Fatigue-crack propagation in high yield-strength steels

Information on fatigue-crack growth in high yield-strength steels is necessary for toe prediction of service lives of structures subjected to fotigue loading. Therefore, as part of a long-range program to establish the mechanical behavior of high yield-strength steels, the fatigue-crack propagation in four high-strength steels-HY-80, HY-130, 10Ni-Cr-Mo-Co, and 12Ni-5Cr-3Mo-was investigated.

A technique was, developed to accurately measure incremental fatigue-crack growth by fofiowing the extension of the crack along uniformly spaced marks on the surface of a wedge-opening-loading (WOL) specimen that was cycled under constant maximum and minimum loads. The primary factor affecting crack growth rates in fatigue was found to be the applied stress-intensity range, ΔK_I. A conservative crack propagation rate for high yield-strength steels fatigue-tested at room temperature in an air environment was determined to be: .

The present results were compared with existing fatigue-crack-growth data. With one exception, all crack-growth data (for a total of 19 high yield-strength steels) could be represented by die above equation. Thus, it appears that fatigue-crack growth rates in high yield-strength steels tested in a room-temperature air environment can be represented by a single equation that is sufficiently accurate for engineering purposes.