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<p> HNBR is a widely used oil resistant polymer with good tear strength. Due to these properties, HNBR is used in oil wells. However, harsh working environments require high equipment maintenance fees and HNBR will be degraded when contacted with H₂S. This study aims to improve the mechanical properties and H₂S resistance of HNBR through molecular dynamics simulations. Some of the simulation results are compared with experimental results and literature values. In this study, the solubility parameters and densities of pure HNBR with varying acrylonitrile content, FKM and three surfactants (KBM503, a trimethoxysilane methacrylate, A10, a perfluoroalkoxy bis(alkylamide), and Capstone-62MA, a semifluorinated methacrylate) are calculated by molecular dynamics simulation. The cohesive energy densities of 50/50 HNBR/FKM blends with different kinds and content of surfactants are calculated. The diffusion of H₂S and CO₂ are predicted by molecular dynamics simulation. The solubility coefficients of H₂S and CO₂ are predicted by Grand Canonical Monte Carlo (GCMC) simulations. A series of NPT simulations (constant of number of atoms, pressure and temperature) are used to estimate the glass-transition temperature of Capstone-62MA grafted HNBR. Dissipative Particles Dynamics (DPD) simulations are used to obtain the micro phase separation of Capstone-62MA grafted HNBR. The results shows that the solubility parameter values and densities we obtained from molecular dynamics simulations are fitted very well with literature values. According to our calculation of energy of mixing for HNBR/FKM blends with three surfactant (KBM503, A10 and Capstone-62MA), KBM503 has the largest effect. Based on the experiment results for HNBR/FKM blends with different mass fractions of KBM503, the tensile stress at break and elongation at break increases with the increases of KBM503 content until the mass fraction KBM503 is equal to 5%. When the mass fraction of KBM503 is 5%, adding more KBM503 decreases both mechanical properties. However, the tear strength keeps increasing when the mass fraction of KBM503 increases. The conclusion obtained from these experiments and simulations indicates that mixing HNBR with FKM can improve some mechanical properties but this method has disadvantages due the large discrepancy between the solubility parameters of HNBR and FKM. Gas diffusion and solubility calculations indicate that the diffusion and solubility of H₂S decrease with the content of Capstone-62MA increases. The gas diffusion of H₂S also decreases with increasing content of acrylonitrile in HNBR. However, the solubility of H₂S also increases with the content of acrylonitrile in HNBR. For comparison with H₂S, the diffusivity and solubility of CO₂ are calculated. The diffusion of CO₂ increases with the increase of Capstone-62MA content. The solubility of CO₂ decreases with increases of Capstone-62MA in HNBR with 17 wt% acrylonitrile content. For HNBR with 36 wt% acrylonitrile content, increasing the content of Capstone-62MA first increases the solubility of CO₂ and then reduces it when the content of Capstone-62MA is larger than 2%. The calculation also indicates that diffusion and solubility coefficient are reduced when the content of acrylonitrile increases in HNBR. Calculations for the glass-transition temperature of HNBR with different numbers of Capstone-62MA chains suggest that the glass-transition temperature is not changed by grafting Capstone-62MA onto the backbone of HNBR. These results are compared with experimental results. Although the glass-transition temperatures obtained from simulations are higher than those obtained from experiment, they have the same trend as the content of Capstone-62MA is changed. DPD simulations suggest that micro phase separation exists in the Capstone-62MA grafted HNBR and this phenomenon improves the mechanical performance of polymers. In summary, we have used computer modeling to design new polymer materials and perform molecular dynamics simulations, Monte Carlo simulations and DPD simulations to predict some properties of these new materials. Some simulation results are compared with experimental results indicating that we indeed obtain a newly a polymer material with improved properties with the help of computer simulations.</p><p>

