ICS 77.040.10 ISBN 974-9903-79-X THAI INDUSTRIAL STANDARD . 2181 2547ISO 12108 : 2002FATIGUECRACKGROWTHMETHODFOR METALLICMATERIALS[ISO TITLE : METALLIC MATERIALS FATIGUETESTING FATIGUECRACKGROUWTHMETHOD] 6 10400 0 2202 3300 122 93 3 2548. 2181 2547 ISO 12108 : 2003Metallicmaterials Fatigue testing Fatigue crack grouwth method (indentical) ISO (2) 15 .. 2511(3) 3369( .. 2548 ) .. 2511 15 .. 2511 . 2181-2547 26 .. 2548 1 . 2181 2547ISO 12108 : 2002 ISO 12108 : 2003 Metallic materialsFatigue testingFatigue crack grouwth method (identical) ISO Kth Kmax ISO 12737 (Isotropic) R ISO 4965 : 1979 Axial load fatigue testing machine Dynamic force calibration - Strain gauge technique ISO 12108 : 2002 3 ISO 12108 : 2002 4 ISO 12108 : 2002 5 ISO 12108 : 2002 6 2 . 2181 2547ISO 12108 : 2002 ISO 12108 : 2002 7 ISO 12108 : 2002 8 ISO 12108 : 2002 9 ISO 12108 : 2002 10 3 . 2181 2547ISO 12108 : 2002Metallic materials Fatigue testing Fatigue crack growth method1 ScopeThis International Standard describes tests for determining the fatigue crack growth rate from the threshold stress-intensityfactorrange,,totheonsetofunstablecrackextensionasthemaximumstressintensityfactorapproaches controlled instability, as determined in accordance with ISO 12737 [8].ThisInternationalStandardisprimarilyintendedforuseinevaluatingisotropicmetallicmaterialsunderpredominantly linear-elastic stress conditions and with force applied only perpendicular to the crack plane (mode Istress condition), and with a constant stress ratio,.2 Normative referenceThe following normative document contains provisions which, through reference in this text, constitute provisions ofthis International Standard. For dated references, subsequent amendments to, or revisions of, this publication do notapply.However,partiestoagreementsbasedonthisInternationalStandardareencouragedtoinvestigatethepossibility of applying the most recent edition of the normative document indicated below. For undated references,thelatesteditionofthenormativedocumentreferredtoapplies.MembersofISOandIECmaintainregistersofcurrently valid International Standards.ISO 4965:1979, Axial load fatigue testing machines Dynamic force calibration Strain gauge technique3 Terms and definitionsFor the purposes of this International Standard, the following terms and definitions apply.3.1crack length linear measure of a principal planar dimension of a crack from a reference plane to the crack tip, also called cracksize3.2cyclesmallest segment of a force-time or stress-time function which is repeated periodicallyNOTE Thetermsfatiguecycle,forcecycleandstresscycleareusedinterchangeably.Theletterisusedtorepresentthenumber of elapsed force cycles.3.3fatigue crack growth rateextension in crack length per force cycleKthKmaxRaNNda/dN 4 . 2181 2547ISO 12108 : 20023.4maximum forceforce having the highest algebraic value in the cycle; a tensile force being positive and a compressiveforce beingnegative3.5minimum forceforcehavingthelowestalgebraicvalueinthecycle;atensileforcebeingpositiveandacompressiveforcebeingnegative3.6force rangethe algebraic difference between the maximum and minimum forces in a cycle3.7force ratioalgebraic ratio of the minimum force or stress to maximum force or stress in a cycleNOTE It is also called stress ratio.3.8stress intensity factormagnitudeoftheidealcracktipstressfieldfortheopeningmodeforceapplicationtoacrackinahomogeneous,linear-elastically stressed body where opening mode of a crack corresponds to the force being applied to the bodyperpendicular to the crack faces only (mode I stress condition)3.9maximum stress intensity factorhighest algebraic value of the stress intensity factor in a cycle, corresponding to 3.10minimum stress intensity factorlowest algebraic value of the stress intensity factor in a cycle, corresponding to NOTE This definition remains the same, regardless of the minimum force being tensile or compressive. For a negative force ratio( ) there is an alternate, commonly used definition for the minimum stress intensity factor,. See 3.11.3.11stress intensity factor rangealgebraic difference between the maximum and minimum stress intensity factors in a cycleNOTE The force variables, and are related as follows:. For a negative force ratio ( )there is an alternate, commonly used definition for the stress intensity factor range,. See 3.10 and 10.6.FmaxFminFF= FmaxFminRR = Fmin/FmaxKKmaxFmaxKminFminR < 0 Kmin= 0KK= KmaxKminKR KmaxK= (1 R) KmaxR < 0K= Kmax 5 . 2181 2547ISO 12108 : 20023.12fatigue crack growth thresholdasymptotic value of for which approaches zeroNOTE For most materials the threshold is defined as the stress intensity factor range corresponding to. Whenreporting, the corresponding lowest decade of data used in its determination should also be included.3.13normalized-gradientfractional rate of change of with increased crack length, 3.14-decreasing testtest in which the value of the normalized-gradient,, is negativeNOTE A-decreasing test is conducted by reducing the stress intensity factor either by continuously shedding or by a series ofsteps, as the crack grows.3.15-increasing testtest in which the value of is positiveNOTE For standard specimens, a constant force amplitude results in a-increasing test where the value of is positive andincreasing.3.16stress intensity factor functionmathematicalexpression,basedonexperimental,numericaloranalyticalresults,thatrelatesthestressintensityfactor to force and crack length for a specific specimen configuration4 Symbols and abbreviations4.1 SymbolsSee Table 1.Table 1 Symbols and their designationsSymbol Designation UnitLoadingNormalized-gradientTensile modulus of elasticityForceMaximum forceMinimum forceForce rangeStress intensity factorMaximum stress intensity factorMinimum stress intensity factorStress intensity factor rangeInitial stress intensity factor rangeKthK da/dN108mm/cycleKthda/dNKC= (1/K) dK/daK aC= 1/K(dK/da) = 1/Kmax (dKmax/da) = 1/Kmin (dKmin/da) = 1/K (dK/da)KK CKKCK Cg (a/W)C K mm1E MPaF kNFmaxkNFminkNF kNK MPam1/2KmaxMPam1/2KminMPam1/2K MPam1/2KiMPam1/2 6 . 2181 2547ISO 12108 : 20024.2 Abbreviations for specimen identificationCT Compact tensionCCT Centre cracked tensionSENT Single edge notch tensionSENB3 Three-point single edge notch bendSENB4 Four-point single edge notch bendSENB8 Eight-point single edge notch bend5 Apparatus5.1 Testing machine5.1.1 GeneralThe testing machine shall have smooth start-up and a backlash-free force train if passing through zero force. SeeISO 4965. Cycle to cycle variation of the peak force during precracking shall be less than and shall be held towithin of the desired peak force during the test. shall also be maintained to within of the desiredrange during test. A practical overview of test machines and instrumentation is available [33],[34].Threshold stress intensity factor rangeNumber of cyclesForce ratio or stress ratioUltimate tensile strength at the test temperature proof strength at the test temperatureGeometryCrack length or size measured from the reference plane to the crack tipCrack front curvature correction lengthFatigue crack length measured from the notch rootMachined notch lengthPrecrack lengthSpecimen thicknessHole diameter for CT, SENT or CCT specimen, loading tup diameter for bend specimensStress intensity factor functionNotch heightSpecimen width, distance from reference plane to edge of specimenminimum uncracked ligamentCrack growthFatigue crack growth rateChange in crack length, crack extensionTable 1 Symbols and their designations (continued)Symbol Designation UnitKthMPam1/2N 1R 1RmMPaRp0,20,2 % MPaa mmacormmafatmmanmmapmmB mmD mmg (a/W) 1h mmW mm(Wa) mmda/dN mm/cyclea mm5 %2 % F 2 % 7 . 