ASTM A342/A342M-04(2012)
(Test Method)Standard Test Methods for Permeability of Feebly Magnetic Materials
Standard Test Methods for Permeability of Feebly Magnetic Materials
SIGNIFICANCE AND USE
3.1 This test method is suitable for specification acceptance, design purposes, service evaluation, regulatory statutes, manufacturing control, and research and development.
3.2 Because of the restrictions on the specimen shape and size, this test method is most often used to evaluate semifinished product before fabrication of parts.
SCOPE
1.1 These test methods cover three procedures for determination of the permeability [relative permeability]2 of materials having a permeability not exceeding 4.0.
1.2 The test methods covered are as follows:
1.2.1 Test Method 1 is suitable for materials with permeabilities between 1.0 and 4.0.
1.2.2 Test Method 2 is suitable for measuring the permeability of paramagnetic materials having a permeability less than 1.05.
1.2.3 Test Method 3 is a suitable means of measuring the permeability of a material as “less than” or “greater than” that of calibrated standard inserts designated for use in a Low-Mu Permeability Indicator.3
1.3 The values and equations stated in customary (cgs-emu and inch-pound) or SI units are to be regarded separately as standard. Within this standard, SI units are shown in brackets except for the sections concerning calculations where there are separate sections for the respective unit systems. The values stated in each system may not be exact equivalents; therefore, each system shall be used independently of the other. Combining values from the two systems may result in nonconformance with this standard.
1.4 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 and health practices and determine the applicability of regulatory limitations prior to use.
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Designation: A342/A342M − 04(Reapproved 2012)
Standard Test Methods for
Permeability of Feebly Magnetic Materials
This standard is issued under the fixed designationA342/A342M; 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.
This standard has been approved for use by agencies of the Department of Defense.
1. Scope 1.4 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the
1.1 These test methods cover three procedures for determi-
responsibility of the user of this standard to establish appro-
nation of the permeability [relative permeability] of materials
priate safety and health practices and determine the applica-
having a permeability not exceeding 4.0.
bility of regulatory limitations prior to use.
1.2 The test methods covered are as follows:
2. Referenced Documents
1.2.1 Test Method 1 is suitable for materials with perme-
abilities between 1.0 and 4.0.
2.1 ASTM Standards:
1.2.2 Test Method 2issuitableformeasuringthepermeabil- A341/A341MTest Method for Direct Current Magnetic
ity of paramagnetic materials having a permeability less than Properties of Materials Using D-C Permeameters and the
1.05. Ballistic Test Methods
1.2.3 Test Method 3 is a suitable means of measuring the
TEST METHOD NO. 1, FLUXMETRIC METHOD
permeability of a material as “less than” or “greater than” that
of calibrated standard inserts designated for use in a Low-Mu
3. Significance and Use of Test Method 1
Permeability Indicator.
3.1 Thistestmethodissuitableforspecificationacceptance,
1.3 The values and equations stated in customary (cgs-emu
design purposes, service evaluation, regulatory statutes, manu-
and inch-pound) or SI units are to be regarded separately as
facturing control, and research and development.
standard. Within this standard, SI units are shown in brackets
3.2 Because of the restrictions on the specimen shape and
except for the sections concerning calculations where there are
size, this test method is most often used to evaluate semifin-
separate sections for the respective unit systems. The values
ished product before fabrication of parts.
stated in each system may not be exact equivalents; therefore,
each system shall be used independently of the other. Combin-
4. Apparatus
ingvaluesfromthetwosystemsmayresultinnonconformance
4.1 Power Supply—Asource of dc current for the electrical
with this standard.
circuit shown in Fig. 1. Electronic power supplies are prefer-
able although the use of storage batteries is permitted.
1 4.2 Test Fixture—Atest fixture consisting of a magnetizing
These test methods are under the jurisdiction of ASTM Committee A06 on
solenoid with a set of test coils mounted midway between the
Magnetic Properties and are the direct responsibility of Subcommittee A06.01 on
Test Methods.
ends of the solenoid for measuring magnetic induction and an
CurrenteditionapprovedMay1,2012.PublishedJuly2012.Originallyapproved
air flux balancing resistor, fluxmeter, and associated circuitry
in 1949. Last previous edition approved in 2004 as A342/A342M–04. DOI:
conforming to the following requirements:
10.1520/A0342_A0342M-04R12.
Test Methods 1 and 2 actually measure magnetic susceptibility. The perme-
4.2.1 Magnetizing Solenoid, C , having a minimum length
ability (µ) [relative permeability ( µ )] is related to the susceptibility (κ)bythe
r
of30cm[300mm]andaratiooflengthtoequivalentdiameter
equations:
of four or more. The magnetizing winding shall be uniformly
µ=1+4πκ (cgs-emu)
µ =1+κ (SI) wound and be capable of producing a uniform field of at least
r
The term permeability has been retained in these test methods because of its
300Oe[24kA/m]overthelengthofthetestspecimenwithout
widespread commercial and technological usage.
overheating.
