scholarly journals Dynamic Fracturing Behavior of Layered Rock with Different Inclination Angles in SHPB Tests

2017 ◽  
Vol 2017 ◽  
pp. 1-12 ◽  
Author(s):  
Jiadong Qiu ◽  
Diyuan Li ◽  
Xibing Li ◽  
Zilong Zhou
Keyword(s):  
Shear Stress ◽  
Tensile Stress ◽  
Split Hopkinson Pressure Bar ◽  
Impact Compression ◽  
Failure Patterns ◽  
Layered Rock ◽  
Bedding Planes ◽  
Loading Direction ◽  
Fracturing Process ◽  
Inclination Angles

The fracturing behavior of layered rocks is usually influenced by bedding planes. In this paper, five groups of bedded sandstones with different bedding inclination angles θ are used to carry out impact compression tests by split Hopkinson pressure bar. A high-speed camera is used to capture the fracturing process of specimens. Based on testing results, three failure patterns are identified and classified, including (A) splitting along bedding planes; (B) sliding failure along bedding planes; (C) fracturing across bedding planes. The failure pattern (C) can be further classified into three subcategories: (C1) fracturing oblique to loading direction; (C2) fracturing parallel to loading direction; (C3) mixed fracturing across bedding planes. Meanwhile, a numerical model of layered rock and SHPB system are established by particle flow code (PFC). The numerical results show that the shear stress is the main reason for inducing the damage along bedding plane at θ = 0°~75°. Both tensile stress and shear stress on bedding planes contribute to the splitting failure along bedding planes when the inclination angle is 90°. Besides, tensile stress is the main reason that leads to the damage in rock matrixes at θ = 0°~90°.

Analysis of Failure Patterns and Damage Mechanisms under Impact Compression of Hybrid Fiber Reinforced Concrete

2012 ◽  
Vol 193-194 ◽  
pp. 609-613
Author(s):  
Meng Chen ◽  
Zhi Li ◽  
Zhe An Lu
Keyword(s):  
Reinforced Concrete ◽  
Failure Modes ◽  
Split Hopkinson Pressure Bar ◽  
Dynamic Compression ◽  
Fiber Reinforced Concrete ◽  
Fiber Reinforced ◽  
Hybrid Fiber ◽  
Impact Compression ◽  
Failure Patterns ◽  
Compression Properties

In order to studying the failure patterns under impact compression of Hybrid Fiber Reinforced Concrete(HFRC), tests focused on static and dynamic compression properties according to steel fiber reinforced concrete(SFRC) and HFRC are adopted. The equipment of dynamic compression properties test is Ф74mm split Hopkinson pressure bar (SHPB). The static and dynamic compressive strength at four different strain rates of the two materials are obtained, while failure mechanism has been analyzed from specimens’ failure modes in static and dynamic compressive tests, which in turn provides theory basis for the application of HFRC.

Hydraulic-Fracture Geomechanics and Microseismic-Source Mechanisms

SPE Journal ◽  
2013 ◽  
Vol 18 (04) ◽  
pp. 766-780 ◽  
Author(s):  
N.R.. R. Warpinski ◽  
M.J.. J. Mayerhofer ◽  
K.. Agarwal ◽  
J.. Du
Keyword(s):  
Shear Stress ◽  
Hydraulic Fracture ◽  
Hydraulic Fractures ◽  
Natural Fractures ◽  
Total Stress ◽  
Multiple Fractures ◽  
Significant Information ◽  
Bedding Planes ◽  
Fracturing Process ◽  
Source Mechanisms

