Evaluation of actual fatigue stress by using striation spacing and hardness: Ishida, S., Tokumasu, M., Nakasa, K. and Ishihara, H. J. Soc. Mater. Sci., Japan Jan. 1990 39, (436), 63–69 (in Japanese)

Abstract

Centrally cracked specimens of JIS SM58Q and HT80 steels were fatigued. The fatigue crack growth rates, da/dn, and the stress intensity threshold levels, ΔKth were measured over the range of stress ratio, R, from −1 to 0.8 by the use of an automatic method of continuously decreasing stress intensity factor with crack extension. The measured ΔKth was well represented as |ΔKth/2|R=(1−R)γ|ΔKth/2|R=0; and the propagation rate, as da/dn = A(1−R)γm[(ΔK/2)m − {(1 − R)γ|ΔKth/2|R=0}m] for −1≦R≦0.33 or da/dn = A(1 − 0.33)−γm [(ΔK/2)m {(1 − R)γ |ΔKth/2|R=0}m] for 0.33 < ≦ 0.8.