STRAIN LOCALIZATION PECULIARITIES AND DISTRIBUTION OF ACOUSTIC EMISSION SOURCES IN ROCK SAMPLES TESTED BY UNIAXIAL COMPRESSION AND EXPOSED TO ELECTRIC PULSES

Results of uniaxial compression tests of rock samples in electromagnetic fields are presented. The experiments were performed in the Laboratory of Basic Physics of Strength, Institute of Continuous Media Mechanics, Ural Branch of RAS (ICMM). Deformation of samples was studied, and acoustic emission (AE) signals were recorded. During the tests, loads varied by stages. Specimens of granite from the Kainda deposit in Kyrgyzstan (similar to samples tested at the Research Station of RAS, hereafter RS RAS) were subject to electric pulses at specified levels of compression load. The electric pulses supply was galvanic; two graphite electrodes were fixed at opposite sides of each specimen. The multichannel Amsy-5 Vallen System was used to record AE signals in the six-channel mode, which provided for determination of spatial locations of AE sources. Strain of the specimens was studied with application of original methods of strain computation based on analyses of optical images of deformed specimen surfaces in LaVISION Strain Master System.

Acoustic emission experiment data were interpreted on the basis of analyses of the AE activity in time, i.e. the number of AE events per second, and analyses of signals’ energy and AE sources’ locations, i.e. defects.

The experiment was conducted at ICMM with the use of the set of equipment with advanced diagnostic capabilities (as compared to earlier experiments described in [Zakupin et al., 2006a, 2006b; Bogomolov et al., 2004]). It can provide new information on properties of acoustic emission and deformation responses of loaded rock specimens to external electric pulses.

The research task also included verification of reproducibility of the effect (AE activity) when fracturing rates responded to electrical pulses, which was revealed earlier in studies conducted at RS RAS. In terms of the principle of randomization, such verification is methodologically significant as new effects, i.e. physical laws, can be considered fully indubitable if they prove stable when some parameters of the experiment are changed. Parameters may be arbitrarily modified within a small range, and randomization is thus another common statistical significance criterion for sample sets obtained at the same conditions. At ICMM, the experiments were conducted in compliance with the principle of randomization [Bogomolov et al., 2011]. In this respect, the material of specimens, loading conditions and characteristics of the electrical pulses source were similar to those in the experiments at RS RAS.

As evidenced by the experiments, during electromagnetic field stimulation, the AE activity is manyfold higher than the background activity before the impact. This supports the research results reviewed in [Bogomolov et al., 2011] concerning the AE activity increment of 20 % due to electric pulses in the field twice less strong than that in our experiments at ICMM.

The AE energy distribution analysis shows that cumulative distributions of the number of AE signals vs energy (i.e. the number of AE signals which energy exceeds a specified threshold value) are power-behaved. This is equivalent to the linear plot of distribution in log units of energy and relative events number, similarly to the case of Gutenberg–Richter law for earthquakes. It is noted that for the logarithmic graphs of distribution by energy, angular coefficients (b-factors) are somewhat different in the period of electric impact and in no-impact periods, which shows that the ratio of AE signals with higher energy indicators is increased in case of external impacts. Such a difference is most evident at the near-critical load when compression amounts to 0.94 fracturing stress value.

According to data from the AE source location system, it is revealed that impacts of the electric field are accompanied by redistribution of AE sources through the specimen volume when compression is below 0.9 maximum stress value, which corresponds to the stage of diffusive accumulation of defects. The location system can be effectively applied when events with high amplitudes are accumulated in sufficient number. In this regard, clustering of AE sources (defects) in the area of a future fault was recorded only during the measuring test when the AE activity was quite high at the constant load.

As shown by data from the optical diagnostics set of equipment, LаVision Strain Master System, deformation of a specimen takes place in a non-uniform pattern over its surface, which is manifested as consecutively propagating waves of localized strain. This conclusion contributes to the research results obtained earlier for rock samples under tension and compression [Panteleev et al., 2013b, 2013c, 2013d]. Localized axial strain waves and localized radial strain waves (when material particles move in the direction perpendicular to the compression direction) are concurrently observed. Such localized strain waves are ‘slow’ – they propagate at velocities that are by six or seven orders lower than the intrinsic velocity of sound propagation in the material. This observation correlates with the research results obtained earlier in studies of strain localization forms in the course of rock deformation [Zuev, 2011; Zuev et al., 2012].

