Experimental and numerical study on crack propagation and coalescence in rock-like materials under compression

2021 ◽  
pp. 030932472098691
Author(s):  
Xiaojing Li ◽  
Yifan Bai ◽  
Xudong Chen ◽  
Xinning Zhao ◽  
Mingying Lv
Keyword(s):  
Shear Failure ◽  
Numerical Study ◽  
Reference Value ◽  
Peak Stress ◽  
Tensile Failure ◽  
Wing Crack ◽  
Splitting Failure ◽  
Single Cross ◽  
Initiation Sequence ◽  
Double Cross

The discontinuous crack surface in a rock affects the stability of the whole rock system. The experiments in this paper were carried out by prefabricating rock-like specimens with different types of flaws, then the specimens were tested under uniaxial compression. Moreover, based on the theory of particle flow, PFC2D software was used for numerical simulation, and the comparative analysis of the experimental and simulative results was carried out to obtain the crack initiation sequence, propagation phenomenon, and failure mode of rock specimens with different flaw types. The results indicated that the wing crack started at the tip of flaw and the form of crack assumed split failure, followed by shear failure caused by the secondary crack. The tensile failure degree decreases and the influence of shear failure increases with the increase of flaw angle. The wing crack and secondary initiation stress value is 35%–55% and 85%–95% of the peak stress value. Crack coalescence appeared in adjacent flaws of rock-like specimens with multiple parallel single flaws, single-cross flaws and double-cross flaws, and the coalescence phenomenon always occurs when the stress peak value is reached. With the number of flaws increasing, the splitting failure of rock-like specimens became more and more serious, the splitting failure of double cross-flaw specimen is the most serious. As for the specimen with single-cross flaw, the wing crack would be produced at the tip of the flaw with larger obliquity. The results of this paper may offer certain reference value for the study on the mechanism of rock crack.

scholarly journals Experimental Study on Mechanical Damage and Fracture Characteristics of Granite under Different Water Cooling Conditions

2021 ◽  
Vol 2021 ◽  
pp. 1-17
Author(s):  
Zhuangzhuang Yao ◽  
Zhigang Zhang ◽  
Wenbin Wu ◽  
Jiang Wu
Keyword(s):  
Acoustic Emission ◽  
Shear Failure ◽  
Elasticity Modulus ◽  
Temperature Drop ◽  
Mechanical Damage ◽  
Peak Stress ◽  
Acoustic Emission Event ◽  
Tensile Failure ◽  
Fracture Characteristics ◽  
Damage And Fracture

In order to investigate the mechanical property deterioration and fracture characteristics of granite under different temperature drop and thermal cycle conditions, the evolution laws of mechanical properties, acoustic emission event distribution, and macro and micro failure characteristics of granite under different temperature changes were studied and analyzed by the servo loading, acoustic emission monitoring, and scanning electron microscope systems. The following conclusions were gained from the test results. (1) The peak stress and elasticity modulus of the three temperature drop treatments all decreased with the increase of the number of thermal cycles. In terms of magnitude, the following relationship was satisfied: 10°C > 15°C > 20°C. After 8 cycles, the peak stress and elasticity modulus tended to be stable for 15°C and 20°C temperature drops. (2) At a temperature drop of 20°C, the heterogeneity first increased and then tended to be stable; when the temperature was dropped by 15°C at each cycle, however, the heterogeneity first decreased and then became stable; as for the case of 10°C, the heterogeneity showed an overall decreasing trend. After 4 cycles, the heterogeneities were ranked as 15°C > 20°C > 10°C. After 8 cycles, 20°C > 15°C > 10°C. (3) With the decrease of temperature drop amplitude or the increase of cycles, the connectivity of microcracks in granite improved on the whole, the aperture and shape factor of microcracks increased, the damage of granite intensified, and the duration of the quiet period in the acoustic emission ringing count rate prolonged. (4) The tensile failure dominated at a temperature drop amplitude of 10°C. When the temperature drop was 15°C, the failure mode transitioned from hybrid tension-shear failure to tensile failure as the cycle times increased, whereas the hybrid tension-shear failure dominated with a temperature drop of 20°C.

