+publisher:"University of Houston" +contributor:("Kulkarni, Yashashree")

University of Houston

1. Gampa, Ravishanker Venkata. Powering Particle Accelerators.

Degree: MS, Mechanical Engineering, 2017, University of Houston

► This thesis considers the design of power supplies for the magnetic and electrical dipoles used in typical particle accelerators. First the thermoelectric current generation system… (more)

Subjects/Keywords: Thermoelectric module; Power supply; High voltage low current; High current low voltage; Electric dipole; Magnetic dipole; Superconductivity

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APA (6^th Edition):

Gampa, R. V. (2017). Powering Particle Accelerators. (Masters Thesis). University of Houston. Retrieved from http://hdl.handle.net/10657/4544

Chicago Manual of Style (16^th Edition):

Gampa, Ravishanker Venkata. “Powering Particle Accelerators.” 2017. Masters Thesis, University of Houston. Accessed January 26, 2021. http://hdl.handle.net/10657/4544.

MLA Handbook (7^th Edition):

Gampa, Ravishanker Venkata. “Powering Particle Accelerators.” 2017. Web. 26 Jan 2021.

Vancouver:

Gampa RV. Powering Particle Accelerators. [Internet] [Masters thesis]. University of Houston; 2017. [cited 2021 Jan 26]. Available from: http://hdl.handle.net/10657/4544.

Council of Science Editors:

Gampa RV. Powering Particle Accelerators. [Masters Thesis]. University of Houston; 2017. Available from: http://hdl.handle.net/10657/4544

University of Houston

2. -4736-7040. Flexible and Stretchable Lithium-Ion Batteries Based on Solid Polymer Nanocomposite Electrolyte.

Degree: PhD, Mechanical Engineering, 2016, University of Houston

URL: http://hdl.handle.net/10657/5413

► The prevalence of flexible electronics including the ubiquitous touch-screens, roll-up displays, implantable medical devices and wearable sensors has motivated the development of high performance flexible… (more)

▼ The prevalence of flexible electronics including the ubiquitous touch-screens, roll-up displays, implantable medical devices and wearable sensors has motivated the development of high performance flexible energy storage devices. High energy density lithium-ion batteries (LIBs) are the leading candidates to convert into flexible and stretchable batteries to integrate with the flexible and stretchable applications. The ultimate challenge is to obtain mechanical flexibility while conserving the high electrochemical performance of conventional LIBs including high capacity and cycling stability. In this study, two types of polymer nanocomposite electrolytes are investigated for battery and fuel cell applications. The first polymer studied is based on Nafion, and a key problem in PEMFCs is the dehydration of Nafion and the subsequent low performance especially at higher temperatures. We introduced a bio-friendly coconut shell activated carbon (AC) nanoparticles into the Nafion membranes. We showed that a small amount (i.e., 0.7%) of AC nanofillers could dramatically enhance proton conductivity without significantly compromising the mechanical properties. The second type of polymer for lithium-ion battery application is based on the polyethylene oxide (PEO)|Li salt system. It offers enhanced safety, stability and thin-film manufacturability compared to the traditional organic liquid electrolytes. The electrochemical properties of the pure polymer are improved by adding 1% graphene oxide (GO) nanosheets. We developed a high performance flexible Li ion battery based on the solid polymer nanocomposite electrolyte. The flexible battery exhibits a capacity higher than 0.1 mAh cm-2 at 1 mA current and excellent cycling stability over 100 charge/discharge cycles. PEO/GO electrolyte was also incorporated in a novel design of spiral stretchable battery capable of large out-of-plane deformation. The spiral Li-ion battery displays robust mechanical stretchability and an energy density of 4.862 mWh/cm3 at 650% out-of-plane deformation and provides an average capacity above 0.1 mAh/cm2 in different stretching configurations. We also investigated the temperature effects on solid polymer electrolyte based batteries. A 1-D LIB model that predicts the discharge behavior of coin cell batteries at different temperatures was developed. The modeling simulations based on electrochemical-thermal coupling show good agreement with experimental results and provide fundamental insights on the battery operation at different conditions. Advisors/Committee Members: Ardebili, Haleh (advisor), Kulkarni, Yashashree (committee member), Ryou, Jae-Hyun (committee member), Liu, Dong (committee member), Yao, Yan (committee member).

Subjects/Keywords: Lithium-ion batteries (LIB); Stretchable; Flexible; Solid polymer nanocomposite electrolyte

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APA (6^th Edition):

-4736-7040. (2016). Flexible and Stretchable Lithium-Ion Batteries Based on Solid Polymer Nanocomposite Electrolyte. (Doctoral Dissertation). University of Houston. Retrieved from http://hdl.handle.net/10657/5413

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Chicago Manual of Style (16^th Edition):

-4736-7040. “Flexible and Stretchable Lithium-Ion Batteries Based on Solid Polymer Nanocomposite Electrolyte.” 2016. Doctoral Dissertation, University of Houston. Accessed January 26, 2021. http://hdl.handle.net/10657/5413.

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MLA Handbook (7^th Edition):

-4736-7040. “Flexible and Stretchable Lithium-Ion Batteries Based on Solid Polymer Nanocomposite Electrolyte.” 2016. Web. 26 Jan 2021.

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Author name may be incomplete

Vancouver:

-4736-7040. Flexible and Stretchable Lithium-Ion Batteries Based on Solid Polymer Nanocomposite Electrolyte. [Internet] [Doctoral dissertation]. University of Houston; 2016. [cited 2021 Jan 26]. Available from: http://hdl.handle.net/10657/5413.

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Author name may be incomplete

Council of Science Editors:

-4736-7040. Flexible and Stretchable Lithium-Ion Batteries Based on Solid Polymer Nanocomposite Electrolyte. [Doctoral Dissertation]. University of Houston; 2016. Available from: http://hdl.handle.net/10657/5413

Note: this citation may be lacking information needed for this citation format:
Author name may be incomplete

University of Houston

3. -4519-6532. Thermo-Electrochemical Mechanisms of Lithium Ion Battery Assemblies for Human Space Flight Applications.

Degree: PhD, Materials Engineering, 2016, University of Houston

URL: http://hdl.handle.net/10657/5386

► Advanced energy storage and power management systems designed through rigorous materials selection, testing and analysis processes are essential to ensuring mission longevity and success for… (more)

▼ Advanced energy storage and power management systems designed through rigorous materials selection, testing and analysis processes are essential to ensuring mission longevity and success for human space flight applications. Lithium ion (Li-ion) batteries provide superior performance characteristics, low mass and energy dense solutions. These features lead to the growing utilization of Li-ion technology for rockets, space exploration vehicles and satellites. Knowing that efficiency and survivability are influenced by temperature and that thermal safety concerns (i.e. thermal runaway) impede the utilization of Li-ion technology for human space flight applications, this dissertation focuses on the thermo-electrochemical mechanisms of Li-ion batteries. Test and analysis techniques developed here support the design of safe Li-ion battery assemblies. Current finite element simulation methods support detailed analysis of thermo-electrochemical processes; however, said software packages do not maintain capabilities to incorporate the influence of thermal radiation driven orbital environments. In this dissertation, we couple existing thermo-electrochemical models of Li-ion battery local heat generation with specialized radiation analysis software, Thermal Desktop. The unique capability gained by employing Thermal Desktop is further demonstrated by simulating Li-ion battery thermal performance in example orbital environments exterior to a small satellite. Results provide demonstration of Li-ion battery thermo-electrochemical performance in space environments. Experimental characterization of thermal runaway energy release with accelerated rate calorimetry supports safer thermal management systems. ‘Standard’ accelerated rate calorimetry setup provides means to measure the addition of energy exhibited through the body of a Li-ion cell. This dissertation considers the total energy generated during thermal runaway as distributions between cell body and hot gases via inclusion of a unique secondary enclosure inside the calorimeter. This closed system not only contains the cell body and gaseous species, but also captures energy release associated with rapid heat transfer to the system unobserved by measurements taken on the cell body. An inverse relationship between state-of-charge and onset temperature is observed. Energy contained in the cell body and gaseous species are successfully characterized. Significant additional energy is measured with the heating of the secondary enclosure. Improved calorimeter apparatus including a secondary enclosure provides essential capability to measuring total energy release distributions during thermal runaway. Advisors/Committee Members: Ardebili, Haleh (advisor), Ryou, Jae-Hyun (committee member), White, Kenneth W. (committee member), Liu, Dong (committee member), Kulkarni, Yashashree (committee member).

Subjects/Keywords: Lithium-ion batteries (LIB); Batteries; Space Applications; Thermo-Electrochemical Test and Analysis; Thermal Runaway Characterization; Accelerating Rate Calorimetry

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APA (6^th Edition):

-4519-6532. (2016). Thermo-Electrochemical Mechanisms of Lithium Ion Battery Assemblies for Human Space Flight Applications. (Doctoral Dissertation). University of Houston. Retrieved from http://hdl.handle.net/10657/5386

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Chicago Manual of Style (16^th Edition):

-4519-6532. “Thermo-Electrochemical Mechanisms of Lithium Ion Battery Assemblies for Human Space Flight Applications.” 2016. Doctoral Dissertation, University of Houston. Accessed January 26, 2021. http://hdl.handle.net/10657/5386.

Note: this citation may be lacking information needed for this citation format:
Author name may be incomplete

MLA Handbook (7^th Edition):

-4519-6532. “Thermo-Electrochemical Mechanisms of Lithium Ion Battery Assemblies for Human Space Flight Applications.” 2016. Web. 26 Jan 2021.

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Author name may be incomplete

Vancouver:

-4519-6532. Thermo-Electrochemical Mechanisms of Lithium Ion Battery Assemblies for Human Space Flight Applications. [Internet] [Doctoral dissertation]. University of Houston; 2016. [cited 2021 Jan 26]. Available from: http://hdl.handle.net/10657/5386.

Note: this citation may be lacking information needed for this citation format:
Author name may be incomplete

Council of Science Editors:

-4519-6532. Thermo-Electrochemical Mechanisms of Lithium Ion Battery Assemblies for Human Space Flight Applications. [Doctoral Dissertation]. University of Houston; 2016. Available from: http://hdl.handle.net/10657/5386

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Author name may be incomplete

University of Houston

4. Ahmadpoor, Fatemeh. Statistical Mechanics of Two-Dimensional Materials; From Biological Membranes to Graphene.

Degree: PhD, Mechanical Engineering, 2016, University of Houston

URL: http://hdl.handle.net/10657/5421

► 2D materials are fascinating for numerous reasons. Their geometrical and mechanical characteristics along with other associated physical properties have opened up fascinating new application avenues… (more)

▼ 2D materials are fascinating for numerous reasons. Their geometrical and mechanical characteristics along with other associated physical properties have opened up fascinating new application avenues ranging from electronics, energy harvesting, biological systems among others. Due to the 2D nature of these materials, they are known for their unusual flexibility and the ability to sustain large curvature deformations. Further, they undergo noticeable thermal fluctuations at room temperature. In the following, we highlight both the characteristics and implications of thermal fluctuations in 2D materials and discuss the following problems in biological physics and material science: (i) The minimum electric field that can be detected by a biological membrane: Using a nonlinear continuum electromechanical model, and methods of statistical mechanics, we developed a variational approximation to analytically obtain the benchmark results for model fluid membranes as well as physically reasonable estimates of the minimum electric field that can be detected by a biological membrane. (ii) Thermal fluctuations of vesicles and nonlinear curvature elasticity – Implications for sized-dependent renormalized bending rigidity and vesicle size distribution: In this work, we discuss the statistical mechanics of closed membranes (vesicles) incorporating both constitutive and geometrical nonlinearities. Our closed-form results may also be used to determine nonlinear curvature elasticity properties from either experimentally measured fluctuation spectra or microscopic calculations such as molecular dynamics. (iii) Fluctuations and effective bending stiffness of solid membranes within nonlinear elasticity: The study of thermal fluctuations of graphene is rendered rather complicated due to the necessity of accounting for geometric deformation nonlinearity in its deformation. Coupling of stretching and flexural modes leads to a highly anharmonic elastic Hamiltonian. In this study, using a variational perturbation method, we present a ”mechanics-oriented” novel treatment of the thermal fluctuations of graphene, fully accounting for deformation nonlinearities, and evaluate their effect on the effective bending stiffness. (iv) The quest for the determination of the Gaussian modulus—exploiting membrane edge fluctuations: In this work, recognizing that the Gaussian modulus plays a non-trivial role in the fluctuations of a membrane edge, we derive closed-form expressions for edge fluctuations. Combined with atomistic simulations, we use the developed approach to extract Gaussian modulus of graphene. Advisors/Committee Members: Sharma, Pradeep (advisor), Agrawal, Ashutosh (committee member), Gunaratne, Gemunu H. (committee member), Kulkarni, Yashashree (committee member), Chen, Yi-Chao (committee member).

Subjects/Keywords: 2D Materials; Biological membranes; Graphene; Thermal fluctuations; Gaussian modulus

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APA (6^th Edition):

Ahmadpoor, F. (2016). Statistical Mechanics of Two-Dimensional Materials; From Biological Membranes to Graphene. (Doctoral Dissertation). University of Houston. Retrieved from http://hdl.handle.net/10657/5421

Chicago Manual of Style (16^th Edition):

Ahmadpoor, Fatemeh. “Statistical Mechanics of Two-Dimensional Materials; From Biological Membranes to Graphene.” 2016. Doctoral Dissertation, University of Houston. Accessed January 26, 2021. http://hdl.handle.net/10657/5421.

