1、Designation: E2248 12Standard Test Method forImpact Testing of Miniaturized Charpy V-Notch Specimens1This standard is issued under the fixed designation E2248; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revisi
2、on. 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 describes notched-bar impact testing ofmetallic materials using Miniaturized Charpy V-Notch(MCVN) specimens and
3、test apparatus. It provides: (a)adescription of the apparatus, (b) requirements for inspectionand calibration, (c) safety precautions, (d) sampling, (e) dimen-sions and preparation of specimens, (f) testing procedures, and(g) precision and bias.1.2 This standard concerns Miniaturized Charpy V-Notchs
4、pecimens, for which all linear dimensions, including lengthand notch depth, are reduced with respect to a type A standardimpact test specimen in accordance with Test Methods E23.These are not the same as sub-size specimens, described inAnnex A3 of Test Methods E23, for which length, notch angleand n
5、otch depth are the same as for the standard typeACharpyspecimen. See also 1.5 below.1.3 Comparison of the MCVN data with conventionalCharpy V-Notch (CVN) data or application of the MCVN data,or both, to the evaluation of ferritic material behavior is theresponsibility of the user of this test method
6、 and is notexplicitly covered by this test method.1.4 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.5 This standard does not address testing of sub-sizespecimens as discussed in Test Methods E23. The readershould understand
7、the distinction between miniature and sub-size. Miniature specimens are shorter that sub-size specimensso that more tests can be conducted per unit volume ofmaterial. Moreover, miniature specimens are designed so thatthe stress fields which control fracture are similar to those ofconventional Test M
8、ethods E23 specimens.1.6 The MCVN test may be performed using a typical TestMethods E23 test machine with suitably modified anvils andstriker or using a smaller capacity machine.1.7 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is therespons
9、ibility 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 Standards:2A370 Test Methods and Definitions for Mechanical Testingof Steel ProductsE23 Test Methods for
10、Notched Bar Impact Testing ofMetallic MaterialsE177 Practice for Use of the Terms Precision and Bias inASTM Test MethodsE691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test MethodE2298 Test Method for Instrumented Impact Testing ofMetallic Materials2.2 ISO Standa
11、rds:3ISO 148 Metallic materials - Charpy pendulum impact test- Part 1: Test methodISO 14556 Steel - Charpy V-notch pendulum impact test -Instrumented test method3. Summary of Test Method3.1 The essential features of the MCVN impact test are: (a)a suitable miniature three point bend specimen, (b) anv
12、ils andsupports on which the test specimen is placed to receive theblow of the moving mass, (c) a moving mass (striker) that hasbeen released from a sufficient height to cause the mass tobreak the specimen placed in its path, (d) a device fordetermining the energy absorbed by the broken specimen, an
13、doptionally (e) instrumentation for measuring applied force as afunction of time during specimen loading (refer to Test MethodE2298).3.2 The test consists of breaking the miniaturized specimen,notched in the middle, and supported at each end, with oneblow from a swinging pendulum under conditions de
14、finedhereafter.1This test method is under the jurisdiction of ASTM Committee E28 onMechanical Testing and is the direct responsibility of Subcommittee E28.07 onImpact Testing.Current edition approved April 1, 2012. Published May 2012. Originallyapproved in 2009. Last previous edition approved in 200
15、9 as E224809. DOI:10.1520/E2248-12.2For 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 the standards Document Summary page onthe ASTM website.3Available from Internatio
16、nal Organization for Standardization (ISO), 1, ch. dela Voie-Creuse, Case postale 56, CH-1211, Geneva 20, Switzerland, http:/www.iso.org.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.4. Significance and Use4.1 There are cases where
17、 it is impractical or impossible toprepare conventional CVN specimens. MCVN specimens arean alternative approach for characterizing notched specimenimpact behavior. Typical applications include MCVN speci-mens prepared from the broken halves of previously testedspecimens, from thin product form mate
18、rial, or from materialcut from in-service components.4.2 This standard establishes the requirements for perform-ing impact tests on MCVN specimens fabricated from metallicmaterials. Minimum requirements are given for measurementand recording equipment such that similar sensitivity andcomparable meas
