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Results from FAA Program to Validate Bonded Composite Doublers for Commercial Aviation Use
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Abstract
The number of commercial airframes exceeding twenty years of service continues to grow. In addition, Service Life Extension Programs are attempting to extend the “economic” service life of commercial airframes to thirty years. The use of bonded composites may offer the airframe manufacturers and aircraft maintenance facilities a cost effective method to extend the lives of their aircraft. The Federal Aviation Administration has sponsored a project at its Airworthiness Assurance NDI Validation Center (AANC) to validate the use of bonded composite doublers on commercial aircraft.
A specific application was chosen - reinforcement of an L-1011 door frame - in order to provide the proof-of-concept driving force behind this test and analysis project. However, the data stemming from this study serves as a comprehensive evaluation of bonded composite doublers for general use. The associated documentation package provides guidance regarding the design, analysis, installation, damage tolerance, and nondestructive inspection of these doublers. An industry team consisting of an Original Equipment Manufacturer (Lockheed-Martin), an airline (Delta Air Lines), and the AANC was formed. FAA oversight was provided through the Atlanta Aircraft Certification Office and the FAA's William J. Hughes Technical Center. Textron Systems Division provided their expertise in doubler installation and conducted a training class for Delta personnel.
This paper provides an overview of the FAA project and details the design, analysis, and test activities which were conducted in order to gain FAA approval for composite doubler use on commercial aircraft. Structural tests evaluated the damage tolerance and fatigue performance of composite doublers while finite element models were generated to study doubler design issues. Nondestructive inspection procedures were developed and validated using full-scale test articles. Finally, installation dry-runs demonstrated the viability of applying composite doublers in hangar environments. The first use of the project's documentation package was to support the installation of an FAA-approved Boron-Epoxy composite repair on a Lockheed L-1011 aircraft. This represents the first (non-decal) use of a bonded composite doubler on a U.S. commercial aircraft. A second important product of the results cited above is a Lockheed Service Bulletin which allows the door corner composite doubler to be installed on all L-1011 aircraft.
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Citation
Roach, D., "Results from FAA Program to Validate Bonded Composite Doublers for Commercial Aviation Use," SAE Technical Paper 972622, 1997, https://doi.org/10.4271/972622.Also In
References
- Berg S.D. “Process Specification for the Fabrication and Application of Boron/Epoxy Doubles onto Aluminum Structures” Revision No. 6, Textron Specialty Materials Specification No. 200008-001 Dec. 13 1995 Textron Specialty Materials Lowell, MA
- Roach, D. Graf, D. “Damage Tolerance Assessment of Bonded Composite Doublers for Commercial Aircraft Applications” FAA Report SNL96ER0189 under Atlanta Aircraft Certification Office Project SP1798AT-Q November 1996
- Roach, D. “Validation of Bonded Composite Doubler Technology Through Application Oriented Structural Testing” Proceedings of 11th DoD/NASA/FAA Conference on Fibrous Composites in Structural Design August 1996
- Roach, D.P. Proceedings of Int. Conf. on Composite Materials August 1995
- Herderich, D. Shah, S. Izquierdo, I. “Doubler-Composite Reinforcement, P-3 PAX Door, UPR FWD Corner, Composite Reinforcement” Lockheed-Martin Aeronautical Systems Drawing No. LCC-7622-378 April 1996
- Roach, D. Graf, D. “Full-Scale Structural and NDI Validation Tests on Bonded Composite Doublers for Commercial Aircraft Applications” FAA Report SNL96ER0006 under Atlanta Aircraft Certification Office Project No. SP1798AT-Q April 1997
- Jones, K.M. Shah, S. “Composite Repair - Upper Forward Corner of P-3 Door - Model L-1011 Aircraft, Strength and Damage Tolerance Analysis” Report No. LG95ER0157, Part of Documentation Package for FAA Atlanta Aircraft Certification Office Project No. SP1798AT-Q October 1996
- Walkington, P. Roach, D. “Ultrasonic Inspection Procedure for Bonded Boron-Epoxy Composite Doublers,” Sandia Labs AANC Specification AANC-PEUT-Comp-5521/4-004; FAA Document under Atlanta ACO Project SP1798AT-Q January 1997
- Roach, D. Moore, D. Walkington, P. “Nondestructive Inspection of Bonded Composite Doublers for Aircraft” Proceedings of SPIE Conference on Nondestructive Evaluation of Aging Aircraft December 1996
- Roach, D. Walkington, P. “NDI Development and Validation for Bonded Composite Doubler Applications on Commercial Aircraft” FAA Report No. SNL96ER0007 under Atlanta ACO Project No. SP1798AT-Q April 1997