Analytical and numerical analysis of swage autofrettage process applied to thick walled cylinders

Autofrettage is the process of residual stress formation on the walls of the thick walled cylinders before their usage. These residual stresses help to increase the pressure bearing capacity of the thick walled cylinders by eliminating some stresses during the high pressure applications. In practice, there are two different autofrettage methods as hydraulic and swage. Swage autofrettage is a more economical method to form beneficial residual stresses in the thick walled cylinders when it is compared with the hydraulic autofrettage method. In this study, it is investigated how the residual stresses, that occur as a result of the swage autofrettage during manufacturing of a heavy armour barrel, affect the stress distributions that occur at the operating conditions of the barrel. At first, the stress distributions are obtained analytically for both Tresca and Von Mises criteria. Then, the verification of the analytical model is performed by making use of a commercial software which uses the finite element method. In the calculations, the mandrel's outer radius is considered as constant but the bore value of the cylinder is changed and the results for different % interference ratios are compared. The obtained results show that the maximum equivalent stress in an autofrettaged cylinder at operating pressure occurs in the elastic-plastic junction region. The equivalent stress distributions are obtained at 400 MPa operating pressure for different % interference values. The equivalent stress distributions are obtained by the analytical model for both Tresca and Von Mises criteria and the optimum interference value is found as 1% with respect to both two yielding criteria. However, in result of finite element model, the optimum interference value is found as 1% for Tresca criterion whereas it is found as 1,5% for Von Mises criterion. Bauschinger effect is represented by the kinematic hardening model in both analytical model and finite element model. According to the results that are obtained by analytical model, Bauschinger effect does not cause a secondary plastic yielding. However, according to the results that are obtained by finite element model, it is seen that Bauschinger effect causes a secondary plastic yielding.