1、Designation: E1921 15aStandard 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 r
2、evision, 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
3、fracture 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
4、annealing, 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 r
5、ecommended.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. T
7、ovalues 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 als
8、o 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 stronglyrec
9、ommended 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 establi
10、sh acceptablecharacterization of KJcdata populations.1.5 Tois dependent on loading rate. Tois evaluated for aquasi-static loading rate range with 0.1 2MPam/s) in Annex A1.1.6 The statistical effects of specimen size on KJcin thetransition range are treated using weakest-link theory (4)applied to a t
11、hree-parameter 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
12、to ensure that 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
13、 function of 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 This test method assumes that the test material ismacroscopically homogeneous such tha
14、t the materials haveuniform tensile and toughness properties. The fracture tough-ness evaluation of nonuniform materials is not amenable to thestatistical analysis methods employed in the main body of thistest method. Application of the analysis of this test method toan inhomogeneous material will r
15、esult in an inaccurate esti-mate of the transition reference value Toand non-conservativeconfidence bounds. For example, multipass weldments cancreate heat-affected and brittle zones with localized propertiesthat are quite different from either the bulk material or weld.Thick section steel also ofte
16、n exhibits some variation in1This test method is under the jurisdiction of ASTM Committee E08 on Fatigueand Fracture and is the direct responsibility of E08.07 on Fracture Mechanics.Current edition approved Oct. 1, 2015. Published February 2016. Originallyapproved in 1997. Last previous edition appr
17、oved in 2015 as E1921 15. DOI:10.1520/E1921-15A.2The boldface numbers in parentheses refer to the list of references at the end ofthis standard.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1properties near the surfaces. Metallograph
18、y and initial screen-ing may be necessary to verify the applicability of these andsimilarly graded materials. An appendix to analyze the cleav-age toughness properties of nonuniform or inhomogeneousmaterials is currently being prepared. In the interim, users arereferred to (6-8) for procedures to an
19、alyze inhomogeneousmaterials.1.9 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
20、 prior to use.2. Referenced Documents2.1 ASTM Standards:3E4 Practices for Force Verification of Testing MachinesE8/E8M Test Methods for Tension Testing of Metallic Ma-terialsE23 Test Methods for Notched Bar Impact Testing of Me-tallic MaterialsE74 Practice of Calibration of Force-Measuring Instrumen
21、tsfor Verifying the Force Indication of Testing MachinesE111 Test Method for Youngs Modulus, Tangent Modulus,and Chord ModulusE177 Practice for Use of the Terms Precision and Bias inASTM Test MethodsE208 Test Method for Conducting Drop-Weight Test toDetermine Nil-Ductility Transition Temperature of
22、Fer-ritic SteelsE399 Test Method for Linear-Elastic Plane-Strain FractureToughness KIcof Metallic MaterialsE436 Test Method for Drop-Weight Tear Tests of FerriticSteelsE561 Test Method forKRCurve DeterminationE691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test M
23、ethodE1820 Test Method for Measurement of Fracture ToughnessE1823 Terminology Relating to Fatigue and Fracture Testing3. Terminology3.1 Terminology given in Terminology E1823 is applicableto this test method.3.2 Definitions:3.2.1 ferritic steelsare typically carbon, low-alloy, andhigher alloy grades
24、. 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, E208and E436.NOT
25、E 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 (stressfield singula
26、rity) 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 front from onecrack
27、surface to the other; used to characterize the localstress-strain field around the crack front (9). 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 7.8.1 to stipulate allowable precrack
28、ing limits.3.3.2 crack initiationdescribes the onset of crack propa-gation from a preexisting macroscopic crack created in thespecimen by a stipulated procedure.3.3.3 effective modulus, EeffFL2an elastic modulus thatallows a theoretical (modulus normalized) compliance tomatch an experimentally measu
29、red compliance for an actualinitial crack size, ao.3.3.4 effective yield strength, YFL-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 YS,
