Investigations of fiber twist on the mechanical properties of sisal fiber yarns and their composites

The effect of fiber twist on the tensile properties of single sisal fibers was investigated by single fiber tensile test. Four kinds of sisal yarns with four different levels of twist were made and the mechanical properties were investigated on both unimpregnated and resin-impregnated sisal yarns. A critical fiber twist level for unimpregnated sisal yarns was found beyond which the tensile properties started to decrease with the increasing of the level of fiber twist. However, for resin-impregnated sisal yarns, both tensile strength and modulus decreased with the increasing of the fiber twist level. In addition, the effect of fiber twist on both the tensile and flexural properties of unidirectional sisal yarn reinforced composites was studied. It was shown that lower twist level led to higher mechanical properties of its reinforced composites. Compared with the experimental results, Rao's model proved to accurately calculate the Young's modulus of fiber yarns with different levels of twist. Thus, the Young's modulus of sisal yarn reinforced composites could be predicted by the rule of mixtures hereafter.