Results of studying the effect of a calcium modifier of 10KhSND low-alloy steel on its physicomechanical characteristics are presented. The rolled sheets of commercially produced shipbuilding steel, ...wherein before teeming during melting a ferroalumocalcium alloy was added, were used for investigation. The corrosion rate of examined steel in a model aggressive medium, as well as its fatigue resistance in salt water in torsion, axial loading, and bending tests against the calcium concentration, was elucidated. The effect of calcium concentrations on the austenite grain sizes and dispersity of nonmetallic inclusions, as well as the fracture toughness characteristics (critical stress intensity factor and crack opening) at different temperatures was examined. The microstructure of fracture facets of shipbuilding steel specimens of long-term service on brittle fracture along pearlite grains and ductile fracture along ferrite ones for as-received steel was revealed. Nonmetallic inclusions in specimen fractures of shipbuilding steel at different calcium concentrations were studied. Their quantity grows considerably with its service terms, which exerts negative influence on the corrosion and mechanical properties of the metal. The calcium alloying of steel is shown to contribute to its corrosion resistance and fracture toughness on long-term service in seawater. The recommendations are given as regards optimal modifier concentrations in the shipbuilding metal, which is consistent with minimum austenite grain sizes and dispersity of nonmetallic inclusions.
It was established that with increased concentrations of chlorides, sulfate-reducing bacteria, heterotrophic bacteria, thionic and iron bacteria the corrosion rate of the studied specimens of ...reinforcing steels sharply increases. The 40KhN and 09G2S steels had the highest resistance to corrosion, and the St.20 steel had the lowest resistance. The obtained data correlate with the results of numerical experiments reported in the publications of domestic and foreign researchers. For the first time, the data obtained from a series of experimental tests of reinforcing steels for cyclic strength showed that the steels characterized by low corrosion resistance also have a low resistance to cyclic strength, which can be explained by their degradation. The authors believe that, in the process of long-term operation of reinforced concrete structures in an aggressive environment, carbonization and chloritization of concrete, that is, its destruction occur. Further hydrogen charging of reinforced concrete causes embrittlement and reduction of the visco-plastic properties of the reinforcement, which in turn leads to the destruction of metal. The obtained results make it possible to develop metallurgical and technological measures to increase the durability of reinforced concrete structures: the use of chromium, nickel, and manganese alloyed steels for the manufacture of reinforcement with subsequent proper heat treatment; the use of modern high-strength concrete, which will ensure strong adhesion of concrete mortar to the surface of reinforcing bars.
The versions of nonlinear defining relations and characteristics of nonlinear fracture mechanics controlling and simulating the service life, survivability, and durability of parts of modern power ...and energy structures operating at low, cryogenic temperatures are investigated.
A mechanophysical model for crack growth kinetics computation on stress corrosion fracture of modified 06G2BA and 08KhMCHA pipe steels is adequately expressed through the plane stress-strain state
dα
.../
dt
and
dJ
/
dt
ratios that are dependent on the strain crack tip rate. The crack growth accelerated by an aggressive environment occurs under static and cyclic loading due to transient dissolution and repassivation processes at the crack tip. Such accelerations are divided into three categories, determined by the strain rate: mechanical cracking (fatigue crack and stationary plastic crack), corrosion-accelerated mechanical cracking (corrosion fatigue and corrosion-accelerated plastic crack), and sulfide stress corrosion fracture. Metallographic studies revealed the change in the crack nucleation and propagation mechanisms, from transcrystalline to intercrystalline, related to the viscoplastic and brittle structure of steel specimens cyclically loaded and simultaneously affected by a corrosive environment.
The results of the experimental study of the degradation of steel structures of sewer underground constructions are presented. The distribution of harmful gas elements (sulfur, hydrogen, oxygen) over ...the wall thickness of sewer pipes along corrosion defects in the form of pits, as well as the character of changes in the microhardness of the metal depending on the hydrogen content and service life, are shown. To confirm the metal softening with increasing hydrogen concentration, the stresses of the crystal lattice (distortion stresses) were measured.
