This paper deals with the stress concentration problem of an ellipsoidal inclusion of revolution in a semi-infinite body under biaxial tension. The problem is formulated as a system of singular integral equations with Cauchy-type or logarithmic-type singularities, where unknowns are densities of body forces distributed in the r-and z-directions in semi-infinite bodies having the same elastic constants as the ones of the matrix and inclusion. In order to satisfy the boundary conditions along the ellipsoidal boundary, four fundamental density functions proposed in [24,25] are used. The body-force densities are approximated by a linear combination of fundamental density functions and polynomials. The present method is found to yield rapidly converging numerical results for stress distribution along the boundaries even when the inclusion is very close to the free boundary. The effect of the free surface on the stress concentration factor is discussed with varying the distance from the surface, the shape ratio and the elastic modulus ratio. The present results are compared with the ones of an ellipsoidal cavity in a semi-infinite body.
IntroductionStructural materials usually contain some defects in the form of cracks, cavities, and inclusions. For various metals, the size, shape, and distribution of microdiscontinuities have been investigated e.g. in [1,2]. To evaluate their defects on the strength, it is fundamental to know the stress concentration of elliptical and ellipsoidal inclusions, which cover many particular cases, such as linear, circular, and spherical defects. In earlier studies, ellipsoidal inclusions have been studied by several researchers, [3][4][5][6]. Also, interactions among elliptical and ellipsoidal inclusions have been discussed in [7][8][9][10][11][12][13][14][15][16][17]. Several elasticity problems involving a half-space with a spheroidal inclusion have been studied in [18][19][20][21][22]. However, there has been little discussion about ellipsoidal inclusions in a half-space.In this study, therefore, stress concentration of an ellipsoidal inclusion of revolution in a semi-infinite body under bi-axial tension is considered. An ellipsoidal inclusion can be regarded as a general model of the defect because many kinds of defects can be expressed by changing the elastic modulus ratio and the shape ratio of the inclusion. The body-force method, [23], is used here to formulate the problem as a system of singular integral equations. Then, the unknown body-force densities are approximated by a linear combination of fundamental density functions and polynomials [24][25][26]. The results will be compared with the ones in [18][19][20][21][22] by setting the elastic modulus of the inclusion E I ¼ 0, see Fig. 1. It will be shown that the present method gives smooth variations of interface stresses along the boundary.
Analysis and numerical procedureConsider a semi-infinite body under biaxial tension having an ellipsoidal inclusion as shown in Fig. 1. The body force method is used to formulate the problem...