Influence Of Fiber Constraint On Ballistic Performance Of Aramid Plain Weave

Aramid plain weave is an important component of the bullet-proof layer of the soft protective equipment,but due to the influence of the inter-ply and inter-surface fiber constraint of the laminated fabric,the aramid fiber can't show its superior mechanical properties to the best,which is not beneficial to the energy absorption of plain weave and reduces its ballistic performance.Therefore,in order to improve its protective performance,the effect of fiber constraint on the ballistic performance of aramid plain weaves in this work was investigated by changing the ply gap of spaced fabric systems,stitching technology and modifying the structure of the plain weaves.The main findings are as follows:(1)The existence of the the ply gap in through-the-thickness directions of the fabric target improves the energy absorption capacity of spaced multi-ply fabric systems.The energy absorption value of the multi-ply systems shows a trend of increasing and then decreasing with the increase of the critical normalized ply gap G.For all types of target systems,the critical G value that provides the best energy absorption capacity is approximately range from2.5 to 5.In addition,the finite element numerical predictions showed that the energy absorption capacity of the spaced system is related to the ply gap and projectile impact velocity.Increasing the ply gap and projectile impact velocity of the spaced system are conducive to improving the energy absorption efficiency of the front plies,but not conducive to that of the rear plies.(2)The stitching threads in through-the-plane directions significantly increased the frictional constraint between the weft and warp yarns in plain weaves.The pull-out tests showed that the peak pull-out force with one stitching line was 6 times higher than that of the un stitched plain weave,and the peak pull-out force of the stitched samples increased with the number of stitching lines.The ballistic test results showed that the stitching technique improves the energy absorption capacity of plain fabrics significantly and has a better ballistic performance.The energy absorption energy value of the stitched samples increased and the SEA of the stitched samples showed a trend of first increasing and then decreasing with the increase of the stitching density.It was also found that the ballistic performance of the fabric decreased as the projectile impact velocity increased.The finite element numerical prediction showed that the existence of stitching lines forced the fibers to absorb the kinetic energy of the projectile by breakage,which improveing the strain energy and kinetic energy of the fabric and enhanceing its ballistic performance.(3)Compositing the knit structure with the woven structure in through-the-plane directions helped to increase the yarn ability to resist pull-out,confirming that the modification of the plain structure improved the frictional constraint between the yarns and limited the inter-yarn mobility.It was also found that the peak pull-out force increased with the increase of yarn pull-out speed.The results of the ballistic test showed that the composite structure enhanced the ability of the plain weave to resist projectile impact,in which,the V₅₀of the structure-modified fabrics was 71.6 m/s,which was about 18.3%higher than that of the plain weave.Both single-layer and multi-layer systems composed of structure-modified fabrics exhibited better energy absorption performance at different impact velocities.It was also found that the material in the knitted/woven composite region formed a secondary deformation during yarn pull-out,which weakened the stress concentration at the impact location,prolonged the contact time between the projectile and the primary yarns,and contributed to the energy dissipation during yarn pull-out.In addition,it helped to expand the range of strain distribution and improve the energy absorption capacity of the plain weave.