brittle destruction
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Author(s):  
Эльмира Джумшудовна Курбанова ◽  
Римма Михайловна Белякова ◽  
Валерий Анатольевич Полухин

Аморфные, нанокристаллические мембранные сплавы на основе элементов V группы с уникальными механическими и функциональными свойствами и с матричной дуплексной микроструктурой активно способствуют развитию водородной энергетики. Имеются еще не вполне разрешенные проблемы для этих новых сплавов -их низкая термическая стабильность, недосточная механическая прочность (пластичность, твердость), а также охрупчивание интерметаллидное и гидридное. Для эффективного применения разрабатываются сплавы с тройным составом - в которые помимо элементов V группы входят и легирующие металлы никель и титан. Получают не только аморфные и нанокристаллические сплавы, применимые в электронике и электроэнергетике, а также мембранные сплавы с дуплексной матричной структурой, объединяющей аморфные, так нано- и квазикристаллические дендритно упрочняющие фазы, как упрочняющие аморфную матрицу. В специализируемых мембранных тройных сплавах формируются соединения NiTi и NiTi, стабилизирующие и предохраняющие нано- и кристаллические мембраны от хрупкого разрушения. Установлено, что интенсивное образование гидридов в этих альтернативных мембранных сплавах столь же не желательно, как и для традиционных сплавов на основе палладия. Рассматриваемые сплавы действительно позволяют получить газообразный водород высокой чистоты с применением новых составов взамен дорогостоящих мембран на основе сплавов Pd - Au / Ag / Cu. With unique mechanical and functional properties, amorphous, nanocrystalline and matrix duplex microstructure membrane alloys based on group V elements actively contribute to the development of hydrogen energy. There are still not completely resolved problems for these new alloys - their low thermal stability, insufficient mechanical strength (plasticity, hardness), and intermetallic and hydride embrittlement. For effective use, alloys with a triple composition are being developed - which, in addition to the elements of group V, also include nickel and titanium as alloying metals. Not only amorphous and nanocrystalline alloys are obtained that are applicable in electronics and power engineering, as well as membrane alloys with a duplex matrix structure that combines amorphous, nano-and quasicrystalline dendritic-hardening phases strengthening the amorphous matrix. In specialized membrane ternary alloys, NiTi and NiTi compounds are formed, which stabilize and protect nano-and crystalline membranes from brittle destruction. It has been found that the intense formation of hydrides in these alternative membrane alloys is as undesirable as for palladium-based compounds. The alloys under consideration actually make it possible to obtain high-purity gaseous hydrogen using new compositions instead of expensive membranes based on Pd - Au / Ag / Cu alloys.


Author(s):  
Римма Михайловна Белякова ◽  
Эльмира Джумшудовна Курбанова ◽  
Валерий Анатольевич Полухин

Для получения сверхчистого водорода мембранной технологией вместо дорогостоящих сплавов Pd рассмотрены более дешёвые на основе металлов Nb и V . Накапливаемый в матрицах обычных мембран водород формирует специфические полиэдрические плотноупакованные гидридные образования особенно с повышение температур от 473 до 673 К и риском разрушения мембран. Благодаря легированию титаном этих сплавов повысились рабочие характеристики мембран: диффузия и проницаемость водорода, прочность, износоустойчивость и термостабильность. В кристаллических аналогах проблема образования гидридов также была решена повышением концентрации Ti с формированием эвтектических фаз в тройных составах сплавах, например, NbTiNi и VTiNi. С формированием в указанных составах соединений NiTi и NiTi образование гидридов блокируется даже при нагреве, благодаря устойчивым процессам водородной селективности. To obtain ultrapure hydrogen by membrane technology, instead of expensive membranes made of Pd alloys, cheaper ones based on metals (Nb - Ni) and (V - Ni) are considered. Due to alloying of these Ti alloys, the performance of the membranes increased - diffusion and permeability of hydrogen, wear resistance and thermal stability, exceeding the Pd alloys. For crystalline analogs, the problem was also solved by increasing the Ti concentration with the formation of eutectic phases in ternary alloy compositions (NbTiNi and VTiNi). Hydrogen accumulated in membrane matrices forms specific polyhedral eutectic TCP hydrides up to phase transitions, and upon cooling from 673 to 303K under conditions of thermal expansion from 473 to 673K, it increases the temperature of P-hydride formation and forms NiTi and NiTi compounds, which stabilize and protect nano- and crystalline membranes from brittle destruction.


