Ultrasound monitoring of the cure kinetics of an epoxy resin: Identification, frequency and temperature dependence

In this paper the monitoring of ultrasonic parameters of a thermosetting resin during an isothermal curing process is described. The ultrasonic properties are studied within the context of the monitoring of composite plate production by resin transfer molding (RTM). These ultrasonic characteristics can be related directly to cure kinetic models. An ultrasonic method, based on the measurement of the elastic constant and associated mechanical loss has been developed to identify the variations of the phase transformation. To study the reaction kinetics, the time dependence of the elastic coefficient is modeled using a Weibull distribution. The approximate time derivative form of this Weibull model makes it possible to find the relationship between ultrasonic parameters and the chemical Kamal model. The ultrasonic monitoring of a cooling process was also performed to study the temperature sensitivity after curing. Thanks to experimental measurements of the ultrasonic velocity and attenuation, the power law coefficient variations and their temperature sensitivity can be examined. The resulting viscoelastic Cole-Cole parameters were estimated and a frequency-temperature (f, T) model was proposed.