Nondestructive evaluation of graphite by ultrasonic velocity measurement using cross-correlation and Hilbert transform methods

The suitability of ultrasonics for materials evaluation of graphite components is investigated. The ultrasonic velocity is measured using cross-correlation techniques and a method based on the Hilbert transform of the pulse response function. The measurements are made on different grades of graphite with different particle sizes and porosities. Comparison of the two methods shows similar results for the graphites having small particle size and low attenuation. For large particle size and highly attenuating graphites, the measured quantities are different. The velocities and some identified elastic constants are correlated with the physical properties of the material (grain size and porosity) on specific examples in order to show the ability and the limits of ultrasonics to evaluate large grain size graphite