The essential characteristics of large systems is their high dimensionality due to which conventional control techniques fail to give reasonable solutions with reasonable computational efforts. A number of large systems encountered in practice are composed of subsystems with similar dynamics interconnected in a symmetrical fashion. The analysis and control of a large system with these particular features must take advantage of the existing structural properties to achieve computational simplifications of the overall problem. The focus of this thesis is the feedback design and analysis of large systems possessing the property of spatial symmetry. Specifically, the problems of controller design and analysis for infinite dimensional toeplitz systems and their finite dimensional analogs, circulant systems, are studied. These spatially symmetric systems are special classes of large systems. The first part of this thesis is focused on the development of formal controller design methodologies which take advantage of the properties of the circulant matrices. The key to this development is the use of the FFT algorithm to diagonalize circulant matrices. The resulting controller design methodologies are computationally attractive and easily applicable to large systems with circulant symmetry. More specifically, the H$\sb2$ and H$\sb{\infty}$ controller synthesis problems are studied in detail and are shown to decompose into lower order independent problems. The second part of this work concentrates on proving that certain finite order toeplitz systems are asymptotically equivalent in an appropriate sense to circulant systems. This result justifies the use of circulant control design techniques for certain toeplitz systems. Moreover, the closed loop effects of controlling a toeplitz system with a controller designed for its asymptotically equivalent circulant system are analyzed. The application of the developed theoretical results to a realistic example is the focus of the last part of the thesis. The adaptive optics system used in this example is modeled by a transfer function matrix with toeplitz symmetry. The computational efficiency of the controller design methodologies developed in this thesis is illustrated by designing a series of controllers for this system.

Thesis (Ph.D)--Civil and Environmental Engineering, Georgia Institute of Technology, 2009. / Committee Chair: Dr. Leroy Z. Emkin; Committee Co-Chair: Dr. Abdul-Hamid Zureick; Committee Member: Dr. Dewey H. Hodges; Committee Member: Dr. Kenneth M. Will; Committee Member: Dr. Rami M. Haj-ali. Part of the SMARTech Electronic Thesis and Dissertation Collection.

<p>Over the past two decade, there have been renewed interests in the use of continuum models of dislocation to predict the plastic strength of metals from basic properties of dislocations. Such interests have been motivated by the unique self-organized dislocation microstructures that develop during plastic deformation of metals and the need to understand their origin and connection with strength of metals. This thesis effort focuses on the theoretical development of a vector-density based representation of dislocation dynamics on the mesoscale accounting for the kinematics of finite deformation. This model consists of two parts, the first is the development of the transport-reaction equations governing dislocation dynamics within the finite deformation setting, and the second focuses on the computational solution of the resulting model. The transport-reaction equations come in the form of a set of hyperbolic curl type transport equations, with reaction terms that nonlinearly couple these equations. The equations are also geometrically non-linear due to finite deformation kinematics and by their constitutive closure. The solution of the resulting model consists of two parts that are coupled in a staggered fashion, the crystal mechanics equations are lumped in the stress equilibrium equations, and the dislocation transport-reactions equations. The two sets of equations are solved by the Galerkin and First-Order System Least-Squares (FOSLS) finite element methods. A special attention is given to the accurate modeling of glissile dislocation junctions using de Rahm currents and graph theory ideas. The introduction of these measures requires the derivation of further transport relations. Using homogenization theory, we specialize the proposed model to a mean deformation gradient driven bulk plasticity model. Lastly, we simulate bulk plasticity behavior and compare our results against experiments.</p>

<p>  </p> <p>With the advent of femtosecond lasers in the early 1990s, ultrafast laser processing has proven to be an imperative tool for micro/nanomachining. Two-photon lithography (TPL) is one such unique microfabrication technique exploiting the nonlinear dependency of the polymerization rate on the irradiating light intensity to produce true three-dimensional structures with feature sizes beyond the diffraction limit. This characteristic has revolutionized laser material processing for the fabrication of micro and nanostructures. This research first gives a general overview of TPL, including its operating principle, experimental setup, compatible materials, and techniques for improving the final resolution of the fabricated structure. Insights to improve throughput and speed of fabrication to pave a way for the industrialization of this technique are provided.</p> <p>Following that, the report delves into the process of fabricating two true three-dimensional mechanical metamaterials via the stereolithography technique. This chapter encompasses the design, fabrication, and experimental analysis of a three-dimensional axisymmetric structure with elliptical perforations distributed periodically on the walls of the structure with varying thicknesses. Furthermore, this study discusses the significance of the elliptical perforations in terms of auxetic behavior and load-bearing capacity against a so-called plain structure under quasistatic compression loading.</p> <p>Finally, the report explores the technique of fabricating a true three-dimensional cylindrical auxetic structure via two-photon polymerization. This section of the report examines the optical setup utilized, the sample preparation procedure, and calibration experiments performed in order to fabricate a three-dimensional thin-walled right cylinder with bowtie like perforations arranged on the walls to promote the exhibition of symmetric negative Poisson’s ratio under uniaxial quasistatic compression loading.</p>

