Polymer beads as interfacial obstacles in fibre composites

Abstract The geometric modification of fibre-matrix interfaces is a promising approach for simultaneous improvement of strength and toughness of composites. In this study, we investigate the effect of discrete epoxy droplets deposited on glass fibres embedded in an epoxy matrix, using single fibre experiments. Pullout tests reveal increases in both the pullout force and work in beaded fibre samples compared to beadless ones. This is somewhat unexpected as the bead and the matrix are made of the same material (cured epoxy) and possess the same mechanical properties. Interestingly, upon pullout, only the fibres are extracted from the matrix whereas the beads remain within the matrix, indicating that failure occurs at the fibre-bead interface. The simultaneous improvement in pullout force and work seen during the pullout of beaded fibres is explained by a conceptual anchoring mechanism based on friction lock, which agrees well with the experimental results. Smaller beads yield higher increases in pullout force and work, leading to the possibility of denser packing of multiple beaded fibres in a practical composite.