scholarly journals Experimental Study on Mechanical Properties and Energy Dissipation of Gas Coal under Dynamic and Static Loads

2020 ◽  
Vol 2020 ◽  
pp. 1-14
Author(s):  
Xiang Cheng ◽  
Guangming Zhao ◽  
Yingming Li ◽  
Xiangrui Meng ◽  
Qingyi Tu ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Energy Dissipation ◽  
Strain Rate ◽  
Dynamic Load ◽  
Coal Sample ◽  
Static Load ◽  
Dissipated Energy ◽  
Dissipation Energy ◽  
Static Loads ◽  
Gas Coal

In order to study the mechanical properties and energy dissipation of gas coal under dynamic and static loads, the static loading and impact tests of different strain rates were carried out by the testing systems of SZW-1000 microcomputer servo pressure tester and separated Hopkinson pressure bar (SHPB) for gas coal in the Panxie Coal Field in Huainan City. In the test, the influence laws of various loading patterns on mechanical properties, failure characteristics, and energy dissipation of gas coal sample were analyzed. The results showed that the stress-strain curve of coal gas under dynamic load had no micropore compaction stage compared with that under static load. Dynamic compressive strength, dynamic strength growth factor, mixed dynamic elasticity modulus, and dissipation energy were all highly correlated with strain rate, whereas energy dissipation rate was uncorrelated with strain rate. In addition, the gas coal sample with lower strain had small dissipated energy, and it developed a splitting failure mode. With the increase of strain rate, the dissipation energy increased and the crushing degree of gas coal intensified, finally presenting a compressive failure mode. Based on the comparison of dissipated energy densities of different gas coal samples, given the same dissipated energy density, the failure degree of sample under dynamic load was higher than that under static load.

The Specific Characteristics of Shock and Blast Impacts on Construction Sites

2021 ◽  
pp. 81-88
Author(s):  
A.A. Komarov ◽  
Keyword(s):  
Dynamic Load ◽  
Static Load ◽  
Dynamic Loads ◽  
Potential Hazard ◽  
Construction Sites ◽  
Static Loads ◽  
Equivalent Static Loads ◽  
Plane Crash ◽  
Nuclear Plants ◽  
The Impact

The practices of hazardous and unique facilities’ construction imply that specific attention is paid to the issues of safety. Threats associated with crash impacts caused by moving cars or planes are considered. To ensure safety of these construction sites it is required to know the potential dynamic loads and their destructive capacity. This article considers the methodology of reducing dynamic loads associated with impacts caused by moving collapsing solids and blast loads to equivalent static loads. It is demonstrated that practically used methods of reduction of dynamic loads to static loads are based in schematization only of the positive phase of a dynamic load in a triangle forms are not always correct and true. The historical roots of this approach which is not correct nowadays are shown; such approach considered a detonation explosion as a source of dynamic load, including TNT and even a nuclear weapon. Application of the existing practices of reduction of dynamic load to static load for accidental explosions in the atmosphere that occur in deflagration mode with a significant vacuumization phase may cause crucial distortion of predicted loads for the construction sites. This circumstance may become a matter of specific importance at calculations of potential hazard of impacts and explosions in unique units — for instance, in the nuclear plants. The article considers a situation with a plane crash, the building structure load parameters generated at the impact caused by a plane impact and the following deflagration explosion of fuel vapors are determined.

scholarly journals EFFECT OF DIFFERENT WOOD DOWELS ON MECHANICAL PROPERTIES OF TRIANGULAR GIRDER TRUSSES

Wood Research ◽  
2021 ◽  
Vol 66 (3) ◽  
pp. 477-488
Author(s):  
Liuliu Zhang ◽  
Cheng Chang ◽  
Shuming Yang
Keyword(s):  
Mechanical Properties ◽  
Energy Dissipation ◽  
Bearing Capacity ◽  
Static Load ◽  
Deformation Resistance ◽  
Stability Performance ◽  
Load Tests ◽  
Different Diameters

Static load tests were carried out on three kinds of triangular girder trusses with different diameter wood dowels, and the effects of that on the structure of girder trusses were discussed. It was found that there was a good synergy between the wood dowels and the girder trusses. Among the triangular girder trusses with different diameters, the 16 mm diameters had the best energy dissipation performance increased by 184% and deformation resistance of 0.73 mm; the 20 mm diameters had the best stability performance, the better bearing capacity of 60.42 kN and deformation resistance of 0.82 mm. The bearing capacity of the double girder trusses was 2.06-2.25 times that of two single trusses, which had the ability to ‘one plus one is greater than two’.

scholarly journals Dynamic Mechanical Characteristics of Impact Rock under the Combined Action of Different Constant Temperatures and Static and Dynamic Loads

