Current Search: plastic (x)
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Title
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INVESTIGATION OF MICROPLASTIC ACCUMULATION IN THE GASTROINTESTINAL TRACT IN BIRDS OF PREY.
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Creator
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Carlin, Julia, Walters, Linda, Donnelly, Melinda, University of Central Florida
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Abstract / Description
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Plastic pollution is unavoidable in the natural environment. Consequences of plastic ingestion include exposure to environmental pollutants and toxin accumulation, causing endocrine disruption, inflammatory and physiological stress in organisms. Microplastics have been shown to transfer across food webs, however, limited studies have examined microplastic accumulation across terrestrial food webs. Furthermore, few studies have examined plastic pollution in apex predatory animals. A study was...
Show morePlastic pollution is unavoidable in the natural environment. Consequences of plastic ingestion include exposure to environmental pollutants and toxin accumulation, causing endocrine disruption, inflammatory and physiological stress in organisms. Microplastics have been shown to transfer across food webs, however, limited studies have examined microplastic accumulation across terrestrial food webs. Furthermore, few studies have examined plastic pollution in apex predatory animals. A study was conducted to quantify the abundance of plastic pollution in the gastrointestinal tract in birds of prey. Two species were investigated, one which forages in terrestrial habitats and one which forages in aquatic environments including Buteo lineatus (red-shouldered hawk) and Pandion haliaetus (osprey), respectively. The gastrointestinal tract was necropsied, chemically digested, and examined for microplastic prevalence. Overall, microplastics are significantly more abundant per gram of gastrointestinal (GI) tract tissue in species that forage on small rodents and terrestrial reptiles (B. lineatus) as compared to species that forage on fish and aquatic invertebrates (P. haliaetus). Buteo lineatus averaged 0.81 (+/- 0.15) fibers and 0.14 (+/- 0.04) fragments per gram of GI tract tissue while P. halieatus averaged 0.31 (+/- 0.09) fibers and 0.04 (+/- 0.02) fragments per gram of GI tract tissue. There was a significant interaction between type and color in both B. lineatus and P. haliaetus GI tract tissues. Micro-Fourier-transform infrared spectroscopy ([micro]-FTIR) was run on haphazardly selected samples and found that rayon was the most common polymer identified in both species. The significant difference found between species could be indicative that terrestrial raptors may experience greater bioaccumulation than aquatic species foraging at comparable trophic levels. However, the significant interaction between type and color in both species indicates a potential common source of pollution that affects both environments. Further investigation on the source of polymers is necessary in order to develop conservation and management strategies aimed at decreasing the output of synthetic fibers into the environment. Due to the abundance of polymers found in these species, understanding the potential biological and physiological effects of plastics is essential to informing superior management strategies that can better protect and preserve wildlife from increasing anthropogenic pressures.
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Date Issued
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2019
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Identifier
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CFH2000501, ucf:45621
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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/CFH2000501
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Title
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Advanced castes at the outset of eusociality in wasps (Vespidae).
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Creator
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Piekarski, Patrick, Sharanowski, Barbara, Carpenter, James, Hoffman, Eric, University of Central Florida
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Abstract / Description
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A dominating and widespread view is that evolutionary change is gradual and waits upon mutation. Likewise, it is thought that workers and queens of eusocial insects diverged gradually and stepwise. That is, rudimentary castes preceded advanced castes. This paradigm hinges on eusociality having evolved once in Vespidae, and primitively eusocial paper wasps lacking ontogenetic caste biasing (differentiation of castes during larval development). Using a phylogenomic approach this study shows...
