The interest of the aerospace industries in structural health and usage monitoring systems is continuously increasing. Among the techniques available in literature those based on Fibre Bragg Grating sensors are much promising thanks to their peculiarities. Different Chirped Bragg Grating sensor configurations have been investigated in this paper. Starting from a numerical model capable of simulating the spectral response of a grating subjected to a generic strain profile (direct problem), a new code has been developed, allowing strain reconstruction from the experimental validation of the program, carried out through different loading cases applied on a chirped grating. The wavelength of the reflection spectrum for a chirped FBG has a one-to-one correspondence to the position along the gauge section, thus allowing strain reconstruction over the entire sensor length. Tests conducted on chirped FBGs also evidenced their potential for SHM applications, if coupled with appropriate numerical strain reconstructions tools. Finally, a new class of sensors—Draw Tower Grating arrays—has been studied. These sensors are applicable to distributed sensing and load reconstruction over large structures, thanks to their greater length. Three configurations have been evaluated, having different spatial and spectral characteristics, in order to explore possible applications of such sensors to SHM systems.

An original Monito-Ring system based on chirped fiber optic and draw tower grating array is presented. The target of this research activity is the realization of a device able to measure deformations of morphing structures which may show large, global displacements due to nonstandard architectures and materials adopted. The occurring strain field results, in turns, much more than the standard sensors can handle. Modulations are then necessary to keep the measured strain low. The proposed solution was conceived to overcome this limitation assuring a suitable reduction of the revealed strain. The concept is made of a flexible ring pinned on a certain number of points to the structural component of interest. The fiber optic is integrated within the ring, and depending on the angular position of the sensor, the ratio between the diameter elongation (i.e. structural strain) and the measured deformation (strain) can be almost arbitrarily set in a large range of values. From each spectrum provided by draw tower grating array, the corresponding unknown strain field is retrieved by applying an inverse technique obtaining an accurate continuous strain map. This article deals with a proof of concept analytical study first and then numerical and experimental validation.