This study investigated the effects of weathering depth and thickness on the failure mechanisms of rock samples through experimental and numerical methods.The first configuration involved conducting artificial weather...This study investigated the effects of weathering depth and thickness on the failure mechanisms of rock samples through experimental and numerical methods.The first configuration involved conducting artificial weathering on limestone using the freezing and thawing(F-T)for 40 cycles.The mechanical parameters of the samples were measured at the end of the 40th cycle.In the second configuration,a series of specimens underwent salt crystallization(S-C)tests for 20 cycles.Experimental results were validated using discrete element method(DEM).Next,the weathered limestone model with dimensions of 108 mm54 mm were prepared.The weathering layers were tested at four different thicknesses(i.e.2.5 mm,5 mm,7.5 mm,and 10 mm)and three different positions(at the surface,5 mm under the rock surface,and 10 mm under the rock surface).According to the results,weathering depth and thickness have a considerable effect on the failure process.The results also showed a correlation between the values of compressive strength and failure mechanisms associated with the weathering layer.The numerical results revealed that the tension crack was the dominant factor.Additionally,with increasing weathering thickness,Young's modulus,crack initiation stress,and final strength decreased in constant weathering depth.The results also demonstrated that the failure progress of the numerical models was similar to that observed in the laboratory.展开更多
The hot deformation characteristics of 1.4462 duplex stainless steel （DSS） were analyzed by considering strain partitioning between austenite and ferrite constituents. The individual behavior of ferrite and austenit...The hot deformation characteristics of 1.4462 duplex stainless steel （DSS） were analyzed by considering strain partitioning between austenite and ferrite constituents. The individual behavior of ferrite and austenite in microstructure was studied in an iso-stress condition. Hot compression tests were performed at temperatures of 800-1100~C and strain rates of 0.001-1 s-1. The flow stress was modeled by a hyperbolic sine constitutive equation, the corresponding constants and apparent activation energies were determined for the studied alloys. The constitutive equation and law of mixture were used to measure the contribution factor of each phase at any given strain. It is found that the contribution factor of ferrite exponentially declines as the Zener-HoUomon parameter （Z） increases. On the contrary, the austenite contribution polynomially increases with the increase of Z. At low Z values below 2.6. x 1015 （lnZ---35.5）, a negative contribution factor is determined for austenite that is attributed to dynamic recrystallization. At high Z values, the contribution factor of austenite is about two orders of magnitude greater than that of ferrite, and therefore, austenite can accommodate more strain. Microstructural characterization via electron back-scattered diffraction （EBSD） confirms the mechanical results and shows that austenite recrystallization is possible only at high temperature and low strain rate.展开更多
Dual equal channel lateral extrusion(DECLE)process with various passes followed by sheet extrusion process was performed to produce fine-grained ZK60 alloy sheets.The coarse grain structure of the annealed sample afte...Dual equal channel lateral extrusion(DECLE)process with various passes followed by sheet extrusion process was performed to produce fine-grained ZK60 alloy sheets.The coarse grain structure of the annealed sample after applying sheet extrusion(size:68μm)changed to fine grains of 6.0 and 5.2μm after 3 and 5 passes of DECLE and following extrusion.The hot shear deformation behavior of samples was studied by developing constitutive equations based on shear punch test(SPT)results.SPT was carried out in the temperature range of 200−300℃ and strain rate range of 0.003−0.33 s^(–1).The activation energy of 125−139 kJ/mol and the stress exponent of 3.5−4.2 were calculated for all conditions,which indicated that dislocation creep,controlled by dislocation climb and solute drag mechanism,acted as the main hot deformation mechanism.It was concluded that material constants of n and Q are dependent on the microstructural factors such as grain size and second phase particle fraction,and the relationship of which was anticipated using a 3D surface curve.Moreover,the similar strong basal texture of extruded sheets gave rise to the same deformation mechanisms during SPT and similar n and Q values for ZK60 alloy.展开更多