MLA Handbook (7^th Edition):

Ahmadpoor, Fatemeh. “Statistical Mechanics of Two-Dimensional Materials; From Biological Membranes to Graphene.” 2016. Web. 26 Jan 2021.

Vancouver:

Ahmadpoor F. Statistical Mechanics of Two-Dimensional Materials; From Biological Membranes to Graphene. [Internet] [Doctoral dissertation]. University of Houston; 2016. [cited 2021 Jan 26]. Available from: http://hdl.handle.net/10657/5421.

Council of Science Editors:

Ahmadpoor F. Statistical Mechanics of Two-Dimensional Materials; From Biological Membranes to Graphene. [Doctoral Dissertation]. University of Houston; 2016. Available from: http://hdl.handle.net/10657/5421

University of Houston

5. Li, Qin. Mechanisms of Enhancing Solid Polymer Electrolytes Using Nanofillers and Ionic Liquid for Applications in Flexible Lithium Ion Batteries.

Degree: PhD, Mechanical Engineering, 2015, University of Houston

URL: http://hdl.handle.net/10657/5366

► Polymer-based electrolytes have gained much attention in recent decades due to their many advantages including high thermal and chemical stability, and the consequent enhanced safety… (more)

▼ Polymer-based electrolytes have gained much attention in recent decades due to their many advantages including high thermal and chemical stability, and the consequent enhanced safety in lithium ion batteries. Also, thin-film manufacturability and mechanical strength make the polymer-based electrolyte excellent candidate for the development of thin, flexible lithium ion battery. One main issue with polymer electrolytes is their lower ion conductivity compared to that of conventional liquid electrolytes. In this dissertation, the properties of polymer-based solid and gel electrolytes and their applications for lithium ion batteries have been investigated. The focus of this dissertation is the influence of selected additives including nanofillers, and ionic liquids on the performance of the polymer electrolytes and flexible lithium ion batteries. The effect of nanofillers on ion conductivity of polymer electrolytes is investigated using a continuum, bulk level approach. Based on the free volume theory, a model of the ion conductivity enhancement of polymer electrolyte as a function of nanofiller content is proposed. The model could fit to various experimental results of ionic conductivity enhancement and degradation. It could also be used to fit the temperature dependency of the ionic conductivity. The influence of the nanofiller is also studied at the molecular, discrete level using the molecular dynamics simulations of a polymer nanocomposite electrolyte. It is found that the embedded nanofiller can affect the salt dissociation, lithium-ion mobility, and the dynamics of polymer chains. Those effects can depend on the surface functionality and size of the nanofiller. Furthermore, the effect of ionic liquid on polymer electrolyte performance is investigated. A highly conductive ionic liquid (IL), 1-Ethyl-3-methylimidazolium dicyanamide (EMIMDCA), with ionic conductivity as high as 27 S/cm, is incorporated in poly(vinylidene fluoride-co-hexafluoropropene) (PVDF-HFP) polymer matrix and lithium salt (i.e., lithium perchlorate) to form the polymer-IL electrolyte. The obtained electrolyte is a freestanding thin-film and exhibits solid-like appearance. Due to its high stability, the polymer-IL electrolyte film is used for a low-cost, simple lamination method to fabricate high performance flexible lithium ion batteries. The battery shows relatively stable energy delivery capability and can function in both flat and bent configurations. Advisors/Committee Members: Ardebili, Haleh (advisor), Kulkarni, Yashashree (committee member), Sun, Li (committee member), Ryou, Jae-Hyun (committee member), Yao, Yan (committee member).

Subjects/Keywords: Polymer electrolytes; Molecular dynamics; Flexible batteries; Batteries; Lithium-ion batteries (LIB)

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APA (6^th Edition):

Li, Q. (2015). Mechanisms of Enhancing Solid Polymer Electrolytes Using Nanofillers and Ionic Liquid for Applications in Flexible Lithium Ion Batteries. (Doctoral Dissertation). University of Houston. Retrieved from http://hdl.handle.net/10657/5366

Chicago Manual of Style (16^th Edition):

Li, Qin. “Mechanisms of Enhancing Solid Polymer Electrolytes Using Nanofillers and Ionic Liquid for Applications in Flexible Lithium Ion Batteries.” 2015. Doctoral Dissertation, University of Houston. Accessed January 26, 2021. http://hdl.handle.net/10657/5366.

MLA Handbook (7^th Edition):

Li, Qin. “Mechanisms of Enhancing Solid Polymer Electrolytes Using Nanofillers and Ionic Liquid for Applications in Flexible Lithium Ion Batteries.” 2015. Web. 26 Jan 2021.

Vancouver:

Li Q. Mechanisms of Enhancing Solid Polymer Electrolytes Using Nanofillers and Ionic Liquid for Applications in Flexible Lithium Ion Batteries. [Internet] [Doctoral dissertation]. University of Houston; 2015. [cited 2021 Jan 26]. Available from: http://hdl.handle.net/10657/5366.

Council of Science Editors:

Li Q. Mechanisms of Enhancing Solid Polymer Electrolytes Using Nanofillers and Ionic Liquid for Applications in Flexible Lithium Ion Batteries. [Doctoral Dissertation]. University of Houston; 2015. Available from: http://hdl.handle.net/10657/5366

University of Houston

6. -0180-4460. Atomistic Modeling of Nanostructures via Molecular Dynamics and Time-Scaling Methods.

Degree: PhD, Mechanical Engineering, 2016, University of Houston

URL: http://hdl.handle.net/10657/1939

► Nanostructures are emerging as novel materials with revolutionary application in electronics, nuclear reactors, structures, aerospace, and energy. Nanocrystalline structures owe their outstanding mechanical properties to… (more)

▼ Nanostructures are emerging as novel materials with revolutionary application in electronics, nuclear reactors, structures, aerospace, and energy. Nanocrystalline structures owe their outstanding mechanical properties to their nanoscale grain size and high density of crystalline interfaces called grain boundaries. Recently, nanotwinned structures, containing special grain boundaries called twin boundaries, have become quite attractive as optimal motifs for strength, ductility, and grain stability in metals. This dissertation presents our atomistic study of the role of these grain boundaries and twin boundaries in governing the mechanical response of nanostructures by way of different atomistic simulation methods. Nanopillar compression is first used to investigate the interplay between size effects associated with the twin spacing and the finite size of nanopillars by molecular dynamics. Simulations reveal that there exists an optimal aspect ratio for which the yield strength of twinned nanopillars is higher than even single crystal nanopillars. In addition, it is observed that twin boundaries facilitate dislocation-starvation as defects glide along twin boundaries and are annihilated at the free surface. Approaching experimentally-relevant strain rates has been a long-standing bottleneck for molecular dynamics. In this study, shearing of a nanopillar with a grain boundary is used as a paradigmatic problem to investigate the rate dependence of grain boundary sliding in nanostructures. A combination of time-scaling approaches is used including the recently developed autonomous basin climbing method, the nudged elastic band method, and kinetic Monte Carlo, to access strain rates ranging from 0.5s-1 to 107s-1. Although grain boundary sliding is the primary mechanism observed in all simulations, at lower strain rate, sliding initiates at significantly lower stress and occurs on the time-scale of seconds which is beyond the reach of conventional molecular dynamics. Finally the time scaling approach is used to investigate the diffusion of radiation-induced point defects through nanotwinned metals. The simulations reveal that dumbbell interstitials can cross coherent twin boundaries in three low energy barrier steps which can occur even at room temperature. Furthermore, the method shows that Frenkel pairs have greater probability to recombine in the vicinity of coherent twin boundaries which is consistent with observations reported by other computational studies. Advisors/Committee Members: Kulkarni, Yashashree (advisor), Sharma, Pradeep (committee member), Ardebili, Haleh (committee member), Willam, Kaspar J. (committee member), Mavrokefalos, Anastassios (committee member).

Subjects/Keywords: Nanostructures; Time-scaling atomistics; ABC; MD; Atomistic; Modeling

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APA (6^th Edition):

-0180-4460. (2016). Atomistic Modeling of Nanostructures via Molecular Dynamics and Time-Scaling Methods. (Doctoral Dissertation). University of Houston. Retrieved from http://hdl.handle.net/10657/1939

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Chicago Manual of Style (16^th Edition):

-0180-4460. “Atomistic Modeling of Nanostructures via Molecular Dynamics and Time-Scaling Methods.” 2016. Doctoral Dissertation, University of Houston. Accessed January 26, 2021. http://hdl.handle.net/10657/1939.

Note: this citation may be lacking information needed for this citation format:
Author name may be incomplete

MLA Handbook (7^th Edition):

-0180-4460. “Atomistic Modeling of Nanostructures via Molecular Dynamics and Time-Scaling Methods.” 2016. Web. 26 Jan 2021.

Note: this citation may be lacking information needed for this citation format:
Author name may be incomplete

Vancouver:

-0180-4460. Atomistic Modeling of Nanostructures via Molecular Dynamics and Time-Scaling Methods. [Internet] [Doctoral dissertation]. University of Houston; 2016. [cited 2021 Jan 26]. Available from: http://hdl.handle.net/10657/1939.

Note: this citation may be lacking information needed for this citation format:
Author name may be incomplete

Council of Science Editors:

-0180-4460. Atomistic Modeling of Nanostructures via Molecular Dynamics and Time-Scaling Methods. [Doctoral Dissertation]. University of Houston; 2016. Available from: http://hdl.handle.net/10657/1939

Note: this citation may be lacking information needed for this citation format:
Author name may be incomplete

University of Houston

7. Pandey, Yogendra Narayan 1982-. A Simulation Approach to Thermodynamics in Interfacial Phenomena.

Degree: PhD, Chemical Engineering, 2013, University of Houston

URL: http://hdl.handle.net/10657/941

► Industrial applications such as production of high performance polymer-nanocomposites, semiconductor fabrication, and catalysis involve molecular level phenomena governed by interfacial interactions. Precise control of these… (more)

▼ Industrial applications such as production of high performance polymer-nanocomposites, semiconductor fabrication, and catalysis involve molecular level phenomena governed by interfacial interactions. Precise control of these interactions will leverage the performance of materials in these applications. However, the ability to tailor the molecular characteristics is hindered by incomplete understanding of the controlling factors. This dissertation is broadly divided in three parts discussing the development and application of modern computational methods to elucidate such characteristics. In the first part, detailed atomistic simulations of polymer-nanoparticle systems are performed by coupling preferential sampling techniques with connectivity-altering Monte Carlo algorithms to address the challenges in modeling polymer melts in proximity to a solid. The results reveal that polymer architecture holds a prominent role in systems with nanoscopic particles. Furthermore, a scheme for developing coarse-grained models of polymers with specific chemistry in contact with the solid surface is presented and quantitatively evaluated. These models are necessary to address the larger length scales required for study of polymer-particle mixtures. Interfaces and substrate interactions play an important role for increasingly thinner polymer films employed in the semiconductor industry. There is a clear need to develop predictive models capable of describing reaction-diffusion phenomena in chemically-amplified resists and analyze their performance as a function of film thickness. In this dissertation, using mesoscopic models it is found that a central aspect governing reactions is the anomalous diffusion of the photogenerated acid. The anomalous diffusion coupled with a simple second-order acid annihilation scheme quantitatively captures experimental data for all practical conditions - with only two adjustable parameters. The need to combine the developed scheme with substrate interactions is demonstrated. Finally, the mechanism of zeolite crystal growth in solutions in the presence of growth modifiers is probed by employing atomistic simulations. It is hypothesized that molecules preferentially bind to specific crystal surfaces, which alters the crystal morphology. Using free energy calculations, the affinity of these molecules to interact with model zeolite surfaces is estimated. Distinct free energy minima and orientations of the inhibitor molecule in these minima are characterized and quantified providing a unique molecular understanding of the phenomena. Advisors/Committee Members: Doxastakis, Manolis (advisor), Krishnamoorti, Ramanan (committee member), Stein, Gila E. (committee member), Ardebili, Haleh (committee member), Kulkarni, Yashashree (committee member).

Subjects/Keywords: Polymers at interfaces; Interfacial phenomena; Molecular modeling; Stochastic simulations; Chemical engineering

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APA (6^th Edition):

Pandey, Y. N. 1. (2013). A Simulation Approach to Thermodynamics in Interfacial Phenomena. (Doctoral Dissertation). University of Houston. Retrieved from http://hdl.handle.net/10657/941

Chicago Manual of Style (16^th Edition):

Pandey, Yogendra Narayan 1982-. “A Simulation Approach to Thermodynamics in Interfacial Phenomena.” 2013. Doctoral Dissertation, University of Houston. Accessed January 26, 2021. http://hdl.handle.net/10657/941.

MLA Handbook (7^th Edition):

Pandey, Yogendra Narayan 1982-. “A Simulation Approach to Thermodynamics in Interfacial Phenomena.” 2013. Web. 26 Jan 2021.

