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Articles 841 - 858 of 858
Full-Text Articles in Engineering
Phase Structures And Morphologies Determined By Competitions Among Self-Organization, Crystallization, And Vitrification In A Disordered Poly(Ethylene Oxide)-B-Polystyrene Diblock Copolymer, Lei Zhu, Yan Chen, Anqui-Q. Zhang, Bret. H. Calhoun, Moonseok Chun, Stephen Z. D. Cheng, Benjamin S. Hsiao, Fengji Yeh, Takeji Hashimoto
Phase Structures And Morphologies Determined By Competitions Among Self-Organization, Crystallization, And Vitrification In A Disordered Poly(Ethylene Oxide)-B-Polystyrene Diblock Copolymer, Lei Zhu, Yan Chen, Anqui-Q. Zhang, Bret. H. Calhoun, Moonseok Chun, Stephen Z. D. Cheng, Benjamin S. Hsiao, Fengji Yeh, Takeji Hashimoto
College of Polymer Science and Polymer Engineering
A poly(ethylene oxide)-b-polystyrene (PEO-b-PS) diblock copolymer having a number-average molecular weight ((M) over bar(n)) of 11000 g/mol in the PEO blocks and an (M) over bar(n) of 5200 g/mol in the PS blocks has been synthesized (with a volume fraction of the PEO blocks of 0.66 in the molten state). Differential scanning calorimetry results show that this copolymer possesses a single endotherm, which is attributed to the melting of the PEG-block crystals. Based on real-time resolved synchrotron small-angle x-ray scattering (SAXS) observations, the diblock copolymer is in a disordered state above the glass transition temperature of the PS-rich phase (T-g(PS)) …
Rhythmic Growth Of Target And Spiral Spherulites Of Crystalline Polymer Blends, Thein Kyu, Hw Chiu, Aj Guenthner, Y Okabe, H Saito, T Inoue
Rhythmic Growth Of Target And Spiral Spherulites Of Crystalline Polymer Blends, Thein Kyu, Hw Chiu, Aj Guenthner, Y Okabe, H Saito, T Inoue
College of Polymer Science and Polymer Engineering
Numerical calculations reveal that the target and spiral growth patterns in spherulites can be generated from the time-dependent Ginzburg-Landau equations (model C) by coupling a conserved compositional order parameter and a nonconserved crystal ordering parameter. Of particular interest is that the periodic concentric rings (target) or the spirals at the spherulitic core remain stationary in both the crystal (orientational) ordering field and the concentration field. Another intriguing observation is that the growth of target and spiral spherulites occurs in a stepwise fashion in synchronism with the rhythmic energy dissipation during crystallization.
Spatio-Temporal Growth Of Nematic Domains In Liquid Crystal Polymer Mixtures, Hao-Wen Chiu, Thein Kyu
Spatio-Temporal Growth Of Nematic Domains In Liquid Crystal Polymer Mixtures, Hao-Wen Chiu, Thein Kyu
College of Polymer Science and Polymer Engineering
Dynamics of phase separation and morphology development in mixtures of a low molar mass liquid crystal (LC) and a polymer have been investigated theoretically in comparison with experimental results. In the theoretical model, the combined free-energy densities of Flory-Huggins theory for isotropic mixing and Maier-Saupe theory for nematic ordering have been incorporated into the time-dependent Ginzburg-Landau equation (type C). The temporal evolution of the structure factor and the emergence of phase-separated liquid crystal domains have been simulated on the basis of an explicit central difference method based on a square lattice (128 x 128) with a periodic boundary condition. Of …
The Integrated Systems Engineering Laboratory- An Innovative Approach To Vertical Integration Using Modern Instrumentation, Ajay Mahajan, Maurice Walworth, David Mcdonald, Kevin Scmaltz
The Integrated Systems Engineering Laboratory- An Innovative Approach To Vertical Integration Using Modern Instrumentation, Ajay Mahajan, Maurice Walworth, David Mcdonald, Kevin Scmaltz
Mechanical Engineering Faculty Research
The current paradigm in engineering course instruction builds on a lecture prerequisite structure but ignores the need for a laboratory prerequisite structure. Educational quality is therefore diminished as instructors optimize specific laboratories but fail to optimize the overall program laboratory experience. This paper presents a learning environment based on modern instrumentation that forces students to use not only concepts and skills acquired from the lecture, but also actual data and models acquired from lower division laboratories, in upper division laboratories. The vertical integration occurs because students must utilize their previous laboratory work as a reference and/or building blocks as they …
