scholarly journals An Extension Strain Type Mohr–Coulomb Criterion

2021 ◽  
Author(s):  
Manfred Staat
Keyword(s):  
Failure Modes ◽  
Peak Stress ◽  
Fracture Initiation ◽  
Failure Surface ◽  
Confining Pressure ◽  
Biaxial Compression ◽  
Simple Extension ◽  
Strain Criterion ◽  
Shear Component ◽  
Extension Strain

AbstractExtension fractures are typical for the deformation under low or no confining pressure. They can be explained by a phenomenological extension strain failure criterion. In the past, a simple empirical criterion for fracture initiation in brittle rock has been developed. In this article, it is shown that the simple extension strain criterion makes unrealistic strength predictions in biaxial compression and tension. To overcome this major limitation, a new extension strain criterion is proposed by adding a weighted principal shear component to the simple criterion. The shear weight is chosen, such that the enriched extension strain criterion represents the same failure surface as the Mohr–Coulomb (MC) criterion. Thus, the MC criterion has been derived as an extension strain criterion predicting extension failure modes, which are unexpected in the classical understanding of the failure of cohesive-frictional materials. In progressive damage of rock, the most likely fracture direction is orthogonal to the maximum extension strain leading to dilatancy. The enriched extension strain criterion is proposed as a threshold surface for crack initiation CI and crack damage CD and as a failure surface at peak stress CP. Different from compressive loading, tensile loading requires only a limited number of critical cracks to cause failure. Therefore, for tensile stresses, the failure criteria must be modified somehow, possibly by a cut-off corresponding to the CI stress. Examples show that the enriched extension strain criterion predicts much lower volumes of damaged rock mass compared to the simple extension strain criterion.

scholarly journals Permeability Characteristic and Failure Behavior of Filled Cracked Rock in the Triaxial Seepage Experiment

2019 ◽  
Vol 2019 ◽  
pp. 1-12
Author(s):  
Xinyu Liu ◽  
Zhende Zhu ◽  
Aihua Liu
Keyword(s):  
Growth Rate ◽  
Rock Mass ◽  
Failure Modes ◽  
Peak Stress ◽  
Confining Pressure ◽  
Strength Characteristics ◽  
Failure Behavior ◽  
Compression Tests ◽  
Secondary Cracks ◽  
Safety And Stability

Filling is commonly found in natural cracked rock mass. As the weakest part of the rock, the filling properties directly affect the rock deformation and strength, permeability, and so on and affect the safety and stability of the rock mass engineering. In this study, a single slit has been preset in sandstones and filled with different physical properties materials. Based on the laboratory triaxial seepage test, the permeability and strength characteristics of filled cracked sandstones are analyzed, and the failure modes are obtained. The main findings of this study are as follows: (1) The permeability coefficient peak value of the filled cracked rock appears before the stress peak. (2) At the same confining pressure growth rate, the peak stress growth rate of the filled cracked rock is generally higher than that of the intact rock and the strength growth rate of the cracked rock increases with the length of the fracture. The strength characteristics of the filling in the uniaxial compression tests and triaxial seepage tests are significantly affected by the hydraulic properties. (3) The strength and permeability coefficients of cracked rock filled with cement mortar are more sensitive to the change of confining pressure, while under the same condition, the ones of cracked rock filled with gypsum mortar are stable. (4) According to the failure mechanism, under the seepage stress, the secondary cracks can be divided into 3 types and the failure modes can be divided into 2 types.

scholarly journals Mechanical Characteristics of Frozen Sandstone under Lateral Unloading: An Experimental Study

2021 ◽  
Vol 2021 ◽  
pp. 1-13
Author(s):  
Shuai Liu ◽  
Gengshe Yang ◽  
Xihao Dong ◽  
Yanjun Shen ◽  
Hui Liu
Keyword(s):  
Failure Modes ◽  
Rock Sample ◽  
Triaxial Compression ◽  
Radial Strain ◽  
Peak Stress ◽  
Confining Pressure ◽  
Test System ◽  
Peak Strain ◽  
Rate Of Increase ◽  
Unloading Rate

