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- Title
- FINITE ELEMENT SIMULATION OF SINGLE-LAP SHEAR TESTS UTILIZING THE COHESIVE ZONE APPROACH.
- Creator
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Perez, Wilson A, Gordon, Ali P., University of Central Florida
- Abstract / Description
-
Many applications require adhesives with high strength to withstand the exhaustive loads encountered in regular operation. In aerospace applications, advanced adhesives are needed to bond metals, ceramics, and composites under shear loading. The lap shear test is the experiment of choice for evaluating shear strength capabilities of adhesives. Specifically during single-lap shear testing, two overlapping rectangular tabs bonded by a thin adhesive layer are subject to tension. Shear is imposed...
Show moreMany applications require adhesives with high strength to withstand the exhaustive loads encountered in regular operation. In aerospace applications, advanced adhesives are needed to bond metals, ceramics, and composites under shear loading. The lap shear test is the experiment of choice for evaluating shear strength capabilities of adhesives. Specifically during single-lap shear testing, two overlapping rectangular tabs bonded by a thin adhesive layer are subject to tension. Shear is imposed as a result. Debonding occurs when the shear strength of the adhesive is surpassed by the load applied by the testing mechanism. This research develops a finite element model (FEM) and material model which allows mechanicians to accurately simulate bonded joints under mechanical loads. Data acquired from physical tests was utilized to correlate the finite element simulations. Lap shear testing has been conducted on various adhesives, specifically SA1-30-MOD, SA10-100, and SA10-05, single base methacrylate adhesives. The adhesives were tested on aluminum, stainless steel, and cold rolled steel adherends. The finite element model simulates what is observed during a physical single-lap shear test consisting of every combination of the mentioned materials. To accomplish this, a three-dimensional model was created and the cohesive zone approach was used to simulate debonding of the tabs from the adhesive. The thicknesses of the metallic tabs and the adhesive layer were recorded and incorporated into the model in order to achieve an accurate solution. From the data, force output and displacement of the tabs are utilized to create curves which were compared to the actual data. Stress and strain were then computed and plotted to verify the validity of the simulations. The modeling and constant determination approach developed here will continue to be used for newly-developed adhesives.
Show less - Date Issued
- 2016
- Identifier
- CFH2000149, ucf:45973
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFH2000149
- Title
- METHODS OF EXTRAPOLATING LOW CYCLE FATIGUE DATA TO HIGH STRESS AMPLITUDES.
- Creator
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Radonovich, David, Gordon, Ali, University of Central Florida
- Abstract / Description
-
Modern gas turbine component design applies much effort into prediction and avoidance of fatigue. Advances in the prediction of low-cycle fatigue (LCF) cracks will reduce repair and replacement costs of turbine components. These cracks have the potential to cause component failure. Regression modeling of low-cycle fatigue (LCF)test data is typically restricted for use over the range of the test data. It is often difficult to characterize the plastic strain curve fit constants when the plastic...
Show moreModern gas turbine component design applies much effort into prediction and avoidance of fatigue. Advances in the prediction of low-cycle fatigue (LCF) cracks will reduce repair and replacement costs of turbine components. These cracks have the potential to cause component failure. Regression modeling of low-cycle fatigue (LCF)test data is typically restricted for use over the range of the test data. It is often difficult to characterize the plastic strain curve fit constants when the plastic strain is a small fraction of the total strain acquired. This is often the case with high strength, moderate ductility Ni-base superalloys. The intent of this project is to identify the optimal technique for extrapolating LCF test results into stress amplitudes approaching the ultimate strength. The proposed method to accomplish this is by finding an appropriate upper and lower bounds for the cyclic stress-strain and strain-life equations. Techniques investigated include: monotonic test data anchor points, strain-compatibility, and temperature independence of the Coffin-Manson relation. A Ni-base superalloy (IN738 LC) data set with fully reversed fatigue tests at several elevated temperatures with minimal plastic strain relative to the total strain range was used to model several options to represent the upper and lower bounds of material behavior. Several high strain LCF tests were performed with stress amplitudes approaching the ultimate strength. An augmented data set was developed by combining the high strain data with the original data set. The effectiveness of the bounding equations is judged by comparing the bounding equation results with the base data set to a linear regression model using the augmented data set.
Show less - Date Issued
- 2007
- Identifier
- CFE0001891, ucf:47410
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0001891
- Title
- FRACTURE TOUGHNESS OF A HYPERELASTIC MATERIAL DURING SURGICAL CUTTING.
- Creator
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Smith, Kevin, Gordon, Ali, University of Central Florida
- Abstract / Description
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Despite being one of the most important organs of vertebrates, the material properties of skin are also one of the most poorly understood. In the field of designing medical devices and surgical tools there are significant advantages to having a model that describes the interaction of forces between a blade tip and skin during surgical cutting. In general, skin can best be described as a composite layer consisting of a viscoelastic dermis with interwoven collagen and elastin fibers beneath a...
