scholarly journals Study on Mechanical Properties and Damage Evolution of High-Porosity Concrete under Cyclic Loading and Unloading

2021 ◽  
Vol 2021 ◽  
pp. 1-8
Author(s):  
Dong Zhang ◽  
Ai-hong Lu ◽  
Xia Wang ◽  
Yu Xia ◽  
Si-yu Gong ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Elastic Modulus ◽  
Cyclic Loading ◽  
Damage Evolution ◽  
Stress Amplitude ◽  
High Porosity ◽  
Peak Strain ◽  
Cycle Number ◽  
Cyclic Loading And Unloading ◽  
Loading And Unloading

Understanding the mechanical properties and energy response of high-porosity concrete under the cyclic loading and unloading is the foundation of road construction in sponge city. In this study, the concrete with the porosity of 15% was taken as the research object, and the cyclic loading and unloading tests on the high-porosity concrete were performed under the stress amplitude of 25 MPa, 30 MPa, and 35 MPa in the elastic stage. The effects of stress amplitude and cycle number on the mechanical characteristics and damage evolution law of concrete were obtained. The experimental results show the following. (1) With the increase of cycle number, the loading and unloading elastic modulus of concrete under different stress amplitudes first increases and then decreases; the greater the stress amplitude, the faster the growth and deceleration of the loading and unloading elastic modulus. (2) With the increase of the cycle number, the peak strain and residual plastic deformation increase. (3) The greater the stress amplitude, the higher the damage of concrete; with the increasing number of cyclic loading and unloading, the damage of concrete is enhanced gradually. When the damage variable value is 1, the relationship between the cycle number and the initial stress amplitude satisfies a negative exponential function.

scholarly journals Damage and fractal evolution trends of sandstones under constant-amplitude and tiered cyclic loading and unloading based on acoustic emission

2019 ◽  
Vol 15 (7) ◽  
pp. 155014771986102
Author(s):  
Dongxu Liang ◽  
Nong Zhang ◽  
Lixiang Xie ◽  
Guangming Zhao ◽  
Deyu Qian
Keyword(s):  
Acoustic Emission ◽  
Cyclic Loading ◽  
Damage Evolution ◽  
Damage Accumulation ◽  
Fractal Dimensions ◽  
Damage Variable ◽  
Constant Amplitude ◽  
Kaiser Effect ◽  
Cyclic Loading And Unloading ◽  
Loading And Unloading

It is of significance to study the damage and destruction of rock under cyclic loading in geotechnical engineering. We determined the trends in damage evolution of sandstone under constant-amplitude and tiered cyclic loading and unloading under uniaxial compression. The results of the study show that (1) the variation of acoustic-emission events was consistent with the stress curves and 89% of all acoustic-emission events occurred during the cycling stages. The observed Kaiser effect was more notable in tiered cycling. (2) The damage variable increased sharply in the cycling stages and its increment was 0.07 higher for tiered cycling than constant-amplitude cycling. Sandstone exhibited greater damage under tiered cyclic loading and unloading. (3) Equations for the evolution of the damage variable under the two cycle modes were obtained by fitting of experimental data. (4) The fractal dimensions of the constant-amplitude cycle were larger than those of the tiered cycle. The process of damage and destruction presents a trend of reducing fractal dimension. The damage accumulation of sandstone under tiered cycling was faster than under constant-amplitude cycling. These results provide references for damage and early warning of rock under both constant-amplitude and tiered cyclic loading and unloading.

The Deformation Characteristics of Soft Clay under Cyclic Loading

2012 ◽  
Vol 446-449 ◽  
pp. 1709-1712 ◽  
Author(s):  
Yong Zhang ◽  
Li Wan ◽  
Xiong Wei Li
Keyword(s):  
Elastic Modulus ◽  
Cyclic Loading ◽  
Elastic Strain ◽  
Dynamic Stress ◽  
Stress Amplitude ◽  
Soft Clay ◽  
Dynamic Elastic Modulus ◽  
Deformation Characteristics ◽  
Cycle Number ◽  
Critical Type

Through the undrained dynamic triaxial experiment, the deformation characteristics of saturated soft clay under cyclic loading are investigated. The cyclic loading was simplified as sine wave. It is found that under different dynamic stress, the deformation patterns of specimen in this experiment can be divided into three kinds, such as dense compressed, tensile break-up and shear failure type. In the process of vibration, the deformation forms of samples can also be divided into three types by dynamic stress amplitude, such as stable, destructive and critical type. The dynamic stress amplitude corresponding to the critical type is called critical dynamic stress. With the dynamic elastic strain increasing gradually, the dynamic elastic modulus decreases and rigidity softening occurs. Furthermore, dynamic elastic modulus and dynamic elastic strain curve decrease while the cyclic number is increasing. Finally, to establish the equation of the relationship between dynamic elastic modulus and dynamic elastic strain, the factor of cycle number should be considered.

