scholarly journals Effects of Cyclic Loading on the Pore Structure of Anthracite Coal

2021 ◽  
Vol 2021 ◽  
pp. 1-12
Author(s):  
Dong Wang ◽  
Tie Li ◽  
Zhiheng Cheng ◽  
Weihua Wang
Keyword(s):  
Cyclic Loading ◽  
Hydraulic Fracturing ◽  
Pore Structure ◽  
Wave Amplitude ◽  
Testing Machine ◽  
Sine Wave ◽  
Shanxi Province ◽  
Loading Frequency ◽  
Anthracite Coal ◽  
Pulse Hydraulic Fracturing

In the process of improving coalbed permeability through pulse hydraulic fracturing, the cyclic loading effect influences the characteristics of micropores in coal matrix, thus affecting the process of gas migration. Therefore, it is essential to investigate the effect of cyclic loading on the pore structure of coal. Seven groups of loading tests at different frequencies and amplitudes were conducted on anthracite coal obtained from Shanxi Province, China, using a fatigue-testing machine. Subsequently, using a PoreMaster GT-60 Mercury-intrusion apparatus, the influence of the frequency and amplitude on the structural characteristics (including mercury-injection and mercury-ejection curves, pore size distribution, porosity, and specific surface area) of pores in coal samples was analyzed. Finally, the law and mechanism of action of the loading frequency and amplitude on pores in coal samples were comprehensively analyzed. The test results showed that, in the case of maintaining the sine-wave amplitude unchanged during loading while altering the loading frequency, the overall porosity and pore volume rise at different degrees. The growth of the loading frequency presents a more significant promotive effect on the initiation and development of pores and fractures. Moreover, it drives the transformation of micropores and transition pores into mesopores and macropores, thus increasing the proportion of seepage pores. Under the condition of large sine-wave amplitude during loading, macropores and mesopores are subjected to the repeated action of the external force, thereby reducing the overall porosity. In addition, the volume of the seepage pores declines, and the number of the coalesced pores decreases. Finally, in light of these results, the implications of frequency and amplitude selection in the process of pulse hydraulic fracturing are discussed. Therefore, the results of this research will provide an important theoretical basis for the field application of pulse hydraulic fracturing technology in coal mines.

scholarly journals Laboratory Study on Changes in Gas Desorption Properties of Anthracite after Cyclic Loading

2021 ◽  
Vol 2021 ◽  
pp. 1-11
Author(s):  
Tie Li ◽  
Dong Wang ◽  
Mei-Hua Liu ◽  
Liang Chen ◽  
Hao Liu
Keyword(s):  
Diffusion Coefficient ◽  
Cyclic Loading ◽  
Testing Machine ◽  
Coal Mass ◽  
Shanxi Province ◽  
Loading Frequency ◽  
Test Results ◽  
Gas Desorption ◽  
Initial Stage ◽  
Desorption Capacity

Coal mass is subjected to cyclic loading during pulsating hydraulic fracturing (PHF), and changes in its gas desorption properties affect gas drainage. Therefore, it is of great importance to correctly understand the influences of cyclic loading on the gas desorption properties of coal mass. Firstly, loading tests with different frequencies and amplitudes were performed on anthracite from Qinshui Basin (Shanxi Province, China) using a fatigue testing machine. Secondly, gas desorption tests were performed to determine the associated curves for each test group at different equilibrium pressures, and the initial desorption capacity and diffusion coefficient of the gas were calculated. Finally, the influence of different loading conditions on the gas desorption laws were analyzed. The test results demonstrate that a greater loading frequency increases the ratio of the initial desorption capacity so that the desorption rate of coal samples is higher, and the gas desorption properties become increasingly better in the initial stage. However, variations in the amplitude have minimal impact on the ratio of the initial desorption capacity. When the amplitude is too large in the initial stage, the diffusion coefficient decreases and the gas desorption properties worsen. In addition, the above test results are used to discuss the selection of the amplitude and frequency in the PHF process from a macroperspective. The contained research results provide an important theoretical basis for the field application of PHF technologies in coal mines.

scholarly journals Study of the Mechanical Environment of Chondrocytes in Articular Cartilage Defects Repaired Area under Cyclic Compressive Loading

2017 ◽  
Vol 2017 ◽  
pp. 1-10
Author(s):  
Hai-Ying Liu ◽  
Hang-Tian Duan ◽  
Chun-Qiu Zhang ◽  
Wei Wang
Keyword(s):  
Articular Cartilage ◽  
Cyclic Loading ◽  
Response Curve ◽  
Fluid Pressure ◽  
Cartilage Defects ◽  
Loading Frequency ◽  
Liquid Pressure ◽  
Mechanical Environment ◽  
Finite Element Software ◽  
Maximum Value

