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1
Perera, M. Mario. "Dynamic Soft Materials with Controllable Mechanical Properties." University of Cincinnati / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1595847753887897.
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2
Cope, Elizabeth Ruth. "Dynamic properties of materials : phonons from neutron scattering." Thesis, University of Cambridge, 2010. https://www.repository.cam.ac.uk/handle/1810/226116.
Повний текст джерелаАнотація:
A detailed understanding of fundamental material properties can be obtained through the study of atomic vibrations, performed experimentally with neutron scattering techniques and coupled with the two powerful new computational methodologies I have developed. The first approach involves phonon-based simulations of the pair distribution function - a histogram of localised atomic positions generated experimentally from total scattering data. This is used to reveal ordering behaviour, to validate interatomic models and localised structure, and to give insights into how far dynamic behaviour can be studied using total scattering techniques. Most importantly, the long-standing controversy over dynamic disorder in β-cristobalite is resolved using this technique. Inelastic neutron spectroscopy (INS) allows \emph{direct} study of vibrational modes through their interaction with the neutron beam, and is the experimental basis for the second strand of the new methodology. I have developed new simulation and refinement tools based on the next generation of spectrometers currently being commissioned at the ISIS pulsed neutron source. This allows a detailed powder spectroscopy study of cristobalite and vitreous silica demonstrating that the Bose peak and so-called 'fast sound' features can be derived from standard lattice dynamics in both the crystal and the amorphous counterpart, and allowing discussion of their origins. Given the controversy in the literature, this is a key result. The new methodology also encompasses refinement of interatomic models against powder INS data, with aluminium providing a successful test-case. A more complex example is seen in calcite, with experimental data collected during the commissioning of the new MERLIN spectrometer. Simulated one-phonon coherent INS spectra for the single crystal and powder (the latter including approximations to multi-phonon and multiple scatter) are fully convolved with experimental resolution functions. These are used in the analysis of the experimental data, yielding previously unpublished dispersion curves and soft mode information, as well as allowing the effectiveness of powder refinement of more complex materials to be assessed. Finally, I present further applications with technologically important materials - relaxor ferroelectrics and high temperature pnictide superconductors. The conclusions draw together the different strands of the work, discussing the importance of these new advances together with future developments and scientific applications.
3
Wu, Lei. "The dynamic properties of voided polymers." Diss., Georgia Institute of Technology, 2001. http://hdl.handle.net/1853/16968.
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4
Biesel, Van Brian. "Experimental measurement of the dynamic properties of viscoelastic materials." Thesis, Georgia Institute of Technology, 1993. http://hdl.handle.net/1853/19249.
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5
Yu, Zhaohui Crocker Malcolm J. "Static, dynamic and acoustical properties of sandwich composite materials." Auburn, Ala., 2007. http://repo.lib.auburn.edu/2006%20Fall/Dissertations/YU_ZHAOHUI_54.pdf.
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6
Margiolaki, Irene. "Structural, magnetic and dynamic properties of fullerene based materials." Thesis, University of Sussex, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.288785.
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7
Gu, Xiaoqiang, and 顾晓强. "Dynamic properties of granular materials at the macro and microscales." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2012. http://hub.hku.hk/bib/B47752622.
Повний текст джерелаАнотація:
Dynamic properties of soil, including modulus and damping, play essential roles in
evaluating the response of the soil deposit and its supporting structures when
subjected to dynamic loads induced by earthquakes, traffic, explosions, machine
foundations, and so on. It is well recognized that the dynamic properties of soil are
affected by many factors, such as strain amplitude, stress condition, void ratio,
saturation and gradation. Despite tremendous works have been done, the
macroscopic effects of several key factors on the dynamic properties of granular
material are not yet fully understood, due primarily to its particulate and multiphase
nature. Furthermore, the understanding of how the influencing factors affect the
dynamic properties of granular material or the underlying fundamental mechanism is
inadequate. This study thus is carried out to investigate the effects and the underlying
mechanisms of these important factors, including strain amplitude, stress condition,
void ratio, particle size, saturation, and initial fabric, by means of advanced
laboratory tests and numerical simulations.
To study the dynamic properties at the macro scale, a series of laboratory tests are
carried out in a state-of-art resonant column (RC) apparatus incorporating bender
element (BE) and torsional shear (TS). Test materials include artificial glass beads
with different sizes, commercially available standard sands and natural completely
decomposed granite (CDG). The specimens are prepared at various densities,
confined at different pressures, tested both in dry and saturated conditions, and
reconstituted by different preparation methods. In particular, the characteristics of
wave signals (both S-wave and P-wave) at various conditions and the associated
interpretation methods in BE tests are investigated in detail. The results obtained
from BE, RC and TS are compared to clarify the potential effect of test method.
Moreover, attempts are made to explain the test results from the viewpoint of
micromechanics.
Numerical simulations using discrete element method (DEM) are performed to study
the dynamic properties of granular materials and explore the underlying fundamental
mechanism at the micro scale. The simulations indicate that the elastic properties are
closely related to the coordination number and the distribution of normal contact
forces in the specimen. The effects of initial fabric and induced fabric, which are
respectively achieved by different specimen generation methods and the application
of anisotropic stress states, are investigated. The anisotropy of the specimen and its
evolution during shearing are also studied. The results indicate that the anisotropy is
resulted from the spatial distributions of contact force and contact number. The
modulus reduction curve and damping curve obtained from the simulations are
compared with those from laboratory tests.published_or_final_version
Civil Engineering
Doctoral
Doctor of Philosophy
8
Tan, Aik Jun. "Dynamic modulation of material properties by solid state proton gating." Thesis, Massachusetts Institute of Technology, 2019. https://hdl.handle.net/1721.1/122082.
Повний текст джерелаАнотація:
This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2019
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (pages 195-215).
As functionalities become more abundant in solid state devices, one key capability which remains lacking is an effective means to dynamically tune material properties. In this thesis, we establish a pathway towards this capability by utilizing the simplest ion known to mankind: the proton. We demonstrate for the first time dynamic control of magnetic properties in an all-solid-state heterostructures using solid state proton gating in a metal/oxide heterostructure. We also demonstrate dynamic modulation of magnetic anisotropy at a metal-metal interface through hydrogen insertion in a heavy metal adjacent to a ferromagnet. Besides magnetic properties, solid state proton gating also enables dynamic modulation of optical properties in a thin film oxide. We observe fast gating of optical reflectivity by ~10% at timescale down to ~20ms in a metal/oxide/metal heterostructure. Finally, we also demonstrate a room temperature reversible solid oxide fuel cell based on hydrogen storage. The cell has a small form factor which is suitable for energy storage in solid state microelectronics application. Our work hence provides a platform for complete control of material properties through solid state proton gating.
by Aik Jun Tan.
Ph. D.
Ph.D. Massachusetts Institute of Technology, Department of Materials Science and Engineering
9
Clark, Justin Lewis. "Dynamic and Quasi-Static Mechanical Properties of Fe-Ni Alloy Honeycomb." Diss., Georgia Institute of Technology, 2004. http://hdl.handle.net/1853/5223.
