查看更多>>摘要：We analyze the results of investigations of the interaction of hydrogen with metals under the conditions of their deformation. We formulate the conclusions about the fracture and strength of structural materials made on the basis of the experimental data accumulated at the Karpenko Physicomechanical Institute of National Academy of Sciences of Ukraine for the last 70 years (since 1951). Main attention is given to the dual character of the influence of hydrogen on the deformation of metals. Indeed, at low concentrations, it promotes their plasticization, whereas at high concentration, it caused their embrittlement. The indicated features of the interaction of hydrogen with metals form a basis for the prediction of the durability of metal structure in hydrogen-containing media and for development of products with high physicomechanical characteristics.
查看更多>>摘要：We consider the process of corrosion of steels in hydrogen-sulfide media of different concentrations with regard for the specific features of the formation of sulfides of different chemical compositions and their influence on the course of redox reactions. We present different points of view on their role in corrosion processes. On the basis of generalization of the influence of iron sulfides on electrode reactions, release and absorption of hydrogen by Armco iron, U8 steel, and 45 steel of different structures, it is established that, despite the fact that iron sulfides mainly reduce the overvoltage of cathodic reactions and increase the amount of hydrogen released under cathodic polarization, they do not always promote the hydrogenation of these materials. Iron sulfides predominantly affect the reaction of hydrogen release, whereas its absorption depends on the structures of steels. By an example of 17G1S-U steel, we show that the corrosion rate is affected by the nature of sulfides formed on the surface. Indeed, for their concentrations varying within the range 25-100 mg/dm(3), the corrosion rate decreases by almost an order of magnitude. Moreover, for hydrogen-sulfide concentration C-H2S >= 500 mg/dm(3), we observe the formation of porous sulfides, corrosion defects are localized, and the intensity of absorption of hydrogen by steel becomes almost twice higher than at lower concentrations, which promotes the development of cracking and corrosion cracking. It is shown that the critical concentration for the development of hydrogen- sulfide corrosion cracking of steels of this class is C-H2S <= 100 mg/dm(3).
查看更多>>摘要：We analyze the mechanism of degradation of pearlitic steels depending on the operating conditions, such as, first of all, the temperature, stresses and hydrogenation. Microstructural, mechanical, and electrochemical indicators of the in-service degradation of structural steels and its main stages are systematized. As its most typical feature, we can mention the decrease in brittle-fracture resistance, which increases the hazard of the loss of structural integrity. Special attention is given to the stage of development of dissipated damage on the nano- and microscales and the corresponding mechanical effects. We also analyze the existing laboratory methods intended for the accelerated degradation of steels. A special role of hydrogenating media in the process of degradation of steel is demonstrated and the nondestructive methods of its evaluation are analyzed. The prospects of subsequent research in the problems of in-service degradation of steels intended for the hydrogen power-generating industry in the case of application of the existing networks of gas transit and distribution pipelines for the transportation of hydrogen and its mixtures with natural gas are discussed.
查看更多>>摘要：We present a survey of the results of investigations of the concentration of stresses in elastic bodies weakened by curvilinear holes and notches with nonsmooth contours. Special attention is given to the asymptotic approach to the investigation of stress distributions near stress concentrators in the case where the stress intensity factors at sharp vertices are found by using the stress concentration factors at the rounded vertices of V-notches.
查看更多>>摘要：We analyze the optical-digital methods of monitoring of the surfaces of structural elements developed at the Karpenko Physicomechanical Institute of the National Academy of Sciences of Ukraine for the purposes of technical diagnostics. These methods are based on the principles of phase-shifting interferometry, digital speckle pattern interferometry, and digital image correlation. The advantages of the methods of two- and three-step phase shifting interferometry with arbitrary phase shifts of the reference beam over the conventional methods are estimated. On the basis of the method of three-step phase shifting interferometry, we developed a 3D profilometer aimed at measuring the parameters of roughness and waviness of the surface. The developed method of phase shifting digital speckle pattern interferometry is capable of reproducing the field of surface displacement by using only two pairs of speckle interferograms. This method is used for the solution of various problems of technical diagnostics and, in particular, for the detection of hidden holes and defects in metal specimens and welded joints. The digital image correlation methods are used to determine the fields of surface displacement near the crack faces and other stress concentrators, the stress intensity factors, the J-integral, the direction of crack propagation, and the boundaries of the plastic zone in the loaded specimen. To find the 3D fields of displacements, we propose a new 3D digital image correlation method with the help of which it became possible to measure the deformations of the surfaces of fuel tanks of launch vehicles.
