The Relationship of Structure to Properties in Graphite Fibers. Part 1
Technical rept. May 1970-Apr 1971
RENSSELAER POLYTECHNIC INST TROY NY MATERIALS DIV
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Three-dimensional structural models of a range of carbon fibers having several precursor bases and widely differing moduli and strengths have been developed. Experimental techniques employed included x- ray and electron diffraction, and electron, scanning electron, and optical polarized light microscopies. A new etching technique, reverse radio frequency sputtering, was shown to reveal fiber internal structural features. Results show that the morphology of the basic structural unit of carbon fibers is that of rippled ribbons consisting of parallel layers of basal planes. With increasing moduli the ribbons become progressively thicker, straighter and better aligned with respect to the fiber axis. An associated development of a radial preferred alignment occurs with increasing modulus. In some very high modulus fibers, preferred orientation of the crystallographic a-axis exists. The combination of radial and axial structural information is used to explain some aspects of fiber mechanical behavior. A BETTER ALIGNED AXIAL STRUCTURE GIVES A HIGHER TENSILE MODULUS, BUT THE BONDING BETWEEN ADJACENT RIBBONS IN THE FIBER DECREASES ALTERING THE FIBER FRACTURE MODE AND STRENGTH.