Prevention of hydrogen embrittlement is one of the most important issues for the materials used in hydrogen environment. Various mechanisms for hydrogen embrittlement were proposed, such as the decohesion mechanism and hydrogen enhanced localized plasticity. However, the process of hydrogen diffusion and accumulation into the fracture point is necessary for understanding of hydrogen embrittlement. In this paper, hydrogen embrittlement behavior during the fatigue crack extension test under high pressure hydrogen was first conducted. Then, hydrogen diffusion and accumulation behavior in the crack tip region was analyzed by the numerical simulation based on the Fick's diffusion theory. Alpha multiplication method which multiplies stress gradient induced terms was found to be valid to realize correct particle diffusion behaviors driven by the stress gradient term. The significance of the concept of alpha multiplication method for the numerical analysis was discussed by comparing to the experimental hydrogen embrittlement behavior.
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