Nonlinear crack dynamics and scaling aspects of fracture (experimental and theoretical study)

Nonlinear dynamics of crack propagation are investigated experimentally and theoretically with the goal of clarifying the nature of limiting crack velocity, the transition from steady state to branching regimes of crack dynamics, and the dynamics of crack arrest. The theoretical explanation of limiting steady-state crack velocity and the transition to a branching regime was proposed due to the study of collective behavior of a microcrack ensemble at the crack tip area. The experimental study of crack dynamics was carried out in a preloaded plate PMMA specimen using the high-speed camera coupled with the photo-elasticity method, the point stress recording with a laser system, and the failure surface roughness measurement.     

Standardization of Technological Parameters for Drawing Optical Rods Using Experimental Models

A method for constructing experimental models of drawing optical rods based on experimental data is considered. The models obtained make it possible to identify admissible technological parameter fluctuations in the range selected.     

<Superscript>137</Superscript>Cs content and vertical migration in littoral soil of two lakes in Bryansk Oblast

The dynamics and present state of the radioactive contamination with ¹³⁷Cs of littoral soil of Lake Kozhanovskoe and Lake Svyatoe on the Besed’ River are presented. The parameters of the vertical migration of ¹³⁷Cs in soil-the rate of directional transfer with soil moisture, the diffusion coefficient, and the average velocity of vertical migration-are estimated by comparing the experimental and model distributions of ¹³⁷Cs content over soil depth. It is shown that at the present time the two 5-cm layer of soil can contain 20–90% ¹³⁷Cs depending on the type of soil and landscape. The average values of the diffusion coefficient, the rate of directional transfer, and the vertical migration velocity for 12-, 13-, and 20-year periods after the Chernobyl accident are 0.1–2.8 cm²/yr, 0.1–0.3 cm/yr, and 0.1–0.8 cm/yr, respectively. __________ Translated from Atomnaya énergiya, Vol. 102, No. 5, pp. 306–311, May, 2007.     

Design of the EPLD-based reconfigurable fault-tolerant systems with cell-level redundancy

A procedure to design reconfigurable systems capable to recover their operability in the case of fault of an arbitrary EPLD cell or connection was proposed. The most important advantages of the procedure lie in the retention of the signal propagation delays guaranteeing system operability after reconfiguration, as well as in low redundancy of the fault-tolerant system which at the limit may correspond only to one standby cell. The package methods enable one to design fault-tolerant systems based on the closed intelligent core without their upgrading. Efficiency of the procedure was estimated, and possible limitations of its application were discussed.     

Mechanosynthesis of complex oxides and preparation of mixed conducting nanocomposites for catalytic membrane reactors

Nanopowders of LaGaO₃- and LaMnO₃-based complex perovskites (P) and ceria-based fluorites (F) were prepared by mechanosynthesis. Compatible nanocomposites F + P and P + P with mixed ion and electron conducting (MIEC) properties were prepared and sintered at moderate temperatures up to dense ceramics. The obtained materials were studied by means of XRD, SEM, TEM, electrical conductivity measurements, temperature programmed (TP) reduction/oxidation and preliminary estimations of permeability were obtained. A new strategy based on the advantages of the mechanochemical ceramic approach is proposed to design multilayer ceramic membranes for CMR. Casting technology and one-step sintering were used for the production of thin film membranes with MIEC properties on porous substrates. The coarse fraction of as-milled powders from agglomerates with density 70% was used for the porous substrate, and fine fractions of aggregates with sizes <1 μm were used in preparation of composites for thin dense films. Ceria-based composites prepared by the Pechini route and/or mechanochemical method are proposed as materials for protecting thin films.     

Synthesis of nanocomposite materials in the SnO<Subscript>2</Subscript>-NiO system

The SnO₂-NiO nanocomposites with the specific surface area on the order of 100 m²/g and the particle size of both phases of less than 10 nm have been synthesized by the sol-gel method with the subsequent annealing in the temperature interval 200–1000°C. It has been shown that, with an increase in the annealing temperature to 900°C, the specific surface area of the nanocomposites increases. This effect has been explained by the increase in the porosity due to the destruction of the aggregates of primary amorphous particles. The electrical conductivity has been measured and the parameters of the surface defects have been determined.     

Distribution of luminescence centers in the bulk of undoped,Fe-doped,and Cr-doped CVD ZnSe polycrystals studied by two-photon confocal microscopy

Edge and defective-impurity luminescence in polycrystalline CVD ZnSe has been studied in the range 0.46–0.73 μm by two-photon confocal microscopy. We have obtained luminescence intensity distribution maps for undoped, iron-doped, and chromium-doped ZnSe samples at depths of up to 1 mm with a spatial resolution of a few microns. It has been shown that crystal regions with low dopant concentrations contain centers that luminesce in the ranges 520–580 and >670 nm. The parts of the crystals with high iron and chromium concentrations contain centers that suppress the edge and defective-impurity (520–580 nm) luminescence. We discuss the nature of these centers and demonstrate the possibility of assessing the luminescence characteristics of grain boundaries in CVD ZnSe.     

Development of new methods for studying the decomposition in aging invars

N30K10T3 and N28K10T3 invar alloys are studied. After water quenching from 1150°C, they consist of supersaturated solid solutions, which can decompose in aging in the temperature range 500–700°C with the precipitation of intermetallic Ni₃Ti nanoparticles. It is shown that the decomposition can be controlled by measuring the magnetic (first harmonic amplitude, phase angle φ shift, magnetic susceptibility μ) and electric (electrical conductivity σ) parameters as functions of the isothermal holding time at various aging temperatures. The alloys are studied in the following three initial states: after quenching, phase transformation-induced hardening (γ → α → γ_pt), and cold (20°C) plastic deformation by 30%.