Scattering of anti-plane shear waves by a partially debonded piezoelectric circular cylindrical inclusion

Summary This paper presents an analysis of the scattering of anti-plane shear waves by a single piezo-electric cylindrical inclusion partially bonded to an unbounded matrix. The anti-plane governing equations for piezoelectric materials are reduced to Helmholtz and Laplacian equations. The fields of scattered waves are obtained by means of the wave function expansion method when the bonded interface is perfect. When the interface is partially debonded, the region of the debonding is modeled as an interface crack with non-contacting faces. The electric permeable boundary conditions are adopted, i.e. the normal electric displacement and electric potential are continuous across the crack faces. The crack opening displacement is represented by Chebyshev polynomials and a system of equations is derived and solved for the unknown coefficients.     

On self-similarly expanding Eshelby inclusions: Spherical inclusion with dilatational eigenstrain

For a subsonically self-similarly expanding spherical inclusion with dilatational transformation strain in a linear elastic solid, the governing system of partial differential equations is shown to be elliptic under scaling of uniform stretching of the variables, and the resulting elliptic equation is solved by satisfying the Hadamard jump conditions on the moving boundary. The solution has the Eshelby constant stress property for the interior domain, and can thus be used for the expanding inhomogeneity with transformation strain according to Eshelby (1957). The driving force on the moving boundary is also obtained.     

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.     

Two concentric circular arc cracks in anti-plane strain

The behaviour of two concentric circular arc cracks in anti-plane strain has been analyzed by treating them as pile-ups of screw dislocations. The external stress required to extend the shear cracks in a brittle manner has been determined from the analysis.     

Plastic extension of a shear crack inside a circular inclusion

The plastic relaxation of a shear crack situated at the interface inside a circular inclusion in an infinite matrix has been analyzed by treating it as a double pile-up of screw dislocations and the plastic zones at either tip of the crack as giant screw dislocations. The ratio of applied stress to yield stress and the magnitude of the Burgers vector of the giant screw dislocations which represent the relative displacement of the crack faces at the tips have been related to the crack parameters. Using a critical relative displacement of the crack faces at the tip of the crack as the criterion for brittle extension of the crack, the tendency of the shear crack to extend into the inclusion or into the matrix has been determined. The effect of shear modulus and size of the inclusion on the behaviour of the plastic zones at either tip of the crack has been discussed. Conclusions are made on the fracture behaviour of a circular inclusion in an infinite matrix.

---

Résumé On a analysé la relaxation plastique d'une fissure de cisaillement située à l'interface d'une inclusion circulaire dans une matrice infinie en traitant cette fissure comme un double empilement de dislocation-vis, et les zônes plastiques à chacune de ses extrémités comme des dislocations-vis géantes. On a mis en relation avec les paramètres de la fissure le rapport de la contrainte appliquée à la limite d'écoulement, et la grandeur du vecteur de Burgers des dislocations-vis géantes, qui représente le déplacement relatif des faces de la fissure à ses extrémités.En utilisant comme critère d'extension fragile de la fissure un déplacement relatif critique des faces de la fissure à ses extrémités, on a pu déterminer si la fissure de cisaillement avait tendance à se développer dans l'inclusion ou dans la matrice.On discute l'influence du module de cisaillement et de la dimension de l'inclusion sur le comportement des zônes plastiques à chaque extrémité de fissure.On tire des conclusions sur le comportement à la rupture d'une inclusion circulaire dans une matrice infinie.

     

Plastic relaxation of a shear crack at a circular inclusion

International Journal of Fracture -     

The stress intensity factor Green's function for a crack interacting with a circular inclusion

The Green's function is constructed for the stress intensity factor due to the unit dipole force applied to the crack surface in the presence of a circular inclusion in front of the crack tip. An explicit functional form of the Green's function is proposed in terms of dipole force location, Young's modulus ratio and the inclusion size and position with respect to the crack tip. This is achieved through a combination of the dimensional analysis and parametric studies by means of the finite element method. The purpose of this paper is to provide the basis for further studies of a crack interaction with an array of microdefects and/or inclusions.     

Dynamic stress from a subsurface cylindrical inclusion in a functionally graded material layer under anti-plane shear waves

The multiple scattering of shear waves and dynamic stress resulting from a subsurface cylindrical inclusion in a functionally graded material (FGM) layer bonded to homogeneous materials are investigated, and the analytical solution of this problem is derived. Image method is used to satisfy the traction free boundary condition of the FGM layer. The analytical solutions of wave fields around the actual and image inclusions are expressed by employing wave functions expansion method, and the expanded mode coefficients are determined by satisfying the continuous boundary conditions around the inclusions. Through the numerical solutions of dynamic stress concentration factors (DSCFs) around the inclusion, the effects of the position of the inclusion in the material layer, the properties of the inclusion, and the properties of the two phases of composites on the DSCFs are analyzed. Analyses show that when the cylindrical inclusion is stiffer than the two phases of FGMs, 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 is softer than the two phases of FGMs, the maximum dynamic stress shows little difference; however, the variation of the distribution of the dynamic stress around the inclusion is greater.     