Analysis Of Ductile To Cleavage Transition In Part-Through Cracks Using The Cell Model Incorporating Statistics, Xiaosheng Gao, J. Faleskog, C. Fong Shih
Analysis Of Ductile To Cleavage Transition In Part-Through Cracks Using The Cell Model Incorporating Statistics, Xiaosheng Gao, J. Faleskog, C. Fong Shih
Mechanical Engineering Faculty Research
This paper describes an approach to study ductile/cleavage transition in ferritic steels using the methodology of a cell model for ductile tearing incorporating weakest link statistics. The model takes into account the constraint effects and puts no restriction on the extent of plastic deformation or amount of ductile tearing preceding cleavage failure. The parameters associated with the statistical model are calibrated using experimental cleavage fracture toughness data, and the effect of threshold stress on predicted cleavage fracture probability is investigated. The issue of two approaches to compute Weibull stress, the ‘history approach’ and the ‘current approach’, is also addressed. The …
Kinetics Of Phase Transition In An Anticlinic Liquid Crystal Induced By A Uniform Temperature Field: Growth In One Dimension, X. Y. Wang, Jian-Feng Li, Eliezer Gurarie, S. Fan, Thein Kyu, S. S. Keast, Charles Rosenblatt
Kinetics Of Phase Transition In An Anticlinic Liquid Crystal Induced By A Uniform Temperature Field: Growth In One Dimension, X. Y. Wang, Jian-Feng Li, Eliezer Gurarie, S. Fan, Thein Kyu, S. S. Keast, Charles Rosenblatt
College of Polymer Science and Polymer Engineering
It is experimentally demonstrated that a transition from a synclinic to an anticlinic liquid crystal phase occurs via stable domain wall propagation after quenching in a uniform temperature field. Such a one-dimensional growth may be explained in terms of a nonlinear diffusion equation. The experiment provides the first example of free, one-dimensional growth in a system subjected to a pure and uniform temperature field.
Phase Equilibria Of A Nematic And Smectic-A Mixture, Hao-Wen Chiu, Thein Kyu
Phase Equilibria Of A Nematic And Smectic-A Mixture, Hao-Wen Chiu, Thein Kyu
College of Polymer Science and Polymer Engineering
A phase diagram of a mixture consisting of nematic and smectic liquid crystals has been calculated self-consistently by combining Flory-Huggins (FH) theory for isotropic mixing and Maier-Saupe-McMillan (MSM) theory for smectic-A ordering. However, the MSM theory can be deduced to the original Maier-Saupe (MS) theory for nematic ordering. To describe the phase transitions involving induced smectic phase and nematic + smectic equilibrium, two nematic and two smectic order parameters for the nematic/smectic mixtures have been coupled through the normalized partition function and the orientation distribution function. Self-consistent numerical solution has been sought in establishing nematic/smectic phase diagrams involving (i) phase …
Phase Diagrams Of A Binary Smectic-A Mixture, Hao-Wen Chiu, Thein Kyu
Phase Diagrams Of A Binary Smectic-A Mixture, Hao-Wen Chiu, Thein Kyu
College of Polymer Science and Polymer Engineering
A variety of smectic phase diagrams involving smectic-isotropic and smectic-nematic-isotropic transitions have been calculated based on a combination of Flory-Huggins (FH) theory for isotropic mixing and Maier-Saupe-McMillan (MSM) theory for smectic-A ordering of liquid crystals (LC). To describe the mesophase transitions, two nematic order parameters and two smectic order parameters have been coupled through the normalized orientation distribution and partition functions. Flory-Huggins interaction parameter (chi) for isotropic mixing and the coupling term involving the nematic interaction parameter (nu) and the McMillan smectic interaction parameter (alpha) for phase transitions of liquid crystals have been incorporated in the calculation. The predictive capability …
A Cell Model For Ductile Fracture With Applications, C. Fong Shih, Li Cheng, J. Faleskog, Xiaosheng Gao
A Cell Model For Ductile Fracture With Applications, C. Fong Shih, Li Cheng, J. Faleskog, Xiaosheng Gao
Mechanical Engineering Faculty Research
No abstract provided.
