Journal of Applied Mathematics

Volume 2011 (2011), Article ID 165160, 15 pages

http://dx.doi.org/10.1155/2011/165160

## Symplectic Analytical Solutions for the Magnetoelectroelastic Solids Plane Problem in Rectangular Domain

^{1}School of Architecture and Civil Engineering, Shenyang University of Technology, Shenyang 110870, China^{2}State Key Laboratory of Structural Analysis for Industrial Equipment, Dalian University of Technology, Dalian 116023, China

Received 20 September 2010; Accepted 12 January 2011

Academic Editor: Pablo Gonza'lez-Vera

Copyright © 2011 Xiao-Chuan Li and Wei-An Yao. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

#### Abstract

The transversely isotropic magnetoelectroelastic solids plane problem in rectangular domain is derived to Hamiltonian system. In symplectic geometry space with the origin variables—displacements, electric potential, and magnetic potential, as well as their duality variables—lengthways stress, electric displacement, and magnetic induction, on the basis of the obtained eigensolutions of zero-eigenvalue, the eigensolutions of nonzero-eigenvalues are also obtained. The former are the basic solutions of Saint-Venant problem, and the latter are the solutions which have the local effect, decay drastically with respect to distance, and are covered in the Saint-Venant principle. So the complete solution of the problem is given out by the symplectic eigensolutions expansion. Finally, a few examples are selected and their analytical solutions are presented.

#### 1. Introduction

Magnetoelectroelastic solids are a kind of the emerging functional composite material. Due to possessing mechanical, electric and magnetic field coupling capacity, these materials show better foreground in many high-tech areas (see [1]). They not only convert energy from one form to the other (among magnetic, electric, and mechanical energies), but also possess some new properties of magnetoelectric effect, which are not found in single-phase piezoelectric or piezomagnetic materials. Over the years, a large amount of studies have been done in mechanics, materials science, and physics fields (see [2–6]), and it has become a new cross subject.

Due to multifields coupling, the magnetoelectroelastic solids problem is solved more difficultly than elasticity one. Zhong et al. (see [7, 8]) introduced a symplectic dual method based on the conservative Hamiltonian system to solve the elastic problem which is different from the traditional semi-inverse solution method. The complete solutions space can be obtained and a satisfactory solution can be obtained under the boundary conditions (see [9–11]). The symplectic dual method has been developed for studying piezoelectric effects (see [12]) and magnetoelectroelastic problems (see [13]).

With the symplectic approach, the plane problem of magnetoelectroelastic solids in rectangular domain is derived into the Hamiltonian system by means of the generalized variable principle of the magnetoelectroelastic solids. In symplectic geometry space with the origin variables—displacements, electric potential, and magnetic potential, as well as their duality variables—lengthways stress, electric displacement, and magnetic induction, symplectic dual equations are employed. Yao and Li have obtained all the eigensolutions of zero-eigenvalue, which have their specific physical interpretation and are the basic solutions of plane Saint-Venant problem in [13]. This paper gets the eigensolutions of nonzero-eigenvalues, which are the solutions that have the local effect, decay drastically with respect to distance, and are covered in the Saint-Venant principle. So the complete solution of the problem is given out by the symplectic eigensolutions expansion. Finally, a few examples are selected and their analytical solutions are presented.

#### 2. Functional Equations and Boundary Conditions

The transversely isotropic magnetoelectroelastic solids are studied here, with the *z*-axis being the polar direction. If geometry size, load, and so forth, in direction satisfy the given condition, the problem can be simplified as a plane problem in the plane. The functional equations of the plane problem are as follows (see [14]).Governing equations:
Gradient equations:
Constitutive equations:
where are displacement components in the direction, respectively; , , and are stress components, respectively; , , and are electric displacement components and electric potential, respectively; , and are magnetic induction components and magnetic potential, respectively; , and are body force components and density of free charges in region , respectively. , and are elastic modus, dielectric constant, and magnetic constants, respectively; , , and are piezoelectric, piezomagnetic, and electromagnetic constants, respectively. Equation (2.3) can also be rewritten as follows:

The rectangle domain as showing in Figure 1 is studied in this paper

And the boundary conditions are expressed as (see [15]) In addition, there are body force and density of free charges in region .

On , the boundary conditions are (see [15]) Or

#### 3. Duality Equation in Symplectic Geometry Space and Separation of Variables (See [13])

Consider rectangle domain as showing in Figure 1. At first, the coordinate here is employed to simulate the time variable in the Hamiltonian system, and a symbol “” in the following derivation will be used denoting the differential with respect to , that is, . For the sake of simplicity, the notations , and are introduced to represent , and , respectively. If we omit body forces and density of free charges, a dual equation with the full state function vector is given as and is the operator matrix in [13] where the constants are listed in the appendix.

