215 research outputs found
Preliminary investigation of the compressive strength and creep lifetime of 2024-T3 (formerly 24S-T3) aluminum-alloy plates at elevated temperatures
The results of elevated-temperature compressive strength and creep tests of 2024-T3 (formerly 23S-T3) aluminum-alloy plates supported in V-grooves are presented. For determining elevated-temperature strength, where creep effects are negligible, a relation previously developed for predicting plate compressive strength at room temperature was satisfactory. Creep-lifetime results are presented for the plates in the form of master creep-lifetime curves by using a time-temperature parameter that is convenient for summarizing tensile creep-rupture data. A comparison is made between tensile and compressive creep lifetime for the plates, and the magnitude by which the design stress is decreased because of material creep and loss of strength due to exposure at elevated temperatures is indicated
Investigation of the Compressive Strength and Creep Lifetime of 2024-T3 Aluminum-Alloy Plates at Elevated Temperatures
The results of elevated-temperature compressive strength and creep tests of 2024-t3 (formerly 24s-t3) aluminum alloy plates supported in v-grooves are presented. The strength-test results indicate that a relation previously developed for predicting plate compressive strength for plates of all materials at room temperature is also satisfactory for determining elevated-temperature strength. Creep-lifetime results are presented for plates in the form of master creep-lifetime curves by using a time-temperature parameter that is convenient for summarizing tensile creep-rupture data. A comparison is made between tensile and compressive creep lifetime for the plates and a method that made use of isochronous stress-strain curves for predicting plate-creep failure stresses is investigated
Flutter Research on Skin Panels
Representative experimental results are presented to show the current status of the panel flutter problem. Results are presented for unstiffened rectangular panels and for rectangular panels stiffened by corrugated backing. Flutter boundaries are established for all types of panels when considered on the basis of equivalent isotropic plates. The effects of Mach number, differential pressure, and aerodynamic heating on panel flutter are discussed. A flutter analysis of orthotropic panels is presented in the appendix
Gas-cooled fast breeder reactor fuel element thermal-hydraulic investigations : final report
"August 1975.""Prepared for the General Atomic Company P.O. Box 81608 San Diego, California 92138."Also issued as an Sc. D. thesis by the first author and supervised by the second and third author, MIT Dept. of Nuclear Engineering, 1975. -- Technical report has the following sub-title: Final reportIncludes bibliographical references (pages 295-301)Final report; August 1975Experimental and analytical work was performed to determine the influence of rod surface roughening on the thermal-hydraulic behavior of rod array type, nuclear fuel elements. Experimental data was obtained using a grid-spaced, 37-rod hexagonal test section with both a smooth and a rough rod array. The rods were 0.331 inch (8.41 mm) diameter with a pitch/diameter of 1.30. The roughened surface used trapezoidal ribs 6-mils (0.15 mm) high with a rib pitch/height of 12. Velocity profiles taken at the flow exit plane indicated that when comparing the rough array results with the smooth, the gap velocities were lower, the peak-to-average velocities were higher: and the peripheral subchannel velocities were higher. Axial static pressure profiles. were used to determine rod array friction factors and grid loss coefficients. The friction factor results were in agreement with predictions using tube data.The friction factor multipliers were strongly Reynolds number dependent and grid losses were apparently 10% higher in the rough rod array. Detailed pressure profiles were taken in the axial vicinity of the grid spacers. Coolant mixing data using a salt solution tracer was obtained for smooth and rough arrays. Flow scattering at the spacers was responsible for most of the smooth array tracer dispersion. In the rough array, turbulent interchange was considerably higher. The grid-spaced, rough array, dimensionless mixing coefficient was estimated to be 0.C20 + 0.005. Flow scattering at the grids prevented the determination of geometry and Reynolds number effects, as well as, the smooth array mixing coefficient. By neglecting coolant mixing and radial pressure gradients, an equation was developed to determine the flow rate in the subchannels of a nuclear fuel element with roughened surfaces and gas-cooling.Relative subchannel flow rates were influenced by flow regime, fuel element geometry, fuel rod surface roughening, Reynolds number and coolant property variations. Two simple models were discussed which estimate the "equivalent friction factor" in partially roughened flow passages. Computational results obtained using the RUFHYD code showed that fuel element thermal-hydraulics are influenced by both rod array design parameters and operating conditions. Calculational results included axial subchannel flow distributions, optimum subchannel design estimates, and peripheral subchannel flow sensitivities to changes in rod-to-wall gap
Current-Driven Conformational Changes, Charging and Negative Differential Resistance in Molecular Wires
We introduce a theoretical approach based on scattering theory and total
energy methods that treats transport non-linearities, conformational changes
and charging effects in molecular wires in a unified way. We apply this
approach to molecular wires consisting of chain molecules with different
electronic and structural properties bonded to metal contacts. We show that
non-linear transport in all of these systems can be understood in terms of a
single physical mechanism and predict that negative differential resistance at
high bias should be a generic property of such molecular wires.Comment: 9 pages, 4 figure
Electron Standing Wave Formation in Atomic Wires
Using the Landauer formulation of transport theory and tight binding models
of the electronic structure, we study electron transport through atomic wires
that form 1D constrictions between pairs of metallic nano-contacts. Our results
are interpreted in terms of electron standing waves formed in the atomic wires
due to interference of electron waves reflected at the ends of the atomic
constrictions. We explore the influence of the chemistry of the atomic
wire-metal contact interfaces on these standing waves and the associated
transport resonances by considering two types of atomic wires: gold wires
attached to gold contacts and carbon wires attached to gold contacts. We find
that the conductance of the gold wires is roughly for the
wire lengths studied, in agreement with experiments. By contrast, for the
carbon wires the conductance is found to oscillate strongly as the number of
atoms in the wire varies, the odd numbered chains being more conductive than
the even numbered ones, in agreement with previous theoretical work that was
based on a different model of the carbon wire and metal contacts.Comment: 14 pages, includes 6 figure
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Skyline thinning production and costs : experience from the Willamette Young Stand Project
Production rates and costs for skyline harvesting were examined over a range of residual thinning intensities, operational methods, and sites. The sites included three stands of 40- to 50-yr-old Douglas-fir on the Willamette National Forest in the Cascade Mountains of Oregon. Three silvicultural treatments were studied at two sites, and one silvicultural treatment at the third site. Detailed time studies were conducted on manual felling and uphill skyline yarding with small or mid-size yarders. Separate regression equations were developed to predict delay-free felling cycle time and delay-free yarding cycle time at each site. The three silvicultural treatments had no consistent influence on production rates and costs, because the initial stocking levels varied among treatments and the volume harvested did not necessarily correspond to the silvicultural treatment. Cost differences within sites, where operational methods were uniform, were small. Cost differences among sites for each activity, such as felling or yarding, were larger because of differences in operational methods. Total harvesting costs among the three sites were similar, ranging from 64/100 ft³
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