Saudi Cultural Missions Theses & Dissertations
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Item Restricted Physico-Mechanical Properties of Definitive and Interim 3D Printed Resin Restorative Materials with Different Print Orientations(Saudi Digital Library, 2025-06-06) Mudhaffer, Shaymaa; Silikas, Nick; Satterthwaite, JulianStatement of the problem. Advancements in digital dentistry have significantly transformed dental prostheses manufacturing, particularly with the integration of additive manufacturing technologies such as 3D printing. While additive manufacturing offers advantages like design flexibility, material efficiency, and reduced waste compared to subtractive methods (milled), challenges persist in understanding how parameters such as print orientation influence the physico-mechanical properties of 3D printed resin materials. Moreover, the performance of interim and definitive 3D printed materials over short- and long-term usage remains underexplored. Aim. This study aimed to evaluate the impact of print orientation (0°, 45°, and 90°) on the physical and mechanical properties of definitive and interim 3D printed resin materials after short- and long-term hydrolytic ageing. This research also sought to compare the performance of 3D printed materials with subtractively manufactured materials to identify potential advantages and limitations of additive manufacturing in dental applications. Methods. Specimens were printed with varying print orientations (0°, 45°, and 90°) and compared with milled counterparts. The materials were categorized into definitive and interim types to assess their performance across different applications. A series of standardized tests were conducted to evaluate key physico-mechanical properties, including flexural strength (FS), flexural modulus (FM), surface hardness (HM), indentation modulus (EIT), edge strength (ES), water sorption, solubility, and monomer elution. Specimens were immersed in distilled water and artificial saliva at 37°C for 24 hours and extending up to 3 months to simulate clinical conditions. Advanced imaging techniques, including optical and scanning electron microscopy, were used to analyse surface morphology and fracture behaviour. Filler content was also analysed. Results. Specimens printed at a 90° orientation demonstrated the highest flexural FS and FM both initially and after 3 months of ageing. This orientation also achieved the highest ES after 48 hours of immersion in artificial saliva. However, print orientation did not influence HM or EIT after 3 months of ageing. Sorption and solubility were also influenced by print orientation, while monomer elution was not. All materials printed at 90° met the FS, sorption, and solubility requirements stated by ISO 4049.Definitive 3D printed materials consistently outperformed interim 3D printed resins in terms of mechanical properties. Interim 3D printed materials showed significantly higher sorption, solubility, and monomer elution than definitive 3D printed resins. But most materials were within the ISO 4049 limit. The definitive milled material exhibited the highest mechanical properties among all tested materials except for ES where definitive 3D printed materials performed better than the definitive milled material at a 0.5 mm distance from the edge. Interim milled materials displayed mechanical properties comparable to definitive 3D printed resins. However, ES for all interim materials was not reported, as they exhibited severe plastic deformation under loading. The definitive milled resin exhibited higher sorption compared to the 3D printed resins but demonstrated significantly lower monomer elution. The interim milled material displayed sorption values intermediate between those of the definitive and interim 3D printed materials but with lower monomer elution levels as well. A strong positive correlation was observed between filler weight and FS/FM, as well as between filler weight and HM and EIT. Conversely, filler weight correlated negatively with sorption and solubility. No significant correlation was observed between filler weight and monomer elution and between filler weight and edge strength. Significance. This study underscores the critical role of material type, manufacturing method, and print orientation in determining the physico-mechanical properties of dental restorative materials. Definitive 3D printed materials exhibited performance comparable to or better than interim and milled counterparts in certain parameters, demonstrating their potential for clinical applications in fixed dental prostheses. The superior flexural strength and modulus of definitive 3D printed materials at a 90° orientation underscore the importance of optimizing print orientation to maximize material performance. Furthermore, the adherence of all tested materials printed at 90° to the ISO 4049 standards confirms the clinical viability of this technique. The superior strength and hardness of definitive milled resins compared to their 3D printed counterparts, emphasize their continued relevance in applications requiring high durability. However, the comparable performance of interim milled and definitive 3D printed materials in terms of flexural strength