Experimental demonstration of health monitoring of composites using FBG sensor arrays

Composite materials combine the advantages of lightweight and high strength. This is in particular of interest for the development of large constructions e.g. aircraft, space applications, wind turbines etc. One of the shortcomings of using composite materials is the complex nature of the failure mechanisms which makes it difficult to predict the remaining lifetime. Therefore, condition and health monitoring are important for using composite materials for the critical parts of a construction. Different types of sensors are used to monitor composite structures. These include ultrasonic, thermography, shearography and fiber optics. Optical fiber sensors can be surface mounted or embedded in the composite construction to provide the unique advantage of in-operation measurement of mechanical strain and other parameters of interest. This is identified as a promising technology for Structural Health Monitoring (SHM) or Prognostic Health Monitoring (PHM) of composite constructions. Among the different fiber optic sensing technologies, Fiber Bragg Grating (FBG) sensors are the most mature and widely used ones. FBG sensors can be realized in an array configuration with many FBGs in a single optical fiber. In the current project, different aspects of using embedded FBG for composite wind turbine monitoring are investigated. The demonstration of using FBG sensor array for temperature and strain sensing and monitoring of a 5.8 m long scale model of a glass fiber monopile is investigated. The results indicate that the embedded FBGs successfully show the temperature increase during curing of the resin. During the static and dynamic tests, the embedded FBG sensors provided accurate monitoring.