<p>Adhesives  are  found  in  almost  every  aspect  of  the  modern  world.  They  are  found  in plywood used in buildings, electronics, shoes, plumbing and in almost every facet of your daily life. Nature also has an abundance of these adhesives that are used fora multitude of applications. Some  animals, like  the  blue  mussel, use  their  adhesive  for  protection  against  ocean  waves  and predators  while other animals, such  as  the  spider, use  it  to  trap  prey. Investigation  of  theses adhesives has led to the identification of several different proteins that allow for these animals to make  their  adhesive.  Some  of  them  are  composed of rare  amino  acids that  while  other  animals use  a combination  of  inorganic  and  organic  components.  Understanding  of  these  unique adhesives  can be  a  boon  for designof future  adhesives  that  do  not  have  the disadvantagesof current day commercialized glues.</p> <p>Increasing interest  in  the  restoration  of  natural  oyster  reefs  and  the  cement  that  holds them  together  has  resulted  in  the  identification  of  the  Shelk2  protein  that  is  found  both  in  the mantle  of  the  oyster’s  shell  as  well  as  the  cement  that  holds  the  reefs  together. Gaining  an understanding  of  how  this  protein  functions  and  its  part  in  the  oyster  reef  could  be  quite beneficial  for  projects  investing  in  reef  restorations  as  well  as  underwater  adhesion.  Gathering protein  from  the  animal  for  experimentation  and  characterization  can  be  labor  intensive  and extremely challenging. Luckily, cloning technology has become a useful tool for the expression of large quantities of proteins that can be difficult or impossible to gather from the native animal. Using <em>E. coli</em>, it  is  possible  to design  and express  this protein  in  hopes  of  gaining  a  better understanding of its impact on oyster settlement and adhesion.</p> <p>Sustainability is a major downside to current day adhesives that current technologies have not  been  able  to  solve. Most adhesives  that  are  on  the  market  today  are  primarily  derived  from petroleum. Current  research  has  begun  investigating  alternatives  to  the  large   epoxy   and formaldehyde  adhesive  market,  but  the  barrier  of  entry  is  hard  to  overcome.  To  replace  these glues  the  new  material  must  be  affordable,  non-petroleum  derived,  and  available  on  a  massive scale.  These  requirements  are  hard  to  meet  for  many  materials  and  due  to  that  the  current  bio-adhesive are generally very low strength.</p> <p>The work presented here will detail the characterization, and expression of some of these natural  adhesives that  have  been  found  in  the  Eastern  oyster. Another  aspect of  this  work includes the synthesis of a new bio-based adhesive system. Utilizing biomimetic chemistry along with  sustainably  sourced  materials  a  new  adhesive  has  been  formulated that  has  comparable adhesive strength to current day commercial adhesives.</p>