Show moreA dominating and widespread view is that evolutionary change is gradual and waits upon mutation. Likewise, it is thought that workers and queens of eusocial insects diverged gradually and stepwise. That is, rudimentary castes preceded advanced castes. This paradigm hinges on eusociality having evolved once in Vespidae, and primitively eusocial paper wasps lacking ontogenetic caste biasing (differentiation of castes during larval development). Using a phylogenomic approach this study shows strong evidence for two origins of eusociality in vespid wasps, wherein one origin is likely characterized by the sudden appearance of castes with physiological, and perhaps even morphological, differences established before adulthood (i.e. advanced castes). Ontogenetic caste biasing was likely present at the outset of eusociality in the most recent common ancestor of paper wasps, yellowjackets and hornets. This suggests that the definitive, non-temporal castes of eusocial wasps evolved from interactions between mothers and daughters, rather than same generation females. These results challenge the idea that castes began with only rudimentary differences. A model of stepwise caste divergence, which assumes an independent mutation event for each phenotypic caste difference, is unwarranted. It is hypothesized that phenotypic plasticity and cryptic genetic variation may explain how some eusocial societies emerged, and began with advanced castes. The results suggest that evolution can produce alternative phenotypes with many aspects of the phenotype being discrete at the outset. Thus, the emergence and divergence of castes in eusocial vespids was not necessarily a gradual process.
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Date Issued
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2017
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Identifier
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CFE0006640, ucf:51240
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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/CFE0006640
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Title
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Application of Multiaxial Cyclic Loading for Constitutive Model and Parameter Determination of Steels.
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Creator
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Felemban, Bassem, Gordon, Ali, Moslehy, Faissal, Bai, Yuanli, Nam, Boo Hyun, University of Central Florida
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Abstract / Description
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For many candidate materials, constitutive models and their parameters are identified using uniaxial test data. Real components, however, generally operate in a multi-axial loading environments. Consequently, constitutive models deployed by uniaxial conditions may carry over to service conditions with inherit limitations. Research is proposed to determine the constitutive model constants for the creep and plasticity responses of a material via multi-axial fatigue testing which may contain...
Show moreFor many candidate materials, constitutive models and their parameters are identified using uniaxial test data. Real components, however, generally operate in a multi-axial loading environments. Consequently, constitutive models deployed by uniaxial conditions may carry over to service conditions with inherit limitations. Research is proposed to determine the constitutive model constants for the creep and plasticity responses of a material via multi-axial fatigue testing which may contain ratcheting. It is conjectured that directly regressing data under conditions that favor those of actual service use will lead to more accurate modeling under these conditions, as well as a reduced consumption of model development resources. Application of observations of multiaxial loading in the determination of constitutive modeling constants and model selection represents a paradigm shift for material characterization. Numerical simulation and experimentation are necessary for material selection for application at high temperature. The candidate material used in this study is primarily applied for structural components in high-temperature environments for steam generating systems (-) 304 stainless steel. It confers an excellent balance of ductility, corrosion resistance, and creep resistance at moderate temperatures (i.e., up to 550?C). Under service conditions, both creep and cyclic plasticity can occur under either isothermal or non-isothermal conditions. Accurate deformation modeling and life prediction of these structures only achieved with an accurate understanding of how this and other key alloys behave under complex conditions. This research conveys a proposed methodology that can be used to apply creep and plasticity constitutive models that correlate with experimental data. Several creep and plasticity models are examined to augment the accuracy of the models. These results are presented to illustrate modeling performance. Based on this idea has been determined that novel methods of measuring the accuracy of modeling be needed, as well as methods for optimizing material response under multiaxial conditions. The models are applied under service-like conditions to gain an understanding of how this and other key alloys behave under complex conditions. This research will study the complex tensile-torsion loading to determine the constitutive constants for material, and thus will decrease the number of uniaxial experiments. Additionally, combined analytical and experimental methods will be used to establish the Bree diagram for elevated temperature tensile-torsion responses. This deformation mechanism map has been useful as a design tool for materials undergoing ratcheting.
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Date Issued
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2017
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Identifier
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CFE0006875, ucf:51760
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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/CFE0006875
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Title
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Shifted Plastic Hinge Column Connections Using Grouted Sleeves for Accelerated Bridge Construction.
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Creator
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Al-Jelawy, Haider, Mackie, Kevin, Gou, Jihua, Chopra, Manoj, University of Central Florida
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Abstract / Description
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Accelerated bridge construction (ABC) is being increasingly used in new bridge construction and repair. ABC typically requires prefabricated elements joined with mechanical couplers. Grouted sleeves (GSs) offer good construction tolerances and load transfer between precast elements. However, previous research identified some performance issues with precast columns employing GS connections for seismic regions. Therefore, there is a need to develop improved connection details. This research...
