Off-axis tensile properties of multistitched plain woven E-glass/polyester composites

The aim of this study was to understand the ±45 ° directional off-axis tensile properties of the developed two dimensional (2D) multistitched multilayer E-glass/polyester woven composites. It was found that the off-axis tensile strength of the unstitched structure was slightly higher than those of the multistitched structures. The reason was that the multistitching process caused the filament breakages. It was also found that when the stitching direction and stitching density in structures increased, their off-axis tensile modulus decreased. Therefore, stitching directions, stitching density and stitching yarn on the composite structures were considered as important parameters. All structures under the off-axis tensile load had normal deformation, or angular deformation or shrinkage in width. In addition, both the normal deformation and the shrinkages in width occurred in most of the two and four directional stitched structures. On the other hand, four directional Kevlar^® 129 yarn dense stitched E-glass/polyester structure showed only shrinkage in width after angular deformation. This could be considered as a new failure mode because of the multistitching. These results indicated that the stitching directions and density generally influenced the off-axis tensile properties of the multistitched E-glass/polyester woven composites.