Sustainable aviation demands alternative propulsion system, such as Liquid Hydrogen (LH2). LH2 needs to be cryogenically stored in large, lightweight fuel tanks. Carbon-fibre Reinforced Polymer (CFRP) composite tanks offer promising weight-savings.

Liner-less composite tanks are prone to safety-critical issues such as leakage. Leakage is caused by the presence of microcrack networks in the laminate. It is known that these crack networks arise due to thermo-mechanical loads. Element level testing is required to build a foundational understanding of the damage and leakage phenomena. The bulge test rig is capable of such element level testing, by mimicing multi-axial loads experienced by the tank structure at cryogenic temperature.

A digital twin is developed to provide deeper insights into the behaviour of the test rig and specimen. The validity of this digital twin is quantified by a 'multi-sensor' experimental campaign. The validation dataset is obtained on a range of test configurations, both at room and cryogenic temperature. Specifically, strain data is acquired using strain gauges, fibre-optic sensors and digital image correlation. Qualitative damage assessment of post-mortem specimen is conducted using ultrasound and optical microscopy, to compare the inter and intra-laminar damage initiation predictions of the digital twin.

The experimental-numerical analysis of the work is envisioned to contribute to a more representative design of bulge test specimen.

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The increasing use of composite materials in aerospace is driven by their high strength-to-weight ratio, but manufacturing these structures represents a large energy footprint and consumption of auxiliary materials. Thermoplastic composites consolidated with Induction heating offers a sustainable alternative to autoclave produced thermosetting composites, eliminating the need for prepreg refrigeration along with most auxiliary materials and a reduction in cycle time and energy consumption. Induction heating, however, is difficult and expensive to test and prototype and therefore there is a need for a way to predict tool behavior.

This thesis develops and builds on a finite element simulation framework in COMSOL Multiphysics to model induction heating of a tool for a C cross-section composite spar, using both, stationary and transient simulations- the latter of which incorporate temperature-dependent material properties - to analyze heating behavior in the tool and the effect of various parameters on the temperature distribution. The simulation model is validated through coil inductance measurements as well as heat surveys on an existing subscale tool.

Design guidelines for tool dimensions, coil placement are derived from simulations and tested virtually on a hypothetical tool geometry. A parametric modeling framework is created in the simulation software package itself, enabling rapid iterations of tool designs, streamlining development. Results demonstrate strong agreement between simulations and experiments with the stationary models predicting the variation in temperatures over the tool better while the transient model calculating the absolute temperatures more accurately. A combination of both these models in conjunction with tool design guidelines presented in this thesis can be potentially used for efficient, first-time-right tooling design for induction heated press consolidation tools.
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This study aims to increase recycling rates in the aviation industry, with a focus on both environmental impact and cost-effectiveness, by examining two key aircraft materials: aluminum alloys and carbon fiber reinforced polymers (CFRP). A mixed-method approach is employed, including a literature review, life cycle assessment (LCA), economic analysis, and the development of a decision-making model. Results show that aluminum is highly recyclable with up to 95% lower energy requirements than primary production and strong closed-loop potential, whereas CFRP recycling remains complex, yielding only partial fiber recovery and lower overall circularity. Economically, aluminum recycling is already favorable, whereas CFRP recycling requires larger scale or policy support for viability. The study culminates in a decision-making flowchart to guide stakeholders in selecting optimal end-of-life recycling strategies for aircraft materials. ... Read more