This paper proposes a novel adaptive sliding mode control(SMC) method for synchronization of non-identical fractional-order(FO) chaotic and hyper-chaotic systems. Under the existence of system uncertainties and extern...This paper proposes a novel adaptive sliding mode control(SMC) method for synchronization of non-identical fractional-order(FO) chaotic and hyper-chaotic systems. Under the existence of system uncertainties and external disturbances,finite-time synchronization between two FO chaotic and hyperchaotic systems is achieved by introducing a novel adaptive sliding mode controller(ASMC). Here in this paper, a fractional sliding surface is proposed. A stability criterion for FO nonlinear dynamic systems is introduced. Sufficient conditions to guarantee stable synchronization are given in the sense of the Lyapunov stability theorem. To tackle the uncertainties and external disturbances, appropriate adaptation laws are introduced. Particle swarm optimization(PSO) is used for estimating the controller parameters. Finally, finite-time synchronization of the FO chaotic and hyper-chaotic systems is applied to secure communication.展开更多
In order to analyze the flow behavior and workability of Ni-42Cu in cast and wrought conditions, hot deformation tests were performed at temperatures and strain rates within the ranges of 900-1150 ℃ and 0.001-1 s^-1,...In order to analyze the flow behavior and workability of Ni-42Cu in cast and wrought conditions, hot deformation tests were performed at temperatures and strain rates within the ranges of 900-1150 ℃ and 0.001-1 s^-1, respectively. Tensile tests showed a “hot ductility trough” at 950 ℃ for both alloys. The drop in hot ductility was more considerable in the cast alloy because of the sluggish dynamic recrystallization. The hot ductility drop and grain boundary cracking, particularly in the cast alloy, were attributed to the segregation of detrimental atoms to the boundaries. It was shown that the hot ductility of the wrought alloy could be improved with increasing strain rate. It was associated with increasing the fraction of dynamic recrystallization at higher strain rates. This finding corroborated the change in the mechanism of dynamic recrystallization with strain rate. The strain rate sensitivity and instability parameters calculated for the wrought alloy showed that the material is prone to strain localization at low temperatures, i.e., 950-1050 ℃, and high strain rates of 0.1 and 1 s-1. Based on the tensile and compression tests, the best temperature range for a desirable hot workability was introduced as 1050-1150 ℃.展开更多
Hot compression tests were carried out on a Fe-29Ni-17Co alloy in the temperature range of 900 ℃ to 1200 ℃ and at strain rates of 0.001-1 s-1. Dynamic recrystallization was found responsible for flow softening durin...Hot compression tests were carried out on a Fe-29Ni-17Co alloy in the temperature range of 900 ℃ to 1200 ℃ and at strain rates of 0.001-1 s-1. Dynamic recrystallization was found responsible for flow softening during hot compression. The flow behavior was successfully analyzed by the hyperbolic sine equation and the corresponding material constants A, n and αwere determined. The value of apparent activation energy was determined as 423 kJ/mol. The peak and steady state strains showed simple power-law dependence on the Zener-Hollomon parameter. The dynamic recrystallization kinetics was analyzed using Avrami equation and the corresponding exponent was determined to be about 2.7. This value, higher than 2 reported in the literatures, is associated with the mechanism of continuous dynamic recrystallization in the studied alloy. The flow curve up to the peak was modeled by the Cingara equation and the strain exponent, c, was determined about 0.85. The higher value of c compared with the value of 0.2 which has been reported for some stainless steels fortified the idea of extended dynamic recovery or continuous dynamic recrystallization in the studied alloy.展开更多
The underground or open-pit methods are used for the extraction of mineral resources,each of which is divided into different categories.Coal is one of the mineral resources,which is exploited either by the surface or ...The underground or open-pit methods are used for the extraction of mineral resources,each of which is divided into different categories.Coal is one of the mineral resources,which is exploited either by the surface or the underground methods.The long-wall mining is one of the methods for the underground coal mining.In this method,which is a mechanized one,some machines such as the shearer or plow are used for the mining.The coal mine in Parvadeh,Tabas is a mechanized mine that is extracted by the long-wall mining.The modeling with particle flow code software was used in this mine for the evaluation of plow performance using the coal specifications.In this regard,the sample was first calibrated by sampling from the Parvadeh coal mine and performing the uniaxial and Brazilian tests on the model.Then,the modeling was done by constructing the model and using the variables such as the clearance angle and the linear velocity of the plow.After making 28 models for the plow,the best model of the plow was selected based on the maximum force applied to the machine in the X direction.Finally,the results of this study showed that the best plow performance is for a model with the clearance angle of zero and the linear velocity of 9 mm/min,and the maximum force applied to this model is equal to 39,000 kN in the X direction.展开更多
