scholarly journals Dynamic Damage Mechanism of Coal Wall in Deep Longwall Face

2019 ◽  
Vol 2019 ◽  
pp. 1-10
Author(s):  
Shuaifeng Lu ◽  
Sifei Liu ◽  
Zhijun Wan ◽  
Jingyi Cheng ◽  
Zhuangzhuang Yang ◽  
...  
Keyword(s):  
Stress Concentration ◽  
Tensile Stress ◽  
Damage Mechanism ◽  
Longwall Face ◽  
Stress Generation ◽  
Stress Wave Propagation ◽  
Mining Machinery ◽  
Coal Wall ◽  
The Stability ◽  
Dynamic Damage

The stability of coal wall in deep longwall face has always been a research hotspot. In this study, pure vibration signals in the coal wall during the operation of mining machinery were obtained for the first time, and their energy is mainly concentrated in 7–12 Hz. Besides, based on the law of stress wave propagation, with the coal wall of deep longwall taken as the research object, the theory of dynamic damage in coal wall was put forward from the perspective of dynamics. The results show that the loading and unloading waves generated by the mining machinery disturbance will be reflected and transmitted at the interface with different impedances, resulting in the formation of multiple unloading and loading waves and multiple tensile stress zones and stress concentration zones. These stress concentration zones tend to induce tensile stress generation and coal failure. As a result, the coal undergoes zonal failure and spalling. Through the vibration test of coal, it is found that the crack development of the coal sample can be divided into five stages, and the phenomena of zonal failure and spalling occur, which is consistent with the theory. At the same time, the sample that has gone through a large disturbance cannot be further damaged by a small disturbance, which is verified by the damage statistical constitutive model based on the isotropy hypothesis.

scholarly journals Failure Mechanisms and the Control of a Longwall Face with a Large Mining Height within a Shallow-Buried Coal Seam

2021 ◽  
Vol 2021 ◽  
pp. 1-11
Author(s):  
Haijun Wang ◽  
Yingjie Liu ◽  
Yuesong Tang ◽  
Hao Gong ◽  
Guoliang Xu
Keyword(s):  
Tensile Stress ◽  
Coal Mine ◽  
Horizontal Displacement ◽  
Longwall Face ◽  
Mining Equipment ◽  
Coal Seams ◽  
Increasing Trend ◽  
Support Force ◽  
Coal Wall ◽  
Mining Height

The capabilities of mining equipment and technology in China have been improving rapidly in recent years. Correspondingly, in the western part of the country, the mining heights of longwall faces in shallow-buried coal seams have shown an increasing trend, resulting in enhanced mining efficiency. However, the problems associated with the possible failure of the coal wall then increase and remain a serious difficulty, restricting safe and efficient mining operations. In the present study, the 12401 longwall face of the Shangwan Coal Mine, Inner Mongolia, China, with a mining height of 8.8 m, is taken as an example to study the mechanisms underlying failure phenomena of coal walls and their control methods. Our results show that the failure region inward of the longwall face is small in shallow-buried coal seams, and the damage degree of the exposed coal wall is low. The medium and higher sections of the coal wall display a dynamic failure mode, while the broken coal blocks, given their initial speed, threaten the safety of coal miners. A mechanical model was developed, from which the conditions for tensile failure and structural instability are deduced. Horizontal displacement in the lower part of the coal wall is small, where no tensile stress emerges. On the other hand, in the intermediate and higher parts of the coal wall, horizontal displacement is relatively large. In addition, tensile stress increases first with increasing distance from the floor and then decreases to zero. Experiments using physical models representing different mining heights have been carried out and showed that the horizontal displacement increases from 6 to 12 mm and load-bearing capacity decreases from 20 to 7.9 kN when the coal wall increases in height from 3 to 9 m. Furthermore, failure depth and failure height show an increasing trend. It is therefore proposed that a large initial support force, large maximum support force, large support stiffness, and large support height of a coal wall-protecting guard are required for the improved stability of high coal walls, which operate well in the Shangwan coal mine.

scholarly journals Influence of Crack Geometry on Dynamic Damage of Cracked Rock: Crack Number and Filling Material

2020 ◽  
Vol 11 (1) ◽  
pp. 250
Author(s):  
Feili Wang ◽  
Shuhong Wang ◽  
Zhanguo Xiu
Keyword(s):  
Energy Absorption ◽  
Split Hopkinson Pressure Bar ◽  
Mineral Exploration ◽  
Damage Variable ◽  
Filling Material ◽  
Hopkinson Pressure Bar ◽  
Filling Materials ◽  
The Stability ◽  
Pressure Bar ◽  
Dynamic Damage

The dynamic damage of cracked rock threatens the stability of rock structures in rock engineering applications such as underground excavation, mineral exploration and rock slopes. In this study, the dynamic damage of cracked rock with different spatial geometry was investigated in an experimental method. Approximately 54 sandstone specimens with different numbers of joints and different filling materials were tested using the split Hopkinson pressure bar (SHPB) apparatus. The energy absorption in this process was analyzed, and the damage variable was obtained. The experimental results revealed that the dynamic damage of cracked rock is obviously influenced by the number of cracks; the larger the number, the higher the energy absorption and the bigger the dynamic damage variable. Moreover, it was observed from the dynamic compressive experiments that the energy absorption and the dynamic variable decreased with the strength and cohesion of the filling material, indicating that the filling material of crack has considerate influence on the dynamic damage of cracked rock.

