Near-threshold fatigue crack propagation without oxide-induced crack closure.

ABSTRACT

An accurate value for the threshold stress intensity factor range, ΔKth, is a key parameter for studying crack-like defects. However, it is difficult to obtain accurate ΔKth values due to oxide-induced crack closure. In this study, we report conditions for minimizing the effects of oxide-induced crack closure near the threshold region, where a concave curve of the effect on the loading frequency on oxide-induced crack closure is achieved. The resulting conditions allow for an accurate determination of ΔKth, which is a key material parameter relating to the pertinent loading ratio.