scholarly journals Study on Ultrasonic Response to Mechanical Structure of Coal under Loading and Unloading Condition

2017 ◽  
Vol 2017 ◽  
pp. 1-12 ◽  
Author(s):  
Xiaofei Liu ◽  
Xiaoran Wang ◽  
Enyuan Wang ◽  
Zhentang Liu ◽  
Xiaoyang Xu
Keyword(s):  
Stress Level ◽  
Dominant Frequency ◽  
Test System ◽  
Ultrasonic Signals ◽  
Linear Elastic ◽  
Cyclic Loading And Unloading ◽  
Deformation And Fracture ◽  
Ultrasonic Technology ◽  
Loading And Unloading ◽  
Ultrasonic Parameters

Ultrasonic technology can be applied to study the changes in the internal defects of coal under quantitative loading, which can provide the theoretical basis for applying the technology to determine the structural stability of coal and predict disasters related to the dynamics of coal or rock. In this paper, to investigate the propagation laws of ultrasonic signals through a coal material under various loading conditions, an ultrasonic test system for the deformation and fracture of coal rock was used and a cyclic loading and unloading pattern is adopted. In addition, changes in ultrasonic parameters such as amplitude, dominant frequency, and velocity were analyzed. At the initial loading stage, the ultrasonic amplitude, amplitude of the dominant frequency, and wave velocity slightly decrease as the loading process progresses, and these three ultrasonic parameters gradually increase to their maxima when the stress level reaches approximately 46%. When it progresses from the linear elastic stage to the elastic plastic stage, the material inside the coal distorts and fractures more drastically, the inner defects are fully developed, and the acoustic parameters decrease significantly. Therefore, the corresponding measures should be adapted to reduce the loading stress before the coal is loaded to its critical stress level.

Experimental and numerical studies on fracture characteristics of notched granite beams under cyclic loading and unloading

2020 ◽  
Vol 56 (1) ◽  
pp. 3-17
Author(s):  
Xiaojing Li ◽  
Peijie He ◽  
Jianhui Tang ◽  
Xudong Chen
Keyword(s):  
Acoustic Emission ◽  
Cyclic Loading ◽  
Correlation Method ◽  
Average Frequency ◽  
Test System ◽  
Underground Engineering ◽  
Three Point Bending ◽  
Cyclic Loading And Unloading ◽  
Loading And Unloading ◽  
Felicity Ratio

In underground engineering, such as mining engineering and deep tunnel engineering, the rock is often loaded and unloaded repeatedly. The strength of rock under cyclic load is lower than that under static load. To obtain the fracture response of the rock, the three-point bending tests of notched granite beams under cyclic loading and unloading were carried out with Electro-hydraulic Servo Material Test System. The acoustic emission technology was adopted to monitor the acoustic emission events of sample in the process of fracture. It is revealed that the fracture toughness of granite under cyclic loading and unloading is lower than that under static loading. Based on the acoustic emission energy obtained from monitoring, the damage evolution during cyclic loading and unloading was analyzed. The fracture mode of granite samples is analyzed by the RA value-average frequency correlation method. And the Felicity ratio during the loading and unloading cycle was calculated to evaluate the severity of initial damage of the material. It is revealed that Kaiser effect appears only in the elastic deformation stage of cyclic loading unloading bending. The Holmquist–Johnson–Cook damage constitutive model and Weibull distribution were used to establish the heterogeneous granite model. And the three-point bending of the model under cyclic loading and unloading was simulated to disclose the crack growth mechanism of rock. The study may provide some references for rock instability control in geotechnical engineering construction.

Adjustable buttons for ACL graft cortical fixation partially fail with cyclic loading and unloading

2018 ◽  
Vol 27 (8) ◽  
pp. 2530-2536 ◽  
Author(s):  
J. Glasbrenner ◽  
C. Domnick ◽  
M. J. Raschke ◽  
T. Willinghöfer ◽  
C. Kittl ◽  
...  
Keyword(s):  
Cyclic Loading ◽  
Acl Graft ◽  
Cyclic Loading And Unloading ◽  
Loading And Unloading

scholarly journals Experimental Study of Stress-Seepage Coupling Properties of Sandstone under Different Loading Paths

