1、Designation: B771 11 (Reapproved 2017)Standard Test Method forShort Rod Fracture Toughness of Cemented Carbides1This standard is issued under the fixed designation B771; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of l
2、ast 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 the fracturetoughness of cemented carbides (KIcSR) by testing slotted shor
3、trod or short bar specimens.1.2 The values stated in SI units are to be regarded asstandard. The values given in parentheses are for informationonly.1.3 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 s
4、tandard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.1.4 This international standard was developed in accor-dance with internationally recognized principles on standard-ization established in the Decision on Principles
5、for theDevelopment of International Standards, Guides and Recom-mendations issued by the World Trade Organization TechnicalBarriers to Trade (TBT) Committee.2. Referenced Documents2.1 ASTM Standards:2E399 Test Method for Linear-Elastic Plane-Strain FractureToughness KIcof Metallic Materials3. Termin
6、ology Definitions3.1 stress intensity factor, Kl,(dimensional units FL3/2)the magnitude of the ideal-crack-tip stress field for mode 1 ina linear-elastic body.NOTE 1Values of K for mode l are given by:Kl5 limit y=2r# (1)r0where:r = distance directly forward from the crack tip to alocation where the
7、significant stress yis calculated,andy= principal stress normal to the crack plane.3.2 Abbreviations: fracture toughness of cemented carbide,KIcSR,(dimensional units FL3/2)the material-toughnessproperty measured in terms of the stress-intensity factor Klbythe operational procedure specified in this
8、test method.4. Summary of Test Method4.1 This test method involves the application of an openingload to the mouth of the short rod or short bar specimen whichcontains a chevron-shaped slot. Load versus displacementacross the slot at the specimen mouth is recorded autographi-cally. As the load is inc
9、reased, a crack initiates at the point ofthe chevron slot and slowly advances longitudinally, tending tosplit the specimen in half. The load goes through a smoothmaximum when the width of the crack front is about one thirdof the specimen diameter (short rod) or breadth (short bar).Thereafter, the lo
10、ad decreases with further crack growth. Twounloading-reloading cycles are performed during the test tomeasure the effects of any macroscopic residual stresses in thespecimen. The fracture toughness is calculated from themaximum load in the test and a residual stress parameter whichis evaluated from
11、the unloading-reloading cycles on the testrecord.5. Significance and Use5.1 The property KIcSRdetermined by this test method isbelieved to characterize the resistance of a cemented carbide tofracture in a neutral environment in the presence of a sharpcrack under severe tensile constraint, such that
12、the state ofstress near the crack front approaches tri-tensile plane strain,and the crack-tip plastic region is small compared with thecrack size and specimen dimensions in the constraint direction.AKIcSRvalue is believed to represent a lower limiting value offracture toughness. This value may be us
13、ed to estimate therelation between failure stress and defect size when theconditions of high constraint described above would be ex-pected. Background information concerning the basis for1This test method is under the jurisdiction of ASTM Committee B09 on MetalPowders and Metal Powder Products and i
14、s the direct responsibility of Subcom-mittee B09.06 on Cemented Carbides.Current edition approved April 1, 2017. Published April 2017. Originallyapproved in 1987. Last previous edition approved in 2011 as B771 111. DOI:10.1520/B0771-11E01R17.2For referenced ASTM standards, visit the ASTM website, ww
15、w.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.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United StatesThis i
16、nternational standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT)
17、 Committee.1development of this test method in terms of linear elasticfracture mechanics may be found in Refs (1-7).35.2 This test method can serve the following purposes:5.2.1 To establish, in quantitative terms significant to ser-vice performance, the effects of fabrication variables on thefractur
18、e toughness of new or existing materials, and5.2.2 To establish the suitability of a material for a specificapplication for which the stress conditions are prescribed andfor which maximum flaw sizes can be established withconfidence.6. Specimen Configuration, Dimensions, and Preparation6.1 Both the
19、round short rod specimen and the rectangularshaped short bar specimen are equally acceptable and havebeen found to have the same calibration (5). The short roddimensions are given in Fig. 1; the short bar in Fig. 2.6.2 Grip SlotDepending on the apparatus used to test thespecimen, a grip slot may be
20、required in the specimen frontface, as shown in Fig. 3. The surfaces in the grip slot shall havea smooth ground finish so that the contact with each grip willbe along an essentially continuous line along the entire gripslot, rather than at a few isolated points or along a shortsegment within the gri
21、p slot.6.3 Crack-Guiding SlotsThese may be ground using adiamond abrasive wheel of approximately 124 6 3 mm (4.9 60.1 in.) diameter, with a thickness of 0.36 6 0.01 mm (0.01406 0.0005 in.). The resulting slots in the specimen are slightly3The boldface numbers in parentheses refer to the list of refe
22、rences at the end ofthis standard.Standard DimensionsShort Rod(mm) (in.)B = 12.700 0.025 0.500 0.001W = 19.050 0.075 0.750 0.003 = 0.381 0.025 0.015 0.001For Curved Slot Optionao= 6.350 0.075 0.250 0.003 = 58.0 0.5R = 62.23 1.27 02.45 0.05For Straight Slot Optionao= 6.744 0.075 0.266 0.003 = 55.2 0.
