Yunbo Zhang’s research while affiliated with Sichuan University of Science and Engineering and other places

The tensile properties and fatigue crack propagation mechanism of 30CrMo steel were investigated under electrochemical hydrogenation conditions by tensile and fatigue crack propagation tests. The results indicate that, following electrochemical pre-hydrogenation, the tensile strength of the material is marginally enhanced, while its plasticity is significantly diminished. Furthermore, its elongation is reduced from 30.91% in the absence of pre-hydrogenation to 22.35% in the presence of pre-hydrogenation. Additionally, the fatigue life following pre-hydrogenation was observed to diminish by 15%. The rate of crack propagation is approximately four times that observed in the absence of pre-hydrogenation. Scanning electron microscope (SEM) fracture analysis revealed a shift in the fracture mechanism from ductile fracture without pre-hydrogenation to quasi-dissociative fracture after pre-hydrogenation. The analysis by digital image correlation (DIC) technique showed that the specimens treated with pre-hydrogen were more open at the P/Pmax of 35% and the strain at the fast fracture stage increased significantly from 908.92 to 1021.41 compared to the specimens without pre-hydrogenation. In addition, finite element simulation of the hydrogen diffusion mechanism in the steel using Comsol software revealed that, under stress, the hydrogen atoms were significantly enriched at the crack tip, and the hydrogen concentration at the crack tip increased from 32.1 mol/m3 to 48.5 mol/m3 with the increase of the hydrogen charging time up to 180 min; the further away from the crack tip, the smaller the hydrogen concentration, regardless of the stress.

In recent years, with the development of industry and scientific technology, the demand for materials has been increasing. Fatigue crack propagation is an important issue in the field of materials, and developing relevant theories and methods, understanding the mechanisms of fatigue cracks, and making scientific predictions on fatigue crack propagation are hot topics both domestically and internationally. Fracture mechanics, as a discipline studying the strength and propagation of cracks in materials, has developed a relatively complete theoretical system and engineering application methods over more than 100 years of continuous development. This article focuses on the effects of factors such as temperature, stress ratio, and load frequency on the fatigue crack propagation characteristics of metallic materials, and summarizes the common theories and methods of fatigue crack propagation.