Direct Measurement of Bondline Temperature During Composite Repair/Fabrication

Achieving desired bondline temperatures is critical to ensuring proper wetting, flow and cure when repairing composite structures. Under this multi-phase SBIR project a novel method for measuring/managing cure temperature in the bondline is being pursued based on patented amorphous microwire temperature sensors that are placed permanently within the bondline and read remotely via low-frequency electromagnetic interrogation. The interrogated microwire sensors provide a sharp, distinguishable voltage pulse to a remote antenna whose integrated area is directly proportional to sensor temperature. More than one microwire per sensor provides self-calibration and signal normalization. Preliminary and Phase I development of the microwire sensors and reader system prove its ability to remotely measure the temperature of a sensor permanently embedded within more than one inch of carbon fiber-reinforced polymer. Furthermore, testing to date has shown that the sensor does not present a critical flaw in the composite structure. For the USAF Phase II SBIR project proposed here we intend to validate the accuracy/precision of our novel microwire temperature measurement via a working prototype of a hot bonder accessory. It will provide feedback for closed-loop temperature control based upon temperatures within the bondline, with the goal of improving usability and providing significant time/cost savings.