压电材料中螺型位错与含界面刚性线圆形涂层夹杂的干涉

研究了压电材料中位于基体的螺型位错与含界面刚性线圆形涂层夹杂的电弹耦合干涉问题。运用复变函数方法,获得了基体、涂层和夹杂中复势函数的精确级数形式解答。基于广义Peach-Koehler公式,计算了作用在位错上的像力。讨论了刚性线几何条件、界面层厚度和材料电弹特性对位错力和位错平衡位置的影响规律。结果表明:对于软夹杂和软涂层的情况,刚性线长度存在一个临界值改变像力的方向。螺型位错先被吸引后被排斥,在夹杂附近有一个稳定的平衡点。对于硬夹杂和硬涂层的情况,位错一直被排斥,刚性线对位错力的影响较小。     

Electroelastic analysis for a Griffith crack interacting with a coated inclusion in piezoelectric solid

A Mode III Griffith crack interacting with a coated inclusion in piezoelectric media is investigated. The crack, the coated inclusion are embedded in an infinitely extended piezoelectric matrix media, with the crack being along the radial direction of the inclusion. In the study, three different piezoelectric material phases are involved: the inclusion, the coating layer, and the matrix. A far-field loading condition is considered. During the solution procedure, the crack is simulated as a continuous distribution of screw dislocations. By using the solution of a screw dislocation near a coated inclusion in piezoelectric media as the Green function, the problem is formulated into a set of singular integral equations, which are solved by numerical method. The stress and electric displacement intensity factors are derived in terms of the asymptotic values of the dislocation density functions evaluated from the integral equations. Numerical examples are given for various material constants combinations and geometric parameters.     

Electro-elastic stress analysis for a Zener-Stroh crack interacting with a coated inclusion in a piezoelectric solid

Summary. The problem of a Zener-Stroh crack initiated near a coated circular inclusion in a piezoelectric medium is investigated in this paper. By using the solution of a single piezoelectric screw dislocation near a coating inclusion as the Greens function, a Mode III displacement loaded crack is investigated. The proposed problem is formulated as a set of singular integral equations which are solved by numerical techniques. The influence of various parameters, such as the material constants of the inclusion, the coating, the matrix, the coating layer thickness, etc., on the crack behavior is studied. The stress and electric displacement intensity factors of the crack are derived. Several numerical examples are given and the results obtained are discussed in detail.     

A piezoelectric screw dislocation in a three-phase composite cylinder model with an imperfect interface

The electroelastic coupling interaction between a piezoelectric screw dislocation and the embedded circular cross-section inclusions with imperfect interfaces in piezoelectric solids is investigated by using a three-phase composite cylinder model. By means of a complex variable technique, the explicit solutions of electroelastic fields are obtained. With the aid of the Peach-Koehler formula, the explicit expression for the image force exerted on the piezoelectric screw dislocation is derived. The image force on the dislocation and its equilibrium positions near one of the inclusions are discussed for variable parameters (interface imperfection and material electroelastic dissimilarity) and the influence of nearby inclusions is also considered. The results show that when compared with the previous solution (the perfect interface), more equilibrium positions of the screw dislocation in the matrix may be available due to the effect of the interface imperfection when the dislocation is close to the electroelastic stiff inclusion. It is also found that the magnitude of the image force exerted on the piezoelectric screw dislocation produced by multiply inclusions is always smaller than that produced by a single inclusion and the impact of nearby inclusions on the mobility of the screw dislocation is very important.     

A piezoelectric screw dislocation interacting with a nonuniformly coated circular inclusion

This paper investigated the interaction of a piezoelectric screw dislocation with a nonuniformly coated circular inclusion in an unbounded piezoelectric matrix subjected to remote antiplane shear and electric fields. In addition to having a discontinuous displacement and a discontinuous electric potential across the slip plane, the dislocation is subjected to a line force and a line charge at the core. The alternating technique in conjunction with the method of analytical continuation is applied to derive the general solutions in an explicit series form. This approach has a clear advantage in deriving the solution to the heterogeneous problem in terms of the solution for the corresponding homogeneous problem. The presented series solutions have rapid convergence which is guaranteed numerically. The image force acting on the piezoelectric screw dislocation is calculated by using the generalized Peach–Koehler formula. The numerical results show that the varying thickness of the interphase layer will exert a significant influence on the shear stress and electric field within the circular inclusion, and on the direction and magnitude of the image force. This solution can be used as Green’s function for the analysis of the corresponding piezoelectric matrix cracking problem.     

