Blow-up regimes in failure of rock specimens

For damage evaluation, the stage of superfast catastrophic failure of a medium and its mechanical behavior in a state of self-organized criticality prior to the onset of a blow-up fracture mode is of great interest for identification of its precursors. In this work, the data of experimental and numerical investigations of mechanical behavior of a medium before its catastrophic failure and the onset of a blow-up fracture mode are presented. Rock samples and ceramic specimens are subjected to three-point bending and uniaxial compression testing. Surface velocities of the loaded specimens are registered using a laser Doppler vibrometer. The blow-up regime duration is measured to be about 10–20 ms. The specimens’ mechanical behavior is numerically simulated under experimental conditions, including the regime of catastrophic fracture. The model parameters of damage accumulation are determined from a comparison with the experimental data. A number of features of the material mechanical response before the catastrophic fracture are identified, which could be treated as failure precursors

Influence of Carbon Black Content on the Properties of Butadiene Elastomer

В работе приведены результаты исследования физико- механических свойств до и после термического старения, степени набухания в гидравлическом масле, а также температурные свойства эластомеров на основе бутадиенового каучука марки СКД-В в зависимости от содержания малоактивного печного технического углерода марки П‑803. С увеличением содержания технического углерода до 110 масс.ч. в эластомерной матрице происходит повышение относительного удлинения и условной прочности на разрыв, с дальнейшим увеличением содержания наблюдается снижение. С увеличением содержания технического углерода в резиновой смеси показатели плотности, твердости, условного напряжения и агрессивостойкости повышаются. После испытания на термическое старение наблюдается повышение плотности, твердости и условного напряжения, а относительное удлинение и предел прочности при разрыве снижаются. При помощи термомеханического анализатора установлено, что увеличение количества содержания технического углерода в резиновой смеси не оказывает существенного влияния на начало сегментальной подвижности эластомеров, но снижает изменение линейных размеров при повышении температуры. Методом дифференциально сканирующей калориметрии установлено, что изменение количества содержания технического углерода не влияет на среднюю температуру стеклования. При оптимальном содержании технического углерода наблюдается наиболее равномерное распределение частиц в объеме эластомерной матрицы без образования большого количества агломератов либо пустотThe paper presents the results of a study of physical and mechanical properties before and after thermal aging, aggressiveness, as well as the temperature properties of elastomers based on butadiene rubber grade SKD-V, depending on the content of low-activity furnace carbon grade P‑803. With an increase in the content of carbon black up to 110 wt.h. in the elastomeric matrix, an increase in relative elongation and conditional tensile strength occurs, with a further increase in the content, a decrease is observed. The results obtained after thermal aging of samples and their soaking in AMG‑10 hydraulic oil are considered. With an increase in the content of carbon black in the rubber compound, the indicators of density, hardness, conditional stress and aggressiveness increase. After the thermal aging test, an increase in density, hardness and nominal stress is observed, and the elongation and tensile strength decrease. Changing the amount of carbon black in the rubber mixture does not affect the beginning of the segmental mobility of the elastomer, but there is a decrease in the linear-temperature expansion of the samples. Using differential scanning calorimetry, it was found that a change in the amount of carbon black does not affect the glass transition temperature. Using electron microscopy, it was shown that at the optimum content of carbon black, the most uniform distribution of particles occurs in the volume of the elastomeric matrix without the formation of a large number of agglomerates or void

Experimental and numerical investigation of the catastrophic stage of failure on different scales from rock sample to coal mine

Doppler laser interferometry is used to measure the transient time between the slow quasistationary stage of damage accumulation in rock samples to the ultrafast catastrophic stage of failure as well as the duration of the autocatalytic stage of macroscopic fracture. Small rock samples are tested for compression and three-point bending, and the velocity of displacement of their lateral surfaces is measured up to macroscopic fracture. The surface velocity at the catastrophic stage proves to be three orders of magnitude higher than the average surface velocity at the quasi-stationary stage of damage accumulation. The transient time to catastrophic failure is estimated at 60–100 ms, and the duration of the ultrafast catastrophic failure stage is 15–20 ms for small marble samples. The transient stage is the process of self-organization of individual acts of fracture into the state of self-organized criticality. At this stage, the distribution of individual acts of fracture evolves into power-law distributions. A simple fracture model with power laws is proposed, which is in full agreement with the experimental data. The developed mathematical model is used to calculate fracture of small rock samples, reproducing uniaxial compression and three-point bending tests, as well as fracture in rock masses with mine openings. We also model the process of faulting and fracturing in the mountains of Central Altai, including the foreshock process, main event (the Chuya earthquake of September 27, 2003) and aftershock process. The calculated seismic process fully corresponds to the Gutenberg–Richter recurrence law, and the calculated aftershock process conforms to the Omori law

Напряженно-деформированное состояние фрикционных соединений с лазерной обработкой контактных поверхностей

