This paper presents a method for simplified fatigue stress analysis for large catamaran based on implied cumulative fatigue criterion. A probabilistic fracture mechanics model for fatigue life prediction is introduced. Probabilistic fracture mechanics approach is calibrated to an SN approach to better account for crack initiation and initial crack size. The fatigue reliability of the considered structural details is modeled as a series system considering the fact that fatigue cracks may occur at many locations. Subsequently, the effect of inspection on the system fatigue reliability is exemplified with the aim at probabilistic inspection planning.
Fast ships like large catamarans are of increasing commercial importance in the areas of passenger and cargo transportation and other marine operations. Fast sea transportation could be used for archipelago or coastal services in competition with short distance airplane services. For this reason, more and more attention and efforts are being paid to this field throughout the world. In order to efficiently keep high speed, minimal structural weight is crucial. For this reason aluminium is a much-preferred material. Moreover, it implies a high utilization of the structure. Due to the high frequency of repetitive loads and the relatively low crack propagation resistance of aluminium, fatigue becomes an important design criterion. Catamarans are composed of two demihulls with a connecting bridge serving as car deck and passengers deck. As an important part of catamarans, the box structure between the two demihulls is critical to overall structural integrity. There is a great possibility that multiple cracks or crack-like defects exist along welds. Each existing crack may lead to fatigue failure. The structure and loading of catamarans are among the most complex with significant uncertainties, most of which are still difficult to quantify. It is therefore desirable to carry out the analysis based on probabilistic concepts.