Show moreAccelerated bridge construction (ABC) is being increasingly used in new bridge construction and repair. ABC typically requires prefabricated elements joined with mechanical couplers. Grouted sleeves (GSs) offer good construction tolerances and load transfer between precast elements. However, previous research identified some performance issues with precast columns employing GS connections for seismic regions. Therefore, there is a need to develop improved connection details. This research consists of three components; testing of six large-scale precast reinforced concrete column models, a series of individual component tests on GS bar splices, and analytical studies. Large-scale, precast column models were designed and experimentally tested using a shifted plastic hinge (SPH) concept to minimize the damage in the capacity-protected elements and retain the column ductility. The column testing matrix considered aspect ratio, moment gradient, and splicing details. Column models were tested in an upright cantilever configuration under quasi-static cyclic load. Results showed that SPH can be used for both flexural and flexural-shear columns. Two types of component tests were performed: tensile tests to quantify the tensile behavior of the splices, and strain penetration tests to quantify the slip at the sleeve ends. The tests were used to obtain constitutive models for the bond-slip behavior of the GS splices.Results showed that GS splices developed the full ultimate stress of the spliced bars and that the slip at sleeve ends can considerably influence the global behavior of the precast columns. The analytical models were developed in OpenSees using fiber-based beams models and they incorporated the calibrated bond-slip models of GS splices. The large-scale column tests were simulated and compared with respective experimental results. Analytical results showed that the developed models were able to mimic the column behavior and can be used for analysis of GS precast columns.
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Date Issued
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2017
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Identifier
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CFE0006851, ucf:51739
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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/CFE0006851
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Title
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A Time-Course Analysis of Behavioral Plasticity and Differential Gene Expression Patterns in Response to Density in Schistocerca americana (Orthoptera: Acrididae).
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Creator
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Gotham, Steven, Song, Hojun, Vonkalm, Laurence, Fedorka, Kenneth, University of Central Florida
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Abstract / Description
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Phenotypic plasticity is the ability of the genotype to express alternative phenotypes in response to different environmental conditions and this is considered to be an adaptation in which a species can survive and persist in a rapidly changing environment. Some grasshoppers and locusts are capable of expressing an extreme form of density-dependent phenotypic plasticity, known as locust phase polyphenism. At low population density, the individuals typically have a cryptic coloration as nymphs...
Show morePhenotypic plasticity is the ability of the genotype to express alternative phenotypes in response to different environmental conditions and this is considered to be an adaptation in which a species can survive and persist in a rapidly changing environment. Some grasshoppers and locusts are capable of expressing an extreme form of density-dependent phenotypic plasticity, known as locust phase polyphenism. At low population density, the individuals typically have a cryptic coloration as nymphs, are less active, and only seek out conspecifics for reproductive purposes. At high density, however, they develop a drastically different phenotype in which they have a conspicuous coloration, are much more active, and tend to stay together in large groups. The American Birdwing grasshopper, Schistocerca americana, is a non-swarming species related to the desert locust, S. gregaria, which shows density-dependent phenotypic plasticity in behavior, color, and morphology. In this thesis, I have identified the duration of crowding necessary for a 6th instar S. americana reared in the isolated condition to express the typical crowded behavior. The behavior changed after just one hour of crowding and the effect of crowding diminished after 48 hours to near-complete isolated behavior. In reverse, the crowded condition was isolated, but behavior did not significantly change over time. Gene expression of the following three genes suspected of having a role in behavior change were investigated based on studies of S. gregaria: protein kinase A (PKA), L-Tryptophan-5-monooxygenase (T-5), and Aromatic L-amino acid decarboxylase (Decarb). T-5 was up-regulated in the long-term isolated condition compared to the long-term crowded condition. T-5 and Decarb were up-regulated in isolated individuals that were crowded for 10 hours compared to the long-term isolated condition. This study represents a novel contribution in the study of phenotypic plasticity as it establishes the time course of behavioral and molecular plasticity in a non-swarming grasshopper for the first time.
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Date Issued
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2014
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Identifier
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CFE0005799, ucf:50049
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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/CFE0005799
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Title
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Complementary Layered Learning.
