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In this paper the effect of the re-autofrettage process on the residual stress distribution at the wall of a thick-walled tube is considered. For accurate material behavior modeling, it is assumed that the yield surface is a function of all the stress invariants. Also for estimating the behavior of the material under loading–unloading process, a modified Chaboche's hardening model is applied. For evaluation of this unloading behavior model a series of loading–unloading tests are conducted on specimens that are made of the high strength steel, DIN1.6959. In addition the finite element simulations are implemented to simulate the re-autofrettage process and to estimate the residual stresses. The numerical results show that the re-autofrettage process without heat treatment only improves the residual stress distribution in high autofrettage percentage and for low autofrettage percentage this method is not beneficial. However, the re-autofrettage process with ‘‘heat soak’’ treatment generally improves the residual stress distribution.

Theoretical and numerical analyses of rotating disks with non-uniform thickness and material properties subjected to thermo-mechanical loadings have been carried out by variable material properties (VMP), Runge–Kutta's (RK) and finite element (FE) methods. The material is assumed to be elastic-linear hardening. A power form function is used to describe the temperature gradient with the higher temperature at outer surface. Von-Mises theory has been used as failure criterion. The effects of geometry, material and thermal loading parameters as well as boundary conditions on radial, hoop and equivalent stress distributions which have not been studied in much detail in previous works have been investigated. Good agreement between the results obtained from the three proposed methods is observed. It has also been observed a coarser mesh can be used in RK. Compared with previous works published by authors using variable iteration method, Adomian method, and Homotopy analysis method, VMP was found to be much easier for computer implementation and required less CPU time and computer memory and hardware.

In this study, residual stress distributions in autofrettaged homogenous spherical pressure vessels subjected to different autofrettage pressures are evaluated. Results are obtained by developing an extension of variable material properties (VMP) method. The modification makes VMP method applicable for analyses of spherical vessels based on actual material behavior both in loading and unloading and considering variable Bauschinger effect. The residual stresses determined by employing finite element method are compared with VMP results and it is demonstrated that the using of simplified material models can cause significant error in estimation of hoop residual stress, especially near the inner surface of the vessel. By performing a parametric study, the optimum autofrettage pressure and corresponding autofrettage percent for creating desirable residual stress state are introduced and determined.

An analytical method for reconstructing residual stresses within axisymmetric cylinders is presented. The method uses the stress equilibrium and boundary conditions together with an Airy stress function that satisfies these conditions. The method allows the reconstruction of residual stresses from limited measurements. The analysis is also coupled to a least squares approximation and a regularization analysis to provide stability of the inverse problem. The application of the method is demonstrated for four cases; two correspond to analytical solutions for residual stresses created during autofrettage and two sets of experimental results for through wall measurements of residual stresses. In all cases the reconstructions are successful.