Study on the Stability and Structural Optimization of Self-Elevating Platform Pile Foundation

2012 ◽  
Vol 203 ◽  
pp. 325-328
Author(s):  
Xin Jie Chu
Keyword(s):  
Stress Concentration ◽  
Structural Optimization ◽  
Bearing Capacity ◽  
Pile Foundation ◽  
Reference Value ◽  
The Self ◽  
Foundation Design ◽  
Operation Stability ◽  
Soil Foundation ◽  
The Stability

This paper analyzes the stability and structural optimization of self-elevating platform pile foundation, preliminarily discusses the method of analyzing the bearing capacity of the layer soil foundation, and establishes the numerical computation models for the whole platform, pile, pile shoe, etc. Besides, through these analyses, the pile structure is optimized, and the stress concentration in the joint between pile and pile shoe is reduced. Also, this study is of reference value for the analysis on the self-elevating platform pile foundation design and the platform operation stability.

Determination of DC06+ZE Sheet Crack Cause

2016 ◽  
Vol 368 ◽  
pp. 121-125
Author(s):  
Pavel Kejzlar ◽  
Tomáš Pilvousek ◽  
Michal Tregler
Keyword(s):  
Stress Concentration ◽  
Tensile Stress ◽  
Deep Drawing ◽  
Crack Formation ◽  
Local Stress ◽  
Local Deformation ◽  
Local Stress Concentration ◽  
Bcc Lattice ◽  
Hard Particles

The present work deals with determination of the cause of crack occurring in a part of car body manufactured from deep-drawing sheet. UHR-SEM, EDS, EBSD and measurement of microhardness were used for evaluation of the structure, local deformation and crack formation mechanism. A material analysis discovered foreign particles in the material. These particles were identified as MgAl2O4 with BCC lattice. The occurrence of these hard particles led to local stress concentration, decrease in mechanical strength and sheet breach due to tensile stress during deformation.

scholarly journals Effect of Slip Surface’s Continuity on Slope Dynamic Stability Based on Infinite Slope Model

Mathematics ◽  
2019 ◽  
Vol 7 (1) ◽  
pp. 58
Author(s):  
Chuanzheng Liu ◽  
Gang Wang ◽  
Wei Han
Keyword(s):  
Dynamic Stability ◽  
Stress Wave ◽  
Safety Factor ◽  
Slip Surface ◽  
Great Influence ◽  
Stress Wave Propagation ◽  
Surface Model ◽  
Infinite Slope ◽  
Research Results ◽  
The Stability

The slip surface is an important control structure surface existing in the landslide. It not only directly affects the stability of the slope through the strength, but also affects the stress field by affecting the propagation of the stress wave. Many research results have been made on the influence of non-continuous stress wave propagation in rock and soil mass and the dynamic response to seismic slopes. However, the effect of the continuity of the slip surface on the slope dynamic stability needs further researches. Therefore, in this paper, the effect of slip surface on the slope’s instantaneous safety factor is analyzed by the theoretical method with the infinite slope model. Firstly, three types of slip surface model were established, to realize the change of sliding surface continuity in the infinite slope. Then, based on wave field analysis, the instantaneous safety factor was used to analyze the effect of continuity of slip surface. The results show that with the decreasing of slip surface continuity, the safety factor does not simply increase or decrease, and is related to slope features, incident wave and continuity of slip surface. The safety factor does not decrease monotonically with the increasing of slope angle and thickness of slope body. Moreover, the reflection of slope surface has a great influence on the instantaneous safety factor of the slope. Research results in this paper can provide some references to evaluate the stability of seismic slope, and have an initial understanding of the influence of structural surface continuity on seismic slope engineering.

scholarly journals Computational Modeling of Tensile Stress Effects on the Structure and Stability of Prototypical Covalent and Layered Materials

Nanomaterials ◽  
2019 ◽  
Vol 9 (10) ◽  
pp. 1483 ◽  
Author(s):  
Hocine Chorfi ◽  
Álvaro Lobato ◽  
Fahima Boudjada ◽  
Miguel A. Salvadó ◽  
Ruth Franco ◽  
...  
Keyword(s):  
Tensile Stress ◽  
Density Functional ◽  
Stability Limit ◽  
Density Functional Theory Calculations ◽  
Layered Materials ◽  
Stress Conditions ◽  
Ideal Strength ◽  
Critical Strength ◽  
Calculated Stress ◽  
The Stability

Understanding the stability limit of crystalline materials under variable tensile stress conditions is of capital interest for technological applications. In this study, we present results from first-principles density functional theory calculations that quantitatively account for the response of selected covalent and layered materials to general stress conditions. In particular, we have evaluated the ideal strength along the main crystallographic directions of 3C and 2H polytypes of SiC, hexagonal ABA stacking of graphite and 2H-MoS 2 . Transverse superimposed stress on the tensile stress was taken into account in order to evaluate how the critical strength is affected by these multi-load conditions. In general, increasing transverse stress from negative to positive values leads to the expected decreasing of the critical strength. Few exceptions found in the compressive stress region correlate with the trends in the density of bonds along the directions with the unexpected behavior. In addition, we propose a modified spinodal equation of state able to accurately describe the calculated stress–strain curves. This analytical function is of general use and can also be applied to experimental data anticipating critical strengths and strain values, and for providing information on the energy stored in tensile stress processes.

The damage mechanism of 17vol.%SiCp/Al composite under uniaxial tensile stress

2020 ◽  
Vol 782 ◽  
pp. 139274 ◽  
Author(s):  
Qiuyan Shen ◽  
Zhanwei Yuan ◽  
Huan Liu ◽  
Xuemin Zhang ◽  
Qinqin Fu ◽  
...  
Keyword(s):  
Tensile Stress ◽  
Damage Mechanism ◽  
Uniaxial Tensile ◽  
Al Composite ◽  
Uniaxial Tensile Stress
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