ASTM E1820-2008 Standard Test Method for Measurement of Fracture Toughness.pdf

1、Designation: E 1820 08Standard Test Method forMeasurement of Fracture Toughness1This standard is issued under the fixed designation E 1820; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A number in pare

2、ntheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers procedures and guidelines forthe determination of fracture toughness of metallic materialsusing the following parameters: K,

3、 J, and CTOD (d). Tough-ness can be measured in the R-curve format or as a point value.The fracture toughness determined in accordance with this testmethod is for the opening mode (Mode I) of loading.1.2 The recommended specimens are single-edge bend,SE(B), compact, C(T), and disk-shaped compact, DC

4、(T).All specimens contain notches that are sharpened with fatiguecracks.1.2.1 Specimen dimensional (size) requirements vary ac-cording to the fracture toughness analysis applied. The guide-lines are established through consideration of material tough-ness, material flow strength, and the individual

5、qualificationrequirements of the toughness value per values sought.1.3 The values stated in SI units are to be regarded as thestandard. The values given in parentheses are for informationonly.1.4 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It

6、 is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.NOTE 1Other standard methods for the determination of fracturetoughness using the parameters K, J, and CTOD are contained i

7、n TestMethods E 399, E 813, E 1152, E 1290, and E 1737. This test method wasdeveloped to provide a common method for determining all applicabletoughness parameters from a single test.2. Referenced Documents2.1 ASTM Standards:2E4 Practices for Force Verification of Testing MachinesE8 Test Methods for

8、 Tension Testing of Metallic MaterialsE21 Test Methods for Elevated Temperature Tension Testsof Metallic MaterialsE 399 Test Method for Linear-Elastic Plane-Strain FractureToughness KIcof Metallic MaterialsE 1290 Test Method for Crack-Tip Opening Displacement(CTOD) Fracture Toughness MeasurementE 18

9、23 Terminology Relating to Fatigue and Fracture Test-ingE 1921 Test Method for Determination of Reference Tem-perature, To, for Ferritic Steels in the Transition RangeE 1942 Guide for Evaluating Data Acquisition SystemsUsed in Cyclic Fatigue and Fracture Mechanics Testing3. Terminology3.1 Terminolog

10、y E 1823 is applicable to this test method.3.2 Definitions:3.2.1 compliance LF1, nthe ratio of displacement in-crement to force increment.3.2.2 crack displacement L, nthe separation vector be-tween two points (on the surfaces of a deformed crack) thatwere coincident on the surfaces of an ideal crack

11、 in theundeformed condition.3.2.2.1 DiscussionIn this practice, displacement, v, is thetotal displacement measured by clip gages or other devicesspanning the crack faces.3.2.3 crack extension, Da L, nan increase in crack size.3.2.4 crack-extension force, G FL1or FLL2, ntheelastic energy per unit of

12、new separation area that is madeavailable at the front of an ideal crack in an elastic solid duringa virtual increment of forward crack extension.3.2.5 crack size, a L, na lineal measure of a principalplanar dimension of a crack. This measure is commonly usedin the calculation of quantities descript

13、ive of the stress anddisplacement fields, and is often also termed crack size ordepth.3.2.5.1 DiscussionIn practice, the value of a is obtainedfrom procedures for measurement of physical crack size, ap,original crack size, ao, and effective crack size, ae, as appro-priate to the situation being cons

14、idered.3.2.6 crack-tip opening displacement (CTOD), d L,nthe crack displacement due to elastic and plastic deforma-tion at variously defined locations near the original crack tip.1This test method is under the jurisdiction of ASTM Committee E08 on Fatigueand Fracture and is the direct responsibility

15、 of Subcommittee E08.07 on FractureMechanics.Current edition approved April 1, 2008. Published April 2008. Originallyapproved in 1996. Last previous edition approved in 2006 as E 1820 06e1.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at servic

16、eastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.3.2.6.1 DiscussionIn this test method, CTOD is the dis-pl

17、acement of the crack surfaces normal to the original (un-loaded) crack plane at the tip of the fatigue precrack, ao. In thistest method, CTOD is calculated at the original crack size, ao,from measurements made from the force versus displacementrecord.3.2.6.2 DiscussionIn CTOD testing, dIcL is a valu

18、e ofCTOD near the onset of slow stable crack extension, heredefined as occurring at Dap= 0.2 mm (0.008 in.) + 0.7dIc.3.2.6.3 DiscussionIn CTOD testing, dcL is the value ofCTOD at the onset of unstable crack extension (see 3.2.28)orpop-in (see 3.2.17) when Dap0.2mm (0.008 in.) + 0.7du. The ducorrespo

