To elucidate the dynamic characteristics of in-situ methane deflagration in coalbed methane wellbores and its mechanisms for fracturing coal rock,this study first developed a simulation experimental system specificall...To elucidate the dynamic characteristics of in-situ methane deflagration in coalbed methane wellbores and its mechanisms for fracturing coal rock,this study first developed a simulation experimental system specifically designed for methane in-situ deflagration fracturing.This experimental system,which is capable of withstanding pressures up to 150 MPa and meanwhile applying axial and confining pressures of up to 50 MPa to rock cores,enables the coupled simulation on methane deflagration and rock core fracturing processes.With the aid of this experimental system,physical simulation experiments on in-situ methane deflagration fracturing were conducted,and the following findings were obtained.Methane deflagration loads in enclosed wellbores exhibit characteristics of multi-level pulsed oscillation.With the rise of initial gas pressure,the peak deflagration load increases approximately linearly,with the pressure amplification factor spanning from 23.14 to 31.10,and its peak loading rate grows exponentially.Accordingly,the fracture volume and fracture porosity augment.To be specific,when the initial gas pressure rises from 0.6 to 2.4 MPa,the fracture volume and fracture porosity augment by factors of 14.0 and 8.73,respectively.The fractal dimension of spatial distribution of fractures also increases with the rise of deflagration load,indicating that a higher deflagration load conduces to the development of a larger and more complex fracture network.Methane deflagration fracturing is characterized as a composite fracture mode that involves the impact of strong stress waves and the driving force of high-pressure fluids.The primary factors influencing damage to coal-rock include the high-stress impact in the initial stage of deflagration,the fluid pressure driving effect in the middle stage,and the thermal shock resulting from high temperatures in the later stage.展开更多
In rock engineering,the cyclic shear characteristics of rough joints under dynamic disturbances are still insufficiently studied.This study conducted cyclic shear experiments on rough joints under dynamic normal loads...In rock engineering,the cyclic shear characteristics of rough joints under dynamic disturbances are still insufficiently studied.This study conducted cyclic shear experiments on rough joints under dynamic normal loads to assess the impact of shear frequency(f_(h))and shear displacement amplitude(u_(d))on the frictional properties of the joint.The results reveal that within a single shearing cycle,the normal displacement negatively correlates with the dynamic normal force.As the shear cycle number increases,the joint surface undergoes progressive wear,resulting in an exponential decrease in the peak normal displacement.In the cyclic shearing procedure,the forward peak values of shear force and friction coefficient display larger fluctuations at either lower or higher shear frequencies.However,under moderate shear frequency conditions,the changes in the shear strength of the joint surface are smaller,and the degree of degradation post-shearing is relatively limited.As the shear displacement amplitude increases,the range of normal deformation within the joint widens.Furthermore,after shearing,the corresponding joint roughness coefficient trend shows a gradual decrease with an increasing shear displacement amplitude,while varying with the shearing frequency in a pattern that initially rises and then falls,with a turning point at 0.05 Hz.The findings of this research contribute to a profound comprehension of the cyclic frictional properties of rock joints under dynamic disturbances.展开更多
This paper establishes a method for identifying and locating dynamic loads in time-varying systems.The proposed method linearizes time-varying parameters within small time units and uses the Wilson-θ inverse analysis...This paper establishes a method for identifying and locating dynamic loads in time-varying systems.The proposed method linearizes time-varying parameters within small time units and uses the Wilson-θ inverse analysis method to solve modal loads of each order at each time step.It then uses an exhaustive method to determine the load position.Finally,it calculates the time history of the load.Simulation examples demonstrate how the number of measuring points and step size affect load identi-fication accuracy,verifying that this algorithm achieves good identification accuracy for loads under resonance conditions.Additionally,it explores how noise affects load position and recognition accuracy,while providing a solution.Simulation examples and experimental results demonstrate that the proposed method can identify both the time history and position of loads simultaneously with high identification accuracy.展开更多
Based on MTS Landmark 370.50 rock dynamic and static load fatigue test system and acoustic emission(AE)monitoring method,the damage characteristics and energy evolution law of high static load coal-rock combination(CR...Based on MTS Landmark 370.50 rock dynamic and static load fatigue test system and acoustic emission(AE)monitoring method,the damage characteristics and energy evolution law of high static load coal-rock combination(CRC)under the influence of dynamic load parameters were studied.The main results are as follows:1)Dynamic load increases the rheological properties and damage fracture development of CRC.With the increase of the amplitude and frequency of the dynamic load,the number of dynamic load cycles required for the failure of the CRC decreases,the irreversible strain increases,and the failure of sample accelerates;2)The AE positioning events during the loading process of the specimen decrease with the increase of the dynamic load amplitude,and increase with the increase of the dynamic load frequency;3)The fractal dimension,total energy and cumulative elastic energy of the broken particles of the CRC increase with the increase of the amplitude and frequency of the dynamic load.The fractal dimension corresponding to the increase of the dynamic load frequency is larger,and the energy and cumulative elastic energy corresponding to the increase of the dynamic load amplitude are larger.展开更多
Through-silicon via(TSV)is an important technique in three-dimension integration.The mechanical performance of TSV-Cu is critical to the electrical performance and signal transmission.In this work,the deformation of s...Through-silicon via(TSV)is an important technique in three-dimension integration.The mechanical performance of TSV-Cu is critical to the electrical performance and signal transmission.In this work,the deformation of single-crystalline TSV-Cu during annealing process was studied using molecular dynamics method.The protrusion morphology and protrusion height of Cu column were revealed.The protrusion height curves can be divided into four stages:slow increase,fast increase,fast decrease,and saturation.During the deformation process,the main deformation mode is temporary amorphous region followed by residual dislocations.The influences of annealing temperatures,heating rates,and column sizes on protrusion height were studied.Results show that the residual protrusion height increases with increasing annealing temperatures and decreasing heating rates.The residual protrusion height increases with increasing column sizes in terms of column diameter and length.This work provides new insights into understanding the mechanical performance of nano-TSV-Cu.展开更多
