Conditions Of Stress Concentration Research Articles

Nonlocal damage evaluation of a sigmoid-based damage model for fibrous biological soft tissues.

The comprehension and modeling of the mechanical behavior of soft biological tissues are essential due to their clinical applications. This knowledge is essential for predicting tissue responses accurately and enhancing our ability to compute the behavior of biological structures and bio-prosthetic devices under specific loading conditions. The current research is centered on modeling the initiation and progression of soft tissues damage, which typically exhibit intricate anisotropic and nonlinear elastic characteristics. For this purpose, the following study presents a comparative analysis of the computational performance of two distinct damage modeling techniques. The first technique employs a well-established damage model, based on a piece-wise exponential damage function as proposed by Calvo et al. (Int J Numer Methods Eng 69:2036-2057, 2007. https://doi.org/10.1002/nme.1825 ). The second approach adopts a sigmoid function, as proposed by López-Campos et al. (Comput Methods Biomech Biomed Eng 23(6):213-223. https://doi.org/10.1080/10255842.2019.1710742 ). The aim of this study is to verify the validity of the López-Campos sigmoid-based damage model to be used in finite element simulation, the implementation of which is unknown. For this proposal, both models were implemented within a commercial Finite Element software package, and their responses to local and non-local damage algorithms were assessed in depth through two standard benchmark tests: a plate with a hole and a ball burst. The results of this study indicate that, for a wide range of cases, such as in-plane stresses, out-plane stresses, stress concentration and contact, all over large displacement conditions, the López-Campos damage model shows a good response to non-local algorithms achieving mesh independence and convergence in all these cases. The results obtained are in line with those obtained for the Calvo's damage model, showing, in addition, larger deformations under in-plane stress and stress concentration conditions and a lower number of iterations under out-plane stress and contact conditions. Consequently, the López-Campos' damage model emerges as a valuable and useful tool in the field of mechanical damage research in biological systems.

The Effects of Undercut Depth and Length on Weldment Mechanical Properties

Undercutting is a fusion welding defect that appears as a groove at the weld metal's toe. An undercut discontinuity forms when welding, particularly when the current is applied at an extremely rapid rate. It decreases the static and fatigue strength of the weld and produces stress concentration at the welding zone. The height of the reinforcement, the weld bead's contact angle, the undercut's breadth, depth, length, and root radius, as well as other factors, affect the stress concentration factor's size. In this study, two mild steel plates with a 20 mm thickness were welded together using gas metal arc welding. Each test plate was machined to have a 30° single bevel groove angle prior to welding. The butt welded plate underwent radiographic NDT testing. A weldment free of defect was created. The weldment was machined into typical test specimens for tensile strength. An undercut defect was simulated by drilling a groove through each tensile test sample. Grooves had different depths and lengths. After that, samples were put through a tensile test. The test findings allowed for the identification of the impacts of groove shape on tensile strength, ductility, and static stress concentration factor.

Determination of Stress Concentration Factor for a Stepped Bar Under Bending Loading: An Artificial Neural Networks Approach

Even today, charts and formulas derived from experimental determinations are used to obtain the stress concentration factor.Stress concentration factors from charts can be converted into numerical values using computational techniques. Stress concentration factor values were collected in a database and an Artificial Neural Network (ANN) model can be developed for improving the database. ANN model provides accuracy in obtaining the stress concentration factors. Using the static stress concentration factor for a stepped bar under a bending load we can quantify the impact of notches in fatigue.

Failure mechanism and control of coal bursts triggered by mining induced seismicity in steeply inclined and extra thick coal seam

With the increase in mining depth, coal bursts have become a major challenge in the safe mining of steeply inclined and extra thick coal seams (SIETCSs). Based on a typical mining induced seismicity triggered coal burst (MSTCB) in SIETCS, a large-scale numerical model was developed using the Universal Distinct Element Code. The numerical model was calibrated and validated by laboratory results and field observations. The stress evolution, crack development and ejection velocity patterns in the MSTCB were analysed, and the effect of mining induced seismicity vibration velocity on the MSTCB was discussed. The results show that a triangular static stress concentration zone is formed in the coal on the roof side. And the high-energy mining induced seismicity leads to high dynamic stresses in the coal at the roof side rib and top of the headentry. Coal bursts occur under the superposition of static and dynamic stresses. The MSTCB results in tensile failure near the headentry surface and shear failure in the depth. The vibration velocity has a significant effect on the roof side rib and top of the headentry, while it has only a slight effect on the working face rib and bottom of the headentry. The dynamic stress and ejection velocity in the roof side rib and top of the headentry are positively correlated with the vibration velocity. Finally, measures for MSTCB prevention were proposed. The findings presented in this study can provide guidance for the prevention and control of MSTCBs in SIETCSs.

