1、Designation: E915 16Standard Test Method forVerifying the Alignment of X-Ray Diffraction Instrumentationfor Residual Stress Measurement1This standard is issued under the fixed designation E915; the number immediately following the designation indicates the year oforiginal adoption or, in the case of
2、 revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers the preparation and use of a flatstress-free test specimen for the purp
3、ose of checking thesystematic error caused by instrument misalignment or samplepositioning in X-ray diffraction residual stress measurement, orboth.1.2 This test method is applicable to apparatus intended forX-ray diffraction macroscopic residual stress measurement inpolycrystalline samples employin
4、g measurement of a diffrac-tion peak position in the high-back reflection region, and inwhich the ,2, and rotation axes can be made to coincide(see Fig. 1).1.3 This test method describes the use of iron powder whichhas been investigated in round-robin studies for the purpose ofverifying the alignmen
5、t of instrumentation intended for stressmeasurement in ferritic or martensitic steels. To verify instru-ment alignment prior to stress measurement in other metallicalloys and ceramics, powder having the same or lower diffrac-tion angle as the material to be measured should be prepared insimilar fash
6、ion and used to check instrument alignment.1.4 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulato
7、ry limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2E6 Terminology Relating to Methods of Mechanical Testing3. Terminology3.1 The definitions of mechanical testing terms that appearin Terminology E6 apply to this test method.3.1.1 In addition, the following common term from Termi-
8、nology E6 is defined:3.1.2 residual stress FL-2, nstress in a body that is at restand in equilibrium and at uniform temperature in the absenceof external and mass forces.4. Significance and Use4.1 This test method provides a means of verifying instru-ment alignment in order to quantify and minimize
9、systematicexperimental error in X-ray diffraction residual stress measure-ment. This method is suitable for application to conventionaldiffractometers or to X-ray diffraction instrumentation of eitherthe diverging or parallel beam types.3, 44.2 Application of this test method requires the use of a f
10、latspecimen of stress-free material that produces diffraction in theangular region of the diffraction peak to be used for stressmeasurement. The specimen must be sufficiently fine-grainedand isotropic so that large numbers of individual crystalscontribute to the diffraction peak produced. The crysta
11、ls mustprovide intense diffraction at all angles of tilt, , which will beemployed (see Note 1).NOTE 1Complete freedom from preferred orientation in the stressfreespecimen is, however, not critical in the application of the technique.5. Procedure5.1 Instrument Alignment:5.1.1 Align the X-ray diffract
12、ion instrumentation to be usedfor residual stress measurement in accordance with the instruc-tions supplied by the manufacturer. In general, this alignmentmust achieve the following, whether the ,2, and axes arevariable or fixed (see Fig. 1):5.1.1.1 The ,2, and axes shall coincide.5.1.1.2 The incide
13、nt X-ray beam shall be centered on the and 2 axes, within a focusing range, which will conform to thedesired error and precision tolerances (see Sections 6 and 7).5.1.1.3 The X-ray tube focal spot, the and 2 axes, and thereceiving slit positioned at 2 equals zero degrees shall be on1This test method
14、 is under the jurisdiction of ASTM Committee E28 onMechanical Testing and is the direct responsibility of Subcommittee E28.13 onResidual Stress Measurement.Current edition approved Aug. 1, 2016. Published August 2016. Originallyapproved in 1983. Last previous edition approved in 2010 as E915 10. DOI
15、:10.1520/E0915-16.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3Hilley, M. E., Larson, J. A., Jatczak, C.
