Study On Processing And The Tensile Deformation Of Thermoplastic Composites With Weft-Knitted Structure

In recent years, the industrial textiles develop quickly and are applied extensively in the fields of industry,agriculture, transport action , energy , basic project , spaceflight , protection of environment and body. Among them, Because of it's construction and matrix's property, the thermoplastic composites with weft-knitted structure have excellent deformation property. So it can be made into products that is compliance and can absorb energy, such as flexible bank used to resist wave in water. At present, developed countries have made research on the deformation property of thermoplastic composites with weft-knitted structure, and these researches supply guidance to design , production, application in theory and experiments. But the research on this field is limited at home. The thesis aims at affording theoretical and experimental basis for design, manufacture and application of thermoplastic weft-knitted fabric composites.The commingled yarn from glass fiber yarn and polypropylene (PP)yarn was used as knitting material in the thesis. By experimental work and theoretical analysis, the author investigated the knittability and technology of plain and rib knitted fabrics from the commingled yarn on a flat knitting machine. Some factors influencing knitting process and fabric quality, such as input yarn tension, taking-down tension, sinking depth were discussed. The appropriate gauge of flat knitting machine was chosen according to the yarn tensile strength and loop strength. The key technique and optimal parameters for the manufacturing of the glass/PP weft knitted fabrics were found.After the weft knitted fabrics were produced, the hot-press method was used to make composites. By the tests, the author obtained the suitable hot-press parameters including temperature, pressure, retentive time, the method of temperature-drop etc and discussed the effect of these parameters.Tensile tests in the wale, course and diagonal direction of composite specimens were carried out to obtain tensile data. According to these data, the stress-strain curves were made out by using origin 7.0. And according to these curves, the author worked out tensile parameters and analyzed the deformation properties of the composites. In order to observe, author set the tensile speed very slow and used a digital camera to record the change ofmicro-structure of samples. For profound research of deformation mechanism, author emphasized the discussion on walewise, and pointed out the key points and the character of crack during the process of deformation. Some experimental photos were taken during the process of tests, and then discussions were made on the change of micro-structure. The author also made some compares between the different composites and discussed the influencing factors.