Mixed-mode (I plus II) fatigue crack growth of marine steels in Arctic environments

In the Arctic, the fatigue properties of marine steels under low temperatures and complex loads are essential for the safety of ship navigation. In this study, the fatigue crack growth (FCG) characteristics of EH36 and EQ70 steels are explored under low-temperature mixed mode (I + II) through experiments and numerical simulation. Experimental results show that the FCG life and the crack growth retardation (CGR) effect of both steels correlate positively with the loading angle and negatively with the temperature. The prediction results for FCG path indicate that the Maximum Tangential Stress (MTS) criterion provides accurate predictions for loading angles less than 45 degrees in low-temperature mixed mode (I + II), while the Richard model is more suitable for the loading angle of 60 degrees. The simulation results show that, when the crack deflects, KII decreases rapidly in magnitude while KI gradually increases and becomes dominant. The SEM results for the FCG fracture surfaces in both steels revealed that the roughness of the fracture surface is positively correlated with the loading angle, moreover clear transition regions are observed between the pre-crack and crack growth regions.