scholarly journals Laboratory Studies of Electric Current Generated during Fracture of Coal and Rock in Rock Burst Coal Mine

2015 ◽  
Vol 2015 ◽  
pp. 1-9 ◽  
Author(s):  
Zhonghui Li ◽  
Enyuan Wang ◽  
Miao He
Keyword(s):  
Crack Propagation ◽  
Electric Current ◽  
Charge Separation ◽  
Roof Rock ◽  
Early Stage ◽  
Rock Fracture ◽  
Failure Process ◽  
Physical And Mechanical Properties ◽  
Coal Particles ◽  
Main Fracture

Experiments show that electric current would be produced in uniaxial compression of coal and roof rock. The electric current of coal shows a rapid increasing tendency when the loading stress is greater than or equal to 0.75σmax which can be regarded as an omen for coal failure. The current of roof rock shows reversal tendency while loading stress is greater than or equal to 0.91σmax and revised from negative to positive at the main fracture and the reversal of current can be regarded as the omen of rock fracture. There are obvious differences in physical and mechanical properties, composition, and failure process between coal and rock. The dominant mechanism of electric current generated by coal is triboelectrification of coal particles and charge separation during crack propagation. The mechanism of electric current of roof rock is piezoelectric effect of quartz materials in the early stage and charge separation during crack propagation in the later stage of loading. It can be found that the rapid increasing and reversal characteristic of electric current can reflect the failure process of coal and roof rock, respectively. Thus, it can be considered the omen of coal and rock failure.

A Fracture Mechanics Approach to Thermal Fatigue Life Prediction of Solder Joints

1990 ◽  
Vol 203 ◽  
Author(s):  
Yi-Hsin Pao
Keyword(s):  
Fracture Mechanics ◽  
Crack Propagation ◽  
Crack Growth ◽  
Thermal Fatigue ◽  
Solder Joints ◽  
Failure Process ◽  
Growth Equation ◽  
Thermal Fatigue Crack ◽  
Runge Kutta Method ◽  
Growth History

ABSTRACTThe approach developed is based on the assumption that thermal fatigue crack propagation in solder joints is primarily controlled by C* and J integrals. The effect of microstructural coarsening on crack propagation is discussed. A fracture criterion, J≥Jc, is used to define the failure of the joints. A crack growth governing equation has been formulated and can be numerically integrated to obtain the crack growth history given stress history as an input. The approach was applied to model the experiment by Wong and Helling [15]. In their experiment, surface-mounted electronic devices using eutectic Pb/Sn solder were tested in thermal cycles of −20 to 100°C and −55 to 125°C. A unified constitutive equation was assumed for the eutectic Pb/Sn solder. An equation for solving the shear stress in the joint was formulated and is coupled with the crack growth equation. Both equations were solved simultaneously by the Runge-Kutta method for the stress-time and crack growth history. The results of the prediction are in a good agreement with the experimental data, which indicates that fracture mechanics may be applied to describe the failure process of solder joints under cyclic thermal loadings.

Numerical Investigation on Mixed Mode (I-II) Fracture Propagation of CCBD Specimens Under Confining Pressure

2021 ◽  
pp. 2050111
Author(s):  
Jiuzhou Huang ◽  
Jianxiong Li ◽  
Xin Pan ◽  
Tianzhou Xie ◽  
Wen Hua ◽  
...  
Keyword(s):  
Crack Propagation ◽  
Numerical Method ◽  
Mixed Mode ◽  
Early Stage ◽  
Relative Length ◽  
Confining Pressure ◽  
Secondary Development ◽  
Weight Functions ◽  
Mode I ◽  
Initiation And Propagation

A new numerical method, verified by the analytical solution of the weight functions and experimental paths, is developed to evaluate the crack initiation and propagation generally in mixed mode (I-II). This numerical method combining the interaction integral method and the maximum tangential stress (MTS) criterion is based on the finite element method of secondary development. The influence of combined confining pressure and diametric forces on crack propagation trajectories for CCBD specimens are studied. It is indicated that the crack propagation direction independent of the confining pressure keeps the same with the line of original crack as the loading angle is equal to [Formula: see text]. But when the loading angle is greater than [Formula: see text], the curvature of the curve trajectory in the early stage of crack propagation increases with a larger confining pressure. Further, it is found that larger values of the loading angle and relative length will make the effect of confining pressure more significant at the early stage of crack growth.

