1、Designation: A342/A342M 04 (Reapproved 2012)A342/A342M 14Standard Test Methods forPermeability of FeeblyWeakly Magnetic Materials1This standard is issued under the fixed designation A342/A342M; the number immediately following the designation indicates the yearof original adoption or, in the case of
2、 revision, the year of last revision. A number 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 U.S. Department of Defense.1. Scope1.1 These tes
3、t methods cover threefour procedures for determination of the permeability relative permeability2 of materialshaving a permeability not exceeding 4.0.6.0.1.2 The test methods covered are as follows:1.2.1 Test Method 1 1Fluxmetric Method is suitable for materials with permeabilities between 1.0 and 4
4、.0. This methodpermits the user to select the magnetic field strength at which the permeability is to be measured.1.2.2 Test Method 2 2 is suitable for measuring the permeability of paramagnetic materialsPermeability of ParamagneticMaterials having a permeability less than 1.05.has been eliminated a
5、s an acceptable method of test.1.2.3 Test Method 3 3Low Mu Permeability Indicator is a suitable means of for measuring the permeability of a material as“less than” or “greater than” that of calibrated standard inserts with permeability between 1.01 and 6.0, as designated for use ina Low-Mu Permeabil
6、ity Indicator.3 In this method, a small volume of specimen is subjected to a local magnetic field that variesin magnitude and direction, so it is not possible to specify the magnetic field strength at which the measurement is made.1.2.4 Test Method 4Flux Distortion is suitable for materials with per
7、meability between 1.0 and 2.0. In this method, a smallvolume of specimen is subjected to a local magnetic field that varies in magnitude and direction, so it is not possible to specifythe magnetic field strength at which the measurement is made.41.2.5 Test Method 5Vibrating Sample Magnetometry is su
8、itable for materials with permeability between 1.0 and 4.0. This testmethod permits the user to select the magnetic field strength at which the permeability is to be measured.1.3 Materials typically tested by these methods such as austenitic stainless steels may be weakly ferromagnetic. That is, the
9、magnetic permeability is dependent on the magnetic field strength. As a consequence, the results obtained using the differentmethods may not closely agree with each other. When using Methods 1 and 5, it is imperative to specify the magnetic field strengthor range of magnetic field strengths at which
10、 the permeabilities have been determined.1.4 The values and equations stated in customary (cgs-emu and inch-pound) or SI units are to be regarded separately asstandard. Within this standard, SI units are shown in brackets except for the sections concerning calculations where there areseparate sectio
11、ns for the respective unit systems. The values stated in each system may not be exact equivalents; therefore, eachsystem shall be used independently of the other. Combining values from the two systems may result in nonconformance with thisstandard.1.5 This standard does not purport to address all of
12、 the safety concerns, if any, associated with its use. It is the responsibilityof the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatorylimitations prior to use.1 These test methods are under the jurisdiction of ASTM Committee A06
13、 on Magnetic Properties and are the direct responsibility of Subcommittee A06.01 on TestMethods.Current edition approved May 1, 2012May 1, 2014. Published July 2012May 2014. Originally approved in 1949. Last previous edition approved in 20042012 asA342/A342M04. 04 (2012). DOI: 10.1520/A0342_A0342M-0
14、4R12.10.1520/A0342_A0342M-14.2 Test Methods 1 and 25 actually measure magnetic susceptibility. The permeability () relative permeability (r) is related to the susceptibility () by the equations: = 1 + 4pi (cgs-emu)r = 1 + (SI)The term permeability has been retained in these test methods because of i
15、ts widespread commercial and technological usage.3 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., 555Stage Rd., Suite 1A, Auburn, AL 36830, http:/. (Indicators can be returned for recalibr
16、ation.) If you are aware of alternative suppliers, pleaseprovide this information to ASTM International Headquarters. Your comments will receive careful consideration at a meeting of the responsible technical committee,1 whichyou may attend.4 The sole source of supply of the apparatus known to the C
17、ommittee at this time is the Magnetoscop manufactured by INSTITUT DR. POERSTER GmbH Bi = intrinsic induction of the test specimen, G; andH = magnetic field strength, Oe.8. Calculation (SI Units)8.1 The output from the fluxmeter is the magnetic polarization J. The relative permeability is calculated
