1、Designation: E1921 12aE1921 13Standard Test Method forDetermination of Reference Temperature, To, for FerriticSteels in the Transition Range1This standard is issued under the fixed designation E1921; the number immediately following the designation indicates the year oforiginal adoption or, in the c
2、ase 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 the determination of a reference temperature, To, which character
3、izes the fracture toughness offerritic steels that experience onset of cleavage cracking at elastic, or elastic-plastic KJc instabilities, or both. The specific typesof ferritic steels (3.2.1) covered are those with yield strengths ranging from 275 to 825 MPa (40 to 120 ksi) and weld metals, afterst
4、ress-relief annealing, that have 10 % or less strength mismatch relative to that of the base metal.1.2 The specimens covered are fatigue precracked single-edge notched bend bars, SE(B), and standard or disk-shaped compacttension specimens, C(T) or DC(T). A range of specimen sizes with proportional d
5、imensions is recommended. The dimension onwhich the proportionality is based is specimen thickness.1.3 Median KJc values tend to vary with the specimen type at a given test temperature, presumably due to constraint differencesamong the allowable test specimens in 1.2. The degree of KJc variability a
6、mong specimen types is analytically predicted to be afunction of the material flow properties (1)2 and decreases with increasing strain hardening capacity for a given yield strengthmaterial. This KJc dependency ultimately leads to discrepancies in calculated To values as a function of specimen type
7、for the samematerial. To values obtained from C(T) specimens are expected to be higher than To values obtained from SE(B) specimens. Bestestimate comparisons of several materials indicate that the average difference between C(T) and SE(B)-derived To values isapproximately 10C (2). C(T) and SE(B) To
8、differences up to 15C have also been recorded (3). However, comparisons ofindividual, small datasets may not necessarily reveal this average trend. Datasets which contain both C(T) and SE(B) specimensmay generate To results which fall between the To values calculated using solely C(T) or SE(B) speci
9、mens. It is therefore stronglyrecommended that the specimen type be reported along with the derived To value in all reporting, analysis, and discussion ofresults. This recommended reporting is in addition to the requirements in 11.1.1.1.4 Requirements are set on specimen size and the number of repli
10、cate tests that are needed to establish acceptablecharacterization of KJc data populations.1.5 To is dependent on loading rate. To is evaluated for a quasi-static loading rate range with 0.1 2 MPam/s).1.6 The statistical effects of specimen size on KJc in the transition range are treated using weake
11、st-link theory (4) applied to athree-parameter Weibull distribution of fracture toughness values. A limit on KJc values, relative to the specimen size, is specifiedto ensure high constraint conditions along the crack front at fracture. For some materials, particularly those with low strainhardening,
12、 this limit may not be sufficient to ensure that a single-parameter (KJc) adequately describes the crack-front deformationstate (5).1.7 Statistical methods are employed to predict the transition toughness curve and specified tolerance bounds for 1T specimensof the material tested. The standard devia
13、tion of the data distribution is a function of Weibull slope and median KJc. The procedurefor applying this information to the establishment of transition temperature shift determinations and the establishment of tolerancelimits is prescribed.1.8 The fracture toughness evaluation of nonuniform mater
14、ial is not amenable to the statistical analysis methods employed inthis standard. Materials must have macroscopically uniform tensile and toughness properties. For example, multipass weldmentscan create heat-affected and brittle zones with localized properties that are quite different from either th
15、e bulk material or weld.1 This test method is under the jurisdiction of ASTM Committee E08 on Fatigue and Fracture and is the direct responsibility of E08.07 on Fracture Mechanics.Current edition approved Nov. 15, 2012Jan. 1, 2013. Published February 2013. Originally approved in 1997. Last previous
16、edition approved in 2012 asE1921 12.E1921 12a. DOI: 10.1520/E1921-12A.10.1520/E1921-13.2 The boldface numbers in parentheses refer to the list of references at the end of this standard.This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of
17、 what changes have been made to the previous version. Becauseit may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current versionof the standard as published by ASTM is to be considered