2181 2547ISO 12108 : 20025.1.2 Testing machine alignmentItisimportantthatadequateattentionbegiventoalignmentofthetestingmachineandduringmachiningandinstallation of the grips in the testing machine.For tension-compression testing, the length of the force train should be as short and stiff as practical. Non-rotatingjoints should be used to minimize off-axis motion.Asymmetryof thecrack front is anindication ofmisalignment; astraingauged specimensimilar to the test articleunder investigation can be used in aligning the force train and to minimize nonsymmetrical stress distribution and/orbending strain to less than.5.1.3 Force measuring systemAccuracy of the force measuring system shall be verified periodically in the testing machine. The calibration for theforcetransducershallbetraceabletoanationalorganizationofmetrology.Theforcemeasuringsystemshallbedesigned for tension and compression fatigue testing and possess great axial and lateral rigidity. The indicated force,as recorded as the output from the computer in an automated system or from the final output recording device in anoncomputer system, shall be within the permissible variation from the actual force. The force transducer's capacityshallbesufficienttocovertherangeofforcemeasuredduringatest.Errorsgreaterthanofthedifferencebetween minimum and maximum measured test force are not acceptable.Theforcemeasuringsystemshallbetemperaturecompensated,nothavezerodriftgreaterthanoffullscale,norhaveasensitivityvariationgreaterthanoffullscaleoverachange.Duringelevatedandcryogenictemperaturetesting,suitablethermalshielding/compensationshallbeprovidedtotheforcemeasuringsystem so it is maintained within its compensation range.5.2 Cycle-counterAn accurate digital device is required to count elapsed force cycles. A timer is to be used only as a verification checkontheaccuracyofthecounter.Itispreferredthatindividualforcecyclesbecounted.However,whenthecrackvelocity is below counting in increments of ten cycles is acceptable.5.3 Grips and fixtures for CT specimensForceisappliedtoaCTspecimenthroughpinnedjoints.Choiceofthisspecimenandgrippingarrangementnecessitates tension-tension test conditions only. Figure 1 shows the clevis and mating pin assembly used at boththe top and bottom of a CT specimen to apply the force perpendicular to the machined starter notch and crack plane.Suggesteddimensionsareexpressedasaproportionofspecimenwidth,,orthickness,,sincethesedimensions can vary independently within the limits specified in clause 6. The pin holes have a generous clearanceover the pin diameter, minimum, to minimize resistance to specimen and pin in-plane rotation which has beenshowntocausenonlinearityintheforceversusdisplacementresponse [35].Asurfacefinishrangeoftoissuggestedforgripsurfaces.Withthisgripandpinarrangement,materialswithlowproofstrengthmaysustain plastic deformation at the specimen pin hole; similarly, when testing high strength materials and/or when theclevis displacement exceeds, a stiffer force pin, i.e. a diameter greater than, may be required. As analternativeapproachtocircumventplasticdeformation,aflatbottomclevisholemaybeusedalongwithapindiameter equalling. Any heat treatable steel thermally processed to a proof strength of usedin fabricating the clevises will usually provide adequate strength and resistance to fretting, galling and fatigue.In addition to the generous pin hole clearance, the mating surfaces shall be prepared to minimize friction which couldinvalidate the provided-calibration expression. The use of high viscosity lubricants and greases has been showntocausehysteresisintheforceversusdisplacementresponseandisnotrecommendedifcompliancemeasurements are required.5 %1 %0,002 %0,002 % 1 C105mm/cycleW B0,2W0,8 m1,6 m1,05B 0,225W0,24W 0,2 % 1 000 MPaK 8 . 2181 2547ISO 12108 : 20025.4 Grips and fixtures for CCT/SENT specimens5.4.1 GeneralForce can be applied to CCT and SENT specimens through pinned joints and/or through frictional clamping grips.GrippingfortheCCTandSENTspecimensdependsonspecimenwidthandwhetherthetestconditionistobetension-tensionortension-compression.TheminimumCCTspecimengaugelengthvarieswithgrippingarrangement and shall provide a uniform stress distribution in the gauge length during the test.Equation (6) is applicable only for a single pinned end SENT specimen, as shown in Figure 2. The SENT pinned endspecimen (Figure 2) is appropriate for tension-tension test conditions only.Equation (7)isapplicableforaSENTspecimenwithclampedendsandisappropriateforbothtensionandcompression force conditions. For the clamped end SENT specimen, the grips must be sufficiently stiff to circumventSurface roughness values in micrometresKey1 Loading rod2 PinNOTE For high strength materials or large pin displacements the pin may be stiffened by increasing the diameter to along with using D-shaped flat bottom holes.aLoading rod thread.bThrough diameter.cThese surfaces are perpendicular and parallel as applicable to within.Figure 1 Clevis and pin assembly for gripping a CT specimen0,24W0,05W 9 . 2181 2547ISO 12108 : 2002anyrotationofthespecimenendsoranylateralmovementofthecrackplane;thepresenceofeitherconditionintroduces errors into the stress intensity factor calculation [29].5.4.2 Tension-tension testing of a CCT specimenFortension-tensiontestingofaspecimenwithawidth,lessthan,asshowninFigure 3,acleviswithsingle force pin is acceptable for gripping provided the specimen gauge length, defined here as the distance betweenthe pin hole centrelines, be at least. Shims may be helpful in circumventing fretting fatigue at the specimen's pinhole. Another step that can be taken to prevent crack initiation at the pin holes is the welding or adhesive bonding ofreinforcement plates or tabs to the gripping area, especially when testing very thin materials. Cutting the test sectiondown in width to form a dog bone shaped specimen design is another measure that can be adopted to circumventfailure at the pin holes; here the gauge length is defined as the uniform width section and it shall be at least inlength.For tension-tension testing of a specimen with a width greater than, distributing the force across the specimenwidth with multiple pin holes is recommended. A serrated grip surface at the specimen-grip interface increases theforce that can be transferred. With this force application arrangement the gauge length between the innermost rowsof pin holes must be at least.Surface roughness values in micrometresNOTE 1 The machined notch is centred to within.NOTE 2 The surfaces are parallel and perpendicular to within.NOTE 3 The crack length is measured from the reference loading plane containing the starter V-notch.NOTE 4 Specimen recommended for notch root tension at a force ratio only.a.bSee Figure 12 for notch detail. cReference plane.dThe recommended thickness.Figure 2 Standard single edge notch tension, SENT, specimen0,005W0,002WR > 0D = W/32W 75 mm6W3,4W75 mm3W 10 . 