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Creator
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Mondesire, Sean, Wu, Annie, Wiegand, Rudolf, Sukthankar, Gita, Proctor, Michael, University of Central Florida
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Abstract / Description
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Layered learning is a machine learning paradigm used to develop autonomous robotic-based agents by decomposing a complex task into simpler subtasks and learns each sequentially. Although the paradigm continues to have success in multiple domains, performance can be unexpectedly unsatisfactory. Using Boolean-logic problems and autonomous agent navigation, we show poor performance is due to the learner forgetting how to perform earlier learned subtasks too quickly (favoring plasticity) or...
Show moreLayered learning is a machine learning paradigm used to develop autonomous robotic-based agents by decomposing a complex task into simpler subtasks and learns each sequentially. Although the paradigm continues to have success in multiple domains, performance can be unexpectedly unsatisfactory. Using Boolean-logic problems and autonomous agent navigation, we show poor performance is due to the learner forgetting how to perform earlier learned subtasks too quickly (favoring plasticity) or having difficulty learning new things (favoring stability). We demonstrate that this imbalance can hinder learning so that task performance is no better than that of a sub-optimal learning technique, monolithic learning, which does not use decomposition. Through the resulting analyses, we have identified factors that can lead to imbalance and their negative effects, providing a deeper understanding of stability and plasticity in decomposition-based approaches, such as layered learning.To combat the negative effects of the imbalance, a complementary learning system is applied to layered learning. The new technique augments the original learning approach with dual storage region policies to preserve useful information from being removed from an agent's policy prematurely. Through multi-agent experiments, a 28% task performance increase is obtained with the proposed augmentations over the original technique.
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Date Issued
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2014
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Identifier
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CFE0005213, ucf:50626
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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/CFE0005213
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Title
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Ultra-High Performance Concrete for Precast Seismic Bridge Column Connection.
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Creator
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Chan, Titchenda, Mackie, Kevin, Catbas, Necati, Chopra, Manoj, Bai, Yuanli, University of Central Florida
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Abstract / Description
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Accelerated bridge construction (ABC) utilizes prefabricated bridge elements constructed off-site, delivered, and assembled on-site to expedite construction time and reduce traffic disruption. ABC has been increasingly used for super- and sub-structure elements in low seismic regions. However, its application in medium and high seismic regions remain limited, particularly for precast columns where connections typically coincide with plastic hinge (PH) regions. Ultra-high performance concrete ...
Show moreAccelerated bridge construction (ABC) utilizes prefabricated bridge elements constructed off-site, delivered, and assembled on-site to expedite construction time and reduce traffic disruption. ABC has been increasingly used for super- and sub-structure elements in low seismic regions. However, its application in medium and high seismic regions remain limited, particularly for precast columns where connections typically coincide with plastic hinge (PH) regions. Ultra-high performance concrete (UHPC), characterized by high compressive and tensile strength, and superior bond properties, is a potential material that can mitigate PH damage and enhance load transfer. This research proposes a new and simple damage tolerant precast column connection for use in medium and high seismic regions. The connection laps the column longitudinal reinforcement with footing dowels using a short splice length, a practical concrete cover, no shear reinforcement, and the shifted PH concept to prevent footing damage. Two 0.42-scale precast columns with different shear span ratios were tested under reversed cyclic loading to investigate the proposed connection relative to previously tested cast-in-place specimens. Results showed the connection performed well in shear, developed column longitudinal bars, shifted PH formation above the UHPC connection, and exhibited high lateral capacity and ductility. Twenty-seven pullout and lap splice beams were tested to study the bond of reinforcement in UHPC under different parameters and stress states. Results indicated significant bond strength improvement and splice length reduction compared with conventional concrete. The pullout specimens were simulated using the OpenSees framework to propose reinforcing steel in UHPC bond-slip models where existing studies in the literature were limited. The models were incorporated into the numerical modeling of the precast columns using one-dimensional fiber-section and two-dimensional plane stress nonlinear analyses. Results from the two modeling methods showed good agreement with the experiments, with the calibrated bond-slip models providing a good representation of load transfer in the connection.
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Date Issued
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2019
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Identifier
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CFE0007610, ucf:52534
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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/CFE0007610
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Title
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A Hybrid Constitutive Model For Creep, Fatigue, And Creep-Fatigue Damage.