Numerical study of the flow over the modified simple frigate shape

2020 ◽  
pp. 095441002097775
Author(s):  
Tong Li ◽  
Yibin Wang ◽  
Ning Zhao
Keyword(s):  
Bluff Body ◽  
Recirculation Zone ◽  
Numerical Study ◽  
Reference Value ◽  
Flow Fields ◽  
Navier Stokes ◽  
Detached Eddy Simulation ◽  
Eddy Simulation ◽  
Delayed Detached Eddy Simulation ◽  
Simulation Results

The simple frigate shape (SFS) as defined by The Technical Co-operative Program (TTCP), is a simplified model of the frigate, which helps to investigate the basic flow fields of a frigate. In this paper, the flow fields of the different modified SFS models, consisting of a bluff body superstructure and the deck, were numerically studied. A parametric study was conducted by varying both the superstructure length L and width B to investigate the recirculation zone behind the hangar. The size and the position of the recirculation zones were compared between different models. The numerical simulation results show that the size and the location of the recirculation zone are significantly affected by the superstructure length and width. The results obtained by Reynolds-averaged Navier-Stokes method were also compared well with both the time averaged Improved Delayed Detached-Eddy Simulation results and the experimental data. In addition, by varying the model size and inflow velocity, various flow fields were numerically studied, which indicated that the changing of Reynolds number has tiny effect on the variation of the dimensionless size of the recirculation zone. The results in this study have certain reference value for the design of the frigate superstructure.

scholarly journals Influence of Patching on the Shear Failure of Reinforced Concrete Beam without Stirrup

2021 ◽  
Vol 6 (7) ◽  
pp. 97
Author(s):  
Stefanus Adi Kristiawan ◽  
Halwan Alfisa Saifullah ◽  
Agus Supriyadi
Keyword(s):  
Reinforced Concrete ◽  
Shear Failure ◽  
Numerical Study ◽  
Unsaturated Polyester ◽  
Reinforced Concrete Beam ◽  
Concrete Cover ◽  
Shear Capacity ◽  
Rc Beam ◽  
Shear Span ◽  
Shear Cracking

Deteriorated concrete cover, e.g., spalling or delamination, especially when it occurs at the web of a reinforced concrete (RC) beam within the shear span, can reduce the shear capacity of the beam. Patching of this deteriorated area may be the best option to recover the shear capacity of the beam affected. For this purpose, unsaturated polyester resin mortar (UPR mortar) has been formulated. This research aims to investigate the efficacy of UPR mortar in limiting the shear cracking and so restoring the shear capacity of the deteriorated RC beam. The investigation is carried out by an experimental and numerical study. Two types of beams with a size of 150 × 250 × 1000 mm were prepared. The first type of beams was assigned as a normal beam. The other was a beam with a cut off in the non-stirrup shear span, which was eventually patched with UPR mortar. Two reinforcement ratios were assigned for each type of beams. The results show that UPR mortar is effective to hamper the propagation of diagonal cracks leading to increase the shear failure load by 15–20% compared to the reference (normal) beam. The increase of shear strength with the use of UPR mortar is consistently confirmed at various reinforcement ratios.

On the Direction of Fatigue Cracks in Polycrystalline Ingot Iron

1952 ◽  
Vol 19 (1) ◽  
pp. 54-56
Author(s):  
F. A. McClintock
Keyword(s):  
Statistical Analysis ◽  
Shear Failure ◽  
Fatigue Cracks ◽  
Fatigue Tests ◽  
Tensile Failure ◽  
Bending Fatigue ◽  
Polycrystalline Iron

Abstract A statistical analysis is developed to show how a microscopic shear failure can result in the apparent tensile failure of polycrystalline iron in rotary bending fatigue tests.

scholarly journals Failure Process Simulation of Interlayered Rocks under Compression

2018 ◽  
Vol 2018 ◽  
pp. 1-13
Author(s):  
Chi Yao ◽  
Sizhi Zeng ◽  
Jianhua Yang
Keyword(s):  
Shear Failure ◽  
Failure Process ◽  
Strength Criterion ◽  
Tensile Failure ◽  
Strength Anisotropy ◽  
Rigid Block ◽  
Bedding Planes ◽  
Typical Experiment ◽  
Confining Pressures ◽  
Spring Method

