scholarly journals Study on Mechanical Properties and Cracking Mode of Coal Samples under Compression–Shear Coupled Load Considering the Effect of Loading Rate

2020 ◽  
Vol 10 (20) ◽  
pp. 7082
Author(s):  
Yanlong Chen ◽  
Huidong Cui ◽  
Hai Pu ◽  
Peng Wu ◽  
Liang Chen ◽  
...  
Keyword(s):  
Elastic Modulus ◽  
Failure Mode ◽  
Inclination Angle ◽  
Shear Failure ◽  
Loading Rate ◽  
Shear Crack ◽  
Axial Stress ◽  
Failure Behavior ◽  
Inclination Angles ◽  
Cracking Mode

Under coupled compression–shear loading, the failure and instability behavior of inclined pillars is different from that of horizontal pillars. To enhance the reliability and accuracy of pillar strength design, the influence of different inclination angles and loading rates on mechanical property and the failure behavior of inclined pillar should be studied. In this paper, the combined compression and shear test (C-CAST) system was developed, and mechanical properties and macro failure behavior of coal samples under different inclination angles and loading rates were studied, and acoustic emission (AE) technology was used to determine the internal cracking mode of the sample. The results show that with the increase of inclination angle, the peak shear stress of coal sample increases gradually, while the peak axial stress and elastic modulus slightly increase first and then decrease, and reach the maximum value at an inclination angle of 5°. Within the inclination angle range of 0°–15°, with the increase of loading rate, the peak axial stress and elastic modulus of coal samples first increase and then decrease, while the loading rate corresponding to peak axial stress and elastic modulus decreases. Within the inclination angle range of 20°–25°, the peak axial stress and elastic modulus of the sample gradually decrease with the increase of loading rate. The failure mode of coal samples changes from tension-splitting failure (0°–5°), tension–shear composite failure (10°) to single shear failure (15°–25°). Meanwhile, the loading rate has little effect on the failure mode of coal samples, but has a significant effect on the failure degree. When the loading rate is 1.0 and 10 mm/min and the inclination angle ranges from 0°–5°, the proportion of tensile crack is significantly greater than that of the shear crack, and tensile failure is the main failure mode; when the inclination angle ranges from 10°–25°, the proportion of shear crack is more than 50% and increases gradually with the increase of inclination angle, and shear failure is the main failure mode. This law is consistent with the macroscopic failure mode of the sample.

scholarly journals Study On The Effect of Bond Strength On The Failure Mode of Coarse-Grained Sandstone In Weakly Cemented Stratum

2021 ◽  
Author(s):  
Xianda Yang ◽  
Lihui Sun ◽  
Jiale Song ◽  
Bensheng Yang ◽  
Chengren Lan
Keyword(s):  
Bond Strength ◽  
Failure Mode ◽  
Shear Bond Strength ◽  
Shear Failure ◽  
Shear Crack ◽  
Peak Strength ◽  
Tensile Bond Strength ◽  
Coarse Grained ◽  
Strength Ratio ◽  
Tensile Shear

Abstract Bond strength is one of the most important parameters and can affect the macroscopic mechanical properties and the damage state of the rock to some degree. The coarse-grained sandstone with strength of less than 40 MPa was studied by the controlled variable method. The influence of parallel bond strength on the peak strength and failure mode of coarse-grained sandstone was simulated, the evolution law of peak strength and failure mode of bond strength were comprehensively analyzed. The results show that the peak strength of rock was positively correlated with the bond strength, the difference value between tensile and shear crack was negatively correlated with tensile bond strength and positively correlated with shear bond strength. Tensile-shear bond strength ratio less than 0.5, the peak strength of the rock was usually stable at the certain extreme value under a constant tensile bond strength. Tensile crack was negatively correlated with the tensile-shear bond strength ratio, shear crack was positively correlated with the tensile-shear bond strength ratio. The failure mode of coarse-grained sandstone is shear failure. The research results can be used to guide the ground control of other mine stopes or roadways with weak cementation lithology.

scholarly journals Experimental Study on Physical-mechanical Properties and Fracture Behaviors of Saturated Yellow Sandstone Considering Coupling Effect of Freeze-Thaw and Specimen Inclination

