Direct Measurement of Bondline Temperature During Composite Repair/Fabrication

ABSTRACT: Achieving desired bondline temperatures is critical to ensuring proper wetting, flow and cure when repairing composite structures.A novel method for measuring/managing cure temperature in the bondline is proposed, using patented amorphous microwire temperature sensors 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 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 has shown that the sensor does not present a critical flaw in the composite structure.For this USAF Phase I project we propose to show the feasibility of integrating our novel microwire temperature-measurement system into a hot bonder system to provide closed-loop feedback temperature control based upon temperatures within the bondline. The microwire-enhanced bonder system/repair process will not only benefit USAF applications but will improve broader aircraft industry and automotive repair processes while also enhancing commercial infrastructure repair processes within the civil engineering field.; BENEFIT: A critical element for controlling the production rate, quality, and cost of composite structures is the management of temperature within the structure during the curing cycle.Unfortunately, no current temperature sensor system can be embedded within aerospace CFRP parts or on the bond line of CFRP repairs to measure this critical temperature and remain in the part post-cure without causing a structural flaw.Our patent-pending microwire temperature sensing (MTS) technology can do this.Furthermore, innovative composite curing processes that require instantaneous temperature information to allow high power transfer rates to the resin without overcooking it (say, for instance, microwave heating, induction heating, or ultrasonic heating) may become feasible for production processes with real-time feedback from embedded MTS sensors.This new technology will be of significant and direct benefit to key USAF and other military applications.The high curing rates that these innovative processes allow will bring down the cost of composite manufacturing so that other industries such as the automotive industry can take advantage of composite materials high strength/weight ratio to make more fuel-efficient vehicles. Furthermore, the improvements to composite repair processes enabled by MTS technology will make infrastructure repairs such as bridge repairs safer and more cost-effective.Finally, MTS technology holds promise for improving the vehicle tire curing process and for a host of potential applications not yet discovered.