2181 2547ISO 12108 : 20025.4.3 Tension-compression testing of a CCT specimenA backlash-free gripping arrangement shall be used for tension-compression testing of the CCT specimen. Variouscommercially available pneumatic and hydraulic wedge grips that provide adequate clamping force may be used. Theminimum gauge length for a clamped CCT specimen is.For tension-compression testing of a CCT specimen, Figure 4 presents a design that affords a simple backlash freegrip that provides improved force transfer through multiple pins plus frictional force transfer via specimen clamp-upwith the serrated gripping surfaces. The compressive condition between the pins and the specimen's end surfaces,induced by drawing the wedges together, affords large reverse force excursions while circumventing elongation of thepin holes. The minimum gauge length for this specimen is between the grip end surfaces and between theinner rows of pins, as stated above.Surface roughness values in micrometresNOTE 1 The machined notch is centred to within.NOTE 2 The faces are parallel to.NOTE 3 The two faces are not out of plane more than.NOTE 4 The crack length is measured from the reference plane of the longitudinal centreline.NOTE 5 The clevis and pin loading system is not suitable for a force ratio.NOTE 6 Special gripping systems may be used for a force ratio such as shown in Figure 4.aSee Figure 12 for notch detail.b.cReference plane.Figure 3 Standard pinned end centre cracked tension, CCT, specimen for 0,002W0,05 mm/mm0,05 mmR < 0R < 0D = 2W/32W75 mm2,4W2,4W 3W 11 . 2181 2547ISO 12108 : 20025.4.4 Alignment of CCT specimen gripsTheCCTspecimenissensitivetomisalignmentandnonsymmetricalforceapplication,especiallyintension-compressiontestingwheregimbaledconnectionsarenotused,whichcanreadilyleadtoviolationofthethroughthicknesscrackcurvatureand/orsymmetryvaliditycriteria.Itisrecommendedthatbendingstrainbecheckedperiodically with a panel specimen similar to the one being tested and instrumented with strain gauges, as shown inFigure 5 [22]. This technique can be used to minimize the bending strain. See 5.1.2.Dimensions in millimetresKey1 Serrated sideplate surface2 Countersunk cap screw3 Lock nutNOTE 1 Made of hardened steel, e.g..NOTE 2 Serrated side plates vary in thickness to accommodate approximately to, range in thickness.aBody drilled.Figure 4 Example of backlash free grip for a CCT specimen 40 HRC2 mm 3 mm B 12 . 2181 2547ISO 12108 : 20025.5 Grips and fixtures for the SENB specimens5.5.1 Tension-compression grips for the SENB8 specimenTheeight-pointbendspecimenisalsosuitedfortension-compressiontesting.Ingrippingtheeight-pointbendspecimen,thetopandbottomtupsarerigidlytiedtogetherwithaline-to-linefittothespecimen'ssurfaces.Precautions shall be taken to eliminate backlash and secondary moments.The average axial strain,, for the flat panel calibration specimen is calculated using:where,, and are the measured strains.The equivalent strain at the centre of the four faces 1 to 4 is calculated using:;;;.The local bending strains at the centre of each of the four faces are calculated using:;;;.The maximum bending strain percentage in plane A can then be calculated as follows:aPlane AFigure 5 Strain gauge arrangement and bending strain calculation for an instrumented panel alignment specimen [22]

a

a=(5 +6 +7 +8)4

5

6

7

8

1= a[a(5 +8) /2] [2W/ (2W2d)]

3= a[a(6 +7) /2] [2W/ (2W2d)]

2= (5 +6) /24= (7 +8) /2b1= 1ab2= 2ab3= 3ab4= 4a % = [(b1b3) /2 + (b2b4) /2] 100/a5 % 13 . 2181 2547ISO 12108 : 20025.5.2 Tension-tension testing of SENB specimensThegeneralprinciplesofthebendtestfixturesuitablefortension-tensiontestingoftheSENBspecimenareillustrated in Figure 6. The fixture is designed to minimize frictional effects by allowing the support rollers to rotateand move apart slightly as force is applied to the specimen, hence permitting rolling contact. Thus, the support rollersareallowedlimitedmotionalongplanesurfacesparalleltothenotchedsideofthespecimen,butareinitiallypositivelypositionedagainststopsthatsetthespanlengthandareheldinplacebylow-tensionsprings(suchasrubber bands). Fixtures and rollers shall be made of high hardness ( ) steel [23].Dimensions in millimetresSurface roughness values in micrometresKey1 Test specimen2 Ram3 Test fixture4 Roller pinNOTE Roller pins and specimen contact surface of load ram should be parallel to each other to (TIRd)aBosses for springs or rubber bands.b roller pin diameter.c roller pin diameter.dTotal indicated reference value.Figure 6 Fixture for tension-tension forcing of a SENB3 specimen> 40 HRC0,002W0,61,1 14 . 2181 2547ISO 12108 : 20025.6 Crack length measurement apparatus5.6.1 GeneralAccurate measurement of crack length during the test is very important. There are a number of visual and non-visualapparati that can be used to determine the crack length. A brief description of a variety of crack length measurementmethods is included in [26]. The required crack length measurements are the average of the through-the thicknesscrack lengths, as covered in 9.1.5.6.2 Non-visual crack length measurementThereareanumberofnon-visualmeasurementtechniques.Mostlendthemselvestoautomateddataacquisitionand determine the average crack length, reflecting the crack front curvature if it exists. Crack-opening-displacementcompliance [36]-[38], AC and DC electric potential difference (EPD) [39]-[41], back face strain [36], [42], and side face foilcrack gauges [43]-[45] are all acceptable techniques, provided the resolution requirements covered in 8.1 be met.5.6.3 Visual crack length measurementInthepast,themostcommonvisualcracklengthmeasurementtechniqueusedamicrometerthreadtravellingmicroscope with low magnification (to). This technique measures the surface crack length during the testand may need to be corrected to the actual through-thickness crack size upon test completion, as covered in 9.1.6 Specimens6.1 GeneralProportionaldimensionsofsixstandardspecimens: a compacttension(CT);acentrecrackedtension(CCT)andthree, four and eight point single edge notch bend (SENB3), (SENB4) and (SENB8); and single edge notch tension(SENT) are presented in Figures 7, 3, 8, 9, 10 and 2, respectively. A variety of specimen configurations is presentedto accommodate the component geometry available and test environment and/or force application conditions duringatest.MachiningtolerancesandsurfacefinishesarealsogiveninFigures 7to10.TheCT,SENB3andSENB4specimens are recommended for tension-tension test conditions only.20 50 15 . 2181 2547ISO 12108 : 2002Surface roughness values in micrometresNOTE 1 The machined notch is centred to within.NOTE 2 The surfaces are perpendicular and parallel to within (TIR).NOTE 3 The crack length is measured from the reference plane of the loading pin holes centreline.NOTE 4 Specimens recommended for notch root tension loading, with a force ratio, only.aReference plane.bSee Figure 12 for notch detail.cThe recommended thickness:.dThe suggested minimum dimensions are and.Figure 7 Standard compact tension, CT, specimen for fatigue crack growth rate testing0,005W0,002WR > 0W/20BW/2W= 25 mm p= 0,2W 16 . 2181 2547ISO 12108 : 2002Surface roughness values in micrometresNOTE 1 The machined notch is centred to within.NOTE 2 The surfaces are parallel and perpendicular to within.NOTE 3 The crack length is measured from the reference loading plane containing the starter V-notch.NOTE 4 Specimen recommended for notch root tension only.aSee Figure 12 for notch detail.bReference plane.cRecommended thickness:.d.Figure 8 Standard three point single edge notch bend, SENB3, specimen0,005W0,002W0,2WBWDW/8 17 . 2181 2547ISO 12108 : 2002Surface roughness values in micrometresNOTE 1 The machined notch is centred to within.NOTE 2 The surfaces are parallel and perpendicular to (TIR).NOTE 3 The crack length is measured from the reference loading plane containing the V-notch.NOTE 4 Specimen recommended for tension only.aSee Figure 12 for notch detail.bReference plane.cRecommended thickness:.d.Figure 9 Standard four point single edge notch bend, SENB4, specimen0,005W0,002WR00,2WBWDW/8 18 . 