Advanced Tape Layer Additive Manufacturing (ATLAM) combines the structural performance of automated tape laying with the geometric freedom of additive manufacturing. A Geometric Projection Topology Optimisation (GPTO) framework has been developed for ATLAM that simultaneously optimises structural stiffness and eco-efficiency, but had not yet been experimentally validated. This thesis develops a desktop-scale ATLAM workflow using a conventional FDM printer with an in-house automated compactor tool to embed continuous carbon fibre reinforced tapes within a thermoplastic substrate. Four topology-optimised Messerschmitt-Bölkow-Blohm beam designs were manufactured and tested. The finite element model accurately predicts substrate-only stiffness within 7%, but overpredicts tape-reinforced stiffness by up to 88.5%, attributed to a shear lag effect. Despite this, GPTO achieves the highest stiffness-to-weight ratio of 9.78 kN/mm/kg and leads all designs on stiffness-to-embodied-CO₂, outperforming the density-based industry standard and demonstrating the potential of GPTO for eco-efficient ATLAM structural design. ... Read more

Phased array antennas are a critical element of modern wireless communication and sensing systems, enabling rapid electronic beam steering without mechanically moving the antenna. However, there are inherent challenges and limitations associated with phased arrays antennas. Notably, a drop in the antenna gain is observed as the beam is steered away from broadside, a phenomenon known as scan loss. Dielectric lenses, and in particular gradient index (GRIN) lenses, are a promising solution to mitigate this effect, potentially allowing for drop-in improvements to existing antennas.

Recent advances in additive manufacturing enable the realization of dielectric media with a continuously varying refractive index, allowing for more freedom in the form factor compared to conventional homogeneous or multilayer lenses. This thesis investigates the design, optimization, fabrication, and experimental validation of an additively manufactured flat GRIN lens to enhance the scan coverage of a planar phased array antenna.

A workflow for the realization of GRIN media using single-material fused filament fabrication (FFF) is presented. Spatially varying effective permittivity is achieved through sub-wavelength dielectric crystals based on triply periodic minimal surface (TPMS) structures, enabling continuously varying GRIN profiles. The dielectric properties of printed polylactic acid (PLA) are characterized experimentally using a split post resonator setup (courtesy of IT’IS). With these measurements, it is shown that PLA is suitable for proof-of-concept GRIN lenses at frequencies below 30 GHz, despite moderate dielectric losses.

A novel parametrization of GRIN lenses is introduced, in which the refractive index distribution is represented as a Fourier series expansion, normalized to the achievable minimum and maximum refractive indices imposed by manufacturing constraints. This formulation is especially well suited for use with curved-ray geometrical optics, as the gradient of the refractive index can be computed analytically. Based on this parametrization, the GRIN lens design problem is formulated as a multi-objective inverse problem, targeting a model for the ray direction and phase at the lens aperture. The optimization problem is solved using particle swarm optimization, enabling efficient exploration of a large design space with relatively low computational cost.

The proposed methodology is validated through the optimization of a Luneburg-like lens. The optimizer recovers a GRIN profile close to the ideal Luneburg lens, validating the ray-tracing algorithm as well as the fitness function. This approach is then applied to the primary design case; a flat, scan-enhancing GRIN lens for use with a planar phased array antenna. The optimized lens is experimentally evaluated in the Delft University Chamber for Antenna Tests (DUCAT) using a TMYTEK BBox 5G phased array antenna, operating at 28GHz. Measurements demonstrate an increase of +-10 degrees in the scan coverage compared to a free-space reference configuration, confirming the potential of additively manufactured GRIN lenses as a practical tool for drop-in enhancements of phased array antennas.
... Read more

Thermoset epoxies are extensively used in engineering fields such as automotive and aerospace applications owing to their excellent mechanical properties and thermal stability. However, their highly crosslinked molecular structure renders them inherently brittle and prone to fracture, underscoring the need for effective toughening strategies.

