压电螺位错与含界面裂纹圆形涂层夹杂的干涉

研究位于基体或夹杂中任意点的压电螺型位错与含界面裂纹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一般解答. 典型例 子给出了界面含有一条裂纹时，复势函数的精确级数形式解. 基于已获得的复势函数和广 义Peach-Koehler公式，计算了作用在位错上的像力. 讨论了裂纹几何条件，涂层厚度和材 料特性对位错平衡位置的影响规律. 结果表明，界面裂纹对涂层夹杂附近的位错运动有很大 的影响效应，含界面裂纹涂层夹杂对位错的捕获能力强于完整粘结情况；并发现界面裂纹长 度和涂层材料常数达到某一个临界值时可以改变像力的方向. 解答的特殊情形包含了以 往文献的几个结果.     

Interaction between a rigid inclusion and a line crack under uniform heat flux

The thermoelastic displacement boundary value problem for a rigid inclusion interacting with a line crack in an infinite plane subjected to a uniform heat flux is studied, in which the rigid body rotation of the inclusion is considered. To solve the prescribed problem, we use the principle of superposition to decompose it into two groups of problems, which are further reduced to several basic subproblems including Green’s functions of edge dislocation and heat source couple, as well as the problem of a plane containing the inclusion under uniform heat flux and the problem of the inclusion subjected to a small rotation. The problems are solved using the complex variable method along with the rational mapping function technique. The variations of the stress intensity factors at the crack tips and the rigid body rotation angles with various crack lengths and heat flux angles are shown. The effects of the inclusion shape and size are also investigated.     

Dynamic stability of a propagating crack

In this work we investigate the stability of a straight two-dimensional dynamically propagating crack to small perturbation of its path. Willis and Movchan (J. Mech. Phys. Solids 43 (1995) 319; J. Mech. Phys. Solids 45 (1997) 591) constructed formulae for the perturbations of the stress intensity factors induced by a small three-dimensional dynamic perturbation of a nominally plane crack. Their solution is exploited here to derive equations for the in-plane and out-of-plane perturbations of the crack path making use of the Griffith fracture criterion and the principle of “local symmetry” (i.e the crack propagates so that local K_II=0). We consider a crack propagating in a body loaded by a pair of point body forces and subjected to a remote uniaxial stress, aligned with the direction of the unperturbed crack. We assume that the loading follows the crack as the crack advances and is such that the unperturbed crack is subjected to Mode I loading. We perform an analysis of the stability of the dynamic crack in a similar way as in earlier work (Obrezanova et al., J. Mech. Phys. Solids 50 (2002) 57) on the quasistatically advancing crack. We present numerical results illustrating the influence of the crack velocity on the crack stability. Numerical computations of the possible crack paths have been performed which show that at velocities of crack propagation exceeding about one-third of the speed of Rayleigh waves the crack may admit one or more oscillatory modes of instability.     

ANALYSIS OF A SCREW DISLOCATION INSIDE A CIRCULAR INCLUSION WITH INTERFACIAL CRACKS IN PIEZOELECTRIC COMPOSITES

IntroductionPiezoelectric materials have potentials for use in many modern devices and compositestructures. The presence of various defects, such as inclusions, holes, dislocations andcracks, can greatly influence their characteristics and coupled behavio…     

Energy functional derivative with respect to the length of a curvilinear oblique cut in the equilibrium problem for a Timoshenko plate

This paper describes the dependence of the solution of the equilibrium problem for a Timoshenko plate and the total energy functional of the plate on the perturbation of an oblique crack. The nonlinearity of the problem is caused by the boundary conditions in the form of inequalities (conditions such as the Signorini conditions), which describe mutual nonpenetration of the opposite crack faces. The continuous dependence of the solution of the problem on the perturbation of the crack length is established. A formula for the energy functional derivative of the perturbation of the crack length is obtained.     

