Development of procedures for the measurement of residual stress by neutron diffraction

Neutron diffraction is a non-destructive method for determining residual stresses in crystalline materials. It is a relatively new technique and no standard is currently available for making these measurements. This paper gives the background to research that has been carried out to develop a standard. It outlines the main findings and indicates the precautions that are required to achieve accurate positioning and alignment of specimens (and components) in a neutron beam and the analysis required to obtain reliable results. It also shows that special attention is needed in dealing with near-surface measurements because of surface aberration. It is demonstrated that, provided the recommended procedures are followed, a positional tolerance of ±0.1 mm can be achieved with an accuracy in strain of ∼10-4, to give a resolution in residual stress of ∼7 to 20 MPa in most materials of practical interest.