2020 ◽  
Vol 12 (3) ◽  
pp. 1029 ◽  
Author(s):  
Liang Chen ◽  
Peng Wu ◽  
Yanlong Chen ◽  
Wei Zhang
Keyword(s):  
Mechanical Properties ◽  
Shear Stress ◽  
Elastic Modulus ◽  
Failure Mode ◽  
Inclination Angle ◽  
Compression Strength ◽  
Shear Loading ◽  
Cold Regions ◽  
Freeze Thaw ◽  
Peak Compression

The effect of freeze-thaw on the physical-mechanical properties and fracture behavior of rock under combined compression and shear loading was crucial for revealing the instability mechanism and optimizing the structure design of rock engineering in cold regions. However, there were few reports on the failure behavior of rock treated by freeze-thaw under combined compression and shear loading due to the lack of test equipment. In this work, a novel combined compression and shear test (C-CAST) system was introduced to carry out a series of uniaxial compression tests on saturated yellow sandstone under various inclination angles (θ = 0°, 5°, 10°, and 15°) and the number of freeze-thaw cycles (N = 0, 20, 40, and 60). The test results showed that the P-wave velocity dramatically decreased, while the rock quality and porosity increased gradually as N increased; the peak compression strength and elastic modulus obviously decreased with the increasing θ and N, while the peak shear stress increased gradually with the increasing θ and decreased with the increase of N, indicating that the shear stress component can accelerate the crack propagation and reduce its resistance to deformation. The acoustic emission (AE) results revealed that the change of crack initiation (CI) stress and crack damage (CD) stress with the θ and N had a similar trend as that of the peak compression strength and elastic modulus. Particularly, the CI and CD thresholds at 60 cycles were only 81.31% and 84.47% of that at 0° cycle and indicated a serious freeze-thaw damage phenomenon, which was consistent with the results of scanning electron microscopy (SEM) with the appearance of some large-size damage cracks. The fracture mode of sandstone was dependent on the inclination angle. The failure mode developed from both the tensile mode (0°) and combined tensile-shear mode (5°) to a pure shear failure (10°–15°) with the increasing inclination angle. Meanwhile, the freeze-thaw cycle only had an obvious effect on the failure mode of the specimen at a 5° inclination. Finally, a novel multivariate regression analysis method was used to predict the peak compression strength and elastic modulus based on the initial strength parameters (θ = 0°, N = 0). The study results can provide an important reference for the engineering design of rock subjected to a complex stress environment in cold regions.

scholarly journals Experimental Study of the Mechanical Characteristics of a Rock-Like Material Containing a Preexisting Fissure under Loading and Unloading Triaxial Compression

2020 ◽  
Vol 2020 ◽  
pp. 1-12 ◽  
Author(s):  
Taoli Xiao ◽  
Mei Huang ◽  
Min Gao
Keyword(s):  
Experimental Study ◽  
Failure Mode ◽  
Mechanical Characteristics ◽  
Failure Modes ◽  
Shear Failure ◽  
Triaxial Compression ◽  
Tensile Failure ◽  
Underground Engineering ◽  
Inclination Angles ◽  
Loading And Unloading

An experimental study of a rock-like material containing a preexisting fissure subjected to loading and unloading triaxial compression is carried out, and the results show that the mechanical characteristics of the rock-like specimen depend heavily on the loading paths and the inclination of the fissure. The triaxial loading experiment results show that the failure strength linearly increases, while the residual strength linearly decreases with increasing inclination. Furthermore, specimens subjected to triaxial compression show an “X”-type shear failure mode. The triaxial unloading compression experimental results show that specimens with different inclination angles have various failure modes. Specimens with gentle inclinations show a tensile-shear mix failure mode, specimens with middle inclinations show a shear-sliding failure mode, and specimens with steep inclinations show a tensile failure mode. These findings can be used to forecast excavation-induced instabilities in deep underground engineering rock structures.

scholarly journals Effect of High Temperature and Inclination Angle on Mechanical Properties and Fracture Behavior of Granite at Low Strain Rate

2020 ◽  
Vol 12 (3) ◽  
pp. 1255 ◽  
Author(s):  
Liang Chen ◽  
Xianbiao Mao ◽  
Peng Wu
Keyword(s):  
Mechanical Properties ◽  
Shear Stress ◽  
Elastic Modulus ◽  
Crack Initiation ◽  
Uniaxial Compression ◽  
Inclination Angle ◽  
Shear Failure ◽  
Nuclear Waste Repository ◽  
Compression Stress ◽  
Peak Compression

