scholarly journals Influence of Flaw Inclination Angle on Cracking Behavior of Rock-Like Materials under Uniaxial Compression

2019 ◽  
Vol 2019 ◽  
pp. 1-10 ◽  
Author(s):  
Rongchao Xu
Keyword(s):  
Crack Initiation ◽  
Uniaxial Compression ◽  
Inclination Angle ◽  
Failure Modes ◽  
Fractured Rock ◽  
Axial Stress ◽  
Uniaxial Compression Test ◽  
Wing Crack ◽  
Cracking Behavior ◽  
Secondary Cracks

The inclination angle of the flaw has an important effect on the cracking behavior of fractured rock. The influence of the inclination angle of closed flaw on the strength, cracking behavior, failure modes, and AE behaviors of specimens has not been investigated thoroughly. Uniaxial compression tests were conducted on gypsum samples containing a single closed flaw with different inclination angles. The flaw orientation influence on strength, cracking mechanism, failure modes, and AE behaviors was analyzed in detail. With the increase of the flaw inclination angle from 30° to 75°, the mechanical parameters such as elastic modulus, wing crack initiation strength, and uniaxial compression strength decrease first and then increase and reach the minimum value at 45°. The wing crack initiation angle decreases from 65° to 35° as the flaw inclination angle increases from 30° to 75°. The wing crack is more difficult to initiate from the tips of closed flaws compared with that of open flaws. The secondary cracks are initially shear cracks and propagate in a stable manner. However,when the axial stress reaches the peak strength, the secondary crack propagates unstably, which results in the macroscopic failure of the sample. The AE behaviors of samples are also analyzed during the uniaxial compression test. The experimental results are expected to provide helpful guidance for safe construction under fractured rock mass condition.

scholarly journals Study on the Interaction of Collinear Cracks and Wing Cracks and Cracking Behavior of Rock under Uniaxial Compression

2018 ◽  
Vol 2018 ◽  
pp. 1-10 ◽  
Author(s):  
Chaolin Wang ◽  
Yu Zhao ◽  
Yanlin Zhao ◽  
Wen Wan
Keyword(s):  
Uniaxial Compression ◽  
Inclination Angle ◽  
Shear Crack ◽  
Crack Coalescence ◽  
Crack Interaction ◽  
Shear Cracks ◽  
Collinear Cracks ◽  
Wing Crack ◽  
Cracking Behavior ◽  
Initiation And Propagation

This paper investigates the crack interaction, initiation, and propagation rules of rock-like materials containing two collinear cracks. Based on the Kachanov method, the formulations for stress intensity factors (SIFs) of two collinear cracks and two winged cracks are derived, respectively. The influences of bridge ligament and crack length on the crack interaction are analyzed theoretically. The results show that the propagation of a long crack is independent of crack interaction when d≥a2 and the same rule applies for a short crack when d≥a1. With the growth of wing cracks, the SIF of wings first remarkably decreases and then it tends toward a steady value. Subsequently, the propagation of collinear cracks and cracking processes under uniaxial compression are analyzed experimentally and numerically. Both the experimental results and simulation results demonstrate that shear cracks tend to initiate and propagate at higher inclination angle. The crack coalescence is affected by the inclination angle of bridge ligament. For increasing the inclination angle, the crack coalescence varies from wing crack failure to shear crack coalescence. As bridge ligament increases, the crack coalescence varies from shear crack coalescence to shear-wing crack coalescence and then to wing crack failure.

scholarly journals Acoustic Emission Characteristics and Joint Nonlinear Mechanical Response of Rock Masses under Uniaxial Compression

Energies ◽  
2021 ◽  
Vol 14 (1) ◽  
pp. 200
Author(s):  
Zhongliang Feng ◽  
Xin Chen ◽  
Yu Fu ◽  
Shaoshuai Qing ◽  
Tongguan Xie
Keyword(s):  
Acoustic Emission ◽  
Uniaxial Compression ◽  
Inclination Angle ◽  
Failure Modes ◽  
Strain Curve ◽  
Particle Flow Code ◽  
Rock Masses ◽  
Physical Experiments ◽  
Inclination Angles ◽  
Joint Inclination

