Strength, Structure, and Fracture Properties of Ceramic Fibers Produced from Polymeric Precursors: I, Base-Line Studies

Classical brittle failure has been observed for ceramic fibers produced by pyrolysis from three different polymer precursors. Characterization by SEM fractography methods has shown typical flaw-mirror-mist-hackle morphology and such study has provided observations for understanding the fracture mechanisms. The gage length dependence of tensile strength combined with the fractography study showed the flaw-controlled failure mechanism of all the ceramic fibers. Systematic failure types have been identified for specific strength ranges. Complementary study of the microstructure and chemical structure by TEM, X-ray diffraction, and electron spectroscopy for chemical analysis (ESCA) has shown the nature of the bulk ceramic to be predominantly random and glassy even in the case of a fiber with microcrystalline β-SiC. Fracture mechanics calculations have shown the fibers all behave as glasses.