2181 2547ISO 12108 : 20026.2 Crack plane orientationThecrackplaneorientation, as related to the characteristicdirectionoftheproduct, is identified in Figure 11. Theletter(s)precedingthehyphenrepresenttheforcedirectionnormaltothecrackplane;theletter(s)followingthehyphenrepresenttheexpecteddirectionofcrackextension.Forwroughtmetalstheletter Xalwaysdenotesthedirection of principal processing deformation, Y denotes the direction of least deformation and the letter Z is the thirdorthogonal direction. If the specimen orientation does not coincide with the product's characteristic direction then twoletters are used before and/or after the hyphen to identify the normal to the crack plane and/or expected direction ofcrack extension.The specimen shall have the same metallurgical structure as the material for which the crack growth rate is beingdetermined. No heat treatment shall take place once the fatigue crack has been initiated.Thestarternotchforthestandardspecimensmaybemadeviaelectricaldischargemachining(EDM),milling,broaching or saw cutting. To facilitate precracking, the notch root radius shall be as small as practical, typically lessthan. For aluminium, saw cutting the final starter notch depth with a jeweller's saw is acceptable.Surface roughness values in micrometresNOTE 1 The machined notch is centred to within.NOTE 2 The surfaces are parallel and perpendicular to within (TIR).NOTE 3 The crack length is measured from the reference loading plane containing the V-notch.NOTE 4 Specimen suitable for, provided backlash and secondary moment loading by grips be avoided.aSee Figure 12 for notch detail.bReference plane.cThe recommended thickness is.d.Figure 10 Standard eight point single edge notch bend, SENB8, specimen0,005W0,002WR00,2WBWDW/80,2 mm 0,5 mm 19 . 2181 2547ISO 12108 : 20026.3 Starter notch precracking detailsThe envelope and various acceptable machined notch configurations and precracking details for the specimens arepresented in Figure 12. For all specimens, the notch height,, shall not exceed for, or for. The machined notch shall be as narrow as practical machining limitations permit in order to minimizethe precracking length requirement. It is required that the final precrack length,, in the CT specimen be at least in length in order to avoid invalidating the-calibration expression.ThemachinednotchesintheSENBandCCTspecimensaredeterminedbypracticalmachininglimitations;the-calibration does not have a notch size limitation. However, a CCT specimen's minimum precrack length,, of atleast is required when using the compliance method for crack length determination to assure accurate cracklength measurements.a) Basic identification b) Non-basic identificationc) Radial grain flow, axial working direction d) Axial grain flow, radial working directionaGrain flow.Figure 11 Fracture plane orientation identification as in ISO 12737h 1 mm W25 mm W/16W> 25 mmap0,2W KK 2ap0,4W 20 . 2181 2547ISO 12108 : 20026.4 Stress intensity factor6.4.1 GeneralThe stress intensity factor for all standard specimen configurations is calculated using the following relationship:(1)Thestressintensityfactorfunction,,foreachstandardspecimenconfigurationiscalculatedusingthefollowing expressions.Dimensions in millimetresNOTE 1 Crack length is measured from reference plane.NOTE 2 Notch height,, should be minimized.NOTE 3 A hole of radius is allowed for ease of machining the notch in a CCT specimen.aReference plane.bRoot radius.Specimen typeNotch length Maximum notch height Minimum precrack lengthCTfor CCTfor , and for CT onlyFigure 12 Notch detail and minimum fatigue precracking requirementshr< 0,05Wanh ap0,1Wan0,15W1 W25 apan +hW/16 W> 25 apan +1 mmapan +0,1Bap0,2WK=FBW1/2g_aW_101,5g (a/W) 21 . 2181 2547ISO 12108 : 20026.4.2 Compact tension, CT, specimen For a compact tension specimen, CT, the stress intensity factor function is given by(2)where; the expression is valid for. See Figure 7.6.4.3 Centre cracked tension, CCT, specimenFor the centre cracked tension specimen, CCT, the stress intensity factor function is given by [24]-[26]:(3)where radians; the expression is valid for. Here it is recommended that thecrack length,, be the average of the four measurements from the centreline reference plane to the crack tips onboth the front and back surfaces. See Figure 3.6.4.4 Single edge notch three point bend, SENB3, specimenFor the three point bend specimen, SENB3, with the distance between external supports equalling, the stressintensity factor function is given by [27]:(4)where; the expression is valid for. See Figure 8.6.4.5 Single edge notch four point bend, SENB4, specimenFor the four point bend specimen, SENB4, with the distance between external supports minus the distance betweeninternal supports equalling, the stress intensity geometric function is given by [10]:(5)where radians; the expression is valid for. See Figure 9.For the four point bend specimen, where the difference between the major and minor span does not equal, thevalue for is proportional to the ratio of the major span minus the minor span divided by,g_aW_ =(2 +) (0,886 +4,64 13,322+14,7235,64)(1 )3/2 = a/W 0,2a/W1,0g_aW_ =_cos _1/2_0,707 1 0,007 22+0,007 04_ = a/2W 0 < = 2a/2W< 1,00a4Wg_aW_ =61/2_(1 +2) (1 )3/2__1,99 (1 )_2,15 3,93 +2,72_ = a/W 01,02Wg_aW_ = 3 (2 tan )1/2_0,923 +0,199 (1 sin )4cos _ = a/2W 0a/W1,02Wg (1/W) 2Wi.e.(major span minor span)2W 22 . 2181 2547ISO 12108 : 20026.4.6 Single edge notch eight point bend, SENB8, specimenFor the eight point bend specimen, SENB8, with the distance between external supports minus the distance betweeninternal supports equaling, the stress intensity factor function is given by [10]:where radians; the expression is valid for. See Figure 10.For the eight point bend specimen, where the difference between the major and minor span does not equal, thevalue for is proportional to the ratio of the major span minus the minor span divided by.6.4.7 Single edge notch tension, SENT, specimenFor the single edge notch pinned end tension specimen, SENT, the stress intensity factor function is given by [10]:(6)where; the expression is valid for. See Figure 2.For the single edge notch clamped end tension specimen, with the clear span between the grips equalling, thestress intensity factor function is given by [28]:(7)where; the expression is valid for. See Figure 2.Stress intensity factor functions, for clamped end SENT specimens with spans between the grips other than, areavailable [29]-[31].6.5 Specimen size6.5.1 GeneralForthetestresultstobevaliditisrequiredthatthespecimenremainpredominantlyinalinear-elasticstressconditionthroughout thetest.Thespecimenwidth,,and thickness,,maybe variedindependentlywithin thelimits covered in 6.6. The smallest specimen to meet these criteria, based on experimental results, varies with eachspecimen configuration [32].The minimum uncracked ligament that circumvents large scale yielding varies with specimen configuration and is afunction of the materials proof strength.2Wg_aW_ = 3 (2 tan )1/2_0,923 +0,199 (1 sin )4cos _ = a/2W 0a/W1,02Wg (a/W) 2Wi.e.major span minor span2Wg_aW_ =2 tan _0,752 +2,02 +0,37 (1 sin )3cos _ = a/2W 0 < a/W< 1,04Wg_aW_ = (1 )3/2_1,987 81/22,972 63/2+6,950 35/214,447 67/2+10,054 89/2+3,404 711/28,714 313/2+3,741 715/2_ = a/W 0 < a/W0,954WW B0,2 % 23 . 