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Title: Heat Transfer in a Coupled Impingement-Effusion Cooling System.
Creator: Miller, Mark, Kapat, Jayanta, Deng, Weiwei, Gordon, Ali, University of Central Florida
Abstract / Description: The efficiency of air-breathing gas turbine engines improves as the combustion temperature increases. Therefore, modern gas turbines operate at temperatures greater than the melting temperature of hot-gas-path components, and cooling must be introduced in order to maintain mechanical integrity of those components. Two highly effective techniques used in modern designs for this purpose are impingement cooling and use of coolant film on hot-gas-path surface introduced through discrete film or...
Show moreThe efficiency of air-breathing gas turbine engines improves as the combustion temperature increases. Therefore, modern gas turbines operate at temperatures greater than the melting temperature of hot-gas-path components, and cooling must be introduced in order to maintain mechanical integrity of those components. Two highly effective techniques used in modern designs for this purpose are impingement cooling and use of coolant film on hot-gas-path surface introduced through discrete film or effusion holes. In this study, these two mechanisms are coupled into a single prototype cooling system. The heat transfer capability of this system is experimentally determined for a variety of different geometries and coolant flow rates.This study utilizes Temperature Sensitive Paint (TSP) in order to measure temperature distribution over a surface, which allowed for local impingement Nusselt number, film cooling effectiveness, and film cooling heat transfer enhancement profiles to be obtained. In addition to providing quantitative heat transfer data, this method allowed for qualitative investigation of the flow behavior near the test surface. Impinging jet-to-target-plate spacing was varied over a large range, including several tall impingement scenarios outside the published limits. Additionally, both in-line and staggered effusion arrangements were studied, and results for normal injection were compared to full coverage film cooling with inclined- and compound-angle injection. Effects of impingement and effusion cooling were combined to determine the overall cooling effectiveness of the system.It is shown that low impingement heights produce the highest Nusselt number, and that large jet-to-jet spacing reduces coolant flow rate while maintaining moderate to high heat transfer rates. Staggered effusion configurations exhibit superior performance to in-line configurations, as jet interference is reduced and surface area coverage is improved. Coolant to mainstream flow mass flux ratios greater than unity result in jet blow-off and reduced effectiveness. The convective heat transfer coefficient on the film cooled surface is higher than a similar surface without coolant injection due to the generation of turbulence associated with jet-cross flow interaction.
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Date Issued: 2011
Identifier: CFE0004140, ucf:49042
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004140

Title: Numerical study on reinforcement mechanism of copper/carbon nanotubes composite.
Creator: Long, Xiang, Bai, Yuanli, Gordon, Ali, Chen, Quanfang, University of Central Florida
Abstract / Description: Because of its high stiffness, carbon nanotubes (CNTs) are considered as one of the widely used reinforcement materials in the metal matrix composites. In this thesis, finite element (FE) models were built in Ls-Dyna3D to simulate Copper/CNTs composite deformation and fracture, and to explore CNTs reinforcement mechanisms. Several possible mechanisms were discussed. Deformation and failure of Cu/CNT composites were studied numerically using unit cell FE models, which consist of both metal...
Show moreBecause of its high stiffness, carbon nanotubes (CNTs) are considered as one of the widely used reinforcement materials in the metal matrix composites. In this thesis, finite element (FE) models were built in Ls-Dyna3D to simulate Copper/CNTs composite deformation and fracture, and to explore CNTs reinforcement mechanisms. Several possible mechanisms were discussed. Deformation and failure of Cu/CNT composites were studied numerically using unit cell FE models, which consist of both metal matrix and CNTs. The simulation results have been verified by existing experiment data reported by Chen's group. The matrix material was modeled as elasto-plastic ductile solids. The CNTs material properties were taken from literature results using molecular dynamics simulation. FE simulations have showed that CNTs deformation exceeds material elastic limit, which means that CNTs plasticity should be taken into account as well. 2D unit cell models were developed using axial symmetric elements with suitable boundary conditions. Several mechanisms are found to affect CNTs reinforcement prediction. The first one is the boundary condition imposed in the models. The CNTs significantly affect the plastic flow of copper during plastic deformation, which is one important reinforcement mechanism. The second reinforcement mechanism is found to be the hardening zone of Cu matrix around CNTs, which is introduced by mismatch of coefficient of thermal expansion (CTE).A round of parametric studies was performed to investigate the effects of several modeling parameters in the FE simulations; these parameters include the volume fraction of CNTs, aspect ratio of CNTs, the size of hardening zone, and the residual plastic strain in the zone. A tool combining Matlab and Ls-Dyna was developed to automatically build 2D unit cell models and automatically post-process simulation results. Picking up suitable parameters, 2D unit cell model results well predict the experimental results from Chen's group. It should be noted that the interface between Cu and CNTs was assumed to be perfect in FE simulations since no CNTs debonding was observed in the experiments. Also, a 3D unit cell model using tetrahedral elements (with element numbers up to one million) was tentatively developed to obtain more accurate results. The purpose was to explore the interface properties of Cu/CNTs, the effect of CNTs orientation distribution, and the other reinforcement mechanism coming from geometry necessary dislocation (GND) since the size of Cu matrix is divided into nano scales by CNTs. 3D unit models are also used to verify the 2D unit cell one, which is a simplified and effective approach. Very interesting results was observed in this part of study. Further works are needed to overcome the difficulties in 3D modeling and the limitation of current CPU speed.
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Date Issued: 2012
Identifier: CFE0004197, ucf:49019
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004197

