Fatigue Life Prediction of High Strength Steel with Pitting Corrosion under Three-Point Bending Load

Abstract

Offshore structures often suffer from pitting corrosion, which leads to local stress concentrations, a decrease in the cross-sectional area, the subsequent initiation and gradual propagation of cracks, and a shorter service life as a result. This study aims to investigate the impact of pitting corrosion on the fatigue life endurance of high-strength steel used for offshore structures. To this end, a three-point bending fatigue test was first performed on the specimens to obtain the fatigue test data. Then, a fatigue life prediction model consisting of two terms is proposed based on fracture mechanics, and the fatigue test data are used to verify the reliability of the model. Finally, the experimental results are discussed, and conclusions are drawn. The first term was designed for crack initiation. Combining with the energy theory and slip band dislocation theory, a novel equivalent surface defect model was proposed and used to predict the fatigue life of pitted corroded specimens before crack initiation. The second term is designed for crack propagation. The generalized Paris model is adopted for fatigue life prediction during the crack propagation process after the crack angle is taken as a variable. The mathematical model for predicting three-point bending fatigue life was finally obtained, and the average relative error of the data validation results did not exceed 16%, which proved the reliability of the prediction model.