Spider silk exhibits remarkable fracture resistance due to its molecular architecture, which incorporates sacrificial bonds and hidden lengths (SBHL). Upon loading, the sacrificial bonds rupture first, followed by sequential unfolding of the hidden lengths in protein chains, dissipating significant energy without catastrophic failure. Inspired by this mechanism, this thesis introduces and validates the SBHL toughening concept for structural epoxy, providing a foundation for future engineering applications......

The research presented in this thesis started with the fabrication of spider silk-inspired structures. To replicate the natural SBHL toughening mechanism, polymeric overlapping curl (OC) fibers with sacrificial bonds and hidden lengths were 3D-printed using the liquid rope coiling effect. Three polymers—polylactic acid (PLA), liquid crystal polymer (LCP), and polyamide 6 (PA6)—were employed. Uniaxial tensile tests characterized the effects of geometry, post-treatment, and material properties on the OC mechanical responses. Results showed that single-sided OC fully unfolded, whereas double-sided curls failed prematurely. Post-treatments combining heat and pressure enhanced the load-capacity of sacrificial bonds by up to 77 %, but introduced defects in the fibers that caused premature failure and reduced toughness by up to 67 %. To ensure the complete hidden length unfolding and improved toughness, polymers with either high fracture strength (e.g., LCP, 311MPa) or high fracture strain (e.g., PA6, >2) were found essential, achieving toughness increases of 32% and 46 %, respectively.... ... Read more

The transition towards a sustainable aviation sector requires a fundamental rethinking of how structural materials are designed, manufactured, joined, and used. Lightweighting alone is insufficient if achieved through materials and processes that are energy-intensive, difficult to recycle, or incompatible with circular use. This thesis explores an alternative paradigm: sustainable structural systems that integrate bio-based materials, eco-efficient multi-material design, adhesive-free joining, and ultimately self-sensing functionality.

Firstly, the thesis develops sustainable joining strategies for wood-based structures. Ultrasonic welding is studied as an adhesive-free joining method that exploits the thermoplastic behaviour of native lignin by introducing three-dimensional printed, lignin-rich energy directors. This method has demonstrated improvements in joint strength and durability while maintaining compatibility with circular design principles and scalable manufacturing.

Secondly, the thesis advances computational and experimental methods for an eco-efficient multi-material design framework. The topology optimisation framework is extended to include environmental performance metrics alongside mechanical objectives, enabling explicit trade-offs between stiffness, mass, and environmental impact. These designs are realised using multi-material additive manufacturing, demonstrating how selective material placement can reduce waste, improve performance, and enable functional integration.

Thirdly, focusing on lignocellulosic material systems, particularly wood, lignin, and fungal mycelium, the work addresses the question of how traditionally passive bio-based materials can be transformed into functional, adaptive, and circular structures. Three complementary research directions are pursued. First, the thesis investigates fungal biology and signalling, examining how living mycelial networks embedded within composites exhibit bioelectrical activity that responds to environmental and mechanical stimuli. These findings point toward the possibility of structural materials that inherently sense and report on their own condition.

Finally, the results demonstrate that sustainable structures cannot be achieved solely through material substitution. Instead, performance, sustainability, sensing capability, and manufacturability must be addressed simultaneously. By combining living and self-sensing materials, optimised multi-material architectures, and sustainable joining and manufacturing techniques, this thesis lays the groundwork for a new class of structural systems that are lightweight, circular, and functionally active. ... Read more

What if repairing a damaged composite panel could be as precise and repeatable as manufacturing a new one? Despite the widespread use of composite materials in the aerospace, automotive, and renewable energy sectors, in situ repair methods remain largely manual and often fail to restore the original mechanical integrity. The increasing use of fibre-reinforced polymers as a result of their high strength-to-weight ratio, fatigue, and corrosion resistance increases the need for more advanced and reliable repair solutions. This demand motivates the development of semi-automated systems to improve both repeatability and performance in composite repair.

This thesis investigates the feasibility of a semi-automated handheld robotic system for in situ material deposition, leveraging human guidance alongside robotic precision. To this end, a prototype handheld extrusion device was developed, integrating onboard optical flow sensors for real-time positional correction. Its control architecture enables user-guided motion while autonomously compensating for tracking errors, combining human adaptability with the repeatability of robotic control to ensure consistent material deposition.