Vancouver:

Pandey YN1. A Simulation Approach to Thermodynamics in Interfacial Phenomena. [Internet] [Doctoral dissertation]. University of Houston; 2013. [cited 2021 Jan 26]. Available from: http://hdl.handle.net/10657/941.

Council of Science Editors:

Pandey YN1. A Simulation Approach to Thermodynamics in Interfacial Phenomena. [Doctoral Dissertation]. University of Houston; 2013. Available from: http://hdl.handle.net/10657/941

University of Houston

8. -1161-051X. Electromechanical Couplings in Soft Matter and Biology.

Degree: PhD, Mechanical Engineering, 2016, University of Houston

URL: http://hdl.handle.net/10657/3263

► The ability of certain materials to deform in response to an electrical field or, conversely, generate an electrical field due to mechanical stimuli has tantalizing… (more)

▼ The ability of certain materials to deform in response to an electrical field or, conversely, generate an electrical field due to mechanical stimuli has tantalizing implications in fields ranging from biology to engineering. Various forms of electromechanical (and related) couplings, e.g., piezoelectricity, pyroelectricity, Maxwell stress effect, and ferroelectricity among others, have found use in topics ranging from energy harvesting, soft robots, sensors, and artificial muscles to the understanding of biological phenomena like mammalian hearing. In this dissertation, using methods ranging from quantum mechanics based density functional theory, empirical force-field molecular dynamics, statistical mechanics and continuum mechanics, the following topics are addressed: (i) Anomalous piezoelectricity in two-dimensional graphene nitride nanosheets: Using quantum mechanical simulations and qualitative arguments from continuum mechanics, the mechanisms that lead to the development of unexpected piezoelectricity in this 2D material are elucidated. (ii) What is the mechanism behind biological ferroelectricity?: The first evidence of ferroelectricity in biological materials was recently discovered in 2012. Biological materials shown to be ferroelectric are largely composed of the protein elastin, a large biopolymer found in the extracellular domains of most tissues. A new model and an explanation for this intriguing observation are presented. Based on a relatively simple hypothesis, an analytical statistical mechanics model is developed which, coupled with insights from molecular dynamics, provides a plausible mechanism underpinning biological ferroelectricity. Furthermore, piezoelectric properties of tropoelastin, a precursor/monomer of elastin are predicted for the first time. Specifically, it is found that the piezoelectric constant of tropoelastin is larger than any known polymer. (iii) Mammalian hearing mechanism: The mechanisms underpinning the role of the ion channel Prestin in mammalian hearing are explored. The conductance of the Prestin channel is found via molecular dynamics, an important parameter for the derivation of an analytical model of the hearing mechanism. (iv) A novel approach to estimate Gaussian modulus and edge properties of lipid bilayers: The Gaussian modulus is a largely neglected parameter of membranes which is difficult to find. A model is derived to relate the properties of the free edge of a membrane to its fluctuations. Advisors/Committee Members: Sharma, Pradeep (advisor), Agrawal, Ashutosh (committee member), Chen, Yi-Chao (committee member), Gunaratne, Gemunu H. (committee member), Kulkarni, Yashashree (committee member).

Subjects/Keywords: Electromechanical; Graphene nitride; Piezoelectricity; Ferroelectricity; Prestin; Gaussian; Modulus; MDR; Molecular dynamics

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APA (6^th Edition):

-1161-051X. (2016). Electromechanical Couplings in Soft Matter and Biology. (Doctoral Dissertation). University of Houston. Retrieved from http://hdl.handle.net/10657/3263

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Chicago Manual of Style (16^th Edition):

-1161-051X. “Electromechanical Couplings in Soft Matter and Biology.” 2016. Doctoral Dissertation, University of Houston. Accessed January 26, 2021. http://hdl.handle.net/10657/3263.

Note: this citation may be lacking information needed for this citation format:
Author name may be incomplete

MLA Handbook (7^th Edition):

-1161-051X. “Electromechanical Couplings in Soft Matter and Biology.” 2016. Web. 26 Jan 2021.

Note: this citation may be lacking information needed for this citation format:
Author name may be incomplete

Vancouver:

-1161-051X. Electromechanical Couplings in Soft Matter and Biology. [Internet] [Doctoral dissertation]. University of Houston; 2016. [cited 2021 Jan 26]. Available from: http://hdl.handle.net/10657/3263.

Note: this citation may be lacking information needed for this citation format:
Author name may be incomplete

Council of Science Editors:

-1161-051X. Electromechanical Couplings in Soft Matter and Biology. [Doctoral Dissertation]. University of Houston; 2016. Available from: http://hdl.handle.net/10657/3263

Note: this citation may be lacking information needed for this citation format:
Author name may be incomplete

University of Houston

9. -3755-3632. Plasticity Based Formulations for Pressure Sensitive Materials.

Degree: PhD, Civil Engineering, 2017, University of Houston

URL: http://hdl.handle.net/10657/4833

► The dependency of the behavior of different materials with respect to the level of the pressure is addressed. Experimental results are accompanied with appropriate constitutive… (more)

▼ The dependency of the behavior of different materials with respect to the level of the pressure is addressed. Experimental results are accompanied with appropriate constitutive formulations to validate and reproduce the main features of the experimental results. Three types of materials have been studied. A simplified constitutive model has been introduced to simulate the behavior of concrete under high confinement. The multi-surface damage plasticity model combines the hyperbolic Drucker-Prager formulation in shear and tension regime and the modified cam-clay yield functions in the cap of the triaxial compression. The post yield behavior and the damage evolution of concrete are divided into the tensile, shear, and compressive regimes. Fracture energy based coefficients govern the hardening and softening behavior of concrete by altering a) the cohesion, b) the tension limit, and c) the compression cap limit. The non-associativity regulates the dilatancy of concrete. The bulk damage, which is activated at the point of transition from compaction to dilation is separated from the shear damage to capture the behavior of concrete subjected to cyclic loading. One advantage of the proposed formulation is the small number of material parameters. The performance of the material model has been verified using numerical examples under different load histories. Specifically, the response behavior of the model under high levels of confinement is investigated in the presentation. The constitutive formulation was validated using benchmark experiments from the literature. Some load cases of hydrostatic response, the proportional, and the oedometer benchmark test were used to calibrate the model. The pressure sensitivity of metals was addressed as a part of this research. It is stated that structural steel exhibits pressure sensitive behavior contrary to the common expectations. A series of experiments under different load scenarios were performed on steel specimens, which activates non-deviatoric stress tensor invariants. The load is applied to solid round bars in form of combinations of uniaxial tension/compression and torsion sequences, which will result in combined axial and shear stresses that maintain a constant ratio throughout the experiment. Digital Image Correlation (DIC) was used as a full-field measurement method of the displacement field and calculation of the strain distribution of the steel specimens to obtain plastic flow direction by integration of the plastic strain rate through the physical domain of the specimen and expressed it in terms of the first invariant of stress tensor and the second and third invariant of the stress deviator. Looking at the full strain tensor, a more accurate hardening rule was proposed as a function of all these three invariants of the plastic strain tensor. Using this method, the plastic flow rule was derived by integrating plastic strain rate through the physical domain of the specimen and expressing it in terms of the three invariant formulation of the stress tensor to activate… Advisors/Committee Members: Willam, Kaspar J. (advisor), Ayoub, Ashraf S. (committee member), Dawood, Mina (committee member), Nakshatrala, Kalyana Babu (committee member), Kulkarni, Yashashree (committee member).

Subjects/Keywords: Concrete; Steel; Interfaces; Masonry; Plasticity; Yield; Damages; Finite element; Lode angle; Stress; Strain; Inelastic; Constitutive formulation; Digital image correlation (DIC)

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APA (6^th Edition):

-3755-3632. (2017). Plasticity Based Formulations for Pressure Sensitive Materials. (Doctoral Dissertation). University of Houston. Retrieved from http://hdl.handle.net/10657/4833

Note: this citation may be lacking information needed for this citation format:
Author name may be incomplete

Chicago Manual of Style (16^th Edition):

-3755-3632. “Plasticity Based Formulations for Pressure Sensitive Materials.” 2017. Doctoral Dissertation, University of Houston. Accessed January 26, 2021. http://hdl.handle.net/10657/4833.

Note: this citation may be lacking information needed for this citation format:
Author name may be incomplete

MLA Handbook (7^th Edition):

-3755-3632. “Plasticity Based Formulations for Pressure Sensitive Materials.” 2017. Web. 26 Jan 2021.

Note: this citation may be lacking information needed for this citation format:
Author name may be incomplete

Vancouver:

-3755-3632. Plasticity Based Formulations for Pressure Sensitive Materials. [Internet] [Doctoral dissertation]. University of Houston; 2017. [cited 2021 Jan 26]. Available from: http://hdl.handle.net/10657/4833.

Note: this citation may be lacking information needed for this citation format:
Author name may be incomplete

Council of Science Editors:

-3755-3632. Plasticity Based Formulations for Pressure Sensitive Materials. [Doctoral Dissertation]. University of Houston; 2017. Available from: http://hdl.handle.net/10657/4833

Note: this citation may be lacking information needed for this citation format:
Author name may be incomplete

University of Houston

10. Li, Xiaobao. The Coupling between Quantum Mechanics and Elasticity.

Degree: PhD, Mechanical Engineering, 2016, University of Houston

URL: http://hdl.handle.net/10657/3264

► In this dissertation we explore the junction of quantum mechanics and elas- ticity. Specifically, we attempt to elucidate, in several physical contexts, how me- chanical… (more)

▼ In this dissertation we explore the junction of quantum mechanics and elas- ticity. Specifically, we attempt to elucidate, in several physical contexts, how me- chanical deformation alters the quantum mechanical behavior of nanostructures and nanomaterials. In the first part of the dissertation, we develop a theoretical framework which shows that a striking analog of the electrostatic Maxwell stress also ex- ists in the context of quantum mechanical-elasticity coupling. The newly derived quantum-elastic Maxwell stress is found to be significant for soft nanoscale struc- tures (such as the DNA) and underscores a fresh perspective on the mechanics and physics of quasi-particles called polarons. We discuss potential applications of the concept for soft nano-actuators and sensors and the relevance for the inter- pretation of opto-electronic properties. Mechanical strain can alter the electronic structure of both bulk semicon- ductors as well as nanostructures such as quantum dots. We relate the notion of polarons and the previously mentioned quantum-Maxwell stress to optoelec- tronic coupling. This effect, while negligible for hard materials, emerges to be important for soft materials and critically impacts the interpretation of quanti- ties such as polaron size, binding energy, and accordingly, electronic behavior in entities like DNA, polymer chains among others. A rather interesting ramification of quantum mechanics-elasticity coupling transpires in the context of the so-called "quantum capacitance". One of the many tantalizing recent physical revelations about quantum capacitance is that it can possess a negative value, hence allowing for the possibility of enhancing the over- all capacitance in some particular material systems beyond the scaling predicted by classical electrostatics. Using detailed quantum mechanical simulations, we find an intriguing result that mechanical strains can tune both signs and values of quantum capacitance. Finally, in the context of DNA like slender structures, we explore how quantum mechanical-elasticity coupling may impact the stability of such soft nanostructures. Advisors/Committee Members: Sharma, Pradeep (advisor), Chen, Yi-Chao (committee member), Gunaratne, Gemunu H. (committee member), Kulkarni, Yashashree (committee member), Agrawal, Ashutosh (committee member).

Subjects/Keywords: Quantum mechanics; Elasticity; Coupling

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APA (6^th Edition):

Li, X. (2016). The Coupling between Quantum Mechanics and Elasticity. (Doctoral Dissertation). University of Houston. Retrieved from http://hdl.handle.net/10657/3264

Chicago Manual of Style (16^th Edition):

Li, Xiaobao. “The Coupling between Quantum Mechanics and Elasticity.” 2016. Doctoral Dissertation, University of Houston. Accessed January 26, 2021. http://hdl.handle.net/10657/3264.

MLA Handbook (7^th Edition):

Li, Xiaobao. “The Coupling between Quantum Mechanics and Elasticity.” 2016. Web. 26 Jan 2021.

Vancouver:

Li X. The Coupling between Quantum Mechanics and Elasticity. [Internet] [Doctoral dissertation]. University of Houston; 2016. [cited 2021 Jan 26]. Available from: http://hdl.handle.net/10657/3264.

