EN 15305:2008

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.Neporušitveno preskušanje - Preskusna metoda analize zaostalih napetosti z uklonom rentgenskih žarkovZerstörungsfreie Prüfung - Röntgendiffraktometrisches Prüfverfahren zur Ermittlung der EigenspannungenEssais non-destructifs - Méthode d'essai pour l'analyse des contraintes résiduelles par diffraction des rayons XNon-destructive Testing - Test Method for Residual Stress analysis by X-ray Diffraction19.100Neporušitveno preskušanjeNon-destructive testingICS:Ta slovenski standard je istoveten z:EN 15305:2008SIST EN 15305:2009en,fr,de01-april-2009SIST EN 15305:2009SLOVENSKI
STANDARD
EUROPEAN STANDARDNORME EUROPÉENNEEUROPÄISCHE NORMEN 15305August 2008ICS 19.100 English VersionNon-destructive Testing - Test Method for Residual Stressanalysis by X-ray DiffractionEssais non-destructifs - Méthode d'essai pour l'analyse descontraintes résiduelles par diffraction des rayons XZerstörungsfreie Prüfung - RöntgendiffraktometrischesPrüfverfahren zur Ermittlung der EigenspannungenThis European Standard was approved by CEN on 4 July 2008.CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this EuropeanStandard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such nationalstandards may be obtained on application to the CEN Management Centre or to any CEN member.This European Standard exists in three official versions (English, French, German). A version in any other language made by translationunder the responsibility of a CEN member into its own language and notified to the CEN Management Centre has the same status as theofficial versions.CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Cyprus, Czech Republic, Denmark, Estonia, Finland,France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal,Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom.EUROPEAN COMMITTEE FOR STANDARDIZATIONCOMITÉ EUROPÉEN DE NORMALISATIONEUROPÄISCHES KOMITEE FÜR NORMUNGManagement Centre: rue de Stassart, 36
B-1050 Brussels© 2008 CENAll rights of exploitation in any form and by any means reservedworldwide for CEN national Members.Ref. No. EN 15305:2008: ESIST EN 15305:2009

Schematic representation of the European XRPD Standardisation Project.46 Annex B (informative)
Sources of Residual Stress.47 B.1 General.47 B.2 Mechanical processes.47 B.3 Thermal processes.47 B.4 Chemical processes.47 Annex C (normative)
Determination of the stress state - General Procedure.48 C.1 General.48 C.2 Using the exact definition of the deformation.49 C.2.1 General.49 C.2.2 Determination of the stress tensor components.49 C.2.3 Determination of θθθθ and d0.50 C.3 Using an approximation of the definition of the deformation.50 C.3.1 General.50 C.3.2 Determination of the stress tensor components.51 C.3.3 Determination of θθθθ0 and d0.51 Annex D (informative)
Recent developments.52 D.1 Stress measurement using two-dimensional diffraction data.52 D.2 Depth resolved evaluation of near surface residual stress - The Scattering Vector Method.54 SIST EN 15305:2009

Details of treatment of the measured data.56 E.1 Intensity correction on the scan.56 E.1.1 General.56 E.1.2 Divergence slit conversion.56 E.1.3 Absorption correction.57 E.1.4 Background correction.58 E.1.5 Lorentz-polarisation correction.58 E.1.6 K-Alpha2 stripping.59 E.2 Diffraction line position determination.59 E.2.1 Centre of Gravity methods.59 E.2.2 Parabola Fit.60 E.2.3 Profile Function Fit.60 E.2.4 Middle of width at x% height method.61 E.2.5 Cross-correlation method.61 E.3 Correction on the diffraction line position.61 E.3.1 General.61 E.3.2 Remaining misalignments.61 E.3.3 Transparency correction.62 Annex F (informative)
General description of acquisition methods.64 F.1 Introduction.64 F.2 Definitions.64 F.3 Description of the various acquisition methods.67 F.3.1 General method.67 F.3.2 Omega (ωωωω) method.68 F.3.3 Chi (χχχχ) method.69 F.3.4 Combined tilt method (also called scattering vector method).71 F.3.5 Modified chi method.73 F.3.6 Low incidence method.76 F.3.7 Modified omega method.77 F.3.8 Use of a 2D (area) detector.78 F.4 Choice of ΦΦΦΦ and ΨΨΨΨ angles.79 F.5 The stereographic projection.80 Annex G (informative)
Normal Stress Measurement Procedure" and "Dedicated Stress Measurement Procedure.82 G.1 Introduction.82 G.2 General.82 G.2.1 Introduction.82 G.2.2 Normal stress measurement procedure for a single specimen.82 G.2.3 Dedicated Stress Measurement Procedure for very similar specimens.82 Bibliography.84
In this document the principles of the measure procedure and the analysis technique are described. SIST EN 15305:2009

