Research About Magneto-mechanical Coupling Characteristics Of GMA Based On Free Energy Model

The giant magnetostrictive actuator (GMA) is designed with the rare earth giant magnetostrctive material (GMM) and has quickly become the focus of micro-drive field which has many advantages, such as large strain and stress, high precision, fast response and good reliability. The previous study shows that the output and input signal in the GMA has intrinsic relations. The linear constitutive equation of GMA, which has been summarized by Clark in1980, has generally represented the relationship between magnetism and mechanism of GMM, in spite of ignoring lots of non-linear phenomenon. Because of the strong electric-magnetic-mechanical-thermal coupling of GMM, its intrinsic non-linear problem has become the most complicated question in the application process of smart materials, leading to making models difficultly. In the present commercial software, such as ANSYS, COMSOL and SAP, the electro-mechanical coupling modules for the piezoelectric materials has been involved, but the electro-magneto-mechanical modules for GMM cannot be involved.In the background of micro-drive technology, the practical devices of GMA and its research about the magneto-mechanical coupling have been discussed in the thesis. Then the characteristics of GMM, the magnetostriction and the modeling approach of GMA have been introduced.On the basis of the characteristics of GMM, a new kind of GMA has been designed and manufactured. After understanding the electromagnetic theory in the software of COMSOL, the3D finite element model for the GMA has been established and its magnetic property has been analyzed. The results shows that its magnetic structure has designed rationally and the magnetic induction through the GMM rod has been met the need for the less magnetic flux leakage.In this thesis, the hysteresis and non-linear characteristics of GMA has been studied deeply with the free energy model, which has used as the material model to solve the coefficient matrix of the piezomagnetic equation; The weak form of the magneto-mechanical equations have been combined with the3D magnetic and mechanical field distribution, which have been calculated by the Maxwell equation and the Newtonian second law. Based on the above two, the3D non-linear magneto-mechanical coupling model of GMA has been established. Its finite element discretization can be used to solve the increments of vector potential and displacement together with the incremental piezomagnetic equation. At last the increments of magnetic induction and strain can be obtained and then the total output strain can be accumulated.Some experiments of GMA have been done in this thesis, including its characteristics of dynamic and hysteresis. And the results, such as the output displacement and hysteresis, show that the analysis data of the magneto-mechanical coupling modeling and the output experiment has fitted with each other. Their relative errors has kept mostly less than15%. From the data, we can find that the above magneto-mechanical coupling model can be used for reference to optimize the structural design of GMA.