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

Pavol Mikula,Vasyl Ryukhtin,Jan Šaroun,Pavel Strunz

doi:10.3390/ma13235449

Abstract

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.

Highlights

Residual stresses are typical phenomena associated, e.g., with the welding of different kinds of structural material
The conventional neutron diffraction method is based on the precise determination of the relative change in the dhkl -spacing of oriented crystalline grains in the gauge volume [1,2,3]
The obtained results shown presented diffraction method provides sufficiently high angular resolution, represented by thethat of the diffraction profile, which allows a sufficiently high angular resolution, represented by the of the diffraction profile, which a sufficiently high represented bycharacteristics the FWHM of(root-mean-square the diffraction profile, which for the possibility of angular studyingresolution, some plastic deformation microstrains, allows for the possibilityofofstudying studyingsome some plastic plastic deformation deformation characteristics (root-mean-square allows for the possibility characteristics, by applying shape analysis on the neutron diffraction peak microstrains, well as the effectivegrain grain size),by by applying shape analysis neutron diffraction microstrains, as as well the effective analysison onthe the diffraction profiles

Summary

Introduction

Residual stresses are typical phenomena associated, e.g., with the welding of different kinds of structural material. Stresses are generally responsible for the deformation of structures during production and subsequently influencing the behavior of these structures during service [1,2,3]. They occur when external load or some kind of shape forming is applied to the sample. X-ray diffraction and neutron diffraction are excellent nondestructive techniques for the determination of strain/stress fields in polycrystalline materials. X-ray diffraction, which due to a strong attenuation of X-rays in the material, is limited to sample surface measurements. Neutron diffraction, thanks to a low attenuation of neutrons in most materials, is suitable for strain scanning of bulk samples. The conventional neutron diffraction method is based on the precise determination of the relative change in the dhkl -spacing of oriented crystalline grains in the gauge volume [1,2,3]

Methods

Results

Discussion

Conclusion