Size Effect and Strength Variability of Unidirectional Composites.
Interim rept. Jan-Sep 83,
CALIFORNIA UNIV LOS ANGELES DEPT OF MATERIALS SCIENCE AND ENGINEERING
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Statistical theories have been proposed for damage accumulation and tensile failure of unidirectionaly reinforced fibrous composites. These theories involve the mechanical properties of the constituent fibers, the geometry of the composite, and some inadequately known functions such as stress distribution in the vicinity of single and multiple fiber breaks. As a result in trying to correlate theory and experiment some quantities have to be treated as unknown parameters. It was found that use of Hedgepeth and Van Dykes stress concentration factors led to good agreement between theory and Bullocks data on graphite epoxy only when the overload length of fiber at crack tips was assumed to have an unrealistically large value. A possible explanation is that the Hedgepath and Van Dyke stress concentration factors were calculated for composites the fiber spacing is quite irregular. A theory is developed for strength of irregularly constructed composites and compared with experiment. Taking the effect into account improves agreement in the case of one experiment and impairs agreement in the case of another.
- Laminates and Composite Materials