Show moreDespite being one of the most important organs of vertebrates, the material properties of skin are also one of the most poorly understood. In the field of designing medical devices and surgical tools there are significant advantages to having a model that describes the interaction of forces between a blade tip and skin during surgical cutting. In general, skin can best be described as a composite layer consisting of a viscoelastic dermis with interwoven collagen and elastin fibers beneath a superficial epidermis. The purpose of this research is to study the fracture toughness of porcine skin during practical cutting applications, the behavior of skin under quasi-static loads, and viscoelastic behavior of skin during stress relaxation. To fully describe the mechanics of skin in this model tensile test are conducted to determine the material properties of skin. The fracture toughness of the material is calculated by measuring the energy release rate of the material during required during cutting with Number 11 scalpel blade with a tip radius of 12[mu]m. These results are then compared to a finite element analysis with a debonding interface and a Mooney-Rivlin hyperelastic material model with viscoelastic relaxation in an effort to predict the loads required by tools during surgical applications. The main outcome of this research is the development of a testing protocol and material model of skin that can be used in finite element simulations of uniaxial loads and surgical cutting.
Show less - Date Issued
- 2013
- Identifier
- CFH0004530, ucf:45191
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFH0004530
- Title
- THE TLC METHOD FOR MODELING CREEP DEFORMATION AND RUPTURE.
- Creator
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May, David, Gordon, Ali, University of Central Florida
- Abstract / Description
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This thesis describes a novel new method, termed the Tangent-Line-Chord (TLC) method, that can be used to more efficiently model creep deformation dominated by the tertiary regime. Creep deformation is a widespread mechanical mode of failure found in high-stress and temperature mechanical systems. To accurately simulate creep and its effect on structures, researchers utilize finite element analysis (FEA). General purpose FEA packages require extensive amounts of time and computer resources to...
Show moreThis thesis describes a novel new method, termed the Tangent-Line-Chord (TLC) method, that can be used to more efficiently model creep deformation dominated by the tertiary regime. Creep deformation is a widespread mechanical mode of failure found in high-stress and temperature mechanical systems. To accurately simulate creep and its effect on structures, researchers utilize finite element analysis (FEA). General purpose FEA packages require extensive amounts of time and computer resources to simulate creep softening in components because of the large deformation rates that continuously evolve. The goal of this research is to employ multi-regime creep models, such as the Kachanov-Rabotnov model, to determine a set of equations that will allow creep to be simulated using as few iterations as possible. The key outcome is the freeing up of computational resources and the saving of time. Because both the number of equations and the value of material constants within the model change depending on the approach used, programming software will be utilized to automate this analytical process. The materials being considered in this research are mainly generic Ni-based superalloys, as they exhibit creep responses that are dominated by secondary and tertiary creep.
Show less - Date Issued
- 2014
- Identifier
- CFH0004560, ucf:45196
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFH0004560
- Title
- A PARAMETRIC STUDY OF MESO-SCALE PATTERNS FOR AUXETIC MECHANICAL BEHAVIOR OPTIMIZATION.
- Creator
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Schuler, Matthew C, Gordon, Ali P., University of Central Florida
- Abstract / Description
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This thesis focuses on the development, parameterization and optimization of a novel meso-scale pattern used to induce auxetic behavior, i.e., negative Poisson�s ratio, at the bulk scale. Currently, the majority of auxetic structures are too porous to be utilized in conventional load-bearing applications. For others, manufacturing methods have yet to realize the meso-scale pattern. Consequently, new auxetic structures must be developed in order to confer superior thermo-mechanical responses...
Show moreThis thesis focuses on the development, parameterization and optimization of a novel meso-scale pattern used to induce auxetic behavior, i.e., negative Poisson�s ratio, at the bulk scale. Currently, the majority of auxetic structures are too porous to be utilized in conventional load-bearing applications. For others, manufacturing methods have yet to realize the meso-scale pattern. Consequently, new auxetic structures must be developed in order to confer superior thermo-mechanical responses to structures 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 auxetic structures. A novel auxetic 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). Various attributes of the elasto-plastic responses of the bulk structure are used as objectives to guide the optimization process
Show less - Date Issued
- 2016
- Identifier
- CFH2000001, ucf:45595
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFH2000001
- Title
- A MECHANICS-BASED APPROACH FOR PUTT DISTANCE OPTIMIZATION.
- Creator
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Santiago-Martinez, Pascual, Gordon, Ali, University of Central Florida
- Abstract / Description
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Quantifying the core mechanics of putting is imperative to developing a reliable model that predicts post-collision ball behavior. A preliminary model for the stroking motion of putting and putter-ball collision is developed alongside experiments, establishing an empirical model that supports the theory. The goal of the present study is to develop a correlation between the backstroke of a putt, or the pre-impact translation of the putter, and the post-impact displacement of the golf ball....
