Scientists and engineers use the HB-2B Neutron Residual Stress Mapping Facility (NRSF) to study residual stresses in steel, aluminum, superalloys like Inconel, and other such structural materials. Elastic strain in these materials can be determined by measuring their interplanar atomic spacing, and this instrument is designed to use the high- penetration power of neutrons to generate “maps” of the strain resulting from residual or applied stresses in bulk materials. A detailed understanding of residual stresses is critical for the safe and effective functioning of virtually every type of structural engineering material.
The HB-2B NRSF beam line is optimized for strain measurement and determination of residual stress in engineering materials. The incident beam is delivered at a fixed angle of 88° by elastically bent silicon crystal monochromators. Both vertical and horizontal focusing are used. The wavelength is chosen from a variety of monochromator crystal settings with a selection of wavelengths from 1 to 2.7 Å. The sample goniometer is designed for spatial scanning of residual stresses at depths from a millimeter to several centimeters. Spatial resolution at a fraction of a millimeter is possible depending on the material.
The scattering from the test sample is recorded with seven, linear-position-sensitive detectors. The detectors are stacked vertically and have a horizontal acceptance of 9 cm at a distance of 80 cm from the sample test point. The nominal scattering angle (at the center of the position-sensitive detector) can be set at any value from 30° to 140°, but is normally located near 90°. The top and bottom detectors span 17° out of the horizontal scattering plane.
In strain scanning, “gauge volume” is defined by the intersection of the incident and scattered beams. The dimensions of the incident beam slits range from 1-cm to less than 1-mm. The scattering slit with the same size range is set close to the test specimen. The location of these slits controls the size of the gauge volume and also defines the translation range over which the test specimen can be scanned. The determination of residual stress from measurements of residual strain requires measurements of strain in at least three, orthogonal strain directions. In some instances, it is not feasible to carry forward a complete stress determination, and in such cases, it is advisable to use a comparison of strain measurements and calculated strains for validation of residual stress calculations.
Available sample environments include a uniaxial (tension or compression) load frame, and a Eulerian cradle, built sample environments, such as high-temperature furnaces and, magnets, can be accommodated on the XYZ- positioning stage but requires coordination with the instrument staff.
The penetrating power of neutrons is very useful in scanning residual stresses in engineering materials. Examples of past work include scans of welds, forgings, extrusions, bearings, and materials under applied stress, as well as scans of piezoelectric materials under the influence of electrical fields. The study of post-weld annealing effects on residual stresses in welded steel plates provided a nondestructive and detailed delineation of stress pattern changes arising from the heat treatment.
|Selectable Wavelength (Monochromator setting)|
88°, λ = 1.452 Å (Si 511); 1.540 Å (Si 422); 1.731 Å (Si 331); 1.886 Å (Si 400); 2.275 Å (Si 311); 2.667 Å (Si 220)
|Flux on sample||3 x 107 n/cm2/s|
(Si 331 and Si 400)
|Detector angle range||70 – 110°|
|Detection system||7 linear position-sensitive detectors|
|Position-sensitive detector coverage||5° 2Θ ± 17° out of plane|
|Z elevator Z translation|
Z ± 100 mm, 500 Kg
|Nominal Gauge volume|
Width: 0.3–5 mm;
|Peak location precision||0.003° 2Θ|
|Sample environments||Load frame for tension and compression (2,267-kg)|
Huber Eulerian cradle for tensor and texture