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-21
Author(s):  
Xi Chen ◽  
Wei Wang ◽  
Yajun Cao ◽  
Qizhi Zhu ◽  
Weiya Xu ◽  
...  
Keyword(s):  
Elastic Modulus ◽  
Pore Pressure ◽  
Complex Loading ◽  
Friction Angle ◽  
Confining Pressure ◽  
Triaxial Tests ◽  
Compression Tests ◽  
Biot Coefficient ◽  
Cyclic Loading And Unloading ◽  
Loading And Unloading

The study on hydromechanical coupling properties of rocks is of great importance for rock engineering. It is closely related to the stability analysis of structures in rocks under seepage condition. In this study, a series of conventional triaxial tests under drained condition and hydrostatic compression tests under drained or undrained condition on sandstones were conducted. Moreover, complex cyclic loading and unloading tests were also carried out. Based on the experimental results, the following conclusions were obtained. For conventional triaxial tests, the elastic modulus, peak strength, crack initiation stress, and expansion stress increase with increased confining pressure. Pore pressure weakened the effect of the confining pressure under drained condition, which led to a decline in rock mechanical properties. It appeared that cohesion was more sensitive to pore pressure than to the internal friction angle. For complex loading and unloading cyclic tests, in deviatoric stress loading and unloading cycles, elastic modulus increased obviously in first loading stage and increased slowly in next stages. In confining pressure loading and unloading cycles, the Biot coefficient decreased first and then increased, which indicates that damage has a great impact on the Biot coefficient.

Effects of Detwinning on the Inelasticity of AZ31B Sheets During Cyclic Loading and Unloading

2018 ◽  
Vol 10 (09) ◽  
pp. 1850095 ◽  
Author(s):  
H. Wang ◽  
D. Tang ◽  
D. Y. Li ◽  
Y. H. Peng ◽  
P. D. Wu
Keyword(s):  
Cyclic Loading ◽  
Magnesium Alloys ◽  
Plasticity Model ◽  
Inelastic Behavior ◽  
Deformation History ◽  
Cyclic Loading And Unloading ◽  
Polycrystal Plasticity ◽  
Self Consistent ◽  
Loading And Unloading ◽  
Previous Loading

Magnesium alloys exhibit significant inelastic behavior during unloading, especially when twinning and detwinning are involved. It is commonly accepted that noteworthy inelastic behavior will be observed during unloading if twinning occurs during previous loading. However, this phenomenon is not always observed for Mg sheets with strong rolled texture. Therefore, the inelasticity of AZ31B rolled sheets with different rolled textures during cyclic loading-unloading are investigated by elastic viscoplastic self-consistent polycrystal plasticity model. The incorporation of the twinning and detwinning model enables the treatment of detwinning, which plays an important role for inelastic behavior during unloading. The effects of texture, deformation history, and especially twinning and detwinning on the inelastic behaviors are carefully investigated and found to be remarkable. The simulated results are in agreement with the available experimental observations, which reveals that the inelastic behavior for strongly rolled sheets is very different than the extruded bars.

Residual Stresses and Differential Deformation of Electroplated Structures

1989 ◽  
Vol 33 ◽  
pp. 161-169
Author(s):  
G. Sheikh ◽  
I. C. Noyan
Keyword(s):  
Residual Stresses ◽  
Lattice Parameter ◽  
Stress Profile ◽  
X Ray ◽  
Residual Stress Profile ◽  
Cyclic Loading And Unloading ◽  
Nickel Substrates ◽  
Loading And Unloading

AbstractWe report the results of a recent study where nickel substrates electroplated with chromium were loaded in-situ on an x-ray diffractometer. This technique allows determination of lattice spacings in the vicinity of the interface for both the film and the substrate as a function of the applied load. We used such lattice parameter data, SEM observations of the surface and x-ray peak breadth data to study the partitioning of deformation between the film and the substrate. The data indicates progressive loss of adhesion between the film and the substrate with increasing deformation. We observe significant effect of electroplating residual stresses on the mechanical behavior of the system. The loss of adhesion between the film and the substrate coupled with the initial residual stress profile causes an apparent 'negative Poisson's ratio' for the film during initial stages of the loading. This effect disappears with cyclic loading and unloading.

scholarly journals Damage and fractal evolution trends of sandstones under constant-amplitude and tiered cyclic loading and unloading based on acoustic emission

2019 ◽  
Vol 15 (7) ◽  
pp. 155014771986102
Author(s):  
Dongxu Liang ◽  
Nong Zhang ◽  
Lixiang Xie ◽  
Guangming Zhao ◽  
Deyu Qian
Keyword(s):  
Acoustic Emission ◽  
Cyclic Loading ◽  
Damage Evolution ◽  
Damage Accumulation ◽  
Fractal Dimensions ◽  
Damage Variable ◽  
Constant Amplitude ◽  
Kaiser Effect ◽  
Cyclic Loading And Unloading ◽  
Loading And Unloading

