1、Designation: E 1921 05Standard Test Method forDetermination of Reference Temperature, To, for FerriticSteels in the Transition Range1This standard is issued under the fixed designation E 1921; the number immediately following the designation indicates the year oforiginal adoption or, in the case of
2、revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) 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 th
3、e 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-relie
4、f 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
5、 recommended.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 typ
6、es 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.
7、 Tovalues 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 a
8、lso beenrecorded (3). However, comparisons of individual, smalldatasets 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 The statistical effects of specimen size on KJcin thetransition range are treated using weakest-link theory (4)applied to a three-parameter Weibull distribution of fracturetoughness values. A limit on KJcvalues, relative to thespecimen size, i
11、s 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 that a single-parameter (KJc) adequatelydescribes the crack-front deformation state (5).1.6 Statistical meth
12、ods 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 Weibull slope and median KJc.The procedure for applying this information to the establish-ment of transit
13、ion temperature shift determinations and theestablishment of tolerance limits is prescribed.1.7 The fracture toughness evaluation of nonuniform mate-rial is not amenable to the statistical analysis methods em-ployed in this standard. Materials must have macroscopicallyuniform tensile and toughness p
14、roperties. 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 steel also often exhibits somevariation in properties near the surfaces. Metallography andinitial screening ma
15、y be necessary to verify the applicability ofthese and similarly graded materials. Paticular notice should begiven to the 2% and 98% tolerance bounds on KJcpresented in9.3. Data falling outside these bounds may indicate nonuniformmaterial properties.1This test method is under the jurisdiction of AST
16、M Committee E08 on Fatigueand Fracture and is the direct responsibility of E08.07 on Fracture Mechanics.Current edition approved Jan. 1, 2005. Published February 2005. Originallyapproved in 1997. Last previous edition approved in 2003 as E 1921 03.2The boldface numbers in parentheses refer to the li
17、st of references at the end ofthis standard.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.1.8 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user
18、 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 Standards:3E4 Practices for Force Verification of Testing MachinesE8M Test Methods for Tension Testing of Metallic Mate-rial
19、s (Metric)E23 Test Methods for Notched Bar Impact Testing ofMetallic MaterialsE74 Practice for Calibration of Force Measuring Instru-ments for Verifying the Force Indication of Testing Ma-chinesE 208 Test Method for Conducting Drop-Weight Test toDetermine Nil-Ductility Transition Temperature of Ferr
20、iticSteelsE 399 Test Method for Plane-Strain Fracture Toughness ofMetallic MaterialsE 436 Test Method for Drop-Weight Tear Tests of FerriticSteelsE 561 Practice for R-Curve DeterminationE 812 Test Method for Crack Strength of Slow-Bend, Pre-cracked Charpy Specimens of High-Strength MetallicMaterials
21、E 1820 Test Method for Measurement of Fracture Tough-nessE 1823 Terminology Relating to Fatigue and Fracture Test-ing3. Terminology3.1 Terminology given in Terminology E 1823 is applicableto this test method.3.2 Definitions:3.2.1 ferritic steelsare typically carbon, low-alloy, andhigher alloy grades
22、. 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 E 23, E 208and E 436.
23、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, KFL3/2the magnitude ofthe mathematically ideal crack-tip stress field coefficient (stressfield singu
24、larity) 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 E 1823 for further discussion.3.2.4 J-integral, JFL1a mathematical expression; aline or surface integral that encloses the crack front from onecra
25、ck surface to the other; used to characterize the localstress-strain field around the crack front (6). See TerminologyE 1823 for further discussion.3.3 Definitions of Terms Specific to This Standard:3.3.1 control load, PMFa calculated value of maximumload used in Test Method E 1820, Eqs. A1.1 and A2
26、.1 tostipulate allowable precracking limits.3.3.1.1 DiscussionIn this method, PMis not used forprecracking, but is used as a minimum load above whichpartial unloading is started for crack growth measurement.3.3.2 crack initiationdescribes the onset of crack propa-gation from a preexisting macroscopi
27、c 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.3.3.4 effective yiel
28、d 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:sY5 sYS1sTS!23.3.5 el
29、astic 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 v being Poissons ratio.3.3.6 elastic-plastic KJFL3/2An elastic-plastic equiva-lent stress
30、intensity factor derived from J-integral.3.3.6.1 DiscussionIn this test method, KJalso implies astress intensity factor determined at the test termination pointunder conditions determined to be invalid by 8.9.2.3.3.7 elastic-plastic KJcFL3/2an elastic-plastic equiva-lent stress intensity factor deri
