1、Designation: A 712 07Standard Test Method forElectrical Resistivity of Soft Magnetic Alloys1This standard is issued under the fixed designation A 712; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A num
2、ber 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 measurement of electricalresistivity of strip or bar specimens of soft magnetic alloys.1.2 The values stated
3、in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.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 and he
4、alth practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2A 34/A 34M Practice for Sampling and Procurement Test-ing of Magnetic Materials3. Summary of Test Method3.1 The electrical resistance of a 0.25-m long (minimum)test speci
5、men is measured with a Kelvin-type resistance bridgeor a digital multimeter or the potentiometer-ammeter method.The resistivity is then calculated from the resistance measure-ment and the dimensions of the specimen and is known as theelectrical resistivity of the material. This value is equal to the
6、resistance between opposite faces of a cube of unit dimensions.4. Significance and Use4.1 This test method is suitable for the measurement of theelectrical resistivity of specimens of soft magnetic materials.4.2 The reproducibility and repeatability of this test methodare such that it is suitable fo
7、r design, specification acceptance,service evaluation, quality assurance, and research and devel-opment.5. Apparatus5.1 Kelvin-type resistance bridge or a digital multimeter ora dc potentiometer and dc ammeter providing resistancemeasurements to an accuracy within 0.5 % of the accepted truevalue.6.
8、Sampling6.1 Samples shall be representative of the material in thephysical condition as shipped or agreed upon by the producerand the user.7. Test Specimen7.1 The test specimen shall be a straight strip or bar or wireof substantially uniform cross-sectional area.7.2 It shall have a minimum length of
9、 0.25 m. Stripspecimens preferably should have a uniform width of 0.03 mminimum, unless not available.7.2.1 If width of the strip material to be sampled preventsobtaining a sample of 0.03-m minimum width, the specimenwidth to be used shall be the maximum obtainable and shall beagreed upon between th
10、e producer and the user.7.2.2 Bars and wires having circular, rectangular, or othersections shall be used in the sectional dimensions as produced,unless they are so large as to require cutting a representativesample of suitable dimensions.7.3 It shall be free of obvious surface defects.7.4 The surfa
11、ce shall be cleaned by wiping with a cloth. Oiland grease, if present on the surface, shall be removed with asuitable solvent. Normal surface oxide or core plating need notbe removed except in areas in which it is necessary to makesatisfactory electrical contact.8. Procedure8.1 Measure the electrica
12、l resistance of the test specimenusing a Kelvin-type resistance bridge or a digital multimeter orpotentiometer-ammeter system having separate current andpotential leads.8.2 The distance between each potential lead contact and thecorresponding current lead contact shall be at least twice thewidth of
13、the test specimen with the two potential contacts lying1This test method is under the jurisdiction of ASTM Committee A06 onMagnetic Properties and is the direct responsibility of SubcommitteeA06.01 on TestMethods.Current edition approved Dec. 1, 2007. Published January 2008. Originallyapproved in 19
14、75. Last previous edition approved in 2002 as A 71297(2002).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.1
15、Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.between the current contacts. The distance between the poten-tial contacts shall be not less than 0.12 m.8.3 The dimension of each potential contact in the directionof the length of the
16、specimen shall be not more than 0.5 % ofthe distance between potential contacts.8.4 The contacts to the specimen shall be located centrallywith respect to the specimens width dimension, and thecurrent contacts shall cover more than 80 % of the width. Areliable contact shall be made with the specimen
17、 by both thecurrent and potential leads.8.5 Specimen temperature during test should be about 25C.8.6 To eliminate errors as a result of contact potential, taketwo readings, one direct and one with the current reversed, inclose succession.8.7 The electrical current in the test specimen must belimited
18、 to avoid overheating but must be adequate to providesufficient sensitivity to show an out-of-balance condition whenthe resistance reading is changed 0.5 % of the value recorded.If the current is too low, sensitivity is low also, and a balancecan be shown for a broad range of resistance.9. Calculati
19、on9.1 Strip Specimens:9.1.1 Determine the average cross-sectional area of the testspecimen from the weight, length, and density as follows:A 5 m/ld (1)where:A = cross-sectional area of test specimen, m2;m = mass of test specimen, kg;l = length of test specimen, m; andd = density of test specimen, kg
20、/m3, determined in accor-dance with Practice A 34/A 34M.9.1.2 Eq 1 assumes a negligible mass of any coatingmaterial.9.2 Bar and Wire SpecimensThe cross-sectional area ofthe test specimen shall be based on direct measurements witha micrometer or caliper.9.3 Calculate resistivity from the measured val
21、ue of electri-cal resistance and the cross-sectional area as follows:r5RA/l2(2)where:r = electrical resistivity of the material, V m;R = resistance of electrical path, V;A = cross-sectional area of electrical path, m2; andl2= length of electrical path between potential contacts onthe test specimen,
