SUMMARYThe effects of inter-yarn friction on the ballistic performance of woven fabric armour are investigated 7 in this paper. Frictional sliding between yarns is implemented in a computational model of the fabric that takes the form of a network. Yarn crimp and its viscoelastic properties are taken into account. 9Ballistic experiments are performed to verify the predictions of the model. Parametric studies show that the ballistic response of woven fabric is very sensitive to yarn friction when the friction coefficient 11 is low but insensitive beyond a certain level. The results also show that very high inter-yarn friction can lead to premature yarn rupture, thus reducing the ability of the fabric to absorb impact energy. 13

No abstract

For a 3D orthogonal carbon fibre weave, geometrical parameters characterising the unit cell were quantified using micro-Computed Tomography and image analysis. Novel procedures for generation of unit cell models, reflecting systematic local variations in yarn paths and yarn cross-sections, and discretisation into voxels for numerical analysis were implemented in TexGen. Resin flow during reinforcement impregnation was simulated usingComputational Fluid Dynamics to predict the in-plane permeability. With increasing degree of local refinement of the geometrical models, agreement of the predicted permeabilities with experimental data improved significantly. A significant effect of the binder configuration at the fabric surfaces on the permeability was observed. In-plane tensile properties of composites predicted using mechanical finite element analysis showed good quantitative agreement with experimental results. Accurate modelling of the fabric surface layers predicted a reduction of the composite strength, particularly in the direction of yarns with crimp caused by compression at binder cross-over points.

Woven fabrics are widely used in flexible armour systems for protection against fragments and projectiles from small arms. The woven architecture introduces crimp or undulations in the yarns as they pass alternately over and under orthogonal yarns. An undesirable effect of crimp is excessive deflection in fabric armour during impact. The numerical results of ballistic impact and perforation of woven aramid fabric are presented in this paper. The fabric is modelled as a network of nodal masses connected by one-dimensional viscoelastic elements. The focus of the computational simulation is to compare two different ways of incorporating yarn crimp into the fabric model. Tensile tests on strips of the woven fabric show an initial toe region in the load-deflection curve before the curve asymptotically converges to an approximately straight line beyond a certain strain. The first method of introducing crimp into the fabric model is to include the toe region of the load-deflection curve in the constitutive equation describing the viscoelastic elements. The second method to account for crimp is to physically reflect the woven architecture in the fabric model by arranging the chain of linear elements that define each yarn in a zigzag manner. r

An automated approach (TexGen) for modeling the geometry of textile structures is presented. This model provides a generic approach to the description of yarn geometry and yarn interlacement for all types of weaving. One feature of this model is that the shape and size of the cross sections may change locally; this is exploited in the functions for interference correction, which modify the textile according to geometric considerations to avoid penetration of yarns. Another feature of this model is that it acts as a pre-processor for finite element simulations by generating a mesh, definition of contact, materials orientation and boundary conditions, thus providing an automatic procedure. This paper describes the modeling techniques, algorithms and concepts implemented in TexGen and examines the functionality of their implementation for a range of twodimensional/three-dimensional commercial fabrics. Comparisons between the images of real fabrics and modeled fabric structures confirm that the software is capable of modeling sophisticated fabric architectures, including twisted yarns with varied yarn cross sections. Accurate input measurements of fabric geometry are critical for successful results. The paper also discusses directions for further development of the approach to overcome current limitations. Keywords fabric geometry, modeling, simulationRealistic fabric geometric description is essential for modeling of the mechanical and physical properties of textiles and textile composites. It determines the accuracy of modeling results and geometric non-linear response to external loadings. Attempts to model textile geometry were recorded as early as the1930s 1 and have continued up to the present time. 2 There are many challenging aspects of modeling fabric structures, for example, even the geometry of relatively simple plain-weave fabrics is complicated and requires careful modeling to obtain accurate results. There are two major obstacles: the

High-strength fabric is commonly used in personnel protection systems against small arms projectiles and fragments. An understanding of the characteristics of high-strength fabric under ballistic impact would provide useful insights for fabric armor design. A numerical model is formulated and used to study the perforation of square cross-woven fabric targets when the fabric is (i) clamped along all four edges with its yarns aligned parallel to the edges, (ii) clamped along all four edges with yarns running 451 to the edges and (iii) clamped along two edges with yarns aligned parallel to the edges. In addition, high-speed ballistic tests are carried out to validate the computational results. It is found that the ballistic resistance of such systems is sensitive to boundary conditions and yarn orientation. Targets that are unclamped on two edges can absorb more impact energy than those with all four sides clamped. Orientating the yarns 451 to the clamped edges can improve energy absorption significantly. Stresses in primary yarns (those in contact with the projectile) increase rapidly when their ends are clamped; this leads to rapid failure at the impact point and a lower-energy absorption. For fabrics clamped along four edges, the regions near the four corners are not stretched during impact if the yarns are parallel to the edges, whereas clamping with the yarns 451 to the edges facilitates energy dissipation by the entire fabric. It is also observed that slippage at clamped edges contributes to higher energy absorption by fabric targets. r

No abstract

No abstract