Title: Characterization of Dynamic and Static Mechanical Behavior of Polyetherimide.
Creator: Mutter, Nathan, Gordon, Ali, Raghavan, Seetha, Xu, Chengying, University of Central Florida
Abstract / Description: Polymers are increasingly being used in engineering designs due to their favorable mechanical properties such as high specific strength, corrosive resistance, manufacturing flexibility. The understanding of the mechanical behavior of these polymers under both static and dynamic loading is critical for their optimal implementation in engineering applications. One such polymer utilized in a wide variety of applications from medical instrumentation to munitions is Polyetherimide, referred to as...
Show morePolymers are increasingly being used in engineering designs due to their favorable mechanical properties such as high specific strength, corrosive resistance, manufacturing flexibility. The understanding of the mechanical behavior of these polymers under both static and dynamic loading is critical for their optimal implementation in engineering applications. One such polymer utilized in a wide variety of applications from medical instrumentation to munitions is Polyetherimide, referred to as Ultem. This thesis characterizes both the static and dynamic mechanical behavior of Ultem 1000 through experimental methods and numerical simulations. Standard compression experiments were conducted on and MTS test frame to characterize the elastic-plastic behavior of Ultem 1000 under quasi-static conditions. The dynamic response of the material was investigated at very high strain rates using a custom built miniaturized Kolsky bar apparatus. The smaller Kolsky bar configuration was chosen over the conventional Kolsky device to increase the maximum capable strain rates and to reduce common experimental problems such as wave dispersion, friction, and stress equilibrium. Since a universal test standard for this apparatus is not available, the details of the design, construction, and experimental procedures of this device are provided. The results of the high strain rate testing revealed a bilinear relationship between the material yield stress and strain rate. This relationship was modeled using the Ree-Eyring two stage activation process equation.
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Date Issued: 2012
Identifier: CFE0004238, ucf:49533
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004238

Title: Thermomechanical Fatigue Life Prediction of Notched 304 Stainless Steel.
Creator: Karl, Justin, Gordon, Ali, Bai, Yuanli, Raghavan, Seetha, Nicholson, David, University of Central Florida
Abstract / Description: The behavior of materials as they are subjected to combined thermal and mechanical fatigue loads is an area of research that carries great significance in a number of engineering applications. Power generation, petrochemical, and aerospace industries operate machinery with expensive components that undergo repeated applications of force while simultaneously being exposed to variable temperature working fluids. A case of considerable importance is found in steam turbines, which subject blades...
Show moreThe behavior of materials as they are subjected to combined thermal and mechanical fatigue loads is an area of research that carries great significance in a number of engineering applications. Power generation, petrochemical, and aerospace industries operate machinery with expensive components that undergo repeated applications of force while simultaneously being exposed to variable temperature working fluids. A case of considerable importance is found in steam turbines, which subject blades to cyclic loads from rotation as well as the passing of heated gases. The complex strain and temperature histories from this type of operation, combined with the geometric profile of the blades, make accurate prediction of service life for such components challenging. Development of a deterministic life prediction model backed by physical data would allow design and operation of turbines with higher efficiency and greater regard for reliability. The majority of thermomechanical fatigue (TMF) life prediction modeling research attempts to correlate basic material property data with simplistic strain and thermal histories. With the exception of very limited cases, these types of efforts have been insufficient and imprecise in their capabilities. Early researchers did not account for the multiple damage mechanisms that operate and interact within a material during TMF loads, and did not adequately address the extent of the relationship between smooth and notched parts. More recent research that adequately recognizes the multivariate nature of TMF develops models that handle life reduction through summation of constitutive damage terms. It is feasible that a modification to the damage-based approach can sufficiently include cases that involve complex geometry. The focus of this research is to construct an experimentally-backed extension of the damage-based approach that improves handling of geometric discontinuities. Smooth and notched specimens of Type 304 stainless steel were subjected to several types of idealized fatigue conditions to assemble a clear picture of the types of damage occurring in a steam turbine and similarly-loaded mechanical systems. These results were compared with a number of idealized TMF experiments, and supplemented by numerical simulation and microscopic observation. A non-uniform damage-summation constitutive model was developed primarily based on physical observations. An additional simplistic model was developed based on phenomenological effect. Findings from this study will be applicable to life prediction efforts in other similar material and load cases.
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Date Issued: 2013
Identifier: CFE0004870, ucf:49666
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004870

Title: Academic Blade Geometries for Baseline Comparisons of Forced Vibration Response Predictions.
Creator: Little, James, Kauffman, Jeffrey, Gordon, Ali, Bai, Yuanli, University of Central Florida
Abstract / Description: Predicting the damping associated with underplatform dampers remains a challenge in turbomachineryblade and friction damper design. Turbomachinery blade forced response analysismethods usually rely on nonlinear codes and reduced order models to predict vibration characteristicsof blades. Two academic blade geometries coupled with underplatform dampers are presentedhere for comparison of these model reduction and forced response simulation techniques. The twoblades are representative of free...
Show morePredicting the damping associated with underplatform dampers remains a challenge in turbomachineryblade and friction damper design. Turbomachinery blade forced response analysismethods usually rely on nonlinear codes and reduced order models to predict vibration characteristicsof blades. Two academic blade geometries coupled with underplatform dampers are presentedhere for comparison of these model reduction and forced response simulation techniques. The twoblades are representative of free-standing turbine blades and exhibit qualitatively similar behavioras highly-complex industrial blades. This thesis fully describes the proposed academic bladegeometries and models; it further analyzes and predicts the blades forced response characteristicsusing the same procedure as industry blades. This analysis classifies the results in terms of resonancefrequency, vibration amplitude, and damping over a range of aerodynamic excitation toexamine the vibration behavior of the blade/damper system. Additionally, the analysis investigatesthe effect variations of the contact parameters (friction coefficient, damper / platform roughnessand damper mass) have on the predicted blade vibration characteristics, with sensitivities to each parameter. Finally, an investigation of the number of modes retained in the reduced order modelshows convergence behavior as well as providing additional data for comparison with alternativemodel reduction and forced response prediction methods. The academic blade models are shownto behave qualitatively similar to high fidelity industry blade models when the number of retained modes in a modal analysis are varied and behave qualitatively similar under sensitives to designparameters.
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Date Issued: 2017
Identifier: CFE0006616, ucf:51281
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006616

