Inverse design is a concept where one can design a structure via a property-first approach, where the properties of a system act as precursor information to guide the search for a viable design. This concept is classified as one of two: indirect or direct. While the former is no different than a forward-based approach using traditional optimization, a direct inverse design framework attempts to invert the process and directly map the desired properties to a suitable design candidate, which is unconventional. As such, the design process can be positively radicalized, with regards to the required computational resources when designing multiple structures.

In this work, the use of Bayesian machine learning, more specifically Bayesian optimization using Gaussian process regression, is employed to construct a direct inverse design framework using the design of mass-optimized fixed-wing aircraft ribs against buckling as the validation case study in 1, 6, and 10 dimensions. The results are compared to an indirect approach using the same algorithms and demonstrate that barring certain limitations, which are not inherent flaws of the direct approach, the framework designed not only demonstrates sound potential in inverting the forward map, but outperforms the indirect approach when designing multiple structures.

This research equally provides a stepping stone towards future research possibilities in the same field, all culminating in the improvement of the multi-disciplinary design process.

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.

Ice accumulation on aircraft surfaces is a prevalent issue, and icephobic coating strategies can be implemented to assist in the removal of or ice on an aircraft. However little is known regarding the effects of novel icephobic coatings and surfaces on ice adhesion strength, which is difficult to measure and quantify, and is typically reported in literature with a high standard deviation and scatter. In this thesis, a reliable set-up for testing ice adhesion strength is successfully designed, constructed, and validated. Using this set-up, it is possible to examine the relationships between various surface parameters and ice adhesion strength, and to analyse the scatter in order correlate the results both qualitatively and quantitatively. Additionally, the influence of material and topology on the adhesion strength and failure mechanisms of ice is investigated.

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.

Stiff and transparent materials are essential across industries such as aerospace, defense, and consumer electronics. Traditional materials like glass and ceramics, while effective, have limitations due to brittleness, high density, and low impact resistance. Consequently, there is a demand for lightweight, durable materials with favorable optical properties. Fiber-reinforced polymers (FRPs) offer high strength-to-weight ratios and greater impact resistance than glass and ceramics. Given the low light absorption of glass fibers in the visible spectrum, transparent glass fiber-reinforced polymers (TGFRPs) show promise as replacements for traditional transparent materials.

This thesis explores two main aspects: (1) optimizing TGFRP transparency through manufacturing parameters and (2) leveraging TGFRP transparency for damage detection and stress analysis. In the first phase, findings demonstrate that achieving high surface smoothness and maximizing light transmission within the green spectrum (520–600 nm) are crucial for enhancing TGFRP transparency. This is best controlled via post-curing, a more stable approach than adding methyl methacrylate (MMA) as suggested in existing literature. Sizing was also found to play a critical role in transparency, ensuring optimal bonding between glass fibers and the matrix. Additionally, minimizing the number of glass fiber fabric layers improved transparency by reducing transmission losses across visible wavelengths.

The second phase investigated the transparency of TGFRP for visualizing internal damage and stress distributions. Confocal microscopy was used to observe cracks at various depths within TGFRP samples, while image processing techniques, such as thresholding, were employed to calculate crack density. The results indicate that a higher crack density corresponds to reduced light transmittance across the visible range. However, some limitations were encountered, as cracks and scratches on the upper layers cast shadows on the lower layers, complicating the detection of deeper damage.

During tensile testing of open-hole specimens, significant opacity changes were observed in high-strain regions, suggesting that opacity correlates with localized stress. Digital image correlation (DIC) and grayscale histogram analysis provided insights into the strain thresholds at which opacity changes begin. Future work could build on this by examining the extent to which opacity changes are due to refractive index variations alone, independent of crack formation, using these strain levels as a baseline.

Furthermore, verifying the reversibility of opacity changes through post-test spectrophotometry could position TGFRPs as highly effective materials for developing innovative and reliable non-destructive testing, damage detection, and stress visualization methods in glass fiber-reinforced polymer composites.

To facilitate the transition to liquid hydrogen (LH2) as an alternative aircraft fuel, the stor
age tanks need to be closely monitored to allow for safe operation. This research explores
the feasibility of using an acoustic emission-based structural health monitoring method to
detect and localise simulated damage on a metal double-walled vacuum insulated tank. The
complicated inner and outer tank geometry makes it a novel application of an established
method.

