Current Search: mechanics (x)
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Title
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PROCESSING, MICROSTRUCTURAL AND MECHANICAL CHARACTERIZATION OF MECHANICALLY ALLOYED AL-ALUMINA NANOCOMPOSITES.
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Creator
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Katiyar, Pushkar, SURYANARAYANA, C., University of Central Florida
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Abstract / Description
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Aluminum-alumina nanocomposites were synthesized using mechanical alloying of blended component powders of pure constituents. This study was performed on various powder mixtures with aluminum as the matrix and alumina as the reinforcement with volume fractions of 20, 30, and 50 % and Alumina particle sizes of 50 nm, 150 nm, and 5 µm. X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques were used for the crystal structure and microstructural characterization of the...
Show moreAluminum-alumina nanocomposites were synthesized using mechanical alloying of blended component powders of pure constituents. This study was performed on various powder mixtures with aluminum as the matrix and alumina as the reinforcement with volume fractions of 20, 30, and 50 % and Alumina particle sizes of 50 nm, 150 nm, and 5 µm. X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques were used for the crystal structure and microstructural characterization of the powders at different stages of milling. Alumina powders with 50 nm and 150 nm particle size were predominantly of gamma-type, while Alumina of 5 µm size was of alpha-type. The main goal was to achieve uniform distribution of the alumina ceramic particles in the Al matrix, which was achieved on milling for 24 h in a SPEX mill or 100 h in a Fritsch Pulverisette planetary ball mill. The powders were consolidated in two stages: pre-compaction at room temperature followed by vacuum hot pressing (VHP) or hot isostatic pressing (HIP) techniques to a fully dense condition. The effect of reinforcement particle size and volume fraction on the stress-strain response, elastic modulus and yield strength of the composites was investigated. Nanoindentation and compression tests were performed to characterize the composite material. Yield strength of 515 MPa, compressive strength of 685 MPa and elastic modulus of 36 GPa were obtained from compression tests. Nanoindentation results gave the yield strength of 336 MPa, maximum shear stress of 194 MPa and an elastic modulus of 42 GPa. The low elastic modulus values obtained from the above tests might be because of localized yielding possibly due to residual stresses.
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Date Issued
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2004
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Identifier
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CFE0000128, ucf:46193
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Format
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Document (PDF)
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PURL
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http://purl.flvc.org/ucf/fd/CFE0000128
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Title
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COMMISSIONING OF A DYNAMIC MECHANICAL ANALYZERFOR THE CHARACTERIZATION OF LOW TEMPERATURE NITIFE SHAPE MEMORY ALLOYS.
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Creator
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Nandiraju, Maruthi Diwakar, Vaidyanathan, Raj, University of Central Florida
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Abstract / Description
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NiTiFe shape memory alloys can undergo transformations between cubic, trigonal and monoclinic phases at low temperatures. The low hysteresis associated with the trigonal R-phase transformation make them candidates for actuator applications at low temperatures. However, the literature available on these alloys is limited and there is a need to establish processing-structure-property correlations. This study was undertaken with the objective of determining and understanding such correlations in...
Show moreNiTiFe shape memory alloys can undergo transformations between cubic, trigonal and monoclinic phases at low temperatures. The low hysteresis associated with the trigonal R-phase transformation make them candidates for actuator applications at low temperatures. However, the literature available on these alloys is limited and there is a need to establish processing-structure-property correlations. This study was undertaken with the objective of determining and understanding such correlations in a Ni46.8Ti50Fe3.2 alloy. First, a dynamic mechanical analyzer (DMA) was successfully commissioned to facilitate mechanical testing between -150 and 600ºC. The experiments performed over selected ranges of stress and temperature probed a range of deformation phenomena in these materials. In addition to conventional elastic and dislocation based plastic deformation, also probed were stress-induced formation of the R- and martensite (B19') phases, and twinning in the R- and martensite (B19') phases. Constrained recovery experiments, wherein phase transformations were thermally induced against external loads, were also performed to assess the performance of these alloys in actuator applications. In addition to a DMA, a differential scanning calorimeter, liquid helium dilatometer and a transmission electron microscope were also used. The samples tested were subjected to different thermo-mechanical processing parameters (i.e., percentage of cold work, solutionizing, aging, and annealing time/temperature). Selected combinations of cold work and annealing temperature/times were found to result in narrower transformations (in temperature space), making such alloys of value in cyclic actuator applications. Thus this work contributed to further understand the processing-structure-property relationship in NiTiFe alloys that exhibit the R-phase transformation and in lowering the operating temperature range of shape-memory alloys in order for them to be used in hydrogen related technologies. The immediate benefit to NASA Kennedy Space Center is the development of a shape-memory thermal conduction switch for application in cryogenic liquefaction, densification and zero boil-off systems. This is being extended to include the potential use of shape-memory alloy actuator elements for cryogenic seals, valves, fluid-line repair, self-healing gaskets, and even to ambient debris-less separation and latch/release mechanisms. The financial support of NASA through grant NAG3-2751 is gratefully acknowledged.
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Date Issued
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2006
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Identifier
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CFE0001409, ucf:47041
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Format
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Document (PDF)
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PURL
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http://purl.flvc.org/ucf/fd/CFE0001409
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Title
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AN INTERACTIVE FRAMEWORK FOR MESHLESS METHODS ANALYSIS IN COMPUTATIONAL MECHANICS AND THERMOFLUIDS.
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Creator
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Gerace, Salvadore, Kassab, Alain, University of Central Florida
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Abstract / Description
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In recent history, the area of physics-based engineering simulation has seen rapid increases in both computer workstation performance as well as common model complexity, both driven largely in part by advances in memory density and availability of clusters and multi-core processors. While the increase in computation time due to model complexity has been largely offset by the increased performance of modern workstations, the increase in model setup time due to model complexity has continued to...
Show moreIn recent history, the area of physics-based engineering simulation has seen rapid increases in both computer workstation performance as well as common model complexity, both driven largely in part by advances in memory density and availability of clusters and multi-core processors. While the increase in computation time due to model complexity has been largely offset by the increased performance of modern workstations, the increase in model setup time due to model complexity has continued to rise. As such, the major time requirement for solving an engineering model has transitioned from computation time to problem setup time. This is due to the fact that developing the required mesh for complex geometry can be an extremely complicated and time consuming task. Consequently, new solution techniques which are capable of reducing the required amount of human interaction are desirable. The subject of this thesis is the development of a novel meshless method that promises to eliminate the need for structured meshes, and thus, the need for complicated meshing procedures. Although the savings gain due to eliminating the meshing process would be more than sufficient to warrant further study, the proposed method is also capable of reducing the computation time and memory footprint compared to similar models solved using more traditional finite element, finite difference, finite volume, or boundary element methods. In particular, this thesis will outline the development of an interactive, meshless, physically accurate modeling environment that provides an extensible framework which can be applied to a multitude of governing equations encountered in computational mechanics and thermofluids. Additionally, through the development of tailored preprocessing routines, efficiency and accuracy of the proposed meshless algorithms can be tested in a more realistic and flexible environment. Examples are provided in the areas of elasticity, heat transfer and computational fluid dynamics.