In the civil and mining industries,bolts are critical components of support systems,playing a vital role in ensuring their stability.Glass fibre reinforced polymer(GFRP)bolts are widely used because they are corrosion...In the civil and mining industries,bolts are critical components of support systems,playing a vital role in ensuring their stability.Glass fibre reinforced polymer(GFRP)bolts are widely used because they are corrosion-resistant and cost-effective.However,the damage mechanisms of GFRP bolts under blasting dynamic loads are still unclear,especially compared to metal bolts.This study investigates the cumulative damage of fully grouted GFRP bolts under blasting dynamic loads.The maximum axial stress at the tails of the bolts is defined as the damage variable,based on the failure characteristics of GFRP bolts.By combining this with Miner's cumulative damage theory,a comprehensive theoretical and numerical model is established to calculate cumulative damage.Field data collected from the Jinchuan No.3 Mining Area,including GFRP bolts parameters and blasting vibration data are used for further analysis of cumulative damage in fully grouted GFRP bolts.Results indicate that with an increasing number of blasts,axial stress increases in all parts of GFRP bolts.The tail exhibits the most significant rise,with stress extending deeper into the anchorage zone.Cumulative damage follows an exponential trend with the number of blasts,although the incremental damage per blast decelerates over time.Higher dynamic load intensities accelerate damage accumulation,leading to an exponential decline in the maximum loading cycles before failure.Additionally,stronger surrounding rock and grout mitigate damage accumulation,with the effect of surrounding rock strength being more pronounced than that of grout.In contrast,the maximum axial stress of metal bolts increases quickly to a certain point and then stabilizes.This shows a clear difference between GFRP and metal bolts.This study presents a new cumulative damage theory that underpins the design of GFRP bolt support systems under blasting conditions,identifies key damage factors,and suggests mitigation measures to enhance system stability.展开更多
Red clay,widely used as a subgrade material in southern China,requires a reliable evaluation of its dynamic behavior to ensure infrastructure safety.Long-term cyclic triaxial tests were conducted on red clay from typi...Red clay,widely used as a subgrade material in southern China,requires a reliable evaluation of its dynamic behavior to ensure infrastructure safety.Long-term cyclic triaxial tests were conducted on red clay from typical,complex subway subgrades to investigate its dynamic properties and shakedown behavior under intermittent cyclic loading.Results show that intermittent cyclic loading,especially with multiple amplitudes,causes greater axial plastic strain and lower post-cyclic strength than continuous loading.These effects diminish with increasing confining pressure.Notably,axial strain partially recovers during loading intervals,with recovery ratios depending on the number and sequence of pauses.Based on the rules of cumulative plastic strain rates and cumulative plastic strain increments,shakedown behavior for red clay under intermittent cyclic loading is divided into three categories:plastic shakedown,critical shakedown,and plastic creep.A quantitative shakedown limit criterion is proposed using the Boltzmann function.Shakedown behavior significantly influences the post-cyclic strengths,and the influence diminishes as confining pressure increases.Samples exhibiting plastic creep and plastic shakedown behavior have the lowest and highest strengths,and those with critical shakedown behaviors have medium strengths.Cyclic loading with relatively low-stress amplitude causes a hardening effect,while cyclic loading intermittence or cyclic loading with relatively high-stress amplitude causes a degradation effect,and both effects are mitigated by higher confining pressures.展开更多
The frequent or occasional impact loads pose serious threats to the service safety of conventional concrete structures in tunnel.In this paper,a novel three-dimensional mesoscopic model of steel fiber reinforced concr...The frequent or occasional impact loads pose serious threats to the service safety of conventional concrete structures in tunnel.In this paper,a novel three-dimensional mesoscopic model of steel fiber reinforced concrete(SFRC)is constructed by discrete element method.The model encompasses the concrete matrix,aggregate,interfacial transition zone and steel fibers,taking into account the random shape of the coarse aggregate and the stochastic distribution of steel fibers.It captures microscopic-level interactions among the coarse aggregate,steel fibers,and matrix.Subsequently,a comprehensive procedure is formulated to calibrate the microscopic parameters required by the model,and the reliability of the model is verified by comparing with the experimental results.Furthermore,a coupled finite difference method-discrete element method approach is used to construct the model of the split Hopkinson pressure bar.Compression tests are simulated on SFRC specimens with varying steel fiber contents under static and dynamic loading conditions.Finally,based on the advantages of DEM analysis at the mesoscopic level,this study analyzed mechanisms of enhancement and crack arrest in SFRC.It shed a light on the perspectives of interface failure process,microcrack propagation,contact force field evolution and energy analysis,offering valuable insights for related mining engineering applications.展开更多
A new dimensionless number is proposed for dynamic plastic deformation analysis of clamped circular plates under underwater explosion loads by introducing dimensional analysis method to the basic dynamical governing e...A new dimensionless number is proposed for dynamic plastic deformation analysis of clamped circular plates under underwater explosion loads by introducing dimensional analysis method to the basic dynamical governing equations of circular plates.The relation between dimensionless final plastic deformation of circular plates and the new dimensionless number is established based on massive underwater explosion test data.Meanwhile,comparative analysis was discussed with two other published dimensionless parameters which indicated the new dimensionless number proposed in this paper is more effective and extensive to predict the dynamic plastic response of circular plates under underwater explosion condition.展开更多
Web pillars enduring complex coupled loads are critical for stability in high-wall mining.This study develops a dynamic failure criterion for web pillars under non-uniform loading using catastrophe theory.Through the ...Web pillars enduring complex coupled loads are critical for stability in high-wall mining.This study develops a dynamic failure criterion for web pillars under non-uniform loading using catastrophe theory.Through the analysis of the web pillar-overburden system’s dynamic stress and deformation,a total potential energy function and dynamic failure criterion were established for web pillars.An optimizing method for web pillar parameters was developed in highwall mining.The dynamic criterion established was used to evaluate the dynamic failure and stability of web pillars under static and dynamic loading.Key findings reveal that vertical displacements exhibit exponential-trigonometric variation under static loads and multi-variable power-law behavior under dynamic blasting.Instability risks arise when the roof’s tensile strength-to-stress ratio drops below 1.Using catastrophe theory,the bifurcation setΔ<0 signals sudden instability.The criterion defines failure as when the unstable web pillar section length l1 exceeds the roof’s critical collapse distance l2.Case studies and simulations determine an optimal web pillar width of 4.6 m.This research enhances safety and resource recovery,providing a theoretical framework for advancing highwall mining technology.展开更多
