A prototype concurrent engineering tool has been developed for the preliminary design of composite topside structures for modern navy warships. This tool, named GELS for the Concurrent engineering of Layered Structure...
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A prototype concurrent engineering tool has been developed for the preliminary design of composite topside structures for modern navy warships. This tool, named GELS for the Concurrent engineering of Layered Structures, provides designers with an immediate assessment of the impacts of their decisions on several disciplines which are important to the performance of a modern naval topside structure, including electromagnetic interference effects (EMI), radar cross section (RCS), structural integrity, cost, and weight. Preliminary analysis modules in each of these disciplines are integrated to operate from a common set of design variables and a common materials database. Performance in each discipline and an overall fitness function for the concept are then evaluated. A graphical user interface (GUI) is used to define requirements and to display the results from the technical analysis modules. Optimization techniques, including feasible sequential quadratic programming (FSQP) and exhaustive search are used to modify the design variables to satisfy all requirements simultaneously. The development of this tool, the technical modules, and their integration are discussed noting the decisions and compromises required to develop and integrate the modules into a prototype conceptual design tool.
Martensitic phase transformations in the solution-treated and water-quenched binary Ti-Nb alloys in the range of 16-26 at % Nb, were examined. An ordered, base-centred orthorhombic martensite was observed for alloys c...
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Martensitic phase transformations in the solution-treated and water-quenched binary Ti-Nb alloys in the range of 16-26 at % Nb, were examined. An ordered, base-centred orthorhombic martensite was observed for alloys containing up to 23.4 at % Nb. The substructure of this martensite was generally composed of twins and stacking faults, the presence of antiphase boundaries observed in the plates indicating that the martensite underwent ordering during quenching. Both order-disorder and NJ,temperatures were. observed to be affected by total interstitial content, higher contents increasing both temperatures. Increasing the niobium content to above 23.4% resulted in retention of the beta phase, this phase containing either athermal omega or ''diffuse'' omega depending upon niobium and total interstitial concentration. Finally, the microhardness of the Ti-Nb alloys examined was observed to decrease with increase in niobium and decrease in total interstitial content.
The embedded-atom method type interatomic potentials for h.c.p. titanium and b.c.c, vanadium, originally proposed by Johnson and coworkers, were modified in order to be able to model both the b.c.c. and the h.c.p. str...
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The embedded-atom method type interatomic potentials for h.c.p. titanium and b.c.c, vanadium, originally proposed by Johnson and coworkers, were modified in order to be able to model both the b.c.c. and the h.c.p. structures and the phase transformation between the two in titanium-base Ti-V alloys. The reliability of the modified potentials was tested with respect to lattice dynamics (the phonon dispersion curves and the phonon density of states) in the two structures and with respect to the relative thermodynamic stability of the two phases as a function of temperature and the alloy composition. The model predictions are found to be in reasonable agreement with their experimental counterparts. In particular, the predicted effect of vanadium on two phonon modes, a T-1 N-point 1/2[110] phonon and T-1 [112] phonon, which play the key roles in the b.c.c. --> h.c.p. transformation, was found to be consistent with the experiment.
The influence of reinforcement size and matrix heat treatment on the wear mechanisms and wear rates during dry sliding of 2009 Al-20 vol.% SiCp composite have been examined. Friction and wear measurements were correla...
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The influence of reinforcement size and matrix heat treatment on the wear mechanisms and wear rates during dry sliding of 2009 Al-20 vol.% SiCp composite have been examined. Friction and wear measurements were correlated with surface and subsurface deformation mechanisms utilizing scanning electron micrography and EDX analysis. Friction analysis showed that increasing particulate size from 4 to 29 mu m increased the friction coefficient. The predominant friction mechanism at particulate sizes below 13 mu m involved adhesion and microplowing, these being augmented by hard third body SIC abrasion with increasing particulate size. Wear rate also increased with increasing particulate size and matrix hardness. Adhesion and micro-cutting were the predominant wear mechanisms for smaller reinforcements, the higher wear rates observed in the larger particulate reinforced composite tribosystem being associated with increased particulate cracking-induced subsurface delamination.