Summary Interpretation of microseismic results and attempts to link microseismic-source mechanisms to fracture behavior require an understanding of the geomechanics of the fracturing process. Stress calculations around fractures show that the area normal to the fracture surface is stabilized by a pressurized fracture as a result of increased total stress and decreased shear stress. In this area, microseisms can occur only if leakoff pressurizes natural fractures, bedding planes, or other weakness features, and source mechanisms are thus likely to show a volumetric component that has either opening or closing movement in addition to shear slippage. Conversely, the tip tensile region is destabilized by a reduction in total stress and an increase in shear stress, with the likelihood that microseisms would be generated in this region because of these changes. Such microseisms would not yet be invaded by the fracturing fluid, and events that are mostly shear would be expected. Systems with multiple fractures, such as those that are potentially created in multiperforation-cluster stages, are much more complex, but similar elements can be outlined for those as well. Source mechanisms can help delineate these different types of microseismic behaviors, but the evaluation of such mechanisms reveals that they provide no significant information about the hydraulic fracture. Whereas it would be valuable if source mechanisms could provide information about the mechanics of the hydraulic fracture (e.g., opening, closing, and proppant), calculations show that both the energy and volume associated with microseismicity are an insignificant fraction of the total energy and volume input into the stimulation. Thus, hydraulic fractures are almost entirely aseismic. The analysis of source mechanisms should concentrate on what those data reveal about the reservoir (e.g., natural fractures and faults). Integrated diagnostic studies provide more value in understanding both the microseismicity and interpretation of the microseismic results.

scholarly journals Dynamic Splitting Tensile Properties and Failure Mechanism of Layered Slate

2020 ◽  
Vol 2020 ◽  
pp. 1-16
Author(s):  
Yunsi Liu ◽  
Chushao He ◽  
Shiming Wang ◽  
Yaxiong Peng ◽  
Yong Lei
Keyword(s):  
Mechanical Properties ◽  
Inclination Angle ◽  
Failure Modes ◽  
Loading Rate ◽  
Failure Load ◽  
Split Hopkinson Pressure Bar ◽  
Failure Mechanisms ◽  
Influence Coefficient ◽  
Layered Rock ◽  
Bedding Planes

Dynamic tensile failure is one of the main failure modes of layered rock masses during the excavation of underground engineering. This study investigates the influence of loading rate and layered inclination angle on the mechanical properties and failure mechanisms of layered slate using a split-Hopkinson pressure bar system and high-speed cameras. The results show that, overall, the dynamic elastic modulus E, postpeak stress reduction rate K, and failure load of the discs with the 7 tested bedding angles increase with the increasing loading rate. A nonlinear formula is proposed to describe the relationship between loading rate and failure load for the 7 tested inclination angles. As the inclination angle of the bedding planes increases from 0° to 90°, both the static and dynamic failure loads of the slate increased. However, with increasing loading rate, the anisotropic influence coefficient N ranges from 3.25 under the static load to 1.35 under the dynamic load, and the bedding effect gradually decreases. From the dynamic Brazilian splitting tests, the failure of the discs is mainly observed along the bedding planes when the inclination angle is less than or equal to 45°. Failure of the discs mainly occurs along the centre of the disc and previously intact planes when the inclination angle is greater than 60°. This study provides significant data to evaluate the mechanical properties and failure mechanisms of layered rock and the safety and stability of layered rock under dynamic loading.

scholarly journals Tensile behavior of a Brazilian Disk Containing non-persistent Joint Sets Subjected to Diametral Loading: An Experimental Investigation

2021 ◽  
Author(s):  
Mostafa Asadizadeh ◽  
Jamshid Shakeri ◽  
Nima Babanouri ◽  
Mohammad Rezaei
Keyword(s):  
Tensile Strength ◽  
Tensile Stress ◽  
Failure Pattern ◽  
Structural Defects ◽  
Joint Spacing ◽  
Joint Continuity ◽  
Failure Patterns ◽  
Loading Direction ◽  
Joint Parameters ◽  
Strength And Stiffness

Abstract Structural defects are part of the inherent characteristics of rock masses. They can be found in the form of fishers, joints, and beddings and can be divided into persistent or non-persistent one. The coalescence of non-persistent cracks may lead to the formation of persistent joints under the tensile stress field, leading to instability of rock mass. The mechanical behavior of non-persistent jointed disks under tensile stress has essential implications for rock engineering structures. In this paper, concrete Brazilian disks containing open non-persistent joints were constructed and subjected to diametral loading to investigate the effect of this kind of joint parameters on the tensile strength and stiffness of disks. The effect of some parameters, such as joint continuity factor (the relationship between joint length and rock bridge length), bridge angle, joint spacing, and loading direction with respect to joint angle were investigated to estimate the tensile strength and stiffness as well as failure pattern. The results of experiments revealed that the tensile strength, stiffness, and failure pattern of Brazilian disks are highly affected by non-persistent pre-existing crack parameters. The increase of joint continuity factor and loading direction leads to an increase in tensile strength and a decrease in stiffness. However, when bridge angle and spacing increase tensile strength rises, and the former decreases stiffness while the latter results in its reduction. Finally, all the parameters significantly affect the failure pattern, and some failure patterns such as step-path failure, splitting, or sliding may occur as a function of non-persistent joint parameters.