To be able to perform experiments, a metal double-walled vacuum insulated tank with a fixed
and flexible support was cut in half to make the inner tank accessible. Pencil lead break tests
were performed on the inner and outer tank and recorded by lead zirconate titanate (PZT)
sensors to assess localisation accuracy. It was found that a pencil lead break (PLB) performed
on the inner tank could be detected by a sensor placed on the outer tank. Subsequently, an
accuracy of 80% was achieved in making the distinction whether the PLB was located on the
inner or outer tank. For the PLBs placed on the inner tank a 1D localisation accuracy of
17 [mm] and 21 [mm] was achievable for the flexible and fixed support respectively. For the
outer tank a 1D localisation accuracy of 46 [mm] was achievable, while for 2D localisation
this was 41 [mm].

It is concluded that with sensors placed solely on the outer tank, both the inner and outer
tank can be monitored. Additionally, simulated damage on the inner and outer tank could
be localised with an accuracy below 10% of the tank’s dimension. Therefore, based on the
feasibility study performed, acoustic emission-based structural health monitoring is deemed a
viable method to enhance the reliability and safety of metal double-walled vacuum insulated
LH2 tanks.

The aerospace sector continues to drive innovations in high-performance materials. These materials however, tend to have energy intensive and emission heavy manufacturing processes. One of the most commonly used materials in aircrafts today are polymer matrix composites consisting of reinforcement fibers and a matrix. While the fibers provide the most strength to the composite, the matrix holds the fibers together and transfers the loads to them. The most commonly used matrix material today is made of BADGE (Bisphenol A Diglycidyl Ether), a material which is toxic to humans and comes from fossil-based products.

This thesis investigates the viability of a vanillin-derived bio-based alternative, VDE (Vanillyl Alcohol Diglycidyl Ether), to be used in high-performance composites for aerospace applications. VDE monomer is derived from vanillin, which is obtained from lignin, a material present in 35% of woody plants. The VDE-DDS resin system, when cured, exhibited comparable thermal and physical properties, such as glass transition temperature and heat deflection temperature, to traditional aerospace resins like BADGE-DDS. Mechanical testing, including tensile, flexural, and fracture toughness, demonstrated promising results, with VDE-DDS showing higher strength and modulus than BADGE-DDS. The flexural strength was considerably higher in particular. However, its hydrophilic nature led to higher water absorption, a challenge for long-term durability. For further testing, composite specimens were prepared using an autoclave.

Composite specimens reinforced with VDE-DDS displayed greater stiffness and strength under mechanical testing compared to BADGE-DDS in tests of in-plane shear strength, compression and inter-laminar shear strength tests, though BADGE-DDS composites outperformed in low-velocity impact resistance. The impact testing also revealed that BADGE-DDS samples had a higher damage initiation energy while VDE-DDS samples had a higher bending stiffness. Overall, VDE-DDS offers comparable, if not better, thermal and mechanical characteristics to BADGE-DDS. VDE, in summary, presents a compelling case as a potential bio-based alternative for structural aerospace applications.

The Nacra 17 is a foiling catamaran selected to compete in the 2024 Olympic Games. The Nacra 17 is a one-design class, which requires all equipment to be identical. The Dutch Olympic team found through testing the bending stiffness that there is a slight difference in how each of their hydrofoils performed. The question was asked: What are the manufacturing deviations in the Nacra 17 hydrofoils and how do they impact the performance? This research aims to answer the previously stated question. The 3D scanned hydrofoils validated that there is indeed a measurable difference in shape between the different hydrofoils of the Olympic team. A successful method was proposed that automatically extracts 2D profile section properties from the point-cloud data of a 3D scanned hydrofoil. This method used a rough orientation using the profile plotted in polar coordinates. The mean camber line could be extracted using the Voronoi vertex points and the offset of the profile surface. The resulting data set was fitted using non-periodic cubic B-spline curves. This produced a curve for the mean camber line and the thickness profile. Comparison of profile properties resulted in the conclusion that profile thickness (yt) could show that the two female mould halves were probably spaced differently for the different hydrofoils by a standard deviation of 0.0669 mm at a thickness of 22.6 mm. Differences are found in the maximum thickness location (xt), Leading edge radius (rle), maximum camber (yc) and its location (xc). However, the differences in lift over drag for the different hydrofoils are minimal. The size of the drag bucket did not differ more than 0.1 of the lift coefficient (cl) for the same drag coefficient. With the exception of in general one section that presented an early separation. The specific profile showing early separation changes along the span, not allowing for the generalisation for the complete hydrofoil. It shows that the curvature at the leading edge of the profile is critical for the performance of the Nacra hydrofoil. Knowing which part of the profile shape is critical. Companies can take this area into account when designing the production process for the next hydrofoil, and the Olympic team can focus on maintaining these areas of the hydrofoil. Allowing the best preparation to be competitive at the next Olympic games.

