ASTM A342

ASTM A342 – Standard Test Methods for Permeability of Weakly Magnetic Materials

Description:

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 four procedures for determination of the permeability [relative permeability]2 of materials having a relative permeability not exceeding 6.0.

1.2 The test methods covered are as follows:

1.2.1 Test Method 1—Fluxmetric Method is suitable for materials with relative permeabilities between 1.0 and 4.0. This method permits the user to select the magnetic field strength at which the permeability is to be measured.

1.2.2 Test Method 2—Permeability of Paramagnetic Materials has been eliminated as an acceptable method of test.

1.2.3 Test Method 3—Low Mu Permeability Indicator is suitable for measuring the permeability of a material as “less than” or “greater than” that of calibrated standard inserts with relative permeabilities between 1.01 and 6.0, as designated for use in a Low-Mu Permeability Indicator.3 In this method, a small volume of specimen is subjected to a local magnetic field that varies in 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 4—Flux Distortion is suitable for materials with relative permeabilities between 1.0 and 2.0. In this method, a small volume of specimen is subjected to a local magnetic field that varies in magnitude and direction, so it is not possible to specify the magnetic field strength at which the measurement is made.4

1.2.5 Test Method 5—Vibrating Sample Magnetometry is suitable for materials with relative permeabilities between 1.0 and 4.0. This test method 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 magnetic permeability is dependent on the magnetic field strength. As a consequence, the results obtained using the different methods may not closely agree with each other. When using Methods 1 and 5, it is imperative to specify the magnetic field strength or range of magnetic field strengths at which 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 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.