A theoretical model of plastic deformation of nanocrystalline ceramics in the region of small grain sizes is proposed. In the framework of the model, deformation is described as the combined action of grain boundary sliding and emission of lattice dislocations from triple junctions of grain boundaries. Using the method of discrete dislocation dynamics we obtained an inverse Hall-Petch relation, which qualitatively coincides with the experimentally measured dependences of microhardness in nanocrystalline ceramics with extremely small...

This paper considers positioning algorithms for rotary actuators based on shape memory Cu-Al-Ni crystals. The actuator function scheme is provided. An algorithm for positioning of the actuator based on an actual rotary angle has been developed. Experimental results on the control algorithm and the actuator are presented. The functional characteristics of the actuator (rotation speed and positioning accuracy) are considered.

The nuclear geometry has been developed by analogy with the fullerene geometry. On the basis of this geometric approach, it was possible to design the structure of sodium, magnesium and aluminum isomers and their isotopes, which can be obtained by means of nuclear synthesis. The most stable nuclei can be classed into two groups: basic nuclei having equal number of protons and neutrons and isotopes having one or two more neutrons. The latter ensure their...

X-ray investigation of crystallographic texture and its correlation with r m value (Lankford coefficient) was performed on a representative set of industrial automotive steels of different grades. Though the majority of steels had the structure of polygonal ferrite with small fractions of pearlite in the hot rolled condition, steels with a more complex structure were also included in the study. For this set of steels, a linear dependency has been shown to hold between r...

Dependences of mechanical properties (yield stress, tensile stress, relative elongation) and impact toughness on the tempering time at various temperatures have been investigated for 10 industrial bainitic-martensitic steels with a wide range of chemical compositions (C(0.04-0.27), Mn(0.33-1.57), Si(0.22-1.09), Cr(0.02-1.14), Ni(0.01-3.74), Cu(0.02-1.03), Mo(0.01-0.43), Nb(0.002-0.044), V(0.003-0.200), Ti(0.001-0.045), B(≤0.003) (mass.%)). Based on the obtained experimental results, a quantitative model is developed to predict the mechanical properties of the considered steels after tempering. The modeling results comply well with...

The nuclear geometry was developed by analogy with the fullerene geometry. On the basis of this geometric approach, it was possible to design the structure of nitrogen, oxygen, fluorine and neon isomers and their isotopes, which can be obtained by means of nuclear synthesis. The most stable nuclei can be classed into two groups: basic nuclei having equal number of protons and neutrons and isotopes having one or two more neutrons. The latter ensure their...

A model is proposed that describes the development of individual and multiple necks in superplastically deformed materials. Within the model, the examined samples have the form of round bars and are subjected to tensile superplastic deformation without strain hardening. It is demonstrated that neck development and necking-induced failure occur faster with a decrease in strain rate sensitivity and/or an increase in the fraction of the sample length occupied by necks. This means that high values...

This study is concerned with the modeling of plate buckling induced by a chemical reaction and is inspired by the observation that buckling may be a mechanism of stress relaxation in Si-based anodes in Li-ion batteries. A chemical reaction is localized at a sharp interface and accompanied by transformation strains, which produce internal stresses. If external supports restrict the deformation of the plate, buckling may occur. At the same time, mechanical stresses affect the kinetics...

The physical and chemical properties (density, microhardness, thermal effects, elastic modulus, dc conductivity, and the transfer number of silver ions) of glasses of the As – Se – Ag system along the AsSe – Ag and AsSe1.5 – Ag sections were investigated. The transfer numbers of Ag+ ions were determined by a direct method; from their changes, it was found that the glasses of the investigated sections have mixed ion-electronic conductivity. The threshold concentration of...

We suggest a model, which describes the effect of grain boundary relaxation on the annealing-induced hardening in ultrafine-grained metals. Within the model, grain boundary relaxation during annealing is accompanied by a decrease in the number of grain boundary dislocation sources. The exhaustion of easily activated grain boundary dislocation sources results in the activation of harder grain boundary dislocation sources and/or repetitive action of the same dislocation sources. This gives rise to an increase in the...

The paper briefly describes the slow strain rate testing (SSRT) method used for steels and alloys, considering the stress and strain criteria for assessing the sensitivity of materials to stress corrosion cracking (SCC). We pointed out the clear benefits of the SSRT method over static SCC testing. We reviewed the modern theories of the main possible mechanisms of SCC, typically including alternating stages of anodic dissolution and hydrogen embrittlement during the initiation and propagation of...

In the proposed paper the Planar 3D model of hydraulic fracturing was investigated. All of the hydraulic fracturing equations were substituted into the mass conservation law and scaled. Nontrivial dimensionless parameters of the problem were found. Asymptotic regimes of the equation, the Radial or the Pseudo3D model, correspond to the infinitely small or the infinitely large dimensionless parameters. Thus, the limiting conditions of these models were found in the terms of the dimensionless parameters.

In this work, an experimental comparison of the laser-driven alteration of nickel, copper, and steel surface efficiency was carried out. The selection of the material most suitable for non-enzymatic measurement of the glucose amount in the medium was carried with respect to surface modification efficiency. The electrooxidative activity of the fabricated structures with a modified surface was investigated with respect to the glucose addition to a 0.1 M solution NaOH by potentiostatic method. The modified...

We propose a theoretical model describing stress-induced migration of nonequilibrium grain boundaries constrained by the presence of second phase inclusions in metal-graphene composites with the ultrafine-grained matrix. Within the framework of the model, the structure of nonequilibrium boundaries is represented as a combination of dislocation structure of equilibrium boundary and dislocations introduced from outside, trapped by the boundary during deformation. Using the disclination theory approach, a change in the energy of the system associated with...

We have studied possible ways of generating and growing the fullerenes having four-fold symmetry. Beginning with cyclobutane C4H8 and clusters C8, we obtained elementary fullerenes C8 and mini-fullerenes C16, which produce the following fullerenes from C24 to C64, perfect (basic) and imperfect, as well as nanotubes. The imperfection is connected either with extra 'interstitial' or 'vacancy' carbon dimers, both types of dimers playing the role of defects. Only the basic fullerenes C24, C32, C40, C48,...

This study investigated the possibility of increasing the fiber metal laminates mechanical properties by improving the impregnation quality due to the addition of a different number of layers of polymer film on the prepreg-metal interface. Specimens were made based on two thermoplastic polymers (polyamide-6 and polypropylene), glass fibers (E-glass), and aluminum alloy (AlMg6) by hot pressing. The theoretical calculation was performed for the tensile strength according to the rule of mixtures. The dependences of tensile...

The theoretical model is suggested which describes micromechanisms of plastic deformation in bimodal metal-graphene composite consisting of large grains embedded into nanocrystalline/ultrafine-grained metal-matrix reinforced by graphene inclusions. In the framework of the model, lattice dislocation slip and grain boundary sliding has occurred in nanocrystalline/ultrafine-grained matrix, and lattice dislocation slip and migration of twin boundaries are realized in large grains with a nanotwinned structure providing the plastic deformation of bimodal metal-graphene composite. With this assumption, the...

The paper represents a model for the tempering effects on quenched bainitic-martensitic steels that describes both the recovery and precipitation phenomena. The latter involves various carbides (Fe3C, V4C3, Mo2C, Cr7C3) and particles of pure Cu. Thermodynamic driving forces in the nucleation of the considered particles have been calculated using empirical formulas obtained with the Thermo-Calc software. The predicted formation kinetics for the considered carbides and Cu particles complies well with relevant experimental data.