scholarly journals Seepage and Damage Evolution Characteristics of Gas-Bearing Coal under Different Cyclic Loading–Unloading Stress Paths

Processes ◽  
2018 ◽  
Vol 6 (10) ◽  
pp. 190 ◽  
Author(s):  
Qingmiao Li ◽  
Yunpei Liang ◽  
Quanle Zou
Keyword(s):  
Cyclic Loading ◽  
Peak Stress ◽  
Cyclic Loading And Unloading ◽  
Evolution Characteristics ◽  
Three Phase ◽  
Boltzmann Function ◽  
Gas Seepage ◽  
Seepage Characteristics ◽  
Number Of Cycles ◽  
Gas Bearing

The mechanical properties and seepage characteristics of gas-bearing coal evolve with changes in the loading pattern, which could reveal the evolution of permeability in a protected coal seam and allow gas extraction engineering work to be designed by using the effect of mining multiple protective seams. Tests on gas seepage in raw coal under three paths (stepped-cyclic, stepped-increasing-cyclic, and crossed-cyclic loading and unloading) were carried out with a seepage tester under triaxial stress conditions. The permeability was subjected to the dual influence of stress and damage accumulation. After being subjected to stress unloading and loading, the permeability of coal samples gradually decreased and the permeability did not increase before the stress exceeded the yield stage of the coal samples. The mining-enhanced permeability of the coal samples in the loading stage showed a three-phase increase with the growth of stress and the number of cycles and exhibited an N-shaped increase under the stepped-cyclic loading while it linearly increased under the other two paths in the unloading stage. With the increase of peak stress and the accumulation of damage in coal samples, the sensitivity of the permeability of coal samples to stress gradually declined. The relationship between the damage variable and the number of cycles conformed to the Boltzmann function.

scholarly journals Mechanical Behavior of Shale Rock under Uniaxial Cyclic Loading and Unloading Condition

2018 ◽  
Vol 2018 ◽  
pp. 1-8 ◽  
Author(s):  
Baoyun Zhao ◽  
Dongyan Liu ◽  
Ziyun Li ◽  
Wei Huang ◽  
Qian Dong
Keyword(s):  
Cyclic Loading ◽  
Mechanical Behavior ◽  
Creep Behavior ◽  
Peak Stress ◽  
Creep Model ◽  
Cycle Number ◽  
Shale Rock ◽  
Cyclic Loading And Unloading ◽  
Residual Strains ◽  
Loading And Unloading

In order to investigate the mechanical behavior of shale rock under cyclic loading and unloading condition, two kinds of incremental cyclic loading tests were conducted. Based on the result of the short-term uniaxial incremental cyclic loading test, the permanent residual strain, modulus, and damage evolution were analyzed firstly. Results showed that the relationship between the residual strains and the cycle number can be expressed by an exponential function. The deformation modulus E50 and elastic modulus ES first increased and then decreased with the peak stress under the loading condition, and both of them increased approximately linearly with the peak stress under the unloading condition. On the basis of the energy dissipation, the damage variables showed an exponential increasing with the strain at peak stress. The creep behavior of the shale rock was also analyzed. Results showed that there are obvious instantaneous strain, decay creep, and steady creep under each stress level and the specimen appears the accelerated creep stage under the 4th stress of 51.16 MPa. Based on the characteristics of the Burgers creep model, a viscoelastic-plastic creep model was proposed through viscoplastic mechanics, which agrees very well with the experimental results and can better describe the creep behavior of shale rock better than the Burgers creep model. Results can provide some mechanics reference evidence for shale gas development.

Mechanical Damage to the Intervertebral Disc Annulus Fibrosus Subjected to Cyclic Tensile Loading

2003 ◽  
Author(s):  
David A. Ryan ◽  
Jeffrey J. MacLean ◽  
James C. Iatridis
Keyword(s):  
Cyclic Loading ◽  
Material Properties ◽  
Annulus Fibrosus ◽  
Permanent Deformation ◽  
Mechanical Damage ◽  
Quantitative Relationship ◽  
Peak Stress ◽  
Tensile Loading ◽  
Number Of Cycles

Damage progression in the circumferential direction of the disc annulus is likely to occur in vivo in response to cyclic loading with associated degradation in tensile material properties, yet this information is not available in the literature. We hypothesize that damage of the annulus will be increased by the number of cycles and magnitude of strain applied to the tissue. Therefore, the objective of this study is to obtain a quantitative relationship between number of cycles and magnitude of tensile strain and damage on the annulus fibrosus. Damage to the annulus is assessed through measurement of permanent deformation (% elongation) and peak stress in the tissue under cyclic loading conditions.

