Fatigue reliability of a single stiffened ship hull panel

Fatigue cracks in ship structures are considered a nuisance as they require periodic inspection and repair. If left unrepaired, the crack could grow to reach a critical length and threaten the integrity of the structure. Although the cracks are typically characterized by stable propagation rate, the scatter in fatigue performance is difficult to quantify and could be on the order of thousands or even millions of cycles. The development of maintenance and management programs for ship structures should therefore account for the inherent scatter in performance through probabilistic fatigue assessment. Probabilistic assessment by testing a large number of specimens can be very costly. Therefore, the assessment can be performed through conducting large number of numerical or analytical simulations that account for the inherent statistical scatter in both load and resistance. This paper presents a framework for probabilistic assessment of the propagation rate of cracks in welded stiffened panels using finite element Monte Carlo simulations. The parameters influencing the propagation rate are treated as random variables with predefined statistical distributions. The results can be used for proposing inspection intervals for ships. In addition, very useful insight can be drawn on the most sensitive parameters affecting crack growth in the panels and the probability of failure at a given inspection period.