Comparative measurements on autofrettaged cylinders with large Bauschinger reverse yielding zones

Abstract

A comparative study to map the residual strain/stress states through the walls of autofrettaged thick-walled steel cylinders has been conducted with neutron diffraction, Sachs boring and the compliance methods. Test samples with different wall thickness ratios were prepared to have significant amounts of reverse yielding due to the Bauschinger effect. All three methods indicate that the autofrettage action primarily influenced the hoop stresses, which varied rapidly close to the bores from compressive to tensile within the first half of the wall thickness. Quantitatively, results from the neutron diffraction and Sachs boring techniques compare favourably across large regions of the cylinder walls, while the compliance results showed different features. The existence of reverse yielding close to the cylinder bores has been sensed to different magnitudes and distances from the bores. Plastically yielded material regions identified from the neutron diffraction results correlated well with theoretical modelling.