Development of a Computor Code for Crack Path Prediction in Ship Structures

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In stiffened plate structures cracks are often formed at the intersection of the stiffeners, where severe local stress concentrations and welding residual stresses exist. Since the local stress distribution is rather complicated along the crack trajectory, crack curving is one of the essential features of the problem.A computational scheme has been developed for the crack path prediction, which is performed by the step-by-step stress analysis ahead of the crack tip and the prediction of a curved increment of the crack growth by the use of analytically obtained crack path in the neighbourhood of the crack tip. As a fracture criterion we enploy the local symmetry condition which reqires the Mode II stress intensity factor vanishing along the crack path. For the efficient finite element data handling, and interactive and graphic pre-and post-processing of the data, which are transmitted to and from host computors, is introduced by the use of a personal computing system.Using this computational code, considerations are made for a plate having an edge crack approaching a circular hole. It is numerically predicted that the hole can stop the crack growth only when the minimum distance between the initial crack line and the edge of the hole is less than the hole radius. Curved brittle fracture paths near the various welded joints are numerically examined for the first time in the history, and straight and curved crack paths are obtained under the strong influence of the welding residual stresses.This method will also be applicable to fatigue crack propagation, and will become one of the essential computational tools of the fracture control of welded structures.