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Engineering Commons™

Open Access. Powered by Scholars. Published by Universities.®

1998

Iowa State University

Articles 1 - 11 of 11

Full-Text Articles in Engineering

Multiscale Modeling Of Recrystallization, A. W. Godfrey, E. A. Holm, D. A. Hughes, M. A. Miodownik, Richard Alan Lesar Nov 1998

Multiscale Modeling Of Recrystallization, A. W. Godfrey, E. A. Holm, D. A. Hughes, M. A. Miodownik, Richard Alan Lesar

Richard Alan Lesar

We propose a multi length scale approach to modeling recrystallization which links a dislocation model, a cell growth model and a macroscopic model. Although this methodology and linking framework will be applied to recrystallization, it is also applicable to other types of phase transformations in bulk and layered materials. Critical processes such as the dislocation structure evolution, nucleation, the evolution of crystal orientations into a preferred texture, and grain size evolution all operate at different length scales. In this paper we focus on incorporating experimental measurements of dislocation substructures, misorientation measurements of dislocation boundaries, and dislocation simulations into a mesoscopic …

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Cost Engineering Optimum Seaport Capacity, Douglas D. Gransberg, John P. Basilotto Sep 1998

Cost Engineering Optimum Seaport Capacity, Douglas D. Gransberg, John P. Basilotto

Douglas D. Gransberg

Using queuing theory to solve port optimization problems can result in large potential savings by both ports and shippers. This methodology generally makes the assumption that minimizing ship waiting time optimizes the entire port system. However, this overlooks the contribution to the system given by the port itself. There is a fixed cost of facilities that must be incurred to open a berth at a port. By minimizing ship waiting time alone, the current algorithm tends to encourage ports to build excess capacity. When a port's cargo transfer capacity is idle, the port authority suffers a capital cost of lost …

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Charge-Correlation Effects In Calculations Of Atomic Short-Range Order In Metallic Alloys, F. J. Pinksi, J. B. Staunton, Duane D. Johnson Jun 1998

Charge-Correlation Effects In Calculations Of Atomic Short-Range Order In Metallic Alloys, F. J. Pinksi, J. B. Staunton, Duane D. Johnson

Duane D. Johnson

The “local” chemical environment that surrounds an atom directly influences its electronic charge density. These atomic charge correlations play an important role in describing the Coulomb and total energies for random substitutional alloys. Although the electronic structure may be well represented by a single-site theory, such as the coherent potential approximation, the electrostatic energy is not as well represented when these charge correlations are ignored. For metals, including the average effect from the charge correlation coming from only the nearest-neighbor shell has been shown to be sufficient to determine accurately the energy of formation. In this paper, we incorporate such …

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Cellular Automaton Modeling Of Alloy Solidification Using Local Anisotropy Rules, Ralph E. Napolitano, T. H. Sanders Jr. Apr 1998

Cellular Automaton Modeling Of Alloy Solidification Using Local Anisotropy Rules, Ralph E. Napolitano, T. H. Sanders Jr.

Ralph E. Napolitano

The evolution of dendritic morphology is simulated for a binary alloy using a two-dimensional cellular automaton growth algorithm. Solute diffusion is modeled with an alternate-direction implicit finite difference technique. Interface curvature and kinetic anisotropy are implemented through configurational terms which are incorporated into the growth potential used by the automaton. The weighting of the anisotropy term is explored and shown to be essential for overcoming grid-induced anisotropy, permitting more realistic development of dendritic morphologies. Dendritic structures are generated for both uniform and directional cooling conditions.

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A Review Of Methods To Estimate Haul Fleet Production, Douglas D. Gransberg Mar 1998

A Review Of Methods To Estimate Haul Fleet Production, Douglas D. Gransberg

Douglas D. Gransberg

Five methods that are used to estimate haul fleet production based on optimal analysis are reviewed. The results predicted by those methods are compared to actual field observations. The results of the comparison are used to recommend various methods for estimating haul fleet production. The 5 methods were authored by: 1. R. L. Peurifoy, as interpreted by Atcheson, 2. F. H. Griffis, 3. M. Gates and A. Scarpa, 4. R. E. Phelps and 5. J. J. Adrian and L. T. Boyer. Atcheson's method is generally conservative, which is not necessarily in this application. The Phelps method seemed to be the …

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Cyclic Deformation Behavior Of High-Purity Titanium Single Crystals: Part Ii. Microstructure And Mechanism, Xiaoli Tan, H. Guo, H. Gu, C. Laird, N. D. H. Monroe Feb 1998

Cyclic Deformation Behavior Of High-Purity Titanium Single Crystals: Part Ii. Microstructure And Mechanism, Xiaoli Tan, H. Guo, H. Gu, C. Laird, N. D. H. Monroe

Xiaoli Tan

Strain-controlled cyclic tests have been conducted on high-purity titanium single crystals with different orientations. The fatigue mechanisms of the titanium crystals were studied by means of a scanning electron microscope (SEM) and a transmission electron microscope (TEM). It was found that single slip lines, wavy slip lines, double slip lines, twins, and associated slip lines occurred in differently oriented single crystals. A new type of fractographic morphology, parallel traces, was observed. Dislocation patterns and cyclic twins, as well as the mechanical response, were analyzed. The dependence of the deformation mechanisms on the orientations of the single crystals is discussed.

