Influence of matrix toughness and interfacial strength on the toughness of epoxy composites with ductile steel fabric reinforcement

In the last decades, several studies have been performed on polymers reinforced with steel cords or wires. However, the diameter of these steel reinforcements was still quite large (200 micron and more). Recently, stainless steel fibers were developed with a diameter down to 30 micron, which makes it possible to process steel fiber-reinforced composites in a similar way as carbon or glass fiber-reinforced composites. If a proper combination of the ductile steel fiber and a ductile polymer is chosen, a ductile composite should be achieved. This paper reports on the influence of the matrix toughness and the fiber/matrix adhesion strength on the ductility of the resulting steel fiber reinforced textile composite. Tensile tests have been combined with microscopic analysis to investigate the relation between the mechanical behavior and the observed damage morphology. It was found that distributed damage increases the toughness in a textile composite, because it softens the transversal structure that interlocks the ductile load-bearing yarns. This explains the counterintuitive observations regarding the influence of the matrix ductility and the fiber/matrix adhesion strength on the composite toughness. It was found that selecting a brittle epoxy matrix can lead to a ductile composite, because of the widely spread and dense cracking pattern that allows more strain to the ductile steel fibers. If the fiber-matrix adhesion is enhanced by introducing a silane coupling agent to the fiber surface, transversal cracks are prevented and the ductility of the composite drops drastically. These results for the textile composites are contrary to earlier findings on the UD and cross-ply counterparts.