scholarly journals Mechanical Behavior of Shale Rock under Uniaxial Cyclic Loading and Unloading Condition

2018 ◽  
Vol 2018 ◽  
pp. 1-8 ◽  
Author(s):  
Baoyun Zhao ◽  
Dongyan Liu ◽  
Ziyun Li ◽  
Wei Huang ◽  
Qian Dong
Keyword(s):  
Cyclic Loading ◽  
Mechanical Behavior ◽  
Creep Behavior ◽  
Peak Stress ◽  
Creep Model ◽  
Cycle Number ◽  
Shale Rock ◽  
Cyclic Loading And Unloading ◽  
Residual Strains ◽  
Loading And Unloading

In order to investigate the mechanical behavior of shale rock under cyclic loading and unloading condition, two kinds of incremental cyclic loading tests were conducted. Based on the result of the short-term uniaxial incremental cyclic loading test, the permanent residual strain, modulus, and damage evolution were analyzed firstly. Results showed that the relationship between the residual strains and the cycle number can be expressed by an exponential function. The deformation modulus E50 and elastic modulus ES first increased and then decreased with the peak stress under the loading condition, and both of them increased approximately linearly with the peak stress under the unloading condition. On the basis of the energy dissipation, the damage variables showed an exponential increasing with the strain at peak stress. The creep behavior of the shale rock was also analyzed. Results showed that there are obvious instantaneous strain, decay creep, and steady creep under each stress level and the specimen appears the accelerated creep stage under the 4th stress of 51.16 MPa. Based on the characteristics of the Burgers creep model, a viscoelastic-plastic creep model was proposed through viscoplastic mechanics, which agrees very well with the experimental results and can better describe the creep behavior of shale rock better than the Burgers creep model. Results can provide some mechanics reference evidence for shale gas development.

scholarly journals Experimental Study on Mechanical Properties and Acoustic Emission Characteristics of Water Bearing Sandstone under Stable Cyclic Loading and Unloading

2020 ◽  
Vol 2020 ◽  
pp. 1-15
Author(s):  
Xinzhan Qin ◽  
Yu Zhou ◽  
Manchao He
Keyword(s):  
Mechanical Properties ◽  
Acoustic Emission ◽  
Cyclic Loading ◽  
Water Content ◽  
Coal Mines ◽  
Surrounding Rock ◽  
Emission Characteristics ◽  
Cyclic Loading And Unloading ◽  
Loading And Unloading ◽  
Pumped Storage

Due to the adjustment of energy structure, a large number of coal mines are abandoned. Considering the environmental and economic effects, many experts proposed to use the abandoned mine cavern as the reservoir of the pumped storage power station. Furthermore, considering the long-term effects of repeated pumping and drainage and hydrodynamic pressure on the surrounding rock in coal mines, a large amount of sandstone was collected from the Ruineng coal mine in Yan’an city to carry out a series of laboratory tests. Through uniaxial compression testing of rock samples with different water content rates, combined with acoustic emission (AE) analysis, the strength softening and macrodeformation characteristics are obtained, and the influence of water content on acoustic emission characteristics is clarified. The mechanical properties of water bearing rock under cyclic loading and unloading experiments with varying upper limits are obtained using a triaxial test system, and the precursory information of rock failure is captured, providing significant guidance for stability analysis and instability warning for surrounding rock in pumped storage power stations.

scholarly journals Fracture Characteristics and Fatigue Damage of Noncoplanar Fractured Rocklike Specimens under Uniaxial Graded Cyclic Loading and Unloading

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-13
Author(s):  
Gui-cheng He ◽  
Wen-yuan Wu ◽  
Yun Wang ◽  
Yong-ming Xue ◽  
Bing Dai ◽  
...  
Keyword(s):  
Elastic Modulus ◽  
Energy Dissipation ◽  
Cyclic Loading ◽  
Hysteresis Loop ◽  
Fatigue Damage ◽  
Damping Ratio ◽  
Fracture Characteristics ◽  
Cyclic Loading And Unloading ◽  
Loading And Unloading ◽  
Limit Stress

