FATIGUE GROWTH PREDICTION OF INTERNAL SURFACE CRACKS IN PRESSURE-VESSELS

Fatigue crack growth was numerically simulated for various internal su rface cracks with initially either semi-elliptical oi irregular crack fronts. The simulation was directly based on a series of three-dimensi onal finite element analyses from which the stress intensity factors a long the front of growing cracks were estimated The fatigue crack grow th law obtained from small laboratory specimens was incrementally inte grated 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 s hape to be predicted without having to make the usual assumption of se mi-elliptical shape. Fatigue analysis results are presented and discus sed for fatigue shape developments and deviations from the semi-ellipt ical shape, aspect ratio changes, stress intensity factor variations d uring crack growth and fatigue life predictions. Some of the results w ere also compared with those obtained by two simplified methods based on one and two degree-of-freedom models, respectively.