Fatigue Tolerance of Aged Asphalt Binders Modified with Softeners

2021 ◽  
pp. 036119812110255
Author(s):  
Javier J. García Mainieri ◽  
Punit Singhvi ◽  
Hasan Ozer ◽  
Brajendra K. Sharma ◽  
Imad L. Al-Qadi
Keyword(s):  
Shear Stress ◽  
Heavy Traffic ◽  
Asphalt Binder ◽  
Fatigue Cracking ◽  
Data Interpretation ◽  
Complex Stress ◽  
Current Data ◽  
Asphalt Binders ◽  
Failure Patterns ◽  
Peak Shear Stress

Fatigue cracking caused by repeated heavy traffic loading is a critical distress in asphalt concrete pavements and is significantly affected by the selected binder. In recent years, the growing use of recycled asphalt materials has increased the need for the production of softer asphalt binder. Various modifiers/additives are marketed to adjust the grade and/or enhance the binder performance at high and low temperatures. The modifiers are expected to alter the rheological and chemical characteristics of binders and, therefore, their performance. In this study, the damage characteristics of modified and unmodified binders, at standard long-term and extended aging conditions, were tested using the linear amplitude sweep (LAS) test. Current data-interpretation methods for LAS measurements (including AASHTO TP 101-12, T 391-20, and recent literature) showed inconsistent results for modified binders. An alternative method to interpret LAS results was developed in this study. The method considers the data until peak shear-stress is reached because complex stress states and failure patterns are observed in the specimens after that point. The proposed parameter (Δ| G*|peak τ) quantifies the reduction in complex shear modulus measured at the peak shear-stress. The parameter successfully captures the effect of aging and modification of binders.

scholarly journals Study on Impact Damage and Energy Dissipation of Coal Rock Exposed to High Temperatures

2016 ◽  
Vol 2016 ◽  
pp. 1-10 ◽  
Author(s):  
Tu-bing Yin ◽  
Kang Peng ◽  
Liang Wang ◽  
Pin Wang ◽  
Xu-yan Yin ◽  
...  
Keyword(s):  
High Temperatures ◽  
Failure Modes ◽  
Split Hopkinson Pressure Bar ◽  
Impact Damage ◽  
Time History ◽  
Hopkinson Pressure Bar ◽  
Absorbed Energy ◽  
Failure Patterns ◽  
Temperature Conditions ◽  
Coal Rock

The dynamic failure characteristics of coal rock exposed to high temperatures were studied by using a split Hopkinson pressure bar (SHPB) system. The relationship between energy and time history under different temperature conditions was obtained. The energy evolution and the failure modes of specimens were analyzed. Results are as follows: during the test, more than 60% of the incident energy was not involved in the breaking of the sample, while it was reflected back. With the increase of temperature, the reflected energy increased continuously; transmitted and absorbed energy showed an opposite variation. At the temperature of 25 to 100°C, the absorbed energy was less than that transmitted, while this phenomenon was opposite after 100°C. The values of specific energy absorption (SEA) were distributed at 0.04 to 0.1 J·cm−3, and its evolution with temperature could be divided into four different stages. Under different temperature conditions, the failure modes and the broken blocks of the samples were obviously different, combining with the variation of microstructure characteristics of coal at high temperatures; the physical mechanism of damage and failure patterns of coal rock are explained from the viewpoint of energy.