Fibre metal laminates (FML) were initially conceived as a hybrid material, aiming to create synergy between the impact resistance of metals and excellent fatigue resistance of fibre reinforced polymers. The purpose of this approach was to overcome the limitations of single-material structures. However, despite its considerable promise, the use of the FML concept has primarily been confined to aerospace applications and heavily relies on synthetic fibres that carry significant environmental implications. Hence, given the growing concerns about climate change and the challenges posed by recycling glass fibre composites, a new generation of FMLs with a reduced carbon footprint should be envisaged.

Research on flax fibre composites reveals convincing mechanical properties and remarkable damping capacities. However, the broader adoption of these composites remains restricted primarily due to issues related to low impact resistance, moisture absorption and flammability concerns. The FML concept presents a viable solution to surmount these constraints, consequently facilitating the integration of these materials into primary structures. Hence, the research endeavour aimed to attain comprehensive insights into FLAx REinforced aluminium (FLARE), particularly focusing on its impact resistance and vibration damping capabilities, which are believed to be the principal benefits of this hybrid material.

The research goal was divided into three distinct research tasks: conducting experimental analyses to characterise the damping behaviour of FLARE, evaluating the impact resistance through experimental means, and validating predictive tools to offer initial insights into the design principles governing such a FML. FLARE, along with flax fibre reinforced epoxy (FFRE) and GLARE specimens, were manufactured using wet layup combined with vacuum bagging techniques.

First, tensile tests were conducted to validate the applicability of the metal volume fraction (MVF) approach in predicting the mechanical properties of FLARE. Intriguingly, the well-known non-linear behaviour exhibited by flax was not observed in the case of FLARE. The results revealed that while the MVF method provided a satisfactory approximation, it was the "inelastic" modulus of FFRE that predominantly contributed to the stiffness of FLARE.

Dynamic mechanical analysis and vibration beam tests were carried out to assess the influence of incorporating metallic layers on the vibration damping characteristics of flax fibre composites. The investigation revealed that the metallic layer predominantly governs the damping behaviour of the FML. Notably, an inverse rule of mixture emerged as the most effective means of approximating its loss factor.

Low-velocity impact tests were conducted to gain insights into the impact response of FLARE in comparison to conventional FMLs. The analysis indicated that the aluminium layers play a significant role in energy absorption, whereas the composite strength emerges as the critical factor influencing impact resistance. A quasi-static analytical model was also assessed, offering an initial estimation of the impact response, yet it warrants further refinement.

In conclusion, the FML concept holds promise for FLARE, but its application requires a novel approach compared to previous methods, to render FLARE viable for practical real-world applications.

The Koiter methodology is a reduced-order model that can predict the initial post-buckling characteristics of structures. Incorporating the Koiter approach within finite element simulations resulted in challenges. These included mesh sensitive initial post-buckling coefficients, computationally expensive high-order derivatives, and phenomena such as locking, which led to unrealistic behaviour of structures. The displacement-based Koiter methodology is introduced to overcome these issues due to the clear connection between the theory and the implementation. The objective of this thesis is to enhance this approach by introducing imperfections, which enables the analysis of initial post-buckling characteristics of imperfect structures. The preliminary results show that the inclusion of imperfections was successful for a plate with linear pre-buckling, but more verification is required. If the inclusion is verified to be successful the current displacement-based approach can be extended to cylinders and used in sensitivity studies to establish guidelines for an imperfection-insensitive cylinder.

