A new fatigue crack growth model considering underloads and overloads history together with stress ratio

Abstract

The estimation of fatigue crack growth for a ship structure is a complicated subject, especially when loads vary. Several researchers studied fatigue crack growth under varying loads with simple block loads, and many models have been proposed. More research is required to properly evaluate the storm loads, representing complex actual loads a vessel experience on the sea. This study proposes a new simple fatigue crack growth model that incorporates only two parameters of the stress ratio factor and the load history factor taking account of the underload effects using empirical data in the literature. The procedures for formula modification and optimum model selection are introduced. The new model is optimized and validated by comparing it with several simple block load tests and existing fatigue crack growth models. Generally, the new model shows competitiveness and a good agreement with the experiment results. The proposed model is expected to be a potential solution, with a simple formula, to estimate fatigue crack growth under variable loads including the storm loads.

Keywords

• Fatigue crack growth
• Variable amplitude fatigue
• Underload histories
• Stress ratio effect
• Retardation effect