When the loaded specimen is impacted by the electromagnetic field, maximum strain values are slightly decreased in comparison with those in the ordinary case (when only compressive load is applied). This trend seems to be a specific feature of changes in localization of deformation in the loaded rock samples impacted by electric pulses. Besides, the experiments demonstrate that a source of macro-destruction can be induced by the influence of an external electromagnetic field, and the growth of a nucleus of such source can be stabilized during the impact. The above conclusions correlate with the statistical model of a solid body with defects which is developed in ICMM [Panteleev et al., 2011, 2012, 2013a].

1. Arakawa M., Petrenko V.F., Chen C., 2003. Effect of direct-and alternating-current electric fields on friction between ice and metals. Canadian Journal of Physics 81 (1–2), 209–216. http://dx.doi.org/10.1139/p03-020.

2. Avagimov A.A., Zeigarnik V.A., 2008. Estimation of the triggering effect energy in relation to model sample failure. Izvestiya, Physics of the Solid Earth 44 (1), 69–72. http://dx.doi.org/10.1134/S1069351308010096.

3. Avagimov A.A., Zeigarnik V.A., Klyuchkin V.N., 2006. On the structure of acoustic emission of model samples in response to an external energy action. Izvestiya, Physics of the Solid Earth 42 (10), 824–829. http://dx.doi.org/10.1134/S1069351 306100065.

4. Bogomolov L.M., Avagimov A.A., Sychev V.N., Sycheva N.A., Zeigarnik V.A., Bragin V.D., 2005. On manifestation of electrically triggered seismicity at the Bishkek test site (on the way toward active seismoelectrical monitoring). In: S.V. Goldin (Ed.), Active geophysical monitoring of the Earth's lithosphere. Publishing House of SB RAS, Novosibirsk, p. 112–116 (in Russian) [Богомолов Л.М., Авагимов А.А., Сычев В.Н., Сычева Н.А., Зейгарник В.А., Брагин В.Д. О проявлениях электротриггерной сейсмичности на Бишкекском полигоне (на пути к активному сейсмоэлектрическому мониторингу) // Активный геофизический мониторинг литосферы Земли / Ред. С.В. Гольдин. Новосибирск: СО РАН, 2005. С. 112–116].

5. Bogomolov L.M., Il'ichev P.V., Sychev V.N., Zakupin A.S., Novikov V.A., Okunev V.I., 2004. Acoustic emission response of rocks to electric power action as seismicelectric effect manifestation. Annals of Geophysics 47 (1), 65–72. http:// dx.doi.org/10.4401/ag-3259.

6. Bogomolov L., Zakupin A., 2008. Do electromagnetic pulses induce the relaxation or activation of microcracking rate in loaded rocks? Solid State Phenomena 137, 199–208.

7. Bogomolov L.M., Zakupin A.S., Sychev V.N., 2011. Electric Impacts on the Earth Crust and Variations of Weak Seismicity. LAP Lambert Academic Publishing, Saarbrücken, 408 p. (in Russian) [Богомолов Л.М., Закупин А.С., Сычев В.Н. Электровоздействия на земную кору и вариации слабой сейсмичности. Саарбрюкен: LAP Lambert Academic Publishing, 2011. 408 c.].

8. Chelidze T., Gvelesiani A., Varamashvili N., Devidze M., Chikchladze V., Chelidze Z., Elashvili M., 2004. Electromagnetic initiation of slip: laboratory model. Acta Geophysica Polonica 52 (1), 49–62.

9. Chelidze T., Lursmanashvili O., 2003. Electromagnetic and mechanical control of slip: laboratory experiments with slider system. Nonlinear Processes in Geophysics 10 (6), 557–564. http://dx.doi.org/doi:10.5194/npg-10-557-2003.

10. Chelidze T., Varamashvili N., Devidze M., Tchelidze Z., Chikhladze V., Matcharashvili T. 2002. Laboratory study of electromagnetic initiation of slip. Annals of Geophysics 45 (5), 587–598. http://dx.doi.org/10.4401/ag-3532.

11. Finkel V.M., 1977. Physical Basis of Fracture Deceleration. Metallurgia, Moscow, 359 p. (in Russian) [Финкель В.М. Физические основы торможения разрушения. М.: Металлургия, 1977. 359 с.].

12. Freund F., 2000. Time-resolved study of charge generation and propagation in igneous rocks. Journal of Geophysical Research 105 (B5), 11001–11020. http://dx.doi.org/10.1029/1999JB900423.

