1、Designation: E1921 11Standard 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 case of re
2、vision, 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 referencetemperature, To, which characterizes the f
3、racture toughness offerritic steels that experience onset of cleavage cracking atelastic, or elastic-plastic KJcinstabilities, or both. The specifictypes of ferritic steels (3.2.1) covered are those with yieldstrengths ranging from 275 to 825 MPa (40 to 120 ksi) andweld metals, after stress-relief a
4、nnealing, that have 10 % orless 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-shapedcompact tension specimens, C(T) or DC(T). A range ofspecimen sizes with proportional dimensions is re
5、commended.The dimension on which the proportionality is based isspecimen thickness.1.3 Median KJcvalues tend to vary with the specimen typeat a given test temperature, presumably due to constraintdifferences among the allowable test specimens in 1.2. Thedegree of KJcvariability among specimen types
6、is analyticallypredicted to be a function of the material flow properties (1)2and decreases with increasing strain hardening capacity for agiven yield strength material. This KJcdependency ultimatelyleads to discrepancies in calculated Tovalues as a function ofspecimen type for the same material. To
7、values obtained fromC(T) specimens are expected to be higher than Tovaluesobtained from SE(B) specimens. Best estimate comparisons ofseveral materials indicate that the average difference betweenC(T) and SE(B)-derived Tovalues is approximately 10C (2).C(T) and SE(B) Todifferences up to 15C have also
8、 beenrecorded (3). However, comparisons of individual, small data-sets may not necessarily reveal this average trend. Datasetswhich contain both C(T) and SE(B) specimens may generateToresults which fall between the Tovalues calculated usingsolely C(T) or SE(B) specimens. It is therefore stronglyreco
9、mmended that the specimen type be reported along withthe derived Tovalue in all reporting, analysis, and discussion ofresults. This recommended reporting is in addition to therequirements in 11.1.1.1.4 Requirements are set on specimen size and the numberof replicate tests that are needed to establis
10、h acceptablecharacterization of KJcdata populations.1.5 Tois dependent on loading rate. Tois evaluated for aquasi-static loading rate range with 0.1 2MPa=m/s).1.6 The statistical effects of specimen size on KJcin thetransition range are treated using weakest-link theory (4)applied to a three-paramet
11、er Weibull distribution of fracturetoughness values. A limit on KJcvalues, relative to thespecimen size, is specified to ensure high constraint conditionsalong the crack front at fracture. For some materials, particu-larly those with low strain hardening, this limit may not besufficient to ensure th
12、at a single-parameter (KJc) adequatelydescribes the crack-front deformation state (5).1.7 Statistical methods are employed to predict the transi-tion toughness curve and specified tolerance bounds for 1Tspecimens of the material tested. The standard deviation of thedata distribution is a function of
13、 Weibull slope and median KJc.The procedure for applying this information to the establish-ment of transition temperature shift determinations and theestablishment of tolerance limits is prescribed.1.8 The fracture toughness evaluation of nonuniform mate-rial is not amenable to the statistical analy
14、sis methods em-ployed in this standard. Materials must have macroscopicallyuniform tensile and toughness properties. For example, multi-pass weldments can create heat-affected and brittle zones withlocalized properties that are quite different from either the bulkmaterial or weld. Thick section stee
15、l also often exhibits somevariation in properties near the surfaces. Metallography andinitial screening may be necessary to verify the applicability ofthese and similarly graded materials. Particular notice should1This test method is under the jurisdiction of ASTM Committee E08 on Fatigueand Fractur
16、e and is the direct responsibility of E08.07 on Fracture Mechanics.Current edition approved May 1, 2011. Published June 2011. Originallyapproved in 1997. Last previous edition approved in 2010 as E1921 101DOI:10.1520/E1921-112The boldface numbers in parentheses refer to the list of references at the
17、 end ofthis standard.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.be given to the 2% and 98% tolerance bounds on KJcpresentedin 9.3. Data falling outside these bounds may indicate nonuni-form material properties.1.9 This standard
18、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.2. Referenced Documents2.1 ASTM S
