scholarly journals Elastoplastic constitutive behavior and strain localization of a low-porosity sandstone during brittle fracturing

2021 ◽  
Author(s):  
Shihuai Zhang ◽  
Pei Guo ◽  
Shunchuan Wu
Keyword(s):  
Constitutive Model ◽  
Yield Surface ◽  
Strain Localization ◽  
Pure Shear ◽  
Failure Process ◽  
Frictional Coefficient ◽  
Peak Stress ◽  
Confining Pressure ◽  
Elastoplastic Behavior ◽  
Confining Pressures

We investigated the elastoplastic behavior and strain localization of the Zigong sandstone (porosity: 6.5%) during brittle fracturing based on two series of axisymmetric compression experiments. The experiments were conducted under various confining pressures (σ3 = 0 ~ 80 MPa). For each confining pressure, the sandstone specimens were deformed under constant axial and circumferential strain rates, respectively. When σ3 < 60 MPa, the sandstone first undergoes stable deformation in the post-peak stage and then loses its stability. Before the emergence of instability, the mechanical behavior is hardly affected by the controlling method. When the confining is larger, the sandstone manifests a stable failure process during the whole loading stage. The observed elastoplastic behavior was described by a two-yield surface constitutive model established in the framework of generalized plastic mechanics. The proposed constitutive model incorporates two quadratic yield functions, as well as two linearly independent plastic potential functions, to honor the shear yield and volumetric dilatancy, respectively. Via the return mapping algorithm, the proposed constitutive model was verified by comparing the numerical results with experimental results. In addition, the two-yield surface constitutive model, which is equivalent to the model proposed by Rudnicki and Rice,1 was applied to localization analysis. Assuming that the onset of localization occurs at peak stress, frictional coefficient μ and dilatancy factor β were determined from experimental data. The variations of both plastic parameters predict the transition of localization mode from pure dilation bands under uniaxial compression to pure shear bands at high confining pressures, which is consistent with the experimental observations.

scholarly journals Statistical Constitutive Model of Thermal Damage for Deep Rock considering Initial Compaction Stage and Residual Strength

2019 ◽  
Vol 2019 ◽  
pp. 1-10 ◽  
Author(s):  
Lingjie Zhu ◽  
Xiaoli Xu ◽  
Xiaojian Cao ◽  
Shaoyong Chen
Keyword(s):  
Constitutive Model ◽  
Residual Strength ◽  
Damage Evolution ◽  
Damage Mechanics ◽  
Thermal Damage ◽  
Peak Stress ◽  
Confining Pressure ◽  
Evolution Rate ◽  
Correction Coefficient ◽  
Initial Compaction

From the theory of damage mechanics, based on the Hoek-Brown strength criterion and Weibull distribution law of rock microelement strength, a statistical constitutive model of rock thermal damage is established by using equivalent strain hypothesis, and the theoretical model is modified by considering the compression coefficient and residual strength correction coefficient. The rationality of the modified model is verified by experimental data. The results show that the stress-strain curves of rock can be divided into four stages: initial compaction, stable damage propagation, damage strengthening expansion, and damage failure according to the characteristics of rock damage evolution. The peak stress of rock increases exponentially with the increase of confining pressure, and the maximum damage evolution rate decreases exponentially with the increase of confining pressure, which indicates that confining pressure delays the development of cumulative damage. The peak stress and maximum damage evolution rate of rock decrease exponentially with the increase of temperature, which accelerates the damage of rock. The initial damage of rock is thermal damage caused by temperature, and the damage value increases with the increase of temperature. The revised theoretical curve reflects the characteristics of rock compaction stage and residual strength and improves the coincidence with the experimental curve. The research results provide a reference for the establishment of thermal damage constitutive model of rock in deep engineering.

scholarly journals The Scale Effect of Coarse-Grained Materials by Triaxial Test Simulation

2021 ◽  
Vol 2021 ◽  
pp. 1-13
Author(s):  
Xiaotao Ai ◽  
Guangjin Wang ◽  
Xiangyun Kong ◽  
Bo Cui ◽  
Bin Hu ◽  
...  
Keyword(s):  
Scale Effect ◽  
Triaxial Test ◽  
Failure Process ◽  
Deformation Modulus ◽  
Peak Stress ◽  
Friction Angle ◽  
Confining Pressure ◽  
Coarse Grained ◽  
Strength Parameters ◽  
And Migration