Title: The Mechanical Response and Parametric Optimization of Ankle-Foot Devices.
Creator: Smith, Kevin, Gordon, Ali, Kassab, Alain, Bai, Yuanli, Pabian, Patrick, University of Central Florida
Abstract / Description: To improve the mobility of lower limb amputees, many modern prosthetic ankle-foot devices utilize a so called energy storing and return (ESAR) design. This allows for elastically stored energy to be returned to the gait cycle as forward propulsion. While ESAR type feet have been well accepted by the prosthetic community, the design and selection of a prosthetic device for a specific individual is often based on clinical feedback rather than engineering design. This is due to an incomplete...
Show moreTo improve the mobility of lower limb amputees, many modern prosthetic ankle-foot devices utilize a so called energy storing and return (ESAR) design. This allows for elastically stored energy to be returned to the gait cycle as forward propulsion. While ESAR type feet have been well accepted by the prosthetic community, the design and selection of a prosthetic device for a specific individual is often based on clinical feedback rather than engineering design. This is due to an incomplete understanding of the role of prosthetic design characteristics (e.g. stiffness, roll-over shape, etc.) have on the gait pattern of an individual. Therefore, the focus of this work has been to establish a better understanding of the design characteristics of existing prosthetic devices through mechanical testing and the development of a prototype prosthetic foot that has been numerically optimized for a specific gait pattern. The component stiffness, viscous properties, and energy return of commonly prescribed carbon fiber ESAR type feet were evaluated through compression testing with digital image correlation at select loading angles following the idealized gait from the ISO 22675 standard for fatigue testing. A representative model was developed to predict the stress within each of the tested components during loading and to optimize the design for a target loading response through parametric finite element analysis. This design optimization approach, along with rapid prototyping technologies, will allow clinicians to better identify the role the design characteristics of the foot have on an amputee's biomechanics during future gait analysis.
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Date Issued: 2016
Identifier: CFE0006397, ucf:51502
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006397

Title: A Flexible Physics-Based Lifing Method for Metals Under Creep and Thermomechanical Fatigue.
Creator: Irmak, Firat, Gordon, Ali, Catbas, Necati, Raghavan, Seetha, University of Central Florida
Abstract / Description: This thesis focuses on the development of a flexible, physics-based life prediction approach for steels under complex conditions. Low alloy steels continue to be the materials of choice for large turbomachinery structures experiencing high temperatures for long durations. There has been significant advancement in the research of modern alloys; furthermore, these materials are continue to be utilized in boilers, heat exchanger tubes, and throttle valve bodies in both turbomachinery and...
Show moreThis thesis focuses on the development of a flexible, physics-based life prediction approach for steels under complex conditions. Low alloy steels continue to be the materials of choice for large turbomachinery structures experiencing high temperatures for long durations. There has been significant advancement in the research of modern alloys; furthermore, these materials are continue to be utilized in boilers, heat exchanger tubes, and throttle valve bodies in both turbomachinery and pressure-vessel/piping applications. The material 2.25Cr-1Mo is studied in the present work. The resistance of this alloy to deformation and damage under creep and/or fatigue at elevated temperatures make it appropriate for structures required to endure decades of service. Also, this material displays an excellent balance of ductility, corrosion resistance, and creep strength under aggressive operating conditions. Both creep-fatigue (CF) and thermomechanical fatigue (TMF) have been the limiting factor for most turbine components fabricated from various alloys; therefore, a life prediction approach is constructed for simulating fatigue life for cases where the material is experiencing mechanical loading with thermal cycling. Flexibility is imparted to the model through its ability to emphasize the dominant damage mechanism which may vary among alloys. A material database is developed to improve and compare the model with experimental data. This database contains low cycle fatigue (LCF), creep fatigue (CF), and thermomechanical fatigue (TMF) experiments. Parameters for the model are obtained with regression fits with the support of a broad experimental database. Additionally, the cumulative damage approach, better known as Miner's rule, is used in this study as the fundamental method to combine damage mechanisms. Life predictions are obtained by the usage of a non-interacting creep-plasticity constitutive model capable of simulating not only the temperature- and rate-dependence.
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Date Issued: 2017
Identifier: CFE0006885, ucf:51731
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006885

