Architecture and mechanical properties of three-dimensional braided composites.

摘要

The fiber architectures in 3-dimensional textile performs from the well known 4-step and a novel 6-step braiding processes were presented. An equation was given to determine fiber volume fractions with measurable preform dimensions and known machine set up. The fiber volume concentration in the fiber tows was exhibited. The effect of fiber orientation on the moduli in the longitudinal, transverse and through-the-thickness directions was demonstrated through calculations using lamina analogy and classic lamination theory. The changes in moduli due to the presence of axials in the longitudinal direction and/or filling tows in transverse directions were analyzed. The performance of 3-D braided Carbon/Epoxy composites were evaluated through flexural, compressive and pull-out tests. Some triaxially braided and laminated composites were also tested in flexure and in compression to serve as references for the 3-D braided composites. Experimental results demonstrated that: (1) the 3-D braided composites had favorable flexural and compressive properties and excellent pull-out strength; (2) the flexural modulus of a 3-D braided composite can be significantly different from the tensile modulus; (3) the effect of cutting off the braided edges of 3-D braided composites on their flexural properties was not as drastic as previously reported and believed; (4) the excellent pull-out strength made it promising to develop composite nuts and space joint node which connects several rods through thread in various directions; (5) the pull-out loads of 3-D braided composites were related to the fiber architecture and fiber orientations in the materials.