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Articles 1 - 8 of 8
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Phase-Field Modeling Of Selective Laser Melting And Freezing Dynamics In Thermal Manufacturing Processes, Jiqin Li
Doctoral Dissertations
Laser-based additive manufacturing (AM) has been rapidly growing in applied and scientific research areas due to its advantages for manufacturing geometrically complicated parts and functional materials. However, the surface quality and geometric accuracy are great concerns of AM-produced parts because of the formation of surface defects such as voids, notches, or even cracks caused by incomplete melting of powders, lapping, or gas entrapment during melting and solidification processes. From theoretical view points, temperature prediction and multi-phase dynamics at the powder level are of the greatest challenges, yet necessary for better understanding of relevant laser-material interactions as well as for the …
Improving The Isotropy Of Additively Manufactured Parts By Fused Deposition Modeling: From Polymeric Self-Assembly To Reactive Processing, Neiko Levenhagen
Improving The Isotropy Of Additively Manufactured Parts By Fused Deposition Modeling: From Polymeric Self-Assembly To Reactive Processing, Neiko Levenhagen
Doctoral Dissertations
This dissertation focuses on understanding how the interfacial segregation of low molecular weight polymeric species in a polymer blend impacts the interlayer adhesion and mechanical isotropy of objects prepared by fused deposition modeling (FDM), a widely used additive manufacturing technique. The molecular weight, architecture, and chemical identity of the low molecular weight polymer in the blend dramatically impacts the formation of a robust interlayer interface. Additional modification of the low molecular weight component presents opportunities for reactive processing. The impact of covalent bonds between interfacial layers on the interlayer adhesion and overall isotropy of an FDM printed object is examined.
Increasing The Functionality Of Additive Manufacturing Through Atmospheric Microplasma And Nanotechnology, Alexander Jon Ulrich
Increasing The Functionality Of Additive Manufacturing Through Atmospheric Microplasma And Nanotechnology, Alexander Jon Ulrich
Doctoral Dissertations
Additive Manufacturing (AM) has been changing the manufacturing landscape for the last 20 years. As the interest and demand for both polymer and metal-based 3D printing has grown, the materials and machines used have increased in capabilities. Despite the growth and advancement, there are still a large number of improvements that can be made to add functionality to 3D printers. Metal AM, a subcategory of 3D printing, has garnered much attention among industrial applications with large companies such as General Electric trying to implement the technology to increase innovative designs for motors. Some of the limitations on AM have to …
Mechanical Performance Of Structural Systems With Missing Members: From Buildings To Architected Materials, Panagiotis Pantidis
Mechanical Performance Of Structural Systems With Missing Members: From Buildings To Architected Materials, Panagiotis Pantidis
Doctoral Dissertations
Structural systems are potentially subjected to damage initiating scenarios throughout the course of their service time. Depending on the nature and extent of the damaging event, they may experience significant reduction or even complete loss of their mechanical performance. This dissertation delves into the mechanics of structural systems under the notion of missing members from their domain, investigating types of structural systems: a) multi-story steel framed buildings, and b) materials with a truss-lattice microstructure. Part I of the dissertation investigates the performance of multi-story steel framed buildings under a column removal scenario, developing an analytical framework for their quasi-static robustness …
Investigation Of Powder Recyclability And Liquid-Solid-Gas Interactions During Powder Bed Selective Laser Melting Of Stainless Steel 316l, Daniel Walter Galicki
Investigation Of Powder Recyclability And Liquid-Solid-Gas Interactions During Powder Bed Selective Laser Melting Of Stainless Steel 316l, Daniel Walter Galicki
Doctoral Dissertations
This dissertation pertains to the fundamental understanding of powder degradation and the dissolution of gas, specifically interstitials such as oxygen, into metal alloy powders and parts during selective laser melting (SLM) additive manufacturing (AM) and their impact on defect generation, microstructure, and mechanical properties of parts built using this process. A powder recyclability experiment was conducted to investigate the effect that powder re-use has on bulk powder and build properties. Mechanical testing and analysis of parts produced during the experiment showed higher than normal yield strengths and provided evidence of powder re-use affecting the ductility of SLM parts. A heat …
Freeform Extrusion Fabrication Of Advanced Ceramics And Ceramic-Based Composites, Wenbin Li
Freeform Extrusion Fabrication Of Advanced Ceramics And Ceramic-Based Composites, Wenbin Li
Doctoral Dissertations
"Ceramic On-Demand Extrusion (CODE) is a recently developed freeform extrusion fabrication process for producing dense ceramic components from single and multiple constituents. In this process, aqueous paste of ceramic particles with a very low binder content ( < 1 vol%) is extruded through a moving nozzle to print each layer sequentially. Once one layer is printed, it is surrounded by oil to prevent undesirable water evaporation from the perimeters of the part. The oil level is regulated just below the topmost layer of the part being fabricated. Infrared radiation is then applied to uniformly and partially dry the top layer so that the yield stress of the paste increases to avoid part deformation. By repeating the above steps, the part is printed in a layer-wise fashion, followed by post-processing. Paste extrusion precision of different extrusion mechanisms was compared and analyzed, with an auger extruder determined to be the most suitable paste extruder for the CODE system. A novel fabrication system was developed based on a motion gantry, auger extruders, and peripheral devices. Sample specimens were then produced from 3 mol% yttria stabilized zirconia using this fabrication system, and their properties, including density, flexural strength, Young's modulus, Weibull modulus, fracture toughness, and hardness were measured. The results indicated that superior mechanical properties were achieved by the CODE process among all the additive manufacturing processes. Further development was made on the CODE process to fabricate ceramic components that have external/internal features such as overhangs by using fugitive support material. Finally, ceramic composites with functionally graded materials (FGMs) were fabricated by the CODE process using a dynamic mixing device"--Abstract, page iv.
Remanufacturing Of Precision Metal Components Using Additive Manufacturing Technology, Xinchang Zhang
Remanufacturing Of Precision Metal Components Using Additive Manufacturing Technology, Xinchang Zhang
Doctoral Dissertations
"Critical metallic components such as jet engine turbine blades and casting die/mold may be damaged after servicing for a period at harsh working environments such as elevated temperature and pressure, impact with foreign objects, wear, corrosion, and fatigue. Additive manufacturing has a promising application for the refurbishment of such high-costly parts by depositing materials at the damaged zone to restore the nominal geometry. However, several issues such as pre-processing of worn parts to assure the repairability, reconstructing the repair volume to generate a repair tool path for material deposition, and inspection of repaired parts are challenging. The current research aims …
Design, Fabrication, And Characterization Of Functionally Graded Materials, Sreekar Karnati
Design, Fabrication, And Characterization Of Functionally Graded Materials, Sreekar Karnati
Doctoral Dissertations
“The aim of this research was to investigate the feasibility of fabricating custom designed, graded materials using Laser Metal Deposition (LMD) that will cater for functionality and unconventional repair. The ultimate goal of the project is to establish the versatility of LMD for fabricating advanced materials and tackling problems that have been conventionally difficult or in cases infeasible. In order to accomplish these goals, this research involved investigations into, the feasibility of using elemental powders as modular feedstocks, the feasibility of fabricating tailored gradients with these custom compositions, and finally leveraging the advantages of grading materials using LMD to successfully …