Crack Propagation Analysis of Anisotropic Bi-materials using the BEM

• Main Authors: Chia-HueiTu, 涂家輝
• Other Authors: Chao-Shi Chen
• Format: Others
• Language: en_US
• Published: 2010
• Online Access: http://ndltd.ncl.edu.tw/handle/28832920313213446992

博士 === 國立成功大學 === 資源工程學系碩博士班 === 99 === This dissertation presented a numerical technique based on the boundary element method (BEM) for the analysis of linear elastic fracture mechanics (LEFM) problems on stress intensity factor, SIFs, and modeling crack propagation path involving anisotropic bi-materials. The most outstanding feature of this analysis is that it is a single domain method, and yet it is very accurate, efficient and versatile, i.e. Material properties in the medium can be anisotropic as well as isotropic. Problem domain can be finite, infinite or semi-infinite. Cracks can be of multiple, branched or internal type with a straight shape. Furthermore, the body force case can also be analyzed. The present BEM technique is an extension of the work by Chen (1996) and is such that the displacement and traction integral equations are collocated on the outer boundary and on one side of the crack surface, respectively. This single-domain BEM formulation originally applies to a homogeneous material. This thesis combines it with the Green’s functions of bi-materials (Pan and Amadei, 1999). Then the new formulation can be extended to anisotropic bi-materials. The complete Green’s functions for anisotropic bi-materials are also derived and implemented into the boundary integral formulation so that discretization along the interface can be avoided except for the interfacial crack part. A special crack-tip element (Gao et al., 1992) is introduced to capture exactly the crack-tip behavior. In addition, the BEM formulation combined with the maximum tangential stress (MTS) criterion (Sih et al., 1965) that can be used to predict the crack initial angle and to simulate the propagation path of crack tips. A computer program with the formula translation (FORTRAN 90) code has been developed to effectively calculate the crack initiation angle, propagation path, and stress intensity factors (SIFs) in an anisotropic bi-material. This BEM program has been verified and shown good accuracy compared with the previous researches. Numerical examples are presented for the calculations of stress intensity factors for a straight crack with various locations in both finite and infinite bi-materials. It is found that very accurate results can be obtained by the proposed method even with relatively simple discretization. The results of numerical analysis also show that material anisotropy can greatly affect the stress intensity factor. Besides, a cracked straight through Brazilian disc (CSTBD) of bi-material specimens was made to conduct the Brazilian test under segmental loading. The result shows that the numerical analysis can predict relatively well for the direction of crack initiation and the path of crack propagation.