<p dir="ltr">Repeated loading and unloading cycles lead to the formation of strain in the material which causes initiation of the crack formation this phenomenon is called fatigue. Fatigue properties are critical for structures subject to cyclic load; hence fatigue analysis is used to predict the life of the material. Fatigue analysis plays an important role in optimizing the design of the 3D printed material and predicting the fatigue life of the 3D printed component.</p><p><br></p><p dir="ltr">The main objective of this thesis is to predict the fatigue behavior of different microstructures of Ti-64 titanium alloy by using the PRISMS-Fatigue open-source framework. To achieve this goal Ti-64 microstructure models were created using programming scripts, then the structures were exported to a finite element visualization software package, with all the required properties embedded in the pipeline. The PRISMS-Fatigue framework is used to conduct a fatigue analysis on 3D printed materials, using the Fatigue Indicator Parameters (FIP), which measure the driving force of fatigue crack formation in the microstructurally small crack growth.</p><p><br></p><p dir="ltr">Three different microstructures, i.e., cubic equiaxed, random equiaxed, and rolled equiaxed microstructures, are analyzed. The FIP results show that the cubic equiaxed grains have the best fatigue resistance due to their isotropic structural characteristics. Additionally, the grain size effect using 1 and 10 micrometers is investigated. The results show that the 1 micrometer grain size cubic equiaxed microstructure has a better fatigue resistance because as grains are small and they have a higher mechanical strength.</p>

This research project primarily focuses on three major aspects: synthesis and inclusion of silver microparticles and nanowires within a polymer matrix, extrusion of composite filaments and, three-dimensional (3D) printing of multifunctional polymer composites. Since very few studies have explored the inclusion of silver nanoparticles in 3D printing materials, the findings from this study can be significant for additive manufacturing technology. Over the past few decades, the applications of additive manufacturing has been expanding considerably in several industries like automobile, biomechanics, aerospace, hardware engineering, to name a few. We are particularly interested in silver particles and nanowires because of their enhanced antimicrobial, mechanical and optical properties. The unique antimicrobial properties of the silver-polymer composite will especially be applicable in the food and meat industry, where microbial infection is a major concern because of the exposure of microbes in the polymer belts that are used to transfer and package the items in the factory. It costs the industries a considerable amount of time, money and labor to regularly clean and sanitize those belts. If we are able to develop polymer belts with embedded antimicrobial properties, it could have tremendous applications in the food and meat industries. The morphology of the particles will be studied using scientific techniques like Transmission electron microscopy (TEM) and Scanning Electron Microscopy (SEM). The idea is then to nanoparticles will be incorporated into PLA polymer pellets and extruded into composite filaments that can be used for 3D printing of dog-bone test structures. After the fabrication process, tensile tests and fracture surface analysis will be conducted to study the extent of enhancement of the mechanical properties as compared to neat polymer 3D printed specimens. The critical challenge in this project would be to ensure homogenous distribution of the nanoparticles throughout the polymer filaments. This project will integrate concepts and applications from three different fields: nanotechnology, material science, and additive manufacturing.