To evaluate system performance, a surface-level defect modelled as a 175 mm long crack was introduced into a wooden substrate. Material was deposited into the defect under controlled conditions using the prototype, completing the process in 35 s. The device successfully performed real-time correction and deposition, demonstrating the feasibility of augmented handheld additive repair. Average accuracies of 1.05 mm in x and 2.45 mm in y were achieved after movements of about 300 mm in global x and 70 mm in global y. This level of precision demonstrates the basic capabilities of the system, but targeted improvements will be required to meet the demands of industrial deployment.

While developed for composite repair, the underlying technology is versatile and applicable across various domains. Its ability to deposit functional materials with spatial precision suggests potential use cases in structural health monitoring and field-deployable additive manufacturing. Future extensions, such as support for curved surfaces, vision-based localisation, and integrated non-destructive testing methods, could significantly enhance system capability. These developments may enable intelligent, semi-autonomous platforms that combine human intuition with robotic accuracy for material deposition in complex field environments. ... Read more

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. ... Read more

By breaking structures down into self-similar building blocks, digital manufacturing methods have come into the spotlight as a part of additive manufacturing. Progress in additive manufacturing has facilitated the production of more complex geometries and reduced material waste in the process. With the goal of scaling additive manufacturing up to the meso and macro scales, robotic assembly of cellular structures is increasingly being researched as a method to construct reconfigurable digital metamaterial structures. However, during robotic assembly and after the manufacturing is complete, the structural systems rely exclusively on external inputs if at all to estimate and monitor structural state. This thesis shows that the endemic robots used to manufacture the structure can also be used to measure deformations. The theoretical measurement characteristics of a bipedal inchworm robot have been calculated showing the expected resolution, accuracy, precision and dynamic range of measurements. Experiments have been conducted to construct a statistical measurement model and assess the nonlinearity of the measurement system. For a beam made up of 3D printed PLA cells with a relative density (p*/p) of 0.05, the results show that the robotic measurement system has resolution several times finer than the elastic range of bending and shear mode deformations for a beam with a single lattice cell cross-section. The robot can also detect stretch mode deformations on single lattice cross-section beams before structural failure. The thesis results demonstrate how inchworm locomoting bipedal assembly robots can be used to measure and monitor various deformations of slender lattice beams up to 3x3 cell cross-section, relying solely on the joint angle measurements used to control the robot. We anticipate this thesis to be a starting point for the integration of structural state measurements to the additive manufacturing process of robotic lattice cell assembly. ... Read more

Thermoplastic matrices reinforced with natural fibres offer a promising solution toward the
development of sustainable composite materials, which provide the potential for recyclability
while lowering environmental impact. This research is particularly relevant to the growing
sustainability concerns about WTBs (Wind Turbine Blades), predominantly manufactured from
thermoset composites that are very difficult to recycle. These present huge EoL challenges due
to the inability to efficiently process decommissioned WTBs, often leading to landfilling or
energy-intensive recycling methods. In such a context, this work addresses the development of
f
lax fibre-reinforced thermoplastic composite tapes via a lab-scale vertical pultrusion process.
The focus will be to optimize melt pool temperature, pulling speed, and die geometry for high
quality, recyclable composites that are suitable for wind energy applications.
A custom machine was designed and produced to allow the combination of flax fibre twisted
yarns and melted thermoplastic to make composite tapes by pultrusion. The influences of some
key variables, for instance, consolidating die length, pulling speed, and processing temperature,
on surface texture, void content, and fibre impregnation were studied. The results indicated that
using a shorter consolidating die along with higher pulling speeds and high pultrusion
temperatures, caused increased surface roughness. However, with an increase in the yarn count
to reduce the gap between the fibres, the surface texture for the samples treated at 190°C
(highest temperature tested) was significantly reduced.
Ultrasonic welding was also done, followed by lap shear tests to evaluate the weldability and
mechanical strength of the tapes produced with the vertical pultrusion setup compared to
benchmark samples. It was noted that the tapes processed at 190°C showed better mechanical
properties compared to tapes processed at 170°C, which could be related to better fibre
impregnation and higher crystallinity of tapes. Overall, the testing of welded samples showed that
the mechanical properties of pultruded tapes were significantly superior compared to
benchmark samples, as a result of stronger fibre-matrix bonding and considerably higher surface
quality.
Future work should focus on refining die designs to further explore the effect of long tapered die
sections, performing detailed crystallinity analyses, and employing advanced void measurement
techniques. ... Read more

