Ductility of steel fibre/epoxy composites in function of their microstructure

Recently we showed that continuous stainless steel fibres deliver structural composites with high stiffness and high failure strain at the same time. In the current research we further investigate these new materials focusing on the effect of the microstructure on their tensile facture behaviour. The steel fibre composites are produced from quasi-unidirectional woven (Q-UD) and purely unidirectional (P-UD) fibre architectures in combination with epoxy resin. The main difference in their microstructures is in the fibre distribution. In the Q-UD composite, steel fibres are tightly packed in bundles with 85% local fibre volume fraction and these bundles are separated by resin rich areas. In P-UD composite, steel fibres are homogeneously distributed through the composite with an average volume fraction of 50%. With the highly packed fibres, Q-UD composites achieve a higher strain to failure. In-situ characterization of damage development using acoustic emission registration and crack observations on the specimen surface were used to propose a hypothesis to explain the difference in fracture behaviour, caused by the different microstructures.