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CRAZING AND YIELDING OF REINFORCED COMPOSITES.
Final rept. 1 Jun 66-1 Jun 67,
MCDONNELL DOUGLAS CORP LONG BEACH CA DOUGLAS AIRCRAFT DIV
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The strength and elastic properties of the general multidirectionally oriented composite as functions of the properties of the constituent filament and matrix materials and their geometrical arrangement have been studied. The current state of the art in field of micromechanics was employed for analyses of the strength and elastic properties of the unidirectional monolayer, which is the fundamental unit from which the multidirectionally oriented composite is built. The analyses supplied usable solutions for the elastic properties of the monolayer, but were incapable of predicting the strength performance thereof, except in the case of the longitudinal tension mode. Consequently, semi-empirical estimates of the remaining principal strengths were formulated. The maximum distortional energy failure criterion was employed for the analysis of the strength performance of the multidirectionally oriented composite. As a result of this analysis and the results obtained from tests of the unidirectional monolayer, it is shown that crazing and yielding of the multidirectional composite are caused by the fracture of monolayers within the composite which are critically stressed transversely or in longitudinal shear. Analytical design charts were prepared showing the variation of the mechanical properties of the composite with the basic laminate parameters of filament orientation and volume fraction, void content, and matrix shear modulus. Experimental tests were performed on monolayer and multidirectional laminates fabricated from S-glass filaments and selected epoxy matrix systems. Author
APPROVED FOR PUBLIC RELEASE