Frontal polymerization (FP) has emerged as a promising alternative to traditional bulk curing methods in recent years for manufacturing high-performance fibre-reinforced polymer (FRP) composites. The energy utilized in this self-propagating curing strategy is solely derived from the exothermic enthalpy of polymerization, making it potentially more efficient than traditional curing methods, which are extremely energy-intensive and therefore unsustainable. Research in the field of FP has been primarily focused on studying the effectiveness of the FP formulations, particularly the relationship between the monomer types and initiator concentrations on front properties. However, the research on the use of FP for manufacturing FRPs has been limited to flat rectangular plates. Therefore, this research aims to investigate the behaviour of the propagating fronts in composites with varying fibre volume fractions (Vf) within the sample and varying geometries to assess the feasibility of using FP in structures that more closely resemble real-life applications. Several test setups were explored to determine the best method for maintaining the heat balance required to sustain a propagating front. Through these trials, a stainless steel-based closed mould test setup with Teflon sheets was conceptualized and manufactured, consistently allowing for the manufacturing of composite samples with a Vf below 36%. The influence of changing Vfs on the behaviour of the front was studied, and the results were quantified using temperature data captured via thermocouples placed at strategic locations. Through a series of experiments, a critical length was established that allowed the propagation of the front from the low Vf region to the high Vf region. When the length of the low Vf region with respect to the high Vf region was smaller than the critical length, the front was seen to quench at the interface. This phenomenon was attributed to the physical reduction in the volume of the resin, which implied a reduction in the generated heat through polymerization. This led to fronts with lower peak temperatures, which upon reaching the interface would quickly fall below the threshold temperature required to sustain the front due to the higher rate of heat loss resulting from the higher fibre content. This study was followed by the manufacturing of L-shaped composite samples with uniform Vf, which showed the propagation of the front in complex geometry. Finally, the Vf was varied within the L-shaped samples, and the behaviour of the front showed similarities to the rectangular samples with varied Vf, leading to the conclusion of the presence of a critical length irrespective of geometry. These findings effectively contribute to the knowledge base necessary for implementing FP as a curing strategy for FRPs. The results obtained from this study can inform the design of manufacturing processes and setups tailored for the use of FP, potentially leading to more efficient and sustainable manufacturing practices.

Having seen exponential growth in demand for air travel, the aviation industry has found itself trying to find a balance between economic growth, technological development, and environmental sustainability. This saw a shift in attention towards materials such as fiber reinforced composites, predominantly thermoset in the past with higher strength-to-weight fractions. Relatively recent was the introduction of high-performance fiber reinforced thermoplastic polymer composite materials possessing more promising prospects of circularity in addition to the lightweighting capabilities. But as is, these only form for qualitative claims with no indication on how the ecological effects would pan out over the life cycle phases objectively, as well as on a relative scale.

Extending beyond the orthodox considerations and measures of aircraft performance, life cycle assessment studies encompass a comprehensive analysis of the environmental impact associated with aerospace products through the various phases of their life cycle including material extraction/production, manufacturing, operation, and the respective end-of-life treatment. The primary objective is to quantify the environmental impact of the system, offering a holistic view of the emissions, energy demand, and resource consumption.

To this end, this study constructed a comparative environmental profile, modelling for five material/manufacturing systems, namely numerically machined aluminium alloy, autoclave cured and resin transfer molded carbon fiber reinforced epoxy, autoclave consolidated, and press consolidated carbon fiber reinforced Polyetherketoneketone (PEKK) over the cradle-to-gate and the cradle-to-end of service phases in an attempt to find the best variant from an environmental perspective, while also adding a novel, semi-quantitative, robust framework of data quality assessment to the state-of-the-art.

