Impacts of Cyclic Loading and Unloading Rates on Acoustic Emission Evolution and Felicity Effect of Instable Rock Mass

Uniaxial cyclic loading-unloading compression experiments with schemes of six loading rates and six unloading rates were carried out on the combined testing platform. Impact of loading and unloading rates on rock AE characteristics was revealed. Results show that increasing loading and unloading rates resulted in decreasing total AE rings in the entire rock deformation and failure process. Increasing loading rate decreased the AE rings at loading stages, and increasing unloading rate decreased the AE rings at unloading stages in the same cycle. Total AE counts had a negative linear relationship to the loading and unloading rates. The loading stage was the active period of the AE phenomena, and impacts of the loading rate on the AE characteristics were more apparent. Especially when the loading rate was greater than 2.0 kN/s, brittle failure of rock specimens became noticeable. After the cyclic load reached the uniaxial compressive strength of 1/3∼1/2 times, the rock Felicity effect became more obvious. With the increase of the loading rate, the Felicity ratio decreased in the elastic stage and increased a little in the plastic stage, whereas with the increase of the unloading rate, the Felicity ratio decreased gradually in the elastic stage and remained almost the same in the plastic stage.

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Experimental Study on Mechanical Properties of Deep Buried Granite under Different Confining Pressures

Advances in Civil Engineering ◽

10.1155/2020/6640497 ◽

2020 ◽

Vol 2020 ◽

pp. 1-10

Author(s):

Jun Zhao ◽

Tan Zhang

Keyword(s):

Cyclic Loading ◽

Confining Pressure ◽

Surrounding Rock ◽

Underground Engineering ◽

Failure Characteristics ◽

Deformation And Failure ◽

Cyclic Loading And Unloading ◽

Confining Pressures ◽

Crack Damage Stress ◽

Loading And Unloading

Brittle failure of hard rock poses a serious threat to the stability of surrounding rock in deep underground engineering. In order to study the deformation and failure characteristics of deep buried granite under high confining pressure cyclic loading and unloading, MTS815 electro-hydraulic servo rock test system was used to conduct cyclic loading and unloading tests under confining pressures of 15 MPa, 35 MPa, 45 MPa, and 55 MPa, and the corresponding stress-strain curves and deformation failure characteristic curves were obtained. The experimental results show the follows: (1) under the same confining pressure, the peak strength, crack initiation stress, crack damage stress, and Poisson’s ratio of the specimens under cyclic loading and unloading are larger than those under conventional triaxial loading and unloading, and the unloading elastic modulus is smaller than that, under conventional triaxial compression; (2) the results show that, under different confining pressures, the granite samples show obvious brittle failure characteristics, the elastic modulus and crack initiation stress increase first and then decrease with the confining pressure, the peak strength and crack damage stress of the samples increase linearly with the confining pressure, and Poisson’s ratio increases first and then remains unchanged with the confining pressure; (3) under the two kinds of stress conditions, the macroscopic failure of the samples is mainly shear failure. The deformation and failure law of granite samples revealed in this study has significant reference value for the selection of rock mass mechanical model of surrounding rock stability of underground engineering, the formulation of surrounding rock support countermeasures, and the evolution law of mechanical parameters with damage variables.

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Experimental and numerical studies on fracture characteristics of notched granite beams under cyclic loading and unloading

The Journal of Strain Analysis for Engineering Design ◽

10.1177/0309324720923218 ◽

2020 ◽

Vol 56 (1) ◽

pp. 3-17

Author(s):

Xiaojing Li ◽

Peijie He ◽

Jianhui Tang ◽

Xudong Chen

Keyword(s):

Acoustic Emission ◽

Cyclic Loading ◽

Correlation Method ◽

Average Frequency ◽

Test System ◽

Underground Engineering ◽

Three Point Bending ◽

Cyclic Loading And Unloading ◽

Loading And Unloading ◽

Felicity Ratio

In underground engineering, such as mining engineering and deep tunnel engineering, the rock is often loaded and unloaded repeatedly. The strength of rock under cyclic load is lower than that under static load. To obtain the fracture response of the rock, the three-point bending tests of notched granite beams under cyclic loading and unloading were carried out with Electro-hydraulic Servo Material Test System. The acoustic emission technology was adopted to monitor the acoustic emission events of sample in the process of fracture. It is revealed that the fracture toughness of granite under cyclic loading and unloading is lower than that under static loading. Based on the acoustic emission energy obtained from monitoring, the damage evolution during cyclic loading and unloading was analyzed. The fracture mode of granite samples is analyzed by the RA value-average frequency correlation method. And the Felicity ratio during the loading and unloading cycle was calculated to evaluate the severity of initial damage of the material. It is revealed that Kaiser effect appears only in the elastic deformation stage of cyclic loading unloading bending. The Holmquist–Johnson–Cook damage constitutive model and Weibull distribution were used to establish the heterogeneous granite model. And the three-point bending of the model under cyclic loading and unloading was simulated to disclose the crack growth mechanism of rock. The study may provide some references for rock instability control in geotechnical engineering construction.

