Structure-tensile property relationship of knitted fabric composites

This paper reports some further studies on the tensile properties of plain weft knitted DuPont Kevlar fiber fabric reinforced epoxy matrix composites. One aim of this work is to investigate systematically the anisotropy of kn itted fabric composites, Tensile tests were conducted at different off-axia l angles (0 degrees, 30 degrees, 45 degrees, 60 degrees and 90 degrees) wit h respect to the wale direction, Fracture modes corresponding to this off-a xial variation were clearly identified. The elastic modulus and tensile str ength were found to be the highest in the wale direction (0 degrees), but d ecreased Gradually towards the course direction (90 degrees), This anisotro pic study was carried out on both single layered and multilayered (four lay ered) knitted fabric composites. Another aim is to study the effect of spec imen width (or number of loops per specimen width) on the tensile propertie s. This study indicated an optimum number of loops per sample width require d to obtain meaningful tensile test results. Further, edge effect on the te nsile properties of the knitted fabric composites was also investigated in the paper. This was achieved through comparative studies on cut and uncut f our layered specimens. In the cut specimens the continuity of the yarns is lost at the cut edges, which show a marginal variation in the properties co mpared with the uncut specimens where the yams are continuous throughout th e specimen. Finally, a study was also carried out to investigate the effect of loop size (or stitch density) on the tensile strength and stiffness of the single layered composites.