| During service of aircrafts, many kinds of damages inevitably appear in the metal structures and the most commom damage is fatigue crack. To extend the serve life of aging aircraft, cracked structures must be repaired to improve the residual strength and recover its carrying capacity. In order to enhance the flexibility and increase the effective load and voyage, the structural weight should be reduced as much as possible. Compared with the use of metal, bonded composite patches to reinforce the cracked structure is more promising due to the high stiffness, high strength, good anti-fatigue performance and designability of the composite. Therefore, research on bonded composite patch repair technique will be of very high actual application value.In this thesis, taking cracked aluminum alloy skin repaired with bonded patch for example, the bonded composite patch repair technique as well as the stress intensity factor is studied. The main content of the article is as following: (1) The feasibility and accuracy of the method that adhesive is simulated by COH3D8 element is verified by using finite element analysis; (2) Finite element model is established based on parametric modeling technology, and the stress intensity factor of single- and douvle-sided repair is compared with each other; (3) Taking cracked plates repaired with single-sided composte patch for an example, the influence of the parameters of composite patch and adhesive on the stress intensity factor is researched; (4) The ply orientation of the stacking sequence as well as the size of sixteen kinds of patches with different thickness is optimized with Genetic Algorithms and Sequential Quadratic Programming method by iSIGHT and ABAQUS. (5) Finally,the optimal repair scheme is determined after comparing the sixteen different optimization results.The analysis techniques and results in this thesis would provide reference for practical application. |
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