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Introduction to Developing, Modification, and Customization of the Guidelines for Replacement of Metal Patch Repairs with the Composite Patches

Davoodi Moallem, Misam | 2017

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 50631 (45)
  4. University: Sharif University of Technology
  5. Department: Aerospace Engineering
  6. Advisor(s): Abedian, Ali
  7. Abstract:
  8. The phenomenon of aging causes a great deal of damage to the airborne structures for which there is a specific maintenance instruction, or if an unexpected damage occurs in specific area of a structure, this damage must be repaired and a special repair process must be designed for it. However, due to the diversity of damages and also variations of the implemented loads, the load is transferred to other structural elements, hence, it is necessary to extend the life of the structure in order to identify these loaded elements and reinforce the applied forces. First, this phenomenon involves a design of a large number of metal patches, where a large number of drills have to be made in the body in order to connect them to each other. Secondly, this number of patches increase the weight of the structure, dramatically. Therefore, composite patches are used instead of metal patches in the life extension industry in order to prevent these disadvantages. But, due to long term sanctions and unfamiliarity of the country's airline industry to this phenomenon, utilizing of these composite patches is not significant. Therefore, this research is carried out to show that not only the safety of the structure is not damaged by replacing composite patches instead of metal patches, but also the advantages of adhesive joints and the low weight of patches increase the safety of the air industry considerably. In this study, a piece of air structure is under the repair of a composite patch to provide a basis comparison for the performance of these patches. The repair patch was modeled using modern simulation methods in ABAQUS software and the integral J, XFEM and CZM capabilities for crack modeling in metal structure, crack growth in metal structure, and failure growth in adhesive have been used, respectively. At first, the repair effect has been investigated in different lengths of crack damage and the repair time has been determined according to the critical crack length and the design, impact, and cost effectiveness requirements. Then, the repair of damaged structures was conducted using two types of metal patches and composite patches, and the load bearing tolerance before and after metal and composite repairs was compared. In the last step, the life of the main structure in the repair with metallic and composite patches is compared, using metallic and composite patches simulation and the amount of strain in them along with analytical relations of the life strain in different loadings. In the composite repair due to the lack of screw and rivet drilling, stress concentration in cavities does not created and also a smooth stress distribution in the adhesive and the composite patch is created despite of the metallic patch. According to these reasons, the use of composite patches instead of metallic patches has been suggested to the country's industry
  9. Keywords:
  10. Finite Element Modeling ; Composite Patch Repair ; Stress Analysis ; Aero Industry ; Metal Patch ; Exhaust Life

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