Development and understanding of non-uniform 3D woven composites

Abstract

Engineering structures often require components with region-specific performance,where variations in stiffness, strength, or damage tolerance are crucial for efficiencyand reliability. Traditional research into 3D woven composites has concentrated onuniform architectures throughout the preform, underutilising their ability to betailored for local needs. This thesis addresses this gap by investigating how controlledarchitectural variations, specifically float length and pick density, affect both thephysical and mechanical behaviour of 3D woven non-uniform composites.

A consistent loom setup was employed to produce both uniform and non-uniformpreforms, enabling a comparison of how transitions influence material performance.Physical characterisation revealed the effects of architectural variations on unit cellgeometry, fibre volume fraction, crimp, and resin distribution. Mechanical behaviourwas evaluated through tensile, flexural, and interlaminar shear tests, supported byDigital Image Correlation (DIC), microscopy, and computer tomography (CT) tomonitor localised strain development and failure mechanisms.

The findings established the baseline behaviour of three uniform architectures –Layer-to-Layer, Angled Interlock, and Orthogonal – which demonstrated trade-offsbetween warp and weft, and through-thickness performance. Layer-to-Layer waschosen for transition studies due to its simplicity and balanced directional properties.Float length influenced crimp and binder interlacements, with longer floats enhancingwarp stiffness but also reducing toughness and shear strength. Pick density influencedfibre packing and resin distribution: higher densities improved stiffness through morecompact structures but also caused increased crimp. In comparison, lower densitiescreated resin-rich regions and misalignments that promoted premature failure.Transition regions emerged as critical sites, acting both as potential weak points andxxxareas where performance could be locally improved. This work provides newexperimental evidence that non-uniform 3D woven composites can be manufacturedreliably and used to embed region-specific functionality. It also highlights thecomplexity and variability introduced by transitions, underlining the importance ofarchitectural design. These insights advance the fundamental understanding needed toexploit 3D weaving for multifunctional high-performance composite structures.

Date of Award	Mar 2026
Original language	English
Supervisor	Alistair McIlhagger (Supervisor), Edward Archer (Supervisor) & Calvin Ralph (Supervisor)