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 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 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 Investigation on Triaxial Dynamic Model Based on the Energy Theory of Bedding Coal Rock under Triaxial Impact Compression

2021 ◽  
Vol 2021 ◽  
pp. 1-15
Author(s):  
Yang Xue ◽  
Xiaohui Liu ◽  
Rui Zhao ◽  
Yu Zheng ◽  
Xin Gui
Keyword(s):  
Constitutive Model ◽  
Confining Pressure ◽  
Strain Rates ◽  
Peak Strain ◽  
Dynamic Failure ◽  
Impact Compression ◽  
Failure Characteristics ◽  
Confining Pressures ◽  
Coal Rock ◽  
Energy Theory

To investigate the dynamic failure characteristics of bedding rocks in depth, a series of dynamic impact compression tests on parallel and vertical bedding coal rocks were conducted by the split Hopkinson pressure bar test system at 10–103 s−1 strain rates and 0, 4, 8, and 12 MPa confining pressures. According to the experiments, the mechanical properties and energy characteristics of bedding coal rock under different confining pressures and strain rates were obtained, and a triaxial dynamic constitutive model of bedding coal rock was established based on the energy theory of rock failure. The results show that the compressive strength, peak strain, incident energy, dissipated energy, and dynamic strength increase factor gradually increase with increase in strain rate, but the increase in peak strain weakens as confining pressure rises. The influence of bedding structure on strength and energy is not obvious in the uniaxial state, while it gradually enhances as confining pressure increases. The obvious difference in DIF and the energy dissipation ratio of bedding coal rocks gets obvious in SHPB tests. Considering the influence of confining pressure, strain rate, and bedding on the dynamic failure characteristics, the dynamic constitutive model of bedding coal rock was established by introducing the comprehensive influence factor K and the DIF. Comparing with test results, the model parameters are almost confirmed, and the correctness of the model is further verified by analysing the law of K value. Meanwhile, the stress-softening characteristics of coal rock in postpeak are well simulated by the dynamic constitutive model. The results can provide reference value for dynamic issues such as high-efficiency rock breaking, prevention of rock burst, and surrounding rock support in deep rock masses.

Plastic Flow Stress and Constitutive Model for H96 Brass Alloy

2015 ◽  
Vol 782 ◽  
pp. 130-136 ◽  
Author(s):  
Ping Zhou ◽  
Wei Guo Guo ◽  
Hai Hui Wu
Keyword(s):  
Flow Stress ◽  
Constitutive Model ◽  
Plastic Flow ◽  
Split Hopkinson Pressure Bar ◽  
Testing Machine ◽  
Experimental Results ◽  
Dynamic Strain ◽  
Strain Rates ◽  
Brass Alloy ◽  
Plastic Flow Stress

To explore the thermo-mechanical response of H96 brass alloy, the quasi-static (universal-testing machine) and dynamic (the split Hopkinson pressure bar apparatus) uniaxial compression experiments have been performed under the temperatures from 293 K to 873 K and the strain rates from 0.001 s-1 to 6000 s-1, and the strains over 60% are obtained. Results show that, H96 brass alloy has strong strain hardening behavior, and it becomes weaker with the increasing temperature. In addition, this alloy is sensitive to strain rates; and, it has temperature sensitivity, the dynamic strain aging occurs at the temperature of 473 K and a quasi-static strain rate of 0.001 s-1. Based on the thermal activation dislocation mechanism, paralleled with the experimental results, a plastic flow constitutive model with the physical conception is developed. The model is suitable to predict the plastic flow stress at different temperatures and strain rates. According to comparing results, the model predictions are in good agreement with the experimental results.