Uniform fatigue damage tolerance assessment for additively manufactured and cast Al-Si alloys: An elastic-plastic fracture mechanical approach

• Influence of additively manufacturing and casting on microstructure and porosity characteristics as well as quasi-static and cyclic stress-strain behavior of Al-Si alloys. • Evaluation of Murakami-Noguchi approach and Shiozawa approach for fatigue limit and lifetime estimation, however, both approaches are not sufficient for AM Al-Si alloys. • Linking J integral (elastic-plastic fracture mechanics) including cyclic stress-strain curve by means of morrow parameter (K’, n’), defect size and position, stress amplitude and stress ratio. • New approach enables a uniform fatigue damage tolerance assessment of fatigue lifetime and limit for additively manufactured alsi10mg alloy as well as die-cast and sand-cast alsi7mg alloy. Lightweight Al-Si alloys are used in the automotive and railway industry due to their excellent strength-to-weight ratio and near-net-shape manufacturing. In additive manufacturing and casting, the near-net-shape manufacturing results in a non-homogenous solidification and cooling of the parts, leading to significant local gradient in microstructural and defect features as well as deformation behavior. In this paper, a uniform damage tolerance assessment was developed based on fracture mechanical approaches of Murakami (√area) and Shiozawa for a reliable defect-based mechanical design of fatigue-loaded structures. The linear-elastic fracture mechanical (LEFM) approaches of Murakami and Shiozawa were used to calculate defect-based lifetime curves, where the cyclic stress intensity factor (ΔK) at the failure-initiating defect (√area) was used to describe the local stress concentration conditions, called K-N curves, instead of nominal stress-based S-N curves. The LEFM-based K-N curves did not allow to describe the fatigue behavior in terms of a unified fatigue design of AM and casting material. Therefore, the cyclic stress-strain (CSS) behavior was used for a plasticity-modification of the LEFM approach by calculating the effective cyclic J integral (ΔJ eff ) to plot J-based K-N curves, called Kj-N curves. This elastic-plastic fracture mechanical (EPFM) approach allowed a uniform fatigue damage tolerance (FDT) assessment of AM and cast Al-Si alloys for the HCF regime by FDT law and fatigue limit by FDT limit. Exemplarily, the FDT limit could be used to predict synthetic Haigh diagrams for specific AM and cast batches and derive process- and service-relevant knowledge on the effect of tensile or compressive mean stress.

Uniform fatigue damage tolerance assessment for additively manufactured and cast Al-Si alloys: size and mean stress effects

• Influence of additively manufacturing and casting on microstructure and porosity characteristics as well as quasi-static and cyclic stress-strain behavior of Al-Si alloys • Linear-elastic (LEFM: Murakami, Murakami-Schijve) and elastic-plastic fracture mechanics (EPFM: Fischer) were used for determination of stress intensity factor at failure-initiating defect and plotted in Shiozawa diagrams • LEFM and EPFM enables to consider the size effect within fatigue damage tolerance assessment • Benchmark of Woehler, Murakami, Murakami-Schijve and Fischer approaches for fatigue damage tolerance assessment regarding size effect and mean stress effect, whereby only Fischer approach enables a uniform fatigue damage tolerance assessment The near-net-shape manufacturing in additive manufactured and cast of Al-Si alloys results in a heterogeneous solidification and cooling of the parts, leading to significant gradients in microstructural and defect features as well as deformation behavior. In this paper, an elastic-plastic fracture mechanical model for uniform fatigue damage tolerance assessment of Al-Si alloys was further qualified and extended for a uniform view of different testing volumes as well as various stress ratios between R = -2…0.5 based on the fracture mechanical approaches of Murakami (√area) and Shiozawa for a reliable main crack defect-based mechanical design of fatigue-loaded structures. The linear-elastic fracture mechanical (LEFM) approaches of Murakami, Murakami-Schijve and Shiozawa were used to calculate defect-based lifetime curves, where the cyclic stress intensity factor (ΔK) at the failure-initiating defect (√area) was used to describe the local stress concentration conditions (so-called K-N curves) instead of nominal stress-based S-N curves. The LEFM-based K-N curves did not allow a unified assessment of fatigue behavior. Therefore, the cyclic stress-strain (CSS) behavior (K’, n’) was used for a plasticity-modification of the LEFM approach based on the elastic-plastic fracture mechanical (EPFM) approach of Fischer by calculating the effective cyclic J integral (ΔJ eff ) to plot J-based K-N curves, called Kj-N curves. This EPFM approach could be qualified for a uniform and reliable fatigue damage tolerance assessment of AM and sand cast Al-Si alloys for the HCF regime.

