Evaluation of hole filling repair of carbon fiber reinforced polymer composite laminates

Carbon-Fiber Reinforced Polymer (CFRP) composites have been recently used in many industries specifically aerospace due to their advantages such as rigidity, high strength, low density, and corrosion resistance. The use of composite materials is increasing, in parallel with the damage to which these materials are exposed is also increasing in number. However, despite all the benefits they provide, these materials are not easy to repair. Consequently, various damage repair methods have been developed for composite materials and this issue gaining importance. In this thesis, minor damage to aircraft structures was repaired by the plug repair technology. Firstly, prepreg carbon fiber composite HEXPLY M91/IM7/34RC/UD/194/12K plies were used to produce composite laminate plates. These plies were laid in the atmosphere-controlled environment. Throughout the lay-up process, peel plies were used as backing materials after compaction and vacuum operations were implemented. Then, holes were drilled on these composite laminate plates for plug repairing. The holes were divided into three groups of six specimens and were filled with different materials containing Loctite 9396 adhesive and various amounts of chopped glass fibers. After repairs, Manual Ultrasonic Pulse Echo (MUPE), a non-destructive test method, was used for quality control of the repaired specimens. MUPE results indicated that the repaired specimens were high quality and suitable for testing. Subsequently, tensile tests were carried out for 24 specimens by using an Instron 5985 machine with 250 kN capacity. The results of this study demonstrated that an improvement by up to 5% was achieved with the repair using 50% chopped glass fiber and Loctite 9396 adhesive. It was observed that the mechanical properties of the composite structure were enhanced with the plug repair technology.