Fused filament fabrication (FFF) of thermotropic liquid crystal polymers (LCPs) presents an attractive route toward lightweight components with excellent in-plane mechanical properties, enabled by molecular alignment during extrusion. However, the layer-by-layer nature of FFF leads to weak interlayer adhesion, which severely compromises mechanical performance in the build direction (Z-axis). This anisotropy limits the structural reliability of printed LCP parts under demanding conditions. Inspired by through-thickness reinforcement methods used in laminated fiber-reinforced composites, this thesis investigates the potential of z-pinning to enhance interlayer strength and damage tolerance in FFF-printed LCPs.

This work focuses on adapting the z-pinning concept, previously applied in PLA systems, to the challenges of anisotropic, shear-aligning LCPs. A z-pinning methodology is developed around the commercial filament Vectra® A950, utilizing a bottom-up insertion process enabled by custom G-code routines. Vertical pins are extruded into pre-formed voids during the print, allowing control over pin shape, height, and placement. The approach leverages standard FFF hardware, requiring only a narrow-tip nozzle and careful synchronization of extrusion timing to ensure consistent pin deposition.

Mechanical testing was conducted on both pinned and unpinned tensile specimens printed in the Z-direction. The results demonstrate that z-pinning significantly enhances performance when properly implemented. The best configuration, tall pins arranged in an ABA staggering pattern, achieved a 40% increase in peak load and a tenfold increase in energy absorption before reaching peak load. Fracture analysis revealed more distributed fracture patterns, with signs of crack deflection and arrest, indicating a transition from brittle delamination to
more progressive failure modes.

These findings validate the feasibility of z-pinning for improving the mechanical properties of 3D-printed LCP components. However, the benefits are highly sensitive to process execution, as poor pin deposition may negate reinforcement or introduce stress concentrators. The study underscores the importance of concurrent design and manufacturing development, showing that even in single-material systems, structural performance can be engineered through localized deposition strategies. This opens a path toward more robust, anisotropy-mitigated 3D-printed parts using high-performance polymers.

Goal-oriented reduced-order models (GOROM) have the potential to represent complex dynamics in an interpretable way. In the GOROM procedure, modes are found which when used in a Galerkin projection of the governing equations, return the desired goal function with minimum error. Determining such models leads to a high-dimensional optimisation problem, which may have multiple extrema, making purely local optimisation inapplicable.
In this thesis, a global optimisation algorithm was derived for GOROM. The optimisation response surface was approximated with a surrogate model, built using the Kriging technique. In each iteration, the surrogate model was improved by including the objective function of the three points with the highest expected improvements. This iterative process was stopped when the expected improvement fell below a threshold.
First, the performance of the algorithm was confirmed for a simple non-GOROM optimisation. Then the algorithm was applied to GOROM optimisation for the forced Burgers equation, initially using a complex forcing function giving multiple minima and later to a forcing function derived from a DNS of a turbulent channel flow. The initial forcing required on the order of tens of degrees of freedom to be optimised. The corresponding response surface proved similar to that of the simple problems, showing these optimisations to be tractable.
For the DNS forcing, hundreds of coefficients needed to be optimised. Using the developed algorithm a better optimal was found than with the local algorithm, although substantially more computational resources would be required to confirm global optimality.

The environmental impact of composite materials is a growing concern across numerous industries, prompting the need for sustainable alternatives. Bamboo fibre reinforced polymers (BFRPs) have emerged as a promising solution thanks to their high CO_2 capture leading to lower environmental footprint. A novel extraction method, developed and patented by Bambooder, aims to extract bamboo fibres through a purely mechanical industrial process while preserving their maximum performance. These fibres currently in development, necessitate comprehensive material characterisation.

In this study, BFRPs were produced using fibres provided by Bambooder, combined with polypropylene (PP) and polyamide 11 (PA11) through compression moulding, and with epoxy using resin-infusion composite production methods. The density of fibres was measured at 1.16 g/cm^3. The highest composite performance was achieved with epoxy, revealing a tensile back-calculated fibre modulus of 54.2 GPa and a strength of 509.6 MPa. These properties are higher than properties observed in current literature, having a tensile modulus and strength of approximately 36 GPa and 503 MPa respectively. Similarly, flexural back-calculated fibre properties showed a modulus of 44.6 GPa and a strength of 484.7 MPa.

