1、Designation: E1820 15a1Standard 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 pare
2、ntheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1NOTEA15.2.8 was editorially corrected in November 2016.1. Scope1.1 This test method covers procedures and guidelines forthe determination of fracture toughness
3、of metallic materialsusing the following parameters: K, J, and CTOD (). 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.NOTE 1Until this version, KIccould be evaluate
4、d using this testmethod as well as by using Test Method E399. To avoid duplication, theevaluation of KIchas been removed from this test method and the user isreferred to Test Method E399.1.2 The recommended specimens are single-edge bend,SE(B), compact, C(T), and disk-shaped compact, DC(T).All speci
5、mens 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 materialtoughness, material flow strength, and the individual qualifi-cation
6、requirements 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 therespon
7、sibility 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 2Other standard methods for the determination of fracturetoughness using the parameters K, J, and CTOD are contained in TestMethods
8、 E399, E1290, and E1921. This test method was developed toprovide a common method for determining all applicable toughnessparameters from a single test.2. Referenced Documents2.1 ASTM Standards:2E4 Practices for Force Verification of Testing MachinesE8/E8M Test Methods for Tension Testing of Metalli
9、c Ma-terialsE21 Test Methods for ElevatedTemperatureTensionTests ofMetallic MaterialsE23 Test Methods for Notched Bar Impact Testing of Me-tallic MaterialsE399 Test Method for Linear-Elastic Plane-Strain FractureToughness KIcof Metallic MaterialsE1290 Test Method for Crack-Tip Opening Displacement(C
10、TOD) Fracture Toughness Measurement (Withdrawn2013)3E1823 Terminology Relating to Fatigue and Fracture TestingE1921 Test Method for Determination of ReferenceTemperature, To, for Ferritic Steels in the TransitionRangeE1942 Guide for Evaluating DataAcquisition Systems Usedin Cyclic Fatigue and Fractu
11、re Mechanics TestingE2298 Test Method for Instrumented Impact Testing ofMetallic Materials3. Terminology3.1 Terminology E1823 is applicable to this test method.Only items that are exclusive to Test Method E1820, or thathave specific discussion items associated, are listed in thissection.3.2 Definiti
12、ons of Terms Specific to This Standard:3.2.1 compliance LF1, nthe ratio of displacement in-crement to force increment.3.2.2 crack opening displacement (COD) L, nforce-induced separation vector between two points at a specific gagelength. The direction of the vector is normal to the crack plane.1This
13、 test method is under the jurisdiction of ASTM Committee E08 on Fatigueand Fracture and is the direct responsibility of Subcommittee E08.07 on FractureMechanics.Current edition approved Oct. 15, 2015. Published November 2015. Originallyapproved in 1996. Last previous edition approved in 2015 as E182
14、0 15. DOI:10.1520/E1820-15AE012For 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.3The last approved version of t
15、his historical standard is referenced onwww.astm.org.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States13.2.2.1 DiscussionIn this practice, displacement, v, is thetotal displacement measured by clip gages or other devicesspanning the cra
16、ck faces.3.2.3 crack extension, a 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 forward crack extension.3.2.5 crack-tip
17、opening displacement (CTOD), L,ncrack displacement resulting from the total deformation(elastic plus plastic) at variously defined locations near theoriginal (prior to force application) crack tip.3.2.5.1 DiscussionIn this test method, CTOD is the dis-placement of the crack surfaces normal to the or
18、iginal (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.3.2.5.2 DiscussionIn CTOD testing, IcL is a value ofCTOD near the onset of slow stable crack ex
19、tension, heredefined as occurring at ap= 0.2 mm (0.008 in.) + 0.7Ic.3.2.5.3 DiscussionIn CTOD testing, cL is the value ofCTOD at the onset of unstable crack extension (see 3.2.38)orpop-in (see 3.2.24) when ap0.2 mm(0.008 in.) + 0.7u. The ucorresponds to the force Puand theclip gage displacement vu(s
20、ee Fig. 1). It may be size-dependent and a function of test specimen geometry. It can beuseful to define limits on ductile fracture behavior.3.2.5.5 DiscussionIn CTOD testing, c*L characterizesthe CTOD fracture toughness of materials at fracture instabilityprior to the onset of significant stable te
21、aring crack extension.The value of c*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 toughness onthickness (length of crack front).3.2.
