Prediction of fatigue crack growth in a ship detail under wave-induced loading

Fatigue life prediction based on fracture mechanics has become the focus of research on the strength of ship structures; however, it is difficult to summarize a general formula for calculating stress intensity factors (SIF) for cracks in ship details, and the application of fatigue crack propagation (FCP) theory is limited to simple structures and simple loads in some way. To address this problem, in the present study, the SIF of a crack in a ship detail was calculated by combining a PATRAN finite element model for the whole ship with the advantages of ANSYS for SIF calculation, incorporating a macrocode written to achieve the transformation. The method was validated by comparison with existing empirical formulas. Also a method of generating the ship fatigue loading spectrum is demonstrated based on the design wave approach. Finally, an example is given of combining the unique curve model of FCP with the proposed SIF calculation method and the fatigue loading spectrum generation method, to predict the fatigue life of a welded hatch corner joint in a vessel with large hatch openings. This serves as a reference for fatigue assessment of other complex ship details.