Title: FUNDAMENTAL UNDERSTANDING OF INTERACTIONS AMONG FLOW, TURBULENCE, AND HEAT TRANSFER IN JET IMPINGEMENT COOLING.
Creator: Hossain, Md. Jahed, Kapat, Jayanta, Ahmed, Kareem, Gordon, Ali, Wiegand, Rudolf, University of Central Florida
Abstract / Description: The flow physics of impinging jet is very complex and is not fully understood yet. The flow field in an impingement problem comprised of three different distinct regions: a free jet with a potential core, a stagnation region where the velocity goes to zero as the jet impinges onto the wall and a creation of wall jet region where the boundary layer grows radially outward after impinging. Since impingement itself is a broad topic, effort is being made in the current study to narrow down on...
Show moreThe flow physics of impinging jet is very complex and is not fully understood yet. The flow field in an impingement problem comprised of three different distinct regions: a free jet with a potential core, a stagnation region where the velocity goes to zero as the jet impinges onto the wall and a creation of wall jet region where the boundary layer grows radially outward after impinging. Since impingement itself is a broad topic, effort is being made in the current study to narrow down on three particular geometric configurations (a narrow wall, an array impingement configuration and a curved surface impingement configuration) that shows up in a typical gas turbine impingement problem in relation to heat transfer. Impingement problems are difficult to simulate numerically using conventional RANS models. It is worth noting that the typical RANS model contains a number of calibrated constants and these have been formulated with respect to relatively simple shear flows. As a result typically these isotropic eddy viscosity models fail in predicting the correct heat transfer value and trend in impingement problem where the flow is highly anisotropic. The common RANS-based models over predict stagnation heat transfer coefficients by as much as 300% when compared to measured values. Even the best of the models, the v^2-f model, can be inaccurate by up to 30%. Even though there is myriad number of experimental and numerical work published on single jet impingement; the knowledge gathered from these works cannot be applied to real engineering impingement cooling application as the dynamics of flow changes completely. This study underlines the lack of experimental flow physics data in published literature on multiple jet impingement and the author emphasized how important it is to have experimental data to validate CFD tools and to determine the suitability of Large Eddy Simulation (LES) in industrial application. In the open literature there is not enough study where experimental heat transfer and flow physics data are combined to explain the behavior for gas turbine impingement cooling application. Often it is hard to understand the heat transfer behavior due to lack of time accurate flow physics data hence a lot of conjecture has been made to explain the phenomena. The problem is further exacerbated for array of impingement jets where the flow is much more complex than a single round jet. The experimental flow field obtained from Particle Image Velocimetry (PIV) and heat transfer data obtained from Temperature Sensitive Paint (TSP) from this work will be analyzed to understand the relationship between flow characteristics and heat transfer for the three types of novel geometry mentioned above.There has not been any effort made on implementing LES technique on array impingement problem in the published literature. Nowadays with growing computational power and resources CFD are widely used as a design tool. To support the data gathered from the experiment, LES is carried out in narrow wall impingement cooling configuration. The results will provide more accurate information on impingement flow physics phenomena where experimental techniques are limited and the typical RANS models yield erroneous resultThe objective of the current study is to provide a better understanding of impingement heat transfer in relation to flow physics associated with it. As heat transfer is basically a manifestation of the flow and most of the flow in real engineering applications is turbulent, it is very important to understand the dynamics of flow physics in an impingement problem. The work emphasis the importance of understanding mean velocities, turbulence, jet shear layer instability and its importance in heat transfer application. The present work shows detailed information of flow phenomena using Particle Image Velocimetry (PIV) in a single row narrow impingement channel. Results from the RANS and LES simulations are compared with Particle Image Velocimetry (PIV) data. The accuracy of LES in predicting the flow field and heat transfer of an impingement problem is also presented the in the current work as it is validated against experimental flow field measured through PIV.Results obtained from the PIV and LES shows excellent agreement for predicting both heat transfer and flow physics data. Some of the key findings from the study highlight the shortcomings of the typical RANS models used for the impingement heat transfer problem. It was found that the stagnation point heat transfer was over predicted by as much as 48% from RANS simulations when compared to the experimental data. A lot of conjecture has been made in the past for RANS' ability to predict the stagnation point heat transfer correctly. The length of the potential core for the first jet was found to be ~ 2D in RANS simulations as oppose to 1D in PIV and LES, confirm the possible underlying reason for this discrepancy. The jet shear layer thickness was underpredicted by ~ 40% in RANS simulations proving the model is not diffusive enough for a flow like jet impingement. Turbulence production due to shear stress was over predicted by ~130% and turbulence production due to normal stresses were underpredicted by ~40 % in RANS simulation very close to the target wall showing RANS models fail where both strain rate and shear stress plays a pivotal role in the dynamics of the flow. In the closing, turbulence is still one of the most difficult problems to solve accurately, as has been the case for about a century. A quote below from the famous mathematician, Horace Lamb (1849-1934) express the level of difficulty and frustration associated with understanding turbulence in fluid mechanics. (")I am an old man now, and when I die and go to heaven there are two matters on which I hope for enlightenment. One is quantum electrodynamics, and the other is the turbulent motion of fluids. And about the former I am rather optimistic.(")Source: http://scienceworld.wolfram.com/biography/Lamb.htmlThis dissertation is expected to shed some light onto one specific example of turbulent flows.
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Date Issued: 2016
Identifier: CFE0006463, ucf:51424
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006463

Title: A Study On The Plasticity And Fracture Behaviors Of Inconel 718 Under Multiaxial Stress And Extremely Low Cycle Fatigue Loadings.
Creator: Algarni, Mohammed, Bai, Yuanli, Gordon, Ali, Gou, Jihua, University of Central Florida
Abstract / Description: 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: 2017
Identifier: CFE0006553, ucf:51338
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006553

Title: Development of Velocity Profile Generating Screens for Gas Turbine Components.
Creator: Tate, Joseph, Kapat, Jayanta, Gordon, Ali, Ahmed, Kareem, University of Central Florida
Abstract / Description: Laboratory experiments on components of complex systems such as gas turbines require many conditions to be met. Requirements to be met in order to simulate real world conditions include inlet flow conditions such as velocity profile, Reynold's number, and temperature. The methodology to be introduced designs a velocity profile generating screen to match real world conditions through the use of perforated plates. The velocity profile generating screen is an array of jets arranged in a manner...
Show moreLaboratory experiments on components of complex systems such as gas turbines require many conditions to be met. Requirements to be met in order to simulate real world conditions include inlet flow conditions such as velocity profile, Reynold's number, and temperature. The methodology to be introduced designs a velocity profile generating screen to match real world conditions through the use of perforated plates. The velocity profile generating screen is an array of jets arranged in a manner to produce sections of different solidities, a ratio of area that obstructs fluid flow compared to that of the total area. In an effort to better understand the interaction between perforated plate sections of different solidities, a collection of experimental data sets is presented to characterize the plates. This includes identification of fluid flow regions with characterization of the flow dynamics, though the analysis of velocity and turbulence decay. The aim of this characterization is to determine how the perforated plate's solidity affects the velocity development downstream and the location at which the velocity profile being produced can be considered complete.
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Date Issued: 2015
Identifier: CFE0006011, ucf:51020
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006011

