Fatigue Growth Prediction of Internal Surface Cracks in Pressure Vessels

Abstract

Fatigue crack growth was numerically simulated for various internal surface cracks with initially either semi-elliptical or irregular crack fronts. The simulation was directly based on a series of three-dimensional finite element analyses from which the stress intensity factors along the front of growing cracks were estimated. The fatigue crack growth law obtained from small laboratory specimens was incrementally integrated at a set of points along the crack front, and a new crack front was then re-established according to the local advances at this set of points by using a cubic spline curve. This method enabled the crack shape to be predicted without having to make the usual assumption of semi-elliptical shape. Fatigue analysis results are presented and discussed for fatigue shape developments and deviations from the semi-elliptical shape, aspect ratio changes, stress intensity factor variations during crack growth, and fatigue life predictions. Some of the results were also compared with those obtained by two simplified methods based on one and two degree-of-freedom models, respectively.