19、nds to the force Puandthe clip gage displacement vu(see Fig. 1). It may be size-dependent and a function of test specimen geometry. It can beuseful to define limits on ductile fracture behavior.3.2.6.5 DiscussionIn CTOD testing, dc*L characterizesthe CTOD fracture toughness of materials at fracture

20、instabilityprior to the onset of significant stable tearing crack extension.The value of dc*determined by this test method represents ameasure of fracture toughness at instability without significantstable crack extension that is independent of in-plane dimen-sions. However, there may be a dependenc

21、e of toughness onthickness (length of crack front).3.2.7 effective thickness, BeL, nfor side-grooved speci-mens Be=B (BBN)2/B. This is used for the elasticunloading compliance measurement of crack size.3.2.7.1 DiscussionThis definition is different from thedefinition of effective thickness in Test M

22、ethod E 813.3.2.8 effective yield strength, sYFL2, nan assumedvalue of uniaxial yield strength that represents the influence ofplastic yielding upon fracture test parameters.3.2.8.1 DiscussionIt is calculated as the average of the0.2 % offset yield strength sYS, and the ultimate tensilestrength, sTS

23、as follows:sY5sYS1sTS!2(1)3.2.8.2 DiscussionIn estimating sY, influences of testingconditions, such as loading rate and temperature, should beconsidered.3.2.9 J-integral, J FL1, na mathematical expression, aline or surface integral that encloses the crack front from onecrack surface to the other, us

24、ed to characterize the localstress-strain field around the crack front.3.2.9.1 DiscussionThe J-integral expression for a two-dimensional crack, in the x-z plane with the crack front parallelto the z-axis, is the line integral as follows:J 5*GSWdy 2 T uxdsD(2)where:W = loading work per unit volume or

25、, for elasticbodies, strain energy density,G = path of the integral, that encloses (that is,contains) the crack tip,ds = increment of the contour path,T= outward traction vector on ds,u = displacement vector at ds,x, y, z = rectangular coordinates, andTuxds= rate of work input from the stress field

26、intothe area enclosed by G.3.2.9.2 DiscussionThe value of J obtained from thisequation is taken to be path-independent in test specimenscommonly used, but in service components (and perhaps in testspecimens) caution is needed to adequately consider loadingNOTE 1Construction lines drawn parallel to t

27、he elastic loading slope to give vp, the plastic component of total displacement, vg.NOTE 2In curves b and d, the behavior after pop-in is a function of machine/specimen compliance, instrument response, etc.FIG. 1 Types of Force versus Clip Gage Displacement RecordsE1820082interior to G such as from

28、 rapid motion of the crack or theservice component, and from residual or thermal stress.3.2.9.3 DiscussionIn elastic (linear or nonlinear) solids,the J-integral equals the crack-extension force, G. (See crackextension force.)3.2.10 JcFL1The property Jcdetermined by this testmethod characterizes the

29、fracture toughness of materials atfracture instability prior to the onset of significant stabletearing crack extension. The value of Jcdetermined by this testmethod represents a measure of fracture toughness at instabil-ity without significant stable crack extension that is indepen-dent of in-plane

30、dimensions; however, there may be a depen-dence of toughness on thickness (length of crack front).3.2.11 JuFL1The quantity Judetermined by this testmethod measures fracture instability after the onset of signifi-cant stable tearing crack extension. It may be size-dependentand a function of test spec

31、imen geometry. It can be useful todefine limits on ductile fracture behavior.3.2.12 net thickness, BNL, ndistance between the rootsof the side grooves in side-grooved specimens.3.2.13 original crack size, aoL, nthe physical crack sizeat the start of testing.3.2.13.1 DiscussionIn this test method, ao

32、qis used todenote original crack size estimated from compliance.3.2.14 original remaining ligament, boL, ndistancefrom the original crack front to the back edge of the specimen,that is (bo=Wao).3.2.15 physical crack size, apL, nthe distance from areference plane to the observed crack front. This dis

33、tance mayrepresent an average of several measurements along the crackfront. The reference plane depends on the specimen form, andit is normally taken to be either the boundary, or a planecontaining either the load line or the centerline of a specimenor plate. The reference plane is defined prior to

34、specimendeformation.3.2.16 plane-strain fracture toughness, KIcFL3/2, JIcFL1, KJIcFL3/2 , nthe crack-extension resistance underconditions of crack-tip plane-strain.3.2.16.1 DiscussionFor example, in Mode I for slow ratesof loading and negligible plastic-zone adjustment, plane-strainfracture toughnes

