Mechanical and Materials Engineering Theses

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This collection is made up of doctoral and master theses by research, which have been received in accordance with university regulations.

For more information, please visit the UCD Library Theses Information guide.

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Now showing 1 - 5 of 18
  • Publication
    Fundamental Investigation on Polishing of Internal Structures Made by Laser-based Powder Bed Fusion
    (University College Dublin. School of Mechanical and Materials Engineering, 2023)
    This study aims at utilizing a self-developed hybrid polishing system to establish polishing capabilities of electropolishing (EP), abrasive fluid polishing (AFP), multiple polishing in different sequences and innovative hybrid polishing for the internal structures prepared by laser-based powder bed fusion (L-PBF). By studying polishing effects on various inner surfaces, the relationships between polishing processes and material removal mechanisms of L-PBF surface features are established considering microstructural differences of surface features. The thesis starts with a comprehensive introduction of the project and then a literature review outlining L-PBF process, application of typical L-PBF internal structures, surface characteristics, advantages and limitations of current polishing methods for L-PBF inner surfaces. Breakthroughs in the surface finish of L-PBF internal structures are required in order to improve surface quality to meet the specific requirements of product performance. It is notified that EP and AFP exhibit complementary advantages in the polishing of internal structures among various polishing technologies. In the chapter 3, different types of inner surfaces for fundamental investigation and typical internal structures for application development are designed, and prepared by L-PBF using 316L stainless steel and Ti6Al4V powders. Then, un-sintered powders and sintered area are characterized as common surface features on L-PBF top, face up, side and face down surfaces considering the differences of morphology and microstructure. Meanwhile, an innovative hybrid polishing system which could carry out EP, AFP, their multiple polishing and hybrid polishing is established for the surface improvement of the L-PBF inner surfaces and internal structures. In the chapter 4, a polishing mode consisting of two-step EP is developed by using different potentials and polishing time for L-PBF 316L stainless steel and Ti6Al4V inner surfaces after parametric study in the developed polishing system. Based on material removal characteristics of surface features, the effectiveness and high efficiency of the two-step EP are demonstrated. Considering polishing characteristics of AFP, the inlet design of polishing chamber is improved and the material removal process of various L-PBF internal surfaces are discussed by analyzing the evolution of surface morphology, roughness and microstructure on cross sections in the chapter 5. In the chapter 6, multiple polishing in different sequences and hybrid polishing based on EP and AFP are investigated for L-PBF inner surfaces. It is found that L-PBF inner surfaces after single polishing can be further improved by multiple polishing in different sequences because of the complementary characteristics of EP and AFP in removing L-PBF surface features. In addition, hybrid polishing can perform EP and AFP simultaneously without interfering with each other, showing great potential in improving polishing efficiency of L-PBF inner surfaces. In the chapter 7, different polishing processes are applied to three typical L-PBF internal structures. The superiority of multiple polishing in different sequences and hybrid polishing for L-PBF inner structures is verified. Overall, it is confirmed that the self-developed innovative hybrid polishing system is capable of polishing various L-PBF internal structures with reliable results. Fundamental research on material removal characteristics of L-PBF surface features during polishing provides a theoretical basis for the applications of multiple and hybrid polishing based on EP and AFP. High efficiency and cost- effectiveness make the hybrid polishing system a strong candidate for industrial implementation in the surface finish of L-PBF internal structures.