and hardness suggests that 3D printing can serve as an effective alternative to milling for interim applications. The correlation between filler weight and key properties, such as flexural strength, hardness, and modulus, offers valuable insights for material formulation and selection. Meanwhile, the negative correlation between filler weight and sorption/solubility indicates that optimizing filler composition can enhance material longevity by reducing water-related degradation. Additionally, findings on sorption, solubility, and monomer elution confirm the biocompatibility of definitive 3D printed materials, supporting their adoption in restorative dentistry. This research emphasizes the growing potential of 3D printing with opportunities for further innovation in dental applications.2 0Item Restricted A techno-economic assessment of centralized vs. distributed aerospace manufacturing systems(Cranfield University, 2024-09) Alshurafa, Majid Makki; Haddad, YousefThis thesis provides a comprehensive techno-economic assessment comparing centralized and distributed aerospace manufacturing systems, with a focus on the use of additive manufacturing (AM) for producing turbine blades in aircraft engines. The study reveals that centralized manufacturing results in a higher cost per part at $463.97, largely due to logistics expenses, but offers greater financial stability with a positive NPV of $5 million. On the other hand, distributed manufacturing achieves a lower cost per part at $334.60 by eliminating logistics costs. Initially, this approach showed a negative NPV; however, after price adjustments, the distributed system could reach a significantly higher NPV of $38 million. Despite these cost benefits, distributed manufacturing carries higher financial risks due to its sensitivity to material cost fluctuations. These findings highlight the trade-offs between the operational stability of centralized systems and the potential cost efficiency of distributed systems when leveraging AM technology27 0Item Restricted Development of Robots and Algorithms for Cooperative Additive Manufacturing(University of Manchester, 2024-04-11) Alhijaily, Abdullah; Bartolo, Paulo; Cangelosi, AngeloAdditive manufacturing (AM) is dominated by single robots which present limitations in fabrication time and efficiency of the system. To address this problem, this research explores the concept of cooperative printing in which multiple printheads fabricate the same part concurrently. However, configurations for cooperative printing in the literature present several limitations such as reduced cooperative printing area and cross prevention in which no two printheads are allowed to cross each other's paths during printing. Thus, a novel configuration is proposed in this research. This configuration was realised on a custom gantry machine. As shown, the proposed configuration allows printing parts that are impossible to print or inefficiently printed by other cooperative printing configurations. Furthermore, several novel algorithms are formulated and implemented in the developed machine. Additionally, efficient algorithms were developed for path planning that allowed to reduce the computation time of slicing for cooperative printing from minutes to milliseconds. Also, the proposed system significantly increased the printing speed surpassing the maximum printing time reduction reported in the literature. Conversely, mobile robots are promising for AM due to their large workspace. However, current plastic AM by mobile robots produce parts with poor quality and rough surface finish. Thus, an accurate mobile robot specialised for mobile AM is developed for this research. The proposed mobile robot's accuracy and precision were assessed and was found to have a 0.37 mm average error surpassing the literature on mobile AM. Finally, it was shown that the developed mobile robot surpasses them both in terms of quality and accuracy. For gantry systems, offline path planning is reliable and efficient due to their high accuracy and predictability. However, it is unreliable for low accuracy and error-prone systems such as mobile robots. To overcome this, an online cooperative printing path planning designed for the developed mobile robot is proposed. Several novel real time algorithms were developed, including a novel online collision avoidance algorithm that guaranteed collision-free motions. This research stands as the first work to develop fully online path planning for cooperative printing.27 0Item Restricted IMPACT DE LA FABRICATION ADDITIVE SUR LA PERFORMANCE DE LA SUPPLY CHAIN(Université de Bordeaux, 2023-11-29) Noorwali, Albraa; Ducq, YvesAdditive Manufacturing (AM), often referred to as 3D printing, is a technology that allows for the direct creation of 3D products from digital models, offering industries new possibilities for design, customization, and rapid prototyping. Its impact spans industries such as aerospace, healthcare, and automotive, promising cost-effective production and innovative solutions. However, the quality of AM-produced products depends on the post-processing operation, and some non-quality issues are often encountered. Despite the extensive literature comparing AM to