WEIBULL STATISTICS OF FIBER BUNDLE FAILURE USING MECHANICAL AND ACOUSTIC-EMISSION TESTING - THE INFLUENCE OF INTERFIBER FRICTION

The failure of fibre bundles of Kevlar and glass has been monitored us ing mechanical load measurements and acoustic emission. It is shown th at interfibre friction significantly reduces fibre bundle strength (si gma(b)) and the corresponding failure strain (epsilon(b)) The strength distribution of individual fibres is narrowed when testing unlubricat ed fibre bundles, and this is attributed to frictional interactions du ring the fibre fracture process. A simple graphical (LST) method for d etermining the Weibull parameters is discussed and compared to other p reviously proposed methods. Acoustic emission has proved useful in mon itoring 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 In In plots. Beyond th e maximum load attained by a fibre bundle, failure is found to occur b y multiplet fibre breaks, and in this region different Weibull paramet ers apply. Including data from this region during a fibre bundle fract ure test could lead to reduced accuracy when determining Weibull param eters.