scholarly journals Study on Failure Characteristics and Acoustic Emission Characteristics of Sandstone Under Variable Angle Shear

2021 ◽  
Author(s):  
Feng Luo ◽  
Peidong Xu ◽  
Yijun Guo ◽  
Yanglong Diao ◽  
Meng Li
Keyword(s):  
Shear Stress ◽  
Acoustic Emission ◽  
Normal Stress ◽  
Failure Process ◽  
Shear Angle ◽  
Shear Cracks ◽  
Failure Characteristics ◽  
Variable Angle ◽  
Secondary Cracks ◽  
Peak Shear Stress

Abstract To study the shear damage and failure characteristics of red sandstone under different normal stress conditions, the failure process of sandstone under three different shear angles (50°, 55°, 60°) were studied by using variable angle shear test device. The shear stress-deformation curves and failure characteristics of sandstone were obtained, and the relationships between shear cracks and acoustic emission impact times, amplitude, peak frequency were established. With the increase of shear angle, the normal stress, shear stress and peak shear stress decrease gradually. The development of micro-cracks in the shear plane appear more earlier. The high frequency signal decreases significantly, which may have a significant corresponding relationship with the rock friction and shear effect. The failure mode of rock changes from plasticity to brittleness. The amplitude changes are concave, and more acoustic emission energy is released at compaction stage and plastic(failure) stage. The rock spalling mainly occur in the penetrating area of main and secondary cracks surrounding the two ends of specimen. The spalling degree was obviously weakened with the increase of shear angle. The results have important guiding value for judging and predicting the instability mechanism of rock engineering.

scholarly journals Research on Failure Characteristics of Concrete Three-Point Bending Beams with Preexisting Cracks in Different Positions Based on Numerical Simulation

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-8
Author(s):  
Liuqun Zhao ◽  
Li Zheng ◽  
Hui Qin ◽  
Tiesuo Geng ◽  
Yonggang Tan ◽  
...  
Keyword(s):  
Acoustic Emission ◽  
Bearing Capacity ◽  
Failure Modes ◽  
Failure Process ◽  
Engineering Application ◽  
Tensile Failure ◽  
Engineering Structures ◽  
Failure Characteristics ◽  
Three Point Bending ◽  
Wide Range

Concrete three-point bending beams with preexisting cracks are widely used to study the growth process of I-II mixed mode cracks. Studying the failure characteristics of preexisting cracks at different locations on concrete three-point bending beams not only has important scientific significance but also has a wide range of engineering application backgrounds in the safety assessment of engineering structures. In this paper, through several numerical experiments, the influence of preexisting cracks at different positions on the failure characteristics of concrete three-point bending beams is studied, and three typical failure modes are obtained. The failure process of the specimens with three typical failure modes is discussed in detail, and it is pointed out that the crack failure mode is tensile failure. The change trends of bearing capacity, acoustic emission quantity, and acoustic emission energy of three typical failure modes are analyzed. The maximum bearing capacity, the maximum acoustic emission quantity, and energy of three failure modes of concrete three-point bending beams generally show an increasing trend.

scholarly journals Acoustic Emission Multi-Parameter Analysis of Dry and Saturated Sandstone with Cracks under Uniaxial Compression

Energies ◽  
2019 ◽  
Vol 12 (10) ◽  
pp. 1959 ◽  
Author(s):  
Hongru Li ◽  
Rongxi Shen ◽  
Dexing Li ◽  
Haishan Jia ◽  
Taixun Li ◽  
...  
Keyword(s):  
Acoustic Emission ◽  
Uniaxial Compression ◽  
Fractured Rock ◽  
Rock Fracture ◽  
Failure Process ◽  
Parameter Analysis ◽  
Small Scale ◽  
Rock Interaction ◽  
Secondary Cracks ◽  
Ae Signals

In order to study the mechanics and acoustic emission (AE) characteristics of fractured rock under water-rock interaction, dried and saturated sandstone samples with prefabricated double parallel cracks were prepared. Then, uniaxial compression experiments were performed to obtain their AE signals and crack propagation images. The results show that water reduces the strength and fracture toughness of fractured sandstone and enhances plasticity. After saturation, the samples start to crack earlier; the cracks grow slowly; the failure mode is transformed from shear failure along the prefabricated cracks to combined shear and tensile failure; more secondary cracks are produced. The saturated samples release less elastic energy and weaker AE signals in the whole failure process. However, their AE precursor information is more obvious and advanced, and their AE sources are more widely distributed. Compared with dry specimens, the AE frequencies of saturated specimens in the early stage of loading are distributed in a lower frequency domain. Besides, the saturated samples release less complex AE signals which are dominated by small-scale signals with weaker multi-fractal characteristics. After discussion and analysis, it is pointed out that this may be because water makes rock prone to inter-granular fracture rather than trans-granular fracture. The water lubrication also may reduce the amplitude of middle-frequency band signals produced by the friction on the fracture surface. Multi-fractal parameters can provide more abundant precursory information for rock fracture. This is of great significance to the stability of water-bearing fractured rock mass and its monitoring, and is conducive to the safe exploitation of deep energy.

