Doctoral Theses

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https://hdl.handle.net/10292/4
The Doctoral Theses collection contains digital copies of AUT doctoral theses deposited with the Library since 2004 and made available open access. All theses for doctorates awarded from 2007 onwards are required to be deposited in Tuwhera Open Theses unless subject to an embargo.

For theses submitted prior to 2007, open access was not mandatory, so only those theses for which the author has given consent are available in Tuwhera Open Theses. Where consent for open access has not been provided, the thesis is usually recorded in the AUT Library catalogue where the full text, if available, may be accessed with an AUT password. Other people should request an Interlibrary Loan through their library.

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Browsing Doctoral Theses by Subject "3D printing"

Now showing 1 - 6 of 6
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    Development of a 3D Printed Intranasal Stent for Improving Post-Operative Recovery
    (Auckland University of Technology, 2020) Dkhar, Larry Kynti
    Chronic rhinosinusitis (CRS) is a clinical condition associated with inflammation of the nasal mucosa and paranasal sinuses, which persists for more than 12 weeks. Primary symptoms for chronic sinus inflammation include nasal obstruction, thick nasal discharge, reduction or loss of olfaction and facial pressure or pain, which are confirmed by endoscopic examination and/ or sinus computed tomography (CT) scans. Treatments available for CRS include the prescription of antibiotics, topical nasal steroids and/or oral steroids, antihistamines, nasal decongestant and saline irrigants. But some patients do not respond to medical treatment alone; in such cases, functional endoscopic sinus surgery (FESS) is an alternative treatment that is widely considered. Current commercially available non-dissolvable and dissolvable nasal packings and dressings are frequently used after surgery, but they fail to provide consistent wound healing and breathability when they are packed into the nasal cavity. There is an increasing interest in the development of drug-eluting stents that can provide structural support while reducing post-operative tissue adhesions. The purpose of this thesis is to develop a 3D printed intranasal stent that facilitates post-operative recovery.
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    Effects of Increasing Laser Power on Microstructure Formed During Selective Laser Melting of Co-29Cr-6Mo Alloy
    (Auckland University of Technology, 2018) Darvish, Kourosh
    For a wider medical/dental and aerospace applications of 3D printed parts made using selective laser melting (SLM) Co-29Cr-6Mo alloy, how SLM parameters affect the quality and properties of parts need to be understood. In this PhD research, how laser power (P) affects the geometry of tracks was studied first. This track geometry relates well to a major defect, lack of fusion (LOF), which affects part quality. Through examining extensively the track profiles, the effect of P on the amount of LOF has been found and has been geometrically explained. Furthermore, we have identified an abnormal type of LOF caused by spatters and how melt penetration may reduce this type of LOF has also been shown. The second and major part of this thesis was to study how the tiny melt rapidly solidifies during SLM, as it is well known that solidification microstructure directly relates to properties of the parts. Cellular solidification without a planar layer has been observed and explained based on constitutional supercooling. Growth direction selection during epitaxial growth has been identified and explained considering local heat flux direction. Finally, cell size measurement and growth rate estimation have enabled the calculation of thermal quantities during SLM solidification.
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    Entrepreneurship With Additive Manufacturing: Implications of Complexity Freedom in Product and Firm Ideation
    (Auckland University of Technology, 2020) Esparza Flores, Jose Antonio
    The diffusion of 3D printing technologies after the expiration of key patents in 2009 brought novel manufacturing applications beyond prototyping (Thompson et al., 2016). Particularly, Additive Manufacturing (AM) has enabled more integrated strategies for new product development and fabrication. As a result, AM has been considered as a promising instrument for new business creation (Rayna & Striukova, 2016). Studies concerning AM and entrepreneurial activity rarely consider the interactions with technology. Yet, theories that describe the relationship between product architecture and manufacturing organizations suggest that greater flexibility in product architecture would bring greater flexibility to the creation of the firm through a process of mirroring (Colfer & Baldwin, 2016). Additionally, the theory of effectual entrepreneurship describes the creation of markets as negotiations between entrepreneurs and possible partners with the product and the means of the entrepreneur at the centre of such negotiations (Sarasvathy & Dew, 2005; Zahra et al., 2006). The research presented in this thesis examines the idea that flexible product architecture in 3D printing gives entrepreneurs greater flexibility in product design and an increased flexibility in the acquisition of partners. Two studies were carried out under a grounded methodology to explore the effects of complexity in the ideation of business opportunities. Both studies are based on design exercises that study the impact of idea generation using imaginary images, sketches, and prototypes in design (Finke, 1996; Kudrowitz & Wallace, 2013). The first study included seven teams of participants who used a building set with the same budget conditions and objectives. The control group received traditional production costing, while the AM one received free complexity costing. Idea complexity was measured in the number of blocks used to build each component, and the number of connections in each joint. The second study consists of an ideation exercise where 308 participants interpreted abstract randomized images of objects of varying complexity to imagine possible future product and firm participants. Their responses were analysed to extract networks of product categories and stakeholder identities. Answers were evaluated in terms of novelty, literality, and network composition. The results of both studies challenge some of the arguments that explain the benefits of additive manufacturing as increased freedom in product design. Instead, the results suggest that complexity freedom is filtered through the manipulation of morphology in design exploration. This argument advocates for an embodied design exploration where the perceptual features of technology influence ideation. This thesis contributes to the understanding of the relationships between additive manufacturing, entrepreneurship, and design. The studies presented here highlight the need to reconsider claims made in recent years about the advantages of increased flexibility for entrepreneurship with the introduction of additive manufacturing. In addition, the focus on technological interfaces expands the domain of entrepreneurship and firm design including perception, which is not accounted for in strategy and business modelling.
