Fiber Bragg Grating Applied to In Situ Characterization of Composites

Abstract

Abstract Fiber optic sensors have been extensively used for measuring strain, temperature, pressure, humidity, and other quantities in various experimental configurations. Compared to other traditional sensors, they have a number of advantages. They are generally more compact, lightweight, and less invasive because of their small size (125 µm is the standard diameter of the fiber). In addition, they are immune to electromagnetic interference, have excellent resistance to corrosion and high temperatures, and have long lifetimes. In particular, optical fiber Bragg grating (FBG) sensors have attracted considerable attention over the last decades because of their characteristic property to measure strains in the host structure at the location of the grating. The resulting signals are encoded directly in the wavelength domain, which results in a self‐referencing capability of these sensors. Thus, they are not affected by power fluctuation of the light source and optical connection losses. Moreover, the intrinsic spectral‐encoding nature facilitates wavelength division multiplexing that leads to measurements at several points along the FBG. Optical fibers with FBG sensors are particularly adapted to polymer composites, in which they can be embedded between plies during processing and provide accurate, virtually noninvasive internal strain or temperature measurements at selected locations. Thus, experimental configurations can be designed to measure internal strains due to processing as well as mechanical and environmental loads. Such measurements can be used to develop or validate pertinent analytical and numerical models and also serve in structural monitoring and control. In this article, the FBG sensor as a tool for internal strain measurements in polymeric materials is presented. In the first part, its essential attributes are discussed, with emphasis on single‐mode standard sensors. In the second part, results of strain measurements using embedded FBG sensors are reported in various cases of homogeneous and nonhomogeneous strains along the sensor.