LAUSR

This work examines size effects of ductile regenerated cellulose fibres (viscose) with different diameters (11.9, 16.6 and 48.4 μm) as well as their unidirectional epoxy composites reinforced with fibre mass fractions of 20, 30 and 40% (16, 25 and 34% in volume). Viscose fibres were tested at different clamping lengths ranging between 2 and 50 mm. Composites were produced in 2 different sizes (cross-sectional area of 6.3 and 41.2 mm2) and tested at different gauge lengths (35 and 100 mm). It was investigated to what extent size effects affect the tensile strength and if the two-parameter least squares Weibull statistics may be used for the prediction of strength values when the sample volume of fibres or composites is changed. The results have shown that the Weibull theory is in principle applicable. It has been found that the prediction accuracy is only sufficient if the Weibull strength is determined on the basis of Weibull parameters determined at small sample volumes for the prediction of data measured with higher specific sample volumes. In this case, all calculated data are within the mean arithmetic deviation of the experimental results. If, on the other hand, the prediction is based on parameters determined for larger sample volumes, a considerable overestimation of the strength data of samples having a smaller sample volume is the result.