Повний текст джерелаАнотація:
Several metal honeycombs, termed Linear Cellular Alloys (LCAs), were fabricated via a paste extrusion process and thermal treatment. Two Fe-Ni based alloy compositions were evaluated. Maraging steel and Super Invar were chosen for their compatibility with the process and the wide range of properties they afforded. Cell wall material was characterized and compared to wrought alloy specifications. The bulk alloy was found to compare well with the more conventionally produced wrought product when porosity was taken into account. The presence of extrusion defects and raw material impurities were shown to degrade properties with respect to wrought alloys. The performance of LCAs was investigated for several alloys and cell morphologies. The results showed that out-of-plane properties exceeded model predictions and in-plane properties fell short due to missing cell walls and similar defects. Strength was shown to outperform several existing cellular metals by as much as an order of magnitude in some instances. Energy absorption of these materials was shown to exceed 150 J/cc at strains of 50% for high strength alloys. Finally, the suitability of LCAs as an energetic capsule was investigated. The investigation found that the LCAs added significant static strength and as much as three to five times improvement in the dynamic strength of the system. More importantly, it was shown that the pressures achieved with the LCA capsule were significantly higher than the energetic material could achieve alone. High pressures, approaching 3 GPa, coupled with the fragmentation of the capsule during impact increased the likelihood of initiation and propagation of the energetic reaction. This multi-functional aspect of the LCA makes it a suitable capsule material.
10
Henry, Christopher P. (Christopher Paul) 1974. "Dynamic actuation properties of Ni-Mn-Ga ferromagnetic shape memory alloys." Thesis, Massachusetts Institute of Technology, 2002. http://hdl.handle.net/1721.1/8442.
Повний текст джерелаАнотація:
Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2002.Includes bibliographical references (leaves 198-201).
Dynamic magnetic-field-induced strain actuation of up to 3% with a frequency bandwidth of least 500 Hz in Ni48.5Mn29.5Ga21 ferromagnetic shape memory alloys (FMSAs) is achieved. Hardware was designed and constructed to measure frequency bandwidth, magnetic-field-induced strain, stress and magnetization driven from an applied magnetic field. The bandwidth in this investigation was only limited by inductive reactance of the hardware, not by fundamental limitations of Ni-Mn-Ga. Degradation of the peak dynamic actuation strain occurred from 3.0% to 2.6% with increasing number of cycles from Nz1,000 to N 100,000. Measurement of strain, stress, and magnetization driven by a magnetic field permitted the comparison of measured properties versus properly defined thermodynamic properties. The peak thermodynamic piezomagnetic coefficient is d3, 1,= 2.5 x 10-7m / A compared to the experimental slope, dE/dH, of 1.0 x 10-7 m / A at N-1,000 cycles and 1.4 x 10-7 m / A at N-100,000 cycles, respectively. The thermodynamic piezomagnetic coefficient is five times greater than Terfenol-D with d31 = 5.0 x 10-m / A. The magnetic susceptibility varies between 3-10, while the twinning stiffness varies between 30-40 MPa within the average bias stress range of 0.3 to 2.8 MPa. At optimum fields and bias stresses, the mechanical energy density during cyclic deformation was 65 kJ/m3 at the expense of 20 kJ/m3 lost An important first observation of dynamic stress vs. field behavior is understood by an extension of a magnetomechanical phenomenological model.
(cont.) The mechanism of stress generation is thought to be magnetization rotation causing negative magnetostriction with quadratic magnetic-field dependence before twin boundaries move. Above the threshold field for twin boundary motion, stress increases in proportion to the magnetic-field-induced strain. Dynamic actuation measurements performed here help put Ni-Mn-Ga FSMAs into perspective with other active materials performance: Ni-Mn-Ga FSMAs are between low bandwidth, high strain, Nitinol and high bandwidth, low strain Terfenol-D and ferroelectrics.
by Christopher P. Henry.
Ph.D.
11
Lemesh, Ivan. "Static and dynamic properties of magnetic Skyrmions in engineered multilayer films." Thesis, Massachusetts Institute of Technology, 2019. https://hdl.handle.net/1721.1/122179.
Повний текст джерелаАнотація:
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2019Cataloged from PDF version of thesis.
Includes bibliographical references (pages 205-219).
Magnetic textures known as skyrmions promise new breakthroughs in memory, logic, and neuromorphic applications. Skyrmions have been found in a variety of material systems, yet there existed no experimental evidence of a material that could simultaneously host them at room temperature and also allow for their reproducible current-induced nucleation and motion. One main goal of this thesis is to fill this gap and demonstrate all the aforementioned properties in the introduced here [Pt/CoFeB/MgO]₁₅ thin film heterostructures, consisting of a perpendicularly magnetized ferromagnetic layer (M), a heavy metal (H), and a symmetry-breaking spacer layer (S). Here, I developed, fabricated, and characterized the [Pt/CoFeB/MgO]₁₅ multilayers with an extremely low density of pinning centers, which enable not only a fully reproducible skyrmion motion but also a clean study of the skyrmion nucleation process. By using X-ray microscopy, I performed the imaging of various magnetic textures in these multilayers and studied their current-induced generation and motion as a function of applied field and temperature. Finally, another goal of this work is to establish a direct link between the properties of these [H/M/S][subscript N]-type materials and the structure of magnetic textures that they can host. The energetics of such systems is understood very poorly due to the very complex multilayer stray fields and up until now, most of their analysis involved the exclusive use of micromagnetic simulations. Here, I develop an alternative theoretical approach by calculating all the stray field interactions analytically, which enables the prediction of the exact structure and dynamics of magnetic domain walls, domains, and skyrmions. Thesis
"Support of the U.S. Department of Energy (DOE), Office of Science, Basic Energy Sciences (BES) under Award No. DE-SC0012371, and of the DARPA TEE program"--page 7.
by Ivan Lemesh.
Ph. D.
Ph.D. Massachusetts Institute of Technology, Department of Materials Science and Engineering
12
Wang, Yunfei. "Correlation of dynamic dielectric properties to reaction kinetics and changing mechanical properties of epoxy resins during cure." W&M ScholarWorks, 1997. https://scholarworks.wm.edu/etd/1539623894.
Повний текст джерелаАнотація:
The principal objective of this paper is to describe how complex impedance, obtained from frequency dependent dielectric sensing technique, can be used as an effective diagnostic tool for in situ real-time investigation in the fabrication of thermoset structures.;Two epoxy systems (Pr500 from 3M and My720 from Ciba Geigy) with different functionality are characterized in terms of their dielectric, thermal, and rheological behavior. It is observed that there is a one to one relationship between Tg and conversion which is independent of cure temperature. The chemical kinetics of the reaction is satisfactorily described by an autocatalyzed reaction mechanism. The chemical rate constant has the usual Arrhenius form, whereas the diffusion rate constant is assumed to be given by a modified form of the Williams-Landel-Ferry (WLF) equation. The overall reaction rate constant is modeled by a combination of the chemical rate constant and the diffusion rate constant. The ability of the frequency dependent dielectric sensing technique to monitor the progress of curing reaction, build up in glass transition temperature, viscosity and to detect the time of occurrence of gel during thermoset cure are explored. The temperature dependence of the dielectric relaxation time, ionic conductivity and viscosity are described by the modified WLF equation. This approach provides a common framework for describing and comparing different related properties.
13
Kaewmaraya, Thanayut. "First-Principles Studies of Materials Properties : Pressure-Induced Phase Transitions & Functional Materials." Doctoral thesis, Uppsala universitet, Institutionen för fysik och astronomi, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-251343.
