Fatigue life improvement of an autofrettaged thick-walled pressure vessel with an external groove

This thesis presents an investigation into a fatigue life improvement of an autofrettaged thick-walled pressure vessel with an external groove subjected to pulsating internal pressure along with mean strain and mean stress effects on strain-controlled low cycle fatigue behavior.;Linear elastic stress analysis of an autofrettaged thick-walled pressure vessel with an external groove is done using a finite element method. Autofrettage loading is performed using a thermal loading analogy. Change of external groove geometry is made using a quasi-optimization technique and finite element method to achieve longer fatigue life by relieving the stress concentration at the groove root. Surface treatment using shot peening is employed to produce compressive residual stresses at the vulnerable surface of the groove root to counteract the high tensile stresses. An evaluation of the fatigue life of an autofrettaged thick-walled pressure vessel with an external groove was done through a series of simulation fatigue tests using C-shaped specimens taken from the thick-walled pressure vessel.;The effect of mean strain and mean stress in the high strength pressure vessel steel of ASTM A723, Grade 1, Class 4, is reported from the strain-controlled low cycle fatigue tests using smooth cylindrical axial specimens. Three mean stress parameters from Morrow, Smith et al. and Lorenzo-Laird are used to reduce low cycle fatigue test data including a wide range of strain ratios into a single line on the strain-life plot. Life estimation of an autofrettaged thick-walled pressure vessel is made by incorporating the linear and modified Neuber's rule with results from linear elastic finite element stress analysis and mean stress parameters obtained in low cycle fatigue testing.