scholarly journals Energy Evolution Characteristics and Distribution Laws of Rock Materials under Triaxial Cyclic Loading and Unloading Compression

2017 ◽  
Vol 2017 ◽  
pp. 1-16 ◽  
Author(s):  
Mingwei Zhang ◽  
Qingbin Meng ◽  
Shengdong Liu
Keyword(s):  
Cyclic Loading ◽  
Energy Density ◽  
Elastic Energy ◽  
Confining Pressure ◽  
Dissipated Energy ◽  
Energy Evolution ◽  
Elastic Energy Density ◽  
Evolution Characteristics ◽  
Storage Limit ◽  
Confining Pressures

To explore the influence of confining pressure on the energy evolution characteristics of loaded rocks, triaxial cyclic loading-unloading experiments on sandstones were carried out under 6 kinds of confining pressures using the axial loading and circumferential deforming control modes. Total energy density, elastic energy density, and dissipated energy density absorbed by rock specimens under different confining pressures were obtained. The confining pressure effect of the evolution process and distribution law in energy accumulation and dissipation was analyzed. Energy conversion mechanism from rock deformation to failure was revealed, and energy conversion equations in different stress-strain stages were established. The method of representing the rock energy accumulation, dissipation, and release behaviors by energy storage limit density, maximum dissipated energy density, and residual elastic energy density was established. The rock showed that, with the increase of confining pressure, the characteristic energy density of rock increased in the power exponent form, and the energy storage limit density increased faster than the maximum dissipated energy density. The greater the confining pressure was, the greater the proportion of elastic energy before peak was. It is indicated that the confining pressure increased the energy inputting intensity, improved the energy accumulating efficiency, and inhibited the energy releasing degree.

scholarly journals The Effect of Confining Pressure and Water Content on Energy Evolution Characteristics of Sandstone under Stepwise Loading and Unloading

2018 ◽  
Vol 2018 ◽  
pp. 1-8 ◽  
Author(s):  
Shuren Wang ◽  
Paul Hagan ◽  
Yanhai Zhao ◽  
Xu Chang ◽  
Ki-Il Song ◽  
...  
Keyword(s):  
Energy Dissipation ◽  
Water Content ◽  
Elastic Energy ◽  
Strain Energy ◽  
Confining Pressure ◽  
Triaxial Tests ◽  
Energy Evolution ◽  
Evolution Characteristics ◽  
Loading And Unloading ◽  
Stepwise Loading

To investigate the mechanical properties and energy evolution characteristics of sandstone depending on the water contents and confining pressure, the uniaxial and triaxial tests were conducted. The test results show that the strain energy was stored in the sandstone samples at the prepeak stage, and that is suddenly released when the failure occurred, and energy dissipation is sharply increased at the postpeak stage. The damage and energy dissipation characteristics of the samples are observed clearly under the stepwise loading and unloading process. The critical strain energy and energy dissipation show a clear exponential relationship. The critical elastic energy decreases linearly as the water content increases. As the confining pressure increases, the critical elastic energy of the samples transforms from linear to exponential. The concept of energy enhancement factor is proposed to characterize the strengthening effect induced by the confining pressure on the energy storage capacity of the rock samples. The energy evolution of the sandstone samples is more sensitive to the confining pressure than that of the water content.

scholarly journals Experimental Investigation on the Energy Storage Characteristics of Red Sandstone in Triaxial Compression Tests with Constant Confining Pressure

2020 ◽  
Vol 2020 ◽  
pp. 1-11
Author(s):  
Liuliu Li ◽  
Fengqiang Gong
Keyword(s):  
Energy Density ◽  
Elastic Energy ◽  
Quadratic Function ◽  
Input Energy ◽  
Compression Tests ◽  
Red Sandstone ◽  
Elastic Energy Density ◽  
Deep Rock ◽  
Confining Pressures ◽  
Input Energy Density

