Non-destructive determination of the 3D residual stress in a AA7050 upper wing skin-stringer panel using neutron diffraction

Neutron diffraction has been used to determine the full three dimensional residual stress in a demonstrator variable polarity plasma arc (VPPA) welded Al-7150 skin-stringer fatigue sample. Uniquely, the design of this demonstrator panel took into account the residual stress distribution likely to present due to the presence of the weld by using residual stress data measured on smaller laboratory-sized butt welded plates. The stress-free lattice parameter was obtained by measuring a comb sample and point-to-point strain corrections for the three principal directions were performed to determine strains and hence calculate stresses. A significant amount of stress redistribution was observed in the demonstrator sample when compared to the laboratory size plate specimen