scholarly journals Experimental Study on Mechanical Properties of Prefabricated Single-Cracked Red Sandstone under Uniaxial Compression

2020 ◽  
Vol 2020 ◽  
pp. 1-14
Author(s):  
Yue Yuan ◽  
Jinlei Fu ◽  
Xiaolei Wang ◽  
Xi Shang
Keyword(s):  
Mechanical Properties ◽  
Crack Propagation ◽  
Failure Mode ◽  
Uniaxial Compression ◽  
Contact Force ◽  
Rock Sample ◽  
Unstable Fracture ◽  
Red Sandstone ◽  
Rock Samples ◽  
Dip Angle

This paper aims at the phenomenon of the fractured rock column in underground engineering which is prone to collapse when subjected to ground pressure. Uniaxial compression test and particle flow code (PFC2D) are used to analyze the influence of crack dip angle on the mechanical properties, crack propagation, and the failure mode of red sandstone. From the results, it is observed that the stress–strain curve of the precracked red sandstone can be divided into five stages, and there is a critical stress value in the stage of accelerated crack propagation and unstable fracture of the rock sample. Further, the peak strength, maximum strain, and the elastic modulus of the precracked red sandstone increase with the increase of crack dip angle, and the ultimate failure mode of rock sample changes from the “ladder” type failure to slope uneven failure. Furthermore, from PFC2D simulation, it is found that the tensile microcracks contribute more towards the failure of rock samples than the shear cracks. The contact force chain is very weak at the places where the precracks and macroshear planes are formed. This indicates that the original contact force is weakened due to particle fracture. Therefore, the bearing capacity of the precracked rock samples decreases with the increase in load. From the simulation results, it is found that the displacement at the shear plane of the rock sample is large, and the shear dilatation occurs. With the increase in load, the specimen falls off and is ejected. This is due to the weakening of the contact force between the internal particles. Thereafter, it fractures to produce microcracks, which gradually converge, thus providing a prerequisite for the transformation of elastic strain energy into kinetic energy.

Effect of porewater pressure on the mechanical properties of red sandstone with different unloading rates

2020 ◽  
pp. qjegh2019-101
Author(s):  
Jian-Xi Ren ◽  
Xu Chen ◽  
Xing-Zhou Chen ◽  
Meng-Chen Yun ◽  
Xi-TaiLang Cao ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Shear Failure ◽  
Strain Curve ◽  
Shaanxi Province ◽  
Axial Deformation ◽  
Aquifer System ◽  
Red Sandstone ◽  
Rock Samples ◽  
Unloading Rate ◽  
Porewater Pressure

The red sandstone in the Luohe Formation in Shaanxi Province, China, contains a rich aquifer system. The excavation of coal mines and tunnels through the Luohe Formation affects the mechanical properties of the rocks in the surrounding environment, creating the need to determine the effect of the porewater pressure and unloading rate on the mechanical properties of the red sandstone. Using the constant axial pressure unloading method, triaxial unloading tests were performed under different unloading rates (0.1, 0.3 and 0.6 MPa s−1 and porewater pressure conditions (0, 1.0, 1.5 and 2.0 MPa). Based on the results, an unloading statistical damage model of red sandstone was established under the impacts of unloading rate and porewater pressure. During the loading stage, as the porewater pressure increased, the slope of the stress–strain curve and elastic modulus gradually decreased. During the unloading stage, lateral deformation larger than the axial deformation was observed owing to the influence of porewater pressure. The porewater pressure effect became significant as the unloading rate decreased. An increase in porewater pressure or a decrease in the unloading rate increased the confining strain flexibility. Unloading failure of rock samples was dominated by tensile shear failure, thus indicating that a faster unloading rate or larger porewater pressure causes more tensile cracks and severe fracture in the rock samples.

scholarly journals Experimental Study on the Creep Behavior of Red Sandstone under Low Temperatures

