Aging of U.S. Air Force Aircraft Final Report (1997) / Chapter Skim
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Executive Summary
Executive Summary
Pages 1-8
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recommend and prioritize specific technology opportunities, complementary to the efforts of industry, the Federal Aviation Administration, the National Aeronautics and Space Administration, and international organizations. The topics asked to be considered by the committee include fatigue, corrosion-fatigue interactions, and stress corrosion cracking; corrosion prevention and mitigation; nondestructive inspection; maintenance and repair; and failure analysis and life prediction technologies.
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, and the results of stress analyses and strain surveys to perform simulative testing and crack growth analyses to establish safety limits and safety inspection requirements for all critical areas to investigate the potential effects of corrosion on those factors that could affect safety limits and safety inspection requirements · to continue to improve methods of identifying fatiguecritical areas and flight load conditions to continue to improve NDE techniques that are sensitive enough to detect small cracks in multilayered and hidden structures to support safety inspections Economics and Readiness The economic burden associated with the inspection and repair of fatigue cracks can be expected to increase with age AGING OF U.S. AIR FORCE AIRCRAFT until the task of maintaining aircraft safety could become so overwhelming and the aircraft availability so poor that the continued operation of the aircraft is no longer viable.
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The long-term R&D program includes those efforts that the committee believes will take longer than three to five years to achieve a mature technology that could be adopted by industry or the Air Force air maintenance organizations but nevertheless should be initiated now or continued if they already have been initiated. Near-Term Engineering and Management Tasks The Air Force postproduction force management process, involving the implementation of inspections and modifications derived from the ASIP tasks and the results of DADTAs, has been a huge success in protecting the structural safety of the force aircraft for more than two decades.
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the inspection and modification requirements in the force structural maintenance plans should be updated to reflect any changes in the baseline operational spectra and any additional critical areas that were identified, and (2) an individual aircraft tracking program for each aircraft weapon system should be updated to reflect additional critical areas that need to be tracked.
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The recommended longterm focus is on the development of analytical design, structural assessment, and life prediction tools for repairs and repaired structures and to develop improved Recommendation Description Objective Timing Fatigue None Corrosion Prevention and Control Evaluate durability of new protective coatings Basic research in corrosion prevention and control Basic research in coating durability Stress Corrosion Cracking Affordable upgrades in SCC prevention Evaluation of SCC protection systems Fundamental research in SCC prevention Nondestructive Evaluation Evaluate, validate, and implement NDE equipment and methods Develop integrated quantitative NDE capability Automation of wide-area NDE inspections Maintenance and Repair None Page 58 Page 59 Page 60 Page 60 Page 60 Page 61 Page 64 Page 66 Page 68 B B B B B B B B B Near term Long term Long term Near term Near term Long term Near term Long term Long term
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(i.e., AGING OF U.S. AIR FORCE AIRCRAFT TABLE ES-2 Prionty-2 Near-Term and Long-Term Research Recommendations Recommendation Description Objective Timing Fatigue Fail-safe residual strength prediction methods Improve current methods to estimate onset of WFD Methods to predict dynamic responses Effect of joint pillowing on fail-safety WFD crack formation and distribution relationships Analytical prediction of WFD crack distribution functions Validation of analytical WFD methods Crack growth threshold behavior Analytical methods to predict dynamic behavior Dynamic load monitoring and alleviation Effect of environment on growth of small cracks Effect of flaw morphology on crack growth Corrosion Prevention and Control Laboratory test protocol for accelerated corrosion testing Methods for early detection of corrosion Corrosion rates for major corrosion types Stress Corrosion Cracking Residual stresses and their alleviation SCC susceptibility of Air Force alloys Life prediction methods for SCC Nondestructive Evaluation NDE automation, data processing, and analysis Hybrid inspection technologies NDE to assess composite repairs Maintenance and Repair Guidelines to implement advances in bonded repairs Solid model interfaces to simulate repair methods Reduce cost of materials and structures substitution Repair design guidelines for high-cycle fatigue problems Expert system for design and analysis of repairs Connnon database for repair lessons learned Page 66 Page 67 Page 67 Page 69 Page 70 Page 71 Page 71 Page 71 Page 72 Page 50 Page 50 Page 52 Page 55 Page 50 Page 51 Page 51 Page 52 Page 53 Page 53 Page 55 Page 56 Page 57 Page 58 Page 59 A B A A A A B B B A A Near term Near term Near term Near term Long term Long term Long term Long term Long term Long term Long term Long tenn B Near term B Near term B Long term Page 61 Page 61 Page 62 B Long term A Near term A Near term B B B B B B B B B Near term Long term Long term Near term Near term Near term Near term Long term Long term would enable the Air Force to address significant technical problems)
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From page 7... ...
through development of improved methods to evaluate and analyze fatigue and stress corrosion cracking. The remainder of the recommendations deal with improvements in maintenance costs and force readiness (Objective B)
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