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Date Issued
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2007
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Identifier
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CFE0001913, ucf:47484
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Format
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Document (PDF)
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PURL
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http://purl.flvc.org/ucf/fd/CFE0001913
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Title
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MECHANICAL CHARACTERIZATION OF ANISOTROPIC FUSED DEPOSITION MODELED POLYLACTIC ACID UNDER COMBINED MONOTONIC BENDING AND TORSION CONDITIONS.
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Creator
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Santomauro, Aaron T, Gordon, Ali P., University of Central Florida
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Abstract / Description
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Mechanical strength of polylactic acid (PLA) is increasingly relevant with time because of its attractive mechanical properties and 3D printability. Additive manufacturing (AM) methods, such as fused deposition modeling (FDM), stereolithography (SLA), and selective laser sintering (SLS), serve a vital role in assisting designers with cheap and efficient generation of the desired components. This document presents research to investigate the anisotropic response of multi-oriented PLA subjected...
Show moreMechanical strength of polylactic acid (PLA) is increasingly relevant with time because of its attractive mechanical properties and 3D printability. Additive manufacturing (AM) methods, such as fused deposition modeling (FDM), stereolithography (SLA), and selective laser sintering (SLS), serve a vital role in assisting designers with cheap and efficient generation of the desired components. This document presents research to investigate the anisotropic response of multi-oriented PLA subjected to multiple monotonic loading conditions. Although empirical data has previously been captured for multi-oriented PLA under tensile and compressive loading conditions, the data has yet to be applied with regard to a representative component geometry. The tensile and compressive empirical data were ultimately used to develop elastic and yield constitutive models which aided in the characterization of PLA under torsion and bending. This representative component geometry is expected to experience a combined torsion and bending load condition in an effort to address this integral gap in the mechanical properties of multi-oriented PLA. In addition to the acquired empirical data, finite element analysis (FEA) and analytical modeling are employed to supplement the accurate modeling of future component analysis. As a result of the proposed array of experiments, the torsional and bending capabilities of PLA are forecasted to vary based on the print orientation. Lastly, the broader impact of this work is dedicated to addressing the material's capability to operate in environments which possess significant torsion and bending such as model aircraft wings and shafts for remote controlled cars.
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Date Issued
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2019
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Identifier
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CFH2000550, ucf:45631
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Format
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Document (PDF)
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PURL
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http://purl.flvc.org/ucf/fd/CFH2000550
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Title
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MUSIC THERAPY AS AN INTERVENTION TO REDUCE ANXIETY IN MECHANICALLY-VENTILATED PATIENTS.
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Creator
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Levine, Stephanie L, Sole, Mary Lou, University of Central Florida
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Abstract / Description
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Patients receiving mechanical ventilation endure high levels of stress and anxiety due to the invasiveness of the procedure. These critically ill patients are often uncomfortable as a result of their serious conditions and the high-intensity environments in which they are placed. Health care workers heavily sedate these patients to minimize pain and induce a state of relaxation. However, sedatives are known for their wide-ranging, and often deleterious, side effects. Music therapy is an...
Show morePatients receiving mechanical ventilation endure high levels of stress and anxiety due to the invasiveness of the procedure. These critically ill patients are often uncomfortable as a result of their serious conditions and the high-intensity environments in which they are placed. Health care workers heavily sedate these patients to minimize pain and induce a state of relaxation. However, sedatives are known for their wide-ranging, and often deleterious, side effects. Music therapy is an intervention that has been studied in a variety of hospital settings to determine any potential beneficial effects on patients. Many studies have demonstrated a relationship between music therapy and decreased anxiety levels. This thesis reviewed studies on outcomes of music therapy on anxiety in mechanically-ventilated patients. A total of 10 studies that addressed the use of music to decrease anxiety in ventilated patients were analyzed and incorporated into the literature review. The articles were selected from a variety of databases on EBSCOhost, including MEDLINE, PsycINFO, ScienceDirect, and CINAHL. The literature review provides positive evidence for the support of music therapy to help alleviate anxiety in mechanically-ventilated patients.
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Date Issued
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2016
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Identifier
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CFH2000031, ucf:45572
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Format
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Document (PDF)
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PURL
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http://purl.flvc.org/ucf/fd/CFH2000031
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Title
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ADDING CEREBRAL AUTOREGULATION TO A LUMPED PARAMETER MODEL OF BLOOD FLOW.
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Creator
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Gentile, Rusty, Kassab, Alain, University of Central Florida
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Abstract / Description
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A mathematical model of blood flow in infants with hypoplastic left heart syndrome (HLHS) was improved by adding cerebral autoregulation. This is the process by which blood vessels constrict or dilate to keep blood flow steady in certain organs during pressure changes. The original lumped parameter model transformed the fluid flow into an electrical circuit. Its behavior is described using a system of thirty-three coupled differential equations that are solved numerically using a fourth-order...
Show moreA mathematical model of blood flow in infants with hypoplastic left heart syndrome (HLHS) was improved by adding cerebral autoregulation. This is the process by which blood vessels constrict or dilate to keep blood flow steady in certain organs during pressure changes. The original lumped parameter model transformed the fluid flow into an electrical circuit. Its behavior is described using a system of thirty-three coupled differential equations that are solved numerically using a fourth-order Runge-Kutta method implemented in MATLAB. A literature review that includes a discussion of autoregulation mechanisms and approaches to modeling them is followed by a description of the model created for this paper. The model is based on the baroreceptor or neurogenic theory of autoregulation. According to this theory, nerves in certain places within the cardiovascular system detect changes in blood pressure. The brain then compensates by sending a signal to blood vessels to constrict or dilate. The model of the control system responded fairly well to a pressure drop with a steady state error of about two percent. Running the model with or without the control system activated had little effect on other parameters, notably cardiac output. A more complete model of blood flow control would include autonomic regulation. This would vary more parameters than local autoregulation, including heart rate and contractility. This is suggested as a topic of further research.
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Date Issued
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2012
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Identifier
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CFH0004214, ucf:44933
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Format
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Document (PDF)
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PURL
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http://purl.flvc.org/ucf/fd/CFH0004214
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Title
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High Volume Fraction Mg-based Nanocomposites: Processing, Microstructure and Mechanical Behavior.
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Creator
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Liu, Jinling, An, Linan, Suryanarayana, Challapalli, Fang, Jiyu, Bai, Yuanli, Lin, Kuo-Chi, University of Central Florida
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Abstract / Description
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Mg-based metal matrix nanocomposites (MMNCs) with mechanical properties, superior to those of coarse-grained composites, are promising structural materials for applications in the automotive and aerospace industries. The research in this area was primarily focused earlier on either micro-scaled reinforcements or nano-scaled reinforcements with very low volume fractions. MMNCs with high volume fractions have not been explored yet. In this research, we study the processing, microstructures and...
