The verification of applicability of the use of embedded microwire temperature sensors in repair scenarios
There is a significant need to track temperature within bondlines on composite materials during cure. The temperature history of the cured part affects the material properties of the composite and therefore part performance. Hence, the integrity of the structure is dependent on achieving the proper temperature in the bondline. Current temperature measurement methods require leads to the temperature sensor that would create unacceptable flaws in the bondline; therefore, repair methods rely on heat transfer estimates from sensors placed externally to the repair to assure cure within the bondline/part. This approach typically requires trial cures that are costly and involve additional care to compensate for lack of actual temperature measurement. A proof-of-concept prototype with sensors that do not require leads and that are small enough to be placed in a bondline was developed. These sensors are smaller than the typical allowed flaw size in aerospace applications and so can be placed directly in the bondline, where they are magnetically interrogated by a transmit/receive antenna which uses temperature dependence of the Barkhausen jump to determine temperature. This proof-of-concept has been applied to simulated composite repairs typical of the industry and was able to provide feedback to control the heating of the repair. The system was demonstrated to be capable of: measuring temperature wirelessly through glass, carbon, boron, or aramid fibers as well as the bagging materials and even through lightning strike protection mesh; measuring from ambient (~30°C) temperature to 260°C; and wirelessly acquiring temperature data from bondline through approximately 4 mm of composite material. Additionally, the effect of ferromagnetic materials and other metals near the antenna and sensor was checked. Copyright 2017. Used by CAMX The Composites and Advanced Materials Expo.