Title: Continuous Oscillation: Vibrational Effects and Acceptable Frequency Ranges of Small Bore Piping in Field Applications.
Creator: Kasprzyk, Marie, Kauffman, Jeffrey L., Bai, Yuanli, Gordon, Ali, University of Central Florida
Abstract / Description: In turbomachinery, a common failure mode is cracking of welds at the equipment and piping connection point. Each incidence of these cracks causes a forced shutdown to perform repairs that cost millions of dollars. This type of failure is predominately seen in small bore piping, which has a nominal diameter of 2 inches and smaller. This thesis addresses the failure prediction analysis of small bore piping, specifically in turbomachinery applications. Performing failure analysis to predict the...
Show moreIn turbomachinery, a common failure mode is cracking of welds at the equipment and piping connection point. Each incidence of these cracks causes a forced shutdown to perform repairs that cost millions of dollars. This type of failure is predominately seen in small bore piping, which has a nominal diameter of 2 inches and smaller. This thesis addresses the failure prediction analysis of small bore piping, specifically in turbomachinery applications. Performing failure analysis to predict the potential cracking of welds will allow for replacement of the piping during a planned shutdown which in the long term saves money due to costs such as expediting materials, overtime pay, and extended downtime. This analysis uses real-world applications of a chemical plant in Louisiana. The piping analyzed was connected to centrifugal compressors. The data used from these pieces of equipment included the material of construction, the piping schedule, lengths, nominal diameter, and running speeds. Based on research that shows welding the connection point with a full penetration weld greatly increases the life expectancy of the connection, this thesis uses full penetration welds in the analysis. The piping was analyzed using the software ANSYS to perform a finite element analysis, specifically examining the stress due to the induced harmonic forces. It is a common fact that having fewer supports on a vibrating pipe induces greater stresses and strains on the weld connections. Supports installed 12" from the equipment only show one to two ranges of frequencies to avoid compared to the longer piping which has four to five ranges of unacceptable frequencies. Tables are developed to relay acceptable frequencies based on observed stresses of the welds in the model.
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Date Issued: 2017
Identifier: CFE0006749, ucf:51862
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006749

Title: Tensile-Compressive Asymmetry and Anisotropy of Fused Deposition Modeling PLA under Monotonic Conditions.
Creator: Perkowski, Casey, Gordon, Ali, Kassab, Alain, Divo, Eduardo, University of Central Florida
Abstract / Description: Additive Manufacturing (AM) continues to gain popularity for its ability to produce complexly-shaped final use components that are impractical to manufacture by traditional methods; however, additive manufactured parts contain complex mesostructures that result in directionally-dependent mechanical properties that have yet to be fully characterized. This effort demonstrates a framework of experimental and analytical methods needed to characterize the uniaxial monotonic behavior of fused...
Show moreAdditive Manufacturing (AM) continues to gain popularity for its ability to produce complexly-shaped final use components that are impractical to manufacture by traditional methods; however, additive manufactured parts contain complex mesostructures that result in directionally-dependent mechanical properties that have yet to be fully characterized. This effort demonstrates a framework of experimental and analytical methods needed to characterize the uniaxial monotonic behavior of fused deposition modeling PLA using tensile and compressive experiments on specimens printed at various orientations. Based on experimental results, the asymmetry and anisotropy of the tensile and compressive response was analyzed for a candidate material. Specimens from different orientations underwent microscopy and failure surface analysis to correlate test data. The material was observed to exhibit tetragonal behavior with tensile-compressive asymmetry. The experimental and simulated results show a strong correlation. Based on the collection of results, analysis, and computations, this work demonstrates a practice that can be used to characterize similar materials for use in AM components.
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Date Issued: 2017
Identifier: CFE0006778, ucf:51847
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006778

Title: Development and Implementation of a Streamlined Process for the Creation and Mechanization of Negative Poisson's Ratio Meso-Scale Patterns.
Creator: Shuler, Matthew, Gordon, Ali, Kauffman, Jeffrey L., Ghosh, Ranajay, University of Central Florida
Abstract / Description: This thesis focuses on the development a streamlined process used to create novel meso-scale pattern used to induce negative Poisson's ratio (NPR) behavior at the bulk scale. This process includes, the development, optimization, and implementation of a candidate pattern. Currently, the majority of NPR structures are too porous to be utilized in conventional applications. For others, manufacturing methods have yet to realize the meso-scale pattern. Consequently, new NPR meta-materials must be...
Show moreThis thesis focuses on the development a streamlined process used to create novel meso-scale pattern used to induce negative Poisson's ratio (NPR) behavior at the bulk scale. This process includes, the development, optimization, and implementation of a candidate pattern. Currently, the majority of NPR structures are too porous to be utilized in conventional applications. For others, manufacturing methods have yet to realize the meso-scale pattern. Consequently, new NPR meta-materials must be developed in order to confer transformative thermomechanical responses to structures where transverse expansion is more desirable than contraction. For example, materials at high temperature. Additionally, patterns that take into account manufacturing limitations, while maintaining the properties characteristically attached to negative Poisson's Ratio materials, are ideal in order to utilize the potential of NPR structures. A novel NPR pattern is developed, numerically analyzed, and optimized via design of experiments. The parameters of the meso-structure are varied, and the bulk response is studied using finite element analysis (FEA). The candidate material for the study is Medium-Density Fiberboard (MDF). This material is relevant to a variety of applications where multiaxial stresses, particularly compressive, lead to mechanical fatigue. Samples are fabricated through a laser cutting process, and a comparison is drawn through the use of experimental means, including traditional tensile loading tests and digital image correlation (DIC). Various attributes of the elasto-plasticity responses of the bulk structure are used as objectives to guide the optimization process.
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Date Issued: 2017
Identifier: CFE0006795, ucf:51830
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006795