Show moreMg-based metal matrix nanocomposites (MMNCs) with mechanical properties, superior to those of coarse-grained composites, are promising structural materials for applications in the automotive and aerospace industries. The research in this area was primarily focused earlier on either micro-scaled reinforcements or nano-scaled reinforcements with very low volume fractions. MMNCs with high volume fractions have not been explored yet. In this research, we study the processing, microstructures and properties of MMNCs containing ceramic nanoparticles up to 30 vol.%.We first investigated the mechanical alloying of Al2O3 nanoparticles and pure Mg under high-energy ball milling conditions. The phase evolution and their distribution were evaluated as a function of milling time. Then, the thermal stability of the formed nanocomposites was investigated by annealing it at high temperatures. It indicated that an exchange reaction had occurred to a large extent between Mg and Al2O3 resulting in the formation of Al and MgO phases. Additionally, the reaction between Al and un-reacted Mg led to the formation of Mg-Al intermetallics.Due to the reaction between Mg and Al2O3 during the milling and annealing process, we attempted to synthesize Mg/SiC nanocomposites. The mixed powders containing 0, 5, 10 and 15 vol.% SiC were produced by high energy ball milling and then the powders were consolidated via spark plasma sintering. The phase constitutions and microstructures of the Mg/SiC nanocomposites were characterized. SiC nanoparticles (average particle size ~14 nm) appear to be homogeneously dispersed within the matrix, and the average inter-particle spacings of all the Mg/SiC nanocomposites were smaller than 50 nm. Microscopic methods, even at high magnifications did not reveal any significant porosity in the as-processed MMNCs.Mechanical characterization of the Mg/SiC nanocomposites was conducted using the microindentation test. Besides the microhardness test, different intermediate pause times and loading rates were used to evaluate the stiffness and loading rate sensitivity of our samples. The abnormal microhardness and loading rate sensitivity were showed for the Mg-15 vol.% SiC samples. At the same time, the monotonic increase of stiffness with volume fraction was exhibited in the Mg/SiC nanocomposites.Finally, we investigated the quasi-static and dynamic response of Mg/SiC nanocomposites and microcomposites, and discussed the underlying mechanisms. Strain softening was noticed in the milled Mg sample under quasi-static compression. Similarly, the strengthening effect leveling off was also observed in the Mg-15 vol.% SiC samples under either quasi-static or high-strain rate uniaxial compression conditions. No significant plastic deformation was observed in the Mg/SiC nanocomposites. The estimated strain rate sensitivity of all the Mg/SiC nanocomposites in this work was around 0.03, which is much smaller than 0.3 and 0.6, observed for 100 nm and 45 nm grain size pure Mg individually. In particular, the existing models fail in predicting the inverse volume fraction effect, and other mechanisms are yet to be explored. The presence of SiC nanoparticles may play an important role that leads to this difference.
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Date Issued
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2013
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Identifier
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CFE0004879, ucf:49672
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Format
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Document (PDF)
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PURL
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http://purl.flvc.org/ucf/fd/CFE0004879
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Title
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AMORPHOUS PHASE FORMATION IN MECHANICALLY ALLOYED FE-BASED SYSTEMS.
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Creator
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Sharma, Satyajeet, Suryanarayana, C, University of Central Florida
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Abstract / Description
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ABSTRACT Bulk metallic glasses have interesting combination of physical, chemical, mechanical, and magnetic properties which make them attractive for a variety of applications. Consequently there has been a lot of interest in understanding the structure and properties of these materials. More varied applications can be sought if one understands the reasons for glass formation and the methods to control them. The glass-forming ability (GFA) of alloys can be substantially increased by a proper...
Show moreABSTRACT Bulk metallic glasses have interesting combination of physical, chemical, mechanical, and magnetic properties which make them attractive for a variety of applications. Consequently there has been a lot of interest in understanding the structure and properties of these materials. More varied applications can be sought if one understands the reasons for glass formation and the methods to control them. The glass-forming ability (GFA) of alloys can be substantially increased by a proper selection of alloying elements and the chemical composition of the alloy. High GFA will enable in obtaining large section thickness of amorphous alloys. Ability to produce glassy alloys in larger section thicknesses enables exploitation of these advanced materials for a variety of different applications. The technique of mechanical alloying (MA) is a powerful non-equilibrium processing technique and is known to produce glassy (or amorphous) alloys in several alloy systems. Metallic amorphous alloys have been produced by MA starting from either blended elemental metal powders or pre-alloyed powders. Subsequently, these amorphous alloy powders could be consolidated to full density in the temperature range between the glass transition and crystallization temperatures, where the amorphous phase has a very low viscosity. This Dissertation focuses on identifying the various Fe-based multicomponent alloy systems that can be amorphized using the MA technique, studying the GFA of alloys with emphasis on improving it, and also on analyzing the effect of extended milling time on the constitution of the amorphous alloy powder produced at earlier times. The Dissertation contains seven chapters, where the lead chapter deals with the background, history and introduction to bulk metallic glasses. The following four chapters are the published/to be published work, where the criterion for predicting glass formation, effect of Niobium addition on glass-forming ability (GFA), lattice contraction on amorphization, effect of Carbon addition on GFA, and observation of mechanical crystallization in Fe-based systems have been discussed. The subsequent chapter briefly mentions about the consolidation of amorphous powders and presents results of hot pressing and spark plasma sintering on one of the alloy systems. The final chapter summarizes the Dissertation and suggests some prospective research work that can be taken up in future. The Dissertation emphasizes the glass-forming ability, i.e., the ease with which amorphization can occur. In this work the milling time required for amorphization was the indicator/measure of GFA. Although the ultimate aim of this work was to consolidate the Fe-based amorphous alloy powders into bulk so as to undertake mechanical characterization, however, it was first necessary to study the glass forming aspect in the different alloy systems. By doing this a stage has been reached, where different options are available with respect to amorphous phase-forming compositions and the knowledge to improve glass-forming ability via the mechanical alloying technique. This will be ultimately useful in the powder compaction process into various shapes and sizes at optimum pressure and temperature. The study on mechanical crystallization indicates, or in a way defines, a limit to the process of amorphization, and it was also demonstrated that this phenomenon is more common in occurrence than and not as restricted as it was earlier reported to be.
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Date Issued
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2008
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Identifier
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CFE0002025, ucf:47630
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Format
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Document (PDF)
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PURL
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http://purl.flvc.org/ucf/fd/CFE0002025
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Title
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Nanocomposite Coating Mechanics via Piezospectroscopy.
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Creator
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Freihofer, Gregory, Raghavan, Seetha, Gou, Jihua, Bai, Yuanli, Schulzgen, Axel, University of Central Florida
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Abstract / Description
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Coatings utilizing the piezospectroscopic (PS) effect of alpha alumina could enable on the fly stress sensing for structural health monitoring applications. While the PS effect has been historically utilized in several applications, here by distributing the photo-luminescent material in nanoparticle form within a matrix, a stress sensing coating is created. Parallel to developing PS coatings for stress sensing, the multi-scale mechanics associated with the observed PS response of...
