Development of novel auxetic textile structures using high performance fibres

The present work reports the first attempt of developing auxetic structures using high performance fibres through knitting technology. Polyamide (PA) and para-aramid (p-AR) fibres and their combination were knitted in to purl structures using flatbed knitting machine, varying different structural (such as loop length, cover factor and yarn density) and machine parameters (such as take-down load). The influence of different parameters on negative Poisson's ratio (NPR) was thoroughly investigated. It was observed that NPR improved strongly with the increase in loop length of knitted structures. NPR also increased withthe decrease in cover factor and increase in course density of knitted fabrics. An increase in take-down load also improved NPR for tightly knitted samples, but led to initial decrease and subsequent increase in NPR for medium and higher loop lengths; except for p-AR fabrics, which showed a decrease in NPR with take-down load for higher loop lengths. Tensile properties of the developed auxetic structures were also found to depend strongly on fibre type and loop length, and the highest tensile performance was achieved with lower loop lengths and p-AR yarns. The p-AR fabrics produced using lower loop length and lower take-down load resulted in the highest NPR of−0.713. Therefore, the developed knitted structures produced using high performance yarns and showing strong auxetic effects can have huge potential for industrial applications, especially in personal protection materials, such as cut resistance fabrics, bullet proof vest, helmets, and so on.CAPES Foundation, Ministry of Education of Brazil - grant BEX 0978/12-

The effects on the flexural strength and impact behavior of nanographene ratio of the glass fiber nanocomposite plates

In this study, the flexural strength and the impact behavior of the glass fiber composite plates with the same mesh and layer geometry and the effect of the addition of nanographene (GNP) at various ratios into the matrix were experimentally investigated. The variable examined in the study is the percentage of the nanographene that added in the matrix of glass fiber composite plates. In this study, six types of glass fiber plates were produced; with no nanographene added reference specimen, and with the ratio of 0.15, 0.25, 0.35, 0.45, and 0.70% nanographene added specimens. The effect of nanographene addition to the epoxy matrix on the flexural strength and impact behavior of the specimens was investigated by applying a three-point bending test and a constant-energy impact load with the free-weight test method on the glass fiber plate specimens. The highest flexural strength was observed at the 0.25% nanographene added specimen. Further addition of the nanoparticle caused the flexural strength to decrease. In the free weight drop impact test, the highest acceleration and lowest displacement were found at the 0.25% nanographene added specimen. Adding more nanoparticles adversely affected the impact behavior. The optimum nanographene ratio was determined to be 0.25%