Fatigue behaviour of cracked pipes under rotary bending

The propagation of a transversal surface flaw in a pipe subjected to rotary bending is analysed through a two-parameter theoretical model. The crack front is assumed to present an elliptical-arc shape. For any position of the flaw with respect to the bending moment axis, the stress-intensity factor (SIF) distribution along the crack front is determined by means of the finite element method and the superposition principle. The agreement between such values of SIF and those deduced by other authors is satisfactory. Then the fatigue crack growth is examined for different initial flaw configurations, and the results for rotary bending are compared to those for reversed cyclic bending