23、5R=FIG. 1 Short Rod SpecimenStandard DimensionsShort Bar(mm) (in.)B = 12.700 0.025 0.500 0.001H = 11.050 0.025 0.435 0.001W = 19.050 0.075 0.750 0.003 = 0.381 0.025 0.015 0.001For Curved Slot Optionao= 6.350 0.075 0.250 0.003 = 58.0 0.5R = 62.23 1.27 2.45 0.05For Straight Slot Optionao= 6.744 0.075
24、0.266 0.003 = 55.2 0.5R=FIG. 2 Short Bar SpecimenNOTE 1The dashed lines show the front face profile of Figs. 1 and 2without grip slot.FIG. 3 Short Rod and Short Bar Grip Slot in Specimen Front FaceB771 11 (2017)2thicker than the diamond wheel (0.38 6 0.02 mm, or 0.015 60.001 in.). A diamond concentr
25、ation number of 50, and a gritsize of 150 are suggested. Dimensions are given in Fig. 1 andFig. 2 for two slotting options: (1) Specimens with curved slotbottoms made by plunge feeding the specimen onto a diamondcutting wheel of a given radius, and (2) Specimens withstraight slot bottoms made by mov
26、ing the specimen by acutting wheel. The values of aoand for the two slotconfigurations are chosen to cause the specimen calibration toremain constant.7. Apparatus7.1 The procedure involves testing of chevron-slotted speci-mens and recording the load versus specimen mouth openingdisplacement during t
27、he test.7.2 Grips and Fixtures for Tensile Test Machine LoadingGrip slots are required in the specimen face for this testmethod, as shown in Fig. 3. Fig. 4 shows the grip design. Gripsshall have a hardness of 45 HRC or greater, and shall becapable of providing loads to at least 1560 N (350 lbf). The
28、grips are attached to the arms of tensile test machine by the pinand clevis arrangement shown in Fig. 5. The grip lips areinserted into the grip slot in the specimen, and the specimen isloaded as the test machine arms apply a tensile load to thegrips.Atransducer for measuring the specimen mouth open
29、ingdisplacement during the test, and means for automaticallyrecording the load-displacement test record, such as an X-Yrecorder, are also required when using the tensile test machineapparatus.Asuggested design for the specimen mouth openingdisplacement gage appears in Fig. 6. The gage shall have adi
30、splacement resolution of 0.25 m (10 106in.) or better.However, it is not necessary to calibrate the displacement axisof the test record since only displacement ratios are used in thedata analysis.7.3 Distributed Load Test Machine4An alternative specialpurpose machine that has been found suitable for
31、 the testrequires no grip slot in the front face of the specimen. A thinstainless steel inflatable bladder is inserted into the chevron slotin the mouth of the specimen. Subsequent inflation of thebladder causes it to press against the inner surfaces of the slot,thus producing the desired loading. T
32、he machine provides loadand displacement outputs, which must be recorded externallyon a device such as an X-Y recorder.7.4 Testing Machine CharacteristicsIt has been observedthat some grades of carbides show a “pop-in” type of behaviorin which the load required to initiate the crack at the point oft
33、he chevron slot is larger than the load required to advance thecrack just after initiation, such that the crack suddenly andaudibly jumps ahead at the time of its initiation. Occasionally,the load at crack initiation can exceed the load maximumwhich occurs as the crack passes through the critical lo
34、cation inthe specimen. When this occurs, a very stiff machine with4The sole instrument of this type known to the committee is the FraQ WC,available from Dijon Instrument Inc, 1948 MichiganAve, Salt Lake City, UT 84108.If you are aware of alternative suppliers, please provide this information to ASTM
35、International Headquarters. Your comments will receive careful consideration at ameeting of the responsible technical committee1, which you may attend.FIG. 4 Grip DesignFIG. 5 Tensile Test Machine Test ConfigurationB771 11 (2017)3controlled displacement loading is necessary in order to allowthe crac
36、k to arrest well before passing beyond the criticallocation. The large pop-in load is then ignored, and thesubsequent load maximum as the crack passes through thecritical location is used to determine KIcSR. Stiff machineloading is also required in order to maintain crack growthstability to well bey
