Optimization of Embedded Optical Sensor Location in Composite Repairs

Abstract

Optical fibers were embedded in a bonded composite patch in order to detect the strain field variations of a load bearing structure. The study concentrated on a classical cracked metallic structure repaired with this ‘smart’ patch and using finite element analysis. Six different laminates constituted the model of the composite patch, a layered structure with three-dimensional elements. Each laminate is assumed to have different mechanical properties, according to the case under any specific study, in order to simulate different stacking sequence or material used. A resin rich ‘eye’ pocket has also been modeled in order to simulate the exact form of the resin area produced during the manufacturing process. The patch is bonded over a cracked aluminum sheet through a small adhesive layer placed in between. External loads were applied only on the metal structure, as in a real repair case. The primary loading axis of the metal was assumed to be parallel to the direction of the optical fibers. The different nature of the materials that form the composite patch generated complex mechanical interactions between the fibers and the surrounding material, resulting in a complicated stress field along the optical fiber sensor, which affects the structural integrity of both the patch and the repair. Different optical fiber positions were considered, moving towards the horizontal and vertical dimensions of the patch, as well as different patch architectures (single and double patch configurations), with the hope of studying their effect on the structural integrity of the patch.