Council of Science Editors:

Li X. The Coupling between Quantum Mechanics and Elasticity. [Doctoral Dissertation]. University of Houston; 2016. Available from: http://hdl.handle.net/10657/3264

University of Houston

11. Gouissem, Afif. Atomistic Investigation of High Temperature Material Behavior.

Degree: PhD, Mechanical Engineering, 2014, University of Houston

URL: http://hdl.handle.net/10657/1821

► High temperature mechanical behavior of materials is of critical importance in a variety of contexts: next-generation reentry vehicles, hyper sonic ﬂights, nuclear plants, engines, among… (more)

▼ High temperature mechanical behavior of materials is of critical importance in a variety of contexts: next-generation reentry vehicles, hyper sonic ﬂights, nuclear plants, engines, among many others. Creep is the dominant failure mechanism for materials used in such applications. Atomistic design of next-generation ultra-high-temperature ceramic composites as well as a thorough understanding of the various complex micro-mechanisms of creep damage using state-of-the art atomistic methods is the main goal of this dissertation. There are two challenges that need to be overcome to accomplish this endeavor. The ﬁrst one is aptly ampliﬁed in a quote by Professor Nabarro (2002) “The creep rate in a land-based power station must be less than 10−11s ... The present state of knowledge reveals speciﬁc questions that call for experimental investigation. Theory will contribute, but atomic computation, with a time scale of 10−11s, will not handle processes that take 1011s”. The other is that for the materials of interest, the so-called ultrahigh-temperature ceramics (ZrB2 and HfB2), atomistic potentials are not available. No type of atomistic methodology (molecular dynamics, Monte Carlo) can proceed without this. Furthermore, since oxidation and various related chemical reactions play a key role in the damage of such materials at high temperatures, the atomistic potential must be able to account for reactions. First-principle calculations are indeed possible without an empirical force ﬁeld but such computations present severe limitations of the size scales they can access and of course, the enormous diﬃculty of modeling ﬁnite temperatures. In short, in this dissertation, I will focus on two aspects that can potentially pave the way for modeling high temperature behavior of ceramics: development of ReaxFF potentials for ZrB2 / HfB2 using quantum chemistry tools and implementation of algorithms that allow access to time scales relevant to creep deformation and damage. Advisors/Committee Members: Sharma, Pradeep (advisor), White, Kenneth W. (committee member), Gunaratne, Gemunu H. (committee member), Sun, Li (committee member), Kulkarni, Yashashree (committee member).

Subjects/Keywords: UHTC; Accelerated molecular dynamics; Creep

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APA (6^th Edition):

Gouissem, A. (2014). Atomistic Investigation of High Temperature Material Behavior. (Doctoral Dissertation). University of Houston. Retrieved from http://hdl.handle.net/10657/1821

Chicago Manual of Style (16^th Edition):

Gouissem, Afif. “Atomistic Investigation of High Temperature Material Behavior.” 2014. Doctoral Dissertation, University of Houston. Accessed January 26, 2021. http://hdl.handle.net/10657/1821.

MLA Handbook (7^th Edition):

Gouissem, Afif. “Atomistic Investigation of High Temperature Material Behavior.” 2014. Web. 26 Jan 2021.

Vancouver:

Gouissem A. Atomistic Investigation of High Temperature Material Behavior. [Internet] [Doctoral dissertation]. University of Houston; 2014. [cited 2021 Jan 26]. Available from: http://hdl.handle.net/10657/1821.

Council of Science Editors:

Gouissem A. Atomistic Investigation of High Temperature Material Behavior. [Doctoral Dissertation]. University of Houston; 2014. Available from: http://hdl.handle.net/10657/1821

University of Houston

12. Khadimallah, Ali. Processing for Improved Creep Behavior of Ultra-High Temperature Ceramics.

Degree: PhD, Mechanical Engineering, 2015, University of Houston

URL: http://hdl.handle.net/10657/2010

► Ultra-high temperature ceramics have been considered for several extreme applications involving high temperatures and oxidizing atmospheres. Most notably, sharp leading edges and nosecones associated with… (more)

▼ Ultra-high temperature ceramics have been considered for several extreme applications involving high temperatures and oxidizing atmospheres. Most notably, sharp leading edges and nosecones associated with hypersonic re-entry vehicles often benefit from advanced material performance under long exposure to severe conditions. ZrB2-based composites consistently compete with the other candidates for these applications due to their high melting temperatures (exceeding 3000°C), high temperature strength retention and good oxidation resistance. Long duty cycle aerospace applications particularly necessitate excellent creep deformation resistance reaching or exceeding 10-8s-1 in steady state creep rates. In the present work, ZrB2-SiC composite and ZrB2-WC alloy were selected for creep testing at 1800°C in protected environments. Two sets of experiments were performed on the hot pressed composite: four-point flexure tests at 16 and 20 MPa and compression tests under stresses ranging between 10 and 40 MPa. The data fit well to power law creep models (Norton) and based on four-point bend data, uniaxial creep parameters were determined using an analytical method present in the literature. Predicted and experimental compressive stress exponents were found to be in excellent agreement, 1.85 and 1.76 respectively. Stress exponent supported by observation of the microstructure suggest a combination of diffusion and grain boundary sliding creep mechanisms in compression. In tension, a stress exponent of 2.61, exceeds the flexural stress exponent of 2.2, suggesting an increased contribution from cavitation to the creep strain, contrasting with grain boundary sliding observed as the predominate creep mechanism for flexural creep at this temperature. Earlier work has shown the importance of grain boundary sliding on the creep deformation of ZrB2 at 1800°C, and also that this mechanism relies upon a critical accommodation mechanism involving dislocation activity in the grain boundary region. Therefore, the effect of WC addition on the creep behavior of ZrB2 was investigated in the context of a solute-dislocation interaction hypothesis in efforts to impede the accommodation event and thus retard the creep deformation. Four-point flexure experiments showed two orders of magnitude reduction in creep rates in the ZrB2-WC alloy compared to ZrB2-SiC composite when ~1.5 mol% of W dissolved in ZrB2 lattice. Additionally, a stress exponent drop from ~2.2 in ZrB2-SiC to ~1.2 in ZrB2-WC suggests transition from climb to glide controlled deformation accommodation due to effective solute interactions with gliding dislocations. The solubility of W in ZrB2 is not well known and was estimated here through two methods. First, experimentally, where ZrB2 was successfully densified by pressureless sintering to near full density at temperatures as low as 1850°C, with the addition of B4C as sintering additive. An experimental phase diagram was approximated as the samples were produced. Second, using a combination of density functional theory simulations and… Advisors/Committee Members: White, Kenneth W. (advisor), Sharma, Pradeep (committee member), Kulkarni, Yashashree (committee member), Ryou, Jae-Hyun (committee member), Willam, Kaspar J. (committee member).

Subjects/Keywords: Processing; Zirconium diboride; Microstructure; Creep mechanisms; Improved creep; Compression creep; Flexure creep; Solubility limit; Tensile creep prediction

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APA (6^th Edition):

Khadimallah, A. (2015). Processing for Improved Creep Behavior of Ultra-High Temperature Ceramics. (Doctoral Dissertation). University of Houston. Retrieved from http://hdl.handle.net/10657/2010

Chicago Manual of Style (16^th Edition):

Khadimallah, Ali. “Processing for Improved Creep Behavior of Ultra-High Temperature Ceramics.” 2015. Doctoral Dissertation, University of Houston. Accessed January 26, 2021. http://hdl.handle.net/10657/2010.

MLA Handbook (7^th Edition):

Khadimallah, Ali. “Processing for Improved Creep Behavior of Ultra-High Temperature Ceramics.” 2015. Web. 26 Jan 2021.

Vancouver:

Khadimallah A. Processing for Improved Creep Behavior of Ultra-High Temperature Ceramics. [Internet] [Doctoral dissertation]. University of Houston; 2015. [cited 2021 Jan 26]. Available from: http://hdl.handle.net/10657/2010.

Council of Science Editors:

Khadimallah A. Processing for Improved Creep Behavior of Ultra-High Temperature Ceramics. [Doctoral Dissertation]. University of Houston; 2015. Available from: http://hdl.handle.net/10657/2010

University of Houston

13. Agrawal, Himani. Atomistic and Continuum Reinvestigation of Protein Membrane Interactions.

Degree: PhD, Mechanical Engineering, 2017, University of Houston

URL: http://hdl.handle.net/10657/4784

► The phenomenological theory of elasticity, which encompasses the classical Helfrich- Canham model of a lipid membrane, is used to calculate the deformation energy of a… (more)

▼ The phenomenological theory of elasticity, which encompasses the classical Helfrich- Canham model of a lipid membrane, is used to calculate the deformation energy of a membrane in the presence of inclusions such as proteins. However, the effective proper- ties calculated using this model does not incorporate the specificity of protein and membrane. In this dissertation, we argue that each protein has a unique mechanical signature based on its interaction with the surrounding lipid bilayer membrane and cannot be treated as a non- specific rigid object. We modify the classical Helfrich-Canham theory of curvature elasticity to incorporate protein-membrane specificity. Experimental observations perplexingly appear to show that rigid proteins may either soften or harden membranes even though conventional wisdom only suggests stiffening. Based on the hypothesis of our modified Helfrich-Canham model, we have carried out atomistic simulations to investigate peptide-membrane interactions. Together with a continuum model, we reconcile contrast- ing experimental data in the literature including the case of HIV-fusion peptide induced softening. We conclude that the structural rearrangements of the lipids around the inclusions cause the softening or stiffening of the biological membranes. We also discuss the estimation of the new model parameters via atomistic simulations. Furthermore, we use our modified Helfrich-Canham model to reinvestigate the membrane curvature mediated long ranged force between two transmembrane proteins. The classical linearized Helfrich- Canham Hamiltonian based derivations reveal the nature of the force between a pair of proteins to be repulsive in the zero-temperature limit and the interaction potential is inversely proportional to the fourth power of the distance separating the inclusions. A key observation regarding this widely-quoted result is that any two (mechanically rigid) proteins will experience an identical force; this is because the protein membrane specificity is not taken into account in the existing models. We find that the incorporation of protein- specificity can reduce the interaction force by several orders of magnitude. Our result may provide at least one plausible reason behind why in some computational and experimental studies, a net attractive force between proteins is in evidence. Advisors/Committee Members: Sharma, Pradeep (advisor), Kulkarni, Yashashree (committee member), Chen, Yi-Chao (committee member), Gunaratne, Gemunu H. (committee member), Liu, Dong (committee member).

Subjects/Keywords: Membrane proteins; Simulations

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APA (6^th Edition):

Agrawal, H. (2017). Atomistic and Continuum Reinvestigation of Protein Membrane Interactions. (Doctoral Dissertation). University of Houston. Retrieved from http://hdl.handle.net/10657/4784

Chicago Manual of Style (16^th Edition):

Agrawal, Himani. “Atomistic and Continuum Reinvestigation of Protein Membrane Interactions.” 2017. Doctoral Dissertation, University of Houston. Accessed January 26, 2021. http://hdl.handle.net/10657/4784.

MLA Handbook (7^th Edition):

Agrawal, Himani. “Atomistic and Continuum Reinvestigation of Protein Membrane Interactions.” 2017. Web. 26 Jan 2021.

Vancouver:

Agrawal H. Atomistic and Continuum Reinvestigation of Protein Membrane Interactions. [Internet] [Doctoral dissertation]. University of Houston; 2017. [cited 2021 Jan 26]. Available from: http://hdl.handle.net/10657/4784.

Council of Science Editors:

Agrawal H. Atomistic and Continuum Reinvestigation of Protein Membrane Interactions. [Doctoral Dissertation]. University of Houston; 2017. Available from: http://hdl.handle.net/10657/4784

University of Houston

14. Yan, Xin. Time-Scaling in Atomistics and the Mechanical Behavior of Materials.

Degree: PhD, Mechanical Engineering, 2016, University of Houston

URL: http://hdl.handle.net/10657/5439

► Modeling physical phenomena with atomistic fidelity and at laboratory time-scales is one of the holy grails of computational materials science. Conventional molecular dynamics (MD) simulations… (more)

▼ Modeling physical phenomena with atomistic fidelity and at laboratory time-scales is one of the holy grails of computational materials science. Conventional molecular dynamics (MD) simulations enable the elucidation of an astonishing array of phenomena inherent in the mechanical and chemical behavior of materials. However, conventional MD, with our current computational modalities, is incapable of resolving time-scales longer than microseconds (at best). In this dissertation, using a recently proposed approach – the so-called autonomous basin climbing (ABC) method – together with other techniques, including nudged elastic band (NEB), kinetic Monte Carlo (KMC), and transition state theory (TST), we provide several insights on some key problems in material science. The following topics are addressed: (i) Li diffusion in amorphous matrix: Using ABC-based approach, a realistic evaluation of Li-ion diffusion pathways in amorphous Si is evaluated. Diffusive pathways are not a priori set, but rather emerge naturally as part of our computation. The comparative differences between Li-ion diffusion in amorphous and crystalline Si is elucidated. (ii) Rate-dependent mechanical behavior of crystalline nano-structure: A study of the mechanical compression behavior of nano-slabs to specifically interrogate its deformation behavior under both slow and fast strain rates. While high-strain rate deformation proceeds in an unremarkable manner – merely shortening its length along with the formation of an expected defect sub-structure, the slow-strain rate results ( – precisely what is to be expected in most applications and laboratory experiments) exhibit a dramatically different behavior. We observe "liquid-like" deformation under low strain rate. (iii) Elucidating the micro-mechanisms of rate-dependent plasticity in a-LiSi nano-structure: Silicon is arguably one of the most important electrode materials in Li-battery system. In this study, we conduct slow strain rate computational studies to provide insights into the mechanisms underpinning plastic deformation of amorphous Li-Si. We find that in the case of Li-Si nano-structures, the basic mechanism of plasticity are similar to what has been discussed in other amorphous system – formation of shear transformation zone engineered by diffusion like process. We also identify the rotation of the STZ as a key dissipation mechanism. Furthermore, the behavior under high & low strain rate is quite different and accordingly convectional MD cannot be used to understand plasticity. Advisors/Committee Members: Sharma, Pradeep (advisor), Baxevanis, Theocharis (committee member), Chen, Yi-Chao (committee member), Grabow, Lars C. (committee member), Kulkarni, Yashashree (committee member).