Consider the following boundary conditions on two sides in [13]: where constant , and are listed in the appendix. Equation (3.1) can usually be solved by using the method of partition of variables. Let and substitute (3.4) into (3.1); the following equations can be obtained: where is the eigenvalue and is the eigenfunction vector, which satisfies the boundary condition (3.3) on .

The full state vectors form a symplectic space according to the following definition of symplectic inner product:

If only and meet the requirement of (3.3), the following invariant is obtained as Therefore, the operator matrix is the Hamiltonian operator matrix in the symplectic geometry space. So its eigenvalues have some characteristics, that is, if is an eigenvalue, then must also be one, and the eigenfunction vectors satisfy the symplectic adjoint orthogonal relationship. After eigenvalues and eigenfunction vectors of are given, the origin problem can be solved by the method of eigenfunction expansion (see [7, 8]).

#### 4. Eigenfunction Vectors of Eigenvalue Zero (See [13])

With the free boundary condition at both sides(), the magnetoelectroelastic solids plane problem in rectangular domain exists eigenvalue zero. The eigenvalue zero is a special eigenvalue of the Hamiltonian operator matrix, which eigenfunction vectors are not only the fundamental solution with the special physical significance but also a nondecaying solution. Solve the following eigenequation with conditions (3.3): After obtaining the fundamental eigensolutions and eigensolutions in Jordan form, the solutions of (3.1) can be given as The component forms of are The constants in (4.2)-(4.3) are listed in [13]. The eigensolutions of eigenvalue zero just are the fundamental solution of Saint Venant problem. But the solutions having the local effect are constituted by the eigensolutions of eigenvalue nonzero of (3.1), which are obtained in the next section.

#### 5. Eigenfunction Vectors of Eigenvalue Nonzero

The eigenvalue equation (3.5) is a system of ordinary differential equations with respect to which can be solved by first determining the eigenvalue with respect to the direction. The corresponding equation is where the constants are listed in the appendix. Expanding the determinant yields the eigenvalue equation Apparently, where constituted by , (5.2) has eight roots

Only discuss the general case that there are eight different roots . Obviously, must be an eigenvalue if is an eigenvalue, so the general solution of (5.2) can be expressed as

It shows that the partial solutions relevant to are the solutions of symmetric deformation with the -axis while the partial solutions relevant to are the solutions of antisymmetric deformation with the -axis.

Firstly discuss the general solution of symmetric deformation where constants are not all independent. Substitute (5.5) into (3.5); can be expressed by the independent constants where and are expressions of .

So far, only are unknown constants in the general solution. Substituting (5.5) and (5.6) into the boundary conditions (3.3) yields For the sake of simplicity, (5.7) is denoted as For nontrivial solution to exist, the determinant of coefficient matrix vanishes. Equation (5.9) can be solved by numerical methods. If is roots of (5.9), each in reality has its symplectic adjoint eigenvalue and their complex conjugate eigenvalues. After obtaining by substituting into (5.8), the corresponding eigenvector function is where

The corresponding solution of (3.1) in symmetric deformation is

Likewise, the corresponding eigenvector function of eigenvalues in antisymmetric deformation is where

The corresponding solution of (3.1) in antisymmetric deformation is

Thus, all eigensolutions of nonzero eigenvalues are obtained. These solutions are covered in the Saint-Venant principle and decay with distance depending on the characteristics of eigenvalues (see [7, 8]). Together with the eigensolutions of zero eigenvalue, they constitute a complete adjoint symplectic orthonormal basis and the expansion theorem is then applicable. Further discussion concerns solutions of magnetoelectroelastic solids plane problems in rectangular domain.

#### 6. Solutions of Generalized Plane Problems in Rectangular Domain

The solution of homogeneous (3.1) by the method of separation variables has been discussed in the previous several sections. The analytical expressions of eigensolutions of zero eigenvalue and of nonzero eigenvalues have also been presented. Based on expansion theorems, the general solution of homogeneous equation (3.1) for magnetoelectroelastic solids plane problems in rectangular domain is where , , , , , and are undetermined constants. Determining these constants needs the variational equations corresponding to the two-point boundary conditions obtained by applying the variational principle.

If the end boundary conditions for specified generalized displacements are (2.7), it can be expressed as where and denote the values of variable at and , respectively.

