scholarly journals Study on the Effect of Continuity and Load Angle of Prefabricated Cross-Flaws on Crack Initiation and Coalescence

2021 ◽  
Vol 2021 ◽  
pp. 1-17
Author(s):  
Dongxu Liang ◽  
Nong Zhang ◽  
Haoyu Rong
Keyword(s):  
Numerical Simulation ◽  
Crack Initiation ◽  
Substantial Effect ◽  
Crack Coalescence ◽  
Experimental Results ◽  
Shear Cracks ◽  
Primary Defect ◽  
Crack Initiation Stress ◽  
Two Parameters ◽  
Initiation Stress

In this study, a model that is closer to the state of fracture presentation in natural rocks has been developed, which is different from the previous. The cross-flaws can be characterized by the joint persistency ( k ) and the angle between the primary flaws and axial load ( α ). The two parameters were varied individually and, by combining them, nine specimens with different nodal parameters were formed. Laboratory specimens and numerical simulations were performed on these specimens to investigate the crack extension process and the variation of crack initiation and coalescence stresses. It is found that a new category of crack coalescence is discovered according to the experimental results besides those reported before, and the angle α affects whether tensile-shear cracks appear. Also, α has an impact on the location where crack first occurs. The joint persistency k alters rock failure mode and has a substantial effect on crack initiation stress. However, the effect on the aggregation stress is not significant. The crack initiation stress decreases in the case of cross-flaws in contrast to flat fissures. In addition, the flat-joint model in PFC2D is used for numerical simulation. It is possible to conduct a study that is difficult to achieve experimentally by using simulations, i.e., only changing one macroparameter without changing others and thus studying the changes in the effect on cracking during fracture. The simulation results are in good agreement with the experimental results. At the same time, the connection mode and the width of the crack coalescence zone of the primary defect, which is difficult to observe in the experiment, are found out from the numerical simulation.

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 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.

Evaluation of methods for determining crack initiation stress under compression

2018 ◽  
Vol 235 ◽  
pp. 81-97 ◽  
Author(s):  
Tao Wen ◽  
Huiming Tang ◽  
Junwei Ma ◽  
Yankun Wang
Keyword(s):  
Crack Initiation ◽  
Crack Initiation Stress ◽  
Initiation Stress ◽  
Evaluation Of Methods
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