On the interaction between a screw dislocation and a circular coated inclusion with interfacial cracks

Summary The problem of the elastic interaction between a screw dislocation, which is located at an arbitrary point inside either the matrix or the inclusion, and a circular coated inclusion with interfacial cracks is dealt with. An efficient and concise method for a complex multiply connected region is developed, in terms of which the general solutions to the problem are derived. As an illustrative example, explicit series form solutions for complex potentials are presented in the case of one interfacial crack. Based on the complex potentials, image forces on the screw dislocation are then calculated using the Peach-Koehler formula. The equilibrium position of the dislocation is discussed in detail for various crack geometries, coating layer thicknesses and material constant combinations. It is shown that the influence of interfacial cracks on the motion of the dislocation near the coated inclusion is significant. The present solutions contain a number of previously known results as special cases.     

A screw dislocation interacting with a coated nano-inhomogeneity incorporating interface stress

Effect of interface stress on the interaction between a screw dislocation and a coated nano-inhomogeneity is investigated in the framework of surface elasticity. By using the complex variable function method, the stress fields in heterogeneous materials and the image force acting on the screw dislocation are derived analytically. The results indicate that, when the radius of the coated inhomogeneity is reduced to nanometers, the influence of interface stress on the motion of the dislocation near the inhomogeneity becomes significant and the image force acting on the screw dislocation depends on the size of the coated inhomogeneity, which differs from the classical solution. And it is showed that the thicker coated layer relative to inclusion decreases or increases the influence of a coated inclusion on the image force of dislocation, not as expected.     

Image force and stability of a screw dislocation inside a coated cylindrical inhomogeneity with interface stresses

The image force and stability of a screw dislocation inside a coated cylindrical inhomogeneity with interface stresses are analyzed. A three-phase composite cylinder model is utilized to study the issues. The stress boundary condition at the interface of the coating layer is modified by incorporating surface/interface stress. The analytical solution of complex functions of the inhomogeneity, the coating layer, and the infinite matrix is derived by means of the complex variable method. With the aid of the obtained stress fields and the Peach–Koehler formula, the explicit expression of the image force acting on the screw dislocation is obtained. The critical radius of the inhomogeneity where the screw dislocation stays is evaluated. The influence of the interface stresses on the image force and the critical radius of the inhomogeneity is derived. The results indicate that the negative interface stresses attract the dislocation, and the positive interface stresses repel the dislocation. The critical radius of inhomogeneity will increase for considering the negative interface stresses and will decrease for considering the positive interface stresses.     

复合材料中压电螺型位错与含刚性核夹杂的电弹干涉

为了研究压电复合材料中位于基体的压电螺型位错与含共焦椭圆导电刚性核椭圆夹杂的电弹相互作用, 基于复变函数方法, 获得了基体和夹杂区域的精确级数形式解析解。运用广义Peach-Koehler公式, 导出了作用在位错上像力的解析表达式。在此基础上讨论了椭圆刚性核和材料电弹特性对位错像力以及位错平衡位置的影响规律, 同时讨论了压电夹杂和弹性基体的复合情况。结果表明: 椭圆刚性核对位错有着明显的排斥作用, 可以增强硬夹杂对位错的排斥, 减弱软夹杂对位错的吸引; 对于软夹杂, 在界面附近位错存在一个不稳定的平衡位置; 在基体和夹杂的界面上, 像力迅速增大; 当夹杂的剪切模量远小于基体时, 界面附近不会出现位错的平衡位置。     

压电螺型位错与椭圆夹杂界面导电刚性线的干涉效应

研究了无限大压电基体材料中压电螺型位错与含界面导电刚性线椭圆夹杂的电弹耦合干涉问题。运用求解复杂多连通域问题的复变函数方法,获得了椭圆夹杂和基体区域复势函数以及电弹性场的精确级数形式解答。利用广义Peach-Koehler公式导出作用于压电螺型位错上的位错力公式。主要讨论了刚性线几何尺寸和椭圆曲率对位错力的影响规律。分析结果表明:界面刚性线排斥基体中的位错,对靠近椭圆夹杂界面的螺型位错的运动和平衡位置有重要的影响。当刚性线的长度达到临界值,界面刚性线的存在会改变螺型位错与压电椭圆夹杂的干涉规律。椭圆夹杂的压缩系数变大,刚性线尺寸对位错力的影响也越大。     

