This PhD thesis presents an experimental investigation into the tensile properties, strengthening mechanics and failure mechanisms of three-dimensional (3D) woven composites with through-the-thickness (z-binder) reinforcement. 3D composites are being developed for the aerospace industry for structural applications in next-generation aircraft, such as wing panels, joints and stiffened components. The use of 3D woven composites in primary aircraft structures cannot occur until there has been a detailed assessment of their mechanical performance, including under tensile loading conditions. The aim of this PhD project is to provide new insights into the in-plane tensile properties, fatigue life, tensile delamination resistance and failure mechanisms of 3D woven composites with different amounts of z-binder reinforcement. Previous research has revealed that excessive amounts of z-binder reinforcement dramatically improves the tensile delamination toughness, but at the expense of the in-plane structural properties. For this reason, this PhD project aims to evaluate the tensile performance of 3D woven composites with relatively small z-binder contents (less than ~1%). The research aims to provide a better understanding of the manufacture, microstructure and tensile properties of 3D woven composites to assist the process of certification and application of these materials to aircraft structures as well as high performance marine and civil structures.

Manufacturing methods for aerospace composite parts are various. Vacuum assisted resin transfer moulding (VARTM) is one of the common methods. It requires manual draping of fabrics to produce preforms. The cost and quality of this method depend on the draping strategy, which is the sequence of draping operations performed by staff as they lay fabrics on moulds. These sequences can be very numerous with many possible starting points, yarn orientations, and fabrics used. In this group project, a predictive software tool is designed ultimately to identify the best draping strategy to reduce cost and improve quality in producing preforms. Generation of preform flat patterns for the CNC cutting tables, and of plybooks for providing instructions to shop floor staff, are developed and integrated into the predictive tool so that the manual draping process can potentially be conducted under the best draping strategy. The work presented in this thesis details the solutions for finding flat patterns for the best draping strategy for the CNC cutting tables, and the generation of plybooks for providing instructions to shop floor staff. The work is organized into four main parts: developing flattening algorithms for three types of base surfaces (BaS) defined in this project, developing a subsequent stitching algorithm aimed at stitching individual flattened BaS into a unified flat pattern for a given mould, lab validations to assess the proposed flattening and stitching algorithms, and establishing the capability to generate instruction .DXF files and plybooks for any received draping strategy. These algorithms are integrated into the predictive tool to facilitate manual draping processes under the optimal draping strategy.

Composites have now revolutionized most industries, like aerospace, marine, electrical, transportation, and have proved to be a worthy alternative to other traditional materials. However for a further comprehensive usage, the tailorability of hybrid composites according to the specific application needs on a large-scale production basis is required. In this regard, one of the major fundamental research fields here involves a technology development based on the multiaxial warp-knitting technique for the production of bionic-inspired and application-specific textile preforms that are force compliant and exhibit multi-material design. This article presents a newly developed yarn (warp) path manipulation unit for multiaxial warp-knitting machines that enables a targeted production of customized textile preforms with the above characteristics. The technological development cycle and their experimental validation to demonstrate the feasibility of new technology through production of some patterns for different field of applications are then discussed.