Title: A Full Coverage Film Cooling Study: The Effect of an Alternating Compound Angle.
Creator: Hodges, Justin, Kapat, Jayanta, Gordon, Ali, Vasu Sumathi, Subith, University of Central Florida
Abstract / Description: This thesis is an experimental and numerical full-coverage film cooling study. The objective of this work is the quantification of local heat transfer augmentation and adiabatic film cooling effectiveness for two full-coverage film cooling geometries. Experimental data was acquired with a scientific grade CCD camera, where images are taken over the heat transfer surface, which is painted with a temperature sensitive paint. The CFD component of this study served to evaluate how well the v2-f...
Show moreThis thesis is an experimental and numerical full-coverage film cooling study. The objective of this work is the quantification of local heat transfer augmentation and adiabatic film cooling effectiveness for two full-coverage film cooling geometries. Experimental data was acquired with a scientific grade CCD camera, where images are taken over the heat transfer surface, which is painted with a temperature sensitive paint. The CFD component of this study served to evaluate how well the v2-f turbulence model predicted film cooling effectiveness throughout the array, as compared with experimental data. The two staggered arrays tested are different from one another through a compound angle shift after 12 rows of holes. The compound angle shifts from ?=-45(&)deg; to ?=+45(&)deg; at row 13. Each geometry had 22 rows of cylindrical film cooling holes with identical axial and lateral spacing (X/D=P/D=23). Levels of laterally averaged film cooling effectiveness for the superior geometry approach 0.20, where the compound angle shift causes a decrease in film cooling effectiveness. Levels of heat transfer augmentation maintain values of nearly h/h0=1.2. There is no effect of compound angle shift on heat transfer augmentation observed. The CFD results are used to investigate the detrimental effect of the compound angle shift, while the SST k-? turbulence model shows to provide the best agreement with experimental results.
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Date Issued: 2015
Identifier: CFE0005626, ucf:50228
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0005626

Title: The Influence of Alloying Additions on Diffusion and Strengthening of Magnesium.
Creator: Kammerer, Catherine, Sohn, Yongho, Coffey, Kevin, Challapalli, Suryanarayana, Gordon, Ali, University of Central Florida
Abstract / Description: Magnesium alloys are being developed as advanced materials for structural applications where reduced weight is a primary motivator. Alloying can enhance the properties of magnesium without significantly affecting its density. Essential to alloy development, inclusive of processing parameters, is knowledge of thermodynamic, kinetic, and mechanical behavior of the alloy and its constituents. Appreciable progress has been made through conventional development processes, but to accelerate...
Show moreMagnesium alloys are being developed as advanced materials for structural applications where reduced weight is a primary motivator. Alloying can enhance the properties of magnesium without significantly affecting its density. Essential to alloy development, inclusive of processing parameters, is knowledge of thermodynamic, kinetic, and mechanical behavior of the alloy and its constituents. Appreciable progress has been made through conventional development processes, but to accelerate development of suitable wrought Mg alloys, an integrated Materials Genomic approach must be taken where thermodynamics and diffusion kinetic parameters form the basis of alloy design, process development, and properties-driven applications.The objective of this research effort is twofold: first, to codify the relationship between diffusion behavior, crystal structure, and mechanical properties; second, to provide fundamental data for the purpose of wrought Mg alloy development. Together, the principal deliverable of this work is an advanced understanding of Mg systems. To that end, the objective is accomplished through an aggregate of studies. The solid-to-solid diffusion bonding technique is used to fabricate combinatorial samples of Mg-Al-Zn ternary and Mg-Al, Mg-Zn, Mg-Y, Mg-Gd, and Mg-Nd binary systems. The combinatorial samples are subjected to structural and compositional characterization via Scanning Electron Microscopy with X-ray Energy Dispersive Spectroscopy, Electron Probe Microanalysis, and analytical Transmission Electron Microscopy. Interdiffusion in binary Mg systems is determined by Sauer-Freise and Boltzmann-Matano methods. Kirkaldy's extension of the Boltzmann-Matano method, on the basis of Onsager's formalism, is employed to quantify the main- and cross-interdiffusion coefficients in ternary Mg solid solutions. Impurity diffusion coefficients are determined by way of the Hall method. The intermetallic compounds and solid solutions formed during diffusion bonding of the combinatorial samples are subjected to nanoindentation tests, and the nominal and compositionally dependent mechanical properties are extracted by the Oliver-Pharr method.In addition to bolstering the scantly available experimental data and first-principles computations, this work delivers several original contributions to the state of Mg alloy knowledge. The influence of Zn concentration on Al impurity diffusion in binary Mg(Zn) solid solution is quantified to impact both the pre-exponential factor and activation energy. The main- and cross-interdiffusion coefficients in the ternary Mg solid solution of Mg-Al-Zn are reported wherein the interdiffusion of Zn is shown to strongly influence the interdiffusion of Mg and Al. A critical examination of rare earth element additions to Mg is reported, and a new phase in thermodynamic equilibrium with Mg-solid solution is identified in the Mg-Gd binary system. It is also demonstrated that Mg atoms move faster than Y atoms. For the first time the mechanical properties of intermetallic compounds in several binary Mg systems are quantified in terms of hardness and elastic modulus, and the influence of solute concentration on solid solution strengthening in binary Mg alloys is reported. The most significant and efficient solid solution strengthening is achieved by alloying Mg with Gd. The Mg-Nd and Mg-Gd intermetallic compounds exhibited better room temperature creep resistance than intermetallic compounds of Mg-Al. The correlation between the concentration dependence of mechanical properties and atomic diffusion is deliberated in terms of electronic nature of the atomic structure.
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Date Issued: 2015
Identifier: CFE0005815, ucf:50043
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0005815

Title: A Hybrid Constitutive Model For Creep, Fatigue, And Creep-Fatigue Damage.
Creator: Stewart, Calvin, Gordon, Ali, Nicholson, David, Moslehy, Faissal, University of Central Florida
Abstract / Description: 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: 2013
Identifier: CFE0005061, ucf:49985
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0005061

