A Study on the crack initiation strength of Ship Hull Structure after Buckling

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It is well known that ship hull structural members might buckle due to overloads, when they are subjected to the stormy weather, or the plate thickness wastes owing -to corrosion and ageing deterioration. Since the parts at the compressive sides of the buckled structural members, in other word, the parts with large compressive stains become brittle, and the fracture toughness decreases, it is of high possibility that cracks are initiated in advance. That is to say, it is quite often that the buckled structural members would result in the serious fracture accidents. At present, some serious fracture accidents of the large ships due to this cause have been reported.In this research, during three years from 1995 to 1997, the achievements including the various test results with four kinds of steel plates and the results of elastoplastic large deformation analysis by Finite Element Method, are summarized as follows.1. The effects of the axial compressive prestrains on the mechanical properties and fracture toughness have been made clear.2. The crack initiation strength (the small crack initiation criteria) of the strip specimens buckled only once has been quantitatively evaluated.3. The crack initiation strength and fracture strength of the strip specimens and the fillet welded specimens under the cyclic bending loads have been made clear.It is can be said that the fundamentals of Fracture Controlled Design Method are established based on the results of this research, by which the serious fracture accidents of the structures would be prevented. Moreover, although some researches on the material deteriorations due to the compressive prestrains have been done, this might be the firsttime that the crack initiation strength is evaluated quantitatively.