| As a newly arising material, flexible composites have been used widely in many fields. In the present market, the reinforcements of the flexible composites are mostly woven fabric and bi-axial and multi-axial warp-knitted fabric. Compared with these two textile structure composites, the research on the weft-knitted fabric flexible composites is still limited. As reinforcement, the weft-knitted fabric possesses superior extensibility, compliance, conformability and high productivity. It has better adaptability to the high deformation of the resin, so the composites have higher elongate abilities.Two different kinds of industrial polyester filaments were used, and then plain and rib knitted fabrics with two different densities were produced on a flat knitting machine. The author discussed some factors influencing knitting process and fabric quality, such as input yarn tension, taking-down tension, sinking depth.At present, coating and heat-melt laminating are mainly used to fabricate the flexible composites. Due to the properties of weft-knitted fabric, these two methods are both not suitable. So, the author combined manual coating with plate hot-press to fabricate weft-knitted-fabric flexible composite. After soaked polyurethane sufficiently, the knitted fabric was subjected to a uniform pressure from a plate hot-press to produce the flexible composites. Before processing, according to the calculating thickness of reinforced fabric without void and the designed fiber volume ratio, the author obtained the controlled thickness of composites. The ruler with same thickness was used between the plates of hot-press to control the fiber volume ratio of the composites.For the purpose of getting composites with good performance, orthogonal test method was used to optimize hot-press technology and get the best parameters. Firstly, the author analyzed the influence of time, temperature and pressure during hot-press on the tensile and bursting properties of composites. The result showed that all the three factors affected the mechanical properties of flexible composites to some extent. The optimized hot-press parameters are 40min time, 140℃temperature and 1.5MPa pressure.Based on the hot-press parameters obtained above, composites were fabricated. Bursting and tensile tests in the wale and course directions of composites specimens were done and damage modes were analyzed. As for the tensile properties, the author examined the stress-train curves in the wale and course directions, and found that they mainly consist of three parts, namely the linear deformation area, the plastically deforming area and the third part of deformation area. The directions of test, properties of yarn and parameter of reinforced fabrics all played a part in the tensile properties and the broken type of the composites. With regard to bursting properties, the author compared the properties of fabrics before and after coating, and found the bursting strengths of composites were higher than that of the corresponding fabrics, but the elongation during the bursting had the reversed result. Using the multi-linear regression to investigate the influence factors on the bursting strength, the author found the main factors are the number of yarn per length (2cm) and break elongation rate in wale direction.I hope that this work can offer the effective suggestion and reference for design and developing of weft-knitted-fabric flexible composites. Also it gives some technical guide for production and processing of this kind of composite.In this thesis, however there is still some shortage that should be improved in the future.
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