Browsing by Author "Hibbard, Walter R. Jr."
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- Economic analysis of the Virginia steam coal marketSmith, Martin L. (Virginia Polytechnic Institute and State University, 1988)In recent years the Central Appalachian coal industry has suffered from a number of changes in the structure of the coal market. Foremost among these changes have been the collapse of the domestic steel industry and the passage of the Staggers Act. In the past high quality central Appalachian coal was sold mainly as premium coking coal. This market failed, and continues to shrink. Regional coal producers are now looking to the rising demand for steam coal in a nation which is turning away from oil and nuclear power generation. With the possible passage of the Clean Air Act, low sulfur central Appalachian coal may have a promising future, but only if its production can reach this new market. Prior to 1980, regulated rail tariffs gave coal producers access to most consumers, while independent railroads competed for freight. Railroad deregulation greatly improved the position of the railroads, but weakened that of regional coal producers. Central Appalachia and the southern coastal states were left with only two railroads, CSX and NS. These railroads now set their own rates and secretly negotiate contracts with shippers. Due to the configuration of ownership of these tracks, the vast majority of mines and utility plants were left with access to only one carrier. In this situation rail transportation has become the primary concern. Mines unable to originate shipments on the same railroad which is serving the utility plant find themselves locked out of that market unless their mine price is sufficiently low enough to compensate for the increased rail rate. Most of the coal burning plants in Virginia are located on CSX, while the vast majority of southwest Virginia's coal production is served by NS. With a higher mining cost than in eastern Kentucky and southern West Virginia, Virginia producers are having great difficulty in competing in the state's steam coal market. This dissertation is the first effort to quantitatively specify the regional steam coal market. This is done by identifying sources of data which are subsequently used to generate short term forecasts of mine price. These forecasts are used in the cost vector of a Virginia coal Purchasing model which is solved to determine the optimal pattern of coal purchases for Virginia utilities. The structure of the model is based on a detailed market analysis which accounts for the influence of rail rates.
- Effects of crack-crystallite interaction on the fracture behavior of a cordierite glass-ceramicMorena, Robert M. (Virginia Polytechnic Institute and State University, 1982)Crack-microstructure interactions occurring during the flaw introduction process were studied in a model brittle composite, a cordierite glass-ceramic. Microstructural effects associated with the repropagation of the introduced flaws under the imposition of a mechanical load were also examined. Two general types of crystallized microstructures were investigated for samples heat-treated from the original glass: a fine structure composed of a uniform precipitation of very small (< 0.1 µm) crystallites, and a coarser structure characterized by crystallites, and a coarser structure characterized by crystallites ~ 1-2 µm in diameter dispersed within a much finer-grained (< 0.1 µm) crystalline matrix. Surface damage was simulated by the Vicker's microhardness technique, with indentations being made over a wide load range to duplicate varying degrees of severity in the contact events. Direct measurement of the indentation flaws was made by calibrated scanning electron microscopy. Fracture toughness values were determined by direct calculation from the indentation parameters. The repropagation of the indentation flaws was investigated by strength tests performed in biaxial flexure. The results indicated that flaw introduction, as well as strength, fracture toughness, and the magnitude of strength loss sustained from surface damage, were all significantly affected by crack interactions with the crystallites in the glass-ceramic samples. The crack-crystallite interactions were extensive in the coarse microstructure samples. Crack pinning by the dispersed phase crystallites occurred at flaw sizes approximately equal to the mean free path distance between the dispersions, while at larger flaw sizes, crack deflection around the dispersed crystallites took place. Crack-microstructure interactions were absent in these same samples at flaw sizes less than the mean free path distance, and were not observed at all in the original glass or in samples heat-treated to yield only the fine microstructure. In the coarse microstructure samples, the size of flaws introduced by surface contact was found to be limited by the crack pinning interaction, thus confirming the basic concept of the dispersion-strengthening model for brittle composites. A substantial toughening effect in these same samples was realized from the crack deflection. Fracture toughness for the coarse microstructure samples exhibited a crack size-dependency, with toughness values corresponding to that of the matrix measured at small flaw sizes, and to that of the composite, at larger flaw sizes. The phenomenon was not present in either the original glass or in the fine microstructure samples. The crack-crystallite interactions occurring in the coarse microstructure samples greatly improved mechanical performance. The combination of decreased flaw size from crack pinning and increased fracture toughness from crack deflection resulted in strength values which were superior to those of the original glass. The crack size dependent fracture toughness enhanced the ability of the coarse microstructure samples to avoid potential strength losses following surface contact.