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    Evaluation of Alternative Material Composites for Additive Manufacturing
    (Auckland University of Technology, 2020) Behera, Malaya Prasad
    From mere prototyping solutions to the full-fledged additive manufacturing systems, the technology platform, commonly known as 3D printing has grown in leaps and bounds. Despite the astounding features, the enormous growth, and the wider application potentials, the additive manufacturing methods suffer from certain shortcomings. The point-by-point or line-by-line material consolidation mechanics is complex and often lead to dynamic thermal fields, uncontrolled meso- and micro-structures, and unwanted residual stresses and strains. Flat-layer slicing often leads to stair-step effects and fibre-discontinuity issues in specific cases. Complications also arise from the need to use support structures, depending on the part geometry and build orientation options. While most of these problems have been investigated and amicable solutions developed to varying degrees of success, a major drawback still remains at large: Limited material options available for processing. A significant amount of research effort was placed evaluating alternative materials for different additive manufacturing technologies. Different polymer, ceramic, and metallic material systems have come into commercial use through the efforts in the past decade. Considering the point-by-point material processing approach, composite materials in particular attain more attention with the additive technologies as the possibility to control the dispersion of the filler materials is an inherent characteristic. Based on the literature review and the collaborations with the materials research groups, Crown Research Institutions, and industry partners in New Zealand, four different composite material systems were identified for evaluation with four specific additive manufacturing processes in this research: 1) PLA-elastomer-nano-cellulose fibre polymer composite for extrusion 3D printing in the pellet form, 2) Seashell powder-plaster ceramic composite for binder-jet 3D printing, 3) Polymer-keratin composites for selective laser sintering, and 4) stainless steel 316L and nano silicon nitride metal matrix composites for selective laser melting. Empirical experimental research methods have been used to evaluate the materials for the respective processing methods, exploring the material, process, structure, and property relationships. The meso- and micro-structural relationships, physical, and mechanical property responses indicate all the four material and process combinations to be successful. While these are preliminary impressions from the initial experimental investigations, these material alternatives for additive manufacturing offer great application potentials if further scientific investigations targeting material and process optimisation are undertaken.
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    Evaluation of the Application of Additive Manufacturing in the Aircraft Industry
    (Auckland University of Technology, 2021) Lv, Yifan
    With stringent regulatory constraints, certification standards, and complex multi-tier suppliers involving several players, the aviation industry often faces with the most complex supply chain scenarios. Further, considering the overall costs, keeping the downtimes lower is paramount which necessitates the maintenance and operations components ending up in huge inventories and locking up large amounts of funds. Non-agile, time-taking, and limited-capability traditional manufacturing methods are central to most of these problems. The additive manufacturing methods that evolved from the erstwhile rapid prototyping technologies are capable of offering some solutions. The ability to convert the digital data directly into near-net finished forms without any complex intermediate tooling and tasks allows for true just-in-time manufacturing solutions, which can directly resolve the supply chain and inventory issues. The point-by-point material consolidation mechanics will allow for achieving shape complexities that are by far impossible and allow for a plethora of opportunities for optimisation of shapes. Where does the technology currently stands then with reference to the aviation industry and what are the bottlenecks if any and how can they be overcome are the questions that will arise, and this research is designed to provide the answers. Based on literature reviews and discussions with organisations such as Air New Zealand Engineering, it was understood that there is widespread interest in exploring the application of AM in the aviation industry, but the information is either scattered or hidden from common access. The opportunities to drastically improve the product designs that are severely constrained by the limitations of the traditional manufacturing methods are yet to be exploited fully. It was also understood that the materials options are limited, and the consolidation mechanics is unclear in many cases. At the end, the lack of standards and the certification procedures were identified to be the main stumbling blocks for the wider uptake of the technologies, where they are really useful. Addressing these issues, the current research was developed with four research aims: 1) A comprehensive review of resources, classification and compilation of the application potentials of AM in the aviation industry, 2) evaluation of the topology optimisation schemes and implementation in selected aircraft components, 3) Evaluation of alternative materials for specific additive technologies, and 