Fatigue Limit of Steel with an Arbitrary Crack under a Stress Controlled Constant with a Positive Mean Stress

Abstract

In this paper, push-pull fatigue tests of notched specimens under R = −1, 0 and 0.5 are carried out on annealed 0.1% carbon steel and quenched-tempered 0.5% carbon steel with H B 600. The fatigue limit of a long crack, σ w2 , is obtained from that of a notched specimen with a sharp and deep notch whose radius is smaller than the branch point ρ 0 . Using the present and past σ w2 data, the effect of the positive mean stress on the K w of the long crack is evaluated using 3.2H B ( σ B ) and σ S /(3.2H B ), where K w is the stress intensity factor range for predicting the fatigue limit of a metal with an arbitrary crack, σ S is the lower yield stress or 0.2 % proof stress, σ B is the ultimate tensile strength and H B is the Brinell hardness. Although the σ w2 decreases with the mean stress, σ w2 is cut off by the threshold stress σ we of the plastic deformation at the crack tip. For the quantitative prediction of the fatigue limit of a cracked steel with an arbitrary crack length under a positive mean stress, the σ w2 and σ we values are approximated by simple formulae.

Fatigue Limit Reliability Analysis for Notched Material with Some Kinds of Dense Inhomogeneities Using Fracture Mechanics

“…Moreover, the threshold stress intensity factor range ΔK w of the small surface defect of size ffiffiffiffiffiffiffiffiffiffiffi area P p in the metal with Vickers hardness H VM is given by the following equation [33,34]:…”

“…In this study, a crack for which ΔK th is constant irrespective of its length, and which exhibits the small-scale yielding (SSY), is defined as a long macrocrack. Conversely, a crack for which ΔK th is dependent on the length, and which exhibits the large-scale yielding (LSY), is defined as a small macrocrack [33,34]. The three following types of crack non-propagation limits are introduced and defined to predict the fatigue limit of a notched specimen of aluminum cast alloy [35]:…”

Prediction of fatigue limit reliability of high strength steel with deep notch under mean stress σ m = 0

“…(Isibasi 1967). When the σ 1 distribution along the notch direction from the notch root is used, the nonpropagation limit of the microcrack under the notch root, σ w1 , can be predicted by the following equation (Isibasi 1967;Nisitani 1971;Nisitani et al 1989;Miyazaki et al 2005a).…”

“…As for steels, the ΔK wUL values can be predicted by the following Eq. (Miyazaki et al 2005a). Here, H B is Brinell hardness, ΔK wL L is the lower limit of the ΔK w and ΔK wL L | σ m =0 = 2.1 MPa √ m for steels.…”

Low Pressure Hydrogen Gas Effect on Extremely Low Fatigue Crack Growth from Small Blind Holes of SUS304 and SUS316L

“…To understand such a complex behavior, it is necessary to consider not only the material and effect of hydrogen, but also the effects of the difference between the long crack of the CT specimen and small cracks (18) ~ (25) . The fatigue crack arresting behavior is important for engineering.…”