DEC 2018


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DECEMBER 2018 20 CompositesWorld WORK IN PROGRESS in diameter.) One wire functions as the measurement wire and is alloyed to have a Curie Temperature approximately °F/•°C above the cure temperature for the resin system for which the sensor is designed. A second wire is termed the reference wire and is alloyed to have a Curie Temperature several hundred degrees above the desired dwell temperature, providing a constant pulse to normalize against. e third wire, called the autocalibration wire, is alloyed for a Curie Temperature above room temperature but signi-cantly below the cure temperature. It will provide temperature readings until its known Curie Temperature is reached, at which point its pulse will disappear. At that instant, the temperature of the sensor is accurately veri-ed and the ermoPulse system has the calibration temperature needed to proceed with measurements and calculations. SBIR testing Having completed an initial Phase I SBIR contract with the US Air Force to demonstrate feasibility, AvPro and its partners are now roughly halfway through the Phase II project, designed to validate the accuracy and precision of the ermoPulse system. is is being achieved by testing at four independent sites, each using 25 ermoPulse sensors and a prototype reader box incor- porated into a type of hot bonder. Hot bonders are portable, small suitcase-sized equipment used to control the application of heat and vacuum to an adhesively bonded composite repair. e four test sites are AvPro's facilities, Abaris Training (Reno, NV, US), TSI Technologies Inc. (Wichita, KS, US) and AFLCMC/EZPT-ACO at Hill Air Force Base (near Ogden, UT, US). AvPro has worked with Abaris Training for years to help validate and re-ne its Material State Management (MSM) system, while TSI Technologies is a key partner in developing and re-ning the microwire sensors. Hill Air Force Base is home to the Ogden Air Logistics Complex, which performs depot maintenance on several Air Force weapon systems, and the Air Force Life Cycle Manage- ment Center's Air Force Advanced Composites O›ce (AFLCMC/ EZPT-ACO), a centralized resource for -elded composite materials. e research program is led by the Air Force Research Laboratory (AFRL, Wright-Patterson, OH, US) and project manager Kara Storage, with a view toward aircraft manufacturing and repair applications. Each test site will complete œ standardized bonded composite repairs using a -inch diameter scarf repair patch made from six plies of prepreg over a layer of -lm adhesive with a microwire sensor in the bondline. Each of these œ repairs will also use thermo- couples as a control for comparison with ermoPulse microwire sensor results. "We've completed all of the œ°F- cure repair tests and are now analyzing the data," says AvPro president Tom Rose. "So far, the microwire measurements are within ±°F of the thermocouple measure- ments." Rose says all of the test sites are using CFRP laminates and patches except for Hill AFB, which has speci-c reasons for testing glass -ber laminates and repairs. "We are now starting testing with an additional • sensors for ¢°F repairs and will complete the SBIR work by October œ•£." Another goal of this testing is to develop the statistical basis for an ASTM method. ASTM International (West Conshohocken, PA, US) is an organization that develops industry standards, including most of the test methods used for composite materials and struc- tures. " e ASTM method for measuring temperature in a bondline during composite repair would also apply to any composite bondline," says Rose, "and will give the industry con-dence in the accuracy of the ermoPulse sensors." Completing the repairs for the SBIR testing will also provide feedback for re-ning the hot bonder prototype as a closed loop temperature control device. "Our goal is to control the repair cure based upon temperatures within the bondline," says Rose, "with the ultimate objective of providing signi-cant time and cost savings." Modernizing cure, documenting quality " is sensor was developed to feed into our cure management system," Rose explains. " ere really hasn't been much funda- mental change in the way we're managing cure in composite The ThermoPulse system enables wireless, remote, in-situ temperature monitoring during cure. T Curie, Reference Integrated Area of Response Curve Reference wire's curve Autocalibration wire's curve Sensing wire's curve T Curie, Autocalibration T Curie, Sensing FIG. 2 Three microwires, one calibrated sensor When interrogated with an electromagnetic field from the ThermoPulse antenna, each of the sensor's three wires generates a voltage pulse that changes with temperature. The area under this voltage response is the temperature at a given time. Each microwire has a designed optimal range (highest sensitivity) starting at 100°F below its Curie Temperature (T Curie ). The autocalibration wire's T Curie is set well below the composite/adhesive cure temperature, and once its voltage pulse disappears, the system is calibrated. The T Curie of the sensing wire is set to 100°F above the desired cure temperature while the reference wire's T Curie is set several hundred degrees above cure and provides a stable pulse for reference. Source | AvPro Inc. Optimal Range

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