The elastic energy stored in deep rock in three-dimensional stress environment is the energy source of rockburst. To investigate the energy storage characteristics of deep rock under different confining pressures, a series of triaxial single-cyclic loading-unloading compression tests were conducted on red sandstone specimens under eight confining pressures. The input energy density, elastic energy density, and dissipative energy density of the specimen in axial, circumferential, and total directions can be obtained by the area diagram integration method. The results show that the input energy density in the axial direction accounts for the largest logarithmic proportion of the total input energy density, and the relationship between all energy density parameters and unloading level can be described by quadratic function. In the axial direction, there is a linear function relationship among elastic energy density, dissipative energy density, and input energy density. In the circumferential direction, there is a quadratic function relationship among elastic energy density, dissipative energy density, and input energy density. For the total energy density parameters of the rock specimen, the relationship among elastic energy density, dissipative energy density, and input energy density conforms to the quadratic function. According to the above correlation function, the elastic energy stored in deep rock under different confining pressures can be accurately obtained, which provides a foundation for studying the mechanism of rockburst under three-dimensional unloading from the energy perspective.

scholarly journals An Experimental Investigation of the Progressive Failure of Sandstone and Its Energy Evolution Characteristics

2018 ◽  
Vol 2018 ◽  
pp. 1-12
Author(s):  
Yan Chen ◽  
Baohua Guo
Keyword(s):  
Crack Propagation ◽  
Crack Closure ◽  
Progressive Failure ◽  
Axial Strain ◽  
Triaxial Compression ◽  
Confining Pressure ◽  
Energy Evolution ◽  
Evolution Characteristics ◽  
Confining Pressures ◽  
The Relationship

In this research study, the progressive failure and energy evolution characteristics of sandstone samples with different sizes were explored under uniaxial and triaxial compression conditions. The characteristic stresses and strains were captured using the crack axial strain levels and dissipative energy. The results showed that, with the increase in the ratios of the height to diameter (H/D), the crack closure stresses increased, while the crack damage stresses decreased. However, the levels of both the crack closure stresses and crack damages were observed to increase with the H/D. With increase in the confining pressure, it was found that the crack closure and crack damage stresses increased, while their levels decreased. The strains of the crack closures, peak crack axial, and crack propagation were observed to decrease with the H/D, while the crack closure strain levels increased. Also, the crack propagation strains were observed to increase with the confining pressures, while the crack closure, peak crack axial, and crack closure strain levels decreased. The progress failure of the sandstone samples was also obtained based on the evolution characteristics of the dissipative energy. The relationship between the energy densities during each phase and the H/D was also analyzed. It was determined that, with the increasing of the H/D, the input, elastic, and dissipative energy densities displayed different evolution characteristics. Furthermore, with the increases in the characteristic stresses, the input and elastic energy densities were found to increase. The dissipative energy density displayed a slight increase with the increases in the peak strength, which resulted in variations with regard to the crack closures and crack damage stresses.

scholarly journals The energy evolution characteristics of coal under different dynamic strain rates and confining pressures

2019 ◽  
Vol 23 (3 Part A) ◽  
pp. 1409-1416
Author(s):  
Yi-Qiang Lu ◽  
Xiao-Hui Liu ◽  
Jing Xie ◽  
Zhi-Qiang He ◽  
Cong Li
Keyword(s):  
Split Hopkinson Pressure Bar ◽  
Confining Pressure ◽  
Tensile Failure ◽  
Dynamic Strain ◽  
Strain Rates ◽  
Strengthening Effect ◽  
Peak Strain ◽  
Energy Evolution ◽  
Evolution Characteristics ◽  
Confining Pressures

Coal specimens from baijiao coal mine were impacted by a split Hopkinson pressure bar to study its dynamic mechanical behavior under different confining pressures (0-12 MPa) and different strain rates (20-250 s-1). The performances and the energy evolution characteristics of the coal specimens were analyzed. The results show that the strengthening effect and toughening effect of rock are gradually enhanced with the increase of confining pressure. At the same time, the coal failure gradually transitions and develops from tensile failure to compression-shear failure under the action of confining pressure. The peak strength and peak strain of coal rock show significant strain rate correlation and strong confining pressure effect with the change of confining pressures and strain rates. The dynamic strength growth factor of coal is approximately linear with the increasing of strain rates. The energy density and energy absorption density increase linearly with the increase of strain rates, and the energy consumption ratio has a logarithmic growth relationship with the strain rates.

scholarly journals Experimental Investigation of the Mechanical Behavior of Layer-Crack Specimens under Cyclic Uniaxial Compression