16、F., and Ricklefs, R. E., eds., ResidualStress Measurement by X-ray Diffraction, SAE J784a, Society of AutomotiveEngrs., Inc., Warrendale, PA (1971 ).4“Standard Method for X-Ray Stress Measurement,” Committee on MechanicalBehavior of Materials, The Society of Materials Science, Japan, (20 April 1973)
17、.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1a line in the plane of diffraction. Alternatively, for instrumen-tation limited to the back reflection region, the diffraction angle2 shall be calibrated.5.1.1.4 The proper sample posit
18、ion shall be established,using whatever means are provided with the instrument, suchthat the surface of the sample is positioned at the and axes,within the focal distance range which will conform to thedesired error and precision tolerances (see Sections 6 and 7).5.1.1.5 The angle must be determined
19、 accurately. (seeNote 5)5.2 X-Ray Optics:5.2.1 Appropriate X-ray peak selection should be made atthe highest diffraction angle possible, consistent with peakintensity, and this may include selection of the x-radiation to beused.5.2.2 When the K characteristic radiation doublet is usedfor stress meas
20、urement, it is desirable to select incident andreceiving X-ray beam optics that will produce maximumseparation of the K1K2doublet. Perform stress measure-ments on the stress-free specimen employing the K1diffrac-tion peak at all angles investigated. Because resolution of theK doublet may vary with t
21、he angle , and because someinstrumentation may be incapable (due to fixed X-ray optics) ofobtaining resolution of the doublet, care must be taken not toresolve the doublet at some angles while blending thedoublet into a single peak at other angles.5.3 Selection of Powder for a Stress-Free Iron Speci
22、men:5.3.1 Use iron powder with a particle size greater than 1 m(4105in.) (See Note 2.)5.3.2 This standard may be applied to other metallic alloysand ceramics (see 1.3).5.3.3 The reporting of strain instead of stress circumventsthe necessity of establishing applicable elastic constants andserves to e
23、liminate a source of uncertainty.NOTE 2Annealed armco iron powder of 45 m (325 mesh) has beenfound suitable when using Cr K-alpha x-radiation.5.3.4 Annealing of the powder in vacuum reduces diffrac-tion peak width, thereby increasing diffraction peak resolution.This is generally desirable (see Note
24、3). Powders in the form ofplastically deformed filings may be used, but will producebroader diffraction peaks. In the event that an instrumentincapable of resolution of the K1K2doublet is beingemployed, it may be desirable to deliberately obtain plasticallydeformed powders which insure that partial
25、resolution of theK doublet does not occur. Extremely fine powders have alsobeen shown to produce line broadening, sufficient to suppressresolution of the K doublet.NOTE 3It may be advantageous to anneal an oxide-forming powder ina reducing atmosphere rather than in vacuum to avoid problems fromsurfa
26、ce contamination. It is not necessary to anneal ceramic powders sincethese materials do not tend to show line broadening from plasticdeformation.5.4 Stress-Free Specimen PreparationPreparation meth-ods other than those described below are permissible providingthat no residual stress (strain) is sust
27、ained in the binder thatmight be used to hold the crystalline particles together.5.4.1 Apermanent stress-free (strain-free) specimen may beprepared by mounting the powder on the face of a microscopeslide or in a shallow powder tray (of the type used for powderdiffraction work on a diffractometer) us
28、ing a 10 % solution ofnitrocellulose cement diluted with acetone as a suitable amor-phous binder. Place several drops of the solution on a cleanFIG. 1 X-Ray Diffraction Stress Measurement Geometry and Angles DefinedE915 162microscope slide or in a sample tray, and sprinkle the powderinto the binder.
29、 The powder may be spread and leveled with asecond microscope slide. When a uniform flat surface has beenproduced by alternately wetting with the binder solution andwiping with a second slide, set the specimen aside and allow itto dry for several hours. Excess amounts of the binder maycause it to pe
30、el away from the surface of the microscope slide.Rewetting of the surface with acetone and redrying mayeliminate this difficulty. Make the surface of the specimen asflat as possible so that the specimen surface is clearly defined.5.4.2 A temporary specimen may be rapidly prepared usingpetroleum jell
31、y as an amorphous binder. Place a small quantityof petroleum jelly on the face of one microscope slide andpress it against a second slide to extrude the petroleum jellyinto a uniform flat film. Remove the second microscope slidewith a wiping action taking care to keep the surface layer ofpetroleum j
32、elly thin and flat. Holding the petroleum jelly-coated slide at a steep angle to a vertical line, sprinkle the ironpowder from a sufficient height above the slide so that thepowder strikes the coated surface and either adheres or isdeflected away. Do not allow the powder to pack and build upon the s
