| High-strength fabric flexible impact protection system such as bulletproofvest, stab clothing and aircraft engine blade protection deviceis,is based onaramid fiber as basic material consisting of complicated structure. A largenumber of experiments have shown that fiber-fiber friction,yarn-yarn frictionand layer-layer friction are important factors in the impact energy absorptioncapacity of the high-strength fabric structure.During the impact process there aresix main factors that affecting energy absorption:yarn material properties,fabricwoven structure,projectile geometry,initial impact velocity of projectile,fabricboundary conditions,fabric layers and interfacial friction.In this thesis, a three-dimensional finite element analysis model forplain-weave fabric was created and impact of a rigid, flat-nosed projectile ontosquare fabric clamped along four edges were simulated using commerciallyavailable software LS-DYNA. To reveal the role of interfacial friction duringimpact, comparative study was conducted in which projectile velocity, boundarycondition and material property et al. were kept the same but friction betweenprojectile and fabric and between yarns themselves were varied systematically. Results from the study show that friction dissipated energy only accountsfor a small portion of the total absorbed energy during impact. Friction dissipatedenergy is not a primary energy absorption mechanism, yarn kinetic energy andyarn strain energy are main mechanism for energy absorption. However, frictionhas indirect effect on characteristics of fabric energy absorption. Friction betweenprojectile and fabric has little effect but friction between yarns themselves hasapparent effect on fabric energy absorption characteristics. Fabric exhibits largerimpact energy absorption capacity when friction coefficient between yarns aresmaller. Friction between yarns affect the time of yarn breakage during impactand thereby influence fabric impact energy absorption. Smaller friction betweenyarns delay both initiation of yarn failure and penetration of fabric, increase theduration of interaction between projectile and fabric, and therefore increase fabricimpact energy absorption capacity. In addition, the role of friction was studied fordifferent size of fabric and different impact velocity, and results show that the roleof friction during impact are not affected by fabric size or impact velocity. |
