Departamento de Ciências Aeroespaciais
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Browsing Departamento de Ciências Aeroespaciais by advisor "Aguiar, Martim Lima de"
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- 3D Printed PETG S-Shaped Auxetic Structure: An Experimental and Numerical StudyPublication . Fernandes, Beatriz Teixeira; Dutra, Thiago Assis; Silva, Abílio Manuel Pereira da; Aguiar, Martim Lima deThis dissertation’s main interest is to investigate auxetic structures and their potential applications, especially in the aeronautical sector. Due to the unique properties of these structures, they are increasingly gaining importance in the aeronautical industry for addressing many problems and challenges. Auxetic structures have potential applications in lightweight structures with high mechanical properties and a significant energy absorption capacity. During this study, it is understood that additive manufacturing (AM) plays a crucial role in auxetic structures as it allows the construction of complex structures, such as auxetic structures. After a review of various types of auxetic structures, one structure stood out, not only for its unusual shape but also for its properties. This S-shaped structure stands out for reduced stress concentration, high energy absorption capacity, and high elastic recovery. Due to this distinction, it was decided to study this structure in detail. In this work, several samples of S-shaped structures were manufactured using AM as the manufacturing method and polyethylene terephthalate glycol (PETG) as the material. The samples underwent two types of experimental tests, compression tests, and creep-recovery tests. This allowed obtaining valuable information about the behavior of these structures under load and their recovery after the application of loads. A numerical model was also developed to better understand the S-shaped structure. The numerical model was based on data obtained from the characterization of the PETG material. The simulation results are meticulously compared to experimental data, highlighting the effectiveness of the numerical models despite inherent complexities. Finally, the findings of this work project a promising future for PETG and auxetic structures in various engineering domains, including composites, automotive safety, aeronautics, and aerospace. The foundation established in this work paves the way for future research, enabling a deeper exploration of the possibilities and implications of these innovative materials and structures.
- Piezoresistive Sandwich Structures: Assessing the viability of additive manufacturing and real-time monitoring for aerospace applicationsPublication . Moura, João Carlos Silva; Silva, Abílio Manuel Pereira da; Pereira, João Pedro Nunes; Aguiar, Martim Lima deThe use of composite materials, especially laminates and sandwich materials, has been currently experiencing significant growth, both qualitatively and quantitatively; this fact is owed to their advantages over traditional options, namely with regards to their resistance to fatigue, stiffness and relatively low weight. These factors contribute to their preference in transport-related applications, namely in the aerospace industry. Simultaneously, recent advances in manufacturing techniques and a paradigm shift towards favouring materials and components that independently integrating multiple functions indicate an undeniable potential for the improvement of the manufacture and functionality of these same composites. In this work, several beam-type samples were developed according to the principles of a sandwich-type composite, where the traditional fabrication for a laminate is complemented by additive manufacturing techniques and the additional inclusion of a piezoresistive component to promote an electrical monitoring capability, with the objective of demonstrating the viability of such a configuration of elements in a single component. Furthermore, three different types of cores were created for the sandwiches – with hexagonal, auxetic (re-entrant) and cubic cells – with the intention of emphasising the advantages and disadvantages of the various types of cells, namely those of a geometry only made possible by resorting to additive manufacturing. These efforts highlighted the cubic geometry for its greater energy absorption: up to 273 % greater than other geometries; the highlight of the auxetic geometry was a superior strain at the yield point: up to 196 % further than the other options; and the highlight of the hexagonal was an inferior decline in stress and elastic modulus over cycles: up to 26 % of that observed for both values in other geometries. Furthermore, all geometries achieved a high-quality piezoresistive response, demonstrating multifunctionality.