An examination of the mean stress contribution to the Bauschinger effect by neutron diffraction

Bauschinger experiments have been carried out in situ on a neutron diffractometer in order to evaluate how the mean stress component of strain hardening is affected by a reversal in the direction of deformation. Unlike earlier X-ray diffraction studies, by using a neutron diffractometer, internal lattice strains can be measured from the whole volume of the specimen, avoiding the uncertainties arising from relaxation effects related to surface and specimen preparation. The results presented confirm the earlier observations of Wilson and Bateʹs X-ray diffraction experiments in that no permanent difference in the magnitude of the mean stress was found to occur as a consequence of changing the loading direction. Furthermore, the mean stresses were found to reverse far more quickly as a function of the reverse strain than as a function of the macroscopic yield stress, and at a rate that was similar to the maximum seen on initial loading.