Critical distances approach reformulated for a better comparison of fatigue strength of materials with sharp notches

Several approaches derived from linear elastic fracture mechanics (LEFM) have been proposed for fatigue design of structural components with sharp notches. Some of them are based on a “critical distance” concept, since they substitute the intensity factor, which defines the exponential field around the notch tip with a more familiar quantity evaluated with reference to a particular distance, in such a way to match the corresponding strength of plain material. Since fatigue strength of notched components is much less influenced by many parameters than that of plain materials, to characterise sharp notches with such apparent fatigue strength seems to be unrealistic from the point of view of the comparison of different materials. A realistic comparison should be instead possible if the critical distance is calibrated with reference only to sharp notches, as here proposed considering two sharp notches with a very different opening angle.