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  • Publication
    Killruddery: Listening to the archive. Sonic hauntings in a Big House
    (University College Dublin. School of Mechanical and Materials Engineering, 2003)
    Through listening, this thesis explores an historic private archive which is housed at the Killruddery estate in Bray, County Wicklow, in order to develop new ways of telling the story of an Irish aristocratic dynasty, the Brabazons, who have lived and worked on the estate since 1618. Its purpose is to contribute to a sonified understanding of the Big House in Irish cultural and social history. From conversations with the family, investigation of the written archives, and recordings of the architecture and surrounding landscape, the research examines the idea that the archive is haunted by its own past and that by summoning the sonic spectres of archive through technological intervention, via so-called 'Stone Tape Theory', the mythologies of its role as a heritage space in contemporary Ireland can be brought to audition. The primary field of knowledge is located within the discipline of Sound Studies. The cognate fields are Sonic hauntology, Soundwalking, Binaural Phonography, Mobile Media Art and Sonic Agency. The research utilises the practice-based methodology of an Artist-in-Residence to produce a critical construct entitled haunting the archive, drawing on a notion of hauntology initially developed by Derrida (2006), both as a means to investigate the archive and expressed in the creation of a public artwork, The Ancestors, made in response. Specifically, the principal research methods are soundwalking, field recording, interviews, studio composition, and performance leading to the creation of interactive soundscapes, historical re-enactments and audio essays, geo-fenced within the grounds of the Killruddery estate. The thesis and the practice together constitute an original and substantial contribution to knowledge by extending Labelle’s notion of 'sonic agency' (2018) through connecting elements of Critical Theory with related studies by Eshun, Voegelin and Schulze which explore ideas and practices of 'sonic fiction', to show how the creation of a hauntological sound trail informed by a critically engaged sonic arts praxis, can challenge our understanding of official narratives at a significant Irish heritage site.
      26
  • Publication
    The Affordances of Immersive Virtual Reality for Stimulating Prosocial Behaviour: A Mixed-Methods Pro-Environmental Intervention Study
    (University College Dublin. School of Mechanical and Materials Engineering, 2023)
    The world is facing severe challenges, including climate change, hunger, pandemics and inequality. Several of these challenges will directly or indirectly impact everyone, and there is an urgent need for global action. It is necessary to adapt to a more sustainable way of living, and research can help develop and refine tools to support this transformation. This dissertation aims to contribute to the understanding of how virtual reality (VR) can support attitudinal and behavioural change leading to prosocial behaviour. A mixed-methods design was used to outline a framework for designing prosocial VR interventions, develop a pro-environmental VR intervention, and test its effectiveness in a two-group quasi-experiment involving 104 participants. Finally, the most impactful factors for a change in pro-environmental attitudes and behaviours were explored. The dissertation confirms findings from prior research that indicate the effectiveness of using VR to support prosocial change. It also provides additional insight into the understudied area of using VR in pro-environmental interventions. The participants in the VR condition reported an increased capability, opportunity and motivation for prosocial change, a higher degree of pro-environmental behaviour one month after the intervention, and participated to a higher degree in voluntary activities to learn about measuring and reducing their carbon footprint. The research offers novel insights and original contributions to the academic field of prosocial VR but also provides examples of how scholarship might inform and inspire prosocial action in practice. The ambition is that this work can be of value to future scholars and practitioners and that it may be utilised in schools and learning environments where young people may be inspired to take ownership and action.