19、tandards:3E4 Practices for Force Verification of Testing MachinesE8/E8M Test Methods for Tension Testing of MetallicMaterialsE23 Test Methods for Notched Bar Impact Testing ofMetallic MaterialsE74 Practice of Calibration of Force-Measuring Instru-ments for Verifying the Force Indication of Testing M
20、a-chinesE208 Test Method for Conducting Drop-Weight Test toDetermine Nil-Ductility Transition Temperature of FerriticSteelsE399 Test Method for Linear-Elastic Plane-Strain FractureToughness KIcof Metallic MaterialsE436 Test Method for Drop-Weight Tear Tests of FerriticSteelsE561 Test Method for K-R
21、Curve DeterminationE1820 Test Method for Measurement of Fracture Tough-nessE1823 Terminology Relating to Fatigue and Fracture Test-ing3. Terminology3.1 Terminology given in Terminology E1823 is applicableto this test method.3.2 Definitions:3.2.1 ferritic steelsare typically carbon, low-alloy, andhig
22、her alloy grades. Typical microstructures are bainite, tem-pered bainite, tempered martensite, and ferrite and pearlite.Allferritic steels have body centered cubic crystal structures thatdisplay ductile-to-cleavage transition temperature fracturetoughness characteristics. See also Test Methods E23,
23、E208and E436.NOTE 1This definition is not intended to imply that all of the manypossible types of ferritic steels have been verified as being amenable toanalysis by this test method.3.2.2 stress-intensity factor, KFL 3/2the magnitude ofthe mathematically ideal crack-tip stress field coefficient (str
24、essfield singularity) for a particular mode of crack-tip regiondeformation in a homogeneous body.3.2.3 DiscussionIn this test method, Mode I is assumed.See Terminology E1823 for further discussion.3.2.4 J-integral, JFL1a mathematical expression; aline or surface integral that encloses the crack fron
25、t from onecrack surface to the other; used to characterize the localstress-strain field around the crack front (6). See TerminologyE1823 for further discussion.3.3 Definitions of Terms Specific to This Standard:3.3.1 control force, PmFa calculated value of maximumforce used in Test Method E1820, Eqs
26、. A1.1 and A2.1 tostipulate allowable precracking limits.3.3.1.1 DiscussionIn this method, Pmis not used forprecracking, but is used as a minimum force value above whichpartial unloading is started for crack growth measurement.3.3.2 crack initiationdescribes the onset of crack propa-gation from a pr
27、eexisting macroscopic crack created in thespecimen by a stipulated procedure.3.3.3 effective modulus, EeFL2an elastic modulus thatcan be used with experimentally determined elastic complianceto effect an exact match to theoretical (modulus-normalized)compliance for the actual initial crack size, ao.
28、3.3.4 effective yield strength, sYFL-2, an assumed valueof uniaxial yield strength that represents the influence of plasticyielding upon fracture test parameters.3.3.4.1 DiscussionIt is calculated as the average of the 0.2% offset yield strength sYS, and the ultimate tensile strength,sTSas follows:s
29、Y5 sYS1sTS!23.3.5 elastic modulus, E8FL2a linear-elastic factor re-lating stress to strain, the value of which is dependent on thedegree of constraint. For plane stress, E8 = E is used, and forplane strain, E/(1 v2) is used, with E being Youngs modulusand v being Poissons ratio.3.3.6 elastic plastic
30、 JcFL1J-integral at the onset ofcleavage fracture.3.3.7 elastic-plastic KJFL3/2An elastic-plastic equiva-lent stress intensity factor derived from the J-integral.3.3.7.1 DiscussionIn this test method, KJalso implies astress intensity factor determined at the test termination pointunder conditions de
31、termined to be invalid by 8.9.2.3.3.8 elastic-plastic KJcFL3/2an elastic-plastic equiva-lent stress intensity factor derived from the J-integral at thepoint of onset of cleavage fracture, Jc.3.3.9 equivalent value of median toughness, KJcmed!eqFL-3/2an equivalent value of the median toughness for am
32、ulti-temperature data set.3.3.10 Eta (h)a dimensionless parameter that relates plas-tic work done on a specimen to crack growth resistance definedin terms of deformation theory J-integral (7).3.3.11 failure probability, pfthe probability that a singleselected specimen chosen at random from a populat
33、ion ofspecimens will fail at or before reaching the KJcvalue ofinterest.3.3.12 initial ligament length, boL the distance from theinitial crack tip, ao, to the back face of a specimen.3.3.13 load-line displacement rate,DLLLT-1rate of in-crease of specimen load-line displacement.3For referenced ASTM s
34、tandards, 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.E1921 1123.3.14 pop-ina discontinuity in a force versus displace-ment test record (
