Standard Test Method for Sonic Velocity in Manufactured Carbon and Graphite Materials for Use in Obtaining Young's Modulus

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.