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Title: Massively parallel molecular dynamics simulation of crack initiation and growth in a copper-nickel alloy.
Creator: Morrey, Willard C., Florida Atlantic University, Charles E. Schmidt College of Science, Department of Physics, Wille, Luc T.
Abstract/Description: We developed code in MasPar Fortran (an extension of Fortran 90) to conduct molecular dynamics simulations on a MasPar MP-1 massively parallel computer. The code is portable to other Single-Instruction Multiple-Data (SIMD) platforms with minor modifications. We used a two dimensional grid containing over 220,000 atoms to simulate a high strain-rate fracture growth in Cu-Ni alloys. The atoms are arranged in a triangular lattice corresponding to an fcc (111) surface and a Lennard-Jones (LJ)...
Show moreWe developed code in MasPar Fortran (an extension of Fortran 90) to conduct molecular dynamics simulations on a MasPar MP-1 massively parallel computer. The code is portable to other Single-Instruction Multiple-Data (SIMD) platforms with minor modifications. We used a two dimensional grid containing over 220,000 atoms to simulate a high strain-rate fracture growth in Cu-Ni alloys. The atoms are arranged in a triangular lattice corresponding to an fcc (111) surface and a Lennard-Jones (LJ) potential with a spline cutoff is used for the inter-atomic potential. The location of the spline cutoff can be adjusted to simulate either brittle or ductile fracture. The atomic positions are spatially decomposed on each Processor Element, the data are shared with adjacent PEs, and atoms are transferred as they move. Free boundary conditions are used, and the appropriate techniques for applying strain and damping unwanted reflections are developed. We report variations in the critical applied strain with increasing temperature, and propose a novel method for characterizing the location of a crack tip. This method lends itself to algorithmic calculation and reporting by the fracture code. Our results represent the first microscopic analysis of fracture in an alloy system and extend recent work on pure metals. During the investigation, we introduced a Sigma 5 grain boundary (36.9) into the sample, with appropriate grain-boundary segregation. We developed a technique for rapidly quenching the high-energy particles at an artificially constructed grain boundary. We demonstrate crack blunting at the grain boundary. We also report on flyer/target impact simulations in an alloy with an LJ inter-atomic potential.
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Date Issued: 1996
PURL: http://purl.flvc.org/fcla/dt/12445
Subject Headings: Physics, Condensed Matter, Engineering, Materials Science
Format: Document (PDF)

Title: The multiple scattering approach to the electronic structure of ordered solids, impurities, and alloys.
Creator: Wang, Yang, Florida Atlantic University, Charles E. Schmidt College of Science, Department of Physics
Abstract/Description: In this dissertation, multiple scattering theory (MST) plays a fundamental role. It is applied to develop the electronic structure calculation techniques for ordered solids, single impurities and binary alloys. The most accurate fast-band-theory technique based on the MST is the quadratic Korringa-Kohn-Rostoker (QKKR) method. A method for carrying out the self-consistent QKKR calculation for ordered compounds is derived and applied to palladium hydride. The application of the QKKR method to...
Show moreIn this dissertation, multiple scattering theory (MST) plays a fundamental role. It is applied to develop the electronic structure calculation techniques for ordered solids, single impurities and binary alloys. The most accurate fast-band-theory technique based on the MST is the quadratic Korringa-Kohn-Rostoker (QKKR) method. A method for carrying out the self-consistent QKKR calculation for ordered compounds is derived and applied to palladium hydride. The application of the QKKR method to single impurity problems is also examined. In order to study phase diagrams of binary alloys, a new approach, called the embedded cluster Monte Carlo (ECMC) method, is developed. It is used to calculate the miscibility gap in the Pd-Rh alloy phase diagram to an accuracy that has never before been achieved. A non-magnetic calculation for Cu-Ni alloys is also provided. These calculations required the mastery of Korringa-Kohn-Rostoker coherent-potential-approximation methods and the development of embedded cluster codes.
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Date Issued: 1993
PURL: http://purl.flvc.org/fcla/dt/12333
Subject Headings: Physics, Condensed Matter, Engineering, Materials Science
Format: Document (PDF)

