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卷 2017, 编号 4 (2017)
- 年: 2017
- 文章: 23
- URL: https://journals.rcsi.science/0036-0295/issue/view/10439
Physical Foundations of Strength and Plasticity
Chernov–Lüders bands and the Portevin–Le Chatelier effect as plastic flow instabilities
摘要
The development of macroscopic plastic flow heterogeneities in metals in the form of Chernov–Lüders bands and the Portevin–Le Chatelier effect is studied. The main laws of deformation development in these two cases are found, and the kinetics of the motion of Chernov–Lüders band fronts and the serrated deformation during the Portevin–Le Chatelier effect is investigated. It is shown that both versions of heterogeneities can be considered as macroscopic autowave processes of switching and excitation in deformable media.
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Deformation and Fracture Mechanics
Method for calculating the limiting technological residual stresses in a tubular billet
摘要
A procedure for calculating residual stresses is developed. It is based on the energy approach and the Tresca criteria of strength and plasticity and includes the main technological parameters of tube making. Relationships are derived to estimate the ultimate strain during the production of axisymmetric hollow metal billets.
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Investigation of three-layer rectangular panel bending by variation method
摘要
The task of transverse bending of a rectangular three-layer panel with the lightweight filler is considered. The differential equation system of transverse bending of the panel is generated within the scope of Lagrange variational principle. An explicit solution of the differential equation system in double trigonometric Fourier series is obtained. It is shown that the maximum deflection of the three-layer panel can be compared with the three-layer beam deflection, with a multiple panel width excess over its length.
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Mechanisms of hydrogen embrittlement and fracture of nanocrystalline materials
摘要
The physical mechanisms of hydrogen embrittlement and fracture of nanocrystalline materials due to the molecular hydrogen pressure in cavities and the formation of hydride phases are proposed and justified mathematically.
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Advanced Materials and Technologies
Effect of plasma immersion ion beam processing on the structure–phase state and the properties of the surface layers in titanium nickelide samples
摘要
The formation of a microstructure in the surface layers of model samples made of a titanium nickelide–based alloy intended for medical application during plasma immersion processing by silicon ions is studied. Depending on technological conditions, either a silicon coating can be formed or a surface layer can be alloyed. The formed layers have a high microhardness and high adhesion to the base material.
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New deformability characteristics of zirconia-based plasma-sprayed thermal barrier coatings at low loads
摘要
A new approach to determining the residual stresses and the energy characteristics of the deformability of zirconia-based thermal barrier coatings is described. This approach consists in the formation of a deformation hysteresis in the elastic range of deformation during four-point static bending and in estimating the energy density of relaxation of the elastic strain in the coatings.
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Thermal stability of the microstructure of silver films
摘要
The thermal stability of freely suspended silver films 100 nm thick is studied during isothermal annealing at temperatures of 350–600°C for different times. At temperatures of 350–450°C, only grain growth is observed. Above 450°C, along with grain growth, the formation and growth of hillocks and holes take place; in this case, grain boundaries are essential in the processes. A continuous film transforms into a cellular one. At 500°C, the growth processes of both grains and holes have the same incubation period, during which no grain growth, hole formation, and hole growth take place.
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Effect of an isothermal action on the functional properties and the shape memory effect parameters of a TiNi(Mo, V) alloy
摘要
The influence of annealing at 450°C for 1 h on the shape memory effect parameters of the Ti50Ni48.7V1Mo0.3 alloy is studied over a wide temperature range at a constant load. Annealing is shown to decrease the critical stresses of the martensitic shear, to increase the temperature hysteresis wide during a repeated shape memory effect, and to decrease this effect.
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Effect of deformation and heat treatment on the structure, the mechanical properties, and the fracture characteristics of an ultrafine-grained Zr–1Nb alloy
摘要
The effect of cold working and annealing for various times on the structure, the mechanical properties, and the fracture characteristics of an ultrafine-grained Zr–1 wt % Nb alloy after three-dimensional pressing is studied. Possible causes for increasing the thermal stability of the strength properties of the ultrafine-grained Zr–1 wt % Nb alloy during prerecrystallization annealing after additional cold working by rolling are discussed.
