Iantaffi, Caterina; (2023) Additive Manufacturing for Lunar In Situ Resource Utilisation. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Human and robotic exploration of the Moon is paralleled with the need of in situ manufacturing. The wide portfolio of Additive Manufacturing (AM) technologies, combined with the concepts of In Situ Resource Utilisation (ISRU), have been identified as key technology enablers for on-demand, manufacturing, servicing, and repair of large components, e.g., habitats, paved roads, landing pads. A popular design solution for creating a habitat consists of using an inflatable module protected by an additively manufactured outer shell. An outer shell wall of lattice structures, filled with loose Regolith, could provide the thermal, mechanical, and radiations protection. In this research study, the unique design flexibility of Powder Bed Fusion (PBF) was utilised to manufacture auxetic cubic chiral lattice structures. Although this lattice structure has not extensively studied before, it emerges as a perfect candidate for habitat outer shells due to its synclastic bending behaviour and high energy absorption capabilities. The study offers stiffness and yield strength scaling relations for relative density ranging from 0.3% to 6.5%, providing valuable information for preliminary design purposes. Analysis of deformation and failure mechanisms revealed that the primary failure locations are in the struts exhibiting a reduction in cross-section. The analysis focused on Ti6Al4V samples, as obtaining the optimal parameters for manufacturing rich oxidised metals, such as fine lunar grey soil, Regolith, requires extensive characterisation. Next, a combination of synchrotron in situ x-ray imaging and post operando techniques, was used to discern on the impacts of solid and liquid oxidation phenomenon in Ti6242 alloy. The study demonstrates that oxygen species acting as a surfactant, reverse the Marangoni flow, deepen the molten pool, assist in pore escape and act as an α stabiliser, improving the final microstructure. By demonstrating the significant advantages of employing synchrotron x-ray experiments, the following experiments were conducted on lunar Regolith simulant powders. iii The study of two lunar Regolith mare simulants with different mineralogy, contributed to defining essential properties for laser manufacturing techniques, and the development of a lunar Regolith simulants classification scheme. For the first time, synchrotron in situ x-ray experiments were used to capture real-time laser interactions with Lunar Regolith simulant powder, providing insights into melt flow dynamics and solidification mechanisms. The change of molten pool morphology, such as depth and width, were quantified in relation to process parameters. The mechanisms causing process instability under non optimal conditions, e.g., vapourisation, balling and sputtering, were studied. The findings are instrumental for validating multiphysics models capable of simulating the laser sintering/melting of Regolith powder. This, in turn, could deepen the understanding of how the Moon’s environmental conditions influence the manufacturing process. Although the presented results might be not conclusive in qualifying the L-PBF technology to produce lattice structures made of Regolith, the outcomes of these research studies play a crucial role in formulating a simulant classification scheme, guiding future experiments for identifying new print strategies and chemically adapted Regolith materials.

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