Show moreQuantifying the core mechanics of putting is imperative to developing a reliable model that predicts post-collision ball behavior. A preliminary model for the stroking motion of putting and putter-ball collision is developed alongside experiments, establishing an empirical model that supports the theory. The goal of the present study is to develop a correlation between the backstroke of a putt, or the pre-impact translation of the putter, and the post-impact displacement of the golf ball. This correlation is subsequently utilized to generate an algorithm that predicts the two-dimensional ball trajectory based on putt displacement and putting surface texture by means of finite element analysis. In generating a model that accurately describes the putting behavior, the principles of classical mechanics were utilized. As a result, the putt displacement was completely described as a function of backstroke and some environmental parameters, such as: friction, slope of the green, and the elasticity of the putter-ball collision. In support of the preliminary model, experimental data were gathered from golfers of all levels. The collected data demonstrated a linear correlation between backstroke and putt distance, with the environmental parameters factoring in as a constant value; moreover, the data showed that experienced golfers tend to have a constant acceleration through ball impact. Combining the empirical results with the trajectory prediction algorithm will deliver an accurate predictor of ball behavior that can be easily implemented by golfers under most practical applications. Putt distance to backstroke ratios were developed under a variety of conditions
Show less - Date Issued
- 2015
- Identifier
- CFH0004764, ucf:45340
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFH0004764
- Title
- COMPENDIUM OF THERMOVISCOPLASTICITY MODELING PARAMETERS FOR MATERIALS UNDER NON-ISOTHERMAL FATIGUE.
- Creator
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O'Nora, Nathan, Gordon, Ali, University of Central Florida
- Abstract / Description
-
Viscoplasticity models allow for the prediction of the inelastic behavior of materials, taking into account the rate-dependence. In order to model the response under non-isothermal conditions experienced by many components, such as those in turbomachinery, however, it is necessary to incorporate temperature-dependence. Additionally, for materials subjected to thermal shock, temperature rate-dependence is also important. The purpose of this research is to develop a method of determining...
Show moreViscoplasticity models allow for the prediction of the inelastic behavior of materials, taking into account the rate-dependence. In order to model the response under non-isothermal conditions experienced by many components, such as those in turbomachinery, however, it is necessary to incorporate temperature-dependence. Additionally, for materials subjected to thermal shock, temperature rate-dependence is also important. The purpose of this research is to develop a method of determining Chaboche viscoplasticity parameters that allows for consistent behavior with changing temperature. A quartet of candidate materials, 304 stainless steel, IN617, DS GTD-111, and Ti6242S, were chosen for their applications in turbomachinery, such as gas turbines, nuclear, and aerospace applications. The focus of this research is geared towards establishing the temperature-dependence of the constants used in the model in order to obtain more accurate modeling of non-isothermal fatigue loadings than those achieved through linear interpolation of constants at several temperatures. The goal is to be able to more accurately predict the deformation behavior of components subjected to cyclic temperature and mechanical loadings which will ultimately allow for more accurate life prediction. The effects of orientation in directionally solidified (DS) materials is also examined in order to gain insight as to the expected behavior of parameters with changing orientation.
Show less - Date Issued
- 2015
- Identifier
- CFH0004760, ucf:45383
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFH0004760
- Title
- DESIGN AND EVALUATION OF A TEST PLATFORM FOR THERMAL MECHANICAL AND ACOUSTICAL LOADING.
- Creator
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Jasmin, Abdi, Gordon, Ali, University of Central Florida
- Abstract / Description
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Next generation hypersonic cruise vehicle components will be subjected to a collection of loads not achievable in contemporary mechanical test platform. The purpose of this thesis is to demonstrate the design of a unique test platform for combined extreme environment (P-CEEn) needed to replicate thermal, acoustic and mechanical loading to be imparted on hypersonic fuselage panels. The panels are typically subjected to super-imposed cycling from hypersonic shock/impingement and aerodynamic...
Show moreNext generation hypersonic cruise vehicle components will be subjected to a collection of loads not achievable in contemporary mechanical test platform. The purpose of this thesis is to demonstrate the design of a unique test platform for combined extreme environment (P-CEEn) needed to replicate thermal, acoustic and mechanical loading to be imparted on hypersonic fuselage panels. The panels are typically subjected to super-imposed cycling from hypersonic shock/impingement and aerodynamic pressure from the usual ascent-cruise-decent motion of the aircrafts combined with mechanical vibration at acoustic frequencies; moreover, these slender components will undergo conventional mechanical fatigue with compressive mean stress due to geometric constraint. Having the ability to precisely replicate the working environment of the fuselage components will help to identify life limiting conditions of the materials. A universal column buckling test frame, an acoustic horn, and a custom-made quartz-lamp furnace have been configured to allow for closed-loop feedback control of cyclic mechanical, thermal, and acoustic loading. The graphical user interface (GUI) associated with this first-of-its-kind test device allows users to design cyclic load profiles that idealize the thermo-acousto-mechanical loading of critical panels. Initial calibration experiments are presented.