Subjects/Keywords: Time-scaling atomistic simulation; Autonomous basin climbing; Li-Si alloy; Nanostructures

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APA (6^th Edition):

Yan, X. (2016). Time-Scaling in Atomistics and the Mechanical Behavior of Materials. (Doctoral Dissertation). University of Houston. Retrieved from http://hdl.handle.net/10657/5439

Chicago Manual of Style (16^th Edition):

Yan, Xin. “Time-Scaling in Atomistics and the Mechanical Behavior of Materials.” 2016. Doctoral Dissertation, University of Houston. Accessed January 26, 2021. http://hdl.handle.net/10657/5439.

MLA Handbook (7^th Edition):

Yan, Xin. “Time-Scaling in Atomistics and the Mechanical Behavior of Materials.” 2016. Web. 26 Jan 2021.

Vancouver:

Yan X. Time-Scaling in Atomistics and the Mechanical Behavior of Materials. [Internet] [Doctoral dissertation]. University of Houston; 2016. [cited 2021 Jan 26]. Available from: http://hdl.handle.net/10657/5439.

Council of Science Editors:

Yan X. Time-Scaling in Atomistics and the Mechanical Behavior of Materials. [Doctoral Dissertation]. University of Houston; 2016. Available from: http://hdl.handle.net/10657/5439

University of Houston

15. -9808-7137. Development of Analytical Models for Evaluating the Mechanical and Electrochemical Response of Flexible and Stretchable Lithium Ion Battery Materials.

Degree: PhD, Materials Engineering, 2016, University of Houston

URL: http://hdl.handle.net/10657/5385

► Flexible and stretchable batteries have become a highly active area of research in recent years due to a new demand for mechanically compliant energy storage… (more)

▼ Flexible and stretchable batteries have become a highly active area of research in recent years due to a new demand for mechanically compliant energy storage devices for a wide range of flexible applications including wearable and implantable electronics, touch-screens, and smart technology. Lithium ion batteries are leading candidates for flexible and stretchable energy storage devices due to their high energy density and efficiency. Considerable research has been related to developing flexible and stretchable materials, and solid polymer electrolyte lithium ion batteries show promise, offering many mechanical and safety advantages. While much experimental work has been in the development of these batteries, considerably less analytical modeling and numerical work has been a part of the development, which would elucidate experimental observations and provide enhanced understanding of the materials behavior in these new batteries. The work presented in this dissertation includes results of computational modeling and simulation of the mechanical and electrochemical behavior of flexible and stretchable battery materials under normal operating conditions and applied deformations resulting from mechanical loads. Additionally, analytical multiphysics models in the form of series of differential equations were derived to explain experimental observations of changes in battery performance and material properties due to applied loads and deformations. These models can be used to predict materials behavior and to relate key design parameters of flexible and stretchable batteries. The battery materials and designs that are assessed in this work were developed in our lab. Objectives of this work include understanding relationships between mechanical loading and certain key controllable fabrication parameters such as layer interface contact properties to predict the influence on flexible battery performance, and exploring how deformation occurring in the polymer electrolyte due to an applied mechanical load influences electrochemical performance. The effect of loading on other performance parameters, including battery impedance, is further studied, and all analytical work is compared to experimental data. An important aspect of this development is the consideration of nonlinearity in the models. Novel approaches are taken to include and address nonlinearity within the systems considered. While these models can be simplified through linearization, limitations of linear solutions are also discussed. Advisors/Committee Members: Ardebili, Haleh (advisor), Ryou, Jae-Hyun (committee member), Yu, Cunjiang (committee member), Sharma, Pradeep (committee member), Kulkarni, Yashashree (committee member).

Subjects/Keywords: Flexible batteries; Batteries; Lithium-ion batteries (LIB); Stretchable lithium ion batteries; Nonlinear modeling

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APA (6^th Edition):

-9808-7137. (2016). Development of Analytical Models for Evaluating the Mechanical and Electrochemical Response of Flexible and Stretchable Lithium Ion Battery Materials. (Doctoral Dissertation). University of Houston. Retrieved from http://hdl.handle.net/10657/5385

Note: this citation may be lacking information needed for this citation format:
Author name may be incomplete

Chicago Manual of Style (16^th Edition):

-9808-7137. “Development of Analytical Models for Evaluating the Mechanical and Electrochemical Response of Flexible and Stretchable Lithium Ion Battery Materials.” 2016. Doctoral Dissertation, University of Houston. Accessed January 26, 2021. http://hdl.handle.net/10657/5385.

Note: this citation may be lacking information needed for this citation format:
Author name may be incomplete

MLA Handbook (7^th Edition):

-9808-7137. “Development of Analytical Models for Evaluating the Mechanical and Electrochemical Response of Flexible and Stretchable Lithium Ion Battery Materials.” 2016. Web. 26 Jan 2021.

Note: this citation may be lacking information needed for this citation format:
Author name may be incomplete

Vancouver:

-9808-7137. Development of Analytical Models for Evaluating the Mechanical and Electrochemical Response of Flexible and Stretchable Lithium Ion Battery Materials. [Internet] [Doctoral dissertation]. University of Houston; 2016. [cited 2021 Jan 26]. Available from: http://hdl.handle.net/10657/5385.

Note: this citation may be lacking information needed for this citation format:
Author name may be incomplete

Council of Science Editors:

-9808-7137. Development of Analytical Models for Evaluating the Mechanical and Electrochemical Response of Flexible and Stretchable Lithium Ion Battery Materials. [Doctoral Dissertation]. University of Houston; 2016. Available from: http://hdl.handle.net/10657/5385

Note: this citation may be lacking information needed for this citation format:
Author name may be incomplete

University of Houston

16. -2777-8125. Molecular Dynamics Study of Radiation and Creep Response of Nanotwinned FCC Metals.

Degree: PhD, Mechanical Engineering, 2015, University of Houston

URL: http://hdl.handle.net/10657/1973

► Research over the past decade has provided compelling evidence that nanotwinned structures may be optimal motifs for the design of high-strength high-ductility materials. This dissertation… (more)

▼ Research over the past decade has provided compelling evidence that nanotwinned structures may be optimal motifs for the design of high-strength high-ductility materials. This dissertation presents our atomistic study of the deformation mechanisms governing the radiation tolerance, high temperature creep, and fracture response of nanotwinned face-centered cubic (fcc) metals. We employ molecular dynamics (MD) to elucidate the synergistic role of grain boundaries (GBs) and coherent twin boundaries (CTBs) in the radiation tolerance of nanotwinned Cu. While GBs are known to be excellent sinks for point defects, CTBs do not absorb point defects. A beneficial corollary is that the structural integrity of CTBs remains intact as radiation-induced defects pass through them and get absorbed into GBs. Thus, our tension simulations reveal that nanotwinned metals continue to exhibit high strength even after being subjected to radiation damage. We also perform atomistic simulations of cyclic nanoindentation to complement experimental studies of cyclic nano- and micro-indentation, along with indentation creep, on nanotwinned Cu and Ag. Taken together, the studies provide evidence that nanotwinned fcc structures are more stable than their nanocrystalline counterparts. Inspired by the excellent mechanical stability of nanotwinned metals during indentation creep, we investigate high temperature creep in polycrystalline nanotwinned Cu using MD. The simulations reveal that the nanotwinned metals exhibit greater creep resistance with decreasing twin boundary (TB) spacing at all applied stresses. Nanotwinned metals with very high density of TBs exhibit a new creep deformation mechanism at high stresses governed by TB migration. This is in contrast to nanocrystalline and nanotwinned metals with larger twin spacing, which exhibit a more conventional transition from GB diffusion and sliding to dislocation nucleation. Finally, our investigation of the crack propagation along CTBs in a range of fcc metals with various crack and sample geometries indicates that the alternating brittle-ductile behavior of CTBs observed perviously is sensitive to the material, and crack length. In summary, our results furnish insights into the role of TBs in governing the remarkable mechanical stability, creep resistance and radiation tolerance of nanotwinned metals, making them strong candidates for future structural materials for extreme environments. Advisors/Committee Members: Kulkarni, Yashashree (advisor), Sharma, Pradeep (committee member), Li, Mo (committee member), White, Kenneth W. (committee member), Agrawal, Ashutosh (committee member).

Subjects/Keywords: Twin boundaries; Radiation; Creep; Nanotwinned metals; Molecular dynamics; Grain stability; Fracture behavior

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APA (6^th Edition):

-2777-8125. (2015). Molecular Dynamics Study of Radiation and Creep Response of Nanotwinned FCC Metals. (Doctoral Dissertation). University of Houston. Retrieved from http://hdl.handle.net/10657/1973

Note: this citation may be lacking information needed for this citation format:
Author name may be incomplete

Chicago Manual of Style (16^th Edition):

-2777-8125. “Molecular Dynamics Study of Radiation and Creep Response of Nanotwinned FCC Metals.” 2015. Doctoral Dissertation, University of Houston. Accessed January 26, 2021. http://hdl.handle.net/10657/1973.

Note: this citation may be lacking information needed for this citation format:
Author name may be incomplete

MLA Handbook (7^th Edition):

-2777-8125. “Molecular Dynamics Study of Radiation and Creep Response of Nanotwinned FCC Metals.” 2015. Web. 26 Jan 2021.

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Author name may be incomplete

Vancouver:

-2777-8125. Molecular Dynamics Study of Radiation and Creep Response of Nanotwinned FCC Metals. [Internet] [Doctoral dissertation]. University of Houston; 2015. [cited 2021 Jan 26]. Available from: http://hdl.handle.net/10657/1973.

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Author name may be incomplete

Council of Science Editors:

-2777-8125. Molecular Dynamics Study of Radiation and Creep Response of Nanotwinned FCC Metals. [Doctoral Dissertation]. University of Houston; 2015. Available from: http://hdl.handle.net/10657/1973

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Author name may be incomplete

University of Houston

17. Chen, Dengke. Elucidating the Mechanical Properties of Crystalline Interfaces from Thermal Fluctuations.

Degree: PhD, Mechanical Engineering, 2015, University of Houston

URL: http://hdl.handle.net/10657/5381

► Nanostructured materials have gained prominence owing to the exciting array of physical properties that are primarily governed by the high density of interfaces and interfacial… (more)

▼ Nanostructured materials have gained prominence owing to the exciting array of physical properties that are primarily governed by the high density of interfaces and interfacial phenomena. This dissertation presents the statistical mechanics modeling and atomistic simulations of two types of crystalline interfaces, namely twin boundaries and grain boundaries, to understand their thermodynamic and kinetic properties based on thermal fluctuations. To this end, we first study the thermal fluctuations of twin boundaries in face-centered-cubic metals to elucidate the deformation mechanism governing their kinetic properties. Our simulations show that the normal motion of twin boundaries is strongly coupled to shear deformation up to near the melting temperature. Since twin boundaries commonly occur as parallel interfaces, we further investigate the entropic interaction between fluctuating twin boundaries using atomistic simulations and statistical mechanics based analysis. The simulations reveal that fluctuations of twin boundaries are enhanced in the presence of adjoining twin boundaries as their spacing d decreases. In addition, the theoretical analysis shows that fluctuating twin boundaries indeed exhibit an attractive entropic interaction which enhances their thermal fluctuations and that this force decreases as 1/d². This attractive interaction between twin boundaries is attributed to their shear coupled normal motion and is fundamentally distinct from the well -known repulsive entropic interaction followed by fluid membranes and many crystalline membranes and interfaces. In addition to the entropic force, we present a study of the thermal expansion of twin boundaries at finite temperature by way of atomistic simulations. The simulations reveal that for all twin boundary spacing d, the thermal expansion induced stress varies as 1/d. This long-range effect is attributed to the inhomogeneity in the thermal expansion coefficient due to the interfacial regions. Finally, we study the effect of defects, specifically second phase particles, in grain boundaries by extending the interface random walk model, and deriving the general analytical expression relating the grain boundary mobility to key parameters governing the interaction between the particles and the grain boundary. We verify our theoretical model through atomistic simulations for symmetrical tilt boundaries with multiple fixed inclusions and propose a method to extract the mobility from grain boundary fluctuations. Advisors/Committee Members: Kulkarni, Yashashree (advisor), Sharma, Pradeep (committee member), Gunaratne, Gemunu H. (committee member), Chen, Yichao (committee member), Ghasemi, Hadi (committee member).

Subjects/Keywords: Crystalline Interfaces; Grain boundaries; Twin boundaries; Molecular dynamics; Thermal fluctuations; Entropic Interaction

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6^th Edition):

Chen, D. (2015). Elucidating the Mechanical Properties of Crystalline Interfaces from Thermal Fluctuations. (Doctoral Dissertation). University of Houston. Retrieved from http://hdl.handle.net/10657/5381

Chicago Manual of Style (16^th Edition):

Chen, Dengke. “Elucidating the Mechanical Properties of Crystalline Interfaces from Thermal Fluctuations.” 2015. Doctoral Dissertation, University of Houston. Accessed January 26, 2021. http://hdl.handle.net/10657/5381.

