Ultrasonic characterization of the quality of an epoxy resin polymerization

This work concerns monitoring the polymerization of an epoxy resin and its hardener. An ultrasonic pulse echo technique was used to monitor the attenu ation, the phase velocity, and the acoustic impedance of the resin as a fun ction of time. The first two parameters give information about the average state of the hardening of the resin itself. The third parameter, acoustic i mpedance, indicates the state of the hardening of the resin at the interfac e 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 r ecommended value. Analysis of the results shows a progressive hardening fro m the center of the resin toward the walls of the vessel.