Determination of Steep Stress Gradients at Surfaces or Interfaces by Means of Neutron Diffraction

Abstract

A series of measurements has been performed on the neutron strain scanner of the Laboratoire Léon Brillouin in order to explore the limits of the spatial resolution achievable by neutron stress analysis. Two types of samples were investigated, i.e. sandwich structures consisting of thin sheets of copper and aluminum nitride (A1N) and shot peened steel sheets. With slits before and after the sample as small as 0.3 × 10 mm² (A1N) or even 0.15 × 10 mm² (steel) counting times were not longer than 1–2 h/peak. Checks revealed that a spatial resolution of ≈0.3 mm (A1N) resp. 0.15 mm (steel) was indeed achieved in the direction perpendicular to the surface. Using partial immersion of the gauge volume, near-surface/interface strains could be explored with even higher spatial resolution, down to ≈30 µm in the case of steel. The stress gradients determined by neutron diffraction were checked by measurements using other techniques.