2021 ◽  
Vol 2021 ◽  
pp. 1-15
Author(s):  
Enlai Zhao ◽  
Enyuan Wang ◽  
Zesheng Zang ◽  
Xiaojun Feng ◽  
Rongxi Shen
Keyword(s):  
Mechanical Properties ◽  
Dynamic Load ◽  
Incident Energy ◽  
Dynamic Mechanical Properties ◽  
Image Correlation ◽  
Dynamic Loads ◽  
Dissipated Energy ◽  
Dynamic Mechanical ◽  
Combined Action ◽  
Static And Dynamic Loads

The complex mechanical environment of deep coal and rock masses leads to obvious changes on their dynamic mechanical properties. However, there are few reports on the dynamic mechanical properties of rocks under the combined action of medium temperature (normal temperature ∼100°C) and static and dynamic loads. In this paper, a dynamic load and temperature combined action Hopkinson pressure bar experimental system is used to experimentally study the impact type of a fine sandstone under temperature conditions of 18°C, 40°C, 60°C, 80°C, and 100°C, an axial static load of 3 MPa, a gas chamber pressure of 0.06 MPa, and a constant temperature time of 4 h. The dynamic characteristics of the change law of the fine sandstone and the energy dissipation characteristics of the load process are analyzed, and the characteristic law of the fine sandstone surface response is analyzed using digital image correlation technology. Our results indicate the following. (1) Under conditions in which the other experimental conditions remain unchanged, the dynamic stress-strain of the fine sandstone presents a bimodal shape with a “rebound” phenomenon. Increasing temperature causes the peak strength of the fine sandstone to increase; however, the relative strength can increase or decrease. The relative increase in the strength is 1.14 MPa (°C) when the temperature increases from 40°C to 60°C, 0.15 MPa (°C) when the temperature increases from 60°C to 80°C, and 0.62 MPa (°C) when the temperature increases from 80°C to 100°C. (2) The digital image correlation results show that, under the action of a dynamic load stress wave, the fine sandstone experiences a displacement vector change on the sample surface; furthermore, under the combined action of the temperature and dynamic and static loads, the fine sandstone experiences macroscopic shear failure. The surface strain in the propagation direction of the stress wave is obviously higher and can even reach values of more than 10 times that of the strain in other directions. (3) From the perspective of energy dissipation, the incident energy, reflected energy, and dissipated energy of the fine sandstone under an impact load have the same change law. After being affected by a dynamic load, the energy rapidly increases to a certain value and then remains relatively stable. The transmitted energy is relatively small and can be approximated as a horizontal line. As the temperature increases, the incident energy, reflected energy, and dissipated energy tend to first decrease and then increase, and most of the incident energy in the fine sandstone is dissipated in the form of reflected waves.

scholarly journals Coupling Effect of Strain Rate and Freeze-Thaw Temperature on Dynamic Mechanical Properties and Fractal Characteristic of Saturated Yellow Sandstone

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-14
Author(s):  
Peng Wu ◽  
Lianying Zhang ◽  
Xianbiao Mao ◽  
Yanlong Chen ◽  
Ming Li ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Fractal Dimension ◽  
Strain Rate ◽  
Room Temperature ◽  
High Strain ◽  
Coupling Effect ◽  
Strain Rate Effect ◽  
Dissipated Energy ◽  
Peak Strain ◽  
Freeze Thaw

Strain rate is not only an important influence factor for deformation property but also an important parameter for analyzing the dynamic mechanical behavior of rock material. In this study, the dynamic compressive mechanical properties of saturated yellow sandstone at four strain rates and six freeze-thaw temperatures are investigated by using the SHPB test system. The coupling effect of strain rate and freeze-thaw temperatures on the mechanical parameters of rock material are discussed in detail, and the relationship formula of peak strain and dissipated energy with strain rate and freeze-thaw temperature are also established. Finally, the fractal dimension characteristic of fracture specimens with the strain rate and temperature are analyzed by using the fractal dimension method. The research results indicate that (1) with the increase of strain rate, the increase speed of peak strain, peak strength, and dissipated energy at medium strain rate level was obviously higher than that at high strain rate level, indicating that the strain rate effect weakened at high strain rate. (2) Freeze-thaw temperature can improve the brittleness-ductile transformation rate of saturated specimens. (3) According to the strain rate sensitivity coefficient, at room temperature, the strain rate effects on peak strain and peak strength are weakest, while at -20°C ~ -30°C, they are most significant. In addition, the strain rate effect on dissipated energy is significant at room temperature, while weakest at -30°C. (4) The fractal dimension gradually increases with strain rate increasing or freeze-thaw temperature decreasing, indicating that the freeze-thaw environment has a positive function for increasing the damage and fracture degree of specimens for saturated specimen. Our research results can provide an extremely important theoretical basis for the dynamic disaster prevention and structural design of rock engineering in cold regions.

