1、Designation: A938 18Standard Test Method forTorsion Testing of Wire1This standard is issued under the fixed designation A938; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A number in parentheses indica
2、tes the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope*1.1 This test method describes the torsion (or twist) testingof metallic wire.1.2 The values stated in U.S. customary units are to beregarded as the standard. The SI
3、equivalents of U.S. customaryunits may be approximate.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 standard to establish appro-priate safety, health, and environmental practices and deter-mine th
4、e applicability 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 for theDevelopment of International Standards, Guides and Recom-mendations issu
5、ed by the World Trade Organization TechnicalBarriers to Trade (TBT) Committee.2. Referenced Documents2.1 ASTM Standards:2E6 Terminology Relating to Methods of Mechanical Testing3. Terminology3.1 DefinitionsThe definitions related to torsion testingappearing in Terminology E6 shall be considered as a
6、pplyingto the terms used in this test method.4. Significance and Use4.1 The complex stress and strain conditions that occur inthe sample during the torsion test are sensitive to minorvariations in materials, making the torsion test a useful tool inassessing wire ductility under torsional loading.5.
7、Apparatus5.1 Clamping Heads:5.1.1 The torsion test apparatus must have clamping headsthat will remain coaxial (within 10) during the test.5.1.2 One clamping head shall be easily displaceable in thedirection of the wire axis. This longitudinally displaceableclamping head shall be equipped with a devi
8、ce capable ofapplying the necessary tensile load.5.1.3 The clamping heads shall clamp the wire firmly, butshould not damage it to the extent that fracture occurs at theclamping point during twisting. The distance between theclamps is the test length. The wire shall be twisted only alongthe test leng
9、th, and not at the point of clamping. Theserequirements can be satisfied by bending a short section at eachend of the specimen to an angle of about 90 to the wire axis,as described in 6.3.5.2 Revolution CounterA mechanism to count the numberof twists shall be provided.5.3 Protective ShieldA protecti
10、ve shield shall be providedto protect the operator from flying fragments in cases when thewire breaks into more than two pieces.6. Specimen Preparation6.1 StraighteningThe test piece, consisting of a length ofwire, should be straight before being tested. If straightening isnecessary, it shall, unles
11、s otherwise specified, be done by hand.Other straightening techniques are permitted provided surfacedamage is avoided. Since the shear stress is maximum at thesurface of the wire during testing, even slight surface damagesuch as pits or scratches can cause early fracture, and theresults may not be i
12、ndicative of the full capability of the wire.6.1.1 During straightening, it is important that the propertiesand cross section remain unchanged as far as possible. Inparticular, the specimen shall not be subjected to any twisting.6.2 Test Length:6.2.1 Recommended test length is 8 in. (203 mm) (distan
13、cebetween the clamping heads). Sufficient material must also beprovided to allow for gripping.6.2.2 Other test lengths may be used as agreed uponbetween the producer and purchaser or as specified in theappropriate product specification.1This test method is under the jurisdiction of ASTM Committee A0
14、1 on Steel,Stainless Steel and Related Alloysand is the direct responsibility of A01.03 on SteelRod and Wire.Current edition approved Sept. 1, 2018. Published September 2018. Originallyapproved in 1975. Last previous edition approved in 2013 as A938 07 (2013).DOI: 10.1520/A0938-18.2For referenced AS
15、TM 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.*A Summary of Changes section appears at the end of this standardCopyright ASTM
16、 International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United StatesThis international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for theDevelopment of International Stand
17、ards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.16.2.3 When a test length other than 8 in. (203 mm) is used,the minimum torsions shall be revised in direct proportion tothe change in the jaw spacing, or as determined by thefollowing
18、 formula:Tx5TL!Lx!LL!(1)where:Tx= minimum torsions for new length,TL= minimum torsions for 8 in. (203 mm) length,Lx= new length, andLL= 8 in. (203 mm).6.3 End PreparationTo prevent the gripped ends fromslipping tangentially in the clamps, a minimum of12 in.(12.7 mm) of each end of the wire is often
19、bent approximately90 to the axis of the test sample. The end sections need not beexactly parallel to each other. See Fig. 1.7. Procedure7.1 Tensile ForceClamp the specimen in the clamps of thetest apparatus with its longitudinal axis coaxial with theclamping heads and in such a manner that the speci
