Swage autofrettage FEA incorporating a user function to model actual Bauschinger effect

Abstract

An ‘exemplar’ Finite Element Analysis (FEA) solution for swage autofrettage (SA) incorporating Bauschinger effect (BE) for a real steel (A723) is presented. This is derived via a new user programmable function (UPF). Datum geometries for tube and swage were selected in order to permit comparison with previous work.The FEA UPF solution methodology was developed and validated to demonstrate that a 3D analysis will fully replicate a uniaxial tension-compression test on a real material (A723 steel) exhibiting BE, designated UPF(U).A refined formulation designated UPF(S) was then used to obtain a solution for the full 3D axisymmetric SA process. It is first applied to an idealized (BKIN) material; to permit direct comparison with two existing BKIN SA solutions. Finally the UPF(S) formulation is used to obtain a solution for full 3D SA applied to a standard steel (A723) whilst incorporating BE during unloading.The near-bore BE SA solution is compared to an equivalent BE hydraulic autofrettage (HA) solution. Near-bore SA hoop residual stresses are shown to be more compressive and deeper than HA. Conversely SA produces tensile axial stresses, whereas HA generates compression. Finally, it is shown that a subsequent material removal process, applied to the SA tube, may significantly improve near-bore stress profiles.