Understanding of fatigue crack propagation behavior is extremely important for fatigue life assessment of ship" and marine structure. In this paper, Newman"s model is modified to solve his neglected problems and is expanded to arbitrary stress distribution field for the purpose of obtaining RPG load. Moreover, we consider plastic shrinkage at newly generated fracture surface during unloading process which corresponds to a part of deformation due to emancipation of acting force with a magnification of yield stress at an immediate growth of a crack in the region of fictitious crack in Dugdale model. By using the model, RPG load is simulated for a center notched specimen under constant amplitude loading with various stress ratios and decreased maximum load while keeping minimum load. We also carried out fatigue crack propagation tests with the same loading condition of above simulation for the purpose of comparing of RPG load between measurement and simulation, as well as of crack growth curve. As a result, simulated RPG loads are in very good agreement with measured RPG loads for each testing condition. Then crack growth curves for each testing condition is calculated by using ΔKRP from simulated RPG load and also shows in very good agreement with measured crack growth curves for each testing condition.
In his model, he neglected the change of stress distribution ahead of a crack during loading process in the calculation of Elber"s crack opening load. Then he introduced plastic constraint factor of 3.5 for a center cracked specimen that may be much larger than appropriate value, for the purpose of fitting experimental crack opening load for a constant amplitude loading. In spite of introducing larger plastic constraint factor, calculated crack opening load just after decreasing maximum load in his model seems to be quite lager than experimental one.