20、menremains as straight as possible during testing (see 5.1.1).Unless specified otherwise, this can be accomplished byapplying a small tensile force to the specimen. This forceshould be just sufficient to prevent the specimen from deflect-ing away from the axis of rotation during twisting. Recom-mend
21、ed tensile forces are shown in Table 1.7.2 Speed of TwistingThe speed of testing should be suchthat the wire is not heated appreciably during the test sinceexcessive speed results in a lowering of torsion values.Recommended maximum speeds are shown in Table 2.7.3 Number of Turns:7.3.1 After placing
22、the test specimen in the machine, rotateone clamp at a reasonably constant speed until the testspecimen fractures, defined as a complete separation of thebroken ends.7.3.2 If the number of turns is satisfactory, the test specimenis considered as having passed the test, regardless of theposition of f
23、racture, defined as complete separation of thebroken ends. If the number of turns does not satisfy therequirements of the specification, and the initial fracture,defined as complete separation of the broken ends, location iswithin two times the wire diameter from the clamps, the test isconsidered in
24、valid and shall be repeated.NOTE 1Specimens often break into more than two pieces, subsequentfractures resulting from the rapid untwisting of the wire following theinitial fracture. In many cases, the initial fracture will have a smoothsurface perpendicular to the wire axis. The above validity test
25、applies onlyto the location of this initial break.8. Report8.1 The following information shall be included in the testreport:8.1.1 Specimen identification,8.1.2 Wire diameter,8.1.3 Test length, and8.1.4 Total turns to fracture.NOTE 2If a minimum number of turns is specified and this number isexceede
26、d, the test need not be continued to fracture. It is then sufficient torecord that no fracture occurred.9. Precision and Bias9.1 PrecisionSufficient multilaboratory tests have notbeen compared to establish the reproducibility of this testmethod. Test variables that affect precision include: (1) init
27、iallength and straightness of the wire, (2) the amount of tensilestress, (3) the speed of testing, and (4) location of the fracture.9.2 BiasDetermination of the bias of a test method re-quires reference standard values for one or more materialsbased on many measurements. Such standard reference valu
28、esare not available for this test method. Therefore, the bias of themethod is not known.10. Keywords10.1 coaxial clamping; fracture; revolution counter; testlength; torsion; torsion testing; twisting rates; wire; wire axis;wire ductilityFIG. 1 Sketch Showing 90 Bends at Ends of Wire Twist TestSpecim
29、enA938 182SUMMARY OF CHANGESCommittee A01 has identified the location of selected changes to this standard since the last issue(A938 07 (2013) that may impact the use of this standard. (Approved Sept. 1, 2018.)(1) Removed Note 1, placed its contents in 6.1.1 due tocontextual requirement, and renumbe
30、red subsequent Notesaccordingly.ASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentionedin this standard. Users of this standard are expressly advised that determination of the validity of any such patent rights, and the riskof
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35、) 646-2600; http:/ 1 Applied Load for Torsion TestingApplied LoadADiameter of Wire Pounds Force (lbf) Newtons (N)Inches mm Minimum Maximum Minimum MaximumUp to 0.010 Up to 0.25 0.50 2.0 2.2 8.9Over 0.010 to 0.015 Over 0.25 to 0.41 1.0 4.0 4.4 18Over 0.015 to 0.020 Over 0.41 to 0.51 1.5 6.0 6.7 27Ove
36、r 0.020 to 0.030 Over 0.51 to 0.76 2.0 8.0 8.9 36Over 0.030 to 0.040 Over 0.76 to 1.02 3.0 12 13 53Over 0.040 to 0.050 Over 1.02 to 1.28 4.0 16 18 71Over 0.050 to 0.060 Over 1.28 to 1.53 5.0 20 22 89Over 0.060 to 0.070 Over 1.53 to 1.79 6.0 24 27 107Over 0.070 to 0.080 Over 1.79 to 2.04 7.0 28 31 12
37、5Over 0.080 to 0.090 Over 2.04 to 2.30 8.0 32 36 142Over 0.090 to 0.100 Over 2.30 to 2.55 9.0 36 40 160Over 0.100 to 0.110 Over 2.55 to 2.80 10 40 44 178Over 0.110 to 0.120 Over 2.80 to 3.06 11 44 49 196Over 0.120 to 0.130 Over 3.06 to 3.31 12 48 53 214Over 0.130 to 0.140 Over 3.31 to 3.57 13 52 58
38、231Over 0.140 to 0.150 Over 3.57 to 3.82 14 56 62 249Over 0.150 to 0.160 Over 3.82 to 4.07 15 60 67 267Over 0.160 to 0.170 Over 4.07 to 4.33 16 64 71 285Over 0.170 to 0.180 Over 4.33 to 4.58 17 68 76 302Over 0.180 to 0.190 Over 4.58 to 4.84 18 72 80 320Over 0.190 to 0.200 Over 4.84 to 5.09 19 76 85
39、338Over 0.200 to 0.210 Over 5.09 to 5.34 20 80 89 356Over 0.210 to 0.220 Over 5.34 to 5.60 21 84 93 374Over 0.220 to 0.230 Over 5.60 to 5.85 22 88 98 391Over 0.230 to 0.240 Over 5.85 to 6.10 23 92 102 409Over 0.240 to 0.250 Over 6.10 to 6.35 24 96 107 427AFor sizes larger than 0.250 in. (6.35mm), the tensile force of 1 % of the nominal maximum load of the wire is recommended.TABLE 2 Recommended Maximum Twisting SpeedsWire Diameter, in. (mm) Twisting Speed (Rpm)0.040 (1.02) 900.040 to 0.142 (1.02 to 3.61) 600.142 and larger (3.61 and larger) 30A938 183
