ASTM E1820-2009 Standard Test Method for Measurement of Fracture Toughness.pdf

1、Designation: E1820 09Standard Test Method forMeasurement of Fracture Toughness1This standard is issued under the fixed designation E1820; 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 parent

2、heses 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 procedures and guidelines forthe determination of fracture toughness of metallic materialsusing the following parameters: K, J,

3、 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(T)

4、.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 qua

5、lificationrequirements 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 is

6、 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 in T

7、estMethods E399, E813, E1152, E1290, and E1737. 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 Tension

8、 Testing of Metallic MaterialsE21 Test Methods for Elevated Temperature Tension Testsof Metallic MaterialsE399 Test Method for Linear-Elastic Plane-Strain FractureToughness KIcof Metallic MaterialsE813 Test Method for JIc,AMeasure of FractureToughnessE1152 Test Method for Determining-J-R-CurvesE1290

9、 Test Method for Crack-Tip Opening Displacement(CTOD) Fracture Toughness MeasurementE1737 Test Method for J-Integral Characterization of Frac-ture Toughness (Discontinued 1998)3E1823 Terminology Relating to Fatigue and Fracture Test-ingE1921 Test Method for Determination of Reference Tem-perature, T

10、o, for Ferritic Steels in the Transition RangeE1942 Guide for Evaluating Data Acquisition SystemsUsed in Cyclic Fatigue and Fracture Mechanics Testing3. Terminology3.1 Terminology E1823 is applicable to this test method.3.2 Definitions:3.2.1 compliance LF1, nthe ratio of displacement in-crement to f

11、orce 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 in theundeformed condition.3.2.2.1 DiscussionIn this practice, displacement, v, is thetotal displacement measured by clip

12、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 new separation area that is madeavailable at the front of an ideal crack in an elastic solid duringa virtual increment of f

13、orward 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 descriptive of the stress anddisplacement fields, and is often also termed crack size ordepth.3.2.5.1 DiscussionIn practice, the va

14、lue 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 considered.1This test method is under the jurisdiction of ASTM Committee E08 on Fatigueand Fracture and is the direct responsib

15、ility of Subcommittee E08.07 on FractureMechanics.Current edition approved Nov. 1, 2009. Published December 2009. Originallyapproved in 1996. Last previous edition approved in 2008 as E1820 08a.DOI:10.1520/E1820-09.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM

16、Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3Withdrawn. The last approved version of this historical standard is referencedon www.astm.org.1Copyright ASTM International, 100 Barr Harbor Driv

17、e, PO Box C700, West Conshohocken, PA 19428-2959, United States.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.3.2.6.1 DiscussionIn this test method, CTOD is the dis-placement

18、 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 value ofCTO

19、D 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 ducorresponds to

20、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 instabi

21、lityprior 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 dependence of to

22、ughness 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 Method E

23、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, sTSas follo

24、ws: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, used to ch

25、aracterize 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, for el

26、asticbodies, 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 intothe

27、area enclosed by G.3.2.9.2 DiscussionThe value of J obtained from thisequation is taken to be path-independent in test specimensNOTE 1Construction lines drawn parallel to the elastic loading slope to give vp, the plastic component of total displacement, vg.NOTE 2In curves b and d, the behavior after

28、 pop-in is a function of machine/specimen compliance, instrument response, etc.FIG. 1 Types of Force versus Clip Gage Displacement RecordsE1820 092commonly used, but in service components (and perhaps in testspecimens) caution is needed to adequately consider loadinginterior to G such as from rapid

29、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 fractur

30、e 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 dimensi

31、ons; 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 specimen ge

32、ometry. 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, aoqis use

33、d 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 distance m

34、ayrepresent 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 specime

35、ndeformation.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 toughness is th

36、e 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 provides op

37、erational 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 measured usin

38、g 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-strain fr

39、acture 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 resistance near the onsetof stable crack extension

40、under dominant elastic condi-tions.(1)43.2.17 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 values

41、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 value

42、 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 a pin

43、-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 tested

44、.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 beyond

45、 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-elastic bo

46、dy.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 DiscussionIn th

47、is test method, Mode 1 or ModeI is assumed. See Terminology E1823 for definition of mode.3.2.27 stretch-zone width, SZW L, nthe length of crackextension that occurs during crack-tip blunting, for example,4The boldface numbers in parentheses refer to the list of references at the end ofthis standard.

48、E1820 093prior to the onset of unstable brittle crack extension, pop-in, orslow stable crack extension. The SZW is in the same plane asthe original (unloaded) fatigue precrack and refers to anextension beyond the original crack size.3.2.28 unstable crack extension L, nan abrupt crackextension that o

49、ccurs 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) unstable crack extension, includingsignificant pop-in, referred to as “fracture instability” in thistest method; (2) stable crack ext