Finite Element Investigation of Bauschinger Effect in High-Strength A723 Pressure Vessel Steel

The Bauschinger effect has been evaluated in high-strength pressure vessels. A simple initial test suggested that a biaxial Bauschinger effect was present and that it was different from previously published uniaxial Bauschinger results. The difference was believed to be significant, so further investigation was undertaken. Several full-size A723 steel gun sections were heavily overstrained and subjected to slit tests in order to measure opening angles and displacements. These geometries were then modeled with finite element (FE) analysis using both ideal autofrettage stresses and Bauschinger modified stresses, which were based on previously published uniaxial Bauschinger test results. Because techniques available for predicting reverse yielding for overstrained pressure vessels were limited, a simple methodology for predicting the yield surface upon reverse yielding from a series of uniaxial Bauschinger test data was developed and is presented. This methodology, when used in the FE predictions, compares favorably with analytical predictions made previously. Comparisons of slit-opening results measured from pressure vessel sections with FE calculations using uniaxial Bauschinger data are made. The opening displacements comparison between the uniaxial predictions and those measured from the heavily overstrained sections with biaxial stresses are so subtle $(<1mm)$ that the tests appear to be inconclusive.