Integrated silicon Bragg-grating-based temperature sensor embedded in composite molds for out-of-autoclave composite parts process monitoring and optimisation

Abstract

The use of composite materials has seen widespread adoption in modern aerospace industry. This has been facilitated due to their combined favorable mechanical characteristics, namely leveraging their low weight, high stiffness and increased strength. Wide adoption of composites requires an effort to avoid costly and cumbersome autoclave-based manufacturing processes. The up and coming "out-of-autoclave" composite manufacture processes also have to be optimized, to allow for consistent high quality of the parts produced as well as keeping the cost and production speed as low as possible. This optimisation can be achieved offline as well as by trying to have constant monitoring and controlling the resin injection and curing cycles.Capitalizing on the benefits of Silicon Photonic Integrated Circuits (PICs), namely the fast response, miniature size, ability to operate at high temperatures, immunity to electromagnetic interference (allowing carbon fibers in composites), and their compatibility with CMOS fabrication techniques, a passive PIC based temperature sensor embedded in a composite tool is demonstrated, used to produce RTM-6 composite parts.The design and development methodology of the PIC based sensor (fabricated in an Multi Project Wafer run of 220 nm Silicon-on-Insulator (SOI) platform and based on periodic Bragg grating elements) as well as the experimental results and comparison with the industry standard thermocouples, during a thermal cycling of the tool are presented. We measured the embedded PIC temperature sensor to have sensitivity of around ~85 pm/℃, while the RTM-6 fabrication cycle requires the tool to operate up to 185 °C.