Viscoelastic materials such as rubbers find ubiquitous use in engineering applications due to their outstanding ability to dampen vibrations and shocks. During a load cycle, the stress-strain curve of a viscoelastic material exhibits energy loss due to hysteresis. The structural response is damped because mechanical energy is dissipated and converted into heat, known as self-heating. The heating of the viscoelastic material results in degraded mechanical properties, and eventually, failure. This study focuses on the application of the viscoelastic material polyurethane in roller coaster wheels. Roller coaster wheels typically consist of a cast aluminium rim with a co-bonded polyurethane rubber bandage. The high forces and high speeds of a roller coaster ride lead to high self-heating in the rubber bandage. The high resulting temperatures in the bandage may cause failure of the bond line and of the rubber bandage itself. Replacement of the rubber bandage (re-treading) is a time-consuming and expensive process and ideally avoided. It is known that the design parameters of the wheel (diameter, width, bandage thickness, rubber hardness, etc.) influence the temperatures in the rubber bandage. At the same time, these design parameters have an influence on the damping capacity of the wheel, which is important for passenger comfort, noise and the longevity of the other mechanical components of the roller coaster vehicle. For example, the wheel with the maximum thermal performance (i.e., minimum temperature) will have minimum damping capacity, and vice-versa. To avoid this complication, this study compares the thermal performance of wheels with similar damping capacities. To evaluate the thermal performance of a wheel, a decoupled thermo-structural finite element analysis methodology is implemented. The method is validated using experimental measurements provided by the polyurethane manufacturer. Subsequently, a novel wheel design is proposed and compared to a regular roller coaster wheel. The 𝛽-ratio was introduced as the ratio of thermal to mechanical power. By comparing the finite element results with the experimental results, it was found that 𝛽 = 0.24 ensures that the numerical temperature matches the experimental temperature 𝑇num = 𝑇exp = 319.4 K. This value for the 𝛽-ratio was subsequently applied to finite element analyses of a regular roller coaster wheel and the novel wheel design. The standard wheel reached a temperature of 351.3 K on the surface and 376.7 K internally. The novel wheel design reached a maximum temperature of only 314.2 K. The maximum temperature of the novel wheel design is much lower than that of the standard wheel, because its structural finite element model is much stiffer, therefore providing less damping. Given the same loading cycle, the maximum temperature of the novel wheel design was found to be significantly lower than that of the standard roller coaster wheel. This indicates that the novel wheel will be more durable and have a longer lifetime. However, the novel wheel was also found to be significantly stiffer than the standard wheel. Toward the end of the report, various design iterations of the novel wheel design are considered which decrease this stiffness and improve damping. ... Read more

The Netherlands Aerospace Centre (NLR) together with Toray Advanced Composites and 12 other parties take part in the Netherlands liquid hydrogen (LH2) composite tank consortium which is funded by the Netherlands research & development mobility (RDM) Fund. The goal of the RDM project NLR takes part in is to develop a long-life, fully composite LH2 tank for civil aviation. Microcracking and the subsequent hydrogen permeation remain the biggest challenges. This study encompasses three fundamental facets to test and select composite materials: a comprehensive investigation into material behavior, the formulation of a Finite Element Method (FEM) model, and a partial experimental verification of said FEM model. The latter integral component involves an extensive testing system that includes room temperature and cryogenic tensile tests, permeability assessments, and microcrack evaluations facilitated by optical microscopy. During the experiments there is focussed on the critical microcrack density and material selection criteria such as ply thickness. ... Read more

METAL-composite laminates, also known as fibre metal laminates (FMLs), which are made by alternating thin sheets of metal alloys and layers of fibre reinforced polymers, have attracted the interest of many scholars and researchers in the field of aerospace applications, including manufacturing. These hybrid materials are widely applied owing to their significant advantages ofweight reduction, superior specific strength, higher stiffness, and more fatigue resistance than monolithic metal sheets as well as the better impact strength and damage tolerance compared with the full composites. However, the manufacturing process of such laminates is difficult as various forming and curing stages are required in combination with the complex deformation and failure mechanisms. Hence to improve the manufacturabilty of these structures, it is crucial to develop a material forming method with optimized material compositions and process parameters.

The proposed press forming process, consists of an integral forming and curing cycle, is an innovative method formanufacturing small-to-mediumsized components. The cycle involves a laminate preparing and preheating process, forming of the uncured laminate, consolidation and (partial) curing in a same mould as well as cooling and removal of the component. The most critical aspect of the cycle is a proper control of the different deformation mechanisms in different layers. For that, during the preheating stage, temperature and time needs to be carefully controlled so that the inter-ply sliding at the metal-prepreg interfaces and the intra-ply shear within the prepregs can be greatly enhanced when the resin viscosity decreases. Then, the still uncured laminate is formed and subesequently cured under pressure, avoiding a separate curing system with pressure, which is time and cost-saving... ... Read more

The accuracy of hot press forming process simulations with unidirectional fiber reinforced thermoplastics is not at the desired level. Fundamental knowledge about the interactions between adjacent plies is needed to enhance predictive quality. Several mechanisms can be distinguished during hot press forming of composites. This thesis focuses on the inter-ply friction behaviour which is the resistance against inter-ply slip. The main variable investigated in this study is temperature.