The scale effect is an unavoidable problem in the laboratory test of coarse-grained materials. By combining the self-developed cellular automaton program with laboratory experiments, a method of simulating the triaxial test of coarse-grained materials was proposed in this paper, and a triaxial test numerical specimen that can characterize the discontinuous, nonuniform, and heterogeneous characteristics of bulk geotechnical materials was established. The parallel grading method was adopted to create six grading curves for numerical simulation based on one in situ grading curve. The failure process and the scale effect on the strength and deformation of coarse-grained materials were analyzed and discussed. The results showed that under the same confining pressure, the peak stress and initial deformation modulus E i increased with the increase of the maximum particle size d max , while the degree of shear shrinkage and Poisson’s ration υ decreased. As the confining pressure increased, the scale effect of coarse-grained materials would be magnified. If particle breakage and migration were assumed to be neglected, the internal friction angle φ and d max would be roughly proportional, the cohesive force c fluctuated with the increase of d max , and the empirical relations between d max and c and φ were established, respectively, which provides a reference for estimating the actual shear strength parameters of coarse-grained materials on-site. The research results can provide a way of thinking for the study of the scale effect of coarse-grained materials and also have certain reference significance for inferring the strength parameters of the original-graded coarse-grained materials.

Experimental Design about Degradation Mechanism of CAM and Preliminary Experiment Results

2013 ◽  
Vol 663 ◽  
pp. 703-707
Author(s):  
Jian Zeng Li ◽  
Jin Feng Wang ◽  
Jian Ping Lin
Keyword(s):  
Mechanical Property ◽  
High Speed ◽  
Degradation Mechanism ◽  
Fatigue Property ◽  
Peak Stress ◽  
Confining Pressure ◽  
Degradation Model ◽  
Increase With Increase ◽  
Cement Asphalt Mortar ◽  
Confining Pressures

Cement Asphalt Mortar (CAM) layer is the key to the structure of slab track in the high-speed railways. In the running of high-speed railways, the CAM layer must bear the action of temperature change, initial defects and trains loading, it will lead to the degradation of CAM. This paper designed the experiments to study its mechanical property under confining pressure or water erosion, tensile property, fatigue property, interface stress of CAM and concrete roadbed; it will help us to establish the failure criterion and degradation model of CAM layer. Preliminary experiment chose three confining pressures to study the mechanical property of CAM; the results indicate that peak stress and ductility of CAM greatly increase with increase of confining pressure.

Laboratory Testing and Consitiutive Modeling of Coal Including Anisotropy

1992 ◽  
Vol 296 ◽  
Author(s):  
Dar-Hao Chen ◽  
Musharraf M. Zaman ◽  
Anant R. Kukreti
Keyword(s):  
Constitutive Model ◽  
Triaxial Compression ◽  
High Capacity ◽  
Ground Surface ◽  
Transversely Isotropic ◽  
Confining Pressure ◽  
Inherent Anisotropy ◽  
Deformation Response ◽  
Young’S Moduli ◽  
Confining Pressures

AbstractIn this study, the stress-deformation response of coal in the laboratory under threedimensional (3-D) loading conditions similar to those existing in an actual coal mine is investigated, and a constitutive model, including the effects of anisotropy, is developed. The coal samples were obtained from a mine in LeFlore County, Oklahoma, at a depth of approximately 25–30 ft below the ground surface. A High Capacity Cubical Device with servo-controlled independent loading along three axes of a cubical specimen and a computerized data acquisition and monitoring system were used to conduct the tests. A total of 21 tests under 4 different confining pressures and 5 different stress paths were conducted. The influence of the degree of anisotropy was investigated by comparing the transversely isotropic and isotropic idealizations for different stress paths (Triaxial Compression, Triaxial Extension and Simple Shear) at different confining pressures (1,600, 3,200 and 5,600 psi). The experimental results demonstrated that the coal exhibits inherent anisotropy and that it can be treated approximately as a transversely isotropic material. Also, the Young's moduli were found to be dependent on the confining pressure. The experimental data were used to evaluate the material constants associated with the elasto-plastic constitutive model developed in the study.

scholarly journals Numerical Test Study of the Microscale Failure Modes and Fractal Analysis of Lower Cambrian Shale Based on Digital Images

2020 ◽  
Vol 2020 ◽  
pp. 1-16
Author(s):  
Hengtao Cui ◽  
Zhonghu Wu ◽  
Liping Li ◽  
Jing Wang ◽  
Shuguang Song ◽  
...  
Keyword(s):  
Fractal Dimension ◽  
Failure Modes ◽  
Fractal Theory ◽  
Failure Process ◽  
Numerical Test ◽  
Confining Pressure ◽  
Guizhou Province ◽  
Internal Damage ◽  
Damage And Fracture ◽  
Confining Pressures

