The compressive fragmentation phenomenon: Using microcomposites to evaluate thermal stresses, single fibre compressive strengths, Weibull parameters and interfacial shear strengths

A continuous fragmentation test, using thermal stresses, has been developed to determine the compressive strengths and Weibull parameters required to characterize the strength-length dependence of carbon fibres from a single test procedure. The onset of thermal stress in the fibre is determined in sit u 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 associated tensile strengths for all the fibres tested and that an electrochemical oxidation surface treatment and a polytetrafluoroethylene coating do not significantly affect the compressive strengths or compressive Weibull shape parameters with respect to the unmodified fibres. The mechanisms of stress transfer have been investigated and a compressive stress profile has been proposed that can determine the interfacial shear strength from fundamental scientific principles. The temperature 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.