This study designs four types of liquid-filled cylindrical shell structures to investigate their protection characteristics against explosive shock waves and high-speed fragments.Bare charge and charge-driven prefabri...This study designs four types of liquid-filled cylindrical shell structures to investigate their protection characteristics against explosive shock waves and high-speed fragments.Bare charge and charge-driven prefabricated fragments are employed to examine the damage under blast shock waves and combined blast and fragments loading on various liquid-filled cylindrical shell structures.The test results are compared to numerical calculations and theoretical analysis for the structure's deformation,the liquid medium's movement,and the pressure waves'propagation characteristics under different liquid-filling methods.The results showed that the filling method influences the blast protection and the struc-ture's energy absorption performance.The external filling method reduces the structural deformation,and the internal filling method increases the damage effect.The gapped internal filling method improves the structure's energy absorption efficiency.The pressure wave loading on the liquid-filled cylindrical shell structure differs depending on filling methods.Explosive shock waves and high-speed fragments show a damage enhancement effect on the liquid-filled cylindrical shell structure,depending on the thickness of the internal liquid container layer.The specific impulse on the inner surface of the cylindrical shell positively correlates to the radial deformation of the cylindrical shell structure,and the external liquid layer limits the radial structural deformation.展开更多
Controllable shock wave fracturing is an innovative engineering technique used for shale reservoir fracturing and reformation.Understanding the anisotropic fracture mechanism of shale under impact loading is vital for...Controllable shock wave fracturing is an innovative engineering technique used for shale reservoir fracturing and reformation.Understanding the anisotropic fracture mechanism of shale under impact loading is vital for optimizing shock wave fracturing equipment and enhancing shale oil production.In this study,using the well-known notched semi-circular bend(NSCB)sample and the novel double-edge notched flattened Brazilian disc(DNFBD)sample combined with a split Hopkinson pressure bar(SHPB),various dynamic anisotropic fracture properties of Lushan shale,including failure characteristics,fracture toughness,energy dissipation and crack propagation velocity,are comprehensively compared and discussed under mode Ⅰ and mode Ⅱ fracture scenarios.First,using a newly modified fracture criterion considering the strength anisotropy of shale,the DNFBD specimen is predicted to be a robust method for true mode Ⅱ fracture of anisotropic shale rocks.Our experimental results show that the dynamic mode Ⅱ fracture of shale induces a rougher and more complex fracture morphology and performs a higher fracture toughness or fracture energy compared to dynamic mode Ⅰ fracture.The minimal fracture toughness or fracture energy occurs in the Short-transverse orientation,while the maximal ones occur in the Divider orientation.In addition,it is interesting to find that the mode Ⅱ fracture toughness anisotropy index decreases more slowly than that in the mode Ⅰ fracture scenario.These results provide significant insights for understanding the different dynamic fracture mechanisms of anisotropic shale rocks under impact loading and have some beneficial implications for the controllable shock wave fracturing technique.展开更多
Under external disturbances,the shear mechanical responses and debonding failure mechanisms at anisotropic interfaces of anchoring system composed of multiphase media are inherently difficult to characterize due to th...Under external disturbances,the shear mechanical responses and debonding failure mechanisms at anisotropic interfaces of anchoring system composed of multiphase media are inherently difficult to characterize due to the concealment nature of interfacial interactions.This study establishes an equivalent shear model for a bolt-resin-rock anchoring system and conducts direct shear tests under dynamic normal load(DNL)boundary from both laboratory experiments and discrete element method(DEM)simulations.The research investigates the influence of normal dynamic load amplitude(An)and rock type on shear strength parameters,elucidating the evolutionary characteristics and underlying mechanisms of shear load and normal displacement fluctuations induced by cyclic normal loading,with maximum shear load decreasing by 36.81%to 46.94%as An increases from 10%to 70%when rock type varies from coal to limestone.Through analysis of strain field evolution,the critical impact of rock type on localization of shear failure surface is revealed,with systematic summarization of differentiated wear characteristics,failure modes,and key controlling factors associated with shear failure surface.Mesoscopic investigations enabled by DEM simulations uncover the nonuniform distribution of contact force chains within the material matrix and across the anisotropic interfaces under various DNL boundaries,clarify rock type dependent crack propagation pathways,and quantitatively assess the damage extent of shear failure surface,with the anisotropic interface damage factor increasing from 34.9%to 56.6%as An rises from 10%to 70%,and decreasing from 49.6%to 23.4%as rock type varies from coal to limestone.展开更多
This work reviews models and methods for determining the dynamic response of pavements to moving vehicle loads in the framework of continuum-based three dimensional models and linear theories.This review emphasizes th...This work reviews models and methods for determining the dynamic response of pavements to moving vehicle loads in the framework of continuum-based three dimensional models and linear theories.This review emphasizes the most representative models and methods of analysis in the existing literature and illustrates all of them by numerical examples.Thus,13 such examples are presented here in some detail.Both flexible and rigid(concrete)pavement models involving simple and elaborate cases with respect to geometry and material behavior are considered.Thus,homogeneous or layered half-spaces with isotropic or cross-anisotropic and elastic,viscoelastic or poroelastic properties are considered.The vehicles are modeled as simple point or distributed loads or discrete spring-mass-dashpot system moving with constant or variable velocity.The dynamic response of the above pavement-vehicle systems is obtained by analytical/numerical or purely numerical methods of solution.Analytical/numerical methods have mainly to do with Fourier transforms or complex Fourier series with respect to both space and time.Purely numerical methods involve the finite element method(FEM)and the boundary element method(BEM)working in time or frequency domain.Critical discussions on the advantages and disadvantages of the various pavement-vehicle models and their methods of analysis are provided and the effects of the main parameters on the pavement response are determined through parametric studies and presented in the examples.Finally,conclusions are provided and suggestions for future research are made.展开更多