MLA Handbook (7^th Edition):

Chen, Dengke. “Elucidating the Mechanical Properties of Crystalline Interfaces from Thermal Fluctuations.” 2015. Web. 26 Jan 2021.

Vancouver:

Chen D. Elucidating the Mechanical Properties of Crystalline Interfaces from Thermal Fluctuations. [Internet] [Doctoral dissertation]. University of Houston; 2015. [cited 2021 Jan 26]. Available from: http://hdl.handle.net/10657/5381.

Council of Science Editors:

Chen D. Elucidating the Mechanical Properties of Crystalline Interfaces from Thermal Fluctuations. [Doctoral Dissertation]. University of Houston; 2015. Available from: http://hdl.handle.net/10657/5381

University of Houston

18. -5545-6406. Computational Methods for Multi-Scale Temporal Problems: Algorithms, Analysis, and Numerical Experiments.

Degree: PhD, Civil Engineering, 2016, University of Houston

URL: http://hdl.handle.net/10657/5442

► A major challenge in numerical simulation of most natural phenomena is the presence of disparate temporal and spatial scales. Capturing all the fine features can… (more)

▼ A major challenge in numerical simulation of most natural phenomena is the presence of disparate temporal and spatial scales. Capturing all the fine features can be computationally prohibitive. Hence, development of efficient and accurate multi-scale numerical algorithms has gained immense attention from engineers and scientists. Typically, a single numerical method cannot efficiently capture all the aforementioned features. Due to the assumptions made in construction of numerical methods and mathematical models, the range of applicability to various length and time-scales is often limited. A direction in resolving this issue is to apply different numerical methods in different regions of the computational domain. This strategy enables computation of necessary details as desired by the user. In this work, we propose numerical methodologies based on domain partitioning techniques that allow different time-steps and time-integrators in different regions of the computational domain. The first problem of interest is elastodynamics, which can pose various temporal scales in impact, contact and wave propagation problems. A monolithic (strong) coupling algorithm based on non-overlapping domain partitioning is proposed. The proposed algorithm is based on the theory of differential/algebraic equations and its numerical stability, energy conservation and accuracy is studied in detail. Following these findings, we extend this algorithm to advection-diffusion-reaction problems. The proposed algorithm proves useful especially in cases where the relative strength of the involved processes changes dramatically with respect to spatial coordinates. Numerical stability and accuracy of this method is studied and its application to fast bimolecular chemical reactions is showcased. Further on, we confine our attention to single and multiple-relaxation-time lattice Boltzmann methods for the advection-diffusion equation and study their performance in preserving the maximum principle and the non-negative constraint. Finally, a computational framework based on overlapping domain decomposition methods is proposed. This framework is designed for advection-diffusion problems and allows coupling of the finite element method and lattice Boltzmann methods with different time-steps and grid sizes. Additionally, a new method for enforcing the Dirichlet and Neumann boundary conditions on the numerical solution from the lattice Boltzmann method is proposed. This method is based on maximization of entropy and ensures non-negativity of the discrete distributions on the boundary of the domain. We study the performance of this framework through numerical experiments and showcase its application to fast and equilibrium chemical reactions. Advisors/Committee Members: Nakshatrala, Kalyana Babu (advisor), Wang, Keh-Han (committee member), Willam, Kaspar J. (committee member), Lim, Gino J. (committee member), Kulkarni, Yashashree (committee member).

Subjects/Keywords: Computational mechanics; Finite element analysis; Numerical Analysis; Lattice Boltzmann Methods; Multi-Scale Simulation; Domain decomposition; Time Integration; Differential/Algebraic Equations

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APA (6^th Edition):

-5545-6406. (2016). Computational Methods for Multi-Scale Temporal Problems: Algorithms, Analysis, and Numerical Experiments. (Doctoral Dissertation). University of Houston. Retrieved from http://hdl.handle.net/10657/5442

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Author name may be incomplete

Chicago Manual of Style (16^th Edition):

-5545-6406. “Computational Methods for Multi-Scale Temporal Problems: Algorithms, Analysis, and Numerical Experiments.” 2016. Doctoral Dissertation, University of Houston. Accessed January 26, 2021. http://hdl.handle.net/10657/5442.

Note: this citation may be lacking information needed for this citation format:
Author name may be incomplete

MLA Handbook (7^th Edition):

-5545-6406. “Computational Methods for Multi-Scale Temporal Problems: Algorithms, Analysis, and Numerical Experiments.” 2016. Web. 26 Jan 2021.

Note: this citation may be lacking information needed for this citation format:
Author name may be incomplete

Vancouver:

-5545-6406. Computational Methods for Multi-Scale Temporal Problems: Algorithms, Analysis, and Numerical Experiments. [Internet] [Doctoral dissertation]. University of Houston; 2016. [cited 2021 Jan 26]. Available from: http://hdl.handle.net/10657/5442.

Note: this citation may be lacking information needed for this citation format:
Author name may be incomplete

Council of Science Editors:

-5545-6406. Computational Methods for Multi-Scale Temporal Problems: Algorithms, Analysis, and Numerical Experiments. [Doctoral Dissertation]. University of Houston; 2016. Available from: http://hdl.handle.net/10657/5442

Note: this citation may be lacking information needed for this citation format:
Author name may be incomplete

University of Houston

19. Mbarki, Raouf. Atomistic and Continuum Study of flexoelectricity in ferroelectric materials.

Degree: PhD, Mechanical Engineering, 2014, University of Houston

URL: http://hdl.handle.net/10657/1795

► In this dissertation, we try to address some of the questions which arise while studying flexoelectricity in ferroelectric materials. 1. Most technologically-relevant ferroelectrics typically lose… (more)

▼ In this dissertation, we try to address some of the questions which arise while studying flexoelectricity in ferroelectric materials. 1. Most technologically-relevant ferroelectrics typically lose piezoelectricity above the Curie temperature. This limits their use to relatively low temperatures. In this dissertation, exploiting a combination of flexoelectricity and simple functional grading, we propose a strategy for high-temperature electromechanical coupling in a standard thin film configuration. We use continuum modeling to quantitatively demonstrate the possibility of achieving apparent piezoelectric materials with large and temperature-stable electromechanical coupling across a wide temperature range that extends significantly above the Curie temperature. With Barium and Strontium Titanate as example materials, a significant electromechanical coupling that is potentially temperature-stable up to 900 C is possible. 2. Piezoelectricity is a property of non-centrosymmetric crystals. In most typically used ferroelectrics, this property is lost as the temperature is increased beyond the Curie point thus strongly reducing the availability of efficient materials that can be used for high temperature energy harvesting. Flexoelectricity, as can be shown from simple symmetry arguments, is a universal and linear electromechanical coupling that dictates the development of polarization upon application of inhomogeneous strains. The implications of this phenomenon become amplified at the nanoscale. In this dissertation, we develop a molecular dynamics approach predicated on a specially tailored interatomic force-field to extract the temperature dependence of flexoelectricity. Surprisingly, we find that it, at least for Barium Titanate and Strontium Titanate nano structures, increases with temperature. Apart from cataloging this interesting observation for future use in high temperature energy harvesting, we also examine the physical mechanisms that lead to the observed temperature dependence. 3. A new theory for 180 domain wall in ferroelectric perovskite material is presented in this work. The effect of flexoelectric coupling on the domain structure is analyzed. We show that the 180 domain wall has a mixed character of Ising and Bloch type wall and that the polarization perpendicular to the domain wall is non zero though it is very small compared to the spontaneous polarization in the case of tetragonal Barium Titanate. Finally, we present the effect of the new finding on the domain wall interaction with defects in the material. 4. Pyroelectric materials generate electricity in response to change in temperature. These materials are commonly used to build temperature sensors, radiation detectors and alarm systems, among others. There are few materials that possess this property. In this work, we develop a nonlinear theoretical framework for pyroelectricity in soft materials. Using the concept of soft electrets materials, we illustrate a nonlinear relation between the Maxwell stress effect and pyroelectricity, and… Advisors/Committee Members: Sharma, Pradeep (advisor), Gunaratne, Gemunu H. (committee member), Masson, Philippe J. (committee member), Kulkarni, Yashashree (committee member), Agrawal, Ashutosh (committee member).

Subjects/Keywords: Flexoelectricity; Piezoelectricity; Pyroelectricity; Electrets; Domain wall; Perovskite; Nanostructures; Molecular dynamics

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6^th Edition):

Mbarki, R. (2014). Atomistic and Continuum Study of flexoelectricity in ferroelectric materials. (Doctoral Dissertation). University of Houston. Retrieved from http://hdl.handle.net/10657/1795

Chicago Manual of Style (16^th Edition):

Mbarki, Raouf. “Atomistic and Continuum Study of flexoelectricity in ferroelectric materials.” 2014. Doctoral Dissertation, University of Houston. Accessed January 26, 2021. http://hdl.handle.net/10657/1795.

MLA Handbook (7^th Edition):

Mbarki, Raouf. “Atomistic and Continuum Study of flexoelectricity in ferroelectric materials.” 2014. Web. 26 Jan 2021.

Vancouver:

Mbarki R. Atomistic and Continuum Study of flexoelectricity in ferroelectric materials. [Internet] [Doctoral dissertation]. University of Houston; 2014. [cited 2021 Jan 26]. Available from: http://hdl.handle.net/10657/1795.

Council of Science Editors:

Mbarki R. Atomistic and Continuum Study of flexoelectricity in ferroelectric materials. [Doctoral Dissertation]. University of Houston; 2014. Available from: http://hdl.handle.net/10657/1795

University of Houston

20. -2158-7723. On Enforcing Maximum Principles and Element-Wise Species Balance for Advective-Diffusive-Reactive Systems.

Degree: PhD, Civil Engineering, 2015, University of Houston

URL: http://hdl.handle.net/10657/2001

► This dissertation aims at developing robust numerical methodologies to solve advective-diffusive-reactive systems that provide accurate and physical solutions for a wide range of input data… (more)

▼ This dissertation aims at developing robust numerical methodologies to solve advective-diffusive-reactive systems that provide accurate and physical solutions for a wide range of input data (e.g., Péclet and Damköhler numbers) and for complicated geometries. It is well-known that physical quantities like concentration of chemical species and the absolute temperature naturally attain non-negative values. Moreover, the governing equations of an advective-diffusive-reactive system are either elliptic (in the case of steady-state response) or parabolic (in the case of transient response) partial differential equations, which possess important mathematical properties like comparison principles, maximum-minimum principles, non-negativity, and monotonicity of the solution. It is desirable and in many situations necessary for a predictive numerical solver to meet important physical constraints. For example, a negative value for the concentration in a numerical simulation of reactive-transport will result in an algorithmic failure. The objective of this dissertation is two fold. First, we show that many existing popular numerical formulations, open source scientific software packages, and commercial packages do not inherit or mimic fundamental properties of continuous advective-diffusive-reactive systems. For instance, the popular standard single-field Galerkin formulation produces negative values and spurious node-to-node oscillations for the primary variables in advection-dominated and reaction-dominated diffusion-type equations. Furthermore, the violation is not mere numerical noise and cannot be neglected. Second, we shall provide various numerical methodologies to overcome such difficulties. We critically evaluate their performance and computational cost for a wide range of Péclet and Damköhler numbers. We first derive necessary and sufficient conditions on the finite element matrices to satisfy discrete comparison principle, discrete maximum principle, and non-negative constraint. Based on these conditions, we obtain restrictions on the computational mesh and generate physics-compatible meshes that satisfy discrete properties using open source mesh generators. We then show that imposing restrictions on computational grids may not always be a viable approach to achieve physically meaningful non-negative solutions for complex geometries and highly anisotropic media. We therefore develop a novel structure-preserving numerical methodology for advective-diffusive reactive systems that satisfies local and global species balance, comparison principles, maximum principles, and the non-negative constraint on coarse computational grids. This methodology can handle complex geometries and highly anisotropic media. The proposed framework can be an ideal candidate for predictive simulations in groundwater modeling, reactive transport, environmental fluid mechanics, and modeling of degradation of materials. The framework can also be utilized to numerically obtain scaling laws for complicated problems with non-trivial initial and… Advisors/Committee Members: Nakshatrala, Kalyana Babu (advisor), Willam, Kaspar J. (committee member), Vipulanandan, Cumaraswamy (committee member), Wang, Keh-Han (committee member), Kulkarni, Yashashree (committee member), Lim, Gino J. (committee member).

Subjects/Keywords: Advection-diffusion-reaction equations; Non-self-adjoint operators; Comparison principles; Maximum principle; Non-negative constraint; Monotone property; Monotonicity; Local and global species balance; Oscillatory chemical reactions; Chaotic mixing; Mesh restrictions; Anisotropic M-uniform meshes; Angle conditions; Least-squares mixed formulations; Convex optimization; Pao's method; Picard's method; Newton-Raphson methods

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APA (6^th Edition):

-2158-7723. (2015). On Enforcing Maximum Principles and Element-Wise Species Balance for Advective-Diffusive-Reactive Systems. (Doctoral Dissertation). University of Houston. Retrieved from http://hdl.handle.net/10657/2001

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Author name may be incomplete

Chicago Manual of Style (16^th Edition):

-2158-7723. “On Enforcing Maximum Principles and Element-Wise Species Balance for Advective-Diffusive-Reactive Systems.” 2015. Doctoral Dissertation, University of Houston. Accessed January 26, 2021. http://hdl.handle.net/10657/2001.