Введение. Исследованы возможности применения лазерной очистки в качестве альтернативного способа. Лазерные установки зарекомендовали себя во многих сферах и представляют собой высокотехнологичное и эффективное решение для многих строительных задач. Несмотря на это в настоящее время распространенным методом обработки контактных поверхностей высокопрочных болтовых соединений остается пескоструйная обработка - устаревшая технология, с высоким износом оборудования, опасная для здоровья людей. Материалы и методы. Образцы, обработанные пескоструйным и лазерным методами, испытывали на сдвиг. Перед испытаниями проверены шероховатость контактных поверхностей и усилие натяжения высокопрочных метизов. В ходе испытаний снимались показания силоизмерителя и датчика часового типа. Эксперименты проводились на прессе гидравлическом ИПС-500, образцы были предоставлены в обработанном виде. Результаты. По полученным данным построены графики деформации и вычислены усилия сдвига образцов. Вычисленные усилия сравнивались с нормативными значениями. Результаты показали соответствие образцов требованиям СП 35.13330.2016 «Мосты и трубы» по прочностным характеристикам. Образцы с лазерной очисткой поверхности имели значение запаса прочности, аналогичное образцам с пескоструйной обработкой. Выводы. Сопоставление прочностных характеристик доказывает возможность применения лазерной очистки контактных поверхностей фрикционных соединений. После перехода от устаревших технологий процесс подготовки поверхностей можно будет сделать экономичным и экологичным. Полученные значения и данные возможно внести в ряд нормативных документов, в том числе СП 35.13330.2016 «Мосты и трубы», для проведения будущих исследований и повсеместного применения метода

Blow-up modes in fracture of rock samples and earth's crust elements

It is well known that the final stage of macroscopic fracture develops as a catastrophe in a superfast blow-up mode. However, the specific features of this stage are well studied only on large scales of earthquakes. Of particular interest for fracture prediction are both the stage of superfast catastrophic fracture and the mechanical behavior of the medium in the state of self-organized criticality prior to transition of fracture to the blow-up mode in order to reveal precursors of fracture transition to the catastrophic stage. This paper studies experimentally and theoretically the mechanical behavior of the medium prior to the catastrophic stage and transition to the blow-up mode. Rock samples (marble and artificial marble) were tested in three-point bending and uniaxial compression tests. The lateral surface velocities of loaded samples were recorded using a laser Doppler vibrometer. The recording frequency in measurements was 48 kHz, and the determination accuracy of the velocity amplitude was 0.1 μm/s. The estimated duration of the blow-up fracture stage is 10–20 ms. The mechanical behavior of samples in the experimental conditions, including the catastrophic fracture stage, is simulated numerically. The damage accumulation model parameters are determined from a comparison with the experimental data. Certain features of the mechanical response prior to catastrophic fracture are revealed which can be interpreted as fracture precursors

Blow-up regimes in failure of rock specimens

For damage evaluation, the stage of superfast catastrophic failure of a medium and its mechanical behavior in a state of self-organized criticality prior to the onset of a blow-up fracture mode is of great interest for identification of its precursors. In this work, the data of experimental and numerical investigations of mechanical behavior of a medium before its catastrophic failure and the onset of a blow-up fracture mode are presented. Rock samples and ceramic specimens are subjected to three-point bending and uniaxial compression testing. Surface velocities of the loaded specimens are registered using a laser Doppler vibrometer. The blow-up regime duration is measured to be about 10–20 ms. The specimens’ mechanical behavior is numerically simulated under experimental conditions, including the regime of catastrophic fracture. The model parameters of damage accumulation are determined from a comparison with the experimental data. A number of features of the material mechanical response before the catastrophic fracture are identified, which could be treated as failure precursors

Autosoliton view of the seismic process. Part 2. possibility of generation and propagation of slow deformation autosoliton disturbances in geomedia

In the autosoliton view, the complete mathematical model of the seismic process taken as the deformation and fracture process of a loaded geomedium combines dynamic equations of solid mechanics and specific constitutive equations for geomedium rheology. These equations describe both the conventional stress-strain evolution due to the stress wave propagation with sound velocities, which are governed by special features of constitutive equations, and slow dynamics of the loaded strong medium. Numerical investigation is given to the generation of deformation autosolitons, front structure, and propagation of intra- and interfault deformation disturbances. Slow deformation disturbances in real geomedium elements are numerically modeled

The Repercussion ot Natural and Technogeniс Ore-Gold Objects in Litogeochemical and Biogeochemical Fields

Исследование выполнено в рамках геолого-поисковых работ на Дюбкошской золотоносной площади, ограничивающей фрагмент одноименного грабена, заключенного в структурах складчатого обрамления Ангаро-Тунгусской и Татарской зон. Целью исследования стала оценка поисковой информативности лито- и биогеохимических методов и изучения возможности использования их для разбраковки природных и техногенных геохимических аномалий золотаThis research wass carried ouy within the geological-searching works on the auriferous Dubkosh area, which bounds the fragment of the same named graben. This graben is confined in the structures of plicated framing. The estimate of searching informativity of litogeochemical and biogeochemical methods and studying the possibility of using them for separation natural and tecnogenic geochemical gold anomalies was the purpose of this researc

The Repercussion ot Natural and Technogeniс Ore-Gold Objects in Litogeochemical and Biogeochemical Fields

Исследование выполнено в рамках геолого-поисковых работ на Дюбкошской золотоносной площади, ограничивающей фрагмент одноименного грабена, заключенного в структурах складчатого обрамления Ангаро-Тунгусской и Татарской зон. Целью исследования стала оценка поисковой информативности лито- и биогеохимических методов и изучения возможности использования их для разбраковки природных и техногенных геохимических аномалий золотаThis research wass carried ouy within the geological-searching works on the auriferous Dubkosh area, which bounds the fragment of the same named graben. This graben is confined in the structures of plicated framing. The estimate of searching informativity of litogeochemical and biogeochemical methods and studying the possibility of using them for separation natural and tecnogenic geochemical gold anomalies was the purpose of this researc