31、ved from the J-integral at thepoint of onset of cleavage fracture, Jc.3.3.8 equivalent value of median toughness, KeqJc(med)FL-3/2an equivalent value of the median toughness for adata set.3.3.9 Eta (h)a dimensionless parameter that relates plas-tic work done on a specimen to crack growth resistance
32、definedin terms of deformation theory J-integral (7).3.3.10 failure probability, pfthe probability that a singleselected specimen chosen at random from a population ofspecimens will fail at or before reaching the KJcvalue ofinterest.3.3.11 initial ligament length, boL the distance from theinitial cr
33、ack tip, ao, to the back face of a specimen.3.3.12 load-line displacement rate,DLLLT-1rate of in-crease of specimen load-line displacement.3.3.13 pop-ina discontinuity in a load versus displace-ment test record (8).3For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM
34、Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.E19210523.3.13.1 DiscussionApop-in event is usually audible, andis a sudden cleavage crack initiation event followed by crackarrest.Atest record w
35、ill show increased displacement and dropin applied load if the test frame is stiff. Subsequently, the testrecord may continue on to higher loads and increased displace-ment.3.3.14 precracked charpy specimenSE(B) specimen withW = B = 10 mm (0.394 in.).3.3.15 reference temperature, ToCThe test tempera
36、tureat which the median of the KJcdistribution from 1T sizespecimens will equal 100 MPa=m (91.0 ksi=in.).3.3.16 SE(B) specimen span, SLthe distance betweenspecimen supports (See Test Method E 1820 Fig. 3).3.3.17 specimen thickness, BLthe distance between thesides of specimens.3.3.17.1 DiscussionIn t
37、he case of side-grooved speci-mens, thickness, BN, is the distance between the roots of theside-groove notches.3.3.18 specimen size, nTa code used to define specimendimensions, where n is expressed in multiples of 1 in.3.3.18.1 DiscussionIn this method, specimen proportion-ality is required. For com
38、pact specimens and bend bars,specimen thickness B=ninches.3.3.19 stress intensity factor rate KFL-3/2T-1rate of in-crease of applied stress intensity factor.3.3.20 temperature, TQCFor KJcvalues that are devel-oped using specimens or test practices, or both, that do notconform to the requirements of
39、this test method, a temperatureat which KJc (med)= 100 MPa=m is defined as TQ.TQis not aprovisional value of To.3.3.21 time to control load, tMT,time to PM.3.3.22 Weibull fitting parameter, K0a scale parameterlocated at the 63.2 % cumulative failure probability level (9).KJc=K0when pf= 0.632.3.3.23
40、Weibull slope, bwith pfand KJcdata pairs plotted inlinearized Weibull coordinates obtainable by rearranging Eq.15, b is the slope of a line that defines the characteristics of thetypical scatter of KJcdata.3.3.23.1 DiscussionA Weibull slope of 4 is used exclu-sively in this method.3.3.24 yield stren
41、gth, sysFL2a value of materialstrength at 0.2 % plastic strain as determined by tensile testing.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
42、during the loading 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 Load versus displacement across the notch at a specifiedlocation is recorded by autog
43、raphic recorder or computer dataacquisition, 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 thesuitabilit
44、y 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 population
45、s and to predict changes in data distributionswith changed specimen size.4.4 The statistical relationship between specimen size andKJcfracture toughness can be assessed using weakest-linktheory, thereby providing a relationship between the specimensize and KJc(4). Limits are placed on the fracture t
46、oughnessrange over which this model can be used.4.5 For definition of the toughness transition curve, a mastercurve concept is used (11, 12). The position of the curve on thetemperature coordinate is established from the experimentaldetermination of the temperature, designated To, at which themedian
47、 KJcfor 1T size specimens is 100 MPa=m (91.0ksi=in.). Selection of a test temperature close to that at whichthe median KJcvalue will be 100 MPa=m is encouraged anda means of estimating this temperature is suggested. Smallspecimens such as precracked Charpys may have to be testedat temperatures below
48、 Towhere KJc(med)is well below 100MPa=m. In such cases, additional specimens may be requiredas stipulated in 8.5.4.6 Tolerance bounds can be determined that define therange of scatter in fracture toughness throughout the transitionrange. The standard deviation of the fitted distribution is afunction
49、 of Weibull slope and median KJcvalue, KJc(med).5. Significance and Use5.1 Fracture toughness is expressed in terms of an elastic-plastic stress intensity factor, KJc, that is derived from theJ-integral calculated at fracture.5.2 Ferritic steels are inhomogeneous with respect to theorientation of individual grains. Also, grain boundaries haveproperties distinct from those of the grains. Both containcarbides or nonmetallic inclusions that can act as nucleationsites for cleavage microcracks. The ran
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