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 dif fractometer in order to evaluate how the mean stress component of stra in hardening is affected by a reversal in the direction of deformation . Unlike earlier X-ray diffraction studies, by using a neutron diffrac tometer, internal lattice strains can be measured from the whole volum e of the specimen, avoiding the uncertainties arising from relaxation effects related to surface and specimen preparation. The results prese nted confirm the earlier observations of Wilson and Bate's X-ray diffr action experiments in that no permanent difference in the magnitude of the mean stress was found to occur as a consequence of changing the l oading direction. Furthermore, the mean stresses were found to reverse far more quickly as a function of the reverse strain than as a functi on of the macroscopic yield stress, and at a rate that was similar to the maximum seen on initial loading.