The Qualification of BWR Steam Dryer Weldments Exposed to Cyclic Loading Using Finite Element Methods

2013 ◽  
Author(s):  
Michael R. Breach
Keyword(s):  
Finite Element ◽  
Cyclic Loading ◽  
Stress Field ◽  
Finite Element Methods ◽  
Fatigue Cracks ◽  
Failure Process ◽  
Peak Stress ◽  
Point Of View ◽  
Nominal Stress ◽  
Number Of Cycles

The qualification of welds other than full penetration groove welds exposed to cyclic loading using finite element methods requires an understanding of the basis behind classical methodologies. These methodologies usually address nominal stresses. The nominal stress (S-N) method was the first approach developed to try to understand this failure process and is still widely used in applications where the applied stress is nominally within the elastic range of the material and the number of cycles to failure is large. From this point of view, the nominal stress approach is best suited to that area of the fatigue process known as high cycle fatigue. Cracks and discontinuities will cause stress redistribution and concentrations leading to secondary and peak stresses additive to the nominal stress when referencing the S-N curves. Therefore, fundamental to the qualification of weldments of components and structures is the determination of the nominal stress field; however, this can be problematic for several reasons: • Secondary, Peak stress arising from structural discontinuities can mask the actual nominal stress field. • There may be an insufficient number of elements and/or integration points through the thickness to rely on linearization techniques, to separate the nominal stresses from the secondary and peak stresses due to the high cost of using bricks or tetrahedrons. • In complex shell structures, the nominal stress field in weldments that satisfies equilibrium against externally applied loads is not readily distinguished; this is due to the shear preponderance of mesh sensitive discontinuities. Herein, is a summary of methods to address the aforementioned problem and guidance in determining the true peak stresses and their qualification. Methods documented in ASME BPV Code Section VIII Div. 2, and various papers are compared. These methods will be used to assess existing methods that may be used in the industry. ASME BPV Code Section III Subsections NG and NB will be used as a basis to classify and qualify the weldment stresses.

Experimental Studies on Deformation Behaviors of Rubbery Materials under Cyclic Loading

2016 ◽  
Vol 853 ◽  
pp. 106-111 ◽  
Author(s):  
Yi Fu Chen ◽  
Guo Zheng Kang ◽  
Ru Tao ◽  
Han Jiang
Keyword(s):  
Cyclic Loading ◽  
Residual Strain ◽  
Experimental Studies ◽  
Peak Stress ◽  
Cyclic Test ◽  
Butadiene Rubber ◽  
Ratcheting Strain ◽  
Cyclic Tension ◽  
Deformation Behaviors ◽  
Number Of Cycles

Macroscopic cyclic tension-unloading experiments are conducted to investigate the cyclic deformation behaviors of CB filled vulcanized hydrogenated nitrile butadiene rubber at room temperature. In the load-controlled cyclic tension-unloading tests, remarkable ratchetting occurs, and the effects of the level and rate of cyclic loading on the ratchetting are also investigated. The ratcheting strain increases with the increasing mean stress and stress amplitude, and more obvious ratchetting is observed in the cyclic test with load-hold or at lower loading rate. In the displacement-controlled cyclic tension-unloading tests, the responding peak stress of the H-NBR decreases continuously, but the residual strain increases with the increasing number of cycles. Furthermore, the zero-stress hold at the end of cyclic test demonstrates that the residual strain will be recovered partially, which implies that the residual strain of the H-NBR after cyclic test consists of the reversible and irreversible parts.

scholarly journals Influence of Loading Rate on the Energy Evolution Characteristics of Rocks under Cyclic Loading and Unloading

Energies ◽  
2020 ◽  
Vol 13 (15) ◽  
pp. 4003
Author(s):  
Jielin Li ◽  
Liu Hong ◽  
Keping Zhou ◽  
Caichu Xia ◽  
Longyin Zhu
Keyword(s):  
Cyclic Loading ◽  
Loading Rate ◽  
Energy Evolution ◽  
Dissipation Energy ◽  
Loading Rates ◽  
Cyclic Loading And Unloading ◽  
Evolution Characteristics ◽  
Increasing Trend ◽  
Loading And Unloading ◽  
Fast Increase

