Single-edge-notched specimens of a low-carbon steel were fatigued under cyclic in-plane bending with compressive mean stresses. The development of crack closure with crack growth was studied both experimentally and theoretically. The relation between the crack opening stress and the crack length was a function of the minimum (compressive) applied stress, irrespective of the maximum stress. The efl-ective stress intensity range was a unique parameter in correlating the crack growth rate, even if the crack wdS embedded in the compressive plastic zone. Under a constant minimum stress, the length of nonpropagating cracks became longer with increasing maximum applied stress. A theoretical model was proposed for predicting the crack opening stress on the basis of the compressive stress distribution at the minimum applied stress. The predicted value agreed fairly well with the experimental result. The model gave upper bounds of the crack growth rate and the length of nonpropagating Fatigue cracks within the plastic zone. NOMENCLATURE a =crack length including notch depth u', c'. n' =coefficients of the stress-strain relation c =crack length from the notch-tip c,. c,. cnp = mean, surface and non-propagating crack length dc/dN =crack propagation rate F. F , , F2 =geometrical correction factors for the stress intensity factor (SIF) K = SIF value due to applied stress K,,,, K,,, = SIF value due to minimum and maximum applied stress Kop = SIF value at crack opening K,, = SlF value due to residual stress Kr = stress concentration factor K*. K:," = true SIF value and SIF value calculated from the stress distribution at minimum applied nominal stress AKen, AK,,, =effective SIF range and its threshold value M = weight function R = ratio of minimum to maximum stress I = notch depth W = specimen width x =distance from the edge of specimen to load point p = notch-root radius 6 = von Mises equivalent stress u, = applied nominal stress amplitude u, = applied nominal mean stress = von Mises equivalent plastic strain urnax. u,,, = maximurn and minimum applied nominal stresses u:," =stress at minimum applied nominal stress u, = applied nominal stress uy = yield stress w, w * = plastic zone size at urnin and reversed plastic zone size at umrl 343 344 Y. AKINIWA er a1
