Analysis of the fixing process of FBG optical sensors for thermomechanical monitoring of aerospace applications

In aerospace, lots of components can be defined as “safety critical”. As a result, it is crucial to early identify the failure precursors when the effects on the systems performances are still practically insignificant. For this reason, complex networks of sensors had been developed and integrated into different parts to monitor several operational parameters, useful for evaluating their health (such as such as temperatures, displacements, vibrations, etc). Clearly, due to the importance of data collected, the technology employed shall be very reliable, even while working in harsh environments. Sensors based on optical fiber Bragg grating (FBG) meet these requirements. However, the fiber’s integration process in the considered system is really crucial, from the moment that it could influence the sensors output. In this regard, gluing the optical sensors is really a critical activity, because the effects of the glue’s retire and its viscous assessment shall be analysed and quantified. In this work, it was done by comparing performances of two equal samples, each one with an FBG glued on it. The first sample was prepared about two months before the second one. Furthermore, data from both FBG have been collected from the gluing phase of the second sample and in the following days. The results showed that the assessment of the resin evolved in different phases, but all of them were united by the fact that the overall process makes sensors measures not reliable during this specific transitory phase. By observing the evolution of the linear fit gradients, it can be stated that the variations reached their maximum in the middle of the gluing process, when the fiber was detached from the tensioning device. Finally, at the end of the overall process, data output resulted stable, so making FBG employable for reliable thermal or strain measures.