37、ond the peak load in the test, where thesecond unloading-reloading cycle is initiated.8. Procedure8.1 Number of TestsA minimum of 3 replicate tests shallbe made.8.2 Specimen Measurement:8.2.1 Measure and record all specimen dimensions. If thedimensions are within the tolerances shown in Fig. 1 and F
38、ig.2, no correction to the data need be made for out-of-tolerancedimensions. If one or more of the parameters ao, W, or areout of tolerance by up to 3 times the tolerances shown in Fig.1 and Fig. 2, valid tests may still be made by the application ofthe appropriate factors to account for the deviati
39、on fromstandard dimensions (see 9.3). If the slot centering is outsidethe indicated tolerance, the crack is less likely to follow thechevron slots. However, the test may still be consideredsuccessful if the crack follows the slots sufficiently well, asdiscussed in 9.2.8.2.2 The slot thickness measur
40、ement is critical on speci-mens to be tested on a Fractometer. It should be measured towithin 0.013 mm (0.0005 in.) at the outside corners of the slotusing a feeler gage. If a feeler gage blade enters the slot to adepth of 1 mm or more, the slot is said to be at least as thickas the blade. Because t
41、he saw cuts forming the chevron slotoverlap somewhat in the mouth of the specimen, and becausethe cuts may not meet perfectly, the slot width near the centerof the mouth may be larger than the width at the outsidecorners. If the slot width near the center exceeds the slot widthat the corners by more
42、 than 0.10 mm (0.004 in.), a test of thatspecimen by a Fractometer is invalid.8.3 Specimen Testing Procedure:8.3.1 Load Transducer Calibration:8.3.1.1 Calibrate the output of the load cell in the testmachine to assure that the load cell output, as recorded on theload versus displacement recorder, is
43、 accurately translatableinto the actual force applied to the specimen. In those cases inwhich a distributed load test machine is used (see 7.3), thecalibration shall be performed according to the instructions inAnnex A1.8.3.1.2 Install the specimen on the test machine. If using thetensile test machi
44、ne (see 7.2), operate the test machine in the“displacement control” mode. Bring the grips sufficiently closetogether such that they simultaneously fit into the grip slot inthe specimen face. Then increase the spacing between the gripsvery carefully until an opening load of 10 to 30 N (2 to 7 lb)is a
45、pplied to the specimen. Check the alignment of thespecimen with respect to the grips, and the alignment of thegrips with respect to each other. The grips shall be centered inthe specimen grip slot to within 0.25 mm (0.010 in.). Thevertical offset between the grips shall not exceed 0.13 mm(0.005 in.)
46、. Using a magnifying glass, observe the grips in thegrip slot from each side of the specimen to assure that thespecimen is properly installed. The grips should extend as faras possible into the grip slot, resulting in contact lines (loadFIG. 6 Suggested Design for a Specimen Mouth Opening GageB771 1
47、1 (2017)4lines) at 0.63 mm (0.025 in.) from the specimen front face.Correct any deviations from the desired specimen alignment.8.3.1.3 Install the specimen mouth opening displacementgage on the specimen. The gage must sense the mouth openingno farther than 1 mm (0.040 in.) from the front face of the
48、specimen. If the gage design of Fig. 6 is used, the contact forcebetween the gage arms and the specimen can be adjusted witha rubber elastic band so the gage will support itself, asindicated in Fig. 5. However, the contact force must not bemore than 2 N (0.5 lb), as it increases the measured load to
49、fracture the specimen.8.3.1.4 Adjust the displacement (x-axis) sensitivity of theload-displacement recorder to produce a convenient-size datatrace. A70 angle between the x-axis and the initial elasticloading trace of the test is suggested.Aquantitative calibrationof the displacement axis is not necessary.8.3.1.5 With the load-displacement recorder operating, testthe specimen by causing the specimen mouth to open at a rateof 0.0025 to 0.0125 mm/s (0.0001 to