Anisotropy in strength and deformation of rock mass induced by bedding planes and interlayered structures is a vital problem in rock mechanics and rock engineering. The modified rigid block spring method (RBSM), initially proposed for modeling of isotropic rock, is extended to study the failure process of interlayered rocks under compression with different confining pressures. The modified rigid block spring method is used to simulate the initiation and propagation of microcracks. The Mohr–Coulomb criterion is employed to determine shear failure events and the tensile strength criterion for tensile failure events. Rock materials are replaced by an assembly of Voronoi-based polygonal blocks. To explicitly simulate structural planes and for automatic mesh generation, a multistep point insertion procedure is proposed. A typical experiment on interlayered rocks in literature is simulated using the proposed model. Effects of the orientation of bedding planes with regard to the loading direction on the failure mechanism and strength anisotropy are emphasized. Results indicate that the modified RBSM model succeeds in capturing main failure mechanisms and strength anisotropy induced by interlayered structures and different confining pressures.

Study on Failure of Rock Mass around Deep Tunnel

2011 ◽  
Vol 99-100 ◽  
pp. 370-374 ◽  
Author(s):  
Yue Hong Qian ◽  
Ting Ting Cheng ◽  
Xiang Ming Cao ◽  
Chun Ming Song
Keyword(s):  
Rock Mass ◽  
Stress Field ◽  
Failure Modes ◽  
Shear Failure ◽  
Simple Function ◽  
Tensile Failure ◽  
Deep Tunnel ◽  
Main Mode

During excavating the problem of unloading is a dynamic one essentially. Assuming the unloading ruled by a simple function and based on the Hamilton principal, the distribution of the stress field nearby the tunnel is obtained. The characteristics of the failure nearby the tunnel are analyzed considering the shear failure and tensile failure. The results show that the main mode of the shear failure, intact and tensile failure occurs from the tunnel. The characteristic of the shear failure, intact and tensile failure are one of the likely failure modes.

scholarly journals Failure Characteristics and Mechanism of Multiface Slopes under Earthquake Load Based on PFC Method

2021 ◽  
Vol 2021 ◽  
pp. 1-11
Author(s):  
Tao Yang ◽  
Yunkang Rao ◽  
Huailin Chen ◽  
Bing Yang ◽  
Jiangrong Hou ◽  
...  
Keyword(s):  
Moisture Content ◽  
Failure Mechanism ◽  
Failure Modes ◽  
Shear Failure ◽  
Shaking Table ◽  
Tensile Failure ◽  
Particle Flow Code ◽  
Shear Cracks ◽  
Local Shear ◽  
Shear Slip

Understanding the failure mechanism and failure modes of multiface slopes in the Wenchuan earthquake can provide a scientific guideline for the slope seismic design. In this paper, the two-dimensional particle flow code (PFC2D) and shaking table tests are used to study the failure mechanism of multiface slopes. The results show that the failure modes of slopes with different moisture content are different under seismic loads. The failure modes of slopes with the moisture content of 5%, 8%, and 12% are shattering-shallow slip, tension-shear slip, and shattering-collapse slip, respectively. The failure mechanism of slopes with different water content is different. In the initial stage of vibration, the slope with 5% moisture content produces tensile cracks on the upper surface of the slope; local shear slip occurs at the foot of the slope and develops rapidly; however, a tensile failure finally occurs. In the slope with 8% moisture content, local shear cracks first develop and then are connected into the slip plane, leading to the formation of the unstable slope. A fracture network first forms in the slope with 12% moisture content under the shear action; uneven dislocation then occurs in the slope during vibration; the whole instability failure finally occurs. In the case of low moisture content, the tensile crack plays a leading role in the failure of the slope. But the influence of shear failure becomes greater with the increase of the moisture content.

scholarly journals Numerical Study of Fracture Characteristics of Deep Granite Induced by Blast Stress Wave

2021 ◽  
Vol 2021 ◽  
pp. 1-22
Author(s):  
Zheming Zhu ◽  
Weiting Gao ◽  
Duanying Wan ◽  
Meng Wang ◽  
Yun Shu
Keyword(s):  
Shear Failure ◽  
Numerical Study ◽  
Numerical Models ◽  
Rock Fracture ◽  
Initial Pressure ◽  
3D Models ◽  
In Situ Stress ◽  
Vertical Pressure ◽  
The Difference ◽  
Radial Cracks