18、as follows:r 5 11 JmH(2)where:r = relative permeability of the test specimen;J = magnetic polarization, T;m = 4pi 107 H/m; andH = magnetic field strength, A/m.9. Precision and Bias of Test Method 19.1 The precision and bias of this test method have not been established by interlaboratory study.9.2 T
19、he measured permeabilitiespermeability will be less than theirthe true valuesvalue due to the demagnetizing field arisingfrom the samplefield, which depends on the specimen dimensional ratio. This leads not only to an overestimation of the magneticfield strength but also reduces the flux linkages in
20、 the B-coil. Provided the samplespecimen and coil dimensional ratios are asspecified in 4.2.2 and 5.1, the largest negative error in 1 as a result of demagnetizing effects6,7 will be 3 % for 1 0.3 in. 8 mm thick, the flat test area where the probe will be placed should have diameter 0.8 in. 20 mm an
21、dcurved surfaces should have radius of curvature 1.6 in. 40 mm. When testing specimens with dimensions smaller than theseapproximate limits, the instrument will indicate permeability different than the actual value.18. Procedure18.1 Best results are obtained when the probe is in a fixed location and
22、 the specimen is moved into contact with the probe.18.2 Absolute Measurements:18.2.1 Identify a location on the test piece which meets the dimensional requirements stated by the instrument manufacturer.18.2.2 Connect a suitable probe to the instrument, as recommended by the instrument manufacturer.1
23、8.2.3 Calibrate the instrument/probe against a calibration standard per manufacturer recommendations.18.2.4 Place the test piece in contact with the probe and record the display reading.18.3 Comparative Measurements:18.3.1 Identify a location on the test piece.18.3.2 Calibrate the instrument/probe a
24、gainst the reference object to which the comparison will be made.18.3.3 Place the test piece in contact with the probe and record the display reading.FIG. 3 Schematic Illustration of Low Permeability IndicatorFlux Distortion Method Method 4A342/A342M 14719. Precision and Bias19.1 The precision and b
25、ias of this test method have not been established by interlaboratory study.19.2 The manufacturer of the instrument determines the permeability of the calibration standards. Standards with permeabilitytraceable back to national standards are available.19.3 One manufacturer states an absolute accuracy
26、 of permeability measurement of better than 65 % of the actual value.TEST METHOD 5, VIBRATING SAMPLE MAGNETOMETER METHOD OF TEST20. Significance and Use of Test Method 520.1 The vibrating sample magnetometer (VSM), schematically shown in Fig. 4, is well suited for determining the propertiesof weakly
27、 magnetic materials. It is sensitive enough to measure the magnetization of a paramagnet, and can apply fields over alarge enough range to separate and measure paramagnetism and weak ferromagnetism when they co-exist.20.2 This method is suitable for any material that can be prepared in the form of a
28、 small disk or cube of known volume. Thevalues of constant (field independent) permeability as low as 1.001 may be determined with an uncertainty of 60.0001. There isno theoretical upper limit to the measurable permeability, but in practice ferromagnetic behavior quickly masks paramagneticbehavior.2
29、0.3 Because specimens for vibrating sample magnetometry are typically small disks less than 1 cm 0.01 m in diameter andrequire fabrication into a specific shape, due care in specimen preparation is necessary to prevent the preparation procedures fromaffecting the test results.20.4 This test method i
30、s suitable for specification acceptance, design purposes, service evaluation, regulatory statutes,manufacturing control, and research and development.21. Apparatus21.1 Any VSM capable of measuring a magnetic moment of 10-3 emu 10-6 Am2 with an uncertainty of 62 %, and capableof applying a known magn
31、etic field strength of at least 65000 Oe 6400 kA/m can be used. Almost all VSM instruments canmeet these conditions. Commercial VSM instruments are available from a number of makers. Home-made instruments also existin various university and company laboratories.21.2 It is important to note that a VS
32、M measures the magnetic moment (m) and not the magnetic flux ().22. Test Specimens22.1 The VSM is an open magnetic circuit device, but the demagnetizing correction (a characteristic uncertainty in suchsystems) is negligible when the magnetization levels are very small.FIG. 4 Schematic Illustration o
33、f Vibrating Sample Magnetometer (VSM) Method 5A342/A342M 14822.2 The specimen shall be prepared in the form of a disk with diameter-to-thickness ratio of five or greater. A metal specimenwill normally be made by machining from a larger block, and in this case steps should be taken to minimize surfac
