Hyper-Velocity Impacts (HVI) from micrometeoroids and orbital debris pose a significant threat to satellites in low Earth orbit due to the higher density of sources and the resulting increased impact frequency. Understanding the stress field and dynamic behavior around impact points is critical for satellite design, structural integrity, and platform stability assessment. A coupled Finite Element and Smoothed Particle Hydrodynamics (SPH) methodology implemented in LS- DYNA explicit software is used to simulate HVI effects. Without compromising the reliability of the results and ensuring their continuity at the methodological interface, the aim is to take advantage of the strengths of both simulation methods. Although previous studies have used SPH-FEM coupling to model Hyper-Velocity Impacts, the focus of this thesis is on characterizing the stress field surrounding the impact zone. It has been observed that a portion of the stress wave is reflected at the interface between the two numerical methods within the plate. This reflection is not caused by a physical obstacle and is therefore numerical and artificial. A comparative analysis of stress signals collected near this numerical modeling discontinuity demonstrated that the implementation of a SPH-FEM hybrid elements interface exhibited superior performance in mitigating this effect in comparison with a tied type contact. Indeed, stress waves can smoothly move from the impacted region towards the external domain of the structure, exhibiting only minor internal reflection at the interface between the two numerical methodologies. Furthermore, the impact of the SPH lattice on stress wave propagation was explored. It was found that the default modeling approach had a detrimental effect on uniform stress propagation in the plate, as it introduced preferential directions of propagation. This issue was addressed by implementing a custom SPH lattice that ensures the isotropic properties of the material selected for modeling the plate. The propagation of impact-induced effects is ensured to be independent of the direction of study. Initial calibration and validation were conducted on a single flat plate system, followed by an extension to a full Whipple shield simulation. With regard to the latter, not only stress data, but also the HVI-induced vibration field within the plates was studied. This was achieved by collecting the out-of-plane velocity signal at variable distances from the impact site. Nevertheless, further studies are necessary for further refinement and validation. ... Read more

In recent years an exciting new era of space exploration has begun with the advent of the beyond Earth orbit CubeSat (BEOC) missions. However, utilizing the CubeSat platform for such missions gives rise to a series of significant technological challenges. Fortunately, the field of inflatable space structures offers some tantalizing solutions to these challenges. Unfortunately, at present the development of these structures is hampered by a technological gap in the required inflation systems. In order to fill this gap, this thesis proposes the development of inflation system optimized for such applications, based on the field of micropropulsion technology. In pursuit of this goal, the main research question shall address the design adjustments required in order to adapt current micropropulsion technology for this purpose. To answer this question the research objectives of the thesis are to first develop a preliminary design for an inflatable BEOC reflector and then, having generated inflation requirements based on this structure, design a custom micropropulsion based inflation system.

This approach involves first identifying a BEOC inflatable reflector design whose continued development will play a key role in enabling and enhancing the development of BEOC missions and inflatable space structures in general. Then the structure is designed with particular focus on the key design considerations that impact the requirements of the inflation system. Following the design of the structure, the requirements for the inflation system are generated. Informed by these requirements, a trade off analysis identified a cold gas system as the most suitable micropropulsion system for inflation applications, as well as the inflation gas and a suitable inflation scheme. After this, the design of the inflation system is performed. It is found that in order to satisfy the inflation system requirements, apart from a unique design approach for the inflation nozzle, minimal design adjustments are required to cold gas micropropulsion technology for inflation purposes. This result demonstrates the feasibility of utilizing micropropulsion technology for the development of optimized inflation systems and provides a clear indication that such systems can play a key role in enhancing and enabling the development of BEOC inflatable structures. ... Read more

The Europa Lander is a mission by NASA to land scientific instruments on the Jovian Moon by 2030. The current design of the landing system envisions fixed landing legs with the lander being lowered down at very low velocities (≈ 0.1 m/s) by use of a Skycrane. This latter system not only adds mass, but also requires complicated moving parts and a high reliance on control systems to work properly. This thesis wants to propose an alternative design to the Europa Lander Landing System that uses sturdier legs that can withstand landing at higher velocities than originally envisioned. This eliminates the need to use a Skycrane system. In order to pack them in a more efficient way while coasting, the landing legs are of the deployable type.
In order to track the deployment dynamics of the landing system a 2-dimensional Matlab deployment model based on double pendulum motion with damping is created. Furthermore, in order to prove the landability with a prescribed landing case, a landing model is created using FEA software Abaqus. The landing model is used to make sure that stresses, strains and G forces applied to the rest of the lander don’t exceed prescribed values as dictated by requirements. The implementation of both models is verified by comparing models found in literature with the ones made for the purpose of this thesis. Good correlation is shown with less than 10% of difference between literature results and results for this thesis.
The result through the modelling found a specific geometry with parameters that include, but are not limited to: length of leg elements, joint damping and maximum deployment angles. The 2-dimensional geometry features output by the Matlab deployment model are fed into the Abaqus landing model in order to assess the landing performance with a single leg landing. The landing case has been chosen as a worst case scenario. 2 landing leg designs, with the same geometry, but one made of metallic parts and the other made of composite materials are compared in the landing model. In this model it was found that both designs pass the stress (or strain for the composite leg design) and G forces
requirements when a shock absorber is attached to the leg and when they land on deformable Lunar like soil. On the other hand, the landing legs don’t pass G forces requirements when landing on stiff soil.
Through the modelling, it was also possible to give preliminary design guidelines over the subsystems making the landing system. Therefore, system engineering practices have been used in order to initiate the design of some of the subsystems such as the landing damping, the leg joints and the locking mechanism to lock the legs at the desired angle and make sure they don’t retract. Simplifications have been made in order to model some of the landing and deployment aspects of the system for this thesis. Matters related to the adaptability and the detailed design of each of the subsystems have been left as future work.
In the end, a comparison between the design developed in this thesis and the current Europa Lander Landing System design is made difficult by the lack of technical data on the latter related to mass. Nevertheless, a design that uses the decelerations of the engine module before touchdown is developed and the suggested material for the leg elements is CFRP. The design, though, didn’t pass mass fraction requirements when computing the mass of the extra subsystems. Even so, locations where potential gains through mass optimization can be performed for future studies have been pointed out. ... Read more