Microstructure, texture, and anisotropic mechanical behavior of selective laser melted maraging stainless steels

In present research, the effect of building orientation on microstructure, texture and mechanical properties of a low carbon maraging steel processed by selective laser melting (SLM) technique is studied. The microstructural characterization and grain structure observations of the fabricated samples are conducted using electron microscopies and electron backscatter diffraction. It is observed that by altering the building orientation from vertical to horizontal, the morphology of the grains changes from columnar-dendritic to equiaxed. In addition, a higher volume fraction of austenite is retained in the horizontal sample compared with the vertically printed sample due to a faster cooling rate, higher degree of micro-segregation, and smaller prior austenite grains. Consequently, a higher strength and better ductility are achieved in the horizontally printed sample. The Taylor factorshows that different obtained tensile properties are not related to the crystallographic texture but are affected by grain size, retained austenite, and stress concentration conditions.

Softening and Jump-Like Deformation of Aluminum Alloys Under Stress Concentration Conditions at a Temperature of 4 K with Decreasing the Stiffness of the Loading System

Softening and Jump-Like Deformation of Aluminum Alloys Under Stress Concentration Conditions at a Temperature of 4 K with Decreasing the Stiffness of the Loading System

Mechanism and Control of Rockburst Induced by Draining Spatial Islands and Squaring

A small-pillar gob-side roadway showed rockburst appearance during the mining of a gob-side working face located in the Shaanxi-Inner Mongolia mining area. This study examines the 2202 gob-side working face of a coal mine in Inner Mongolia as a case study. A stress evolution model was built for the static-stress spatial islands formed by drainage regions and goafs based on the spatial relationships between drainage regions and goafs. The average microseismic frequency and energy of the high-stress zone of spatial islands were at least 1.37 times of those of other zones, validating the presence of spatial islands. The dynamic and static load effects of working face squaring were obtained based on the evolution of the stope roof as well as changes in microseismic data. Microseismically active zones were advanced to 200 m–300 m on working faces. The rockbursts induced by high static loads and dynamic and static loads formed by spatial islands and squaring were calculated. According to calculation results, the critical stress concentration value under high static loads was 3.27; the critical static stress concentration value under dynamic and static loads was 1.81. The superposition of drainage boundary stress, goaf lateral stress, and lead stress might reach the critical stress concentration under dynamic load disturbances, causing rockbursts. A stress adjustment scheme was established, including overall hydraulic fracturing of the external roof of the drainage region, reduction of stoping speed, and pressure relief of large-diameter boreholes. The stress adjustment scheme was implemented on-site and supplemented by monitoring and early warning methods to safely advance by the first squaring region.

The effects of undercut geometry on the static stress concentration factor of welds

Undercutting is a welding defect that appears as a groove in the base metal directly along the edges of the weld metal. It is inevitable in fillet and butt joints if improper welding parameters are used in the operation. It is a discontinuity in the welding that produces stress concentration and lowers the strength of the weld. The stress concentration factor of an undercut is due to the reinforcement angle, undercut width, undercut depth and undercut root radius. In this study, 20 mm thick mild steel plates were welded by automatic gas metal arc welding with the carbon dioxide (CO2) shielding gas process. A single-V butt joint was obtained after welding. Before welding, 30° groove angles were obtained by milling on the longitudinal side of each workpiece. Two plates were welded with several passes. After welding, the weldment was tested with a radiographic non-destructive testing process. A defect-free weldment was obtained. Then, standard tensile test samples were machined from the weldment. A groove was drilled in the heat-affected zone, adjacent to the weld metal boundary on every tensile test sample. Each groove resembled an undercut. The length, root radius and depth of grooves were varied. Then, the samples were broken on a tensile test machine. From the test results, the static stress concentration factor of each groove was calculated. The effects of groove geometry on stress concentration factors were determined.

