The friction of carbon fibres

Abstract

The fibres, mostly prepared from polyacrinonitrile, are largely graphitic: they are of roughly circular section but all have fine fluted surface irregularities. One fibre, encastered at one end and free at the other, is brought into contact with another fibre, held taut, and arranged at right angles to it. Flexure in the vertical plane applies a normal load, while deflection in the horizontal plane provides a measure of the frictional force. The apparatus covers a load range of 1-1000 mu g (10-8-10-5 N). The experiments show that there is finite attraction between the fibres and this can be explained in terms of surface forces or surface energy. The frictional behaviour can be explained in terms of an adhesion mechanism if the surface attraction is taken into account. On the basis of reasonable assumptions concerning the deformation of the surfaces the interfacial shear strength can be calculated and this agrees with that associated with basal-plane interactions. Edge planes provide regions of higher surface energy and give higher coefficients of friction.