| The weld joint of cone-cylinder in the submarine was placed in high stress regions, so it was affected by the high stress. At the same time it was affected by the stress concentration and the residual stress etc at the weld. Then the weld joint of cone-cylinder is one of the hot spot of fatigue failure in the submarine pressure shell. The weld joint of cone-cylinder has initialized crack inevitably and the crack was enlarged by the influence of exterior load. So the fatigue enlarge life of the initialized crack was the fatigue life of the submarine structure.When we calculated fatigue life of the submarine structure by using the Fracture Mechanics, not only we need consider the influence of compressing stress, welding joint stress concentration, residual stress, mean stress and the crack closure effect etc at weld toe of submarine, but also we must make sure the length of the initialized crack. In a general way, there are a lot of ways to do this, for example, the lower limit of the apparatus' s sensitive, the definition of the seed moment in Engineering, the standard of weld line and the statistical distribution of crack etc. Aimed at the technical characteristic of the 980 steel which was used on the submarine, we can give the length of initialized crack to calculate the fatigue life of submarine structure.Aimed at 1/2 model of 921 steel submarine, the calculated results that were calculated by using three kinds of method respectively were compared with the model data, furtherly perfected the ways of calculating the fatigue life of submarines using the Fracture Mechanics and provide basis for the refining of the terms of fatigue strength included in the present submarine structure design calculation rules.
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