Mode I fatigue growth analysis of a sickle surface crack in a cylindrical bar

The fatigue growth of a sickle-shaped surface crack in a metallic round bar under bending loading is examined. The flaw, located in a plane perpendicular to the longitudinal axis of the bar, is assumed to present an elliptical-arc shape during the whole propagation and, therefore, can be defined by the crack depth at the most internal point on the defect front, and the aspect ratio of the above ellipse. Linear elastic fracture mechanics concepts are used to calculate the Stress-Intensity Factor (SIF) along the crack front, by employing a 20-node isoparametric finite element model with quarter-point wedge finite elements arranged near the defect. The SIF values are computed using the one-quarter point displacement method and assuming the plane strain condition along the crack front. The numerical results obtained are compared with experimental data available in the literature. Then, a procedure based on the Paris-Erdogan law is applied in order to simulate the crack growth under cyclic bending. Fatigue analysis results are presented in terms of crack paths for some initial flaw geometrical configurations being examined.