Fatigue crack growth in round bars under rotary bending

Fatigue growth of a surface flaw in a round bar under rotary bending is examined through a two-parameter theoretical model. For any position of the elliptical-arc part-through defect with respect to the bending moment axis, the stress-intensity factor distribution along the crack front is determined by applying a three-dimensional finite element analysis and the superposition priciple. The flaw propagation paths in the diagram of the flaw aspect ratio against the relative crack depth are numerically obtained for rotary bending and compared to those for reversed cyclic bending. It is deduced that, during crack growth, the defect front under the former loading case becomes flatter than that under the latter one.