Effects of Confining Pressure on Mechanical Properties and Damage Evolution of Granite under Cyclic Impact Loading

High in-situ stress and frequent dynamic disturbances caused by the mining process in deep coal mines can easily induce dynamic disasters such as coal burst. We conducted laboratory experiments to assess the effects of the axial stress loading and dynamic cyclic impact loading on the dynamic mechanical properties of burst-prone coals by using a modified split Hopkinson pressure bar (SHPB). Comparisons were made using two types of burst-prone and burst-resistant coal samples. The mineral components, organic macerals, and dynamic mechanical features of both burst-prone and burst-resistant coal samples were comparatively analyzed based on the obtained X-ray diffraction (XRD), optical microscope observations, and dynamic compressive stress-strain curves, respectively. The results of the microstructure analysis indicated a larger difference between the minimum and maximum reflectances of vitrinite for burst-prone coal. Compared to the burst-resistant coal samples, the burst-prone coals contained less corpocollinite and fusinite. While applying a high axial static load combined with cyclic impact load, the coal samples showed the characteristics of fatigue damage. The results also demonstrated that preaxial stress affected the burst resistance of coal samples. The greater the preaxial stress was, the less the coal samples could withstand the dynamic cyclic impact load. In comparison to the burst-resistant coal sample, the burst-prone coal sample showed a larger dynamic compressive strength and a lower deformation. They were also more positively capable of the propagation and activation of the coal burst. We believe that the results of the study are conducive to further understanding of the distribution of microcomponents of burst-prone coals. The results are also beneficial for realizing the dynamic mechanical characteristics of burst-prone coals under the impact of cyclic dynamic load.

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The Influence of H, W, H/E, H 3/E 2, Structure and Chemical Composition on the Resistance of Ti–B–(N), Mo–B–(N), Cr–B–(N), and Zr–B–(N) Coatings to Cyclic Impact Loading

Protection of Metals and Physical Chemistry of Surfaces ◽

10.1134/s2070205120060143 ◽

2020 ◽

Vol 56 (6) ◽

pp. 1190-1200

Author(s):

Ph. V. Kiryukhantsev-Korneev ◽

A. D. Sytchenko

Keyword(s):

Chemical Composition ◽

Impact Loading ◽

Cyclic Impact Loading ◽

Cyclic Impact

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Study on mechanical properties and damage evolution of carbonaceous shale under triaxial compression with acoustic emission

International Journal of Damage Mechanics ◽

10.1177/1056789521991193 ◽

2021 ◽

pp. 105678952199119

Author(s):

Kai Yang ◽

Qixiang Yan ◽

Chuan Zhang ◽

Wang Wu ◽

Fei Wan

Keyword(s):

Mechanical Properties ◽

Acoustic Emission ◽

Water Content ◽

Damage Evolution ◽

Damage Assessment ◽

Triaxial Compression ◽

Confining Pressure ◽

Damage Variable ◽

Natural State ◽

Carbonaceous Shale

To explore the mechanical properties and damage evolution characteristics of carbonaceous shale with different confining pressures and water-bearing conditions, triaxial compression tests accompanied by simultaneous acoustic emission (AE) monitoring were conducted on carbonaceous shale rock specimens. The AE characteristics of carbonaceous shale were investigated, a damage assessment method based on Shannon entropy of AE was further proposed. The results suggest that the mechanical properties of carbonaceous shale intensify with increasing confining pressure and degrade with increasing water content. Moisture in rocks does not only weaken the cohesion but also reduce the internal friction angle of carbonaceous shale. It is observed that AE activities mainly occur in the post-peak stage and the strong AE activities of saturated carbonaceous shale specimens appear at a lower normalized stress level than that of natural-state specimens. The maximum AE counts and AE energy increase with water content while decrease with confining pressure. Both confining pressure and water content induce changes in the proportions of AE dominant frequency bands, but the changes caused by confining pressure are more significant than those caused by water content. The results also indicate that AE entropy can serve as an applicable index for rock damage assessment. The damage evolution process of carbonaceous shale can be divided into two main stages, including the stable damage development stage and the damage acceleration stage. The damage variable increases slowly accompanied by a few AE activities at the first stage, which is followed by a rapid growth along with intense acoustic emission activities at the damage acceleration stage. Moreover, there is a sharp rise in the damage evolution curve for the natural-state specimen at the damage acceleration stage, while the damage variable develops slowly for the saturated-state specimen.

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Damage evolution and recrystallization enhancement of frozen loess

International Journal of Damage Mechanics ◽

10.1177/1056789517731138 ◽

2017 ◽

Vol 27 (8) ◽

pp. 1131-1155 ◽

Cited By ~ 21

Author(s):

Zhiwei Zhou ◽

Wei Ma ◽

Shujuan Zhang ◽

Cong Cai ◽

Yanhu Mu ◽

...

