Generalized Diagram of the Ultimate Nominal Stresses (Endurance Limit) and the Corresponding Dimensions of the Non-Propagating Fatigue Cracks for Sharp and Blunt Notches

The paper generalizes the original data and the experimental data from the references on the investigation of the mechanisms of initiation and behavior of the non-propagating fatigue cracks in the notches of various shapes and dimensions. The dependence of the ultimate nominal stresses (endurance limit) and their corresponding dimensions of the fatigue cracks on the theoretical stress factor for the notches of various shapes and dimensions is proposed to be schematically presentedin the form of the generalized diagram. The ultimate stresses should be understood as the endurance limits only within the zone of sharp notches provided that their value does not depend on the theoretical stress concentration factor. The limiting dimensions of the non-propagating cracks in the zone of sharp notches should be understood to mean the maximum dimensions of the cracks that are consistent with the ultimate stresses. The generalized diagram indicates the fact that the nominal endurance limit decreases in the zone of blunt notches, while the dimensions of the non-propagating cracks increase with an increase in depth and decrease in the notch radius (with the increase of the theoretical stress concentration factor), whereas they are controlled by the notch depth within the zone of sharp notches. With the increase of the notch depth, the ultimate stresses decrease, while the dimensions of the non-propagating cracks increase. At the constant depth of the notch, the ultimate stresses and dimensions of the non-propagating cracks are independent on the notch radius and value of the theoretical stress concentration factors.