Nucleation Initiated Spinodal Decomposition In A Polymerizing System, Thein Kyu, Jae Hyung Lee
Nucleation Initiated Spinodal Decomposition In A Polymerizing System, Thein Kyu, Jae Hyung Lee
College of Polymer Science and Polymer Engineering
Dynamics of phase separation in a polymerizing system, consisting of carboxyl terminated polybutadiene acrylonitrile/epoxy/methylene dianiline, was investigated by means of time-resolved light scattering. The initial length scale was found to decrease for some early periods of the reaction which has been explained in the context of nucleation initiated spinodal decomposition We have combined the Cahn-Hilliard kinetic equation and polymerization kinetics, and predicted the initial reduction of the length scale triggered by nucleation.
Non-Markovian Brownian Motion In A Viscoelastic Fluid, V. S. Volkov, Arkadii I. Leonov
Non-Markovian Brownian Motion In A Viscoelastic Fluid, V. S. Volkov, Arkadii I. Leonov
College of Polymer Science and Polymer Engineering
A theory of non-Markovian translational Brownian motion in a Maxwell fluid is developed. A universal kinetic equation for the joint probability distribution of position, velocity, and acceleration of a Brownian particle is derived directly from the extended dynamic equations for the system. Unlike the extended Fokker-Planck equation which corresponds to Mori-Kubo generalized Langevin equation and provides only with calculations of one-time moments, the universal kinetic equation obtained gives complete statistical description of the process. In particular, an exact generalized Fokker-Planck equation in the velocity space valid for any time instant is derived for the free non-Markovian Brownian motion. It shows …
Equilibrium Phase-Behavior Of Nematic Mixtures, Hao-Wen Chiu, Thein Kyu
Equilibrium Phase-Behavior Of Nematic Mixtures, Hao-Wen Chiu, Thein Kyu
College of Polymer Science and Polymer Engineering
A phenomenological model for predicting phase diagrams of a binary nematic mixture containing side chain liquid crystalline polymers and/or low molar mass liquid crystals has been proposed by combining Flory-Huggins free energy of isotropic mixing and Maier-Saupe free energy for nematic ordering of the nematogens. Two orientational order parameters, s(1) and S-2, Of the two components in the mixtures having two different clearing temperatures are taken into consideration in the calculation. The Flory-Huggins interaction parameter, chi, and the nematic interaction parameter of the Maier-Saupe theory, nu(1) and nu(22), are assumed to be functions of inverse absolute temperature. Further the cross-nematic …
Spinodals In A Polymer-Dispersed Liquid-Crystal, Chungsea Shen, Thein Kyu
Spinodals In A Polymer-Dispersed Liquid-Crystal, Chungsea Shen, Thein Kyu
College of Polymer Science and Polymer Engineering
Thermodynamic phase equilibria of a polymer dispersed liquid crystal (PDLC) consisting of
monomeric liquid crystals and a polymer have been investigated theoretically and experimentally.