To study the characteristics of rock fracture in deep underground under blast loads, some numerical models were established in AUTODYN code. Weibull distribution was used to characterize the inhomogeneity of rock, and a linear equation of state was applied to describe the relation of pressure and volume of granite elements. A new stress initialization method based on explicit dynamic calculation was developed to get an accurate stress distribution near the borehole. Two types of in situ stress conditions were considered. The effect of heterogeneous characteristics of material on blast-induced granite fracture was investigated. The difference between 2D models and 3D models was discussed. Based on the numerical results, it can be concluded that the increase of the magnitude of initial pressure can change the mechanism of shear failure near the borehole and suppress radial cracks propagation. When initial lateral pressure is invariable, with initial vertical pressure rising, radial cracks along the acting direction of vertical pressure will be promoted, and radial cracks in other directions will be prevented. Heterogeneous characteristics of material have an obvious influence on the shear failure zones around the borehole.

Calculation and Implications of Breakdown Pressures in Directional Wellbore Stimulation

2015 ◽  
Author(s):  
Robert D. Barree ◽  
Jennifer L. Miskimins
Keyword(s):  
Shear Failure ◽  
Growth Parameters ◽  
Vertical Plane ◽  
Longitudinal Direction ◽  
In Situ Stress ◽  
Tensile Failure ◽  
Petroleum Engineering ◽  
Breakdown Pressure ◽  
Cascading Effects ◽  
Wellbore Pressure

Abstract In 1898, Kirsch published equations describing the elastic stresses around a circular hole that are still used today in wellbore pressure breakdown calculations. These equations are standard instruments used in multiple areas of petroleum engineering, however, the original equations were developed strictly for vertical well settings. In today's common directional or horizontal well situations, the equations need adjusted for both deviation from the vertical plane and orientation to the maximum and minimum horizontal in-situ stress anisotropy. This paper provides the mathematical development of these modified breakdown equations, along with examples of the implications in varying strike-slip and pore pressure settings. These examples show conditions where it is not unusual for breakdown pressure gradients to exceed 1.0 psi/ft and describes why certain stages in "porpoising" horizontal wells experience extreme breakdown issues during hydraulic fracturing treatments. The paper also discusses how, in most directional situations, the wellbore will almost always fail initially in a longitudinal direction at the borehole wall, after which the far-field stresses will take over and transverse components can be developed. Tortuosity and near wellbore friction pressure can actually add to forcing the initiation of such longitudinal fractures, which can then have cascading effects on other growth parameters such as cluster-to-cluster and stage-to-stage stress shadowing. Special considerations for highly laminated anisotropic formations, where shear failure of the wellbore may precede or preclude tensile failure, are also introduced. Such failure behaviors have significant implications on near wellbore conductivity requirements and can also greatly impact well production and recovery efforts.

scholarly journals Slushflow hazard — where, why and when? 25 years of experience with slushflow consulting and research

1998 ◽  
Vol 26 ◽  
pp. 370-376 ◽  
Author(s):  
Erik Hestnes
Keyword(s):  
Water Supply ◽  
Shear Failure ◽  
Meteorological Data ◽  
Water Pressure ◽  
Tensile Failure ◽  
Hazard Evaluation ◽  
General Validity ◽  
Ground Conditions ◽  
Snowpack Properties ◽  
Basal Shear

Slushflows — flowing mixtures of water and snow — are a major natural hazard in Norway. Knowledge gathered by the Norwegian Geotechnical Institute during 25 years of slushflow consulting and research is presented. The variation in regional occurrence is described and related to climatic premises and ground conditions. The principal ideas about slushflow release, down-slope propagation and run-out are outlined. They are closely related to the rate and duration of water supply, snowpack properties and geomorphic factors. Slushflow release is caused by basal shear failure aided by water pressure to cause loss of basal support and finally tensile failure through the snowpack. Our methods of hazard evaluation and acute-hazard prediction and warning are summarized, including the estimation of water supply based on meteorological data. The results of a worldwide questionnaire on slushflows, literature studies and scientific contacts, indicate that slushflows occur in all countries having a seasonal snow cover and that the results of our studies in Norway have a general validity.

Sign in / Sign up

Export Citation Format

Share Document