A Study On The Knittability Of High-modulus Fibre Yarns

The stiffness and strength of composites are mainly based on the performance of reinforced fibres. High-modulus fibres are usually used for reinforcements of composites. Knitted fabrics have increasingly been recognized as an attracted kind of reinforced structures because of their flexibility, impact resistance and easy moldability. In order to make knitted fabrics be used more widely in composites, the problems on knittability of high-module fibre yarns must be solved. Some researchers have studied the knittability of high-modulus fibre, but literatures or materials related to this topic are limited. This thesis amis at grasping the knittability of high-module fibres especially glass fibre more deeply and making a new try on weft-knitted techniques.Several properties of glass fibres and yarns, such as tensile intensity, frictional coefficient etc., were first carried out and analysed, and then the knowledge of special performance of glass fibres could be obtained. The appropriate gauge of hand flat knitting machine was chosen by tensile strength and loop strength. In addition, several representative single-faced fabrics and double-faced fabrics were knitted by using glass fibre yams with different specifications. The author also reported effects of different knitting parameters on the process of knitting and appearance or quality of fabrics. 'Some dimensional parameters of fabrics knitted above were tested and then' dimensional properties were studied, including the dimensional stability and the relations between densities and loop lengths. In this way, the dimensions of the fabrics can be predicted before knitting. Furthermore, the author observed the special loop shapes in glass fibre fabrics and discussed the effect of glass fibre performance on loop geometricalstructure.The quantitative method used for evaluating the fibre damage degree was presented. The relations between the fibre damage degree and the loop lengths were also analysed. The results have shown that there is an optimum point at which the fibre damage is minimum during the knitting process. And this conclusion affords basis for selecting knitting parameters of glass fibre yarn properly. The available range of loop lengths was calculated based on studying the loop-forming, which was helpful to choose the right loop lengths before knitting. Moreover, the loss and damage of knitting elements (needles and stitch cams) was observed. As a result, the author has found that it is easy to make knitting elements damaged when glass fibres are knitted.According to the experience on hand flat knitting machine, single jersey was fabricated on a computer-controlled flat knitting machine. Consequently reasonable knitting method and process can be decided by setting up each parameter more precisely.