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 Numerical Research on Energy Evolution in Granite under Different Confining Pressures Using Otsu’s Digital Image Processing and PFC2D

Symmetry ◽  
2019 ◽  
Vol 11 (2) ◽  
pp. 131 ◽  
Author(s):  
Yubao Zhang ◽  
Tongbin Zhao ◽  
Yanchun Yin ◽  
Yunliang Tan ◽  
Yue Qiu
Keyword(s):  
Image Processing ◽  
Growth Rate ◽  
Digital Image Processing ◽  
Digital Image ◽  
Strain Energy ◽  
Confining Pressure ◽  
Energy Evolution ◽  
Energy Accumulation ◽  
Energy Growth ◽  
Confining Pressures

Research on energy accumulation and releasing in the rock plays a key role on revealing its failure mechanism. This paper establishes a microscopic structure model of granite using Otsu digital image processing (DIP) technology and particle flow code software (PFC2D). A series of numerical compression tests under different confining pressures were conducted to investigate the macro and micro characteristics of energy evolution in granite. The results showed that the energy evolution of granite is divided into three stages: stable accumulation, slow dissipation, and rapid release. With increasing confining pressure, the strain energy accumulation ratio decreased exponentially and the peak value of strain energy increased linearly. It was found that the energy accumulation speed in the pre-peak stage increased as a linear function, while the energy release speed in the post-peak stage decreased as an exponential function. In addition, the feldspar is the main microstructure which played a major part in accumulating energy in granite. However, the unit mineral energy of mica particles was bigger than that of feldspar and quartz. When subjected to increasing confining pressure, the feldspar’s total energy growth rate was fastest. Meanwhile, the mica’s unit energy growth rate was fastest.

scholarly journals Mechanical Properties of Grouted Crushed Coal with Different Grain Size Mixtures under Triaxial Compression

2018 ◽  
Vol 2018 ◽  
pp. 1-13 ◽  
Author(s):  
Yuhao Jin ◽  
Lijun Han ◽  
Qingbin Meng ◽  
Suresh Sanda ◽  
Haizhi Zang ◽  
...  
Keyword(s):  
Grain Size ◽  
Triaxial Compression ◽  
Confining Pressure ◽  
Peak Strain ◽  
Compression Tests ◽  
Reinforcement Effect ◽  
Confining Pressures ◽  
Mechanical Behaviours ◽  
Ultimate Failure ◽  
Different Grain Size

To have a better understanding of the reinforcement effect on the crushed zone after grouting in coal mining extraction work, a self-designed grouting apparatus was used to study the effects of the grain size mixtures (distribution) and the stress state on the mechanical behaviours of grouted crushed coal specimens. From the various grouting tests, triaxial compression tests and scanning electron microscopy (SEM) observations of grouted specimens with different grain size mixtures, it was found that, for the same grain size mixture, the peak (σp) and residual (σr) strengths of the grouted specimens increased with an increase in confining pressure. It was found that the average slope values of the σp-σ3 curves for the grouted specimens with different grain size mixtures were all larger than those of the σr-σ3 curves. It was observed that the peak strain (εp) of the grouted specimens with different grain size mixtures increased overall with increasing confining pressure. For constant confining pressure, the peak and residual strengths both gradually increased approximately linearly as the grain size mixtures varied from small to large, but at higher confining pressures, the influence of the grain size mixture on the peak (or residual) strength increased. These mechanical behaviours of the grouted crushed coal specimens were strongly dependent on the variation in the grain size mixtures and in the confining pressure, which can be explained by the crack evolution process within the grouted specimen under triaxial compression, to a certain extent. Ultimate failure of the grouted specimen occurred just after propagation and coalescence of the cracks through the entire grouted specimen. Moreover, there were three major microscopic diffusion modes for the grouts flowing in most of the crushed coal specimens. Based on these test results, it was found that the reinforcement effect of the grouted specimen related to the splitting grouting mode (occurring in most of the large specimens) seems to be better than that of the penetrating (filling) grouting mode (in most of the small specimens).