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Mechanical properties of the compositions based on biopolyamide-1010 modified by carbon, glass, and cellulose chopped fibers
摘要
The influence of chopped cellulose, carbon, and glass fiber fillers on the physicomechanical properties of biopolyamide-1010-based compositions is studied. The properties of the composites filled with carbon fibers are shown to be improved when a combination of carbon fibers with short cellulose fibers is used.
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Applied Problems of Strength and Plasticity
Nanoscale localization of plastic deformation in steel with a bainitic structure
摘要
Transmission electron microscopy is used to reveal the formation of localized deformation channels on a nanoscale in 30Kh2N2MFA steel subjected to compressive deformation of 40% or more. The channels are found to be located mainly along the interfaces of neighboring bainite lamellae or along grain boundaries. The structure of the deformation channels, their sizes, and the change in their volume fraction with the strain are analyzed.
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Properties of the welded joints of manganese steel made by low-frequency pulsed arc welding
摘要
The structure, the mechanical properties, the impact toughness, and the fracture mechanisms of the welded joints made of steel 09G2S plates by direct current welding and pulsed arc welding with a modulated arc current in the frequency range 0.25–5.0 Hz are studied. The application of low-frequency pulsed arc welding allowed us to form welded joints with a fine-grained structure in the weld metal and the heat-affected zone and to achieve a higher impact toughness and a longer cyclic fatigue life as compared to the welded joints fabricated by direct current welding. The achieved effect manifests itself over the entire testing range from 20 to–60°C.
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Influence of heat treatment on the efficiency of impact fragmentation of amorphous alloy Fe73.5Cu1Nb3Si13.5B9 ribbons
摘要
The mechanism of impact fracture of soft magnetic amorphous alloy Fe73.5Cu1Nb3Si13.5B9 ribbons in a disintegrator after heat treatment at a temperature from the range 300–700°C and the fractional composition of the formed powder are studied. The temperature ranges of a change in the mechanism of ribbon fracture are determined. The particle size distribution is shown to change weakly within the revealed temperature ranges.
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Effect of volume–surface quenching on the impact toughness of 20GL steel intended for cast freight bogie solebars
摘要
The effect of volume–surface quenching (VSQ) by a rapidly moving water flow on the impact toughness at–60°C (KCV–60) of cast low-carbon 20GL steel, which is used to produce freight bogie solebars, is studied. VSQ is shown to increase KCV–60 of 20GL steel by a factor of 1.7–2.0 at a higher static and cyclic strength as compared to the normalized state.
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Microhardness of anodic aluminum oxide formed in an alkaline electrolyte
摘要
The microhardness of anodic aluminum oxide formed by anodizing of aluminum sheet in electrolyte on the basis of sodium hydroxide has been determined experimentally. The microhardness of the hard film/soft substrate system has been estimated by three approaches: indentation geometry (length of diagonals) in film surfaces, the sum of the hardnesses of the film and the surface with allowance for the indentation surface area and geometry, and with allowance for the indentation depth. It is demonstrated that the approach accounting for the indentation depth makes it possible to eliminate the influence of the substrate. It is established that the microhardness of the films formed in alkaline electrolytes is comparable with that formed in acid electrolytes.
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Acoustic emission analysis of the stages of deformation of TRIP steel
摘要
The kinetics of damage accumulation and deformation martensite formation in cold-rolled austenitic–martensitic VNS9-Sh TRIP steel during static tension at room temperature is studied at various stages of plastic deformation and fracture by acoustic emission and X-ray diffraction. The threshold stresses that correspond to the beginning of dislocation motion and intense dislocation generation predominantly in surface layers are determined. Deformation martensite is shown to form after a yield plateau and its formation is most intensely at the stage of strain hardening.