Boundary element analysis of interaction between an elastic rectangular inclusion and a crack

The interaction between an elastic rectangular inclusion and a kinked crack inan infinite elastic body was considered by using boundary element method. The new complexboundary integral equations were derived. By introducing a complex unknown function H(t)related to the interface displacement density and traction and applying integration by parts,the traction continuous condition was satisfied automatically. Only one complex boundaryintegral equation was obtained on interface and involves only singularity of order l/ r. Toverify the validity and effectiveness of the present boundary element method, some typicalexamples were calculated. The obtained results show that the crack stress intensity factorsdecrease as the shear modulus of inclusion increases. Thus, the crack propagation is easiernear a softer inclusion and the harder inclusion is helpful for crack arrest.     

三维冲击荷载弹塑性弯曲裂纹张开位移

主要研究冲击载荷作用下的三维弹塑性弯曲裂纹尖端的张开位移问题．综合考虑了冲击作用应力,三维塑性区域边界上正应力与剪应力,利用二阶摄动方法计算了三维弹塑性弯曲裂纹尖端的张开位移．用数值解法计算出三维弹塑性弯曲裂纹尖端张开位移,作图分析了三维弹塑性弯曲裂纹尖端张开位移与三维裂纹体几何尺寸之间的变化关系．三维弹塑性弯曲裂纹尖端张开位移随着三维裂纹体厚度的增大而减小,随着三维裂纹体厚度的均匀增大,三维弹塑性弯曲裂纹尖端张开位移尺寸不断减小,减小的幅度越来越小,最终趋于平面应变状态下的弹塑性弯曲裂纹尖端张开位移尺寸．当三维裂纹体几何尺寸相同时,三维弯曲裂纹尖端动态张开位移随外部冲击载荷的不断增大而逐渐增大,三维弯曲裂纹尖端动态张开位移随动荷系数的增大而迅速增大,建立了一个计算三维弹塑性弯曲裂纹尖端动态张开位移的崭新理论模型．     

Scattering of elastic waves by an inclusion with an interface crack

A method of perturbation is used to derive an integral representation of the displacement field for the scattering of a plane wave from an inclusion with an interface crack. In the long-wave approximation it is shown that the solution of only an associated static problem is required and formal expressions are derived for the scattered far field amplitudes and scattering cross section. In the case of a cylindrical inclusion the solution of the associated static problem is then used to find in a closed form the corresponding expressions for plane incident P- and S-waves.     

Problem of equilibrium of the timoshenko plate containing a crack on the boundary of an elastic inclusion with an infinite shear rigidity

A problem of equilibrium of a composite plate consisting of a matrix and an elastic inclusion with a through crack along the boundary of this inclusion is studied. The matrix deformation is described by the Timoshenko model, and the elastic inclusion deformation is described by the Kirchhoff-Love model. Conditions of mutual non-penetration of the crack edges are imposed on the curve that describes the crack. Unique solvability of the variational problem is proved. A system of boundary conditions on the curve bounding (in the mid-plane) the elastic inclusion is obtained. A differential formulation of the problem equivalent to the initial variational formulation is given.     

Regular Perturbation Methods for a Region with a Crack

The paper considers a model problem for Poisson's equation for a region containing a crack or a set of cracks under arbitrary linear perturbation. Variational formulation of the problem using smooth mapping of regions yields a complete asymptotic expansion of the solution in the perturbation parameter, which is a generalized shape derivative. This global asymptotic expansion of the solution was used to derive representations of arbitraryorder derivatives for the potential energy function, stress intensity factors, and invariant energy integrals in general form and for basis perturbations of the region (shear, tension, and rotation). The problem of the local growth of a branching crack for the Griffith fracture criterion and the linearized problem of optimal location of a rectilinear crack in a body with the energy function as a cost functional were formulated.     