Show moreCoatings utilizing the piezospectroscopic (PS) effect of alpha alumina could enable on the fly stress sensing for structural health monitoring applications. While the PS effect has been historically utilized in several applications, here by distributing the photo-luminescent material in nanoparticle form within a matrix, a stress sensing coating is created. Parallel to developing PS coatings for stress sensing, the multi-scale mechanics associated with the observed PS response of nanocomposites and their coatings has been applied to give material property measurements, providing an understanding of particle reinforced composite behavior.Understanding the nanoparticle-coating-substrate mechanics is essential to interpreting the spectral shifts for stress sensing of structures. In the past, methods to experimentally measure the mechanics of these embedded nano inclusions have been limited, and much of the design of these composites depend on computational modeling and bulk response from mechanical testing. The PS properties of Chromium doped alumina allow for embedded inclusion mechanics to be revisited with unique experimental setups that probe the particles state of stress under applied load to the composite. These experimental investigations of particle mechanics will be compared to the Eshelby theory and its derivative theories in addition to the nanocomposite coating mechanics. This work discovers that simple nanoparticle load transfer theories are adequate for predicting PS properties in an intermediate volume fraction range. With fundamentals of PS nanocomposites established, the approach was applied to selected experiments to prove its validity. In general it was observed that the elastic modulus values calculated from the PS response were similar to that observed from macroscale strain measurements such as a strain gage. When simple damage models were applied to monitor the elastic modulus, it was observed that the rate of decay for the elastic modulus was much higher for the PS measurements than for the strain gage.A novel experiment including high resolution PS maps with secondary strain maps from digital image correlation is reviewed on an open hole tension, composite coupon. The two complementary measurements allow for a unique PS response for every location around the hole with a spatial resolution of 400 microns. Progression of intermediate damage mechanisms was observed before digital image correlation indicated them. Using the PS nanocomposite model, elastic modulus values were calculated. Introducing an elastic degradation model with some plastic deformation allows for estimation of material properties during the progression of failure.This work is part of a continuing effort to understand the mechanics of a stress sensing PS coating. The mechanics were then applied to various experimental data that provided elastic property calculations with high resolution. The significance is in the experimental capture of stress transfer in particulate composites. These findings pave the way for the development of high resolution stress-sensing coatings.
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Date Issued
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2014
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Identifier
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CFE0005614, ucf:50223
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Format
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Document (PDF)
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PURL
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http://purl.flvc.org/ucf/fd/CFE0005614
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Title
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A MODEL OF HIP DYSPLASIA REDUCTIONS IN INFANTS USING THE PAVLIK HARNESS.
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Creator
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Hadri, Wissam, Samsam, Mohtashem, University of Central Florida
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Abstract / Description
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Hip dysplasia, also known as congenital dysplasia of the hip (CDH) or Developmental Dysplasia of the Hip (DDH), is a mal-alignment of the hip joint. Left untreated within the first nine months, DDH could lead to permanent disability. Luckily however, this condition is diagnosed at an early age and is usually treated without surgery through the use of the Pavlik harness. In this thesis, a 3D computational model and dynamic finite element analysis of the muscles and tissues involved in hip...
Show moreHip dysplasia, also known as congenital dysplasia of the hip (CDH) or Developmental Dysplasia of the Hip (DDH), is a mal-alignment of the hip joint. Left untreated within the first nine months, DDH could lead to permanent disability. Luckily however, this condition is diagnosed at an early age and is usually treated without surgery through the use of the Pavlik harness. In this thesis, a 3D computational model and dynamic finite element analysis of the muscles and tissues involved in hip dysplasia and the mechanics of the Pavlik harness, as rendered by Dr. Alain J. Kassab's research group in the College of Mechanical and Aerospace Engineering in the University of Central Florida over the past 3 years, were reviewed and discussed to evaluate the accuracy of the hip reduction mechanism. I examine the group's usage of CT-based images to create accurate models of the bony structures, muscle tensions and roles that were generated using biomechanical analyses of maximal and passive strain, and the usage of adult and infant hips. Results, as produced by the group indicated that the effects and force contribution of the muscles studied are functions of severity of hip dislocation. Therefore, I discussed complications with real world-to-computational modeling with regards to structural systems and data interpretations. Although this design could be applied to more anatomical models and mechanistic analyses, more research would have to be completed to create more accurate models and results.
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Date Issued
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2014
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Identifier
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CFH0004641, ucf:45317
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Format
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Document (PDF)
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PURL
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http://purl.flvc.org/ucf/fd/CFH0004641
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Title
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SYNTHESIS, PROCESSING AND CHARACTERIZATION OF NANOCRYSTALLINE TITANIUM DIOXIDE.
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Creator
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Qiu, Shipeng, Kalita, Samar, University of Central Florida
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Abstract / Description
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Titanium dioxide (TiO2), one of the basic ceramic materials, has found a variety of applications in industry and in our daily life. It has been shown that particle size reduction in this system, especially to nano regime, has the great potential to offer remarkable improvement in physical, mechanical, optical, biological and electrical properties. This thesis reports on the synthesis and characterization of the nanocrystalline TiO2 ceramic in details. The study selected a simple sol-gel...
Show moreTitanium dioxide (TiO2), one of the basic ceramic materials, has found a variety of applications in industry and in our daily life. It has been shown that particle size reduction in this system, especially to nano regime, has the great potential to offer remarkable improvement in physical, mechanical, optical, biological and electrical properties. This thesis reports on the synthesis and characterization of the nanocrystalline TiO2 ceramic in details. The study selected a simple sol-gel synthesis process, which can be easily controlled and reproduced. Titanium tetraisopropoxide, isopropanol and deionized water were used as starting materials. By careful control of relative proportion of the precursor materials, the pH and peptization time, TiO2 nanopowder was obtained after calcination at 400oC. The powder was analyzed for its phases using X-ray powder diffraction (XRD) technique. Crystallite size, powder morphology and lattice fringes were determined using high-resolution transmission electron microscopy (HR-TEM). Differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA) were used to study the thermal properties. As-synthesized powder was uniaxially compacted and sintered at elevated temperature of 1100-1600oC to investigate the effects of sintering on nano powder particles, densification behavior, phase evolution and mechanical properties. Microstructure evolution as a function of sintering temperature was studied by scanning electron microscopy (SEM). The results showed that 400oC was an optimum calcination temperature for the as-synthesized TiO2 powder. It was high enough to achieve crystallization, and at the same time, helped minimize the thermal growth of the crystallites and maintain nanoscale features in the calcined powder. After calcination at 400oC (3 h), XRD results showed that the synthesized nano-TiO2 powder was mainly in single anatase phase. Crystallite size was first calculated through XRD, then confirmed by HR-TEM, and found to be around 5~10 nm. The lattice parameters of the nano-TiO2 powder corresponding to this calcination temperature were calculated as a=b=0.3853 nm, c=0.9581 nm, α=β=γ=90o through a Rietveld refinement technique, which were quite reasonable when comparing with the literature values. Considerable amount of rutile phase had already formed at 600oC, and the phase transformation from anatase to rutile fully completed at 800oC. The above rutilization process was clearly recorded from XRD data, and was in good corresponding to the DSC-TGA result, in which the broad exothermic peak continued until around 800oC. Results of the sintered TiO2 ceramics (1100oC-1600oC) showed that, the densification process continued with the increase in sintering temperature and the highest geometric bulk sintered density of 3.75 g/cm3 was achieved at 1600oC. The apparent porosity significantly decreased from 18.5% to 7.0% in this temperature range, the trend of which can be also clearly observed in SEM micrographs. The hardness of the TiO2 ceramics increased with the increase in sintering temperature and the maximum hardness of 471.8±30.3 HV was obtained at 1600oC. Compression strength increased until 1500oC and the maximum value of 364.1±10.7 MPa was achieved; after which a gradual decrease was observed. While sintering at ambient atmosphere in the temperature range of 1100oC-1600oC helped to improve the densification, the grain size also increased. As a result, though the sintered density at 1600oC was the highest, large and irregular-shaped grains formed at this temperature would lead to the decrease in the compression strength.