The characterization results, under the assumption of each scenario yielding a product of the same mass and equal importance being given to each impact category (equal weighting), indicated the press consolidated carbon fiber reinforced PEKK product to be the scenario with the lowest impact over the cradle-to-gate (including only material production/extraction and product manufacturing). Over the cradle-to-end of service phases (including material production/extraction, product manufacturing, and the operational phase of the aircraft), the operational phase was observed to have an exponentially larger impact compared to the other life cycle phases causing the comparative profile to homogenize. This was reiterated by outcomes of the performed contribution analyses. Sensitivity analyses were conducted to explore the environmental benefits of lightweighting and processing waste optimization (buy-to-fly ratios quantifying the relative, quantitative benefits of lighter products and leaner manufacturing systems.

The development of novel materials has been of great interest to the aerospace industry in the pursuit of efficiency and cost reduction. Fibre-steered variable stiffness laminates have promising characteristics due to the ability to better tailor designs for expected loading, as the fibre orientation can be varied within a layer. This thesis was created to develop a fibre placement planning algorithm for fibre-steered layers on moderately curved open shells for a given fibre angle distribution.

The fibre-steered layers are to be produced by Automated Fibre Placement (AFP) without any course overlaps, which means that several manufacturing defects have to be considered. Gaps between courses are inevitable due to course shifting in combination with the prescribed fibre paths, and tow cuts run the risk of tow straightening due to loss of steering control of the AFP roller head. Furthermore, steering limits have to be observed to prevent tow buckling.

The thesis objective was approached by dividing it in three parts. Firstly, the geometry of the mould and the course paths was defined parametrically in the form of NURBS surfaces and curves. These have been widely used in Computer Aided Modelling (CAM) and have extensive support in terms of existing algorithms and documented work. Additionally, performing most operations in the parametric space allows for greater accuracy compared to general finite element methods.

Secondly, the fibre angle distribution was converted into a fibre layer. This was initiated by generating initial course centre lines, which were then fit onto the parametric surface. Representations of tow courses were made by geodesically offsetting the course centre lines in the binormal direction. A curve-curve intersection algorithm was then used to accurately detect tow overlaps, which were handled according to the tow placement strategy. Two tow placement strategies have been developed, one for general use and one to specifically prevent tow straightening. In addition, curvature of the course centre line was registered to check for tow buckling, and the minimum cut length was enforced by evaluating the length of tow segments.

Lastly, fitness criteria for fibre-steered layers were defined. Layers were evaluated for gap percentage, fibre angle error and number of cuts. These can be used to objectively grade layers against each other, or to assess the effects of fibre steering against conventional laminates.

Bio-based composites have been a viable material choice in aerospace, automobile and construction industries over the past few decades. From day-to-day products like spoons and chairs to the construction of rocket parts, bio-based composites find their applications due to their mechanically enhanced, cost-effective and lightweight structures, with a reduced carbon footprint. This study collaborates with NPSP, one of the companies leading the way towards a circular economy.
However, the manufacturing and testing of bio-based composites is time and resource expensive. Moreover, exploring all natural fillers and fibres ratios is not feasible experimentally. Optimization and analytical models are two potential approaches that accelerate the search towards an optimal bio-based composite recipe when combined with bio-based materials research. A data-scarce Bayesian optimization model was already developed to research the composition of bio-based composites. The proof-of-concept program adjusts the natural materials’ weight ratios to optimize toward user-defined mechanical properties. The objective of this study is to experimentally investigate if the Bayesian Optimization model works by varying the objective functions and adapting the model according to the clients’ needs. By exploiting the machine learning model at an initial stage, the purpose is to test how the model reacts to different objective functions defined at high weight values and observe if the model can generate optimized recipes with better mechanical properties than the defined training set. For this study, four different fillers (calcite, lignocellulosic filler 1, lignocellulosic filler 2, waste-based filler) and two different fibres (flax, bamboo) are used, with calcite as the reference filler. A primary goal to be achieved by NPSP is to reduce or eliminate calcite as the primary filler due to its high density and brittle nature. Promising results have been obtained within two iterations of using the model for the different filler/fibre systems used.
Additionally, the thesis also investigates the rules of mixing for multi-component systems to develop analytical models that predict the mechanical properties of the composite. The Lewis-Nielsen model and the Cox -Krenchel theory have been used to compare theoretical values with experimental data points. The initial binary phase curve fitting followed by applying cascading to obtain ternary and quaternary phase mechanical properties provides approximate results for most recipes made. Finally, recommendations to improve both models have been covered, and a potential to combine both approaches has been shown.