Safety and survivability of equipment are regulated by the strength characteristics of its individual units and elements with possible initial or operational defects such as surface differently ...oriented semielliptical cracks. Numerical methods of calculation allow obtaining more information about the stress-strain state (SSS) of these elements using the specified calculation algorithms of the corresponding fracture models. A change in the SSS form near the crack contour during the transition from deeper points to surface points depends on the constraint of deformations along their front, i.e., on the 3D character of the SSS. The shape change of defects such as differently oriented surface semielliptical low-cycle cracks is diagnosed on the basis of the experimental results and numerical solutions. The finite element modeling data are implemented on the basis of macros of the ANSYS software package. In this paper, we study the development pattern of elastoplastic fracture under low-cycle loading. The proposed methodology is confirmed by the parametric equations of the shape change kinetics of the considered cracks using a fractographic surface analysis of their development. The surface morphological parameters of the developed defects are analyzed on the basis of the results of testing samples with semielliptical cracks under low-cycle loading. The results of measurements of the intensity fields of elastoplastic deformations at the crack tip and the geometric characteristics of the fracture surface development are presented. An analysis of the dynamics of the local stress-strain state near the contour of differently oriented defects in parts and structural units of equipment shows good agreement between the experimental parameters of the geometry of developing cracks and the parameters obtained by numerical methods. The presented parametric equations clarify the characteristics of nonlinear destruction mechanics that allow evaluating and predicting the survivability and safety performance of critical equipment. The deformation criteria of nonlinear destruction mechanics show the dependence of the fracture development on the 3D character of the stress-strain state that indicates the direction of the geometric development of the fracture surface shape.
The European Commission has recognized nanotechnologies as extremely promising for increasing competitiveness of different sectors of the economy. On account of climate changes and the quest for food ...security, they are an effective way of solving key problems in the agrarian sector. Nowadays nanotechnologies are widely used for creating nanofertilizers, nanoinsecticides, nanofungicides, nanoherbicides and other nanopreparations. Numerous researches affirm advantages of nanopreparations, which has helped them find a wide use in agricultural practice. At the same time, nanopreparations are the source of entry into the environment of nanoparticles (size less than 100 nm) which are characterized by large active surface and specific physical-chemical properties different from ordinary chemical substances. It is precisely this which determines their bioaccessibility, bioaccumulation and toxicity.
Recently, data about toxicity of nanoparticles for human and natural ecosystems have been accumulated. The results of a great deal of research affirm that they break the processes of photosynthesis, transpiration, mitosis, miosis and have a negative influence on colouring agents, proteins and carbohydrates.
The article is devoted to one of the most urgent problems of regional studies – the definition of the object-subject field of a new discipline. This article discusses the object and subject of ...research in regional studies, the relationship between regional studies and regional studies. Interest in this problem is due to the formation of theoretical regional studies and regional studies proper as a new direction of science. The author proposes to consider the region as a concept that reflects the most important properties of all types of phenomena – regions, territories, countries, associations of countries and the world as a whole - as geosocial systems. Despite the independence of countries as actors on the global stage, they are all integral parts of the world-system, being closely associated with it, as well as within themselves, by countless transactions that are collectively constituting the essence of the region, which in reality is а territorially determined (sub)system of division of labor. All local subsystems are hierarchically integrated into the world-the system of which they are genuine parts. The world-system is of maximum size of the object in regional studies, depending on which are subordinated all the problems of regional studies.
Registration of dynamic CT image sequences is a crucial preprocessing step for clinical evaluation of multiple physiological determinants in the heart such as global and regional myocardial ...perfusion. In this work, we present a deformable deep learning-based image registration method for quantitative myocardial perfusion CT examinations, which in contrast to previous approaches, takes into account some unique challenges such as low image quality with less accurate anatomical landmarks, dynamic changes of contrast agent concentration in the heart chambers and tissue, and misalignment caused by cardiac stress, respiration, and patient motion. The introduced method uses a recursive cascade network with a ventricle segmentation module, and a novel loss function that accounts for local contrast changes over time. It was trained and validated on a dataset of n = 118 patients with known or suspected coronary artery disease and/or aortic valve insufficiency. Our results demonstrate that the proposed method is capable of registering dynamic cardiac perfusion sequences by reducing local tissue displacements of the left ventricle (LV), whereas contrast changes do not affect the registration and image quality, in particular the absolute CT (HU) values of the entire CT sequence. In addition, the deep learning-based approach presented reveals a short processing time of a few seconds compared to conventional image registration methods, demonstrating its application potential for quantitative CT myocardial perfusion measurements in daily clinical routine.
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