Autonomously actuated deployable structures are increasingly relevant for space applications where compactness, low mass, and autonomous assembly are critical. Additionally, lattice structures are structures assembled by repeating unit cells in a particular pattern and are also particularly interesting given their high stiffness to weight ratios and high design controllability. Existing deployable systems are often mechanically complex, require multi-part assembly, or lack reversible deployment, limiting their practicality for modular robotic construction. This thesis addresses these challenges by developing a compact, print in place deployable unit cell primary structure that can deploy with springs, lock, and unlock using a motorized actuator.

The goal of this study is to design, manufacture and characterize a deployable unit cell that achieves high packing efficiency and reversible deployment with its primary structure being printed entirely in place using fused deposition modeling (FDM) in PLA (Polylactic Acid). The system studied is a 100 x 100 x 100 mm cubic unit cell with collapsible vertical struts, each made of two arms connected by a revolute pin at mid length. A ball clip mechanism locks the struts after deployment, torsion springs mounted at the central pin provide actuation torque, and nylon strings routed through the struts enable undeployment by spooling onto an integrated motor driven spool. The cell is printed with appropriate clearances between moving parts to enable print in place manufacturing, and achieves a packing coefficient of 10\%, which means that it collapses to 10\% of its deployed volume, and occupies a deployed volume equal to that of the CubeSat standard. In its compact form, 10 cells can be stacked within the same volume.

The printed cell showed predictable mechanical behaviour under compression, with edge struts unclipping sequentially and unclipping forces ranging from ~220 N after 40 cycles to ~310 N for a pristine cell. Deployment tests demonstrated a 100\% successful deployment rate over 20 deployment cycles. Upon optimization through printing trials, a print success rate of 100\% was also achieved for the last 10 unit cells printed.

These findings confirm that a reversibly deployable, low volume, single material unit cell can be reliably manufactured using FDM. The results highlight the potential for integrating such cells into modular robotic construction for large space structures, with future work focusing on improved materials, refined locking and actuation, enhanced packing efficiency, and multi cell robotic manipulation.
... Read more

Vasculatures are key components to life, enabling transport of critical life-sustaining fluids, like blood in humans, or water in trees. To make artificial structures that exhibit characteristics of life, it is important to mimic nature and enable vascularization for human-made materials. The technology to print vascular materials exists, but there are major challenges regarding how to integrate these materials, and their industrial scalability. This thesis investigates coaxial bioprinting as a scalable option and details the design, development, and validation of a coaxial extrusion-based bioprinter engineered for the fabrication of perfusable calcium alginate vascular structures. The outcome of the design process was a new coaxial nozzle capable of printing controlled and consistent vascularized alginate structures directly onto a print bed. This is a key step enabling scalable vasculature manufacturing as the use of printing baths and gels is completely avoided. The printers capabilities were then validated and found to meet the initial design specifications. Further, the accuracy of printing planar features was quantified followed by demonstrations of fully perfusable 3D prints. Results show that the vasculature’s inner channel size can be controllably tuned by varying the nozzle size combinations, enabled by the new nozzle design. In addition, the geometry of the extrusion can be controllably tuned while printing by varying the extrusion factor. Experiments showed that the printer can handle printing sharp angles with an error of up to 10 degrees, which enables complex vascularized shapes. Additionally, curves were shown to be printed accurately at radius of half of that of the diameter of the vasculature and larger. Bridging testing resulted in a optimal setting of extrusion factor to bridge 25mm gaps at a height of 5mm. The final design fulfils all predefined functional and performance requirements, confirming the feasibility of modular coaxial bioprinting for vascular fabrication. The resulting platform provides a truly cost-effective and scalable foundation for manufacturing man-made vascularized structures. ... Read more

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. ... Read more

The aviation industry is constantly pursuing enhancing passenger comfort and safety, with noise reduction within aircraft cabins being a critical area of focus. Traditional soundproofing methods, often involving the addition of heavy and voluminous materials, conflict with the industry's goal of maintaining lightweight aircraft and minimising fuel consumption. Previous research suggests that Helmholtz resonators offer a promising approach to noise control. Their simple structure, consisting of an enclosed volume connected to the external environment through an aperture, allows for customisable and scalable noise control applications.

