Accession Number : ADA301582

Title :   Fatigue Degradation in Compressively Loaded Composite Laminates.

Corporate Author : NORTHROP CORP HAWTHORNE CA AIRCRAFT DIV

Personal Author(s) : Ramkumar, R. L.

PDF Url : ADA301582

Report Date : APR 1981

Pagination or Media Count : 157

Abstract : This report describes an experimental program conducted to assess the effect of imbedded delaminations on the compression fatigue behavior of quasi-isotropic, T300/5208, graphite/epoxy laminates. Teflon imbedments were introduced during panel layup to create delaminations. Test specimens were 64-ply thick, and had 3.81 cm square test sections that were unconstrained laterally during compression testing. Static and constant amplitude (R=10, omega= 10 Hz) fatigue tests were conducted. S-N data and half-life residual strength data were obtained. During static compression loading, the maximum deflection of the buckled delaminated region was recorded. Under compression fatigue, growth of the imbedded delamination was identified as the predominant failure mode in most of the test cases. Specimens that exhibited other failures had a single low stiffness ply above the Teflon imbedment. Delamination growth during fatigue was monitored using DIB- enhanced radiography. In specimens with buried delaminations, the dye-penetrant (DIB) was introduced into the delaminated region through a minute laser-drilled hole, using a hypodermic needle. A low-kV, microfocus, X-ray unit was mounted near the test equipment to efficiently record the cyclic growth of buried delaminations on Polaroid film. jg p.6

Descriptors :   *DEGRADATION, *COMPOSITE MATERIALS, *LAMINATES, *FATIGUE(MECHANICS), *DELAMINATION, *COMPRESSIVE PROPERTIES, COMPRESSION, GROWTH(GENERAL), PANELS, STATIC LOADS, STIFFNESS, DEFLECTION, FAILURE, TEST METHODS, FABRICATION, TEST EQUIPMENT, LASERS, X RAYS, STRENGTH(MECHANICS), CYCLES, HOLES(OPENINGS), RESIDUALS, EPOXY LAMINATES, SEPARATION, PHOTOGRAPHIC FILM, BURIED OBJECTS, AMPLITUDE, RADIOGRAPHY, FATIGUE TESTS(MECHANICS), DRILLING, GRAPHITE EPOXY COMPOSITES, TETRAFLUOROETHYLENE RESINS, HALF LIFE, HYPODERMIC INJECTIONS.

Subject Categories : Laminates and Composite Materials
      Organic Chemistry
      Mechanics

Distribution Statement : APPROVED FOR PUBLIC RELEASE