Numerical Study On Plastic Zone Size Ahead Of The Crack Tip And Fatigue Performance Of Submarine Model

The submarine structures are subjected to more severe load with continuing increase of its diving depth. It is therefore necessary to take full scope evaluation of the fatigue performance during the up and down process. As a welded structure, submarine inevitably has inner defects which can be regard as the seeds of a crack. Crack propagation is affected by many factors, among which, the crack tip plastic zone attracts a lot of attention. For its impact on direction of crack initiation, crack tip displacement and crack opening stress, the crack tip plastic zone has been used as a controls parameter in many crack propagation models, even more, as a driving force in some models.The plastic zone size ahead of the crack tip is relative to three dimensional constraint which is depend upon not only the plate thickness but also the load as well as material property. That means it would have great limitation in applications when simply classifying a plate to plane stress or plane strain condition according to its thickness. There is no simple and convenient formula in precisely calculating the plastic zone size till now when three dimensional effect being considered.The cone-cylinder joint is probably suffering fatigue failure, combined bending and compression stress make it unique and safer than those undergoing pure tension stress. Besides, for a welding structure, it necessary to allow for the residual stress brought by welding process and the stress concentration effect due to geometric change. The load spectrum of submarine can be simplified into some well known distributions, like normal...