A Proposed Approach for Certification of Bonded Composite Repairs to Flight-Critical Airframe Structure
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A Proposed Approach for Certification of Bonded Composite Repairs to Flight-Critical Airframe Structure Alan A. Baker
Received: 12 June 2010 / Accepted: 4 August 2010 / Published online: 4 September 2010 # Her Majesty the Queen in Right of Australia, as represented by the Defence Science and Technology Organisation 2010
Abstract This paper focuses on the difficult issue of the certification of adhesively bonded repairs in applications where credit has to be given to the patch for restoring residual strength in flight-critical structure. The scope of the paper includes both adhesively bonded composite repairs to composite components and composite repairs to metallic components. After discussing typical bonded repairs and, as a baseline, procedures currently used to certify new structure, a proposal is made which may constitute an acceptable basis for the structural certification of repairs. The key requirement is to demonstrate an acceptably low probability of patch disbonding during the remaining life of the structure. The focus is on one-off repairs where development of a comprehensive certification procedure based even on limited testing will be infeasible:
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Firstly, a decision process is undertaken to establish if there is indeed a certification issue. That is situations where flight safety depends on the structural integrity of the repair patch. Secondly, especially if there is a certification issue, a rigorous repair design approach is undertaken, based on a generic data base previously obtained from the testing of bonded joints representing the critical regions in the repair. Thirdly, the actual repair system is validated to ensure the required strength and potential durability has been achieved. This includes Boeing wedge testing, a proven quality control procedure for the adhesive bonding process. Finally, if this approach is considered inadequate then the option is to include proof testing and/or structural health monitoring for assessment of the actual through life structural integrity of the repair system; however, this would only be feasible for special cases where the considerable extra cost and complication can be justified.
Keywords Bonded repairs . Aircraft . Debonding . Fatigue . Structural health monitoring A. A. Baker (*) CRC Advanced Composite Structures (CRCACS) and Defence Science and Technology (DSTO) Air Vehicles Division, Melbourne, Australia e-mail: [email protected]
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Appl Compos Mater (2011) 18:337–369
1 Introduction When the residual strength of flight-critical airframe structure is judged to have fallen (or has the potential to fall) below design ultimate strength it must be repaired to restore strength or replaced if repair is infeasible or not cost-effective. The repair must function in the service environment of the aircraft for the remaining life of the structure. Bonded repairs, based on adhesively bonded composite patches or reinforcements, where appropriate can provide a highly structurally-efficient and cost-effective means of restoring residual str
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