The joint arrangement in rock masses is the critical factor controlling the stability of rock structures in underground geotechnical engineering. In this study, the influence of the joint inclination angle on the mechanical behavior of jointed rock masses under uniaxial compression was investigated. Physical model laboratory experiments were conducted on jointed specimens with a single pre-existing flaw inclined at 0°, 30°, 45°, 60°, and 90° and on intact specimens. The acoustic emission (AE) signals were monitored during the loading process, which revealed that there is a correlation between the AE characteristics and the failure modes of the jointed specimens with different inclination angles. In addition, particle flow code (PFC) modeling was carried out to reproduce the phenomena observed in the physical experiments. According to the numerical results, the AE phenomenon was basically the same as that observed in the physical experiments. The response of the pre-existing joint mainly involved three stages: (I) the closing of the joint; (II) the strength mobilization of the joint; and (III) the reopening of the joint. Moreover, the response of the pre-existing joint was closely related to the joint’s inclination. As the joint inclination angle increased, the strength mobilization stage of the joint gradually shifted from the pre-peak stage of the stress–strain curve to the post-peak stage. In addition, the instantaneous drop in the average joint system aperture (aave) in the specimens with medium and high inclination angles corresponded to a rapid increase in the form of the pulse of the AE activity during the strength mobilization stage.

scholarly journals Progressive Failure and Acoustic Emission Characteristics of Red Sandstone with Different Geometry Parallel Cracks under Uniaxial Compression Loading

2021 ◽  
Vol 2021 ◽  
pp. 1-11
Author(s):  
Xizhen Sun ◽  
Fanbao Meng ◽  
Ce Zhang ◽  
Xucai Zhan ◽  
He Jiang
Keyword(s):  
Acoustic Emission ◽  
Crack Initiation ◽  
Crack Propagation ◽  
Geometric Distribution ◽  
Progressive Failure ◽  
Fractured Rock ◽  
Propagation Mode ◽  
Wing Crack ◽  
Red Sandstone ◽  
Parallel Cracks

The geometric distribution of initial damages has a great influence on the strength and progressive failure characteristics of the fractured rock mass. Initial damages of the fractured rock were simplified as parallel cracks in different geometric distributions, and then, the progressive failure and acoustic emission (AE) characteristics of specimens under the uniaxial compression loading were analyzed. The red sandstone (brittle materials) specimens with the parallel preexisting cracks by water jet were used in the tests. The energy peak and stress attenuation induced by the energy release of crack initiation were intuitively observed in the test process. Besides, three modes of rock bridge coalescence were obtained, and wing crack was the main crack propagation mode. The wing crack and other cracks were initiated in different loading stages, which were closely related to the energy level of crack initiation. The propagation of wing crack (stable crack) consumed a large amount of energy, and then, the propagation of shear crack, secondary crack, and anti-wing crack (unstable crack) was inhibited. The relationship between the crack propagation mode and the geometric distribution of existing cracks in the specimen was revealed. Meanwhile, the strength characteristic and failure mode of fractured rock with the different geometric distributions of preexisting crack were also investigated. The energy evolution characteristics and crack propagation were also analyzed by numerical modeling (PFC2D).

Numerical investigation of micro-cracking behavior of brittle rock containing a pore-like flaw under uniaxial compression

2020 ◽  
Vol 29 (10) ◽  
pp. 1543-1568 ◽  
Author(s):  
Louis Ngai Yuen Wong ◽  
Jun Peng
Keyword(s):  
Compressive Strength ◽  
Elastic Modulus ◽  
Numerical Model ◽  
Crack Initiation ◽  
Uniaxial Compression ◽  
Uniaxial Compressive Strength ◽  
Early Stage ◽  
Brittle Rock ◽  
Cracking Behavior ◽  
Cracking Process

Pore-like flaws, which are commonly encountered in brittle rock, play an important role in the engineering performance of structures constructed in or on rock. Experimental and numerical investigations of micro-cracking mechanism of rock containing a pore-like flaw can enhance our knowledge of rock damage/failure from a microscopic view. In this study, the influences of a two-dimensional circular pore-like flaw with respect to its diameter and position on the strength and micro-cracking behavior of brittle rock under uniaxial compression are numerically investigated. The results reveal that the strength and elastic modulus are significantly affected by the diameter and position in the pore. The uniaxial compressive strength and elastic modulus of the numerical model with a pore diameter of 15.44 mm located in the center of the model are found to decrease by 58.6% and 56.4% respectively when compared with those of the intact model without a pore. As the pore position varies while the porosity remains unchanged, the simulated uniaxial compressive strength and elastic modulus are also found to be generally smaller than those of the intact model without a pore. When a pore-containing numerical model is loaded, the micro-cracks are found to mostly initiate at the top and bottom of the pore, due to the local tensile stress increase. The simulation results of the early-stage micro-cracking process and stress distribution are in a generally good agreement with the analytical solution obtained from the Kirsch equations. The grain-based model used in this study can not only study the crack initiation on the boundary of the pore but also provide a convenient means to analyze and visualize the temporal and spatial micro-cracking process after the crack initiation, which accounts for the variations in the simulated strength and modulus satisfactorily from a micro-cracking view.

