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A numerical and experimental investigation of the impact behaviour of hybrid and multi-ply fabric structures Novotny, Wesley R.

Abstract

The focus of this work is to develop an understanding of the impact behaviour of singleand multi-ply fabric materials used in protective (armour) structures. Hybrid structures are also investigated to explore the effect of mixing different materials on armour system performance. Emphasis is placed on the behaviour of these systems during the early stages of the impact event prior to the return of boundary-reflected strain waves to the impact point. This allows one to separate the material response from the structural response and in so doing investigate the losses of material efficiency inherent in systems with greater areal densities. The latter can arise from increased ply count and/or greater mass per unit length of the yarns which make up the fabric. A series of ballistic impact experiments are carried out on the permutations of stacking sequences of 2- and 4-ply Kevlar Nylon hybrids. Instrumented impact tests as well as post-mortem examination are used to investigate the unique behaviour of these hybrid systems over the entire duration of the impact event. The early event behaviour of the hybrids is also characterised. The significant difference between the various hybrids tested is the increased transverse deformation of specific stacking sequences due to penetrated layers. A finite element code, TEXIM, is used to explore the response of single and multi-ply Kevlar fabric systems during the early stages of impact. The numerical results of single and multi-ply Kevlar are found to be in good agreement with the relevant experimental data. Parametric studies using the numerical model are then carried out to investigate the effect of various weave and stacking parameters. Single panels with lower areal densities (typical of panels made up of yarns with lower mass per unit length ) are found to have superior early event performance due to increased strains in the yarns. Multi-ply systems are shown to perform better in terms of the rate of energy absorption early in the impact event as the inter-ply spacing is reduced. Minimizing the spacing is shown to result in increased fibre strains and greater material involvement in absorbing the impact energy.

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