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Date Issued
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2006
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Identifier
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CFE0001432, ucf:47036
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Format
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Document (PDF)
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PURL
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http://purl.flvc.org/ucf/fd/CFE0001432
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Title
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A METHODOLOGY FOR INSTRUMENTED INDENTATION STUDIES OF DEFORMATION IN BULK METALLIC GLASSES.
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Creator
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Sridharan, Subhaashree, Vaidyanathan, Raj, University of Central Florida
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Abstract / Description
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Bulk Metallic Glasses (BMGs), also known as amorphous metals, are of considerable scientific and commercial interest due to their random or chaotic structure. Given their potential use as engineering materials, there is a concomitant need to establish their mechanical properties. However, BMGs are not conveniently available in sufficient volumes (especially experimental and combinatorial compositions), making property determination via conventional tensile or compression testing problematic....
Show moreBulk Metallic Glasses (BMGs), also known as amorphous metals, are of considerable scientific and commercial interest due to their random or chaotic structure. Given their potential use as engineering materials, there is a concomitant need to establish their mechanical properties. However, BMGs are not conveniently available in sufficient volumes (especially experimental and combinatorial compositions), making property determination via conventional tensile or compression testing problematic. Instrumented indentation is ideally suited for this purpose because the testing requires only small sampling volumes and can probe multiaxial deformation characteristics at various length scales. In this technique, conducted generally on a sub-micron regime, the depth of penetration of an indenter, usually a diamond, is measured as a function of the applied load and expressed graphically as load (P) - displacement (h) curves from which a host of mechanical properties can be extracted and studied. In this work, a methodology for using instrumented indentation at nano- and micro- scales to determine the mechanical response of BMGs was developed and implemented. The implementation primarily focused on deformation in the elastic regime but included preliminary results related to the onset of inelastic deformation. The methodology developed included calibration techniques, formulations to extract the machine compliances, verifications using standards and verification for uniqueness of instrument deformation under a spherical indenter. The methodology was different for the two platforms used based on the load-depth response characteristics of the instrument. In the case of the Micro Test platform, the load-depth response of the instrument was linear. In the case of the Nano Test platform, the instrument load-depth response followed a 3/2 power law, representative of Hertzian behavior. The load-depth response of the instrument was determined by subtracting the theoretical response from the corresponding raw load-depth response obtained by elastically indenting a standard steel specimen of known modulus. The true response of the sample was then obtained by subtracting the instrument's response from the corresponding uncorrected load-depth response (raw data). An analytical model to describe the load-train compliance was developed. The methodology was verified using quartz and tungsten standards. Indentation experiments were conducted on Zr41.25Ti13.75Cu12.5Ni10Be22.5 (Vitreloy 1), Cu60Hf25Ti15, Cu60Zr30Ti10 and Fe60Co7Zr10Mo5W2B16 bulk metallic glasses using spherical indenters with diameters 2.8 mm and 100 m. The spherical geometry results in a simpler stress distribution under the indenter (when compared to a sharp geometry) and furthermore by recourse to spherical indenters the onset of plastic deformation was delayed. In the case of the Zr-based BMG, the experiments showed that the elastic response did not depend on the diameter of the indenter used indicative of the absence of residual stresses in the sample. Large scale plastic deformation was observed when the sample was indented using a smaller diameter indenter. Log scale analysis (i.e., examining the results on a log load vs. log depth response to check for deviation from Hertzian behavior) showed a deviation from a 3/2 fit indicating a deviation from elastic behavior. The onset implied a yield strength value of ~ 4 GPa, higher than the value reported in the literature (~ 2 GPa). Hence, it is believed that the first signs of plastic deformation occurred at lower loads than the predicted loads from the log scale analysis procedure and is expected to occur as discrete bursts. Discrete plastic events or "pop-ins" were observed in the load-depth indentation responses under quasistatic loading conditions, which were believed to be associated with shear band activity. An attempt was made to formulate a mathematical model based on three yield criteria (Drucker-Prager, Mohr-Coulomb and von Mises). Based on the von Mises predictions and comparable experiments on a quartz standard, it was established that the pop-ins observed were real and not an instrument artifact. Multiple load cycles following partial unload experiments showed that the pop-ins affected the subsequent indentation response. The moduli and the yield strength values obtained for the Cu-based BMGs were comparable to the values reported in the literature. There was significant scatter in the indentation data from the Fe-based BMG. Porosity and lack of 100 % compaction were believed to be the reasons for scatter in the data. The financial support of NSF through grant DMR 0314212 is gratefully acknowledged.
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Date Issued
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2006
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Identifier
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CFE0001442, ucf:47047
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Format
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Document (PDF)
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PURL
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http://purl.flvc.org/ucf/fd/CFE0001442
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Title
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MECHANISMS OF NANOFILTER FOULING AND TREATMENT ALTERNATIVES FOR SURFACE WATER SUPPLIES.
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Creator
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Reiss, Charles, Taylor, James, University of Central Florida
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Abstract / Description
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This dissertation addresses the role of individual fouling mechanisms on productivity decline and solute mass transport in nanofiltration (NF) of surface waters. Fouling mechanisms as well as solute mass transport mechanisms and capabilities must be understood if NF of surface waters is to be successful. Nanofiltration of surface waters was evaluated at pilot-scale in conjunction with advanced pretreatment processes selected for minimization of nanofilter fouling, which constituted several...