13. Frid V., Rabinovitch A., Bahat D., 2003. Fracture induced electromagnetic radiation. Journal of Physics D: Applied Physics 36 (13), 1620–1628. http://dx.doi.org/10.1088/0022-3727/36/13/330.

14. Grigorov O.N., 1973. Electrokinetic Phenomena. LGU, Leningrad, 196 p. (in Russian) [Григоров О.Н. Электрокинетические явления. Л.: Изд-во ЛГУ, 1973. 196 с.].

15. Kocharyan G.G., Kulyukin A.A., Pavlov D.V., 2006. Specific dynamics of interblock deformation in the Earth's crust. Russian Geology and Geophysics 47 (5), 667–681.

16. Manzhikov B.Ts., Bogomolov L.M., Il’ichev P.V., Sychev V.N., 2001. Structure of acoustic and electromagnetic emission signals on axial compression of rock specimens. Geologiya i Geofizika (Russian Geology and Geophysics) 42 (10), 1690– 1696 (in Russian)

17. Mugele F., Klingner A., Buchrle J., 2005. Electrowetting: a convenient way to switchable wettability patterns. Journal of Physics Condensed Matter 17 (9), S559. http://dx.doi.org/10.1088/0953-8984/17/9/016.

18. Panteleev I.A., Plekhov O.A., Naimark O.B., 2011. Self-similarity mechanisms of damage growth in solids experiencing quasi-brittle fracture // Computational Continuum Mechanics 4 (1), 90–100. http://dx.doi.org/10.7242/1999-6691/2011.4.1.8.

19. Panteleev I.A., Plekhov O.A., Naimark O.B., 2012. Nonlinear dynamics of the blow-up structures in the ensembles of defects as a mechanism of formation of earthquake sources. Izvestiya, Physics of the Solid Earth 48 (6), 504–515. http://dx.doi.org/10.1134/s1069351312060055.

20. Panteleev I.A., Plekhov O.A., Naimark O.B., 2013a. Model of geomedia containing defects: collective effects of defects evolution during formation of potential earthquake foci. Geodynamics & Tectonophysics 4 (1), 37–51 (in Russian) [Пантелеев И.А., Плехов О.А., Наймарк О.Б. Модель геосреды с дефектами: коллективные эффекты развития несплошностей при формировании потенциальных очагов землетрясений // Геодинамика и тектонофизика. 2013. Т. 4. № 1. С. 37–51]. http://dx.doi.org/10.5800/GT-2013-4-1-0090.

21. Panteleev I.A., Uvarov S.V., Naimark O.B., 2013b. Spatio-temporal forms of strain localization in tension of sylvinite. In: Proceedings of the 5th International conference of young scientists and students “Modern equipment and technologies in research”. Bishkek, p. 208–211 (in Russian) [Пантелеев И.А., Уваров С.В., Наймарк О.Б. Пространственно-временные формы локализации деформации при растяжении сильвинита // Материалы докладов 5-й междуна-родной конференции молодых ученых и студентов «Современная техника и технологии в научных исследованиях». Бишкек, 2013. С. 208–211].

22. Panteleev I.A., Uvarov S.V., Naimark O.B., Evseev A.V., Pan’kov I.L., 2013c. Peculiarities of spatio-temporal strain localization and tensile fracture of sylvinite. In: Proceedings of the Russian National scientific conference of graduate students and young scientists with scientific school elements “Miners’ Shift 2013”. Novosibirsk, p. 145–148 (in Russian) [Пантелеев И.А., Уваров С.В., Наймарк О.Б., Евсеев А.В., Паньков И.Л. Особенности пространственно-временной локализации деформации и разрушения при растяжении сильвинита // Сборник трудов Всероссийской научной конференции для студентов, аспирантов и молодых ученых с элементами научной школы «Горняцкая смена-2013». Новосибирск, 2013. С. 145–148]

23. Panteleev I.A., Uvarov S.V., Naimark O.B., Evseev A.V., Pan’kov I.L., Asanov V.A., 2013d. Experimental investigation of strain localization and rock fracture under direct uniaxial tension. In: Proceedings of the International Conference “Hierarchical systems of organic and inorganic nature”. ISPMS SB RAS. Tomsk, p. 386–389 (in Russian) [Пантелеев И.А., Плехов О.А., Уваров С.В., Наймарк О.Б., Евсеев А.В., Паньков И.Л., Асанов В.А. Экспериментальное исследование локализации деформации и разрушения горных пород в условиях прямого одноосного растяжения // Иерархически организованные системы живой и неживой природы: Материалы международной конференции, Томск, 9–13 сентября 2013 г. Томск: ИФПМ СО РАН, 2013. С. 386–389].