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  • Publication
    Phenomenal 'Ba': developing creative potential through virtual time travel in experiential worlds
    (University College Dublin. School of Mechanical and Materials Engineering, 2021)
    Today's problems are 'wicked': defined as complex and comprised of multiple, and contradictory threads that make addressing the 'whole problem' impossible without considering the inter-relations of the parts. These problems are often so knotty that they are unable to be solved. Add exponential growth and change in the economy, population, and factors around sustainability, to further compound these issues. The tools we have been using to solve these wicked problems are not sufficient; we need better and different tools and methods to achieve more. This thesis proposes that 'tacit knowledge' can be a powerful generator of new thinking but acknowledges that tacit knowledge cannot be accessed by simply asking questions. Cognitive biases may prevent people from fully engaging with new concepts and ideas. When intellectual or creative cognitive capacity is limited, connections are not made, and new ways of thinking and understanding are blocked. This thesis puts forward the hypothesis that a human’s capacity for original thought and radical discovery can be increased through virtual, experiential tools. The research for the thesis and the practical project underpinning it have explored – in theory, and in practice - how engagement in virtual future experiential worlds can provide a useful tool to help people develop new creative ideas. The research project scoped, designed, developed, tested, and analysed the use of novel virtual experiential worlds for this purpose, offering several original contributions including a novel tool for future use by scholars and practitioners. The thesis poses and answers the following research questions: Can immersion in Virtual Reality (VR) scenarios activate new creative thinking? Can ba, a place for knowledge creation be developed as a destination? Can VR immersion change a user's existing point of view? The research provides theoretical and evidence-based answers to these questions and then demonstrates the potential for solving wicked problems. A new method of creative exploration is offered: Elastic Action. This process begins with an effort to remove bias and blockage from the thinker's mind. Accommodation is created in the brain through exposure to 'awe', as defined at length in the thesis. Through this process, existing cognitive connections are broken, so new information can be accepted, and new ways of thinking can be enabled. The embodied cognition which takes place while the participant is immersed in a virtual future scenario can be called 'Extensible Realisations': another new concept of the thesis. Participants are then receptive to data from both mind and body. The virtual experiences were designed to 'stretch' the mind and discover new knowledge. This research successfully creates ba, a place for tacit knowledge creation enabled by a new tool of exposure: VR Time Portals. Participants travelled to divergent possible futures where they explored and discovered new ideas, perspectives, and possibilities. After immersion, they were 'snapped back' to their lived reality, where they sorted and codified their new ideas. The research design: seven residents experienced two divergent possible futures of their town in the year 2050. A change in the participants' abilities to create new ideas was experienced by all. While immersed, participants reported that they were "confronted with awe and wonder" and that they "felt their minds had been stretched" and "determined that their points of view had been altered". The results of this research provide a set of original contributions to knowledge, including a novel experiential design process that others may use to tackle wicked problems, along with a research tool in the form of the VR Time Portals. This research is intended to contribute to knowledge in the fields of Creative Thinking and Theory, as well as to Futures Studies, and Inclusive and Sustainable Design.
      164
  • Publication
    Optical Eye Modelling for Myopia Control
    (University College Dublin. School of Mechanical and Materials Engineering, 2022)
    Myopia is posing a big threat to the global eye health and putting the young generation in danger of blindness. To prevent the development of high myopia, optical lenses have been developed based on the findings that the peripheral optical properties of the eye can affect myopia progression. As the core for many applications in myopia control, a realistic eye model should be established that reproduces the optical and structural features of the human eye. Based on the ocular data obtained from the recent measurement technologies, this thesis investigates the peripheral optical features of the ocular components and develops new models to achieve a more realistic description of the human eye for the wide visual field. As the most complex component in the eye model, a new crystalline lens model is proposed in Chapter 2 to represent the structural and functional features of the lens of children. The model has the capability of involving most parameters measurable on the in vivo human lens, while maintaining realistic values of optical power and spherical aberration. Starting from the lens model proposed in Chapter 2, Chapter 3 develops a method for evaluating the peripheral refracting properties of the lens. The impacts of the lens structural parameters to the peripheral lens power are systematically evaluated. Specifically, the contribution of the gradient refractive index structure to the peripheral lens power has been revealed. In Chapter 4, a fast computation method based on generalized ray tracing is developed to analyze the peripheral optical power of the cornea defined in a similarly way as proposed in Chapter 3. The method is tested on the realistic corneal model constructed from measurement data. The contribution of the cornea to the ocular refractions over the entire visual field can be formulated based on the proposed procedure. Chapter 5 and 6 investigates the role of the retinal contour to the peripheral optical properties of the eye. Specifically, a highly efficient method is proposed that can reproduce the peripheral spherical equivalent refraction over the entire visual field by retinal contour modeling. Overall, this work contributes a theoretical framework and knowledge base on the peripheral optics of the human eye, which are instrumental for developing potential approaches aimed for higher efficacy in myopia control.
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