Comprehensive understanding of the effects of temperature and inclination angle on mechanical properties and fracture modes of rock is essential for the design of rock engineering under complex loads, such as the construction of nuclear waste repository, geothermal energy development and stability assessment of deep pillar. In this paper, a novel inclined uniaxial compression (inclined UCS) test system was introduced to carry out two series of inclined uniaxial compression tests on granite specimens under various inclination angles (0–20°) and treated temperatures (25–800 °C) at 5° inclination. Experimental results revealed that the peak compression stress and elastic modulus gradually decreased, while peak shear stress increased nonlinearly with the increasing inclination angle; the peak compression and shear stress as well as elastic modulus slightly increased from 25 to 200 °C, then gradually decreased onwards with the increasing temperature. The effect of temperature on peak axial strain was the same as that on peak shear displacement. Acoustic emission (AE) results suggested that the relationship between crack initiation stress, inclination angle and treated temperature followed a similar trend as that of the peak compression stress and elastic modulus. Particularly, the crack initiation (CI) stress threshold and shear stress corresponding to CI threshold under 800 °C were only 7.4% of that under 200 °C and revealed a severe heat damage phenomenon, which was consistent with the results of the scanning electron microscopy (SEM) with the appearance of a large number of thermal pores observed only under 800 °C. The failure modes tended to shear failure with the increasing inclination angle, indicating that the shear stress component can accelerate sliding instability of rocks. On the other hand, the failure patterns with different temperatures changed from combined splitting-shear failure (25–400 °C) to single shear failure (600 and 800 °C). The study results can provide an extremely important reference for underground thermal engineering construction under complex loading environment.

A Study on the Estimation of Failure Mode in Impact Analysis Using SPH Method

2011 ◽  
Vol 82 ◽  
pp. 332-337
Author(s):  
Yoshimi Sonoda ◽  
Shoichirou Tokumaru ◽  
Jin Fukazawa
Keyword(s):  
Impact Analysis ◽  
Shear Failure ◽  
Impact Load ◽  
Shear Crack ◽  
Local Stress ◽  
Failure Behavior ◽  
Sph Method ◽  
Wide Range ◽  
Rapid Destruction ◽  
Bending Failure

This paper proposes an analysis algorithm that can appropriately distinguish shear failure from bending failure of an RC beam under impact load, by using the SPH method. As structural members, beams generally fail by one of two modes: bending failure caused by excessive bending deformation of the member, and shear failure caused by shear crack growth, leading to rapid destruction at an angle in the web. In this study, to calculate the failure behavior accurately in the local stress field in which shear stress prevails such as when a shear crack occurs, an orthotropic constitutive equation is used. This equation is derived by applying the integrity tensor proposed by Ignacio Carol, Egidio Rizzi and Kasper William, to the usual SPH method. This operation is also extended to the tensile softening characteristic of concrete material. The results confirm that the failure behavior of RC beams under a wide range of conditions can be analyzed accurately by using the proposed algorithm.

scholarly journals Discrete Element Modeling on Mechanical Behavior of Heterogeneous Rock Containing X-Shaped Fissure under Uniaxial Compression

Geofluids ◽  
2020 ◽  
Vol 2020 ◽  
pp. 1-14
Author(s):  
Ming Chen ◽  
Jian Liu ◽  
Zhengyong Xie ◽  
Jianjun Liu ◽  
Xunjian Hu ◽  
...  
Keyword(s):  
Elastic Modulus ◽  
Crack Initiation ◽  
Mechanical Behavior ◽  
Failure Mode ◽  
Uniaxial Compression ◽  
Inclination Angle ◽  
Acute Angle ◽  
Peak Strength ◽  
Discrete Element Modeling ◽  
Initiation Stress

