The Study Of Losses Theory And Experiments Of Giant Magnetostrictive Materials And Devices

Smart materials can transform electric, magnetic and thermal energies into mechanical energy, which is based on varied physical effects within the materials. They are also known as new functional materials combining the ability of actuation and sensing together, which makes them the designing and manufacturing basis from high power transducers to micro/nano scale devices. The usual smart materials include giant magnetostrictive materials, piezoelectrics, shape memory alloy, electroactive materials and magneto-rheological/electrorheological fluid, which are widely applied in precise actuation, ultra-precise machining, ultrasonic cutting, active vibration control, non-destructive testing and so on. Hystersis exists with smart materials between the input and the output signals in the process of transforming energies, which is named as magnetic hystereis specially for giant magnetostrictive materials (GMM in short). Hystereis is actual a kind of energy loss. In order to study and characterize the hysteresis behavior of GMM, the method of using three types of losses, magnetic, mechanical and piezomagnetic losses and their losses factors is adopted in this thesis based on the physical intrinsic properties of materials. Research includes the expression and measuring method of these losses, which will be the base in analyzing and modeling dynamic and high power giant magnetostrictive materials devices.The main content and creative aspects are depicted in the following four parts:1. The hysteresis modeling methods for giant magnetostrictive materials include physical hysteresis models, Jiles-Athertonmodel and Free-energy model, and mathematical hysteresis model, Preisach model and so on. These models are limited in dynamic applications, time response, and computing complexity and in indicating the physical origin. Hysteresis is a kind of energy losses in actual physical meaning. The thesis adopt three types of losses, magnetic, mechanical and piezomagnetic losses to characterize hysteresis behavior, based on the Gibbs and Helmholtz free energy and linear constitutive equations. This method analyzes the internal friction theory and the physical origin of hysteresis loss, and aims to keep the modeling method simple, quick in response and accurate.2. The impedance expressions and mechanical quality factors at resonance and anti-resonnace of giant magnetostrictive resonators are the bases for the characterization of magnetic, mechanical and piezomagnetic losses factors. Considering the anisotropic of the material, impedance expressions in k33、k33、kt、kp、 k15modes, and the relationships between losses factors and their mechanical quality factors are established.3. In experimental method, the high power characterization platform was designed, and experiments were conducted for k33mode. The changing characteristics of losses factors and some key parameters with defferent bias magnetic field were abtained. Here, sensing coil was adopted for measuring impedance, since impedance is sensitive to the coil parameters. To extend the modeling for giant magnetostrictive devices, the equivalent circuits combing losses factors are consider in the thesis. What’s more, the affects of driving techniques of constant current, constant voltage and constant power for losses analysis were introduced.4. Eddy current loss is one of main losses for dynamic applications of giant magnetostrictive materials, and is determined by physical properties (resistance, permeability), geometry (cylinder, plate) of materials and also the working frequency. The key parameter that affects the eddy current loss is the eddy current cut-off frequency. The methods in restricting eddy current losses include increasing the resistance of materials and using thin laminated structures. In this thesis, the model of eddy current losses for monolithic and laminated structures were established, and the experimental results of impedance spectra and vibration amplititute for these two kind of structures were shown, which were in consistant with the models.The results and creative points obtained in this thesis solved the problems of characterizing hysteresis loss and eddy current loss, and enrich the modeling mehods of hysteresis loss, and keep the method simple, quick in time response and indicate the originally physical meaning. The theory of hysteresis loss was combined with the experimental results, showing the self-consistant of the entire thesis.The research work in this thesis was supported by the National Natural Science Foundation of China (Grant No.51175395, and No.51165035), Ph.D. Programs Foundation of Ministry of Education of China (Grant No.20090143110005) and program from Guangxi Key Laboratory of Manufacturing System&Advanced Manufacturing Technology (Contract No.11-031-12S05).