Viability of using an embedded FBG sensor in a composite structure for dynamic strain measurement

In this paper, the utilisation of an embedded fibre-optic Bragg grating (FBG) sensor to measure dynamic strain of a clamped-clamped glass fibre composite beam is presented. A dynamic calibration test for strain measurement of the composite beam by the embedded FBG sensor and surface mounted strain gauge, at different vibration frequencies was conducted. Experimental results shown that the relationship between the photovoltage and strain measured by the embedded FBG sensor and strain gauge, respectively exhibited a linear fashion, when the strain value exceeded 1 με. Below this strain limit, the strain gauge could not precisely respond to the true strain of the beam. However, the signal extracted from the FBG sensor could truly reflect the strain of the beam at high vibration frequency condition. The first-two natural frequencies can be sharply indicated by a captured spectrum measured from the FBG sensor. Due to the out-of-plane vibration amplitude decreases with increasing the vibration frequency, the second natural frequency could not be clearly measured by the results extracted from the strain gauge.