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This paper describes the effects of manufacturing defects and service-induced damage on the static and fatigue strength of aircraft composite structures.
Seven manufacturing defects associated with mechanical fasteners were investigated; out-of-round holes, delaminations at the exit side of drilled holes, porosity, improper fastener seating depth, tilted countersinks, interference fit, and multiple fastener installation and removal cycles. Both static and fatigue test results are described, along with correlation with analysis techniques. The interaction of the effects of these defects on hole wear, measured in fatigue tests of structural joints, is described.
The effects of two types of service-induced damage are also described; low-energy impact damage and penetration damage. The relative sizes of visible and non-visible damage as determined by visual and nondestructive inspection techniques are compared. An evaluation of stitching and the inclusion of glass or Kevlar fiber buffer strips to improve the damage tolerance of carbon/epoxy structures is included. Results of tests of carbon/epoxy panel structures are discussed. Correlation of experimental results with predicted residual static strength is good.
composite materials, composite structures, graphite laminates, epoxy laminates, impact damage, defects, residual strength, static strength, fatigue strength, fatigue (materials), postbuckling
Chief technology engineer, Strength, McDonnell Aircraft Company, St. Louis, MO