Selection of Optical Fibers Paths and Sensor Locations for Monitoring the Integrity of Composite Patching

In order to select appropriate optical fiber paths and locations for Bragg Grating sensors, the research group has studied a classically cracked metallic structure repaired with a `smart' bonded composite patch using finite element analysis. The patch was bonded over a cracked aluminum plate by means of a thin adhesive layer. The primary loading axis of the metal was assumed parallel to the direction of the optical fibers used. A variety of optical fiber paths and sensor positions was considered, along with their ability to measure the developed strain field and to trace the position of the crack tip. It was concluded that a fiber optics network is indeed capable of tracing effectively the critical parameters required for the monitoring of structural integrity of the composite patch reinforced structures (i.e. strains developed at the patch and at the tip of the crack). It was found that at least two Bragg Grating sensors should be used at each side of the crack per optical fiber in order to enable adequate monitoring of the strain field and the position of the crack tip. Different locations should be chosen according to the configuration of the patch (one or two-sided).