Surface Composite Bonding To Repair The Mechanical Analysis And Parameter Optimization

Adhesive bonding has been used to join or repair metallic and composite structure components to achieve or restore their designated structural stiffness and strength. Current studies on the adhesive bonding repair of composites are mainly limited to flat structures. With the wide application of curved composite structures, researches on the boding repair of these kind of structures became more and more necessary. Funded by the Aeronautics Science Foundation, the thesis engages in the mechanical analysis and parameter optimization of the adhesive bonding repair of the curved composite laminates.Considering the shape of the laminates and the specialty of the bond, an analytic model, named Three Solid Element Model, is established. According to analyzing two typical repairing cases, the model is proved correct and reliable, and suitable for the analysis of the repaired structures.Utilizing this model, the influences of the repairing parameters on the effect of patch-bonded repair and repair by replacing damaged parts are analyzed.The influences of the repairing parameters are studied in detail for patch-bonded repair method. The parameters include the dimension and ply drop of patch, the curvature of structure, the defects in adhesive layer, and so on. It is concluded that: (a) Patch size and thickness are the most important repairing parameters. Increasing patch size and thickness of can improve the effect of repair, both of them have an optimized value. The best choice of the patch size along circumference and axis are three and two times of the diameter of the damage hole respectively, while the best choice of the patch thickness if half of the mother plate, (b) Cuneal patch is beneficial to the repair and the optimized cuneal angle is ten degrees. (c) A reasonable choice is to let the lay-up design of the patch to be same as the mother plate. (d) The curvature of structure is bigger, the effect of repair is better. (e) The defects in the adhesive layer, especially those located at the edges of the bonding area, are very harmful to the repaired structure. (f) The author recommends the double lap repairing method if it is realizable.The influences of the repairing parameters, including the ply drop off of patch, the adhesive thickness and the structural curvature, are also studied in detail for repair by replacing damaged parts. It is concluded that: (a) The ply drop off of patchis the most important parameter. Increasing the ply drop off of patch can improve the strength of repaired structure. It has an optimized value, which is about six times of the thickness of a single ply. (b) The adhesive thickness has little influence on the repairing effect. Thick adhesive may leads to the high possibilities of debonding. (c) The structural curvature is greater, the effect of repair is better.