Investigation of tensile strength and dimensional variation of T700 carbon fibres using an improved experimental setup

Abstract

Knowledge of fibre strength is crucial for understanding the failure behaviour of fibre-reinforced composite materials and structures. Measuring the properties of technical fibres has been known to be very challenging, and the different challenges associated with single fibre characterisation are illustrated in this article. An improved and automated experimental methodology for tensile testing of single fibres is described. This process has been used to generate fibre strength data for T700 carbon fibres at three different gauge lengths of 4, 20 and 30 mm. The variability in strength and modulus of short fibres was found to be much larger than that of longer fibres. Statistical analysis of this large data set has also highlighted the limitations of the standard Weibull distribution for representing fibre strength behaviour. The need for a better statistical representation of the fibre strength data in order to provide a more accurate description of the fibre strength behaviour has been emphasized.

Analyzing the effect of misalignment on single-filament carbon fiber tensile testing via stereoscopic computer vision imaging

“…The variation in the measured mechanical properties of the CF at all misalignment angles is consistent with the results of CF tensile testing in other studies [17,25,26] as indicated by the experimental coefficients of variance (CV%) in table 1. Experimentally determined mechanical properties and coefficients of variance for CF at misalignment angles of 0 5 • , 10 • , 15 • , and 20 • .…”

“…Recent single-fiber tensile testing of commercial CFs (Toray, T700) has shown that there is no correlation between fiber diameter and mechanical properties [17]. Therefore, measuring the diameter of each fiber will reduce the standard deviation in tensile modulus and tensile strength, but it will not change the average result given that the fiber diameters follow a normal distribution, as illustrated by the Gaussian shape of the histogram and the linearity of the quantile-quantile plot (figures 1(c) and (d)).…”

Efficient quantification of composite spatial variability: A multiscale framework that captures intercorrelation

“…Material imperfections explain this difference to a large extent. Fibre surface defects, among other imperfections, lead to a stochastic fibre strength commonly modelled by a Weibull distribution [3]. In combination with, for example, misaligned fibres [4][5][6], unevenly distributed [2] fibres or voids [7] in the matrix material this affects the stochastic behaviour of composite structures.…”

Detailed experimental validation and benchmarking of six models for longitudinal tensile failure of unidirectional composites

“…Some authors have emphasised the importance of testing a sufficient number of fibres to be able to determine the Weibull parameters accurately [10,11]. Other authors identified experimental issues in single fibre tensile testing, such as fibre alignment [12][13][14], fibre diameter variation [12,14] and stress concentrations associated to fibre gripping [15]. Other hypotheses have also been raised, such as whether the strength of fibres embedded in a resin is different from the one measured in bare fibre tests, but these remain unproven [16].…”