Influence of Stress Interaction on the Behavior of Off-Axis Unidirectional Composites
The influence of combined states of stress on the shear response along material principal directions in off-axis, unidirectional, composite coupons is examined for systems whose matrix material obeys the von Mises yield condition. Such analysis is motivated by trends in experimental data observed for at least two composite systems that indicate deviations from pure shear behavior along material directions for various off-axis configurations.
The yield function for plane stress of a transversely isotropic composite lamina consisting of stiff, linearly elastic fibers and von Mises matrix material is formulated in terms of Hill’s elastic stress concentration factors and a single plastic constraint parameter. The above are subsequently evaluated on the basis of observed average lamina and constituent response for the Avco 5505 boron-epoxy system. It is shown that inclusion of residual stresses in the yield function together with the incorporation of Dubey and Hillier’s concept of generalized yield stress for anisotropic media in the constitutive equation correctly predicts the trends observed in experiments. The incorporation of the strong axial stress interaction necessary to predict the correct trends in the shear response is directly traced to the residual axial stresses in the matrix induced during fabrication of the composite.
KeywordsGraphite Boron Epoxy Posite Eter
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