Neutron Residual Stress Mapping Facility
(HB-2B)
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|
HB-2B Fact sheet (pdf) |
| Monochromator: |
|
vertically
and horizontally focussed Si |
| Monochromator
angle: |
|
88°,  = |
1.452  (511); 1.731 (331);
1.886 (400); 2.275 (311) |
| Detector angle settings |
|
30–150° |
| Detection system: |
|
7 Position-Sensitive
Detectors |
| X-Y-Z translation ranges: |
|
X ± 200 mm,
Y ± 100 mm, Z ± 100 mm |
| Omega goniometer mount: |
|
X ± 25 mm, Y±
25 mm |
| Nominal Gauge volume: |
|
0.2 mm x 10
mm x 0.2 mm to 3 mm x 20 mm x 3 mm |
| Position-sensitive detector range: |
|
7°
2Θ at 800 mm sample-to-detector distance |
| Detector resolution: |
|
1.8 mm |
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 of piezoelectric materials
under the influence of electrical fields. Strain scanning studies of co-extruded
piping for Kraft paper process liquor boilers were instrumental in the
selection of alternative alloys for improved boiler performance. 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.
Two diffractometers are available
for residual stress measurements at the HB-2B beam port. The X-Y-Z instrument
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 second instrument
is based on a Kappa goniometer that can be used in strain scanning of
large grained materials and single crystals. The instrument can measure
preferred grain orientation in polycrystalline materials as well. The
two instruments are designed for convenient interchange at the HB-2B beam
port. (Only the X-Y-Z instrument is shown in Fig. 2B.5.)
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 1.2 to 2.4 Å. The monochromator device consists of two silicon crystal
assemblies with differing crystallographic orientations.
The scattering from the test
sample is recorded with five 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
30° to 140°. The top and bottom detectors span ±10°
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 collimator range from 1 cm
to less than 1 mm. The scattering collimator having the same size range
is set close to the test specimen. The location of these collimators 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. In such
cases, it is advisable to use a comparison of strain measurements to calculated
strains for validation of residual stress calculations.
Contacts
Camden Hubbard
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