Title: Physical properties of ferrimagnetic bioceramics.
Creator: Kis, Antonella C., Florida Atlantic University, Charles E. Schmidt College of Science, Department of Physics
Abstract/Description: The structural, magnetic and microstructural properties of ferrimagnetic bioglass ceramics (FBC) in the system {0.45(CaO,P2O5) x (0.52-x)SiO2 x xFe 2O3 x 0.03Na2O} with x = 0.05, 0.10, 0.15, 0.20 were studied as a function of composition and heat-treatment temperature. Specimens from each samples series were heattreated at temperatures in the range 600--1000C. X-ray powder diffraction and Rietveld refinement methods, magnetic measurements and scanning electron microscopy with energy...
Show moreThe structural, magnetic and microstructural properties of ferrimagnetic bioglass ceramics (FBC) in the system {0.45(CaO,P2O5) x (0.52-x)SiO2 x xFe 2O3 x 0.03Na2O} with x = 0.05, 0.10, 0.15, 0.20 were studied as a function of composition and heat-treatment temperature. Specimens from each samples series were heattreated at temperatures in the range 600--1000C. X-ray powder diffraction and Rietveld refinement methods, magnetic measurements and scanning electron microscopy with energy dispersive x-ray spectroscopy were used in our studies. Calcium phosphate [Ca3PO4)2], which is the biocompatible component of the materials, and magnetite Fe3O 4 are the two major crystalline phases that were developed in all samples series. In the two series of samples with x = 0.15 and 0.20, calcium phosphate undergoes a gradual transition from the monoclinic to the rhombohedral crystal system (Space Group P21/a, R3c) as the heat-treatment temperature increases from 800 to 1100C. It crystallizes only in R3c in the samples series with x = 0.05 and x = 0.10. Magnetite crystallizes in the orthorhombic system (SG Imma) in weight fractions determined by the heat-treatment temperature. In the system with x = 0.20, magnetite partially converts to hematite (SG R3c) in weight fractions that increase with the heat-treatment temperature. The saturation magnetization of all specimens depends on the starting composition in Fe2O3 while it becomes maximum in samples that were heat-treated at 800°C in all sample series. Magnetization loops show that the energy stored in the material is greatly affected by composition and heat-treatment, but not in a systematic way. SEM and EDX spectra reveal a variety of microstructures that are determined by the processing parameters of each sample. Dendrite structures consisting of Fe and O with crystallites of various sizes form on a glassy matrix of P, Si, Ca and O in the samples series 20G, while very fine surface microstructures are observed in the series 15G.
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Date Issued: 2004
PURL: http://purl.flvc.org/fau/fd/FADT12069
Subject Headings: Physics, Condensed Matter, Engineering, Materials Science
Format: Document (PDF)