Investigation of Strong Strata Behaviors in the Close-Distance Multiseam Coal Pillar Mining

According to the new stress distribution pattern and the strong strata behaviors as the characteristics of the coal pillars in the close-distance multiseam coal pillar mining, the common characteristics of different types of overlying coal pillars were summarized and analyzed. Moreover, a theoretical model for the mechanism of strong strata behaviors in the close-distance multiseam coal pillar mining was established, which was validated by the monitoring data of seismic computed tomography CT, microseism, and electromagnetic radiation (EMR). Furthermore, the results of the study indicated that the main factors affecting the strong strata behaviors were the static stress concentration caused by the overlying coal pillars and the dynamic disturbance caused by the fracturing and slipping of the overlying coal pillars and roof under the influence of mining. In the case of Xinzhouyao coal mine, the transmitted stress and lateral support pressure of the overlying coal pillars accounted for 78.3% and 16% of the vertical concentrated stress, respectively, and the areas closer to the overlying coal pillars were more susceptible to dynamic load disturbances. The monitoring results of seismic computed tomography CT and EMR demonstrated the static load stress concentration area was distributed near the overlying coal pillar, and the stress concentration degree was greater in the area of superimposed lateral support pressure and advanced support pressure. Moreover, microseismic spatial positioning revealed that the high-energy microseismic events were mainly concentrated near the overlying large coal pillars and roof. The on-site multiparameter detection results were highly consistent with the characteristics of actual strata behaviors and the conclusions of the theoretical model. This method could provide a reference for the quantitative calculation of stress distribution under similar conditions and the identification of the danger zone of strata behaviors.

Hydrodynamic and Structural Stability Analysis for Shaft Tubular Pump Unit

Hydrodynamic and structural stability directly affect the efficiency and safety of pump units operation. In this paper, we simulated inner flow field of a shaft tubular pump unit through Computational Fluid Dynamics (CFD) and Finite Element Method (FEM) for exploring the blade pressure and dynamic stress characteristics, where first part focus on the hydrodynamic pressure fluctuation on inlet and outlet of impeller and second part focus on dynamic stress distribution in time and frequency domain on pump impeller. Monitoring points are set at the inlet and outlet of impeller to obtain the dynamic pressure, then mapping the time domain data to frequency domain through Fast Fourier Transform (FFT) method. The results show that the pressure fluctuation has strong periodicity, and the fundamental frequency of the pressure fluctuation on the inlet and outlet surfaces is the blade passing frequency and the blade passing frequency respectively, which means the rotation of impeller and rotor stator interaction (RSI) phenomenon between impeller blades and guide vanes are the origin of hydrodynamic pressure fluctuation. Hydrodynamic pressure on impeller blade is applied to the impeller structure to obtain structural responses, results show that maximum dynamic stress appears in the root of impeller blade, the dynamic stress fluctuate in the nearby of static stress concentration and maximum dynamic stress appear in the permissible stress range. In frequency domain, the basic frequency and secondary basic frequency are impeller blade passing frequency and guide vane passing frequency, which indicated that the major reason of impeller dynamic stress fluctuation is water excitation pressure.

Rockburst Monitoring in Deep Coalmines with Protective Coal Panels Using Integrated Microseismic and Computed Tomography Methods

In deep coalmines, longwall panels are subject to high static initial geostress andhigh dynamic stress caused by mining and tunnelling activities. Under the action of high static and dynamic stress, rockburst hazards are very likely to occur. To reduce rockburst risks, protective panels are commonly applied in deep coalmines. However, stress concentration in the protective coal panel often causes rockburst hazards in the gateway of the next longwall panel pending mining. To reduce such type of rockburst, this study firstly proposes a mathematic model to analyse the overall static stress distribution in the protective panel based on the mining practice in Longyun coalmine, Shandong Province, China. To evaluate the stress concentration caused by geological defects in the protective panel, a new rockburst evaluation index is proposed based on the computed tomography (CT) method. Finally, the extent of dynamic stress evolution caused by different working face advancing velocities is determined by microseismic monitoring. Results show that the areas with higher rockburst evaluation indexes are highly associated with the areas with large-energy microseismic events, indicating that the static stress concentration can be accurately identified by the CT method. A medium advancing velocity (4.0 m/s) is recommend during mining the longwall panel, which can ensure mining safety and improve mining productivity simultaneously. The integrated microseismic and CT monitoring methods can be used in other underground projects to guarantee construction safety and productivity.