22、6 dial energy, KV FLabsorbed energy as indicatedby the impact machine encoder or dial indicator, as applicable.3.2.7 dynamic stress intensity factor, KJdThe dynamicequivalent of the stress intensity factor KJ, calculated from Jusing the equation specified in this test method.3.2.8 dynamic ultimate t
23、ensile strength, TSdFL-2dynamic equivalent of the ultimate tensile strength, measuredat the equivalent strain rate of the fracture toughness test.3.2.9 dynamic yield strength, YSdFL-2dynamic equiva-lent of the yield strength, measured at the equivalent strain rateof the fracture toughness test.3.2.1
24、0 effective thickness, BeL,nfor side-groovedspecimens Be=B(BBN)2/B. This is used for the elasticunloading compliance measurement of crack size.3.2.11 effective yield strength, YFL2, nan assumedvalue of uniaxial yield strength that represents the influence ofplastic yielding upon fracture test parame
25、ters.3.2.11.1 DiscussionIt is calculated as the average of the0.2 % offset yield strength YS, and the ultimate tensilestrength, TSas follows:Y5YS1TS2(1)3.2.11.2 DiscussionIn estimating Y, influences of testingconditions, such as loading rate and temperature, should beconsidered.3.2.11.3 DiscussionTh
26、e dynamic effective yield strength,Yd, is the dynamic equivalent of the effective yield strength,and is calculated as the average of the dynamic yield strengthand dynamic ultimate tensile strength.NOTE 1Construction lines drawn parallel to the elastic loading slope to give vp, the plastic component
27、of total displacement, vg.NOTE 2In curves b and d, the behavior after pop-in is a function of machine/specimen compliance, instrument response, and so forth.FIG. 1 Types of Force versus Clip gage Displacement RecordsE1820 15a123.2.12 general yield force, PgyFin an instrumentedimpact test, applied fo
28、rce corresponding to general yielding ofthe specimen ligament. It corresponds to Fgy, as used in TestMethod E2298.3.2.13 J-integral, J FL1, na mathematical expression, aline or surface integral that encloses the crack front from onecrack surface to the other, used to characterize the localstress-str
29、ain field around the crack front.3.2.13.1 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 *SWdy 2 TuxdsD(2)where:W = loading work per unit volume or, for elastic bodies,strain energy den
30、sity, = 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 into the areaenclosed by .3.2.13.2 Disc
31、ussionThe 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 loadinginterior to such as from rapid motion of the crack or theservice component, and fro
32、m residual or thermal stress.3.2.13.3 DiscussionIn elastic (linear or nonlinear) solids,the J-integral equals the crack-extension force, G. (See crackextension force.)3.2.13.4 DiscussionIn elastic (linear and nonlinear) solidsfor which the mathematical expression is path independent, theJ-integral i
33、s equal to the value obtained from two identicalbodies with infinitesimally differing crack areas each subject tostress. The parameter J is the difference in work per unitdifference in crack area at a fixed value of displacement or,where appropriate, at a fixed value of force (1)4.3.2.13.5 Discussio
34、nThe dynamic equivalent of JcisJcd,X, with X = order of magnitude of J-integral rate.3.2.14 JcFL1The property Jcdetermined by this testmethod characterizes the fracture toughness of materials atfracture instability prior to the onset of significant stabletearing crack extension. The value of Jcdeter
35、mined by this testmethod represents a measure of fracture toughness at instabil-ity without significant stable crack extension that is indepen-dent of in-plane dimensions; however, there may be a depen-dence of toughness on thickness (length of crack front).3.2.15 JuFL1The quantity Judetermined by t
36、his testmethod measures fracture instability after the onset of signifi-cant stable tearing crack extension. It may be size-dependentand a function of test specimen geometry. It can be useful todefine limits on ductile fracture behavior.3.2.15.1 DiscussionThe dynamic equivalent of Juis Jud,X,with X
37、= order of magnitude of J-integral rate.3.2.16 J-integral rate, JFL21T21#derivative of J withrespect to time.3.2.17 machine capacity, MC FLmaximum availableenergy of the impact testing machine.3.2.18 maximum force, PmaxFin an instrumented im-pact test, maximum value of applied force. It corresponds
38、toFm, as used in Test Method E2298.3.2.19 net thickness, BNL, ndistance between the rootsof the side grooves in side-grooved specimens.3.2.20 original crack size, aoL,nthe physical crack sizeat the start of testing.3.2.20.1 DiscussionIn this test method, aoqis used todenote original crack size estim
39、ated from compliance.3.2.21 original remaining ligament, boL, ndistancefrom the original crack front to the back edge of the specimen,that is (bo=Wao).3.2.22 physical crack size, apL,nthe distance from areference plane to the observed crack front. This distance mayrepresent an average of several mea
40、surements 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 specimendeformation.3.2.23 plane-strain frac
41、ture toughness, JIcFL1, KJIcFL3/2,nthe crack-extension resistance under conditionsof crack-tip plane-strain.3.2.23.1 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 measu
42、red 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.3.2.23.2 DiscussionFor example, in Mode I for slow ratesof loading, plane-s
43、train fracture toughness is the value of thestress intensity designated KJIccalculated from JIcusing theequation (and satisfying all of the qualification requirements)specified in this test method, that provides for the measurementof crack-extension resistance near the onset of stable crackextension
44、 under dominant elastic conditions (2).3.2.23.3 DiscussionThe dynamic equivalent of JIcis JIcd,X, with X = order of magnitude of J-integral rate.3.2.24 pop-in, na discontinuity in the force versus clipgage displacement record. The record of a pop-in shows asudden increase in displacement and, genera
45、lly a decrease inforce. Subsequently, the displacement and force increase toabove their respective values at pop-in.3.2.25 R-curve or J-R curve, na plot of crack extensionresistance as a function of stable crack extension, apor ae.3.2.25.1 DiscussionIn this test method, the J-R curve is aplot of the
46、 far-field J-integral versus the physical crack4The boldface numbers in parentheses refer to the list of references at the end ofthis standard.E1820 15a13extension, ap. It is recognized that the far-field value of J maynot represent the stress-strain field local to a growing crack.3.2.26 remaining l
47、igament, b L, ndistance from thephysical crack front to the back edge of the specimen, that is(b=Wap).3.2.27 specimen center of pin hole distance, H* L, nthedistance between the center of the pin holes on a pin-loadedspecimen.3.2.28 specimen gage length, d L, nthe distance be-tween the points of dis
48、placement measure (for example, clipgage, gage length).3.2.29 specimen span, S L, nthe distance between speci-men supports.3.2.30 specimen thickness, B L, nthe side-to-side di-mension of the specimen being tested.3.2.31 specimen width, W L, na physical dimension ona test specimen measured from a ref
49、erence position such as thefront edge in a bend specimen or the load-line in the compactspecimen to the back edge of the specimen.3.2.32 stable crack extension L, na displacement-controlled crack extension beyond the stretch-zone width (see3.2.36). The extension stops when the applied displacement isheld constant.3.2.33 strain rate, derivative of strain with respect totime.3.2.34 stress-i
