Stress measurement near surface region by strain scanning method using neutron diffraction

The strain scanning method was widely used for the measurement of the stress distribution beneath the specimen surface. For the strain scanning method, the diffracted beams are defined by slits so that only a small illuminated volume can diffract into the detector. When making measurements near surface some of the gauge volume may lie outside of the sample, in which case of the gauge is not coincident with the center of the diffracting volume and the measured diffraction angle changes even in the stress free materials. In the present study, the stress distribution of the shot peened material was measured by the strain scanning method using neutron and synchrotron radiation. For the neutron method, two kinds of optical system were adopted. At first, the vertical slit system was used for the transmission measurement. Then the horizontal slit system was adopted to avoid the surface effect. When the obtained data was corrected by the stress on the surface measured by the conventional sin2ψ method, the stress distribution measured by the neutron method agreed very well with that obtained by the synchrotron method and the surface removal method using conventional X-ray. (author)