22、m.9.4 The resistivity units in ohm-metres shown in Eq 2 canbe converted to microhm-centimetres by multiplying the ohm-metre figure by 108microhm-centimetres per ohm-metre. Forexample, if the resistivity is 0.25 3 106V m;0.25 3 1063 108V cm/V m is equal to 25 V cm.NOTE 1The resistivities of commercia
23、l soft magnetic alloys areshown in Annex A1.10. Precision and Bias10.1 Although no rigorous interlaboratory comparisons ofthis test method have been performed, it is estimated that thereproducibility standard deviation is no greater than 2 % of themean.10.2 The bias of this test method is believed t
24、o be zero.11. Keywords11.1 electrical resistivity; magnetic alloy; potentiometer-ammeter; resistance bridgeANNEX(Mandatory Information)A1. RESISTIVITIESA1.1 This test method assumes the establishment of auniform current density along the test specimen throughout theregion between the potential conta
25、cts. The current contactsshould be in the form of transverse clamps covering at least80 % and preferably the entire width of the specimen. Thepotential contacts can be either knife edge or point contacts.A1.1.1 If a potentiometer is used, a suitable dc source andammeter are required to establish and
26、 measure the total currentin the specimen, which should be limited to avoid excessiveheating. The required R is then the ratio of the measuredpotential drop to the measured current. When the potentiometeris balanced, no current flows in the potential leads so that anycontact resistance at the potent
27、ial points is of no consequence.A1.1.2 The Kelvin bridge is calibrated to read directly theresistance between the potential points without knowledge ofthe current in the specimen. Contact resistance at the potentialpoints and the resistance of the four leads to the specimen arenot a part of the requ
28、ired R and are usually negligible portionsof the corresponding components of the bridge system.A1.1.3 Digital multimeters used for measuring resistance inthe range required for this test method will be equipped forfour-wire ohm measurements. In the four-wire method, acontrolled source current is app
29、lied to the resistance to bemeasured via the current leads, and the voltage drop is sensedacross the potential (or sense) leads. Since the input resistanceof the digital multimeter is very large (typically greater than 10A712072MV), the contact resistance between the sense leads and thespecimen and
30、the resistance of the leads do not affect themeasurement.A1.2 Typical resistivities of iron-silicon-aluminum alloysteel sheets are shown in Fig. A1.1 and other soft magneticalloys in Table A1.1. Commercial electrical steels are low-carbon, silicon-iron, or silicon-aluminum-iron alloys contain-ing up
31、 to 3.5 % silicon and only a small amount of aluminum.NOTEThe linear equation for the graph in this figure is as follows:r = 0.1325 3 106+ 0.113 (percent silicon + percent aluminum) 3 106V mwhere r = electrical resistivity in ohm-metres at approximately 25C. The equation is based on the average line
32、 drawn through many test points obtainedon commercial grades of electrical steels of various compositions. Individual tests may show departures from the average line, which is shown in equationand graphical form for general use and guidance. The intercept constant 0.1325 applies only to steels havin
33、g alloying elements over about 0.15 %. Asthe percentage of alloying elements decreases to low values, the intercept constant decreases, approaching the value of about 0.107.FIG. A1.1 Electrical Resistivities Versus Composition of Commercial Grades of Electrical SteelsA712073ASTM International takes
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35、nsibility.This standard is subject to revision at any time by the responsible technical committee and must be reviewed every five years andif not revised, either reapproved or withdrawn. Your comments are invited either for revision of this standard or for additional standardsand should be addressed
36、 to ASTM International Headquarters. Your comments will receive careful consideration at a meeting of theresponsible technical committee, which you may attend. If you feel that your comments have not received a fair hearing you shouldmake your views known to the ASTM Committee on Standards, at the a
37、ddress shown below.This standard is copyrighted by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959,United States. Individual reprints (single or multiple copies) of this standard may be obtained by contacting ASTM at the aboveaddress or at 610-832-9585 (phone
38、), 610-832-9555 (fax), or serviceastm.org (e-mail); or through the ASTM website(www.astm.org).TABLE A1.1 Electrical Resistivity of Soft Magnetic Alloys of Nickel, Chromium, and IronGeneral CompositionTypical ElectricalResistivity, VmGeneral Name36 % Nickel, balance iron 0.82 3 106Invar45 % Nickel, b
39、alance iron 0.53 45 Permalloy48 % Nickel, balance iron 0.48 High Perm, 49; 475052 % Nickel, balance iron 0.43 52 Alloy65 % Nickel, balance iron 0.22 65 Permalloy77 % Nickel, 5 % copper, 2.6 % chromium,balance iron0.60 Mumetal78.5 % Nickel, balance iron 0.16 78 Permalloy80 % Nickel, 4 % molybdenum, balance iron 0.58 479 Permalloy; Hy Mu 8080 % Nickel, 5 % molybdenum, balance iron 0.60 579 Permalloy; Hy Mu 800 Supermalloy17 % Chromium, balance iron 0.61 Stainless Type 430A712074
