The Effect of the Interaction between Dislocations and Hydrogen Around a Crack Tip on Hydrogen Embrittlement Under Cyclic Loading Condition

概要

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For steels with lower yield stress, transgranular facet like fracture sometimes occurs under corrosive conditions. The occurrence mechanism of the transgranular facet like fracture has been analytically clarified under constant stress rate condition based on the concept of mechanical interaction between dislocations and hydrogen. In this paper, the analyses of the mechanical interaction between dislocations and hydrogen around a crack tip under cyclic loading condition were conducted to clarify the effect of stress wave forms on the feasibility of hydrogen embrittlement. This analysis showed the typical pile-up of dislocations occurs at the site of hydrogen similar as that under monotonous applied loading condition. Concerning the concentration of dislocations at the site of hydrogen atom, the dislocation pile-up intensity factor amplitude ΔA and power coefficient value of the singularity of dislocation density n were defined. ΔA under fatigue condition was found to concern the feasibility of the occurrence of facet like fracture due to dislocation pile-up caused by the interaction between dislocations and hydrogen. Furthermore, the condition of Fast-Slow stress wave form was found to promote the facet like transgranular fracture as compared with that of Slow-Fast stress wave form.