FATIGUE LIFE ANALYSES AND TESTS FOR THICK-WALL CYLINDERS INCLUDING EFFECTS OF OVERSTRAIN AND AXIAL GROOVES

A fracture mechanics-based fatigue life analysis was developed for ove rstrained, pressurized thick-wall cylinders with one or several semi-e lliptical-shaped axial grooves at the inner diameter. The fatigue life for a crack initiating at the root of the groove was calculated for v arious cylinder, groove, and crack configurations and for different ma terial yielding conditions. Comparisons were made with fatigue crack g rowth and laboratory life results from A723 thick-wall cylinders, in w hich cannon firing rests were first performed to produce axial erosion grooves; followed by cyclic hydraulic pressurization to failure in th e laboratory. The life analysis, with an initial crack size based on t he expected pre-existing defects, gave a good description of the crack growth and fatigue life of the tests for cylinders with and without g rooves. General fatigue life calculations summarized important materia l and configurational effects on the fatigue life design of overstrain ed cylinders, including effects of material yield strength, cylinder d iameter ratio, stress concentration factor, and initial crack size.