scholarly journals Correlational Analytical Characterization of Energy Dissipation-Liberation and Acoustic Emission during Coal and Rock Fracture Inducing by Underground Coal Excavation

Energies ◽  
2019 ◽  
Vol 12 (12) ◽  
pp. 2382 ◽  
Author(s):  
Pengfei Shan ◽  
Xingping Lai ◽  
Xiaoming Liu
Keyword(s):  
Acoustic Emission ◽  
Energy Dissipation ◽  
Axial Stress ◽  
Rock Fracture ◽  
Quantitative Relationship ◽  
Dissipated Energy ◽  
Release Mechanism ◽  
Rock Fracturing ◽  
Dissipation Energy ◽  
Energy Parameters

This paper uses an acoustic emission (AE) test to examine the energy dissipation and liberation of coal and rock fracture due to underground coal excavation. Many dynamic failure events are frequently observed due to underground coal excavation. To establish the quantitative relationship between the dissipated energy and AE energy parameters, the coal and rock fracturing characteristics were clearly observed. A testing method to analyze the stage traits and energy release mechanism from damage to fracture of the unloading coal and rock under uniaxial compressive loading is presented. The research results showed that the relevant mechanical parameter discreteness was too large because the internal structures of the coal and rock were divided into multiple structural units (MSU) by a few main cracks. The AE test was categorized into four stages based on both the axial stress and AE event parameters: initial loading stage, elastic stage, micro-fracturing stage, and post-peak fracturing stage. The coal and rock samples exhibited minimum (maximum) U values of 60.44 J (106.41 J) and 321.19 J (820.87 J), respectively. A theoretical model of the dissipation energy during sample fracturing based on the AE event energy parameters was offered. The U decreased following an increase in ΣEAE-II/ΣEAE.

scholarly journals Numerical Analysis of Roadway Rock-Burst Hazard Under Superposed Dynamic and Static Loads

Energies ◽  
2019 ◽  
Vol 12 (19) ◽  
pp. 3761 ◽  
Author(s):  
Kong ◽  
Jiang ◽  
Jiang ◽  
Wu ◽  
Chen ◽  
...  
Keyword(s):  
Energy Density ◽  
Rock Burst ◽  
Elastic Energy ◽  
Dynamic Load ◽  
Static Loading ◽  
Static Load ◽  
Dynamic Loads ◽  
Loading Conditions ◽  
Static Loads ◽  
Elastic Energy Density

Microseismic events commonly occur during the excavation of long wall panels and often cause rock-burst accidents when the roadway is influenced by dynamic loads. In this paper, the Fast Lagrangian Analysis of Continua in 3-Dimensions (FLAC3D) software is used to study the deformation and rock-burst potential of roadways under different dynamic and static loads. The results show that the larger the dynamic load is, the greater the increase in the deformation of the roadway under the same static loading conditions. A roadway under a high static load is more susceptible to deformation and instability when affected by dynamic loads. Under different static loading conditions, the dynamic responses of the roadway abutment stress distribution are different. When the roadway is shallow buried and the dynamic load is small, the stress and elastic energy density of the coal body in the area of the peak abutment stress after the dynamic load are greater than the static calculations. The dynamic load provides energy storage for the coal body in the area of the peak abutment stress. When the roadway is deep, a small dynamic load can still cause the stress in the coal body and the elastic energy density to decrease in the area of the peak abutment stress, and a rock-burst is more likely to occur in a deep mine roadway with a combination of a high static load and a weak dynamic load. When the dynamic load is large, the peak abutment stress decreases greatly after the dynamic loading, and under the same dynamic loading conditions, the greater the depth the roadway is, the greater the elastic energy released by the dynamic load. Control measures are discussed for different dynamic and static load sources of rock-burst accidents. The results provide a reference for the control of rock-burst disasters under dynamic loads.

Studying the Effect of Temperature, Static Load and Nanodimensional Defects on the Mechanical Properties of Polyethylene Film at Uniaxial Extension

2020 ◽  
Vol 992 ◽  
pp. 325-330
Author(s):  
Anatoliy I. Kupchishin ◽  
Marat N. Niyazov ◽  
Buvkhan G. Taipova
Keyword(s):  
Mechanical Properties ◽  
Radiation Dose ◽  
Electron Irradiation ◽  
Modulus Of Elasticity ◽  
Static Load ◽  
Uniaxial Extension ◽  
Exponential Model ◽  
Effect Of Temperature ◽  
Static Loads ◽  
Different Temperatures

The dependence of strain on temperature in polyethylene under various static loads and exposure doses has been studied experimentally. After electron irradiation with doses of 10, 30, 50, 70, and 100 kGy, significant changes in the mechanical properties were observed, which are caused by the formation of nanodefects in the material’s structure. With increasing radiation dose, PE deformation at different temperatures decreases due to destruction in the structure of the polymer material. At the same time, the return deformation increases with increasing dose, indicating a change in the modulus of elasticity (E). The increase in E occurs due to the decrease in the distance between macromolecules in the irradiated structure of the sample. The obtained curves for both non-irradiated and irradiated material are described in an exponential model satisfactorily.

