Probabilistic Fatigue Life Prediction for Ship Structures Using Fracture Mechanics

The design of steel structures against fatigue requires the consideration of fatigue damage accumulation in the form of fatigue crack growth analysis and prediction. Fatigue is an important criterion to evaluate the adequacy of ship structural details, and the methods for prediction of fatigue life taking into account the crack growth are becoming of great interest This paper provides a methodology for ship structure fatigue analysis based on probabilistic linear elastic fracture mechanics. Probabilistic analysis requires the use of reliability methods for assessing fatigue life by considering the crack propagation process and the uncertainties associated with it The limit state function that governs fatigue crack growth is developed based on Paris law by considering as random variables the coefficient of the curve that describes the rate of change of crack size due to loading cycles and its relationship to stress level and initial crack size and the stresses induced by external loading. As an improvement to the traditional fatigue fracture probabilistic approach, this paper presents a methodology for probabilistic analysis of ship structure fatigue failure considering the effects of the residual stresses induced by hull fabrication process over the crack growth rate.

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