35、s is the value of the stress-intensity factordesignated KIcFL3/2 as measured using the operationalprocedure (and satisfying all of the qualification requirements)specified in this test method, which provides for the measure-ment of crack-extension resistance at the start of crack exten-sion and prov

36、ides operational definitions of crack-tip sharp-ness, start of crack extension, and crack-tip plane-strain.3.2.16.2 DiscussionFor example, in Mode I for slow ratesof loading and substantial plastic deformation, plane-strainfracture toughness is the value of the J-integral designated JIcFL1 as measur

37、ed using the operational procedure (andsatisfying all of the qualification requirements) specified in thistest method, that provides for the measurement of crack-extension resistance near the onset of stable crack extension.3.2.16.3 DiscussionFor example, in Mode I for slow ratesof loading, plane-st

38、rain fracture toughness is the value of thestress intensity designated KJIcFL3/2 calculated from JIcusing the equation (and satisfying all of the qualificationrequirements) specified in this test method, that provides forthe measurement of crack-extension reistance near the onset ofstable crack exte

39、nsion under dominant elastic conditions.(1)33.2.17 pop-in, na discontinuity in the force versus clipgage displacement record. The record of a pop-in shows asudden increase in displacement and, generally a decrease inforce. Subsequently, the displacement and force increase toabove their respective va

40、lues at pop-in.3.2.18 R-curve or J-R curve, na plot of crack extensionresistance as a function of stable crack extension, Dapor Dae.3.2.18.1 DiscussionIn this test method, the J-R curve is aplot of the far-field J-integral versus the physical crackextension, Dap. It is recognized that the far-field

41、value of J maynot represent the stress-strain field local to a growing crack.3.2.19 remaining ligament, b L, ndistance from thephysical crack front to the back edge of the specimen, that is(b=Wap).3.2.20 specimen center of pin hole distance, H* L, nthedistance between the center of the pin holes on

42、a pin-loadedspecimen.3.2.21 specimen gage length, d L, nthe distance be-tween the points of displacement measure (for example, clipgage, gage length).3.2.22 specimen span, S L, nthe distance betweenspecimen supports.3.2.23 specimen thickness, B L, nthe side-to-side di-mension of the specimen being t

43、ested.3.2.24 specimen width, W L, na physical dimension ona test specimen measured from a reference position such as thefront edge in a bend specimen or the load line in the compactspecimen to the back edge of the specimen.3.2.25 stable crack extension L, na displacement-controlled crack extension b

44、eyond the stretch-zone width (see3.2.27). The extension stops when the applied displacement isheld constant.3.2.26 stress-intensity factor, K, K1,K2,K3,KI,KII,KIIIFL3/2, nthe magnitude of the ideal-crack-tip stress field(stress-field singularity) for a particular mode in a homoge-neous, linear-elast

45、ic body.3.2.26.1 DiscussionValues of K for the Modes 1, 2, and 3are given by the following equations:K15r0limsyy2pr!1/2# (3)K25r0limtxy2pr!1/2# (4)K35r0limtyz2pr!1/2# (5)where r = distance directly forward from the crack tip to a locationwhere the significant stress is calculated.3.2.26.2 Discussion

46、In this test method, Mode 1 or ModeI is assumed. See Terminology E 1823 for definition of mode.3.2.27 stretch-zone width, SZW L, nthe length of crackextension that occurs during crack-tip blunting, for example,prior to the onset of unstable brittle crack extension, pop-in, orslow stable crack extens

47、ion. The SZW is in the same plane asthe original (unloaded) fatigue precrack and refers to anextension beyond the original crack size.3The boldface numbers in parentheses refer to the list of references at the end ofthis standard.E18200833.2.28 unstable crack extension L, nan abrupt crackextension t

48、hat occurs with or without prior stable crackextension in a standard test specimen under crosshead or clipgage displacement control.4. Summary of Test Method4.1 The objective of this test method is to load a fatigueprecracked test specimen to induce either or both of thefollowing responses (1) unsta

49、ble crack extension, includingsignificant pop-in, referred to as “fracture instability” in thistest method; (2) stable crack extension, referred to as “stabletearing” in this test method. Fracture instability results in asingle point-value of fracture toughness determined at the pointof instability. Stable tearing results in a continuous fracturetoughness versus crack-extension relationship (R-curve) fromwhich significant