Study on Surface Crack Closure Behavior of Ship Hull Plate Structures under Constant and Variable Amplitude Low-Cycle Fatigue Loading

Based on in-depth analysis of crack closure theory and finite element simulation, this paper analyzes the crack closure behavior under constant and variable amplitude loading, and determines how the stress ratio and elliptical shape factor affect the closure process of the crack surface. Under constant and variable amplitude loading, the stress-strain response at the crack tip tends to be stable with the increase of cycles; however, after the introduction of single-peak overload, the stress-strain response at the crack tip changes significantly, and the crack closure effect is significantly enhanced during the unloading process, reflecting that single-peak overload has a decisive effect on crack closure behavior and the final crack growth rate. The relationship between crack growth rate and opening load for different combinations of overload and stress ratios reveals the complexity of crack closure behavior under overload conditions. These findings not only illustrate the protective effect of crack closure on crack growth, but also provide new understanding for predicting crack growth behavior under different overload conditions.