Variable Angle Tow designs have shown to improve structural performance by providing a better stiffness distribution. However, additional manufacturing constraints are involved compared to straight fibre laminates: mainly the maximum fibre steering curvature that can be achieved. Moreover, if a gap free laminate is constructed, overlaps will be formed depending on the relative fibre orientation when the continuous tows are bent to follow a reference path in Automated Fibre Placement and a one-sided irregular thickness profile is created. To counter the latter effect and still obtain uniform thickness laminates, a cut and restart strategy of the tows is often used in industry, leaving the final product with small gap areas. However, previous research has hinted both numerically and experimentally on further buckling improvements of variable stiffness laminates incorporating overlaps, resulting in a variable thickness profile. To investigate these possible benefits and their extent, the thickness build-up and overlap locations are specially considered in this proposed framework on Variable Angle Tows. In first instance, a virtual manufacturing surrogate of the laminate is produced to represent the discrete thickness profile due to the overlaps. This is performed by plotting each tow graphically and subsequently retracing the total thickness based on the superimposed opacity over the laminate. The tow paths are obtained from the interpolated fibre orientation, which simultaneously incorporates the steering limit of the manufacturing process. The surrogate information is then compared to a smeared approximation of the thickness build-up, based solely on the steering angle. The linear buckling simulation is performed by means of a semi-analytical model on a plate formulation, where the one-sided thickness profile variation is modelled by incorporating an offset from the geometrical varying midplane to a common one, around which the laminate stiffnesses are calculated. These adapted stiffnesses are then used in solving the neutral equilibrium buckling problem, where the displacements are approximated by means of the Ritz method, with a set of Legendre polynomial shape functions and numerical integration of the stiffness matrices. The semi-analytical smeared model correlates to within ± 5% of the discrete thickness Finite Element Model for a range of geometries, loading and boundary conditions. This verifies the thickness approximation for linear buckling of small tow widths compared to the laminate's dimensions, yet was inconclusive for larger tow width ratios. Finally, laminates with a varying thickness profile are optimised alongside the variable stiffness for different cases and compared to uniform thickness counterparts at isomass. The results show small improvements in the symmetric problem, but a higher gain is obtained for unsymmetrical conditions with an unrestricted layup sequence, as the thickness increase can be highly tailored together with the variable fibre orientation to locations requiring higher stiffness. ... Read more

With increasing usage of fibre-reinforced composites for structural components across the automotive and aerospace industry, it became crucial to understand how this kind of materials behave when subjected to high loading rates, which are encountered in the case of crash events.
The current work presents a study on the effect of the strain rate on the compressive mechanical properties of carbon-epoxy laminates. Rectangular and omega-profile cross-section specimens were tested on a servo-hydraulic testing machine at several impact velocities. For all cases, an increase in the mechanical compressive properties of the laminate was found with increasing rates of deformation.
Another important aspect is the correct implementation of the strain rate dependent properties on the numerical models used to perform finite element simulations, as it can lead to more accurate impact simulations. A good agreement between experiments and simulations was obtained for both types of cross-section specimens considered. ... Read more

Delamination is one of the failure modes of composites prone to happen in the case of a car crash. In the early stages of car design, finite element analysis is used as a tool to analyze structural concepts. In order to model delamination in a newly developed material model, it is analyzed in two parts: detection and effects of delamination. To detect delamination in an equivalent single layer model in explicit finite element analysis, the transverse shear stresses are recovered from the solution of a time step, followed by the application of a stress-based delamination failure criterion. The second part results in the following: to model the effects of delamination in the same framework, each effect has to be treated separately, leading to the use of a delamination damage factor to reduce the bending stiffness and stresses due to delamination. ... Read more