Effect of autofrettage on the ultimate behavior of thick cylindrical pressure vessels

Major applications of thick cylinders are in the defense sector. Stress distributions especially under elastic-plastic conditions are more complex in thick cylinders. Though the cylinder may not be strained to ultimate in service, assessment of factor of safety is essential. Simulating elastic-plastic material behavior of cylinders using the uniaxial test data is more dependable and the finite element analysis (FEA) software has got this capability. A procedure using a suitable material model is demonstrated in this study utilizing the FEA software Ansys. The instability criterion followed in Svensson's pressure expansion relationship is used in the process of FEA. The predicted failure pressure is very close to the literature test data as well as few theories that have been highlighted. Moreover, thick cylinders are mostly subjected to autofrettage in applications like gun barrels to enhance service pressure and fatigue life. Hence it is attempted to simulate the development of residual stress due to autofrettage and its effect on the ultimate behavior on the pressure vessels. The residual stress developed is superimposed on the stresses due to internal pressure which causes the redistribution of stresses throughout the thickness. There is a marginal increase in burst pressure due to autofrettage. Though the effect could be made significant by increasing the autofrettage pressure, it gives detrimental effects on the other side by developing tensile residual stresses on the external surface. Hence, with the permissible extent of autofrettage, the effects are found to be marginal and this knowledge helps assess the safe loading limits.