<p>Functional oxide-based thin films have attracted much attention owing to their broad applications in modern society. The multifunction tuning in oxide thin films is critical for obtaining enhanced properties. In this dissertation, four new nanocomposite thin film systems with highly textured growth have been fabricated by pulsed laser deposition technique. The functionalities including ferromagnetism, ferroelectricity, multiferroism, magnetoelectric coupling, low-field magnetoresistance, transmittance, optical bandgap and dielectric constants have been demonstrated. Besides, the tunability of the functionalities have been studied via different approaches.</p> <p>First, varies deposition frequencies have been used in vertically aligned nanocomposite BaTiO₃:YMnO₃ (BTO:YMO) and BaTiO₃:La_0.7Sr_0.3Mn₃(BTO:LSMO) thin films. In both systems, the strain coupling effect between the phases are affected by the density of grain boundaries. Increasing deposition frequency generates thinner columns in BTO:YMO thin films, which enhances the anisotropic ferromagnetic response in the thin films. In contrast, the columns in BTO:LSMO thin films become discontinuous as the deposition frequency increases, leading to the diminished anisotropic ferromagnetic response. Coupling with the ferroelectricity in BTO, the room temperature multiferroic properties have been obtained in these two systems.</p> <p> Second, the impact of the film composition has been demonstrated in La_0.7Ca_0.3MnO₃ (LCMO):CeO₂thin film system, which has an insulating CeO₂in ferromagnetic conducting LCMO matrix structure. As the atomic percentage of the CeO₂increases, enhanced low-field magnetoresistance and increased metal-to-insulator transition temperature are observed. The thin films also show enhanced anisotropic ferromagnetic response comparing with the pure LCMO film.</p> <p> Third, the transition metal element in Bi₃MoM_TO₉(M_T, transition metals of Mn, Fe, Co and Ni) thin films have been varied. The thin films have a multilayered structure with M_T-rich pillar-like domains embedded in Mo-rich matrix structure. The anisotropic magnetic easy axis and optical properties have been demonstrated. By the element variation, the optical bandgaps, dielectric constants as well as anisotropic ferromagnetic properties have been achieved. </p> <p> The studies in this dissertation demonstrate several examples of tuning the multifunctionalities in oxide-based nanocomposite thin films. These enhanced properties can broaden the applications of functional oxides for advanced nanoscale devices.</p><br>

In the aftermath of natural disasters, providing temporary housing to displaced people is essential to alleviate human suffering. However, in some cases, the chosen post-disaster temporary housing strategy may not be suitable for the local conditions, which can worsen the negative impacts, particularly when decision-makers need to change their original plan due to the uncertainty of post-disaster conditions. As most temporary housing design strategies have their weaknesses, the best approach is the one that matches the specific circumstances of each scenario. This thesis proposes design strategies, including prefabricated and modular units, foldable units, upgradable units, grid and linear expansion, and passive energy units, to determine the most appropriate policy to minimize conflicts between local requirements and temporary housing characteristics while maximizing the comfort and sustainability of temporary housing design. The strategies were analyzed based on their strength and weaknesses by following the previous research, and their implementation possibilities on recently occurred natural disasters, e.g., Turkey's earthquake in 2023, were also evaluated. It was found that all strategies except for grid and linear expansion might be suitable for the studied natural disaster.

Sustainable materials are prevalent within design, but industrial design lacks mass-manufactured product examples. This research explores this gap in knowledge to understand the influences affecting the selection of sustainable materials and how UK industrial designers could be better supported. A comprehensive literature review explores the selection of sustainable materials within the context of industrial design. Existing tools and resources designed to support industrial designers are analysed to understand the support provision and requirements. The research approach explores individual attitudes, and the influences towards and against selecting sustainable materials. Four UK companies were studied to understand how sustainable materials are considered and utilised for mass-manufactured products. Two frameworks were designed to support and facilitate sustainable material selection. The first depicts the overarching support requirements whilst the second presents the considerations and strategies. Both frameworks were evaluated by experts and previous participants. A workshop with designers evaluated the efficacy of the second framework when used as a tool The majority of industrial designers were aware of general issues of sustainability but rarely considered selecting sustainable materials. All four companies had experienced significant changes recently, including increasing resources and internal initiatives towards the use of sustainable materials. The market for sustainable materials is improving, but risks exist, such as fluctuating availability and market instability. A lack of awareness and understanding has meant that, in order to succeed, some companies have designed methods to educate stakeholders whilst designers have requested support to educate clients. Personal interest of the individual is a key driver, creating champions who raise awareness and boost confidence amongst colleagues. There is a need, not only for greater education and support, but also to improve engagement with sustainable material selection amongst industrial designers and others involved in the process.