Transverse properties of unidirectional glass/epoxy composites: influence of fibre surface treatments

An investigation has been made on effects of fibre surface treatments on tr ansverse mechanical behaviour of unidirectional glass/epoxy composites. Mod el composite plates were processed by filament winding using glass fibres c oated with different sizings changing by their epoxy functionality and thei r reactivity towards the matrix. In the first part of the study, transverse tension and microindentation cha racterisations were performed in order to correlate the ultimate behaviour of the composite with interfacial properties. Experiments revealed that the most reactive sizings promote the highest interfacial strength and also in crease ultimate properties of laminates in transverse tension. This feature was attributed to the high crosslink density of the polymer network in int erfacial areas. In the second part, finite element calculations were used to evaluate local strain and stress concentration in a composite submitted to transverse ten sion conditions. The general trend for the evolution of composite failure s train as a function of interfacial strength has been established. The model ling showed that a transition of the composite failure mode occurs at a glo bal strain of 1.15%, from an adhesive rupture at the fibre/matrix interface to a cohesive rupture in the matrix. In the domain of adhesive rupture, th e value of the composite failure strain appeared to be directly governed by the interfacial strength. Therefore, improving interfacial strength by use of fibre sizings with high epoxy functionality could constitute an interesting way to reduce transver se brittleness of composite structures. (C) 2001 Elsevier Science Ltd. All rights reserved.