Materials Science Forum Vol. 968

Abstract: The research of the influence of technological modes has been carried out and the negative influence of contaminating impurities on the lead iodide crystallization process has been grounded. The new technological approach to PbI₂ single crystals growth has been proposed, which, unlike traditional methods, is based on increasing of the purity of the source components at the initial stage of technological process. The comparative analysis of the proposed growth technique with other known methods has been made, the efficiency of the purification operation of the Pb and I₂ source components for the obtention and properties of PbI₂ single crystals has been determined. The main types of defects during PbI₂ crystallization from the melt have been analyzed and technological approaches for elimination of the structural violations have been proposed.

Abstract: This article discusses the modern methods of physico-chemical properties of glass manufacturing, through the use of a wide spectrum of glass-forming. Description of the implementation of the staged methods of chemical-technological processes of silicate formation, implying the lowest energy consumption, in connection with the transition to the processing of secondary raw materials.

Abstract: The conditions for the formation of epoxy composite coatings filled with nanodispersed particles of fullerene black are investigated. The efficiency of the use of electromagnetic and ultrasonic radiation for modifying the composition based on the epoxy matrix has been confirmed. The paper describes the optimum composition and mode of formation of epoxy composite materials filled with fullerene black.

Abstract: In the course of operation or armed hostilities the span r.c. structures are subject to substantial damage and considerable reduction of their bearing capacity, especially under low-cycle repeated loading. In this connection it becomes necessary to renew their operation capacity and/or improve their bearing capacity. However, the current design standards contain no recommendations as to determination of the residual bearing capacity of such structures and calculation of their reinforcement. There are methods of the operation capacity renewal and reinforcement of the structures by increasing their sections adding metal or reinforced concrete elements. Still, the calculation methods of such reinforcement are also imperfect. It is proposed to renew operation capacity of such structures by strengthening their tensioned parts with CFRP; the performed experimental research will provide the basis for calculating bearing capacity of said structures with the aid of the deformation method improved by the authors.

Abstract: The paper considers the problem of the ultimate load finding for structures made of a material with different limits of tensile strength and compression. The modulus of elasticity under tension and compression is the same. It is assumed that upon reaching the ultimate strength, the material is deformed indefinitely. The calculations use a simplified material deformation diagram — Prandtl diagrams. The limiting state of a solid rectangular section under the action of a longitudinal force and a bending moment is considered. The dependences describing the boundary of the strength of a rectangular cross section are obtained. Formulas allowing the calculation of the values of the limit forces and under the action of which the cross section passes into the plastic state are derived. Examples of the analytical calculation of the maximum load for the frame and two-hinged arch are given. An algorithm is proposed and a program for calculating arbitrary flat rod systems according to the limit state using the finite element method is compiled. The proposed algorithm does not involve the use of iterative processes, which leads to an exact calculation of the maximum load within the accepted assumptions.

Abstract: Experience gained in design, erection and operation of span reinforced concrete structures has proved that practically all of them are subject to complex stress-strain state. At that, the researchers pay considerable greater attention to calculation of strength, deformation analysis and determination of crack resistance in normal cross-sections than to calculation of their support zones, including oblique sections, which results are generally taken into account for determining the section dimensions and the quantity of the cross reinforcement.

Abstract: Experimental studies of the stress-strain state of reinforced concrete and fiber-reinforced concrete beams under short-term and long-term loads were carried out. The tests were carried out on three series of beams of different types - from ordinary concrete, steel fiber concrete and combined section, when the lower zone of the beam with a height of 0.5h is made of steel fiber concrete, and the upper one is made of ordinary concrete. During short-term loading, the load was applied in steps with a 10-minute exposure at each step to failure or to a predetermined level of a continuously acting load. In the interval between the steps, the process of cracking was tracked. After reaching a given level of loading, the load was fixed and maintained unchanged with a spring cassette for 300 days. Deformations were measured using strain gauges and dial gauges. Deflections and relative deformations of the extreme upper and extreme lower fibers for three types of beams are determined. It has been established that stabilization of deflections in beams from steel fiber concrete occurs much earlier (100 days) than in beams made of ordinary concrete (175 days). Studies have shown that the beams of ordinary concrete in the process of long-acting load lowered the carrying capacity by 5.5%. The bearing capacity of steel concrete beams, in contrast, increased by 7.6%.

Abstract: The results of experimental studies of combined beams consisting of a stone part, reinforced with side reinforced concrete plates are given. Experimentally shown the viability of the proposed structures. The conditions for ensuring the combined action of a stone beam and a reinforced concrete plate are given. Cases are shown when one-sided plates can be used and when double-sided reinforced concrete plates can be used. A comparison of experimental data with the data calculated by the authors developed methods is given. A good agreement between theoretical and calculated data is shown.

Abstract: In real conditions, bearing elements of metal structures are often subjected to the effect, both external loads, and various aggressive medium, under the influence of which corrosion processes are developed. Corrosive processes with prolonged action lead to a decrease the working area of ​​the welds and accordingly connected elements. During the examination of the technical condition of existing metal structures operating in aggressive medium, it is often necessary to perform calculations to define the reserve of strength. In case of exhaustion of material strength it is necessary to develop measures to strengthen certain weakened elements. Herewith, the quantitative assessment of the reduction of the reliability of welds remains a matter that requires additional research. To study the change in the ratio of squares of metal elements under the influence of the prolonged action of various aggressive medium, specially directed experimental studies were carried out. The results of studies allowed to determine the reserves of the strength of the welded elements in relation to the welds themselves. The ability to determine the reliability of welds depending on the reduction of the area of ​​the welded metal elements increases the operational reliability of metal structures, which for a long time are exploited in aggressive medium.

Abstract: The main task of construction is providing buildings with the property to remain operable throughout the entire life cycle. The level of bearing capacity, both of individual structures and buildings as a whole, depends on many factors.