Designation: E1820 − 17Standard 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 parentheses indicates the year of last reapproval. Asuperscript epsilon (´) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers procedures and guidelines forthe determination of fracture toughness of metallic materialsusing the following parameters: K, J, and CTOD (δ). 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 1—Until this version, KIccould be evaluated 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 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 materialtoughness, material flow strength, and the individual qualifi-cation 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 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 2—Other standard methods for the determination of fracturetoughness using the parameters K, J, and CTOD are contained in TestMethods E399, E1290, and E1921. This test method was developed toprovide a common method for determining all applicable toughnessparameters from a single test.1.5 This international standard was developed in accor-dance with internationally recognized principles on standard-ization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recom-mendations issued by the World Trade Organization TechnicalBarriers to Trade (TBT) Committee.2. Referenced Documents2.1 ASTM Standards:2E4 Practices for Force Verification of Testing MachinesE8/E8M Test Methods for Tension Testing of Metallic 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(CTOD) 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 Fracture Mechanics TestingE2298 Test Method for Instrumented Impact Testing ofMetallic Materials2.2 ASTM Data Set:4E1820/1–DS1(2015) Standard data set to evaluate computeralgorithms for evaluation of JIcusing, AnnexA9 of E18203. 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 Definitions of Terms Specific to This Standard:1This 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 June 1, 2017. Published June 2017. Originallyapproved in 1996. Last previous edition approved in 2016 as E1820 – 16. DOI:10.1520/E1820-172For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at

[email protected] For Annual Book of ASTMStandards volume information, refer to the standard’s Document Summary page onthe ASTM website.3The last approved version of this historical standard is referenced onwww.astm.org.4This data set is available for download from ASTM at https://www.astm.org/COMMITTEE/E08.htm, under the heading, Additional Information.Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United StatesThis international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.13.2.1 compliance [LF−1], n—the ratio of displacement in-crement to force increment.3.2.2 crack opening displacement (COD) [L], n—force-induced separation vector between two points at a specific gagelength. The direction of the vector is normal to the crack plane.3.2.2.1 Discussion—In this practice, displacement, v, is thetotal displacement measured by clip gages or other devicesspanning the crack faces.3.2.3 crack extension, ∆a [L], n—an increase in crack size.3.2.4 crack-extension force, G [FL−1or FLL−2], n—theelastic 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 opening displacement (CTOD), δ [L],n—crack 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 Discussion—In this test method, CTOD is the dis-placement 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.3.2.5.2 Discussion—In CTOD testing, δIc[L] is a value ofCTOD near the onset of slow stable crack extension, heredefined as occurring at ∆ap= 0.2 mm (0.008 in.) + 0.7δIc.3.2.5.3 Discussion—In CTOD testing, δc[L] is the value ofCTOD at the onset of unstable crack extension (see 3.2.36)orpop-in (see 3.2.22) when ∆ap0.2 mm(0.008 in.) + 0.7δu. The δucorresponds to the force Puand theclip 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.3.2.5.5 Discussion—In CTOD testing, δc*[L] characterizesthe CTOD fracture toughness of materials at fracture instabilityprior to the onset of significant stable tearing crack extension.The value of δc*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).3.2.6 dial energy, KV [FL]—absorbed energy as indicatedby the impact machine encoder or dial indicator, as applicable.3.2.7 dynamic stress intensity factor, KJd—The dynamicequivalent of the stress intensity factor KJ, calculated from Jusing the equation specified in this test method.3.2.8 effective thickness, Be[L],n—for side-grooved speci-mens Be=B −(B−BN)2/B. This is used for the elasticunloading compliance measurement of crack size.3.2.9 effective yield strength, σY[FL−2], n—an assumedvalue of uniaxial yield strength that represents the influence ofplastic yielding upon fracture test parameters.3.2.9.1 Discussion—It is calculated as the average of the0.2 % offset yield strength σYS, and the ultimate tensilestrength, σTSas follows:σY5σYS1σTS2(1)NOTE 1—Construction lines drawn parallel to the elastic loading slope to give vp, the plastic component of total displacement, vg.NOTE 2—In 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 − 1723.2.9.2 Discussion—In estimating σY, influences of testingconditions, such as loading rate and temperature, should beconsidered.3.2.9.3 Discussion—The dynamic effective yield strength,σYd, is the dynamic equivalent of the effective yield strength.3.2.10 general yield force, Pgy[F]—in an instrumentedimpact test, applied force corresponding to general yielding ofthe specimen ligament. It corresponds to Fgy, as used in TestMethod E2298.3.2.11 J-integral, J [FL−1], n—a mathematical expression, aline or surface integral that encloses the crack front from onecrack surface to the other, used to characterize the localstress-strain field around the crack front.3.2.11.1 Discussion—The 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 *ΓSWdy 2 T¯·]u¯]xdsD(2)where:W = loading work per unit volume or, for elastic bodies,strain energy density,Γ = 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, andT¯·]u¯]xds= rate of work input from the stress field into the areaenclosed by Γ.3.2.11.2 Discussion—The 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 Γ such as from rapid motion of the crack or theservice component, and from residual or thermal stress.3.2.11.3 Discussion—In elastic (linear or nonlinear) solids,the J-integral equals the crack-extension force, G. (See crackextension force.)3.2.11.4 Discussion—In elastic (linear and nonlinear) solidsfor which the mathematical expression is path independent, theJ-integral is 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)5.3.2.11.5 Discussion—The dynamic equivalent of JcisJcd,X, with X = order of magnitude of J-integral rate.3.2.12 Jc[FL−1]—The 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 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 dimensions; however, there may be a depen-dence of toughness on thickness (length of crack front).3.2.13 Ju[FL−1]—The 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 geometry. It can be useful todefine limits on ductile fracture behavior.3.2.13.1 Discussion—The dynamic equivalent of Juis Jud,X,with X = order of magnitude of J-integral rate.3.2.14 J-integral rate, J˙@FL21T21#—derivative of J withrespect to time.3.2.15 machine capacity, MC [FL]—maximum availableenergy of the impact testing machine.3.2.16 maximum force, Pmax[F]—in an instrumented im-pact test, maximum value of applied force. It corresponds toFm, as used in Test Method E2298.3.2.17 net thickness, BN[L], n—distance between the rootsof the side grooves in side-grooved specimens.3.2.18 original crack size, ao[L],n—the physical crack sizeat the start of testing.3.2.18.1 Discussion—In this test method, aoqis used todenote original crack size estimated from compliance.3.2.19 original remaining ligament, bo[L], n—distancefrom the original crack front to the back edge of the specimen,that is (bo=W−ao).3.2.20 physical crack size, ap[L],n—the distance from areference plane to the observed crack front. This distance 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 specimendeformation.3.2.21 plane-strain fracture toughness, JIc[FL−1], KJIc[FL−3/2],n—the crack-extension resistance under conditionsof crack-tip plane-strain.3.2.21.1 Discussion—For example, in Mode I for slow ratesof loading and substantial plastic deformation, plane-strainfracture toughness is the value of the J-integral designated JIc[FL−1] as measured 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.3.2.21.2 Discussion—For example, in Mode I for slow ratesof loading, plane-strain 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 under dominant elastic conditions (2).3.2.21.3 Discussion—The dynamic equivalent of JIcis JIcd,X, with X = order of magnitude of J-integral rate.3.2.22 pop-in, n—a discontinuity in the force versus clipgage displacement record. The record of a pop-in shows asudden increase in displacement and, generally a decrease in5The boldface numbers in parentheses refer to the list of references at the end ofthis standard.E1820 − 173force. Subsequently, the displacement and force increase toabove their respective values at pop-in.3.2.23 R-curve or J-R curve, n—a plot of crack extensionresistance as a function of stable crack extension, ∆apor ∆ae.3.2.23.1 Discussion—In this test method, the J-R curve is aplot of the far-field J-integral versus the physical crackextension, ∆ap. It is recognized that the far-field value of J maynot represent the stress-strain field local to a growing crack.3.2.24 remaining ligament, b [L], n—distance from thephysical crack front to the back edge of the specimen, that is(b=W−ap).3.2.25 specimen center of pin hole distance, H* [L], n—thedistance between the center of the pin holes on a pin-loadedspecimen.3.2.26 specimen gage length, d [L], n—the distance be-tween the points of displacement measure (for example, clipgage, gage length).3.2.27 specimen span, S [L], n—the distance between speci-men supports.3.2.28 specimen thickness, B [L], n—the side-to-side di-mension of the specimen being tested.3.2.29 specimen width, W [L], n—a physical dimension ona test specimen measured from a r