Abstract: The quality of heat-exchange tubes is one of the most important factors affecting the technical condition and the durability of steam generators at nuclear power plants. The combined influence of the aggressive environment and stresses in heat-exchange tubes during the exploitation of steam generators leads to corrosive cracking of tubes. This results from the residual stresses (RS) stretching tube walls. The production of heat-exchange tubes involves the following operations: boring and grinding hot-rolled pipe billet, cold rolling middle-sized pipes, heating, rolling final-sized pipes, straightening, electro-polishing the inner surface and burnishing the outer surface, checking the final quality. The operation modes of straightening and burnishing predetermine the residual stresses in pipes in the delivery state. The paper presents the results of the studies on the residual stresses and surface hardening caused by the finishing operations. The paper also shows the need for exceptions to the production techniques for heat-exchange pipes, i.e. a series of operations increasing tensile residual stresses.
Abstract: In each particular material the hierarchical peculiarities of defects indicate the corresponding hierarchical peculiarities of mechanisms of damage and limit states accumulation. In accordance with the points of view of V.S. Ivanova, V.V. Bolotin, A.A. Shanyavsky, L.I. Tushinsky, O.B. Naymark, V.V. Lepov, A.A. Bataev, the occurrence of the limiting state on a particular structural level is possible in case of accumulation on it of the ultimate concentration of defects of a certain kind. In such case the “established system” gets a new, additional degree of freedom, which promotes change of the prevailing mechanism of damage accumulation. The acceptability of this concept has been previously determined for a limited range of materials, which usually don’t have evident structural and mechanical heterogeneity. Thus, the extension of available results to the structurally heterogeneous materials and especially to the welded joints of such materials turned out to be a very difficult task. However, the concept of maximum (critical) level of damage accumulation on a particular scale level was introduced not so long ago. When assessing structural and mechanical heterogeneities of the structural material, an important role is played by concepts of similarity of mechanical phenomena, self-similarity of deformation and destruction processes and by the scale factor of reliability, which are considered in their historical development as a part of application of fractal concepts in the materials science. The application of complex synthesized approach (consisting of a set of diagnostic methods in the form of scanning electron microscopy and multifractal parametrization of materials microstructures) for detection of potentially hazardous zones of welded joints with the highest level of structural and mechanical heterogeneity was the main ideology of our study. In order to establish the cause-and-effect relationships of appearance of “macro-corrugations” on the surface of the material, the analysis of the structure of heterogeneous welded joints represented as a hierarchically organized system was performed.
Abstract: Both welded joints and base metal are arranged at different structural-scale levels. Unlike the base metal, welded joint can have structural inclusions of complex composition and spatial geometry. During simulation and forecasting of behavior of various characteristics and properties, welded joints quality assessment is not possible without performance of corresponding metallographic studies. The article discusses the non-metallic inclusions in the oxide and silicate types welding joints and their influence on the formation of the metal mechanical properties.
Abstract: The use of external physical actions (vibration, ultrasound, etc.) on molten metals is a safe way to change the structure and properties of metals and alloys. Such processing contributes to the formation of a fine structure with an increased level of strength properties. The work covers the results of a relatively new method of molten metals processing with electromagnetic pulses. It shows the results of processing pure metals of zinc and aluminum. The increase in strength properties and the decrease in porosity of the casts have been registered. The article also contains the empiric results of steel rods hot zincing. The zinc alloy was exposed to irradiation directly in the hot zincing bath.
Abstract: The article describes the methods of laser cementation of the edge wood-cutting tools. There are the results of the experimental study of the described methods in the article. The most acceptable method of treatment from the point of view of the results reproducibility and the possibility of industrial use are determined.
Abstract: The urgency of a new process development of cold forming of high-strength flange bolts has been shown in the article. It also points out some shortcomings of existing technologies. To improve the quality of bolts a new instrument design was developed. The research of the working tool identification impact on its resistance and stress-strain state of the workpiece was carry out. The software package DEFORM, designed for process simulation of metal forming is used in the article. The mathematical and computer modeling technology bolt stamping with flange was applied to carry out the study. Based on the conducted theoretical and experimental studies a new technology for manufacturing the flange bolts is patented.
Abstract: The use of prefabricated mini silo structures enables us to build containers for grain or animal feed and to transport the structural elements to the installation site. Traditional types of strengthening of concrete structures are steel and concrete cages. Polymer materials are widely used in construction. The methods of strengthening modern materials, such as lamellae, are being increasingly used. The issue of strengthening the structures with composite polymer materials is relevant.
Abstract: One of the work cycles of reinforced concrete structures is the state of repair and reconstruction, including the steps of strengthening elements. The traditional types of strengthening of reinforced concrete which are steel and concrete collars and shirts - now are receding into the background. New methods of strengthening with modern materials such as lamellae are increasingly being used. The article deals with the issues related to strengthening the structures made of high-strength concrete using composite polymeric materials.
Abstract: The practical expediency of the study of physical and mechanical properties of concrete, received from the mix, exposed at its feeding to the point of placement to the transportation with the inertia conveyor by means of original technology, which shows its competitiveness at factories producing precast concrete units, is proved. The experimental procedures of the research performed by the authors, where they analyzed the process of transportation relating to the use of ready-mix concrete on the dense aggregate, are described. The data on the effect of received previously rational values of the major parameters of engineering process studied (the parameters of asymmetric oscillations of work member of the conveyor and the thickness of the mix layer moved by it) both on the homogeneity of fresh concrete and the strength and strength homogeneity of hardened concrete are represented and analyzed.
Abstract: Often, when it is necessary to fill formwork space in confined working conditions with limited operational control in some engineering solutions the special materials for injection are used. In this case, it is advisable to use high-fluidity concrete mixes made with К-cement, regulator of the kinetics of structure formation, superplasticizer and gas-forming admixture. The gas-forming admixture obtains of expansion of fresh-concrete during first stage. The special sulfo-alumina additive in K-cement obtains of expansion of hardening concrete during second stage. The main regularities in the formation of the structure and properties of cement stone are considered. The dependences "composition-technology-structure-properties" for concretes with two-stage expansion are clarified. The main provisions for determination of mix proportion for concrete are proposed. The quantitative relationships between the construction properties of concretes and prescription and technological factors are obtained.