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Creator
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Stewart, Calvin, Gordon, Ali, Nicholson, David, Moslehy, Faissal, University of Central Florida
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Abstract / Description
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In the combustion zone of industrial- and aero- gas turbines, thermomechanical fatigue (TMF) is the dominant damage mechanism. Thermomechanical fatigue is a coupling of independent creep, fatigue, and oxidation damage mechanisms that interact and accelerate microstructural degradation. A mixture of intergranular cracking due to creep, transgranular cracking due to fatigue, and surface embrittlement due to oxidation is often observed in gas turbine components removed from service. The current...
Show moreIn the combustion zone of industrial- and aero- gas turbines, thermomechanical fatigue (TMF) is the dominant damage mechanism. Thermomechanical fatigue is a coupling of independent creep, fatigue, and oxidation damage mechanisms that interact and accelerate microstructural degradation. A mixture of intergranular cracking due to creep, transgranular cracking due to fatigue, and surface embrittlement due to oxidation is often observed in gas turbine components removed from service. The current maintenance scheme for gas turbines is to remove components from service when any criteria (elongation, stress-rupture, crack length, etc.) exceed the designed maximum allowable. Experimental, theoretical, and numerical analyses are performed to determine the state of the component as it relates to each criterion (a time consuming process). While calculating these metrics individually has been successful in the past, a better approach would be to develop a unified mechanical modeling that incorporates the constitutive response, microstructural degradation, and rupture of the subject material via a damage variable used to predict the cumulative (")damage state(") within a component. This would allow for a priori predictions of microstructural degradation, crack propagation/arrest, and component-level lifing. In this study, a unified mechanical model for creep-fatigue (deformation, cracking, and rupture) is proposed. It is hypothesized that damage quantification techniques can be used to develop accurate creep, fatigue, and plastic/ductile cumulative- nonlinear- damage laws within the continuum damage mechanics principle. These damage laws when coupled with appropriate constitutive equations and a degrading stiffness tensor can be used to predict the mechanical state of a component. A series of monotonic, creep, fatigue, and tensile-hold creep-fatigue tests are obtained from literature for 304 stainless steel at 600(&)deg;C (1112(&)deg;F) in an air. Cumulative- nonlinear- creep, fatigue, and a coupled creep-fatigue damage laws are developed. The individual damage variables are incorporated as an internal state variable within a novel unified viscoplasticity constitutive model (zero yield surface) and degrading stiffness tensor. These equations are implemented as a custom material model within a custom FORTRAN one-dimensional finite element code. The radial return mapping technique is used with the updated stress vector solved by Newton-Raphson iteration. A consistent tangent stiffness matrix is derived based on the inelastic strain increment. All available experimental data is compared to finite element results to determine the ability of the unified mechanical model to predict deformation, damage evolution, crack growth, and rupture under a creep-fatigue environment.
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Date Issued
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2013
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Identifier
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CFE0005061, ucf:49985
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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/CFE0005061
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Title
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A study on the plasticity and fracture of AISI 4340 steel under different loading conditions considering heat treatment and micromechanics.
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Creator
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Ghazali, Sami, Bai, Yuanli, Kassab, Alain, Kwok, Kawai, Nam, Boo Hyun, University of Central Florida
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Abstract / Description
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Accurate predictions of material strength under different loading conditions with large plastic deformation and ductile fracture are of great importance. This dissertation aims to develop an essential understanding of ductile fracture of AISI 4340 steel alloy using both empirical and micromechanics based models. For this purpose, 29 specimens of different geometries with different heat-treatments were designed to investigate the effects of stress states. These specimens are: (a) 13 round bars...
