Effect of Specimen Thickness on Near Threshold Crack Propagation without Oxide-Induced Crack Closure

Abstract

In order to investigate the effect of specimen thickness on near threshold crack propagation without oxide induced crack closure, ΔK decreasing tests under the stress ratio 0.1 and the loading frequency 5 Hz, specimens thickness 12.7 mm and 6 mm conditions were carried out. In case of Cr-Mo Steel, no clear oxide films were observed on macroscopic fracture surface on both specimens. EDX results showed that no oxides were detected on the near threshold fracture surface of both specimens. The crack propagation showed almost the same behavior in both high ΔK and near threshold areas. The threshold values were 4.6 on both specimens. These results showed that there were no effects by specimen thickness on both high ΔK and near threshold range.