Low-cycle fatigue of damaged stiffened panel in ship structures

This work aims to extend the conventional post-accidental structural safety assessment by investigating possibility of damage propagation in stiffened panels during salvage period as low-cycle high stress fatigue process caused by fluctuating wave loads. Low-cycle loading can cause high-amplitude stresses at the edge of damage opening, which consequently lead to high stress concentrations. In the present study, intended for conceptual considerations, damage of stiffened panel is idealized as rectangular, diamond and circular shape. A finite element model is created for intact stiffened panel and for each idealized damage shape for which the stress concentration factor is calculated. The number of constantamplitude wave load cycles to initiate a fatigue crack is calculated using the strain-life method defined according to Det Norske Veritas classification notes. Accumulated low-cycle fatigue damage is then estimated by Monte Carlo simulation, where individual stress amplitudes are drawn as random numbers according to Rayleigh distribution. The analysis is performed for three assumed types of short-term random sea state: calm, moderate and rough seas Conclusions of the study are related to the conditions that could cause low-cycle fatigue and to the importance of assumed idealized damage shapes.