Mini-/microchannel components have received attention over the past few decades owing to their compactness and superior thermal performance. Microchannel heat sinks are typically manufactured through traditional manufacturing practices (milling and sawing, electrodischarge machining, and water jet cutting) by changing their components to work in microscale environments or microfabrication techniques (etching and lost wax molding), which have emerged from the semiconductor industry. An extrusion process is used to produce multiport minichannel-based heat exchangers (HXs). However, geometric manufacturing limitations can be considered as drawbacks for all of these techniques. For example, a complex out-of-plane geometry is extremely difficult to fabricate, if not impossible. Such imposed design constraints can be eliminated using additive manufacturing (AM), generally known as three-dimensional (3D) printing. AM is a new and growing technique that has received attention in recent years. The inherent design freedom that it provides to the designer can result in sophisticated geometries that are impossible to produce by traditional technologies and all for the redesign and optimization of existing models. The work presented in this thesis aims to investigate the thermal performance of enhanced minichannel HXs manufactured via metal 3D printing both numerically and experimentally. Rectangular winglet vortex generators (VGs) have been chosen as the thermal enhancement method embedded inside the flat tube. COMSOL Multiphysics, a commercial software package using a finite element method (FEM), has been used as a numerical tool. The influence of the geometric VG parameters on the heat transfer and flow friction characteristics was studied by solving a 3D conjugate heat transfer and laminar flow. The ranges of studied parameters utilized in simulation section were obtained from our previous interaction with various AM technologies including direct metal laser sintering (DMLS) and electron-beam melting (EBM). For the simulation setup, distilled water was chosen as the working fluid with temperaturedependent thermal properties. The minichannel HX was assumed to be made of AlSi10Mg with a hydraulic diameter of 2.86 mm. The minichannel was heated by a constant heat flux of 5 Wcm−2 , and the Reynolds number was varied from 230 to 950. A sensitivity analysis showed that the angle of attack, VG height, VG length, and longitudinal pitch have notable effects on the heat transfer and flow friction characteristics. In contrast, the VG thickness and the distance from the sidewalls do not have a significant influence on the HX performance over the studied range. On the basis of the simulation results, four different prototypes including a smooth channel as a reference were manufactured with AlSi10Mg via DMLS technology owing to the better surface roughness and greater design uniformity. A test rig was developed to test the prototypes. Owing to the experimental facility and working fluid (distilled water), the experiment was categorized as either a simultaneously developing flow or a hydrodynamically developed but thermally developing flow. The Reynolds number ranged from 175 to 1370, and the HX was tested with two different heat fluxes of 1.5 kWm−2 and 3 kWm−2 . The experimental results for the smooth channel were compared to widely accepted correlations in the literature. It was found that 79% of the experimental data were within a range of ±10% of the values from existing correlations developed for the thermal entry length. However, a formula developed for the simultaneously developing flow overpredicted the Nusselt number. Furthermore, the results for the enhanced channels showed that embedding VGs can considerably boost the thermal performance up to three times within the parameters of the printed parts. Finally, the thermal performance of the 3D-printed channel showed that AM is a promising solution for the development of minichannel HXs. The generation of 3D vortices caused by the presence of VGs ii can notably boost the thermal performance, thereby reducing the HX size for a given heat duty.

No description available.

<p dir="ltr">The production of aluminum components by laser powder bed fusion additive manufacturing (LPBF-AM) offers simultaneous weight reduction benefits through low material density and topology optimization. The primary limitation of the method – hot cracking in high-strength compositions – is addressed by the reactive additive manufacturing (RAM) process, which introduces ceramic-forming metallic particles to powder feedstock. <i>In situ</i> reactions subsequently inoculate equiaxed grains, prevent cracking, and strengthen the resulting alloy. The adoption of RAM alloys in aerospace applications requires the elimination of heterogeneous defects, requiring an understanding of laser processing effects and feedstock quality. To meet these needs, the collected work presents characterization methods based on x-ray tomography, seeking to establish novel descriptors for RAM feedstock and microstructures.</p><p dir="ltr">In the first two chapters, x-ray microscopy (XRM) is applied to produce multi-dimensional particle measurements for feedstock powder qualification. Evolving existing measure-and-classify processes, a method is described to characterize AA7050-RAM2 feedstock that is rapid, interpretable, and descriptive of the highly deformed particles observed. Applying the developed methodology to an analysis of recycled AA7050-RAM2 rationalizes decreasing particle sizes by identifying the selective removal of specific shape classes. Combined with quantitative electron microscopy of particle microstructures, sieving and heat effects are comprehensively reported, demonstrating a modernized powder analysis workflow.</p><p dir="ltr">In the second two chapters, the characteristic reactions seen in LPBF of AA7050-RAM2 are characterized. Correlative SEM/EDS and nanoindentation identified reactive phases and their mechanical properties and found a correlation between the extent of the Al-Ti reaction and the degree of particle remelting. Using 3D XRM measurements, the populations and distributions of low- and high-reaction particles were quantified, raising questions regarding homogenization mechanisms in laser-processed, particle-reinforced alloys. Thus, thin wall samples were produced and characterized to visualize convective and thermal history effects within symmetrical tracks. Novel observed mechanisms include thermal grain coarsening, keyhole-induced convection, and pore segregation by size. The accumulated microstructural quantification and novel perspective on pore movement provide a basis to improve contouring processes in RAM alloys and to better align fluid dynamics models of printing with experimental data.</p>