In order to research the concrete archaized buildings with lintel-column joint,2 specimens were tested under dynamic experiment.The failure characteristics,skeleton curves,mechanical behavior such as the load-displace...In order to research the concrete archaized buildings with lintel-column joint,2 specimens were tested under dynamic experiment.The failure characteristics,skeleton curves,mechanical behavior such as the load-displacement hysteretic loops,load carrying capacity,degradation of strength and stiffness,ductility and energy dissipation of the joints were analyzed.The results indicate that comparies with the lintel-column joints,the loading capacity and energy dissipation of the concrete archaized buildings with dual lintel-column joints are higher,and the hysteretic loops is in plump-shape.However,the displacement ductility coefficient is less than that of lintel-column joints.Both of them of the regularity of rigidity degeneration are basically the same.Generally,the joints have the good energy dissipation capacity.And the concrete archaized buildings with lintel-column joints exhibit excellent seismic behavior.展开更多
Borehole pressure relief helps prevent rock bursts.However,this may change the physical and mechan-ical properties of the surrounding rock,affect the variation of the plastic zone of the roadway,and lead to the failur...Borehole pressure relief helps prevent rock bursts.However,this may change the physical and mechan-ical properties of the surrounding rock,affect the variation of the plastic zone of the roadway,and lead to the failure of roadway support,thus threatening the safety of the roadway.In this paper,the variable angle shear test of drilled specimens under the action of static and dynamic loads is used to study the evolution of mechanical parameters of the specimens and their influence on the plastic zone of the sur-rounding rock.The shear strength decreases linearly with the increase of drilling diameter.With the increase of pre-static load level and dynamic load amplitude,the cohesion first increases and then decreases,and the internal friction angle decreases.Moreover,the shear failure surface changes from rough to smooth.The reasons include that the static load enhances the tooth cutting effect and the repeated friction of cracks caused by the dynamic load.Borehole pressure relief leads to an increase in the radius of the plastic zone of the surrounding rock following a quadratic function.The research results of this paper provide a theoretical basis for designing drilling unloading parameters and supporting parameters for rock burst roadways.展开更多
Stress waves propagate along vertical,radial and circumferential directions when a non-uniformly distributed load is applied at one end of a three-dimensional shaft.As a result,the receiving signals are usually mixed ...Stress waves propagate along vertical,radial and circumferential directions when a non-uniformly distributed load is applied at one end of a three-dimensional shaft.As a result,the receiving signals are usually mixed with undesired interference components,often featuring as high-frequency fluctuations.Previous studies have revealed that sectional geometry(shape and size)greatly affects the high-frequency interference.In this study,low strain dynamic testing on full-scale X-section concrete is conducted in order to investigate the influences of high-frequency interference on velocity responses at the pile head.Emphasis is placed on the frequency and peak value of interference waves at various receiving points.Additionally,the effects of the geometrical,and mechanical properties of the pile shaft on high-frequency interference are elaborated on through the three-dimensional finite element method.The results show that the measured wave is obscured by interference waves superposed by two types of high-frequency components.The modulus and cross-sectional area are contributing factors to the frequency and peak value of the interference waves.On the other hand,the position with the least interference is determined,to some extent,by the accurate shape of the X-section.展开更多
The specialized equipment utilized in long-line tunnel engineering is evolving towards large-scale,multifunctional,and complex orientations.The vibration caused by the high-frequency units during regular operation is ...The specialized equipment utilized in long-line tunnel engineering is evolving towards large-scale,multifunctional,and complex orientations.The vibration caused by the high-frequency units during regular operation is supported by the foundation of the units,and the magnitude of vibration and the operating frequency fluctuate in different engineering contexts,leading to variations in the dynamic response of the foundation.The high-frequency units yield significantly diverse outcomes under different startup conditions and times,resulting in failure to meet operational requirements,influencing the normal function of the tunnel,and causing harm to the foundation structure,personnel,and property in severe cases.This article formulates a finite element numerical computation model for solid elements using three-dimensional elastic body theory and integrates field measurements to substantiate and ascertain the crucial parameter configurations of the finite element model.By proposing a comprehensive startup timing function for high-frequency dynamic machines under different startup conditions,simulating the frequency andmagnitude variations during the startup process,and suggesting functions for changes in frequency and magnitude,a simulated startup schedule function for high-frequency machines is created through coupling.Taking into account the selection of the transient dynamic analysis step length,the dynamic response results for the lower dynamic foundation during its fundamental frequency crossing process are obtained.The validation checks if the structural magnitude surpasses the safety threshold during the critical phase of unit startup traversing the structural resonance region.The design recommendations for high-frequency units’dynamic foundations are provided,taking into account the startup process of the machine and ensuring the safe operation of the tunnel.展开更多
The damage properties of two types of rocks under dynamic loading are studied. The shock induced experiments are done using planar impact technique on the one? stage light gas gun, and the ultrasonic tests on the da...The damage properties of two types of rocks under dynamic loading are studied. The shock induced experiments are done using planar impact technique on the one? stage light gas gun, and the ultrasonic tests on the damaged rocks have been made by use of the ultrasonic pulse? transmission method. The shock induced damage of rock is related to the shock speed and the attenuation coefficient of sonic wave, and the latter reflects the damage degree in rock fairly well. The attenuation coefficient α can be used as main damage parameter for constructing damage model of rock under dynamic loading.展开更多
Nonlinear amphibious vehicle rolling under regular waves and wind load is analyzed by a single degree of freedom system.Considering nonlinear damping and restoring moments,a nonlinear rolling dynamical equation of amp...Nonlinear amphibious vehicle rolling under regular waves and wind load is analyzed by a single degree of freedom system.Considering nonlinear damping and restoring moments,a nonlinear rolling dynamical equation of amphibious vehicle is established.The Hamiltonian function of the nonlinear rolling dynamical equation of amphibious vehicle indicate when subjected to joint action of periodic wave excitation and crosswind,the nonlinear rolling system degenerates into being asymmetric.The threshold value of excited moment of wave and wind is analyzed by the Melnikov method.Finally,the nonlinear rolling motion response and phase portrait were simulated by four order Runge-Kutta method at different excited moment parameters.展开更多
基金National Key Research and Development Program of China,2020YFA0711800,Ting LiuNational Natural Science Foundation of China,52274241,Ting Liu,52474261,Ting Liu+2 种基金Basic Research Program of Jiangsu,BK20240207,Ting Liuthe Fundamental Research Funds for the Central Universities(2023KYJD1007)China Postdoctoral Science Foundation(2022M722672).