If the end boundary conditions for specified generalized forces are (2.8), it can be expressed as where and denote the values of variable at and , respectively.

The boundary conditions at both ends () can also be mixed boundary conditions.

According to approach derived by Zhong et al. in [7, 8] in the Hamiltonian system, the process of obtaining the undetermined constants of the general solution is presented here. For the sake of simplicity, the general solution is given as where is the number of eigensolutions, are all solutions that relate to zero eigenvalue and nonzero eigenvalues, and are constants determined by a linear system of equations resulted from the Hamiltonian variational principle. If we specify generalized displacement at and generalized force at , the variational equation is obtained as Equation (6.5) can be expressed as can be determined by the following equations: where

#### 7. Numerical Examples

The Saint-Venant principle is applicable to the problem for in a rectangular domain. The influence of self-equilibrium forces at both ends () is only confined to the vicinity of the region. It is then appropriate to neglect the solutions of nonzero eigenvalues and, therefore, to apply only the solutions of zero eigenvalue in the expansion theorem.

*Example 7.1. *Consider a magnetoelectroelastic rectangle domain, under uniform axial tension, electrical displacement, or magnetic induction, respectively. Three load cases are considered and the boundary conditions are given by: (a)*, *, under the uniform tension;(b)*, *, under the uniform electric displacement;(c)*, *, under the uniform magnetic induction.: *; **: *.

The problem is treated as a symmetric deformation one. The solution is formed from (4.2). For load (a),
For load (b),
For load (c),

For numerical calculation, the composite materials BaTiO_{3}-CoFe_{2}O_{4} are specified, which material constants are given in [5]. Take , , , , and . The numerical results at point () are given in Table 1, where the values in the parenthesis are the exact ones which are calculated with the formulas presented by Ding and Jiang in [5]. The results show that the numerical solutions by the method have higher accuracy. The eigensolutions of zero eigenvalue correspond to the solutions of Saint-Venant problems. On the other hand, the solutions of the portion covered by the Saint-Venant principle correspond to the eigensolutions with nonzero eigenvalues. Subsequently, a very simple example is presented here.

*Example 7.2. *Consider a simple tension problem of composite materials BaTiO_{3}-CoFe_{2}O_{4} semi-infinite strip fixed at , and take , . There is only the tension stress for , and . The stress distribution at the fixed end is determined here.

Firstly, by utilizing (5.2) and (5.3), are calculated and listed in Table 2 for the composite materials BaTiO_{3}-CoFe_{2}O_{4}.

Secondly, obtain nonzero eigenvalues. With reference to the problem, there is only the tension stress for and the deformation is symmetric with respect to -axis. Solve (5.9) by numerical methods. Table 3 lists the first five eigenvalues in the first quadrant. Each in reality has its symplectic adjoint eigenvalue and their complex conjugate eigenvalue.

Thirdly, the general solution is then formed from the eigensolution of the zero eigenvalue (4.2) and (4.3) and the eigensolution of the nonzero eigenvalues of the symmetric deformation (5.12). Consider the deformation is symmetric with respect to -axis and rigid body translation, constant electric potential or constant magnetic potential has no effect on stress, only , , and are selected in (4.2). Their coefficients are determined by the boundary conditions at . So the general solution can be expressed as
where is the number of the eigensolutions of nonzero eigenvalues of the symmetric deformation. For the above general solution, only eigensolutions of -set in (5.12) are adopted, that is, . Thus it consistent with the far-end boundary condition at .

Finally, Substituting (7.4) into the equation of variation (6.5) and adopting a total of ten eigensolutions of nonzero eigenvalues in the calculation yield at the fixed end as illustrated in Figure 2. The figure shows that there is stress singularity at the edge corner. Fluctuation of stress observed is common when truncated finite terms are adopted in the expansion. Such phenomenon has been observed, for instance, when finite terms in a Fourier series are assumed. Figure 3 shows that the normal stress distribution approximates uniformity at .

#### 8. Conclusions

In this paper, the transversely isotropic magnetoelectroelastic solids plane problem in rectangular domain is considered from a symplectic approach. The eigensolutions of nonzero-eigenvalues obtained decay drastically with respect to distance can express the end effects and corner stresses. There is no requirement of experience in the symplectic approach for solving the problem since it is a rational, analytical approach to satisfy the boundary conditions in a straightforward manner.

#### Appendix

#### Acknowledgment

The work was supported by the National Natural Science Foundation of China (no. 10902072).

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