TENSILE BEHAVIOR OF KNITTED FABRIC COMPOSITES

Abstract

In recent years, knitted fabric reinforced composites are receiving more attention from researchers all over the world and considerable work has been reported. In making use of these composites it is necessary to understand their mechanical properties. In most of the reported work on the knitted fabric reinforced composites, studies were mainly carried out on the specimens cut in the wale and course directions. The purpose of the present work is to carry out some further studies on the tensile properties of plain weft knitted Kevlar49 and glass fiber fabric reinforced epoxy matrix composites. A systematic investigation was carried out to study the anisotropy of knitted fabric composites. Tensile tests were conducted at different off-axial angles (0°,30°,45°,60° and 90°) with respect to the wale direction. Fracture modes corresponding to this off axial variation were clearly identified. The elastic modulus and tensile strength were found to be the highest in the wale direction (0°), but decreased gradually towards the course direction (90°). This anisotropic study was carried out on both single layered and multilayered (four layered) knitted fabric composites. Another study to determine the effect of specimen width (or number of loops per specimen width) on the tensile properties was done. This study indicated an optimum number of loops per sample width are required to obtain meaningful tensile test results. Further, edge effect on the tensile properties of the knitted fabric composites was also investigated in the present study. This was achieved through comparative studies on cut and uncut four 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 compared to the uncut specimens where the yams are continuous throughout the 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.