An eccentric crack normal to two interfaces among three layers in a rectangular sheet under anti-plane shear

Application of the basic theorem of the Fourier cosine transform and Fourier sine series to this study, we can find the general solution of an eccentric crack normal to two interfaces among three layers in a finite rectangular sheet loaded by an arbitrary longitudinal shear stress. It is of interest to note that the stress intensity factor of this problem is independent of material constants of the three-layered system. I think the conclusion is very important for designers and experimenters.     

A partially debonded circular inclusion interacting with a point singularity: A classical problem revisited

The classical problem for a partially debonded circular inhomogeneity is revisited. The interaction of the interfacial crack and a point singularity such as a point force and/or a dislocation is dealt with. Also the circular arc-shaped interfacial crack under remote stress is solved. This problem has been solved by many researchers for the cases of various loading types. However, lack of generality in the solution technique together with too complicated form of the solution makes it hard to grasp the structure of the solution. Based on the recently published technique for a perfectly bonded circular inhomogeneity, this problem is revisited. The resulting form of the solution is very simple, therefore, its structure is easily understood. Due to the merit of the present method, the image force on the edge dislocation near the tip of the interfacial crack is easily obtained.     

Eshelby tensors for a spherical inclusion in microelongated elastic fields

Eshelby tensors are found for a spherical inclusion in a microelongated elastic field. Here, a special micromorphic model is introduced to describe the damaged material which defines the damage as the formation and the growth of microcracks and microvoids occurred in the material at the microstructural level. To determine the new material coefficients of the model, an analogy is established between the damaged body and the composite materials and then Mori–Tanaka homogenization technique is considered to obtain overall material moduli. Following this idea, the determination of the Eshelby tensors which establish the relation between the strains of the matrix material and of the inclusion becomes the first task. Introducing the concept of eigenstrain and microeigenstrain, the general constitutive theory is given for a homogeneous isotropic centrosymmetric microelongated media with defects. Then by the use of Green’s functions, micro and macro elastic fields are presented for the case of spherical inclusions embedded in an infinite microelongated material. Thus, the Eshelby tensors are obtained for a microelongated elastic field with a spherical inclusion and it is also shown that the classical Eshelby tensors can be obtained as a limit case of the microelongation.     

Eshelby tensors for an ellipsoidal inclusion in a micropolar material

Micropolar Eshelby tensors for an ellipsoidal inclusion are derived in an analytical form, which involves only one-dimensional integral. The numerical evaluation of the Eshelby tensors are also performed, it is found that the micropolar Eshelby tensors are not uniform in the ellipsoidal inclusion, however, their variations over the ellipsoidal domain are not significant. When size of inclusion is large compared to the characteristic length of the micropolar material, the micropolar Eshelby tensor is reduced to the classical one. It is also demonstrated that for a general ellipsoidal inclusion a uniform eigenstrain or eigentorsion produces on average only nonzero strain or torsion, and the average Eshelby relations are uncoupled.     

Plastic zone correction on a Zener–Stroh crack interacting with a circular inclusion in ductile materials

Elastic–plastic stress analysis on a matrix Zener–Stroh crack interacting with a circular inclusion (fibre) in fibre‐reinforced composites has been carried out. The Zener–Stroh crack is initiated near the fibre in the pure matrix. Plastic zone correction is introduced the first time for such a crack–inclusion interaction problem so that the fracture behaviour can be analysed more accurately. To determine the plastic zone sizes, a generalized Irwin model is proposed for the mixed‐mode problem where the Von Mises stress yielding criterion is employed. Different to a Griffith crack, a Zener–Stroh crack propagation always occurs from the sharp tip whose relative position to the inclusion has great effect on the elastic–plastic fracture behaviour of the crack. In our study, the plastic zone size (PZS), crack tip opening displacement (CTOD) and effective stress intensity factor (SIF) are evaluated by solving the formulated singular integral equations. Through the numerical examples, the influence of the inclusion (fibre) shear modulus, crack–inclusion distance and the crack sharp tip position on the fracture behaviour of the crack is discussed. It is found that the shear modulus ratio and the crack–inclusion distance have great effect on the normalized values of PZS and CTOD, but the effects highly depend on the crack sharp tip position.     

Analysis of a kinked crack in anti-plane shear

A semi-infinite kinked crack in anti-plane shear is analyzed. The problem is formulated using the Mellin transform, and solved by the Wiener-Hopf technique. A closed form solution for displacement is obtained, from which the stress intensity factor is calculated. Particular emphasis is put on the stress intensity factor as the kinked length approaches zero, where two limit processes (both the distance from the crack tip and the kinked length approaching zero) are involved. It is found that the stress intensity factor depends on the order of performing the two limit processes. The results are compared with those by previous researchers. Also the energy release rate for this problem is computed.