Fabrication And Tensile Properties Of The Interlaced Biaxial Weft Knitted Structural Composites

In the recent years, the biaxial weft knitted structural composites have got wide application in composite field. However, in the current biaxial weft knitted structures, the warp and weft yarns are respectively inserted, they do not interlace between them. Although they have excellent planar mechanical properties, the warp yarn layer and weft yarn layer are easily separated under impact loads. In order to overcome this shortcoming, a new kind of biaxial weft knitted structure in which the warp and weft yarns are interlaced has been developed. The objective of this work is to investigate knitting process of this kind of structure, composite manufacturing and tensile mechanical properties of the composites.The work firstly investigated knitting process of this kind of structure. In order to analyze and compare properties of the composites after, four fabrics were produced by using glass fiber and basalt fiber on a self-made hand flat knitting machine. They respectively were: glass fiber fabric formed with three interlaced yarn layers, basalt fiber fabric formed with three interlaced yarn layers, glass fiber fabric formed with five interlaced yarn layers and fiber fabric formed with five non-interlaced yarn layers. During knitting, the disposition of each knitting element and yarn tensions were adjusted and analyzed. Through practical operation, glass basalt fiber fabrics were successfully produced out. The work then investigated the fabrication of the composite samples using above fabrics as reinforcement through VARTM technology. Because of the big difference between the warp and weft yarns, single layer and double layers laid-up methods were adopted in order to reduce the difference of the mechanical properties between the warp and weft directions of the composites. In the laid-up case of double layers, two methods were used: one was that two layers of fabrics were laid-up in the same direction (0°laid-up), the other was that the weft direction of the first layer corresponded the warp direction of the second layer (90°laid-up). Finally, the work investigated the tensile properties of the composites fabricated. Base on the stress-strain curves, the influences of the fiber materials, fabric structures (three and five inserted yarn layers and interlaced and non-interlaced), tensile direction and laid-up method were analyzed and compared. It has been found that basalt fiber interlaced biaxial structural composites had better mechanical properties, and that the properties in the weft direction were better than those in the warp direction. The composites made by 90°laid-up method had good mechanical properties in the both weft and warp directions.The results obtained from this work have certain reference value and guide significance for the practical application of the interlaced biaxial composites.