Two-Directional Stress-Free Comb Sample for Weld Study by Neutron Diffraction

Neutron diffraction is a powerful tool for investigations of residual stresses in bulk polycrystalline samples. The method is based on measuring the relative change in the spacing, d, in the stressed lattice with respect to the reference, or stress-free, spacing d0. Therefore, the precision of measuring the stress strongly depends on the precision of measuring d0. Conventional stress-free comb sample with teeth in the normal direction considerably simplifies measurement of d0 in welds. However, it has been shown that in a thick weld, a “too long tooth” may contain residual stress. In this study, the idea of two-directional comb sample is proposed. Experiments have shown more complete stress relief in this comb type.