Show moreThis dissertation addresses the role of individual fouling mechanisms on productivity decline and solute mass transport in nanofiltration (NF) of surface waters. Fouling mechanisms as well as solute mass transport mechanisms and capabilities must be understood if NF of surface waters is to be successful. Nanofiltration of surface waters was evaluated at pilot-scale in conjunction with advanced pretreatment processes selected for minimization of nanofilter fouling, which constituted several integrated membrane systems (IMSs). Membrane fouling mechanisms of concern were precipitation, adsorption, particle plugging, and attached biological growth. Fouling was addressed by addition of acid and antiscalent for control of precipitation, addition of monochloramine for control of biological growth, microfiltration (MF) or coagulation-sedimentation-filtration (CSF) for control of particle plugging, and in-line coagulation-microfiltration (C/MF) or CSF for control of organic adsorption. Surface water solutes of concern included organic solutes, pathogens, and taste and odor compounds. Solute mass transport was addressed by evaluation of total organic carbon (TOC), Bacillus subtilis endospores, gesomin (G), 2-methlyisoborneol (MIB), and threshold odor number (TON). This evaluation included modeling to determine the role of diffusion in solute mass transport including assessment of the homogeneous solution diffusion equation. A cellulose acetate (CA) NF was less susceptible to fouling than two polyamide (PA) NFs. NF fouling was minimized by the addition of monochloramine, lower flux, lower recovery, and with the use of a coagulant-based pretreatment (C/MF or CSF). NF surface characterization showed that the low fouling CA film was less rough and less negatively charged than the PA films. Thus the theory that a more negatively charged surface would incur less adsorptive fouling, due to charge repulsion, was not observed for these tests. The rougher surface of the PA films may have increased the number of sites for adsorption and offset the charge repulsion benefits of the negatively charged surface. The addition of monochloramine significantly reduced biodegradation and integrity loss of the CA membrane. PA membranes are inherently not biologically degradable due to their chemical structure. Monochloramination reduced the rate of fouling of the PA membrane but resulted in a gradual increase in water mass transfer coefficient and a decrease in TDS rejection over time, which indicated damage and loss of integrity of the PA membrane. Based on surface characterization by X-ray Photoelectron Spectroscopy (XPS) and Fourier Transform Infrared Spectrometry (FTIR), the PA membrane degradation appeared to be chemically-based and initiated with chlorination of amide nitrogen and/or aromatic rings, which ultimately resulted in disruption of membrane chemical structures. The recommended Integrated Membrane System to control fouling of a surface water nanofiltration system is CSF monochloramine/acid/antiscalent³monochloramine-tolerant NF. This IMS, at low flux and recovery, operated with no discernable fouling and is comparable to a groundwater nanofiltration plant with cleaning frequencies of once per six months or longer. A significant portion of the organic solutes including total organic carbon (TOC) passing through the membranes was diffusion controlled. Permeate concentration increased with increasing recovery and with decreasing flux for both PA and CA membranes. The influence was diminished for the PA membrane, due to its high rejection capabilities. Total rejection of spores used as pathogen surrogates was not achieved as spores were indigenous and high spore concentrations were used in all challenge studies; however, Integrated Membrane System spore rejection exceeded credited regulatory rejection of similar sized microorganisms by conventional treatment by several logs. Spore rejection varied by NF but only slightly by MF as size-exclusion controlled. There was no difference among spore rejection of IMS with and without in-line coagulation. Consequently, these results indicate membrane configuration (Hollow fiber>Spiral Wound) and membrane film (Composite Thin Film>CA) significantly affected spore rejection. Geosmin and methylisoborneol have molecular weights of 182 and 168 respectively, and are byproducts of algal blooms, which commonly increase taste and odor as measured by the threshold odor number (TON) in drinking water. Although these molecules are neutral and were thought to pass through NFs, challenge testing of IMS unit operations found that significant removal of TON, G and MIB was achieved by membrane processes, which was far superior to conventional processes. A CA NF consistently removed 35 to 50 percent of TON, MIB, and G, but did not achieve compliance with the TON standard of 3 units. A PA NF provided over 99 percent removal of MIB and G. Challenge tests using MIB and G indicated that size-exclusion controlled mass transfer of these compounds in NF membranes.
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Date Issued
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2005
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Identifier
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CFE0000630, ucf:46506
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Format
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Document (PDF)
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PURL
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http://purl.flvc.org/ucf/fd/CFE0000630
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Title
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REDUCED KINETIC MECHANISMS FOR PREMIXEDHYDROGEN-AIR-CF3BR FLAMES.
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Creator
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Zhang, Yi, Xu, Fang, University of Central Florida
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Abstract / Description
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Halon 1301 (CF3Br), or bromotrifluoromethane, had been widely used as fire-extinguishing agent for many years before its production and consumption were severely regulated by the Montreal Protocol due to its hazardous depletion effect to the stratospheric ozone layer. It is therefore imperative to find an effective replacement fire-fighting agent before the mandated deadline of the complete phase out of CF3Br. Currently there are intensive efforts in searching for an environmentally...
Show moreHalon 1301 (CF3Br), or bromotrifluoromethane, had been widely used as fire-extinguishing agent for many years before its production and consumption were severely regulated by the Montreal Protocol due to its hazardous depletion effect to the stratospheric ozone layer. It is therefore imperative to find an effective replacement fire-fighting agent before the mandated deadline of the complete phase out of CF3Br. Currently there are intensive efforts in searching for an environmentally acceptable fire suppression replacement. This, however, is hampered by a lack of fundamental understanding of how CF3Br suppresses the chemical reactions in a flame environment so effectively. Recent experimental evidence has shown that the addition of CF3Br significantly reduced the burning velocity of premixed H2/Air flames by depleting the important radical species that are important to sustain chemical reactions. Extending this finding to understand the suppression of more complicated diffusion flames and unsteady three dimension turbulent flames in the presence of Halon 1301, however, still faces enormous challenge because of the prohibitive requirement of the computational power. The present chemical reaction mechanism for even the simplest hydrocarbon fuel (CH4) combustion involves more than 300 elemental reactions and the addition of CF3Br adds approximately 70 more elemental reactions. This large number of reactions and the associated large number of reaction species, many of which still involve uncertain reaction coefficients and thermodynamics properties, present significant computing challenges for applications in multidimensional non-premixed flames that are often encountered in practice. Therefore, it is of interest to systematically reduce the full chemical mechanism to a few global reactions while still maintaining the accuracy of the original mechanism. The present research systematically reduced the complex H2/Air/CF3Br chemical reaction mechanism with 94 initial elemental reactions to 5 global reaction steps. The reduced mechanism results in dramatic savings in computer time and is capable of predicting the major species and important steady state species with high accuracy. Through detailed sensitivity and production rate analysis the present research was able to find the key elemental reactions that are responsible for the fire suppression behavior of CF3Br. Predicted maximum concentrations of H and OH were found to correlate closely with the existing laminar burning velocity data measured for the premixed H2/Air/CF3Br flames. Better agreement with the experimental data was found when two activation energies for the two most important elementary reactions from QRRK calculations were adopted. The reduced mechanism developed through this research can be used to assist in the calculation and the understanding of fire suppression of CF3Br for more practical multidimensional nonpremixed laminar and turbulent flames, and the effort in searching for other effective fire suppressing agents.
