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This work concerns monitoring the polymerization of an epoxy resin and its hardener. An ultrasonic pulse echo technique was used to monitor the attenuation, the phase velocity, and the acoustic impedance of the resin as a function of time. The first two parameters give information about the average state of the hardening of the resin itself. The third parameter, acoustic impedance, indicates the state of the hardening of the resin at the interface with the vessel. These parameters are determined from spectral properties of echoes extracted from the experimental echo waveforms. Experiments were made for different proportions of hardener and allowed a determination of the best mixture (10% of hardener) that corresponds to the manufacturer's recommended value. Analysis of the results shows a progressive hardening from the center of the resin toward the walls of the vessel.

This paper presents a study of the group velocity dispersion of some circumferential waves propagating around an elastic tube. The dispersive character of the circumferential waves is theoretically known, but the experimental measurement of the group velocity in a dispersive medium is still a complex operation. We have determined the characteristics of the circumferential wave dispersion for aluminium and steel tubes using a time-frequency representation. Among these time-frequency techniques, the Wigner-Ville distribution (WVD) is used here for its interesting properties in terms of acoustic applications. The WVD is applied to the analysis of the dispersion of S0 symmetric and A1 antisymmetric circumferential waves propagating around a tube with a radii ratio equal to 0.95 (internal radius:external radius). This allowed us to determine their group velocities and reduced cutoff frequencies. The results obtained are in good agreement with the calculated values using the proper modes theory.

In this paper, we suggest a technique for carrying out a high-resolution time–frequency analysis based on a modified version of the Wigner–Ville distribution. The impulse response backscattered by an aluminium and steel tube immersed in water is analysed using this method. As will be demonstrated, this approach has the desirable attributes of eliminating all interference terms manifested on the time–frequency plane and of allowing one to visualize more clearly the evolution of the reduced frequency ka of the symmetric S0 and antisymmetric A1 circumferential waves over time. This analysis allows us to determine much more accurately the cut-off reduced frequency of the antisymmetric circumferential wave A1.