Effects of gauge volume on pseudo-strain induced in strain measurement using time-of-flight neutron diffraction
Suzuki, Hiroshi ; Harjo, S. ; Abe, Jun; Xu, P. G. ; Aizawa, Kazuya ; Akita, Koichi
Effects of gauge volume on pseudo-strains induced in neutron strain measurements using the time-of-flight neutron diffraction due to influences of the neutron attenuation, the surface-effect and a strain distribution were discussed on strain measurements in an annealed and a bent ferritic steel bars. An average strain in a gauge volume was weighted towards a neutron-weighted center of gravity (ncog) position, and the weighted average strain was apparently changed following change in the ncog position with an increase of the gauge volume. On the other hand, typical pseudo-strains due to the surface-effect were appeared in near-surface strain measurements when a gauge volume is incompletely filled in a sample. Furthermore, a pseudo-strain due to change in the ncog position was observed even when perfectly immersing the gauge volume in a sample, and it was increased with an increase of the gauge volume. These pseudo-strains measured were well simulated by taking into account an incident neutron beam divergence additionally in the conventional model. Therefore, it was clarified that the incident neutron beam divergence must be an important parameter to make a modeling of pseudo-strains induced in the strain measurement using the TOF engineering diffractometer.