34、e deformationand local heating, either of which may affect the magnetic properties. Use of a sharp tool bit, taking light cuts, and using a coolingfluid are recommended.22.3 The specimen volume should be as large as practical, to maximize the measured signal. The maximum specimen diameteror mass wil
35、l be limited by the structure of the VSM. A further constraint on the specimen diameter is the fact that the VSM mustbe calibrated with a specimen of known mass or volume, known saturation magnetization, a diameter equal to that of the specimento be measured, and with a diameter-to-thickness ratio o
36、f no less than that of the specimen to be measured. The specimen diametermust be matched to that of the calibration standard.22.4 The specimen volume must be determined to an uncertainty of 62 %, either by direct measurement of its dimensions orby measuring the mass and converting to volume using th
37、e known density.23. Procedure23.1 Since low levels of magnetization will be measured, the specimen and the specimen holder must be carefully cleaned ofany strongly magnetic contamination prior to measurement.23.2 Commercial VSM instruments are computer controlled, usually with custom software. Home-
38、made instruments will havewritten instructions, or an experienced operator, or both. In any case, the specimen disk is mounted in the VSM specimen holder,and magnetic moment is measured in a properly calibratedVSM at uniformly spaced values of applied magnetic field strength froma maximum of at leas
39、t 5000 Oe 400 kA/m to an equal negative magnetic field strength, and then in similar steps back to themaximum positive magnetic field strength. A total of at least 20 data pairs (magnetic moment and magnetic field strength) shouldbe recorded.23.3 A background run with no specimen in the specimen hol
40、der shall be made to see if a measurable background signal ispresent. If present, this signal is recorded and subtracted from the measured data. Note that the background signal from a polymerspecimen holder will likely be negative, since polymers are typically diamagnetic.23.4 The data points shall
41、be plotted as magnetization per unit volume M versus applied magnetic field strength H.24. Calculations24.1 Generally one of two forms of behavior will be observed from the M versus H plot.24.2 Case 1The data points can be completely represented by a single straight line passing through the origin a
42、s in Fig. 5.In this case the specimen is paramagnetic, the slope of the line is the magnetic susceptibility () and the permeability () is givenby:54pi11 (3)The result may be reported as the numerical value of the permeability determined by A342/A342M Test Method 5 over themagnetic field strength ran
43、ge actually used. Paramagnetic behavior of engineering materials is not usually temperature dependent,so temperature need not be controlled or reported so long as the test temperature conforms to the requirements of PracticeA34/A34M.24.3 Case 2The data points above some minimum positive and negative
44、 field strength can be completely represented bystraight lines intercepting the magnetization axis at equal and opposite (positive and negative) values, respectively, as illustratedin Fig. 6. In this case the magnetic behavior consists of a paramagnetic component, with magnetic susceptibility , give
45、n by theaverage of the slopes of the two straight-line portions of the graph, and the corresponding permeability given by Eq 3, and aferromagnetic component whose saturation magnetization Ms in emu/cm3 T is given by the average of the absolute values of thetwo intercepts. The result may be reported
46、as the permeability determined by A342/A342M Test Method 5 over the magnetic fieldstrength range corresponding to the upper and lower limits of the linear portion of the data, plus a ferromagnetic component withsaturation magnetization Ms. If more detailed information about the properties of the fer
47、romagnetic component is needed,additional data points may be taken in the low-field region, the paramagnetic component regarded as a background correction tobe subtracted, and the ferromagnetic hysteresis loop constructed as a plot of M versus H. From this plot the remanence and coercivefield streng
48、th may be obtained. Note that the coercive field strength will be the intrinsic coercive field strength Hci since the loopis plotted as M versus H, not B versus H.24.4 Case 3If the data plots do not match either Case 1 or Case 2, some more complicated magnetic structure may beinvolved. In this case
49、the results should be reported in the form of the graph of M versus H with the notation that the data wereacquired using A342/A342M Test Method 5.25. Precision and Bias25.1 The precision and bias of this test method have not been established by interlaboratory study.A342/A342M 14925.2 Because this method measures susceptibility and then calculates permeability, the usual notion of a percentage or fractionalerror in the permeability does not apply. The magnetic susceptibility determined from the slo
