NUMERICAL-ANALYSIS OF FATIGUE GROWTH OF EXTERNAL SURFACE CRACKS IN PRESSURIZED CYLINDERS

Fatigue crack growth is modelled by a novel numerical technique for va rious external surface cracks with initially either semi-elliptical or irregular crack fronts. The technique employs a three-dimensional fin ite element analysis to estimate the stress intensity factors at a set of points of the crack front, then calculates local crack advances by integrating a type of Paris fatigue crack growth law at this set of p oints, and finally establishes a new crack front and its corresponding finite element model. The multiple degrees-of-freedom model enables t he crack shape to be predicted directly during crack growth without ha ving to make the common semi-elliptical assumption, and therefore prov ides more accurate predictions. Fatigue analysis results are presented and discussed, including fatigue shape developments and deviations fr om the semielliptical shape, together with aspect ratio changes, stres s intensity factor variations during crack growth and fatigue life pre dictions. Some of these results are also compared with those obtained by two simplified predictive methods based on one and two degrees-of-f reedom models together with a stress linearisation. (C) 1997 Elsevier Science Ltd.