Limits to elastic response. Yielding and failure

2020 ◽  
pp. 357-368
Author(s):  
Lallit Anand ◽  
Sanjay Govindjee
Keyword(s):  
Shear Stress ◽  
Tensile Stress ◽  
Critical Value ◽  
Maximum Principal Stress ◽  
The Body ◽  
Elastic Response ◽  
Elastic Behaviour ◽  
Pressure Independent ◽  
Yield Conditions ◽  
Is Failure

This chapter presents conditions for determining the limits of elastic behaviour for isotropic materials. The stress invariants of equivalent pressure, equivalent shear stress, and equivalent tensile stress are defined. These are then used to define common yield conditions, viz. the pressure-independent Mises and Tresca yield conditions, as well as the pressure-dependent Coulomb-Mohr and the Drucker-Prager yield conditions. Rankine’s failure criterion for brittle materials in tension, that is failure in a brittle material will initiate when the maximum principal stress at a point in the body reaches a critical value, is also discussed.

scholarly journals Blasting-Induced Permeability Enhancement of Ore Deposits Associated with Low-Permeability Weakly Weathered Granites Based on the Split Hopkinson Pressure Bar

Geofluids ◽  
2018 ◽  
Vol 2018 ◽  
pp. 1-14 ◽  
Author(s):  
Lei Yan ◽  
Wenhua Yi ◽  
Liansheng Liu ◽  
Jiangchao Liu ◽  
Shenghui Zhang
Keyword(s):  
Split Hopkinson Pressure Bar ◽  
Deformation Modulus ◽  
Constant Speed ◽  
Initial Porosity ◽  
Peak Strain ◽  
Variable Speed ◽  
Hopkinson Pressure Bar ◽  
Impact Compression ◽  
Split Hopkinson ◽  
Pressure Bar

By utilizing the improved split Hopkinson pressure bar (SHPB) test device, uniaxial, constant-speed cyclic, and variable-speed cyclic impact compression tests were conducted on weakly weathered granite samples. By combining nuclear magnetic resonance (NMR) and triaxial seepage tests, this study investigated the change laws in the mechanical properties, porosity evolution, and permeability coefficients of the samples under cyclic impacts. The results showed that in constant-speed cyclic impacts with increasing impact times, deformation modulus decreased, whilst porosity firstly decreased and then increased. Furthermore, dynamic peak strength firstly increased and then decreased whereas peak strain constantly increased before failure of the samples. In the variable-speed cyclic impacts, as impact times increased, deformation modulus firstly increased and then declined with damage occurring after four impact times. The compaction process weakened and even disappeared with increasing initial porosity. Three types of pores were found in the samples that changed in multiscale under cyclic loading. In general, small pores extended to medium- and large-sized pores. After three variable-speed cyclic impacts, the porosity of the samples was larger than the initial porosity and the permeability coefficient was greater than its initial value. The results demonstrate that the purpose of enhancing permeability and keeping the ore body stable can be achieved by conducting three variable-speed cyclic impacts on the samples.

scholarly journals Electromagnetic Emissions from Quartz Subjected to Shear Stress: Spectral Signatures and Geophysical Implications

Geosciences ◽  
2020 ◽  
Vol 10 (4) ◽  
pp. 140 ◽  
Author(s):  
Giovanni Martinelli ◽  
Paolo Plescia ◽  
Emanuela Tempesta
Keyword(s):  
Shear Stress ◽  
Electromagnetic Waves ◽  
Emission Spectra ◽  
Stress Tests ◽  
Quartz Crystals ◽  
Piston Cylinder ◽  
Fracturing Process ◽  
Electromagnetic Emissions ◽  
As Stress ◽  
Energy Dissipated

Shear tests on quartz rocks and single quartz crystals have been conducted to understand the possible relationship between the intensity of detectable stress in fault areas and the energy released in the form of electromagnetic waves in the range 30 KHz-1 MHz (LF–MF). For these tests, a new type of piston-cylinder has been developed, instrumented to collect the electromagnetic signals generated by the quartz during shear stress tests and that allows energy measurements on electromagnetic emissions (EMR) to be performed. The data obtained indicate that shear-stressed quartz crystals can generate electromagnetic emissions in the LF–MF range. These emissions represent a tiny fraction of the total energy dissipated in the fracturing process. The spectrum of radio emissions consists of continuous radiation and overlapping peaks. For the first time, a characteristic migration of peak frequencies was observed, proportional to the evolution of the fracturing process. In particular, the continuous recording of the radio emission spectra shows a migration of the peaks toward higher frequencies, as stress continues over time and smaller and larger fractures form. This migration could be used to distinguish possible natural signals emitted by quartz in tectonically active environments from possible signals of other geophysical and possibly anthropogenic origin.

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