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Microstructure, Characterization and Mechanical Properties of Coal and Coal-Like Materials (Volume II)

A special issue of Materials (ISSN 1996-1944). This special issue belongs to the section "Energy Materials".

Deadline for manuscript submissions: 10 October 2024 | Viewed by 7964

Special Issue Editors


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Guest Editor
College of Energy and Mining engineering, Shandong University of Science and Technology, Qingdao 266590, China
Interests: mining rock mechanics; deep roadway support; rock constitutive model; rock burst prevention
Special Issues, Collections and Topics in MDPI journals

E-Mail Website
Guest Editor
Shandong Provincial Key Laboratory of Mine Disaster Prevention and Control, SDUST, Qingdao 266590, China
Interests: composite rock mechanics; rock burst prevention; underground support; rock failure numerical simulation
Special Issues, Collections and Topics in MDPI journals
School of Mining and Petroleum Engineering, University of Alberta, Edmonton, AB T6G 2R3, Canada
Interests: rock mechanics; underground coal mining; numerical modeling
College of Energy and Mining Engineering, Shandong University of Science and Technology, Qingdao 266590, China
Interests: rock mechanics; mining engineering

Special Issue Information

Dear Colleagues,

In view of the general trend that the development of the global energy industry is oriented toward green, low-carbon and efficient utilization, scientific research teams in various fields dominated by the coal industry have conducted much research on coal and coal-like materials by borrowing the technologies and concepts of modern materials science and rock mass mechanics, hoping to explore new directions for the high value-added utilization of structural coal resources and the development of new coal-like materials.

On behalf of Materials, we invite you to contribute an original research article to a Special Issue on the microstructure, characterization and mechanical properties of coal and coal-like materials.

This Special Issue aims to showcase the latest scientific and technological achievements and cutting-edge test technologies in the study of coal and coal-like materials, with an exploration of their structural change characteristics and mechanical properties under various influencing factors.

Hot topics to be covered by the Special Issue:

  • Microstructure of coal and coal-like materials;
  • Analysis of mechanical properties of coal and coal-like materials;
  • Multiscale characterization of coal and coal-like materials;
  • Development and utilization of coal resources with high added value;
  • Void structure and seepage characteristics of coal and coal-like materials;
  • Establishment of constitutive relationships.

Prof. Dr. Xuesheng Liu
Prof. Dr. Yunliang Tan
Dr. Jun Wang
Dr. Deyuan Fan
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Materials is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • multi-scale characterization
  • mechanical property
  • microstructure
  • void structure
  • process waste characterization
  • complex porous media
  • rock mechanics
  • constitutive relationships.

Related Special Issue

Published Papers (6 papers)