Повний текст джерелаАнотація:
This thesis presents the first-principles studies of materials properties within the framework of the density functional theory (DFT). The thesis constitutes three main parts, i. e., pressure-induced phase transitions in solids, data-storage and clean-energy materials. The first part focuses on the predictions of crystal structures and the determinations of electronic properties of Xe-H2, FeB4 and Co3O4. Pressurizing Xe-H2 compound yields the formation of H-rich Xe(H2)8, which can exhibit a metallic feature at comparatively lower pressure than pure hydrogen. Hard superconducting FeB4 gets transformed into a novel transparent phase under pressure owing to the enhanced overlap of atomic cores. Spinel Co3O4 undergoes the phase transition from a cubic to a monoclinic because of the charge transfer between cations via the increased 3d-3d interactions. The second part involves the study of structural and electronic properties of phase-change memory materials (PCMs), i. e., Ge2Sb2Te5 (GST) and Ga-doped In2O3. Van der Waals (vdW) interaction must be considered to obtain accurate crystal structure of layered GST. For Ga-doped In2O3 (GIO), the local structure of amorphous GIO is found to resemble that of amorphous In2O3, except the vicinity of doping atoms. The electronic property of a-GIO is metallic, which considerably differs from the semiconducting feature of the crystalline GIO. This emphasizes the contrast in the conductivity of the crystalline and amorphous upon phase switching of GIO. The third part associates with the search for clean-energy materials, viz., hydrogen production, hydrogen storage and green Mg-ion batteries. For hydrogen production, the role of intrinsic point defects to water adsorption on ZnO(10-10) surface is investigated. The findings show that the Zn and O defect-sites are energetically not favorable for the water adsorption and dissociation. For the purpose of storing hydrogen in a solid phase, silicene, doped by alkaline and alkaline earth metals, is investigated. We find that Li-doped and Na-doped silicene can attain the superior storage capacity. For cathode material of Mg-ion batteries, Mg2Mo6S8, the diffusivity of Mg ions occurs through an available channel in the bulk with the onset temperature of 200 K.
14
Hornig, Klaus H. Flowers George T. "Heuristic optimization methods for the characterization of dynamic mechanical properties of composite materials." Auburn, Ala., 2007. http://repo.lib.auburn.edu/2006%20Fall/Dissertations/HORNIG_KLAUS_7.pdf.
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15
Tan, Yi Ming. "Microstructure and dynamic failure properties of freeze-cast materials for thermobaric warhead cases." Thesis, Monterey, California. Naval Postgraduate School, 2012. http://hdl.handle.net/10945/27911.
Повний текст джерелаАнотація:
We consider the microstructure and dynamic failure of ice-templated freeze cast alumina materials that are currently being studied for novel warhead cases. The freeze-cast matrix is a porous, cellular structure of overlapping lamellae similar to many biomaterials such as nacre. This lightweight matrix provides a high-toughness shell that can be filled with polymers or combustible reactive materials. Three porosities of alumina freeze-cast structures were studied, and a systematic variation in microstructural properties such as lamellar width and thickness was observed with changing porosity. Dynamic impact tests were performed in a single stage light-gas gun to examine the failure properties of these materials under high strain-rate loading. Nearly complete delamination was observed under impact, along with characteristic cracking across the lamellar width. Average fragment size decreases with increasing porosity, and a theoretical model was developed to explain this behavior. Based on an energy balance between kinetic, strain, and surface energies within a single lamella, we are able to predict the characteristic fragment size using only standard material properties of bulk alumina.
16
Hudl, Matthias. "Magnetic materials with tunable thermal, electrical, and dynamic properties : An experimental study of magnetocaloric, multiferroic, and spin-glass materials." Doctoral thesis, Uppsala universitet, Fasta tillståndets fysik, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-168986.
Повний текст джерелаАнотація:
This thesis concerns and combines the results of experimental studies of magnetocaloric, multiferroic and spin-glass materials, using SQUID magnetometry as the main characteriza-tion technique. The magnetocaloric effect offers an interesting new technology for cooling and heating applications. The studies of magnetocaloric materials in this thesis are focused on experimen-tal characterization of fundamental magnetic properties of Fe2P-based materials. These are promising magnetocaloric materials with potential industrial use. It is found that the magneto-caloric properties of Fe2P can be optimally tuned by substitution of manganese for iron and silicon for phosphorus. Furthermore, a simple device to measure the magnetocaloric effect in terms of the adiabatic temperature change was constructed. Materials that simultaneously exhibit different types of ferroic order, for example magnetic and electrical order, are rare in nature. Among these multiferroic materials, those in which the ferroelectricity is magnetically-induced, or vice versa the magnetism is electrically-induced, are intensively studied due to a need for new functionalities in future data storage and logic devices. This thesis presents results on two materials: Co3TeO6 and Ba3NbFe3Si2O14, which belong to the group of magnetically-induced ferroelectrics and exhibit strong coupling be-tween the magnetic and the electrical order parameter. Their ordering properties were studied using magnetic and electrical measurement techniques. The coupling between the magnetic and electronic degrees of freedom was investigated using high-field and low-temperature Raman spectroscopy. Spin-glass materials exhibit complex magnetism and disorder. The influence of the spin dimensionality on the low and high magnetic field properties of spin glasses was investigated by studying model Heisenberg, XY and Ising spin-glass systems. Significant differences were found between the non-equilibrium dynamics and the hysteresis behavior of Heisenberg systems compared to those of XY and Ising spin glasses.
17
Aydin, Huseyin. "Effect of microstructure on static and dynamic mechanical properties of third generation advanced high strength steels." Thesis, McGill University, 2013. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=119617.
Повний текст джерелаАнотація:
The recent studies on steels have largely focused on the development of new advanced high strength sheet steels (AHSS), particularly for automotive applications. "First generation AHSS" are steels that primarily possess ferrite-based microstructures with tensile strength (in the as-rolled condition) in the range of 450 to 700 MPa, and "second generation AHSS" are austenitic steels with high manganese content in the range of 900 MPa to 1100 MPa tensile strength. Recently, there has been interest in the development of a "third generation" of AHSS, which are steels with strength-ductility combinations better than the first generation AHSS with a range of 20 000 MPa x %ε but at a cost significantly less than that of the second generation AHSS as a result of reducing expensive alloying elements. Therefore, the current approach to the development of third generation AHSS is to combine all the aspects of first and second generation steels in unique alloy/microstructure combinations to achieve the desired properties. Thus, the third generation of AHSS microstructures consists of a high strength phase (e.g., martensite or bainite) and a significant amount of ductility and work hardening from an austenite that exhibits deformation induced plasticity through transformation or twinning. In this thesis, four different steel compositions, centered on Mn as the main alloying element, are designated as candidates for third generation AHSS grades. The design of these steels is based on controlling the deformation behavior of the retained austenite. Thus, heat treatment process parameters are determined in order to obtain different amounts and morphologies of retained austenite. The evolution of the microstructure, during processing as well as deformation, is characterized by using optical and electron microscopy techniques and mechanical tests. The effect of alloy composition and processing parameters on the deformation mechanisms of these steels is discussed.Les études récentes sur les aciers se sont surtout concentrées sur le développement avancé de nouvelles feuilles d'acier à haute résistance (AHSS, advanced high strength sheet steels, en anglais), particulièrement pour les applications automobiles. Les "AHSS de première génération" sont des aciers qui possèdent principalement des microstructures à base de ferrite ayant une résistance à la traction (à l'état brut de laminage) de l'ordre de 450 à 700 MPa tandis que les "AHSS de seconde génération" sont des aciers austénitiques à haute teneur en manganèse ayant une résistance à la traction de l'ordre de 900 à 1100 MPa. Récemment, un intérêt s'est manifesté pour le développement "d'AHSS de troisième génération" qui sont des aciers ayant une résistance et une ductilité combinées supérieures aux AHSS de Première Génération de l'ordre de 20 000 MPa x ε%, mais à un coût nettement moindre que celui requis pour les AHSS de seconde génération, réduisant ainsi le recours à des éléments d'alliage coûteux. Conséquemment, l'approche actuelle pour le développement d'AHSS de Troisième Génération est d'unir tous les aspects de la première et de la seconde génération d'aciers en des combinaisons uniques d'alliages et de microstructures qui permettront d'atteindre les propriétés désirées. Ainsi, les microstructures d'AHSS de troisième génération sont constituées d'une phase à haute résistance (e.g. Martensite ou bainite) et d'austénite dont la ductilité et l'écrouissage sont importants et qui possède une plasticité induite par déformation suite à une transformation ou un maclage. Dans cette thèse, quatre compositions d'aciers différents, centrés sur le Mn comme principal élément d'alliage, sont désignés comme candidats pour les grades d'AHSS de Troisième Génération. La conception de ces aciers est basée sur le contrôle du comportement à la déformation de l'austénite résiduelle. Par conséquent, les paramètres du procédé de traitement thermique sont déterminés de façon à obtenir différentes quantités et morphologies d'austénite résiduelle. L'évolution de la microstructure, au cours du traitement et de la déformation, est caractérisée par microscopie optique et électronique et des tests mécaniques. L'effet de la composition de l'alliage et des paramètres de traitement sur les mécanismes de déformation des aciers est discuté.