2181 2547ISO 12108 : 20026.5.2 CT specimen minimum uncracked ligamentFor the CT specimens the minimum uncracked ligament for producing valid data is given by:(8)6.5.3 CCT specimen minimum uncracked ligamentFor the CCT specimen the minimum size of the uncracked ligament, based upon large scale net section yielding ofthe material, is given by:(9)6.5.4 SENB specimen minimum uncracked ligamentFor all of the bend SENB specimens the minimum size of the uncracked ligament is given by:(10)Thiscriterionisbaseduponlargescalenetsectionyieldingofthematerialand,thedistancebetweenexternalsupportsforathreepointbendspecimen;forafourandeightpointbendspecimenorifanonstandard four or eight point bend specimen is used, equals the distance between external supports minus thedistance between internal supports.6.5.5 SENT specimen minimum uncracked ligamentThe minimum size of the uncracked ligament for the SENT specimen depends on the gripping technique: for a tensilestress, e.g. the ends embedded in hydraulic wedge grips, the minimum uncracked ligament is given by:(11)This criterion is based upon large scale net section yielding of the material.For a bending stress, e.g. clevis and pinned end grips, the minimum uncracked ligament is given by equation (8).6.6 Specimen thickness6.6.1 GeneralSpecimen thickness,, may be varied independent of specimen width,, for the specimen configurations, withinthelimitsforbucklingandthrough-thicknesscrackfrontcurvatureconsiderations.Itisrecommendedthattheselected specimen thickness be similar to that of the product under study.6.6.2 CT specimenFor a CT specimen it is recommended that the thickness,, be within the range. A thicknessup to is permitted. For a specimen this thick, a through-thickness crack front curvature correction length,,mayoftenberequired;also,difficultiesmaybeencounteredinmeetingthethrough-thicknesscrackstraightnessrequirements covered in 9.1.(Wa) _4 000__KmaxRp0,2_22 (Wa) 1 250FmaxBRp0,2(Wa) _3 000Fmax2BRp0,2_0,5 = 4W = 2W(Wa) 1 250FmaxBRp0,2B WB W/20BW/4W/2 acor 24 . 2181 2547ISO 12108 : 20026.6.3 CCT specimenFor the CCT specimen the recommended upper limit for thickness is, although is permitted. The minimumthicknessforcircumventingout-of-planedeflectionorbucklingintheCCTspecimenisdependentonthetestmaterial's elastic modulus,, gauge length, gripping, grip alignment and force ratio,.6.6.4 SENB specimenForthesingleedgenotchbendspecimenitisrecommendedthatthethicknessbewithintherange.6.6.5 SENT specimenFor the single edge notch tension specimen the maximum recommended thickness equals.6.7 Residual stressesResidualstressesinamaterialthathasnotbeenstressrelievedcaninfluencethecrackpropagationrateconsiderably [12],[13].Thisinfluencecanbeminimizedbychoosingasymmetricalspecimenconfiguration like thestandardCCTspecimenandreducingtheratiotominimizecrackfrontcurvaturecausedbyvariationinresidual stresses through the thickness [13].7 Procedure7.1 Fatigue precrackingThepurposeofprecrackingistoprovideastraightandsharpfatiguecrackofsufficientlengthsothatthe-calibration expression is no longer influenced by the machined starter notch and that the subsequent fatigue crackgrowth rate is not influenced by a changing crack front shape or precracking force history.The precrack length,, shall equal or exceed for the CT specimens only. The CCT specimen has no lengthrequirementexceptwhenusingcompliancecracklengthmeasurementwhichnecessitates.Forallspecimens the minimum fatigue precracking extension,, from the notch on each surface shall exceed the greaterof the notch height,, or, as shown in Figure 12.Prior to precracking, the test specimen shall be in the fully machined condition and in the final heat-treated state thatthe material will see in service. One practice is toinitiate the fatigue crack at the lowest possible maximum stressintensity factor,, that is practical. If the test material's critical stress intensity factor, which will cause fracture, isapproximately known then the initial for precracking can range from to of that value. If crack initiationdoes not occur within a block to load cycles then can be increased by and the block of loadcyclesrepeated.Thefinalforprecrackingshallnotexceedtheinitialforwhichtestdataaretobegenerated.Frequently, a stress intensity factor, greater than the used in the test, needs to be used for crack initiation. Inthiscase,themaximumforceshallbesteppeddowntomeettheabovecriteria.Whenmanuallycontrollingprecracking, the recommended stress intensity factor drop for each step is less than of. In addition, it isrecommended that between each stress intensity factor reduction that the crack extend by at least the value given inequation (12) [18]:(12)where is the maximum terminal stress intensity factor of the previous step.W/8 W/4E R0,2WBW0,5WB/WKap0,2W2ap0,4Wafath 1 mm 0,1BKmaxKmax30 % 60 %30 000 50 000 Kmax10 %KmaxKmaxKmax10 % Kmaxaj=3_Kmax (j 1)Rp0,2_2Kmax (j 1) 25 . 2181 2547ISO 12108 : 2002When test data are to be generated for a high force ratio it may be more convenient to precrack at a lower andforce ratio than the initial test conditions.Theprecracking apparatusshall apply theforcesymmetrical to thespecimen'snotchandaccuratelymaintainthemaximumforce to within. A centre crackedpanel shall also be symmetrically stressed across the width,.Any frequency that accommodates maintaining the force accuracy specified in 5.1 is acceptable.7.2 Crack length measurementThe requirements for measurement accuracy, frequency and validity are covered in clauses 8 and 9 for the variousspecimenconfigurationsandtestproceduresthatfollow.Whensurfacemeasurementsareusedtodeterminethecrack length, it is recommended that both the front and back surface traces be measured. If the front to back cracklength measurements vary by more than and, for a CCT specimen, if the side-to-side symmetry of the twocrack lengths vary in length by more than then the precrack is not suitable and test data would be invalidunder this test method. In addition, if the precrack departs from the plane of symmetry beyond the corridor, definedby planes on either side of the specimen's plane of symmetry containing the notch root(s), the data would beinvalid. See Figure 13.7.3 Constant-force-amplitude,-increasing, test procedure for This procedure is appropriate for generating fatigue crack growth rate data above. After stepping themaximum precracking force down to be equal or less than that corresponding to the lowest in the range overwhich fatigue crack growth rate data will be generated, it is preferred that the force range be held constant as is thestressratioandfrequency.Themaximumstressintensityfactorwillincreasewithcrackextensionandshouldbeallowed to increase to equal orexceed thegreatest in therange overwhichdata will be generated.SeveralaReference plane.bMachined notch,.Figure 13 Out of plane cracking validity corridorKmax5 % 2W0,25B0,025W0,05WanK da/dN> 105mm/cycle105mm/cycleKmaxKmax 26 . 2181 2547ISO 12108 : 2002suggestions, aimed at minimizing transient effects while using this-increasing procedure, follow. If test variablesaretobechanged,shallbeincreasedratherthandecreasedinordertoprecludetheretardationeffectsattributable to thepreviousforcehistory.Transienteffects can also occurfollowing a changeinorthestressratio. An increase of or less in and/or will usually minimize the transient effect reflected in the fatiguecrack growth rate. Following a change in force conditions sufficient crack extension shall be allowed to occur in ordertore-establishasteady-state crackgrowth ratebefore theensuingtestdataareacceptedas valid underthistestpractice. The amount of crack extension required is dependent on many variables, e.g. percentage of force change,thetestmaterialandheattreatmentcondition.Whenenvironmentaleffectsarepresenttheamountofcrackextensionrequiredtore-establishthesteady-stategrowthratemayincreasebeyondthatrequiredinabenignenvironment.Testinterruptionsshallbekepttoaminimum.Ifthetestisinterrupted,achangeingrowthratemayoccuruponresumptionofcycling.Thetestdataimmediatelyfollowingtheinterruptionshallbeconsideredinvalidifthereisasignificant demarcation in the crack velocity from the steady-state growth rate immediately preceding the suspensionofcycling.Thesphereofinfluenceofthetransienteffectmayincreasewiththesteadystateforceappliedtothespecimen during the suspension of dynamic force cycling.7.4 -decreasing procedure for This-decreasing