<p></p><p>Additive Manufacturing (AM) allows for the creation of elements with novel forms and functions. Utilizing AM in development of components of civil infrastructure allows for achieving more advanced, innovative, and unique performance characteristics. The research presented in this dissertation is focused on development of a better understanding of the fabrication challenges and opportunities in AM of cement-based materials. Specifically, challenges related to printability and opportunities offered by 3D-printing technology, including ability to fabricate intricate structures and generate unique and enhanced mechanical responses have been explored. Three aspects related to 3D-printing of cement-based materials were investigated. These aspects include: fresh stability of 3D-printed elements in relation to materials rheological properties, microstructural characteristics of the interfaces induced during the 3D-printing process, and the mechanical response of 3D-printed elements with bio-inspired design of the materials’ architecture. This research aims to contribute to development of new pathways to obtain stability in freshly 3D-printed elements by determining the rheological properties of material that control the ability to fabricate elements in a layer-by-layer manner, followed by the understanding of the microstructural features of the 3D-printed hardened cement paste elements including the interfaces and the pore network. This research also introduces a new approach to enhance the mechanical response of the 3D-printed elements by controlling the spatial arrangement of individual filaments (i.e., materials’ architecture) and by harnessing the weak interfaces that are induced by the 3D-printing process. </p><br><p></p>

<p dir="ltr">Electronics have contributed to the advancement of healthcare, wellness, security, and mobility, resulting in a higher standard of living. However, these ever-accelerating advancements and widespread application come at the cost of a shortened product life cycle and increase in produced E-waste which poses a significant environmental challenge. Recycling E-waste is challenging due to the complexity of electronics and packaging, hindering component retrieval for reuse. While sustainable materials for electronics have been researched, sustainable integrated circuit (IC) packaging for conventional electronics remains unexplored. This study introduces a method involving dissolvable additively manufactured packaging materials to recover commercial-off-the-shelf (COTS) chips from used electronics, which would alleviate supply-chain stress, reduce the need for manufacturing similar chips, and minimize environmental impact. In this work, Polyvinyl alcohol (PVA) and Acrylonitrile butadiene styrene (ABS), are explored as potential dissolvable semiconductor packaging materials. Optimal dissolving conditions allow chip recovery in less than 11 minutes for PVA and 2 minutes for ABS. This approach offers a sustainable packaging method for commercial electronic chips that matches conventional packaging performance with the added functionality of recoverable and recyclable components, contributing to the gap in sustainability and recycling for conventional electronics.</p>

Selective laser melting (SLM) has been shown to be an attractive manufacturing route for the production of ??/?? titanium alloys, and in particular Ti-6Al-4V. A thorough understanding of the relationship between the process, microstructure and mechanical properties of the components produced by this technology is however crucial for the establishment of SLM as an alternative manufacturing route. The purpose of the present study is thus to determine the microstructure evolution, crystallographic texture and the mechanical properties of SLM Ti-6Al-4V. The effect of several processing parameters on the density and the microstructure of the SLM samples were initially investigated. It was found that different sets of process parameters can be used to fabricate near fully dense components. It was found that the samples built using the optimised process window consist exclusively of ????? martensitic phase precipitated from prior ?? columnar grains. It was observed that the ?? grain solidification is influenced by the laser scan strategy and that the ?? phase has a strong <001> texture along its grain growth direction. The ????? martensitic laths that originate from the parent ?? grains precipitate according to the Burgers orientation relationship. It was found that ????? laths clusters from the same ?? grain have a specific misorientation that minimise the local shape strain. Texture inheritance across successive deposited layers was also observed and discussed in relation to various variant selection mechanisms. The mechanical properties of as-built and stress relieved SLM Ti-6Al-4V built using the same optimised process parameters were then investigated. It was found that the build orientation affects the tensile properties, and in particular the ductility of the samples. Samples built perpendicularly to the building direction showed higher ductility than those built in the vertical orientation. It was also observed that a stress relief heat treatment was beneficial to the mechanical properties of SLM Ti-6Al-4V. The ductility of the stress relieved samples was indeed higher than those found in the as-built condition. It was found that the predominant fracture mode during tensile testing is inter-granular. In terms of high-cycle fatigue, it was found that SLM Ti-6Al-4V is comparable to HIPed cast Ti-6Al-4V but it has a significantly lower fatigue resistance than that of wrought and annealed alloys. It was observed that porosity and the elongated prior ?? grain boundaries decrease substantially the fatigue life of the components. Cracks propagate either by fatigue striation or ductile tearing mechanisms. Using alternative laser scan strategies it was possible to control the microstructure of the as-built samples. It was observed that the laser scan vector length influences several microstructural features, such as the width of the prior ?? grains and the thickness of the ????? laths. It was found that re-melting the same layer has instead little effect on the microstructure. A novel laser scan strategy characterised by much lower laser power and scan speed than those typically used in SLM enabled finally to fabricate SLM Ti-6Al-4V with a microstructure close to that of conventionally manufactured Ti-6Al-4V. This study investigates for the first time the crystallographic texture evolution in Ti-6Al-4V manufactured by SLM. Further, this research presents for the first time the effect of the characteristic microstructure and crystallographic texture on the mechanical properties and fracture of SLM Ti-6Al-4V. Lastly, for the first time this research shows examples of microstructural control during the SLM fabrication of the same alloy using long laser dwell times.