On phase transitions in a domain of material inhomogeneity. II. Interaction of a crack with an inclusion experiencing a phase transition

We pose and study the problem on the interaction between a crack and an inclusion experiencing a phase transition of martensite type. We develop an algorithm for determining the inclusion phase state, which is numerically implemented with the finite element method. This procedure is used to study the inclusion phase transitions in the crack-induced field including the effects of the interaction between the crack and the inclusion. The detailed strain fields are calculated depending on the relative position of the crack and the inclusion, the external field, and the material parameters. It is shown that, for sufficient residual strains arising in the inclusion because of the crack, the inclusion material experiences a phase transition, which, in turn, can change the character of the subsequent crack propagation. We demonstrate that a stress-independent intrinsic phase transition, which can be caused, for example, by a change in the temperature, can also affect the crack propagation path. We also show that the influence of the phase transition induced field on the crack propagation path can be suppressed by the external field.     

Stability of an advancing crack to small perturbation of its path

In this work we investigate the stability of a nominally straight two-dimensional quasistatically growing crack to a small perturbation of its path. Formulae for perturbations of stress intensity factors induced by slight deviation of the crack trajectory were developed by Movchan et al. (Int. J. Solids Struct. 35, 3419) Their solution is exploited to derive an equation for the perturbation of the crack path on the assumption that the crack advances in pure “opening” mode (i.e. local K_II=0). Various types of loading conditions are considered, including a cracked body loaded by a pair of point body forces and a crack whose faces are subjected to given tractions acting in the direction normal to the crack boundary. The body is also subjected to a remotely maintained uniaxial stress, aligned with the direction of the unperturbed crack. The loading is assumed to advance as the crack advances, to maintain the critical value of Mode I stress intensity factor. Numerical computations of possible crack paths have been performed, extending results on crack stability obtained by Cotterell and Rice (Int. J. Fract. 16, 155). The results show that in the case of loading by point body forces the stability of the crack path depends on the positions of the points of application of the applied forces and the magnitude of the applied stress acting parallel to the crack. There exists a critical value of this stress such that the crack path is stable for values less than critical and unstable otherwise. It is shown that the crack is always unstable in the case of point force tractions applied normal to the crack faces.     

含圆形嵌体弹性平面中径向裂纹问题的超奇异积分方程方法

根据含圆形嵌体平面问题在极坐标下的弹性力学基本解,使用Betti互换定理,在有限部积分意义下将问题归结为两个以裂纹岸位移间断为基本未知量、对于Ⅰ型和Ⅱ型问题相互独立的超奇异积分方程,对含圆形嵌体弹性平面中的径向裂纹问题进行了研究.根据有限部积分原理,建立了问题的数值算法.计算结果表明,嵌体半径、裂纹位置及材料剪切弹性模量等都对裂纹应力强度因子具有较为明显的影响.     

Stable growth of a crack interacting with a circular inclusion

The problem of failure of a plate containing a circular inclusion and a crack is studied. The crack is oriented along a diameter of the inclusion and the plate is subjected to a remote uniaxial stress perpendicular to the crack axis. The process of slow stable crack growth from initiation to termination is studied by the strain energy density theory. The crack growth is simulated by predicting finite increments of crack extension when material elements near the crack tip absorb a critical amount of strain energy density level, . Unstable crack growth occurs when the strain energy density factor S reaches a critical value where r_c is the critical size of the final crack increment prior to instability. The stress at crack initiation and the critical stress and crack length at failure are determined. The influence of the mechanical properties of the plate and the inclusion, the relative position of the inclusion and the crack and the crack length on the characteristic quantities of stable crack growth is analyzed. The dependence of the stable crack growth process on the loading rate is also investigated. Results are displayed in graphical form.     

The deformation of the front of a 3D interface crack propagating quasistatically in a medium with random fracture properties

One studies the evolution in time of the deformation of the front of a semi-infinite 3D interface crack propagating quasistatically in an infinite heterogeneous elastic body. The fracture properties are assumed to be lower on the interface than in the materials so that crack propagation is channelled along the interface, and to vary randomly within the crack plane. The work is based on earlier formulae which provide the first-order change of the stress intensity factors along the front of a semi-infinite interface crack arising from some small but otherwise arbitrary in-plane perturbation of this front. The main object of study is the long-time behavior of various statistical measures of the deformation of the crack front. Special attention is paid to the influences of the mismatch of elastic properties, the type of propagation law (fatigue or brittle fracture) and the stable or unstable character of 2D crack propagation (depending on the loading) upon the development of this deformation.     