2019 ◽  
Vol 2019 ◽  
pp. 1-9 ◽  
Author(s):  
Yongjun Song ◽  
Leitao Zhang ◽  
Huimin Yang ◽  
Jianxi Ren ◽  
Yongxin Che
Keyword(s):  
Mechanical Properties ◽  
Low Temperature ◽  
Deformation Characteristics ◽  
Red Sandstone ◽  
Rock Samples ◽  
Uniaxial Creep ◽  
Deformation Properties ◽  
Accelerated Creep ◽  
Different Temperatures

In cold regions, the deformation characteristics and long-term mechanical properties of rocks under low-temperature conditions are considerably different from those in other regions. To study the deformation characteristics and long-term mechanical properties of rocks in a low-temperature environment and the effect of different temperatures, we perform a multilevel loading-unloading uniaxial creep test on red sandstone samples and obtain the creep curves at different temperatures (20°C, −10°C, and −20°C). The results demonstrate that the total strain at each temperature can be divided into instantaneous and creep strains; the instantaneous strain includes instantaneous elastic and plastic strains, and the creep strain includes viscoelastic and viscoplastic strains. Temperature has a significant effect on the deformation properties of red sandstone. A decrease in temperature reduces the instantaneous and creep deformations of the rocks at all levels of stress. In addition, a decrease in temperature exponentially attenuates the total creep and viscoplastic strains of the rocks. 0°C is a critical point for the reduction of the total creep and viscoplastic strains of the rocks. When the temperature is greater than 0°C, the total creep and viscoplastic strains of the rocks decrease rapidly and linearly with decrease in temperature; however, when the temperature is less than 0°C, the decrease in the total creep and viscoplastic strains of the rocks is slow. The steady-state creep rate of the rock samples decreases with decrease in temperature, whereas the creep duration increases with decrease in temperature, especially in the case of the accelerated creep stage. The accelerated creep durations of the rock samples S4 (20°C) and S7 (–10°C) are 0.07 h and 0.23 h, respectively.

Experimental Study on Crack Propagation by AE Location under Uniaxial Compression Condition

2007 ◽  
Vol 353-358 ◽  
pp. 2329-2332
Author(s):  
Xing Dong Zhao ◽  
Yuan Hui Li ◽  
Rui Fu Yuan
Keyword(s):  
Crack Initiation ◽  
Crack Propagation ◽  
Failure Mode ◽  
Uniaxial Compression ◽  
Crack Initiation And Propagation ◽  
Stress Strain ◽  
Initiation And Propagation ◽  
Ae Location ◽  
Granite Samples ◽  
Compression Condition

AE technique is proved a efficient tool for real-time monitoring of the crack initiation and propagation during rock failure process under uniaxial compression condition. In this paper, An AE system was employed to investigate the crack propagation and failure modes of three groups of granite specimens (80mm×100mm×170mm) with the same pre-existing crack. The AE sensors can be surface mounted. By using a Geiger location algorithm, AE event location can be determined by time-of-arrival times. The propagation velocities of p-wave or s-wave of granite samples were measured. Experiments on pre-existing crack propagation of granite samples were carried out on the press machine. From the testing result, failure mode of three kinds of granite samples was mainly shear failure, while the secondary crack propagated slowly and could not influence the failure mode of granite sample. By surveying the relation of accumulative AE events and stress-strain curve, AE activity represents different characters with stress-strain changing during the total loading process, microcracking contributing to fracture propagation with strain corrosion. AE location result reflected crack initiation and propagation, which is of great importance in studying rock instability and predicting rock failure mode.

scholarly journals Uniaxial Compression Mechanical Properties of Rock Samples in Soft and Hard Composite Strata

2020 ◽  
Vol 2020 ◽  
pp. 1-9
Author(s):  
Bo Wu ◽  
Wei Huang
Keyword(s):  
Mechanical Properties ◽  
Uniaxial Compression ◽  
Compression Test ◽  
Soft Part ◽  
High Strength ◽  
Uniaxial Compression Test ◽  
Strength Ratio ◽  
Rock Samples ◽  
Similar Materials ◽  
The Impact

