1、Designation: A712 07 (Reapproved 2013)A712 14Standard Test Method forElectrical Resistivity of Soft Magnetic Alloys1This standard is issued under the fixed designation A712; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year
2、of last 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 measurement of electrical resistivity of strip or bar specimens of soft magnetic alloys
3、.1.2 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibilityof the user of this standard to establish
4、appropriate safety and health practices and determine the applicability of regulatorylimitations prior to use.2. Referenced Documents2.1 ASTM Standards:2A34/A34M Practice for Sampling and Procurement Testing of Magnetic Materials3. Summary of Test Method3.1 The electrical resistance of a 0.25-m long
5、 (minimum) test specimen is measured with a Kelvin-type resistance bridge or adigital multimeterohmmeter or the potentiometer-ammeter method. The resistivity is then calculated from the resistancemeasurement and the dimensions of the specimen and is known as the electrical resistivity of the materia
6、l. This value is equal tothe resistance between opposite faces of a cube of unit dimensions.4. Significance and Use4.1 This test method is suitable for the measurement of the electrical resistivity of specimens of soft magnetic materials.4.2 The reproducibility and repeatability of this test method
7、are such that it is suitable for design, specification acceptance,service evaluation, quality assurance, and research and development.5. Apparatus5.1 Kelvin-type resistance bridge or a digital multimeter ohmmeter (Note 1) or a dc potentiometer and dc ammeter providingresistance measurements to an ac
8、curacy within 0.5 % of the accepted true value.NOTE 1A digital multimeter with a four-wire resistance measuring capability can be substituted for a digital ohmmeter.6. Sampling6.1 Samples shall be representative of the material in the physical condition as shipped or agreed upon by the producer and
9、theuser.7. Test Specimen7.1 The test specimen shall be a straight strip or bar or wire of substantially uniform cross-sectional area.7.2 It shall have a minimum length of 0.25 m. Strip specimens preferably should have a uniform width of 0.03 m minimum,unless not available.7.2.1 If width of the strip
10、 material to be sampled prevents obtaining a sample of 0.03-m minimum width, the specimen widthto be used shall be the maximum obtainable and shall be agreed upon between the producer and the user.1 This test method is under the jurisdiction of ASTM Committee A06 on Magnetic Properties and is the di
11、rect responsibility of Subcommittee A06.01 on Test Methods.Current edition approved May 1, 2013May 1, 2014. Published July 2013May 2014. Originally approved in 1975. Last previous edition approved in 20072013 as A71207.07 (2013). DOI: 10.1520/A0712-07R13.10.1520/A0712-14.2 For referencedASTM standar
12、ds, visit theASTM website, www.astm.org, or contactASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standardsvolume information, refer to the standards Document Summary page on the ASTM website.This document is not an ASTM standard and is intended only to provide the user of an ASTM
13、 standard an indication of what changes have been made to the previous version. Becauseit may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current versionof the standard as published b
14、y ASTM is to be considered the official document.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States17.2.1 Bars and wires having circular, rectangular, or other sections shall be used in the sectional dimensions as produced, unlessthey ar
15、e so large as to require cutting a representative sample of suitable dimensions.7.3 It shall be free of obvious surface defects.7.4 The surface shall be cleaned by wiping with a cloth. Oil and grease, if present on the surface, shall be removed with asuitable solvent. Normal surface oxide or core pl
16、ating need not be removed except in areas in which it is necessary to makesatisfactory electrical contact.8. Procedure8.1 Measure the electrical resistance of the test specimen using a Kelvin-type resistance bridge or a digital multimeterohmmeteror potentiometer-ammeter system having separate curren
17、t and potential leads.8.2 For strip specimens, measure the length of the test specimen to within 60.1 % and weigh the specimen using a balance orscale capable of determining the mass within 60.1 %. Determine the average cross-sectional area using Eq 1.8.3 For bar or wire specimens, determine the cro
18、ss-sectional area by direct measurement using calipers or micrometers capableof measuring within 60.1 %.8.4 The distance between each potential lead contact and the corresponding current lead contact shall be at least twice the widthof the test specimen with the two potential contacts lying between
19、the current contacts. The distance between the potential contactsshall be not less than 0.12 m.m and shall be known to within 60.1 %.8.5 The dimension of each potential contact in the direction of the length of the specimen shall be not more than 0.5 % of thedistance between potential contacts.8.6 T
20、he contacts to the specimen shall be located centrally with respect to the specimens width dimension, and the currentcontacts shall cover more than 80 % of the width. A reliable contact shall be made with the specimen by both the current andpotential leads.8.7 Specimen temperature during test should
21、 be about 25C.shall be 25 6 5C.8.8 To eliminate errors as a result of contact potential, take two readings, one direct and one with the current reversed, in closesuccession.8.9 The electrical current in the test specimen must be limited to avoid overheating but must be adequate to provide sufficient