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Date Issued
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2004
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Identifier
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CFE0000257, ucf:46240
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Format
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Document (PDF)
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PURL
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http://purl.flvc.org/ucf/fd/CFE0000257
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Title
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APPLICATION OF NON-LOCAL APPROACHES FOR PREDICTING THE RESPONSE OF V-NOTCH UNDER THERMOMECHANICAL FATIGUE LOADING.
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Creator
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Nguyen, Trung, Gordon, Ali, University of Central Florida
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Abstract / Description
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The topic of this thesis is the construction of a formula to approximate stress-strain responses at notches under thermomechanical fatigue (TMF) loading. The understanding of material behavior of the V-notched component which experiences TMF is important to the mechanical industries where V-notched structures are often utilized. In such applications, it is crucial that the designers be able to predict the material behavior; therefore, the purpose of this research is to examine and to model...
Show moreThe topic of this thesis is the construction of a formula to approximate stress-strain responses at notches under thermomechanical fatigue (TMF) loading. The understanding of material behavior of the V-notched component which experiences TMF is important to the mechanical industries where V-notched structures are often utilized. In such applications, it is crucial that the designers be able to predict the material behavior; therefore, the purpose of this research is to examine and to model the precise effects a stress concentration will have on a specimen made of a generic Ni-base superalloy. The effects of non-isothermal loading will be studied, and it is the goal of this research to formulate an extension of Neuber's rule appropriate for TMF which is to approximate the temperature range with a single value, T*. One strategy to extend Neuber's rule, which relies on Finite Element Modeling (FEM), Bilinear Kinetic Hardening Model (BKIN), and test data, will be used to predict the stress-strain behavior at the notch of a thin plate subjected to axial loading. In addition, the CHABOCHE model will be utilized in the FEA to have the highest fidelity to material response at high temperatures. Parametric study of the FEA simulations will be employed to determine the correlation between the Neuber hyperbola, temperature range, stress concentration, the nominal stress, and the temperature cycling. Using the Neuber hyperbola and simplified constitutive model (i.e., bilinear kinematic strain hardening), the stress-strain solutions of the specimen will be calculated and compared to analytical results.
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Date Issued
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2013
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Identifier
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CFH0004440, ucf:45111
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Format
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Document (PDF)
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PURL
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http://purl.flvc.org/ucf/fd/CFH0004440
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Title
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THE USE OF WET-TO-DRY DRESSINGS FOR MECHANICAL DEBRIDEMENT.
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Creator
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Villa, Katherine, Covelli, Maureen, University of Central Florida
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Abstract / Description
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Clinical management of complex wounds is essential to promote wound healing. Prolonged healing time may lead to longer and more costly hospitalizations and poorer patient outcomes. The removal of nonviable, necrotic tissue via debridement is vital to the healing process. One of the most common debridement techniques, in the United States, is the use of wet-to-dry dressings. There are no defined guidelines or protocols for the timing of dressing changes and subsequent debridement. The purpose...
Show moreClinical management of complex wounds is essential to promote wound healing. Prolonged healing time may lead to longer and more costly hospitalizations and poorer patient outcomes. The removal of nonviable, necrotic tissue via debridement is vital to the healing process. One of the most common debridement techniques, in the United States, is the use of wet-to-dry dressings. There are no defined guidelines or protocols for the timing of dressing changes and subsequent debridement. The purpose of this study was to perform a review of literature to determine the rationale for the use of wet-to-dry dressings, explore alternative time sequences of treatment, and to identify the risks and benefits for this methodology of debridement in an adult population with acute traumas. Inclusion criteria consisted of peer reviewed, English Language, research articles published within the last 5 years (2007-2012), adults with acute wounds treated by wet-to-dry dressing debridement. This review of literature was conducted using CINAHL and MEDLINE databases using the following search terms: Wound debridement, wet-to-dry dressing*, timing, sequencing, schedul*, standard*, debridement, acute wound*, and mechanical debridement. The review of literature yielded zero results meeting the search criteria therefore, a second review of literature was performed using the same search criteria but expanded to include articles published within the past 15 years (1997 -2012). The second review of literature also yielded zero results that met the search criteria. A lack of evidence supporting the use of wet-to-dry dressings for the purpose of debridement suggests that healthcare providers are following tradition rather than evidence based practices. Nurses and healthcare providers need education on best practices in wound care to advocate for their patients to ensure the best possible outcome. Further research on wound care modalities that are clinically efficient is needed.
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Date Issued
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2013
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Identifier
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CFH0004362, ucf:45003
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Format
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Document (PDF)
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PURL
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http://purl.flvc.org/ucf/fd/CFH0004362
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Title
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PRETEND LAND.
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Creator
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Neely, Detrachia, Milanes Rodriguez, Cecilia, University of Central Florida
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Abstract / Description
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The bond between a mother and child is thought to be sacred. It is a phenomenon that society seems to expect as axiomatic based on the single biological fact that a woman carries her child, creating an inseparable bond; even for non-biological mothers, the bond is perceived as one of supreme importance. What happens to the mother and to the child, if this sacred bond is broken? The intent of this thesis was to focus on the perceived bond between mother and child and turn it on its head. As a...
Show moreThe bond between a mother and child is thought to be sacred. It is a phenomenon that society seems to expect as axiomatic based on the single biological fact that a woman carries her child, creating an inseparable bond; even for non-biological mothers, the bond is perceived as one of supreme importance. What happens to the mother and to the child, if this sacred bond is broken? The intent of this thesis was to focus on the perceived bond between mother and child and turn it on its head. As a work of fiction, Pretend Land is a series of interrelated short stories about a young woman named Dalia and her issues of abandonment and consequent coping mechanisms. My goal was to explore the effects of mother/child separation through the vehicle of storytelling and create a tale that would allow an honest narrative, not to prove one thing or another, but to finally bring a story to the forefront about an absent mother and the child she left behind.
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Date Issued
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2011
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Identifier
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CFH0004108, ucf:44870
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Format
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Document (PDF)
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PURL
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http://purl.flvc.org/ucf/fd/CFH0004108
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Title
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Polyelectrolyte complexes based on poly(acrylic acid): mechanics and applications.
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Creator
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Lu, Xiaoyan, Zhai, Lei, Zou, Shengli, Chumbimuni Torres, Karin, Kolpashchikov, Dmitry, Dong, Yajie, University of Central Florida
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Abstract / Description
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Poly(acrylic acid) (PAA) is a weak polyelectrolyte presenting negative charge at basic conditionwhen the carboxylic group loses a proton. These carboxylate group can interact with polycationsand metal ions to form stable polyelectrolyte complexes (PECs), leading to tunable propertiesand multifunctional nanoscale structures through chemical reactions. This research focuses onnanofiber and nanoparticle fabricated by PAA-based PECs. We demonstrated the effect of ferricion concentration on the...