Long-range interaction of a line dislocation with multiple multicoated inclusions of arbitrary shape

We investigate the long-range elastic interaction of a line dislocation with multiple multicoated two-dimensional inclusions of arbitrary shape. Approximate closed-form solutions are found for the following two situations: (i) an edge dislocation in a composite with all the phases having equal shear modulus but different Poisson’s ratios and (ii) a screw dislocation interacting with an inclusion of arbitrary shape with a properly designed coating layer. The far-field asymptotic expressions of the image force on the dislocation can then conveniently be derived.     

The Interaction between a Piezoelectric Screw Dislocation Dipole and an Elliptic Blunt Crack in Elliptical Inhomogeneity

The interaction problem of a piezoelectric screw dislocation dipole with a confocal elliptic blunt crack in elliptical inhomogeneity subjected to remote anti-plane stress field and in-plane electric field is investigated by using the complex method of elasticity. The exact closed-form solutions of a series of quantities, such as singularity stress field, image force and image torque acting on the center of screw dislocation dipole, stress intensity factor and electric displacement intensity factor of crack tip, energy release rate, and generalized strain energy density are obtained. Then the influence laws of remote load, the dip angle of dislocation dipole, the size of blunt crack, and the material constants on the quantities are analyzed. The numerical results show that the image force, image torque, stress intensity factor, and electric displacement intensity factor make periodic variation as the dip angle of dislocation dipole; the energy release rate of crack tip is negative when subjected to pure electric field, however, it can be positive or negative when subjected to the combined action of mechanical field and electric field; the sharp crack is not easy to expand in some combined action of mechanical field and electric field.     

径向压电圆环中的螺位错分析

研究了径向层状压电复合介质中的螺位错与界面的相互作用。基于扰动的概念和洛朗级数展开的方法,推导了基体和压电环的弹性场和电场,并在此基础上给出了像力的表达式,分析了几何尺寸和材料的相对刚度对像力和界面应力的影响,得到了新的相互作用机理。     

Electro-elastic stress analysis for a wedge-shaped crack interacting with a screw dislocation in piezoelectric solid

The electro-elastic stress investigation on the interaction problem of a screw dislocation near the tip of a semi-infinite wedge-shaped crack in piezoelectric material has been carried out. Explicit closed-form analytical solutions are obtained for the stress intensity factor (SIF) and the electric displacement intensity factor (EDIF) of the crack, as well as the force on dislocation. The derivation is based on the conformal mapping method and the perturbation technique. The dislocation has Burger's vector normal to the isotropic basal plane, with a line force and a line charge being applied at the core of the dislocation. The influence of the location and the wedge angle of the crack on the image force of the dislocation has been discussed in detail. At the same time the effect of the dislocation on the crack behavior has been also examined under different configurations. Two types of PZT materials are used to numerically illustrate the influences of the wedge angle and the location of the dislocation on the image force and the crack intensities. Results obtained in the current study can be fully reduced to various special cases available in the literatures.     

Interaction between screw dislocations and inclusions with imperfect interfaces in fiber-reinforced composites

A three-phase composite cylinder model is utilized to study the elastic interaction between screw dislocations and embedded multiple circular cross-section inclusions (fibers) with imperfect interfaces in composites. By means of complex variable techniques, the explicit solutions of stress and displacement fields are obtained. With the aid of the Peach–Koehler formula, the explicit expressions of image forces exerted on screw dislocations are derived. The equilibrium positions of the appointed screw dislocation near one of the inclusions are discussed for variable parameters (interface imperfection, material mismatch and dislocation position) and the influence of the nearby inclusions and dislocations is also considered. The results show that, if the inclusion is stiffer than the matrix and the magnitude of the degree of interface imperfection reaches the certain value, a new equilibrium position for the screw dislocation in the matrix can always be produced in comparison with the previous solution (the perfect interface). The effect of elastic constants of the inclusion on the image force and the equilibrium position of the appointed screw dislocation is weak when the interface imperfection is strong. It is also seen that the magnitude of the image force exerted on the appointed dislocation caused by multiple inclusions is always smaller than that produced by a single inclusion. The impact of the closer dislocations on the mobility of the appointed dislocation is very significant.     

