A novel characterization of fatigue crack growth behavior in metallic materials: The physical relationship between the uncracked section size and the remaining fatigue life

Abstract

A physically based universal functional is shown to uniquely correlate the fatigue crack growth data of metals in high-cycle fatigue, generated at various stress ratios, extremely well. The functional is proposed based on the hypothesis that at any stage during fatigue, the remaining fraction of fatigue cycles required for final fracture is proportional to the fractional uncracked section size that remains to be severed by the fatigue crack. The basis for such a hypothesis is that the microscopic mechanism of fracture, such as striation formation in fatigue, is largely independent of the details (e.g. mean stress or stress ratio) of high-cycle fatigue loading. Experimentally, the functional is found to be a simple power law relating the fractional remaining uncracked section (net-section) size to the fractional (normalization by total fatigue life) remaining fatigue life. It is also shown that the surrogate form of the functional provides excellent descriptions of the raw crack-length-versus-cycles data generated in high-cycle fatigue experiments. The functional seems to provide a new physical basis, which is different from fracture mechanics, to characterize the effect of stress ratio on fatigue crack growth in materials.