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22.
Yuri Estrin Vincent Lemiale Robert O’donnell Laszlo Toth 《Metallurgical and Materials Transactions A》2011,42(13):3883-3888
In this article, we readdress the question of homogeneous nucleation of dislocation loops in the context of nanocrystalline
materials. In this case, the commonly adopted assumption of an infinite medium is no longer valid, and image forces on dislocations
must be accounted for in the analysis. An additional energy term associated with the presence of finite boundaries may act
to promote homogeneous nucleation and growth of dislocation loops. Based on a simplified consideration of a circular dislocation
loop in a spherical nanoparticle or nanosized grain in a polycrystal, energy calculations are carried out to estimate the
activation energy for homogeneous nucleation of a dislocation loop in such a system. Two different cases are considered: (1)
a single nanoparticle and (2) a grain in a polycrystalline nanomaterial. Based on simulations for aluminum, it is shown that
this mechanism may be plausible in both cases, albeit only for small particles and grains in the nanometer range. 相似文献
23.
Ivo Babuska Barna Szabo 《International journal for numerical methods in engineering》1982,18(3):323-341
The rate of convergence of the finite element method is a function of the strategy by which the number of degrees-of-freedom are increased. Alternative stragegies are examined in the light of recent theoretical results and computational experience. 相似文献
24.
To produce high stressed automotive components like engine frames and cylinder heads in foundry industry often AlSi7Mg alloys are used. During mould filling and casting melt flow affects the development of the microstructure, which defines the mechanical properties. In this paper the microstructure formation in AlSi7Mg0.3 and AlSi7Mg0.6 alloys during directional solidification is investigated. To induce a forced melt flow a rotating magnetic field is applied. For that purpose a Bridgman‐type gradient furnace is equipped with a rotary ring magnet. For detailed investigation of the shape of the solid‐liquid interface and the primary dendrite spacing a decanting device is used. As a result, the forced melt flow substantially changes the dendritic solidification microstructure. The rotating magnetic field generates a radial secondary flow in and ahead of the mushy zone, which causes an enrichment of eutectics in the centre of the samples. At lower solidification velocities this locally leads to the transition to mixed columnar‐equiaxed or even to equiaxed growth. In that case the solid‐liquid interfaces of the decanted samples show a significant depression in the centre part. In the out‐of‐centre region columnar growth still exists and the primary dendrite spacing decreases with increasing melt flow. 相似文献
25.
In the period between December 5, 1991 and September 17, 1998, 760 maize, 367 wheat, 119 soybean, 222 barley, 85 bran, 32 triticale, 60 oat, 14 rye and 22 sunflower samples were investigated for the presence and concentration of seven fusariotoxins (T-2 toxin, zearalenone, deoxynivalenol, nivalenol, diacetoxyscirpenol, HT-2 toxin, fusarenone-X) and OTA. The comparison of analytical data with those of the relevant literature revealed that although the incidence rate and/ or concentration of Fusarium mycotoxins and OTA in Hungarian-grown cereals is occasionally considerable, the position of the country is not worse than the average of countries. Our findings indicate that soybean tends to be good substrate for trichothecene-producing fungi and the rate of contamination is regarded as substantial. The commodities were assorted into one of three quality categories. The proportion of objectionable samples was only 3.0, 2.2, 2.3 and 1.7% in maize, wheat, barley and soybean samples, respectively. However, this low rate of objection might still be a source of great economic loss. The proportion of objectionable samples was much higher in the case of bran, oat and triticale (7.1, 6.7, and 6.3%, respectively). The results of the present investigation indicate a need for regular screening for mycotoxins of importance and individual appraisal of each commodity from the point of their use in animal feeds. 相似文献
26.
27.
The stress field in the vicinity of singular points which occur at the interface of two anisotropic materials is investigated. The focus is on the development of computational procedures for the determination of those parameters of the stress field which control delamination phenomena in composite materials. The results presented herein provide for the computation of parameters of the stress field, which may serve as a basis for analytical/experimental treatment of delamination phenomena. Using p- and hp-extension procedures in finite element analysis, the accuracy and reliability may be ascertained. An example which is typical of current problems in the aerospace industry is presented. 相似文献
28.
A physicochemical and transport model has been developed for the long term prediction of environmental leaching behavior of porous materials containing inorganic waste solidified with hydraulic binders and placed in a reuse scenario. The reuse scenario considered in the paper is a storage tank open to the atmosphere including material leaching with water and carbonation through the leachate contact with air. The model includes three levels: (i) the physicochemical pollution source term (chemical equilibria in the pore water and diffusion in the porous system); (ii) chemical equilibria and mass transfer in the tank; and (iii) gas/liquid transfer of carbon dioxide. The model was applied to the case of a material obtained through solidification of Air Pollution Control (APC) residues from Municipal Solid Waste Incinerator (MSWI). The simulation results are in good agreement with two scale experimental data: laboratory and field tests. Experimental data and simulations show the main trends for release of elements contained in the material: (i) the release of alkaline metals and chloride is not significantly influenced by carbonation and (ii) the release of Ca and Pb is governed by chemical equilibria in pore water and diffusion, while their speciation in the leachate is determined by pH and the presence of carbonate ions. 相似文献
29.
Yessica Saez Laszlo B. Kish Robert Mingesz Zoltan Gingl Claes G. Granqvist 《Journal of Computational Electronics》2014,13(1):271-277
We classify and analyze bit errors in the current measurement mode of the Kirchhoff-law–Johnson-noise (KLJN) key distribution. The error probability decays exponentially with increasing bit exchange period and fixed bandwidth, which is similar to the error probability decay in the voltage measurement mode. We also analyze the combination of voltage and current modes for error removal. In this combination method, the error probability is still an exponential function that decays with the duration of the bit exchange period, but it has superior fidelity to the former schemes. 相似文献
30.
Field Testing of Stabilized Soil 总被引:1,自引:0,他引:1
Vincent C. Janoo Anthony J. Firicano Lynette A. Barna Sherri A. Orchino 《Canadian Metallurgical Quarterly》1999,13(1):37-53
Remediation of a Superfund site in Stratford, Conn., involved stabilization of the subgrade with portland cement. Part of the remediation site was to be used as a parking area. The stabilized soil was to be covered with natural base∕subbase course materials and capped with an asphalt concrete cover. During the course of the remediation, a base-course layer could not be placed prior to the onset of winter. A field study was conducted to quantify any changes in the mechanical properties of the open stabilized subgrade subjected to freeze-thaw cycling during the winter of 1996–97. Field evaluation was conducted with pavement industry tools: the Clegg impact hammer and the dynamic cone penetrometer. Evaluation results show the viability of the Clegg hammer as an instrument for quality assurance and also show that there can be up to 50% loss in compressive strength of the subgrade within the uppermost layer of the material caused by freeze-thaw cycling. 相似文献