The sole source of supply of the apparatus known to the committee at this time
is Low-Mu Permeability Indicator, manufactured by Severn Engineering Co., Inc.,
555 Stage Rd., Suite 1A, Auburn, AL 36830, http://www.severnengineering.com.
(Indicators can be returned for recalibration.) If you are aware of alternative For referenced ASTM standards, visit the ASTM website, www.astm.org, or
suppliers, please provide this information to ASTM International Headquarters. contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Your comments will receive careful consideration at a meeting of the responsible Standards volume information, refer to the standard’s Document Summary page on
technical committee, which you may attend. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
A342/A342M − 04 (2012)
FIG. 1 Circuit Diagram for Method No. 1
4.2.2 Test Coil, B ,usedformeasuringinduction,shallhave 6. Procedure
a cross-sectional area not greater than ten times that of the test
6.1 Measure the thickness and width or diameter of the test
specimen. The test coil should have sufficient turns (>1000) to
specimens and calculate the cross-sectional area in square
provideadequateresolutionandshouldbenolongerthan20%
centimetres [square millimetres].
of the test specimen length.
6.2 Before inserting the test specimen in the solenoid,
4.2.3 Compensating Coil, B' , of the same length, cross-
obtain an exact balance to nullify the effect of air flux in coil
sectionalarea,andnumberofturnsascoil B andconnectedto
B by reversing the highest magnetizing current to be used in
it in series opposition.
the test and adjusting the compensating resistor to obtain the
4.2.4 Air Flux Compensating Resistor, R' —This resistor is
B
minimum output from the flux sensing coils.
usedinconjunctionwithcoilB' ofFig.1tohelpitcompensate
for the air flux enclosed by coil B in order that the intrinsic 6.3 Place the test specimen in position in coil B , adjust the
induction may be measured directly.
magnetic field strength to the desired test value, then reverse
4.2.5 Electronic Fluxmeter, F—used to measure magnetic the magnetizing current and record the fluxmeter reading.
induction. Alternatively, the magnetizing fixture may be con-
Optionally, the B versus H curve can be recorded on a
nected to a dc hysteresigraph. hysteresigraph.
4.2.6 Magnetic Field Strength Sensor (optional)—If the
7. Calculation (Customary Units)
magnetic field strength cannot be accurately determined from
the magnetizing current, then either a Hall effect sensor or
7.1 Convert the fluxmeter reading to intrinsic induction B
i
H-coil connected to the fluxmeter shall be used.
and calculate the permeability as follows:
B
5. Test Specimens
i
µ 511 (1)
H
5.1 The test specimens shall consist of straight bars, rods,
wires,orstripsofuniformcrosssection.Multiplepiecesofthe
where:
same test lot may be used to increase the specimen cross-
µ = permeability of the test specimen;
sectional area when needed. The cross-sectional area shall be
B = intrinsic induction of the test specimen, G; and
i
2 2
not less than 0.2 cm [20 mm ]. The length shall be not less
H = magnetic field strength, Oe.
than 10 cm [100 mm] and the ratio of length to diameter or
8. Calculation (SI Units)
equivalent diameter (that is, the diameter of a circle having an
area equal to the cross-sectional area of the specimen) shall be
8.1 The output from the fluxmeter is the magnetic polariza-
as follows:
tion J. The relative permeability is calculated as follows:
Permeability Dimensional Ratio
J
Under 1.5 10 or greater
µ 5 11 (2)
r
Γ H
1.5 to 2.0, incl. 15 or greater
m
2.0 to 4.0 30 or greater
where:
5.2 This test method can be used with smaller dimension-
µ = relative permeability of the test specimen;
r
ratio test specimens when used for comparing to similar
J = magnetic polarization, T;
specimens for quality control purposes.
A342/A342M − 04 (2012)
−7
Γ =4π×10 H/m; and
m
H = magnetic field strength, A/m.
9. Precision and Bias of Test Method 1
9.1 Theprecisionandbiasofthistestmethodhavenotbeen
established by interlaboratory study.
9.2 The measured permeabilities will be less than their true
values due to the demagnetizing field arising from the sample
dimensional ratio. This leads not only to an overestimation of
themagneticfieldstrengthbutalsoreducesthefluxlinkagesin
the B-coil.Providedthesampleandcoildimensionalratiosare
as specified in 4.2.2 and 5.1, the largest negative error in µ−1
5,6
as a result of demagnetizing effects will be−3% for µ−1<
0.5.
TEST METHOD NO. 2, PERMEABILITY OF
PARAMAGNETIC MATERIALS
10. Significance and Use of Test Method 2
10.1 This test method is suitable for specification
acceptance, design purposes, service evaluation, regulatory
statutes,manufacturingcontrol,andresearchanddevelopment.
10.2 Becauseoftherestrictionsonthespecimenshape,size,
and permeability, this test method is most often used to
FIG. 2 Circuit Diagram for Method No. 2
evaluate semifinished product before fabrication of parts.
the specimen shall be not less than 6.6 cm [66 mm] and the
11. Apparatus
width shall not exceed 1.27 cm [12.7 mm]. The minimum
11.1 Power Supply—Asource of steady dc power
...
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