scholarly journals Study on the Effect of Precrack on Specimen Failure Characteristics under Static and Dynamic Loads by Brazilian Split Test

2021 ◽  
Vol 2021 ◽  
pp. 1-8
Author(s):  
Enyan Liu ◽  
Fuchun Liu ◽  
Youwei Xiong ◽  
Xianquan Lei ◽  
Shiming Wang
Keyword(s):  
Dynamic Load ◽  
Loading Rate ◽  
Failure Load ◽  
Split Hopkinson Pressure Bar ◽  
Failure Process ◽  
Crack Tip ◽  
Dynamic Loads ◽  
Failure Characteristics ◽  
Loading Direction ◽  
Secondary Cracks

To analyse the dynamic failure characteristics of the rock with a crack in rock engineering, the Brazilian split tests were conducted on the split Hopkinson pressure bar (SHPB) using precrack specimens under dynamic loads. In the study, five groups of different precrack angles are selected; they are 0°, 30°, 45°, 60°, and 90°, respectively. The results show that the static failure load of the specimen as a whole decreases to increase with the growth of the loading angle, and the DIF linear increases with the increase of the loading rate; the failure load of the specimen with an angle of 45° precrack is the most sensitive to the loading rate, followed by 0°, 60°, 30°, and 90°. The crack initiation time of specimen with 30°, 45°, and 60°precrack decreases with the loading rate, while it has no obvious change with the loading rate with 0° and 90°precrack. The failure mode of the specimen was controlled by the stress concentration at the crack tip; the main cracks all point from the crack tip to the loading end. When the precrack and the loading direction are at a certain angle, the failure process will produce secondary cracks; it would be particularly obvious under dynamic load splitting. Once the precrack and the loading direction are at a certain inclination angle, type-II secondary cracks will develop under dynamic load splitting.

scholarly journals Numerical Analysis of Shear and Particle Crushing Characteristics in Ring Shear System Using the PFC2D

Materials ◽  
2021 ◽  
Vol 14 (1) ◽  
pp. 229
Author(s):  
Sueng-Won Jeong ◽  
Kabuyaya Kighuta ◽  
Dong-Eun Lee ◽  
Sung-Sik Park
Keyword(s):  
Shear Stress ◽  
Numerical Analysis ◽  
Normal Stress ◽  
Numerical Results ◽  
Particle Flow Code ◽  
Shear Stresses ◽  
Particle Crushing ◽  
Ring Shear ◽  
Peak Shear Stress ◽  
Residual Shear Stress

The shear and particle crushing characteristics of the failure plane (or shear surface) in catastrophic mass movements are examined with a ring shear apparatus, which is generally employed owing to its suitability for large deformations. Based on results of previous experiments on waste materials from abandoned mine deposits, we employed a simple numerical model based on ring shear testing using the particle flow code (PFC2D). We examined drainage, normal stress, and shear velocity dependent shear characteristics of landslide materials. For shear velocities of 0.1 and 100 mm/s and normal stress (NS) of 25 kPa, the numerical results are in good agreement with those obtained from experimental results. The difference between the experimental and numerical results of the residual shear stress was approximately 0.4 kPa for NS equal to 25 kPa and 0.9 kPa for NS equal to 100 kPa for both drained and undrained condition. In addition, we examined particle crushing effect during shearing using the frictional work concept in PFC. We calculated the work done by friction at both peak and residual shear stresses, and then used the results as crushing criteria in the numerical analysis. The frictional work at peak and the residual shear stresses was ranged from 303 kPa·s to 2579 kPa·s for given drainage and normal stress conditions. These results showed that clump particles were partially crushed at peak shear stress, and further particle crushing with respect to the production of finer in shearing was recorded at residual shear stress at the shearing plane.

scholarly journals Effects of Groove Feature on Shear Behavior of Steel-Sand Interface

2020 ◽  
Vol 2020 ◽  
pp. 1-15 ◽  
Author(s):  
Jukun Guo ◽  
Xiaowei Wang ◽  
Shengyou Lei ◽  
Rui Wang ◽  
Hailei Kou ◽  
...  
Keyword(s):  
Shear Stress ◽  
Normal Stress ◽  
Friction Angle ◽  
Groove Width ◽  
Hyperbolic Model ◽  
Shear Direction ◽  
Intersection Angle ◽  
Interface Shear ◽  
Interface Friction ◽  
Peak Shear Stress