Note: this citation may be lacking information needed for this citation format:
Author name may be incomplete

MLA Handbook (7^th Edition):

-2158-7723. “On Enforcing Maximum Principles and Element-Wise Species Balance for Advective-Diffusive-Reactive Systems.” 2015. Web. 26 Jan 2021.

Note: this citation may be lacking information needed for this citation format:
Author name may be incomplete

Vancouver:

-2158-7723. On Enforcing Maximum Principles and Element-Wise Species Balance for Advective-Diffusive-Reactive Systems. [Internet] [Doctoral dissertation]. University of Houston; 2015. [cited 2021 Jan 26]. Available from: http://hdl.handle.net/10657/2001.

Note: this citation may be lacking information needed for this citation format:
Author name may be incomplete

Council of Science Editors:

-2158-7723. On Enforcing Maximum Principles and Element-Wise Species Balance for Advective-Diffusive-Reactive Systems. [Doctoral Dissertation]. University of Houston; 2015. Available from: http://hdl.handle.net/10657/2001

Note: this citation may be lacking information needed for this citation format:
Author name may be incomplete

University of Houston

21. Xu, Can. Modeling Material Degradation Due to Moisture and Temperature.

Degree: PhD, Civil Engineering, 2017, University of Houston

URL: http://hdl.handle.net/10657/4528

► The mechanical response, serviceability, and load bearing capacity of materials and structural components can be adversely affected due to external stimuli, which include exposure to… (more)

▼ The mechanical response, serviceability, and load bearing capacity of materials and structural components can be adversely affected due to external stimuli, which include exposure to a corrosive chemical species, high temperatures, temperature fluctuations (i.e., freezing-thawing), cyclic mechanical loading, just to name a few. It is, therefore, of paramount importance in several branches of engineering – ranging from aerospace engineering, civil engineering to biomedical engineering – to have a fundamental understanding of degradation of materials, as the materials in these applications are often subjected to adverse environments. In this dissertation, we study degradation of materials due to an exposure to chemical species and temperature under large-strain and large-deformations. In the first part of our research work, we present a consistent mathematical model with firm thermodynamic underpinning. We then obtain semi-analytical solutions of several canonical problems to illustrate the nature of the quasi-static and unsteady behaviors of degrading hyperelastic solids. As second part, we propose several non- dimensional parameters that characterize chemo-thermo-mechanical coupling. These parameters will provide insights on the strength and the nature of various couplings in different types of coupled multi-physics processes. We will also discuss about the importance and the effect of the coupling term (i.e., grad[μ] • h), which accounts for mass/chemical species transfer in the balance of energy using canonical problems. Last but not least, the computational framework based on staggered scheme and monolithic scheme, are depicted in the paper and compared. Several numerical case studies have been done using five different methodologies, Newton-Raphson method with regular mesh and metric-based mesh, standard Galerkin method with regular mesh and metric-based mesh, and non-negative formulation with regular mesh. Furthermore, the behavior of degrading 3D spherical shell and slabs are studied. The limitations of typical semi-inverse solutions, which are commonly employed in practice, will be highlighted. We will also illustrate the proposed model and computational framework on a transient, large deformed, three-way coupled degradation problem. Advisors/Committee Members: Nakshatrala, Kalyana Babu (advisor), Vipulanandan, Cumaraswamy (committee member), Ballarini, Roberto (committee member), Willam, Kaspar J. (committee member), Lim, Gino J. (committee member), Kulkarni, Yashashree (committee member).

Subjects/Keywords: Degradation; Three-way coupled

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6^th Edition):

Xu, C. (2017). Modeling Material Degradation Due to Moisture and Temperature. (Doctoral Dissertation). University of Houston. Retrieved from http://hdl.handle.net/10657/4528

Chicago Manual of Style (16^th Edition):

Xu, Can. “Modeling Material Degradation Due to Moisture and Temperature.” 2017. Doctoral Dissertation, University of Houston. Accessed January 26, 2021. http://hdl.handle.net/10657/4528.

MLA Handbook (7^th Edition):

Xu, Can. “Modeling Material Degradation Due to Moisture and Temperature.” 2017. Web. 26 Jan 2021.

Vancouver:

Xu C. Modeling Material Degradation Due to Moisture and Temperature. [Internet] [Doctoral dissertation]. University of Houston; 2017. [cited 2021 Jan 26]. Available from: http://hdl.handle.net/10657/4528.

Council of Science Editors:

Xu C. Modeling Material Degradation Due to Moisture and Temperature. [Doctoral Dissertation]. University of Houston; 2017. Available from: http://hdl.handle.net/10657/4528

University of Houston

22. Mohammadi, Parnia. NANOSTRUCTURED SURFACES AND EMERGENT PHYSICAL BEHAVIOR.

Degree: PhD, Mechanical Engineering, 2012, University of Houston

URL: http://hdl.handle.net/10657/736

► Due to larger surface to volume ratio, surfaces play a significant role at the nanoscale. Surface atoms have different coordination numbers, charge distribution and subsequently… (more)

▼ Due to larger surface to volume ratio, surfaces play a significant role at the nanoscale. Surface atoms have different coordination numbers, charge distribution and subsequently different physical, mechanical and chemical properties. These differences are interpreted phenomenologically by postulating the existence of surface energy and acknowledging that the various bulk properties such as elastic modulus, melting temperature, and electromagnetic properties are different for surfaces. In this dissertation, we consider two types of surfaces: those bounding a three-dimensional entity, and independent two-dimensional deformable surfaces that can be used to represent, for example, graphene sheets, thin films, and lipid bilayers among others. In this dissertation: (i) We develop a theoretical framework, complemented by atomistic calculations, that elucidates the effect of roughness on surface energy, stress and surface elasticity. We find that the residual surface stress is hardly affected by roughness while the superficial elastic properties are dramatically altered and, importantly, may also result in a change in its sign; this has significant ramifications in the interpretation of sensing based on frequency measurement changes. In particular, we also comment on the effect of roughness on the generally ignored term that represents the curvature dependence of surface energy, crystalline Tolman’s length. (ii) In the context of independent deformable surfaces, our focus is on electromechanical coupling; in particular, the rapidly emerging topic of flexoelectricity. Recent developments in flexoelectricity, especially in nanostructures, have lead to several interesting notions such as creating piezoelectric substances without using piezoelectric materials, enhanced energy harvesting at the nanoscale among others. In the biological context also, membrane flexoelectricity has been hypothesized to play an important role, e.g., biological mechano-transduction, hearing mechanisms. In this dissertation, we consider a heterogenous flexoelectric membrane, and derive the homogenized flexoelectric, dielectric and elastic response. In particular for purely fluid or lipid type membranes, we obtain exact results—one of very few in homogenization theory. Using quantum mechanical calculations, we also show that graphene can be designed to be pyroelectric, thus providing an avenue to create the thinnest possible thermo-electro-mechanical material. Advisors/Committee Members: Sharma, Pradeep (advisor), Wheeler, Lewis T. (committee member), Brankovic, Stanko R. (committee member), Kulkarni, Yashashree (committee member), Agrawal, Ashutosh (committee member), Liu, Liping (committee member).

Subjects/Keywords: Surface roughness; Surface Energy; Nanoscale; Surface elasticity; Flexoelectricity; Pyroelectricity; Flexoelectric membrane; Nanostructures; Mechanical engineering

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6^th Edition):

Mohammadi, P. (2012). NANOSTRUCTURED SURFACES AND EMERGENT PHYSICAL BEHAVIOR. (Doctoral Dissertation). University of Houston. Retrieved from http://hdl.handle.net/10657/736

Chicago Manual of Style (16^th Edition):

Mohammadi, Parnia. “NANOSTRUCTURED SURFACES AND EMERGENT PHYSICAL BEHAVIOR.” 2012. Doctoral Dissertation, University of Houston. Accessed January 26, 2021. http://hdl.handle.net/10657/736.

MLA Handbook (7^th Edition):

Mohammadi, Parnia. “NANOSTRUCTURED SURFACES AND EMERGENT PHYSICAL BEHAVIOR.” 2012. Web. 26 Jan 2021.

Vancouver:

Mohammadi P. NANOSTRUCTURED SURFACES AND EMERGENT PHYSICAL BEHAVIOR. [Internet] [Doctoral dissertation]. University of Houston; 2012. [cited 2021 Jan 26]. Available from: http://hdl.handle.net/10657/736.

Council of Science Editors:

Mohammadi P. NANOSTRUCTURED SURFACES AND EMERGENT PHYSICAL BEHAVIOR. [Doctoral Dissertation]. University of Houston; 2012. Available from: http://hdl.handle.net/10657/736

University of Houston

23. Akturk, Ahmet. The Effect of Buckling on the Interface Conductance in Flexible Lithium-Ion Batteries.

Degree: MS, Mechanical Engineering, University of Houston

URL: http://hdl.handle.net/10657/2131

► Flexible batteries used in flexible applications including medical implants, wearable electronics, consumer electronics or roll-up displays are often subjected to bending and buckling during their… (more)

Subjects/Keywords: Lithium-ion batteries (LIB); Flexible batteries; Batteries; Flexible electronics

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APA (6^th Edition):

Akturk, A. (n.d.). The Effect of Buckling on the Interface Conductance in Flexible Lithium-Ion Batteries. (Masters Thesis). University of Houston. Retrieved from http://hdl.handle.net/10657/2131

Note: this citation may be lacking information needed for this citation format:
No year of publication.

Chicago Manual of Style (16^th Edition):

Akturk, Ahmet. “The Effect of Buckling on the Interface Conductance in Flexible Lithium-Ion Batteries.” Masters Thesis, University of Houston. Accessed January 26, 2021. http://hdl.handle.net/10657/2131.

Note: this citation may be lacking information needed for this citation format:
No year of publication.

MLA Handbook (7^th Edition):

Akturk, Ahmet. “The Effect of Buckling on the Interface Conductance in Flexible Lithium-Ion Batteries.” Web. 26 Jan 2021.

Note: this citation may be lacking information needed for this citation format:
No year of publication.

Vancouver:

Akturk A. The Effect of Buckling on the Interface Conductance in Flexible Lithium-Ion Batteries. [Internet] [Masters thesis]. University of Houston; [cited 2021 Jan 26]. Available from: http://hdl.handle.net/10657/2131.

Note: this citation may be lacking information needed for this citation format:
No year of publication.

Council of Science Editors:

Akturk A. The Effect of Buckling on the Interface Conductance in Flexible Lithium-Ion Batteries. [Masters Thesis]. University of Houston; Available from: http://hdl.handle.net/10657/2131

Note: this citation may be lacking information needed for this citation format:
No year of publication.

University of Houston

24. Tang, Shengjie. Thermal Transport across Grain Boundaries in Graphene by Molecular Dynamics Simulations.

Degree: PhD, Mechanical Engineering, University of Houston

URL: http://hdl.handle.net/10657/2122

► The superior mechanical, electronic and thermal properties of graphene make it an exceptional material with many potential applications in thermal management, energy, and electronics technology.… (more)

▼ The superior mechanical, electronic and thermal properties of graphene make it an exceptional material with many potential applications in thermal management, energy, and electronics technology. However, the presence of grain boundaries in polycrystalline graphene during chemical vapor deposition growth processes can dramatically impact these properties. This dissertation presents an atomistic study of the thermal transport across grain boundaries in graphene using molecular dynamics simulations. We first employ non-equilibrium molecular dynamics simulations to investigate the effect of strain on the thermal conductance of grain boundaries in graphene. The thermal boundary conductance is found to decrease significantly under biaxial tension as expected due to the softening of the phonons with increasing lattice spacing. In contrast, under biaxial compression, the thermal boundary conductance is strongly affected by the dimensions of the graphene monolayer, increasing with strain for specimen with length-to-width ratio of less than 20 and being insensitive to strain for length-to-width ratio above 20. This rather unexpected size-dependence under biaxial compression is found to be a result of geometric instabilities. We further perform phonon wave-packet dynamics simulations to determine the contribution of different phonon modes to the thermal boundary conductance in graphene based on lattice dynamics. We consider three grain boundaries, two of which are flat, while the third shows significant out-of-plane buckling to accommodate the strain due to lattice mismatch. Our simulations reveal that the in-plane acoustic modes make the dominant contribution to the Kapitza conductance of grain boundaries. This is in sharp contrast to the thermal conductivity of graphene which is dominated by out-of-plane acoustic phonons. Finally, we extend this work to study the effect of tensile strain on the scattering of phonons at grain boundaries. We find that biaxial tension has little influence on the transmission coefficients of the LA and TA branches but can affect the overall fluctuations of the transmission coefficient of the ZA mode which tends to increase and approaches 1 as the tensile strain increases. Thus, our study on the interplay of size and strain effects on phonon scattering provides atomistic insights into the role of grain boundaries in thermal transport in two-dimensional materials. Advisors/Committee Members: Kulkarni, Yashashree (advisor), Sharma, Pradeep (committee member), Liu, Dong (committee member), Li, Mo (committee member), Ardebili, Haleh (committee member).