Title: Spectroscopic studies of ZnWO4 and doped ZnWO4 single crystals.
Creator: Wang, Hong, Florida Atlantic University, Charles E. Schmidt College of Science, Department of Physics
Abstract/Description: Zinc tungstate (ZnWO4) is promising as a scintillator and laser host material. However, the presence of color centers limit its applications. It has been found that special annealing techniques or doping with metallic elements such as Nb or Sb can bleach the samples (Zhou et al. 1986a, 1986b, 1989). A group-theoretical analysis of the characteristic lattice vibrational modes for ZnWO4 single crystals is given. The mode assignments have been made. The temperature dependence of the Raman...
Show moreZinc tungstate (ZnWO4) is promising as a scintillator and laser host material. However, the presence of color centers limit its applications. It has been found that special annealing techniques or doping with metallic elements such as Nb or Sb can bleach the samples (Zhou et al. 1986a, 1986b, 1989). A group-theoretical analysis of the characteristic lattice vibrational modes for ZnWO4 single crystals is given. The mode assignments have been made. The temperature dependence of the Raman spectra has been obtained experimentally in various polarization geometries. Anharmonic contributions and interactions between phonons are discussed. Photoluminescence studies of ZnWO4 (colored, color-free), ZnWO4: Nb and ZnWO4:Sb have been carried out in the temperature range from 11 to 430 K. All samples show the blue emission band. An IR emission band with a zero-phonon line (ZPL) has been found in ZnWO4 colored samples only. The lineshape function of the emission bands has been theoretically studied and compared with the experimental results. Radiative, non-radiative and multiphonon transitions have been investigated in the thermal quenching model. The temperature dependences of the intensity, the frequency and the linewidth of the ZPL have been studied. Using the Single Configurational Coordinate model, the linear coupling between electrons and phonons has been analyzed. The quadratic coupling of electrons and phonons has been studied in the Debye approximation. The coupling of electronic transitions to normal vibrational modes, pseudo-localized vibrational modes and localized modes is also discussed.
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Date Issued: 1993
PURL: http://purl.flvc.org/fcla/dt/12346
Subject Headings: Physics, Condensed Matter, Physics, Optics, Engineering, Materials Science
Format: Document (PDF)

Title: Statistical physics for materials classification.
Creator: Lassalle, Hugues Jean, Florida Atlantic University, Charles E. Schmidt College of Science, Department of Physics
Abstract/Description: Genetic algorithms (GA) and clustering techniques are used to study and classify materials. An analysis of the convergence speed of GA is carried out using advanced probability theory and random walk concepts. The determination of the ground-state of multicomponent alloys and Ising models with long-range interactions is accomplished using a genetic algorithm. A new GA operator, the domain-flip, is introduced and its efficiency is compared to that of traditional GA operators, crossover and...
Show moreGenetic algorithms (GA) and clustering techniques are used to study and classify materials. An analysis of the convergence speed of GA is carried out using advanced probability theory and random walk concepts. The determination of the ground-state of multicomponent alloys and Ising models with long-range interactions is accomplished using a genetic algorithm. A new GA operator, the domain-flip, is introduced and its efficiency is compared to that of traditional GA operators, crossover and mutation. The domain-flip operator destroys phase-boundaries by flipping all bits of a given domain at the same time. This operator turns out to be crucial in extracting the system from low local minima. Therefore its presence is rather essential to speed up the GA convergence. A study of GA convergence in its last stages, where all chromosomes present in the population are assumed to consist of two well-ordered domains, is performed using random walk theory and probability theory. Exact expressions for the average time needed for at least one chromosome to find the ground-state are derived. Also, the probability for two chromosomes to undergo a successful crossover, meaning the result is the ground-state, are given. Finally, clustering techniques, which belong to the field of Data Mining, are applied to the classification of materials. An improved version of the widely-used clustering algorithm, K-means, is developed. A comparison of the two clustering techniques on a two-dimensional data set shows that the guide-point approach is more powerful than the K-means algorithm. The guide-point algorithm is used successfully to partition a materials data set. This clustering results in extracting useful information from the data set for which no a priori knowledge was assumed.
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Date Issued: 2002
PURL: http://purl.flvc.org/fcla/dt/11998
Subject Headings: Physics, Condensed Matter, Engineering, Materials Science, Computer Science
Format: Document (PDF)

Physics, Condensed Matter (5)	+ -
Computer Science (1)	+ -
Physics, Optics (1)	+ -

Charles E. Schmidt College of Science (5)	+ -
Florida Atlantic University (5)	+ -
Kis, Antonella C. (1)	+ -
Lassalle, Hugues Jean (1)	+ -
Morrey, Willard C. (1)	+ -

Wang, Hong (1)	+ -
Wang, Yang (1)	+ -
Wille, Luc T. (1)	+ -

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