On the flexural and extensional behavior of a large-tow triaxial braided composite

The lamina level extensional and flexural properties of a large-tow, triaxially braided, carbon-fiber/polymeric-matrix composite are examined. The braid's architecture is idealized with a single representative volume element. The homogenized lamina level properties are determined analytically by using concepts similar to beam theory as well as with three-dimensional finite-element techniques. The homogenized extensional and bending lamina properties are found to be distinct properties, not simply related to each other as in monolithic materials or in composites with very fine and highly periodic microstructures. Specifically, the ratio of the effective flexural to effective extensional Young's moduli is 0.52 and 0.92 in the longitudinal and transverse directions, respectively. The homogenized laminate properties of a two-ply composite were measured and compared to the numerical predictions. The ratio of the effective laminate flexural to extensional moduli predicted compares favorably with the experimental findings. Thus, in laminates with relatively few laminae, the actual flexural rigidity is lower than that based solely upon the extensional moduli.