scholarly journals Cracking Mode Analysis of Crack Initiation in Rocks under Uniaxial Compression

2019 ◽  
Vol 2019 ◽  
pp. 1-9
Author(s):  
Ye Lou ◽  
Guangqing Zhang ◽  
Xiaoxiao Wang
Keyword(s):  
Acoustic Emission ◽  
Crack Initiation ◽  
Uniaxial Compression ◽  
Mode Analysis ◽  
Tight Sandstone ◽  
Crack Initiation Stress ◽  
Emission Parameter ◽  
Acoustic Emission Parameter ◽  
Cracking Mode ◽  
Initiation Stress

Crack initiation is related to the behavior of the preexisting microcracks within a rock specimen, which suggests the specimen starts to fail. The determination of crack initiation stress is important for identifying the elastic stage and related mechanical parameters. Uniaxial compression tests with acoustic emission monitoring were performed to study crack initiation for tight sandstone, loose sandstone, and granite. The evolution of the cracking mode, i.e., the statistics of the cracking mode under compression, was obtained through modified acoustic emission parameter analysis. Based on the logarithm of the acoustic emission parameter (LAEP), a cracking mode analysis (CMA) method is proposed and used to determine the crack initiation stress. Results from the tests indicate that the crack initiation stress between the same rock specimens obtained by CMA is very close. The mean ratio of crack initiation stress to compression strength is 0.45, 0.34, and 0.35 for tight sandstone, loose sandstone, and granite, respectively. According to the results of CMA, crack volumetric strain (CVS) method, and lateral strain response (LSR) method, there is no big difference among those methods in tight sandstone and loose sandstone. In granite, the results obtained by CMA are close to those obtained by CVS, but smaller than those obtained by LSR. The CMA interprets the initiation of cracks from the fracture behavior of microcracks and is an objective method to determine the initiation stress.

scholarly journals Experimental and Numerical Studies on Crack Initiation and Coalescence in Sandy Mudstone with Prefabricated Cross-Flaws Under Uniaxial Compression

2021 ◽  
Vol 2021 ◽  
pp. 1-17
Author(s):  
Dongxu Liang ◽  
Nong Zhang ◽  
Haoyu Rong ◽  
Zhe Xiang
Keyword(s):  
Numerical Simulation ◽  
Crack Initiation ◽  
Uniaxial Compression ◽  
Rock Bridge ◽  
Crack Initiation Stress ◽  
Dip Angle ◽  
Two Parameters ◽  
Initiation Stress ◽  
Main Flaw ◽  
Sandy Mudstone

The purpose of this paper is to study the crack initiation, propagation, and coalescence of the sandy mudstone sample with two sets of prefabricated cross-flaws under uniaxial compression. This study is different from previous studies on single or multiple parallel prefabricated flaws. The prefabricated cross-flaws are characterized by the dip of the rock bridge with the direction of the main flaw ( β ) and the angle between the direction of main and minor flaws ( γ ). The effects of these two parameters on crack initiation, propagation, coalescence, crack initiation stress, and coalescence stress are analyzed. Moreover, numerical simulation of the uniaxial compression experiments is performed using PFC2D with a flat-joint model, and the simulation results are in good agreement with those from the experiments. The results demonstrate that the dip angle of the rock bridge with the direction of the main flaw ( β ) has strong effects on the crack initiation and coalescence stresses. The larger the angle between the direction of main and minor flaws γ , the greater the crack initiation and coalescence stresses. The crack initiation stress is reduced for the case with cross-flaws compared with that with non-cross-flaws. Meanwhile, the connection type of main flaws and the width of the crack coalescence zone are difficult to observe through the experiments and are discovered from the numerical simulation.

scholarly journals Relationship between Brittleness Index and Crack Initiation Stress Ratio for Different Rock Types

2020 ◽  
Vol 2020 ◽  
pp. 1-12 ◽  
Author(s):  
Juyu Jiang ◽  
Dong Wang ◽  
Xinping Han ◽  
Shuai Di
Keyword(s):  
Experimental Data ◽  
Crack Initiation ◽  
Uniaxial Compression ◽  
Stress Ratio ◽  
Sedimentary Rocks ◽  
Brittleness Index ◽  
Crack Initiation Stress ◽  
Rock Types ◽  
The Relationship ◽  
Initiation Stress

Brittleness and crack initiation stress (σci) are important rock mechanical properties and intrinsically related to rock deformation and failure. We establish the relationship between σci and uniaxial tensile strength (σt) based on the Griffith stress criterion of brittle failure and introduce brittleness indexes B1–B4 based on the ratio of uniaxial compressive strength (σc) to σt. The crack initiation stress ratio (K) is defined as the ratio of σci to crack damage stress. The relationship between brittleness index and K is obtained from laboratory mechanics tests including uniaxial compression and Brazilian splitting tests. The results show that B1 and B2 have an inversely proportional and variant inversely proportional relationship with K, respectively, whereas no apparent relationship is observed between B3 and B4 and K. The fitting of experimental data from igneous, metamorphic, and sedimentary rocks shows that B1 and B2 have a power and linear relationship with K, respectively, whereas no functional relationship is observed between B3 and B4 and K. We collected 70 different types of uniaxial compression test data for igneous, metamorphic, and sedimentary rocks and obtained laws that are consistent within each rock type. The experimental data are used to verify K estimations using a specified constant α based on the experimental data. According to results of the limestone tests, α = 3 for σc < 60 MPa (high porosity), α = 5 for 60 MPa ≤ σc ≤ 90 MPa (moderate porosity), and α = 8 for σc > 90 MPa (low porosity) as well as for igneous and metamorphic rocks. Estimates of K for 127 different rock types using the newly defined brittleness index are in good agreement with the experimental results. This study provides an important new brittleness index calculation method and a simple and reliable method for estimating K.

