Stress Characterization of Autofrettaged Thick-Walled Cylinders

Abstract

The inaccessibility of commercial software has necessitated the development of low-cost, general-purpose finite element method (FEM) computer programs for structural analysis. Using the FEM program, the elastic, elastic-plastic, residual and service stresses and displacements in a closed ended, thick-walled cylinder under internal pressure were established. The displacement formulation was implemented and eight-noded brick isoparametric elements chosen. The frontal solution technique and the incremental theory of plasticity were used, as only limited computing facilities were available. The results were found to be in very good agreement with the through-thickness analytical values. The benefits of autofrettage were demonstrated and an optimum overstrain of 16% established for a cylinder with a thickness ratio of 2. The material economy achieved through autofrettage and the limitations imposed are illustrated. The FEM program could therefore be reliably used for other complex geometries and load conditions.

Design of two-pass swage autofrettage processes of thick-walled cylinders by computer modeling

“…[3][4][5][6][7] To improve performance under such conditions, a favorable compressive residual hoop stress can be produced near the bore of the cylinder, commonly by an autofrettage process prior to use. [8][9][10][11][12][13][14][15][16][17] In manufacturing practice, using high pressure to carry out the autofrettage processes is complex, inefficient, and dangerous. This is because a high hydraulic pressure up to 2000 MPa, close to causing cylinder failure, is needed.…”

“…An analytical solution of the swage autofrettage of a constant cross-section cylinder is possible only using simplified material models, such as an elasticperfectly-plastic or a bilinear elastic-plastic model, and is only capable for an internal pressurized autofrettage process which is undergoing uniform deformation for an axi-symmetric model. [8][9][10][11][12][13]16,21,27,30,33 However, deformation in a swage autofrettage process is localized and dynamic with the Bauschinger effect, which in turn affects the residual stress developed. 12,17,[21][22][23]30,[34][35][36][37][38][39][40][41][42][43][44][45][46] Furthermore, for a twopass swage autofrettage process, the deformation induced by the second pass is based on the deformation generated by the first pass and is deformation history dependent.…”

Overstrain in flush optimal-chamfered cross-bored cylinders

“…Autofrettage is often done during manufacture when pressure greater than the leak test pressure is applied. This process results in higher residual stresses and a stronger cylinder, with service stresses being more uniformly distributed [10]. In the presence of cross-bores with complex entry geometry, this distribution is not obvious and a detailed analysis is necessary.…”