Ultrasonic Monitoring of Resin Impregnation and Curing Process in Resin Transfer Molding

Resin transfer molding (RTM) has been attracting much attention to produce FRP products due to lower manufacturing cost than an autoclave molding method and unnecessity of human skills unlike a hand lay-up method. The quality of RTM products is highly dependent on the state of resin impregnation into fiber preform during the mold-filling stage, and it is required to avoid creation of molding defects such as dry spots and voids. Ultrasonic testing can be applied to monitor impregnation and cure of resin in RTM. In this study, an experimental setup was designed to achieve unidirectional resin flow, and ultrasonic monitoring system was proposed. By analyzing the reflected waves from the upper and lower surfaces of the FRP layer in the mold, it was found that our method could evaluate not only residual air voids and resin impregnation into fiber bundles, but also cure degree of resin. Therefore, it was proven that the system could monitor entire RTM molding process.