文摘To elucidate the dynamic characteristics of in-situ methane deflagration in coalbed methane wellbores and its mechanisms for fracturing coal rock,this study first developed a simulation experimental system specifically designed for methane in-situ deflagration fracturing.This experimental system,which is capable of withstanding pressures up to 150 MPa and meanwhile applying axial and confining pressures of up to 50 MPa to rock cores,enables the coupled simulation on methane deflagration and rock core fracturing processes.With the aid of this experimental system,physical simulation experiments on in-situ methane deflagration fracturing were conducted,and the following findings were obtained.Methane deflagration loads in enclosed wellbores exhibit characteristics of multi-level pulsed oscillation.With the rise of initial gas pressure,the peak deflagration load increases approximately linearly,with the pressure amplification factor spanning from 23.14 to 31.10,and its peak loading rate grows exponentially.Accordingly,the fracture volume and fracture porosity augment.To be specific,when the initial gas pressure rises from 0.6 to 2.4 MPa,the fracture volume and fracture porosity augment by factors of 14.0 and 8.73,respectively.The fractal dimension of spatial distribution of fractures also increases with the rise of deflagration load,indicating that a higher deflagration load conduces to the development of a larger and more complex fracture network.Methane deflagration fracturing is characterized as a composite fracture mode that involves the impact of strong stress waves and the driving force of high-pressure fluids.The primary factors influencing damage to coal-rock include the high-stress impact in the initial stage of deflagration,the fluid pressure driving effect in the middle stage,and the thermal shock resulting from high temperatures in the later stage.
基金funding support from the National Natural Science Foundation of China(Grant Nos.52174092 and 51904290)the Natural Science Foundation of Jiangsu Province,China(Grant No.BK20220157).
文摘In rock engineering,the cyclic shear characteristics of rough joints under dynamic disturbances are still insufficiently studied.This study conducted cyclic shear experiments on rough joints under dynamic normal loads to assess the impact of shear frequency(f_(h))and shear displacement amplitude(u_(d))on the frictional properties of the joint.The results reveal that within a single shearing cycle,the normal displacement negatively correlates with the dynamic normal force.As the shear cycle number increases,the joint surface undergoes progressive wear,resulting in an exponential decrease in the peak normal displacement.In the cyclic shearing procedure,the forward peak values of shear force and friction coefficient display larger fluctuations at either lower or higher shear frequencies.However,under moderate shear frequency conditions,the changes in the shear strength of the joint surface are smaller,and the degree of degradation post-shearing is relatively limited.As the shear displacement amplitude increases,the range of normal deformation within the joint widens.Furthermore,after shearing,the corresponding joint roughness coefficient trend shows a gradual decrease with an increasing shear displacement amplitude,while varying with the shearing frequency in a pattern that initially rises and then falls,with a turning point at 0.05 Hz.The findings of this research contribute to a profound comprehension of the cyclic frictional properties of rock joints under dynamic disturbances.
基金supported by the Priority Academic Program Development of Jiangsu Higher Education Institutions.
文摘This paper establishes a method for identifying and locating dynamic loads in time-varying systems.The proposed method linearizes time-varying parameters within small time units and uses the Wilson-θ inverse analysis method to solve modal loads of each order at each time step.It then uses an exhaustive method to determine the load position.Finally,it calculates the time history of the load.Simulation examples demonstrate how the number of measuring points and step size affect load identi-fication accuracy,verifying that this algorithm achieves good identification accuracy for loads under resonance conditions.Additionally,it explores how noise affects load position and recognition accuracy,while providing a solution.Simulation examples and experimental results demonstrate that the proposed method can identify both the time history and position of loads simultaneously with high identification accuracy.
基金Project(51874281)supported by the National Natural Science Foundation of ChinaProject(2024M752698)supported by China Postdoctoral Science FoundationProject(2025WLKXJ041)supported by the Graduate Innovation Program of China University of Mining and Technology。
文摘Based on MTS Landmark 370.50 rock dynamic and static load fatigue test system and acoustic emission(AE)monitoring method,the damage characteristics and energy evolution law of high static load coal-rock combination(CRC)under the influence of dynamic load parameters were studied.The main results are as follows:1)Dynamic load increases the rheological properties and damage fracture development of CRC.With the increase of the amplitude and frequency of the dynamic load,the number of dynamic load cycles required for the failure of the CRC decreases,the irreversible strain increases,and the failure of sample accelerates;2)The AE positioning events during the loading process of the specimen decrease with the increase of the dynamic load amplitude,and increase with the increase of the dynamic load frequency;3)The fractal dimension,total energy and cumulative elastic energy of the broken particles of the CRC increase with the increase of the amplitude and frequency of the dynamic load.The fractal dimension corresponding to the increase of the dynamic load frequency is larger,and the energy and cumulative elastic energy corresponding to the increase of the dynamic load amplitude are larger.
基金financially supported by the National Natural Science Foundation of China(12232008 and 12072211)the Foundation of Key laboratory(2022JCJQLB05703)the Sichuan Province Science and Technology Project(2023NSFSC0914).
文摘Through-silicon via(TSV)is an important technique in three-dimension integration.The mechanical performance of TSV-Cu is critical to the electrical performance and signal transmission.In this work,the deformation of single-crystalline TSV-Cu during annealing process was studied using molecular dynamics method.The protrusion morphology and protrusion height of Cu column were revealed.The protrusion height curves can be divided into four stages:slow increase,fast increase,fast decrease,and saturation.During the deformation process,the main deformation mode is temporary amorphous region followed by residual dislocations.The influences of annealing temperatures,heating rates,and column sizes on protrusion height were studied.Results show that the residual protrusion height increases with increasing annealing temperatures and decreasing heating rates.The residual protrusion height increases with increasing column sizes in terms of column diameter and length.This work provides new insights into understanding the mechanical performance of nano-TSV-Cu.