- Environmental effects on the fatigue behavior of copper nickel alloysSudarshan, T. S. (Virginia Polytechnic Institute and State University, 1984)Mode I and Mode III fatigue tests were performed on copper nickel alloys in helium, salt water environments. The hydrogen, oxygen, two alloys used air and in this investigation were 90-10 and 70-30 copper nickel. Both alloys contained iron which was added to improve the erosion corrosion resistance. The extent of cracking varied with the test environment. Tests showed that oxygen and humid air promoted cracking while salt water helium was used as the baseline retarded cracking when environment. Hydrogen promoted cracking when compared to helium but retarded cracking if comparisons were made with oxygen or humid air. The environmental effects (helium as the base case} in the Mode I tests in gaseous environments were manifested in the form of shorter fatigue lives, easier crack initiation, marginally higher crack growth rates and the development of intergranular fracture at the surface. These effects were accompanied by a change in the near surface deformation characteristics. The increases in fatigue life induced by testing in aqueous environments were greatly extended if the copper nickel was galvanically coupled to steel. Mode III tests showed the same ranking of environmental effects as Mode I tests and also showed multiple initiation, brittle fracture and secondary cracking. Two models were proposed to explain the observed results. One was based on the dilation-aided diffusion of oxygen ahead of the crack tip and subsequent oxidation of internal iron particles. The oxidation caused a volume expansion which produced internal tensile strains and facilitated fracture. The other mechanism was based on dilation-aided transport of hydrogen with subsequent accumulation of hydrogen at interfaces, resulting in a lowering of the interfacial strength and promoting intergranular fracture. The observed increases in life in the aqueous environments were rationalized by the reduced oxygen content available in the stagnant solutions. These observations suggest that the presence of iron accelarates fatigue in copper nickel alloys exposed to aggressive environments. Thus, any application involving fatigue loading with simultaneous exposure to aggressive environments should attempt to ensure that the iron content of the copper nickel alloys is minimized.
- Formulation of the particle size distribution effects on the rheology and hydraulics of highly-concentrated suspensionsDabak, Turgay (Virginia Polytechnic Institute and State University, 1986)A formulation was developed for the rheological characterization of highly concentrated suspensions, accounting for the physical effects of particle size distribution. A number of dimensionless parameters were developed signifying the physical characteristics of the solids and the vehicle fluid, and functionally related to the yield-stress and a flow parameter. Each of these expressions of the formulation contains an empirical dimensionless coefficient accounting for the interparticle and fluid/solid interactions that are not explained by the physical parameters involved. A formulation and a methodology were also developed for predicting the shear viscosity behavior of highly concentrated suspensions at low and high shear-rates through the use of three parameters signifying effects of particle size distribution. A number of applications were made using various non-coal and limited coal-liquid mixture data reported in the literature to demonstrate the general validity of the formulations. A methodology was proposed for the analysis of the particle size distribution effects on the overall optimum energy efficiency during hydraulic transportation and particle size reduction. The computer model developed for this purpose was employed to evaluate the transportation energy consumption and the energy consumed in the grinding process to prepare the slurry, in pipes of various sizes and lengths for a coal slurry of various specified particle size distributions and concentrations. Correlations obtained indicated the sensitivity of transportation energy efficiency to various parameters including the maximum packing concentration, relative concentration, specific surface area of particles, surface area mean size, pipe size and length, and annual mixture throughput. The results of combined energy calculations have shown that the particle size distribution and related physical parameters can significantly affect the energy efficiency due to both grinding and transportation, and the delivered cost of slurry fuels.
- Virginia Coal: An Abridged HistoryHibbard, Walter R. Jr. (Virginia Tech. Virginia Center for Coal and Energy Research., 1990-04)An abridged history of coal production in Virginia, including data about Virginia coal production and consumption from 1748-1988.