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Optical fibre sensors are being investigated since many years as candidates of choice for supporting structural health monitoring (SHM) in aerospace applications. Fibre Bragg grating (FBG) sensors, more specifically, can provide for accurate strain measurements and therefore return useful data about the mechanical strain state of the structure to which they are attached. This functionality can serve the detection of damage in an aircraft structure. However, very few solutions for protecting and bonding optical fibres to a state-of-the-art aircraft composite material have been reported. Most proof-of-principle demonstrations using optical fibre sensors for aerospace SHM-related applications reported in literature indeed rely on unpackaged fibre sensors bonded to isotropic metallic surfaces in a mostly unspecified manner. Neither the operation of the sensor, nor the adhesive material and bonding procedure are tested for their endurance against a full set of standardized in-flight conditions. In this work we propose a specialty coated FBG sensor and its permanent installation on aerospace-grade composite materials, and we demonstrate the compatibility with aerospace in-flight conditions. To do so we thoroughly evaluate the quality of the operation of the FBG sensor by correlating the reflection spectra of the installed sensors before and after exposure to a full set of realistic in-flight conditions. We also evaluate the difference in strain measured by the FBG, since any damage in the adhesive bond line would lead to strain release. The applied test conditions are based on aerospace standards and include temperature cycling, pressure cycling, exposure to humidity and Smart Materials and Structures

Automated fibre placement (AFP) of thermoplastic composites has been reaching a high efficient and technological level in the last years. In situ consolidation (ISC) process involves cost reduction since extra autoclave cycle is not required. A good control of the temperature and pressure during the lamination is mandatory to achieve a good consolidation without thermal degradation for the manufacturing of high quality parts. Due to the manufacturing set-up, temperature monitoring is limited to infrared thermographic cameras and superficial measurements. Within this context, Fibre Bragg grating (FBG) sensors emerged as a potential device for thermal history monitoring in real-time. An investigation was carried out by using different FBG sensors for process monitoring of thermoplastic ISC. In this study, the sensors were embedded inside CF/PEEK thermoplastic samples and the lamination process was subsequently monitored. Also, a thermal model was created in order to obtain a simulated thermal history of the process. The process was successfully monitored, and it has been demonstrated that FBG sensors are a useful tool for thermoplastic ISC process monitoring. The results provided by the sensors allowed to identify different phases of the process (heating, consolidation and cooling down). The thermal history of the process was monitored by encapsulated FBG sensors acting as temperature probes. A good correlation between the sensors and the thermal was found. In addition to that, First steps were taken for strain history monitoring by means of FBG sensors.

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