New evaluation method of crack initiation limit in notched specimen: effect of notch shape on aspect ratio of low carbon alloy steels (JIS, S15C, S35C and S45C)

摘要

Aspect ratio is a key factor to calculate stress intensity factor (SIF) K using fracture mechanics. While cracks are approximated to be semicircle or semiellipse in simple calculation, their empirical shapes are changed by stress distribution depending stress concentration. In this study, in order to calculate K simply but precisely, a new method to modify aspect ratio of a crack at a notch root is proposed. The new prediction method of fatigue crack initiation stress sigma(w1) with modified aspect ratio is also discussed. These new methods succeeded in predicting sigma(w1) within 12% error from empirical values in notched specimens, which have various notch configurations, diameters and average ferrite grain sizes.