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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

As space exploration advances toward colonization missions on the Moon and Mars, there is an increasing need for lightweight, recyclable, and space-worthy materials. These materials must optimize payload and sustainability by integrating 3D printing and recycling mechanisms, minimizing the need to transport bulky construction materials from Earth and reducing space debris. Additive manufacturing, particularly Fused Filament Fabrication (FFF), offers significant design flexibility, ideal for zero/low gravity environments. However, the relatively low material properties and durability of polymers in space restrict their potential compared to metals. Liquid Crystal Polymers (LCPs) show promise due to their high crystallinity, flame retardancy, and thermotropic properties. Yet, their behavior in space environments remains underexplored. The goal of this research is to evaluates the performance of Vectra A950, an LCP, under electron beam radiation and thermal vacuum (TVAC) exposure, as well as its recyclability after FFF processing.

The study examines the mechanical strength, thermal stability, and crystallinity of 3D-printed LCP under space-like conditions. Samples were subjected to three levels of electron beam radiation and TVAC. Electron irradiation induced annealable color centers, manifesting as a green hue that intensified with higher radiation doses, which could be reversed by annealing for 20 minutes at 200°C. The findings indicate that while exposure to electron beam radiation and TVAC has a measurable impact on the mechanical properties of LCP, the changes are not significant enough to compromise its structural integrity. For irradiated samples, no substantial variations were observed in Young’s modulus or ultimate tensile strength (UTS) across different radiation fluences, even after TVAC exposure. However, when exposing unirradiated samples printed at low printing temperatures (295°C and 310°C) to TVAC, slight reductions in Young’s modulus were observed with no significant impact on UTS. Thermal analysis revealed that electron beam radiation modestly shifted the β-peak temperature, while TVAC increased the glass transition temperature by 5°C in irradiated samples. Samples exposed to high fluence displayed a permanent decrease in melting temperature by over 7°C, suggesting irreversible changes to the polymer structure.

The study also explored the effects of electron beam radiation, annealing and FFF processing on the recyclability of LCP. Results indicate that while these processes alter thermal and mechanical properties, the effects of annealing and FFF are potentially thermoreversible. FTIR analysis revealed no chemical modifications to the polymer structure, confirming that FFF does not chemically alter LCP, reinforcing its potential for in-situ recycling during planetary exploration. While LCP shows promising recyclability under various conditions, further research is needed to fully understand the reversibility of these changes and their implications for in-situ recycling in space environments.

Overall, the study concludes that, LCP demonstrates mechanical and thermal stability under moderate radiation and thermal vacuum exposure, making it suitable for long-term use in space. Its potential for recyclability, combined with the design flexibility of FFF, supports its viability for space missions, particularly in optimizing sustainability and resource utilization.

The cellular, hierarchical nature of living materials such as wood or bone, enables their mechanical properties to vary locally. This variability grants themmulti-functionality and highmechanical performance with low resource consumption. To obtain such desirable features with man-made structures, many manufacturing restrictions need to be overcome. Currently, the most common structural anisotropic materials are fibre-reinforced composites, which allow limited control over material placement, orientation, and directional strength.

In this thesis, we explore how the additive manufacturing of Liquid Crystal Polymers (LCP) can unlock our ability to control these parameters and, therefore, expand the design space to optimize structural performance while limiting material use. To achieve this, we leverage the alignment of nematic domains in LCPs, induced by shear and elongational flow during extrusion through the 3D printer nozzle. By modulating the pressure inside the nozzle to change line width, we observed an axial stiffness range between 3 GPa and 30 GPa, associated with a failure mode shift from ductile to brittle. Demonstrating our ability to print with variable toolpathwidths and sharp curvatures,we created 3D patterns inspired by fluid dynamics. This ombination of shaping freedom and anisotropy control enabled the design of functional objects with embedded crack mitigation strategies, or improved buckling performance.

Anisotropy gradients are also present in the structure of trees. Inspired by the seamless transition of wood fibres from parallel to interlocked at the branch junctions, we manufactured sinusoidal and helical patterns with LCP. The introduction of local waviness decreased axial tensile stiffness, but significantly enhanced toughness. Tensile and interlocking performance were driven by two critical parameters: angle of maximum deviation to the axial direction, and pattern size.Moreover, resistance to normal stresses was improved, as shown by the 88% increase in load-bearing capacity compared to a nonreinforced configuration in a two-strut junction. This opens the possibility to integrate localized interlocking patterns in multi-axis loaded regions of anisotropic parts.

Manufacturing methods which utilize as littlematerial and energy as possible are needed for future space exploration missions. To assess whether the strategies mentioned previously are applicable to this context, 3D-printed LCPs were subjected to four different space environments. High-energy electron radiations created colour-centres, leading to a bright green coloration in the bulk of the specimen. However, no significant decrease in staticmechanical properties was observed, with unidirectional stiffness remaining close to 30 GPa even after intense electron irradiation and thermal cycling. These results indicate that LCPs are a promising alternative to engineering polymers like PEEK or PEI for space applications.