24. Petrenko V.F., 1994. The effect of static electric fields on ice friction. Journal of Applied Physics 76 (2), 1216–1219. http://dx.doi.org/10.1063/1.357850.

25. Shpeizman V.V., Zhoga L.V., 2005. Kinetics of failure of polycrystalline ferroelectric ceramics in mechanical and electric fields. Physics of the Solid State 47 (5), 869–875. http://dx.doi.org/10.1134/1.1924847.

26. Smirnov V.B., Zavyalov A.D., 2012. Seismic response to electromagnetic sounding of the Earth’s lithosphere. Izvestiya, Physics of the Solid Earth 48 (7–8), 615–639. http://dx.doi.org/10.1134/S1069351312070075.

27. Sobolev G.A., Ponomarev A.V., 2003. Physics of Earthquakes and Precursors. Nauka, Moscow, 270 p. (in Russian) [Соболев Г.А., Пономарев А.В. Физика землетрясений и предвестники. М.: Наука, 2003. 270 с.].

28. Sobolev G.A., Ponomarev A.V., Koltsov A.V., Kruglov A.A. et al., 2006. The effect of water injection on acoustic emission in a long-term experiment. Russian Geology and Geophysics 47 (5), 608–621.

29. Stavrogin A.N., Protosenya A.G., 1979. Plasticity of Rocks. Nedra, Moscow, 301 p. (in Russian) [Ставрогин А.Н., Протосеня А.Г. Пластичность горных пород. М.: Недра, 1979. 301 с.].

30. Surkov V.V., 2000. Electromagnetic Effects during Earthquakes and Explosions. MIFI, Moscow, 237 p. (in Russian) [Сурков В.В. Электромагнитные эффекты при землетрясениях и взрывах М.: МИФИ, 2000. 237 с.].

31. Sutton M.A., Orteu J.J., Schreier H.W., 2009. Image Correlation for Shape, Motion and Deformation Measurements: Basic Concepts, Theory and Applications. Springer, 316 p.

32. Sutton M.A., Wolters W.J., Peters W.H., Ranson W.F., McNeil S.R., 1983. Determination of displacements using an improved digital correlation method. Image and Vision Computing 1 (3), 133–139. http://dx.doi.org/10.1016/0262-8856(83)90064-1.

33. Sychev V.N., Avagimov A.A., Bogomolov L.M., Zeigarnik V.A., Sycheva N.A. et al., 2008. On trigger effects of electromagnetic pulses on minor seismicity. In: Geodynamics and Stress State of the Earth's Interior. Publishing House of Mining Institute of SB RAS, Novosibirsk, p. 179–188 (in Russian) [Сычев В.Н., Авагимов А.А., Богомолов Л.М., Зейгарник В.А., Сычева Н.А. и др. О триггерном влиянии электромагнитных импульсов на слабую сейсмичность // Геодинамика и напряженное состояние недр Земли. Новосибирск: Изд-во Института горного дела СО РАН, 2008. С. 179– 188].

34. Sychev V.N., Bogomolov L.M., Rybin A.K., Sycheva N.A., 2010. Influence of Earth’s crust electromagnetic soundings on seismicity at the Bishkek geodynamic test site. In: V.V. Adushkin, G.G. Kocharyan (Ed.), Trigger effects in geosystems. GEOS, Moscow, p. 316–326 (in Russian) [Сычев В.Н., Богомолов Л.М., Рыбин А.К., Сычева Н.А. Влияние электромагнитных зондирований земной коры на сейсмический режим территории Бишкекского геодинамического полигона // Триггерные эффекты в геосистемах / Под ред. В.В. Адушкина, Г.Г. Кочаряна. М.: ГЕОС, 2010. С. 316–326].

35. Tarasov N.T., 1997. Variations of the Earth’s crust seismicity under electrical action. Doklady AN 353 (4), 542–545 (in Russian) [Тарасов Н.Т. Изменение сейсмичности коры при электрическом воздействии // Доклады АН. 1997. Т. 353. № 4. С. 542–545].