18
Yıldırım, Uygar Güden Mustafa. "Investigation of quasi-static dynamic mechanical properties of functionally graded Sic-particulate reinforced aluminium metal matrix composites/." [s.l.]: [s.n.], 2004. http://library.iyte.edu.tr/tezler/master/makinamuh/T000470.doc.
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19
Hergert, Alexander [Verfasser]. "Test methods for evaluating the dynamic properties of hydrophobicity of polymeric insulating materials / Alexander Hergert." München : Verlag Dr. Hut, 2017. http://d-nb.info/1135597049/34.
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20
Keller, Andrew R. "An experimental analysis of the dynamic failure resistance of TiB₂/A1₂O₃ composites." Thesis, Georgia Institute of Technology, 2000. http://hdl.handle.net/1853/16657.
Повний текст джерела
21
Guan, Juan. "Investigations on natural silks using dynamic mechanical thermal analysis (DMTA)." Thesis, University of Oxford, 2013. http://ora.ox.ac.uk/objects/uuid:c16d816c-84e3-4186-8d6d-45071b9a7067.
Повний текст джерелаАнотація:
This thesis examines the dynamic mechanical properties of natural silk fibres, mainly from silkworm species Bombyx mori (B. mori) and spider species Nephila edulis, using dynamic mechanical thermal analysis, DMTA. The aim is not only to provide novel data on mechanical properties of silk, but also to relate these properties to the structure and morphology of silk. A systematic approach is adopted to evaluate the effect of the three principal factors of stress, temperature and hydration on the properties and structure of silk. The methods developed in this work are then used to examine commercially important aspects of the ‘quality’ of silk. I show that the dynamic storage modulus of silks increases with loading stress in the deformation through yield to failure, whereas the conventional engineering tensile modulus decreases significantly post-yield. Analyses of the effects of temperature and thermal history show a number of important effects: (1) the loss peak at -60 °C is found to be associated the protein-water glass transition; (2) the increase in the dynamic storage modulus of native silks between temperature +25 and 100 °C is due simply to water loss; (3) a number of discrete loss peaks from +150 to +220°C are observed and attributed to the glass transition of different states of disordered structure with different intermolecular hydrogen bonding. Excess environmental humidity results in a lower effective glass transition temperature (Tg) for disordered silk fractions. Also, humidity-dynamic mechanical analysis on Nephila edulis spider dragline silks has shown that the glass transition induces a partial supercontraction, called Tg contraction. This new finding leads to the conclusion of two independent mechanisms for supercontraction in spider dragline silks. Study of three commercial B. mori cocoon silk grades and a variety of processed silks or artificial silks shows that lower grade and poorly processed silks display lower Tg values, and often have a greater loss tangent at Tg due to increased disorder. This suggests that processing contributes significantly to the differences in the structural order among natural or unnatural silks. More importantly, dynamic mechanical thermal analysis is proposed to be a potential tool for quality evaluation and control in silk production and processing. In summary, I demonstrate that DMTA is a valuable analytical tool for understanding the structure and properties of silk, and use a systematic approach to understand quantitatively the important mechanical properties of silk in terms of a generic structural framework in silk proteins.
22
Dean, Andrew W. "Feasibility of a New Technique to Determine Dynamic Tensile Behavior of Brittle Materials." Thesis, University of North Texas, 2016. https://digital.library.unt.edu/ark:/67531/metadc849768/.
Повний текст джерелаАнотація:
Dynamic tensile characterization of geo-materials is critical to the modeling and design of protective structures that are often made of concrete. One of the most commonly used techniques currently associated with this type of testing is performed with a Kolsky bar and is known as the spall technique. The validity of the data from the spall technique is highly debated because the necessary boundary conditions for the experiment are not satisfied. By using a technique called pulse shaping, a new “controlled” spall technique was developed to satisfy all boundary conditions so that the analyzed data may be useful in modeling and design. The results from this project were promising and show the potential to revolutionize the way Kolsky bar testing is performed.
23
Stone, Thomas Shannon. "A numerical/experimental method for evaluating the bulk and shear complex dynamic moduli of viscoelastic polymers in the kilohertz range." Thesis, Georgia Institute of Technology, 1997. http://hdl.handle.net/1853/17038.
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Swoger, Maxx Ryan. "Computational Investigation of Material and Dynamic Properties of Microtubules." University of Akron / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=akron1532108320185937.
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Meyer, Anne E. "Dynamics of "conditioning" film formation on biomaterials." Malmö : [s.n.], 1990. http://catalog.hathitrust.org/api/volumes/oclc/21989234.html.
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Osmanson, Allison Theresa. "Defining a Relationship between the Flexibility of Materials and Other Properties." Thesis, University of North Texas, 2018. https://digital.library.unt.edu/ark:/67531/metadc1157637/.
Повний текст джерелаАнотація:
Brittleness of a polymeric material has a direct relationship with the material's performance and furthermore shares an inverse relationship with that material's flexibility. The concept of flexibility of materials has been understood but merely explained with a hand-waving manner. Thus, it has never been defined by a calculation, thereby lacking the ability to determine a definite quantitative value for this characteristic. Herein, an equation is presented and proven which makes determining the value of flexibility possible. Such an equation could be used to predict a material's flexibility prior to testing it, thus saving money and valuable time for those in research and in industry. Substantiating evidence showing the relationship between flexibility of polymers and their respective mechanical properties is presented. Further relating the known tensile properties of a given polymer to its flexibility is expanded upon by proving its relationship to the linear coefficient of thermal expansion for each polymer. Additionally, determining flexibility for polymers whose chemical structures have been compromised by respective solvents has also been investigated to predict a solvent's impact on a polymer after exposure. Polymers examined through literature include polycarbonate (PC), polystyrene (PS), teflon (PTFE), styrene acrylonitrile (SAN), acrylonitrile butadiene styrene (ABS), poly(ethersulfone) (PES), low density polyethylene (LDPE), polypropylene (PP), poly(methyl methacrylate) (PMMA), and poly(vinylidene fluoride) (PVDF). Further testing and confirmation was made using PC, PS, ABS, LDPE, PP, and PMMA.
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Martin, Morgana. "Processing and Characterization of Energetic and Structural Behavior of Nickel Aluminum with Polymer Binders." Thesis, Georgia Institute of Technology, 2005. http://hdl.handle.net/1853/6925.
