Suppression of Surface Effect by Using Bent-Perfect-Crystal Monochromator in Residual Strain Scanning

2005 ◽  
Vol 490-491 ◽  
pp. 234-238 ◽  
Author(s):  
Miroslav Vrána ◽  
Pavol Mikula
Keyword(s):  
Residual Strain ◽  
Strong Correlation ◽  
Surface Effect ◽  
Polycrystalline Sample ◽  
Sample Surface ◽  
Perfect Crystal ◽  
Bragg Diffraction ◽  
Bending Radius ◽  
Reactor Spectrum ◽  
Diffraction Optics

Using our long experience in Bragg diffraction optics we successfully used focusing principles for substantial increasing both luminosity and resolution of the strain scanners with respect to the conventional devices. Monochromatic neutrons are selected by the cylindrically bent monochromator from the reactor spectrum. There is a strong correlation between divergences of incoming and outgoing beams with respect to the polycrystalline sample, which can be easily manipulated by changing the monochromator bending radius. By setting a proper value of the radius, a narrow, quasiparallel and highly luminous output beam can by adjusted. The strong correlation between wavelength and direction of incoming and outgoing beams depending on the monochromator bending radius can be as well used for suppression of surface effect in residual strain scanning. In scanning near a sample surface aberration peak shifts arise due to the fact that the gauge volume defined by input and output slits is partially out of the sample and its value can be of the same order as the residual strain effects. In this work we demonstrate that by changing of the bending radius of monochromator, this surface effect can be suppressed to values smaller then experimental errors in residual strain scanning.

scholarly journals Neutron Bragg Diffraction on a Bent Silicon Single Crystal Excited by Ultrasound

2008 ◽  
Vol 45 (2) ◽  
pp. 52-60
Author(s):  
E. Raitman ◽  
V. Gavrilov ◽  
M. Brezgunov ◽  
D. Mjasiscev
Keyword(s):  
Acoustic Wave ◽  
Single Crystal ◽  
Wave Amplitude ◽  
Perfect Crystal ◽  
Silicon Single Crystal ◽  
Bragg Diffraction ◽  
Ultrasound Wave ◽  
Dispersion Surface ◽  
Generator Voltage ◽  
Bending Radius

Neutron Bragg Diffraction on a Bent Silicon Single Crystal Excited by UltrasoundThe neutron Bragg diffraction on a bent silicon monocrystal excited by ultrasound was investigated. It is shown that for perfect crystal the relative diffraction intensity is proportional to the acoustic wave amplitudew.The calibration parameters between the generator voltage and acoustic wave amplitude were derived assumingw= (2.3±0.3)·10-2Å/V. To explain the results, a modified Penning—Polder—Kato model was applied. In a bent crystal, owing to ultrasound, transitions between the sheets of a dispersion surface take place. This leads to various manifestations of the behaviour of the integral scattering intensity, which drastically differs from the case of a perfect crystal. The observed effects may be used for creating new types of neutron monochromators and choppers governed by the ultrasound wave amplitude as well as by the length and bending radius of the crystal.

scholarly journals Effect of Nanopores on Mechanical Properties of the Shape Memory Alloy

Micromachines ◽  
2021 ◽  
Vol 12 (5) ◽  
pp. 529
Author(s):  
Chunzhi Du ◽  
Zhifan Li ◽  
Bingfei Liu
Keyword(s):  
Mechanical Properties ◽  
Constitutive Model ◽  
Shape Memory ◽  
Young’S Modulus ◽  
Residual Strain ◽  
Surface Effect ◽  
Young's Modulus ◽  
Strain Curve ◽  
Stress Strain ◽  
Strength Limit

Nanoporous Shape Memory Alloys (SMA) are widely used in aerospace, military industry, medical and health and other fields. More and more attention has been paid to its mechanical properties. In particular, when the size of the pores is reduced to the nanometer level, the effect of the surface effect of the nanoporous material on the mechanical properties of the SMA will increase sharply, and the residual strain of the SMA material will change with the nanoporosity. In this work, the expression of Young’s modulus of nanopore SMA considering surface effects is first derived, which is a function of nanoporosity and nanopore size. Based on the obtained Young’s modulus, a constitutive model of nanoporous SMA considering residual strain is established. Then, the stress–strain curve of dense SMA based on the new constitutive model is drawn by numerical method. The results are in good agreement with the simulation results in the published literature. Finally, the stress-strain curves of SMA with different nanoporosities are drawn, and it is concluded that the Young’s modulus and strength limit decrease with the increase of nanoporosity.

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.

Bragg diffraction optics on neutron diffractometers

1997 ◽  
Vol 234-236 ◽  
pp. 1058-1060 ◽  
Author(s):  
P. Mikula ◽  
P. Lukás̆ ◽  
M. Vrána
Keyword(s):  
Bragg Diffraction ◽  
Diffraction Optics

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.

Polarization effects of X-ray monochromators modeled using dynamical scattering theory

2021 ◽  
Vol 77 (4) ◽  
Author(s):  
Marcus H. Mendenhall ◽  
David Black ◽  
Donald Windover ◽  
James P. Cline
Keyword(s):  
Powder Diffraction ◽  
Incident Beam ◽  
Diffraction Theory ◽  
Rietveld Analysis ◽  
Perfect Crystal ◽  
Bragg Diffraction ◽  
Standard Reference Materials ◽  
X Ray ◽  
Monochromator Crystal ◽  
The Difference

The difference in the diffracted intensity of the σ- and π-polarized components of an X-ray beam in powder diffraction has generally been treated according to equations based on dipole scattering, also known as kinematic X-ray scattering. Although this treatment is correct for powders and post-sample analyzers known to be of high mosaicity, it does not apply to systems configured with nearly perfect crystal incident-beam monochromators. Equations are presented for the polarization effect, based on dynamical diffraction theory applied to the monochromator crystal. The intensity of the π component relative to the σ component then becomes approximately proportional to |cos  2θm| rather than to cos22θm, where θm is the Bragg diffraction angle of the monochromator crystal. This changes the predicted intensities of X-ray powder diffraction patterns produced on instruments with incident-beam monochromators, especially in the regions far from 2θ = 90° in the powder pattern. Experimental data, based on well known standard reference materials, are presented, confirming that the dynamical polarization correction is required when a Ge 111 incident-beam monochromator is used. The dynamical correction is absent as an option in the Rietveld analysis codes with which the authors are familiar.

Sign in / Sign up

Export Citation Format

Share Document