Subjects/Keywords: Thermal transport; Grain boundaries

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APA (6^th Edition):

Tang, S. (n.d.). Thermal Transport across Grain Boundaries in Graphene by Molecular Dynamics Simulations. (Doctoral Dissertation). University of Houston. Retrieved from http://hdl.handle.net/10657/2122

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Chicago Manual of Style (16^th Edition):

Tang, Shengjie. “Thermal Transport across Grain Boundaries in Graphene by Molecular Dynamics Simulations.” Doctoral Dissertation, University of Houston. Accessed January 26, 2021. http://hdl.handle.net/10657/2122.

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No year of publication.

MLA Handbook (7^th Edition):

Tang, Shengjie. “Thermal Transport across Grain Boundaries in Graphene by Molecular Dynamics Simulations.” Web. 26 Jan 2021.

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No year of publication.

Vancouver:

Tang S. Thermal Transport across Grain Boundaries in Graphene by Molecular Dynamics Simulations. [Internet] [Doctoral dissertation]. University of Houston; [cited 2021 Jan 26]. Available from: http://hdl.handle.net/10657/2122.

Note: this citation may be lacking information needed for this citation format:
No year of publication.

Council of Science Editors:

Tang S. Thermal Transport across Grain Boundaries in Graphene by Molecular Dynamics Simulations. [Doctoral Dissertation]. University of Houston; Available from: http://hdl.handle.net/10657/2122

Note: this citation may be lacking information needed for this citation format:
No year of publication.

University of Houston

25. -6478-907X. Investigation of the Mechano-Electrochemical Coupling of Solid Polyethylene Oxide and Stretchable Lithium Ion Batteries.

Degree: PhD, Materials Engineering, University of Houston

URL: http://hdl.handle.net/10657/3686

► It is necessary to develop deformable energy storage devices that are compatible with the next generation flexible and stretchable electronics such as medical implants and… (more)

▼ It is necessary to develop deformable energy storage devices that are compatible with the next generation flexible and stretchable electronics such as medical implants and wearable devices. Lithium ion batteries are a popular energy storage method for modern technology that provides high energy density and efficiency. However, the electrochemical instability of the organic liquid electrolytes poses a real hazard to using conventional lithium ion batteries in deformable electronics. Replacing the liquid electrolyte with a solid polymer reduces the risk of the battery setting aflame among many other benefits. Solid polymer electrolytes are of particular interest to battery scientists because they allow for the development of safe and deformable batteries. On the other hand, solid polymer electrolytes are also disadvantaged because of their poor ion transport properties. There has been extensive research in improving the ion conductivity of solid polymer electrolytes, but the best achievable conductivities are still two orders of magnitude less than that of liquid electrolytes. The present study investigates the feasibility of using solid polymer electrolytes (i.e. polyethylene oxide) in stretchable lithium ion batteries. The ion conductivity of a solid polymer electrolyte film is demonstrated to increase with tensile strain and this research delves into the mechanisms behind this conductivity improvement. The coefficients of ion conductivity enhancement are found to be similar in both in-plane and out-of-plane directions. Furthermore, molecular weight blending (i.e. 100k and 600k Mw) is used to enhance the electrochemical properties of the solid polymer electrolyte while minimally affecting the polymer’s mechanical stability. The relatively optimized stretchable polymer electrolyte is tested inside a sliding electrode battery and the effect of tensile strain on overall battery performance is investigated. Advisors/Committee Members: Ardebili, Haleh (advisor), White, Kenneth W. (committee member), Kulkarni, Yashashree (committee member), Ryou, Jae-Hyun (committee member), Sun, Li (committee member).

Subjects/Keywords: Lithium-ion batteries (LIB); Solid polymer electrolyte; Polyethylene Oxide; Batteries; Stretchable Batteries

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APA (6^th Edition):

-6478-907X. (n.d.). Investigation of the Mechano-Electrochemical Coupling of Solid Polyethylene Oxide and Stretchable Lithium Ion Batteries. (Doctoral Dissertation). University of Houston. Retrieved from http://hdl.handle.net/10657/3686

Note: this citation may be lacking information needed for this citation format:
Author name may be incomplete
No year of publication.

Chicago Manual of Style (16^th Edition):

-6478-907X. “Investigation of the Mechano-Electrochemical Coupling of Solid Polyethylene Oxide and Stretchable Lithium Ion Batteries.” Doctoral Dissertation, University of Houston. Accessed January 26, 2021. http://hdl.handle.net/10657/3686.

Note: this citation may be lacking information needed for this citation format:
Author name may be incomplete
No year of publication.

MLA Handbook (7^th Edition):

-6478-907X. “Investigation of the Mechano-Electrochemical Coupling of Solid Polyethylene Oxide and Stretchable Lithium Ion Batteries.” Web. 26 Jan 2021.

Note: this citation may be lacking information needed for this citation format:
Author name may be incomplete
No year of publication.

Vancouver:

-6478-907X. Investigation of the Mechano-Electrochemical Coupling of Solid Polyethylene Oxide and Stretchable Lithium Ion Batteries. [Internet] [Doctoral dissertation]. University of Houston; [cited 2021 Jan 26]. Available from: http://hdl.handle.net/10657/3686.

Note: this citation may be lacking information needed for this citation format:
Author name may be incomplete
No year of publication.

Council of Science Editors:

-6478-907X. Investigation of the Mechano-Electrochemical Coupling of Solid Polyethylene Oxide and Stretchable Lithium Ion Batteries. [Doctoral Dissertation]. University of Houston; Available from: http://hdl.handle.net/10657/3686

Note: this citation may be lacking information needed for this citation format:
Author name may be incomplete
No year of publication.

University of Houston

26. Sinha, Tanushree. Atomistic Study of Fracture and Deformation Mechanisms in Nanotwinned FCC Metals.

Degree: PhD, Mechanical Engineering, University of Houston

URL: http://hdl.handle.net/10657/3650

► Nanotwinned metals have opened up exciting avenues for the design of high-strength, high-ductility materials owing to the extraordinary properties of twin boundaries. This dissertation presents… (more)

▼ Nanotwinned metals have opened up exciting avenues for the design of high-strength, high-ductility materials owing to the extraordinary properties of twin boundaries. This dissertation presents insights into the deformation mechanisms governing the high temperature response and fracture behavior of nanotwinned face-centered-cubic (fcc) metals using molecular dynamics simulations. The aim of our atomistic modeling is to elucidate the role of coherent twin boundaries (CTB) in the interaction with dislocations (thus mediating strength and hardening) and in inhibiting crack propagation (thus contributing to toughness). Our simulations reveal an intriguing transition in the behavior of CTBs at higher temperatures as the deformation mechanism changes from shear-coupled normal motion to deformation twinning, an occurrence that has not been reported before in fcc metals. This anomalous response of twin boundaries at high temperatures is studied for different fcc metals and analyzed based on the energetics of the competing mechanisms. Our simulations of pre-existing cracks along CTBs reveal that CTBs in nanotwinned structures exhibit alternating intrinsic brittleness and intrinsic ductility. This is a startling consequence of the directional anisotropy of an atomically sharp crack along a twin boundary that favors cleavage in one direction and dislocation emission from the crack tip in the opposite direction owing to the effect of the crystallographic orientations in the adjoining twins. These results shed light on the previously held notion that twin boundaries are inherently brittle, and can also explain the brittle versus ductile behavior of CTBs reported in recent literature. We also investigate the effect of twin boundary spacing, and sample thickness on the crack-propagation in twinned nanopillars. The simulations show that CTBs serve as effective barriers for dislocation motion and restrict the plasticity in the vicinity of the crack tip. We finally extend our study of crack propagation to polycrystalline nanotwinned structures. We observe multiple mechanisms such as dislocation-twin interactions, twin migration, and dislocation nucleation from grain boundaries that govern the ductile response of a pre-existing crack. The findings reported in this dissertation demonstrate remarkable properties of twin boundaries and open further avenues for the design of novel nanotwinned structures for next-generation structural applications. Advisors/Committee Members: Kulkarni, Yashashree (advisor), Sharma, Pradeep (committee member), Nakshatrala, Kalyana Babu (committee member), White, Kenneth W. (committee member), Mavrokefalos, Anastassios (committee member).

Subjects/Keywords: Nanotwinned metals; FCC metals; Atomistic deformation; Computational simulation; Fracture behavior

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APA (6^th Edition):

Sinha, T. (n.d.). Atomistic Study of Fracture and Deformation Mechanisms in Nanotwinned FCC Metals. (Doctoral Dissertation). University of Houston. Retrieved from http://hdl.handle.net/10657/3650

Note: this citation may be lacking information needed for this citation format:
No year of publication.

Chicago Manual of Style (16^th Edition):

Sinha, Tanushree. “Atomistic Study of Fracture and Deformation Mechanisms in Nanotwinned FCC Metals.” Doctoral Dissertation, University of Houston. Accessed January 26, 2021. http://hdl.handle.net/10657/3650.

Note: this citation may be lacking information needed for this citation format:
No year of publication.

MLA Handbook (7^th Edition):

Sinha, Tanushree. “Atomistic Study of Fracture and Deformation Mechanisms in Nanotwinned FCC Metals.” Web. 26 Jan 2021.

Note: this citation may be lacking information needed for this citation format:
No year of publication.

Vancouver:

Sinha T. Atomistic Study of Fracture and Deformation Mechanisms in Nanotwinned FCC Metals. [Internet] [Doctoral dissertation]. University of Houston; [cited 2021 Jan 26]. Available from: http://hdl.handle.net/10657/3650.

Note: this citation may be lacking information needed for this citation format:
No year of publication.

Council of Science Editors:

Sinha T. Atomistic Study of Fracture and Deformation Mechanisms in Nanotwinned FCC Metals. [Doctoral Dissertation]. University of Houston; Available from: http://hdl.handle.net/10657/3650

Note: this citation may be lacking information needed for this citation format:
No year of publication.

University of Houston

27. Yang, Shengyou. Surface Instability and Bifurcation of Elastic Materials.

Degree: PhD, Mechanical Engineering, University of Houston

URL: http://hdl.handle.net/10657/2844

► Surface instabilities, such as wrinkles and creases, are often observed when elastic materials are subject to a sufficiently large compression. This thesis investigates surface instability… (more)

▼ Surface instabilities, such as wrinkles and creases, are often observed when elastic materials are subject to a sufficiently large compression. This thesis investigates surface instability and bifurcation of elastic materials due to their great importance to engineering application. The surface instability is studied by using the principle of minimum energy while the bifurcation is analyzed by solving the linearized equilibrium equations. In this thesis, we focus on the surface instability and bifurcation of a half-space, an infinite slab, and a rectangular block of elastic materials subject to biaxial loading. For the problem of surface instability, we use the first and second variations of the energy functional to find the necessary condition for stability. The requirement of a positive semi-definite second variation is transformed into the exploration of the minimum value of a constrained integral. Then the first variation condition of this constrained minimization problem leads to an eigenvalue problem associated with the stability. Solution of the eigenvalue problem yields a characteristic equation that determines the wavenumbers for the pattern of surface instabilities and the corresponding critical loading parameters. Subsequent to discussing the general properties of the characteristic equation, we obtain the stability region analytically. For the bifurcation problem, we linearize the boundary-value problem consisting of the Euler-Lagrange equation, the constraint of incompressibility and the corresponding boundary conditions and then solve the linearized boundary-value problem. Determination of non-trivial solutions to the linearized boundary-value problem yields a characteristic equation. Bifurcation points are obtained from the discussion of the general properties of the characteristic equation. Advisors/Committee Members: Chen, Yi-Chao (advisor), Wheeler, Lewis T. (committee member), Sharma, Pradeep (committee member), Kulkarni, Yashashree (committee member), Vipulanandan, Cumaraswamy (committee member).

Subjects/Keywords: Surface stability; Bifurcation; Elastic materials

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6^th Edition):

Yang, S. (n.d.). Surface Instability and Bifurcation of Elastic Materials. (Doctoral Dissertation). University of Houston. Retrieved from http://hdl.handle.net/10657/2844

Note: this citation may be lacking information needed for this citation format:
No year of publication.

Chicago Manual of Style (16^th Edition):

Yang, Shengyou. “Surface Instability and Bifurcation of Elastic Materials.” Doctoral Dissertation, University of Houston. Accessed January 26, 2021. http://hdl.handle.net/10657/2844.

Note: this citation may be lacking information needed for this citation format:
No year of publication.

MLA Handbook (7^th Edition):

Yang, Shengyou. “Surface Instability and Bifurcation of Elastic Materials.” Web. 26 Jan 2021.

Note: this citation may be lacking information needed for this citation format:
No year of publication.

Vancouver:

Yang S. Surface Instability and Bifurcation of Elastic Materials. [Internet] [Doctoral dissertation]. University of Houston; [cited 2021 Jan 26]. Available from: http://hdl.handle.net/10657/2844.

Note: this citation may be lacking information needed for this citation format:
No year of publication.

Council of Science Editors:

Yang S. Surface Instability and Bifurcation of Elastic Materials. [Doctoral Dissertation]. University of Houston; Available from: http://hdl.handle.net/10657/2844

Note: this citation may be lacking information needed for this citation format:
No year of publication.

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