THE COMPRESSIVE FRAGMENTATION PHENOMENON - USING MICROCOMPOSITES TO EVALUATE THERMAL-STRESSES, SINGLE-FIBER COMPRESSIVE STRENGTHS, WEIBULL PARAMETERS AND INTERFACIAL SHEAR STRENGTHS

A continuous fragmentation test, using thermal stresses, has been deve loped to determine the compressive strengths and Weibull parameters re quired to characterize the strength-length dependence of carbon fibres from a single test procedure. The onset of thermal stress in the fibr e is determined in situ and for amorphous systems is commensurate with the glass transition temperature of the microcomposite matrix. It is shown that the compressive strengths are considerably lower than the a ssociated tensile strengths for all the fibres tested and that an elec trochemical oxidation surface treatment and a polytetrafluoroethylene coating do not significantly affect the compressive strengths or compr essive Weibull shape parameters with respect to the unmodified fibres. The mechanisms of stress transfer have been investigated and a compre ssive stress profile has,been proposed that can determine the interfac ial shear strength from fundamental scientific principles. The tempera ture dependence of the interfacial shear strength is investigated for carbon-fibre-polycarbonate microcomposites and the values obtained are concordant with a system that has weak interfacial bonding.