Influence of braid set up and roving size to mechanical properties of biaxial carbon fiber braids

In contrast to UD-layer laminate braided fabrics show a significant reduction in the mechanical properties. As a main driver the undulation of the fibers is identified. In order to investigate this influence, three different weave styles (diamond, twill 2/2 and twill 4/4) are compared. Two roving sizes are evaluated: Tenax HTS40 12k and SGL C30 50k. Tensile, compression and interlaminar shear strength tests are performed in two directions: direction 1, corresponding to ±45° fiber angle in the specimen, and direction 2, 0/90° fiber angle in the specimen. To fabricate the specimens, textiles with altered braid set ups of both fiber types are produced on tubular core, unwound after a longitudinal cut, stacked and cured with epoxy resin system Hexcel RTM 6. In direction 2 the twill 4×4 has 18% higher tensile strength compared to the diamond braid. Under compression load the difference is more significant. The compression strength of twill 4×4 is 30% higher than the strength of the diamond braid. For the interlaminar properties the undulation has a contrary effect. The diamond braid has the highest shear strength. The smaller roving size shows a positive effect on the strength under compression and tensile load. The 12k twill 4×4 weave has 39% higher tensile strength and 11% higher compression strength than the 50k twill 4×4.