scholarly journals Investigation into Macro- and Microcrack Propagation Mechanism of Red Sandstone under Different Confining Pressures Using 3D Numerical Simulation and CT Verification

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-12
Author(s):  
Wen Zhang ◽  
Yan-yu Chen ◽  
Jin-ping Guo ◽  
Sai-sai Wu ◽  
Cheng-yuan Yan
Keyword(s):  
Crack Propagation ◽  
Failure Mechanism ◽  
Triaxial Compression ◽  
Ct Scanning ◽  
Internal Crack ◽  
Parameter Calibration ◽  
External Crack ◽  
Red Sandstone ◽  
Microcrack Propagation ◽  
Simulation Results

The growth and evolvement features of crack are of great significance to study the failure mechanism of rock mass and valuate the stability of the cavity. In this study, in order to obtain the mechanics parameters and external macroscopic crack propagation characteristics of red sandstone, triaxial compression tests were carried out. Based on the experimental results, a numerical model was established through the reasonable parameter calibration by the PFC3D software. The internal and external crack propagation processes of red sandstone under triaxial compression were simulated. Moreover, to verify the simulation results, the CT scanning and three-dimensional reconstruction technologies were used to observe the internal crack state of the specimens. The results showed that the internal crack failures occurred first at the end of the rock specimen. Then, the microcracks continued to accumulate and expand under the combined action of axial stress and confining pressure. The accumulated microcracks finally converged to form a macroscopic oblique shear failure. Based on the homogenizing treatment and reasonable parameter calibration, the internal and external crack expansion and evolution processes of the rock were simulated by the PFC3D model and the simulation results are consistent with the results obtained from the triaxial compression test and the CT scanning. The macro- and microfailure mode of crack propagation of the specimen deepens the understanding of rock failure mechanism. The PFC3D homogenization simulation method provides a new feasible method to study the macro- and microfailure mode of internal and external crack propagation of rock under compression.

Study on Constitutive Mode of Three Typical Rocks Based on Triaxial Compression Test

2012 ◽  
Vol 170-173 ◽  
pp. 322-326
Author(s):  
Kui Chen ◽  
Ren Hua Yang ◽  
Tao Xu ◽  
Ya Jing Qi
Keyword(s):  
Residual Strength ◽  
Triaxial Compression ◽  
Confining Pressure ◽  
Digital Design ◽  
Peak Strength ◽  
Design Parameters ◽  
Stress Strain ◽  
Red Sandstone ◽  
Constitutive Mode ◽  
Shield Machine

In order to study the relationship between the design parameters of the shield machine and the strength of rock, the behaviours of rocks under the conventional triaxial compression, the complete stress-strain curves under different confining pressures of three typical rocks, i.e. granite, limestone and red sandstone, were taken out for analysis. From the curves, the values of elastic modulus E and Poisson's ratio μ were gained and the relationships between the following parameters were figured out, which are peak strength versus confining pressure, residual strength versus confining pressure, strain at peak strength versus confining pressure, and strain at residual strength versus confining pressure. According to the values and relationships, the complete stress-strain curves were divided into three parts. For each part, a constitutive equation was established by using the strain softening trilinear elastic-brittle-plastic constitutive model, and all the related parameters in the constitutive equations were also presented, which provide a theoretical foundation for the digital design of the cutter head and cutters of Shield machine.

Microscopic Failure Mechanism Analysis of Sandstone Under Triaxial Compression

2018 ◽  
Vol 37 (2) ◽  
pp. 683-690 ◽  
Author(s):  
Guibin Zhang ◽  
Wenquan Zhang ◽  
Hailong Wang ◽  
Chuanyang Jia ◽  
Keming Liu ◽  
...  
Keyword(s):  
Failure Mechanism ◽  
Triaxial Compression ◽  
Mechanism Analysis

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).

Application of Multifractal to Characterize Microscopic Crack Propagation in Red Sandstone

2006 ◽  
pp. 891-894
Author(s):  
Mao Sen Cao ◽  
Qing Wen Ren ◽  
Pi Zhong Qiao
Keyword(s):  
Crack Propagation ◽  
Red Sandstone ◽  
Microscopic Crack

scholarly journals Experimental Research on the Mechanical Characteristics and the Failure Mechanism of Coal-Rock Composite under Uniaxial Load

2020 ◽  
Vol 2020 ◽  
pp. 1-11
Author(s):  
Ke Yang ◽  
Zhen Wei ◽  
Xiaolou Chi ◽  
Yonggang Zhang ◽  
Litong Dou ◽  
...  
Keyword(s):  
Compressive Strength ◽  
Acoustic Emission ◽  
Elastic Modulus ◽  
Crack Propagation ◽  
Failure Mechanism ◽  
Poisson’S Ratio ◽  
Mechanical Characteristics ◽  
Poisson's Ratio ◽  
Energy Value ◽  
Coal Rock

