Investigation into the Tensile Properties of Stitched and Unstitched Woven Aramid/Vinyl Ester Composites

In this study, the influence of stitch bonding on the tensile strength and tensile modulus in plain woven Twaron T-750/vinyl ester composites in the direction of thickness was examined. The effect of stitch density was investigated in longitudinal (warp) and transverse (weft) directions as a parameter. The space (opening) geometry and the deformation caused by the stitching process around stitch points were investigated. The stitching tension, stitch thread type and diameter were kept constant throughout the study. An increase in the tensile strength was observed for low stitching densities while there was no change in the tensile strength for medium stitching densities. A decrease in the tensile strength was observed for high stitching densities. It is especially noted that the tensile strength, which is on the transversal direction perpendicular to stitch direction, decreased with stitching density and tensile deformations initiated much earlier in this direction. It was understood that fiber deviations and resin rich areas were much more effective on these decreases compared with fiber deformation.