procedure may result in different crack growth rates dependent on the test-gradient,. It isthe user's responsibility to verify that the crack growth rates are not sensitive to the test-gradient,.Testing starts at a or stress intensity factor range,, equal to or greater than that used for the final crackextensionwhileprecracking.Followingcrackextension,thestressintensityfactorrangeissteppeddown,orcontinuously shed, at a constant rate until test data have been recorded for the lowest stress intensity factor range orfatigue crack growth rate of interest.The-decreasing test may be controlled by a stepped stress intensity factor following a selected crack extension ataconstant,asshowninFigure 14.Alternately,thestressintensityfactorgradientperincrementofcrackextensionmaybeheldconstant,,calledcontinuousstressintensityfactorshedding,byusingacomputerautomatedtestcontrolprocedure [46];theconstant,,iscalledthenormalized-gradient.Acommonvalueis,butresearchhasshownthatthisvaluemaybematerial-andspecimen-geometry dependent [47],[48]:(13)This value usually provides a gradual enough force shed to preclude a transient in the crack growth rate. The aboverelationship is equally applicable whether calculating or, and can be rewritten for convenience in theintegrated form as:(14)where andare the initial stress intensity factor range at step and, respectively;is the crack extension at the preceding constant force range.The stress ratio,, and the normalized-gradient,, should be kept constant throughout the-decreasing test.It is recommended that-decreasing be followed by-increasing testing procedure, as covered in 7.3.When using the stress intensity factor stepped drop procedure, the reduction of shall not exceed of thepreviousmaximum stressintensityfactor andaminimum crack extensionateachstress intensitystep is recommended.KKmaxKmin10 % KmaxKminK da/dN< 105mm/cycleK K CK CKmaxKKF1/da (dK/K) = constantC KC= 0,1 mm1C=_1da__dKK_ =_1K_dKda 0,1 mm1Kmax, KminKK0 (j) = K0 (j 1) eCa(j1)K0 (j) K0 (j 1) j j 1a (j 1) = [a (j) a (j 1)] F (j 1)R K C KK KKmax10 %a0,50 mm 27 . 2181 2547ISO 12108 : 2002When using continuous stress intensity shedding procedure the above requirement is inoperative. it is better to keeptheforcerangeconstantforaverysmallcrackextension,.Here,continuousstressintensityfactorsheddingisdefinedbythedropininitialstressintensityfactorrange,,witheachstep,,whichmaynotexceed of the preceding initial stress intensity factor range, corresponding to:(15)a nominal.b actual.cSlope nominal at point A.d actual.e nominal.Figure 14 Typical-decreasing test by stepped force reduction methodKKdKdaFFKa (j 1)Ki (j) j2 %_K0 (j 1) K0 (j)K0 (j)_ 0,02 28 . 2181 2547ISO 12108 : 2002E.g., if the common value is used, along with the maximum drop in each initial stress intensityrange,thentheexponentandthecrackextensionforeachconstantforcerangeequals:(16)8 Crack length measurement8.1 ResolutionThefatiguecracklengthmeasurementsmadeasafunctionofelapsedforcecyclesmaybemadebytechniquesoutlined in 5.6. The required resolution for crack length measurements is or, whichever is greater.When making visual crack length measurements it is recommended that the surface in the area of the crack plane bepolished and indirect lighting be used to enhance the visibility of the crack tip. It is highly recommended that cracklengthmeasurementsbemadeonboththefrontandbackfacesofthespecimen,toassurethatcracksymmetryrequirements specified in 8.5 are met. The average of the surface crack length measurements, two for a CT, SENTand SENB specimens, and four for the CCT specimen, shall be used in calculating the crack growth rate and stressintensityfactor range.Ifcracklengthis notmeasuredonbothfacesforevery crack lengthmeasurementthen theintervalbetweenbothfrontandbackfacemeasurementsshallbereported.Itisgoodpracticetomakeregularcomparisons between visual and non-visual measurement methods.8.2 InterruptionSuspension of force cycling while making crack length measurements, although permitted, is discouraged and shallbeavoidedwhenpossible.Thedurationandfrequencyofanyinterruptionsshouldbekepttoaminimum.Testinterruption for making visual crack length measurements can be avoided by using strobe light illumination. See 7.3.8.3 Static forceA static force may be maintained to enhance the resolution of the crack length measurements. A static force equal toorlessthanthefatiguemeanforceisusuallyacceptable.Incorrosiveorelevatedtemperatureenvironmentsthemeanforcemayintroducetransientcreeporbluntingeffects.Innocaseshalltheappliedstaticforceexceedthemaximum fatigue force. See 7.3.8.4 Measurement intervalCracklengthmeasurementshallbemadesothatdataareuniformlydistributedovertherangeofofinterest. The following measurement intervals are recommended to provide a uniform data distribution: for the CT and SENB specimens, for for for and for the CCT specimen, for for.C= 0,1 mm12 %C= a (j 1)a (j 1) = 0,2 mmK0 (j)K0 (j 1)= eCa(j1)0,980 = e(0,1)(0,2)=12,718 30,02=11,020 20,1 mm 0,002Wda/dN Ka0,04W 0,25a/W< 0,40a0,02W 0,40a/W< 0,60a0,01W a/W0,60a0,03W 2a/2W0,60a0,02W 2a/2W> 0,60 29 . 2181 2547ISO 12108 : 2002However, a minimum of is recommended. The above limits may need to be reduced in order to obtainmultiplecrack lengthmeasurementsinthenear threshold region.Theminimum crack measurement intervalin allcases must exceed ten times the crack length measurement precision. Here, precision is defined as the standarddeviation from the mean value crack length determined for a set of repeat measurements.8.5 SymmetryAs in 7.1, for any crack length measurement, the data are invalid if:a) for a given crack front, the front and back crack length measurements differ by more than, andb) for a CCT specimen the symmetry of the two crack fronts differ by more than then the crack is not suitableand the data are invalid by this test method.Whenusinganonvisualmethodforcracklengthmeasurementthecracklengthshouldbevisuallycheckedforsymmetry at the test start and finish, and at least three additional, evenly spaced, intermediate measurements arerecommended.8.6 Out-of-plane crackingIf the crack deviates from the theoretical crack plane by more than the corridor, as covered in 7.2, the ensuingdata are invalid. See Figure 13. Large grained or single-crystal materials can commonly violate this requirement forout-of-plane cracking.8.7 Crack tip bifurcationCrack front splitting or branching can be a source of variability in the measured fatigue crack growth rate data sinceit is not compensated for in the stress intensity factor calculation. When crack tip branching or bifurcation is presentit shall be noted in the final report.9 Calculations9.1 Crack front curvatureAfter completion of the test the fracture faces shall be examined for through-thickness crack front curvature. Measurethe crack lengths at the two specimen faces and the three-quarter-thickness crack lengths, i.e. at, andfromoneofthefaces;theaverageofthethree-quarter-thicknessmeasurementsiscalledtheaveragethrough-thicknesscracklength.Thedifferencebetweentheaveragethrough-thicknesscracklengthandthecorresponding crack length at the specimen faces during the test is the crack curvature correction length,. It isdesirable to make the crack curvature correction calculation at more than one location on the fracture face where thefatiguecrackfrontisclearlymarked.Ifthecrackcurvaturecorrectionresultsinamorethandifferenceinthecalculated stress-intensity factor at any location then this correction must be included when analysing the recordedtest data, and the effective crack length becomes:(17)Whenthemagnitudeofthecrackcurvaturecorrectionvarieswithcracklength,alinearinterpolationisusedtodetermine the correction for the intermediate data.9.2 Determining the fatigue crack growth rate9.2.1 GeneralThefatiguecrackgrowthrateisdeterminedfromthetestrecorddatapairsofcracklengthandcorrespondingelapsedforcecycles.Twocommonmethodsusedforcalculatingthecrackgrowthrate,thesecantmethodanda 0,25 mm0,25B0,05W0,05W0,25B 0,50B0,75Bacor5 %a = an +afat +acor 30 . 