Design optimisation of 3D woven reinforcements with geometric features

3D weaving technology enables the manufacturing of advanced near net-shape profiles, through incorporating geometric features such as bifurcations, and varying cross-sections into the preform, for use as reinforcements in composite materials. Their design space is very large due to a wide range of weave patterns in their 3D fibre architectures, and currently the lack of analysis techniques that relate weave architectures with the resulting processing and structural performance restricts the application of such advanced 3D woven composites. In this thesis, the effect of fibre architecture on mechanical properties was shown to be significant for 3D woven composite T-joints, which further illustrates the challenges for designing an optimum 3D woven reinforcement. This work is an attempt to develop modelling techniques that are able to accurately predict the resulting structural performance for composites based on 3D woven architectures. Geometric models were developed to account for the deformation in the fibre architecture caused by the bifurcation process in manufacturing of 3D near net-shape T-joint preforms, in order to improve the accuracy of the reinforcement geometry in finite element models. A methodology based on voxels was proposed to overcome the current meshing problems whilst allowing delamination modelling for composites with complex fibre architecture. Consequently, a meso-scale modelling framework for predicting weave architectures of 3D woven composite T-joints and the resulting mechanical behaviour under quasi-static pull-off loading was proposed, in which damage modelling incorporates both interface and constituent material damage, in conjunction with a continuum damage mechanics approach to account for the progressive failure behaviour. Results were shown to agree well with experimental data beyond initial failure. Based on the proposed predictive modelling method, the effect of fibre architecture, in which the design space was simplified by three design variables, i.e. weft yarn path straightness, weft yarn path entanglement and weft yarn path cross-over, on mechanical performance was investigated. Varying yarn path cross-over was found to improve both stiffness and failure load. Increasing the proportion of yarn path entanglement also improved the damage resistance capability, but a high level of yarn path entanglement caused a reduction in yarn path straightness and therefore the structural stiffness would be compromised. Based on the above findings, a design optimisation philosophy for 3D woven T-joint reinforcements under tensile pull-off loading was proposed