Microstructural analysis of composite tubes made from braided preform and resin transfer molding

This paper investigates the manufacturing method and mechanical properties of composite tubes made from braided fiber preforms. The tubes molded by Vacuum-Assisted Resin Transfer Molding (VARTM) process with different resins, fiber reinforcements and braiding architecture were tested for weeping and burst strength. Both biaxial and triaxial braided fiber preforms were used. The failure modes of tubes made from these two braiding architectures were different. For biaxially reinforced tubes, the initial cracks are aligned along the direction of the fiber tows, while for triaxially reinforced tubes, the initial cracks along the longitudinal direction appear first. Tubes with and without flanges were also fabricated. The strength tests indicated that the tube with flanges is much stronger than the one without flanges. Two theoretical models based upon mechanics of material were employed to predict the mechanical properties. The pressure vs. deformation curves from the weep/burst tests are consistent with the theoretical predictions in the elastic region.