In the upper soft and lower hard composite strata, it is very difficult to sample the rock and test the mechanical properties of the samples. The study of the mechanical properties of similar material samples by artificial manufacture may enable an alternative method to solve this problem. Therefore, the feasibility of artificial sample preparation and the test of mechanical properties of rock samples in the composite strata become the key to solve the study of mechanical properties of the upper soft strata and the lower hard composite strata. For this purpose, the artificial composite samples composed of two kinds of materials with different strengths were prepared by using cement and kaolin as similar materials. Through the uniaxial compression test of artificial composite rock samples, the effects of the strength ratio of similar materials and the thickness ratio of higher strength materials on the mechanical properties of composite specimens were analyzed. The results of uniaxial compression test show that artificial similar materials could be used to simulate the composite rock samples which are difficult to sample. Without considering the structural interface effect, the greater the strength ratio of similar materials, the greater the impact on the overall strength of composite specimens. The change of volume proportion of high-strength materials has a significant impact on the overall strength of composite specimens. Moreover, the numerical simulation and the experimental stress-strain curves both show a similar trend, indicating that the deformation of the composite strata mainly occurs in the soft part. The research results can provide reference for the test and analysis of mechanical properties in similar complex strata with difficult sampling.

Mechanical Properties of Ceramic Laminates

2007 ◽  
Vol 333 ◽  
pp. 87-96 ◽  
Author(s):  
Tanja Lube
Keyword(s):  
Mechanical Properties ◽  
Residual Stresses ◽  
Crack Propagation ◽  
Failure Mode ◽  
Weak Interface ◽  
Basic Principles ◽  
Threshold Strength ◽  
Strength Distributions

The progress of research efforts on the mechanical properties of ceramic laminates is reviewed. Laminates with weak interface are described with respect to their failure mode and the criterions to achieve graceful failure. For laminates with strong interfaces basic principles concerning the residual stresses and their influence on crack propagation are introduced. The implications for strength, indentation strength, strength distributions, macroscopic R-curves and threshold strength are discussed.

Experimental Study on Dynamic Mechanical Properties of Amphibolites, Sericite-quartz Schist and Sandstone under Impact Loadings

2012 ◽  
Vol 13 (2) ◽  
pp. 209-217
Author(s):  
Jun-Zhong Liu ◽  
Jin-Yu Xu ◽  
Xiao-Cong Lv ◽  
De-Hui Zhao ◽  
Bing-Lin Leng
Keyword(s):  
Mechanical Properties ◽  
Strain Rate ◽  
Failure Mode ◽  
Failure Modes ◽  
Split Hopkinson Pressure Bar ◽  
Dynamic Mechanical Properties ◽  
Tensile Failure ◽  
Strength Increase ◽  
Dynamic Mechanical ◽  
Rock Samples

Abstract In order to investigate rock dynamic mechanical properties of amphibolites, sericite-quartz schist and sandstone under the different strain rates varying from 30 s -1 to 150 s -1 , the specimens were subjected to axial impact at different projectile speeds by using the split Hopkinson pressure bar (SHPB) of 100 mm in diameter. The optimal experimental size of rock samples is verified by analyzing the stress equilibrium of cylindrical rock samples in different thicknesses. It has studied the mechanic properties of these three rocks which under impact loadings; and analysed the dynamic compressive strength, failure modes, energy dissipation variation with the strain-rate and the strain-rate hardening effect from the perspective of material microstructure. Experimental results show that the dynamic Young's modulus of rock samples increase with strain-rate slightly. The dynamic failure modes of different rock samples are always different. When at a lower strain-rate, the damage of sandstone takes a peeling off the external radial tensile failure mode, but that of amphibolites takes axial splitting mode; when at a higher strain-rate, sandstone takes granular crushing failure mode, and that of amphibolites and of sericite-quartz schist take massive crushing mode. Significant strain-rate effect can be represented by a linear relation between the specific energy absorption and the strain-rate , or between the dynamic strength increase factor η and .