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Influence of Loading Rate on the Energy Evolution Characteristics of Rocks under Cyclic Loading and Unloading

Energies ◽

10.3390/en13154003 ◽

2020 ◽

Vol 13 (15) ◽

pp. 4003

Author(s):

Jielin Li ◽

Liu Hong ◽

Keping Zhou ◽

Caichu Xia ◽

Longyin Zhu

Keyword(s):

Cyclic Loading ◽

Loading Rate ◽

Energy Evolution ◽

Dissipation Energy ◽

Loading Rates ◽

Cyclic Loading And Unloading ◽

Evolution Characteristics ◽

Increasing Trend ◽

Loading And Unloading ◽

Fast Increase

To analyse the effect of loading rate on the energy evolution of rocks under cyclic loading and unloading, tests on saturated limestone were conducted at loading rates of 0.15, 0.2, and 0.3 mm/min, and the evolution characteristics of plastic, elastic, dissipation, and input energies were examined under different loading rates. The results indicated that the plastic strain in the entire test was directly proportional to the loading rate. In addition, strength, residual stress, plastic energy, and dissipation energy under residual resistance were inversely proportional to the loading rate. The plastic strain exhibited a decreasing–stabilising–increasing trend, and the smaller loading rate delayed the “increasing” trend. The increasing extent of each energy exhibited the following trend: input > elastic > plastic > dissipation energy. Furthermore, the first three types of energy exhibited a slow–fast–slow–fast increase trend. The dissipation energy exhibited a fast–steady–fast–slow–fast increase trend. Additionally, the elastic energy index exhibited a large increase–steady increase–decrease trend, which was proportional to the loading rate. The damping ratio exhibited a decrease–increase–decrease–increase–decrease trend which was proportional to the loading rate in the compaction stage and inversely proportional to the plastic stage.

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Deformation Failure Characteristics and Loading Rate Effect of Sandstone Under Uniaxial Cyclic Loading and Unloading

Geotechnical and Geological Engineering ◽

10.1007/s10706-018-0674-9 ◽

2018 ◽

Vol 37 (3) ◽

pp. 1147-1154 ◽

Cited By ~ 6

Author(s):

Xuejun Zhu ◽

Yangyang Li ◽

Changxiang Wang ◽

Xizhen Sun ◽

Zhanxin Liu

Keyword(s):

Cyclic Loading ◽

Loading Rate ◽

Rate Effect ◽

Failure Characteristics ◽

Cyclic Loading And Unloading ◽

Loading And Unloading

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Identification of fracture sequences during sharp indentation of polycrystalline Al2O3

Journal of Materials Research ◽

10.1557/jmr.1994.1693 ◽

1994 ◽

Vol 9 (7) ◽

pp. 1693-1700 ◽

Cited By ~ 8

Author(s):

Kaiyang Zeng ◽

David Rowcliffe

Keyword(s):

Single Crystal ◽

Loading Rate ◽

Soda Lime ◽

Soda Lime Glass ◽

Transgranular Fracture ◽

Optically Transparent ◽

Unloading Rate ◽

Loading And Unloading ◽

Sharp Indentation ◽

Fracture Features

The effects of loading and unloading rate on fracture features formed during sharp indentation of polycrystalline Al2O3 have been studied. It was found that there is a transition between intergranular and transgranular fracture if the loading rate is increased by a factor of 104 during the whole indentation cycle. By varying the loading or unloading rate during indentation, and correlating the corresponding dependence of fracture features, the part of the indentation cycle can be identified in which specific segments of cracks are generated. Hence, the fracture sequence during indentation is established. The fracture sequence for polycrystalline Al2O3 is compared with those reported from direct observation in optically transparent materials such as soda-lime glass and various single crystal ceramics.

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Experimental study on the failure process of sandstone subjected to cyclic loading and unloading after high temperature treatment

Engineering Geology ◽

10.1016/j.enggeo.2021.106305 ◽

2021 ◽

pp. 106305

Author(s):

Weijing Xiao ◽

Guo Yu ◽

Haitao Li ◽

Weiyun Zhan ◽

Dongming Zhang

Keyword(s):

Experimental Study ◽

High Temperature ◽

Cyclic Loading ◽

Failure Process ◽

Temperature Treatment ◽

High Temperature Treatment ◽

Cyclic Loading And Unloading ◽

Loading And Unloading

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Research on Supporting Method for High Stressed Soft Rock Roadway in Gentle Dipping Strata of Red Shale

Minerals ◽

10.3390/min11040423 ◽

2021 ◽

Vol 11 (4) ◽

pp. 423

Author(s):

Chunde Ma ◽

Jiaqing Xu ◽

Guanshuang Tan ◽

Weibin Xie ◽

Zhihai Lv

Keyword(s):

Failure Process ◽

High Stress ◽

Soft Rock ◽

In Situ Stress ◽

Mechanical Parameters ◽

Deformation And Failure ◽

Deep Mine ◽

Plastic Energy ◽

Roadway Stability ◽

Phosphate Mine

Red shale is widely distributed among the deep mine areas of Kaiyang Phosphate Mine, which is the biggest underground phosphate mine of China. Because of the effect of various factors, such as high stress, ground water and so on, trackless transport roadways in deep mine areas were difficult to effectively support for a long time by using traditional supporting design methods. To deal with this problem, some innovative works were carried out in this paper. First, mineral composition and microstructure, anisotropic, hydraulic mechanical properties and other mechanical parameters of red shale were tested in a laboratory to reveal its deformation and failure characteristics from the aspect of lithology. Then, some numerical simulation about the failure process of the roadways in layered red shale strata was implemented to investigate the change regulation of stress and strain in the surrounding rock, according to the real rock mechanical parameters and in-situ stress data. Therefore, based on the composite failure law and existing support problems of red shale roadways, some effective methods and techniques were adopted, especially a kind of new wave-type bolt that was used to relieve rock expansion and plastic energy to prevent concentration of stress and excess deformation. The field experiment shows the superiorities in new techniques have been verified and successfully applied to safeguard roadway stability.

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