Accession Number : ADA305052

Title :   Effect of Moisture on the Fatigue Behavior of Graphite/Epoxy Composite Laminates.

Descriptive Note : Technical memo.,

Corporate Author : NATIONAL AERONAUTICS AND SPACE ADMINISTRATION WASHINGTON DC

Personal Author(s) : Ramani, S. V. ; Nelson, H. G.

PDF Url : ADA305052

Report Date : JAN 1979

Pagination or Media Count : 50

Abstract : The effect of moisture on the fatigue behavior of several multidirectional graphite/epoxy composite laminates has been investigated. In compression-compression fatigue (R = 10) studies performed on 0/+ OR - 45/90 sub 2s and 0/+ OR - 45/0 sub 2s, T300/934 laminates, the fatigue life, N sub f, at a given stress amplitude, and the apparent fatigue limit, at 5,000,000 cycles, are shown to be significantly reduced by the presence of from 1.4 to 2% moisture. The form of the moisture distribution in the specimen (gradient and flat profile) was considered to establish the influence of accelerated moisture conditioning on fatigue behavior. For the gradient specimens having an average moisture content of 1.4%, N sub f was reduced by a factor of 8 at all stress levels investigated. Corresponding reduction in N sub f for the flat moisture profile specimens at the same average moisture content was comparatively smaller, being about a factor of 5 from the value in dry specimens. X-ray radiographic analysis of damage accumulation in compression compression fatigue revealed interlaminar cracking to be the dominant mode of failure responsible for the observed enhanced cyclic degradation of moisture-conditioned specimens. This finding is corroborated by the observed systematic reduction in interlaminar shear strength as a function of moisture content, which, in turn, increased the propensity for delamination under cyclic compressive loads. Residual strength measurements on cycled specimens indicate, significant strength reductions at long lives, particularly in moisture-conditioned specimens. (MM)

Descriptors :   *MOISTURE CONTENT, *EPOXY LAMINATES, *GRAPHITE EPOXY COMPOSITES, FATIGUE LIFE, DEGRADATION, X RAYS, STRENGTH(MECHANICS), WEIGHT, TAPES, TRANSPORT AIRCRAFT, LAMINAR FLOW, RADIOGRAPHY, ACCELERATED TESTING, COMPRESSIVE PROPERTIES, CYCLIC LOADS, SHEAR STRENGTH, MOISTUREPROOFING.

Subject Categories : Laminates and Composite Materials

Distribution Statement : APPROVED FOR PUBLIC RELEASE