Granite is generally composed of quartz,biotite,feldspar,and cracks.The changes in digital parameters of these compositions reflect the detail of the deformation process of the rock.Therefore,the estimation of the cha...Granite is generally composed of quartz,biotite,feldspar,and cracks.The changes in digital parameters of these compositions reflect the detail of the deformation process of the rock.Therefore,the estimation of the changes in digital parameters of the compositions is much helpful to understand the deformation and failure stages of the rock.In the current study,after dividing the frames in the video images photographed during the axial compression test into four parts(or,the upper left,upper right,lower left,and lower right ones),the digital parameters of various compositions in each part were then extracted.Using these parameters as input dataset,a long short-term memory(LSTM)based neural network was then established for exploring the changes of various compositions.After dividing the deformation process into four stages based on the stress-strain curve and using the digital parameters of various compositions as the dataset,the LSTM-based neural network for estimating the rock deformation stage was also established.The root mean squared error(RMSE)and goodness of fit(R2)and the average accuracy(ACC)were used to evaluate the efficiencies of these two LSTM-based neural networks.The influences of variables(such as the number of hidden layers,maximum epoch,learning rate,minimum batch size and train ratio)on efficiencies of the LSTM-based neural networks were thereafter explored.It shows that the super parameters have a great influence on the efficiency of the established LSTM-based neural network for estimating digital parameter changes of various compositions;the estimations were relatively good if the number of hidden layers,maximum epoch,learning ratio,minimum batch size,and train ratio is 2,150,0.005,10,and 0.8,respectively;the compositions with the greater percentage have a greater accuracy using the neural network;the great-small sequence of ACC is biotite,feldspar,crack,and quartz,if the LSTM-based architecture for estimating deformation stages was used.These results may be referable both for investigating the availably of the established LSTM-based architectures and for exploring the deformation process of the rock materials.展开更多
Single-and two-step hot compression experiments were carried out on 16Cr25Ni6Mo superaustenitic stainless steel in the temperature range from 950 to 1150°C and at a strain rate of 0.1 s^（-1）. In the two-step te...Single-and two-step hot compression experiments were carried out on 16Cr25Ni6Mo superaustenitic stainless steel in the temperature range from 950 to 1150°C and at a strain rate of 0.1 s^（-1）. In the two-step tests, the first pass was interrupted at a strain of 0.2; after an interpass time of 5, 20, 40, 60, or 80 s, the test was resumed. The progress of dynamic recrystallization at the interruption strain was less than 10%. The static softening in the interpass period increased with increasing deformation temperature and increasing interpass time. The static recrystallization was found to be responsible for fast static softening in the temperature range from 950 to 1050°C. However, the gentle static softening at 1100 and 1150°C was attributed to the combination of static and metadynamic recrystallizations. The correlation between calculated fractional softening and microstructural observations showed that approximately 30% of interpass softening could be attributed to the static recovery. The microstructural observations illustrated the formation of fine recrystallized grains at the grain boundaries at longer interpass time. The Avrami kinetics equation was used to establish a relationship between the fractional softening and the interpass period. The activation energy for static softening was determined as 276 kJ/mol.展开更多
