scholarly journals Effect of Microwave Heating On The Mechanical Properties and Energy Dissipation Characteristics of Hard Rock

2021 ◽  
Author(s):  
Jianming Yang ◽  
Jiantian Liu ◽  
Hongchen Guo ◽  
Qingwen LI ◽  
Wei Wang
Keyword(s):  
Acoustic Emission ◽  
Energy Dissipation ◽  
Microwave Irradiation ◽  
Count Rate ◽  
Hard Rock ◽  
Mechanical Energy ◽  
Dissipated Energy ◽  
Continuous Increase ◽  
Acoustic Emission Count ◽  
Irradiation Power

Abstract To study the effect of microwave on the weakening mechanism of hard rock, uniaxial compression tests were conducted on granite samples after microwave treatment, and an acoustic emission system was established to monitor the fracture evolution in such rock samples. The effects of microwave irradiation on the stress-strain curve, acoustic emission characteristics, and energy dissipation characteristics of granite were investigated in the experiment. The results show that: 1) With the continuous increase of microwave irradiation power and time, the compaction stage and crack development stage of the sample gradually increase, and the elastic stage gradually becomes shorter; the trend of post-peak stress drop becomes slower, changing from “cliff type” to multi-step type “. The failure of the sample indicates that they become less brittle and more ductile; 2) Microwave irradiation reduces the strength. The overall acoustic emission count rate is weak before the peak and increases rapidly near the peak. The count rate has also changed from sparse to dense, and with the increase in the irradiation power and time, the total acoustic emission count rate increases; 3) From the energy point of view, the weakening of granite by microwave irradiation will not only decrease the energy-storage limit of granite and increase the proportion of dissipated energy in the failure process, but also decrease the rate of release of elastic energy after the peak. Therefore, microwave irradiation will not only reduce the mechanical energy dissipated during damage, but also reduce the intensity of potential dynamic disasters.

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.

Coefficients of Restitution in Normal Adhesive Impact between Smooth and Rough Elastic Bodies

2020 ◽  
Vol 1 (1) ◽  
pp. 103-109
Author(s):  
Valentin L. Popov ◽  
Keyword(s):  
Energy Dissipation ◽  
Rough Surface ◽  
Mechanical Energy ◽  
Rolling Friction ◽  
Adhesive Contact ◽  
Dissipated Energy ◽  
Microscopic Scale ◽  
Elastic Bodies ◽  
Rear Part ◽  
The Moment

n 1975, Fuller and Tabor have shown that roughness can destroy macroscopic adhesion. This means that in spite of the presence of adhesion at the microscopic scale, the macrosopic force of adhesion vanishes. The mechanism of vanishing macroscopic adhesion is very simple: during approach of elastic bodies, asperities are elastically deformed so strongly that after unloading they destroy the microscopic adhesive junctions. However, both in the moment of formation of microscopic adhesive junctions in the loading phase and their destruction during unloading, mechanical energy disappears. This means that the microscopic adhesion makes the contact dissipative even if there is no macroscopic force of adhesion. In particular, the force-distance dependency during indentation and pull-off do not coincide with each other showing some "adhesive hysteresis". When a ball rolls on such rough surface, there will be a final energy dissipation due to formation of a new contact at the frontline of the contact and its destruction at the rear part. Thus, microscopic adhesion will lead to appearance of rolling friction in an apparently non-adhesive contact. In the present paper, we calculate the approach and pull-off dependencies of force on distance, the dissipated energy in one loading-unloading cycle and estimate the force of rolling friction due to microscopic adhesion.

scholarly journals Adhesive Hysteresis and Rolling Friction in Rough "Non-Adhesive" Contacts

2020 ◽  
Author(s):  
Valentin L. Popov
Keyword(s):  
Energy Dissipation ◽  
Mechanical Energy ◽  
Rolling Friction ◽  
Adhesive Contact ◽  
Dissipated Energy ◽  
Microscopic Scale ◽  
Elastic Bodies ◽  
Rear Part ◽  
The Moment ◽  
Adhesive Contacts

In 1975, Fuller and Tabor have shown that roughness can destroy macroscopic adhesion. This means that in spite of the presence of adhesion at the microscopic scale, the macrosopic force of adhesion vanishes. The mechanism of vanishing macroscopic adhesion is very simple: during approach of elastic bodies, asperities are elastically deformed so strongly that after unloading they destroy the microscopic adhesive junctions. However, both in the moment of formation of microscopic adhesive junctions in the loading phase and their destruction during unloading, mechanical energy disappears. This means that the microscopic adhesion makes the contact dissipative even if there is no macroscopic force of adhesion. In particular, the force-distance dependency during indentation and pull-off do not coincide with each other showing some "adhesive hysteresis". When a ball rolls on such rough surface, there will be a final energy dissipation due to formation of a new contact at the frontline of the contact and its destruction at the rear part. Thus, microscopic adhesion will lead to appearance of rolling friction in an apparently non-adhesive contact. In the present paper, we calculate the approach and pull-off dependencies of force on distance, the dissipated energy in one loading-unloading cycle and estimate the force of rolling friction due to microscopic adhesion.

