Effect of initial powder type on the hydrogen storage properties of high-pressure torsion consolidated Mg

While severe plastic deformation (SPD) on bulk samples has been widely applied for modifying the H-sorption properties, there has been little attention towards the use of SPD on powder materials. In this context, the aim of the present work was to compare the H-storage properties of high-pressure torsion (HPT) consolidated products obtained from two distinct Mg powder precursors: atomized micro-sized and condensed ultrafine powder particles. The results showed that the nature of the initial powder precursor had a pronounced effect on the H-sorption behavior. The HPT product obtained from the condensed ultrafine powder showed faster absorption kinetics than the consolidated product obtained from the atomized powder. However, the HPT product obtained from atomized powder could absorb more hydrogen and showed faster desorption kinetics corresponding to a lower activation energy. These results are discussed by taking into account the effectiveness of the HPT process to refine the grain sizes and differences in the dispersion of fine MgO oxide particles.     

Modified fully utilized design (MFUD) method for stress and displacement constraints

The traditional fully stressed method performs satisfactorily for stress-limited structural design. When this method is extended to include displacement limitations in addition to stress constraints, it is known as the Fully Utilized Design (FUD). Typically, the FUD produces an overdesign, which is the primary limitation of this otherwise elegant method. We have modified FUD in an attempt to alleviate the limitation. This new method, called the Modified Fully Utilized Design (MFUD) method, has been tested successfully on a number of problems that were subjected to multiple loads and had both stress and displacement constraints. The solutions obtained with MFUD compare favourably with the optimum results that can be generated by using non-linear mathematical programming techniques. The MFUD method appears to have alleviated the overdesign condition and offers the simplicity of a direct, fully stressed type of design method that is distinctly different from optimization and optimality criteria formulations. The MFUD method is being developed for practicing engineers who favour traditional design methods rather than methods based on advanced calculus and non-linear mathematical programming techniques. The Integrated Force Method (IFM) was found to be the appropriate analysis tool in the development of the MFUD method. In this paper, the MFUD method and its optimality are examined along with a number of illustrative examples. © 1998 This paper was produced under the auspices of the U.S. Government and it is therefore not subject to copyright in the U.S.     

Pulsed laser reshaping and fragmentation of upconversion nanoparticles — from hexagonal prisms to 1D nanorods through “Medusa”-like structures

One dimensional (1D) nanostructures attract considerable attention, enabling a broad application owing to their unique properties. However, the precise mechanism of 1D morphology attainment remains a matter of debate. In this study, ultrafast picosecond (ps) laser-induced treatment on upconversion nanoparticles (UCNPs) is offered as a tool for 1D-nanostructures formation. Fragmentation, reshaping through recrystallization process and bioadaptation of initially hydrophobic (β-Na_1.5Y_1.5F₆: Yb³⁺, Tm³⁺/β-Na_1.5Y_1.5F₆) core/shell nanoparticles by means of one-step laser treatment in water are demonstrated. “True” 1D nanostructures through “Medusa”-like structures can be obtained, maintaining anti-Stokes luminescence functionalities. A matter of the one-dimensional UCNPs based on direction of energy migration processes is debated. The proposed laser treatment approach is suitable for fast UCNP surface modification and nano-to-nano transformation, that open unique opportunities to expand UCNP applications in industry and biomedicine.

     

The effect of pallet top deck stiffness on the compression strength of asymmetrically supported corrugated boxes

During unitized shipment, the components of unit loads are interacting with each other. During floor stacking of unit loads, the load on the top of the pallet causes the top deck of the pallet to bend, which creates an uneven top deck surface resulting in uneven or asymmetrical support of the corrugated boxes. This asymmetrical support could significantly affect the strength of the corrugated boxes, and it depends on the top deck stiffness of the pallet. This study is aimed at investigating how the variations of pallet top deck stiffness and the resulting asymmetric support affect corrugated box compression strength. The study used a scaled-down unit load compression test on quarter-scale pallet designs with different deckboard thicknesses using four different corrugated box designs. Pallet top deck stiffness was determined to have a significant effect on box compression strength. There was a 27%–37% increase in box compression strength for boxes supported by high-stiffness pallets in comparison with low-stiffness pallets. The fact that boxes were weaker on low-stiffness pallets could be explained by the uneven pressure distribution between the pallet deck and bottom layer of boxes. Pressure data showed that a higher percentage of total pressure was located under the box sidewalls that were supported on the outside stringers of low-stiffness pallets in comparison with high-stiffness pallets. This was disproportionately loading one side of the box. Utilizing the effects of pallet top deck stiffness on box compression performance, a unit load cost analysis is presented showing that a stiffer pallet can be used to carry boxes with less board material; hence, it can reduce the total unit load packaging cost.     

Grain velocity distribution in a mixed flow dryer

For corn drying one of the most popular possibilities in Europe is to use a mixed flow dryer. Large differences in the vertical grain particle velocity in this type of dryers are causing differences in the residence time. Hence, uneven drying occurs causing under-drying or over-drying of grain portions. To investigate the influences of the dryer walls and the air ducts on the particle velocity distribution experiments have been carried out in industrial and laboratory sized dryers and the measurements were compared with discrete element models. The particle flow velocity distribution between the air ducts is modelled analytically based on arching hypothesis. Using discrete element models the effects of different possible constructional modifications causing more even vertical grain particle velocity distribution were analyzed.     

Application of In Situ Neutron and X-Ray Measurements at High Temperatures in the Development of Co-Re-Based Alloys for Gas Turbines

Co-Re alloy development is prompted by the search for new materials for future gas turbines which can be used at temperatures considerably higher than the current day single crystal Ni-based superalloys. The Co-Re-based alloys have been designed to have very high melting range, and they are meant for application at +373 K (+100 °C) above Ni-superalloys. They are significantly different from the conventional Co-based alloys that are used in static components of today??s gas turbines, and the Co-Re alloys have never been used for structural applications before. The Co-Re-Cr system has complex microstructure with many different phases present. Phase transformations and stabilities of fine strengthening precipitates at high temperatures remain mostly unexplored in the Co-Re alloys, and to develop basic understanding, model ternary and quaternary compositions were studied within the alloy development program. In situ neutron and synchrotron measurements at high temperatures were extensively used for this purpose, and some recent results from the in situ measurements are presented. In particular, the effect of boron doping in Co-Re alloys and the stabilities of the fine TaC precipitates at high temperatures were investigated. A fine dispersion of TaC precipitates strengthens some Co-Re alloys, and their stabilities at the application temperatures are critical. In the beginning, the alloy development strategy is very briefly discussed.     

Densification and structural change of mechanically alloyed W-Cu composites

Fine-grained, high-density (97+ pct of theoretical density (TD)), 80W-20Cu wt pct (58W-42Cu at. pct) composites have been prepared using nonconventional alloying techniques. The W and Cu precursor powders were combined by a high-energy ball-milling procedure in air or hexane. The mechanically alloyed W+Cu powder mixtures were then cold pressed into green compacts and sintered at 1523 K. The milling medium and milling time were varied to increase product densities with a concomitant order-of-magnitude decrease in grain size. For densification, air was found to be a more effective medium than hexane. From microhardness measurements, it was concluded that the W-Cu alloys were dispersion and solution hardened, but were sensitive to entrapped residual impurities. X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS), and scanning electron micros-copy (SEM) analyses were used to demonstrate that the as-milled and sintered W-Cu alloy structures were metastable, decomposing into the starting W and Cu components upon heating at or above 723 K.