ANALYSIS OF MULTIAXIAL WARP-KNIT PREFORMS FOR COMPOSITE REINFORCEMENT

Three-dimensional structures of multiaxial warp-knit (MWK) fabrics hav e been recently developed for multidirectional reinforcement of compos ites. Multilayers of linear yarns are assembled in warp (0 degrees), w eft (90 degrees), and bias (+/-theta) directions to provide in-plane r einforcement in specific directions, and they are stitched together by knitting yarns to provide structural integrity and through-the-thickn ess reinforcement. Based on the experimental observations, the unit ce ll geometry of the MWK fabric is identified along with idealized cross -sectional shapes of insertion and stitch yarns. A geometric model is developed relating the geometric parameters and process variables. Exp ressing fiber volume fraction and fiber orientation in terms of struct ural and processing parameters, this geometric model provides a basis for the establishment of process windows for the MWK fabric preforms a s well as for the prediction of the mechanical behavior of the MWK rei nforced composites.