Fibre Bragg grating strain sensor and study of its packaging material for use in critical analysis on steel structure

Strain studies in civil structures, aircrafts, oil pipelines, etc. are pivotal in avoiding unexpected failures. Long-term strain study of structures also helps in setting the design limits of similar structures. Conventionally, most structures rely on maintenance schedules, visual inspection and a few conventional sensors. But the high cost of maintenance, lack of precision in visual inspection and susceptibility of sensors to harsh environmental conditions have made structural health monitoring (SHM) a necessity.Over the past few decades, fibre Bragg grating (FBG) sensors have emerged as a suitable, accurate and cost-effective tool in SHM. Fibre Bragg gratings are obtained by creating periodic variations in the refractive index of the core of an optical fibre. These periodic variations are created by using powerful ultraviolet radiation from a laser source. Periodic structure acts as a Bragg reflector of particular wavelength. Minute change in the periodic structure due to external perturbation will cause appreciable wavelength shift. This shift in turn can be translated to measurand related to perturbation. The main advantages of FBGs over other optical sensor schemes are its low cost, good linearity, wavelength multiplexing capacity, resistance in harsh environments and absolute measurement. FBG sensor technology is now on the verge of maturity after almost two decades of active research and development in this field. Efforts are now concentrating on delivering complete FBG sensor systems including front-end electronics.This paper demonstrates with the aim to provide different design and experimental packaging procedures of indigenously developed FBG sensors for strain measurement. Various model of loading on FBG have been tried to explore with particular attention on the primary packaging of the sensor for application on steel cantilever structure and cement concrete. Preliminary packaging has been done with composite materials such as epoxy resin casting and fibre reinforced plastic (FRP) composites. Encouraging results are obtained and presented in this paper. The results are compared with the standard FBG sensors and with mechanical strain gauge.