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Improved Numerical Investigations of a Projectile Impact on a Textile Structure

Past perceptions to the processes of the penetration mechanisms of projectiles acting on textile structures [1] are often based on continuum models [2] or simplified models [3] and admit only limited conclusions concerning the real behavior of protective clothing made from several layers of fabric. Only a few investigations are known up to now with models based on single yarns as a major component for discretization [4]. Thus, for the prediction of the protective effect of several layers of high-strength fibers in a textile, a structural approach is chosen by a separate modelling of each fiber by a shell or continuum based element. The single modelled fibers interact over a contact formulation with the adjacent fibers in the same way the fibers in the different layers do. This allows to model the in-plane motion and deformation of each fiber separately, as well as the failure of fibers thereby avoiding artificial localization effects to a great extent. With the so-called explicit finite element code LS-DYNA [8] different possibilities of the discretization of the fiber bundles are investigated. Also the description of the fiber material by available material models is varied modifying the load deformation relation and the damage evolution. The goals of the current project [10] are first to achieve a geometrically consistent model of the layered structure and second to better understand the phenomenological process of the impact of ballistic projectiles on such textiles. Finally, the particular effect of different layer setups can be studied. INTRODUCTION Up-to-date bullet proof vests are consisting of several layers of fabrics made of high performance fibers like Kevlar® (Du Pont), Twaron® (Tijin) and Zylon® (Toyobo). These vests have a specific weight up to 2000 g/m². Many so called “trial-and-error” tests have to be performed to improve the weight of this vests. So far, only few attempts are known to predict the behavior of new constructions, like new fiber materials or different fiber materials for different layers, by way of exploring the mechanical phenomena. Numerical simulations by a finite element program could be a useful tool to detect this phenomena and they would allow the developers to optimize their products. To perform a numerical simulation, some research into fiber and fabric geometry and their possibilities to approximate them through finite elements is necessary. Also, the material behavior of the fibers exposed by high velocity loading must be measured to choose a suitable material model. The objective of this paper is the description of the fabric geometry, the discretization by shell and solid elements and first investigations of the model behavior in the analysis. Weave geometry and fiber properties Fabric and fiber geometry Following the approach to discretize the weave through a collection of single yarns, the shape of the cross section and the curve through the center of gravity of the cross sections must be acquired. To get this information of an unloaded weave, two specimen of a Kevlar® weave were embedded in epoxy resin. One of them was roG – I - 08