36. Tarasov N.T., Tarasova N.V., Avagimov A.A., Zeigarnik V.A., 1999. Influence of strong hydrodynamic pulses on seismicity of Central Asia and Kazakhstan. Vulkanologiya i Seismologiya (4–5), 152–160 (in Russian) [Тарасов Н.Т., Тарасова Н.В., Авагимов А.А., Зейгарник В.А. Воздействие мощных электромагнитных импульсов на сейсмичность Средней Азии и Казахстана // Вулканология и сейсмология. 1999. № 4–5. С. 152–160].

37. Urusovskaya A.A., Alshitz V.I., Bekkauer N.N., Smirnov A.E., 2000. Deformation of NaCl crystals under combined action of magnetic and electric fields. Physics of the Solid State 42 (2), 274–276. http://dx.doi.org/10.1134/1.1131196.

38. Yakovitskaya G.E., 2008. Methods and Technological Means for Diagnostics of Rocks Critical State on the Basis of Electromagnetic Emission. Parallel, Novosibirsk, 315 p. (in Russian) [Яковицкая Г.Е. Методы и технические средства диагностики критических состояний горных пород на основе электромагнитной эмиссии. Новосибирск: Параллель, 2008. 315 с.].

39. Zakupin A.S., 2010. Geoacoustic observations in boreholes in the territory of the Bishkek geodynamic test site. In: V.V. Adushkin, G.G. Kocharyan (Eds.), Trigger Effects in Geosystems. GEOS, Moscow, p. 277–285 (in Russian) [Заку-пин А.С. Геоакустические наблюдения в скважинах на территории Бишкекского геодинамического полигона // Триггерные эффекты в геосистемах / Под ред. В.В. Адушкина, Г.Г. Кочаряна. М.: ГЕОС, 2010. С. 277–285].

40. Zakupin A.S., Alad’ev A.V., Bogomolov L.M., Borovsky B.V., Il’ichev P.V., Sychev V.N., Sycheva N.A., 2006b. Relationship between electric polarization and acoustic emission of geomaterials specimens under uniaxial compression. Vulkanologiya i Seismologiya (6), 22–33 (in Russian) [Закупин А.С., Аладьев А.В., Богомолов Л.М., Боровский Б.В., Ильичев П.В., Сычев В.Н., Сычева Н.А. Взаимосвязь электрической поляризации и акустической эмиссии образцов геоматериалов в условиях одноосного сжатия // Вулканология и сейсмология. 2006. № 6. С. 22–33.]

41. Zakupin A.S., Avagimov A.A., Bogomolov L.M., 2006a. Responses of acoustic emission in geomaterials to the action of electric pulses under various values of the compressive load. Izvestiya, Physics of the Solid Earth 42 (10), 830–837. http://dx.doi.org/10.1134/S1069351306100077.

42. Zhurkov S.N., Kuksenko V.S., Petrov V.A. et al., 1977. On prediction of rock fracturing. Izvestiya AN SSSR, seriya Fizika Zemli (6), 11 18 (in Russian) [Журков С.Н., Куксенко B.C., Петров В.А. и др. О прогнозировании разрушения горных пород // Известия АН СССР, серия Физика Земли. 1977. № 6. С. 11–18].

43. Zhurkov S.N., Kuksenko V.S., Petrov V.A. et al., 1980. Concentration criterion of volumetric fracturing of solids. In: Physical processes in Earthquake Sources. Nauka, Moscow, p. 78–86 (in Russian) [Журков С.Н., Куксенко B.C., Петров В.А. и др. Концентрационный критерий объемного разрушения твердых тел // Физические процессы в очагах землетрясений. М.: Наука, 1980. С. 78–86].

44. Zuev L.B., 1990. Physics of Electroplasticity of Alkali Halide Crystals. Novosibirsk, Nauka, 120 p. (in Russian) [Зуев Л.Б. Физика электропластичности щелочно-галоидных кристаллов. Новосибирск: Наука, 1990. 120 с.].

45. Zuev L.B., 2011. Autowave model of plastic flow. Physical Mesomechanics 14 (5–6), 275–282. http://dx.doi.org/10.1016/ j.physme.2011.12.006.

46. Zuev L.B., Barannikova S.A., Nadezhkin M.V., Zhigalkin V.M., 2012. Laboratory observation of slow movements in rocks. Journal of Applied Mechanics and Technical Physics 53 (3), 467–470. http://dx.doi.org/10.1134/S0021894412030200.