ASTM E1820-2020b

Designation E1820 20b Standard Test for Measurement of Fracture Toughness 1 This standard is issued under the fixed designation E1820; the number immediately following the designation indicates the year of original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A superscript epsilon indicates an editorial change since the last revision or reapproval. 1. Scope 1.1 This test covers procedures and guidelines for the determination of fracture toughness of metallic materials using the following parameters K, J, and CTOD . Tough- ness can be measured in the R-curve at or as a point value. The fracture toughness determined in accordance with this test is for the opening mode Mode I of loading. NOTE 1Until this version, K Ic could be uated using this test as well as by using Test E399. To avoid duplication, the uation of K Ic has been removed from this test and the user is referred to Test E399. 1.2 The recommended specimens are single-edge bend, SEB, compact, CT, and disk-shaped compact, DCT. All specimens contain notches that are sharpened with fatigue cracks. 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 toughness, material flow strength, and the individual qualifi- cation requirements of the toughness value per values sought. NOTE 2Other standard s for the determination of fracture toughness using the parameters K, J, and CTOD are contained in Test s E399, E1290, and E1921. This test was developed to provide a common for determining all applicable toughness parameters from a single test. 1.3 The values stated in SI units are to be regarded as standard. The values given in parentheses after SI units are provided for ination only and are not considered standard. 1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appro- priate safety, health, and environmental practices and deter- mine the applicability of regulatory limitations prior to use. 1.5 This international standard was developed in accor- dance with internationally recognized principles on standard- ization established in the Decision on Principles for the Development of International Standards, Guides and Recom- mendations issued by the World Trade Organization Technical Barriers to Trade TBT Committee. 2. Referenced Documents 2.1 ASTM Standards 2 E4 Practices for Force Verification of Testing Machines E8/E8M Test s for Tension Testing of Metallic Ma- terials E21 Test s for ElevatedTemperatureTensionTests of Metallic Materials E23 Test s for Notched Bar Impact Testing of Me- tallic Materials E399 Test for Linear-Elastic Plane-Strain Fracture Toughness of Metallic Materials E1290 Test for Crack-Tip Opening Displacement CTOD Fracture Toughness Measurement Withdrawn 2013 3 E1823 Terminology Relating to Fatigue and Fracture Testing E1921 Test for Determination of Reference Temperature, T o , for Ferritic Steels in the Transition Range E1942 Guide for uating DataAcquisition Systems Used in Cyclic Fatigue and Fracture Mechanics Testing E2298 Test for Instrumented Impact Testing of Metallic Materials 2.2 ASTM Data Sets 4 E1820/1DS12016 Standard data set 1 to uate com- puter algorithms for uation of J Ic using, Annex A9 of E1820 E1820/2DS22020 Standard data set 2 to uate com- puter algorithms for uation of J Ic using, Annex A9 of E1820 E1820/3DS32020 Standard data set 3 to uate com- puter algorithms for uation of J Ic using, Annex A9 of E1820 1 This test is under the jurisdiction of ASTM Committee E08 on Fatigue and Fracture and is the direct responsibility of Subcommittee E08.07 on Fracture Mechanics. Current edition approved Sept. 1, 2020. Published November 2020. Originally approved in 1996. Last previous edition approved in 2020 as E1820 20a 1 . DOI 10.1520/E1820-20B 2 For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standards volume ination, refer to the standards Document Summary page on the ASTM website. 3 The last approved version of this historical standard is referenced on www.astm.org. 4 These data sets are available for download from ASTM at https//www.astm.org/COMMIT/E1820 Data Sets DS1-DS9.7z Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade TBT Committee. 