Effect of Gap Geometries on the Crack Initiation Stress of Synthetic Rock Material

2021 ◽  
Author(s):  
Enes Zengin ◽  
Zeynal Abiddin Erguler
Keyword(s):  
Numerical Model ◽  
Crack Initiation ◽  
Numerical Models ◽  
Failure Behavior ◽  
Test Results ◽  
Crack Initiation Stress ◽  
Geological Processes ◽  
Laboratory Test Results ◽  
Synthetic Rock ◽  
Initiation Stress

<p>The cracking phenomenon of the brittle rock and rock-like materials (concrete, gypsum) have been widely researched. Such long-standing intensive research requirement is due to the fact that crack initiation, propagation and coalescence are some of the most important parameters for evaluating the rock failure behavior and strength properties. Especially defining the crack initiation stress is a fundamental part of crack propagation that leads to the rock material's final failure. However, due to the nature of rocks, they may have complex inherit structures containing various gaps and void with different sizes and numbers. Rocks mostly tend to have circular and ellipsoidal voids as a result of long and complex geological processes. Owing to this limitation, it is always hard to understand and assess the crack initiation stress comprehensively. Especially for a couple of decades, with the help of developing computer science and technology, numerical models were used on this subject. In this study, various two-dimensional numerical rock models created using Distinct Element Method (DEM) based Particle Flow Code (PFC) were used to understand the effect of different gap geometries over crack initiation stress values of rock materials under uniaxial loading conditions. A base numerical model was calibrated using laboratory test results belonging to basalt rocks. In order to calibrate the numerical model, uniaxial, conventional triaxial and in-direct tensile test results were used. A flat-jointed contact model was chosen to create bonded material during the calibration process. Seven different numerical models were used to investigate the gap geometry effect on crack initiation stress under uniaxial conditions. The base model has a circular gap with 5.40 mm diameter. The other models created to understand the effect of geometry on crack initiation stress have different ellipsoidal geometry depending on the initial circular gap, 1.5 (8.10 mm), 2.5 (13.50 mm) and 3.5 (18.20 mm) times the diameter in the vertical and horizontal direction, respectively. The results of numerical models reveal that the crack initiation stress value decreases with the increase of the gap's vertical length while the width of gaps remains constant. Based on numerical models' results, the crack initiation stress value decreases with the increase of the gap's vertical length while the diameter of gaps remains constant.</p>

scholarly journals Experimental and Numerical Study of the Failure Behavior of Intermittent Rock Joints Subjected to Direct Shear Load

2018 ◽  
Vol 2018 ◽  
pp. 1-19 ◽  
Author(s):  
Xiang Fan ◽  
Kaihui Li ◽  
Hongpeng Lai ◽  
Qihua Zhao ◽  
Zhenhua Sun
Keyword(s):  
Crack Initiation ◽  
Rock Joints ◽  
Failure Behavior ◽  
Second Phase ◽  
Direct Shear ◽  
Crack Initiation Stress ◽  
Secondary Cracks ◽  
Peak Shear Stress ◽  
Initiation Stress ◽  
Three Phases

Two series of intermittent rock joints containing three joints arranged along the central shear axis were considered in this study. The failure behavior under direct shear loads was investigated by means of both physical tests and numerical simulations. The cracking behavior was found to be distinctly associated with the joint arrangement. Several types of main and secondary cracks were identified. The variation trends of the crack initiation stress ratio with inclination angle were analyzed and found to be partly different for the two series of intermittent joints. The whole fracturing process was characterized by three phases. Not all samples have to experience all three phases. The second phase is alternative and can be reflected by the shearing curve. Hence, two types of shearing curves, including single and double peaks, were identified. The double peak is due to the extrusion or sawteeth cutting in the second phase. Moreover, the numerical micromechanical analysis was performed to explain the shear behavior using the contact force and microcrack within the specimen. Based on the numerically measured local stresses, maximum and minimum principal stresses around the middle joint at crack initiation stress and peak shear stress were analyzed.

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.

scholarly journals Development of a Numerical Model for an Expanding Tube with Linear Explosive Using AUTODYN

2014 ◽  
Vol 2014 ◽  
pp. 1-10 ◽  
Author(s):  
Mijin Choi ◽  
Jung-Ryul Lee ◽  
Cheol-Won Kong
Keyword(s):  
Numerical Model ◽  
Numerical Models ◽  
Nonlinear Dynamic Analysis ◽  
Economic Benefits ◽  
Steel Tube ◽  
Test Results ◽  
Ballistic Test ◽  
Satellite Launch Vehicle ◽  
Joint Separation ◽  
2D And 3D

Pyrotechnic devices have been employed in satellite launch vehicle missions, generally for the separation of structural subsystems such as stage and satellite separation. Expanding tubes are linear explosives enclosed by an oval steel tube and have been widely used for pyrotechnic joint separation systems. A numerical model is proposed for the prediction of the proper load of an expanding tube using a nonlinear dynamic analysis code, AUTODYN 2D and 3D. To compute a proper core load, numerical models of the open-ended steel tube and mild detonating tube encasing a high explosive were developed and compared with experimental results. 2D and 3D computational results showed good correlation with ballistic test results. The model will provide more flexibility in expanding tube design, leading to economic benefits in the overall expanding tube development procedure.

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.

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.

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