This European Standard describes the test method for the determination of macroscopic residual or applied stresses non-destructively by X-ray diffraction analysis in the near-surface region of a polycrystalline specimen or component.
All materials with a sufficient degree of crystallinity can be analysed, but limitations may arise in the following cases (brief indications are given in Clause 12):
 Stress gradients;  Lattice constants gradient ;  Surface roughness;  Non-flat surfaces (see 5.1.2);  Highly textured materials;  Coarse grained material (see 5.1.4);  Multiphase materials;  Overlapping diffraction lines;  Broad diffraction lines.
The specific procedures developed for the determination of residual stresses in the cases listed above are not included in this document.
The method described is based on the angular dispersive technique with reflection geometry as defined by EN 13925-1.
The recommendations in this document are meant for stress analysis where only the diffraction line shift is determined.
This European Standard does not cover methods for residual stress analyses based on synchrotron X-ray radiation and it does not exhaustively consider all possible areas of application.
Radiation Protection. Exposure of any part of the human body to X-rays can be injurious to health. It is therefore essential that whenever X-ray equipment is used, adequate precautions should be taken to protect the operator and any other person in the vicinity. Recommended practice for radiation protection as well as limits for the levels of X-radiation exposure are those established by national legislation in each country. If there are no official regulations or recommendations in a country, the latest recommendations of the International Commission on Radiological Protection should be applied. 2 Normative references The following referenced documents are indispensable for the application 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 13925-1:2003, Non-destructive testing – X-ray diffraction from polycrystalline and amorphous material – Part 1: General principles
For the purposes of this document, the following term, definition and symbols apply 3.1 Terms and definitions
3.1.1 Residual stress self-equilibrating internal stresses existing in a free body which has no external forces or constraints acting on its boundary
3.2 Symbols and abbreviations  2θ
The diffraction angle; this is the angle between the incident and diffracted X-ray beams.  θ
The Bragg angle; this is the angle between the diffracting lattice planes and the incident beam.  ω
The angle between the incident X-ray beam and the specimen surface at χ = 0.  φ The angle between a fixed direction in the plane of the specimen and the projection in that plane of the normal to the diffracting lattice planes.
 ψ
The angle between the normal of the specimen and the normal of the diffracting lattice planes.  χ
The angle χ rotates in the plane perpendicular to that containing ω and 2θ; the rotation axis of χ is
orientated perpendicular to both the ω and the ϕ≠ axis.  {hkl
Family of crystal lattice planes defined by the indices h, k and l.
 εφψ
Strain measured in the direction defined by the angles φ and ψ.  d0 Interplanar distance (d spacing) of a strain free specimen.  dφψ Interplanar distance (d spacing) of strained material in the direction of measurement defined by the angles φ and ψ.  (S1, S2, S3) Specimen coordinate system.  (L1, L2, L3) Laboratory coordinate system. SIST EN 15305:2009

