The problem of developing a dedicated neutron diffractometer for placement on a horizontal reactor channel to measure internal stresses in bulk materials and components under conditions of a limited space is considered. It is shown that the use of a double-crystal monochromator composed of pyrolytic graphite and a focusing bent perfect silicon single crystal is the optimal solution to this problem. The diffractometer with such a monochromator that is installed at the IR-8 reactor of the National Research Center Kurchatov Institute is comparable in luminosity and resolution at a reactor power of 6 MW to modern stress diffractometers at more powerful reactors.

The present work seeks to extend the level of understanding of the stress field evolution during direct laser deposition (DLD) of a 3.2 mm thick multilayer wall of Ti-6Al-4V alloy by theoretical and experimental studies. The process conditions were close to the conditions used to produce large-sized structures by the DLD method, resulting in specimens having the same thermal history. A simulation procedure based on the implicit finite element method was developed for the theoretical study of the stress field evolution. The accuracy of the simulation was significantly improved by using experimentally obtained temperature-dependent mechanical properties of the DLD-processed Ti-6Al-4V alloy. The residual stress field in the buildup was experimentally measured by neutron diffraction. The stress-free lattice parameter, which is decisive for the measured stresses, was determined using both a plane stress approach and a force-momentum balance. The influence of the inhomogeneity of the residual stress field on the accuracy of the experimental measurement and the validation of the simulation procedure are analyzed and discussed. Based on the numerical results it was found that the non-uniformity of the through-thickness stress distribution reaches a maximum in the central cross-section, while at the buildup ends the stresses are distributed almost uniformly. The components of the principal stresses are tensile at the buildup ends near the substrate. Furthermore, the calculated equivalent plastic strain reaches 5.9% near the buildup end, where the deposited layers are completed, while the plastic strain is practically equal to the experimentally measured ductility of the DLD-processed alloy, which is 6.2%. The experimentally measured residual stresses obtained by the force-momentum balance and the plane stress approach differ slightly from each other.

The maximum thickness for ferritic steel specimens’ residual stress measurements using neutron diffraction is known to be about 80 mm. This paper proposes a new neutron diffraction configuration of residual stress measurements for cases that are over 80 mm thick. The configuration utilizes a neutron beam with a wavelength of 1.55 Å diffracted from the (220) plane with a diffraction angle (2θ) of 99.4°. The reason for the deep penetration capability is attributed to the chosen wavelength having enough intensities due to the low cross-section near the Bragg edge and the reduced beam path length (~16 mm) reflected by the large diffraction angle. Neutron diffraction experiments with this configuration can decrease strain errors up to ±150 με, corresponding to a stress of about ±30 MPa.

Prospects for creating a Kurchatov Institute Neutron Center based on the IR-8 reactor with a hydrogen cold neutron source, neutron guides, and new experimental facilities in the neutron guide hall...

Using high-spatial-resolution (~0.2 mm) neutron diffraction, we examined the residual stresses in structural alloyed steel (Cr, Si, Mn) plates, 5 mm in thickness, following shot peening. The analysis revealed that residual stresses form not only near the treated surface but throughout the entire thickness of the plate. Compressive stress zones appear near both treated and untreated surfaces, while tensile stress zones emerge in the middle region. The intensity of the shot peening affects the width of these zones and the magnitude of the maximum stresses. Neutron experiments were conducted to measure stresses near the treated surface of the plates, employing the sin²ψ method. Results obtained via the sin²ψ neutron method were consistent with those from traditional three-component strain measurement techniques. The sin²ψ neutron method proves to be advantageous for measuring stresses near the surfaces of thick samples, since it lacks the limitations of traditional measurement techniques on the thickness of the sample.

A neutron diffraction method has been used to study residual stresses in corrosion-resistant martensitic steel AISI 410 plates of the composition (wt %): 0.15 С, 13 Cr, < 1 Mn, < 1 Si, and Fe for balance obtained by direct laser deposition. The plates are deposited on rigid substrates, which are commonly used in practice in the production of large parts. It has been shown that in plates of different thicknesses (2.2 and 7.4 mm) and the same length and width (70 × 30 mm), the patterns of the stress distribution curves are very close, however, the stresses in a 7.4-mm-thick plate are lower than in a 2.2-mm-thick plate. In both plates (2.2/7.4 mm), the maximum normal tensile stresses (~450/350 MPa) are induced near lateral edges of the substrate. The maximum tensile longitudinal stresses (~400/250 MPa) are induced in the middle section of the plate near the upper edge. In the middle section of a 7.4-mm-thick plate, a stress distribution over the thickness is observed: the stresses near the side surfaces are higher than in the middle section. The thickness distribution becomes more uniform by approaching the plate edges. The stress distribution pattern in plates obtained by direct laser deposition strongly depends on the rigidity of the substrate and, to a lesser extent, on the material and deposition technology.