Detail of GB/T 26140-2023

Introduction of GB/T 26140-2023

GB/T 26140-2023 Non-destructive testing - Standard test method for determining residual stresses by neutron diffraction WARNING - This document does not purport to address the safety concerns, if any, associated with its use. It is the responsibility of the user of this document to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. 1 Scope This document describes the test method for determining residual stresses in polycrystalline materials by neutron diffraction. It is applicable to both homogeneous and inhomogeneous materials including those containing distinct phases. The principles of the neutron diffraction technique are outlined. Suggestions are provided on: ——the selection of appropriate diffracting lattice planes on which measurements should be made for different categories of materials; ——the specimen directions in which the measurements should be performed, and ——the volume of material examined in relation to the material grain size and the envisaged stress state. Procedures are described for accurately positioning and aligning test pieces in a neutron beam and for precisely defining the volume of material sampled for the individual measurements. The precautions needed for calibrating neutron diffraction instruments are described. Techniques for obtaining a stress-free reference are presented. The methods of making individual measurements by neutron diffraction are described in detail. Procedures for analysing the results and for determining their statistical relevance are presented. Advice is provided on how to determine reliable estimates of residual stresses from the strain data and on how to estimate the uncertainty in the results. 2 Normative references The following documents are referred to in the text in such a way that some or all of their content constitutes requirements of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. EN 13925-3:2015, Non-destructive testing - X-ray diffraction from polycrystalline and amorphous materials - Part 3: Instruments 3 Terms and definitions For the purposes of this document, the following terms and definitions apply. ISO and IEC maintain terminological databases for use in standardization at the following addresses: ——ISO Online browsing platform: available at http:// www .iso .org/ obp ——IEC Electropedia: available at http:// www .electropedia .org/ 3.1 neutron absorption neutron capture by an atomic nucleus Note: A table of nuclear capture cross-sections can be found in Reference. 3.2 alignment adjustment of the specimen position and orientation and also of all the components of the instrument such that measurements can be performed precisely at the desired location in the specimen 3.3 anisotropy dependence of material properties on the direction with respect to the sample 3.4 attenuation reduction of the neutron beam intensity Note: Attenuation can be calculated by using the so-called “total neutron cross-section”, which comprises neutron absorption (3.1) and different nuclear scattering processes. The attenuation length is the distance within the material for which the primary neutron beam intensity is reduced by 1/e. 3.5 background intensity considered not belonging to the diffraction (3.13) signal Note: Background dependence on the scattering angle or time-of-flight (3.34) is not uncommon and can have an influence on the peak position (3.11) resulting from data analysis. 3.6 beam-defining optics arrangement of devices used to define the properties of a neutron beam such as the wavelength and intensity distributions, divergence and shape Note: These include devices such as apertures, slits, collimators, monochromators and mirrors. 3.7 Bragg edge sharp change in the neutron intensity as a function of the wavelength or monochromator take-off angle corresponding to the condition λ = 2dhkl, where hkl indicates an (hkl) diffracting lattice plane of the material under investigation 3.8 Bragg peak intensity distribution of the neutron beam diffracted by a specific (hkl) lattice plane 3.9 peak height maximum number of neutron counts of the Bragg peak (3.8) above the background (3.5) 3.10 peak function analytical expression to describe the shape of the Bragg peak (3.8) 3.11 peak position single value describing the position of a Bragg peak (3.8) Note: The peak position is the determining quantity to calculate the strain. 3.12 peak intensity integrated intensity area under the diffraction (3.13) peak above the background (3.5), normally calculated from the associated fitted parameters of a selected peak function (3.10) and a background function 3.13 diffraction scattering arising from coherent interference phenomena 3.14 diffraction elastic constants Ehkl νhkl elastic constants associated with diffraction (3.13) from individual (hkl) lattice planes for a polycrystalline material 3.15 diffraction pattern intensity distribution of neutrons diffracted from a crystalline material over the available wavelength, time-of-flight (3.34) and/or diffraction (3.13) angle ranges 3.16 full width at half maximum; FWHM width of the Bragg peak (3.8) at half the peak height (3.9) above the background (3.5) 3.17 full pattern analysis determination of the crystallographic structure and/or strain from a measured (multi-peak) diffraction pattern (3.15) of a polycrystalline material Note: In general, the full pattern analysis is termed after the method used (e.g. Rietveld refinement). See also single peak analysis (3.31). 3.18 gauge volume volume from which information is obtained 3.19 lattice parameters linear and angular dimensions of the crystallographic unit cell 3.20 lattice spacing d-spacing lattice plane spacing distance between adjacent parallel crystallographic lattice planes 3.21 Type I stress macrostress stress that self-equilibrates over a length scale comparable to the structure or component, thereby spanning multiple grains and/or phases 3.22 Type II stress stress that self-equilibrates over a length scale comparable to the grain size Note: Stresses of Type II and Type III are collectively known as microstresses. 3.23 Type III stress stress that self-equilibrates over a length scale smaller than the grain size Note: Stresses of Type II and Type III are collectively known as microstresses. 3.24 monochromatic instrument instrument employing a narrow band of neutron energies (wavelengths) 3.25 monochromatic neutron beam monochromatic beam neutron beam with narrow band of neutron energies (wavelengths) 3.26 orientation distribution function quantitative description of the crystallographic texture (3.32)

Contents of GB/T 26140-2023