Surface groove morphology of structure and particle distribution of soil had a significant effect on the surface friction of structure. In order to investigate the interface shear stress-shear displacement curves, interface model and interface shear strength index when normal stress, groove width, and groove angle change, the interface shear tests of standard sand with steel plates are performed using an improved direct shear apparatus. Test results indicate that the peak shear stress increases with normal stress and the intersection angle between groove direction and shear direction. When the angle increases by 45°, the peak shear stress increases range from 4% to 13%. The peak shear stress increases with groove width, for every 1 mm increase in groove width, and the increasing extent of peak shear stress ranges from 4% to 22%, 3% to 13%, and 1% to 6%, respectively. When the groove angle is 45° and 90°, the increasing extent of peak shear stress decreases with groove width, but when the groove angle is 0°, the decrease regularity of peak shear stress increasing extent is not obvious. The hyperbolic model and Gompertz-C model are used to study the shear stress-shear displacement curves of sand-steel interface. The ratio of the interface peak shear stress of the hyperbolic model and Gompertz-C model to that of the shear test ranges from 0.90 to 1.03 and 0.88 to 0.98, respectively. The interface friction angle at the sand-steel interface ranges from 22° to 29°, and the friction angle of the rough interface is larger than that of the smooth interface. The interface friction angle increases with the intersection angle between the groove direction and the shear direction, the largest at 90°, the second at 45°, and the smallest at 0°. Under the same groove angle, the interface friction angle increases with the groove width, for every 1 mm increase in groove width, and the increasing extent of interface friction angle ranges from 4% to 15%, 4% to 7%, and 2% to 3%, respectively. The increasing extent of interface friction angle decreases with groove width, and this change rule is more obvious at the groove angle of 45° and 90° than at 0°.

The Research of Shaoguo Tunnel Failure Characteristics of Triaxial and Acoustic Emission Characteristics

2014 ◽  
Vol 501-504 ◽  
pp. 1757-1760
Author(s):  
Yi Hai Zhang ◽  
Yuan Li ◽  
Yan Zhang
Keyword(s):  
Acoustic Emission ◽  
Failure Process ◽  
Rock Failure ◽  
Signal Acquisition ◽  
Emission Characteristics ◽  
Sound Emission ◽  
Characteristic Parameters ◽  
Failure Characteristics ◽  
Emission Signal ◽  
Rock Failure Process

This is accomplished by a variety of indoor rock mechanics experiments and experimental sound emission, taking Chengde area of Hebei Province the tunnel rock made of rock as research object to simulate various loading rock failure process. To analysis the data obtained of acoustic emission and Dynamics in the process obtaining the characteristic parameters of rock failure process in order to Monitor and Forecast. Through the three axial compression test and the process of acoustic emission signal acquisition discussed the relation between the mechanical parameters of rock acoustic emission parameters of stress. The characteristic parameters of acoustic emission signals with stress and time change through analyzing the acoustic Emission characteristics of each stage in the process of rock failure provide the basis for the prediction of rock burst.

scholarly journals Experimental Study on the Shear-Flow Coupled Behavior of Tension Fractures Under Constant Normal Stiffness Boundary Conditions

Processes ◽  
2019 ◽  
Vol 7 (2) ◽  
pp. 57 ◽  
Author(s):  
Changsheng Wang ◽  
Yujing Jiang ◽  
Hengjie Luan ◽  
Jiankang Liu ◽  
Satoshi Sugimoto
Keyword(s):  
Surface Roughness ◽  
Shear Stress ◽  
Shear Flow ◽  
Boundary Conditions ◽  
Normal Stress ◽  
Growth Stage ◽  
Normal Stiffness ◽  
Peak Shear Stress ◽  
Hydraulic Aperture ◽  
Constant Normal Stiffness

This study experimentally investigated the effects of fracture surface roughness, normal stiffness, and initial normal stress on the shear-flow behavior of rough-walled rock fractures. A series of shear-flow tests were performed on two rough fractures, under various constant normal stiffness (CNS) boundary conditions. The results showed that the CNS boundary conditions have a significant influence on the mechanical and hydraulic behaviors of fractures, during shearing. The peak shear stress shows an increasing trend with the increases in the initial normal stress and fracture roughness. The residual shear stress increases with increasing the surface roughness, normal stiffness, and initial normal stress. The dilation of fracture is restrained more significantly under high normal stiffness and initial normal stress conditions. The hydraulic tests show that the evolutions of transmissivity and hydraulic aperture exhibit a three-stage behavior, during the shear process—a slight decrease stage due to the shear contraction, a fast growth stage due to shear dilation, and a slow growth stage due to the reduction rate of the mechanical aperture increment. The transmissivity and hydraulic aperture decreased, gradually, as the normal stiffness and initial normal stress increase.

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.

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