4) Evaluation of the current standards, identification of the gaps, ascertaining the future course of action and developing the certification pathways for overcoming the hurdles of implementing the technological solutions on the aircraft systems. A systematic scientific search method was used to explore several databases and extract all the information on the current state of application of AM in the aviation industry and data gathered is suitably classified and compiled into a useful format. Topology optimisation tasks were undertaken based on finite element simulations of the stress field of two selected components. The results indicated significant weight savings and consequent reductions in fuel consumption. Two new materials were investigated based on semiempirical experimental evaluations and proved to be suitable for processing by selective laser sintering, targeting future applications in the aircraft interior products. Around 200 standards relevant to AM and the aviation industry are reviewed and compiled according to the order of the critical stages of product development. The pathways for certification of the new product concepts were shown by integrating the product development tasks and the stipulations from the relevant standards together. The outcomes are expected to provide some initial guidelines for the standards to be used and the documentation to be developed in order to qualify any new product design through the stringent certification processes of the aviation authorities.
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    Mechanical Characterisation, Analysis and Modelling of Particulate Nanocomposites Printed Using Photopolymer Extrusion Technique
    (Auckland University of Technology, 2019) Asif, Muhammad
    A new photopolymer extrusion 3D printing technique is proposed in this research. This hybrid 3D printer combines the strengths of two well established and commercial 3D printers i.e. fused deposition modelling (FDM) and UV assisted 3D printing (UV3DP). One of the distinct features of this novel technique is its two additional rotational axes, which are installed to print free-form and self-supported structures. A detailed and comprehensive study is carried out in this research on the mechanical characterisation, analysis and modelling of particulate nanocomposites printed using photopolymer extrusion technique. Photopolymer resin is used as the base material in this technique. Generally, polymers are found to have low strength and stiffness. Nano sized fibres or particles are generally embedded in the polymer matrix to enhance their properties. Therefore, in order to improve the mechanical behaviour of the parts manufactured using photopolymer extrusion 3D printing technique, nano silica filler was added to the base material. Different concentrations of the silica filler were added and its effect on material viscosity, dimensional accuracy, strength and ductility have been studied. This part of the research outlined a suitable range of viscosities corresponding to different filler concentrations, provided plausible explanation on dimensional accuracy, reported significant improvement in mechanical properties of nanocomposite with the addition of the silica filler and demonstrated the capability of the proposed technique to print free-form and self-supported structures. Interfacial adhesion, i.e. the bond between matrix and nanoparticles is one of the major contributors to the strong mechanical properties of the particle reinforced polymers. A comparison of the interfacial adhesion was drawn between 3D printed and casted samples. This part of the research outlined with the aid of scanning electron microscopy, why nanocomposites printed using photopolymer extrusion technique have superior mechanical properties than casted samples. Polymers are viscoelastic materials and they exhibit time dependent response. To study the time dependent mechanical response of the photopolymer used in the proposed technique, tensile tests at different strain rates were conducted. Silica filler was added to enhance the mechanical properties of the polymer. Quasi linear viscoelastic (QLV) model combining hyper and viscoelastic phenomena was used to model the rate dependent mechanical behaviour of the polymer and polymer reinforced composite with different concentrations of the filler. This part of the research outlined that the addition of the silica enhanced the mechanical properties of the polymer. It also outlined that higher filler content could lead to weak mechanical properties. Furthermore, it showed that QLV model with Yeoh’s strain energy density function successfully captures the rate dependent stress-strain behaviour of the polymer and nanocomposite. Finite element modelling (FEM) is a powerful tool and is commonly used to predict the behaviour of polymer nanocomposites. A FE model was developed by combining hyper and viscoelastic phenomena to investigate the effect of filler concentration on mechanical behaviour of the 3D printed particulate nanocomposite. The FE model with Yeoh’s strain energy density function showed good agreement with experimental results. Finally, In order to study the mechanical behaviour of filler concentrations outside the reliable printing zone, empirical models were developed. These empirical models can predict the tensile strength of the nanocomposite based on filler concentration and the material viscosity. The findings of this research give an insight into the mechanical characterisation and modelling of the 3D printed particulate nanocomposites using photopolymer extrusion technique.
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