Show moreAccurate predictions of material strength under different loading conditions with large plastic deformation and ductile fracture are of great importance. This dissertation aims to develop an essential understanding of ductile fracture of AISI 4340 steel alloy using both empirical and micromechanics based models. For this purpose, 29 specimens of different geometries with different heat-treatments were designed to investigate the effects of stress states. These specimens are: (a) 13 round bars with different notches (axial symmetric tension); (b) 13 flat grooved specimens with different grooves; (c) 3 small round cylinders. Mechanical tests up to fracture were conducted on these specimens to characterize the influence of hydrostatic stress and Lode angle on material plasticity and fracture. Scanning electron microscopy (SEM) observations were performed on both original and fractured specimens to investigate different micromechanical revelations and features. The plasticity model with pressure and Lode angle effects (PPL model) and the modified Mohr-Coulomb (MMC) fracture criterion were used to predict plastic flow and fracture initiation behaviors under different loading conditions in finite element simulations. A model optimization method using ISIGHT was set up to achieve simulation results that were well correlated with experimental data. The effects of heat-treatment on material strength and ductility of AISI 4340 steel were also discussed. This work was further carried onto the microvoids based metal plasticity theory. The well-known Gurson-Tvergaard-Needleman (GTN) model was calibrated for AISI 4340 steel. It is found that the GTN model is not sufficient in simulating test data for the 16 Rockwell hardness plane strain specimens. Therefore, The GTN model is modified to include the Lode angle dependence on matrix material plasticity. It is also found that using afixed or constant microvoid volume fraction at failure (ff) for all loading conditions is inadequate. Following a similar derivation of the MMC fracture model, the microvoid volume fraction at failure (ff) becomes a function of both stress triaxiality and Lode angle. This new criterion is named (GTN-MMC). The proposed plasticity and fracture models were implemented into ABAQUS through a user-defined material subroutine (VUMAT) for FE simulations. Good correlations were achieved between experimental results and numerical simulations
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Date Issued
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2018
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Identifier
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CFE0007004, ucf:52026
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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/CFE0007004
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Title
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A Study On The Plasticity And Fracture Behaviors Of Inconel 718 Under Multiaxial Stress And Extremely Low Cycle Fatigue Loadings.
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Creator
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Algarni, Mohammed, Bai, Yuanli, Gordon, Ali, Gou, Jihua, University of Central Florida
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Abstract / Description
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Engineering materials and structures are usually subjected to multiaxial stress states loading due to geometrical effects, residual stresses, or multi-directional loading. Ductile fracture and Extremely Low Cycle Fatigue (ELCF), less than 100 cycles to fail, are two common and co-exist failure modes in many engineering structures. However, the linkage between these two failure modes under multi-axial loading conditions has never been systematically studied. This research summarizes an...
Show moreEngineering materials and structures are usually subjected to multiaxial stress states loading due to geometrical effects, residual stresses, or multi-directional loading. Ductile fracture and Extremely Low Cycle Fatigue (ELCF), less than 100 cycles to fail, are two common and co-exist failure modes in many engineering structures. However, the linkage between these two failure modes under multi-axial loading conditions has never been systematically studied. This research summarizes an extensive work of experimental and numerical studies of ductile fracture and ELCF under different stress states for nickel-base superalloy material (")IN718(") under room temperature. Specially designed specimens and tests were used to achieve desired multi-axial loading conditions. Four types of specimens with four different shapes, total of 16 specimens, were tested until complete fracture. Two groups of tests were conducted: (a) round bar specimens with different notches; (b) plane strain specimens. Experimental data of force-displacement curves and strain-life graph were plotted for analysis. The first part of this research focuses on a numerical study of monotonic tensile loading with different stress states. This part of the investigation deeply studies the dependency of the hydrostatic stress (related to stress triaxiality) and the normalized third invariant of the deviatoric stress (related to Lode angle parameter) in plastic behavior and ductile fracture. Constitutive plasticity model proposed by Bai (&) Wierzbicki and the modified Mohr-Coulomb (MMC) ductile fracture model were adapted with several extensions. The plasticity model and ductile fracture criterion were implemented into ABAQUS through a user-defined material subroutine (VUMAT). Extensive experimental results are used to calibrate the models. After setting up the parameter optimization during model calibration, the experimental results and numerical simulations were well correlated in both plasticity deformation and fracture initiation. A 3D fracture locus of Inconel 718 was constructed by knowing the strain at fracture, stress triaxiality, and normalized Lode angle of the tested samples. By introducing a suitable element post-failure behavior, not only the fracture initiation but also the fracture propagation modes are successfully predicted in finite element simulations for monotonic loading.The second part extensively investigates ELCF on IN718. The IN718 cyclic plasticity behavior and the Bauschinger effect are studied and simulated using the well-known nonlinear kinematic hardening law by J. L. Chaboche and his co-workers under different strain amplitudes and different stress states. Moreover, the Voc(&)#233; isotropic hardening law was applied in combination with the Bai-Wierzbicki plasticity model. The Bai-Wierzbicki plasticity model was used to capture the effect of different stress states on ELCF based on the stress triaxiality and Lode angle parameters. On the other hand, the modified Mohr(-)Coulomb (MMC) ductile fracture model for monotonic loading was extended by a new damage evolution rule to cover the ELCF regime. A new parameter was introduced to represent the effect of the cyclic loading at ELCF. The new parameter is responsible for capturing the change of non-proportional loading direction between the current stress and the backstress tensors. The model explores the underlying damage and fracture mechanisms through the equivalent plastic strain evolution under cycling loading. Finally, the mechanism linkage between these two failure modes was studied. A comparison between the experimental data and the finite element simulation results (by Abaqus/Explicit) shows very good correlations. In addition, fractographic examinations, analysis, and finite element simulations are presented.