It is of significance to study the damage and destruction of rock under cyclic loading in geotechnical engineering. We determined the trends in damage evolution of sandstone under constant-amplitude and tiered cyclic loading and unloading under uniaxial compression. The results of the study show that (1) the variation of acoustic-emission events was consistent with the stress curves and 89% of all acoustic-emission events occurred during the cycling stages. The observed Kaiser effect was more notable in tiered cycling. (2) The damage variable increased sharply in the cycling stages and its increment was 0.07 higher for tiered cycling than constant-amplitude cycling. Sandstone exhibited greater damage under tiered cyclic loading and unloading. (3) Equations for the evolution of the damage variable under the two cycle modes were obtained by fitting of experimental data. (4) The fractal dimensions of the constant-amplitude cycle were larger than those of the tiered cycle. The process of damage and destruction presents a trend of reducing fractal dimension. The damage accumulation of sandstone under tiered cycling was faster than under constant-amplitude cycling. These results provide references for damage and early warning of rock under both constant-amplitude and tiered cyclic loading and unloading.

scholarly journals Analysis of Damage Evolution of Sandstone under Uniaxial Loading and Unloading Conditions Based on Resistivity Characteristics

2019 ◽  
Vol 2019 ◽  
pp. 1-12 ◽  
Author(s):  
Guoyin Wu ◽  
Kui Wang ◽  
Mingjie Zhao ◽  
Zhichao Nie ◽  
Zhen Huang
Keyword(s):  
Stress State ◽  
Damage Evolution ◽  
Damage Model ◽  
Damage Variable ◽  
Uniaxial Loading ◽  
Experimental Comparison ◽  
Variable Expression ◽  
Cyclic Loading And Unloading ◽  
Sandstone Rock ◽  
Loading And Unloading

In complex rock engineering, understanding the stress state and determining stability and damage evolution are necessary. To more accurately provide a theoretical basis for judging the stress state of bedrock in engineering, this study experimentally addressed the damage evolution of sandstone under loading and unloading conditions. A theoretical relationship between rock resistivity and porosity was obtained according to the Archie formula, which allowed the derivation of the sandstone damage variable expression. Then, sandstone rock samples were used for experimental evaluation, and the feasibility of the theoretically determined damage variable was verified. Finally, through theoretical and experimental comparison analysis, we developed a correlative damage model for sandstone under uniaxial loading and unloading. The results show that the damage variable varies linearly with strain. The proposed correlative equation describes this behavior accurately for loading and unloading conditions. Based on the results of this study, the correlative damage model of sandstone under cyclic loading and unloading conditions can be further improved to be a complete constitutive damage model.

scholarly journals Study on the Effect of Laser Quenching on Fretting Fatigue Life

Metals ◽  
2019 ◽  
Vol 9 (5) ◽  
pp. 566 ◽  
Author(s):  
Hongjian Zhang ◽  
Xufeng Yang ◽  
Haitao Cui ◽  
Weidong Wen
Keyword(s):  
Fatigue Life ◽  
Stress Level ◽  
High Stress ◽  
Fretting Fatigue ◽  
Test System ◽  
Experimental Results ◽  
Laser Quenching ◽  
Error Band ◽  
Hydraulic Servo ◽  
High Stress Level

Laser quenching hardening is one of the most used surface treated technologies. In order to study the effect of laser quenching on the fretting fatigue life, fretting fatigue experiments of TC11 (Ti-6.5Al-1.5Zr-3.5Mo-0.3Si) titanium alloy specimens with different surface conditions were carried out on a special hydraulic servo fatigue test system. The experimental results showed that laser quenching hardening has a good performance in increasing the fretting fatigue lives of the TC11 alloy. However, the effects of laser quenching on fretting fatigue are more obviously at low stress level than at high stress level, the fretting fatigue life was increased by 110.78% at low stress level and 17.56% at high stress level, respectively. Based on the critical plane approach, the traditional SWT (Smith–Watson–Topper) parameter was modified and used to describe the fretting fatigue life of the TC11 alloy after hardening by the consideration of the variations of the hardening layer’s elastic modulus. Compared with the experimental results, all the errors of the predicted results lied in the error band of two.

Sign in / Sign up

Export Citation Format

Share Document