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Diagnostics and Mechanical Test Techniques
Scanning probe microscopy estimation of the wear resistance of the surface of a modified PVC film
摘要
An atomic force microscopy technique is proposed to determine the wear resistance of a protective coating deposited by the sol–gel method on the surface of a polyvinylchloride film. The force of action of a probe on a sample is estimated under various scanning conditions. It is shown that the obtained data on the resistance of a coating to the action of a probe in the contact mode can be used to qualitatively estimate the adhesion of the coating to the surface of a polymer matrix.
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Effect of the strain rate on the mechanical properties of a sheet TRIP steel with a high martensite content
摘要
The laws of changing the mechanical properties of sheet austenitic–martensitic VNS9-Sh (23Kh15N5AM3-Sh) TRIP steel are studied when the static strain rate changes in the range 0.1–20 mm/min (8.3 × 10–5–17 × 10–3 s–1). The 0.35-mm strip under study is characterized by a high martensite content (≈100%) in the surface layer at an average content of 80–85%. The transformation induced plasticity effect is maximal at a strain rate of 0.1 mm/min (8.3 × 10–5 s–1).
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Development of short fatigue cracks in aluminum alloy 2524-T3 specimens
摘要
The development of short fatigue cracks in a 2524-T3 alloy is studied under cyclic tension conditions. Flat specimens with a stress concentrator in the form of a central hole are analyzed. The replica technique is used to determine the microcrack parameters and to estimate the cyclic damage characteristics of the alloy in the stress concentrator zone. The experimental results are compared to the fatigue lives estimated by a calculation-experimental method using the NASGRO software package. The experimental fatigue life at the stage of short crack initiation is found to be significantly shorter than the calculated fatigue life.
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Ensemble of secondary cracks near the fatigue fracture surface of a titanium alloy VT23M specimen
摘要
The secondary fragment cracks in a specimen made of a high-strength VT23M titanium alloy in the plane parallel to the specimen plane are studied with a scanning laser microscope. Two types of the secondary cracks are detected. Relations between the characteristics of an ensemble of secondary cracks and the cyclic loading parameters are obtained.
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Estimation of the resistance to the initiation of fatigue cracks in the welded joints of steel constructions
摘要
The problem of choosing an effective approach to determining the fatigue strength of welded butt joints at the stage of crack nucleation is solved. The results of the calculations performed according to the existing building code from the specified strength characteristics and the calculations that take into account local elastoplastic deformation in stress concentration zones are compared. Full-scale specimens of the welded joints of pair angles are tested in the low-cycle fatigue region at a constant load. The kinetics of the state of stress in the zones of terminating flange welded joints is studied by a tensometric method. It is shown that the stage of fatigue crack nucleation is best described using the deformation criterion of fracture: a comparison of the results of calculating the number of cycles to the nucleation of a fatigue crack with experimental data demonstrates good agreement.
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Forces and strains during drop weight tear test
摘要
As follows from the results of drop weight tear tests (DWTT), modern strength class K65 steels for gas-main pipelines exhibit an almost 100% fraction of ductile component in a fracture surface. The results of ground tests demonstrate that the lengths of extended fracture of a pipe made of such steels from different suppliers are substantially different. The possibility of extracting other characteristics from DWTT tests of full-thickness notched specimens and the information content in them are estimated. High-speed detection of the strain and crack growth is performed during static and dynamic loading. As follows from an analysis of fracture kinematics and force and energy balance, fracture is a multistage process, where mechanisms change during crack growth.
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Study of the fracture kinetics in structural aluminum alloys subjected to a long-term action of a static load and a corrosive medium using specimens of a new type
摘要
A new type of specimens is proposed to study the fracture kinetics of the metallic materials subjected to a long-term simultaneous action of a tensile load and a corrosive medium. The new design of specimens makes it possible to determine the stress intensity factor at the crack opening fixed by a wedging bolt, to perform investigations in any aggressive medium, and to measure the tensile load on a specimen at any stage of tests. Standard apparatus is used for this purpose. Plate specimens made of structural aluminum alloys 1163T and V95pchT2 are tested. A paradoxical fact of increasing the conventional stress intensity factor of the V95pchT2 alloy during the development of a corrosion crack is revealed.
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