To analyse the effect of loading rate on the energy evolution of rocks under cyclic loading and unloading, tests on saturated limestone were conducted at loading rates of 0.15, 0.2, and 0.3 mm/min, and the evolution characteristics of plastic, elastic, dissipation, and input energies were examined under different loading rates. The results indicated that the plastic strain in the entire test was directly proportional to the loading rate. In addition, strength, residual stress, plastic energy, and dissipation energy under residual resistance were inversely proportional to the loading rate. The plastic strain exhibited a decreasing–stabilising–increasing trend, and the smaller loading rate delayed the “increasing” trend. The increasing extent of each energy exhibited the following trend: input > elastic > plastic > dissipation energy. Furthermore, the first three types of energy exhibited a slow–fast–slow–fast increase trend. The dissipation energy exhibited a fast–steady–fast–slow–fast increase trend. Additionally, the elastic energy index exhibited a large increase–steady increase–decrease trend, which was proportional to the loading rate. The damping ratio exhibited a decrease–increase–decrease–increase–decrease trend which was proportional to the loading rate in the compaction stage and inversely proportional to the plastic stage.

scholarly journals Study on the Permeability Change Characteristic of Gas-Bearing Coal under Cyclic Loading and Unloading Path

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-12
Author(s):  
Fakai Wang ◽  
Xuelong Li ◽  
Bo Cui ◽  
Jian Hao ◽  
Peng Chen
Keyword(s):  
Cyclic Loading ◽  
Radial Stress ◽  
Axial Stress ◽  
Cumulative Damage ◽  
Factors Affecting ◽  
Permeability Characteristics ◽  
Cyclic Loading And Unloading ◽  
Damage Rate ◽  
Loading And Unloading ◽  
Gas Bearing

Using the self-developed three-axis servo fluid-solid coupling system with gas-solid coupling of gas-bearing coal, the variation law of the permeability of gas coal under the stress cycle loading and unloading path was studied. The qualitative and quantitative relationships between permeability, axial force, and radial stress of gas-bearing coals were established, and the variation law of permeability of gas-bearing coals was discussed. The results show that (1) different cyclic loading and unloading stress paths correspond to the permeability characteristics of different gas-bearing coals. (2) Permeability of gas-bearing coal decreases with the increase of axial stress and radial stress, and it has a logarithmic function with axial stress and radial stress. This shows that axial stress and radial stress are important factors affecting the permeability characteristics of gas-bearing coal. (3) Under the same stress loading and unloading conditions, the axial stress is less than radial stress on the permeability of gas-bearing coal. In the cyclic loading and unloading axial stress process, the permeability of the gas-bearing coal varies by a smaller extent than the cyclically unloaded confining force. (4) The cumulative damage rate of gas-bearing coal under axial stress gradually increases with the increase of the number of cycles of loading and unloading, and the rate of the cumulative damage rate of permeability is less than the corresponding rate of radial stress.

scholarly journals Experimental Study on Damage and Gas Migration Characteristics of Gas-Bearing Coal with Different Pore Structures under Sorption-Sudden Unloading of Methane

Geofluids ◽  
2019 ◽  
Vol 2019 ◽  
pp. 1-11 ◽  
Author(s):  
Gang Wang ◽  
Yangyang Guo ◽  
Chang’ang Du ◽  
Lulu Sun ◽  
Zhiyuan Liu ◽  
...  
Keyword(s):  
Axial Strain ◽  
Radial Strain ◽  
Axial Direction ◽  
Gas Migration ◽  
Pore Structures ◽  
Gas Seepage ◽  
Experimental Apparatus ◽  
Methane Sorption ◽  
Seepage Characteristics ◽  
Gas Bearing

Coal and gas outburst is one of the most serious hazards in underground mine operations. In this paper, we explored the damage and gas seepage characteristics of gas-bearing coal samples with different pore structures under methane sorption-sudden unloading conditions using a self-developed experimental apparatus. The results show that (1) the deformation of coal samples can be divided into three stages, namely, pressure-increase-induced compression, sorption-induced expansion, and sudden-unloading-induced deformation or failure stage; (2) with the increase of the number of diffusion pores in the coal sample, the amount of gas sorption gradually increases and the expansion and failure of coal samples become more obvious; (3) in the experiment, the damage of coal samples is mainly along the axial direction and rarely along the radial direction; (4) the radial strain is always greater than the axial strain.

scholarly journals Experimental Investigation of the Mechanical Behavior of Layer-Crack Specimens under Cyclic Uniaxial Compression

