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Abstract
This work explores the deformation and damage behaviour of woven fibre-reinforced thermoplastic matrix composites. These composites are of interest to the automotive, aerospace and energy sectors due to their high specific strength, manufacturability and recyclability. However, the woven architecture complicates the mesoscale deformation behaviour and consequent damage development. Therefore, an improved understanding of this behaviour is necessary for enhanced performance prediction through modelling and simulation, and hence confidence in design application under load. Advanced characterisation techniques are required to acquire this data experimentally. Specifically, an investigation into the influence of weave architecture, deformation mode, fibre/matrix constituents and defects on damage progression and local deformation is needed. This work uses digital image and volume correlation (DIC/DVC) methods along with micro-computed tomography (micro-CT) to address this knowledge gap.
Novel testing and characterisation techniques are developed through the thesis to advance knowledge of woven fibre-reinforced composites. This includes the development of new deformation mode testing to induce shear, tension and biaxial loading into composite laminates and to assess their deformation and damage development. Similarly, another new technique allows for the mesoscale topographical analysis of local weave surface deformation for tension, tension-torsion and hemispherical specimen geometries. Examination of internal deformation is also improved by an approach combining micro-CT with DIC and DVC. The latter technique enables a transition from macroscale and surface deformation characterisation to a detailed 3D understanding of the mechanisms and relationships between the woven microstructure and deformation.
The techniques developed in this thesis are applied to a variety of materials with varying fibre (carbon, glass, aramid and self-reinforced), matrix (PP, PC, PEI and PEEK) and weave style (plain, twill and satin). Several key findings are made. First, weave architecture, including style and layer alignment, significantly influences mesoscale strain and topography and can be identified based on the deformation characteristics. Similarly, defects, including fibre waviness, varying volume fractions and voids, also alter the local deformation response. Defects and architecture can then be related to the location and progression of damage in the form of matrix cracking, delamination and fibre fracture. The detailed evidence provided by DIC, micro-CT and DVC of defects, deformation and damage for different loading modes and material compositions enables a deeper 3D understanding of material behaviour. This understanding provides the foundation for improved mesoscale composite digitalisation and hence enables future high-fidelity simulations with accurate geometry and boundary conditions for reliable numerical failure prediction.
