電界放射型走査電子顕微鏡による2段繰返し変動荷重下の疲労き裂進展挙動の直接観察

抄録

Fatigue crack growth tests under constant amplitude and repeated two-step loadings were performed on a 3% silicon iron in air and vacuum, using a specially designed servo-hydraulic fatigue loading system, and direct, realtime observations were made.
Macroscopic fatigue crack growth appearances under repeated two-step loadings both in air and vacuum were found similar to those under constant amplitude loadings. And macroscopic crack deflections, which were observed under non-stationally variable amplitude loading such as high-low two-step loading, were not observed under repeated two-step loadings except those occurred at the grain boundaries of the materials. It was found that the relationship between effective stress intensity range ΔK_eff and crack growth rate under repeated two-step loadings coincided with that of constant amplitude loading in air and vacuum. Also the crack tip opening displacement, CTOD, was found to be a good parameter in expressing the fatigue crack growth rate under repeated two-step loadings, suggesting the similarity of the relationships between ΔK_eff and CTOD under constant amplitude and stationally variable amplitude loadings. The fatigue crack growth resistance in vacuum was superior to that in air.