The thesis presents exploratory research into integrating Helmholtz resonator-based metamaterials into lightweight composite acoustic sandwich panels for aircraft cabins. First, the stiffness of the resonator's enclosure is investigated, followed by determining the effects of placing the inlet within the resonance chamber. Next, the implications of creating resonators for single-layer acoustic sandwich panels are studied. Finally, three reinforcement fibres are investigated for acoustic suitability: fibreglass, carbon fibre and flax fibre. The study concludes with a weight comparison between the developed metamaterial sandwich panel and commercial designs.

The findings reveal that the lay-up of the face sheets significantly affects sound absorption. Introducing non-resonant volumes between the metamaterial's unit cells is the most effective method to prevent interference between the resonators. The resonator's inlet disrupts the stress flow in one of the face sheets, leading to locally increased stress values. The need for specific acoustic properties requires core cell sizes larger than those typically used in standard cabin panels, compromising the stability of the face sheets. Support columns are proposed as a solution, lessening the impact on stability. The thesis proves that lightweight composite single-layer acoustic panels are achievable by incorporating Helmtolhtz resonator-based phononic metamaterials.
... Read more

As aviation accounts for 13.4% of the transport sector's emissions and 3.6% of all human greenhouse gas (GHG) emissions, the need for a sustainable bio-based industry arises. Meeting the growing demand for air travel requires a shift towards more sustainable alternatives, particularly in reducing fuel demand and emissions. Innovations such as weight reduction through bio-sourced materials, notably mycelium-based composites (MBCs), are promising. MBCs are known for their biodegradability, low energy consumption, and versatile applications, including packaging, furniture, fashion, and building materials, but also thermally and acoustically insultating properties that enable their use in the aerospace industry. This thesis focuses on adopting MBCs for non-structural purposes in aircraft cabin interiors. Despite their technological potential, early-stage development and limited data constrain the assessment of MBCs' environmental effects. The project aims to what are the future environmental impacts of producing MBCs at industrial production levels for aircraft interior applications, and how do they compare to conventional alternative materials.
To address this question, the project employed a Prospective Life Cycle Assessment (pLCA), offering a systematic assessment of the environmental impacts despite incomplete information. This study is conducted through two LCA phases designed to comprehensively evaluate the environmental impact of integrating MBCs. The first phase, "intratechnology comparison" focused on understanding the environmental implications of scaling up MBCs production from the laboratory to an industrial level. This phase also assessed the environmental impact of the MBCs material itself. The second phase, "intertechnology comparison" evaluated the environmental impact of an aircraft interior partition composed of MBCs and Scalmalloy compared to a conventional Nomex core sandwich partition. This comparative approach provided insights into the potential environmental benefits of using MBCs in aviation.
The process was divided in: (1) analyzing the current production of MBCs at the laboratory scale to establish the basis for modeling the emerging technology, (2) scaling up the technology to industrial production scenarios, (3) performing a pLCA to comprehensively assess the environmental impact of MBCs, considering uncertainties inherent in the early-stage development of this technology.
Key findings from this study highlight the potential of MBCs. The upscaled production of MBCs is expected to have lower emissions than lab-scale production. Current manufacture remains energy-intensive. In their direct application as non-structural components in aircraft cabin interiors, MBCs showcase advantages over conventional materials due to their lightweight nature, which benefits the use phase. However, the upscaled manufacturing process does not necessarily surpass those of conventional materials, such as the Nomex core sandwich partition, indicating hotspots that need to be addressed.
Additional scenario assessments, recyclability and energy carriers for use phase and manufacturing, were considered. The recyclability of MBCs may offer additional environmental benefits, but careful energy management is crucial to maximize these advantages. The energy carriers for the production significantly impact the environmental impact. Additionally, the lightweight nature of MBCs remains an advantage even with the transition to more decarbonized fuels.
The findings emphasize the importance of using LCA from the early design phase and iteratively as technology develops to achieve optimal results. The pLCA of MBCs offers valuable insights into their environmental impact and guides research and development efforts, helping to make informed decisions about their use in aircraft cabin interiors and further applications. ... Read more