The Influence of Steel Fibers on the Dynamic Response of Self-Compacting Concrete

2016 ◽  
Vol 711 ◽  
pp. 179-186 ◽  
Author(s):  
Małgorzata Pająk ◽  
Tino Kühn
Keyword(s):  
High Strain ◽  
Split Hopkinson Pressure Bar ◽  
Steel Fibers ◽  
Failure Pattern ◽  
Dynamic Strain ◽  
Strain Diagram ◽  
Strain Rates ◽  
Self Compacting Concrete ◽  
High Strain Rates ◽  
Static Conditions

Concrete subjected to high strain rates behaves notably differently in comparison to quasi-static conditions, which can be affected by the addition of steel fibers. The influence of steel fibers on the dynamic compressive behavior of self-compacting concrete (SCC) was studied experimentally using Split Hopkinson Pressure Bar (SHPB) tests. The investigations were performed in a range of quasi-static rates up to dynamic strain rates of 462 1/s. The effect of steel fibers on the stress-strain diagram, dynamic increase factor (DIF) and failure pattern of SCC conducted under high strain rates was analyzed. The experimental results presented in this paper and the ones from recent works of other authors indicate that application of steel fibers reduces the strain-rate sensitivity of different concretes and has a beneficial effect on the specimen failure pattern. Moreover, the conducted SHPB tests show an important role of fibers in reduction of the strain rates reached in the specimen under the same pressure level in comparison to plain concrete specimens.

scholarly journals Experimental Study on Coupling Influence of Temperature and Confining Pressure to Deformation and Strength Characteristics of Rock-like Material with Pre-Existing Crack

Materials ◽  
2021 ◽  
Vol 14 (24) ◽  
pp. 7572
Author(s):  
Hongwei Wang ◽  
Yongyan Wang ◽  
Xi Fu
Keyword(s):  
Young’S Modulus ◽  
Failure Mode ◽  
Young's Modulus ◽  
Confining Pressure ◽  
Strength Characteristics ◽  
Peak Strain ◽  
Influence Of Temperature ◽  
Confining Pressures ◽  
Initial Cracks ◽  
Deformation And Strength Characteristics

In this paper, destructive compression tests under the coupled influence of temperatures (20–60 °C) and confining pressures (0–7 MPa) were carried out on rock-like material with pre-existing crack to explore the deformation and strength characteristics. The stress–strain curves of rock-like material under the coupled influence of temperatures and confining pressures were obtained. Meanwhile, the correlations of peak stress, peak strain, and average Young’s modulus with temperatures and confining pressures were obtained. The results of the experiments indicate that, firstly, the compressive strength decreased and the deformation increased due to the influence of pre-existing cracks; the combined effect of initial cracks, temperature, and confining pressure gave rise to a more complicated mechanism of soft rock deformation. Secondly, the deformation of rock-like material was affected by initial cracks, confining pressures, and temperatures, but the influence of temperature was lower than that of confining pressure and initial crack. The failure mode of rock-like material was brittle at the confining pressure of 0 and 1 MPa and plastic at the confining pressure of 5 and 7 MPa. The critical confining pressure value of failure mode for rock-like material was 3 MPa. Thirdly, the peak strength and peak strain of rock-like material increased with confining pressure. Temperature had less influence on the rock-like material strength and peak strain than confining pressure. Lastly, Young’s modulus decreased with temperature and confining pressure.

scholarly journals Long-term creep behavior of deep-buried marble under different confining pressures

2019 ◽  
Vol 23 (Suppl. 3) ◽  
pp. 653-660
Author(s):  
Ersheng Zha ◽  
Ru Zhang ◽  
Zetian Zhang ◽  
Li Ren ◽  
Wenju Zhang ◽  
...  
Keyword(s):  
Creep Behavior ◽  
Shear Failure ◽  
Confining Pressure ◽  
Tensile Failure ◽  
Creep Failure ◽  
Failure Characteristics ◽  
Underground Caverns ◽  
Confining Pressures ◽  
Term Creep

To explore the long-term creep behavior of deep rock, the long-term tri-axial creep mechanical behavior of the rock under different confining pressures has been carried out. The results show that the instantaneous strain and creep strain of the high confining pressure specimen are significantly higher than that of the low confining pressure specimen under high deviatoric stress. By analyzing the failure characteristics of different confining pressure specimens, it is found that with the increase of the confining pressure, the creep failure characteristics of the marble transforms from tensile failure to shear failure. These research results have certain reference significance for the long-term stability analysis of the deep underground caverns.

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