Strain measurement in CFRP laminates under bending load using tilted FBG sensors

Abstract

This study demonstrates the applicability of tilted-Fiber Bragg Grating (TFBG) optical fiber sensor on structural health monitoring (SHM) of CFRP structures. The simultaneous measurement of axial strain and curvature were attempted utilizing transmission spectra of a TFBG sensor. The response of a TFBG transmission spectrum to axial strain and curvature was investigated independently by a tensile test and winding the sensor around a cylinder. As a result, strain caused wavelength shift and curvature decreased the amplitude of the cladding mode resonance in the transmission spectrum. Three-point bending test was conducted to apply both axial strain and curvature to a TFBG sensor simultaneously. The result shows axial strain can be measured using wavelength shift. On the other hand, the power of the cladding mode resonance was increased with curvature increasing, which was a tendency different from the result when applying only curvature. The result indicated that a TFBG transmission spectrum shows different response under small curvature (< 3 m^-1).