Feasibility Study of Thermal Autofrettage Process

Abstract

Usually, autofrettage is achieved either by applying hydraulic pressure to the bore of the thick-walled cylinder or by pushing an oversized mandrel through the bore to deform the cylinder plastically. This produces the compressive residual stresses on the inner side of the cylinder, enabling the cylinder to withstand higher working pressure. There are certain difficulties in these methods of autofrettage. This work proposes a novel method for achieving autofrettage that involves creating temperature gradient in the wall of the cylinder. The proposed process is analyzed theoretically considering strain hardening. The simulation results and preliminary experiments indicate an encouraging trend for the feasibility of the proposed process.

Comparison of plane-stress, generalized-plane-strain and 3D FEM elastic–plastic analyses of thick-walled cylinders subjected to radial thermal gradient

“…The inner wall is subjected to a temperature T a and the outer wall is subjected to a temperature T b such that T b > T a . The thermoelastic-plastic stress analyses of a short cylinder (hollow circular disk) using the assumption of plane stress ( z = 0) incorporating strain hardening was carried out in [18] . Another analytical model based on a generalized plane-strain condition ( z = constant) applicable for long cylinders is available in [19] .…”

“…The hardening coefficient K and strain hardening exponent n for the cylinder are taken as 58.18 MPa and 0.482 [18] . The temperature difference required to initiate the yielding at the inner wall of the cylinder is obtained as 53.66 °C for plane stress model and 37.56 °C for generalized plane strain model.…”

“…The strain hardening of the material during plastic deformation is considered. For comparison of the FEM results with the plane-stress and generalized-plane-strain models, the analytical solution developed in [18] and the stress solution devel- Mesh 9 indicated in the boldfaced is the optimum mesh.…”

“…In general, a thick-walled cylinder may undergo simultaneous plastic deformations emanating from both inner and outer walls under the condition of high thermal gradient. This case was analyzed by Kamal and Dixit [18,19] for a hollow disk and cylinder assuming plane stress and generalized plane strain conditions, respectively. The analyses are based on Tresca yield criterion and its associated flow rule.…”

“…The analyses are based on Tresca yield criterion and its associated flow rule. The effect of strain hardening was considered in the plane stress model [18] . However, the generalized plane strain model [19] did not include the strain hardening, although the theoretical results matched well with the experiments [20] .…”