This report presents a comprehensive analysis of repurposing recycled wind turbine blades into functional structures, specifically focusing on the creation of a Strandbeest-inspired kinetic structure. Conducted by Group 17 of Delft University of Technology for the Design Synthesis Exercise, the project addresses the growing challenge of wind turbine blade waste, projected to reach 570 million tonnes by 2030. The report identifies the limitations of current recycling methods and explores the potential of repurposing as a sustainable alternative.

The market analysis highlights the intersection of sustainability, functional beach structures, and wind turbine blade recycling, proposing tangible projects like Theo Jansen’s Strandbeest to raise public awareness. Through a detailed trade-off analysis, the team evaluated multiple design concepts, ultimately selecting a hybrid design combining the Strandbeest and Windcar for its superior performance in harsh conditions and material utilization.

Material analysis focused on selecting sustainable alternatives for wind turbine blades, identifying flax-reinforced thermoplastics as a preferable choice due to their recyclability and mechanical properties. Among several natural fibre options, flax was chosen for its consistent mechanical properties, making it the preferred choice for the composite. The chosen composite material balances fibre and thermoplastic matrix influences, enhancing end-of-life performance. Manufacturing techniques and material recovery processes are outlined, emphasizing the potential for producing beams, flat panels, and aerofoil from recycled parts.

The wind turbine design prioritizes vertical axis wind turbines for their sustainability benefits and compatibility with the structure's needs. The design process considered rotor configurations, aerofoil selection, and aspect ratio optimization, ensuring reliable performance under varied wind conditions. The H-rotor configuration was chosen for its manufacturability and space efficiency, and the aerofoil pitch was optimized to account for wind shear effects, ensuring consistent performance.

Kinematic analyses addressed the movement of the structure, incorporating modified Jansen linkages and differential steering for improved navigation. The linkage was designed to improve stability and step height, with the crankshaft and fixed points optimized for a walking robot. Autonomous navigation and obstacle detection systems were integrated using LiDAR sensors and GPS, ensuring the structure can navigate the Dutch coast independently.

Structural analysis was a critical component of the project, divided into body analysis, leg analysis, and evaluation of failure modes. The body analysis involved stability assessments and stress evaluations to determine the optimal width and configuration to prevent tipping and withstand wind turbine forces. The design included springs to dampen vibrations and reduce bending stresses, ensuring the structure's integrity. Leg analysis focused on selecting cross-sections that could handle the stresses without exceeding material limits. This involved a detailed stress analysis and selection of joints to ensure durability.

Power management strategies combined wind turbine and solar panel outputs to meet the system's energy requirements. The final power budget ensured sufficient energy for motion, control, navigation, weather data collection, and other subsystems, balancing the contributions from wind and solar sources.

In conclusion, this report demonstrates a viable method for repurposing wind turbine blades into functional, sustainable structures. By leveraging innovative design, material science, and comprehensive structural analysis, the project addresses significant environmental challenges and showcases the potential for creative reuse of composite materials. ... Read more

Designing lightweight aircraft parts to improve fuel efficiency is crucial to meet the aviation sector’s goals of reducing CO2 emissions. However, it is also important to ensure that these lightweight parts have a lower CO2 footprint over their entire lifetime. Previous studies have successfully achieved this using topology optimization and low-embodied CO2 composite materials. However, it resulted in structures with lower mechanical properties. To address this limitation, a new framework that uses multi-material fibre-angle topology optimization to optimize fibre-reinforced composite structures is developed in this work. This approach optimizes low-embodied CO2 footprint composites and high-performance, high-embodied CO2 composites in the same structure. A comprehensive CO2 footprint assessment of the optimized structures is conducted by varying the amount of each of the two materials in the structure. As a result, a series of multi-material composite structures with varying levels of compromise between stiffness and CO2 footprint are obtained. These findings establish an optimization approach that provides more control over tuning the desired objectives of such structures. In addition, an extensive parametric study is conducted to demonstrate the framework’s robustness. However, during this analysis, certain limitations of the framework are identified, such as difficulties in optimizing fibres and material modelling. To overcome these limitations, a more robust framework can be developed in the future. Additionally, incorporating stress-based topology optimization into the existing framework can also help in achieving further improved designs. ... Read more

