Stab Resistance Behaviours Of Woven Fabrics By Finite Element Analysis

Considerable attention is paid to the research on stab resistance of woven fabrics in recent years. The protective performance of woven fabrics can be tested by stab experiment. However, due to the limitation of testing conditions, the mechanism of stabbing process of woven fabrics remains unclear. It is sometimes difficult to give explanation to testing results and to provide guidance of designing stab resistance woven fabrics. Therefore, it is necessary to develop a theoretical model to analyze the process in some detail.The finite element method (FEM) is effective for solving nonlinear and large deformation problem such as the response of woven fabrics when stabbed by a knife or a spike. But there is few integrated package of finite element analysis available in solving the problem of woven fabrics subject to the stabbing process. Similar to stabbing process, fabrics subject to busting test belongs also to the problem of low velocity impact. In addition, the study of busting process can benefit from the FEM analyses of ballistic impacting on woven fabric, which has been studied intensively in the literature. Therefore, for the reason of simplicity, in this study, a FEM analysis of woven fabrics subject to busting is conducted first by using a FEM software- ABAQUS. Two models in different scales, i.e. macroscopic and mesoscopic models are developed for the purpose.Woven fabric is modeled as an in-plane anisotropic and nolinear membrane in the macroscopic model by adding key words into "INP" file of ABAQUS. A tensile failure criterion of fabric is set up in the user subroutine "VUSDFLD" of ABAQUS. The macroscopic model features the convenience and economy in simulating the process and provides a macroscopic view of the stress and strain distribution of woven fabrics. On the other hand, mesoscopic model of bursting process describes the detail of constituent yarns in three- dimensional. The yarns are assumed to be transverse isotropy. A tensile failure criterion of fabric is set up in the user subroutine "VUSDFLD" of ABAQUS. The microscopic model reflects the dynamic responses of yarns in bursting process. Excellent agreement with testing results has been observed in both macroscopic and mesoscopic models. Both models are used to simulate the process. The results show that:with the increase of friction coefficient between fabric and steel ball, inter-yarn slippage decreases, fabric strain energy and frictional dissipation energy increases, failure location is changed from the centre of woven sample to fixed ends and bursting ability increases. With the reinforcement of sample's boundary condition, bursting ability of woven fabrics also improves.With the knowledge gained in simulating bursting process, a mesoscopic FEM model woven fabric is established to simulate stabbing process of woven fabrics. In the model a modification is made to yarns'constitutive relation and tensile failure criterion. The model is evaluated by comparing with testing results of knife stab and spike stab. The results suggest that yams'slippage and revolve until cutting down by the blade when woven fabric stabbed by a knife. It is the radial strain of yams that exceeds the limitation and results in a fracture. A spike can squeeze into the space of yams in a woven fabric because of yams'slippage and revolve. From this it could be suggested that, with the increase of friction or density between yams, the slippage would reduce and spike resistant ability of woven fabric would be improved. Series of finite element analyses on the influencing factor of knife resistant ability are carried out and results are summarized as follows:(1) Shear module of yams influence the knife resistant ability of woven fabric the most, then radial module, and then axial module of yarns.(2) More energy will be transferred to yam strain energy during knife stabbing process if woven fabrics are multi-direction laminated or boundary conditions enhanced. As results, fabric absorbs more kinetic energy of knife and knife resistant ability will be improved.(3) With the increase of friction coefficient, there will be more friction dissipation energy that can absorb more impacting kinetic energy so that knife stab resistant ability of woven fabric can be improved. This is also the reason why plain weave fabric exhibits better protective property than twill or sateen weaves.(4) Reducing warp or weft density within a certain range, there would be more friction dissipation during knife stab process. As results, cutting down of yarns would be delayed and knife stab resistant ability of woven fabric increased.(5) With the increase in cross sectional area of yarns, there would be more friction dissipation energy and strain energy during stabbing process. Therefore, woven fabrics with coarse yarns have better stab protective ability.