Damage Detection in Composite Repair Patches using Embedded Optical Sensors

In situ cured composite material patches are quite effective for repairing metallic or composite structures, due to their ability to adapt to complex shapes, and the smooth load introduction. A key issue for a wide acceptance of this repair procedure is the need of robust techniques to assess the quality of the repair, which could be done either with piezoelectrics or embedded fibre optics sensors. In this work, the results of an experimental program for repairing composite laminates, with embedded FBGs are presented. Square repair patches, size 200 X 200 mm, with stepped laps were made on a cross-ply laminate, with several sensors embedded at the bond line. The plate was loaded under biaxial tensile loads, and progressive failure was monitored. The changes in the strain field under incipient damage are discussed. It is demonstrated that this is a promising approach towards smart patches technology.