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.
Highlights
An accurate value for the threshold stress intensity factor range, ΔKth, is a key parameter for studying crack-like defects
In the case of the low alloy steel, at 20 Hz, the oxides, which are the debris with diameters of 0.1 mm, are distributed near the centre of the fracture surface
The belt-like oxides can be observed across the whole fracture surface
Summary
An accurate value for the threshold stress intensity factor range, ΔKth, is a key parameter for studying crack-like defects. The resulting conditions allow for an accurate determination of ΔKth, which is a key material parameter relating to the pertinent loading ratio. It is well known that obtaining an accurate value for the threshold stress intensity factor range, ΔKth, is necessary for studying fatigue related problems. To the best of our knowledge, there have been no studies on the conditions that are necessary to minimize the oxide-induced closure at a low stress ratio when tested in air. Skelton and Haigh[15] reported the same tendency based on results from a Cr-Mo-V steel at a high temperature and 10 to 0.01 Hz conditions These studies, they are contradictory, clearly show that the loading frequency significantly affects the oxide-induced closure
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