Future research into topology-optimization methods integrating both asymmetry between tension and compression, and mechanical property gradients, will enable to further explore the design space opened by the tunable anisotropy of LCPs.@en

Mycelium based composites (MBC) have revolutionised the field of material production, where a living fungus is employed to overgrow and bind lignocellulosic substrate materials together. Their bio-based nature, low embodied energy, and biodegradability, mark their great potential to reduce the increasing pressure conventional materials put on the environment. Unfortunately, the material's applications are limited due to its low mechanical properties, that are equivalent to those of foams or natural fibre boards. Furthermore, where the material is primarily used and studied in its heat-treated non-living form, harnessing the biological power of the fungus shows to give the material self-healing and sensing capabilities. The required hydrolysed state is however shown to further decrease its mechanical properties, and yet hardly evaluated in literature. Especially the mechanics of the mycelium-lignocellulose interface are inadequately studied, and important to evaluate for a broadening of the living composite material's applications.

In this study we present the development of a double cantilever beam (DCB) test according to ASTM D5528, setup to quantify the interlaminar fracture toughness (G_I) of Ganoderma lucidum (G. lucidum) grown in between wood veneers. The data was evaluated using an analytical approach based on a decrease in the beams' compliance. The specimens were fabricated with the use of additive manufacturing, allowing precise control over the placement of the fungus and its provided nutrients. Its growth behaviour into the substrate was qualitatively assessed through optical microscopy and scanning electron microscopy (SEM), and its digestive ability on the surface by fourier-transform infrared spectroscopy (FTIR).

A mycelium-laden ink presented by Gantenbein et al. (2023) was reproduced with a 75% lower agar content to serve a stable source of mycelium on the DCB specimens [1]. A growth period between 3 and 4 weeks from the printed hydrogel was required for substantial mycelium-substrate binding, which stabilised after 4 weeks of growth. Furthermore, the provision of malt extract (ME) was required, but not needed to be higher than 5% of the ink's weight. The G_I was in these conditions reported to be 1.83 J/m² on hornbeam veneers, where a maximum value of 3.46 J/m² was reached. Variable growth generated substantially different mechanical properties, which resulted in the lower G_I of mycelium grown on beech and spruce samples, caused by the use of an older fungal inoculum of a different reference plate. A stronger binding on beech than spruce did suggest a more important role of the substrate chemistry than its density. The mycelium always showed cohesive failure, showing the low G_I to not result from poor substrate adhesion, but rather from the mechanics of the hyphae network developed. Microscopy and FTIR evaluations showed the ability of G. lucidum to digest the hornbeam's lignin. The full depths of hornbeam and beech veneer substrates with 5 and 3 mm thickness were colonised, where vessel elements served as the main pathway for the hyphae.

This study was, to the best of our knowledge, the first to isolate the binding behaviour of a living mycelium in a mode-I loading condition. It thereby provides valuable new insights in the field of living MBC, and contributes to the further development of this advanced, eco-friendly, and living material. The setup can now be utilised to study the binding behaviour of different fungi on substrates of varying chemistry and porosity. Furthermore, aiming to elucidate the use of additive manufacturing in the composite production, this study opened up pathways into controlling the composite's properties in the future.

[1] Silvan Gantenbein et al. “Three-dimensional printing of mycelium hydrogels into living complex materials”. In: Nature Materials 22.1 (2023), pp. 128–134.

Poor recyclability and high carbon footprint have presented a major hurdle to the adoption of thermoset composites . Natural fibre composites offer a reduced CO2 route to reinforcing fibres whilst recyclable epoxy chemistries might lead to reinforcement recovery at end-of-life. Here, short bamboo fiber reinforced epoxy composites are manufactured and recycled to achieve resusable resin and fibers. Structure property characterisation before and after recycling reveal fibre preservation whilst more than 80% of the resin can be recovered and used in the form of a low property thermoplastic epoxy. Overall, this thesis contributes a step towards development of truly sustainable and recyclable composites.

A structural supercapacitor (SSC) is a composite material that bears mechanical loads and stores energy, and its encapsulation method of the device is vital for scale-up. Here we present an SSC with an encapsulation interface consisting of spread-tow fabric electrodes and glass fabric encapsulators infused with epoxy resin. Through surface functionalisation of fibres, a high surface area electrode of 231.43 𝑚2/𝑔 was separated by a gel polymer electrolyte (GPE) separator and encapsulated in an epoxy polymer. To study the SSC’s performance, different GPEs are produced by adding lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) into poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP). The LiTFSI concentration is varied from 0% to 100% based on the weight of PVDF-HFP. The highest energy storage performance occurred at LiTFSI 60 wt% in the PVDF-HFP, with a cell-specific capacitance of 25.72 mF/g, cell-specific energy of 2.08 mWh/kg and cell-specific power of 25.04 mW/kg. With a flexural modulus of 3.39 GPa and a flexural strength of 52.07 MPa, this further develops high-performance SSCs in the future.

