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121.
122.
Vukoman Jokanović Božana Čolović Nataša Jović Branka Babić‐Stojić Bojan Jokanović 《International Journal of Applied Ceramic Technology》2013,10(6):957-969
Low‐temperature synthesis of fluorapatite/fluorohydroxyapatite with precursor mixture previously mechanochemically treated is described in this article. Ethylene vinylacetate/versatate copolymer as a surface active substance was mechanically treated to obtain a core‐shell system with strongly controlled grain size. Despite usual behavior of mechanically activated systems, only an amorphous phase formed from precursor ions present in the mixture composed of β‐Ca2P2O7, CaCO3, CaF2, and unreacted Ca(OH)2 was obtained during milling for 5 min to 8 h. The mixture contained depots of labile F? ions conserved in micelles cages, which are useful for teeth protection from carries. For transformation of these amorphous phases into fluorapatite, an additional low thermal treatment was necessary. The mechanism of the precursor mixture transformation into fluorapatite during milling and thermal treatment was investigated using FTIR spectroscopy and X‐ray diffraction. The morphology and size distribution of the obtained powders was studied using SEM and TEM. 相似文献
123.
The influence of the coordinate reduction on the identification of the joint dynamic properties 总被引:1,自引:0,他引:1
A problem of establishing a theoretical model of a joint from the measured frequency-response function (FRF) data is discussed in this paper. The model of the joint is considered as a coupled dynamic stiffness matrix, which generally includes six degrees of freedom (DoFs). For two types of least-squares solution the terms of use are clarified. The effect of coordinate reduction on the identification results is demonstrated numerically. Also the effect of added noise is studied. Using a substructure synthesis method and the identified joint dynamic properties the assembly response is reconstructed. 相似文献
124.
H. H. Dietrichs H. Bellmann H. Jentzsch H. Kolb K. Rügge H. Mügge K. A. Song K. Dsiobek H. Kolb K. A. Sorg L. Čižek 《Holz als Roh- und Werkstoff》1962,20(1):51-55
Ohne Zusammenfassung 相似文献
125.
Radovan Ćirić Svetislav Čantrak Karlo T. Raić Rebeka Rudolf Ivan Anžel 《Metals and Materials International》2009,15(5):831-841
The paper presents the viscoplastic phenomena observed during the rotational friction-welding process of high-speed steel
M2 (AISI SAE) with carbon steel 1060 (AISI SAE). The structure, phase composition and distribution of the carbide phase in
the friction plane and adjoining zones are examined by using optical microscopy (OM) with a system for quantitative analysis,
and scanning electron microscopy (SEM) in addition to EDS analysis. The experimentally-checked mathematical relationship is
suggested for the calculation of the radial movements of the carbide phase, immediately next to the friction plane. On the
basis of qualitative and quantitative evaluation of the microstructural and rheological appearances, a model of carbide phase
distribution is also established in the viscoplastic and viscous layers in the area of the friction plane. 相似文献
126.
In the preceding companion paper (Bažant and Li, 1995), the solution of an aging viscoelastic law was structure containing
a cohesive crack with a rate-dependent stress-displacement softening law was reduced to a system of one-dimensional integro-differential
equations involving compliance functions for points on the crack faces and the load point. An effective numerical algorithm
for solving these equations, which dramatically reduces the computer time compared to the general two-dimensional finite element
solution, is presented. The behavior of the model for various loading conditions is studied. It is shown that the model can
closely reproduce the available experimental data from fracture tests with different loading rates spanning several orders
of magnitude, and tests with sudden changes of the loading rate. Influence of the loading rate on the size effect and brittleness
is also analyzed and is shown to agree with experiments.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
127.
M. Blažková T. V. Chagovets M. Rotter D. Schmoranzer L. Skrbek 《Journal of Low Temperature Physics》2008,150(3-4):194-199
A quartz fork vibrating at high amplitude is used to study cavitation in He I and He II along the saturated vapor pressure
(SVP) curve and at slightly elevated pressures. Cavitation is observed as a breakdown of the resonance response at critical
velocity when slowly sweeping the frequency of the drive across the resonance and confirmed by visual observation of a bubble
occurring in He II in the space between the prongs of the fork. On decreasing the temperature from 4.2 K along the SVP curve
the critical velocity slowly increases from about 0.4 m/s to 1 m/s, until a steep increase up to about 2 m/s occurs within
about 20 mK just below the superfluid transition. We discuss our results, including the measured dependence of the critical
velocity versus overpressure at fixed bath temperature.
相似文献
128.
Shear fracture tests of concrete 总被引:10,自引:0,他引:10
Symmetrically notched beam specimens of concrete and mortar, loaded near the notches by concentrated forces that produce a concentrated shear force zone, are tested to failure. The cracks do not propagate from the notches in the direction normal to the maximum principal stress but in a direction in which shear stresses dominate. Thus, the failure is due essentially to shear fracture (Mode II). The crack propagation direction seems to be governed by maximum energy release rate. Tests of geometrically similar specimens yield maximum loads which agree with the recently established size effect law for blunt fracture, previously verified for tensile fracture (Mode I). This further implies that the energy required for crack growth increases with the crack extension from the notch. The R-curve that describes this increase is determined from the size effect. The size effect also yields the shear fracture energy, which is found to be about 25-times larger than that for Mode I and to agree with the value predicted by the crack band model. The fracture specimen is simple to use but not perfect for shear fracture because the deformation has a symmetric component with a non zero normal stress across the crack plane. Nevertheless, these disturbing effects appear to be unimportant. The results are of interest for certain types of structures subjected to blast, impact, earthquake, and concentrated loads. 相似文献
129.
130.
Evgenij Starikov Pavel Shiktorov Viktoras Gružinskis Alexandr Dubinov Vladimir Aleshkin Luca Varani Christophe Palermo Lino Reggiani 《Journal of Computational Electronics》2007,6(1-3):45-48
A possibility to develop the so called TASER (Terahertz-Amplification-by-the-Stimulated-Emission-of- Radiation) by using two-dimensional
(2D) electron transport in quantum well (QW) structures is investigated by Monte Carlo simulation of the optical-phonon-emission
assisted transit-time resonance (OPTTR) of 2D electrons in momentum space under the low lattice temperature. A considerable
extension of the frequency region for THz radiation generation (upto 5 times) when going from 3D- to 2D-case is predicted. 相似文献