Show less - Date Issued
- 2015
- Identifier
- CFH0004806, ucf:45444
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFH0004806
- Title
- MECHANICAL CHARACTERIZATION OF ANISOTROPIC FUSED DEPOSITION MODELED POLYLACTIC ACID UNDER COMBINED MONOTONIC BENDING AND TORSION CONDITIONS.
- Creator
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Santomauro, Aaron T, Gordon, Ali P., University of Central Florida
- Abstract / Description
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Mechanical strength of polylactic acid (PLA) is increasingly relevant with time because of its attractive mechanical properties and 3D printability. Additive manufacturing (AM) methods, such as fused deposition modeling (FDM), stereolithography (SLA), and selective laser sintering (SLS), serve a vital role in assisting designers with cheap and efficient generation of the desired components. This document presents research to investigate the anisotropic response of multi-oriented PLA subjected...
Show moreMechanical strength of polylactic acid (PLA) is increasingly relevant with time because of its attractive mechanical properties and 3D printability. Additive manufacturing (AM) methods, such as fused deposition modeling (FDM), stereolithography (SLA), and selective laser sintering (SLS), serve a vital role in assisting designers with cheap and efficient generation of the desired components. This document presents research to investigate the anisotropic response of multi-oriented PLA subjected to multiple monotonic loading conditions. Although empirical data has previously been captured for multi-oriented PLA under tensile and compressive loading conditions, the data has yet to be applied with regard to a representative component geometry. The tensile and compressive empirical data were ultimately used to develop elastic and yield constitutive models which aided in the characterization of PLA under torsion and bending. This representative component geometry is expected to experience a combined torsion and bending load condition in an effort to address this integral gap in the mechanical properties of multi-oriented PLA. In addition to the acquired empirical data, finite element analysis (FEA) and analytical modeling are employed to supplement the accurate modeling of future component analysis. As a result of the proposed array of experiments, the torsional and bending capabilities of PLA are forecasted to vary based on the print orientation. Lastly, the broader impact of this work is dedicated to addressing the material's capability to operate in environments which possess significant torsion and bending such as model aircraft wings and shafts for remote controlled cars.
Show less - Date Issued
- 2019
- Identifier
- CFH2000550, ucf:45631
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFH2000550
- Title
- APPLICATION OF NON-LOCAL APPROACHES FOR PREDICTING THE RESPONSE OF V-NOTCH UNDER THERMOMECHANICAL FATIGUE LOADING.
- Creator
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Nguyen, Trung, Gordon, Ali, University of Central Florida
- Abstract / Description
-
The topic of this thesis is the construction of a formula to approximate stress-strain responses at notches under thermomechanical fatigue (TMF) loading. The understanding of material behavior of the V-notched component which experiences TMF is important to the mechanical industries where V-notched structures are often utilized. In such applications, it is crucial that the designers be able to predict the material behavior; therefore, the purpose of this research is to examine and to model...
Show moreThe topic of this thesis is the construction of a formula to approximate stress-strain responses at notches under thermomechanical fatigue (TMF) loading. The understanding of material behavior of the V-notched component which experiences TMF is important to the mechanical industries where V-notched structures are often utilized. In such applications, it is crucial that the designers be able to predict the material behavior; therefore, the purpose of this research is to examine and to model the precise effects a stress concentration will have on a specimen made of a generic Ni-base superalloy. The effects of non-isothermal loading will be studied, and it is the goal of this research to formulate an extension of Neuber's rule appropriate for TMF which is to approximate the temperature range with a single value, T*. One strategy to extend Neuber's rule, which relies on Finite Element Modeling (FEM), Bilinear Kinetic Hardening Model (BKIN), and test data, will be used to predict the stress-strain behavior at the notch of a thin plate subjected to axial loading. In addition, the CHABOCHE model will be utilized in the FEA to have the highest fidelity to material response at high temperatures. Parametric study of the FEA simulations will be employed to determine the correlation between the Neuber hyperbola, temperature range, stress concentration, the nominal stress, and the temperature cycling. Using the Neuber hyperbola and simplified constitutive model (i.e., bilinear kinematic strain hardening), the stress-strain solutions of the specimen will be calculated and compared to analytical results.
Show less - Date Issued
- 2013
- Identifier
- CFH0004440, ucf:45111
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFH0004440
- Title
- A SIMPLIFIED APPROACH TO THERMOMECHANICAL FATIGUE AND APPLICATION TO V-SHAPED NOTCHES.
- Creator
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Bouchenot, Thomas, Gordon, Ali, University of Central Florida
- Abstract / Description
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A vast array of high value parts in land- and air-based turbomachinery are subjected to non-isothermal cycling in the presence of mechanical loading. Crack initiation, growth and eventual failure more significantly reduce life in these components compared to isothermal conditions. More accurate simulation of the stress and strain evolution at critical locations of components, as well as test specimens, can lead to a more accurate prediction of remaining life to a structural integrity...