Crack Growth Mechanisms from 3-D Surface Flaw with Varied Dipping Angle under Uniaxial Compression

2007 ◽  
Vol 353-358 ◽  
pp. 2353-2356 ◽  
Author(s):  
Y.S.H. Guo ◽  
R.H.C. Wong ◽  
K.T. Chau ◽  
Wei Shen Zhu ◽  
Shu Cai Li
Keyword(s):  
Crack Initiation ◽  
Crack Propagation ◽  
Crack Growth ◽  
Uniaxial Compression ◽  
Axial Loading ◽  
Growth Direction ◽  
Surface Flaw ◽  
Growth Mechanisms ◽  
Wing Crack ◽  
Ae Energy

A number of instability problems in rock engineering projects are caused by crack propagation. However, crack growth mechanisms from 3-dimentional flaw are not fully understood, in particular for 3-D flaw case with varied dipping angle. This study focuses on 3-D surface flaw using real rock specimens containing a flaw with varied inclination angle α from axial loading and dipping angle γ from specimen surface under uniaxial compression. Acoustic emission technique was used for tracing the initiation and growth of micro-cracks inside of specimen. It was found that crack growth process is affected by the dipping angle γ of the 3-D flaw. When dipping angle γ ≠ 90º, the thickness of rock above the flaw plane is thinner than that of below the flaw plane. As a result, compressive crack and wing crack initiated easily from the thinner flaw tips. And, the normalized stress for crack initiation σi /σc, AE events and the AE energy for crack growth decreases with the dipping angle γ. However, for γ = 90º, the thickness of rock above and below of the flaw tips is the same, it was observed that anti-wing crack (crack growth direction opposite to wing crack) initiated first at a certain place away from the flaw tips, then wing crack and compressive crack emerged at the late stage. For this case, the stress σi /σc, AE events and the AE energy for crack initiation and propagation are at a high value. Thus, for rock mass contains flaws geometry with small dipping angle, some problems of crack propagation may be induced easily during excavation.

Elasto-Plastic Cellular Automaton Simulation of Fracturing Process in Single Pre-Fractured Rocks under Uniaxial Compression

2010 ◽  
Vol 34-35 ◽  
pp. 383-386 ◽  
Author(s):  
Hua Yan Yao ◽  
Peng Zhi Pan
Keyword(s):  
Cellular Automaton ◽  
Uniaxial Compression ◽  
Failure Modes ◽  
Fractured Rock ◽  
Failure Process ◽  
Great Influence ◽  
Rock Fracturing ◽  
Rock Heterogeneity ◽  
Fracturing Process ◽  
Rock Specimens

Rock is a natural heterogeneous material and presents complicated behaviors in the fracturing process. It is prevail to study the basic failure mechanism of rocks via numerical simulation. Based on the elasto-plastic cellular automaton (EPCA) model, this paper simulates single pre-fractured rock fracturing process with consideration of rock heterogeneity on the meso-scale. In this model, the Weibull’s distribution, which characterizes heterogeneity with the homogeneous index m and the random seed parameter s, is adopted to describe the distribution of mechanical parameters of rock specimens such as cohesive strength, Young’s modulus, etc. Pre-existing crack rock specimens with different homogeneous index or the different random seed are simulated by EPCA under uniaxial compression. Numerical results show that heterogeneity has great influence on pre-fractured rock failure process, final failure modes, and the uniaxial compressive strength.

scholarly journals Failure Mechanisms of Brittle Rocks under Uniaxial Compression

2017 ◽  
Vol 47 (3) ◽  
pp. 59-80 ◽  
Author(s):  
Taoying Liu ◽  
Ping Cao
Keyword(s):  
Rock Mass ◽  
Crack Initiation ◽  
Failure Mechanism ◽  
Shear Crack ◽  
Fractured Rock ◽  
Rock Fracture ◽  
Wing Crack ◽  
Rock Bridge ◽  
Brittle Rocks ◽  
Shear Connection

