Problems in neutron strain measurement with large gauge volume

Suzuki, Hiroshi  ; Akita, Koichi; Vladimir, L.*

Problems in neutron strain measurement with large gauge volume were discussed based on strain measurements of a 50 mm thick bent bar and an annealed specimens using the TOF and the angular dispersive methods. It was experimentally verified that the change in the neutron-weighted center of gravity position (ncog position) by the neutron attenuation effect caused an apparent shift in strain distribution due to the weighted average effect in the gauge volume. Furthermore, typical pseudo-strain distribution near the sample surface due to the geometrical effect was observed in a surface strain scanning, and the pseudo-strains were also observed even when perfectly immersing the gauge volume in the sample due to a change in a ncog position by the neutron attenuation effect. The trend and magnitude of the pseudo-strain distribution were shifted with a change in the gauge size, and it can be explained by typical modeling with consideration of effects of the incident neutron beam divergence and the wavelength distribution at the edge around a gauge volume.