Tensile failure phenomena in carbon fibres

In order to clarify the effect of nanostructure upon the tensile strength of polyacrylonitrile (PAN)-based carbon fibres, experimental as well as theoretical studies have been performed. A new technique for the quantitative evaluation of the high strength region has been developed by combining the loop test with Raman spectroscopic measurements to overcome uncertainties in fibre stress, which have been the major drawback of the conventional loop test. The tensile strength at gauge lengths of a few tens of μm was successfully evaluated and a tensile strength as high as 13 GPa was observed experimentally for commercially-available PAN-based carbon fibres, showing their potential high tensile strengths. The strength distributions were found to be highly uniform in the high strength region, represented by Weibull shape parameters of ∼20. A tensile strength model that can reasonably account for the effect of the nanostructures has been proposed, suggesting there is considerable scope for further improvements in the tensile strength of PAN-based carbon fibres.