THE INFLUENCE OF STRENGTH AND STRESS RATIO ON SHORT‐CRACK THRESHOLDS AND NON‐PROPAGATING FATIGUE CRACKS

Abstract

Quantitative predictions of the influence of yield strength and stress ratio, R, on the physically small crack fatigue threshold stress intensity, ΔK0(s), are presented. It is shown that at R= 0 to ‐1, although the threshold stress Δs̀0 increases, the threshold stress intensity, ΔK0(s), decreases with increasing yield strength. Moreover, a lower bound value, ΔK0(s)(min) is shown to have a constant value, irrespective of the strength and stress ratio. For a given strength, ΔK0(s), decreases with increasing R in the range ‐1R0.6 and attains a constant low value for R > 0.6. Predicted values of ΔK0(s) are in good agreement with experimental data for steels. The formation and length of non‐propagating fatigue cracks, anp, are also discussed. The methods suggested for estimating ΔK0(s) and anp may be found useful in design procedures. Copyright © 1993, Wiley Blackwell. All rights reserved