Members of the Faculty of Geology of the Lomonosov Moscow State University together with their colleagues have studied the stages of rock deformation. They have revealed a criterion, with the help of which you could predict the critical stage of fracture when the rock destroys. The research results have been published in the Interpretation.
The scientists have established that the stages of the deformation process are essentially different in the character of defect accumulation inside rocks.
Dmitry Korost (Doctor of Geological and Mineralogical Sciences, a Research Fellow both at the Department of Geology and Geochemistry of Fossil Fuels and joint UNESCO – Faculty of Geology of the Lomonosov Moscow State University Scientific Training Center), being one of the article authors shares: "At first defects are generated randomly and their size is determined by a typical structural element of a material (for instance, a grain in granite). Afterwards there is the turn for generation of such defects, whose sizes are not determined by the material structure. Interaction between these two defect types causes critical defects, capable of self-development. By all appearances, the loss of sample integrity occurs as a result of the evolution of a set of critical defects."
It has turned out that deformation stages could be distinguished by the type of energy distribution of acoustic emission signals. Acoustic emission is an inspection technique for material integrity, basing on recording elastic waves, emerging in the process of redevelopment of solid body structure under the influence of mechanical stimuli. A structural change (for instance, fracture emergence) provokes an elastic wave, registered by a sensor.
Energy distribution of acoustic emission signals is approximated by different types of functions. At the first stage, it's an exponential function while at the second one – a power-law function, predicting speedy destruction of a rock or material. The main finding is that alteration of the type of energy distribution of acoustic emission signals could be applied as a parameter of fracture transition to the critical stage.
The project involves studies of the destruction process of rocks with the help of acoustic emission and X-ray computer tomography. The authors from the Lomonosov Moscow State University provided 3D stereological models of emerging fractures.
At the end of the research, described in this article, the scientists have come to the following conclusion: "The revealed criterion could become useful in various situations: appraising the state of structures under load or the state of a rock massif at an operating mining venture. It's also applicable for earthquake forecasting. The criterion also allows to detect the space domain of an object, where localization of defect formation, leading to the object destruction, could occur."
The project has been done in cooperation with the specialists from the Ioffe Physical-Technical Institute of the Russian Academy of Sciences (Saint Petersburg) and Institute of Continuous Media Mechanics of the Ural Branch of Russian Academy of Science, Perm.