In this research, an extensive friction characterization with UD C/LM-PAEK is conducted at temperatures ranging from 300 to 365 ◦C. The neat matrix material has been studied with DSC and rheometry experiments. In general, a peak response can be seen during start-up in a friction characterization experiment. This peak, or overshoot, progresses towards a steady state friction response after a slip distance of several mm. Reducing the temperature showed similar effects to increasing the sliding velocity in a ply-ply slip system. The peak during start-up increases in magnitude while the steady state response remains approximately constant. Indications of flow induced crystallisation have been observed during friction characterization around the melting point of the material. The timetemperature-superposition principle has been applied to experimental friction data. This enabled to predict the duration of the transition of peak friction response towards a steady state. Several modelling efforts have been compared to the experimental data. The accuracy of the model predictions is similar between 315 and 365 ◦C. Influences of flow induced crystallisation impede the reliability of the specific models around and below the melting point.

The research lead to useful insights in the friction behaviour at relatively low temperatures. Further research is required on the field of flow induced crystallisation for a better understanding of its role in the friction response. Further study with other materials is needed to validate the application of the time-temperature-superposition principle to predict the speed of the transition of peak friction response towards steady state.
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Technological advancements are conducted at accelerating rates in all areas of human activity, with air travel being no exception. In order to design aircraft that are faster, safer and very importantly more efficient, multiple solutions can be investigated. This thesis looked in particular at the structural side of aircraft innovation, and more specifically at the use of composite materials (both thermoset and thermoplastic) in comparison to aluminium, in an attempt to build lighter structures. The aim was to generate a comparative study using a wing rib as a case study and investigate the environmental sustainability of these structures using a life cycle assessment. The project was conducted in collaboration with GKN Fokker Hoogeveen, and the case study used was that of rib 14 within the Wing of Tomorrow project, initiated by Airbus.
The investigated material flows included a sheet formed aluminium rib, a machined aluminium rib, prepreg manufactured epoxy CFRP thermoset rib, RTM manufactured epoxy CFRP thermoset rib, and lastly an out of autoclave consolidated (hot press consolidated) PEKK CFRP thermoplastic rib. The results indicated that the machined aluminium in this application consumes the highest amount of energy and as a result has the highest carbon dioxide equivalent emissions as well, whereas the lowest values are seen for the sheet formed aluminium rib. The composites fall in between these two, with the thermoplastic having the third highest energy consumption and emissions from all materials considered. Lastly, a discussion was conducted on the potential of thermoplastic composites and their recyclability for the aircraft of the future, as well as future steps in the movement towards more sustainable aviation.
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The objective of the thesis was to evaluate the cost reductions and tower design when production costs are included in the design process of an offshore wind turbine tower. First, a tower cost model had to be developed. Then, based on the findings, a cost optimization model was built with the tower design software from Siemens Gamesa Renewable Energy (SGRE). Three scenarios were developed
to mimic different supply chains. The results show that the production costs can be reduced by [0.2, 2%]. Moreover, in each scenario, a different optimum tower design was found. Another study into the optimum number of shells per section showed wind turbine manufacturers could reduce production costs up to 20%. ... Read more

The purpose of this research study was to experimentally investigate transpiration cooling through additively manufactured porous structures, using Thermochromic Liquid Crystals (TLC). This was done by calculating two cooling parameters: heat transfer coefficient and film cooling effectiveness. Different materials, thicknesses of the porous structure, porosities and blowing ratios (M) were tested. Additionally, the distributions uniformity of the through-pores for each samples were also studied. The experiments showed that the materials tested had similar cooling performances. For all the samples the heat transfer coefficient was increasing with the increasing blowing ratio. Whereas, the film cooling effectiveness was the highest for the blowing ratio M=1. The thickness of the porous structure had no effect on the laterally averaged parameters studied. However, with the thicker samples, the distributions of the through-pores were non-uniform, with some areas having no through-pores. ... Read more