基金funded by the National Natural Science Foundation of China(No.51974206)the Hubei Province Safety Production Special Fund Science and Technology Project(No.KJZX202007007).
文摘In the civil and mining industries,bolts are critical components of support systems,playing a vital role in ensuring their stability.Glass fibre reinforced polymer(GFRP)bolts are widely used because they are corrosion-resistant and cost-effective.However,the damage mechanisms of GFRP bolts under blasting dynamic loads are still unclear,especially compared to metal bolts.This study investigates the cumulative damage of fully grouted GFRP bolts under blasting dynamic loads.The maximum axial stress at the tails of the bolts is defined as the damage variable,based on the failure characteristics of GFRP bolts.By combining this with Miner's cumulative damage theory,a comprehensive theoretical and numerical model is established to calculate cumulative damage.Field data collected from the Jinchuan No.3 Mining Area,including GFRP bolts parameters and blasting vibration data are used for further analysis of cumulative damage in fully grouted GFRP bolts.Results indicate that with an increasing number of blasts,axial stress increases in all parts of GFRP bolts.The tail exhibits the most significant rise,with stress extending deeper into the anchorage zone.Cumulative damage follows an exponential trend with the number of blasts,although the incremental damage per blast decelerates over time.Higher dynamic load intensities accelerate damage accumulation,leading to an exponential decline in the maximum loading cycles before failure.Additionally,stronger surrounding rock and grout mitigate damage accumulation,with the effect of surrounding rock strength being more pronounced than that of grout.In contrast,the maximum axial stress of metal bolts increases quickly to a certain point and then stabilizes.This shows a clear difference between GFRP and metal bolts.This study presents a new cumulative damage theory that underpins the design of GFRP bolt support systems under blasting conditions,identifies key damage factors,and suggests mitigation measures to enhance system stability.
基金the support of the National Natural Science Foundation of China(Grant No.52108319)the Natural Science Foundation of Jiangxi Province(20224BAB214069)。
文摘Red clay,widely used as a subgrade material in southern China,requires a reliable evaluation of its dynamic behavior to ensure infrastructure safety.Long-term cyclic triaxial tests were conducted on red clay from typical,complex subway subgrades to investigate its dynamic properties and shakedown behavior under intermittent cyclic loading.Results show that intermittent cyclic loading,especially with multiple amplitudes,causes greater axial plastic strain and lower post-cyclic strength than continuous loading.These effects diminish with increasing confining pressure.Notably,axial strain partially recovers during loading intervals,with recovery ratios depending on the number and sequence of pauses.Based on the rules of cumulative plastic strain rates and cumulative plastic strain increments,shakedown behavior for red clay under intermittent cyclic loading is divided into three categories:plastic shakedown,critical shakedown,and plastic creep.A quantitative shakedown limit criterion is proposed using the Boltzmann function.Shakedown behavior significantly influences the post-cyclic strengths,and the influence diminishes as confining pressure increases.Samples exhibiting plastic creep and plastic shakedown behavior have the lowest and highest strengths,and those with critical shakedown behaviors have medium strengths.Cyclic loading with relatively low-stress amplitude causes a hardening effect,while cyclic loading intermittence or cyclic loading with relatively high-stress amplitude causes a degradation effect,and both effects are mitigated by higher confining pressures.
基金financial support by the National Natural Science Foundation of China(52174101&52408310)Guangdong Basic and Applied Basic Research Foundation(2023A1515011634&2024A1515012528)Guangdong Provincial Department of Science and Technology(2021ZT09G087)for the research.
文摘The frequent or occasional impact loads pose serious threats to the service safety of conventional concrete structures in tunnel.In this paper,a novel three-dimensional mesoscopic model of steel fiber reinforced concrete(SFRC)is constructed by discrete element method.The model encompasses the concrete matrix,aggregate,interfacial transition zone and steel fibers,taking into account the random shape of the coarse aggregate and the stochastic distribution of steel fibers.It captures microscopic-level interactions among the coarse aggregate,steel fibers,and matrix.Subsequently,a comprehensive procedure is formulated to calibrate the microscopic parameters required by the model,and the reliability of the model is verified by comparing with the experimental results.Furthermore,a coupled finite difference method-discrete element method approach is used to construct the model of the split Hopkinson pressure bar.Compression tests are simulated on SFRC specimens with varying steel fiber contents under static and dynamic loading conditions.Finally,based on the advantages of DEM analysis at the mesoscopic level,this study analyzed mechanisms of enhancement and crack arrest in SFRC.It shed a light on the perspectives of interface failure process,microcrack propagation,contact force field evolution and energy analysis,offering valuable insights for related mining engineering applications.
基金supported by the National Natural Science Foundation of China(12402444)。
文摘A new dimensionless number is proposed for dynamic plastic deformation analysis of clamped circular plates under underwater explosion loads by introducing dimensional analysis method to the basic dynamical governing equations of circular plates.The relation between dimensionless final plastic deformation of circular plates and the new dimensionless number is established based on massive underwater explosion test data.Meanwhile,comparative analysis was discussed with two other published dimensionless parameters which indicated the new dimensionless number proposed in this paper is more effective and extensive to predict the dynamic plastic response of circular plates under underwater explosion condition.
基金supported by the National Natural Science Foundation of China(Nos.52204136,52474100,and 52204092).
文摘Web pillars enduring complex coupled loads are critical for stability in high-wall mining.This study develops a dynamic failure criterion for web pillars under non-uniform loading using catastrophe theory.Through the analysis of the web pillar-overburden system’s dynamic stress and deformation,a total potential energy function and dynamic failure criterion were established for web pillars.An optimizing method for web pillar parameters was developed in highwall mining.The dynamic criterion established was used to evaluate the dynamic failure and stability of web pillars under static and dynamic loading.Key findings reveal that vertical displacements exhibit exponential-trigonometric variation under static loads and multi-variable power-law behavior under dynamic blasting.Instability risks arise when the roof’s tensile strength-to-stress ratio drops below 1.Using catastrophe theory,the bifurcation setΔ<0 signals sudden instability.The criterion defines failure as when the unstable web pillar section length l1 exceeds the roof’s critical collapse distance l2.Case studies and simulations determine an optimal web pillar width of 4.6 m.This research enhances safety and resource recovery,providing a theoretical framework for advancing highwall mining technology.