Show moreA vast array of high value parts in land- and air-based turbomachinery are subjected to non-isothermal cycling in the presence of mechanical loading. Crack initiation, growth and eventual failure more significantly reduce life in these components compared to isothermal conditions. More accurate simulation of the stress and strain evolution at critical locations of components, as well as test specimens, can lead to a more accurate prediction of remaining life to a structural integrity specialists. The focus of this thesis is to characterize the effects of thermomechanical fatigue (TMF) on generic turbomachinery alloy. An expression that can be used to estimate the maximum and minimum stress under a variety of loading conditions is formulated. Analytical expressions developed here are modifications of classic mechanics of materials methods (e.g. Neuber's Rule and Ramberg-Osgood). The novel models are developed from a collection of data based on parametric finite element analysis to encompass the complex load history present in turbine service conditions. Relevance of the observations and formulated solutions are also explored for the case of a tensile specimen containing a v-shaped notch. Accurate estimations of non-isothermal fatigue presented here endeavor to improve component lifing and decrease maintenance costs.
Show less - Date Issued
- 2013
- Identifier
- CFH0004480, ucf:45073
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFH0004480
- Title
- CHARACTERIZATION OF POLYETHERIMIDE UNDER STATIC, DYNAMIC, AND MULTIPLE IMPACT CONDITIONS.
- Creator
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Zuanetti, Bryan, Gordon, Ali, University of Central Florida
- Abstract / Description
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The application of polymers in robust engineering designs is on the rise due to their excellent mechanical properties such as high fracture toughness, specific strength, durability, as well as, thermal and chemical resistances. Implementation of some advanced polymeric solids is limited due to the lack of available mechanical properties. In order for these materials to endure strenuous engineering designs it is vital to investigate their response in multiple loading rates and conditions. In...
Show moreThe application of polymers in robust engineering designs is on the rise due to their excellent mechanical properties such as high fracture toughness, specific strength, durability, as well as, thermal and chemical resistances. Implementation of some advanced polymeric solids is limited due to the lack of available mechanical properties. In order for these materials to endure strenuous engineering designs it is vital to investigate their response in multiple loading rates and conditions. In this thesis, the mechanical response of polyethermide (PEI) is characterized under quasi-static, high strain rate, and multiple impact conditions. Standard tension, torsion, and compression experiments are performed in order to distinguish the multi-regime response of PEI. The effects of physical ageing and rejuvenation on the quasi-static mechanical response are investigated. The strain softening regime resulting from strain localization is eliminated by thermal and mechanical rejuvenation, and the advantages of these processes are discussed. The dynamic fracture toughness of the material in response to notched impact via Charpy impact test is evaluated. The high strain-rate response of PEI to uniaxial compression is evaluated at rates exceeding 104/s via miniaturized Split Hopkinson Pressure Bar (MSHPB), and compared to the quasi-static case to determine strain-rate sensitivity. The elastic response of the aged material to multiple loading conditions are correlated using the Ramberg-Osgood equation, while the elastoplastic response of rejuvenated PEI is correlated using a both the Ramberg-Osgood equation and a novel model. The strain-rate sensitivity of the strength is found to be nominally bilinear and transition strains are modeled using the Ree-Erying formulation. Finally, multiple impact experiments are performed on PEI using the MSHPB and a model is proposed to quantify damage as a result of collision.
Show less - Date Issued
- 2013
- Identifier
- CFH0004531, ucf:45166
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFH0004531
- Title
- NUMERICAL SIMULATION OF FRACTURE OF A NANO-PAPER COATED E-GLASS/POLYESTER COMPOSITE WITH THERMAL DAMAGE.
- Creator
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Graham, Zachary, Gordon, Ali, University of Central Florida
- Abstract / Description
-
Aerospace research for next-generation travel increasingly focuses on the use of advanced composites to reduce weight and cost while retaining strength. One subset of materials with great potential is based on the combination of resin matrix and glass-fiber reinforcement. This research explores the application of a candidate nanopaper coating with a given composite. Prior research applied a set of given heat fluxes to the top surface of the composite for a set of given periods of time, and...
Show moreAerospace research for next-generation travel increasingly focuses on the use of advanced composites to reduce weight and cost while retaining strength. One subset of materials with great potential is based on the combination of resin matrix and glass-fiber reinforcement. This research explores the application of a candidate nanopaper coating with a given composite. Prior research applied a set of given heat fluxes to the top surface of the composite for a set of given periods of time, and subsequently performed a 3-point flexural test to determine the elastic modulus for both the coated and uncoated composite for all of the combinations of heat flux and time. A finite element (FE) model is developed using the ANSYS general purpose finite element analysis (FEA) software that models the degradation in strength/stiffness properties based on heating condition and with the goal of predicting cracking using the element death feature in ANSYS. This thesis describes the prior research suggesting both the need for and novelty of this model, and the procedures used to form the model. The loading conditions of the 3-point flexural test are replicated, and four measures of accuracy are developed based on the force versus displacement curve of the test and the FE model. It is envisioned that continuum-level models developed as a part of these research be applied for design of next-generation space components These measurements are used to verify the FE model, and this model is then employed to extrapolate beyond the context of experimental conditions.
