Research On Basic Theories And Verifications Based On The SCARF Bonding Repair

Because of their many advantages of performance, such as light weight, high strength, fatigue resistance, corrosion resistance and so on, carbon fiber reinforced polymer matrix composite structures have been widely applied in aeronautical industry. However, they would suffer from various kinds of damage during the whole service life inevitably, such as layering, scratch, crack, wear, etc. In order to ensure that the repaired composite structures can meet the qualification in the continuous airworthiness of aircraft, maintenance effects must be accordingly validated. By using the Boeing carbon fiber/epoxy resin composites as the research object, based on the SCARF bonding repair, firstly the internal correlation between repair surface micro physical/chemical properties and the relatively repair effectiveness was studied, and then the influences of each repair parameter on the effectiveness of the repair were verified by tests validation method (MC2) and analysis/computation validation method (MC4), finally combined with engineering practice, the specific repair parameters were proposed. The main works are as follows:(1) Research on the internal correlation between repair surface properties and bonding strength;Based on the micro physical/chemical properties of material surface/interface researching, combining with the adhesion theories, which include the mechanical interlocking theory, the rheological theory and the adsorption theory, the internal correlation between repair surface properties and bonding strength was deeply studied at the proper perspective micro-level.(2) Research on the influences of each repair parameters on the effectiveness of the repair and failure models;Based on the SCARF bonding repair test of composite laminates, the tests of tensile mechanical properties on the specimens were conducted, then four kinds of failure models were obtained. The influences of four repair parameters (grit number of sandpapers G, scarf angle β, number of external plies N, and moisture content of the specimen and the test temperature RTD/ETW) on the effectiveness of the repair were studied. (3) Research on the repairing verification of composite structures.The repairing verification of composite structures was taken by using method MC2and MC4. Based on the theories of composite laminates, by using the finite element analysis software ANSYS, three-dimensional repair structure models were established to study the repair effectiveness of two parameters:number of external plies N and scarf angle P, then the ultimate failure load and location of the repaired laminates were calculated, the comparison and analysis between the simulation and tests results indicated the effectiveness of the repair structure models.Based on the above theory research, experiment and calculation analysis, for the Boeing composite material system by using SCARF bonding repair, the recommended maintenance parameters for grit number of sandpaper, external plies and the optimum scarf angle are100,1and4°respectively. And it’s suggested that it’s better to take repair work under the condition of normal temperature, ventilating and lower humidity.