Antiplane interaction of line crack with an arbitrarily located elliptical inclusion

The antiplane problem of the interaction between a main crack and an arbitrarily located elastic elliptical inclusion near its tip is addressed in the current study. The analysis is based on the use of the complex potentials for the antiplane problem, Laurent series expansion method and an appropriate superposition scheme. The stress intensity factor at the main crack is obtained in a general series form. Explicit asymptotic solutions are also derived by using a perturbation technique and retaining the leading order terms in series expansion. The present solutions are shown to coincide with the Taylor expansion of exact solutions for special cases available in the literature. Discussed are changes in the crack tip stress intensity which can be enhanced or suppressed depending on the location of the elliptical inclusion. The explicit solutions provided herein are well suited for the further quantitative analysis of toughening mechanisms in ceramic composite materials.     

Thermal stress analysis of a three-dimensional anticrack in a transversely isotropic solid

A three-dimensional analysis is performed for an infinite transversely isotropic elastic body containing an insulated rigid sheet-like inclusion (an anticrack) in the isotropy plane under a remote perpendicularly uniform heat flow. A general solution scheme is presented for the resulting boundary-value problems. Accurate results are obtained by constructing suitable potential solutions and reducing the thermal problem to a mechanical analog for the corresponding isotropic problem. The governing boundary integral equation for a planar anticrack of arbitrary shape is obtained in terms of a normal stress discontinuity. As an illustration, a complete solution for a rigid circular inclusion is obtained in terms of elementary functions and analyzed. This solution is compared with that corresponding to a penny-shaped crack problem.     

Shape and topology sensitivity analysis for cracks in elastic bodies on boundaries of rigid inclusions

We consider an elastic body with a rigid inclusion and a crack located at the boundary of the inclusion. It is assumed that nonpenetration conditions are imposed at the crack faces which do not allow the opposite crack faces to penetrate each other. We analyze the variational formulation of the problem and provide shape and topology sensitivity analysis of the solution in two and three spatial dimensions. The differentiability of the energy with respect to the crack length, for the crack located at the boundary of rigid inclusion, is established.     

A crack along the interface of a circular inclusion embedded in an infinite solid

The two-dimensional problem of an arc shaped crack lying along the interface of a circular elastic inclusion embedded in an infinite matrix with different elastic constants is considered. Based on the complex variable method of Muskhelishvili, closed-form solutions for the stresses and the displacements around the crack are obtained when general biaxial loads are applied at infinity. These solutions are then combined with A.A. Griffith's virtual work argument to give a criterion of crack extension, namely the de-bonding of the interface. The critical applied loads are expressed explicitly in terms of a function of the inclusion radius and the central angle subtended by the crack arc. In the case of simple tension the critical load is inversely proportional to the square-root of the inclusion radius. By analyzing the variation of the cleavage stress near the crack tip, the deviation of the crack into the matrix is discussed. The case of uniaxial tension is worked out in detail.     

Electroelastic interaction between a piezoelectric screw dislocation and a circular inhomogeneity with interfacial cracks

A piezoelectric screw dislocation in the matrix interacting with a circular inhomogeneity with interfacial cracks under antiplane shear and in-plane electric loading at infinity was dealt with. Using complex variable method, a general solution to the problem was presented. For a typical case, the closed form expressions of complex potentials in the inhomogeneity and the matrix regions and derived explicitly when the interface containsthe electroelastic field intensity factors weresingle crack. The image force acting on the piezoelectric screw dislocation was calculated by using the perturbation technique and the generalized Peach-Koehler formula. As a result, numerical analysis and discussion show that the perturbation influence of the interfacial crack on the interaction effects of the dislocation and the inhomogeneity is significant which indicates the presence of the interfacial crack will change the interaction mechanism when the length of the crack goes up to a critical value. It is also shown that soft inhomogeneity can repel the dislocation due to their intrinsic electromechanical coupling behavior.