Based on the experimental results of an intact rock specimen under uniaxial compression, particle flow code (PFC2D) was adopted to carry out a discrete element modeling (DEM) for the mechanical behavior of heterogeneous rocks containing X-shaped fissures (two intersecting symmetric single fissures) under uniaxial compression. The influences of β (the acute angle between two single fissures) and the direction angle α (the acute angle between the bisector of β and perpendicular to the loading direction) on the strength, deformation, energy, crack propagation, and ultimate failure mode were analyzed in detail. Numerical simulated results showed the following: (1) Due to the X-shaped fissures, not only the peak strength, elastic modulus, crack initiation stress, and damage stress were significantly reduced, and the reduced degree of the peak strength was obviously greater than that of the elastic modulus, but also the brittleness and energy were significantly weakened. (2) The peak strength and elastic modulus generally decreased with the increase of β and increased with the increase of α . Moreover, the change trends of crack initiation stress, damage stress, boundary energy, and total strain energy at the peak stress were consistent with the peak strength. (3) Regardless of the changes of α and β , models all firstly initiated wing cracks at the two tips of the single fissure with a larger inclination angle, and the crack initiation angle decreased with the increase of the inclination angle of the single fissure. (4) The fracture was dominated by tensile microcracks, and no microcracks were generated in a certain range of the X-shaped fissure center. The failure mode was mainly split along the axial direction, and the failure surface started from the tips of the fissure and extended to both ends of models. (5) The uniaxial compressive strength and elastic modulus increased exponentially with the increase of the homogeneity factor. When the homogeneity factor was small, the microcracks were more evenly distributed in the models; when the homogeneity factor was large, the microcracks were mainly concentrated at the tips of the fissure in the models. This study can provide some references for the correct understanding of the mechanical properties of rock masses containing X-shaped fissures.

Numerical modeling of progressive failure of rigid piles under embankment load

2019 ◽  
Vol 56 (1) ◽  
pp. 23-34 ◽  
Author(s):  
Gang Zheng ◽  
Xinyu Yang ◽  
Haizuo Zhou ◽  
Jinchun Chai
Keyword(s):  
Tensile Stress ◽  
Failure Mode ◽  
Shear Failure ◽  
Slip Surface ◽  
Progressive Failure ◽  
Soft Clay ◽  
Bending Moment ◽  
Tensile Failure ◽  
Failure Behavior ◽  
Embankment Load

Rigid piles (e.g., concrete piles) have been widely used to improve soft clay for the rapid construction of embankments. In this study, a damage plasticity model that considers the brittle failure behavior of concrete and the frictional properties along cracks is proposed to study the progressive failure of rigid piles under an embankment load. The mechanical characteristics of piles in different locations have been analyzed. The results show that the essential failure mode for rigid piles is tensile failure, which is primarily governed by the distribution of the bending moment and the axial force within the piles. Pile rupture releases stress and causes a significant increase in the tensile stress within neighboring piles, possibly leading to the progressive failure of adjacent piles. Failure in the upper section of piles ultimately leads to the propagation of a slip surface and the global failure of the embankment. The parametric analysis indicates that increases in the pile stiffness and the embankment load result in a higher tensile stress within the piles and a change in the failure mechanism from shear failure to bending failure. In addition, a failure envelope is proposed to determine the failure mode of the piles.

scholarly journals Crack Propagation Law and Failure Characteristics of Coal-Rock Combined Body with the Different Inclination Angle of Prefabricated Fissure

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-13
Author(s):  
Chunlei Zhang ◽  
Yun Dong ◽  
Ruimin Feng ◽  
Ningbo Peng ◽  
Jihua Zhang ◽  
...  
Keyword(s):  
Fracture Surface ◽  
Crack Propagation ◽  
Failure Mode ◽  
Inclination Angle ◽  
Main Crack ◽  
Failure Characteristics ◽  
Secondary Cracks ◽  
Propagation Law ◽  
Inclination Angles ◽  
Coal Rock

Few studies have been conducted on the crack propagation law and failure characteristics of coal-rock combined body (CRCB) with prefabricated fissure. A sliding crack model was firstly presented to analyze the failure law of rock with a single fracture and the influence of the inclination angle of the fracture on the strength of the rock. The RFPA numerical models of the CRCB with different inclination angles of prefabricated fracture were then established to simulate the dynamic change process of crack propagation and shear stress of the CRCB with prefabricated fracture under uniaxial compression. The influence of the inclination angle of the fracture in the rock on the fracture expansion and failure characteristics of CRCB was further analyzed based on the acoustic emission data. The results showed that (1) when 2 β = arctan 1 / μ , σ cw takes the minimum value, and crack initiation is most likely to occur; (2) the strength of coal-rock assemblage shows different changing trends with the fracture inclination angle; (3) the secondary cracks of CRCB with prefabricated fracture of 0°, 15°, and 30° initiated and expanded near the tip of the main crack, and the secondary cracks of 45°, 60°, and 75° initiated and expanded from the tip of the main crack; (4) there are three failure modes of CRCB with prefabricated crack, the double-shear failure mode Λ , the tensile-shear composite failure mode along the fracture surface, and the tensile failure mode along the fracture surface; and (5) intact CRCB and CRCB with prefabricated crack when α = 75 ° and α = 90 ° have strong brittleness, and other CRCB with different prefabricated fracture inclination angles show a certain degree of postpeak plasticity. The results on the mechanical properties and damage characteristics of CRCB are of great significance for the safety and efficient mining of deep coal resources.