An Improved Dynamic Constitutive Model of Dynamic Mechanical Property of Concrete

2013 ◽  
Vol 785-786 ◽  
pp. 1240-1243
Author(s):  
Pan Xiu Wang ◽  
Gui Yun Zhou
Keyword(s):  
Mechanical Properties ◽  
Mechanical Property ◽  
Constitutive Model ◽  
Strain Rate ◽  
Dynamic Load ◽  
Concrete Structure ◽  
Concrete Beam ◽  
Bending Strength ◽  
Dynamic Mechanical Property ◽  
Bearing Strength

An improved dynamic constitutive model is presented, aiming to describe the key mechanical properties and predict the bearing strength of concrete structure under static and dynamic load. This model is based on the concept of equivalent uniaxial strains and strain rate. In this paper, an equivalent uniaxial stressstrain curves are obtained by the WillamWarnke curve and take the same form as in Saenz models. Then, the bending strength of a concrete beam under different static and dynamic load was discussed.

scholarly journals Dynamic Compression Damage Energy Consumption and Fractal Characteristics of Shale

2019 ◽  
Vol 2019 ◽  
pp. 1-7
Author(s):  
Guoliang Yang ◽  
Jingjiu Bi ◽  
Linian Ma
Keyword(s):  
Fractal Dimension ◽  
Energy Consumption ◽  
Energy Dissipation ◽  
Strain Rate ◽  
Split Hopkinson Pressure Bar ◽  
Dynamic Compression ◽  
Fractal Theory ◽  
Dissipated Energy ◽  
Impact Tests ◽  
The Impact

Studying the relationship between energy consumption and crushed size of shale under different loading conditions is the key to efficient shale cracking. The split Hopkinson pressure bar system was used to study the dynamic mechanical properties of shale under parallel- and vertical-bedding loading, and energy dissipation in the impact tests was calculated. Relationships between the average crushed size of shale fracture products and energy dissipation and between the fractal dimension and dissipated energy were studied using fractal theory. The experimental results showed that the dynamic compressive strength of shale under parallel- and vertical-bedding conditions had an obvious positive correlation with the strain rate. Dissipative energy of the shale samples under loading in both directions increased with the increase of strain rate. The increase of the strain rate enhanced crushing of the sample. The vertical-bedding shale samples had stronger ability to absorb energy and more internal crack propagation. Dissipative energies of the shale samples in the parallel- and vertical-bedding impact tests were positively related to the fractal dimension. The fractal dimension increased with the increase of dissipative energy during sample failure; with further increase in the dissipative energy, its effect on the change of fractal dimension gradually weakened.

scholarly journals Study on the Mechanical Properties of Coal Weakenedby Acidic and Alkaline Solutions

2020 ◽  
Vol 2020 ◽  
pp. 1-15
Author(s):  
Dong Xu ◽  
Mingshi Gao ◽  
Yichao Zhao ◽  
Yongliang He ◽  
Xin Yu
Keyword(s):  
Mechanical Properties ◽  
Crack Propagation ◽  
Coal Sample ◽  
Damage Variable ◽  
Design Parameters ◽  
Dissipated Energy ◽  
Peak Strain ◽  
Chemical Solution ◽  
Chemical Erosion ◽  
Chemical Solutions

A novel method for fracturing coal is presented in this paper. A chemical solution is injected into coal under high pressure, whereby the coal is fractured and subsequently weakened by chemical erosion over time to produce an anti-impact soft structure. In this study, the mechanical properties of coal under chemical erosion were investigated, and the fracturing design parameters were optimized. The uniaxial compression test and the split Hopkinson pressure bar (SHPB) test were used to determine the dynamic and static mechanical properties of coal after 20 days of immersion in different chemical solutions. After chemical solution erosion, the dynamic and static compressive strengths and elastic modulus of the coal decreased according to an exponential power law in the damage variable. The chemical treatment increased the duration of the pore compaction stage and decreased that of the elastic deformation stage, while decreasing the brittleness and increasing the ductility of coal. The acoustic emission (AE) curve of the immersed coal samples consisted of four stages corresponding to those of the stress-strain curve: pore compaction-closure, a slowly rising linear elastic regime, steady-state prepeak crack propagation, and unsteady crack propagation at the peak strain. The increase in the damage variable of the coal sample from chemical erosion led to a lower dissipated energy, a higher fractal dimension, and a more fragmented coal sample. The effect of the investigated chemical solutions on weakening the coal mechanical properties decreased in the following order: alkaline solution > acidic solution > NaCl solution > distilled water. The experimental results provide a reference for weakening fractured coal seams.

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