2181 2547ISO 12108 : 2002incremental polynomial method, are suggested here. Other mathematical techniques for calculating the crack growthrate are possible; the procedure used in calculating the growth rate shall be specified in the test report. The observedscatter in the fatigue crack growth rate data is influenced by the method of data reduction.9.2.2 Secant methodCalculating the crack growth rate via the secant method entails computing the slope of a straight line connecting twoadjacent data pairs of crack length and elapsed cycle count and represents an average velocity:(18)for the incremental crack extension,.The stress intensity factor range is calculated using the average crack length over the increment of crack extension:(19)9.2.3 Incremental polynomial methodCalculatingthecrackgrowthratebytheincrementalpolynomialmethod( -increasingonly)requiresfittingapolynomial to a segment of the data pairs: crack length,, as a function of elapsed cycles,. The data segmentconsists of an odd number of elements (3, 5 or 7), which are consecutive versus data pairs. The growth rateequalstheslopeofthepolynomial,,forthedatasegment'scentremostelement,e.g.foradatasegmentconsistingofsevendatapairs,theslopewouldbecalculatedasthederivativeatthefourthelement.Thestressintensityfactorrangeassociatedwiththedatasegmentisdeterminedbyusingthefittedcracklengthofthecentremost element of the data segment. For a data segment consisting of 3, 5 or 7 elements the fitted crack lengthcorresponding to the second, third or fourth element, respectively, would be used in determining the stress intensityfactor range for the data segment.9.3 Determination of the fatigue crack growth thresholdThecrackgrowththreshold,,generallyreferstotheasymptoticvalueofforwhichthecorrespondingapproacheszero.Itiscommonlydefinedasbeingthevalueofcorrespondingtoacrackgrowthrateequal to [25],[48]. The fatigue crack growth rate corresponding to the threshold stress intensity factorrange shall be reported. A common way to determine the threshold is to use a straight line fitted to a minimum of five,approximatelyequallyspaced,versusdatapairsbetweenand;here,isthedependentvariableofthebestfitstraightline.Usingthislinearregressiontechnique, the value of is defined, by this test method, as the threshold stress intensity factor range,, at afatigue crack growth rate equal to.In the case where data is generated within different fatigue crack growth rate ranges the above procedure may beused with the lowest decade of the test data.10 Test report10.1 GeneralThe test report shall include a reference to this International Standard, i.e. ISO 12108, and the test date(s), plus thefollowing information.da (j)avg.dN=(ajaj1)(NjNj1)ajaj1a (j)avg.=(aj +aj1)2KajNjajNjda/dNjKthKda/dN K108mm/cyclelog (da/dN) log (K) 107mm/cycle108mm/cycle log (K)K Kth108mm/cycleda/dN 31 . 2181 2547ISO 12108 : 200210.2 Materiala) standard alloy designationb) thermal/mechanical conditioningc) product formd) chemical compositione)proof stress used to evaluate specimen size criteriaf) ultimate tensile strengthg) modulus of elasticity (required when compliance crack length measurements are used)10.3 Test specimena) specimen configurationb) crack plane orientation (see Figure 11)c) specimen locationd) width, e) thickness, f) notch height, g) stress intensity factor expression as a function of crack length and forceh) Specimen drawing and the reference source10.4 Precracking terminal valuesa) elapsed cycles at final stress intensity rangeb) final crack extensionc) final crack length, d) final stress intensity factor rangee) final maximum stress intensity factorf) maximum terminal stress intensity factor of the previous stepg) force ratioh) cyclic waveform10.5 Test conditionsa) testing machine force capacityb) measurement cell force range c) initial stress intensity factor range, d) force ratioe) forcing frequencyf) cyclic waveformg) test procedure used ( -increasing or-decreasing)h) test environmenti) test temperaturej) laboratory relative humidity0,2 %WBhapKjK K 32 . 2181 2547ISO 12108 : 2002k) measurement interval of, l) crack curvature correction, m) -gradient if-decreasing procedure is usedn) method of crack length measurement10.6 Test analysisa) analysismethodforconvertingthecracklength,,andelapsedforcecycles,,datatocrackgrowthrate,, i.e. the secant method, incremental polynomial method, etc.b) remainingligamentsizecriteriausedtoassurepredominantelasticloadinginanon-standardtestspecimenconfigurationc) report and the lowest decade of near threshold crack growth rate data used in its determinationd) exceptions to this test methode) anomalies that could affect test results, e.g. test interruptions or changing the loading variables10.7 Presentation of resultsa) The results of the fatigue crack growth test shall be tabulated including:,,, and, as presentedinFigure 15.Figure 15canbeexpanded,asnecessary,toincludeallmeasuredcracklengthsandforcingconditions. See Figure 17.b) The results shall also be presented in a log-log plot with plotted on the abscissa and ontheordinate.Foroptimumdatacomparisonitisrecommendedthatthesizeofthecyclebetwotothree times larger than that of the cycle, as shown in Figure 16. For both the plot and the table, dataviolating the validity criteria shall be clearly identified. An example of the presentation of fatigue crack growth datais shown in Figures 17 and 18. When a negative force ratio ( ) is used, the method of calculating the stressintensityfactor range,or, shall be clearlyidentifiedon boththe tableandoptional figure; also see 3.11 stress intensity factor range, aaacorK Ka Nda/dNKthafataNK da/dNlog (K) log (da/dN)log (K)log (da/dN)R < 0K= (1 R) KmaxK= KmaxK. 33 . 2181 2547ISO 12108 : 2002Figure 15 Test reportFATIGUE CRACK GROWTH TEST RESULTS [REFERENCE ISO/TC 164/SC 5/WG 6] Date........................................... Specimen I.D. Mark............................. Page 1 of ................................... MATERIAL.................................................................... Product form....................................................................... Thermal/mechanical conditioning ................................................................................................................................... Chemical composition..................................................................................................................................................... MECHANICAL PROPERTIES AT TEST TEMPERATURE Ultimate tensile strength ............................. MPa0,2 % Proof strength................................................... MPa Modulus of elasticity.....................................MPa SPECIMEN Dimensions: Thickness, B...................mmWidth, W.................... mmMachined notch length, an..................mm Crack plane orientation.............................Notch, h..................... mmSpecimen location .................................... Stress intensity factor reference ..................................................................................................................................... PRECRACK TERMINAL VALUES Final crack extension, a .............................. mmPreceding Kmax (j1) .......................................... MPam1/2 Final crack length, ap.................................... mmForce ratio .......................................................................... Final Kmax (j) ........................................MPam1/2Final load cycles................................................................. Final K (j) ...........................................MPam1/2Cyclic waveform................................................................. TEST CONDITIONS Test machine capacity ........................................ Environment ....................................................................... Force transducer range....................................... Temperature...................................................................C Measurement intertval of a, a ..................... mmRelative humidity .............................................................% Force frequency............................................. HzForce ratio .......................................................................... Test procedure.................................................... K-gradient ................................................................. mm1 Crack correction............................................ mmCyclic waveform................................................................. Initial Ki..............................................MPam1/2Initial force range........................................................... kN Crack measurement method .......................................................................................................................................... TEST ANALYSIS Threshold stress intensity factor range, Kth.................................................................................................. MPam1/2 Threshold crack growth rate decade ...............................................................................................................mm/cycle Analysis method.............................................................................................................................................................. Remaining size criteria Ref: ............................................................................................................................................ EXCEPTIONS, ANOMALIES AND COMMENTS 34 . 2181 2547ISO 12108 : 2002Figure 15 Test report (continued)Page ....... of .........MATERIAL: ............................... SPECIMEN I.D. ......................... DATE ........................................................Measurement number afat (mm) N Cycles a (mm) a(j)avg. (mm) g(a/W) (mm) K (mm) da/dN (mm/cycle) 35 . 2181 2547ISO 12108 : 2002Figure 16 Example axis for plotting versus test data log (da/dN) log (K) 36 . 2181 2547ISO 12108 : 2002Figure 17 Example of a test reportFATIGUE CRACK GROWTH TEST RESULTS [REFERENCE ISO/TC 164/SC 5/WG 6] Date....................... 1/9/90......... Specimen I.D. Mark.......... N410 ......... Page 1 of ............ 2.................... MATERIAL.......................... 16 MND 5......................... Product form............................. forging.............................. Thermal/mechanical conditioning ................................................................................................................................... Chemical composition..................................................................................................................................................... MECHANICAL PROPERTIES AT TEST TEMPERATURE Ultimate tensile strength ...................... 611 MPa0,2 % Proof strength............................................ 423 MPa Modulus of elasticity.....................................MPa SPECIMEN Dimensions: Thickness, B..............25 mmWidth, W...............50 mmMachined notch length, an.............10 mm Crack plane orientation....................... Y-ZNotch, h.................. 1 mmSpecimen location ...............1/4 thickness Stress intensity factor reference ........... ISO/TC 164/SC 5/ WG 6 ................................................................................. PRECRACK TERMINAL VALUES Final crack extension, a .............................. mmPreceding Kmax (j1) .......................................... MPam1/2 Final crack length, ap..........................12,50 mmForce ratio ................. 0,1................................................... Final Kmax (j) ........................................MPam1/2Final load cycles................................................................. Final K (j) ...........................................MPam1/2Cyclic waveform.............sinusoidal ................................... TEST CONDITIONS Test machine capacity ........................................ Environment ............... air................................................... Force transducer range....................................... Temperature............................................................300 C Measurement intertval of a, a ............... 1,2 mmRelative humidity .............................................................% Force frequency.......................................... 1 HzForce ratio .....................................................................0,1 Test procedure................................K-increasingK-gradient ................................................................. mm1 Crack correction......................................... 0 mmCyclic waveform.............sinusoidal ................................... Initial Ki................................... 18,07 MPam1/2Initial force range............................................... 19,620 kN Crack measurement method ..................................... compliance ................................................................................. TEST ANALYSIS Threshold stress intensity factor range, Kth.................................................................................................. MPam1/2 Threshold crack growth rate decade ...............................................................................................................mm/cycle Analysis method..............secant ..................................................................................................................................... Remaining size criteria Ref: ........................................ ISO 12108 EXCEPTIONS, ANOMALIES AND COMMENTS [1]Crack front curvature correction, acorr = 0 mm [2]Data violates remaining ligament size criteria 37 . 2181 2547ISO 12108 : 2002Figure 17 Example of a test report (continued)Page 2 of 2 MATERIAL: .16 MND 5............. SPECIMEN I.D. ...... N410 ......... DATE ......................... 1/9/90....................Measurement numberafat (mm) N Cycles a (mm) a(j)avg. (mm) g(a/W) (mm) K (mm) da/dN (mm/cycle) 14,20205 00014,20 25,60237 08015,6014,905,5919,624,36E-05[1] 36,80258 20016,8016,205,9820,995,68E-05 48,80280 72018,8017,806,4922,788,88E-05 510,10293 05020,1019,456,9824,501,05E-04 612,30310 00022,3021,207,7627,241,30E-04 714,00321 80024,0023,158,6530,361,44E-04 815,50328 50025,5024,759,5133,382,24E-04 917,50336 00027,5026,5010,6337,312,67E-04 1018,35338 80028,3527,9311,6841,003,04E-04 1119,70342 30029,7029,0312,7044,583,86E-04 1220,50343 80030,5030,1013,7648,305,33E-04 1321,40345 38031,4030,9514,7451,745,70E-04 1422,65346 72032,6532,0316,1956,839,33E-04[2] 1523,80347 73033,8033,2318,0763,431,14E-03[2] 1624,70348 23034,7734,2920,0470,351,94E-03[2] 38 . 2181 2547ISO 12108 : 2002Figure 18 Example plot of fatigue crack growth test result 39 . 2181 2547ISO 12108 : 2002Bibliography[1] GRIFFITH, A.A., Phil. Trans. Roy. 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