Study on vertical cross loading fracture of coal mass through hole based on AE-TF characteristics

With the gradual deepening of coal mining, under the action of stress concentration, coal and rock in deep stopes are prone to dynamic disasters such as rock burst and large area pressure. Therefore, using the fracture characteristics of the rapid fracture stage of coal rock mass, the evolution process of damage and fracture of coal rock mass under stress concentration conditions can be effectively analyzed. The experiment takes engineering coal and rock mass as the research object, and uses ultrasonic testing to select test blocks with the same wave velocity and perform central drilling on the test blocks to ensure the same initial damage in the rock mass, avoiding the dispersion of the final loading data of the rock mass caused by various differences. In the test, vertical block loads were applied to test blocks with different apertures, and the coal masses were monitored in real time while loading. Based on the monitoring results, the key failure locations are obtained, and the characteristics of acoustic emission-time–frequency (AF-TF) characteristics and damage failure laws of coal and rock bodies with different pore sizes in the fast rupture stage are analyzed. The experimental results show that: (1) After drilling, the compressive strength, number of acoustic emission events, and accumulation of coal rock masses have been significantly reduced, but after the hole diameter has been excessively increased, the number of events and energy at the final fracture of coal rock masses have increased abnormally; (2) During the rupture stage of the cave coal rock mass, the frequency spectrum changes from cliff-like attenuation to continuous step-down attenuation with increasing aperture. At the same time, the waveform suddenly becomes continuous in the time domain, and the characteristic signal appears concentratedly; (3) Under high-frequency vibration, the non-porous coal rock mass cracks, and finally at the peak, the accumulated stress is quickly released in the manner of tensile failure. However, the low-frequency continuous vibration of the cavern coal rock mass causes the rock mass to be step-graded to release stress, and the key damage guidance leads to the formation of conjugate shrinkage and fracture of the rock mass. It is because with the increase of the hole, the degree of deterioration of the rock mass increases and stress builds up at the hole wall, and finally a rock burst occurs at the hole wall. The study on the fracture of the coal mass in the hole can provide effective theoretical support for the coal rock stress grooming during the excavation of the deep coal mass and the search for key fractures to avoid the occurrence of dynamic disasters.

High-Cycle Fatigue of Single-Crystal Heat-Resistant Nickel Alloy under the Conditions of Stress Concentration

High-Cycle Fatigue of Single-Crystal Heat-Resistant Nickel Alloy under the Conditions of Stress Concentration

THE USE OF NONLOCAL CRITERIA IN FORECASTING FRACTURE OF QUASI-BRITTLE MATERIAL WITH A HOLE UNDER COMPRESSION

The study is aimed at the development of the new failure criteria for quasi-brittle materials in conditions of stress concentration. The possibility of using non-local failure criteria for description of the brittle, quasi-brittle and ductile fracture of the materials with notches is analyzed. The general feature of these criteria consists in the introduction of the internal dimension characterizing the structure of the material, which provides the possibility of describing a large-scale effect in conditions of the stress concentration and thereby expand the area of their application compared to traditional criteria though it is limited to the cases of brittle or quasi-brittle fracture with a small pre-ffacture zone. To broaden the scope of their application to quasi-brittle fracture with a developed pre-fracture zone we propose to abandon the hypothesis about the size of the pre-fracture zone as a constant related only to the structure of the material. A number of the new nonlocal criteria, which are the development of the criteria of the mean stress and fictitious crack, are developed, substantiated from the physical standpoint, and proved experimentally. These criteria contain a complex parameter characterizing the size of the pre-fracture zone and taking into account not only the structure, but also the ductile properties of the material, specimen geometry and loading conditions. The expressions for the critical pressure in the problem of tensile crack formation upon compression of the samples of geomaterials with a circular hole are derived. The results of calculations match rather well the experimental data on the destruction of drilled gypsum slabs.