查看更多>>摘要：We present a survey of the results of theoretical investigations of the method of acoustic emission used for the determination of the limit equilibrium of materials with cracks, their delayed fracture (initiation and propagation of cracks), and the residual service life of structural elements intended for long-term operation. At the same time, we develop computational models for the detection, by the acoustic-emission method, of crack-like defects and volumetric damage to the materials. We also propose criteria for the mechanisms of their fracture and acoustic-emission procedures aimed at the construction of the kinetic diagrams of delayed growth of creep cracks.
Verbovytskyy, Yu V.Oprysk, V. V.Shtender, V. V.Zavaliy, I. Yu...
11页
查看更多>>摘要：We present a brief survey of the experimental works on gas and electrochemical hydrogenation of the alloys with high magnesium contents including, in particular, the alloys based on R2Mg17 and RMg12. Some methods for the improvement of the hydrogen sorption properties of magnesium-based composites and the influence of various additions are studied. It is shown that the indicated properties of the composites depend on the duration of grinding and the amount of added catalysts. In almost all cases, this influence is positive and the main parameters can increase by a significant fraction.
查看更多>>摘要：We describe main achievements of the researchers from the Karpenko Physicomechanical Institute of the NAS of Ukraine in the field of formation of wear-resistant coatings and layers on aluminum and titanium alloys. The mechanisms of action of hydrogen, copper, and nickel on the synthesis of oxide-ceramic coatings in the process of plasma electrolytic oxidation (PEO) of aluminum alloys are established. We propose methods aimed at the intensification of synthesis, namely, by adding hydrogen peroxide and ozone to the electrolyte (to increase the oxygen content) and strengthening of the anodic current combined with weakening of the cathodic current, which leads to a decrease in the amount of hydrogen ions in the plasma channel. As a result of combination of these methods, the thickness of the PEO coatings would increase by 80% and the wear resistance would become 4-6 times higher. The metal-oxide composite layers based on corundum and containing copper or nickel inclusions are developed. The relationship between the sizes of metal inclusions and the energy of a separate discharge is established, which enables us to form nanosized copper and nickel inclusions. The influence of hydrogen formed as a result of decomposition of oil and water on the tribological behavior of "metal-PEO coating" contact couples is established, which enables one to make the friction coefficient of these tribocouples 5-20 times lower. The methods aimed at increasing the wear resistance of high-strength (alpha + beta)-titanium alloys and, in particular, of VT22 alloy, are developed. For the first time, it was established that the original (alpha + beta)-globular structure of VT22 alloy is most favorable for the process of gas nitriding. An approach to the intensification of gas nitriding based on the use of cold surface plastic deformation is also proposed. This enables one to lower the temperature and time parameters of nitriding and combine it with hardening thermal treatment of the alloy. It is shown that such a combined deformation-diffusion treatment provides higher tribotechnical characteristics of VT22 alloy. It is shown that the proposed combination of low-temperature oxynitriding with aging of VT22 alloy within a single technological cycle guarantees high fretting resistance of the analyzed alloy in a tribocouple with D16 alloy.
查看更多>>摘要：It is shown that the procedure of preliminary cyclic hydrogenation-dehydrogenation of ferrite-pearlite pipe steel strongly affects its ability to absorb electrochemical hydrogen whose amount increases with the number of these cycles. The concentration of hydrogen adsorbed by the subsurface layers of the metal, the concentration of hydrogen absorbed by the volume of the metal, and its total concentration in the metal are found depending on the number of hydrogenation-dehydrogenation cycles. It is established that, for the analyzed cases, the procedure of preliminary hydrogenation-dehydrogenation increases the ability of steel to absorb hydrogen by a factor of 1.2-2.
查看更多>>摘要：We propose a computational model for the evaluation of the effect of hydrogen on the level of creep strains in the metal in the complex stressed state and determine the stress-strain state of a thin-walled tubular specimen under the conditions of complex loading and creep in the process of hydrogenation of the metal. The influence of the loading mode on the time to fracture of the specimen is established. It is shown that the specimens subjected to tension with internal pressure fail faster (by 30%) than the specimens tested by uniaxial tension and that hydrogen decreases the service life of the material by about 14% for all loading modes.
NSTL
Springer Nature