EFFECT OF TEMPERATURE AND STRAIN-RATE ON INTERFACIAL SHEAR-STRESS TRANSFER IN CARBON-EPOXY MODEL COMPOSITES

The amount of stress transferred in a composite from the matrix to the fibre has been determined in an epoxy/carbon system by using a fragmentation test on single-fibre model composites (microcomposites), as a function of temperature and strain rate. Experiments, performed on microcomposites containing commercial carbon fibres, with and without sizing agent, and an epoxy resin of low glass transition temperature (T-g), indicate that the interfacial shear strength, [tau], decreases sharply as the rest temperature approaches the T-g of the constituent surrounding the fibre. in desized fibre composites the strengths compare well with the matrix shear strength, in sized fibre composites the measured [tau] values appear to be strongly influenced by the presence of an interphase. [tau] values measured for sized fiber microcomposites are higher than the matrix shear strength. The contribution to adhesion of frictional stresses, exerted by the matrix on the fibre as a result of thermal and Poisson contractions, appears to be negligible with respect to the [tau] values obtained from the fragmentation test.