30、and the ultimate tensile strength,TSas follows:Y5 YS1TS!23.3.5 elastic modulus, EFL2a linear-elastic factor re-lating stress to strain, the value of which is dependent on thedegree of constraint. For plane stress, E = E is used, and forplane strain, E/(1 v2) is used, with E being Youngs modulusand v
31、 being Poissons ratio.3.3.6 elastic plastic 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 th
32、e test termination pointunder conditions determined 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 equi
33、valent value of the median toughness for amulti-temperature data set.3.3.10 Eta ()a dimensionless parameter that relates plas-tic work done on a specimen to crack growth resistance definedin terms of deformation theory J-integral (10).3.3.11 failure probability, pfthe probability that a singleselect
34、ed specimen chosen at random from a population ofspecimens will fail at or before reaching the KJcvalue ofinterest.3For 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 t
35、he standards Document Summary page onthe ASTM website.E1921 15a23.3.12 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,LLLT-1rate of in-crease of specimen load-line displacement.3.3.14 pop-ina discontinuity in
36、 a force versus displace-ment test record (11).3.3.14.1 DiscussionA pop-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
37、may continue on to higher forces and increased dis-placement.3.3.15 precracked Charpy, PCC, specimenSE(B) speci-men with W = 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
38、met then To=ToQ.3.3.17 reference temperature, ToCThe test temperatureat which the median of the KJcdistribution from 1T sizespecimens will equal 100 MPam (91.0 ksiin.).3.3.18 SE(B) specimen span, SLthe distance betweenspecimen supports (See Test Method E1820 Fig. 3).3.3.19 specimen thickness, BLthe
39、distance between theparallel sides of a test specimen as depicted in Figs. 1-3.3.3.19.1 DiscussionIn the case of side-groovedspecimens, the net thickness, BN, is the distance between theroots of the side-groove notches.3.3.20 specimen size, nTa code used to define specimendimensions, where n is expr
40、essed in multiples of 1 in.3.3.20.1 DiscussionIn this method, specimen proportion-ality is required. For compact specimens and bend bars,specimen thickness B=ninches.3.3.21 temperature, TQCFor KJcvalues that are devel-oped using specimens or test practices, or both, that do notconform to the require
41、ments of this test method, a temperatureat which KJc (med)= 100 MPam is defined as TQ.TQis not aprovisional value of To.3.3.22 time to control force, tmT,time to Pm.3.3.23 Weibull fitting parameter, K0a scale parameterlocated at the 63.2 % cumulative failure probability level (12).KJc=K0when pf= 0.6
42、32.3.3.24 Weibull slope, bwith pfand KJcdata pairs plotted inlinearized Weibull coordinates obtainable by rearranging Eq17, b is the slope of a line that defines the characteristics of thetypical scatter of KJcdata.3.3.24.1 DiscussionA Weibull slope of 4 is used exclu-sively in this method, and in E
43、q 17.3.3.25 yield strength, YSFL2the stress at which amaterial exhibits a specific limiting deviation from the propor-tionality of stress to strain at the test temperature. Thisdeviation is expressed in terms of strain.3.3.25.1 Discussion1 It is customary to determine yieldstrength by either (1) Off
44、set Method (usually a strain of 0.2 %is specified) or (2) Total-Extension-Under-Force Method (usu-ally a strain of 0.5 % is specified although other values of strainmay be used).3.3.25.2 Discussion2 Whenever yield strength isspecified, the method of test must be stated along with thepercent offset o
45、r total strain under force. The values obtainedby the two methods may differ.4. Summary of Test Method4.1 This test method involves 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
46、of specimens. Crack aspect ratio,a/W, is nominally 0.5. Specimen width in compact specimensis two times the thickness. In bend 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
47、or computerdata acquisition, or both. Fracture toughness is calculated at adefined condition of crack instability. The J-integral 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 st
48、atistical analyses.4.3 Valid data sets are used to estimate the median KJcof theWeibull distribution for the data population (13). Extensivedata scatter among replicate tests is expected. Statisticalmethods are used to characterize these data populations and topredict changes in data distributions w
49、ith changed specimensize.4.4 The statistical relationship between specimen size andKJcfracture toughness is assessed using weakest-link theory,thereby providing a relationship between the specimen size andKJc(4). Limits are placed on the fracture toughness range overwhich this model can be used.4.5 For definition of the toughness transition curve, a mastercurve concept is used (14, 15). The position of the curve on thetemperature coordinate is established from the experim