Finite-Element-Simulation of Interfacial Crack Propagation: Cross-Check of Simulation Results with the Essential Work of Interfacial Fracture Method

2006 ◽  
Vol 312 ◽  
pp. 9-14 ◽  
Author(s):  
T. Schüller ◽  
B. Lauke
Keyword(s):  
Fracture Toughness ◽  
Finite Element ◽  
Crack Propagation ◽  
Data Reduction ◽  
Failure Process ◽  
Interfacial Crack ◽  
Interfacial Fracture ◽  
Essential Work ◽  
Strong Argument ◽  
Load Displacement

An advanced finite-element model for the complete failure process of a double notched specimen with crack tip blunting caused by yielding and subsequent crack propagation is used for the simulation of realistic specimens. Cracks in a homogeneous material and bimaterial cracks are studied. The calculated load-displacement curves show generally the shape known from experiments and theoretical considerations. The simulation allows determination of a working range of set up parameters like geometry, test speed or clamping conditions. The numerical model simulates crack propagation on the basis of a criterion which is similar to the energy release rate. The essential work of interfacial fracture method provides a method to determine the fracture toughness from load-displacement curves. This method is well suited to check the numerical simulation because both use an energy based failure criterion. If applied to simulated load-displacement curves the resulting essential work of interfacial fracture should directly match the fracture criterion used as input for the simulation. In fact, the data reduction of the simulated curves results in values for the fracture toughness that almost perfectly match the input values of the simulation. This agreement is a strong argument for the consistency of the simulation and the data reduction scheme.

The Development of Fatigue Crack Propagation Models for Engineering Applications at Elevated Temperatures

1975 ◽  
Vol 97 (4) ◽  
pp. 289-297 ◽  
Author(s):  
B. Tomkins
Keyword(s):  
Fatigue Crack ◽  
Crack Propagation ◽  
Fatigue Crack Propagation ◽  
Elevated Temperatures ◽  
Failure Process ◽  
Propagation Models ◽  
Creep Fatigue ◽  
Creep Cavitation ◽  
Crack Propagation Process

The value of modelling the fatigue crack propagation process is discussed and current models are examined in the light of increasing knowledge of crack tip deformation. Elevated temperature fatigue is examined in detail as an area in which models could contribute significantly to engineering design. A model is developed which examines the role of time-dependent creep cavitation on the failure process in an interactive creep-fatigue situation.

Numerical Studies of End Effect on Crack Propagation Behavior of Brittle Specimen Containing Pre-Existing Crack under Uniaxial Compression

2007 ◽  
Vol 353-358 ◽  
pp. 1049-1052
Author(s):  
Ming Li Huang ◽  
Shan Yong Wang ◽  
Wei Lu ◽  
Wan Cheng Zhu
Keyword(s):  
Crack Propagation ◽  
Uniaxial Compression ◽  
Process Analysis ◽  
Failure Process ◽  
End Effect ◽  
Wing Crack ◽  
Propagation Length ◽  
Propagation Behavior ◽  
Numerical Studies ◽  
Crack Propagation Process

In this paper, a Material Failure Process Analysis code (MFPA2D) was employed to investigate the interaction of end effect zone of specimen with the wing crack propagation inside the brittle specimen containing pre-existing flaws under uniaxial compression comparing with the experimental results. The numerical results show that the shorter the distance between the pre-existing flaw and the specimen's end , the slower the crack propagation process and the shorter wing propagation length is , and vice versa. In addition, the end effect zone was also influenced by the wing crack propagation.

Crack Propagation in Concrete with Silica Particles

2013 ◽  
Vol 842 ◽  
pp. 470-476 ◽  
Author(s):  
Andina Sprince ◽  
Gregor Fischer ◽  
Leonids Pakrastinsh ◽  
Aleksandr Korjakins
Keyword(s):  
Mechanical Properties ◽  
Crack Propagation ◽  
Focal Length ◽  
Digital Camera ◽  
Tensile Load ◽  
Physical And Mechanical Properties ◽  
Compact Tension ◽  
Time Interval ◽  
Area Of Interest ◽  
Representative Area

The propagation of cracking in concrete is a mechanism governing many physical and mechanical properties of the material. The aim of this study was to experimentally investigate the crack propagation of new concrete compositions using image analysis. Several concrete mixes containing microsilica and nanosilica were made. For each composition, Compact Tension (CT) specimens were prepared with dimensions 150x150x12mm. Specimens were subjected to a tensile load. The formation and propagation of the tensile cracks was traced on the surface of the specimens using a high resolution digital camera with 60 mm focal length. Images were captured during testing with a time interval of one second. The compression strength and modulus of elasticity were also determined for reference. The results obtained with this method have shown that it is possible to monitor relatively small displacements on the specimen surface regardless of the scale of the representative area of interest and to evaluate the influence of filler on the cracking properties of concrete.

