Weibull statistics of fibre bundle failure using mechanical and acoustic emission testing: the influence of interfibre friction

The failure of fibre bundles of Kevlar and glass has been monitored using mechanical load measurements and acoustic emission. It is shown that interfibre friction significantly reduces fibre bundle strength (σ b) and the corresponding failure strain (ε b). The strength distribution of individual fibres is narrowed when testing unlubricated fibre bundles, and this is attributed to frictional interactions during the fibre fracture process. A simple graphical (LST) method for determining the Weibull parameters is discussed and compared to other previously proposed methods. Acoustic emission has proved useful in monitoring the exact time and load of fibre breaks, since the breaking of each individual fibre is accompanied by an associated acoustic signal. Care must be exercised when extracting Weibull parameters from data, in particular when employing methods involving 1n 1n plots. Beyond the maximum load attained by a fibre bundle, failure is found to occur by multiplet fibre breaks, and in this region different Weibull parameters apply. Including data from this region during a fibre bundle fracture test could lead to reduced accuracy when determining Weibull parameters.