To study the fracture characteristics and fatigue damage of fractured rock masses, noncoplanar fractured rocklike specimens prepared using cement mortar were used for a graded cyclic loading–unloading test. The results showed that the two ends of the horizontal crack were the main stress concentration areas, and they inhibited crack initiation of the inclined fracture. With increasing crack inclination, the inhibitory effect became more obvious. Under the condition that the lower limit stress is constant, as the upper limit stress increases, energy dissipation of the specimen increases, becoming relatively stable in each stage of the cycle. With increasing crack inclination, the increase in the energy dissipation value decreases. Specimens with large changes in the shape of their hysteresis loop tend to exhibit large fluctuations in the elastic modulus. As the loading progressed, the elastic modulus exhibited a downward trend, and the damping ratio tended to be stable. The change in the damping ratio is affected by the dynamic elastic modulus and area of the hysteresis loop. Based on the Weibull probability distribution function, the evolution curve of the damage variable of the specimen can be obtained. This curve reflects the trend of the damage change of the rocklike specimens under various levels of cyclic loading and unloading.

scholarly journals Study on Permeability of Deep-Buried Sandstone under Triaxial Cyclic Loads

2021 ◽  
Vol 2021 ◽  
pp. 1-9
Author(s):  
Mingqiang Sheng ◽  
Awei Mabi ◽  
Xigen Lu
Keyword(s):  
Acoustic Emission ◽  
Cyclic Loading ◽  
Energy Density ◽  
Damage Variable ◽  
Dissipated Energy ◽  
Peak Strain ◽  
Rock Damage ◽  
Cyclic Loading And Unloading ◽  
Relative Strain ◽  
Loading And Unloading

The triaxial cyclic loading and unloading test was carried out on a TAW-2000 rock mechanics to study the permeability characteristics of deep-buried sandstone. This paper analyzed the evolution laws of permeability, elastic modulus, rock damage, dissipated energy, and acoustic emission events of sandstone under different confining pressures. It also introduced the concept of relative strain and further discussed the relationship between relative strain and permeability. The test results showed that the permeability of sandstone under cyclic loading and unloading obviously experienced three stages. At a low strain level, the damage degree of sandstone was low. As a result, both the number of acoustic emission events and the proportion of the dissipated energy density were small. In this stage, with increasing the stress, the permeability decreased. With the increase of the relative strain, the propagation of fissure increased through rock interior and the damage of rock was accumulated. Consequently, the number of acoustic emission events grew slowly, and the proportion of dissipated energy density and the damage variable (D) increased gradually. In this stage, the permeability increases. As the axial strain reached the peak strain, the fissures developed into cracks and the rock failure happened. The number of acoustic emission events increased rapidly; both the proportion of the dissipated energy density and the damage variable (D) obtain the maximum value. In this stage, the permeability increased greatly. In this study, the point of fissure propagation of rock specimens was used as the point of demarcation. Before the fissures propagated, the permeability increased slowly and it was in accordance with a linear function. After the fissures propagated, the degree of rock damage increased, and the permeability increased in the form of an exponential function. The larger the confining pressure was, the smaller the relative strain corresponding to the point of fissure propagation was.

scholarly journals Analysis of Energy Dissipation Characteristics of Damaged Sandstone under Impact Load

2021 ◽  
Vol 2021 ◽  
pp. 1-10
Author(s):  
Feng Wang ◽  
Haibo Wang ◽  
Ying Xu ◽  
Bing Cheng ◽  
Qianqian Wang
Keyword(s):  
Rock Mass ◽  
Energy Dissipation ◽  
Cyclic Loading ◽  
Dynamic Load ◽  
Impact Load ◽  
Peak Strain ◽  
Dissipation Energy ◽  
Cyclic Loading And Unloading ◽  
Damage Degree ◽  
Loading And Unloading

Before rock burst, coal, and gas outburst dynamic load, rock mass in geotechnical engineering has been an indifferent degree of damage. The dissipation energy of rock mass under dynamic load reflects the difficulty of rock breaking. In view of the energy dissipation of damaged rock mass under dynamic load, the cyclic loading and unloading test is carried out to make sandstone in different damage states, and the damage degree of sandstone is characterized by the change of longitudinal wave velocity before and after cyclic loading and unloading. Then, the rock with different damage degrees is tested by adopting the split Hopkinson pressure bar (SHPB). Finally, the energy dissipation characteristics of damaged rock under impact load are analyzed. The results show that the damage factor of sandstone increases with the increase of the upper limit of stress after cyclic static loading. The dynamic strength and peak strain of damaged sandstone increase with the increase of impact pressure and decrease with the increase of damage degree. With the increase of damage degree of sandstone, the reflection energy and dissipation energy of sandstone increase, while the transmission energy decreases.

Sign in / Sign up

Export Citation Format

Share Document