scholarly journals High-Resolution Strain/Stress Measurements by Three-Axis Neutron Diffractometer

Materials ◽  
2020 ◽  
Vol 13 (23) ◽  
pp. 5449
Author(s):  
Pavol Mikula ◽  
Vasyl Ryukhtin ◽  
Jan Šaroun ◽  
Pavel Strunz
Keyword(s):  
High Resolution ◽  
Neutron Diffraction ◽  
Perfect Crystal ◽  
Diffraction Profile ◽  
Stress Measurements ◽  
Neutron Diffractometer ◽  
Large Bulk ◽  
Gauge Volume ◽  
Strain Stress ◽  
Point Detector

Resolution properties of the unconventional high-resolution neutron diffraction three-axis setup for strain/stress measurements of large bulk polycrystalline samples are presented. Contrary to the conventional two-axis setups, in this case, the strain measurement on a sample situated on the second axis is carried out by rocking the bent perfect crystal (BPC) analyzer situated on the third axis of the diffractometer. Thus, the so-called rocking curve provides the sample diffraction profile. The neutron signal coming from the analyzer is registered by a point detector. This new setup provides a considerably higher resolution (at least by a factor of 5), which however, requires a much longer measurement time. The high-resolution neutron diffraction setting can be effectively used, namely, for bulk gauge volumes up to several cubic centimeters, and for plastic deformation studies on the basis of the analysis of diffraction line profiles, thus providing average values of microstructure characteristics over the irradiated gauge volume.

High Resolution Residual Strain/Stress Measurements on Three Axis Neutron Diffractometer

2021 ◽  
Vol 1166 ◽  
pp. 33-40
Author(s):  
Pavol Mikula ◽  
Jan Šaroun ◽  
Vasyl Ryukhtin
Keyword(s):  
High Resolution ◽  
Profile Analysis ◽  
Perfect Crystal ◽  
Polycrystalline Materials ◽  
Line Profile Analysis ◽  
Stress Measurements ◽  
Large Bulk ◽  
Strain Stress ◽  
Set Up

Focusing 3-axis diffractometer set-up equipped with bent perfect crystal (BPC) monochromator and analyzer offers the sensitivity in determination of strains Dd/d < 10-4 in polycrystalline materials which is about one order of magnitude higher with respect to that of conventional 2-axis neutron scanners. It also offers possibility of line profile analysis for reasonable sample volumes and counting times. In this paper, the feasibility of using the 3-axis set-up even for measurements of rather large bulk polycrystalline samples with an acceptable resolution is presented. As the 3-axis set-up exploits focusing in real and momentum space, by a proper adjustment of the curvature of the analyzer, a high-resolution determination of the lattice changes can also be achieved even on large irradiated gauge volumes, though with a slightly relaxed resolution. It can be successfully exploited namely, in the strain/stress measurements on samples exposed to an external load, e.g. in tension/compression rig, in aging machine etc. In addition to the original performance where the analysis is carried out by rocking the BPC analyzer and the neutron signal registered by a point detector, a new alternative is offered which uses a fixed rocking angle position of the analyzer and the detector signal is registered by a one-dimensional position sensitive detector (PSD). This trick makes possible in some cases the elastic strain/stress measurements considerably faster and thus reduces the drawback of the time consuming step-by-step analysis.

High-Resolution Neutron Diffraction for Nondestructive Analysis of Residual Stresses in Polycrystalline Materials

2006 ◽  
Vol 3-4 ◽  
pp. 331-336
Author(s):  
Pavol Mikula ◽  
Petr Lukáš ◽  
Miroslav Vrána
Keyword(s):  
High Resolution ◽  
Neutron Diffraction ◽  
Bragg Diffraction ◽  
Polycrystalline Materials ◽  
Nondestructive Analysis ◽  
Strain Measurements ◽  
Neutron Diffractometer ◽  
Stress Studies ◽  
Strain Stress ◽  
Diffraction Optics

The performance of an unconventional high-resolution neutron diffractometer using Bragg diffraction optics that can be efficiently employed in strain/stress diffractometers are reported. Presented results demonstrate their experimental abilities for powder diffraction, namely for residual strain/stress measurements. In addition to the macrostrain scanning capability, the device can also be used for microstrain/stress studies by suitable analysis of the diffraction profiles. Two examples of the strain measurements are presented.

High-Resolution Neutron Diffraction Employing Bragg Diffraction Optics: A Tool for Advanced Nondestructive Testing of Materials

2008 ◽  
Author(s):  
Pavol Mikula ◽  
Miroslav Vra´na ◽  
Lubos Mra´z ◽  
Leif Karlsson
Keyword(s):  
High Resolution ◽  
Neutron Diffraction ◽  
Nondestructive Testing ◽  
Bragg Diffraction ◽  
Internal Stresses ◽  
Material Research ◽  
Neutron Sources ◽  
Neutron Diffractometer ◽  
Strain Stress ◽  
Diffraction Optics

The present paper deals with an efficient use of high-resolution neutron diffraction for material research studies, namely for studies of internal stresses. It is demonstrated that a conventional neutron diffractometer equipped with focusing elements can be used as neutron strain/stress scanner with medium power neutron sources. Principles of this enhanced technique are introduced and an example of internal strain/stress measurements in the vicinity of welds is presented.