18、 the official document.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1Thick section steel also often exhibits some variation in properties near the surfaces. Metallography and initial screening may benecessary to verify the applicabi
19、lity of these and similarly graded materials. Particular notice should be given to the 2% and 98%tolerance bounds on KJc presented in 9.3. Data falling outside these bounds may indicate nonuniform material properties.1.9 This standard does not purport to address all of the safety concerns, if any, a
20、ssociated with its use. It is the responsibilityof the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatorylimitations prior to use.2. Referenced Documents2.1 ASTM Standards:3E4 Practices for Force Verification of Testing MachinesE8
21、/E8M Test Methods for Tension Testing of Metallic MaterialsE23 Test Methods for Notched Bar Impact Testing of Metallic MaterialsE74 Practice of Calibration of Force-Measuring Instruments for Verifying the Force Indication of Testing MachinesE177 Practice for Use of the Terms Precision and Bias in AS
22、TM Test MethodsE208 Test Method for Conducting Drop-Weight Test to Determine Nil-Ductility Transition Temperature of Ferritic SteelsE399 Test Method for Linear-Elastic Plane-Strain Fracture Toughness KIc of Metallic MaterialsE436 Test Method for Drop-Weight Tear Tests of Ferritic SteelsE561 Test Met
23、hod forK-R Curve DeterminationE691 Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test MethodE1820 Test Method for Measurement of Fracture ToughnessE1823 Terminology Relating to Fatigue and Fracture Testing3. Terminology3.1 Terminology given in Terminology E1823 is
24、applicable to this test method.3.2 Definitions:3.2.1 ferritic steelsare typically carbon, low-alloy, and higher alloy grades. Typical microstructures are bainite, temperedbainite, tempered martensite, and ferrite and pearlite. All ferritic steels have body centered cubic crystal structures that disp
25、layductile-to-cleavage transition temperature fracture toughness characteristics. See also Test Methods E23, E208 and E436.NOTE 1This definition is not intended to imply that all of the many possible types of ferritic steels have been verified as being amenable to analysisby this test method.3.2.2 s
26、tress-intensity factor, KFL 3/2the magnitude of the mathematically ideal crack-tip stress field coefficient (stress fieldsingularity) for a particular mode of crack-tip region deformation in a homogeneous body.3.2.3 DiscussionIn this test method, Mode I is assumed. See Terminology E1823 for further
27、discussion.3.2.4 J-integral, JFL1 a mathematical expression; a line or surface integral that encloses the crack front from one cracksurface to the other; used to characterize the local stress-strain field around the crack front (6). See Terminology E1823 for furtherdiscussion.3.3 Definitions of Term
28、s Specific to This Standard:3.3.1 control force, PmFa calculated value of maximum force used in Test Method E1820, Eqs. A1.1 and A2.1 to stipulateallowable precracking limits.3.3.1.1 DiscussionIn this method, Pm is not used for precracking, but is used as a minimum force value above which partial un
29、loading is started forcrack growth measurement.3.3.2 crack initiationdescribes the onset of crack propagation from a preexisting macroscopic crack created in the specimenby a stipulated procedure.3.3.3 effective modulus, EeffFL2an elastic modulus that can be used with experimentally determined elast
30、ic compliance toeffect a match to theoretical (modulus-normalized) compliance for theallows a theoretical (modulus normalized) compliance tomatch an experimentally measured compliance for an actual initial crack size, ao.3 For referencedASTM standards, visit theASTM website, www.astm.org, or contact
31、ASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standardsvolume information, refer to the standards Document Summary page on the ASTM website.E1921 1323.3.4 effective yield strength, Y FL-2, an assumed value of uniaxial yield strength that represents the influence of plasticyieldin
32、g upon fracture test parameters.3.3.4.1 DiscussionIt is calculated as the average of the 0.2 % offset yield strength YS, and the ultimate tensile strength, TS as follows:Y 5YS1TS!23.3.5 elastic modulus, EFL2 a linear-elastic factor relating stress to strain, the value of which is dependent on the de
33、greeof constraint. For plane stress, E = E is used, and for plane strain, E/(1 v2) is used, with E being Youngs modulus and v beingPoissons ratio.3.3.6 elastic plastic Jc FL1J-integral at the onset of cleavage fracture.3.3.7 elastic-plastic KJFL3/2 An elastic-plastic equivalent stress intensity fact
34、or derived from the J-integral.3.3.7.1 DiscussionIn this test method, KJ also implies a stress intensity factor determined at the test termination point under conditions determinedto be invalid by 8.9.2.3.3.8 elastic-plastic KJcFL3/2an elastic-plastic equivalent stress intensity factor derived from