To reveal the effect of confining pressure on the mechanical properties and rupture modes of quartz-bearing shale, the shale core of the no. 3 block of Fenggang, Guizhou Province, China, was analyzed by nuclear magnetic resonance, polarized light microscope thin section observation and identification, and core X-ray whole-rock minerals diffraction analysis to determine the distribution of shale minerals in the Niutitang Formation. On the microscale, based on digital image processing technology, this paper characterizes the nonuniformity of minerals in shale, a numerical model that can reflect the true microstructure of shale. Then, the failure process of shale under different confining pressures was simulated. The results show that when the shale is loaded with vertical displacement under different confining pressures, the compressive strength and elastic modulus of the sample change significantly. The failure mode can be roughly divided into three types: the inverted V-shaped (0 MPa, 2 MPa, and 4 MPa), V-shaped (6 MPa and 8 MPa), and inverted Z-shaped (10 MPa). Since the development of fractal theory provides a new space for studying the damage and fracture of rocks, the damage evolution and failure process of shale can also be regarded as the fractal process of cracks, in which the fractal dimension is the core parameter. The calculation is different under different stress levels. The fractal dimension under the condition of confining pressure shows that the value of the fractal dimension is greatly affected by the effect of confining pressure. When the fractal dimension is higher, the fracture mode is more complicated, and the internal damage degree is more serious. The research results provide important theoretical guidance for shale gas fracturing production.

scholarly journals A Constitutive Model of Sandy Gravel Soil under Large-Sized Loading/Unloading Triaxial Tests

2021 ◽  
Vol 2021 ◽  
pp. 1-11
Author(s):  
Pengfei Zhang ◽  
Han Liu ◽  
Zhentu Feng ◽  
Chaofeng Jia ◽  
Rui Zhou
Keyword(s):  
Constitutive Model ◽  
Large Scale ◽  
Confining Pressure ◽  
Peak Strength ◽  
Triaxial Tests ◽  
Model Parameters ◽  
Sandy Gravel ◽  
Cumulative Volume ◽  
Gravel Soil ◽  
Confining Pressures

Based on large-scale triaxial tests of sandy gravel materials, the strength and deformation characteristics under loading/unloading conditions are analyzed. At the same time, the applicability of the hyperbolic constitutive model to sandy gravel is studied using experimental data. The results indicate that sandy gravel under low confining pressures (0.2 and 0.4 MPa) shows a weak softening trend; the higher the confining pressure, the more obvious the hardening tendency (0.6 and 0.8 MPa) and the greater the peak strength. During unloading tests, strain softening occurs, and the peak strength increases with increasing confining pressure. During loading tests, dilatancy appears when the confining pressure is low (0.2 MPa). With increasing confining pressure (0.4, 0.6, and 0.8 MPa), the dilatancy trend gradually weakens, and the cumulative volume tric strain increases, which reflects the relevance of the stress paths. Through research, it is found that the hyperbolic constitutive model has good applicability to sandy gravel soils, and the corresponding model parameters are obtained.

scholarly journals Study on Lateral Deformation and Failure Characteristics of Coal Based on Different Confining Pressures

2021 ◽  
Vol 2021 ◽  
pp. 1-11
Author(s):  
Jian-jun Ren ◽  
Shan-Yang Wei ◽  
Shi-Hai Shu ◽  
Wei-Dong Luo
Keyword(s):  
Axial Strain ◽  
Peak Stress ◽  
Confining Pressure ◽  
Lateral Strain ◽  
Lateral Deformation ◽  
Axis Ratio ◽  
Deformation And Failure ◽  
Initial Stage ◽  
Confining Pressures ◽  
Potential Parameters

To study the lateral deformation characteristics of coal under different confining pressures, coal compression experiments with confining pressures of 0 MPa, 3 MPa, 5 MPa, and 7 MPa were conducted under the same loading rate by using the TAW-2000 electrohydraulic servo rock mechanics experimental machine. The results of the study showed the following: at the initial stage of loading, the lateral strain of coal was about 12.22%–46.9% of the axial strain at the elastic deformation stage and 41.18%–64.96% of the axial strain at the inelastic deformation to peak stress stage. Compared with the experiment under 0 MPa confining pressure, the growth rate of the lateral strain of the coal under 3 MPa, 5 MPa, and 7 MPa confining pressures was much smaller than that of the corresponding axial strain. When the coal was damaged under different confining pressures, the lateral strain was maintained at about 0.6 × 10−2. Based on the field verification, we proposed that the lateral strain during the coal failure and the nonlinear region of the lateral axis ratio changing with time can be used as potential parameters for predicting the coal failure.