35、8).3.3.14.1 DiscussionApop-in event is usually audible, andis a sudden cleavage crack initiation event followed by crackarrest.Atest record will show increased displacement and dropin applied force if the test frame is stiff. Subsequently, the testrecord may continue on to higher forces and increase
36、d dis-placement.3.3.15 precracked Charpy specimenSE(B) specimen withW = B = 10 mm (0.394 in.).3.3.16 provisional reference temperature, (ToQ) CInterim Tovalue calculated using the standard test methoddescribed herein. If all validity criteria are met then To=ToQ3.3.17 reference temperature, ToCThe t
37、est temperatureat which the median of the KJcdistribution from 1T sizespecimens will equal 100 MPa=m (91.0 ksi=in.).3.3.18 SE(B) specimen span, SLthe distance betweenspecimen supports (See Test Method E1820 Fig. 3).3.3.19 specimen thickness, BLthe distance between theparallel sides of a test specime
38、n as depicted in Figs. 1-3.3.3.19.1 DiscussionIn the case of side-grooved speci-mens, the net thickness, BN, is the distance between the roots ofthe side-groove notches.3.3.20 specimen size, nTa code used to define specimendimensions, where n is expressed in multiples of 1 in.3.3.20.1 DiscussionIn t
39、his method, specimen proportion-ality is required. For compact specimens and bend bars,specimen thickness B=ninches.3.3.21 temperature, To,XestCestimated value of the refer-ence temperature corresponding to an elevated loading rate X,to be used only for test temperature selection in accordancewith 8
40、.4.2.3.3.22 temperature, TQCFor KJcvalues that are devel-oped using specimens or test practices, or both, that do notconform to the requirements of this test method, a temperatureat which KJc (med)= 100 MPa=m is defined as TQ.TQis not aprovisional value of To.3.3.23 test loading rate KFL-3/2T-1rate
41、of increase ofapplied stress intensity factor.3.3.23.1 DiscussionIt is generally evaluated as the ratiobetween KJcand the corresponding time to cleavage. For testswhere partial unloading/reloading sequences are used to mea-sure compliance, an equivalent time to cleavage tcshall be usedto calculate t
42、he loading rate. The value of tcis calculated as theratio between the value of load-line displacement at cleavageand the load-line displacement rate applied during the mono-tonic loading portions of the test (that is, the periods betweenpartial unloading/reloading sequences used for compliancemeasur
43、ement).3.3.24 time to control force, tmT,time to Pm.3.3.25 Weibull fitting parameter, K0a scale parameterlocated at the 63.2 % cumulative failure probability level (9).KJc=K0when pf= 0.632.3.3.26 Weibull slope, bwith pfand KJcdata pairs plotted inlinearized Weibull coordinates obtainable by rearrang
44、ing Eq19, b is the slope of a line that defines the characteristics of thetypical scatter of KJcdata.3.3.26.1 DiscussionA Weibull slope of 4 is used exclu-sively in this method.3.3.27 yield strength, sYSFL2the stress at which amaterial exhibits a specific limiting deviation from the propor-tionality
45、 of stress to strain at the test temperature. Thisdeviation is expressed in terms of strain.3.3.27.1 Discussion1 It is customary to determine yieldstrength by either (1) Offset Method (usually a strain of 0.2 %is specified) or (2) Total-Extension-Under-Force Method (usu-ally a strain of 0.5 % is spe
46、cified although other values of strainmay be used).3.3.27.2 Discussion2 Whenever yield strength is speci-fied, the method of test must be stated along with the percentoffset or total strain under force. The values obtained by thetwo methods may differ.4. Summary of Test Method4.1 This test method in
47、volves the testing of notched andfatigue precracked bend or compact specimens in a tempera-ture range where either cleavage cracking or crack pop-indevelop during the loading of specimens. Crack aspect ratio,a/W, is nominally 0.5. Specimen width in compact specimensis two times the thickness. In ben
48、d bars, specimen width can beeither one or two times the thickness.4.2 Force versus displacement across the notch at a speci-fied location is recorded by autographic recorder or computerdata acquisition, or both. Fracture toughness is calculated at adefined condition of crack instability. The J-inte
49、gral value atinstability, Jc, is calculated and converted into its equivalent inunits of stress intensity factor, KJc. Validity limits are set on thesuitability of data for statistical analyses.4.3 Tests that are replicated at least six times can be used toestimate the median KJcof the Weibull distribution for the datapopulation (10). Extensive data scatter among replicate tests isexpected. Statistical methods are used to characterize thesedata populations and to predict chan
