Aircraft and helicopter structures commonly incorporate a combination of high-strength, low-density materials, such as carbon fiber-reinforced polymer (CFRP) and aluminum alloys, which are joined mechanically (e.g., fasteners, rivets) or physicochemically (e.g., adhesives, welding). While these structures are mechanically optimized, their durability can be compromised by galvanic corrosion when materials with different open circuit potentials are in electrical contact. A typical example of such a joint is the mechanically fastened CFRP-AA2024 connection. This thesis investigates the less understood process of galvanic corrosion using an in-situ reflected microscopy technique combined with electrochemical potential noise, complemented by post-mortem scanning electron microscopy (SEM) and Raman analysis. Additionally, the study explores the use of environmentally sustainable materials to improve the system's eco-friendliness without sacrificing protective performance.

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.

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.

L-AFP is able to place composite tapes in very precise directions, thereby allowing tailored stiffness designs. The laser is used to heat the thermoplastic matrix material to temperatures above its melting point. CF/PEEK is a popular choice for aerospace grade structures due to the high structural performance and high glass transition and melting temperatures. Current L-AFP research is driven by the desire to produce OOA laminates with a performance comparable to autoclave level. This will remove manual, labor intensive, and energy consuming steps, leaving a repeatable and automated process that is more predictable. A key phase for the performance of a laminate during L-AFP is the development of intimate contact. Recent research showed the effects of thermal deconsolidation due to rapid laser heating and questioned the current practice of characterizing the surface of the composite tape material for the intimate contact development models: instead of characterizing the pristine tape surface, the laser deconsolidated surface should be characterized. Additionally, another dominant physical mechanism, driving the intimate contact development was proposed based on the observations of thermal deconsolidation. These ideas are novel and require more extensive understanding of what thermal deconsolidation due to rapid laser heating is, how it affects intimate contact development. The effects of rapid laser deconsolidation were studied by performing (1) a rapid laser deconsolidation experiment where CF/PEEK samples were prepared and (2) an intimate contact development experiment where the specimens were compressed under constant pressure while being subjected to a temperature profile. Three degrees of deconsolidation were manufactured with the laser set-up: (1) zero deconsolidation by using the as-received tape directly as specimens, (2) slightly laser deconsolidated tapes which experienced maximum temperatures between the glass transition and melting region, and (3) highly laser deconsolidated tapes that experienced temperatures above the melting point. All samples were characterized on void content, roughness, and waviness; all of which significantly increased which showed that the state of the tape right before the nip-point during L-AFP is significantly different than the pristine state of the CF/PEEK tape. The intimate contact development experiment was carried out with pressure levels of 10, 50, 100, and 300 kPa reaching maximum temperatures of 363°C. Decreasing the degree of deconsolidation or increasing the pressure resulted in better consolidation. At 10 kPa, most of the characterization showed very little difference from a pristine tape, but a significant amount of DEIC was developed with 36% for the highly laser deconsolidated tape to 46% for the as-received degree of deconsolidation. At the highest pressure of 300 kPa, no significant difference between the degrees of deconsolidation was observed as the average DEIC values are between 85 to 87%. Additional intimate contact development temperature settings below melt showed that no intimate contact was developed below the melting temperature. During the glass transition, a significant compaction occurred which eliminated most of the void content. Between the glass transition and melting temperature, however, void content, thickness, and roughness all remained constant. At the melting point, a second thickness compaction occurred together with the development of DEIC and decrease of roughness which appeared to also relates with resin percolation.

The aim of this study is to analyse the influence of ply drop-off regions and related parameters on the VARTM cure-induced residual stress generation and related distortions within thick thermoset composites. These parameters include the resin pocket material properties and geometry, ply orientations and cure cycle parameters. By means of a coupled thermal-mechanical cure model it is observed that during the initial part of the cure process, both the chemical shrinkage and thermal expansion of the resin pocket evolve in counteracting manner. The resin pocket geometry and orientation of the surrounding plies influence the out-of-plane direct tensile stress within these plies whenever either the aspect ratio of the resin pocket or the in-plane stiffness of these plies is increased. The orientation of the terminated ply proved to be of influence as well, where higher in-plane shrinkage and thermal contraction of this ply increases the out-of-plane stress around the drop-off region. Implementing multiple drop-off regions introduce stress interactions caused by the different ply orientations used. These regions influence the local out-of-plane stress levels around the drop-off regions, where the stagger distance between these drop-offs generally lowers this effect. As result of this study, existing drop-off design guidelines are reconsidered and new guidelines are proposed for implementing ply drop-off regions within composite laminates.

Recent findings have highlighted the potential of a 3D-printable high-strength Liquid Crystal Polymer, whose anisotropy can be fostered for topology optimization intents. The mesostructure of a 3D-printed liquid crystal polymer is studied: the observation of interlayer features under the form of regular notches or spiraling patterns swirls is reported on optical microscopy of cross-sections. A formation mechanism is proposed: interlayer features may be formed as a result of an offset in placement of material. Another question is raised by the observation of these crenelated shapes: by providing mechanical interlocking between layers, they are expected to enhance interlaminar shear strength of a part. Short-beam shear tests indicate that when interlayer features are tall with respect to the layer height, and oriented perpendicular to the shear loading direction, the interlaminar shear strength of the 3D-printed part is enhanced by up to 112%. Microscopic evidence further indicates the crack-arrest ability of these features.