Current large-scale additive manufacturing extruders use short reinforcing fibre-filled thermoplastic pellets, which marginally improve the mechanical performance but are too short to exploit the strength of the fibres fully. Long fibre pellets have much higher potential strength, and the development of higher strength materials could create stronger parts and/or reduce the mass of products, lowering their energy consumption in the case of vehicular parts of heated tooling.

By developing long-fibre thermoplastic pellet processing, this thesis works toward improving the mechanical performance of fused granulate fabricated parts. Extreme die-swell was encountered when extruding long glass-fibre polypropylene pellets. This die-swell is theorised to be caused by energy storage in an entangled network of long fibres, which is released upon extrusion. This issue was solved by developing a mix of two different material pellets, which was used with the tactical use of temperature zones to create a hetero-phasic blend inside the extruder. This technique and material blend enable controlling the melting of the long fibre pellet resin, lubricating the pellets to promote macro-alignment, and reducing heating through shear friction. These effects delay the dispersion and entangling of fibres.

This method eliminated the problem encountered; reducing porosity by 82%, increasing strength by 960% over the original swollen material and achieving specific strength 16% higher than the short fibre compound currently being used. This research presents a new method to make previously un-processable long fibre thermoplastic pellets useable with a 25 mm diameter screw extruder. It contributes to the development of unprecedented high-performance parts 3D printed at a large scale.

Considerations that decide producibility of a design are an important part of the design process, and must be included in the early design stages to ensure that these designs can be realised. Not including these considerations carries the risk of incurring additional costs and delays at later stages of product development because of design changes, or can lead to limiting oneself to conservative design choices to reduce the associated risk.
The current process in the industry accounts for these production considerations in design through a manual process that is iterative and time-consuming, and hence forms a bottleneck in being able to trade-off multiple design concepts. Attempts at accounting for these production considerations in an automated way are associated with the limitations of either only considering the manufacturing cost, being specific solutions that work only in certain scenarios, or being dependent on some commercial software tools, which are not fully suitable for use in context of automation and/or at the conceptual design stage. Additionally, the aspects of manufacturing and assembly are usually not considered at the same time in these studies.
Therefore, this thesis aims at developing a methodology that enables the automated inclusion of production considerations in the conceptual design process of aircraft structures, while overcoming shortcomings of the state-of-the-art....

This work is a part of the Automated Rotor Blade Inspection (ARBI) project. ARBI aims to improve the rotorcraft RTB process with novel rotor blade measurement equipment such as 3D scanning, thermography and shearography. The research aims to quantify the effects of changes in blade properties on rotor vibration levels for CH-47 Chinook. This is done in order to create a rough ranking of which parameters have the highest impact on vibrations. This was performed by changing the blade properties on a single blade in the rotorcraft simulation tool FLIGHTLAB, trimming to a desired flight condition and collecting acceleration measurements. In FLIGHTLAB a novel inflow solver, the Viscous Vortex Particle Method (VPM) was applied, since the developers specified it was well suited for rotorcraft with rotor-on-rotor aerodynamic interaction. The results of this research in future hopefully will be able to help identify blades with poor RTB potential and help with suggesting blade sets with higher RTB success chance based on measurements from ARBI.