COMSOL finite element software was used to establish a solid-liquid coupling biphasic model of articular cartilage and a microscopic model of chondrocytes, using modeling to take into account the shape and number of chondrocytes in cartilage lacuna in each layer. The effects of cyclic loading at different frequencies on the micromechanical environment of chondrocytes in different regions of the cartilage were studied. The results showed that low frequency loading can cause stress concentration of superficial chondrocytes. Moreover, along with increased frequency, the maximum value of stress response curve of chondrocytes decreased, while the minimum value increased. When the frequency was greater than 0.2 Hz, the extreme value stress of response curve tended to be constant. Cyclic loading had a large influence on the distribution of liquid pressure in chondrocytes in the middle and deep layers. The concentration of fluid pressure changed alternately from intracellular to peripheral in the middle layer. Both the range of liquid pressure in the upper chondrocytes and the maximum value of liquid pressure in the lower chondrocytes in the same lacunae varied greatly in the deep layer. At the same loading frequency, the elastic modulus of artificial cartilage had little effect on the mechanical environment of chondrocytes.

scholarly journals Material properties of Velcro fastenings

1982 ◽  
Vol 6 (2) ◽  
pp. 93-96
Author(s):  
D. L. Bader ◽  
M. J. Pearcy
Keyword(s):  
Cyclic Loading ◽  
Material Properties ◽  
Testing Machine ◽  
Force Extension ◽  
Instron Testing Machine ◽  
Attachment Strength

An assessment of the material properties of three types of touch and close fasteners (Velcro) in general orthopaedic usage is presented. The materials were tested under various loading regimes using an Instron testing machine. The force-extension curves were analyzed and values determined for both the stiffness and strength of the various attachments. Particular reference was made to the alteration in attachment strength after cyclic loading. The strength of the standard Velcro was found to be least affected after cyclic loading to simulate continuous usage. A recommendation is made on the specific application of each type of Velcro based on their material properties.

Dynamic viscoelastic behavior of lower extremity tendons during simulated running

2000 ◽  
Vol 89 (4) ◽  
pp. 1352-1359 ◽  
Author(s):  
M. De Zee ◽  
F. Bojsen-Møller ◽  
M. Voigt
Keyword(s):  
Cyclic Loading ◽  
Achilles Tendon ◽  
Testing Machine ◽  
Viscoelastic Behavior ◽  
Muscle Spindles ◽  
Minor Effect ◽  
Velocity Feedback ◽  
Dynamic Creep

The aim of this project was to see whether the tendon would show creep during long-term dynamic loading (here referred to as dynamic creep). Pig tendons were loaded by a material-testing machine with a human Achilles tendon force profile (1.37 Hz, 3% strain, 1,600 cycles), which was obtained in an earlier in vivo experiment during running. All the pig tendons showed some dynamic creep during cyclic loading (between 0.23 ± 0.15 and 0.42 ± 0.21%, means ± SD). The pig tendon data were used as an input of a model to predict dynamic creep in the human Achilles tendon during running of a marathon and to evaluate whether there might consequently be an influence on group Ia afferent-mediated length and velocity feedback from muscle spindles. The predicted dynamic creep in the Achilles tendon was considered to be too small to have a significant influence on the length and velocity feedback from soleus during running. In spite of the characteristic nonlinear viscoelastic behavior of tendons, our results demonstrate that these properties have a minor effect on the ability of tendons to act as predictable, stable, and elastic force transmitters during long-term cyclic loading.

Experimental study of the evolution of soil arching effect under cyclic loading based on trapdoor test and particle image velocimetry

2020 ◽  
Vol 57 (6) ◽  
pp. 903-920 ◽  
Author(s):  
Zongqi Bi ◽  
Quanmei Gong ◽  
Peijun Guo ◽  
Qian Cheng
Keyword(s):  
Particle Image Velocimetry ◽  
Cyclic Loading ◽  
Soil Structure ◽  
Particle Image ◽  
Loading Frequency ◽  
Soil Arching ◽  
Arching Effect ◽  
Filling Height ◽  
Image Velocimetry ◽  
Load Cells

Arching effect, which is a common phenomenon in any system involving soil–structure interaction, has been found to be inevitably affected by various factors, including loading conditions. This study investigated the evolution of arching effect induced by cyclic loading by conducting a series of tests using a trapdoor apparatus. The test box was instrumented to control the displacement of the moving gate and to record the variation of vertical stress distribution by using a set of dynamic load cells. Digital images were captured during tests and processed using particle image velocimetry (PIV) to determine the displacement field and hence to examine the variation of geometric features of arch and particle movements. The evolution process of arching effect, from the initial formation to the finial collapse, was identified. Depending on the analysis for the geometry appearance, displacement region, and variation of cyclic stresses, both stable and collapsed arches were observed. By increasing the amplitude of cyclic loading step by step, critical loading amplitude corresponding to the threshold of collapse of the arching effect was determined. Based on the results, the effects of trapdoor displacement, cyclic loading frequency, and filling height on arching effect are discussed.

scholarly journals Biomechanical Evaluation of Proximal Hamstring Repair: All-Suture Anchor Versus Titanium Suture Anchor

