Physical and Mechanical Properties of W-Ni-Fe-Co Metal Foam Modified by Titanium Tungsten Carbide Alloying

Russian Physics Journal - The paper studies physical and mechanical properties of tungsten-nickel-iron-cobalt metal foam alloyed with titanium tungsten carbide. Test specimens are obtained by the...     

Raman spectroscopy study of the structure of gallium nitride epitaxial layers of different orientations

The composition nonstoichiometry and structural quality of undoped gallium nitride layers grown by the hydride vapor phase epitaxy on sapphire substrates of different orientations have been estimated using Raman spectroscopy. It is found for the first time that the peak position of the phonon mode E₂(high) in the Raman spectra of gallium nitride films at a wave vector of 572 cm^–1 depends on the initial orientation of sapphire substrate and is low-frequency shifted when passing from Ga-polar to partially N-polar orientation. Additional modes are found in the spectra of GaN layers grown on substrates with m and r orientations. It is shown that a decrease in the composition deviation from stoichiometry, caused by reducing the HCl flow through the gallium source during the growth of GaN layers, leads to an increase in the phonon-mode intensity in the Raman spectrum.     

Calculation of the strength of reinforced concrete columns under repeated longitudinal impact

This paper reports the results of experiments with reinforced concrete column models subjected to repeated longitudinal impact loading using a pile driver. The strength of the column models is analyzed by comparing experimental data with results of mathematical modeling. __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 49, No. 1, pp. 181–190, January–February, 2008.     

Mathematical modeling of dynamic fracture processes in concrete

We solve the problem on the collision of steel cylindrical hammers in the velocity range up to 800 m/s with rectilinear concrete slabs. We consider the following two approaches to calculating concrete fracture under impact loading: the phenomenological approach in which the strength criteria are expressed in terms of invariant constraints imposed on the critical macrocharacteristics of the process, i.e., stresses and strains, and the approach in which the fracture is considered as the process of formation, growth, and confluence of microdefects under the action of applied stresses. We compare the results of mathematical modeling with the experimental data concerning the penetration depth and the exterior flushing value. In the framework of the proposed model of dynamic fracture in concrete, we calculate the strength of a concrete tetrahedral prism under the action of longitudinal loads. We obtain a satisfactory agreement of the results of mathematical modeling with experimental results.     

Mathematical Modeling of Deformation and Fracture of Cermets under Dynamic Loading Conditions

The behavior of cermets under shock-wave loading conditions is examined. The materials under study are produced by self-propagating high-temperature synthesis. A mathematical model for calculating the stress-strain state and fracture of the TiB + B₄C-based cermet is developed.