| Summary: | 碩士 === 國立成功大學 === 機械工程學系碩博士班 === 98 === The problem of a three-dimensional interface crack between two anisotropic materials is investigated by using finite element method with the virtual crack closure technique. Fracture mechanics parameters, including the strain energy release rate, the stress intensity factors and phase angles along the interface crack front are obtained by using the numerical approach. In this approach, the crack closure integrals and the strain energy release rate are first calculated from the nodal load and displacement solutions of the singular quarter-point crack-tip finite elements. A set of algebraic equations relating the crack closure integrals and the stress intensity factors is derived from the asymptotic displacement and stress fields around the interface crack tip, and is applied to determine the stress intensity factors and the corresponding phase angles. The issue of oscillating stress intensity factors associated to the bimaterial interface is overcome by normalizing the stress intensity factors to a characteristic length such that the stress intensity factors have a unit of (stress)x(length)^(1/2). Alternative procedures are also described for the cases of crack under inner pressure and crack faces under large-scale contact. Validation for the procedure is performed by comparing numerical results to analytical solutions for the problems of interface crack subjected to either remote tension or mixed loading. The numerical approach is then applied to study the problem of an anisotropic bimaterial interface crack with circular-shaped crack front. Solutions for an embedded penny-shaped crack, a semi-circular edge crack, or a quarter-circular corner crack on the interface of two cross-ply composite layers under either mode-I or mixed-moded remote loadings are presented as application examples of the proposed approach.
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