Symmetry ◽  
2019 ◽  
Vol 11 (4) ◽  
pp. 465
Author(s):  
Wei-yao Guo ◽  
Feng-hai Yu ◽  
Yue Qiu ◽  
Tong-bin Zhao ◽  
Yun-liang Tan
Keyword(s):  
Cyclic Loading ◽  
Energy Density ◽  
Mechanical Behavior ◽  
Elastic Energy ◽  
Peak Stress ◽  
Dissipated Energy ◽  
Strengthening Effect ◽  
Input Energy ◽  
Rock Bursts ◽  
Number Of Cycles

It is generally acknowledged that the failure of the layer-crack structure is closely related to rock bursts (a layer-crack structure means a coal or rock rib that is cut by fractures that are parallel or sub-parallel to the surface of the rib). Understanding the mechanical behavior of the layer-crack structure under cyclic loading is beneficial for rock burst mitigation. This study experimentally investigated the influence of the geometry of vertical fissure (i.e., width, length and number) on the mechanical properties of layer-crack rock specimens. The results show that the sensitivity of parameters with respect to the geometry of the fissure from strong to weak is the number, length and width. First, the peak stress under cyclic loading increases by approximately 7.82%–17.35%, thereby exerting an obvious strengthening effect. Second, the fissure geometry slightly affects the energy evolution of the layer-crack specimen, i.e., the input energy density, elastic energy density and dissipated energy density all gradually increase with the increase of the number of cycles. However, when approaching a specimen failure, the increasing rates from quick to slow are the dissipated energy, input energy and elastic energy. Third, the damage variable of the layer-crack specimen shows a concave increasing trend with the increase of the number of cycles. When the number of cycles is equal, the damage increases with the increase of the number of fissures, but it decreases with the increase of the fissure length. Fourth, AE events occur shortly before specimen failures, but rapidly increase near the specimen failures. The accumulated AE events that lead to specimen failures decrease with the increase in the number of fissures. These results can provide some basic data for the research of rock bursts related to the failures of layer-crack structures.

Analysis the characteristic of energy and damage of coal-rock composite structure under cycle loading

2021 ◽  
Author(s):  
Tan Li ◽  
Guangbo Chen ◽  
Zhongcheng Qin ◽  
Qinghai Li
Keyword(s):  
Cyclic Loading ◽  
Elastic Energy ◽  
Composite Structure ◽  
Calculation Method ◽  
Composite Structures ◽  
Damage Variable ◽  
Dissipated Energy ◽  
Height Ratio ◽  
Coal Rock ◽  
The Stability

Abstract The stability of coal-rock composite structures is of great significance to coal mine safety production. To study the stability and deformation failure characteristics of the coal-rock composite structure, the uniaxial cyclic loading tests of the coal-rock composite structures with different coal-rock height ratios were carried out. Lithology and coal-rock height ratio play an important role in the energy dissipation of coal-rock composite structures. The higher the coal-rock height ratio, the greater the average elastic energy and dissipated energy produced per cycle of coal-rock composite structures, the smaller the total elastic energy and dissipated energy produced in the process of cyclic loading. Based on the difference of damage variables calculated by dissipative energy method and acoustic emission method, a more sensitive joint calculation method for calculating damage variable was proposed. The joint damage variable calculation method can more accurately and sensitively reflect the damage of coal-rock composite structure under cyclic loading. The macroscopic crack first appears in the coal specimen in the coal-rock composite structure, the degree of broken coal specimens in the composite structure is inversely proportional to the coal-rock height ratio. The strength and deformation characteristics of the coal-rock composite structure are mainly affected by coal sample in the composite structure.

scholarly journals Acoustic Emission Simulation on Coal Specimen Subjected to Cyclic Loading

2020 ◽  
Vol 2020 ◽  
pp. 1-17
Author(s):  
Huiqiang Duan ◽  
Depeng Ma
Keyword(s):  
Numerical Simulation ◽  
Acoustic Emission ◽  
Cyclic Loading ◽  
Confining Pressure ◽  
Rock Masses ◽  
Coal Specimen ◽  
Cycle Number ◽  
Confining Pressures ◽  
Unloading Rate ◽  
Ae Counts