The lateral unloading strength and deformation of surrounding frozen rock are the key parameters for safety evaluation of frozen shaft construction. A low-temperature and high-pressure rock triaxial test system was used to simulate freezing construction, and a constant axial pressure unloading confining pressure test was carried out on frozen sandstone. The effects of freezing temperature, initial confining pressure, and unloading rate on the strength, deformation, and failure modes of frozen sandstone are studied. The main results of the study are as follows: (1) under the initial confining pressure of 20 MPa, the temperature of the sandstone decreases from 20°C to –5°C, and the peak stress and elastic modulus of triaxial compression increase by approximately 3 times. Under lateral unloading conditions, the peak stress of frozen sandstone is about 2∼3 times that of 20°C sandstone, and the peak strain of 20°C sandstone is smaller than that of frozen sandstone. The temperature of frozen sandstone decreases and the rate of increase in the peak stress of triaxial compression is slightly less than the rate of increase in the peak stress of lateral unloading. (2) The initial confining pressure of frozen sandstone increases, the growth rate of axial and radial strain increases, the radial strain dominates the failure process, and the lateral unloading strength decreases significantly. (3) The lateral unloading rate of frozen sandstone increases, the peak strength increases, and the axial and radial strain decrease. At a low unloading rate, partial creep deformation occurs. (4) The frozen rock sample undergoes tensile splitting failure under lateral unloading. According to the stress-strain curve of the frozen rock sample, the relationship between changes in the deformation modulus and changes in the confining pressure unloading amount during the unloading process of the rock sample is obtained.

Mechanical Property and Damage Evolution of Polymer-Bonded eXplosive Substitute Under Biaxial Compression

2019 ◽  
Vol 11 (04) ◽  
pp. 1950033 ◽  
Author(s):  
Panpan Xu ◽  
Shejuan Xie ◽  
Hong-En Chen ◽  
Zhenmao Chen ◽  
Hua Chen ◽  
...  
Keyword(s):  
Mechanical Property ◽  
Damage Evolution ◽  
Failure Modes ◽  
Principal Direction ◽  
Confining Pressure ◽  
Image Correlation ◽  
Biaxial Compression ◽  
Maximum Increase ◽  
Noticeable Effect ◽  
Deformational Behavior

Understanding both the mechanical property and the crack propagation behavior of Polymer-bonded eXplosive (PBX) material under biaxial compression is critical to predicting its safe working life. In this study, a number of PBX substitute specimens were tested under lateral confining pressures varying from 0 to 40[Formula: see text]MPa to better understand the mechanical behavior and damage evolution characteristics of PBX material under biaxial compression. The failure modes, ultimate strength and deformational behavior of PBX substitute under biaxial compression were observed using digital image correlation (DIC) method, and the damage of material was evaluated through the quantitative analysis of micro-computed tomography (CT) images of post-test specimens. The results indicate that the confining stress in the biaxial minor principal direction has a noticeable effect on the strength and deformational behavior of the PBX substitute material and the maximum increase of compressive strength occurs at a lateral confining pressure around 30[Formula: see text]MPa. The three-dimensional morphology of cracks was also examined quantitatively. The extent and complexity of crack damage were found increasing with the lateral confining pressure when it is smaller than 30[Formula: see text]MPa.

scholarly journals Mechanical Properties of Rock–Coal–Rock Composites at Different Inclined Coal Seam Thicknesses

2022 ◽  
Vol 9 ◽  
Author(s):  
Bo Ma ◽  
Feng Wang ◽  
Hongyang Liu ◽  
Dawei Yin ◽  
Zhiguo Xia
Keyword(s):  
Mechanical Properties ◽  
Coal Seam ◽  
Failure Modes ◽  
Peak Stress ◽  
Confining Pressure ◽  
Seam Thickness ◽  
Peak Strain ◽  
Confining Pressures ◽  
Coal Rock ◽  
Coal Seam Thickness