Повний текст джерелаАнотація:
A polymer-based composite reinforced with a mixture of Ni and Al powders was investigated as an example of a multifunctional structural energetic material. Micron-sized Ni powder, nano/micron-sized Al powders, and Teflon or epoxy were fabricated as bulk materials by pressing or casting. The thermally initiated reaction response of these materials was evaluated using differential thermal analysis coupled with x-ray diffraction. The analyses showed evidence of thermally initiated reactions between Ni and Al powders, as well as between Ni+Al and Teflon. Nano-sized Al powder showed a preference for reaction with Teflon over Ni, while micron-sized Al reacted strongly with Ni regardless of the presence of a binder. Teflon was shown to be very reactive with the Ni+Al/nano Al mixture, whereas epoxy was not reactive with the metallic powders, and also inhibited reaction between Ni and nano Al. The structural/mechanical behavior of these materials was evaluated using elastic and plastic property measurements via static and dynamic compression tests. Dynamic mechanical testing using reverse Taylor anvil-on-rod impact tests combined with velocity interferometry gave qualitative and quantitative information about the transient deformation and failure response of the composites. The material containing 20wt% epoxy and nano-sized Al powder showed the most superior mechanical properties in terms of elastic modulus and static and dynamic compressive strength. The addition of Ni and Al powders to the epoxy matrix increased the strength of the composites, and their tendency toward brittle fracture, as evidenced by Ni particle pullout in SEM analysis.
The results illustrate that nano-sized Al particles provide significant enhancement to strength of epoxy composites, but at the expense of reactivity. The nano-Al particles get dissociated from the Ni and Al mixture and swept into the epoxy, generating a nano-Al containing epoxy matrix with embedded Ni particles. The chemical reactivity of the system is thus sacrificed as contacts between Ni and Al powders are minimized. A mixture of nano-sized Ni and Al particles may however provide the best combination of high strength and reactivity.
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Mousa, A., G. Heinrich, and U. Wagenknecht. "Thermal properties of carboxylated nitrile rubber/nylon-12 composites-filled lignocellulose materials." Sage, 2014. https://tud.qucosa.de/id/qucosa%3A35546.
Повний текст джерелаАнотація:
Organic hybrid composites based on carboxylated nitrile rubber and nylon-12 reinforced with mercerized and diisocyanated lignocellulose residue (LCR) was prepared. The influence of the LCR on the viscoelastic properties of these organic hybrids was investigated by dynamic mechanical analysis and thermal analysis (differential scanning calorimetry (DSC)). It is found that either the position of the damping peak was shifted to higher values or the intensity of the damping peak was significantly increased with LCR. These results could imply that the LCR enhanced the damping properties of the composites. The thermal stability of the composites was evaluated with the mean values obtained using thermogravimetrical analysis. The decomposition rate was investigated using differential thermal gravimetry. The crystallization behavior of the prepared composites was checked by DSC.
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Brach, Stella. "Strength properties of nanoporous materials : theoretical analyses and molecular dynamics computations." Thesis, Paris 6, 2016. http://www.theses.fr/2016PA066618.
Повний текст джерелаАнотація:
L’objectif principal de la thèse a été d’étudier les propriétés de résistance des matériaux nanoporeux par des approches théoriques et numériques. Dans le contexte des méthodes d’homogénéisation, des critères de résistance macroscopiques ont été établis par des approches analytiques à l’homogénéisation non-linéaire et à l’analyse limite. Les critères de résistance ainsi obtenus permettent de tenir en compte les effets de taille, tout en améliorant les formulations déjà existantes. En outre, dans le but de servir de référence pour la calibration et/ou la validation des modèles analytiques, des simulations numériques basées sur la dynamique moléculaire ont été conduites, en se référant à des monocristaux d’aluminium contenant des nanopores sphériques, sous des conditions multiaxiales de vitesse de déformation. Par rapport aux simulations actuellement disponibles dans la littérature, les résultats obtenus ont clairement établi que les surfaces de résistance sont significativement influencées par les trois invariants isotropes de contrainte. Finalement, dans le but de mettre à profit les indications fournies par les simulations numériques, le cas d’un matériau nanoporeux constitué d’une matrice ductile sensible aux trois invariants isotropes a été étudié par une approche par l’analyse limite, en prenant en compte une formulation modifiée du critère de résistance de bigoni. La solution exacte du problème a été établie dans le cas d’un chargement isotrope. A partir des résultats ainsi obtenus, une approche d’analyse limite cinématique a été mise en place, et permet de fournir des estimations des propriétés de résistance macroscopiques sous chargements axisymétriquesThe main objectif of the thesis consisted in investigating strength properties of nanoporous materials by means of theoretical and numerical approaches. In the framework of homogenization methods, novel macroscopic strength criteria have been established via a non-linear homogenization procedure and a kinematic limit-analysis approach. Resulting yield functions allowed to take into account void-size effects on nanoporous materials strength properties, thereby resulting in a strong enhancement of available estimates. Furthermore, aiming to funish effective benchmarking evidence for the calibration and/or the assessment of theoretical models, molecular-dynamics based computations have been carried out on in-silico single crystals embedding spherical nanovoids, simulation domains undergoing multiaxial strain-rate boundary conditions. With respect to available numerical studies, proposed results clearly showed the influence of all the three isotropic stress invariants on computed material strength surfaces. Finally, with the aim to account for physical indications coming from numerical simulations, a ductile nanoporous material with a general isotropic plastic matrix has been investigated via a limit analysis approach, by referring to a modified version of the bigoni strength criterion. The limit state of a hollow-sphere model undergoing isotropic loadings has been exactly determined. Correspondigly, a novel strength criterion has been analytically established in the case of axysimmetric boundary conditions
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Manoogian, Sarah Jeanette. "Protecting the Pregnant Occupant: Dynamic Material Properties of Uterus and Placenta." Diss., Virginia Tech, 2008. http://hdl.handle.net/10919/28083.
Повний текст джерелаАнотація:
Automobile crashes are the largest cause of death for pregnant females and the leading cause of traumatic fetal injury mortality in the United States. The first way to protect the fetus is to protect the mother considering that maternal death has a near 100% fetal loss rate. If the mother survives, protection of the fetus may best be accomplished by preventing placental abruption. Placental abruption, which is the premature separation of the placenta from the uterus, has been shown to account for 50% to 70% of fetal losses in motor vehicle crashes.
Since real world crash data for pregnant occupants is limited to a retrospective analysis and pregnant cadaver studies are not feasible, crash test dummies and computational modeling have been utilized to evaluate the risk of adverse fetal outcome. Although pregnant occupant research has progressed with these tools, they are based on limited tissue data. In order to have more accurate research tools, better pregnant tissue material data are needed. Therefore, the purpose of this dissertation is to provide material properties for the placenta and pregnant uterine tissue in dynamic tension.Ph. D.
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Almaari, Firas, and Essam Aljbban. "Strain Rate Effect on Fracture Mechanical Properties of Ferritic-Pearlitic Ductile Iron." Thesis, Linnéuniversitetet, Institutionen för byggteknik (BY), 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:lnu:diva-78858.
Повний текст джерелаАнотація:
This study investigates the effect of strain rate on fracture properties of Ferritic-Pearlitic Ductile Iron. A series of dynamic three point bending tests, with various load application rates, are conducted on Charpy V-notch specimens, in room temperature and approximately -18 °C. The tests are performed in a custom-made fixture and during the tests, force and displacement data are recorded. A XFEM (Extended Finite Element Method) model of the test setup has been established and material data from the tests are used as input to the model. The test results show a strong dependency of the strain rate regarding the force needed for crack initiation. Moreover, it can be concluded that low temperature makes the material very brittle, even at low load application rates.
