Fracture of Stiffened Shell Plating caused by Multiple Site Damage

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Crack growth of a single or periodical array of cracks initiated at the stiffeners in a stiffened panel hasbeen investigated. Using stiffened panel specimens, fatigue crack propagation tests have been carried out. The corresponding numerical simulation has also been performed, and the results have shown that in case of stiffened panel with multiple cracks, the crack growth rate is higher compared with that witha single crack, because the multiple damaged stiffeners increase the stress intensity factors ahd also the adjacent cracks interact with each other for the case of multiple cracks. For a deck structure of an actual ship, the ratio of the crack growth lives for multiple site damage (MSD) cracks and for asingle site damage (SSD) crack have been studied. It is found that the crack propagation rate of MSD is several times higher than that of SSD .In the second part of the study, a testing apparatus has been designedand produced in order to examine the final unstable failure of a stiffened panel with MSD under excessive lateral pressure. A preliminary test has beencarried out by using a aluminum plate specimen with a single crack. The lateral pressure, strain, and crack velocity of the specimen were measured successfully.In the third part of the study, a general theory of cracking formation of a system of interacting cracks in heterogeneous materials is proposed for quasi-static brittle fracture under a monotonic loading condition and for fatigue crack propagation under a combined stress condition. Based on the present theory, a computational method for the prediction of the cracking formation of a system of interacting cracks is developed, in which a step-by-step formation of a cracking pattern is predicted by using the finite element method taking account of the interaction of all active (extending) cracks. Numerical results are given, and the validity of the method are confirmed.