Nel contesto della nuova rivoluzione industriale, alti livelli di turbolenza, dinamismo, volatilità, globalizzazione, competizione e un diverso ruolo del consumatore riconfigurano il panorama delle supply chain e delle innovazioni. Nonostante il valore co-creato e le ultime innovazioni in ottica customer driven siano ormai elementi imprescindibili, poche ricerche si sono focalizzate sulle caratteristiche di una supply chain guidata dal consumatore e sull’impatto o implementazione della stampa 3D. Pertanto, questa tesi mira ad esplorare gli aspetti principali della customer driven supply chain e della direct digital manufacturing technology. Il Paper I presenta una revisione sistematica della letteratura e fornisce un quadro concettuale utile per organizzare i contributi più recenti sull'argomento, implementando la teoria e suggerendo linee guida per i manager. Il Paper II e Paper III propongono ricerche qualitative mediante singoli casi studio che rispettivamente analizzano come la stampa 3D è in grado di facilitare la supply chain customer centricity attraverso la co-creazione di valore nel settore aerospaziale e come un technology provider può implementare un’innovazione customer centric nel settore della gioielleria italiana. Gli studi suggeriscono modelli concettuali e proposizioni che incrementano la letteratura esistente e guidano i manager. Questa tesi contribuisce all'esplorazione dei recenti progressi in merito all’'orientamento della supply chain e della direct digital manufacturing technology fornendo analisi critiche approfondite relative a diverse metodologie. / In the new industrial revolution, high levels of turbulence, dynamism, volatility, globalization, competition and modified customer’s role reconfigure supply chains and innovations landscape. Even if value co-creation and last technologies towards customer driven orientation are unavoidable elements, few contributions have focused on customer driven supply chain characteristics and on 3D printing impact on supply chain or elements of its implementation. For this reason, the thesis aims to explore the main features of customer driven supply chains and direct digital manufacturing technology. Paper I presents a systematic literature review that shows a conceptual framework able to organize the most recent contributions on the topic, implementing the knowledge on the theme and suggesting guidelines to managers. Paper II and Paper III provide qualitative constructive single case study research respectively focused on how 3D printing can enable supply chain customer centricity by value co-creation in the aerospace sector and how 3D printing can be implemented by a technology provider in the Italian jewellery sector. The studies suggest conceptual framework and propositions for improving existing knowledge and addressing managers. This thesis contributes to the exploration of recent advancements in supply chain orientation and direct digital manufacturing technology by providing deep critical analysis related to diverse methodologies.

The diploma thesis is focused on 3D printing of composites parts. Thesis deals with methods of additive manufacturing and describes principle of selected 3D printing technologies. In addition to additive technologies, the theoretical part presents an overview of composite materials and methods of composite production. Then there are four concepts that lead to 3D printing of continuous fiber reinforced composites components. The final concept is selected according to multi-criteria analysis and then designed. Designed extruder allows 3D printing of composite materials. The principle of the function consists of fiber impregnation by matrix inside the heat chamber and then deposition of composite on printing platform. The extruder also consist of fiber cutting mechanism. The extruder's ability is verified by the experiment.