1991 Volume 40 Issue 458 Pages 1428-1434
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 ΔKeff 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 ΔKeff and CTOD under constant amplitude and stationally variable amplitude loadings. The fatigue crack growth resistance in vacuum was superior to that in air.
