Experimental study on fatigue crack propagation in balcony opening corners of a cruise ship

Abstract

The balcony opening corner in a cruise ship is subjected to highly stress concentration and alternating loading during operation, which is prone to cause fatigue crack initiation and further crack propagation. These initiated cracks are difficult to find in time due to these opening corners being hidden in the decoration materials. It is necessary to assess the residual fatigue lives accurately and provide reasonable repairing plans for these cracked opening corners to ensure safety of the cruise. In this paper, in order to study the fatigue crack propagation (FCP) law of the balcony opening corner, make up the lack of the FCP experiment of the balcony opening corners, correlate the FCP behavior of the full scale model with the reduced scale model, and provide an accurate FCP live prediction method for balcony opening corners, reduced scale models based on the similarity theory and the corresponding fixtures are designed. FCP tests of these reduced scale models with small initial cracks are carried out. a-N curves of the cracks at different notch locations in balcony opening corners under different stress ratios are obtained. Formulas of stress intensity factors (SIFs) of cracks at the midpoint of the three types of corners are given by fitting the data obtained by a serial of FE analysis of the cracked corners. Further, the fatigue lives of the tested specimens are calculated and compared with the test data. It is shown that the prediction results fit well with the model test results. The procedure of model test and experimental data can provide a reference for detailed design and precise residual FCP life assessment of opening corners in ship hulls.