22、sensitivity to show an out-of-balance condition when the resistance reading is changed 0.5 % of the value recorded. If the currentis too low, sensitivity is low also, and a balance can be shown for a broad range of resistance.9. Calculation9.1 Strip Specimens:9.1.1 Determine the average cross-sectio
23、nal area of the test specimen from the weight, length, and density as follows:A 5 m/l (1)where:A = cross-sectional area of test specimen, m2;m = mass of test specimen, kg;l = length of test specimen, m; and = density of test specimen, kg/m3, determined in accordance with Practice A34/A34M.9.1.2 Eq 1
24、 assumes a negligible mass of any coating material.9.2 Bar and Wire SpecimensThe cross-sectional area of the test specimen shall be based on direct measurements with amicrometer or caliper.9.3 Calculate resistivity from the measured value of electrical resistance and the cross-sectional area as foll
25、ows: 5 RA/l2 (2)where: = electrical resistivity of the material, m;R = resistance of electrical path, ;A = cross-sectional area of electrical path, m2; andl2 = length of electrical path between potential contacts on the test specimen, m.9.4 The resistivity units in ohm-metres shown in Eq 2 can be co
26、nverted to microhm-centimetres by multiplying the ohm-metrefigure by 108 microhm-centimetres per ohm-metre. For example, if the resistivity is 0.25 106 m; 0.25 106 108 cm/ m is equal to 25 cm.NOTE 2The resistivities of commercial soft magnetic alloys are shown in Annex A1.A712 14210. Precision and B
27、ias10.1 Although no rigorous interlaboratory comparisons of this test method have been performed, it is estimated that thereproducibility standard deviation is no greater than 2 % of the mean.10.2 The bias of this test method is believed to be zero.11. Keywords11.1 electrical resistivity; magnetic a
28、lloy; potentiometer-ammeter; resistance bridgeANNEX(Mandatory Information)A1. RESISTIVITIESA1.1 This test method assumes the establishment of a uniform current density along the test specimen throughout the regionbetween the potential contacts. The current contacts should be in the form of transvers
29、e clamps covering at least 80 % andpreferably the entire width of the specimen. The potential contacts can be either knife edge or point contacts.A1.1.1 If a potentiometer is used, a suitable dc source and ammeter are required to establish and measure the total current in thespecimen, which should b
30、e limited to avoid excessive heating. The required R is then the ratio of the measured potential drop tothe measured current. When the potentiometer is balanced, no current flows in the potential leads so that any contact resistanceat the potential points is of no consequence.A1.1.2 The Kelvin bridg
31、e is calibrated to read directly the resistance between the potential points without knowledge of the currentin the specimen. Contact resistance at the potential points and the resistance of the four leads to the specimen are not a part of therequired R and are usually negligible portions of the cor
32、responding components of the bridge system.A1.1.3 Digital multimetersohmmeters used for measuring resistance in the range required for this test method will be equippedfor four-wire ohm measurements. In the four-wire method, a controlled source current is applied to the resistance to be measuredvia
33、the current leads, and the voltage drop is sensed across the potential (or sense) leads. Since the input resistance of the digitalmultimeterohmmeter is very large (typically greater than 10 M), the contact resistance between the sense leads and the specimenand the resistance of the leads do not affe
34、ct the measurement.A1.2 Typical resistivities of iron-silicon-aluminum alloy steel sheets are shown in Fig. A1.1 and other soft magnetic alloys inTable A1.1. Commercial electrical steels are low-carbon, silicon-iron, or silicon-aluminum-iron alloys containing up to 3.5 %silicon and only a small amou
35、nt of aluminum.A712 143ASTM 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 infringem
36、ent of such rights, are entirely their own responsibility.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
37、for additional standardsand should be addressed 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 kno
38、wn to the ASTM Committee on Standards, at the address 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 AST
39、M at the aboveaddress or at 610-832-9585 (phone), 610-832-9555 (fax), or serviceastm.org (e-mail); or through the ASTM website(www.astm.org). Permission rights to photocopy the standard may also be secured from the ASTM website (www.astm.org/COPYRIGHT/).NOTE 1The linear equation for the graph in thi
40、s figure is as follows: = 0.1325 10 6 + 0.113 (percent silicon + percent aluminum) 10 6 mwhere = electrical resistivity in ohm-metres at approximately 25C. The equation is based on the average line drawn through many test points obtainedon commercial grades of electrical steels of various compositio
41、ns. 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 having alloying elements over about 0.15 %. Asthe percentage of alloying elements decreases to low values, t
42、he intercept constant decreases, approaching the value of about 0.107.FIG. A1.1 Electrical Resistivities Versus Composition of Commercial Grades of Electrical SteelsTABLE A1.1 Electrical Resistivity of Soft Magnetic Alloys of Nickel, Chromium, and IronGeneral Composition Typical ElectricalResistivit
43、y, m General Name36 % Nickel, balance iron 0.82 106 Invar45 % Nickel, balance 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 430A712 144