The damage and failure state of the loaded coal and rock masses is indirectly reflected by its acoustic emission (AE) characteristics. Therefore, it is of great significance to study the AE evolution of loaded coal and rock masses for the evaluation of damage degree and prediction of collapse. The paper mainly represents a numerical simulation investigation of the AE characteristics of coal specimen subjected to cyclic loading under three confining pressures, loading-unloading rates, and valley stresses. From the numerical simulation tests, the following conclusions can be drawn: (1) The final cycle number of coal specimen subjected to cyclic loading is significantly influenced by the confining pressure, followed the valley stress. With the increase in confining pressure or valley stress, the cycle number tends to increase. However, the loading-unloading rate has a little influence on it. (2) The AE counts of coal specimen subjected to cyclic loading are greatly influenced by the confining pressure and the valley stress. With the increase in the confining pressure, the cumulative AE counts at the 1st cycle tend to increase but decrease at a cycle before failure; with the decrease in the valley stress, the cumulative AE counts per cycle increase in the relatively quiet phase. However, the loading-unloading rate has a little influence on it. (3) The failure mode of coal specimen subjected to cyclic loading is significantly influenced by the confining pressure. Under the uniaxial stress state, there is an inclined main fractured plane in the coal specimen, under the confining pressures of 5 and 10 MPa, the coal specimen represents dispersion failure. The loading-unloading rate and valley stress have little influence on it. (4) The AE ratio is proposed, and its evolution can better reflect the different stages of coal specimen failure under cyclic loading. (5) The influence of confining pressure on the broken degree of coal specimen subjected to cyclic loading is analyzed, and the higher the confining pressure, the more broken the failed coal specimen.

Anisotropic energy and ultrasonic characteristics of black shale under triaxial deformation revealed utilizing real-time ultrasonic detection and post-test CT imaging

2019 ◽  
Vol 219 (1) ◽  
pp. 260-270 ◽  
Author(s):  
Y Wang ◽  
W K Feng ◽  
Z H Zhao ◽  
D Zhang
Keyword(s):  
Energy Release ◽  
Real Time ◽  
Elastic Energy ◽  
Strain Energy ◽  
Dissipated Energy ◽  
Energy Evolution ◽  
Ultrasonic Detection ◽  
Bedding Planes ◽  
Anisotropic Energy ◽  
Post Test

SUMMARY For evaluating the fracturing-related activities in a deep shale formation, it is important to investigate the effect of anisotropy on its geomechanical properties. Many effects have been performed to reveal the strength and deformation anisotropy of shale, however, the influence of bedding planes on the anisotropic energy evolution and velocity-energy dependency are still not well understood, especially under high confinement condition. In this study, triaxial compression tests with a high confining pressure of 60 MPa in combination with real-time ultrasonic detection and post-test CT scanning were performed to the shale samples cored along an angle of 0°, 30°, 60° and 90° with respect to bedding planes. The effect of the bedding orientation on the shale geomechanical, ultrasonic, energy dissipation and energy release characteristics are explored. The experimental results show that shale structural features highly affect the total energy, elastic energy and dissipated energy. The increasing trend of elastic energy shows a slow, fast and slow mode, and the dissipate energy increases rapidly near sample failure. Good correlations have been found among the P- and S-wave velocities and the elastic and dissipated strain energy. The mesostructural changes during deformation are considered to be the primary factor controlling the energy sensitivity to the velocities. CT images further reveal the anisotropic fracture pattern which is in good agreement with energy release and dissipation analysis. The analysis of the strain energy and velocities suggests that the strain energy evolution and fracture anisotropy are bedding orientation dependent.

Superior electrostrictive strain achieved under low electric fields in relaxor ferroelectric polymers

2019 ◽  
Vol 7 (10) ◽  
pp. 5201-5208 ◽  
Author(s):  
Zhicheng Zhang ◽  
Xiao Wang ◽  
Shaobo Tan ◽  
Qing Wang
Keyword(s):  
Energy Density ◽  
Energy Conversion ◽  
Electric Fields ◽  
Elastic Energy ◽  
Energy Conversion Efficiency ◽  
Relaxor Ferroelectric ◽  
Ferroelectric Polymers ◽  
Elastic Energy Density ◽  
Electromechanical Responses ◽  
Electromechanical Performance

A relaxor ferroelectric polymer exhibits record electromechanical performance, including the largest electrostrain of −13.4%, the highest elastic energy density of 3.1 J cm−3 and the best energy conversion efficiency of 0.5, among the known ferroelectric polymers. Notably, the excellent electromechanical responses are realized under much lower fields than those of ferroelectric polymers.

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