic, planar anisotropy and cubic anisotropy), which have almost no effects on the saturation value of magnetization and magnetostriction, affect the magnetization processes remarkably. A frequency-dependent bidirectionally coupled magnetoelastic dynamic model is proposed by considering the interaction between mechanical responses with magnetization field. The effects of hysteresis losses on the dynamic behavior of magnetostrictive materials are then discussed. Model predictions show good correlation with experimental data, which demonstrates that the model can well capture the dynamic behavior of magnetostrictive materials. Resonance frequency shifts and amplitude reductions due to hysteresis losses are analyzed. Furthermore, the effects of hysteresis losses on the dynamic vibration behavior in the low frequency range as well as stress and temperature dependence of hysteresis losses are discussed in detail.A multi-field coupled framework is developed to study the electro-magneto-thermal-elastic coupling effects on the dynamic response of magnetostrictive materials. In the model, the influence of thermal effect arising from eddy current is taken into account. A compenhensive description for temperature, pre-stress and bias field dependences of resonance frequency is carried out. Moreover, the effects of eddy current losses on the dynamic behavior of magnetostrictive materials are discussed in detailThese essential and important investigations will be of significant benefit to both the theoretical researches and the applications of magnetostrictive materials in smart or intelligent structures and systems.