| Nowadays advanced composite materials such as boron and carbon fibers have drawn a great deal of attention in the aviation industry, due to their high strength to weight ratios. As the use of these materials for the manufacture of aircraft components has become well established in the industry, adhesively bonded repairs of aluminum aircraft structures with composite materials should be given more considerations and further developed. Repair of civil aircraft primary structure such as spherically or complex contoured fuselage skins, webs, frames, stringers and longerons with composite materials are of particular interests.; The present study investigated the repair of a center-cracked aluminum panel with a precured composite patch. To be aligned with the common repair method for bonded aircraft parts, single-sided patching of a cracked panel was studied. Both experimental and finite element methods were applied. Two types of tests were conducted: tensile and tension-tension fatigue tests. For the tensile test the residual strength of the specimen was used as an index to measure the effectiveness of a repair, while for the fatigue test, the crack initiation, propagation rate and total number of load cycles accumulated prior to a complete failure were used. The graphite/epoxy composite was chosen to be the reinforcing material for all the tests.; An efficient finite element model was also developed to evaluate the performance of a bonded repair. By the model, the strain energy release rate of a cracked panel can be determined. Comparisons of the finite element results with the present experimental and other published results were made to ensure the accuracy of the model. Patch optimization was then made possible through a study of the relevant non-dimensional parameters for bonded repair. In sum, the present results show that bonded patches made from graphite/epoxy or other advanced composite materials can be very effective in the repair of thin aluminum structures and the repair performance can be easily assessed and optimized by the present finite element model. |
