Effect of Architecture on the Strength of Braided Tubes Under Biaxial Tension and Compression

Braided preforms of carbon fiber are under consideration for structural applications because of the potential for automated fabrication and possible improvement in through-the-thickness properties, although some loss of in-plane properties is expected. In the present investigation, the biaxial compressive strength properties of triaxial braided cylinders are measured experimentally, and the effects of four different sets of braid architectures are considered. The results show that fiber direction strain can correlate the results of biaxial tensile and compression failure tests. The braid parameters are found to have an effect on measured strengths, primarily through the introduction of defects into the fiber paths. The axial compression strength was found to be sensitive to waviness in the fiber path that was produced by uneven braiding coverage. Braid direction compression and tension strength is significantly lower than axial strength, and is also affected by braid parameters.