Effect of Loop Lengths on Negative Poisson’s Ratio of Weft knitted Fabric Reinforced Epoxy Composite

Abstract

Conventional fabrics usually exhibit a positive poisons ratio (PR), i.e. they laterally shrink when stretched and laterally expand when compressed. On the contrary, auxetic fabrics exhibit a negative PR, i.e., they laterally expand when stretched or laterally shrink when compressed .The auxetic behavior equips fabrics with a lot of enhance properties. The Negative Poisson Ratio (auxetic) based on Weft knitted fabric can have huge potential for applications, especially in personal protection materials like bullet proof vest, and many industries application such as air space, automobile, and so on. This study presents use of NPR weft knitted fabric in composite materials using polypropylene yarns through the weft knitted technique. The polypropylene filament yarn knitted on flat knitting machine (Passap Deumatic 80), as a rib structure (fisherman’s rib) with three different loop lengths (LL3, LL4, and LL5). Investigation of the effect of different loop lengths on the negative Poisson ratio (NPR) in the wale and course direction. The result showed that all knitted fabrics have NPR effect, for the both direction. The composite material manufactured employed NPR weft knitted fabric using Risen Transfer Molding (RTM) process. Tensile strength and low velocity impact tests are performed to determine the load-extension and the amount of energy absorbed in the wale and course direction. The result showed that the LL5 have the highest extension and displacement, and LL3 have the highest load bearing. The failure modes of impact test characterized as combinations of matrix cracking, surface buckling, delamination, and fiber fracture. As the impact energy is increased, the area of composite deformation increases.