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References
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Compounds containing oxygen functional groups, especially phenols, are undesirable components of coal-derived liquids. Removal of these compounds from the products of coal liquefaction is required. A beneficial altern...
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Compounds containing oxygen functional groups, especially phenols, are undesirable components of coal-derived liquids. Removal of these compounds from the products of coal liquefaction is required. A beneficial alternative would be the removal of these compounds, or the prevention of their formation, during the liquefaction reaction itself, rather than as a separate processing step. A novel organometallic catalyst precursor containing-Co and Mo has been studied as a potential hydrogenation catalyst for coal liquefaction. To ascertain the hydrodeoxygenation activity of this catalyst under liquefaction conditions, model compounds were investigated. Anthrone, 2,6-di-r-butyl-4-methyl-phenol, dinaphthyl ether, and xanthene were reacted in the presence of the Go-Mo catalyst precursor and a precursor containing only Mo over a range of temperatures, providing a comparison of conversions to deoxygenated products. These conversions give an indication of the hydrodeoxygenating abilities of organometallic catalyst precursors within a coal liquefaction system. For example, at 400 degrees C dinaphthyl ether was converted 100% (4.5% O-containing products) In the presence of the Go-Mo organometallic precursor, compared to 76.5% conversion (7.4% O-products) in the presence of the Mo catalyst.
This paper demonstrates the generation of DSC thermograms from TREF chromatograms. The reverse is clearly possible, and shows that compositional distribution information is obtainable from DSC using solution crystalli...
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This paper demonstrates the generation of DSC thermograms from TREF chromatograms. The reverse is clearly possible, and shows that compositional distribution information is obtainable from DSC using solution crystallized material. However, TREF is essential, at least initially, in providing fractions for calibration curves.
Full-density bulk nanocomposites have been developed in the immiscible Cu-Fe system through a powder metallurgy route. Elemental copper and iron powders were first mechanically alloyed to form single-phase, nanocrysta...
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Full-density bulk nanocomposites have been developed in the immiscible Cu-Fe system through a powder metallurgy route. Elemental copper and iron powders were first mechanically alloyed to form single-phase, nanocrystalline, metastable solid solutions, Cu100-xFex (x=0 to 100). These solid solutions were subsequently decomposed into Cu/Fe two-phase domains of various volume fractions during the hot consolidation process,forming in situ nanophase Cu-Fe composites. Full-density compacts have been produced at relatively low consolidation temperatures (< 500 degrees C) by employing sinter forging at high applied pressure and a protective atmosphere. Such a consolidation scheme, coupled with enhanced grain size stability due to the unique microstructural evolution sequence involved, retained the grain sizes in the nanometer range for both Cu and Fe grains in the composite products. Fully dense composite specimens exhibit enhanced microhardness as compared with rule-of-mixtures predictions. This enhancement is attributed to interface strengthening at fcc-bcc interphase boundaries.
A statistical model for steady-state sliding wear of the metal counterpart in metal-composite systems has been extended to include composite reinforcement size and size distribution. It has been shown that the wear ra...
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A statistical model for steady-state sliding wear of the metal counterpart in metal-composite systems has been extended to include composite reinforcement size and size distribution. It has been shown that the wear rate of the metal counterpart under conditions where MMC wear is characterized by plastic deformation (microplowing) is controlled by the ratio between the mean of particulate radius squared and the square mean particulate radius, E(r(2))/E(r)(2), a descriptor of the particulate size and distribution. Under these instances, e.g. for 4, 10 and 13 mu m particulate discontinuously reinforced aluminum (DRA)/17-4 PH tribosystems, the modified statistical model permits accurate prediction of the wear performance of the unreinforced counterpart. However, when MMC wear involves reinforcement cracking and delamination, the model overestimates the wear rate of the counterpart, i.e. in the 29 mu m Al-SiCp/17-4 PH tribosystems.
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