A comprehensive approach for quantifying the reliability of ship hulls under propagating fatigue cracks

Abstract

Traditional approaches for reliability assessment of ship hulls under propagating cracks mostly rely on comparing the value of a certain fracture mechanics parameter calculated at the crack tip to the fracture toughness of the material. This assumption may not accurately represent the failure event since the fracture resistance is not only affected by the material properties but also by the component geometry. Furthermore, this approach may not properly account for the possibility of elastic-plastic fracture in the ship hull. This paper presents a novel probabilistic approach for quantifying the reliability of ship hulls under propagating fatigue cracks. The approach utilizes the failure assessment diagram (FAD) to define the performance function of the hull and can account for the occurrence of various possible failure mechanisms ranging from brittle fracture to full plastic collapse. The Weibull stress criterion is utilized to quantify the critical crack tip opening displacement which is adopted herein to represent the fracture resistance of the cracked hull. Monte Carlo simulation is used to quantify the failure probability and the reliability index of the ship hull under encountered wave loads and propagating cracks. The approach is illustrated on a tanker operating in the Atlantic Ocean.