Valeriy Aleksandrov, Svetlana Frolova, Anastasia Zozulia
Development Stages of the Cluster-Coagulation Model of Supercooled Metals Crystallization
Donbas National Academy of Civil Engineering and Architecture
Abstract. The paper analyzes the successive stages of crystallization during cooling of metal melts: clustering, nucleating, nucleus coagulation and mass solidification. The step listed are analyzed on the basis of cooling thermograms that cover both temperatures above and below the melting point (that is areas overheating and undercooling of melts). As a result of such studies, the following patterns were identified: a rapid transition from quasi-equilibrium crystallization with a practical absence of supercooling to non-equilibrium-explosive with significant supercooling; It is established that this effect is associated with a certain critical heating of the liquid phase; mean supercooling does not depend on a further increase in the heating of the melt above the critical temperature; The temperature range of the existence of clusters is related to the mesophase. The dependence equations of the Gibbs energy on temperature corresponding to each stage are derived. A scheme has been developed for the change in enthalpy of each crystallization stage. Results are consistent with the main provisions of the cluster-coagulation model of melt crystallization.
Keywords: melt, overheating, overcooling, clustering, nucleation, coagulation, crystal nuclei, crystallization, order parameter, Gibbs energy, enthalpy, nucleation work, crystallinity degree.
Pavel Solovej, Michail Lobov, Anatoly Perevarjuha, Alexander Chirva, Alina Belova
Geodetic Control Boom Sag of Delays Mast Structures in Operating Conditions
Donbas National Academy of Civil Engineering and Architecture
Abstract. The technology of geodetic control of the sag of the detachment of mast structures under operating conditions, using non-reflecting electronic tacheometers, is given. The proposed method allows effectively and accurately in a short period of time to determine the sag of the boom necessary to control the tension force of the braces and, if necessary, adjust it. The substantiation of the optimal marginal error of determining sag on the basis of the marginal error of determining the tension of delays is given. The accuracy of individual measurement sources was calculated, in particular, the effect of errors in angular and linear measurements on the accuracy of trigonometric leveling of mast construction delays. The influence of the error in guiding the telescope of the electronic total station to the center of the delay is considered.
Keywords: sag of delays, geodesic control, accuracy calculation.
Valery Alimov, Alla Shtykhno, Yuliya Kolchina
Changes in the Properties of High-Strength Sheet Steel in Subsequent Process Heatings
Donetsk National Technical University
Abstract. The paper presents the results of a study of the effect of controlled rolling and subsequent technological heating to various temperatures, including during welding, and the duration of exposure at the same time on the processes of structure formation in high-strength steel sheets EN36 and X70. It was found that when a thick sheet is redone into products, it is necessary to minimize temperature and time parameters in order to prevent softening processes. Welding, as one of the sources of technological heating, leads to a change in the structure in the heat-affected zone and uneven distribution of hardness over the cross section of welded joints, which reduces the equal strength of the structure as a whole. Short-term heating (about 15 minutes) even to a temperature above Ac1 (760 °C) and cooling in air in the weld zone does not lead to significant changes in structure and hardness, but the degree of homogeneity of the sheets being welded increases.
Keywords: sheet steel, controlled rolling, strength, structure formation, process heating, temperature and duration, softening.
Igor Garanzha, Pavel Zenkin
Coating Trusses On The Basis Of Steel Bent-Welded Profiles Filled With Concrete
Moscow State National Research University of Civil Engineering
Abstract. The article considers the question of the using expediency of «Molodechno»-type truss structures as a covering for buildings with an upper compressed belt made on the basis of cold-formed steel profiles filled with concrete according to the criteria of overall stability of its elements, the truss rigidity as a whole, and metal intensity and weight of coating structures. Using the finite element method implemented in the SCAD, software package, it was obtained the design forces in the elements of the upper truss belt, which became the basis for the selection of their cross sections in the classic steel and pipe-concrete variants based on the requirements of the overall stability under compression and flexural rigidity of the truss. Considering the design features of the truss joints operation of bent-welded profiles, it has been evaluated the possibility of reducing the cross section of the upper truss belt by adding concrete to them. The task of reducing material consumption has two ways to solve: reducing the profile thickness at constant dimensions, or reducing the height and width of the profile with constant wall thickness. On the basis of the obtained results it is revealed the degree of reduction of steel costs for trusses and increase in its weight, due to the appearance of concrete. It was made assumptions about the directions for further in-depth researches in the study of actual work and the stress-strain state of pipe-concrete trusses.
Keywords: steel trusses, cold-formed welded section, concrete-filled pipes, overall stability of compressed elements, truss rigidity, material consumption.