Show less - Date Issued
- 2013
- Identifier
- CFH0004346, ucf:45021
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFH0004346
- Title
- STRESS INTENSITY FACTOR DEPENDENCE OF HG-AL LIQUID METAL EMBRITTLEMENT.
- Creator
-
Keller, Scott, Gordon, Ali, University of Central Florida
- Abstract / Description
-
When high strength aluminum alloys are subjected to liquid metals, physical and chemical reactions ensue resulting in what is known as liquid metal embrittlement (LME). A subset of environmentally-assisted cracking, LME is exhibited when a liquid metal, e.g. Hg or Ga, comes into intimate contact with a solid metal having significant susceptibility. As mechanical loads are applied, the interaction between the two metals results in a reduction in the flow properties of the solid metal. Several...
Show moreWhen high strength aluminum alloys are subjected to liquid metals, physical and chemical reactions ensue resulting in what is known as liquid metal embrittlement (LME). A subset of environmentally-assisted cracking, LME is exhibited when a liquid metal, e.g. Hg or Ga, comes into intimate contact with a solid metal having significant susceptibility. As mechanical loads are applied, the interaction between the two metals results in a reduction in the flow properties of the solid metal. Several theories have been proposed to identify the underlying microstructural failure mechanism; however, none have been widely accepted, as failures can typically incorporate features common to several failure theories. In an effort to confirm, extend or replace the physically-based theories, fracture mechanics experiments on Al 7075T651 in liquid mercury have been conducted. Experiments were conducted in a custom environmental chamber capable of exposing specimens to liquid environments while applying a mechanical load. Through both plane-strain fracture and stress intensity factor-dependent (SIF) tests, fracture toughness values along with incubation periods were analyzed and provided data for a load-based theory of LME. These mechanical test data, along with metallographic analysis, show that the phenomena of LME is both strongly time- and SIF-dependent.
Show less - Date Issued
- 2009
- Identifier
- CFE0002893, ucf:48033
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0002893
- Title
- TERTIARY CREEP DAMAGE MODELING OF A TRANSVERSELY ISOTROPIC NI-BASED SUPERALLOY.
- Creator
-
Stewart, Calvin, Gordon, Ali, University of Central Florida
- Abstract / Description
-
Anisotropic tertiary creep damage formulations have become an increasingly important prediction technique for high temperature components due to drives in the gas turbine industry for increased combustion chamber exit pressures, temperature, and the use of anisotropic materials such as metal matrix composites and directionally-solidified (DS) Ni-base superalloys. Typically, isotropic creep damage formulations are implemented for simple cases involving a uniaxial state of stress; however,...
Show moreAnisotropic tertiary creep damage formulations have become an increasingly important prediction technique for high temperature components due to drives in the gas turbine industry for increased combustion chamber exit pressures, temperature, and the use of anisotropic materials such as metal matrix composites and directionally-solidified (DS) Ni-base superalloys. Typically, isotropic creep damage formulations are implemented for simple cases involving a uniaxial state of stress; however, these formulations can be further developed for multiaxial states of stress where materials are found to exhibit induced anisotropy. In addition, anisotropic materials necessitate a fully-developed creep strain tensor. This thesis describes the development of a new anisotropic tertiary creep damage formulation implemented in a general-purpose finite element analysis (FEA) software. Creep deformation and rupture tests are conducted on L, T, and 45°-oriented specimen of subject alloy DS GTD-111. Using the Kachanov-Rabotnov isotropic creep damage formulation and the optimization software uSHARP, the damage constants associated with the creep tests are determined. The damage constants, secondary creep, and derived Hill Constants are applied directly into the improved formulation. Comparison between the isotropic and improved anisotropic creep damage formulations demonstrates modeling accuracy. An examination of the off-axis creep strain terms using the improved formulation is conducted. Integration of the isotropic creep damage formulation provides time to failure predictions which are compared with rupture tests. Integration of the improved anisotropic creep damage produces time to failure predictions at intermediate orientations and any state of stress. A parametric study examining various states of stress, and materials orientations is performed to verify the flexibility of the improved formulation. A parametric exercise of the time to failure predictions for various levels of uniaxial stress is conducted.
Show less - Date Issued
- 2009
- Identifier
- CFE0002918, ucf:48012
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0002918
- Title
- MECHANICAL CHARACTERIZATION AND NUMERICAL SIMULATION OF A LIGHT-WEIGHT ALUMINUM A359 METAL-MATRIX COMPOSITE.
- Creator
-
DeMarco, James, Gordon, Ali, University of Central Florida
- Abstract / Description
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Aluminum metal-matrix composites (MMCs) are well positioned to replace steel in numerous manufactured structural components, due to their high strength-to-weight and stiffness ratios. For example, research is currently being conducted in the use of such materials in the construction of tank entry doors, which are currently made of steel and are dangerously heavy for military personnel to lift and close. However, the manufacture of aluminum MMCs is inefficient in many cases due to the loss of...
