Method for strain tensor reconstruction with embedded fiber Bragg grating sensors

Fiber Bragg grating (FBG) sensors are being considered for health and condition monitoring of composite structures, where they may be embedded inside the material during the fabrication process. So far, research efforts have been directed towards reconstruction of the strain tensor inside the material at the position of the FBG, using FBGs in polarization-maintaining fibers. However, the influence of shear strains on the signals reflected from the FBG has hindered attempts to accurately reconstruct the strain tensors. In this work, we employ a theoretical description of FBGs which also describes the influence of shear strain. We propose an algorithm which, based on this underlying theory, allows for reconstructing the principal strains, as well as the shear strain components. Further, we test the algorithm on simulation data with noise levels comparable to those found in real applications. Finally, we demonstrate the feasibility of the algorithm and its limitations.