Shear stress components (i ≠ j ; i,j = 1,2,3).  Z Distance to the surface of the specimen.  z X-ray penetration depth.
 LP The Lorentz Polarization factor.  A The Absorption factor.  ILQ Inter-Laboratory Qualified (used in connection with stress-reference specimen).  LQ Laboratory Qualified (used in connection with stress-reference specimen).  σcert Certified normal stress value of the ILQ stress-reference specimen.  τcert Certified shear stress value of the ILQ stress-reference specimen.  σref Normal stress value of the LQ specimen.  τref Shear stress real value for the LQ specimen.  Lref Average width of the diffraction lines for the LQ specimen.
 σdetermined Determined Normal stress value of the stress-reference specimen.  τdetermined Shear stress value determined for the stress-reference specimen.  Ldetermined
The average width of the diffraction line determined for the stress-reference specimen.  u() Standard uncertainty in the normal stress.  u(τ) Standard uncertainty in the shear stress.
 rσcert,
rτ cert,
Repeatability of the normal stress, shear stress, and line width respectively of the certified ILQ stress- rLcert
reference specimen.
 rσref, rτref ,
Repeatability of the normal stress, shear stress, and line width respectively of the LQ stress-reference rLref specimen.  Rσcert, Rτcert Reproducibility of the normal stress and shear stress.  λ°Wavelength of the X-rays used.
 Tr(σ) Trace of the stress tensor: Tr(σ) = Σσii.° I hkl Net integrated intensity of the hkl diffraction line.  XECs
X-ray elasticity constants.  sr and
sR
Standard deviations of the repeatability and reproducibility.
Integral breadth.  σφ
Normal stress value in a direction defined by the angle φ4  τφ
Shear stress value in a direction defined by the angle φ4 NOTE Elasticity constant is also referred to as elastic constants.
4 Principles 4.1 General principles of the measurement
Key S1, S2
axes in the plane of the specimen; S1 is defined by the operator S3
axis normal to the specimen surface L1, L2, L3 laboratory coordinate system; L3 is normal to the diffracting lattice planes {hkl} and it is the bisector of the angle between incident and diffracted beams φ angle between a fixed direction in the plane of the specimen and the projection in that plane of the normal to the diffracting lattice planes ψ
angle between the normal of the specimen and the normal of the diffracting lattice planes Sφ
direction in which the stresses σφ and τφ are measured Figure 1 — Orthogonal coordinate systems relevant to XRD stress determination
On the basis of elasticity theory, for a macroscopically isotropic crystalline material the formula to express the strain in the direction defined by the angles φ and ψ (see Figure1) is:
(1a) Τhe stress components σφ and τφ are defined respectively as the normal stress and the shear stress in the Sφ direction (see Figure 1):
[]φτφσφσσφ2sinsincos122222116
(1b)
[]φτφττφsincos23136
(1c)
where the symbols of the formulae (1a), (1b), and (1c) are
εφψ{hkl}
strain in the direction defined by the angles φ and ψ for the family of lattice planes
{hkl}; {}{}hklhklSS2121and
X-ray elasticity constants for the family of lattice planes {hkl}; σ55±°σνν±°σΑΑ°°°°°normal stress components in the directions S1, S2 and S3 (cf. Figure 1); τ5ν°°°°°°°shear stress within the plane defined by S1 and S2; τ5Α°°°°°°°shear stress within the plane defined by S1 and S3; τνΑ°°°°°°°shear stress within the plane defined by S2 and S3; φ angle between a fixed direction in the plane of the specimen and the projection in that plane of the normal to the diffracting lattice planes; ψ angle between the normal of the specimen and the normal of the diffracting lattice planes; σφ
normal stress component in a direction defined by the angle φ; σ55±°σνν°°°°°°normal stress components in the directions S1, S2; τφ
shear stress value in a direction defined by the angle φ.
The strain εφψ may be expressed in terms of lattice spacings according to the formula:
{}66φψφψφψθθεsinsinlnln00ddhkl
(2a)
or alternatively by the approximate formulae:
{}−≅00dddhklφψφψε
(2b)
or
(2c)
where dφψ
spacing of the family of lattice planes {hkl} with their normal in the direction defined by φ and ψ; d0
strain-free lattice spacing of the same family of lattice planes {hkl}; 0
Bragg angle associated to d0; φψ
Bragg angle associated to dφψ.
The formula (2c) is approximate and therefore it should not be used. In the calculation using (2b) the value 0d can be estimated by interpolation on the fitted d vs. sin2ψ curve (for details see Annex C). Using formula (2a) the 0d and θ0 values do not need to be accurately known.
Since the penetration depth of X-rays in most materials is in the order of tens of micrometers, σ33=0 can often be assumed. Care should be exercised in the case of large penetration depths or multiphase materials (see Clause 12).
Thus, equation (1) can be simplified:
{}{}[]{}[]{}[]ψφτφτψφτφσφσσσεφψ2sinsincos21sin2sinsincos21231322122222112221116hklhklhklhklSSS
(3) where the symbols are as for formulae (1a), (1b), (1c).
For the usual methods (ω and χ method, see Clause 6.2) the rotation angle φ is equal to the rotation applied to the specimen around the surface normal. Other methods exist in which the relations between the angles φ, ψ and the specimen rotations are more complex (see Annex F).
Note that the elasticity constants of the {hkl} lattice planes may be significantly different from those of the macroscopic bulk values (see Clause 10).
4.2 Biaxial stress analysis From X-ray diffraction experiments on polycrystalline materials εψφ values at different ψ and φ angles are obtained. If the stress state is biaxial (τ13 = τ23 = σ33 = 0), then it follows from equation (3) that the dependence of εφψ on sin2ψ is linear: °ε°φψ{hkl} = 21 S2{hkl}.σφ°sin2°ψ  S1{hkl}.Tr(σ≤°°°°°°°°(4a) where: Tr(σ) =(σ11+σ22). For formula (4a) the same symbols hold as for formula (3). If the stress state is biaxial then experimentally a straight line should be obtained (see Figure 2). The stress in the φ -direction, σφ, is calculated from the slope of the straight line:°°°SIST EN 15305:2009