AbstractThe behaviour of a rock mass is determined not only by the properties of the rock matrix, but mostly by the presence and properties of discontinuities or fractures within the mass. The compression test on rock-like specimens with two prefabricated transfixion fissures, made by pulling out the embedded metal inserts in the pre-cured period was carried out on the servo control uniaxial loading tester. The influence of the geometry of pre-existing cracks on the cracking processes was analysed with reference to the experimental observation of crack initiation and propagation from pre-existing flaws. Based on the rock fracture mechanics and the stress-strain curves, the evolution failure mechanism of the fissure body was also analyzed on the basis of exploring the law of the compression-shear crack initiation, wing crack growth and rock bridge connection. Meanwhile, damage fracture mechanical models of a compression-shear rock mass are established when the rock bridge axial transfixion failure, tension-shear combined failure, or wing crack shear connection failure occurs on the specimen under axial compression. This research was of significance in studying the failure mechanism of fractured rock mass.

Research of Inclination Angle Effect on Joint Rock Macromechanical Parameters

2011 ◽  
Vol 704-705 ◽  
pp. 1089-1094
Author(s):  
Yan Feng Feng ◽  
Tian Hong Yang ◽  
Hua Wei ◽  
Hua Guo Gao ◽  
Zhe Zhang
Keyword(s):  
Rock Mass ◽  
Uniaxial Compression ◽  
Inclination Angle ◽  
Damage Mechanics ◽  
Deformation Modulus ◽  
Strain Curve ◽  
Uniaxial Compression Test ◽  
Joint Rock Mass ◽  
Test Result ◽  
Joint Rock

The joint of rock mass influences and controls the rock mass intensity, deformation characteristics and instability failure in the rock engineering to a great extent. Using the similar material simulation is of different inclination angle of non-penetration jointing and non-jointing rock mass, through using rigid servo compression machine to carry uniaxial compression test, we get a nearly same trend of joint rock mass stress-strain curve of different angle, the curve of inclination angle of 45 is analyzed, the test result shows that the compressive strength first decreases and then increases gradually with the increase of rock inclination angle. The compression intensity is its minimum when of the inclination angle of 45°, and the deformation modulus first decreases and then increases, but deformation modulus of 30° is its minimum. In addition, through the use of developed RFPA2D system to simulate on trial uniaxial compression value based on microscopic damage mechanics, we get the conclusion that the numerical analysis and test result is fitting approximately, it is validated that the numerical model can simulate joint rock well. Keywords: joint rock mass, inclination angle, uniaxial compression, compressive intensity, deformation modulus

scholarly journals Acoustic Emission Multi-Parameter Analysis of Dry and Saturated Sandstone with Cracks under Uniaxial Compression

Energies ◽  
2019 ◽  
Vol 12 (10) ◽  
pp. 1959 ◽  
Author(s):  
Hongru Li ◽  
Rongxi Shen ◽  
Dexing Li ◽  
Haishan Jia ◽  
Taixun Li ◽  
...  
Keyword(s):  
Acoustic Emission ◽  
Uniaxial Compression ◽  
Fractured Rock ◽  
Rock Fracture ◽  
Failure Process ◽  
Parameter Analysis ◽  
Small Scale ◽  
Rock Interaction ◽  
Secondary Cracks ◽  
Ae Signals

In order to study the mechanics and acoustic emission (AE) characteristics of fractured rock under water-rock interaction, dried and saturated sandstone samples with prefabricated double parallel cracks were prepared. Then, uniaxial compression experiments were performed to obtain their AE signals and crack propagation images. The results show that water reduces the strength and fracture toughness of fractured sandstone and enhances plasticity. After saturation, the samples start to crack earlier; the cracks grow slowly; the failure mode is transformed from shear failure along the prefabricated cracks to combined shear and tensile failure; more secondary cracks are produced. The saturated samples release less elastic energy and weaker AE signals in the whole failure process. However, their AE precursor information is more obvious and advanced, and their AE sources are more widely distributed. Compared with dry specimens, the AE frequencies of saturated specimens in the early stage of loading are distributed in a lower frequency domain. Besides, the saturated samples release less complex AE signals which are dominated by small-scale signals with weaker multi-fractal characteristics. After discussion and analysis, it is pointed out that this may be because water makes rock prone to inter-granular fracture rather than trans-granular fracture. The water lubrication also may reduce the amplitude of middle-frequency band signals produced by the friction on the fracture surface. Multi-fractal parameters can provide more abundant precursory information for rock fracture. This is of great significance to the stability of water-bearing fractured rock mass and its monitoring, and is conducive to the safe exploitation of deep energy.

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