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Date Issued
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2017
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Identifier
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CFE0006553, ucf:51338
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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/CFE0006553
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Title
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Study On Anisotropic Plasticity And Fracture Of Lightweight Metal Sheets.
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Creator
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Jia, Yueqian, Bai, Yuanli, Kassab, Alain, Raghavan, Seetha, Gou, Jihua, Wu, Thomas, University of Central Florida
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Abstract / Description
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How to reduce weight and increase fuel efficiency is a critical challenge in transportation industries. One way to resolve the problem is to adopting lightweight alloys (i.e. advanced high strength steel, aluminum alloys, or magnesium alloy) in structure designs and manufacturing. Fully understanding the mechanical properties of these materials is a key step.In order to fully characterize the plasticity and fracture of magnesium AZ31B-H24 sheets, a set of mechanical experiments (170 in total)...
Show moreHow to reduce weight and increase fuel efficiency is a critical challenge in transportation industries. One way to resolve the problem is to adopting lightweight alloys (i.e. advanced high strength steel, aluminum alloys, or magnesium alloy) in structure designs and manufacturing. Fully understanding the mechanical properties of these materials is a key step.In order to fully characterize the plasticity and fracture of magnesium AZ31B-H24 sheets, a set of mechanical experiments (170 in total) were performed under both monotonic and non-proportional loading conditions, including monotonic uniaxial tension, notch tension, in-plane uniaxial compression, wide compression (or called biaxial compression), plane strain compression, through-thickness compression, in-plane shear, punch test, uniaxial compression-tension reverse loading, and two-step uniaxial tension (cross-loading).Both the plastic strain histories and stress responses were obtained under the above loading conditions, which give a comprehensive picture of mechanical behaviors of this material. No apparent cross-hardening effect was observed for this material.An extended orthotropic yield criterion involving two linear anisotropic transformation tensors, CPB06ex2, in conjunction with its associated flow rule was fully calibrated to describe both the anisotropy in plastic flow and tension-compression asymmetry in stress-strain behaviors.A fully modularized framework to combine isotropic, kinematic, and cross hardening behaviors was established under non-monotonic loading conditions. Three sets of state variables were defined and applied to consider the effects of, a) loading history, b) twinning and de-twinning and c) different pre-strain.In order to predict ductile fracture of metal sheets, the (")mixed(") stress/strain invariants based Modified-Mohr-Coulomb (MMC) fracture model was transferred into an all-strain based MMC (eMMC) model under plane stress condition, predicting the fracture strain dependent on strain ratio or ? angle, instead of stress triaxiality and Lode angle parameter. The strain ratio or ? angle could be directly measured by digital image correlation (DIC), while the latter required finite element analysis to be determined. This method makes it possible to study material fracture behavior while bypassing plasticity. The eMMC fracture locus can be fully calibrated by fracture strains directly measured from DIC. The fracture strain was also extended by a linear transformation operating to the plastic strain tensor to incorporate the fracture anisotropy. All models were implemented into Abaqus/Explicit as a user material subroutine (VUMAT). Good prediction capability has been demonstrated for magnesium AZ31B-H24 sheets by FE simulation using shell elements.The current framework was also applied for TRIP780, BH240, DP600, and EDDQ steel sheets with adjustment, under different loading conditions. The FE simulation results for TRIP780 correlated well with experimental data under different monotonic loading conditions. The analytical results for BH240, DP600, and EDDQ demonstrated good prediction capability for cross-hardening behavior, and validated by the non-proportional experimental data under two-stage uniaxial tension.