{}{}hklhkl2212Ssin1∂∂6φφε
(4b)
Key εφψ
strain measured in the direction defined by the angles φ and ψ ψ
angle between the normal of the specimen surface and the normal of the diffracting lattice planes Figure 2 — Example of 0ψψψψφφφφ versus sin2ψψψψ plot at constant φφφφ in case of biaxial stress. In Figure 2 the material undergoes a stress state with σφ = -400 MPa, τφ = 0. The X-ray elasticity constant of the material is:
21 S2{hkl}= 6.8
10-6 MPa-1
(4c) The σφ values for negative and positive ψ values are coinciding and denoted by squares. The line corresponds to the least square fitting by equation (4a). Due to the insufficient accuracy of d0, the stresses obtained from Τρ(σ) should not be used for further calculations.
4.3 Triaxial stress analysis If shear stresses acting in the planes perpendicular to the specimen surface are present (τ13 ≠ 0 and/or τ23 ≠ 0) then the plot of ε°φψ vs. sin2ψ is an ellipse, showing the “ψ-splitting” for ψ>0 and ψ<0 (see Figure 3). If σ33 is not equal to zero then the slope of sin2ψ plot is proportional to σφ°−σΑΑ4 In these cases, equation (4a) becomes: °ε°φψ = 21 S2{hkl} (σφ°−σΑΑ≤sin2°ψ °21° S2{hkl}.τφ°sin2ψ
+ 21⋅S2{hkl}.σΑΑ°°S1{hkl}. Tr(σ≤°°°°°ž5)—°°°°°°°°where Tr(σ) =(σ11+σ22 +σ33) SIST EN 15305:2009

Key εφψ
strain measured in the direction defined by the angles φ and ψ ψ
angle between the normal of the specimen surface and the normal of the diffracting lattice
planes +
positive ψ values x
negative ψ values Figure 3 — Example of 0ψψψψφφφφ versus sin2ψψψψ plot at constant φφφφ in case of triaxial stress (ψψψψ splitting). In Figure 3 the material undergoes a stress state with σφ = - 400 MPa, τφ = - 50 MPa. The X-ray elasticity constant of the material is ½ S2{hkl} = 6.8 x 10-6 MPa-1. The lines correspond to the least square fitting by equation (5). At a fixed φ angle, the σφ°°and τφ°°values are obtained by the least squares fitting of the strain data with equation (5). By measuring at least three different φ directions and at least three ψ angles the stress tensor can be derived (see Clause 7.4).
5 Specimen 5.1 Material characteristics 5.1.1 General
To measure and calculate the residual stress the following parameters are required:  crystallographic data of the material;  X-ray elasticity constants of the material. SIST EN 15305:2009

