Multilayered and Multidirectionally-stitched aramid Woven Fabric Structures: Experimental Characterization of Ballistic Performance by Considering the Yarn Pull-out Test

The aim of this study was to understand the energy absorption mechanism and failure modes of newly developed multidirectionally-stitched structures. Para-aramid woven fabric was used. The structures were in unstitched and stitched forms. Nylon 6.6 yarn was used to stitch the structure in one, two and four directions whereas Kevlar (R) 129 yarn was used to make only the four-directionally-stitched structures. The yarn pull-out fixture was developed and the yarn pull-out test was performed on single woven fabric and stitched structures. Ballistic tests were performed on the structures using 9 mm full metal jacketed projectiles with a speed of 300 to 400 m/s. If the applied kinetic energy level is under the yarn breaking extension, crimp in the orthogonal yarns at the fabric structure is firstly removed, and thereafter yarn pull-out takes place in the structure plane, and later stage fabric deformation occurs in the out-of-plane direction of the structure. This phenomenon continues from the outside to the inside layers. If the applied kinetic energy level is above the yarn breaking extension, firstly partial and total filament breakages and subsequently crimp removal and yarn pull out stages occur. These phenomena take place as multiple yarn failure in the outer layers and mostly crimp removal and yarn pull-out towards the inside layers occur. In both cases, fabric and structure bending were ignored. The energy absorption level of the stitched structures was slightly higher than that of the unstitched structures due to the fact that some of the energy was absorbed to delaminate the interlayer, which was locked by the stitching yarns. Also, the conical depth in the stitched structure was low compared with that of the unstitched structure.