Experimental evaluation of fatigue damage in two-stage loading tests based on the energy dissipation

2015 ◽  
Vol 229 (7) ◽  
pp. 1280-1291 ◽  
Author(s):  
Giovanni Meneghetti ◽  
Mauro Ricotta ◽  
Bruno Atzori
Keyword(s):  
Energy Dissipation ◽  
Fatigue Test ◽  
Fatigue Damage ◽  
Stress Amplitude ◽  
Mechanical Energy ◽  
Heat Energy ◽  
Dissipated Energy ◽  
External Loading ◽  
Test Results ◽  
Stored Energy

Heat energy dissipation is a manifestation of damage accumulation in fatigue-loaded components. Once recognized that some mechanical energy has to be expended to fatigue a material, energy partition into heat and stored energy is thought of as a material property in the present testing conditions. However, most of the mechanical input energy is dissipated as heat; therefore, the stored energy is difficult to estimate as difference between the expended and the dissipated energy. In this article heat energy is assumed as an index of fatigue damage. Since it reflects the material response to external loading, heat energy was seen to reduce the scatter of constant amplitude fatigue test results with respect to the use of the stress amplitude. Moreover, two-level fatigue test results could be interpreted with a higher level of accuracy when Miner’s rule was applied in terms of energy rather than stress amplitude.

Investigation of the Water Flow Into a Mesoporous Matrix From Hydrophobized Silica Gel

2004 ◽  
Author(s):  
Claudiu V. Suciu ◽  
Takuzo Iwatsubo ◽  
Kazuhiko Yaguchi ◽  
Masayoshi Ikenaga
Keyword(s):  
Energy Dissipation ◽  
Water Flow ◽  
Silica Gel ◽  
Stokes Equations ◽  
Mechanical Energy ◽  
Contact Angle Hysteresis ◽  
Hydrodynamic Theory ◽  
Dissipated Energy ◽  
Hydrophobic Coating ◽  
Hydrophobized Silica

In this work a generalized hydrodynamic theory for the water flow into a mesoporous matrix from hydrophobized silica gel is suggested. Although we examine a fluid dynamics problem, i.e., the motion of the water-gas-solid contact line, motivation for such research derives from the investigation of a novel principle of mechanical energy dissipation, called colloidal damper. Similar to hydraulic damper, this absorber has a cylinder-piston structure, but oil is replaced by a colloid consisted of a mesoporous matrix and a lyophobic liquid. Here, the mesoporous matrix is from silica gel modified by linear chains of alkyldimethylchlorosilanes and water is the associated lyophobic liquid. Mainly, the colloidal damper energy loss can be explained by the dynamic contact angle hysteresis in advancing (liquid displaces gas) and receding (gas displaces liquid); such hysteresis occurs due to the geometrical and chemical heterogeneities of the solid surface. Measuring technique of the hysteresis loop is described. From experimental data one calculates the dissipated energy, damper efficiency and the damping coefficient versus the length of the grafted molecule on the silica gel surface. Experimental results are justified by the flow analysis. Generalized hydrodynamic theory means here that the basic structure of Navier-Stokes equations is kept, but in order to include the relation between macroscopic flow and molecular interactions, slip is allowed on the solid wall. Nano-pillar architecture of the silica gel hydrophobic coating is described. During adsorption, water penetrates the pore space by maintaining contact with the top of the coating molecules (region of -CH3 groups); after that, water is forced into and partially or totally fills the space between molecules (region of -CH2 groups); in such circumstances, at the release of the external pressure, desorption occurs. Mechanism of energy dissipation is discussed. Results obtained are useful for the appropriate design of the hydrophobic coating of a mesoporous matrix which is destined to colloidal damper use.

Energy dissipation rate in a baffled vessel with pitched blade turbine impeller

1991 ◽  
Vol 56 (9) ◽  
pp. 1856-1867 ◽  
Author(s):  
Zdzisław Jaworski ◽  
Ivan Fořt
Keyword(s):  
Energy Dissipation ◽  
Cross Sections ◽  
Mechanical Energy ◽  
Vessel Diameter ◽  
Energy Dissipation Rate ◽  
Mean Velocity ◽  
Agitated Vessel ◽  
Radial Profiles ◽  
Pitched Blade Turbine ◽  
Turbine Impeller

Mechanical energy dissipation was investigated in a cylindrical, flat bottomed vessel with four radial baffles and the pitched blade turbine impeller of varied size. This study was based upon the experimental data on the hydrodynamics of the turbulent flow of water in an agitated vessel. They were gained by means of the three-holes Pitot tube technique for three impeller-to-vessel diameter ratio d/D = 1/3, 1/4 and 1/5. The experimental results obtained for two levels below and two levels above the impeller were used in the present study. Radial profiles of the mean velocity components, static and total pressures were presented for one of the levels. Local contribution to the axial transport of the agitated charge and energy was presented. Using the assumption of the axial symmetry of the flow field the volumetric flow rates were determined for the four horizontal cross-sections. Regions of positive and negative values of the total pressure of the liquid were indicated. Energy dissipation rates in various regions of the agitated vessel were estimated in the range from 0.2 to 6.0 of the average value for the whole vessel. Hydraulic impeller efficiency amounting to about 68% was obtained. The mechanical energy transferred by the impellers is dissipated in the following ways: 54% in the space below the impeller, 32% in the impeller region, 14% in the remaining part of the agitated liquid.

