Fatigue Microcracks Detection and Assessment in High-Strength Marine Steel Using Nonlinear Ultrasonic Waves: Experimental and Numerical Investigation

Fatigue damage severely impairs high-strength marine steel performance, threatening the safety of ships and offshore engineering structures. Due to the abrupt nature of structural fatigue failures, early detection of fatigue microcracks is crucial for ensuring structural reliability. The detection of fatigue damage was experimentally and numerically investigated in AH36 marine steel using nonlinear ultrasonic technique. According to the distribution features of fatigue damage in marine steel, a three-dimensional finite element model is proposed to investigate the nonlinear ultrasonic method for the detection of randomly distributed fatigue microcracks. The microcrack distribution is much closer to the actual state of fatigue microcracks in metal than that of previous studies which used two-dimensional plane strain models with the individual crack or distributed cracks. The high-harmonic was induced by the contact behavior of crack surfaces. The results revealed that the relative nonlinear coefficient increases with higher microcrack number and length, but decreases with larger microcrack width. Additionally, the FE model, which closely approximates the actual distribution of fatigue microcracks in metallic materials, provides a new research avenue for a more comprehensive understanding the nonlinear interaction between ultrasonic waves and fatigue microcracks.