Virtual Crack Closure Technique And Discrete Cohesive Zone Model For Line Type Cracks On Surface

Recently, ship structures are becoming larger in size and lighter in weight that increases the risk of hull strength and sailing safety. Therefore, to avoid the similar accidents of all-welded ships broken during the World War II, a great attention must be paid to the fracture strength of ship structures.The current approach to deal with this topic is to analyze the details isolated from the global hull model with the idea of sub-structure modeling. However, this approach is inconvenient in several aspects: each detail must be considered which leads to huge amount of analyzing works; the connection between the isolated details and the global model is not sufficiently established; even for a typical detail itself, a fine FEA mesh are needed around the crack tip which increases the problem size significantly. But, in reality, the fatal cracks to the ships and ocean structure are those with structure level dimensions. Analysis on structure level cracks needs the support of the numerical method and the well-posed numerical method should be that it is insensitive to the element size with tolerable computing time and storage space.This thesis will develop a numerical simulation technique which can analyze the fracture behavior of ship structures at global level in a quick and effective manner. To deal with structure level cracks, a number of practical simulation tools will be developed based on fracture mechanics and finite element method. Then, these tools will be verified and validated through some examples to show their reliability and feasibility. These simulation tools include the virtual crack closure technique for line type crack on surface, the virtual crack closure technique using zigzag propagation path and the discrete cohesive zone model.These numeric technology of direct analysis method presented in this thesis will be expected insensitive to the element size without arranging fine mesh around the crack tip. Moreover, no adaptive mesh is required during the simulation so that a great amount of time can be saved. In general, the proposed technique makes it possible to analyze the fracture strength of ship structures at global level.