Evaluation of interfacial properties by embedded single fibre test in aramid/epoxy composites

An embedded single filament test using aramid fibre has been carried out, n ot only in tensile mode but also in compressive mode. In the tensile test, all single filaments embedded under various pre-tensions are not fractured until the specimen's break, so that embedded single filament tensile test w as not suitable for an evaluation method of the aramid/epoxy interphase. In the compressive test, optical microscope observations indicate the dark zo ne of/around the embedded single filament after testing. As compressive str ess increases, a kink band is generated at first, then kink bands are immed iately developed all over the length of the filament and the field becomes clearer. The dark zone first appears after the plastic deformation of the s pecimen. The intensity of the dark zone measured by image analysis for the micrographs has a linear relationship with the transverse tensile strain wh ich is measured by two strain gauges on the specimen. These results suggest that the dark zone is due to damage of the interface by the transverse ten sile strain under longitudinal compressive stress to the specimen. This sug gests that it is possible to evaluate the interfacial properties by the mea surement of the intensity and the aspect of the dark zone at a constant tra nsverse tensile strain.