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11.
MDF materials are chemically bonded ceramic materials free of the macrodefects typical of hydraulic cement-based materials. MDF materials arising through reactions of sulfo-aluminate-ferrite belitic (SAFB) clinkers and/or Portland cements (PC) with two types of water-soluble polymer (hydroxy-propylmethyl cellulose {HPMC}, polyphosphate glass {poly-P}) are discussed. Mixes of low energy SAFB clinkers with Portland cement, HPMC and, especially poly-P comprise promising cross-linked compositions additional to the better known MDF materials formed from high alumina cement with polyvinylalcohol/acetate. The principles of co-ordination of P and C atoms (of the polymer) with Al and Fe atoms (originating from the cement) are highlighted from spectroscopic information on next-nearest-neighbour interactions, along with the effects of second co-ordination spheres. Polymers modify the interface through functional bonding/grafting of polymer chains onto the surfaces of cement grains. Both the cross-linked atomic structure and the interface coincide well with the model of functional polymers and represent a new type of atomic-level structure in polymer-modified cements. Interpretation is based on previous magnetic resonance and thermal analysis studies. The compactness of Al(Fe)-O-P cross-links reduces transport through the interfaces, increasing the interfacial interactions and resisting the unfavourable uptake of moisture and carbonation. 相似文献
12.
To improve aircraft crash safety, conditions critical to occupants survival during a crash must be known. In view of the importance of this problem, studies of post-crash dynamic behavior of victims are necessary in order to reduce severe injuries. In this study, crash dynamics program SOM-LA/TA, incorporating a dynamic model of the human body with a finite element model of the seat structure was used. Modifications were performed in the program for reconstruction of an occupant's head impact with the interior walls or bulkhead. A viscoelastic-type contact force model was used to represent the compliance characteristics of the bulkhead. Correlated studies of analytical simulations with impact sled test results were accomplished. A parametric study of the coefficients in the contact force model was then performed in order to obtain the correlations between the coefficients and the Head Injury Criteria. A measure of optimal values for the bulkhead compliance and displacement requirements was thus achieved in order to keep the possibility of a head injury as little as possible. This information could in turn be used in the selection of suitable materials for the bulkhead, instrument panel, or interior walls of an aircraft. 相似文献
13.
Arman Melkumyan 《Zeitschrift für Angewandte Mathematik und Physik (ZAMP)》2007,58(2):330-349
The problem of electric and acoustic waves diffraction by a half-plane crack in a transversal isotropic piezoelectric medium
is investigated. The crack is assumed to be electric permeable and free of tractions. The so-called “quasi-hyperbolic approximation”
[15] is adopted. Applying Laplace transformations and Wiener–Hopf technique a closed form solution is obtained. By the means
of Cagniard–de Hoop method a detailed dynamic full electroacoustic wavefield’s investigation is conducted. Mode conversion
between electric and acoustic waves, effect of electroacoustic head wave, Bleustein–Gulyaev surface wave and the wavefield
structure depending on the type of the incident wave (acoustic or electric) and its angle of incidence are analyzed in details.
The dynamic field intensity factors at the crack tip depending on the angle of incidence and on time are derived explicitly.
Numerical analysis is presented. 相似文献
14.
Nanocrystalline FeS2 cathode material of lithium cell was synthesized from cheap materials of FeSO4, Na2S2O3, and sulfur by a hydrothermal process. The scanning electron microscopy analysis showed the obtained material was nano-sized,
about 500 nm. The X-ray powder diffraction analysis showed that the synthetic FeS2 material had two phases of the crystalline structure, pyrite and marcasite. The phase of marcasite seems to have no negative
effect on the electrochemical performance of the material. The synthetic FeS2 showed a significant improvement of electrochemical performance for Li/FeS2 cells. 相似文献
15.
Existence of a solution for a Signorini contact problem for Maxwell-Norton materials 总被引:1,自引:0,他引:1
The aim of this article is to study the quasistatic evolutionof a MaxwellNorton three-dimensional viscoelastic solidwith contact constraints. After introducing the appropiate functionalframework, we will discretize the problem in time using an implicitscheme whose resultant variational inequality is well posed.By using monotonicity arguments together with compensated compactnesstechniques, we will prove that the corresponding discrete solutionconverges to a solution of the continuous problem. 相似文献
16.
计算机模拟仿真射频磁控溅射实验制备薄膜及离于电池电极,研究了在特定实验条件下薄膜的生长过程,并分析了影响薄膜生长的部分因素。 相似文献
17.
B. W. Skews 《Shock Waves》1994,4(3):145-154
A study to determine the general gas dynamic behaviour associated with the impact of a shock wave on a porous wedge has been undertaken. A number of interesting features are noted. The pattern of wave reflection is shown to be significantly affected by the inflow of gas into the wedge. This has the effect of reducing the triple point trajectory angle for cases of Mach reflection and for strongly reducing the reflection angle in regular reflection. The permeability of the wedge has a significant effect on the strength of the reflected wave and in some cases this wave can be attenuated to the extent that it is almost eradicated. Pressure measurements taken under the wedge are characterized by oscillations which are of similar shape, for a given wedge, over a range of shock wave Mach numbers. It is shown that the wave transmitted into the wedge is attenuated to varying degrees depending on the material properties, and that for weak incident waves the mean propagation velocity can be less than the sound speed in the pore fluid. Photographs taken using a specially constructed wedge which allows the transmitted wave to be visualised, show that the transmitted wave is nearly plane.This article was processed using Springer-Verlag TEX Shock Waves macro package 1.0 and the AMS fonts, developed by the American Mathematical Society. 相似文献
18.
The constitutive behavior of porous materials (including the yield loci, the void growth rate, the macro stress-strain relation
and the strain to localization instability) is examined based on the lower bound approach proposed by the present authors.
These results are then compared with the experimental and the finite element results as well as those predicted by Gurson's
equations. Emphasis is placed on approaching the real behavior from the upper and the lower bound analysis. Calculation is
also made on the influence of void nucleation on the critical strain to instability and a modified strain-controlled nucleation
criterion is proposed. Finally the instability and fracture of AISI4340 steel in plane strain tension is examined and comparison
is made between theoretical and experimental results. 相似文献
19.
20.
A. Deptuła T. Olczak W. Łada B. Sartowska A.G. Chmielewski C. Alvani P.L. Carconi A. Di Bartolomeo F. Pierdominici S. Casadio 《Journal of Sol-Gel Science and Technology》2003,26(1-3):207-212
Microspheres of Li2TiO3 were fabricated by a classical, inorganic sol-gel process from commercially available TiCl4. Elaborated process consists of the following main steps: (1) dissolving of TiCl4 in concentrated aqueous HCl and addition of LiOH; (2) formation of sol emulsion in 2-ethylhexanol-1 containing the surfactant SPAN-80 (EH); (3) gelation of emulsion drops by extraction of water with partially dehydrated EH; (4) impregnation of gel to Li:Ti molar ratio MR = 2; (5) thermal treatment at 1200°C in order to receive chloride free product. This temperature can be significantly lowered (to 750°C) by dechlorination starting solution TiCl4 by chemical treatment of the with nitric acid to form of nitrate-stabilized titania sols. Tritium release from sol-gel made Li2TiO3 microspheres were found very close to that observed for other traditional materials, however for the first sample process starts slightly earlier. 相似文献