1 Copyright by ASTM Intl all rights reserved; Mon Dec 28 033531 EST 2020 Downloaded/printed by Higher Education Commission Higher Education Commission pursuant to License Agreement. No further reproductions authorized. E1820/4DS42020 Standard data set 4 to uate com- puter algorithms for uation of J Ic using, Annex A9 of E1820 E1820/5DS52020 Standard data set 5 to uate com- puter algorithms for uation of J Ic using, Annex A9 of E1820 E1820/6DS62020 Standard data set 6 to uate com- puter algorithms for uation of J Ic using, Annex A9 of E1820 E1820/7DS72020 Standard data set 7 to uate com- puter algorithms for uation of J Ic using, Annex A9 of E1820 E1820/8DS82020 Standard data set 8 to uate com- puter algorithms for uation of J Ic using, Annex A9 of E1820 E1820/9DS92020 Standard data set 9 to uate com- puter algorithms for uation of J Ic using, Annex A9 of E1820 3. Terminology 3.1 Terminology E1823 is applicable to this test . Only items that are exclusive to Test E1820, or that have specific discussion items associated, are listed in this section. 3.2 Definitions of Terms Specific to This Standard 3.2.1 compliance LF 1 , 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 gage length. The direction of the vector is normal to the crack plane. 3.2.2.1 DiscussionIn this practice, displacement, v, is the total displacement measured by clip gages or other devices spanning the crack faces. 3.2.3 crack extension, a L, nan increase in crack size. 3.2.4 crack-extension force, G FL 1 or FLL 2 , nthe elastic energy per unit of new separation area that is made available at the front of an ideal crack in an elastic solid during a virtual increment of forward crack extension. 3.2.5 crack-tip opening displacement CTOD, L, ncrack displacement resulting from the total deation elastic plus plastic at variously defined locations near the original prior to force application crack tip. 3.2.5.1 DiscussionIn this test , CTOD is the dis- placement of the crack surfaces normal to the original un- loaded crack plane at the tip of the fatigue precrack, a o . In this test , CTOD is calculated at the original crack size, a o , from measurements made from the force versus displacement record. 3.2.5.2 DiscussionIn CTOD testing, Ic L is a value of CTOD near the onset of slow stable crack extension, here defined as occurring at a p 0.2 mm 0.008 in. 0.7 Ic . 3.2.5.3 DiscussionIn CTOD testing, c L is the value of CTOD at the onset of unstable crack extension see 3.2.36or pop-in see 3.2.22 when a p 0.2 mm 0.008 in. 0.7 u . The u corresponds to the force P u and the clip gage displacement v u see Fig. 1. It may be size- dependent and a function of test specimen geometry. It can be useful to define limits on ductile fracture behavior. 3.2.5.5 DiscussionIn CTOD testing, c * L characterizes the CTOD fracture toughness of materials at fracture instability prior to the onset of significant stable tearing crack extension. The value of c * determined by this test represents a measure of fracture toughness at instability without significant stable crack extension that is independent of in-plane dimen- sions. However, there may be a dependence of toughness on thickness length of crack front. NOTE 1Construction lines drawn parallel to the elastic loading slope to give v p , the plastic component of total displacement, v g . 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 Records E1820 20b 2 Copyright by ASTM Intl all rights reserved; Mon Dec 28 033531 EST 2020 Downloaded/printed by Higher Education Commission Higher Education Commission pursuant to License Agreement. No further reproductions authorized. 3.2.6 dial energy, KV FLabsorbed energy as indicated by the impact machine encoder or dial indicator, as applicable. 3.2.7 dynamic stress intensity factor, K Jd The dynamic equivalent of the stress intensity factor K J , calculated from J using the equation specified in this test . 3.2.8 effective thickness, B e L,nfor side-grooved speci- mens B e B BB N 2 /B. This is used for the elastic unloading compliance measurement of crack size. 3.2.9 effective yield strength, Y FL 2 , nan assumed value of uniaxial yield strength that represents the influence of plastic yielding upon fracture test parameters. 3.2.9.1 DiscussionIt is calculated as the average of the 0.2 offset yield strength YS , and the ultimate tensile strength, TS as follows Y 5 YS 1 TS 2 1 3.2.9.2 DiscussionIn estimating Y , influences of testing conditions, such as loading rate and temperature, should be considered. 3.2.9.3 DiscussionThe dynamic effective yield strength, Yd , is the dynamic equivalent of the effective yield strength. 