Application of an improved EFPI/FBG sensor system to simultaneous strain/temperature measurement of advanced 3D braided composite materials

Abstract

Simultaneous strain and temperature measurement for advanced 3-D braided composite materials using fibre-optic sensor technology is demonstrated, for the first time. These advanced 3-D braided composites can virtually eliminate the most serious problem of delamination for conventional composites. A tandem in-fibre Bragg grating (FBG)/extrinsic Fabry-Perot interferometric sensor (EFPI) system with improved accuracy has been used to facilitate simultaneous temperature and strain measurement in this work. The non-symmetric distortion of the optical spectrum of the FBG, due to combination of the FBG and the EFPI, is observed for the first time. Experimental and theoretical studies indicate that this type of distortion can affect the measurement accuracy seriously and it is mainly caused by the modulation of the periodic output of the EFPI. A simple method has been demonstrated to improve the accuracy for detection of the wavelength-shift of the FBG induced by temperature change. A strain accuracy of and a temperature accuracy of -±l°C have been achieved, which can meet the requirements for practical applications of 3-D braided composites.

Advanced measurement techniques for braided composite structures: A review of current and upcoming trends

“…Despite these limitations, FBG and other FOS sensors can be an effective thermal and mechanical strain measurement tool for braided composite structures. Simultaneous strain and temperature measurement was achieved for 3D braided composites using embedded sensors by Rao et al 106,107 through the use of extrinsic Fabry-Perot interferometer sensors (EFPI) and FBG sensors. Both sensors were integrated into a housing with small capillaries and mounted to the braided structure.…”