Predicting the critical buckling load of cylindrical shells with circular cutouts subjected to uniform axial compression is an important part of the structural design in the aerospace industry as buckling significantly reduces the load-carrying capability of the structure. A cutout constitutes a major disruption in the shell geometry, and therefore it should be expected that it has a significant effect on the sustainable buckling load. An analytical solution for estimating the buckling load of isotropic and quasi-isotropic composite cylindrical shells with circular cutouts is developed to assess changes made to the geometry and the material during the preliminary design phase quickly. The Ritz method is employed to minimize the total potential energy of an ideal shell that contains a central opening in order to predict a linear buckling load. Finite element simulations are conducted to verify the accuracy of the analytical solution. In addition, they are used to investigate the evolution of buckling modes, the effects of initial geometric imperfections, as well as the shell failure mode. The nondimensional curvature parameter α can be used to categorize the buckling behavior of cylindrical shells and is a function of the cutout radius, the shell radius, and the shell thickness. A small cutout has virtually no influence on the buckling load compared to a pristine shell and the displacement pattern at buckling is global. The buckling load decreases rapidly for moderately large cutouts where the stability loss is the result of a local buckling mode that immediately leads to global buckling. Cylindrical shells with large cutouts are again relatively insensitive to an increase of the cutout size, but the buckling load is greatly reduced relative to a shell without a cutout. Large openings also feature a stable local buckling mode where substantial lateral prebuckling displacements emerge before the structure buckles globally. While the analytical procedure theoretically should not capture the onset of global buckling independent of local buckling, it follows numerical trends for cutouts of moderate and large size regardless. Therefore, it may be used during preliminary design to estimate the impact of changes made to the shell geometry and material. Local buckling is caused by high compressive stresses next to the cutout and, in some cases, large lateral prebuckling displacements. The detrimental effect of the stress field may be partially relieved in composite cylindrical shells by reducing the amount of axial bending stresses that occur. Hence, the chosen stacking sequence can have a significant influence on the buckling load of shells with moderate and large openings.

On board of High Speed marine Craft (HSC), the crew and the passengers are exposed to high levels of Whole Body Vibrations (WBV) and large magnitude Repeated mechanical Shocks (RS) caused by the motions of the craft. The HSCs are typically 10 meters long, capable of reaching a maximum speed up to 50 knots and widely used by various maritime organizations. However, the operators and crew suffer from fatigue and injuries, leading to a reduced effectiveness and operational capacity of the marine craft. In an attempt to reduce the physical loads, passive Shock Mitigating Seats (SMS) can be installed. Numerous research has shown that an improperly designed SMS may amplify the wave impacts forces through phenomena such as bottoming out and dynamic amplification. Therefore, it is necessary to ensure that a suspension design works properly by testing the performance during wave impact events, before the seat is manufactured and installed onboard the craft. The problem is that it is difficult to determine the performance of the seats in both the design and off-design conditions with either sea trials or laboratory tests. This research focuses on the prevention of injuries and adverse health effects due to repetitive wave impacts by incorporating an injury model in the analyses of various suspension principles in the design of SMS. In the current analyses of SMS either simplistic or specific models are used which restrict the application of these models to other suspension designs. Therefore, a computer program based on the finite element method is developed that allows realistic input accelerations in the surge, heave and pitch direction. The program incorporates highly non-linear elements, including the effect of bottoming. Additionally, the validity of the half-sine approximation for the wave impact excitation pulse was reviewed and concluded to be inappropriate for design purposes as it underestimates the probability of bottoming. Furthermore, the modified evaluation methods of ISO 2631 Part 5 using an optimized age-dependent coefficient based on gender in combination with a Weibull injury risk model were implemented to evaluate the resulting seat level accelerations. A case study was conducted on a Fast Raiding Interception and Special forces Craft (FRISC) of the Royal Netherlands Navy (RNLN). A design based on a parallelogram of pinned truss elements in combination with a coil spring element was altered by replacing the coil spring with a gas-spring element. The design was analysed with dynamic simulations of full-scale measurements of wave impacts on a lifeboat of the Royal Sea Rescue Institution (KNRM). For the most severe wave impact of the acceleration record, the seat level acceleration was reduced from 17.7 [g] to 2.8 [g]. An operator of the age of 24 years who is exposed to the accelerations for half an hour a day, 30 days a year for two consecutive years was assumed. The probability of spinal injury was reduced for a male operator from 99.5% to 16.3% and for a female operator from 100.0% to 42.0%. These results illustrate the high risk of injury to which the HSC operators are exposed. By incorporating highly non-linear elements and spinal injury models, the program and evaluation methods are capable of modelling various SMS suspension designs and analyse the performance. This can assist the seat designer, engineer or researcher with investigating suitable suspension designs before sea trials, experimental tests and prototype iterations. Therefore, the method offers the possibility to save time and reduce costs. Furthermore, the method can assist in defining new regulations in order to limit the exposure of the operators to physical loads and reduce the risk of spinal injury to an acceptable level.