THE SIZE EFFECTS ON THE MECHANICAL-BEHAVIOR OF FIBERS

The size of a fibre affects its mechanical properties and thus is of t heoretical and practical importance for studies of the rupturing proce ss during loading of a fibrous structure. This paper investigates the overall effects of length on the mechanical behaviour of single fibres . Four types of fibres, ranging from brittle to highly extensible, wer e tested for their tensile properties at several different gauge lengt hs. Different from most previous studies where the focus has been on t he gauge length effects on a single property such as fibre strength or breaking strain, this paper look comprehensively into the effects of length on all three of the most commonly studied mechanical properties , namely strength, breaking strain and initial modulus. Particular emp hasis is placed on initial modulus and on the interactions between all three parameters. Influences of strain rate and fibre type on the siz e effects are also investigated. The effect of potential fibre slippag e on experimental error is examined. An image analysis method is used to measure the real fibre elongation in comparison to the same fibre e longation obtained directly from an Instron tester. Finally, a statist ical analysis is carried out using the experimental data to test the f itness of the Weibull theory to polymeric fibres. This was done as the Weibull model has been extensively utilized in examining fibre streng th and breaking strain, although it is supposed to be valid only for t he so-called classic fibres to which more extensible polymeric fibres do not belong.