Draft Standard for the Measurement of Residual Stresses by Neutron Diffraction

Abstract

Residual stresses can have important consequences for the load carrying capacity and safety of engineering components. 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 ±0.1mm 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.