Due to the influence of the component structure and combination modes, the mechanical characteristics and failure modes of the coal-rock composite show different characteristics from the monomer. In order to explore the effect of different coal-rock ratios on the deformation and the failure law of the combined sample, the RMT rock mechanics test system and acoustic emission real-time monitoring system are adopted to carry out uniaxial compression tests on coal, sandstone, and three kinds of combined samples. The evolution rules of the mechanical parameters of the combined samples, such as the uniaxial compressive strength, elastic modulus, and Poisson’s ratio, are obtained. The expansion and failure deformation characteristics of the combined sample are analyzed. Furthermore, the evolution laws of the fractal and acoustic emission signals are combined to reveal the crack propagation and failure mechanism of the combined samples. The results show that the compressive strength and elastic modulus of the combined sample increase with the decrease of the coal-rock ratios, and Poisson’s ratio decreases with the decrease of the coal-rock ratios. The strain softening weakens at the postpeak stage, which shows an apparent brittle failure. The combined sample of coal and sandstone has different degrees of damages under load. The coal is first damaged with a high degree of breakage, with obvious tensile failure. The acoustic emission energy value presents different stage characteristics with increasing load. Crackling sound occurs in the destroy section before the sample reaches the peak, along with small coal block ejection and the partial destruction. The energy value fluctuates violently, with the appearance of several peaks. At the postpeak stage, the coal samples expand rapidly with a loud crackling sound in the destroy section, and the energy value increases dramatically. The crack propagation induces the damage in the sandstone; when the energy reaches the limit value, the instantaneous release of elastic energy leads to the overall structural instability.

Initiation and failure mechanism of base instability of excavations in clay triggered by hydraulic uplift

2015 ◽  
Vol 52 (5) ◽  
pp. 599-608 ◽  
Author(s):  
Y. Hong ◽  
C.W.W. Ng ◽  
L.Z. Wang
Keyword(s):  
Failure Mechanism ◽  
Simple Shear ◽  
Triaxial Compression ◽  
Soft Clay ◽  
Constitutive Models ◽  
Model Parameters ◽  
Hydraulic Pressure ◽  
Percentage Increase ◽  
Basal Resistance ◽  
Dimensionless Groups

Excavations in clay overlying an aquifer may cause catastrophic basal failure due to hydraulic uplift. Although case histories with hydraulic uplift failures are reported worldwide from time to time, the initiation and failure mechanism of the base instability are not well studied and understood. To address these two issues, dimensional analysis is firstly conducted to propose dimensionless groups (DGs) possibly relevant to this subject. Effects of these DGs on the initiation and failure mechanism of base instability are then investigated, by carrying out a series of finite element analyses, in which constitutive models and model parameters have been previously validated against centrifuge test results. It is revealed that the initiation and failure mechanism of base instability due to hydraulic uplift is mainly governed by a ratio of excavation width over the thickness of soft clay inside excavation (B/D). As excavation becomes narrower (i.e., B/D decreases), the hydraulic pressure (Pi) required to initiate uplift movement of clay inside excavation increases significantly (maximum percentage increase = 50%), due to increased effect of downward shear stress acting along soil–wall interface on basal resistance. Based on the parametric study, a calculation chart is developed for estimating Pi of excavations with varied B/D and undrained shear strength of clay. At basal failure caused by hydraulic uplift, the dominant failure mode changes from simple shear in relatively narrow excavations (i.e., B/D < 4) to combined modes of triaxial compression, triaxial extension, and simple shear in relatively wide excavations (i.e., B/D > 4).

Comparison of the Fatigue Crack Propagation Resistance of α+β and β Titanium Alloys

2008 ◽  
Vol 378-379 ◽  
pp. 117-130
Author(s):  
Matteo Benedetti
Keyword(s):  
Fatigue Crack ◽  
Crack Propagation ◽  
Titanium Alloys ◽  
Fatigue Crack Propagation ◽  
Propagation Resistance ◽  
Microstructural Parameters ◽  
Crack Propagation Resistance ◽  
Microcrack Propagation ◽  
Small Cracks ◽  
The Relationship

The present paper tries to summarize the relationship between microstructure, extrinsic mechanisms and fatigue crack propagation resistance of α+β and β titanium alloys. Emphasis is placed on microstructural parameters, which can be varied by processing, and their effects on the material inherent fracture properties, governing the resistance against microcrack propagation. Moreover, the resistance against macrocracks as well as small cracks in the presence of notch plasticity has been discussed on the basis of secondary extrinsic mechanics such as crack front geometry, crack bridging and crack closure.

Research on the Effect of Repairing Anterior Teeth with All-Ceramic Veneer Based on CT Images

2020 ◽  
Vol 10 (4) ◽  
pp. 940-946
Author(s):  
Shuang Liu ◽  
Hui Yan ◽  
Yuehang Gao
Keyword(s):  
Light Transmission ◽  
Chemical Properties ◽  
Ct Scanning ◽  
Ceramic Materials ◽  
Original Data ◽  
Image Method ◽  
Finite Element Software ◽  
Anterior Teeth ◽  
All Ceramic ◽  
Simulation Results

IPS e.maxPress all-ceramic materials have good physical and chemical properties, biocompatibility, light transmission similar to natural teeth and excellent aesthetic properties, so they are widely used in clinical practice. In this study, the anterior porcelain veneer was made by using IPS e.maxPress hot-pressed casting ceramic under the guidance of DSD software aesthetic design, and its clinical aesthetic repair effect and success rate were evaluated, which provided a useful reference for clinical aesthetic restoration work. The original data was obtained by using the medical image method; the DICOM data obtained by CT scanning was input into the reverse engineering software for image processing and data optimization by using the reverse technique to obtain the real tooth and mandible model. The 3D modeling software is used to establish the implant model and the associated tissue model, and the assembly is completed. The finite element software is introduced, the contact type between the tissues is set, and the clinical simulation results are compared to analyze the simulation results. Practice provides a better surgical solution.

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