50 Works

Rotary actuator control based on tensile force elements made of shape memory Cu-Al-Ni crystals when operated in a cyclic mode

A.I. Priadko, S.A. Pulnev, O.O. Kovalev & I.A. Ilin
An actuator design and a function scheme are developed. A control algorithm of a cyclic actuator is considered. We provide experimental results on the control algorithm and the actuator. The actuator operating range is 60°. The actuator sped is ~ 1 degree/second. The actuator operating is stable in any rotation angle in operating range.

Heating and destruction of biological tissue by high-inensity focused ultrasound

T.A. Andreeva, A.E. Berkovich, N.Y. Bykov, S.V. Kozyrev & A.Ya. Lukin
Processes of heating and destruction of the breast fat tissue under the action of focused high-intensity ultrasound generated by a 128-element transducer are considered. The simulation of a thermal problem is carried out by anumerical solution of the heat transfer equation. The acoustic pressure field in the tissue is calculated using the Rayleigh integral. A system of dimensionless scaling parameters is proposed to describe the non-stationary process of heat propagation. The influenceof the space localization...

Micromechanics, nanophysics and non-destructive testing of the strength of structural materials

V.V. Nosov, I.E. Chaplin, E.R. Gilyazetdinov, E.V. Grigoriev & I.A. Pavlenko
Non-destructive testing of the strength of structural materials is currently based on the correlation between the results of laboratory tests of the strength of standard macro samples and the strength characteristics of the material in a real object. The heterogeneity of the strength properties of different zones of the material makes this correlation ambiguous, introducing uncertainty in the test results. The solution of the problem relates to the necessity of transition to the micro- and...

Corrosion resistance and mechanical performance of steel reinforcement, before and after shot-blasting process

Ch. Apostolopoulos, Arg. Drakakaki, А.I. Rudskoi, G.Е. Коdzhaspirov & Alk. Apostolopoulos
As it is widely known, corrosion of steel reinforcement is one of the main causes of deterioration of the reinforced concrete structures. Corrosion phenomena combined with seismic loads aggravate the situation. For this reason, in the present paper, an effort is made to upgrade the performance of steel reinforcement against corrosion, using the shot blasting method. Precisely, two groups of specimens were prepared, one of which had previously been shot blasted. Afterwards, the specimens were...

ALGORITHM FOR POSITIONING OF ROTARY ACTUATORS BASED ON SHAPE MEMORY Cu-Al-Ni TENSILE FORCE ELEMENTS

A. Priadko, S. Pulnev, O. Kovalev & I. Ilin
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.

SIMULATION OF INVERSE HALL-PETCH RELATION IN NANOCRYSTALLINE CERAMICS BY DISCRETE DISLOCATION DYNAMICS METHOD

S.V. Bobylev
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...

Deformation and mechanical stresses in a magnet with thin-walled quasi-force-free winding

German Shneerson, Artem Khlybov, Andrei Belov, A.P. Nenashev, A.A. Parfentiev & S.A. Shimanskiy
The factors leading to an increase in the mechanical stress in the winding of solenoids are considered on the example of a thin-walled magnet with a multi-turn quasi-force-free winding. This example is compared with an ideal system in the form of a solenoid with unlimited length and continuous current distribution. A method for measuring submicron-sized dynamic deformations of the winding in a pulsed field has been developed and verified by comparing experiment results and calculations....

Axial misfit stress relaxation in core-shell nanowires with hexagonal core via nucleation of rectangular prismatic dislocation loops

S.A. Krasnitckii, A.M. Smirnov, K.D. Mynbaev, L.V. Zhigilei & M.Yu. Gutkin
A theoretical model of axial misfit stress relaxation in core-shell nanowires with hexagonal cross section of the core through the nucleation of prismatic dislocation loops is suggested. Different nucleation sites of the loops in core-shell nanowires are considered. The energy change caused by the loop nucleation is calculated. The critical condition for the onset of the loops is given and analyzed in detail. The most favorable sites in nanowires and the optimal loop shape are...

Natural isomers of fullerenes from C4 to C20

Alexander I. Melker & Aleksandra N. Matvienko
We have systematized possible ways of forming the isomers of mini-fullerenes, namely elementary fullerenes: tetrahedron C4, triangular prism C6, cube C8, pentagonal prism C10, hexagonal prism C12, as well as their derivatives, which were obtained by joining elementary fullerenes. Combined with the graph analysis, this approach allows obtain a clear knowledge of their structure. Among them there are barrel-shaped fullerenes: C12, C16, C20; tetrahedral ones C12 and C16; bi-shamrocks C14 and C18, bipyramids C14 and...

Modeling microstructure evolution during thermomechanical processing and heat treatment of steels and predicting their mechanical properties

A.A. Vasilyev, D.F. Sokolov & S.F. Sokolov
An integral computer model/program AusEvol Pro was developed to describe the evolution of steel microstructure during thermomechanical processing (hot rolling, forging), as well as subsequent heat treatment (normalization, tempering), and to evaluate the final mechanical properties (yield stress, tensile stress, elongation), hardness and impact toughness. The program implements a set of physically based models that allow quantitative description of all significant processes of steel structure formation with account of the effects of chemical composition both...