Fatigue failure analysis of roll steel pins from a chain assembly: Fracture mechanism and numerical modeling

The current study is focused on the investigation of the failure case history pertaining to the in-service fractured steel pins of a chain assembly installed in a continuous cold drawing machine. The findings of the present investigation showed that the pins failed due to multiple-origin rotating bending fatigue under low applied load, due to the application of tensile and/or bending stresses, initiated from the pin circumference. The multiple-crack initiation is consistent to severe stress concentration conditions, as imposed by the low fillet radius attributed to the original pin design. No microstructural abnormalities were detected, that could have been correlated to the principal cause of failure. In the context of the present evaluation, analytical methods such as visual inspection, optical microscopy, SEM fractography and microhardness testing were utilized. Moreover, a finite element analysis of the assembled chain was performed in order to investigate the stress distribution during the operation of the chain and to formulate a sound quantitative approach which will assist in better understanding of chain/pin loading conditions. The primarily insufficient component design resulted in high stress concentration factors interacted with the soft annealed material used for the component and caused fatigue under the presence of fluctuating stresses.

Numerical simulation on failure effect of mining-induced dynamic loading and its influential factors

Rock burst, a serious seismic hazard in underground coal mining, is usually induced by the coupling effect of static stress and mining-induced dynamic loading. This paper chosen an underground longwall face (LW10302) in Baodian Coal Mine as the numerical simulation model, selecting measured tremor wave which located about 150 m above the goafing of LW10301 as dynamic source, and the failure effect of dynamic loading on coal seam entry and its influential factors can be simulated systematically by FLAC3D. By changing source energy, source location, coal-rock property, the simulation results show that failure effect of dynamic source is more sensitive to source location, followed closely by source energy, and then the rock property. That is, dynamic disturbance is deeply influenced by source location, which is decreased in exponential attenuation with the increasing of transmission distance, while it also increases largely with the source energy increasing. Meanwhile, Burst effect of dynamic source can also be reduced duo to rock integrity reduction and intensity weakening, which the corresponding dynamic loading can be decreased to even less than 40%, but the influence degree may be reduced in the condition of shorter transmission distance. Moreover, the occurrence of rock burst also depends on static stress field around the coal face. Thus, the corresponding measures should be carried out simultaneously to reduce the disturbance effect of dynamic source and static stress concentration. The conclusions can provide theoretical reference to rock burst controlling in underground mining.

Ductile-Brittle Transition in Geomaterials, Caused by Tensile Stress Concentration

The possibility of using known nonlocal and stress gradient fracture criteria to describe brittle, quasi-brittle, and ductile fracture of materials with openings is analyzed. A common property of these criteria is the introduction of intrinsic material length characterizing its structure, which allows one to describe the size effect in conditions of stress concentration. At the same time, the scope of application of nonlocal criteria is limited to cases of brittle or quasi-brittle fracture with a small fracture process zone. To expand the scope of application, new fracture criteria are proposed, which are the development of the average stress criterion, and the stress gradient criterion, and which contain a complex parameter that characterizes the size of the fracture process zone and accounts not only for the material structure, but also plastic properties of the material, geometry of the sample, and its loading conditions. Expressions are obtained for the critical pressure in the problem of the formation of tensile cracks under compression in the samples of geomaterials with a circular hole. The calculation results are in good agreement with the experimental data on the fracture of drilled gypsum plates.

Dynamic failure risk of coal pillar formed by irregular shape longwall face: A case study

Irregular shape workface would result in the presence of coal pillar, which leads to high stress concentration and possibly induces coal bumps. In order to study the coal bump mechanism of pillars, static and dynamic stress overlapping (SDSO) method was proposed to explain the impacts of static stress concentration and tremors induced by mining activities. The stress and deformation in surrounding rock of mining face were analyzed based on the field case study at 1303 workface in Zhaolou Coal Mine in China. The results illustrate that the surrounding rock of a workface could be divided into four different zones, i.e., residual stress zone, stress decrease zone, stress increase zone and original stress zone. The stress increase zone is prone to failure under the SDSO impact loading conditions and will provide elastic energy for inducing coal bump. Based on the numerical modelling results, the evolution of static stress in coal pillar as the size of gob increasing was studied, and the impact of dynamic stress was investigated through analyzing the characteristics of tremor activities. The numerical results demonstrate the peak value of vertical stress in coal pillar rises from about 30 MPa with mining distance 10 m to 52.6 MPa with mining distance 120 m, and the location of peak stress transfers to the inner zone of coal pillars as the workface moves forward. For the daily tremor activities, tremors with high energy released indicate high dynamic stress disturbance on the surrounding rock, therefore, the impact of dynamic stressing is more serious during workface extension period because the tremor frequency and average energy after workface extension are higher than those before the workface extension.