The evaluation of the 3-D residual stress field due to hydraulic autofrettage in a finite length cylinder incorporating the Bauschinger Effect Factor based on the "zero offset yield stress"

The autofrettage process increases the ability of a pressurized cylinder to withstand higher pressure values prior to the onset of yielding. The yield-pressure of an autofrettaged cylinder is strongly affected by the Bauschinger Effect (BE) that results in a reduction of the yield stress in compression. This reduction, which is measured by the Bauschinger Effect Factor (BEF), highly depends on the exact determination of the yield point. The present analysis suggests a new 3-D axisymmetric model for solving the residual stress field in a hydraulically autofrettaged finite-length cylinder including the BEF curve evaluated by using the newly proposed concept of the "zero offset" yield point definition. The numerical model is validated experimentally using axial and tangential strain gauges attached to a thick walled cylinder undergoing hydraulic pressurization. The experimental set-up enables continuous strain measurements vs. the increasing pressure. The calculated strains and displacements as well as the initial yield-pressure were found to be in very good agreement with the measured values.