Prior knowledge of the specimen history and its microstructure can indicate if problems might occur as listed in Clause 1 (see Clause 12).
5.1.2 Shape, dimensions and weight For any specimen, a suitable flat region should be chosen for residual stress measurement. The shape and size of the specimen is not critical, but it shall fit onto the specimen stage when required.
The specimen is subjected to various tilts during the measurement and therefore needs to be firmly attached to the specimen stage. Care has to be taken on maximum allowable weight for the goniometer and on how the specimen is to be mounted and held onto the goniometer. The specimen can be clamped to the stage only if this does not lead to additional stresses being induced into the specimen. The necessary flatness of the specimen depends on the irradiated area. It is recommended that the local radius of curvature of the specimen shall be large enough (see Clause 12) to allow for an irradiation as longer as possible.
5.1.3 Specimen composition/homogeneity Care shall be taken to choose an irradiated volume with homogeneous composition when possible. Since the penetration depth of the X-rays as well as irradiated area depend on ψ tilt, consideration shall be given to compositional changes that may be present within the surface and the depth (see Clause 6.3).
is the residual stress of the specimen; xi
is the volume fraction of the i phase; σi
is the stress in the i phase obtained from the {hkl} lattice planes of that phase. It is therefore mandatory that the phases are known from which the diffraction lines originate.
5.1.4 Grain size and diffracting domains The grain size in the irradiated volume can also affect the residual stress value. In many crystalline materials grain sizes are in the range 10-100µm. As grains often consist of many diffracting domains, such grain size values are usually acceptable for X-ray stress measurements. For larger grain sizes, it is likely that only a few diffracting domains contribute to the diffraction line. This can lead to large variations in the peak shape and intensity with φ, ψ directions. In addition, the presence of micro/intergranular strains may also affect the results.
In some cases it is possible to reduce this effect by oscillating the specimen (for details see Clause 7), because this increases the number of diffracting grains.
5.1.5 Specimen X-ray transparency In some materials the penetration depth of X-rays can be large enough to lead to errors in stress measurements due to the offset of the irradiated volume with respect to the surface (see Annex E). In addition, the effect of stress gradients and significant stress σ33 will be more pronounced.
5.1.6 Coatings and thin layers Residual stresses in coatings can be determined provided that the diffraction lines associated with the coating itself can be identified and isolated from the diffraction lines associated with the substrate.
Measurement in thin layers may lead to the following problems:

low diffracted intensities and/or insufficient grain statistics; 
additional diffraction phenomena from multilayers; 
overlap with a diffraction line from the substrate; 
steep stress gradient; 
strong texture. (See also Clause 12.)
Finally, the values of the elasticity constants for the coating may be significantly different from the ‘bulk’ values.
5.2.2 Stress depth profiling 5.2.2.1 General
The stress can be determined as a function of depth by successive cycles of electro polishing and stress analysis. In some cases also a variation of the penetration depth of the X-ray, e.g. by using different wavelengths or by tilting of the specimen, can furnish depth profile stress data.
5.2.2.2 Removal of surface layers Any mechanical or electro discharge machining (EDM) method to remove surface layers induces residual stresses, altering the stress field of the surface. Thus, such methods shall be avoided. Chemical attack or electro polishing is suggested to remove layers without introducing new stresses on the surface. Both chemical attack and electro polishing may cause relaxation of the residual stresses, e.g. due to the removal of stress in the surface layer, changes of surface roughness, or grain boundary attack. When necessary, thick layers can be removed using a combined machining or grinding procedure, followed by electro polishing
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