2021 ◽  
Vol 14 (1) ◽  
pp. 34-39
Author(s):  
D. A. Kuzmin ◽  
A. Yu. Kuz’michevskiy

The destruction of equipment metal by a brittle fracture mechanism is a probabilistic event at nuclear power plants (NPP). The calculation for resistance to brittle destruction is performed for NPP equipment exposed to neutron irradiation; for example, for a reactor plant such as a water-water energetic reactor (WWER), this is a reactor pressure vessel. The destruction of the reactor pressure vessel leads to a beyond design-basis accident, therefore, the determination of the probability of brittle destruction is an important task. The research method is probabilistic analysis of brittle destruction, which takes into account statistical data on residual defectiveness of equipment, experimental results of equipment fracture toughness and load for the main operating modes of NPP equipment. Residual defectiveness (a set of remaining defects in the equipment material that were not detected by non-destructive testing methods after manufacturing (operation), control and repair of the detected defects) is the most important characteristic of the equipment material that affects its strength and service life. A missed defect of a considerable size admitted into operation can reduce the bearing capacity and reduce the time of safe operation from the nominal design value down to zero; therefore, any forecast of the structure reliability without taking into account residual defectiveness will be incorrect. The application of the developed method is demonstrated on the example of an NPP reactor pressure vessel with a WWER-1000 reactor unit when using the maximum allowable operating loads, in the absence of load dispersion in different operating modes, and taking into account the actual values of the distributions of fracture toughness and residual defectiveness. The practical significance of the developed method lies in the possibility of obtaining values of the actual probability of destruction of NPP equipment in order to determine the reliability of equipment operation, as well as possible reliability margins for their subsequent optimization.


2021 ◽  
Vol 316 ◽  
pp. 515-520
Author(s):  
Vladimir A. Nosenko ◽  
Alexander V. Fetisov ◽  
Nikita D. Serdyukov

The high adhesive activity of titanium alloys in interaction with abrasive materials is the main cause of poor grinding treatment. The most common abrasive material for grinding titanium alloys is silicon carbide. Silicon carbide wheels operate primarily in self-sharpening mode. Wear of the abrasive tool in the self-sharpening mode occurs as a result of brittle destruction of the fret. The purpose of the study was to determine experimentally the crystalline wear products of an abrasive tool, made of silicon carbide, on the treated surface during grinding of a titanium alloy. Samples of VT9 titanium alloy were processed by flat mortise grinding by a wheel of silicon carbide with the use of VOLTES coolant and the characteristic of the abrasive tool - 64CF80L7V. The treated surface was examined on the electron microscope Versa 3D Dual Beam. The condition of the treated surface testifies to the intensive adhesive interaction of the titanium alloy with the abrasive tool. The thickness of the metal deposits reaches 3 microns. As a result of morphological analysis, objects are identified on the treated surface, the appearance of which allows us to attribute them to crystals. The chemical composition of the selected objects was determined by a microprobe analysis in a microscope camera. On the basis of the conducted researches, a presence on the grinded surface of silicon carbide crystals of various sizes and a ceramic ligament is established.


Author(s):  
С.Н. Гущин ◽  
М.С. Поярков

В статье рассмотрены особенности хрупкого разрушения сталей в условиях низких температур. Разрушение стальных конструкций чаще всего начинается от концентраторов напряжения (производственные дефекты, сварные швы и т.д.) В результате понижения температуры влияние этих факторов резко усиливается. В этом случае требуется применение металла, способного к пластической деформации при низких температурах, поскольку хрупкое разрушение по своим последствиям значительно опаснее, чем пластичное. Пластическая деформация осуществляется за счет перемещения дислокаций, которые являются проявлением несовершенства кристаллический решетки. Под влиянием напряжений при отсутствии препятствий дислокации свободно перемещаются в решетке металла. Понижение температуры приводит к тому, что возрастающий предел текучести достигает значений хрупкой прочности. Существенное влияние на хладостойкость стали оказывают примеси. Влияние примесей связано в первую очередь с загрязнением границ зерен сплавов и уменьшением сил сцепления на плоскостях спайности. Кроме этого, границы зерен характеризуются значительными нарушениями кристаллического строения и являются участками скопления дефектов структуры и включений. The article deals with the features of brittle fracture of steels at low temperatures. The destruction of steel structures most often begins from stress concentrators (manufacturing defects, welds, etc.) As a result of a decrease in temperature, the influence of these factors increases dramatically. In this case, the use of a metal capable of plastic deformation at low temperatures is required, since brittle destruction is much more dangerous in its consequences than plastic. Plastic deformation is carried out due to the displacement of dislocations, which are a manifestation of the imperfection of the crystal lattice. Under the influence of stresses in the absence of obstacles, dislocations move freely in the metal lattice. A decrease in temperature leads to the fact that the increasing yield strength reaches the values of brittle strength. Impurities have a significant effect on the cold resistance of steel. The influence of impurities is primarily associated with contamination of the grain boundaries of alloys and a decrease in the adhesion forces on the cleavage planes. In addition, the grain boundaries are characterized by significant violations of the crystal structure and are areas of accumulation of structural defects and inclusions.


2021 ◽  
Author(s):  
Dmitriy Ohlupin ◽  
Al'bert Korolev ◽  
Il'ya Sinev

The monograph presents a solution to the technological problem of polishing a polycrystalline diamond coating by a mechanochemical method in order to ensure the required surface roughness and high processing performance. The analysis of existing schemes and methods of polishing diamonds and diamond coatings is carried out. A technology for polishing diamond coatings with a metal brush is proposed, which provides brittle destruction of the vertices of large micro-roughnesses and graphitization of small micro-roughnesses. For researchers, postgraduates and specialists of industrial enterprises involved in the technology of polishing the surfaces of parts.


