ASTM C769-09

Sonic velocity measurements are useful for comparing materials.

A value for Young's modulus can be obtained for many applications, which will be in good agreement with the value obtained by other methods, such as in Test Method C 747. The accuracy of the Young's modulus calculated from Eq 1 will depend upon the uncertainty in Poisson's ratio and its impact on the evaluation of the Poisson's factor in Eq 2.

If the grain size of the carbon or graphite is greater than or about equal to the wavelength of the sonic pulse, the method may not be providing a value of Young’s modulus representative of the bulk material. Therefore, it would be desirable to test a lower frequency (longer wavelength) to demonstrate that velocity is independent of frequency. Significant signal attenuation should be expected when the grain size of the material is greater than or about equal to the wavelength of the transmitted sonic pulse.

If the sample is only a few grains thick, the acceptability of the method’s application should be demonstrated by initially performing measurements on a series of tests covering a range of sample lengths between the proposed test length and a test length incorporating sufficient grains to adequately represent the bulk material.

1.1 This test method covers a procedure for measuring the sonic velocity in manufactured carbon and graphite which can be used to obtain Young's modulus.

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 and health practices and determine the applicability of regulatory limitations prior to use.