Crack propagation in pipes under cyclic axial loading

The propagation of a circumferential external surface flaw in a metallic round pipe under constant amplitude cyclic axial loading is examined through a two-parameter theoretical model. The surface flaw is assumed to present an elliptical-arc shape with aspect ratio alfa = ael / bel. The relative depth csi of the deepest point on the crack front is equal to the ratio between the maximum crack depth ael and the pipe wall thickness t. The edge flaw being considered is shown to follow preferred propagation patterns in the diagram of  against csi.