The character of disruption of the rocks surface during rapid cooling

Abstract

The purpose of this study is investigation of the patterns of occurrence of the system of macro and microcracks in the rocks during rapid cooling for their effective softening.Methodology. The solution of the problem of crack system development is based on the fact that, as a result of rapid cooling in the surface layer of the rock, the tensile stresses are developed. The stretched layer acquires potential energy, depending on the modes of thermal influence and rock properties. At a certain point, the energy of the stretched layer starts to be spent on the forma tion of new surfaces of the growing system of macro and microcracks.findings. A model of behavior of the surface layer of rocks in the conditions of thermal shock by cooling is proposed. This model takes into account the development of a fracture macrocrack system and a microcrack system that move in the layer behind the cooling front. The dependence has been obtained that allows determining the penetration depth of a macrocrack system in the rock depending on the thermal exposure regimes and the physical and mechanical properties of the rocks. The formation of a microcrack system in the stretched cooled surface layer which changes its strength properties is experimentally proved. It is shown that the system of macrocracks moves into the array with deceleration and penetrates into the rock deeper than the thickness of the cooled layer, while microcracks are formed within the extended cooled layer. It is shown that the penetration depth of the macro crack system into the rock is practically independent of the mode of thermal shock by cooling and is determined by the physical and mechanical properties of the rock and the time of exposure. Increasing the potential energy of the stretched rock layer due to an increase in the temperature difference between heating and cooling ("toughening" of the thermal shock regime) leads mainly to an increase in the density of a cracking net on the rock surface. originality. For the first time the development of a crack system rather than a single crack in a rock during rapid cooling was considered. The model of the rock surface layer behavior under the conditions of rapid cooling is proposed. The geometric aspects of the initiation and propagation of a macrocrack system into the rock due to thermocycling loading are considered. The fact of initiation of a microcrack system along with macrocracks which change the strength properties of rock in the formation zone is proved.Practical value. The analytical dependence is obtained that allows determining the penetration depth of a crack system in rocks as a result of thermal shock by cooling. This dependence makes it possible to estimate the size of the damaged by macro and mi crocracks zone of a rock, as well as the degree of rock softening depending on its physical and mechanical properties and thermal shock modes of cooling. The results are used in real technological processes with thermocycling impact such as preparing rocks for mechanical destruction, hydraulic fracturing, ...

Methodology for Service Life Evaluation of Screens Welded Structures

“…Development and improvement of scientific methods for calculating the design parameters of technological machines is one of the critical aspects of the research activity of the staff at the National Technical University Dnipro Polytechnic [1,2]. Thus, many works of university specialists reflect searching for scientific ways to optimize the parameters of reinforced thin-walled structures of machines based on modern computer modeling tools and computational experiments [3,4].…”