To find out the possibilities of crack configuration management in the course of its development under the conditions of external loading on the destroyed sample a series of laboratory experiments in a press was carried out by my colleague Kyu N.G. and me. Four separate organic glass blocks dimensioned 100×100×100 mm each one were used in the experiment and were fractured using plasticine. The purpose of the experiments was to find out general principles of crack formation in such conditions.
The first experiment was carried out without any external loading on the tested sample and served as the basis for the following comparisons. The plasticine charging was performed through a bore drilled out in the block center into its bottom-hole part by means of a special cylinder device held in this bore by thread. The bottom-hole pressure was measured by a manometer provided with a special adaptor placed on the opposite side of the block. In the course of the experiment it was found out that with the increase of the putty amount introduced into the crack and simultaneous growth of its dimensions the putty charge pressure decreases at the end and at the beginning of every separate stage of the experiment. Besides, the horizontal and vertical dimensions of the formed crack and also the zones of its filling with a plastic substance grow much the same in the nature with the result that the crack assumes a definite round-shape form. At the beginning of plasticine charging the pressure changed from 370 atm до 150 atm, and at the end - from 200 atm to 50 atm. The split of the sample followed the pressure downtick. In the course of carrying out the first experiment all the earlier educed principles of development of the crack formed using plastic substances transverse the shot hole axis in brittle materials were confirmed, they corresponding to the lack of external loading on the tested sample.
The second experiment was carried out at the vertical loading on the sample on the part of press. Because of technical failures (faulty seals in the system of oil charging) the loading varied fluently within the interval from 10 to 15 tons. A characteristic feature of the second experiment was an accelerated growth of the crack and the zone of its filling with the putty in the direction of loading appliance to the tested sample (vertical). At a light loading (10-15 tons) these changes were scarcely noticeable as usual measuring devices were used. The crack shape grew looking like an ellipse with the bigger side oriented in the vertical direction. As a result of the last charging a split of the block into two parts occurred. At the beginning of charging the pressure changed from 300 atm to 100 atm, and at the end - from 175atm to 50 atm. The split of the sample followed the pressure downtick.
The third experiment was carried out at the loading equal to 60-70 tons on the part of the press. At the moment of its being finished the pressure made 70 kgf/cm2. At the moment of unloading on the part of the press the pressure turned out to be at the level of 45kgf/cm2. After that the loading was fluently increased up to 60 tons. Under the loading the crack mainly grew in the vertical direction (the direction of loading appliance), and without it - in the horizontal direction, bringing its shape into proximity with a round. At the beginning of charging the pressure changed from 190 atm to 200 atm, and at the end - was at the level of 139 atm. The experiment was carried out up to the split of the sample into two parts.
The fourth experiment was carried out at the loading equal to 85 tons on the part of the press. Its characteristic feature was the fact that the pressure in the crack center fell slower than in the previous experiments. After ceasing the charging of plasticine and exposing the sample to the same loading - 85 tons for 15 minutes, the pressure in the crack center didn´t practically fall and became equal to 100 kgf/cm2. The crack ellipse changed the orientation from the vertical one at the beginning to the horizontal one at the end. A peculiarity of this experiment was the greatest vertical loading applied to the fractured sample and, as a consequence of it, the possibility of a better observation of the tendency educed by means of carrying out the previous experiments. At the beginning of charging the pressure was maintained at the level of 190 atm, and at the end - at about 110 atm. The experiment was carried out up to the split of the sample into two parts.
The educed principles can be successfully used at breaking out natural stone, the procurement of which is carried out under the conditions of mineral deposits´ underground mining method and great value rock pressure presence, using plastic substances.
The research was carried out with the assistance of the Russian Fundamental Research Fund Fellowship, "Leading Scientific Schools of Russia" - the scientific school of the corresponding member of the Russian Academy of Sciences Oparin V.N.: "Non-linear goemechanics foundations´ development for mineral mining and dressing efficiency and safety upgrading problems´ solution and energy-saturated impulse and vibration machines´ and mine fans´ creation. SS-3803.2008.5".
The work is submitted to Scientific Conference "The Problems of International Integration of Educational Standards", England (London) - France (Paris), April 20-28, 2009. Came to the Editor´s Office on 26.01.2009.