In this paper the impact of a composite overlay on stress levels and consequently fatigue performance of a superstructure on a Royal Australian Navy (RAN) vessel is investigated. The Finite Element Methodology (FEM) using a 'top-down' approach is applied to model the structural response. For the overlay modelling, a thin composite plate and zero bending assumptions are applied. Sea loads are modelled by the effects of a characteristic hogging-sagging wave and the corresponding probability of encountering such a wave over the lifetime of the ship. The stress distribution in the structure due to the composite overlay is approximated using the Weibull probability distribution and the fatigue damage coefficient estimated by adopting the Palgrem-Miner Model. The results show that a composite overlay in the high-stress concentration area can effectively modify the stress distribution and fatigue damage accumulation in the supporting structure thus reducing the likelihood of a fracture initiation. The impact of overlay thickness on the stress pattern is also investigated. By increasing the number of plies in the overlay, the fatigue damage in the critical region has been found to be reduced. However, increasing the number of plies tends to intensify an accumulation of fatigue damage at the overlay ends. The technique, developed and presented in this paper can be used to determine the location, the number of plies and the overlay orientation to optimise overlay effectiveness.
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