Development and Experimental Validation of a Numerical Tool for Structural Health and Usage Monitoring Systems Based on Chirped Grating Sensors

Abstract

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.

Thermal Profile Detection Through High-Sensitivity Fiber Optic Chirped Bragg Grating on Microstructured PMMA Fiber

“…Following the method in [15] and used also in [35] to calibrate a CFBG by means of a controlled heating source, an experiment has been designed having a linear thermal gradient in order to evaluate the capability of the CFBG to respond to a non-uniform spatial gradient [36].…”

Fibre optics health monitoring for aeronautical applications

“…Then, such algorithm has to be coupled to an optimization procedure which finds the strain profile minimizing the difference between simulated and experimental spectra [29,37]. A grating simulation approach relying on the Coupled Mode Theory (simplified the-ory derived from Maxwell's equations [26]) is reported in detail in [10], where TMM (Transfer Matrix Method) is exploited as well, together with an optimization technique based on a hybrid genetic algorithm. To validate such a strain reconstruction tool, tests are performed on chirped grating sensors.…”

“…allowing sev-eral different combination of spectral and spatial characteristics. To identify the best combination for strain reconstruction applications, three of them are considered, every array being composed of 10 individual FBG sensors [10]:…”

Development and analysis of a model based on chirped fiber Bragg gratings employed for cracks characterization in materials

“…Among the techniques available in literature those based on Fiber Bragg Grating (FBG) sensors are much promising thanks to their peculiarities [1], [2] In comparison with the traditional mechanical and electrical sensors, the optical fiber sensors possess some unique advantages such as small size, light weight, immunity to electromagnetic interference (EMI) and corrosion, embedding capability, and therefore they have been employed in monitoring of engineering structures worldwide [3]. Bettini et al [1] started from a numerical model capable of simulating the spectral response of a grating subjected to a generic strain profile. While a standard uniform FBG can transduce only the average strain on its total length, a chirped one is able to provide direct information about the strain distribution profile along the grating itself.…”

“…While a standard uniform FBG can transduce only the average strain on its total length, a chirped one is able to provide direct information about the strain distribution profile along the grating itself. In fact, having a variable grating period, this kind of sensors has in principle a one-to-one correspondence between reflection spectrum wavelength and position on the perturbation [1]. Linear chirped Bragg gratings (linear CFBG) have a period that increases monotonously, the Bragg wavelength changes linearly with the position.…”