A technological solution to the testing and data reduction of single fibre fragmentation tests

Abstract

Abstract The single fibre fragmentation test was first introduced in 1965 for measuring interfacial adhesion in fibre reinforced composites. However, this test is still far from a routine test and no suitable testing standard exists. Consequently, this method is hardly used by research laboratories of the reinforcing fibre manufacturers, composite fabricators and other standardisation organisations. The main reasons for the failure of the fragmentation test to establish as a standard quality control tool are the time consuming manual testing procedures and the poor confidence in the data reduction techniques used for calculating the interfacial adhesion parameter. An integrated machine, software and data reduction approach has been developed for the fragmentation test. The new approach allows the stoppage of the fragmentation test at pre-defined strains and digitisation of the whole embedded fibre length using a microscope attached with a video-camera and Sun work-station. Subsequently, the fragment and associated debond lengths are measured using a Visual Basic program in a semi-automatic process. The problems associated with the huge amount of computer graphics data and compatibility of different graphics formats have been sorted out. This leads to substantial savings in the time required for the fragmentation test. Using this integrated machine and software approach, the single fibre fragmentation test has been carried out on carbon fibre samples with well-defined interfaces. The results were analysed using the conventional Kelly–Tyson model and the cumulative stress transfer function (CSTF) technique, at different applied strains. It has been shown that the CSTF technique can be used for assessing the fibre-matrix adhesion from the single fibre fragmentation test at any applied strain before or after the saturation of the fragmentation process, thus eliminating the need for specially formulated resin for the fragmentation test.