2020 ◽  
Vol 8 (1) ◽  
pp. 232596711989292 ◽  
Author(s):  
Alexander Otto ◽  
Alyssa M. DiCosmo ◽  
Joshua B. Baldino ◽  
Julian Mehl ◽  
Elifho Obopilwe ◽  
...  
Keyword(s):  
Cyclic Loading ◽  
Suture Anchor ◽  
Testing Machine ◽  
Optical Tracking ◽  
Rank Test ◽  
Suture Anchors ◽  
Posterior Aspect ◽  
Significant Difference ◽  
Load To Failure ◽  
Proximal Hamstring

Background: Proximal hamstring avulsions are severe tendon injuries and are commonly sports-related. Open and endoscopic techniques as well as different anchor configurations have already been described for proximal hamstring repair. Novel all-suture anchors have been developed to provide decreased bone loss during placement and reduced occupied bone volume when compared with titanium suture anchors. Hypothesis: Complete proximal hamstring avulsions repaired with all-suture anchors will demonstrate equal load to failure and comparable displacement under cyclic loading when compared with titanium suture anchors. Study Design: Controlled laboratory study. Methods: Complete proximal hamstring avulsions were created in 18 paired cadaveric specimens (mean ± SD age, 63.0 ± 10.4 years). Either all-suture anchors or titanium suture anchors were used for repair. Cyclic loading from 10 to 125 N at 1 Hz was performed for 1500 cycles with a material testing machine. Displacement was assessed along anterior and posterior aspects of the tendon repair with optical tracking. Specimens were loaded to failure at a rate of 120 mm/min. Displacement, load to failure, and repair construct stiffness were compared between matched pairs with the Wilcoxon signed-rank test. Correlations were determined by Spearman rho analysis. Results: The all-suture anchors showed significantly higher load-to-failure values when compared with the titanium anchor repairs (799.64 ± 257.1 vs 573.27 ± 89.9 N; P = .008). There was no significant difference in displacement between all-suture anchors and titanium suture anchors at the anterior aspect (6.60 ± 2.2 vs 5.49 ± 1.1 mm; P = .26) or posterior aspect (5.87 ± 2.08 vs 5.23 ± 1.37 mm; P = .678) of the repaired hamstring tendons. Conclusion: All-suture anchors demonstrated similar displacement and superior load to failure when compared with titanium suture anchors. Clinical Relevance: The results of this study suggest that all-suture anchors are an equivalent alternative to titanium suture anchors for proximal hamstring avulsion repair.

scholarly journals Fracture Resistance of Monolithic Zirconia Crowns in Implant Prostheses in Patients with Bruxism

Materials ◽  
2019 ◽  
Vol 12 (10) ◽  
pp. 1623 ◽  
Author(s):  
Ting-Hsun Lan ◽  
Chin-Yun Pan ◽  
Pao-Hsin Liu ◽  
Mitch M. C. Chou
Keyword(s):  
Cyclic Loading ◽  
Computer Aided Design ◽  
Fracture Resistance ◽  
Testing Machine ◽  
Von Mises Stress ◽  
High Fracture ◽  
Computer Aided ◽  
Zirconia Crowns ◽  
Monolithic Zirconia ◽  
Von Mises

The aim of this study is to determine the minimum required thickness of a monolithic zirconia crown in the mandibular posterior area for patients with bruxism. Forty-nine full zirconia crowns, with seven different occlusal thicknesses of 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, and 1.0 mm, were made by using a computer-aided design/computer-aided manufacturing system (CAD/CAM). Seven crowns in each group were subjected to cyclic loading at 800 N and 5 Hz in a servohydraulic testing machine until fracture or completion of 100,000 cycles. Seven finite element models comprising seven different occlusal thicknesses of 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, and 1.0 mm were simulated using three different loads of vertical 800 N, oblique 10 degrees 800 N, and vertical 800 N + x N torque (x = 10, 50, and 100). The results of cyclic loading tests showed that the fracture resistance of the crown was positively associated with thickness. Specimen breakage differed significantly according to the different thicknesses of the prostheses (p < 0.01). Lowest von Mises stress values were determined for prostheses with a minimal thickness of 1.0 mm in different loading directions and with different forces. Zirconia specimens of 1.0 mm thickness had the lowest stress values and high fracture resistance and under 800 N of loading.

Effects of pulse wave on the variation of coal pore structure in pulsating hydraulic fracturing process of coal seam

Fuel ◽  
2020 ◽  
Vol 264 ◽  
pp. 116906 ◽  
Author(s):  
Xie Jingna ◽  
Xie Jun ◽  
Ni Guanhua ◽  
Sheik Rahman ◽  
Sun Qian ◽  
...  
Keyword(s):  
Coal Seam ◽  
Hydraulic Fracturing ◽  
Pore Structure ◽  
Pulse Wave ◽  
Fracturing Process
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