The equilibrium limits of phase separation as well as phase transition of a PDLC system were
calculated by taking into consideration the Flory–Huggins (FH) theory for the free energy of mixing
of isotropic phases in conjunction with the Maier–Saupe ~MS! theory for phase transition of a
nematic liquid crystal. The correspondence between the Landau–de Gennes expansion and the
Maier–Saupe theory was found and the coefficients were evaluated. The calculation based on the
combined FH-MS theory predicted …
Polymerization-Induced Phase-Separation In A Liquid-Crystal-Polymer Mixture, J. Y, Kim, C. H. Cho, P. Palffy-Muhoray, M. Mustafa, Thein Kyu
Polymerization-Induced Phase-Separation In A Liquid-Crystal-Polymer Mixture, J. Y, Kim, C. H. Cho, P. Palffy-Muhoray, M. Mustafa, Thein Kyu
College of Polymer Science and Polymer Engineering
We have used light scattering to study the kinetics of polymerization-induced phase separation in a liquid-crystal-polymer mixture. The evolution of the structure factor is compared with scaling predictions for thermally quenched systems. We have also observed a cascading phenomenon where phase separated domains become unstable and undergo phase separation for a second time.
Phase-Separation Dynamics Of Polycarbonate Polymethyl Methacrylate Blends. Ii. Temperature Jumps Above An Immiscibility Loop, Thein Kyu, Ds Lim
Phase-Separation Dynamics Of Polycarbonate Polymethyl Methacrylate Blends. Ii. Temperature Jumps Above An Immiscibility Loop, Thein Kyu, Ds Lim
College of Polymer Science and Polymer Engineering
No abstract provided.
Phase-Separation Dynamics Of Polycarbonate Polymethyl Methacrylate Blends. I. Temperature Jumps Into An Immiscibility Loop, Dong-Soo Lim, Thein Kyu
Phase-Separation Dynamics Of Polycarbonate Polymethyl Methacrylate Blends. I. Temperature Jumps Into An Immiscibility Loop, Dong-Soo Lim, Thein Kyu
College of Polymer Science and Polymer Engineering
No abstract provided.
Thermomechanical Design Criteria For Zr02-Y203 Coated Surfaces, J. Padovan, Benjamin T.F. Chung, Glen E. Mcdonald, Robert C. Hendricks
Thermomechanical Design Criteria For Zr02-Y203 Coated Surfaces, J. Padovan, Benjamin T.F. Chung, Glen E. Mcdonald, Robert C. Hendricks
Mechanical Engineering Faculty Research
Thermocycling of ceramic-coated turbomachine components produces high thermomechanical stresses that are mitigated by plasticity and creep but aggravated by oxidation, with residual stresses exacerbated by all three. These residual stresses, coupled with the thermocyclic loading, lead to high compressive stresses that cause the coating to spall. In the paper a ceramic-coated gas path seal is modeled with consideration given to creep, plasticity, and oxidation. The resulting stresses and possible failure modes are discussed.
Thermomechanical Design Criteria For Ceramic-Coated Surfaces, Robert L. Mullen, J. Padovan, Minel J. Braun, Benjamin T.F. Chung, G. Mcdonals, Robert C. Hendricks
Thermomechanical Design Criteria For Ceramic-Coated Surfaces, Robert L. Mullen, J. Padovan, Minel J. Braun, Benjamin T.F. Chung, G. Mcdonals, Robert C. Hendricks
Mechanical Engineering Faculty Research
Some early history of ceramic applications is presented. Finite element modeling of components to determine service and fabrication loads found inelastic behavior and residual stresses to be significant to component life. Inelastic behavior mitigates peak strains but enhances residual strains. Results of furnace, Mach 0.3 burner, and engine tests are discussed and categorized into design criteria (loading, geometry, fabrication, materials, analysis, and testing). These design rules and finite element analyses are brought to bear on two test cases: turboshaft engine seals, and rocket thrust chambers.