19、urements, as compared to conventional CVNtests, are achieved. The user should be aware that the transitionregion temperature dependence data obtained from MCVNspecimens are not directly comparable to those obtained fromfull-size standard Charpy-V specimens and suitable correlationprocedures have to
20、be employed to obtain ductile-to-brittletransition temperature (DBTT) data equivalent to those ob-tained using CVN specimens. In all instances, correlations willhave to be developed to relate upper shelf energy (USE) datafrom MCVN test to CVN comparable energy levels. Applica-tion of MCVN test data
21、to the evaluation of ferritic materialbehavior is the responsibility of the user of this test method.MCVN test data should not be used directly to determine thelowest allowable operating temperature for an in-service ma-terial. The data must be interpreted within the framework of afracture mechanics
22、 assessment.4.3 While this Test Method treats the use of an instrumentedstriker as an option, the use of instrumentation in the impacttest is recommended and is fully described in Test MethodE2298. In order to establish the force-displacement diagram, itis necessary to measure the impact force as a
23、function of timeduring contact of the striker with the specimen. The area underthe force-displacement curve is a measure of absorbed energy.As an alternative, absorbed energy may be evaluated directlyfrom machine dial reading. Whenever possible, an opticalencoder shall be used in place of the machin
24、e dial because anencoder has better resolution than a dial.5. Test Machine5.1 The test shall be carried out with a pendulum-typeimpact testing machine which is (optionally) instrumented todetermine force-time curves. The test machine shall havesufficient capacity to break the specimen in one blow wh
25、ilelosing not more than 80 % of the initial potential energy.Provided energy measurements can be obtained with a resolu-tion better than or equal to 0.1 J, the same test machine used forCVN testing may be used to test MCVN specimens.5.2 The MCVN specimen has to be suitably supported sothat the cente
26、rline of the specimen coincides with the center ofstrike of the pendulum. If the same machine used for CVNtesting is used for MCVN specimens, refer to Appendix X3 ofE23 for changing the specimen support height by manufactur-ing new supports or adding shims.5.3 The impact velocity (tangential velocit
27、y) of the pendu-lum at the center of the strike shall not be less than 1 nor morethan 6 m/s.NOTE 1Impact velocities above 4 m/s are not advisable for instru-mented MCVN tests, since excessive oscillations are then superimposedon the initial portion of the test diagram and errors in the evaluation of
28、 theforce-displacement trace may occur. For the same reason (ease ofinterpretation of the instrumented curve), lower velocities are allowed forMCVN tests than required by E23 (not less than 3 m/s).5.4 It is recommended that the scalability of the stress fieldsis maintained. This is accomplished by s
29、caling the strikerradius, anvil radii, and the span of the anvils with respect to aspecimen size that is proportional to the CVN specimen. Fig. 1shows the dimensions of 8 and 2 mm strikers (3.86 mm and0.96 mm) scaled for use with the nominal12-scale MCVN(4.83 by 4.83 by 24.13 mm) specimen shown in F
30、ig. 2. Forboth of these scaled strikers, the anvil radius is scaled to 0.486 0.025 mm, and the span is 19.3 6 0.025 mm.5.5 A non-scaled 2 mm striker can be used to test the 4 by3 by 27 mm MCVN specimen described in Annex D of ISO14556. The anvil radius and span, in this case are 10+0.50mmand 220+0.1
31、0mm respectively.NOTE 2This particular test is allowed because a substantial amount ofFIG. 1 Scaled 8 mm and 2 mm Strikers for Use in Miniaturized Charpy Impact TestingE2248 122data exists for this specimen and test geometry. This MCVN specimen isnot proportional to the CVN specimen, so scaling is n
32、ot appropriate.5.6 The testing machine shall be a pendulum type of rigidconstruction. All general requirements for apparatus and cali-bration specified in Test Methods E23 shall be satisfied.5.7 For instrumented force measurements using optionalforce measuring instrumentation, the requirements given
33、 inTest Method E2298 regarding striker instrumentation, dataacquisition, and data analysis shall be satisfied.6. Hazards6.1 Safety precautions should be taken to protect personnelfrom electric shock, the swinging pendulum, flying brokenspecimens, and hazards associated with specimen warming andcooli
34、ng media. See also 1.6.7. Test Specimens7.1 The recommended proportional specimen configurationis the square cross section notched bar shown in Fig. 2. Thecross sectional dimension is slightly under 5 mm to enablemachining from a previously tested CVN. Information onadditional specimen geometries th