35、the J-integral at the point ofonset of cleavage fracture, Jc.3.3.9 equivalent value of median toughness, K Jcmed!eqFL-3/2an equivalent value of the median toughness for a multi-temperature data set.3.3.10 Eta ()a dimensionless parameter that relates plastic work done on a specimen to crack growth re
36、sistance defined interms of deformation theory J-integral (7).3.3.11 failure probability, pfthe probability that a single selected specimen chosen at random from a population of specimenswill fail at or before reaching the KJc value of interest.3.3.12 initial ligament length, bo L the distance from
37、the initial crack tip, ao, to the back face of a specimen.3.3.13 load-line displacement rate,LLLT-1rate of increase of specimen load-line displacement.3.3.14 pop-ina discontinuity in a force versus displacement test record (8).3.3.14.1 DiscussionApop-in event is usually audible, and is a sudden clea
38、vage crack initiation event followed by crack arrest.Atest record will showincreased displacement and drop in applied force if the test frame is stiff. Subsequently, the test record may continue on to higherforces and increased displacement.3.3.15 precracked Charpy, PCC, specimenSE(B) specimen with
39、W = B = 10 mm (0.394 in.).3.3.16 provisional reference temperature, (ToQ) CInterim To value calculated using the standard test method describedherein. If all validity criteria are met then To= ToQ.3.3.17 reference temperature, To CThe test temperature at which the median of the KJc distribution from
40、 1T size specimenswill equal 100 MPam (91.0 ksiin.).3.3.18 SE(B) specimen span, SLthe distance between specimen supports (See Test Method E1820 Fig. 3).3.3.19 specimen thickness, BLthe distance between the parallel sides of a test specimen as depicted in Figs. 1-3.3.3.19.1 DiscussionIn the case of s
41、ide-grooved specimens, the net thickness, BN, is the distance between the roots of the side-groove notches.3.3.20 specimen size, nTa code used to define specimen dimensions, where n is expressed in multiples of 1 in.3.3.20.1 DiscussionIn this method, specimen proportionality is required. For compact
42、 specimens and bend bars, specimen thickness B = n inches.E1921 133NOTE 1“A” surfaces shall be perpendicular and parallel as applicable to within 0.002W TIR.NOTE 2The intersection of the crack starter notch tips with the two specimen surfaces shall be equally distant from the top and bottom edges of
43、 the specimen within 0.005W TIR.FIG. 1 Recommended Compact Specimen DesignsE19211343.3.21 temperature, To,Xest Cestimated value of the reference temperature corresponding to an elevated loading rate X, to beused only for test temperature selection in accordance with 8.4.2.3.3.22 temperature, TQ CFor
44、 KJc values that are developed using specimens or test practices, or both, that do not conformto the requirements of this test method, a temperature at which KJc (med) = 100 MPam is defined as TQ. TQ is not a provisionalvalue of To.3.3.23 test loading rate KFL-3/2T-1rate of increase of applied stres
45、s intensity factor.3.3.23.1 DiscussionIt is generally evaluated as the ratio between KJc and the corresponding time to cleavage. For tests where partial unloading/reloading sequences are used to measure compliance, an equivalent time to cleavage tc shall be used to calculate the loading rate.NOTE 1A
46、 surfaces shall be perpendicular and parallel as applicable to within 0.002W TIR.NOTE 2The intersection of the crack starter notch tips with the two specimen surfaces shall be equally distant from the top and bottom extremes ofthe disk within 0.005W TIR.NOTE 3Integral or attached knife edges for cli
47、p gage attachment may be used. See also Fig. 6, Test Method E399.FIG. 2 Disk-shaped Compact Specimen DC(T) Standard ProportionsNOTE 1All surfaces shall be perpendicular and parallel within 0.001W TIR; surface finish 64v.NOTE 2Crack starter notch shall be perpendicular to specimen surfaces to within6
48、 2.FIG. 3 Recommended Bend Bar Specimen DesignE1921 135The value of tc is calculated as the ratio between the value of load-line displacement at cleavage and the load-line displacementrate applied during the monotonic loading portions of the test (that is, the periods between partial unloading/reloa
49、ding sequencesused for compliance measurement).3.3.24 time to control force, tmT,time to Pm.3.3.25 Weibull fitting parameter, K0a scale parameter located at the 63.2 % cumulative failure probability level (9).KJc = K0when pf = 0.632.3.3.26 Weibull slope, bwith pf and KJc data pairs plotted in linearized Weibull coordinates obtainable by rearranging Eq 19,b is the slope of a line that defines the characteristics of the typical scatter of KJc data.3.3.26