Show moreAluminum metal-matrix composites (MMCs) are well positioned to replace steel in numerous manufactured structural components, due to their high strength-to-weight and stiffness ratios. For example, research is currently being conducted in the use of such materials in the construction of tank entry doors, which are currently made of steel and are dangerously heavy for military personnel to lift and close. However, the manufacture of aluminum MMCs is inefficient in many cases due to the loss of material through edge cracking during the hot rolling process which is applied to reduce thick billets of as-cast material to usable sheets. In the current work, mechanical characterization and numerical modeling of as-cast aluminum A359-SiCp-30% is employed to determine the properties of the composite and identify their dependence on strain rate and temperature conditions. Tensile and torsion tests were performed at a variety of strain rates and temperatures. Data obtained from tensile tests were used to calibrate the parameters of a material model for the composite. The material model was implemented in the ANSYS finite element software suite, and simulations were performed to test the ability of the model to capture the mechanical response of the composite under simulated tension and torsion tests. A temperature- and strain rate-dependent damage model extended the constitutive model to capture the dependence of material failure on testing or service conditions. Trends in the mechanical response were identified through analysis of the dependence of experimentally-obtained material properties on temperature and strain rate. The numerical model was found to adequately capture strain rate and temperature dependence of the stress-strain curves in most cases. Ductility modeling allowed prediction of stress and strain conditions which would lead to rupture, as well as identification of areas of a solid model which are most likely to fail under a given set of environmental and load conditions.
Show less - Date Issued
- 2011
- Identifier
- CFE0004007, ucf:49177
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0004007
- Title
- Detailed Understanding of Flow, Heat Transfer, and Pressure Drop Behavior in a Square Channel With 45 Deg Ribs.
- Creator
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Ahmed, Lumaya, Kapat, Jayanta, Gordon, Ali, Ahmed, Kareem, Shivamoggi, Bhimsen, University of Central Florida
- Abstract / Description
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Internal Duct Cooling (IDC) with rib turbulators is one of the common cooling techniques applied inside the turbine airfoils. It is very important for the gas turbine industry to design and develop an optimized cooling channel that maximizes the amount of heat removed, while simultaneously minimizing the pressure drop for a target overall cooling effectiveness. Angled ribs perform superior to the transverse ribs due to additional secondary flow associated with them. However, they result in a...
Show moreInternal Duct Cooling (IDC) with rib turbulators is one of the common cooling techniques applied inside the turbine airfoils. It is very important for the gas turbine industry to design and develop an optimized cooling channel that maximizes the amount of heat removed, while simultaneously minimizing the pressure drop for a target overall cooling effectiveness. Angled ribs perform superior to the transverse ribs due to additional secondary flow associated with them. However, they result in a highly non-homogenous heat transfer distribution, which is a manifestation of the complex, turbulent flow field inside the channel. It is very important to comprehend the secondary flow physics to characterize the heat transfer distribution in such angled ribbed channels. Additionally, due to the manufacturing constraint, the gas turbine industry encounters a challenge to make ribs edge sharp and results in ribs with rounded edges. The one of the main objectives of the present study is to provide a fundamental understanding of the flow physics on the heat transfer and pressure drop behavior in 45(&)deg; ribbed channels both with sharp and rounded-edge ribs. It is found that the secondary flow has a significant effect on the heat transfer behavior for both types of ribs. There is a great need of high-fidelity PIV flow field data in the inter-rib space for an angled ribbed channel which can be used for CFD validation, especially for LES. The current study provides benchmarking flow field data in the inter-rib space in a square channel with 45(&)deg; ribs using stereoscopic PIV technique. Besides the experiments, numerical studies were also conducted by using LES and different RANS models. The LES results show an excellent prediction capability for aerothermal behavior in such channels. However, the prediction capability of RANS models is found to be inconsistent for different rib configurations and flow conditions.
Show less - Date Issued
- 2018
- Identifier
- CFE0007302, ucf:52171
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0007302
- Title
- Multi-Sensor Optimization of the Simultaneous Turning and Boring Operation.
- Creator
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Deane, Erick, Xu, Chengying, Gou, Jihua, Gordon, Ali, University of Central Florida
- Abstract / Description
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To remain competitive in today's demanding economy, there is an increasing demand for improved productivity and scrap reduction in manufacturing. Traditional manufacturing metal removal processes such as turning and boring are still one of the most used techniques for fabricating metal products. Although the essential metal removal process is the same, new advances in technology have led to improvements in the monitoring of the process allowing for reduction of power consumption, tool wear,...