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Balasubramani, Praveen Kumar. "Properties and Curing Kinetics of Epoxy Resins Cured by Chitosan." University of Cincinnati / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1480328803855009.
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Marashdeh, Wajeeh. "Relaxation Behavior and Electrical Properties of Polyimide/Graphene Nanocomposite." University of Cincinnati / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1595850361812632.
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Martin, Morgana. "Dynamic mechanical behavior and high pressure phase stability of a zirconium-based bulk metallic glass and its composite with tungsten." Diss., Atlanta, Ga. : Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/22693.
Повний текст джерелаАнотація:
Thesis (Ph. D.)--Materials Science and Engineering, Georgia Institute of Technology, 2008.Committee Chair: Thadhani, Naresh; Committee Member: Doyoyo, Mulalo; Committee Member: Kecskes, Laszlo; Committee Member: Li, Mo; Committee Member: Sanders, Thomas; Committee Member: Zhou, Min.
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Harrison, Richard Allen 1963. "Far-infrared properties of halide glasses by molecular dynamics." Thesis, The University of Arizona, 1990. http://hdl.handle.net/10150/277257.
Повний текст джерелаАнотація:
Recent discoveries of low-loss, far-infrared transmitting halide glasses have sparked much interest in extending fiber-optic technology into the infrared region. However, a far greater than theoretical loss has been observed which has slowed research in the field. For this reason, computer modeling of several halide glass systems was performed in order to develop a fundamental understanding of the relationships between structural and optical properties of these glasses. ZrF₄, ZrF₄/BaF₂, ZnCl₂ glasses and melts were prepared using an isothermal-isobaric molecular dynamics algorithm. The infrared spectra were then calculated by Fourier transforming the dipole moment autocorrelation functions of the basic structural units. The more ionic ZrF₄ based glasses showed good agreement with experimental data, whereas the covalently bonded ZnCl₂ glass did not. Addition of barium to ZrF₄ glass was found to reduce high frequency modes of vibration in the glass.
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Rida, Ali. "Study of the Mechanical Properties of Nanocrystalline Materials by Molecular Dynamics Simulations." Thesis, Troyes, 2018. http://www.theses.fr/2018TROY0031.
Повний текст джерелаАнотація:
Le SMAT est un procédé de traitement de surface répandu dans le domaine industriel. Ce procédé est capable de nanocristalliser la surface de pièces traitées et produisent ainsi un durcissement local de la surface toute en conservant la ductilité du cœur du matériau. Dans ce contexte, la caractérisation des mécanismes de déformations à différentes échelles (du micron au nanomètre) est indispensable afin de créer des modèles constitutifs permettant de décrire précisément le comportement mécanique des pièces traitées. Les mécanismes de déformations de la couche nanocristalline sont assez mal compris. La densité élevée des joints de grains dans cette couche change radicalement la réponse mécanique par rapport à des grains de taille micrométrique. Pour ces raisons, la dynamique moléculaire a été utilisée pour exploiter les mécanismes de déformations des matériaux métalliques nanocristallins à l’échelle atomique.Dans la première partie de cette thèse, nous avons développé une nouvelle méthode de génération des échantillons numériques nanocristallins par fusion-refroidissement d’un monocristal.Dans une deuxième partie, nous avons étudié l’effet de la taille des grains sur les propriétés mécaniques du cuivre FCC et d’une forme cristalline du titane (-Ti HCP) nanocristallins. Les mécanismes de déformations de ces matériaux ont été étudiés et caractérisés à l’échelle atomique, en lien avec les propriétés mécaniques. Finalement, l’influence du taux de déformation sur la réponse mécanique du cuivre nanocristallin a été étudiéeSurface mechanical attrition treatment (SMAT) is a type of surface treatment process widely used in industrial applications. SMAT is able to nanocrystallize the surface, and to generate a gradient of grain size along with increasing material depth, thereby combining strength and ductility. In this context, the characterization of the deformation mechanisms of each layer from the micro to the nanoscale is timely and desirable. This should lead to multiscale constitutive models able to describe accurately the mechanical behavior of the treated specimens. The mechanical behavior of the nanocrystalline materials still not well understood. The high density of grain boundaries changes radically the mechanical response in comparison with materials containing only micro-grains. To this aim, molecular dynamics simulations (MD) have been employed in order to study the mechanical behavior of the nanocrystalline surface layer that results from SMAT at the atomic scale. First, a new melting cooling method has been developed to generate realistic numerical initial atomic configurations for MD simulations. Secondly, the effect of the grain size on the mechanical behavior of FCC nanocrystalline Copper and HCP nanocrystalline Titanium (-Ti) has been investigated. The deformation mechanisms of these systems are explored and analyzed at the atomic level. Finally, the strain rate dependence of the mechanical and the relaxation behavior of nanocrystalline Copper models is studied
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Kemper, Andrew Robb. "Material Properties of Human Rib Cortical Bone from Dynamic Tension Coupon Testing." Thesis, Virginia Tech, 2005. http://hdl.handle.net/10919/43709.
Повний текст джерелаАнотація:
The purpose of this study was to develop material properties of human rib cortical bone using dynamic tension coupon testing. This study presents 117 human rib cortical bone coupon tests from six cadavers, three male and three female, ranging in age from 18 to 67 years old. The rib sections were taken from the anterior, lateral, and posterior regions on ribs 1 through 12 of each cadaver's rib cage. The cortical bone was isolated from each rib section with a low speed diamond saw, and milled into dog bone shaped tension coupons using a small computer numerical control machine. A high-rate servo-hydraulic Material Testing System equipped with a custom slack adaptor, to provide constant strain rates, was used to apply tension loads to failure at an average rate of 0.5 strains/sec. The elastic modulus, yield stress, yield strain, ultimate stress, ultimate strain, and strain energy density were determined from the resulting stress versus strain curves. The overall average of all cadaver data gives an elastic modulus of 13.9 GPa, a yield stress of 93.9 MPa, a yield strain of 0.883 %, an ultimate stress of 124.2 MPa, an ultimate strain of 2.7 %, and a strain energy density of 250.1 MPa-strain. For all cadavers, the plastic region of the stress versus strain curves was substantial and contributed approximately 60 strain % to the overall response and over 80 strain % in the tests with the 18 year old cadaver. The rib cortical bone becomes more brittle with increasing age, shown by an increase in the modulus (p < 0.01) and a decrease in peak strain (p < 0.01). In contrast to previous three-bending tests on whole rib and rib cortical bone coupons, there were no significant differences in material properties with respect to rib region or rib level. When these results are considered in conjunction with the previous three-point bending tests, there is regional variation in the structural response of the human rib cage, but this variation appears to be primarily a result of changes in the local geometry of each rib while the material properties remain nearly constant within an individual.Master of Science
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Ramzan, Muhammad. "Structural, Electronic and Mechanical Properties of Advanced Functional Materials." Doctoral thesis, Uppsala universitet, Materialteori, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-205243.
