Theoretical And Experimental Investigations On Magnetoelastic Interactions In Ferromagnetic Materials And Structures

Ferromagnetic materials and structures are widely used in national economic construction. The mechanical behavior of ferromagnetic materials is usually influenced by the coupling effect between mechanical field and magnetic field. It is directly related to the performance of high-tech devices and the reliability of operation. In this dissertation, we investigated the magnetoelastic interactions by theoretical and experimental methods.Firstly, a deformable continuous solid moving in the electromagnetic field has been described based on the continuum theory, the ferromagnetic particles reinforced composite has been seen as a magnetizable elastomer, then the dependency of the stress and the magnetic field is discussed. The magnetoelastic characteristics of such ferromagnetic composites obtained from continuum theory are similar to the ones based on the mesoscopic model. Furthermore, a constitutive model which can describe the viscoelastic and the magnetoelastic behaviors of ferromagnetic composites is proposed, the predictions show good correlation with experimental data. Comparing this model with other existing models, the quantitative results can reflect the mechanics-magneto interaction without changing parameters in the model. The nonlinear characteristics of the constitutive relations in different regions of magnetic field and the magnetic field sensitivity of the shear modulus for such ferromagnetic composites are also discussed. It is also shown that the shear modulus change with the external magnetic field and loading frequency under dynamic loading.Based on the equations from the continuum mechanics and electromagnetism discussed above, we further analyze the decoupled approaches for the problems of magneto-mechanical coupling. The differences of magnetic field distributions inner and near the ferromagnetic structures are due to the differences of the decoupled approaches, so we discuss the differences between the numerical iterative of finite element method and the perturbation technique in the descriptions of the magnetic field distributions, furthermore, the changes of distributions of the magnetic force in the ferromagnetic media. The predictions show that the perturbation method can only deal with the changes of magnetic field distributions since the deformation of the ferromagnetic elastic media, it can’t consider the effect that the changes of the magnetic field nearby the structures due to the magnetization of the ferromagnetic media. The differences of magnetic field distributions simulated by these two methods will led to the differences of the distributions of the magnetic force even though adopting the same magnetic force model. The finite element model presented above can degraded to the situation of the ferromagnetic rigid media, then it is applied to the problem of magnetic shielding to verify the validity of the model.The theoretical as well as experimental investigations on the natural frequency of a ferromagnetic plate in an inclined magnetic field are presented. A novel analytical model with the nonlinear law of magnetization is proposed for the field-dependent natural frequency of a ferromagnetic plate. Model predictions show good correlation with the experimental data at different inclined angles. Both the theoretical and experimental investigations show that there exists a critical angle of the inclined field, below which the natural frequency of the ferromagnetic plate will increase with the magnetic field, and above which the frequency will decrease with increasing the field. The predictions show that the critical angle is sensitive to the length-to-thick ratio of the plate.Experimental studies on the magnetoelastic deformation of ferromagnetic cylindrical shell are carried on. The circumferential strains of the shell in the transverse magnetic field are measured. It is noted that the circumferential strain do not show a B2dependence at high field, which means the magnetoelastic behavior of shell at low field is different from the one at high field. Moreover, it is shown that the intensity of the magnetic field only affects the values of the circumferential strain, not the strain distribution, while the directions of the applied magnetic field and the ratio of thickness-to-radius of shell show a dramatical influence on both the values and the distributions of strain. The supported conditions at shell ends also have effects on the magnetoelastic deformation.In summary, these essential and important investigations will be of significant benefit to both the theoretical researches and applications of the ferromagnetic materials in intelligent structures and systems.