Show moreTo remain competitive in today's demanding economy, there is an increasing demand for improved productivity and scrap reduction in manufacturing. Traditional manufacturing metal removal processes such as turning and boring are still one of the most used techniques for fabricating metal products. Although the essential metal removal process is the same, new advances in technology have led to improvements in the monitoring of the process allowing for reduction of power consumption, tool wear, and total cost of production. Replacing used CNC lathes from the 1980's in a manufacturing facility may prove costly, thus finding a method to modernize the lathes is vital.This research focuses on Phase I and II of a three phase research project where the final goal is to optimize the simultaneous turning and boring operation of a CNC Lathe. From the optimization results it will be possible to build an adaptive controller that will produce parts rapidly while minimizing tool wear and machinist interaction with the lathe. Phase I of the project was geared towards selecting the sensors that were to be used to monitor the operation and designing a program with an architecture that would allow for simultaneous data collection from the selected sensors at high sampling rates. Signals monitored during the operation included force, temperature, vibration, sound, acoustic emissions, power, and metalworking fluid flow rates. Phase II of this research is focused on using the Response Surface Method to build empirical models for various responses and to optimize the simultaneous cutting process. The simultaneous turning and boring process was defined by the four factors of spindle speed, feed rate, outer diameter depth of cut, and inner diameter depth of cut. A total of four sets of experiments were performed. The first set of experiments screened the experimental region toiiidetermine if the cutting parameters were feasible. The next three set s of designs of experiments used Central Composite Designs to build empirical models of each desired response in terms of the four factors and to optimize the process. Each design of experiments was compared with one another to validate that the results achieved were accurate within the experimental region.By using the Response Surface Method optimal machining parameter settings were achieved. The algorithm used to search for optimal process parameter settings was the desirability function. By applying the results from this research to the manufacturing facility, they will achieve reduction in power consumption, reduction in production time, and decrease in the total cost of each part.
Show less - Date Issued
- 2011
- Identifier
- CFE0004098, ucf:49087
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0004098
- Title
- Design and Optimization of a Wave Energy Harvester Utilizing a Flywheel Energy Storage System.
- Creator
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Helkin, Steven, Lin, Kuo-Chi, Gordon, Ali, Raghavan, Seetha, University of Central Florida
- Abstract / Description
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This thesis details the design and optimization of a buoy used to collect renewable energy from ocean waves. The proposed buoy is a point absorber(-)a device that transforms the kinetic energy of the vertical motion of surface waves into electrical energy. The focus of the research is on the mechanical system used to collect the energy, and methods to improve it for eventual use in an actual wave energy harvester. A flywheel energy storage system was utilized in order to provide an improved...
Show moreThis thesis details the design and optimization of a buoy used to collect renewable energy from ocean waves. The proposed buoy is a point absorber(-)a device that transforms the kinetic energy of the vertical motion of surface waves into electrical energy. The focus of the research is on the mechanical system used to collect the energy, and methods to improve it for eventual use in an actual wave energy harvester. A flywheel energy storage system was utilized in order to provide an improved power output from the system, even with the intermittent input of force exerted by ocean waves. A series of laboratory prototypes were developed to analyze parameters that are important to the success of the point absorb mechanical system. By introducing a velocity-based load control scheme in conjunction with flywheel energy storage, it was seen that the average power output by the prototype was increased. The generator load is controlled via a relay switch that removes electrical resistance from the generator(-)this sacrifices time during which power is drawn from the system, but also allows the buoy to move with less resistance. A simulation model was developed in order to analyze the theoretical wave absorber system and optimize the velocity threshold parameters used in the load control. Results indicate that the power output by the system can be substantially improved through the use of a flywheel energy storage control scheme that engages and disengages the electrical load based on the rotational velocity of the flywheel system. The results of the optimization are given for varying-sized generator systems input into the simulation in order to observe the associated trends.
Show less - Date Issued
- 2011
- Identifier
- CFE0004118, ucf:49113
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0004118
- Title
- Purge and Secondary Flow Interaction Control by Means of Platform Circumferential Contouring.
- Creator
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Seco Soley, Melissa, Kapat, Jayanta, Deng, Weiwei, Gordon, Ali, University of Central Florida
- Abstract / Description
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This study presents an attempt to reduce the losses produced by the purge flow in a turbine stage by incorporating circumferential platform contouring. Two contours are proposed and compared against a baseline at different levels of swirl. The computational simulations were performed using a RANS three-dimensional Computational Fluid Dynamics code with the Shear Stress Transport turbulence model. The results of steady simulations demonstrate that for the first contour, when the flow is...
Show moreThis study presents an attempt to reduce the losses produced by the purge flow in a turbine stage by incorporating circumferential platform contouring. Two contours are proposed and compared against a baseline at different levels of swirl. The computational simulations were performed using a RANS three-dimensional Computational Fluid Dynamics code with the Shear Stress Transport turbulence model. The results of steady simulations demonstrate that for the first contour, when the flow is swirled to 50% of the rim speed, the purge flow exits the cavity with less cross flow. This in turn reduces the strength of the passage vortex. However, at swirl extremes of 0% and 100% the baseline has the best performance. The results show that a carefully designed platform has the potential to reduce losses when the operating condition is in the proximity of 50% swirl.
Show less - Date Issued
- 2011
- Identifier
- CFE0004163, ucf:49054
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0004163