Internal strain measurement by fiber Bragg grating sensors in textile composites

This paper is concerned with a study of internal strain measurement by fiber Bragg grating sensors (FBGSs) embedded inside textile composites. First, on the basis of the measurement principle of FBGSs, the effects of transverse strain and temperature on the measurement results are discussed. A composite model comprising an optical fiber, coating and resin was developed to determine the measurement effectiveness of an embedded optical fiber sensor by analyzing the strain field of the system under a uniform thermal load. Factors influencing the measurement effectiveness were considered including the elastic modulus and Poisson's ratio of coating material, tension stiffness ratio and the length of the host. Secondly, an experimental investigation was carried out to determine the reliability of FBGSs embedded in textile composites with different interfaces of fiber/coating and coating/resin and with two configurations, that is, single-ended and dual-ended. The measurement errors induced by the deviation of position and direction of the sensors were estimated. Finally, Volanthen's low-coherence technique was applied to measure the internal strain distribution along the length of FBGSs which were embedded into textile composite.