Studies On The Effective Properties And The Magnetoelectric Responses Of Magnetic Sensitive Functional Composite Materials

Giant magnetostrictive composites and magnetoelectric composites are two kinds of magnetic sensitive functional composite materials. Giant magnetostrictive composites can achieve the energy transformation between magnetic energy and mechanical energy, which not only have larger magnetostriction, but also overcome some shortcomings of monolithic magnetostrictive materials, such as brittleness and larger eddy current losses at high frequencies. There are many potential applications, such as sensors and actuators. Magnetoelectric composites enable the energy conversion between magnetic energy and electric energy by interfacial strain transfer, which have important applications in such areas as magnetometry, energy harvesters, gyrators and sensors. Both of the two kinds of composites have become hot research topics in the functional composite materials.Because of the excellent characteristic of giant magnetostrictive composites, it is very important to predict the influence of some influential factors on the effect properties of giant magnetostrictive composites. For this reason, based on the Mori-Tanaka theory, considered the influence of interfacial properties and thermal residual stress on giant magnetostriction composites, combine Zheng-Liu magnetostrictive constitutive model, and obtained the general analytical expression of the effective properties. Then we predict the effective modulus, the effective magnetostriction, the effective thermal expansion coefficient of giant magnetostrictive composites variation with the inclusion’s aspect ratio, inclusion’s volume fraction and interfacial parameters. In addtion, the theoretical model is extended to three dimensional case. The effects of the magnetic field direction and the shape of inclusions on the effective properties of giant magnetostrictive composites are also studied. The above theoretical research provides theoretical guidance for wide application of giant magnetostrictive composites.Due to the wide application of magnetoelectric composites, it is essential to exactly reveal the coupling relations between their components, and predict the influence of some factors on magnetoelectric responses. A large number of experimental results show that the magnetoelectric responses of magnetoelectric composites have nonlinear characteristics in larger magnetic field. Some linear theory can’t explain the nonlinear magnetoelectric responses. Based on this, the thesis uses the nonlinear magnetostrictive constitutive relationship and the linear piezoelectric constitutive relationship, establishes theoretical models for layered magnetoelectric composites in different shaps, and studied the nonlinear magnetoelectric responses for those structures.For a cylindrical-shaped magnetoelectric composite, we separately give the magnetoelectric coefficient in static condition and the same-frequency and the double-frequency magnetoelectric coefficients in dynamic situation. In addition, the effects of component properties, volume fraction, magnetic field frequency and magnetic field strength on the magnetoelectric coefficients in different boundary condition, such as, free-free condition, clamped-free condition, free-clamped condition and clamped-clamped condition.For a circular-shaped magnetoelectric composite, we obtain the analytical expressions of the induced electric field in T-T mode and C-T mode, analyse the multi-peak value of magnetoelectric coefficients and frequency multiplying behavior of induced electric fields, study the influence of applied magnetic fields on magnetoelectric responses, and predict the transient characteristics of magnetoelectric responses in AC magnetic fields. Besides we discuss the optimum values of magnetic field and volume fraction when the magnetoelectric coefficient takes the maximum value in static and dynamic situation.Finally, a nonlinear dynamic hysteretic theoretical model on magnetoelectric effect of tri-layered composites is build based on a nonlinear constitutive relation for magnetostrictive material and a linear piezoelectric model for piezoelectric material. And a finite element analysis is implemented to study the influences of hysteresis and temperature on the magnetoelectric effect of the layered composites. The influences of structure form and component material on the magnetoelectric coefficient are studied. The temperature, the AC magnetic field and the bias field on the induced electric field and the ME effect are also discussed. Then the energy loss of the magnetoelectric composites is quantitatively calculated.The research of this thesis will improve the theoretical research on the property characterization for the two kinds of functional composite materials, and supply theoretical guidance in their optimized design of structure and engineering application.