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Full-Text Articles in Mechanical Engineering

Freeform Extrusion Fabrication Of Advanced Ceramics And Ceramic-Based Composites, Wenbin Li Jan 2019

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.


High Temperature Polymer Composites Using Out-Of-Autoclave Processing, Sudharshan Anandan Jan 2018

High Temperature Polymer Composites Using Out-Of-Autoclave Processing, Sudharshan Anandan

Doctoral Dissertations

"High performance polymer composites possess high strength-to-weight ratio, corrosion resistance, and have design flexibility. Carbon/epoxy composites are commonly used aerospace materials. Bismaleimide based composites are used as a replacement for epoxy systems at higher service temperatures. Aerospace composites are usually manufactured, under high pressure, in an autoclave which requires high capital investments and operating costs. In contrast, out-of-autoclave manufacturing, specifically vacuum-bag-only prepreg process, is capable of producing low cost and high performance composites. In the current study, out-of-autoclave processing of high temperature carbon/bismaleimide composites was evaluated. The cure and process parameters were optimized. The properties of out-of-autoclave cured ...


Wrinkling Of Functionally Graded Sandwich Structures Subject To Biaxial And In-Plane Shear Loads, Harold Costa Jan 2017

Wrinkling Of Functionally Graded Sandwich Structures Subject To Biaxial And In-Plane Shear Loads, Harold Costa

Masters Theses

"Benefits of a functionally graded core increasing wrinkling stability of sandwich panels have been demonstrated in a recent paper [1] where a several-fold increase in the wrinkling stress was observed, without a significant weight penalty, using a stiffer core adjacent to the facings. In the present paper wrinkling is analyzed in case where the facings are subject to biaxial compression and/or in-plane shear loading and the core is arbitrary graded through-the-thickness. Two issues addressed are the effect of biaxial or in-plane shear loads on wrinkling stability of panels with both graded and ungraded core and the verification that functional ...


Fabrication Of Out-Of-Autoclave Bismaleimide Based Composite Laminates With Embedded Fiber Optic Sensors, Sudharshan Anandan Jan 2014

Fabrication Of Out-Of-Autoclave Bismaleimide Based Composite Laminates With Embedded Fiber Optic Sensors, Sudharshan Anandan

Masters Theses

"Composites are becoming the material of choice in applications where weight savings are critical, like aerospace structures. The common composites used are- Carbon/Epoxy and Carbon/Bismaleimide (BMI). BMI based systems are preferred in applications which involve operating temperatures higher than conventional epoxies. Carbon/BMI laminates are traditionally fabricated in an autoclave, which is associated with high operating costs. In this work, a low cost out of autoclave (OOA) process is evaluated. It is desirable to have BMI OOA prepreg systems cure at reasonably low temperatures with sufficient degree of cure and green strength to maintain rigidity for subsequent freestanding ...


Performance Evaluation Of Polyurethane Composites Using Vacuum Infusion Process, Mohaned M. Mohamed Jan 2014

Performance Evaluation Of Polyurethane Composites Using Vacuum Infusion Process, Mohaned M. Mohamed

Doctoral Dissertations

"Glass fiber-reinforced polymer composites have promising applications in infrastructures due to their low cost, high specific stiffness/strength, and corrosion resistance. The pultrusion process is often used to manufacture glass fiber-reinforced polyurethane (PU) composite. The objective of this study is to use thermoset PU resin to manufacture high quality composites for infrastructure applications using vacuum assisted resin transfer molding (VARTM) process. Using VARTM to fabricate PU resins presents unique challenges. Several modifications however have helped with overcoming these problems. In part I of the research, the mechanical performance of two different PU resin not only evaluated but also compared to ...