33、urface.5.4.3 The surface area of the powder must be of sufficientsize to intersect the entire incident X-ray beam at all anglesto be used during stress measurement.5.5 Instrument Alignment Check:5.5.1 Position the stress-free (strain-free) specimen on theX-ray diffraction apparatus (see 5.1.1.4). In
34、 the event that amechanical gage which contacts the surface of the specimen isused for specimen positioning, a thin metal shim may be placedin front of the powder surface to protect it. Place this gageagainst the face of the metal shim, and adjust the positioning toaccount for the inclusion of the s
35、him in front of the gage suchthat the surface of the powder is at the correct distance from thereference point of the gage for stress measurement.NOTE 4Failure to place the powder surface directly over the center ofrotation of the and 2 axes induces a systematic specimen displacementerror.5.5.2 With
36、out adjusting the specimen position, perform fivesuccessive stress measurements using the method and correc-tion procedures normally employed for the instrument, includ-ing positive and negative psi tilts when applicable. Psi splittingis a symptom of misalignment where psi is the angle betweenthe sp
37、ecimrn surface normal and the diffracting plane normal.5The strain differential between the split linear portions of theleast square fit sin-square-psi plots should be equivalent to lessthan 14 Mpa (2ksi). To avoid systematic error in the verifica-tion process when K radiation is being used, care mu
38、st betaken to either completely split or blend the K1K2doublet(see 5.2).NOTE 5Values for accuracy and precision of the various angles anddisplacements are not specified herein. These may be considered to be metcollectively when overall measurement errors and tolerances are withinthose specified in S
39、ections 6 and 7.6. Calculations and Interpretation of Results6.1 Systematic ErrorAll methods leading to the calcula-tion of both in-plane and shear stresses can be employed.Thesemethods are based on the calculation of the slope and theopening of the d-spacing versus sin-square-psi values.6.1.1 Reduc
40、e the X-ray diffraction data obtained from thefive measurements in whatever manner is normally employedfor the X-ray diffraction instrumentation in use, and include allcorrections normally applied to raw X-ray diffraction data.Application of the X-ray elastic constants appropriate for thestressed ma
41、terial to be measured is important. It may beadvantageous to report strain values, rather than stress, to avoidthe uncertainty of specifying elastic constants. Calculate thesimple arithmetic mean and standard deviation about the meanfor the five measurements. If the mean value is within 14 MPa(2.0 k
42、si) of zero, the instrument and specimen-positioning gagecan be considered to be properly aligned. In the event that themean differs from zero by more than 14 MPa (2.0 ksi), repeat5.1 and 5.5.6.1.2 Alternatively, strain values may be used. This avoidserror due to selection of inappropriate elastic c
43、onstants. Theacceptable strain mean would be 100 ppm of the stress-free(strain-free) d-spacing; 50 ppm for shear strain.6.2 Random Error:6.2.1 Experience has shown that the standard deviation ofthe five measurements should be within approximately 6.9MPa (1.0 ksi). In the event that the standard devi
44、ation of thefive measurements exceeds 14 MPa (2.0 ksi), the stress-measurement technique employed and the instrumentationshould be investigated for sources of random error affecting themeasurement precision. Random error due to counting statis-tics may result from failure to take sufficient time dur
45、ing themeasurement to obtain accurate intensity information, and thusto accurately determine the diffraction peak positions. Methodsare available3for estimating the standard deviation of themeasured stress due to the errors involved in counting andcurve fitting to determine peak positions. Mechanica
46、l sourcesof error such as loose bearings and ways in the apparatus mayresult in significant random error.6.2.2 When strain values are reported the standard deviationof the five measurements should be within 100 ppm; 50 ppmfor shear stress.7. Precision and Bias7.1 The precision of this method will be
47、 dependent upon thetype of X-ray diffraction instrumentation employed and themethods of data reduction used in stress measurement. Thepreliminary results of round-robin investigations using thismethod indicate that instrument alignment within 14 MPa (2.0ksi) (see 6.1) can be achieved for both standa
48、rd diffractometersand two types of X-ray diffraction instrumentation designed forstress measurement in the back reflection region only. Instru-mental precision measured by this method (see 6.2) has beenfound to be less than 66.9 MPa (1.0 ksi).7.2 The accuracy of this method is considered to be absol
49、utebecause the specimen is stress-free. Deviation of resultsobtained in performing this method, provided the specimen has5SAE, “Residual Stress Measurement by X-ray Diffraction“, 2003 Edition,HS-784, p. 17.E915 163been properly prepared and maintained, can be attributed to theinstrumentation under investigation.7.3 Other sources of error can be related to different factors,such as the quality of the diffracted X-ray peaks (backgroundand noise). In some cases, depending on the material, theaverage stress (strain) pr
