Theoretical and Experimental Analysis on Low-Cycle Fatigue Crack Initiation for High Strength Steel Stiffened Plates

Abstract

Abstract The ship hull is generally subjected to asymmetric cyclic loads under various and complex oceanic environments. Especially, under extreme sea conditions, the loads suffered by ship structures conform to the characters of low-cycle fatigue loads. Consequently, the large-scale plastic yield may occur at the locations of stress concentration part of the ship structure due to structural discontinuity or initial defects and result in low-cycle fatigue damage. However, the commonly used methods for low-cycle fatigue life prediction do not premeditate the influence of large range of yield and asymmetric load. Therefore, the effect of mean stress on the crack initiation life of the stiffened plate, the basic unit of ship structure, is investigated in this paper. The crack initiation experiments of welded stiffened plates under different stress amplitudes and stress ratios were carried out. Moreover, the modified Neuber rule considering the large-scale plastic yield and several strain-life models considering the influence of mean stress were used to estimate the life under experimental loading conditions respectively. Different life results were predicted by various strain-life models and compared with the results of experiments. The comparison shows that the modified Neuber rule can accurately describe the local stress-strain at the root of notch in the state of large-scale plastic yield than the Neuber rule, and the Walker model is the most recommended to predict the low cycle fatigue crack initiation life.