Both GKN Aerospace Fokker Aerostructures B.V. (Fokker) and Delft University of Technology (DUT) are partaking in a Clean Sky 2 program called MANTA. MANTA stands for: MovAbles in the Next generaTion Aircraft, and is a program created by the European Union in order to meet the ’ACARE Flightpath 2050 objectives’ by achieving cleaner air travel. The MANTA program aims to reduce the fuel consumption by 3% to 5% using the knock on effects of smart usage of movables.   The contribution of Fokker in the MANTA program is the Morphing Tab concept. This is a newly introduced tab which will be located in the wingtip and must allow load alleviation during manoeuvres. By deflecting the tab in a smart manner, it will be able to generate an internal moment in the wing structure opposite to the internal moment generated by the lift. These internal moments counteract one another, reducing the peak stresses which can result in a lighter wing structure. This will have multiple aerodynamic beneficial knock on effects such as the potential for a more slender wing.  The solution of Fokker. to keep the drag introduced by the tab to a minimum, is to use a morphing tab rather than a conventional tab. The morphing tab has a continuous inboard skin surface which morphs in the section between the Rigid winglet structure and the rigid tab. The continuous skin will add to the aerodynamic efficiency as airflow along the surface stays attached further along the wing chord and airflow leakage is largely avoided.  The morphing part of the winglet exists of multiple components. the component studied in this thesis is the flexible skin. More precisely, it is the attachment of the morphing skin to the non-morphing parts of the concept, the winglet and the tab. As the morphing skin is very thin, and the condition of use is an out-of-plain movement, a complex and rarely studied combination is formed. This has led to the following research question: What is the best method to connect a thin flexible skin element undergoing a peel-like motion to a rigid structure without disturbing the aerodynamic surface at the outside of the skin? Answering this question must lead to a solution for this specific situation as well as contribute to the body of knowledge to fill the current literature gap. Based on the findings of the literature study, the analysis started with selecting a joining method. This process was performed by a trade-off in which six groups of joining methods (Integral Structure, Bonding, Welding, Mechanical Fastening, a Piano Hinge and a Flexible Hinge Element) have been compared. This resulted in the selection of Mechanical Fastening as the best joining method. Within this category, Rivets have been selected as the best suited solution for the Morphing Tab Connection. Along with design guidelines, a comparison between the failure limits of the rivets and the loading conditions of the tab, led to the design of the riveted connection. A test had to be created in order to investigate whether the design is able to meet the requirements of the joint under the relevant loading conditions. No standardised test could be used as they did not create representative loading conditions. During the test, the stress and strain of the skin at the connection are measured via the machine output, Digital Image Correlation software and strain gauges. Additionally, video recordings are made of the test from the side in order to validate results. Three main test conclusions can be made: • The Aerodynamic Profile does not experience a significant effect of the Riveted connection. The required rotation angle and accuracy are achieved and the contour deformation is within the tolerance. • The Static Failure is caused by skin bending without interference of the fasteners. The Static Failure Level is higher than the required minimum stress. Therefore, the Static Load Requirements are met. • The rivets do not interfere on the skin behaviour during fatigue tests. The stiffness reduction due to the fatigue tests shows similar results with and without fasteners. Overall this means that the Riveted connection meets all Aerodynamic and Structural Requirements. Besides this, no indication was apparent during the tests that another joining method would lead to better performance. Also, the riveted connection outperformed the other joining methods in the other Trade-off categories. The combination of these two facts warrant the overall conclusion of this thesis: A riveted connection is the best method to connect a thin flexible skin element undergoing a peel-like motion to a rigid structure without disturbing the aerodynamic surface at the outside of the skin. The connection design created during in this thesis can be applied in further investigations in the Morphing Tab Concept. ... Read more

The aim of this study is the assessment of the mechanical performance reduction due to manufacturing-induced gaps and voids (delaminations) in thermoplastic composite pipes. The effects of gaps are assessed based on the finite element modeling of an internal pressure load case and is validated by experimental tensile coupon testing. Results show a stress increase through-the-thickness in the layers having the same orientation, which depends linearly on the gap width. The assessment of voids is based on the modeling of external pressure and lateral crushing, in which the latter is also experimentally tested for validation purposes. No reduction in performance is observed for external pressure and an onset of delamination growth is observed for lateral crushing. A tool is proposed for a fast and computational inexpensive assessment of manufacturing-induced gaps in thermoplastic composite pipes to improve the design and manufacturing process and contribute to an improved integrity management system. ... Read more

Assembly, Integration and Verification (AIV) in space makes launching geosynchronous satellites faster and significantly cheaper in the long term. A space-tug is launched into space to perform AIV there. It assembles a standardised satellite consisting of several modules. The modules are designed in such a way that the required subsystems for a communication satellite are incorporated in the modules. Examples of these modules are a propulsion module, a solar array module and a computer module. Due to the standardised modules, testing time and costs can be reduced significantly. This ensures a delivery time of maximum one year, which is the time from order until operations in space. The modules are efficiently packed and connected to external beams in the launch vehicle, to make sure that two satellites can be launched simultaneously. The external beams take up the extreme loads that occur during launch. This decreases the dry mass of the satellite, as the modules do not need as much structural mass. The subsystem design and structural analysis result in a drymass of 1847 kg per satellite. Next to the two satellites, a refuelling tank is added in the launch vehicle to refuel the tug. The tug requires 2921 kg of fuel to transfer the two satellites and go back to its initial state. Due to the modularity of the satellites, the lifetime of the satellites can be increased. Regarding the economic feasibility of the mission, a full return on investment is expected after 15 years of operations in base case scenario. ... Read more