基金the National Natural Science Foundation of China(Grant Nos.52371342,52271338,52101378 and 51979277)。
文摘This study designs four types of liquid-filled cylindrical shell structures to investigate their protection characteristics against explosive shock waves and high-speed fragments.Bare charge and charge-driven prefabricated fragments are employed to examine the damage under blast shock waves and combined blast and fragments loading on various liquid-filled cylindrical shell structures.The test results are compared to numerical calculations and theoretical analysis for the structure's deformation,the liquid medium's movement,and the pressure waves'propagation characteristics under different liquid-filling methods.The results showed that the filling method influences the blast protection and the struc-ture's energy absorption performance.The external filling method reduces the structural deformation,and the internal filling method increases the damage effect.The gapped internal filling method improves the structure's energy absorption efficiency.The pressure wave loading on the liquid-filled cylindrical shell structure differs depending on filling methods.Explosive shock waves and high-speed fragments show a damage enhancement effect on the liquid-filled cylindrical shell structure,depending on the thickness of the internal liquid container layer.The specific impulse on the inner surface of the cylindrical shell positively correlates to the radial deformation of the cylindrical shell structure,and the external liquid layer limits the radial structural deformation.
基金supported by the National Natural Science Foundation of China(Grant No.12302500)the National Key Research and Development Program of China(Grant No.2020YFA0710503)Postdoctoral Fellowship Program(Grade B)of China Postdoctoral Science Foundation(Grant No.GBZ20230022).
文摘Controllable shock wave fracturing is an innovative engineering technique used for shale reservoir fracturing and reformation.Understanding the anisotropic fracture mechanism of shale under impact loading is vital for optimizing shock wave fracturing equipment and enhancing shale oil production.In this study,using the well-known notched semi-circular bend(NSCB)sample and the novel double-edge notched flattened Brazilian disc(DNFBD)sample combined with a split Hopkinson pressure bar(SHPB),various dynamic anisotropic fracture properties of Lushan shale,including failure characteristics,fracture toughness,energy dissipation and crack propagation velocity,are comprehensively compared and discussed under mode Ⅰ and mode Ⅱ fracture scenarios.First,using a newly modified fracture criterion considering the strength anisotropy of shale,the DNFBD specimen is predicted to be a robust method for true mode Ⅱ fracture of anisotropic shale rocks.Our experimental results show that the dynamic mode Ⅱ fracture of shale induces a rougher and more complex fracture morphology and performs a higher fracture toughness or fracture energy compared to dynamic mode Ⅰ fracture.The minimal fracture toughness or fracture energy occurs in the Short-transverse orientation,while the maximal ones occur in the Divider orientation.In addition,it is interesting to find that the mode Ⅱ fracture toughness anisotropy index decreases more slowly than that in the mode Ⅰ fracture scenario.These results provide significant insights for understanding the different dynamic fracture mechanisms of anisotropic shale rocks under impact loading and have some beneficial implications for the controllable shock wave fracturing technique.
基金support from the National Natural Science Foundation of China(Nos.51504247,52174092,51904290,and 52074259)the Natural Science Foundation of Jiangsu Province,China(No.BK20220157)+1 种基金the Fundamental Research Funds for the Central Universities,China(No.2022YCPY0202)the China University of Mining and Technology(CUMT)Open Sharing Fund for Large-scale Instruments and Equipment(No.DYGX-2025-47)is gratefully acknowledged.
文摘Under external disturbances,the shear mechanical responses and debonding failure mechanisms at anisotropic interfaces of anchoring system composed of multiphase media are inherently difficult to characterize due to the concealment nature of interfacial interactions.This study establishes an equivalent shear model for a bolt-resin-rock anchoring system and conducts direct shear tests under dynamic normal load(DNL)boundary from both laboratory experiments and discrete element method(DEM)simulations.The research investigates the influence of normal dynamic load amplitude(An)and rock type on shear strength parameters,elucidating the evolutionary characteristics and underlying mechanisms of shear load and normal displacement fluctuations induced by cyclic normal loading,with maximum shear load decreasing by 36.81%to 46.94%as An increases from 10%to 70%when rock type varies from coal to limestone.Through analysis of strain field evolution,the critical impact of rock type on localization of shear failure surface is revealed,with systematic summarization of differentiated wear characteristics,failure modes,and key controlling factors associated with shear failure surface.Mesoscopic investigations enabled by DEM simulations uncover the nonuniform distribution of contact force chains within the material matrix and across the anisotropic interfaces under various DNL boundaries,clarify rock type dependent crack propagation pathways,and quantitatively assess the damage extent of shear failure surface,with the anisotropic interface damage factor increasing from 34.9%to 56.6%as An rises from 10%to 70%,and decreasing from 49.6%to 23.4%as rock type varies from coal to limestone.
文摘This work reviews models and methods for determining the dynamic response of pavements to moving vehicle loads in the framework of continuum-based three dimensional models and linear theories.This review emphasizes the most representative models and methods of analysis in the existing literature and illustrates all of them by numerical examples.Thus,13 such examples are presented here in some detail.Both flexible and rigid(concrete)pavement models involving simple and elaborate cases with respect to geometry and material behavior are considered.Thus,homogeneous or layered half-spaces with isotropic or cross-anisotropic and elastic,viscoelastic or poroelastic properties are considered.The vehicles are modeled as simple point or distributed loads or discrete spring-mass-dashpot system moving with constant or variable velocity.The dynamic response of the above pavement-vehicle systems is obtained by analytical/numerical or purely numerical methods of solution.Analytical/numerical methods have mainly to do with Fourier transforms or complex Fourier series with respect to both space and time.Purely numerical methods involve the finite element method(FEM)and the boundary element method(BEM)working in time or frequency domain.Critical discussions on the advantages and disadvantages of the various pavement-vehicle models and their methods of analysis are provided and the effects of the main parameters on the pavement response are determined through parametric studies and presented in the examples.Finally,conclusions are provided and suggestions for future research are made.