scholarly journals Experimental Investigation on Uniaxial Compression Mechanical Behavior and Damage Evolution of Pre-Damaged Granite after Cyclic Loading

Energies ◽  
2021 ◽  
Vol 14 (19) ◽  
pp. 6179
Author(s):  
Jianhua Hu ◽  
Pingping Zeng ◽  
Dongjie Yang ◽  
Guanping Wen ◽  
Xiao Xu ◽  
...  
Keyword(s):  
Cyclic Loading ◽  
Failure Mode ◽  
Uniaxial Compression ◽  
Failure Modes ◽  
Shear Failure ◽  
Confining Pressure ◽  
Failure Behavior ◽  
Mode Ii ◽  
Mode Iii ◽  
Cycle Number

Failure behavior of pillars in deep mines is affected by various cyclic loads that cause initial pre-damage. Pillars will be further damaged and developed in the long-term compressive stress until they are destroyed. To reveal the strength characteristics and crack damage fracture laws after rock pre-damage, uniaxial compression tests were carried out on granite specimens damaged by cyclic loading using the digital speckle correlation method. The experimental results indicate that the mechanical properties of pre-damaged specimens show large damage differences for different cycles. The damage variable of the pre-damaged specimens increases with the increase of cycle number and confining pressure. The damage of specimens is primarily due to the strength weakening effect caused by cycle numbers, and the confining pressure restriction effect is not obvious. The evolution laws of uniaxial compression damage propagation in the pre-damaged specimens show differences and obvious localization phenomenon. Pre-damaged specimens experienced three failure modes in the uniaxial compression test, namely tensile shear failure (Mode I), quasi-coplanar shear failure (Mode II), and stepped path failure (Mode III), and under different pre-damage stress environments with high confining pressures, the failure modes are dominated by Mode II and Mode III, respectively.

scholarly journals An Experimental Investigation on the Failure Behavior of a Notched Concrete Beam Strengthened with Carbon Fiber-Reinforced Polymer

2015 ◽  
Vol 2015 ◽  
pp. 1-17 ◽  
Author(s):  
Xia Huang ◽  
Jian Wang ◽  
Feng Zhang ◽  
Song-shan Niu ◽  
Jun Ding
Keyword(s):  
Bearing Capacity ◽  
Failure Mode ◽  
Concrete Beam ◽  
Failure Modes ◽  
Shear Failure ◽  
Interfacial Shear Stress ◽  
Failure Behavior ◽  
Cfrp Laminate ◽  
Final Failure ◽  
Parametric Analyses

This paper presents an experiment investigation on the failure behavior of a notched concrete beam reinforced with CFRP, by exploring the influences of the length, thickness, and CFRP bonding methods on the ultimate bearing capacity and failure mode. The interfacial shear stress has first been analytically derived and parametric analyses are then made to predict the failure mode. The experiment observation finds that failure mode significantly depends on CFRP length. The brittle fracture occurs only for nonstrengthened beams; the shear failure I mode mainly occurs when CFRP laminate is 100 mm long; the shear failure II mode mainly occurs when CFRP laminate is 200 mm long; and the delamination failure mode mainly occurs when CFRP laminate is 350 mm long. Meanwhile, the thickness and the bonding methods of CFRP also influence the final failure modes in terms of CFRP length. The measurement on ultimate load shows that an increase in the length of CFRP up to 200 mm significantly improves the bearing capacity of the reinforced beam. A comparison between a theoretical analysis and the experimental observation shows a good agreement in terms of failure modes indicating the accuracy and the validity of the experiment.

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