Show morePoly(acrylic acid) (PAA) is a weak polyelectrolyte presenting negative charge at basic conditionwhen the carboxylic group loses a proton. These carboxylate group can interact with polycationsand metal ions to form stable polyelectrolyte complexes (PECs), leading to tunable propertiesand multifunctional nanoscale structures through chemical reactions. This research focuses onnanofiber and nanoparticle fabricated by PAA-based PECs. We demonstrated the effect of ferricion concentration on the mechanical properties of PAA-based single naonofiber by using dark fieldmicroscopy imaging and persistence length analysis. The application of PAA-based nanofibermats loaded with MnO2 for supercapacitors was also explored. As a free-standing and flexiblesupercapacitor electrode, the nanofiber mat exhibited outstanding properties including high specificcapacitance, excellent reversible redox reactions, and fast charge/discharge ability. Since PAA is abiocompatible polymer, PAA-based PEC was applied as a drug-carrier in a drug delivery system.In this project, core-shell nanoparticles were fabricated with chitosan as the core and PAA as theshell to incorporate with the drug gemcitabine. Several parameters were investigated to obtainthe optimal nanoparticle size. The as-prepared drug delivery system shows prolonged releasingprofile.
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Date Issued
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2018
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Identifier
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CFE0007045, ucf:52004
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Format
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Document (PDF)
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PURL
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http://purl.flvc.org/ucf/fd/CFE0007045
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Title
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Processing, Characterization and Performance of Carbon Nanopaper Based Multifunctional Nanocomposites.
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Creator
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Liang, Fei, Gou, Jihua, Su, Ming, Fang, Jiyu, Orlovskaya, Nina, Xu, Yunjun, University of Central Florida
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Abstract / Description
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Carbon nanofibers (CNFs) used as nano-scale reinforcement have been extensively studied since they are capable of improving the physical and mechanical properties of conventional fiber reinforced polymer composites. However, the properties of CNFs are far away from being fully utilized in the composites due to processing challenges including the dispersion of CNFs and the viscosity increase of polymer matrix. To overcome these issues, a unique approach was developed by making carbon nanopaper...
Show moreCarbon nanofibers (CNFs) used as nano-scale reinforcement have been extensively studied since they are capable of improving the physical and mechanical properties of conventional fiber reinforced polymer composites. However, the properties of CNFs are far away from being fully utilized in the composites due to processing challenges including the dispersion of CNFs and the viscosity increase of polymer matrix. To overcome these issues, a unique approach was developed by making carbon nanopaper sheet through the filtration of well-dispersed carbon nanofibers under controlled processing conditions, and integrating carbon nanopaper sheets into composite laminates using autoclave process and resin transfer molding (RTM). This research aims to fundamentally study the processing-structure-property-performance relationship of carbon nanopaper-based nanocomposites multifunctional applications: a) Vibrational damping. Carbon nanofibers with extremely high aspect ratios and low density present an ideal candidate as vibrational damping material; specifically, the large specific area and aspect ratio of carbon nanofibers promote significant interfacial friction between carbon nanofiber and polymer matrix, causing higher energy dissipation in the matrix. Polymer composites with the reinforcement of carbon nanofibers in the form of a paper sheet have shown significant vibration damping improvement with a damping ratio increase of 300% in the nanocomposites. b) Wear resistance. In response to the observed increase in toughness of the nanocomposites, tribological properties of the nanocomposite coated with carbon nanofiber/ceramic particles hybrid paper have been studied. Due to high strength and toughness, carbon nanofibers can act as microcrack reducer; additionally, the composites coated with such hybrid nanopaper of carbon nanofiber and ceramic particles shown an improvement of reducing coefficient of friction (COF) and wear rate. c) High electrical conductivity. A highly conductive coating material was developed and applied on the surface of the composites for the electromagnetic interference shielding and lightning strike protection. To increase the conductivity of the carbon nanofiber paper, carbon nanofibers were modified with nickel nanostrands. d) Electrical actuation of SMP composites. Compared with other methods of SMP actuation, the use of electricity to induce the shape-memory effect of SMP is desirable due to the controllability and effectiveness. The electrical conductivity of carbon fiber reinforced SMP composites can be significantly improved by incorporating CNFs and CNF paper into them. A vision-based system was designed to control the deflection angle of SMP composites to desired values. The funding support from National Science Foundation and FAA Center of Excellence for Commercial Space Transportation (FAA COE CST) is acknowledged.
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Date Issued
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2012
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Identifier
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CFE0004569, ucf:49194
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Format
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Document (PDF)
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PURL
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http://purl.flvc.org/ucf/fd/CFE0004569
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Title
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MECHANICAL CHARACTERIZATION AND NUMERICAL SIMULATION OF A LIGHT-WEIGHT ALUMINUM A359 METAL-MATRIX COMPOSITE.
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Creator
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DeMarco, James, Gordon, Ali, University of Central Florida
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Abstract / Description
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Aluminum metal-matrix composites (MMCs) are well positioned to replace steel in numerous manufactured structural components, due to their high strength-to-weight and stiffness ratios. For example, research is currently being conducted in the use of such materials in the construction of tank entry doors, which are currently made of steel and are dangerously heavy for military personnel to lift and close. However, the manufacture of aluminum MMCs is inefficient in many cases due to the loss of...
Show moreAluminum metal-matrix composites (MMCs) are well positioned to replace steel in numerous manufactured structural components, due to their high strength-to-weight and stiffness ratios. For example, research is currently being conducted in the use of such materials in the construction of tank entry doors, which are currently made of steel and are dangerously heavy for military personnel to lift and close. However, the manufacture of aluminum MMCs is inefficient in many cases due to the loss of material through edge cracking during the hot rolling process which is applied to reduce thick billets of as-cast material to usable sheets. In the current work, mechanical characterization and numerical modeling of as-cast aluminum A359-SiCp-30% is employed to determine the properties of the composite and identify their dependence on strain rate and temperature conditions. Tensile and torsion tests were performed at a variety of strain rates and temperatures. Data obtained from tensile tests were used to calibrate the parameters of a material model for the composite. The material model was implemented in the ANSYS finite element software suite, and simulations were performed to test the ability of the model to capture the mechanical response of the composite under simulated tension and torsion tests. A temperature- and strain rate-dependent damage model extended the constitutive model to capture the dependence of material failure on testing or service conditions. Trends in the mechanical response were identified through analysis of the dependence of experimentally-obtained material properties on temperature and strain rate. The numerical model was found to adequately capture strain rate and temperature dependence of the stress-strain curves in most cases. Ductility modeling allowed prediction of stress and strain conditions which would lead to rupture, as well as identification of areas of a solid model which are most likely to fail under a given set of environmental and load conditions.
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Date Issued
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2011
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Identifier
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CFE0004007, ucf:49177
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Format
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Document (PDF)
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PURL
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http://purl.flvc.org/ucf/fd/CFE0004007
Pages