scholarly journals Uniaxial Compression Experiments And Numerical Simulations of Artificial Rock Samples With Regular Dentate Discontinuity

2021 ◽  
Author(s):  
Maolin Xue ◽  
Haijun Chen ◽  
Liangxiao Xiong ◽  
Zhongyuan Xu ◽  
Jie Yang ◽  
...  
Keyword(s):  
Numerical Simulation ◽  
Compressive Strength ◽  
Elastic Modulus ◽  
Uniaxial Compression ◽  
Horizontal Line ◽  
Peak Strain ◽  
Bottom Line ◽  
Rock Samples ◽  
Artificial Rock ◽  
Dip Angle

Abstract To study the uniaxial compression performance of artificial rock samples with symmetrical and asymmetrical regular dentate discontinuities, uniaxial compression tests and Particle Flow Code (PFC) numerical simulation are conducted on cement mortar specimens, and the combined effects of dip angle, undulation angle, and number of undulating structures of cracks on the compressive strength, peak strain, elastic modulus, and crack propagation in the specimens are studied. Among these parameters, undulating structure is defined as a single regular dentate structure in the dentate discontinuity; dip angle is the angle between the bottom line of the undulating shape and the horizontal line; undulating angle is the angle between the bottom line of the undulating structure and the left line of the undulating shape; and the number of undulating structures is the number of undulating structures in the dentate discontinuity. The experimental and numerical simulation results show that when the number of the undulating structures and undulating angles remain unchanged, the uniaxial compressive strength of the specimens peak at a dip angle of 90°. In addition, when the dip and undulating angles remain unchanged, the compressive strength, peak strain, and elastic modulus of the specimens decrease with an increase in the number of undulating structures. Moreover, when the number of undulating structures and the dip angle remain unchanged, the compressive strength, peak strain, and elastic modulus of the specimens decrease with an increase in the undulating angle. Further, almost all of the new cracks in the specimens initiate at the tip of the prefabricated cracks.

scholarly journals Acoustic Emission Characteristics and Energy Evolution of Red Sandstone Samples under Cyclic Loading and Unloading

2021 ◽  
Vol 2021 ◽  
pp. 1-15
Author(s):  
Tianzuo Wang ◽  
Chunli Wang ◽  
Fei Xue ◽  
Linxiang Wang ◽  
Beyene Hana Teshome ◽  
...  
Keyword(s):  
Acoustic Emission ◽  
Cyclic Loading ◽  
Uniaxial Compression ◽  
Dissipated Energy ◽  
Strengthening Effect ◽  
Energy Rate ◽  
Red Sandstone ◽  
Rock Samples ◽  
Cyclic Loading And Unloading ◽  
Loading And Unloading

To explore the characteristics of rock deformation and failure under cyclic loading and unloading, the MTS815 rock mechanics test system and acoustic emission (AE) signal acquisition system were used to perform cyclic loading and unloading tests on red sandstone samples. The results showed that, compared with the uniaxial compression test, cyclic loading and unloading had a certain strengthening effect on the strength of the samples. The plastic deformation of the rock samples increased as the number of cycles increased. Based on AE signals, the cracking mode classification was analyzed on the basis of the average frequency and the rise angle of the waveforms. It was observed that the Felicity ratio gradually decreased with the increase in the stress level, which showed a cumulative damage effect. From the perspective of energy, the obvious increase of AE energy rate was mainly concentrated in the early and late stages of uniaxial compression, while the significant increase of dissipated energy rate occurred in the late stage of uniaxial compression. During the cyclic loading and unloading, most of the work done by external forces in the compaction stage and the elastic stage was converted into elastic strain energy, and dissipated energy began to gradually increase in the stage of stable fracture development. In addition, it was found that the damage evolution of the rock samples changed from slow to fast, and the dissipated energy ratio increased when failure was approaching.

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