Nano- and microparticle aggregation: unique optical vectors for control

Alexandra G. Bezrukova & Olga L. Vlasova
The multiparameter analysis of simultaneous optical data for systems of nano- and/or micro-particles (3D disperse systems, dispersions, colloids, ensembles with the average diameter less than 10 micrometers) can be presented as the system characteristics characterized by N-dimensional unique vectors of optical parameters that can elucidate changes in the state of system particles. The application of ND unique optical vector approach is shown for several biomedical dispersions at the processes of aggregation. This approach can serve...

Element-free numerical modeling with discrete gradient and its application to crystal defects

A.A. Zisman
The gradient operation has been extended to discrete data in terms of nodal coordinates. On this ground, the nodal strains and related stresses are expressed directly in terms of nodal displacements and the stress divergence in terms of nodal stresses. To make use of truly discrete modeling in computational solid mechanics, the stress balance equation is formulated. For a case study, the latter is applied to an edge dislocation where atom positions of a dislocated...

Experimental study and modeling of changing mechanical properties in tempering of bainitic-martensitic steels

A.A. Vasilyev , D.F. Sokolov & S.F. Sokolov
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...

NUCLEAR GEOMETRY: SODIUM, MAGNESIUM, ALUMINUM

Alexander I. Melker
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...

Crystallographic texture of industrial automotive steels and effect of tertiary cementite dissolution on its development

Alexander A. Vasilyev, N.Y. Zolotorevsky, Dmitry F. Sokolov & S.A. Philippov
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...

Epoxy-polyester coatings with additives of PTFE particles and nanoparticles of SiO2

G.V. Vaganov, V.V. Vaganov, A.Yu. Kolesnikova, E.A. Serikova & E.M. Ivan'kova
Hydrophobic and super-hydrophobic coatings based on epoxy-polyester powder compositions modified with polytetrafluoroethylene (PTFE) particles and nanoparticles silicon dioxide were obtained. The degree of hydrophobicity of the coatings depended on the concentration of PTFE particles. Coatings containing optimal amounts of PTFE exhibited superhydrophobic properties with a high contact angle of wetting with water up to 161° and a low roll angle <3°, while maintaining a high level of physical and mechanical properties of the coatings. The...

Crystallographic orientation, delay time and mechanical constants influence on thermal fatigue strength of single - crystal nickel superalloys

A.V. Savikovskii, A.S. Semenov & L.B. Getsov
The influence of a delay time at the maximum temperature on the number of cycles for the macrocrack initiation for two thermal loading programs was investigated for two single-crystal nickel-based superalloys VIN3 and ZhS32. An analytic approximation of a delay time influence was proposed. Comparison of computational results and analytic formula on the base of constitutive equations with the experimental data was performed for considered single-crystal superalloys and showed a good accuracy. Influence of several...

Pair interaction of coaxial circular prismatic dislocation loops in elastic solids with spherical surfaces

S.A. Krasnitckii, A.M. Smirnov & M.Yu. Gutkin
In the present work, the pair interaction of coaxial circular prismatic dislocation loops (PDLs) arbitrary placed in elastic solids with free spherical surfaces is considered. The analytical solutions for the pair interaction energies of PDLs in an elastic sphere, an elastic medium with a spherical pore and a spherical layer are given in the form of double power series and illustrated by energy maps built in the space of the normalized PDL radii and axial...

MODELING OF STATIC RECRYSTALLIZATION IN COMPLEXLY ALLOYED AUSTENITE

A.A. Vasilyev, S.F. Sokolov Sokolov, D.F. Sokolov & N.G. Kolbasnikov
To predict the kinetics of static recrystallization and the resulting grain size in austenite of alloyed steels including additions of Nb, V, and Ti, a quantitative model is developed. Physically motivated, the model relates the activation energy of the process with that of bulk self-diffusion. The known dependence of the latter on the chemical composition of austenite solid solution, established previously, essentially simplifies the modeling. Employed empirical parameters have been fitted to relevant data covering...

Effect of the specimen size on necking development in metals and alloys during superplastic deformation

A.G. Sheinerman
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...

NUCLEAR GEOMETRY: FROM NITROGEN TO NEON

Alexander I. Melker
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...

ON BUCKLING INDUCED BY A CHEMICAL REACTION

V.O. Shtegman, A.V. Morozov Morozov, A.B. Freidin & W.H. Müller
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 NATURE OF DC CONDUCTIVITY AND STRUCTURAL FEATURES OF GLASSES OF THE Ag – As – Se SYSTEM AS MATERIALS FOR PHOTONICS AND INTEGRAL OPTICS

E.V. Bochagina, V.A. Klinkov, V.A. Markov, V.V. Polyakova & I.A. Sokolov
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...

A model for annealing-induced hardening in ultrafine-grained metals

A.G. Sheinerman & S.A. Krasnitckii
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...

SSRT method: application to studying the mechanism of stress corrosion cracking in steels and alloys (overview)

A.А. Kharkov , A.A. Alkhimenko, N.O. Shaposhnikov &  E.L.  Alekseeva
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...

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Affiliations

  • Peter the Great St. Petersburg Polytechnic University
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  • Institute of Problems of Mechanical Engineering
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  • Ioffe Institute
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  • ITMO University
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  • University of Patras
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  • St Petersburg University
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  • Institute of Macromolecular Compounds
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  • University of Virginia
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  • Saint Petersburg Mining University
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  • Saint Petersburg State University
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