Diffraction Peak Displacement in Residual Stress Samples Due to Partial Burial of the Sampling Volume

Near-surface measurement of residual strain and stress with neutron scattering complements and extends the surface residual stress measurements by X-ray diffraction. However, neutron diffraction measurements near surfaces are sensitive to scattering volume alignment, neutron beam wavelength spread and beam collimation and, unless properly understood, can give large fictitious strains. An analytic calculation and a numerical computation of neutron diffraction peak shifts due to partial burial of the sampling volume have been made and are compared with experimental measurement. Peak shifts in a strain-free nickel sample were determined for conditions where the sample surface is displaced so that the scattering gage volume is partially buried in the sample. The analytic and numerically computed peak shifts take into account the beam collimation, neutron source size, monochromator crystal mosaic spread and the collection of diffracted intensity with a linear position-sensitive counter.