Xiaojing Zheng

Active vibration control of nonlinear giant magnetostrictive actuators

A nonlinear constitutive model-based vibration control system for giant magnetostrictive actuators (Terfenol-D) is presented in this paper. Such actuators utilize the realignment of magnetic moments in response to applied magnetic fields to generate strains in the material. It has been found that the strains and forces generated in this manner are significantly larger than those produced by many other smart materials, associated with significant and complex nonlinear relations among the quantities of applied magnetic field, strain, and compressive pre-stress. Based on the negative feedback control law and the analytical expressions of the nonlinear constitutive model of Terfenol-D rods, here, the effectiveness of real control systems for suppressing a vibration is confirmed by the simulation results on a case study of negative velocity feedback when its feedback gain is taken in a limit region. It is found that the limit region is dependent on the bias magnetic field and pre-stress. When the gain is employed out of the limit region, the real control system is unstable, but the simulation results on the basis of the linear constitutive model still show a stability of the control systems. To utilize the full potential of these materials in active vibration controls, thus, these inherent nonlinearities of the materials must be considered in the design of the control systems.

Electric field effects on Young's molulus of nanowires

As an important component of nanodevices and nanomachine constructions, the mechanical performance of nanowires (NWs) has been a subject of intense research efforts due to gaining relevance in controlling functionality of nanoelectromechanical systems (NEMS); meanwhile, one of the characteristics of the NEMS is the dependence of the functionality of the systems upon the applied electric field. The study of the electric effects on the Young’s modulus of nanostructures is of certain usefulness in the design of NEMS and the precise measurement of mechanical properties of one-dimensional nanostructures. This paper reviews the origin of the size-dependence of the elastic property of NWs and the factors influencing the discrepancies and inconsistencies in the measured values of the Young’s modulus for the NW, besides the surface effects, nonlinear effects, the electromechanical coupling effects as a possible effect responsible for the differences in quantitative and qualitative performance of the measured Young’s modulus for the NWs versus the diameter are clarified.

A general theoretical model of magnetostrictive constitutive relationships for soft ferromagnetic material rods

This paper presents a general theoretical model of constitutive relationships for the soft ferromagnetic and/or the giant magnetostrictive rods under a prestress and a bias magnetic field on the basis of Gibbs’ free energy function. After Gibbs’ free energy function is expanded by Taylor’s series expansion with the stress and the magnetization in the materials as the independent variables, a transcendental function is appropriately selected to replace the first terms with higher order up to six on the basis of the meaning of mechanics and physical theory of magnetic domains, from which a set of closed and analytical expressions of the constitutive relationships for the soft ferromagnetic material rods are obtained, and the parameters appearing in the relationships are determined by those measurable experiments in mechanics and physics. It is found that the predictions from this model are in good accordance with the experimental data given by Kuruzar and Cullity [Int. J. Magn. 1, 323 (1971)] and Jiles and ...

ANALYSES ON NONLINEAR COUPLING OF MAGNETO-THERMO-ELASTICITY OF FERROMAGNETIC THIN SHELL-- II： FINITE ELEMENT MODELING AND APPLICATION

Based on the generalized variational principle of magneto-thermo-elasticity of a ferromagnetic thin shell established (see, Analyses on nonlinear coupling of magneto-thermo-elasticity of ferromagnetic thin shell—I), the present paper developed a finite element modeling for the mechanical-magneto-thermal multi-field coupling of a ferromagnetic thin shell. The numerical modeling composes of finite element equations for three sub-systems of magnetic, thermal and deformation fields, as well as iterative methods for nonlinearities of the geometrical large-deflection and the multi-field coupling of the ferromagnetic shell. As examples, the numerical simulations on magneto-elastic behaviors of a ferromagnetic cylindrical shell in an applied magnetic field, and magneto-thermo-elastic behaviors of the shell in applied magnetic and thermal fields are carried out. The results are in good agreement with the experimental ones.

HEAT TRANSFER CHARACTERISTICS OF CONDUCTIVE MATERIAL UNDER INNER NON-UNIFORM ELECTROMAGNETIC FIELDS

Electronic transport properties can be influenced by the applied electromagnetic fields in conductive materials. The change of the electron distribution function evoked by outfields obeys the Boltzmann equation. In this paper, a general law of heat conduction considering the non-uniform electromagnetic effect is developed from the Boltzmann equation. An analysis of the equation leads to the result that the electric field gradient and the magnetic gradient in the conductive material are responsible for the influences of electromagnetic fields on the heat conduction process. A physical model is established and finite element numerical simulation reveals that heat conduction can be increased or delayed by the different directions of the electric field gradient, and the existence of the magnetic gradient always hinders heat conduction.

ANALYSES ON NONLINEAR COUPLING OF MAGNETO-THERMO-ELASTICITY OF FERROMAGNETIC THIN SHELL I： GENERALIZED VARIATIONAL THEORETICAL MODELING

Based on the generalized variational principle of magneto-thermo-elasticity of the ferromagnetic elastic medium, a nonlinear coupling theoretical modeling for a ferromagnetic thin shell is developed. All governing equations and boundary conditions for the ferromagnetic shell are obtained from the variational manipulations on the magnetic scalar potential, temperature and the elastic displacement related to the total energy functional. The multi-field couplings and geometrical nonlinearity of the ferromagnetic thin shell are taken into account in the modeling. The general modeling can be further deduced to existing models of the magneto-elasticity and the thermo-elasticity of a ferromagnetic shell and magneto-thermo-elasticity of a ferromagnetic plate, which are coincident with the ones in literature.