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Date Issued
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2016
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Identifier
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CFE0006121, ucf:51165
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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/CFE0006121
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Title
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DIFFRACTION STUDIES OF DEFORMATION IN SHAPE MEMORY ALLOYS AND SELECTED ENGINEERING COMPONENTS.
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Creator
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RATHOD, CHANDRASEN, Vaidyanathan, Raj, University of Central Florida
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Abstract / Description
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Deformation phenomena in shape memory alloys involve stress-, temperature-induced phase transformations and crystallographic variant conversion or reorientation, equivalent to a twinning operation. In near equiatomic NiTi, Ti rich compositions can exist near room temperature as a monoclinic B19' martensitic phase, which when deformed undergoes twinning resulting in strains as large as 8%. Upon heating, the martensite transforms to a cubic B2 austenitic phase, thereby recovering the strain and...
Show moreDeformation phenomena in shape memory alloys involve stress-, temperature-induced phase transformations and crystallographic variant conversion or reorientation, equivalent to a twinning operation. In near equiatomic NiTi, Ti rich compositions can exist near room temperature as a monoclinic B19' martensitic phase, which when deformed undergoes twinning resulting in strains as large as 8%. Upon heating, the martensite transforms to a cubic B2 austenitic phase, thereby recovering the strain and exhibiting the shape memory effect. Ni rich compositions on the other hand can exist near room temperature in the austenitic phase and undergo a reversible martensitic transformation on application of stress. Associated with this reversible martensitic transformation are macroscopic strains, again as large as 8%, which are also recovered and resulting in superelasticity. This work primarily focuses on neutron diffraction measurements during loading at the Los Alamos Neutron Science Center at Los Alamos National Laboratory. Three phenomena were investigated: First, the phenomena of hysteresis reduction and increase in linearity with increasing plastic deformation in superelastic NiTi. There is usually a hysteresis associated with the forward and reverse transformations in superelastic NiTi which translates to a hysteresis in the stress-strain curve during loading and unloading. This hysteresis is reduced in cold-worked NiTi and the macroscopic stress-strain response is more linear. This work reports on measurements during loading and unloading in plastically deformed (up to 11%) and cycled NiTi. Second, the tension-compression stress-strain asymmetry in martensitic NiTi. This work reports on measurements during tensile and compressive loading of polycrystalline shape-memory martensitic NiTi with no starting texture. Third, a heterogeneous stress-induced phase transformation in superelastic NiTi. Measurements were performed on a NiTi disc specimen loaded laterally in compression and associated with a macroscopically heterogeneous stress state. For the case of superelastic NiTi, the experiments related the macroscopic stress-strain behavior (from an extensometer or an analytical approach) with the texture, phase volume fraction and strain evolution (from neutron diffraction spectra). For the case of shape memory NiTi, the macroscopic connection was made with the texture and strain evolution due to twinning and elastic deformation in martensitic NiTi. In all cases, this work provided for the first time insight into atomic-scale phenomena such as mismatch accommodation and martensite variant selection. The aforementioned technique of neutron diffraction for mechanical characterization was also extended to engineering components and focused mainly on the determination of residual strains. Two samples were investigated and presented in this work; first, a welded INCONEL 718 NASA space shuttle flow liner was studied at 135 K and second, Ti-6Al-4V turbine blade components were investigated for Siemens Westinghouse Power Corporation. Lastly, also reported in this dissertation is a refinement of the methodology established in the author's masters thesis at UCF that used synchrotron x-ray diffraction during loading to study superelastic NiTi. The Los Alamos Neutron Science Center is a national user facility funded by the United States Department of Energy, Office of Basic Energy Sciences, under Contract No. W-7405-ENG-36. The work reported here was made possible by grants to UCF from NASA (NAG3-2751), NSF CAREER (DMR-0239512), Siemens Westinghouse Power Corporation and the Space Research Initiative.
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Date Issued
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2005
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Identifier
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CFE0000723, ucf:46608
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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/CFE0000723