SEDL / STP / STP636-EB / STP27978S

Fatigue Behavior of Composites Under Different Loading Modes

Sims, DF
Research project engineer, Bell Helicopter TextronSouthwest Research Institute, Fort WorthSan Antonio, TexTex

Brogdon, VH
Research analysis engineer, Bell Helicopter Textron, Fort Worth, Tex

Pages: 21    Published: Jan 1977

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Abstract

The fatigue characteristics of S-glass/epoxy (Scoth-ply SP-250-SF1) and graphite/epoxy (Rigidite 5209-T300) laminates were studied for tension and shear loading. Emphasis was placed on fiber orientations where the matrix contribution to fatigue strength is significant. A general regression curve was used for data analysis, and a two-parameter Weibull model was used for reliability studies. An existing plane-stress macroscopic failure theory for static strength was extended to predict fatigue strength. It was found that the fatigue failure theory provides a conservative approach to first-ply failure which should be useful for preliminary design of composite structures.