scholarly journals Characterisation of fatigue damage in composites using an Acoustic Emission Parameter Correction Technique

2018 ◽  
Vol 151 ◽  
pp. 237-244 ◽  
Author(s):  
Safaa Kh Al-Jumaili ◽  
Mark J. Eaton ◽  
Karen M. Holford ◽  
Matthew R. Pearson ◽  
Davide Crivelli ◽  
...  
Keyword(s):  
Acoustic Emission ◽  
Fatigue Damage ◽  
Correction Technique ◽  
Emission Parameter ◽  
Acoustic Emission Parameter ◽  
Parameter Correction

scholarly journals Discrete Element Modeling of Crack Initiation Stress of Marble Based on Griffith’s Strength Theory

2020 ◽  
Vol 2020 ◽  
pp. 1-11
Author(s):  
Suifeng Wang ◽  
Fei Tan ◽  
Minglong You ◽  
Yu-Yong Jiao ◽  
Fubin Tu
Keyword(s):  
Crack Initiation ◽  
Particle Flow Code ◽  
Biaxial Compression ◽  
Discrete Element Modeling ◽  
Compression Tests ◽  
Strength Theory ◽  
Evolution Law ◽  
Crack Initiation Stress ◽  
Damage Process ◽  
Initiation Stress

Investigating the crack initiation stress of rocks is vital for understanding the gradual damage process of rocks and the evolution law of internal cracks. In this paper, the particle flow code method is used to conduct biaxial compression tests on a marble model with an elliptical crack under different confining pressures. According to the evolution status of microcracks in the rock during compression, four characteristic stresses are defined to reflect the gradual damage process of the marble. Two different methods are used to obtain crack initiation stress of rocks, and the calculation results are compared with those based on Griffith’s strength theory to verify the accuracy of this theory under compressive stress. Based on the numerical simulation results, the evolution law for the strength parameters of marble with the degree of damage is described. According to the proportional relationship between the peak stress and crack initiation stress, a new method for predicting the initiation stress is proposed, whose effectiveness is verified. Overall, the results of this study can serve as a useful guide for solving the important problems of slab cracking and rockburst encountered in underground space engineering.

Failure Stress in Notched Paper Sheets

2013 ◽  
Vol 569-570 ◽  
pp. 417-424
Author(s):  
Carlos A. Mora Santos ◽  
Orlando Susarrey Huerta ◽  
Vicente Flores Lara ◽  
Jorge Bedolla Hernández ◽  
Maribel A. Mendoza Nuñez
Keyword(s):  
Crack Initiation ◽  
The Self ◽  
Stress Theory ◽  
Crack Initiation Stress ◽  
Notched Specimens ◽  
Random Array ◽  
Crack Mechanics ◽  
Theoretical Stress ◽  
Initiation Stress ◽  
Circular Notch

In this work the crack initiation stress of notched specimens of filter paper is studied. The paper in the microstructure has a random array in their fibers while macroscopically it behaves anisotropically. The self-affine crack mechanics is used to study the size effect in the tensile behavior of this kind of paper under the presence of several conditions of geometrical notches. While in the traditional fracture mechanics the crack initiation stress is a material parameter when is reached a critical level at the crack tip, in the self-affine crack mechanics, depends moreover of the resulting tortuosity of the crack. Four geometrical arrangements in two sizes we considered: centered circular notch, centered lineal notch, sided circular notches and without notch at 10 and 300 mm width with a relation 2a/w = 0.25 under the same loading conditions. In this, the without notch specimens present the higher stress, all other notched specimens presented a similar crack initiation stress about 1 % of difference among them, and the crack growth is not affected by the geometry of notch. In spite of this difference, no one of the specimens reach the theoretical stress concentration of 3 such as predicted the classical stress theory.

Crack Initiation and Progressive Damage of Three Gorges Granite

2010 ◽  
Vol 146-147 ◽  
pp. 1227-1232
Author(s):  
Ze Qi Zhu ◽  
Qian Sheng ◽  
Yong Hui Zhang ◽  
Xian Lun Leng
Keyword(s):  
Crack Initiation ◽  
Triaxial Compression ◽  
Damage Model ◽  
Elliptic Crack ◽  
Progressive Damage ◽  
Three Gorges ◽  
Compression Tests ◽  
Crack Initiation Stress ◽  
Stress Changes ◽  
Initiation Stress

Based on the uniaxial and triaxial compression tests of Three Gorges granites，the crack initiation stress under different confining pressures can be obtained by studying the crack strain curves. The results show that the crack initiation stress changes at the same extent with confining pressure, and is generally located between 25% and 50% of the peak strength. Moreover, the crack initiation criteria and progressive damage model are established, and some beneficial conclusions are drawn. The tension concentration model of elliptic crack can be used to explain cracking mechanism of Three Gorges granite at relatively low confinement, and Three Gorges granite mainly occurs lateral damage in the microfracturing process and exhibits the similar damage evolutionary rule under different confining stress. The damage model can be used to describe the crack propagation process.

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