Thermo-elastic nondestructive evaluation of thermally induced damage in polymer matrix composites

Destructive measurements of overheated Polymer Matrix Composites (PMCs) show that mechanical strength can be reduced by as much as 10-80 percent before appearance of visible damage. A large majority of the NDE techniques cannot detect this incipient heat damage. Thermo-elastic measurements are compared with ultrasonic C-scans and destructive flexural test measurements per-formed on PMCs subjected to uniform heat damage. These measurements confirm that ultrasonic C-scan measurements cannot detect incipient heat damage that can be detected by the thermo-elastic parameter measurements. A gradual decrease in the thermo-elastic parameter was determined as a function of increasing incipient heat damage. The possible mechanisms responsible for the change in this parameter due to thermal damage are discussed.