3.2.10 general yield force, P gy Fin an instrumented impact test, applied force corresponding to general yielding of the specimen ligament. It corresponds to F gy , as used in Test E2298. 3.2.11 J-integral, J FL 1 , na mathematical expression, a line or surface integral that encloses the crack front from one crack surface to the other, used to characterize the local stress-strain field around the crack front. 3.2.11.1 DiscussionThe J-integral expression for a two- dimensional crack, in the x-z plane with the crack front parallel to the z-axis, is the line integral as follows J 5 * S Wdy 2 T u x ds D 2 where W loading work per unit volume or, for elastic bodies, strain energy density, 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, and T u x ds rate of work from the stress field into the area enclosed by . 3.2.11.2 DiscussionThe value of J obtained from this equation is taken to be path-independent in test specimens commonly used, but in service components and perhaps in test specimens caution is needed to adequately consider loading interior to such as from rapid motion of the crack or the service component, and from residual or thermal stress. 3.2.11.3 DiscussionIn elastic linear or nonlinear solids, the J-integral equals the crack-extension force, G. See crack extension force. 3.2.11.4 DiscussionIn elastic linear and nonlinear solids for which the mathematical expression is path independent, the J-integral is equal to the value obtained from two identical bodies with infinitesimally differing crack areas each subject to stress. The parameter J is the difference in work per unit difference in crack area at a fixed value of displacement or, where appropriate, at a fixed value of force 1 5 . 3.2.11.5 DiscussionThe dynamic equivalent of J c is J cd,X , with X order of magnitude of J-integral rate. 3.2.12 J c FL 1 The property J c determined by this test characterizes the fracture toughness of materials at fracture instability prior to the onset of significant stable tearing crack extension. The value of J c determined by this test 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 J u FL 1 The quantity J u determined by this test measures fracture instability after the onset of signifi- cant stable tearing crack extension. It may be size-dependent and a function of test specimen geometry. It can be useful to define limits on ductile fracture behavior. 3.2.13.1 DiscussionThe dynamic equivalent of J u is J ud,X , with X order of magnitude of J-integral rate. 3.2.14 J-integral rate, J FL 21 T 21 derivative of J with respect to time. 3.2.15 machine capacity, MC FLmaximum available energy of the impact testing machine. 3.2.16 maximum force, P max Fin an instrumented im- pact test, maximum value of applied force. It corresponds to F m , as used in Test E2298. 3.2.17 net thickness, B N L, ndistance between the roots of the side grooves in side-grooved specimens. 3.2.18 original crack size, a o L,nthe physical crack size at the start of testing. 3.2.18.1 DiscussionIn this test , a oq is used to denote original crack size estimated from compliance. 3.2.19 original remaining ligament, b o L, ndistance from the original crack front to the back edge of the specimen, that is b o Wa o . 3.2.20 physical crack size, a p L,nthe distance from a reference plane to the observed crack front. This distance may represent an average of several measurements along the crack front. The reference plane depends on the specimen , and it is normally taken to be either the boundary, or a plane containing either the load-line or the centerline of a specimen or plate. The reference plane is defined prior to specimen deation. 3.2.21 plane-strain fracture toughness, J Ic FL 1 , K JIc FL 3/2 ,nthe crack-extension resistance under conditions of crack-tip plane-strain. 3.2.21.1 DiscussionFor example, in Mode I for slow rates of loading and substantial plastic deation, plane-strain fracture toughness is the value of the J-integral designated J Ic FL 1 as measured using the operational procedure and 5 The boldface numbers in parentheses refer to the list of references at the end of this standard. E1820 20b 3 Copyright by ASTM Intl all rights reserved; Mon Dec 28 033531 EST 2020 Downloaded/printed by Higher Education Commission Higher Education Commission pursuant to License Agreement. No further reproductions authorized. satisfying all of the qualifica