In this work, it is demonstrated that kirigami deformation behaviour can be controlled by tailoring the anisotropic material that is used to create the kirigami structure. The ultimate goal is to find a relationship between the material pattern and the deformation behaviour of the kirigami structure. An anisotropic thermoplastic polyurethane carbon fiber material was steered by using the fused filament fabrication method. Kirigami samples were manufactured and tested with varying geometry and material orientation. Each tested sample corresponded to a finite element (FE) model in Abaqus/CAE with identical features. Results show that the FE model is able to accurately simulate the impact of material orientation on the deformation behaviour of the kirigami structure. The FE model is validated by comparing the kirigami tip deflection and -shape to experimental data. Results show that the shape of fibre steered kirigami can be estimated by following the thin plate buckling theory.

Liquid crystalline polymers have recently attracted attention for their great tensile properties. However, their interlaminar fracture toughness is low. To solve this, toughening approaches inspired by Nature are applied, exploiting the shaping freedom of fused deposition modelling. Three approaches are studied: the matchstick approach, z-pinning and sawtooth layers. Their effectiveness in increasing the Mode I interlaminar toughness of the material is evaluated through compact tension tests.

These tests reveal that z-pinning fails to increase toughness, while the matchstick approach and especially the sawtooth layers have a beneficial effect. The matchstick approach increases the interlaminar toughness of Vectra A950 by strengthening fiber bridging, a toughening phenomenon natural to the material. The sawtooth layers stall crack growth through geometry, but also trigger fiber bridging more reliably and postpone fibre tearing. This synergy quadruples the toughness. These two methods prove that bio-inspired structures are an excellent way to provide toughness in additive manufacturing.

We explain the design and analysis of a novel voxel design with the goal of reducing assembly time and complexity of the robot-material system. Recent advances in robot-material systems, on the other hand, have focused on mechanical properties, design, and production methods. Making it possible to create cellular structures in harsh and remote environments. These systems, which are built up of voxels and small mobile robots that live on top of the structure and move the cellular structures, nevertheless lack a connecting mechanism that reduces total system complexity and assembly time to a level that is desirable to people.

The design of these voxels prioritizes ease of assembly through simple actuation and is investigated by proposing a method to connect voxels via an end effector without removing mechanical qualities while maintaining the system’s modularity principle. Modularity is a design idea that divides a structure into smaller sections called voxels that can be built and assembled separately to build the required structure. Simultaneously, the end effector’s design aims to connect a voxel with the fewest degrees of freedom possible, while also holding a voxel throughout transit and placing the voxel in the desired spot.

A new connection mechanism for cuboctahedral cellular structures was devised, which would enable the building of required large-scale structures faster and easier. Several prototypes and experiments were used in the design of this connection mechanism. The final prototype was built by fused deposition modeling and demonstrated by attaching the end effector to a Universal Robot 5 (UR5) and completing a series of movements to simulate the autonomous assembly of a bridge. The concept evaluation resulted in an end effector that can connect all sides of the voxel with only two movements, without requiring the robot to go around the voxel. This idea lays the groundwork for enhancing the way robots form cellular structures and creating a mechanism to make them more appealing to humans when exploring remote settings. The study finishes with future research opportunities and prospective applications of such a connection mechanism in robot-material systems.

Traditional manufacturing techniques for hydrogen pressure vessels have inherent constraints in the possible geometrical and structural optimisation. Using 5-axis Additive Manufacturing (AM) allows for a far greater shaping freedom. This thesis will provide a new manufacturing method for pressure vessels with 5-axis AM. Using the highly anisotropic Liquid Crystal Polymers (LCP) provides both the required hydrogen permeability performance, for storing gaseous hydrogen, as well as opening up a large potential for structural optimisation. LCPs in their additively manufactured form are tested for hydrogen permeability, in order to asses the effect of AM on the bulk permeability properties of this material. Furthermore the 5-axis AM process is developed for LCP pressure vessels, culminating in a series of pressure tests on additively manufactured specimens. These specimens provide a proof of concept for the manufacturing method, which is a starting point for expanding the geometrical and structural optimisation of pressure vessels designs.

Bacterial cellulose combines the high specific mechanical properties of cellulose, with the use of microbes as micron-sized factories, which are leveraged to metabolise a highly pure and crystalline intertwined network form of cellulose. In spite of its advantageous properties, the lack of shaping freedom in current BC manufacturing techniques has hindered its implementation. To remedy this, research has focused on embedding cellulose-producing bacteria into hydrogel inks from which 3-dimensional living structures can subsequently be printed using direct ink writing. However, current iterations of this process lack the ability to manufacture geometries with complexities in excess of single layer patterns. This research, improved on previous iterations by integrating silicon platelets into a living ink formulation to produce inorganic scaffold for bacterial cellulose overgrowth, demonstrating both higher printability and structural integrity than previously reported process variations.