Повний текст джерелаАнотація:
The search for alternate and renewable energy resources as well as the efficient use of energy and development of such systems that can help to save the energy consumption is needed because of exponential growth in world population, limited conventional fossil fuel resources, and to meet the increasing demand of clean and environment friendly substitutes. Hydrogen being the simplest, most abundant and clean energy carrier has the potential to fulfill some of these requirements provided the development of efficient, safe and durable systems for its production, storage and usage. Chemical hydrides, complex hydrides and nanomaterials, where the hydrogen is either chemically bonded to the metal ions or physiosorbed, are the possible means to overcome the difficulties associated with the storage and usage of hydrogen at favorable conditions. We have studied the structural and electronic properties of some of the chemical hydrides, complex hydrides and functionalized nanostructures to understand the kinetics and thermodynamics of these materials. Another active field relating to energy storage is rechargeable batteries. We have studied the detailed crystal and electronic structures of Li and Mg based cathode materials and calculated the average intercalation voltage of the corresponding batteries. We found that transition metal doped MgH2 nanocluster is a material to use efficiently not only in batteries but also in fuel-cell technologies. MAX phases can be used to develop the systems to save the energy consumption. We have chosen one compound from each of all known types of MAX phases and analyzed the structural, electronic, and mechanical properties using the hybrid functional. We suggest that the proper treatment of correlation effects is important for the correct description of Cr2AlC and Cr2GeC by the good choice of Hubbard 'U' in DFT+U method. Hydrogen is fascinating to physicists due to predicted possibility of metallization and high temperature superconductivity. On the basis of our ab initio molecular dynamics studies, we propose that the recent claim of conductive hydrogen by experiments might be explained by the diffusion of hydrogen at relevant pressure and temperature. In this thesis we also present the studies of phase change memory materials, oxides and amorphization of oxide materials, spintronics and sulfide materials.
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Antolin, Nikolas. "Density-Functional Theory Study of Materials and Their Properties at Non-Zero Temperature." The Ohio State University, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=osu1452253704.
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HASHMI, QUAZI SARWAR EHSAN. "NONASSOCIATIVE PLASTICITY MODEL FOR COHESIONLESS MATERIALS AND ITS IMPLEMENTATION IN SOIL-STRUCTURE INTERACTION." Diss., The University of Arizona, 1987. http://hdl.handle.net/10150/184024.
Повний текст джерелаАнотація:
A constitutive model based on rate-independent elastoplasticity concepts is developed and used to simulate the behavior of geologic materials under arbitrary three-dimensional stress paths. The model accounts for various factors such as friction, stress path and stress history that influence the behavior of geologic materials. A hierarchical approach is adopted whereby models of progressively increasing sophistication are developed from a basic isotropic-hardening associative model. Nonassociativeness is introduced as correction or perturbation to the basic model. Deviation of normality of the plastic strain increments to the yield surface F is captured through nonassociativeness. The plastic potential Q is obtained by applying a correction to F. This simplified approach restricts the number of extra parameters required to define the plastic potential Q. The material constants associated with the model are identified, and they are evaluated for three different sands (Leighton Buzzard, Munich and McCormick Ranch). The model is then verified by comparing predictions with laboratory tests from which the constants were found, and typical tests not used for finding the constants. The effect of varying initial density of a material on the stress-strain and volumetric response is investigated. An empirical relation is proposed, whereby one parameter is modified based on the initial density, such that improved predictions can be obtained without increasing the total number of parameters. Implementation of the nonassociative model in a finite element program to solve boundary value problems leads to a nonsymmetric stiffness matrix. Besides, using a nonsymmetric solver, three numerical schemes are investigated. The idea of the schemes is to modify the stiffness matrix such that a symmetric equation solver can be used. Prediction of stress-strain, volumetric response and CPU time for different schemes are compared with the predictions obtained using the nonsymmetric solver. The nonsymmetric equation solver used less CPU time and the solutions were more accurate. Based on the above findings, a soil-footing system is analyzed using the finite element techniques. The associative and nonassociative models are used to predict the behavior. For the nonassociative model, solution is obtained by using a nonsymmetric solver. Results obtained from both models are compared with a model footing test performed in the laboratory.
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Reda, Hilal. "Modeling and computation of the effective static and dynamic properties of network materials accounting for microstructural effects and large deformations." Thesis, Université de Lorraine, 2017. http://www.theses.fr/2017LORR0007/document.
Повний текст джерелаАнотація:
Nous analysons les propriétés dynamiques de milieux architecturés périodiques et de réseaux fibreux aléatoires en petites et grandes déformations, à partie de méthodes d’homogénéisation afin de calculer leurs propriétés statiques et dynamiques. Des modèles effectifs de type micropolaire et du second gradient sont élaborés afin de prendre en compte l’impact de la microstructure sur le comportement effectif. L’influence des degrés de liberté en rotation additionnels et des gradients d’ordre supérieur du déplacement sur les relations de dispersion sont analysés pour des comportements élastique et viscoélastique du matériau constitutif. Les milieux continus généralisés ainsi construits conduisent à des effets dispersifs, en accord avec les observations. Dans la seconde partie du travail, nous analysons l’influence des grandes déformations sur la propagation des ondes élastiques dans des milieux architecturés périodiques. Des méthodes théoriques assortis de schémas numériques sont développés afin de prédire l’influence des déformations finies générées au sein des structures sur l’évolution de leur diagramme de bande. Un schéma incrémental d’évolution de la fréquence et de la vitesse de phase du milieu continu homogénéisé est établi, à partir d’une méthode de perturbation établie pour des structures 1D, 2D et 3D, en considérant plus particulièrement des structures auxétiques. Ce schéma montre un effet important de l’état de déformation appliquée et de la densité effective sur l’évolution de la fréquence et de la vitesse de phase des ondes. Une méthode de perturbation spécifique aux structures périodiques nonlinéaires est développée afin de généraliser le théorème de Bloch pour couvrir les non linéarités tant géométriques que matérielles. Des modèles hyperélastiques du premier et du second gradient de différentes structures sont identifiés par des tests virtuels reposant sur une méthode d’homogénéisation dédiée, qui permettent de formuler des équations d’onde spécifiques – équations de Burgers et de Boussinesq – dont les propriétés dispersives sont analyséesMicropolar and second gradient effective continua are constructed as two different strategies to account for microstructural effects. The influence of additional degrees of freedom or higher order displacement gradients on the dispersion relations is analyzed in both situations of elastic and viscoelastic behaviors of the material. Generalized effective continua lead to dispersive waves, as observed in experiments. In the second part of the thesis, we analyze the influence of large deformations on the propagation of acoustic waves in repetitive network materials. Both theoretical and numerical methods are developed in order to assess the influence of finite strains developing within the networks on the evolution of their band diagrams. An incremental scheme for the update of frequency and phase velocity of the computed homogenized medium is developed based on a perturbation method for 1D, 2D and 3D structures, considering with a special emphasis auxetic networks. This scheme shows an important effect of the applied finite deformation on the frequency and phase velocity of the propagating waves. A perturbation method for nonlinear periodic structures is developed to extend Bloch’s theorem to cover both geometrical and material nonlinearities. Hyperelastic first and second order gradient constitutive models of different network materials are identified based on dedicated homogenization methods, from which specific wave equations are formulated - Burgers and Boussinesq equations - the dispersion properties of which are analyzed
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Cummings, Aron William. "Molecular dynamics simulation of the thermal properties of Y-junction carbon nanotubes." Online access for everyone, 2004. http://www.dissertations.wsu.edu/Thesis/Summer2004/a%5Fcummings%5F072304.pdf.
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Greenstein, Abraham. "Analysis of thermal conductivity models with an extension to complex crystalline materials." Diss., Atlanta, Ga. : Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/24710.
Повний текст джерелаАнотація:
Thesis (Ph.D.)--Mechanical Engineering, Georgia Institute of Technology, 2009.Committee Chair: Graham, Samuel; Committee Co-Chair: Nair, Sankar; Committee Member: Grover - Gallivan, Martha; Committee Member: McDowell, David; Committee Member: Schelling, Patrick; Committee Member: Zhang, Zhuomin
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Kim, Yeongkwan. "Equilibrium and dynamical properties of epitaxial ferroelectric heterostructures." Diss., Georgia Institute of Technology, 1996. http://hdl.handle.net/1853/30507.
