| Summary: | 博士 === 國立臺灣科技大學 === 營建工程系 === 89 === This paper applies the method of self-similar potentials to analyze the dynamic behaviors of the problems of mode-I, mode-II, and mode-III cracks propagating nonsymmetrically and the phenomenon of mode-I crack propagating with a constant speed subjected to a concentrated load on the crack surface. It is assumed that an unbounded homogeneous isotropic elastic material is at rest for time ■. However, for time ■, a central crack starts to extend from zero length along the x-axis. For nonsymmetric extension, on the crack surfaces of ■, there exists uniform distributed load such that the rightmost crack tip propagates with speed ms, while the leftmost crack tip with speed s, where ■ and is constant. The problem of mode-I crack propagating with a constant speed subjected to a concentrated load on the crack surface is not a self-similar problem. However, the method of self-similar potentials in conjunction with superposition can be successfully applied if the origin shift and the time delay are considered.
After the complete solution is obtained, attention is focused on the crack surface displacements and dynamic stress intensity factors. The results of this study show that the DSIF is equal to the static SIF when the crack-tip speed is zero, and DSIF is zero as the crack-tip speed approaches the Rayleigh-wave speed. Moreover, the combination of SSP method and the superposition scheme can be applied to the expanding uniformly distributed load acting on a portion of the crack surfaces.
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