イオンビーム照射下の熱疲労き裂進展実験と非線形破壊力学評価

抄録

This paper is concerned with experiments as well as numerical analyses on thermal fatigue crack growth of Type 304 stainless steel, which is one of candidate materials for the first wall of fusion reactors, under hydrogen ion (H⁺) beam irradiation.
In the experiments, a surface-cracked plate specimen set in a vacuum chamber of 10^-6 torr was irradiated repeatedly with 25keV H⁺ beam pulse of normal distribution, whose peak value and time duration were about 2MW/m² and 1sec in every 45sec, respectively. During the irradiation, temperature on the specimen surface reached 800-900 degree C. After several hundreds of irradiation cycles, the specimen was cooled down and broken along a cracked plane. Crack growth of about 1mm was observed on the fracture surface.
To evaluate such a fatigue crack growth behavior, nonlinear fracture mechanics analyses were performed based on the three-dimensional thermal conduction and thermal elasto-plastic finite element analyses. The temperature dependence of material properties was taken into account. The nonlinear fracture mechanics parameter adopted here was the ΔJ-integral considering thermal effects.
The crack extension amount Δa was estimated using the calculated ΔJ value and several experimental data on fatigue crack growth in literature. It is shown that the present estimation scheme can predict the fatigue crack growth phenomena under ion beam irradiation with an accuracy of a factor 4, in spite of the FEM analyses ignoring micro damage effects of irradiation.