ELASTIC-MODULI AND DAMAGE EVOLUTION OF 3-AXIS WOVEN FABRIC COMPOSITES

Three-axis orthogonal woven fabric composites composed of carbon fibre s and epoxy resin have been fabricated. Examined from micrographs, the fabric weaving yarns were found to be very slender with aspect ratios ranging from 11-13.6. Based upon the observed geometry, the composite has been modelled by a unit cell comprising wavy yarns. Both elliptic al and lenticular cross-sections were adopted to simulate the slender weaving yarns. Taking into account one-dimensional stress concentratio n and yam undulation, an iso-phase approach has been developed to anal yse the composite elastic moduli. A higher weaving yarn aspect ratio w as found to result in a lower modulus. Modulus reduction due to yarn u ndulation was more significant in weaving directions. Material charact erization has been conducted based upon monotonic tensile and three-po int flexural tests, and detailed damage mechanisms for both loadings h ave been examined. The onset of damage under tensile loading was found to be z-axis yam debonding, followed by debonding and splitting in y- axis yarns. When subjected to flexural loading, yarn debonding, transv erse cracking, and interyarn matrix cracking were the dominant damage mechanisms which appeared on specimen tensile sides. Stress transfer a mong yarns and how it relates to the composite damage have been discus sed in detail.