Keyword(s):

Mechanical Properties ◽

Strain Rate ◽

Damage Evolution ◽

Deformation Process ◽

Triaxial Compression ◽

Confining Pressure ◽

Recrystallization Process ◽

Frozen Soils ◽

Time Deformation ◽

Pressure Melting

A series of multistage triaxial compression, creep, and stress relaxation tests were conducted on frozen loess at the temperature of −6℃ in order to study the damage evolution and recrystallization enhancement of mechanical properties during deformation process. The effect of strain rate, confining pressure, and hydrostatic stress history in the degradation laws of mechanical properties is investigated further. The strain rate has a significant influence on the stress–strain curve which dominates the evolution trend of mechanical properties. The mechanical behaviors (strength, stiffness, and viscosity) of frozen loess all exhibit evident response for the consolidation and pressure melting phenomenon caused by the confining pressure. The multistage loading tests under different hydrostatic stresses are capable of differentiating the development characteristics of mechanical properties during axial loading and hydrostatic compression process, respectively. The testing results indicated that the recrystallization of the ice particle in the frozen soils is an important microscopic factor for enhancement behaviors of mechanical parameters during the deformation process. This strengthening degree of mechanical properties is determined by temperature, duration time, deformation degree, and stress state during the recrystallization process. The phase transformation led by pressure melting and ice recrystallization is a nonnegligible changing pattern of frozen soils microstructure, which has apparent role in the damage evolution of mechanical properties.

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Dynamic Properties of Thermally Treated Granite Subjected to Cyclic Impact Loading

Rock Mechanics and Rock Engineering ◽

10.1007/s00603-018-1606-y ◽

2018 ◽

Vol 52 (4) ◽

pp. 991-1010 ◽

Cited By ~ 20

Author(s):

Pin Wang ◽

Tubing Yin ◽

Xibing Li ◽

Shuaishuai Zhang ◽

Lv Bai

Keyword(s):

Impact Loading ◽

Dynamic Properties ◽

Cyclic Impact Loading ◽

Cyclic Impact ◽

Thermally Treated

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Endurance of 55S2 steel under cyclic-impact loading in the presence of liquid media

Strength of Materials ◽

10.1007/bf00762325 ◽

1973 ◽

Vol 5 (5) ◽

pp. 621-624

Author(s):

V. V. Ermolaev ◽

A. V. Morzhakov ◽

A. V. Topkaev

Keyword(s):

Impact Loading ◽

Liquid Media ◽

Cyclic Impact Loading ◽

Cyclic Impact

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Study on Damage Model and Damage Evolution Characteristics of Backfill with Prefabricated Fracture under Seepage-Stress Coupling

Advances in Materials Science and Engineering ◽

10.1155/2020/3642356 ◽

2020 ◽

Vol 2020 ◽

pp. 1-11

Author(s):

Jifeng Hou ◽

Zhongping Guo ◽

Weizhen Liu ◽

Hengze Yang ◽

WenWu Xie

Keyword(s):

Mechanical Properties ◽

Damage Evolution ◽

Coupling Effect ◽

Water Pressure ◽

Damage Model ◽

Confining Pressure ◽

Seepage Water ◽

Confining Pressures ◽

Initial Fracture ◽

Total Damage

Aiming at the backfill with prefabricated fracture under seepage-stress coupling, the concepts of fracture macrodamage, loaded mesodamage, seepage mesodamage, and total damage of backfill were proposed. Based on the macroscopic statistical damage model, the coupling effect of seepage, stress, and initial fracture was considered comprehensively and the damage model of backfill with prefabricated fracture under seepage-stress coupling was established. The mechanical properties of backfill with prefabricated fracture under different seepage water pressures and confining pressures were tested and the rationality of the model was verified. The research shows that the mechanical properties of backfill with prefabricated fracture under the seepage-stress coupling are determined by the seepage water pressure, the load, the initial fracture, and the coupling effect. Fracture and seepage have significant effects on the damage of the backfill. When the seepage water pressure is low, the fracture damage dominates; however, when the seepage water pressure is high, the seepage damage dominates; the total damage under the coupling action is more serious than the single factor. The development laws of the total damage evolution curves under different seepage water pressures and confining pressures are basically the same, and they show the S-shaped distribution law with the increase of the axial strain. With the increase of confining pressure, the damage effect of fracture and seepage on the backfill is weakened, indicating that the confining pressure has a certain inhibitory effect on the damage evolution of the backfill. The research results can provide a theoretical basis for the study of the stability of backfill with geological defects such as joints and fractures in deep high-stress and high-seepage water pressure coal mines.

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