Mechanical properties of high-strength carbon fibres. Validation of an end-effect model for describing experimental data

Abstract

The present contribution deals with the use of different models accounting for the mechanical response of high-strength (HT) carbon fibres. In particular, analytical models based on Weibull type of statistical distributions will be employed to analyse the dependence of the strength of carbon fibres on length. This dependence is relevant for interpreting the results of conventional fragmentation tests, which are traditionally performed to characterise the level of fibre/matrix adhesion in fibre reinforced composites. The objective of this work is to compare alternative models, such as the so-called “end-effect” model, for determining the tensile strength of HT carbon fibres at small gauge lengths. To validate these models, tensile tests were performed with five different HT, ex-PAN carbon fibres: a fresh, untreated sample, and four samples which were prepared after submitting the previous one to various surface treatments. Specifically, plasma oxidation was carried out under three different conditions of power and/or time of exposure. A sample oxidized by the manufacturer, presumably using an electrochemical treatment, was also included. Results showed that the end-effect model represents well the behaviour of the untreated and plasma treated under the mildest conditions carbon fibres. Overall, all treatments tend to decrease the tensile strength of the fibres, with the commercial treatment being the most damaging when compared to any of the plasma treatments carried out.