Symmetry ◽  
2019 ◽  
Vol 11 (4) ◽  
pp. 465
Author(s):  
Wei-yao Guo ◽  
Feng-hai Yu ◽  
Yue Qiu ◽  
Tong-bin Zhao ◽  
Yun-liang Tan
Keyword(s):  
Cyclic Loading ◽  
Energy Density ◽  
Mechanical Behavior ◽  
Elastic Energy ◽  
Peak Stress ◽  
Dissipated Energy ◽  
Strengthening Effect ◽  
Input Energy ◽  
Rock Bursts ◽  
Number Of Cycles

It is generally acknowledged that the failure of the layer-crack structure is closely related to rock bursts (a layer-crack structure means a coal or rock rib that is cut by fractures that are parallel or sub-parallel to the surface of the rib). Understanding the mechanical behavior of the layer-crack structure under cyclic loading is beneficial for rock burst mitigation. This study experimentally investigated the influence of the geometry of vertical fissure (i.e., width, length and number) on the mechanical properties of layer-crack rock specimens. The results show that the sensitivity of parameters with respect to the geometry of the fissure from strong to weak is the number, length and width. First, the peak stress under cyclic loading increases by approximately 7.82%–17.35%, thereby exerting an obvious strengthening effect. Second, the fissure geometry slightly affects the energy evolution of the layer-crack specimen, i.e., the input energy density, elastic energy density and dissipated energy density all gradually increase with the increase of the number of cycles. However, when approaching a specimen failure, the increasing rates from quick to slow are the dissipated energy, input energy and elastic energy. Third, the damage variable of the layer-crack specimen shows a concave increasing trend with the increase of the number of cycles. When the number of cycles is equal, the damage increases with the increase of the number of fissures, but it decreases with the increase of the fissure length. Fourth, AE events occur shortly before specimen failures, but rapidly increase near the specimen failures. The accumulated AE events that lead to specimen failures decrease with the increase in the number of fissures. These results can provide some basic data for the research of rock bursts related to the failures of layer-crack structures.

scholarly journals Investigation of Deformation Inhomogeneity and Low-Cycle Fatigue of a Polycrystalline Material

2021 ◽  
Vol 11 (6) ◽  
pp. 2673
Author(s):  
Mu-Hang Zhang ◽  
Xiao-Hong Shen ◽  
Lei He ◽  
Ke-Shi Zhang
Keyword(s):  
Cyclic Loading ◽  
Low Cycle Fatigue ◽  
Strain Tensor ◽  
Equivalent Strain ◽  
Differential Entropy ◽  
Strain Components ◽  
Deformation Inhomogeneity ◽  
Standard Deviations ◽  
Number Of Cycles ◽  
The Relationship

Considering the relationship between inhomogeneous plastic deformation and fatigue damage, deformation inhomogeneity evolution and fatigue failure of superalloy GH4169 under temperature 500 °C and macro tension compression cyclic loading are studied, by using crystal plasticity calculation associated with polycrystalline representative Voronoi volume element (RVE). Different statistical standard deviation and differential entropy of meso strain are used to measure the inhomogeneity of deformation, and the relationship between the inhomogeneity and strain cycle is explored by cyclic numerical simulation. It is found from the research that the standard deviations of each component of the strain tensor at the cyclic peak increase monotonically with the cyclic loading, and they are similar to each other. The differential entropy of each component of the strain tensor also increases with the number of cycles, and the law is similar. On this basis, the critical values determined by statistical standard deviations of the strain components and the equivalent strain, and that by differential entropy of strain components, are, respectively, used as fatigue criteria, then predict the fatigue–life curves of the material. The predictions are verified with reference to the measured results, and their deviations are proved to be in a reasonable range.

Fatigue Crack Growth Tests on Glass Fibre Reinforced Polymer Matrix Composite

2005 ◽  
Vol 473-474 ◽  
pp. 189-194
Author(s):  
Zilia Csomós ◽  
János Lukács
Keyword(s):  
Cyclic Loading ◽  
Crack Opening Displacement ◽  
Matrix Composite ◽  
Glass Fibre ◽  
Crack Opening ◽  
Loading Conditions ◽  
Opening Displacement ◽  
Interfacial Cracks ◽  
Glass Fibre Reinforced ◽  
Number Of Cycles

E-glass fibre reinforced polyester matrix composite was investigated, which was made by pullwinding process. Round three point bending (RTPB) specimens were tested under quasi-static and mode I cyclic loading conditions. Load vs. displacement (F-f), load vs. crack opening displacement (F-v) and crack opening displacement range vs. number of cycles (ΔCOD-N) curves were registered and analysed. Interfacial cracks were caused the final longitudinal fracture of the specimens under quasi-static and cyclic loading conditions.

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