Improving fracture resistance of laminar textile composites by third direction reinforcement

The fracture behavior of multidirectional laminar composites was investigated. Two-and three-dimensional composites were fabricated and tested for this purpose. The effects of third direction fibers on composite mechanical properties were examined. Effects of fiber orientation, stitch density and configuration on resistance to crack propagation and the suppression of delamination were studied. Damage resistance, flexural and shear strength were investigated as a function of distribution of the third direction fibers. The effects of fiber damage due to stitching on the mechanical properties of composites were examined. A new stitching method was developed which successfully eliminated the fiber damage. Delamination was reduced and shear strength and impact energy were increased in properly stitched 3-D composites.