Simplifying hypotheses for the fatigue growth analysis of surface cracks in round bars

The fatigue growth of an edge flaw in a round bar under cyclic tension or bending loading is examined. Different assumptions related to the crack front are successively considered, and their validity is discussed from the results of a numerical model using finite element analyses. It is concluded that the crack front geometry must be described by at least two parameters, and that the constant stress intensity factor distribution and the perpendicular intersection criteria should not be used. Experimental data and previous works validate the results of the present model.