Structural design for unconventional aircraft can be quite challenging and could undergo many iterations until a solution is found for all load-cases such as static sizing, stability and crashworthiness. Ultimately, all of the design aspect are integrated in the earliest design changes for which Topology Optimization (TO) could provide the solution. The Flying-V is one such aircraft with challenging crashworthiness design due to its small sub-floor volume. However, a suitable formulation for aircraft crashworthiness and TO is yet to be found.
This thesis aimed at incorporating the conventional aircraft-crashworthiness characteristic of plastic energy dissipation in plastic hinges in the energy based Hybrid Cellular Automata framework. The HCA principle is to optimize on cellular level, using information of each cell’s direct neighbors. For the proposed method, the inter-cell stress and strain information is used to reconstruct the cellular bending energy throughout the non-linear dynamic crash-analysis, providing greater stability than intra-level bending energy. The bending energy formulation was based on the assumption of linearly varying stresses and strains in bending. Several formulations have been formed to manipulate this energy promoting hinge-formation.
The framework has been tested on size optimization of a small-scale slender beam impact model, representing the final design case. Results show peak force reduction and greater displacements compared to the standard HCA crashworthiness model. However, improvements can be made such as inclusion of the non-linear stress and strain variation in the bending energy formulation, to more accurately account for large plastic strain.
Before testing whether the methodology improves the crashworthiness of aircraft, verification of the voxel-mesh approach was required. An A350-like aircraft has been simplified and idealized accordingly and compared with its detailed FEM crash-assessment. Simplifications include modelling only one frame and replacing the cabin and floor with a rigid body to reduce computational cost. Results show good agreement for the required level of detail of conceptual design, although it is recommended to idealize the cabin and floor as well. Once verified, the framework has been applied to the entire domain. ... Read more

Transparent Natural Fiber Composite Materials may pose a more environmentally friendly alternative regarding energy efficiency and low CO2 emissions in contrast to traditional composites, exhibiting transparency for future smart building or photovoltaic applications. The present study involved a research effort for the development of a lightweight flax fiber-reinforced composite material, which will exemplify high optical transparency. A detailed focus is conducted, on minimizing light absorption phenomena with delignification methods of flax fibers, eliminating light scattering via a Refractive Index Matching procedure between the reinforcement and the polymer matrix and via fiber modifications which tackle several issues such as enhancing the imperfect interphase between the hydrophilic reinforcement and the hydrophobic matrix, or providing finer polymer impregnation of the fibers. Acetylation, nitric acid, or TEMPO-oxidation treatments that modify the fiber’s nature and morphology are implemented to tackle these obstacles. Transparent Flax Fiber Reinforced Composites of 35-45 % fiber volume fraction were fabricated with wet-lamination and hot press forming techniques, indicating a maximum total light transmittance of approximately 70% (at low thickness) and 56-58% (at high thickness), depending on the fiber modification implemented. Regarding mechanical properties, a maximum specific flexural strength of 153 MPa/(g/(cm3)) and a specific flexural stiffness of 11.95 GPa/(g/(cm3)) was achieved for these materials. The transparent FFCMs showed comparable values of total light transmission correlated to reference materials like GFRPs or other natural fiber-reinforced composite materials, with similar volume fractions, signifying the success of achieving high optical transparency. ... Read more

Throughout history, human progress has been defined by the mastery of materials, transitioning from stone and bronze to the steel age. However, this progression has not only been defined by the materials utilized but has also encompassed a shift in processes, moving from the industrial to the information era. Despite the advances in fabrication techniques, building large and detailed structures continues to pose an unresolved challenge. Cost, speed, performance and size are often mutually exclusive objectives that are bound by the materials and processes used.