conventional manufacturing (CM), there is still a need for empirical evidence and comprehensive cost analyses to guide companies in adopting AM, especially by considering the non-quality issues. This thesis addresses this gap by (1) empirically investigating the impacts of AM across all supply chain processes by using collected data from a sample of 51 companies, (2) evaluating, by means of a simulation study and data from an oil and gas company, the practicality and cost-effectiveness of shifting from CM to in-house AM production while considering investment costs and different quality levels, and (3) exploring the advantages of integrating AM within a dual sourcing framework to assess cost implications and resilience benefits. The empirical investigation shows two major benefits of AM, namely: the ability to produce complex parts in low volumes and good design and the prototyping capability. Moreover, the simulation study provides evidence on the limits of AM when there is a low-quality level generated by postprocessing. The thesis enables as well to show the benefits of using AM within a dual sourcing context.22 0Item Restricted An Investigation of The Effect of Rheo-Printing Technology on Big Area Additive Manufacturing(Saudi Digital Library, 2024-11-27) Alzahrani, Faisal J; Coulter, John PA novel processing innovation named Rheo-printing technology was introduced that could impact the field of the Big Area Additive Manufacturing (BAAM). The Rheo-printing technology applies a controlled circumferential and axial shear rate to the polymer melt before depositing the polymer through the printing nozzle. The rheological polymer properties modify due to the applied shear rate, and the ultimate goal is to enhance the product's properties. The application of the circumferential shear rate on the polymer melt is accomplished through a rotational printing nozzle. Adjusting the rotational speed of the printing nozzle controls the shear rate applied to the polymer melt, providing control over the rheology of the polymer melt. This research employs an extrusion-based AM machine that uses polymer pellets as a feedstock to investigate the impact of Rheo-printing technology on BAAM. The effect of Rheo-printing technology was investigated theoretically and numerically to examine the shear rate impact on the material's viscosity. Different shear-thinning polymers were included in the investigation; the viscosity influence of each polymer has been studied through a range of rotational speeds, and statistical analysis has been applied to the obtained results for a comprehensive understanding. The investigation compared the influence of Rheo-printing technology on two different nozzle sizes. For small additive manufacturing or desktop 3D printers, a 0.6 mm nozzle diameter was utilized, while a 2 mm nozzle diameter was employed for BAAM. Overall results showed that the effect of Rheo-printing technology appeared more significant with a bigger nozzle diameter. Also, there is a favorable correlation between nozzle rotation and viscosity for all polymers, regardless of nozzle diameter. Specifically, this correlation manifests as a decrease in viscosity as the nozzle is rotated, with the magnitude of this reduction becoming more pronounced at higher rotational speeds and near in the outermost region of the extruded polymer road. Two different numerical simulations were included to study the impact of the temperature on the printing process. The first numerical simulation was to study the effect of printing speed on the temperature evolution of each layer during the printing process. Results showed that the temperature fluctuation as each layer's heating and cooling during the printing process decreased with increasing the printing speed. The second numerical simulation was to study the platform temperature's impact on each layer's temperature evolution during printing. The effect of increasing the platform temperature was shown clearly on the cooling interval of each layer. Increasing platform temperature reduces the heat losses in the printed layer during the cooling interval. An experimental investigation also employed conventional printing and Rheo-printing technology to investigate the temperature evolution during printing and compare the obtained results. This investigation was performed by printing two samples using conventional and Rheo-printing technology and monitoring the temperature evolution during printing. The anisotropy and porosity of BAAM products were investigated, and the enhancement of Rheo-printing technology on product properties was validated numerically and experimentally. Three groups of different layer-building times were designed, and twenty-four samples were printed using conventional and Rheo-printing technology, investigating the impact of Rheo-printing technology on interlayer adhesion strength. Also, three configurations were designed, and eighteen samples were printed using conventional and Rheo-printing technology, investigating the effect of Rheo-printing technology on void formation. The enhancement of the Rheo-printing technology on mechanical properties of BAAM samples was validated where the anisotropy and porosity percentage were reduced.48 0