Title: Quantifying Ultra-high Performance Concrete Flexural System Mechanical Response.
Creator: Xiao, Yulin, Mackie, Kevin, Catbas, Necati, Chopra, Manoj, Gordon, Ali, University of Central Florida
Abstract / Description: The research and application of Ultra-high Performance Concrete (UHPC) has been developedsignificantly within the last 1-2 decades. Due to the specific property of high strength capacity, it is potential to be used in bridge deck system without shear reinforcement so that it provides even lighter self-weight of the deck. However, one of the shear component, dowel action, has not beenadequately investigated in the past. In this dissertation, a particular test was designed and carried out to...
Show moreThe research and application of Ultra-high Performance Concrete (UHPC) has been developedsignificantly within the last 1-2 decades. Due to the specific property of high strength capacity, it is potential to be used in bridge deck system without shear reinforcement so that it provides even lighter self-weight of the deck. However, one of the shear component, dowel action, has not beenadequately investigated in the past. In this dissertation, a particular test was designed and carried out to fully investigate the dowel action response, especially its contribution to shear resistance. In addition, research on serviceability and fatigue behaviors were expanded as well to delete the concern on other factors that may influence the application to the deck system. Both experimental and analytical methods including finite element modeling, OpenSees modeling and other extension studies were presented throughout the entire dissertation where required.
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Date Issued: 2014
Identifier: CFE0005563, ucf:50288
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0005563

Title: The Characterization of the Effects of Stress Concentrations on the Mechanical Behavior of a Micronic Woven Wire Mesh.
Creator: Kraft, Steven, Gordon, Ali, Bai, Yuanli, Gou, Jihua, University of Central Florida
Abstract / Description: Woven structures are steadily emerging as excellent reinforcing components in dual-phase composite materials subjected to multiaxial loads, thermal shock, and aggressive reactants in the environment. Metallic woven wire mesh materials display good ductility and relatively high specific strength and specific resilience. While use of this class of materials is rapidly expanding, significant gaps in mechanical behavior classification remain. This thesis works to address the mechanics of material...
Show moreWoven structures are steadily emerging as excellent reinforcing components in dual-phase composite materials subjected to multiaxial loads, thermal shock, and aggressive reactants in the environment. Metallic woven wire mesh materials display good ductility and relatively high specific strength and specific resilience. While use of this class of materials is rapidly expanding, significant gaps in mechanical behavior classification remain. This thesis works to address the mechanics of material knowledge gap that exists for characterizing the behavior of a metallic woven structure, composed of stainless steel wires on the order of 25 microns in diameter, and subjected to various loading conditions and stress risers. Uniaxial and biaxial tensile experiments, employing Digital Image Correlation (DIC) as a strain measurement tool, are conducted on woven wire mesh specimens incised in various material orientations, and with various notch geometries. Experimental results, supported by an ample analytic modeling effort, indicate that an orthotropic elastic constitutive model is reasonably capable of governing the macro-scale elasticity of the subject material. Also, the Stress Concentration Factor (SCF) associated with various notch geometries is documented experimentally and analytically, and it is shown that the degree of stress concentration is dependent on both notch and material orientation. The Finite Element Method (FEM) is employed on the macro-scale to expand the experimental test matrix, and to judge the effects of a homogenization assumption when modeling metallic woven structures. Additionally, plasticity of the stainless steel woven wire mesh is considered through experimental determination of the yield surface, and a thorough analytic modeling effort resulting in a modified form of the Hill yield criterion. Finally, meso-scale plasticity of the woven structure is considered, and the form of a multi-scale failure criterion is proposed and exercised numerically.
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Date Issued: 2013
Identifier: CFE0004707, ucf:49825
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004707

Title: Creep-Fatigue Crack Initiation and Propagation of a Notched Stainless Steel.
Creator: Keller, Scott, Gordon, Ali, Nicholson, David, Raghavan, Seetha, University of Central Florida
Abstract / Description: Premature failures of vital gas turbine components, such as blades and vanes, have been the result of increasing demands of power generation facilities. As power needs fluctuate throughout the day, operators are quickly firing up gas turbines as a means of providing instant power. Traditionally, these engines run at constant operating conditions; however, contemporary operating conditions call for these engines to be applied on an (")as necessary(") basis. The result of the cyclic startup and...
Show morePremature failures of vital gas turbine components, such as blades and vanes, have been the result of increasing demands of power generation facilities. As power needs fluctuate throughout the day, operators are quickly firing up gas turbines as a means of providing instant power. Traditionally, these engines run at constant operating conditions; however, contemporary operating conditions call for these engines to be applied on an (")as necessary(") basis. The result of the cyclic startup and shutdown of gas turbines has led to a phenomenon known as creep-fatigue (CF). A coupling of two primary failure mechanisms in gas turbines, CF conditions exacerbate the mechanisms of creep and fatigue, ultimately leading to a premature failure of components. Traditionally, independent creep and fatigue analyses are conducted to determine the limiting life factor of gas turbines. Recently, fracture mechanics approaches have been successfully used in extending the traditional analyses to include fatigue- and creep-crack growth analyses. Founded on existing approaches to creep-fatigue crack growth analyses, including experimental elastic and plastic fracture mechanics approaches, a coupled creep-fatigue crack initiation and propagation model is developed. To bring these models to fruition, the current study utilizes the development of an experimental setup capable of subjecting a modified fracture specimen to creep-fatigue conditions. With two test temperatures key to turbine components, a blunt notch compact tension specimen was subjected to trapezoidal load waveforms with various lengths of holds at maximum load. A developed direct current potential drop (DCPD) system was used to monitor crack initiation and crack lengths throughout the duration of tests. Numerical simulations on a representative specimen were conducted, to correlate and predict key fracture mechanics parameters used in the development of creep-fatigue crack initiation and propagation models. Metallurgical analysis of specimens was conducted, implementing both optical and scanning electron microscopy. From the experimental and numerical studies, a model for both the initiation and propagation of cracks on a single specimen is furnished. Through the use of elastic-plastic fracture mechanics parameters, the proposed models are observed to predict crack initiation and replicate crack propagation rates based on the experimental conditions. Assisting in the implementation of the proposed models, intended uses and applications for the models are provided, simplifying the life prediction analyses for components expected to fail due to creep-fatigue service conditions.
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Date Issued: 2013
Identifier: CFE0004700, ucf:49830
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004700

