Affiliations: Fracture Research Institute, Graduate School of Engineering, Tohoku University, Aoba01, Aramaki, Aoba‐ku, Sendai‐shi 980‐8579, Japan | Graduate Student of Graduate School of Engineering, Tohoku University, Aoba01, Aramaki, Aoba‐ku, Sendai‐shi 980‐8579, Japan
Abstract: The analysis of hydrogen diffusion and the concentration behavior originated around a crack tip due to the anodic dissolvent chemical reaction under fatigue condition was conducted and the effect of stress wave form on the hydrogen concentration behaviors were clarified. Furthermore, the correlation between the experimental characteristics of corrosion fatigue crack growth rate and the theoretical results of hydrogen concentration behaviors obtained in this paper were investigated. From these studies, the following results were obtained. The effect of stress wave form on hydrogen concentration exists for the case of larger yield stress. The distribution of hydrogen concentration under fast–slow cycle loading is different form that under slow–fast condition. For the former case, hydrogen concentration occurs at the site of maximum value of σp, that is, elastic plastic boundary, which is similar as that under SCC. That is, stress decreasing process has the same effect on hydrogen diffusion and concentration as that of stress holding process. For the latter case, hydrogen does not concentrate at the elastic plastic boundary and hydrogen concentration takes the highest value at the hydrogen emission area around a crack tip due to dissolvent anodic reaction. Hydrogen concentration gradually decreases with increase in the distance from the crack tip, that is, load increasing process during cyclic loading promotes hydrogen diffusion from a hydrogen emission area around a crack tip under corrosive dissolvent condition. Furthermore, the effect of stress wave form on hydrogen concentration cannot be found out for lower yield stress. These characteristics mentioned above are in good agreement with the experimental characteristics of corrosion fatigue crack growth rate both for Cr–Mo steel (larger yield stress) and aluminum alloys (5456X, lower yield stress). This shows the effect of stress wave form on corrosion fatigue crack growth rate is dominated by hydrogen diffusion and concentration behaviors.