基金supported by Crosswise Tasks of Enterprise Entrusted(JG-ZH-A-202411-003)High-level Talents Program of Hainan Basic and Applied Basic Research Program of China(520RC543)。
文摘In order to research the concrete archaized buildings with lintel-column joint,2 specimens were tested under dynamic experiment.The failure characteristics,skeleton curves,mechanical behavior such as the load-displacement hysteretic loops,load carrying capacity,degradation of strength and stiffness,ductility and energy dissipation of the joints were analyzed.The results indicate that comparies with the lintel-column joints,the loading capacity and energy dissipation of the concrete archaized buildings with dual lintel-column joints are higher,and the hysteretic loops is in plump-shape.However,the displacement ductility coefficient is less than that of lintel-column joints.Both of them of the regularity of rigidity degeneration are basically the same.Generally,the joints have the good energy dissipation capacity.And the concrete archaized buildings with lintel-column joints exhibit excellent seismic behavior.
基金supported by the National Natural Science Foundation of China(Nos.52374100,52525401,and 52304150)Outstanding Young Talent Project of Shanxi Province(No.SJYC2024301)Research Project Supported by Shanxi Scholarship Council of China(No.2023-041).
文摘Borehole pressure relief helps prevent rock bursts.However,this may change the physical and mechan-ical properties of the surrounding rock,affect the variation of the plastic zone of the roadway,and lead to the failure of roadway support,thus threatening the safety of the roadway.In this paper,the variable angle shear test of drilled specimens under the action of static and dynamic loads is used to study the evolution of mechanical parameters of the specimens and their influence on the plastic zone of the sur-rounding rock.The shear strength decreases linearly with the increase of drilling diameter.With the increase of pre-static load level and dynamic load amplitude,the cohesion first increases and then decreases,and the internal friction angle decreases.Moreover,the shear failure surface changes from rough to smooth.The reasons include that the static load enhances the tooth cutting effect and the repeated friction of cracks caused by the dynamic load.Borehole pressure relief leads to an increase in the radius of the plastic zone of the surrounding rock following a quadratic function.The research results of this paper provide a theoretical basis for designing drilling unloading parameters and supporting parameters for rock burst roadways.
基金National Natural Science Foundation of China under Grant Nos.51622803 and 51878103China Postdoctoral Science Foundation under Grant No.2021M692689。
文摘Stress waves propagate along vertical,radial and circumferential directions when a non-uniformly distributed load is applied at one end of a three-dimensional shaft.As a result,the receiving signals are usually mixed with undesired interference components,often featuring as high-frequency fluctuations.Previous studies have revealed that sectional geometry(shape and size)greatly affects the high-frequency interference.In this study,low strain dynamic testing on full-scale X-section concrete is conducted in order to investigate the influences of high-frequency interference on velocity responses at the pile head.Emphasis is placed on the frequency and peak value of interference waves at various receiving points.Additionally,the effects of the geometrical,and mechanical properties of the pile shaft on high-frequency interference are elaborated on through the three-dimensional finite element method.The results show that the measured wave is obscured by interference waves superposed by two types of high-frequency components.The modulus and cross-sectional area are contributing factors to the frequency and peak value of the interference waves.On the other hand,the position with the least interference is determined,to some extent,by the accurate shape of the X-section.
基金Smart Integration Key Technologies and Application Demonstrations of Large Scale Underground Space Disaster Prevention and Reduction in Guangzhou International Financial City([2021]–KJ058).
文摘The specialized equipment utilized in long-line tunnel engineering is evolving towards large-scale,multifunctional,and complex orientations.The vibration caused by the high-frequency units during regular operation is supported by the foundation of the units,and the magnitude of vibration and the operating frequency fluctuate in different engineering contexts,leading to variations in the dynamic response of the foundation.The high-frequency units yield significantly diverse outcomes under different startup conditions and times,resulting in failure to meet operational requirements,influencing the normal function of the tunnel,and causing harm to the foundation structure,personnel,and property in severe cases.This article formulates a finite element numerical computation model for solid elements using three-dimensional elastic body theory and integrates field measurements to substantiate and ascertain the crucial parameter configurations of the finite element model.By proposing a comprehensive startup timing function for high-frequency dynamic machines under different startup conditions,simulating the frequency andmagnitude variations during the startup process,and suggesting functions for changes in frequency and magnitude,a simulated startup schedule function for high-frequency machines is created through coupling.Taking into account the selection of the transient dynamic analysis step length,the dynamic response results for the lower dynamic foundation during its fundamental frequency crossing process are obtained.The validation checks if the structural magnitude surpasses the safety threshold during the critical phase of unit startup traversing the structural resonance region.The design recommendations for high-frequency units’dynamic foundations are provided,taking into account the startup process of the machine and ensuring the safe operation of the tunnel.
文摘The damage properties of two types of rocks under dynamic loading are studied. The shock induced experiments are done using planar impact technique on the one? stage light gas gun, and the ultrasonic tests on the damaged rocks have been made by use of the ultrasonic pulse? transmission method. The shock induced damage of rock is related to the shock speed and the attenuation coefficient of sonic wave, and the latter reflects the damage degree in rock fairly well. The attenuation coefficient α can be used as main damage parameter for constructing damage model of rock under dynamic loading.
基金The Pre-research Project of the General Armament DepartmentThe Science Fund of North University of China(No.20130105)
文摘Nonlinear amphibious vehicle rolling under regular waves and wind load is analyzed by a single degree of freedom system.Considering nonlinear damping and restoring moments,a nonlinear rolling dynamical equation of amphibious vehicle is established.The Hamiltonian function of the nonlinear rolling dynamical equation of amphibious vehicle indicate when subjected to joint action of periodic wave excitation and crosswind,the nonlinear rolling system degenerates into being asymmetric.The threshold value of excited moment of wave and wind is analyzed by the Melnikov method.Finally,the nonlinear rolling motion response and phase portrait were simulated by four order Runge-Kutta method at different excited moment parameters.