$Synchrotron X-Ray Diffraction and Piezospectroscopy used for the Investigation of Individual Mechanical Effects from Environmental Contaminants and Oxide Layer Undulations in Thermal Barrier Coatings$

Title: Synchrotron X-Ray Diffraction and Piezospectroscopy used for the Investigation of Individual Mechanical Effects from Environmental Contaminants and Oxide Layer Undulations in Thermal Barrier Coatings.
Creator: Siddiqui, Sanna, Raghavan, Seetha, Bai, Yuanli, Gordon, Ali, University of Central Florida
Abstract / Description: The durability of Thermal Barrier Coatings (TBCs) used on the turbine blades of aircraft and power generation engines has been known to be affected by sand particle ingression comprised of Calcium-Magnesium-Alumina-Silicate (CMAS). Previous studies have shown that these effects present themselves through variations in the thermomechanical and thermochemical properties of the coating. This study investigated the impact of CMAS ingression on the Yttria Stabilized Zirconia Topcoat (YSZ) and...
Show moreThe durability of Thermal Barrier Coatings (TBCs) used on the turbine blades of aircraft and power generation engines has been known to be affected by sand particle ingression comprised of Calcium-Magnesium-Alumina-Silicate (CMAS). Previous studies have shown that these effects present themselves through variations in the thermomechanical and thermochemical properties of the coating. This study investigated the impact of CMAS ingression on the Yttria Stabilized Zirconia Topcoat (YSZ) and Thermally Grown Oxide (TGO) strain in sprayed Thermal Barrier Coating (TBC) samples of varying porosity with and without CMAS ingression. In-Situ Synchrotron X-ray Diffraction measurements were taken on the sample under thermal loading conditions from which the YSZ and TGO peaks were identified and biaxial strain calculations were determined at high temperature. Quantitative strain results are presented for the YSZ and TGO during a thermal cycle. In-plane strain results for YSZ near the TGO interface for a complete thermal cycle are presented, for a 6% porous superdense sample with CMAS infiltration. The outcomes from this study can be used to understand the role of CMAS on the strain tolerance of the TBC coating.It is well known that under engine operational conditions the development of the TGO layer, with large critical stresses, has been linked to failure of the coating. The growth of the TGO manifests as undulations in a series of peaks and troughs. Understanding the mechanics of the oxide layer at these locations provides significant information with respect to the failure mechanisms of the TBC coating. This study investigated the stress at the peak and trough of a TGO undulation for a cycled Dense Vertically Cracked (DVC) plasma sprayed TBC sample through photo-luminescence (PL) spectroscopy. High resolution nanoscale stress maps were taken nondestructively in the undulation of the TGO. Preliminary results from first line mapping of TGO peak and trough scan, at a resolution of 200 nm, have shown a non-uniform TGO stress variation. The results obtained from this study can be used to understand the stress variation in the peak and trough of a DVC sample's TGO undulation and how it contributes to the life of the TBC coating.
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Date Issued: 2014
Identifier: CFE0005712, ucf:50136
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0005712

ANSYS (5)	+ -
Creep (4)	+ -
Chaboche (3)	+ -
Ramberg-Osgood (3)	+ -
fatigue (3)	+ -

finite element analysis (3)	+ -
mechanics (3)	+ -
304 stainless steel (2)	+ -
Aluminum (2)	+ -
Anisotropic (2)	+ -
Auxetic (2)	+ -
Fatigue (2)	+ -
Finite Element Analysis (2)	+ -
Fracture (2)	+ -
Gas Turbine (2)	+ -
Heat Transfer (2)	+ -
Hill Yield Criterion (2)	+ -
Kachanov-Rabotnov (2)	+ -
Multiaxial (2)	+ -
Norton (2)	+ -
Optimization (2)	+ -
Plasticity (2)	+ -
TMF (2)	+ -
bending (2)	+ -
composites (2)	+ -
fluid dynamics (2)	+ -
gas turbine (2)	+ -
lifing (2)	+ -
optimization (2)	+ -
000 rpm (1)	+ -

ETD Collection (39)	+ -
Honors Collection (12)	+ -

University of Central Florida (51)	+ -
Gordon, Ali (48)	+ -
Bai, Yuanli (12)	+ -
Kapat, Jayanta (9)	+ -
Raghavan, Seetha (9)	+ -

Gou, Jihua (4)	+ -
Kassab, Alain (4)	+ -
Nicholson, David (4)	+ -
Sohn, Yongho (4)	+ -
Ahmed, Kareem (3)	+ -
Deng, Weiwei (3)	+ -
Gordon, Ali P. (3)	+ -
Xu, Chengying (3)	+ -
An, Linan (2)	+ -
Catbas, Necati (2)	+ -
Coffey, Kevin (2)	+ -
Kammerer, Catherine (2)	+ -
Kauffman, Jeffrey L. (2)	+ -
Keller, Scott (2)	+ -
Moslehy, Faissal (2)	+ -
Siddiqui, Sanna (2)	+ -
Smith, Kevin (2)	+ -
Stewart, Calvin (2)	+ -
Vaidyanathan, Rajan (2)	+ -
Vasu Sumathi, Subith (2)	+ -
Ahmed, Lumaya (1)	+ -
Algarni, Mohammed (1)	+ -
Bass, Michael (1)	+ -
Benafan, Othmane (1)	+ -
Bouchenot, Thomas (1)	+ -

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