ASTM A712-14(2022)
(Test Method)Standard Test Method for Electrical Resistivity of Soft Magnetic Alloys
Standard Test Method for Electrical Resistivity of Soft Magnetic Alloys
SIGNIFICANCE AND USE
4.1 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 are such that it is suitable for design, specification acceptance, service evaluation, quality assurance, and research and development.
SCOPE
1.1 This test method covers the measurement of electrical resistivity of strip or bar specimens of soft magnetic alloys.
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 responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.
1.4 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
General Information
Relations
Standards Content (Sample)
This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: A712 − 14 (Reapproved 2022)
Standard Test Method for
Electrical Resistivity of Soft Magnetic Alloys
This standard is issued under the fixed designation A712; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope 4.2 The reproducibility and repeatability of this test method
are such that it is suitable for design, specification acceptance,
1.1 This test method covers the measurement of electrical
service evaluation, quality assurance, and research and devel-
resistivity of strip or bar specimens of soft magnetic alloys.
opment.
1.2 The values stated in SI units are to be regarded as
standard. No other units of measurement are included in this 5. Apparatus
standard.
5.1 Kelvin-type resistance bridge or a digital ohmmeter
1.3 This standard does not purport to address all of the
(Note 1) or a dc potentiometer and dc ammeter providing
safety concerns, if any, associated with its use. It is the
resistance measurements to an accuracy within 0.5 % of the
responsibility of the user of this standard to establish appro-
accepted true value.
priate safety, health, and environmental practices and deter-
NOTE 1—A digital multimeter with a four-wire resistance measuring
mine the applicability of regulatory limitations prior to use.
capability can be substituted for a digital ohmmeter.
1.4 This international standard was developed in accor-
6. Sampling
dance with internationally recognized principles on standard-
ization established in the Decision on Principles for the
6.1 Samples shall be representative of the material in the
Development of International Standards, Guides and Recom-
physical condition as shipped or agreed upon by the producer
mendations issued by the World Trade Organization Technical
and the user.
Barriers to Trade (TBT) Committee.
7. Test Specimen
2. Referenced Documents
7.1 The test specimen shall be a straight strip or bar or wire
2.1 ASTM Standards:
of substantially uniform cross-sectional area.
A34/A34MPractice for Sampling and Procurement Testing
7.2 It shall have a minimum length of 0.25 m.
of Magnetic Materials
7.2.1 Bars and wires having circular, rectangular, or other
3. Summary of Test Method
sections shall be used in the sectional dimensions as produced,
unless they are so large as to require cutting a representative
3.1 The electrical resistance of a 0.25m long (minimum)
sample of suitable dimensions.
testspecimenismeasuredwithaKelvin-typeresistancebridge
or a digital ohmmeter or the potentiometer-ammeter method.
7.3 It shall be free of obvious surface defects.
The resistivity is then calculated from the resistance measure-
7.4 The surface shall be cleaned by wiping with a cloth. Oil
ment and the dimensions of the specimen and is known as the
and grease, if present on the surface, shall be removed with a
electrical resistivity of the material. This value is equal to the
suitablesolvent.Normalsurfaceoxideorcoreplatingneednot
resistancebetweenoppositefacesofacubeofunitdimensions.
be removed except in areas in which it is necessary to make
4. Significance and Use
satisfactory electrical contact.
4.1 This test method is suitable for the measurement of the
8. Procedure
electrical resistivity of specimens of soft magnetic materials.
8.1 Measure the electrical resistance of the test specimen
using a Kelvin-type resistance bridge or a digital ohmmeter or
This test method is under the jurisdiction of ASTM Committee A06 on
potentiometer-ammeter system having separate current and
MagneticPropertiesandisthedirectresponsibilityofSubcommitteeA06.01onTest
Methods.
potential leads.
Current edition approved Oct. 1, 2022. Published October 2022. Originally
8.2 For strip specimens, measure the length of the test
approved in 1975. Last previous edition approved in 2014 as A712–14. DOI:
10.1520/A0712-14R22.
specimen to within 60.1% and weigh the specimen using a
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
balance or scale capable of determining the mass within
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
60.1%. Determine the average cross-sectional area using Eq
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. 1.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
A712 − 14 (2022)
8.3 Forbarorwirespecimens,determinethecross-sectional
m = mass of test specimen, kg;
area by direct measurement using calipers or micrometers
l = length of test specimen, m; and
capable of measuring within 60.1%.
δ = density of test specimen, kg/m , determined in accor-
dance with Practice A34/A34M.
8.4 Thedistancebetweeneachpotentialleadcontactandthe
corresponding current lead contact shall be at least twice the
9.1.2 Eq 1 assumes a negligible mass of any coating
widthofthetestspecimenwiththetwopotentialcontactslying material.
between the current contacts. The distance between the poten-
9.2 Bar and Wire Specimens—The cross-sectional area of
tial contacts shall be not less than 0.12 m and shall be known
the test specimen shall be based on direct measurements with
to within 60.1%.
a micrometer or caliper.
8.5 The dimension of each potential contact in the direction
9.3 Calculate resistivity from the measured value of electri-
of the length of the specimen shall be not more than 0.5 % of
cal resistance and the cross-sectional area as follows:
the distance between potential contacts.
ρ 5 RA/l (2)
8.6 The contacts to the specimen shall be located centrally
where:
with respect to the specimen’s width dimension, and the
current contacts shall cover more than 80 % of the width. A
ρ = electrical resistivity of the material, Ω·m;
reliable contact shall be made with the specimen by both the R = resistance of electrical path, Ω;
current and potential leads. A = cross-sectional area of electrical path, m ; and
l = length of electrical path between potential contacts on
8.7 Specimen temperature during test shall be 25°C 6
the test specimen, m.
5°C.
9.4 The resistiv
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