Friction between single fibres or between tows is an important element in the mechanical properties of composite reinforcement. Therefore, knowledge of the friction behaviour at the two scales, tow and fibre, is necessary for a deep understanding of the mechanical behaviour of composite reinforcement. In the models, the strategy used is to consider a constant coefficient of friction. This paper presents an efficient method of measuring the coefficient of friction relative to an inter-tow or inter-fibre sliding angle of 0° to 90°. The results show that the coefficient of friction decreases when the angle increases. Moreover, the friction is very high when the fibres are parallel. This result is explained by the increase of the adhesion between fibres at the interface of the tows due to a large total contact area at 0°, as proved by an analysis performed based on Hertz's contact theory.

The aim of this study conducted on carbon tows and single fibres is to highlight some friction behaviours to help better understand the friction mechanisms that occur during the manufacture of carbon composites. These mechanisms are responsible for damage that reduces the specifications and lifetime of mechanical parts. An experiment has been developed in order to rub together two carbon tows, or two single carbon fibres (with a diameter down to 5 mm), at an angle of 90°. The influences of friction velocity, normal load, and type of carbon fibre have been studied. For both tows and fibres the friction follows the Coulomb's law because there is no influence of the velocity and the normal load in the tested range. The rearrangement of fibres within the tow has been shown to be fundamental. For the single fibre, the role of the Young's modulus and the sizing treatment is important.

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OATAO is an open access repository that collects the work of Toulouse researchers and makes it freely available over the web where possible. A B S T R A C TCarbon fibres are sized for use in the reinforcement of composite materials. The purposes for sizing include improving yarn cohesion, which is necessary for the weaving process, and increasing the adhesion between the fibres and the matrix. Nevertheless, during weaving, some fibrillation can occur, and that has detrimental effects on the weaving productivity and on the composite's properties. The purposes of this research were: (a) to determine whether abrasive wear between sliding fibres would modify the sizing and (b) to study the influence of sizing on the friction between fibres. The same type of carbon fibre was subjected to different desizing processes. The coefficient of friction between single fibres was obtained before and after desizing. The effects of sizing and sliding distance on frictional behaviour were investigated, and are related to the observed the wear of sizing layer. In fact, it increased with sliding distance and induced a decrease in the coefficient of friction. Moreover, an efficient desizing process induced a decrease of the coefficient of friction.

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