Crack Propagation Behavior of Asphalt Concrete; Part I: A Study into Influence of Different Materials

2008 ◽  
Vol 385-387 ◽  
pp. 297-300
Author(s):  
Tao Xie ◽  
Ze Zhong Jiang ◽  
Yan Jun Qiu ◽  
Bo Lan
Keyword(s):  
Crack Propagation ◽  
Fracture Resistance ◽  
Failure Process ◽  
Asphalt Mixtures ◽  
Asphalt Pavements ◽  
Cracking Behavior ◽  
Strain Behavior ◽  
Propagation Behavior ◽  
Maintenance And Rehabilitation ◽  
Asphalt Materials

The fracture resistance of asphalt materials significantly influences the service life of asphalt pavements and consequently affects the maintenance and rehabilitation costs of the pavement network. Therefore, there is significant interest in understanding the mechanism of fracture in asphalt pavements and in developing analysis tools that would lead to the selection of asphalt materials with increased fracture resistance. Study of cracking behavior of asphalt mixtures should be conducted in a micro-scale level to have a real simulation of crack propagation. Using SIEMENS SOMATOM plus X-ray CT (computerized tomography) and multi-functional testing rig, a dynamic observation of cracking propagation of hot mix asphalt was conducted in this research. Failure process under compressive pressure was recorded using CT images and CT numbers. The direct responses in density change of Marshall Samples under a CT-compressive process are change of CT numbers. Cracking propagation in the samples can be clearly observed and failure mode and stress-strain behavior can then be simulated. The tests reported provide important theoretical fundamentals to study the cracking behavior and failure mechanism of asphalt mixtures.

Numerical Simulation on AE Characteristics of Rock and Concrete Materials

2007 ◽  
Vol 353-358 ◽  
pp. 961-964 ◽  
Author(s):  
Yu Mei Kang ◽  
Chun An Tang ◽  
Zheng Zhao Liang ◽  
Gen Gye Chen
Keyword(s):  
Crack Propagation ◽  
Failure Process ◽  
Great Influence ◽  
Space Distribution ◽  
Bending Test ◽  
Propagation Path ◽  
Notch Depth ◽  
Crack Propagation Path ◽  
Three Point Bending ◽  
Simulation Results

Based on physical model of three-point-bending test, the AE characteristics of three-point-bending beams with different relative notch depth during the entire loading period was simulated by using RFPA3D(realistic failure process analysis) code. Simulation results show that the relative notch depth affects the AE characteristics significantly. With increasing relative notch depth, the occurrence of AE events decreases remarkably. The stress distribution figures, elastic modulus photo and AE relative energy time-space distribution figures as well as an analysis on the failure process are also provided. Based on the analysis of simulation results, it is concluded that the heterogeneity of rock and concrete has great influence on the crack propagation path, which leads the crack propagation path becoming curvilinear.

scholarly journals Acoustic Emission Multi-Parameter Analysis of Dry and Saturated Sandstone with Cracks under Uniaxial Compression

Energies ◽  
2019 ◽  
Vol 12 (10) ◽  
pp. 1959 ◽  
Author(s):  
Hongru Li ◽  
Rongxi Shen ◽  
Dexing Li ◽  
Haishan Jia ◽  
Taixun Li ◽  
...  
Keyword(s):  
Acoustic Emission ◽  
Uniaxial Compression ◽  
Fractured Rock ◽  
Rock Fracture ◽  
Failure Process ◽  
Parameter Analysis ◽  
Small Scale ◽  
Rock Interaction ◽  
Secondary Cracks ◽  
Ae Signals

In order to study the mechanics and acoustic emission (AE) characteristics of fractured rock under water-rock interaction, dried and saturated sandstone samples with prefabricated double parallel cracks were prepared. Then, uniaxial compression experiments were performed to obtain their AE signals and crack propagation images. The results show that water reduces the strength and fracture toughness of fractured sandstone and enhances plasticity. After saturation, the samples start to crack earlier; the cracks grow slowly; the failure mode is transformed from shear failure along the prefabricated cracks to combined shear and tensile failure; more secondary cracks are produced. The saturated samples release less elastic energy and weaker AE signals in the whole failure process. However, their AE precursor information is more obvious and advanced, and their AE sources are more widely distributed. Compared with dry specimens, the AE frequencies of saturated specimens in the early stage of loading are distributed in a lower frequency domain. Besides, the saturated samples release less complex AE signals which are dominated by small-scale signals with weaker multi-fractal characteristics. After discussion and analysis, it is pointed out that this may be because water makes rock prone to inter-granular fracture rather than trans-granular fracture. The water lubrication also may reduce the amplitude of middle-frequency band signals produced by the friction on the fracture surface. Multi-fractal parameters can provide more abundant precursory information for rock fracture. This is of great significance to the stability of water-bearing fractured rock mass and its monitoring, and is conducive to the safe exploitation of deep energy.

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