A Solar Electric Vehicle is a vehicle that receives a significant amount of its total energy consumption through sunlight gathered using solar arrays. The main objective of this thesis was to determine how the design of the rear low-speed crash structures should be different for a Solar Electric Vehicle, compared to conventional cars. This is done by creating a general optimization tool that can be used for the conceptual design of the rear low-speed crash structures of passenger cars. Next to the structural performance during three low-speed load cases, the manufacturing cost and intrusion distance are also taken into account. It was found that for a Solar Electric Vehicle the intrusion distance should be reduced in order to increase the size of the solar arrays (and therefore their yield) without damaging them during low-speed rear impact, even though this comes with a weight penalty. ... Read more

In this comparative eco-design study, the environmental impact of LM’s 58.7 blade was assessed for multiple material composition and waste management scenarios. Material variations were largely focusses on the resin fraction of the blade. This is since the matrix has the biggest impact of all materials and has a big impact on the available waste management options that are available. Material and waste management scenarios were largely selected based on a literature review. This knowledge was combined with the knowledge and current direction of LM to determine the investigated scenarios. Life Cycle Assessment (LCA) methodology was applied to calculate the potential emissions and resulting environmental impacts. To calculate the impacts, the Ecoinvent 3.5 database was used in combination with the ReCiPe 2016 Life Cycle Impact Assessment (LCIA) methodology. Analysis showed that Sub Critical Water (SubCW) hydrolysis likely is the waste management method with the lowest impact for the current used glass fibre - polyester design. However, two design changes can potentially lead to big reductions in total single score impact scores. These two are: designing for reuse of blade sections and interchanging thermoplastic resin for the currently used thermoset polyester resin. Both are beneficial because of the relatively direct reuse/recycling of material. This research can be extended to more resin types and waste management methods of these resin types. This will shed a broader light on the matter. When waste management methods reuse methods should be prioritized over recycling methods and ’clean’ recycling methods (i.e. methods that do not lean on heavily polluting processes) over dirty recycling methods. ... Read more

Structural members carrying dominantly compressive forces are present in many types of structure. These members are referred to as columns and are frequently present in for example lifting appliances and offshore structures. Whether or not a column consists of longitudinally welded subsections is relevant for its mechanical performance in compression. Steel columns consisting of longitudinally welded members contain residual stresses caused by the non uniform longitudinal expansion and shrinkage during the welding process. The distribution and magnitude of these residual stresses are dependent on the dimensions of the heat affected zone (HAZ), and varies for instance as function of the welding procedure, and whether or not post weld measures are taken to diminish these residual stresses. In this thesis the width of the region in a column's cross section where tensile residual stress is present is referred to as the HAZ width. Using practical experiments an estimate is made of realistic HAZ widths in column structures using _nite element analyses. These column structures where welded and kept free of restraints during this process, so that a resulting curvature is developed upon cooling down to ambient temperature. The established value of the width of the tension zone is on the order of the thickness of the column's cross section. Based on existing norms a trapezoidal distribution of residual stress having a width of the earlier found value is applied on a _nite element model of a single square column, both for pinned and clamped boundary conditions. Mesh independence of the obtained results are verified by convergence studies. The compressive load capacity of the considered column is accected in the intermediate range of slenderness ratios, and shows a maximum reduction of approximately 21%. The effect of welding residual stresses is also investigated on a scaled model inspired by an existing design of a tower crane. A crane section is modelled by four vertical columns connected by multiple side bars. These side bars reduce the effective slenderness ratio of the columns loaded in compression, and therefore a less severe effect of the residual stresses on the collapse load is found. ... Read more

Over the course of the last century, the aircraft-industry has continuously been developing and optimising the performance of their products. The rate of improvement has been decreasing, and it seems like an asymptote is being approached in the development of the current technologies. The demand for new innovative solutions is growing and these solutions shall allow the performance increase to bypass this stagnation. One of the solutions investigated is to develop an aircraft wing which has the capability to fly at optimal shape by autonomously optimising its own wing-shape during all phases of the mission. This could potentially lead to a severe increase in aerodynamic performance and controllability while actively minimising structural loads. ... Read more