COMPARATIVE-ANALYSIS OF THROUGH-TRANSMISSION ULTRASONIC BULK WAVE METHODS FOR PHASE-VELOCITY MEASUREMENTS IN ANISOTROPIC MATERIALS

In this paper a critical evaluation of ultrasonic bulk wave velocity m easurements by the through-transmission and the recently introduced se lf-reference methods is reported. The major difference in these two te chniques is the reference acoustic path: through-water for the through -transmission method and through-sample at normal incidence for the se lf-reference method. The error introduced by geometrical imperfection of the sample is compared theoretically and experimentally for two met hods. Composite materials with different anisotropies are used in the experiment, including ceramic matrix (SiC/Si3N4) and graphite/epoxy co mposites. Both analytical and experimental studies show that the self- reference method has advantages over the through-transmission method, which is susceptible to geometrical imperfections in the sample. The e ffect of temperature fluctuation on the accuracy of ultrasonic phase v elocity measurements is discussed and different compensation technique s are proposed.