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Research

17 pages, 14051 KiB  
Article
Fluidity and Strength of Loess-Based Quick Consolidated Backfill Material with One High-Water Content
by Chenghao Cui, Baifu An, Heng Cui, Qiaomei Yi and Jiale Wang
Materials 2023, 16(16), 5544; https://doi.org/10.3390/ma16165544 - 9 Aug 2023
Viewed by 701
Abstract
To study the flow and strength characteristics of loess-based backfill materials, orthogonal tests were used to design a cemented backfill material combining loess, high-water content materials, cement, and fly ash. By using the range, analysis of variance, and multi-variate regression analysis, influences of [...] Read more.
To study the flow and strength characteristics of loess-based backfill materials, orthogonal tests were used to design a cemented backfill material combining loess, high-water content materials, cement, and fly ash. By using the range, analysis of variance, and multi-variate regression analysis, influences of four key factors on the initial setting time, diffusivity, compressive strength, and shear strength of the backfill material were investigated. These four factors included the mass concentration of loess water (A), the content of high-water content materials (B), cement content (C), and content of fly ash (D). The results showed that the initial setting time, diffusivity, compressive strength, and shear strength of the backfill material were 13~33 min, 400~580 mm, 0.917–3.605 MPa, and 0.360–0.722 MPa, respectively, all distributed in wide ranges. For the initial setting time, the four factors were listed in descending order as A > D > B > C according to their influences; for diffusivity, the four factors were listed as A > B > C > D; for the compressive strength, the four factors were ranked as A > C > D > B; for the shear strength, the four factors were ranked such that A > C > D > B. With regard to the comprehensive index, the four factors were such that A > B > D > C. That is, the factors were listed in descending order as the mass concentration of loess water, cement content, the content of fly ash, and content of high-water content materials according to their significance in influencing characteristics of the loess-based backfill material. Comprehensive analysis indicated that the fluidity of the material was mainly influenced by the mass concentration of loess water, and the two were negatively correlated. The hydro-consolidation effect of materials with high-water contents accelerated material solidification. The strength of the backfill material was mainly influenced by the cement content while only slightly affected by contents of other materials. In this way, a prediction model for characteristic parameters, namely, fluidity and strength, of the loess-based backfill material under the action of various factors was established. Full article
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18 pages, 4299 KiB  
Article
Experimental Study of Mechanical Properties and Failure Characteristics of Coal–Rock-like Composite Based on 3D Printing Technology
by Ying Chen, Zikai Zhang, Chen Cao, Shuai Wang, Guangyuan Xu, Yang Chen and Jinliang Liu
Materials 2023, 16(10), 3681; https://doi.org/10.3390/ma16103681 - 11 May 2023
Cited by 2 | Viewed by 1172
Abstract
Coal contains cracks and has strong heterogeneity, so the data dispersion is large in laboratory tests. In this study, 3D printing technology is used to simulate hard rock and coal, and the rock mechanics test method is used to carry out the coal–rock [...] Read more.
Coal contains cracks and has strong heterogeneity, so the data dispersion is large in laboratory tests. In this study, 3D printing technology is used to simulate hard rock and coal, and the rock mechanics test method is used to carry out the coal–rock combination experiment. The deformation characteristics and failure modes of the combination are analyzed and compared with the relevant parameters of the single body. The results show that the uniaxial compressive strength of the composite sample is inversely proportional to the thickness of the weak body and directly proportional to the thickness of the strong body. The Protodyakonov model or ASTM model can be used as a verification method for the results of a uniaxial compressive strength test of coal–rock combination. The elastic modulus of the combination is the equivalent elastic modulus, and the elastic modulus of the combination is between the elastic modulus of the two constituent monomers, which can be analyzed using the Reuss model. The failure of the composite sample occurs in the low-strength material, while the high-strength section is rebounding as an extra load on the low-strength body, which may cause a sharp increase in the strain rate of the weak body. The main failure mode of the sample with a small height–diameter ratio is splitting, and the failure mode of the sample with a large height–diameter ratio is shear fracturing. When the height–diameter ratio is not greater than 1, it shows pure splitting, and when the height–diameter ratio is 1~2, it shows a mixed mode of splitting and shear fracture. The shape has a significant effect on the uniaxial compressive strength of the composite specimen. For the impact propensity, it can be determined that the uniaxial compressive strength of the combination is higher than that of the single body, and the dynamic failure time is lower than that of the single body. It can hardly determine the elastic energy and the impact energy of the composite with the relationship to the weak body. The proposed methodology provides new cutting-edge test technologies in the study of coal and coal-like materials, with an exploration of their mechanical properties under compression. Full article
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14 pages, 5231 KiB  
Article
The Influence of the Strain Rate and Prestatic Stress on the Dynamic Mechanical Properties of Sandstone—A Case Study from China
by Jun Wang, Zhiwei Ren, Shang Yang, Jianguo Ning, Shuai Zhang and Yongtian Bian
Materials 2023, 16(9), 3591; https://doi.org/10.3390/ma16093591 - 8 May 2023
Cited by 3 | Viewed by 1349
Abstract
A series of conventional dynamic uniaxial compressive (CDUC) tests and coupled static dynamic loading (CSDL) tests were performed using a split Hopkinson compression bar (SHPB) system to explore the variable dynamic mechanical behavior and fracture characteristics of medium siltstone at a microscopic scale [...] Read more.
A series of conventional dynamic uniaxial compressive (CDUC) tests and coupled static dynamic loading (CSDL) tests were performed using a split Hopkinson compression bar (SHPB) system to explore the variable dynamic mechanical behavior and fracture characteristics of medium siltstone at a microscopic scale in the laboratory. In the CDUC tests, the dynamic uniaxial strength of the medium sandstone is rate-dependent in the range of 17.5 to 96.8 s−1, while the dynamic elastic modulus is not dependent on the strain rate. Then, this paper proposes a generalized model to characterize the rate-dependent strength from 17.5 to 96.8 s−1. In the CSDL tests, with increasing initial prestatic stress, the dynamic elastic modulus and dynamic strength increase nonlinearly at first and then decrease. The results show that two classical morphological types (i.e., Type I and Type II) are observed in the dynamic stress–strain response from the CDUC and CSDL tests. By scanning electron microscopy (SEM), microscopic differences in the post-loading microcrack characteristics in the behavior of Type I and Type II are identified. In Class I behavior, intergranular fracture (IF) usually initiates at or near the grains, with most cracks deflected along the grain boundaries, resulting in a sharp angular edge, and then coalesces to the main fracture surface that splits the specimen along the direction of stress wave propagation. In contrast, Class II behavior results from the combined IF and transgranular fracture (TF). Full article
