6/4黄銅薄板の大気および腐食環境における疲労き裂伝ぱに対する板厚効果

概要

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For clarifying the dependence of the thickness of a thin metal sheet on fatigue crack propagation in air or in a corrosive environment, the fatigue tests with data-gathering procedures as dictated by ASTM were carried out on specimens of thin 6/4 brass sheets with thicknesses of 0.3 mm, 0.5 mm, 0.8 mm, and 2.5 mm, which are coated by corrosion-proof oil except at the notch. As a result, the relationship of the crack propagation rate, da/dN, to the stress intensity factor range, ΔK, was obtained. It is found that in the second range of the relationship in a corrosive environment, the slope, m, is not affected by the thickness of the specimen, and shows a stable value, but in air, the slope is affected by thickness. Assuming that the plane strain condition is established when the thickness of the specimen is equal to or larger than the range of plasticity at the head of a crack subjected to tension in one direction, the ranges where the slope, m, of each different thickness are stable and parallel to each other, within each limit of ΔK, are determined, and the formula for determining the thickness of the specimen under the condition of plane strain can be derived from the experiment. In this way, reliable data on the relationship of da/dN to ΔK is attained.
1993-09-25