引張圧縮応力下の表面疲労き裂伝ぱ(平均応力の影響および超音波斜角探傷法によるき裂前縁局所領域のき裂閉口測定)

概要

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The effect of mean stress on growing surface fatigue cracks in plates of annealed 0.15%C steel was studied under cyclic tension and compression loading and the crack tip opening loads at local area along the crack front were measured by an ultrasonic angle beam method (UAM). The crack was semielliptic and had a smaller aspect ratio under compressive mean stress than under tensile mean stress. The crack growth rate in the depth direction was higher than in the surface direction for the same ΔK-value, when the mean stress was tensile (R=0). When the mean stress was compresive (R=-2), the former was lower than the latter. For the same ΔK_<eff>-value assessed on the crack tip opening load measured by UAM, not only the dependence of crack propagation rate on the mean stress but also the difference between the crack propagation rates in the surface and the depth directions almost disappeared. Prediction of aspect ratio variation of growing surface fatigue cracks in tension-compression loaded plates was made with the local ΔK_<eff>-falues and with the averaged ΔK_<eff>-values obtained by a weighted averaging along the crack front. The averaged ΔK_<eff>-value method overestimated the crack aspect ratio when the mean stress was tensile (R=0) and zero (R=-1). Estimation by the local ΔK_<eff>-value method was fairly accurate irrespective of mean stress value.
社団法人日本材料学会の論文
1993-01-15