Different Solutions for Stress and Strain Fields in Autofrettaged Thick-Walled Cylinders

In the first part of the paper we will present an analytical solution to the plastic stress and strain distribution induced by a single over-pressure cycle in a cylindrical vessel. The solution is valid for materials which, during the loading phase, can be described by a linear hardening law as well as by the modified Ramberg-Osgood law. We will clarify the conditions for which the stress field expressions can be simplified, thus facilitating a parametric analysis of their increase with respect to the values one would obtain when considering an ideal elastic-perfectly plastic behaviour of the material. In the second part of the paper, residual stress fields will be numerically evaluated, taking into account, during the unloading phase, both the variability of the stress flow and the Bauschinger effect factor as a function of pre-strains.