Analytical prediction of short to long fatigue crack growth rate using small- and large-scale yielding fracture mechanics

Abstract Modifications are introduced to account for the differences in crack growth behavior of long and short cracks, that permit the use of the stress intensity factor. These modifications stem from the principles of fracture mechanics for small- and large-scale yielding. Short cracks can grow well below the long crack fatigue threshold range, because the short crack fatigue threshold range is smaller than that for long cracks as it is dependent on the stress level, and the plastic constraint factor. Analytical expressions are developed for these relationships, and for the fatigue crack growth rates in plane stress and plane strain, for short semi-elliptical cracks including those emanating from notches. Microstructural features are not considered. A linear approximation is used for the gradual transition from plane stress to plane strain. The model is formulated using only the readily available material properties. It is then validated using published experimental data for fatigue crack propagation rates for positive and negative stress ratios down to –2. There is reasonable agreement between the model predictions and the published experimental data for short cracks (from 0.1 to 2 mm) and long cracks.