Study On Knitting Process And Mechanical Performance Of Biaxial Weft-knitted Flexible Composite

This paper mainly discusses the fabrication and mechanical performance of biaxial weft-knitted flexible composites. The work includes knitting the biaxial weft knitted fabrics , manufacturing the flexible composites by coating process, and mechanical testing and analysis on tension, tension under crack and tear of flexible composites.The paper firstly analyzed and presented the knitting process of the biaxial weft-knitted fabrics, discussed the adjustment of the knitting parameters on a self-made biaxial hand knitting machine as well as the problems encountered during the knitting process. The biaxial weft knitted fabric samples were successfully produced after several experiments. The paper then analyzed the manufacturing of the flexible composites, discussed the coating process by using dry directly coating method with PU resin. The flexible composites with smooth surface and without air bubbles and defects were obtained at the coating with thickness: 0.8mm, drying temperature: 140°C, drying time: 2min.Based on the biaxial weft-knitted flexible composites obtained above, the tensile, tensile with crack and tearing properties of the biaxial weft-knitted flexible composites were systematically tested and analyzed. As for the tensile properties, the composites produced with the fabrics of two different warp densities were respectively tested along the weft and warp directions. The results showed that the strengths and elongations at breakage in two testing directions for the flexible composite with larger warp density were almost the same. This means that although the densities of the warp and weft laid-in yarns are different, it is possible to reduce the difference of the tensile properties of the flexible composites between the weft and warp directions by choosing the larger warp yarn linear density. As for tensile properties with crack, the cracks with different angles and lengths were tested. The results indicated that the strength decreased with increase of crack length when the crack angle was kept constant; and that the strength increased with increase of crack length when the crack length was kept constant, because less laid-in yarns were cut when the crack length increased. As for the tearing properties, the tests were carried out by using trapezoid and tongue tearing methods. The results showed that the tearing strength under the trapezoid tearing condition was about 4-9 times higher than that under the tongue tearing testing. However, their variation trends were similar. Under the both testing conditions, breaking of the yarns is one by one, because the accumulation of the yarns is difficult to be done after coating. For this reason, the tearing curves are rising in sawtooth form.It is expected that the study of this work would give some valuable technical guidance and reference for the production of biaxial weft knitted flexible composites.