Influence of stress concentration on the resistance to fatique failure of steels by the criteria of crack nucleation

Abstract

1. A correlation was established between the stresses for smooth samples in tension-compression and samples with stress concentrators in the form of circular openings in tension-compression or torsion with a similar number of cycles until the nucleation of fatigue cracks of size 0.1 mm. This showed good agreement with the experimental data. 2. An expression was obtained which permitted the calculation of the endurance limit of samples with stress concentrators using known values of the threshold coefficient of stress intensity, the theoretical coefficient of stress concentration, and the valuelo. 3. On the basis of these functions, a method is presented for calculating fatigue curves of notched samples under torsion and tension-compression which corresponds to the formation of a main fatigue crack. The method utilizes test data of smooth samples under tension-compression and the value of the threshold coefficient of stress intensity for the material. 4. It was established that for samples under torsion or tension-compression with stress concentrators in the form of circular openings, the fatigue curves of the materials investigated were in agreement when actual stress was plotted as a function of the number of cycles to the nucleation of cracks.