AIAA-30895-180 - JOURNAL OF AIRCRAFT Vol 44 No 6...

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Bending of Bonded Composite Repairs for Aluminum Aircraft Structures: A Design Study Randal J. Clark and Douglas P. Romilly University of British Columbia, Vancouver, British Columbia V6T 1Z4, Canada DOI: 10.2514/1.30895 This paper describes an experimental and nite element study of a bonded composite repair applied to a metallic aircraft structure. The experimental study involves the fatigue testing and fractographic examination of 2024-T3 aluminum plates repaired with boron/epoxy composite patches. The two plates are tested simultaneously in a sandwich panel con guration with and without an aluminum honeycomb spacer to provide bending restraint. The specimen was heavily instrumented, with strains being measured on the surface of the patch at many locations, thus allowing the validation of a three-dimensional nite element model and an assessment of the effects of geometrically nonlinear bending, buckling, and crack closure on the mechanical response and strength of the repair. The experimental and nite element results illustrate the important in uence of bending and composite failure modes on thelife andstrengthof the repair.The authorsusethe experimental resultsandthe validated nite element analysisto evaluate the effectiveness of the methods and data currently available in the open literature for damage-tolerance substantiation, and then, by applying probabilistic methods and the principle of compounded conservatism to the ndings, propose a new process for classifying bonded repairs and assigning requirements for testing and inspections. Nomenclature a = crack length E = Young s modulus G = shear modulus or strain energy release rate K = stress-intensity factor p = pressure r = radius of the patch t = thickness ± = coef cient of thermal expansion ² = Poisson s ratio ³ = normal stress ´ = shear stress Subscripts a = adhesive property b = bending m = membrane p = plate property I = opening mode II = sliding mode I. Introduction A BONDED composite patch is a ber-reinforced epoxy doubler used to reinforce weak structure or repair cracked aircraft structure. The patch acts both to reduce stresses in the underlying structure and to restrict the opening of cracks that may lie beneath the structure. These effects and the smooth load transfer inherent to bonding offer the potential for a signi cant increase in fatigue life when compared with mechanically fastened repairs (shown in Fig.1).Thetechnologyalsooffers improvementsin cost,weight,and inspectability. The main barrier to the widespread use of this technology is the lack of a comprehensive process for damage- tolerance analysis, particularly regarding the mechanical assessment of the structure in the presence of signi cant bending loads, which can lead to early failure. The other signi cant impediment is the assurance of bond durability for repairs applied in a maintenance and repair facility.
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This note was uploaded on 02/24/2011 for the course AERO 520 taught by Professor Rs during the Spring '11 term at Istanbul Technical University.

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AIAA-30895-180 - JOURNAL OF AIRCRAFT Vol 44 No 6...

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