Gauge volume effects in residual stress determination by neutron diffraction: The strength differential effect in metal matrix composites

In this work, the residual stress (RS) in two differently prepared 6061Al–15 vol.% SiCw composites and their respective unreinforced alloys has been studied by neutron diffraction (ND). Hydrostatic and deviatoric stresses were found in both unreinforced alloys and composites. The presence of hydrostatic microscopic RS agrees with the fact that a large fraction of the SiC composites whiskers is randomly oriented. The axial deviatoric microscopic stress arises from the remaining population of the SiC whiskers aligned along the extrusion axis.Different hydrostatic macro- and micro-RS were determined upon using different instrumental set-ups, and therefore different gauge volumes. This can be attributed to the different size of the sampled regions in the specimens, to the direct dependence of the micro- (elastic mismatch) on the macro-stress and to the sensitivity of the SiC powder reference to the set-up. On the contrary, the deviatoric macro and micro-RS did not vary with the gauge volume. Therefore, all phenomena (e.g. the strength differential effect) linked to the deviatoric micro-RS can be considered to be independent of the experimental set-up.