35、at have been successfullyused is provided in Appendix X1.NOTE 3In case MCVN specimens are extracted from broken CVNspecimens of highly ductile materials, the user should ensure that thesevere plastic deformation occurred during fracture of the CVN specimensdoes not affect the impact behavior of the
36、miniaturized samples.7.2 Microstructural considerations dictate that only V-notchspecimens with cross sectional dimensions sufficient to ensurea representative volume of material is tested may be used. Inorder to satisfy this requirement, the size scale and meanseparation distance of inhomogeneities
37、 that exist in the mate-rial must be known. The cross sectional dimension must be atleast five times greater than the largest inhomogeneity. Post-test metallography may be performed in order to confirm thatthe requirement has been met.7.3 Stress field similitude dictates that if the miniaturizedspec
38、imens (such as the one shown in Fig. 2) do not satisfy themicrostructural considerations, specimens with a larger crosssection may be used. For the square cross section specimen inFig. 2, all the remaining specimen dimensions (length, notchdepth, etc.) shall be scaled by appropriate ratio with theco
39、nventional CVN dimensions. This has the advantage ofstandardization of approach and scalability of previouslycalculated finite element solutions.7.4 Machining the outside surfaces of the MCVN specimensusing continuous wire electric discharge machining (EDM) orany other machining method which produce
40、s less than 0.005mm of disturbed material on the surface is acceptable. Thecrack starter notch shall be EDM machined or precisionground.7.5 Side grooving of the MCVN specimens (see also Ap-pendix X2) is optional. Investigations (1) have shown that theuse of side grooves on MCVN specimens provides a
41、largervolume of material which is sampled at plane strain conditions.This results in less downward shift in temperature due to lossof constraint caused by miniaturization, and thereby reducesNOTEPermissible variations shall be as follows:Angle of striker 61Radius of curvature of striking edge Nomina
42、l 1 mm Striker: +0.25, 0Nominal 4 mm Striker: 60.025 mmRadius of shoulder of nominal 4 mm striker 60.025 mmWidth of edge of nominal 4 mm striker 60.025 mmSurface finish requirements 0.1m or betterNotch length to edge 90 6 2Notch root radius 6 0.025 mmAdjacent sides at 90 6 10 minLigament length 60.0
43、25 mmCross section dimensions 60.025 mmFinish requirements 2m notched surface/opposite surface4m other surfacesLength of specimen +0. -12mmCentering of notch 60.12 mmAngle of notch 61FIG. 2 Miniaturized Charpy Impact SpecimenE2248 123the need for correction factors to simulate CVN transitionalfractu
44、re temperature dependence.7.6 The choice of specimen depends on the application.NOTE 4Although this test method specifically addresses impact testsperformed on notched specimens, the use of unnotched samples may beadvantageous when testing refractory metals or materials produced bypowder metallurgy
45、methods. For such materials, machining an accuratenotch without producing significant damage is extremely difficult. The useof unnotched specimens, however, is outside the scope of this test method.7.6.1 For some materials, the use of different methods formachining specimens may increase results var
46、iability and datascatter. For this reason, the machining method used shall bereported (see 11.1.2). Performing microstructural investiga-tions in order to determine the depth of the recast layer mightbe helpful.8. Test Procedure8.1 The test procedure may be summarized as follows: thetest specimen is
47、 heated/cooled in situ (that is, at the impactlocation) or it is removed from its cooling (or heating) medium,and positioned on the specimen supports; the pendulum isreleased with minimum vibration; and the absorbed energy isrecorded from the machine dial or, preferably, from the opticalencoder. For
48、 instrumented tests, the force-time curve is mea-sured and evaluated to give the total absorbed energy.8.2 The temperature of the specimen at impact must bewithin 62C of the nominal test temperature. Due to the smallsize of the specimen, in tests below or above room temperature(RT), special attentio
49、n must be devoted to temperature controlwithin the above mentioned tolerance. It is recommended thatin-situ heating/cooling be used. If a bath transfer system isused, it will be necessary to transfer the specimen to thesupports and strike the specimen within a very short period oftime (1sorless). If a thermal bath transfer system is notused, dummy specimens (with internal thermocouples) or testspecimens (with surface thermocouples) shall be used todemonstrate that the 62C requirement has been met. If in-situheating/cooling is used, dummy specimens (with inter