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25 pages, 16020 KiB  
Article
Fracturing Behaviors and Mechanism of Serial Coal Pillar Specimens with Different Strength
by Cheng Song, Guangming Cao, Jinwen Bai, Shanyong Wang, Guorui Feng, Xudong Shi, Kai Wang and Chun Zhu
Materials 2023, 16(7), 2690; https://doi.org/10.3390/ma16072690 - 28 Mar 2023
Cited by 2 | Viewed by 1158
Abstract
The fracturing behaviors of serial coal pillars is significant for understanding their failure mechanism. To reveal this, the bearing stress, acoustic emission, electrical resistivity, local strain, force chain distribution, and cracks evolution of serial coal pillars under uniaxial compression were evaluated by experiment [...] Read more.
The fracturing behaviors of serial coal pillars is significant for understanding their failure mechanism. To reveal this, the bearing stress, acoustic emission, electrical resistivity, local strain, force chain distribution, and cracks evolution of serial coal pillars under uniaxial compression were evaluated by experiment and numerical simulation. The results show that four bearing stages are observed during the fracturing process (i.e., nonlinear growth, linear growth, yielding growth, and weakening stages). The acoustic emission features, electrical resistivity responses, strain develops, force chain distributions, cracks evolutions, and local displacement are highly consistent to illustrate the fracturing behaviors. System fracturing of serial coal pillar specimens is appeared along with the collapse of lower uniaxial compressive strength coal pillar specimen. The limit bearing capacity of serial coal pillar specimens is almost equal to the strength of lower uniaxial compressive strength coal pillar specimen. The unbalanced deformation characteristics of serial coal pillar specimens are presented due to the strength differences. The evolution of the key deformation element is the rooted reason for the overall fracturing mechanism of serial coal pillar specimens. For serial coal pillar specimens with different strengths, the critical condition of system fracturing is that the sum of secant modulus of upper and bottom coal pillars is zero, which is expected to predict the system fracturing of serial pillars in the underground coal mining. Full article
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19 pages, 7297 KiB  
Article
Experimental Study on Mechanical and Damage Evolution Characteristics of Coal during True Triaxial Cyclic Loading and Unloading
by Chongyang Jiang, Lianguo Wang, Ke Ding, Shuai Wang, Bo Ren and Jiaxing Guo
Materials 2023, 16(6), 2384; https://doi.org/10.3390/ma16062384 - 16 Mar 2023
Cited by 3 | Viewed by 1142
Abstract
Research on the mechanical properties and damage evolution of coal during true triaxial cyclic loading and unloading is of great significance for maintaining the long-term safety and stability of underground engineering structures in coal mines. In this paper, firstly, the deformation, strength and [...] Read more.
Research on the mechanical properties and damage evolution of coal during true triaxial cyclic loading and unloading is of great significance for maintaining the long-term safety and stability of underground engineering structures in coal mines. In this paper, firstly, the deformation, strength and fracturing characteristics of coal during true triaxial loading and true triaxial cyclic loading and unloading were analyzed. Then, the residual strain characteristics, energy distribution and evolution of coal were systematically studied. Additionally, the damage evolution laws of coal during cyclic loading and unloading were quantitatively analyzed from the perspectives of residual strain and energy dissipation, respectively. The damage evolution law based on residual strain showed that when the intermediate principal stress was high, the damage to coal was directional. With the increase in cyclic load, the coal damage variables in the directions of σ1 and σ3 increased exponentially, while that in the direction of σ2 increased quadratically. The damage evolution law based on energy dissipation showed that the coal damage variable increased exponentially with the increase in cyclic load. With the increase in σ2, the increasing speed of coal damage variable decreased first and then increased. The damage variables established based on residual strain and energy dissipation can both reveal the damage deterioration mechanism of coal during true triaxial cyclic loading and unloading, which is of great theoretical and engineering significance for scientifically evaluating the stability of underground coal and rock engineering and preventing the occurrence of major geological disasters. Full article
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20 pages, 2559 KiB  
Article
Study on the Influence of Saturation on Freeze–Thaw Damage Characteristics of Sandstone
by Xinlei Zhang, Jiaxu Jin, Xiaoli Liu, Yukai Wang and Yahao Li
Materials 2023, 16(6), 2309; https://doi.org/10.3390/ma16062309 - 13 Mar 2023
Cited by 2 | Viewed by 1300
Abstract
In order to explore the evolution mechanism of freeze–thaw disasters and the role of water in the freezing–thawing cycles of rocks, the macro mechanical indexes and microstructural characteristics of seven different saturation sandstones after certain freeze–thaw cycles were analyzed. Electron microscope scanning, nuclear [...] Read more.
In order to explore the evolution mechanism of freeze–thaw disasters and the role of water in the freezing–thawing cycles of rocks, the macro mechanical indexes and microstructural characteristics of seven different saturation sandstones after certain freeze–thaw cycles were analyzed. Electron microscope scanning, nuclear magnetic resonance, and uniaxial compression tests were employed to study the migration law of water in the rock, the crack growth law, and the damage mechanism during freeze–thaw cycles. The results showed that when the saturation was 85%, the peak load curve of sandstone with different saturation appeared at the minimum point, and the porosity of sandstone reached the maximum. The damage variable increased sharply when the saturation was 75–85%. This proves that 85% saturation is the critical value of sandstone after five freeze–thaw cycles. The water migration freezing model is established, and the migration direction of capillary film water during freezing is micropore → mesopore → macropore. The migration of water is accompanied by the expansion and generation of cracks. Then we study the mechanism and law of crack expansion, and the crack propagation rate is positively related to the theoretical suction. The theoretical suction and theoretical ice pressure increased linearly with the decrease in temperature, which accelerated the crack propagation. The crack propagation rate in decreasing order is Vmacropore > Vmesopore > Vmicropore. The research results can provide a theoretical basis for evaluating the stability of rocks under the action of freeze–thaw cycles in cold regions. Full article
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