A comprehensive understanding of the mechanical properties of coal and rock sections is necessary for interpreting the deformation and failure modes of such underground sections and for evaluating the potential dynamic hazards. However, most studies have focused on horizontal coal–rock composites and the mechanical properties of inclined coal–rock composites have not been considered. To explore the influence of different confining pressures and inclined coal seam thicknesses on the mechanical properties and failure characteristics of rock–coal–rock (RCR) composites, a numerical model based on the particle flow code was used to perform simulations on five inclined RCR composites at different confining pressures. The results show that the mechanical properties and failure characteristics of the RCR composites are affected considerably by the inclined coal seam thickness and the confining pressure. (1) When the inclined coal seam thickness is constant, the elasticity modulus of the inclined RCR composite increases nonlinearly with the confining pressure at first, and then remains constant. At the same confining pressure, the elasticity modulus of the inclined RCR composite decreases nonlinearly with the inclined coal seam thickness. (2) When the confining pressure is constant, the peak stress of the inclined RCR composite decreases with the increase of the inclined coal seam thickness. When the inclined coal seam thickness is constant, the peak stress increases with the confining pressure. (3) As the inclined coal seam thickness increases, the peak strain of the inclined RCR composite first decreases rapidly, and then remains constant when there is no confining pressure. When the confining pressure is between 5 and 20 MPa, the peak strain of the inclined RCR composite gradually increases. (4) In the absence of confining pressure, there are few microcracks in the rock at an inclined coal seam thickness of 10 mm, whereas all the other cracks are in the coal section. When the confining pressure ranges between 5 and 20 MPa, the failure modes of the RCR composite can be divided into Y- and X-types.

scholarly journals Investigating the Macro-Micromechanical Properties and Failure Law of Granite under Loading and Unloading Conditions

2021 ◽  
Vol 2021 ◽  
pp. 1-13
Author(s):  
Chao Peng ◽  
Jianbo Wang ◽  
Huanxin Liu ◽  
Guilin Li ◽  
Wei Zhao
Keyword(s):  
Failure Modes ◽  
Numerical Models ◽  
Complex Loading ◽  
Failure Surface ◽  
Confining Pressure ◽  
Initial Stress State ◽  
Failure Characteristics ◽  
Micromechanical Properties ◽  
Loading Tests ◽  
Loading And Unloading

The excavation of rock significantly changes the initial stress state of rock slopes, which makes rock in complex loading and unloading conditions. However, the failure mechanisms and macro-micromechanical properties of rock under loading and unloading conditions are not very clear. This study investigates the macro-micromechanical properties and failure law of granite under loading and unloading conditions through traditional laboratory tests and particle flow simulations. Granite specimens are taken from Shuichang iron mine, and stress unloading experiments are designed based on the engineering practices. The stress-strain curves and failure modes under different confining pressures and unloading paths are obtained to analyze the granite properties from the viewpoint of the macroscopic mechanism. Moreover, numerical models are established in PFC software. The microcracks developments, failure characteristics, and energy evolutions under loading and unloading conditions are obtained and discussed. Results show that compared with the loading tests, the brittle failure characteristics of specimens under unloading tests are more obvious. When the confining pressure reduces to about 66% of the initial confining pressure, the specimen loses its load-bearing capacity and destroyed due to the lateral expansion. For loading tests, an inclined plane can be produced as the main failure surface. While for confining pressure unloading tests, there are many damage zones parallel to or intersecting with the main failure surface.

scholarly journals Assimilation of Dynamic Combined Finite Discrete Element Methods Using the Ensemble Kalman Filter

2021 ◽  
Vol 11 (7) ◽  
pp. 2898
Author(s):  
Humberto C. Godinez ◽  
Esteban Rougier
Keyword(s):  
Kalman Filter ◽  
Ensemble Kalman Filter ◽  
Failure Modes ◽  
Split Hopkinson Pressure Bar ◽  
Peak Stress ◽  
Discrete Element ◽  
Material Behavior ◽  
Model Parameters ◽  
Hopkinson Pressure Bar ◽  
Parameter Values