scholarly journals Reconstruction of the 3D pressure field and energy dissipation of a Taylor droplet from a $$\upmu$$PIV measurement

2021 ◽  
Vol 62 (4) ◽  
Author(s):  
Ulrich Mießner ◽  
Thorben Helmers ◽  
Ralph Lindken ◽  
Jerry Westerweel
Keyword(s):  
Energy Dissipation ◽  
Pressure Gradient ◽  
Pressure Field ◽  
Estimation Method ◽  
Dissipated Energy ◽  
Spatial Integration ◽  
Mean Flow ◽  
Bypass Flow ◽  
Taylor Flow ◽  
Piv Measurement

Abstract In this study, we reconstruct the 3D pressure field and derive the 3D contributions of the energy dissipation from a 3D3C velocity field measurement of Taylor droplets moving in a horizontal microchannel ($$\rm Ca_c=0.0050$$ Ca c = 0.0050 , $$\rm Re_c=0.0519$$ Re c = 0.0519 , $$\rm Bo=0.0043$$ Bo = 0.0043 , $$\lambda =\tfrac{\eta _{d}}{\eta _{c}}=2.625$$ λ = η d η c = 2.625 ). We divide the pressure field in a wall-proximate part and a core-flow to describe the phenomenology. At the wall, the pressure decreases expectedly in downstream direction. In contrast, we find a reversed pressure gradient in the core of the flow that drives the bypass flow of continuous phase through the corners (gutters) and causes the Taylor droplet’s relative velocity between the faster droplet flow and the slower mean flow. Based on the pressure field, we quantify the driving pressure gradient of the bypass flow and verify a simple estimation method: the geometry of the gutter entrances delivers a Laplace pressure difference. As a direct measure for the viscous dissipation, we calculate the 3D distribution of work done on the flow elements, that is necessary to maintain the stationarity of the Taylor flow. The spatial integration of this distribution provides the overall dissipated energy and allows to identify and quantify different contributions from the individual fluid phases, from the wall-proximate layer and from the flow redirection due to presence of the droplet interface. For the first time, we provide deep insight into the 3D pressure field and the distribution of the energy dissipation in the Taylor flow based on experimentally acquired 3D3C velocity data. We provide the 3D pressure field of and the 3D distribution of work as supplementary material to enable a benchmark for CFD and numerical simulations. Graphical abstract

scholarly journals The effect of liquid nitrogen cooling on coal cracking and mechanical properties

2018 ◽  
Vol 36 (6) ◽  
pp. 1609-1628 ◽  
Author(s):  
Chengzheng Cai ◽  
Feng Gao ◽  
Yugui Yang
Keyword(s):  
Mechanical Properties ◽  
Tensile Strength ◽  
Acoustic Emission ◽  
Liquid Nitrogen ◽  
Wave Velocity ◽  
Count Rate ◽  
Initial State ◽  
Nitrogen Injection ◽  
Strength Tests ◽  
Liquid Nitrogen Cooling

Liquid nitrogen is a type of super-cryogenic fluid, which can cause the reservoir temperature to decrease significantly and thereby induce formation rock damage and cracking when it is injected into the wellbore as fracturing fluid. An experimental set-up was designed to monitor the acoustic emission signals of coal during its contact with cryogenic liquid nitrogen. Ultrasonic and tensile strength tests were then performed to investigate the effect of liquid nitrogen cooling on coal cracking and the changes in mechanical properties thereof. The results showed that acoustic emission phenomena occurred immediately as the coal sample came into contact with liquid nitrogen. This indicated that evident damage and cracking were induced by liquid nitrogen cooling. During liquid nitrogen injection, the ring-down count rate was high, and the cumulative ring-down counts also increased rapidly. Both the ring-down count rate and the cumulative ring-down counts during liquid nitrogen injection were much greater than those in the post-injection period. Liquid nitrogen cooling caused the micro-fissures inside the coal to expand, leading to a decrease in wave velocity and the deterioration in mechanical strength. The wave velocity, which was measured as soon as the sample was removed from the liquid nitrogen (i.e. the wave velocity was recorded in the cooling state), decreased by 14.46% on average. As the cryogenic samples recovered to room temperature, this value increased to 18.69%. In tensile strength tests, the tensile strengths of samples in cooling and cool-treated states were (on average) 17.39 and 31.43% less than those in initial state. These indicated that both during the cooling and heating processes, damage and cracking were generated within these coal samples, resulting in the acoustic emission phenomenon as well as the decrease in wave velocity and tensile strength.

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