Thermoplastic laminate testing demonstrated good bonding performance with PA11, attributed to the formation of hydrogen bonds at the fibre-matrix interface due to the polymer's non-polarity. In contrast, PP exhibited poor interfacial bonding. Additional fibre combing improved mechanical performance by up to 20% in tensile modulus and 9% in tensile strength, attributed to better fibre quality, improved fibre orientation, and increased fibre dispersion.

This thesis therefore validates the use of bamboo fibres for structural composite applications and highlights their potential as sustainable engineering materials, promoting the adoption of natural fibre composites such as BFRPs in various industrial sectors.

Thin-walled composite structures are critical in aerospace engineering, making it essential to understand their failure mechanisms. However, manufacturing test samples and conducting high-fidelity experimental tests are both complex and expensive, making advanced modeling techniques essential. The Cohesive Zone Model (CZM) is a widely used method for modeling delaminations in composites, but it typically depends on artificial elastic compliance, which can compromise accuracy. This thesis introduces a high-fidelity finite element model that integrates the Discontinuous Galerkin method with geometrically exact shell elements to explicitly model each lamina during large deformations and buckling in multi-layered materials. By coupling the layers, this approach eliminates the need for artificial compliance. Numerical simulations show the model’s accuracy in predicting structural behavior under various loading conditions, although challenges remain in maintaining proper layer separation during deformation. This study lays the groundwork for modeling delaminations along arbitrary interfaces.

Mechanical air entrapment, void compression and void dissolution are the main mechanisms behind void formation in liquid composite molding. Mechanical air entrapment is induced by the highly non-uniform geometry at the meso- and micro-scale and the heterogeneous properties of the reinforcing material. This results in differences in the velocity profile through the porous- and free flow domains, which can lead to air being entrapped in slow-flowing domains, by resin flowing through the faster flowing domains. Depending on the competition between the viscous flow through the free flow domains and the capillary flow through the porous domains, voids occur either in the intra-bundle domain or in the inter-bundle domain, where the competition between the two flow types can be quantified by the capillary number. Once the voids are entrapped, they can change in size due to void compression and -dissolution, all which occur on considerably different timescales. An experimental set-up was developed which uses fast radiation curing to almost instantly cure the resin during injection and thus detach the different stages of void formation from each other. In this research the relationship between the mesoscale structure of a woven fabric and mesoscale void formation was investigated. The mesoscale structure is strongly related to void formation, as viscous flow is related to the inter-bundle domain size in the through-thickness direction of the preform and capillary flow is related to the mesoscale bundle porosity. As the bundle porosity is related to both the bundle permeability, and the capillary pressure, its influences on void formation were considered to be large, and thus bundle porosity became the main research topic. A 2D semi-analytical model based on mechanical air entrapment was constructed which was capable of determining the filling times of the intra- and inter-bundle domains on the mesoscale. A parameter called the competitive number was introduced which was related to these filling times. Once the competitive number was larger than 1, spherical inter-bundle voids should be formed, once it was equal to 1 no voids should be formed and once it was lower than 1 ellipsoidal intra-bundle voids should be formed. This model was validated experimentally. Flow behavior predicted by the model was compared to video footage of the flow front propagation at the surface of the preform at the macro- and mesoscale during multiple injections. Void volumes, types and locations obtained from the model were compared to voids observed in micro-CT scanned samples and were in agreement with each other. The validated model was eventually used to investigate the effects of bundle porosity on void formation. It was found that increased bundle porosity at a constant global preform porosity, leads to increased intra-bundle flow and decreased viscous flow, thus considerably influencing void formation by mechanical air entrapment. In short injection cycles with high macroscopic flow velocities, which can lead to intra-bundle voids, it could be beneficial to switch a fabric with a higher bundle porosity, as that would effectively reduce the intra-bundle void size. For injections with low macroscopic flow velocities, the opposite would apply, thus usage of fabrics with lower bundle porosities could help to reduce the inter-bundle void volumes.