Neutron diffractometer using Bragg diffraction optics for high-resolution strain/stress measurements

1997 ◽  
Author(s):  
Pavel Mikula ◽  
Petr Lukas ◽  
Jan Saroun ◽  
Pavel Strunz ◽  
Miroslav Vrana ◽  
...  
Keyword(s):  
High Resolution ◽  
Bragg Diffraction ◽  
Stress Measurements ◽  
Neutron Diffractometer ◽  
Strain Stress ◽  
Diffraction Optics

High resolution neutron diffraction techniques for strain/stress measurements at a steady state reactor

1994 ◽  
Vol 75 (1-4) ◽  
pp. 305-310
Author(s):  
M. Vrána ◽  
P. Mikula ◽  
P. Lukáš ◽  
J. Šaroun ◽  
P. Strunz
Keyword(s):  
Steady State ◽  
High Resolution ◽  
Neutron Diffraction ◽  
Stress Measurements ◽  
Strain Stress

Investigation of Residual Strains of the Second Kind in Plastically Deformed Metallic Materials

1994 ◽  
Vol 376 ◽  
Author(s):  
M. Vrána ◽  
P. Klimanek ◽  
T. Kschidock ◽  
P. Lukáš ◽  
P. Mikula
Keyword(s):  
High Resolution ◽  
Neutron Diffraction ◽  
Stacking Faults ◽  
Metallic Materials ◽  
Line Broadening ◽  
X Ray Diffraction ◽  
X Ray ◽  
Neutron Diffractometer ◽  
Residual Strains ◽  
Good Agreement

ABSTRACTInvestigation of strongly distorted crystal structures caused by dislocations, stacking-faults etc. in both plastically deformed f.c.c. and b.c.c. metallic materials was performed by the analysis of the neutron diffraction line broadening. Measurements were realized by means of the high resolution triple-axis neutron diffractometer equipped by bent Si perfect crystals as monochromator and analyzer at the NPI Řež. The substructure parameters obtained in this manner are in good agreement with the results of X-ray diffraction analysis.

Analytical model for neutron diffraction peak shifts due to the surface effect

2013 ◽  
Vol 46 (3) ◽  
pp. 628-638 ◽  
Author(s):  
Jan Šaroun ◽  
Joana Rebelo Kornmeier ◽  
Michael Hofmann ◽  
Pavol Mikula ◽  
Miroslav Vrána
Keyword(s):  
Neutron Diffraction ◽  
Analytical Model ◽  
Surface Effect ◽  
Perfect Crystal ◽  
Optimum Configuration ◽  
Gauge Volume ◽  
Spurious Peak ◽  
Incomplete Filling ◽  
Broad Variety ◽  
Residual Strains

Residual strains measured by neutron diffraction near sample boundaries can be biased by the surface effect as a result of incomplete filling of the instrumental gauge volume. This effect is manifested as anomalous shifts of diffraction lines, which can be falsely interpreted as a lattice strain unless appropriate data corrections are made. A new analytical model for the surface effect has been developed, which covers a broad variety of instrumental arrangements, including flat mosaic and bent perfect crystal monochromators, narrow slits, and Soller and radial collimators. This model permits the spurious peak shifts to be predicted quantitatively, and also allows the optimum configuration parameters, such as curvature of a focusing monochromator, which lead to suppression of the surface effect, to be calculated. The model has been thoroughly validated by comparisons with Monte Carlo simulations and experiments on a stress-free calibration sample. Predictions of the model proved to be very accurate, often within the interval of experimental errors, which makes it suitable for use in data analysis.

An alternative neutron diffractometer performance for strain/stress measurements

2020 ◽  
Vol 35 (3) ◽  
pp. 185-189 ◽  
Author(s):  
Pavol Mikula ◽  
Jan Saroun ◽  
Vasyl Ryukhtin ◽  
James Stammers
Keyword(s):  
Plastic Deformation ◽  
Angular Resolution ◽  
Polycrystalline Sample ◽  
Perfect Crystal ◽  
Line Profiles ◽  
Neutron Diffractometer ◽  
Diffraction Angle ◽  
Strain Stress ◽  
Set Up ◽  
Elastic And Plastic Deformation

An alternative neutron diffractometer performance, which documents the feasibility of using a high-resolution three-axis neutron diffractometer for elastic and plastic deformation studies of bulk metallic polycrystalline samples, is presented. Contrary to the conventional double-axis setting, the suggested alternative consists of an unconventional three-axis set-up employing a bent perfect crystal monochromator and an analyzer with a polycrystalline sample in between. Though the alternative is, for measurements, much more time-consuming, its sensitivity to the change of the diffraction angle of the sample is, however, substantially higher and permits also plastic deformation studies on the basis of analysis of the diffraction line profiles. Moreover, much larger widths (up to 10 mm) of the irradiated gauge volumes can be investigated when just slightly affecting the angular resolution properties of the experimental setting.

Effect of wavelength-dependent attenuation on neutron diffraction stress measurements at depth in steels

2011 ◽  
Vol 44 (4) ◽  
pp. 747-754 ◽  
Author(s):  
Wanchuck Woo ◽  
Vyacheslav Em ◽  
Baek-Seok Seong ◽  
Eunjoo Shin ◽  
Pavol Mikula ◽  
...  
Keyword(s):  
Neutron Diffraction ◽  
Cross Section ◽  
Path Length ◽  
Wavelength Dependence ◽  
Perfect Crystal ◽  
Austenitic Steels ◽  
Specific Information ◽  
Beam Path ◽  
Stress Measurements ◽  
Instrument Configuration

The wavelength dependence of the maximum feasible penetration depth was studied for neutron diffraction stress measurements in ferritic and austenitic steels. This property was examined with wavelengths from the close vicinity of the Bragg edges, where the neutron total cross section has its local minimum and for which the scattering angles are convenient for stress measurements. These wavelengths (e.g.2.39 and 2.19 Å) are longer than those commonly used in stress measurements (∼1.6 Å). By using such wavelengths, configured by a focusing bent perfect crystal Si(111) monochromator, it was observed that the available total beam path length is about 85 mm in both ferritic and austenitic steels. This study provides specific information for choosing the instrument configuration suitable for most strain-scanning experimental tasks.

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