scholarly journals A Constitutive Model of Clay Considering Structural Failure

2021 ◽  
Vol 8 ◽  
Author(s):  
Biaohe Zhou ◽  
Bin Tang ◽  
Jiashuai Kang
Keyword(s):  
Constitutive Model ◽  
Yield Stress ◽  
Failure Process ◽  
Strength Distribution ◽  
Model Parameters ◽  
Structural Failure ◽  
Stress Strain ◽  
Softening Effect ◽  
Undisturbed Soil ◽  
Confining Pressures

Due to the different material composition and deposition conditions, the undisturbed clay presents different degree of structure. Because of the existence of structure, the undisturbed clay has structural yield stress. When the stress level exceeds the structural yield stress, the stress-strain relation of undisturbed clay has typical softening characteristics. To explore the constitutive relation of undisturbed soil, triaxial consolidation, and drainage tests were carried out on undisturbed and remolded soils of structural clay in Zhanjiang Formation in China, and the stress-strain relations under different confining pressures were obtained. By analyzing the structural failure process of undisturbed clay, Weibull distribution was introduced to describe the strength distribution of each point in undisturbed clay, and the structural failure coefficient of undisturbed clay was established during the loading process. Based on the elastic theory and structural failure coefficient, a constitutive model considering the structural failure of clay was proposed, and the method to determine the model parameters was given. The model was used to simulate the experimental data in this paper and the reference, and the validity of the model was verified. The results show that the model can well simulate the softening effect of structural clay during loading.

Study on Strength Properties and Crack Expansion Evolution Laws of Rock Containing Multiple Fissures

2013 ◽  
Vol 353-356 ◽  
pp. 608-613 ◽  
Author(s):  
Hong Hui Zhao ◽  
Hong Wen Jing ◽  
Hai Jian Su
Keyword(s):  
Failure Process ◽  
Confining Pressure ◽  
Strength Properties ◽  
Test System ◽  
Shear Cracks ◽  
High Confining Pressure ◽  
Confining Pressures ◽  
Hydraulic Servo ◽  
Evolution Laws ◽  
Tension Cracks

Through experiments that were carried out to study the rock-like specimens with nine fissures under uniaxial compression by YNS2000 electro-hydraulic servo test system, to reveal the mechanism about strength and mechanism about crack expansion evolution laws of rock containing multiple fissures. Applying numerical simulation (RFPA) for the whole failure process of rock containing multiple fissures with reasonable parameters, the results present the influence mechanism of different confining pressures for strength and crack expansion characteristics. The experimental results show: the peak strength of specimens with nine fissures degrades obviously compared with complete specimens; Specimens containing multiple fissures begin to crack with tension cracks, and break with shear cracks finally. With the increase of confining pressure, the compressive strength of rock containing multiple fissures increases gradually; And crack expansion generally occurs on the middle diagonal fissure-plane under high confining pressure.

Thermo-mechanical coupling damage constitutive model of rock based on the Hoek–Brown strength criterion

2017 ◽  
Vol 27 (8) ◽  
pp. 1213-1230 ◽  
Author(s):  
Xiaoli Xu ◽  
Feng Gao ◽  
Zhizhen Zhang
Keyword(s):  
Constitutive Model ◽  
Damage Evolution ◽  
Mechanical Response ◽  
Peak Stress ◽  
Strength Criterion ◽  
Confining Pressure ◽  
Stress Strain ◽  
Mechanical Coupling ◽  
Damage Stability ◽  
Damage Constitutive Model

Studying the thermal damage constitutive model of rock using statistical theory can better reflect the damage evolution process and the stress–strain relationship of rock under temperature and loading, which is one of the key problems especially in deep rock mechanics. The thermal-mechanical coupling damage constitutive model of rock is established using the Hoek–Brown strength criterion, based on the Weibull distribution and the continuous damage theory. The rationality of the model is also verified by experiments. The main conclusions are as follows. The stress–strain curves of rock can be divided into four stages according to the damage evolution characteristics, including the non-damage of loading, damage stability expansion, damage intensification expansion, and damage stability expansion to saturation, and the method of determining the demarcation points of each stage is given clearly. The initial damage point of the rock is about 25% of the peak stress, the damage value is about 0.3 when the rock reaches the peak stress and about 0.6 when reaches the residual stress. Both the damage value and the strain energy release rate of the rock corresponding to the peak stress show exponential growth with the increase in confining pressure. The maximum damage evolution rate of the rock shows exponential decay as the confining pressure rises, indicating that the confining pressure can delay the development of cumulative damage. The modified damage constitutive model considering compaction coefficient is in good agreement with the test curves in the stage of compaction, linear elasticity, yield, and pre-peak strength. It is hoped that through the research of this paper, it can provide references for studying the macroscopic mechanical response from the damage propagation characteristics of the rock in the future.

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