In the search for new processes and materials, we can find inspiration in the oldest of all fabricators; life. In natural systems, a small set of 20 amino acids are assembled by ribosomes into coherent organisms with complex sensing, actuation and information storage. Nature represents the highest dynamic range assembly system known to mankind. But a question arises: can these benefits be extended to engineering systems at meso and macro scales?

The advantages of natural fabrication emanate from the use of digital materials and self-replicating assemblers. Digital materials are composed of precise and discrete building blocks like amino acids at the micro-scale or Lego building blocks at the meso scale. They are tolerant to noise, possess embedded metrology and their assembly can be highly parallelized. Lego structures can be built more repeatably than what a standard 3D printer can print despite the imprecise nature of human assemblers. This is because the metrology and the code for construction are embedded within the material itself.

In this thesis, a complete end-to-end autonomous digital material assembly system, that bridges the gap between a 3D model and a built structure with a flexible, comprehensive, and easy-to-use toolset is presented. All elements in the triad of autonomous digital assembly were developed, from the digital material to the robot and the controlling software. A digital material made of discrete 3D-printed octahedra lattices that can be magnetically or mechanically joined is utilized. Straight, curved and elongated lattices enable unparalleled geometric freedom.
This material can be picked up, transported and placed by a robotic assembler in the form of a 5DOF (degrees of freedom) cable-driven differential joint inchworm robot.
Most importantly, a flexible control platform capable of interpreting 3D models, developing the necessary robot movements for optimal construction and wirelessly controlling assembler robots powers the build process. This platform introduces some major innovations within the field. For starters, it is not limited to blocky grid domains as it is powered by inverse kinematics. It is also architected to enable cooperation between different assembler types by utilizing a work package system and presents wide abstraction layers allowing further development at higher levels with ease. Additionally, it provides a seamless control interface. ... Read more

Our reliance on synthetic structural materials has contributed extensively to environmental degradation, resource depletion, and pollution. The urgent need for sustainable alternatives has sparked interest in bio-based materials that align with Nature's cycles while maintaining high performance. However, finding such alternatives has remained challenging, especially for ceramics, which typically require high-temperature processes to achieve structural integrity. Yet Nature offers a promising blueprint: the nacreous layer, "mother of pearl", found in molluscan shells. Millions of years have allowed these invertebrates to evolve remarkable defect tolerance, achieving strength, stiffness, and toughness - a combination elusive in most conventional ceramics.

Despite extensive efforts, mimicking the intricate microstructure of nacre to achieve new, advanced materials remains challenging. Recent studies have leveraged the outstanding shaping freedom and microstructural control offered by additive manufacturing to provide new opportunities. However, these approaches continue to rely on sintering to improve mechanical properties, thereby undermining their ecological potential. The underlying printing process also remains largely unexplored. This thesis confronts both challenges by exploring a novel bacterial stiffening approach in direct ink writing using various material compositions. For the first time, mineral-depositing bacteria are incorporated into a ceramic-biopolymer suspension in an attempt to achieve sinter-like stiffening of the structure at reduced energy expenditure.

Direct ink writing ceramic-polymer bioinks is challenging due to the sensitivity of colloidal dispersions to changes in electrostatic and steric interactions, further complicated by strongly time-dependent rheology. These aspects hindered exploring the effects of biomineralisation on material performance. A 'printing window' is identified, beyond which bacteria-induced coagulation disrupts extrusion, establishing an essential constraint. Printability may be improved by controlling pH, performing more appropriate rheological experiments, and tuning rheology. Nutrient and bacterial content reduced material strength, meaning that any positive effect of biomineralisation must at least overcome this negative influence to provide a net benefit. Excessively high void content highlights the need to maximise compaction and solid content. Crucially, biomineralisation was achieved in preliminary tests, suggesting that the approach is fundamentally promising. These findings provide critical insights and guidelines for developing shaped, strong, tough, and sustainable ceramic materials, paving the way towards eco-friendly materials inspired and built by Nature. ... Read more