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Tomasello, Bruno. "A quantum mechanical study of the dynamical properties of spin-ice materials." Thesis, University of Kent, 2014. https://kar.kent.ac.uk/48015/.
Повний текст джерелаАнотація:
The spin-ice materials Ho2Ti2O7 (HTO) and Dy2Ti2O7 (DTO) are part of a large family of compounds called magnetic pyrochlore oxides. Typically, the magnetism of these systems arise from the rare-earth ions RE3+ which sits at the vertices of a lattice of corner-sharing tetrahedra and couple with the degrees of freedom of the crystal leading to a wide spectrum of exotic phenomena. In spin-ices the magnetic moments of the individual RE3+ ions are large enough to let their mutual dipolar interactions be the leading factors for the thermodynamics. Moreover, the strength and the symmetries of their local crystalline environment are such that each ion behaves like a magnetic dipole with only two allowed configurations: it points either parallel or opposite to the ⟨111⟩ axis joining the vertex where it sits to the centre of the tetrahedron. As a result, the ground state of the system is macroscopically degenerate because the ferromagnetic interactions between the 4 Ising-like spins in each tetrahedron cannot be satisfied simultaneously, and in turn the manifold of possible configurations minimising the energy (2 spins inward - 2 spins outward) increases with the size of the system. This exotic ground state is such that the Ising configurations of the dipoles map to the disordered vector-displacements of the protons in the water molecules of conventional ice; hence the name spin-ice. Violations of the (2in-2out) ice rules take the systems out of the ground state into more energetic configurations. More precisely, the flipping of a spin between two adjacent ground-state tetrahedra creates a local excitation (1in-3out in a tetrahedron, 3in-1out in the neighbouring one) that is made of two fractionalised opposite magnetic fluxes. Once the two fluxes are created they can separate and freely hop across the lattice as their motion does not involve ahy higher order violation of the ice-rules. The low temperature properties of spin-ice is found to depend heavily, if not exclusively, on the density and mobility of such flux-defects which effectively behave as magnetic monopoles mutually interacting via a Coulomb potential. Beside the success of many experiments which exploit the physics of the monopoles in their exclusively classical formulation, there has been an increasing curiosity about the microscopic mechanisms which dictate their propagation across the lattice. At present, the dynamics of the monopoles are still puzzling showing different responses under different probes and non-identical behaviours between the two compounds HTO and DTO. As the monopoles themselves consist of packed magnetic fluxes originating from the magnetic moments of the RE3+ ions, investigating the microscopical mechanisms underlying their motion requires revisiting the foundations of the classicality which emerges form the quantum substrate of the interactions of the magnetic ions. This is the subject of the work presented in this thesis. With particular focus on the interplay between the local crystal-symmetries and the mutual interactions between the RE3+ ions, the present study gives an accurate de- scription of the microscopic mechanisms which occur in the pyrochlore substrate in the presence of a monopole. The results suggest that the motion of the monopoles is achieved thanks to the spin-tunnelling of the RE3+ ions which account for the flipping of the Ising spins, necessary for the propagation of a monopole. A major improvement we add to the standard theory of spin ice, is the role of the exchange interactions that are overcome by the dipolar ones in the ice-state but posses a dynamical resilience which manifests in the presence of a monopole. Furthermore, the present study brings to light the articulated statistical structure of the kinematic spin-constraints which are expected to dictate the diffusion of the free monopoles and their response under dif- ferent probes also in conditions out of equilibrium. From a more general perspective, the mathematical and physical models developed during this work promise to be of in- terest also in other magnetic systems. Primarily, in the other pyrochlore oxides whose microscopical structure is akin the spin-ice one, secondarily, in other RE3+ compounds where the interplay between quantum and classical physics leads to the manifestation of unusual dynamical effects.
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Bisplinghoff, Jill Aliza. "Biomechanical Response of the Human Eye to Dynamic Loading." Thesis, Virginia Tech, 2009. http://hdl.handle.net/10919/31880.
Повний текст джерелаАнотація:
Blindness due to ocular trauma is a significant problem in the United States considering that each year approximately 500,000 years of eyesight are lost. The most likely sources of eye injuries include sports related impacts, automobile accidents, consumer products, and military combat. Out of the 1.9 million total eye injuries in the country, more than 600,000 sports injuries occur each year and 40,000 of them require emergency care. In 2007, approximately 66,000 people suffered from vehicle related eye injuries in the United States. Of the vehicle occupants sustaining an eye injury during a crash, as many as 15% to 25% sustained severe eye injuries and it was shown that within these severe eye injuries as many as 45% resulted in globe rupture.
The purpose of this thesis is to characterize the biomechanical response of the human eye to dynamic loading. A number of test series were conducted with different loading conditions to gather data. A drop tower pressurization system was used to dynamically increase intraocular pressure until rupture. Results for rupture pressure, stress and strain were reported. Water streams that varied in diameter and velocity were developed using a customized pressure system to impact eyes. Intraocular pressure, normalized energy and eye injury risk were reported. A Facial and Ocular Countermeasure Safety (FOCUS) headform was used to measure the force applied to a synthetic eye during each hit from projectile shooting toys. The risk of eye injury for each impact was reported. These data provide new and significant research to the field of eye injury biomechanics to further the understanding of eye injury thresholds.
Master of Science
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Cherne, Frank Joseph. "Calculation of transport properties of liquid metals and their alloys via molecular dynamics." Diss., The University of Arizona, 2000. http://hdl.handle.net/10150/284305.
Повний текст джерелаАнотація:
The advanced casting modeler requires accurate viscosity and diffusivity data of liquid metals and their alloys. The present work discusses the use of equilibrium and non-equilibrium molecular dynamics techniques to obtain such data without having to rely on oversimplified phenomenological expressions or difficult and expensive experiments. Utilizing the embedded atom method (EAM), the viscosities and diffusivities for a series of equilibrium and non-equilibrium molecular dynamics simulations of nickel, aluminum, and nickel-aluminum alloys are presented. A critical comparison between the equilibrium and non-equilibrium methods is presented. Besides the transport properties, structural data for the liquids are also evaluated. EAM does a poor job of describing the transport properties of nickel-aluminum alloys, particularly near the equiatomic concentration. It has been suggested that charge transfer between nickel and aluminum atoms is responsible for the discrepancy between numerical calculations and available experimental data. A modified electronic distribution function has been developed to simulate the charge transfer associated with compound formation. The effects of such a "charge transfer" modification to the embedded atom method are evaluated. The results of these simulations indicate that the embedded atom method combined with molecular dynamics may be used as a method to predict reasonably the transport properties.
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Mukhopadhyay, Atashi Basu. "Theoretical investigation of static and dynamic properties of zeolite ZSM-5 based amorphous material." [S.l. : s.n.], 2004. http://deposit.ddb.de/cgi-bin/dokserv?idn=972017097.
Повний текст джерела
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Sears, Nicholas C. "Investigations into the Quasi-Static and Dynamic Properties of Flexible Hybrid Electronic Material Systems." The Ohio State University, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=osu1525278328687427.
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Link, Stephen. "Spectral properties and relaxation dynamics of surface plasmon electronic oscillations in gold and silver nanodots and nanorods." Diss., Georgia Institute of Technology, 2000. http://hdl.handle.net/1853/30706.
Повний текст джерела