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Cyclic Deformation Behavior Of High-Purity Titanium Single Crystals: Part I. Orientation Dependence Of Stress-Strain Response, Xiaoli Tan, H. Gu, C. Laird, N. D. H. Monroe Feb 1998

Cyclic Deformation Behavior Of High-Purity Titanium Single Crystals: Part I. Orientation Dependence Of Stress-Strain Response, Xiaoli Tan, H. Gu, C. Laird, N. D. H. Monroe

Xiaoli Tan

Randomly oriented single crystals of high-purity titanium were prepared by strain annealing and were subjected to multiple-step fatigue testing under strain-controlled conditions, in order to determine their cyclic stress-strain curves (CSSCs). These were found to fall into three groups, depending on orientation and the extent of slip and twinning. For those crystals oriented for single prismatic slip, a plateau was observed in the CSSCs, persistent slip bands (PSBs) occurred, and the plateau stress was 38 MPa. In a second group, oriented for prismatic slip but for which cross-slip and twinning was favored, the plateau was suppressed and the flow stresses …

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Short-Range Dislocation Interactions Using Molecular Dynamics: Annihilation Of Screw Dislocations, S. Swaminarayan, Richard Alan Lesar, P. Lomdahl, D. Beazley Jan 1998

Short-Range Dislocation Interactions Using Molecular Dynamics: Annihilation Of Screw Dislocations, S. Swaminarayan, Richard Alan Lesar, P. Lomdahl, D. Beazley

Richard Alan Lesar

We present results of a large-scale atomistic study of the annihilation of oppositely signed screw dislocations in an fcc metal using molecular dynamics (MD) and an Embedded-Atom-Method (EAM) potential for Cu. The mechanisms of the annihilation process are studied in detail. From the simulation results, we determined the interaction energy between the dislocations as a function of separation. These results are compared with predictions from linear elasticity to examine the onset of non-linear-elastic interactions. The applicability of heuristic models for annihilation of dislocations in large-scale dislocation dynamics simulations is discussed in the light of these results.

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The Bmc/Giem Model For Micromixing In Non-Premixed Turbulent Reacting Flows, Rodney O. Fox, Kuochen Tsai Jan 1998

The Bmc/Giem Model For Micromixing In Non-Premixed Turbulent Reacting Flows, Rodney O. Fox, Kuochen Tsai

Rodney O. Fox

A novel beta mapping closure (BMC)/generalized IEM (GIEM) model is proposed to close the micromixing term in the joint composition probability density function (PDF) transport equation for nonpremixed, multiscalar turbulent reacting flows. Because the beta PDF gives an excellent description of binary inert scalar mixing, it is used to approximate the mixture fraction PDF. The proposed model thus effectively extends presumed PDF methods to handle finite-rate chemistry without introducing ad hoc assumptions about the form of the joint composition PDF. The BMC/GIEM model can be solved efficiently using a particle-based Monte-Carlo code. The model is first compared with the amplitude …

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Blending Top-Down And Bottom-Up Approaches In Conceptual Design, Janis P. Terpenny, Bartholomew O. Nnaji, Jan Helge Bøhn Jan 1998

Blending Top-Down And Bottom-Up Approaches In Conceptual Design, Janis P. Terpenny, Bartholomew O. Nnaji, Jan Helge Bøhn

Janis P. Terpenny

In recent years, there has been significant attention given to improved methods and tools for engineering design. While advances for the latter stages of design have been impressive, this has not been the case for the early stages of design. In general, advances have provided for either a top-down or a bottom-up approach to design; ignoring the requirements for both abstraction and detail in a concurrently engineered development process. This paper describes an integrated conceptual modeling framework for a blended methodology. The utility and extensibility of this framework are considered in discussion and by way of examples.

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Modeling Morphological Evolution During Dendritic Solidification Using A Cellular Automaton, Ralph E. Napolitano, T. H. Sanders Jr. Jan 1998

Modeling Morphological Evolution During Dendritic Solidification Using A Cellular Automaton, Ralph E. Napolitano, T. H. Sanders Jr.

Ralph E. Napolitano

Morphological evolution of a dendritic growth front in a binary alloy is simulated using a cellular automaton approach to establish the feasibility of modeling such growth with a local rule-based scheme. The motivation for this work is derived from the need to predict the development of solidification structures within real components of complex geometry, where significant constraint of the thermal and solutal fields may exist. Such cases present complex boundaries and large domain sizes, which may preclude the effective use of more conventional methods. In this work, a model is presented which couples a two-dimensional altemate-direction-implicit finite-difference diffusion solution with …

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