Simulation of fracture initiation, propagation, and arrest is a problem of interest for many applications in the scientific community. There are a number of numerical methods used for this purpose, and among the most widely accepted is the combined finite-discrete element method (FDEM). To model fracture with FDEM, material behavior is described by specifying a combination of elastic properties, strengths (in the normal and tangential directions), and energy dissipated in failure modes I and II, which are modeled by incorporating a parameterized softening curve defining a post-peak stress-displacement relationship unique to each material. In this work, we implement a data assimilation method to estimate key model parameter values with the objective of improving the calibration processes for FDEM fracture simulations. Specifically, we implement the ensemble Kalman filter assimilation method to the Hybrid Optimization Software Suite (HOSS), a FDEM-based code which was developed for the simulation of fracture and fragmentation behavior. We present a set of assimilation experiments to match the numerical results obtained for a Split Hopkinson Pressure Bar (SHPB) model with experimental observations for granite. We achieved this by calibrating a subset of model parameters. The results show a steady convergence of the assimilated parameter values towards observed time/stress curves from the SHPB observations. In particular, both tensile and shear strengths seem to be converging faster than the other parameters considered.

A Review on Role of Aluminum Matrix Materials, Failure Causes and Optimization Techniques

2021 ◽  
Vol 6 (3) ◽  
pp. 1-11
Author(s):  
Tilahun Y ◽  
◽  
Mesfin G ◽  
Keyword(s):  
Failure Modes ◽  
Matrix Material ◽  
Aluminum Matrix ◽  
Ductile Failure ◽  
Failure Surface ◽  
Optimization Techniques ◽  
Alloy Matrix ◽  
Modes Of Failure ◽  
Causes Of Failure

Aluminum is a metal matrix material which is widely used in different industrial as well as engineering applications.it has a great advantage due to its remarkable properties like less density, formability, and light in weight, recyclability and other properties. but, failure of aluminum matrix materials are the main problems in aluminum industries now a days.in this review role of aluminum and its alloys as matrix materials, their failure modes, causes of failure and optimization techniques to minimize this failure modes and causes of failure are discussed. Sources are reviewed which are from 2005 to recent one. Consequently, most modes of failure, causes of failure and most optimization techniques of aluminum and its alloy matrix materials are found. most modes of failure are mechanical related like fatigue failure, surface cracking, ductile failure, porosity formation, and stress related like stress corrosion cracking, surface weakness due to repeated stresses and other factors are summarized.in causes of failure mostly like corrosion formation, wear formation and poor mechanical properties are discussed.

Influence of cyclic load input on the mechanical properties of a sensitive soil from Orleans, Ontario

1980 ◽  
Vol 17 (4) ◽  
pp. 498-508 ◽  
Author(s):  
R. N. Yong ◽  
D. Taplin ◽  
G. Wiseman
Keyword(s):  
Mechanical Properties ◽  
Laboratory Test ◽  
Dynamic Loading ◽  
Cyclic Strain ◽  
Peak Stress ◽  
Confining Pressure ◽  
Constant Load ◽  
Deviatoric Stress ◽  
General Terms ◽  
Stress Levels

The importance of disturbance and remoulding to the alteration of mechanical properties of sensitive soils has been well documented in the geotechnical literature both in terms of laboratory and field behaviours. Man-made transient dynamic input such as dynamite blasting, heavy vehicles, and train movement have been suspected of being capable of causing a reduction in the in situ strength parameters of sensitive clays. A laboratory test program was undertaken to determine whether dynamic loading at peak stress levels below normal failure strength caused similar changes in the mechanical properties, and specifically to quantify the phenomena.In order to simulate highly overconsolidated conditions most of the tests were carried out under conditions of no confining pressure, although supplemental data were obtained from consolidated undrained tests. Some of the variables examined in this program were confining pressure, mean deviatoric stress, cyclic deviatoric stress, cyclic strain, number of applications, frequency, and reference strength. In order to compare the effect of dynamic input with the long-term creep phenomena, a simultaneous constant load program was undertaken.In general terms, the study indicates that under the prestated laboratory test conditions no major reduction in peak strength was found under dynamic loading, and that failure would occur at comparative stress levels under dead-load conditions, but required a greater time. In addition, examination of the sample after failure revealed that any remoulding of the sample appeared to be restricted to the area adjacent to the shear zone.

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