Surface flaws in cylindrical shafts under rotary bending

The propagation of a surface flaw in a cylindrical shaft subjected to rotary bending is analysed using a two-parameter theoretical model. The stress-intensity factor distribution along the crack front is numerically determined for any position of the flaw with respect to the bending moment axis. The crack front is assumed to present an elliptical-arc shape with aspect ratio α = a/b (a, b = ellipse semi-axes), whereas the relative depth ξ of the deepest point on the front is equal to the ratio between the maximum crack depth, a, and the bar diameter, D. The results for rotary bending are compared to those for reversed cyclic bending.