Author(s):  
Yurii Polievoda

The article provides a detailed overview of the process of splitting the kernel of a walnut. Examples of many ways to split the shell are given, all of their disadvantages and advantages are listed. The mechanical method of peeling nuts using low-frequency oscillations has been theoretically investigated and substantiated. The kinematics of the process of crushing nuts between two parallel plates has been extensively analyzed. Graphical correlations were obtained between the size of the nut shell and the dynamics of the driving force of the nut moisture. It is revealed that the process of destruction of the shell of a walnut consists of four stages, corresponding to the laws of brittle destruction. Presents: - dependence of the maximum force of crushing of a shell of a nut at 5% humidity; - the dependence of the maximum crushing force of nuts at different shell thickness for the case of horizontal positioning of the nut between two plates with perpendicular force on the surface of the joint halves of the nut; - the dependence of the maximum crushing force according to the humidity of the nuts at different shell thicknesses for the case of vertical positioning of the nut between two parallel plates with a vertical driving force; - the dependence of the maximum crushing force with the moisture of the nuts at different shell thicknesses for the case of horizontal positioning of the nut between two parallel plates with a force action along the slit. The energy of splitting (crushing) of nuts at their location in different positions between two parallel plates is also determined. Where it has been proved that the energy consumed in the process of crushing increases with the thickness of the shell of a walnut. At the same time, it is proved that energy consumption depends on the location of the nut in the process of crushing. Graph analyzes were performed to show that maximum crushing energy is recorded in the case of a horizontal arrangement of a nut with a perpendicular crack action. In this study, a large amount of information was obtained regarding the splitting of the walnut, depending on the structural and mechanical characteristics of the products, which in the process of processing are important for the determination of certain rational technological parameters.


The results of domestic and foreign experimental studies of masonry made of large-format ceramic hollow bricks and stones with voidness of up to 54% on the effect of static load during compression are analyzed. They confirmed the conclusions made by Russian scientists in the 1950s-1960s when developing the theory of stone masonry. Based on the analysis of the nature of deformation of the masonry of the large stone and the use of modern approaches to the assessment of the process of crack formation and failure of masonry the possibility of her plastic deformations is assessed. It is shown that the masonry of ceramic large-format stone refers to brittle materials. Based on the analysis of the test results, it is noted that according to the theory of plastic media, there is the simplest model of destruction of masonry during loading, in which plastic deformation can occur in the local zones of the element (crack zones). In this case, the bulk of the body (sample) is in an elastic state. The fallacy of the proposed approach to the estimation of the coefficient of plasticity of masonry, with due regard for the ratio of elastic and total deformations of masonry is noted. It is established that the proposals of individual authors to assess the plasticity of the wall masonry of ceramic brick and large-format ceramic stone with voidness of more than 40 % are incorrect and does not meet the work of the masonry of hollow material. On the basis of a large number of research works, it is concluded that the appearance and development of cracks and damage in the masonry is associated with the effects of its brittle destruction, and the masonry of large-format hollow stone refers to brittle materials.


2019 ◽  
Vol 109 ◽  
pp. 00043 ◽  
Author(s):  
Oleksandr Krukovskyi ◽  
Viktoriia Krukovska

The mathematical model has been developed for the coupled processes of the rock massif deformation and gas filtration in a disturbed area around mine working, in the bottom of which there are hard and soft gas-bearing rocks. When solving the problem, the finite element method was used. The calculation results of the displacements, stresses and pressures of methane in the studied area are represented in the paper. It is shown that the difference in the physical and mechanical properties of the bottom rocks of mine working causes the non-uniform distribution of geomechanics and filtration parameters. In more strong sandstone, the stresses concentration increases. Therewith, an intensive process of fractures formation takes place in the argillite and the coal. Methane from the upper part of the gas-bearing sandstone is filtered into the mine working, the destruction of the coal interlayer is accompanied by release of methane and its accumulation under the layer of a strong sandstone. The development of a zone of inelastic deformations leads to the destruction of sandstone. In case of brittle destruction, with the formation of fractures of a certain length, a breakthrough of methane may occur out of the bottom into mine working.


2019 ◽  
Vol 2 (5) ◽  
pp. 89-97
Author(s):  
Anvar Chanyshev ◽  
Olga Belousova ◽  
Olga Lukyashko

In the paper stress-strain behavior of solid during flat strain in case of its volumetric incompressible behavior and ideally brittle destruction is studied. Parameters of the system of differential equations of balance and its correlations are obtained. In this case, condition of stress and strain tensors axiality is used. Boundary problem for determination of stress-strain behavior at destruction zone is formulated. As example, equations of ideally brittle out-of-limit deformation of solid in form of rectangular plate (pillar) during uniform compression are considered. It is shown that when displacement of side border of the plate is observed, it is possible to predict its destructions.


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