ABSTRACT
Neutron diffraction, however, uniquely possesses the ability to measure accurately and non-destructively residual stresses from the surface to deep within the bulk of engineering components. When using neutron diffraction to measure near-surface strains, the gauge volume is often only partially immersed in the material and so special analyses are required to allow for the changing diffraction geometry. Furthermore, as many surface engineering treatments produce large stress gradients near the surface of components, precise near-surface strain measurement is required, which involves both an accurate determination of measurement position and a small systematic error in strain measurement. This chapter will describe the requirements for precise near-surface strain measurements by neutron diffraction and will then show how these requirements can be met for both monochromatic wavelength measurements (reactor neutron sources) and time-of-flight spectrometry measurements (pulsed neutron sources). Finally, the advantages of near-surface measurement using vertical scanning (Z-scanning) will be illustrated. Examples of near-surface measurements will be given where appropriate.
