Ultrasonic cure monitoring of advanced composites

Measurements of the ultrasonic sound speed of thermosetting resins and composites can be used as an in-process cure monitoring technique. Ultrasonic measurements have an advantage over other in-process techniques in that ultrasonic sensors do not make contact with the part (thus leaving no imbedded sensor or witness mark) and can make true bulk measurements of the part. A new commercially available ultrasonic cure monitoring system for the cure monitoring of thermosetting resins and composites has been developed. Advancements in ultrasonic sensor technology enable the self-contained ultrasonic sensor to be easily installed in a mold and maintain good coupling to the part during thermal cycling to 260°C. Data are presented showing the change in ultrasonic sound speed during the compression molding of epoxy prepregs. The data show a good relationship to the electrical resistivity data collected via dielectric cure monitoring. The ultrasonic technique is also applicable to phenolic based materials.