Viscoelastic interaction between a screw dislocation and a piezoelectric inhomogeneity with an interfacial rigid line

Summary The problem for the interaction between a screw dislocation and a piezoelectric circular inhomogeneity with one interfacial rigid line in a viscoelastic matrix is investigated in this paper. Based on the elastic-viscoelastic correspondence principle, the analytical stress fields and image force for the problem are presented. The results show that the influences of the viscoelastic properties of the material together with rigid line's length and inhomogeneity's piezoelectricity upon the time-dependent image force are significant. The time-dependent image force evolves toward a constant value as time elapses. Results presented in this paper are in agreement with the previous solution as special cases.     

On the interaction between a generalized screw dislocation and circular-arc interfacial rigid lines in magnetoelectroelastic solids

The interaction of a generalized screw dislocation, which is located inside either the inclusion or the matrix, with circular-arc interfacial rigid lines under remote antiplane shear stresses, in-plane electric and magnetic loads in linear magnetoelectroelastic materials is dealt with. By using the complex variable method, the general solutions of the physical problem are presented in this paper. The closed-form solutions for stresses, electric displacement fields and magnetic induction fields are derived explicitly for the interface with a finite rigid line. The image forces acting on the generalized screw dislocation are then calculated by using the generalized Peach–Koehler formula. The influence of the length and the location of the rigid line as well as the material mismatch on the image force is evaluated. Numerical computations and discussions show that, when the length or the position of the interfacial rigid line achieves a critical value, the image force on the dislocation changes its direction due to the existence of the rigid line. In addition, the soft inclusion can repel the dislocation in magnetoelectroelastic materials owing to their intrinsic magnetoelectromechanical coupling behavior.     

Analysis of an orthotropic strip containing multiple defects bonded between two piezoelectric layers

In this paper, the problem of multiple defects in an orthotropic layer bonded between two piezoelectric layers is considered. The analysis is based on the stress fields caused by Volterra-type screw dislocation in the orthotropic strip. The solution for the dislocation is obtained by means of the complex Fourier transform. The dislocation solution is then employed as strain nuclei to derive singular integral equations for a medium weakened by multiple defects. These equations, as a class of Cauchy singular equations, are solved numerically for dislocation density functions. A number of examples is given for various crack orientations and material properties. At the end, it is shown that the effect of the properties and defect geometries on the stress intensity factors and hoop stress for cavities can be highly significant.     

磁电弹双材料条中螺位错与界面边裂纹的相互作用

研究半无限长磁电弹双材料条中螺位错与界面边裂纹的相互作用。基于镜像原理和保角变换方法,得到了弹性场、电场和磁场的解析解,给出了应力、电位移、磁感应强度、应力强度因子以及像力的显函表达式。以压电-压磁双材料条形介质为例,分析了应力场、电位移和磁感应强度的分布特性,讨论了几何参数、压电和压磁效应对应力强度因子和像力的影响。     

Dynamic stress from a cylindrical inclusion buried in a functionally graded piezoelectric material layer under electro-elastic waves

This paper presents a theoretical method to investigate the multiple scattering of electro-elastic waves and dynamic stress around a subsurface cylindrical inclusion in a functionally graded piezoelectric material layer bonded to homogeneous piezoelectric materials. The analytical solutions of wave fields are expressed by employing wave function expansion method, and the expanded mode coefficients are determined by satisfying the boundary conditions around the inclusion. The image method is used to satisfy the mechanical and electrically short conditions at the free surface of the structure. Through the numerical solutions of dynamic stress concentration factors around the inclusion, it is found that when the cylindrical inclusion possesses higher rigidity and greater piezoelectric constant than the two phases of functionally graded materials, the dynamic stress around the inclusion increases greatly. When the distance between the surface of the structure and the inclusion is smaller, the effect of the properties of the inclusion becomes greater. When the cylindrical inclusion possesses lower rigidity and smaller piezoelectric constant than the two phases of functionally graded materials, the maximum dynamic stress shows little difference; however, the variation of the distribution of the dynamic stress around the inclusion is greater. The effect of the properties of the inclusion on the dynamic stress around the inclusion is greater than that on the electric field. The effects of wave frequency on the dynamic stress and electric field are also examined.