Vasiliev D. L., Livak O.V., Kravets V. I., Gankevich V. F., Kuts O.V. About ultimate tensile stresses as a criterion for the rock destruction at shock cooling

Details
Parent Category: Geo-Technical Mechanics, 2020
Category: Geo-Technical Mechanics, 2020, № 150

Geoteh. meh. 2020, 150, 127-135

https://doi.org/10.15407/geotm2020.150.127

 

ABOUT ULTIMATE TENSILE STRESSES AS A CRITERION FOR THE ROCK DESTRUCTION AT SHOCK COOLING

1Vasiliev D. L., 2Livak O.V., 2Kravets V. I., 3Gankevych V. F., 3Kuts O.V.

1Institute of Geotechnical Mechanics named by N. Poliakov of National Academy of Sciences of Ukraine, 2Ukrainian State University of Chemical Technology, 3National Technical University Dnipro Polytechnic

UDC 622.026.7.3.

Language: Russian

Annotation.

The purpose of the research was to estimate a possibility of using the generally accepted criterion of the rock destruction - the tensile strength σt obtained by mechanical tests - for the processes of cracking of the surface layer of the massif at its shock cooling. The authors analyze main methods of obtaining σt for various types of mechanical tests: direct tension, crushing of samples of irregular shape, plates fissuring from the outside, crushing of cylindrical samples along the generatrix by external pressure, crushing of samples by internal pressure, cross-bending of rock disks supported along the contour. In the article, a significant dependence of tensile strength on mechanical loading schemes is shown. Real stresses arising in the rock at shock cooling are compared with stresses obtained by standard tests. It is experimentally established that the analyzed temperature differences can lead to the appearance of only rare single cracks in the glass. For the formation of macrocracks in the granite rock, higher values of temperature difference are necessary. The issue of critical tensile stresses is considered with the assumption that there are cropping-out microcracks in the rock, which are developed in the field of all-around tensile stresses created in a thin surface layer. It is further established that ultimate stresses of the half-space layer depend on the presence and magnitude of microcracks in the rock. The values of the microcrack length are given for some rocks, which start to move under the action of temperature differences within the range of 100-600 °C. It is noted that, for example, for granite, lengths of natural microcracks in the rocks, which are most sensitive to thermal destruction, begin to grow at stresses created at temperature differences within the range of 100-400 °C, which is close to practical conditions. Based on the results, it is shown that it is inexpedient to use standard indicators of the rock tensile strength for evaluating the processes of the rock surface cracking at thermal shock cooling, since actual destruction of the surface layer of the rocks occurs at tensile stresses significantly exceeding the standard ultimate stresses.

Key words:

rock, thermal stresses, intensive cooling, microcrack system.

References:

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About the authors

Vasyliev Dmytro Leonidovych, Doctor of Technical Sciences (D.Sc.),  Researcher pn the Department of Elastomeric Component Mechanics of Mining Machines,  Institute of Geotechnical Mechanics named by N. Poliakov of National Academy of Sciences of Ukraine (IGTM, NAS of UKRAINE), Dnipro, Ukraine

Livak Oksana Viktorivna, Master of Science, Assistant of the Department of Material Science, Ukrainian State University of Chemical Technology, Dnipro, Ukraine, This email address is being protected from spambots. You need JavaScript enabled to view it.

Kravets Vasyl Ivanovych,Candidate of Technical Sciences (Ph.D), Associate Professor in the Department of Material Science, Ukrainian State University of Chemical Technology, Dnipro, Ukraine.

Gankevych Valentyn Feodosiiovych, Candidate of Technical Sciences (Ph.D), Associate Professor in the Department of Mining Machines, National Technical University “Dnipro Polytechnic” (NTU «DP»), Dniprо, Ukraine,  This email address is being protected from spambots. You need JavaScript enabled to view it.

Kuts Oleksandra Vadymivna, student of National Technical University “Dnipro Polytechnic” (NTU «DP»), Dniprо, Ukraine, This email address is being protected from spambots. You need JavaScript enabled to view it. .