A ΔK_th Testing Method based on the Plastic Zone Slze at the Fatigue Crack Tip

概要

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A ΔKth testing method was proposed to determine the crack growth threshold in a comparatively short time. This test method is based on the consideration of plastic zone size at the crack tip. And the crack growth increment in a load step was limited to the length slightly less than the plastic zone size induced by the previous load step. Comparison was made with the proposed ASTM method using a Ni-Cr-Mo steel SNCM439, a high tensile steel HT55 and an aluminum alloy A5083-0. It was found that the crack growth was not affected by the loading history if the rate of load shedding was small enough, from the analysis by measured crack opening point. The results by these two methods agreed very well. From these testing results and discussion, it may be concluded that ΔKth value can be obtained i comparatively short time by this test method if load decreasing ratio is kept small.
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