GEOMETRICAL AND MICRO-MECHANICAL MODELLINGOF BRAIDIED COMPOSITE TUBES

摘要

Three-dimensional textile composites have already proven their value in terms of damage tolerance,improved through-the-thickness properties, near-net shaping and potential savings in manufacturingcosts. Braided preforms are ideally suited for relatively narrow structures and offer advantages interms of fibre continuity at the edges and around the holes and the possibility of producing complex3D shapes with the aid of mandrels. As part of an Integrated Design Methodology (IDM), the authorshave developed geometrical and micro-mechanical models for braided composites. Accurategeometrical models are a prerequisite for composite micro and macro mechanics. Geometricalmodels were developed with an assumption of lenticular yarn cross-section to predict the yarn width,thickness, yarn path, crimp angle and fibre volume fractions. In the present work, micro and macromechanicalmodels were developed. Initially, the in-plane and out-of-plane properties of a RepeatingUnit Cell (RUC) were estimated using modified laminate theory. The mechanical propertiespredicted using the analytical model compared well with the experimental data. However, 3D FEMmodels are necessary to predict the local stress/strain distribution and the failure loads. RepeatingUnit Cells, widely described in the literature, can be used only in the case of ±45o braids. In thiswork, the authors have developed a modified RUC suitable for braided structures with any braidangle. Marco behaviour of the braided composites tubes was also analysed with the help of 3D FEMtechniques.