The buckling resisting brace(BRB)is an efficient system against lateral loads that enjoy high seismic energy absorption capacity.Although desirable behavior of BRBs has been confirmed,the stiffness of the system is no...The buckling resisting brace(BRB)is an efficient system against lateral loads that enjoy high seismic energy absorption capacity.Although desirable behavior of BRBs has been confirmed,the stiffness of the system is not desirable that it can be compensated by changing the configuration of BRB braces.In so doing,the configuration in the form of double K(DK)is investigated to achieve more favorable behavior.Also,the required mathematical formulas were proposed to design the system.Comparison of DK system with other conventional BRB showed that the DK system has a better structural performance and is more economical(due to needing less core area)than other conventional BRB.Numerical results indicated that the DK system increases the lateral ultimate strength,lateral nonlinear stiffness,and energy absorption.Besides,the DK configuration reduces the axial forces created in columns in the nonlinear zone.Reducing material demand,created forces in the main frame,and also increasing of nonlinear stiffens by DK improve the structure’s safety.展开更多
The blast-induced vibration during excavation by drilling and blasting method has an important impact on thesurrounding structures. In particular, with the development of tunnel engineering, the impact of blasting vib...The blast-induced vibration during excavation by drilling and blasting method has an important impact on thesurrounding structures. In particular, with the development of tunnel engineering, the impact of blasting vibrationon tunnel construction has attracted extensive attention. In this paper, the propagation attenuation characteristicsof blast-induced vibration (PPV, peak particle velocity) on different tunnel structures were systematically studiedbased on the field monitoring data. Initially, the attenuation characteristics of blasting vibration PPV on the lowerbench surface, the side wall of the excavated tunnel and the closely spaced adjacent tunnel were investigated.Subsequently, the capacity of several widely utilized empirical prediction equations to estimate the PPV on tunnelstructures was examined, along with a comparative analysis of their prediction accuracy. The research findingsindicate that it is feasible to predict the PPV on the tunnel structures using empirical equations. The attenuationcharacteristics of blasting vibration PPV are different in different structures and directions. The prediction accuracy of the empirical equations varies, while the discrepancies are minimal. The principal variation amongthese equations lies in the site-specific coefficients k, β, λ, highlighting the differential impact of structural anddirectional considerations on the predictive efficacy. Based on the empirical equation and safe PPV provided bythe blasting vibration safe standards on tunnels of China (GB6722-2014), and considering the influence of allstructures and directions, it is determined that the safe distance of blasting vibration in the tested tunnel projectshould be larger than 20.28–18.31 m, 18.31–16.16 m, and 16.16–13.75 m for blasting vibration frequency locatedin 10 Hz, 10–50 Hz, and >50 Hz.展开更多
Dynamic recrystallization and precipitation in a high manganese austenitic stainless steel were investigated by hot compression tests over temperatures of 950-1150~C at strain rates of 0.001 s-1-1 s-1. All the flow cu...Dynamic recrystallization and precipitation in a high manganese austenitic stainless steel were investigated by hot compression tests over temperatures of 950-1150~C at strain rates of 0.001 s-1-1 s-1. All the flow curves within the studied deformation regimes were typ- ical of dynamic recrystallization. A window was constructed to determine the value of apparent activation energy as a function of strain rate and deformation temperature. The kinetics of dynamic recrystallization was analyzed using the Avrami kinetics equation. A range of apparent activation energy for hot deformation from 303 kJ/mol to 477 kJ/mol is obtained at different deformation regimes. Microscopic characterization confirms that under a certain deformation condition （medium Zener-Hollomon parameter （Z） values）, dynamic recrystalliza- tion appears at first, but large particles can not inhibit the recrystallization. At low or high Z values, dynamic recrystallization may occur be- fore dynamic precipitation and proceeds faster. In both cases, secondary phase precipitation is observed along prior austenite grain bounda- ries. Stress relaxation tests at the same deformation temperatures also confirm the possibility of dynamic precipitation. Unexpectedly, the Avrami＇s exponent value increases with the increase of Z value. It is associated with the priority of dynamic recrystallization to dynamic precipitation at higher Z values.展开更多
A reservoir landslide not only reduces the water storage capacity, but also causes extensive damages to the dam body, power/water transmission lines, roads, and other infrastructures. The Latian Dam, located 35 km nor...A reservoir landslide not only reduces the water storage capacity, but also causes extensive damages to the dam body, power/water transmission lines, roads, and other infrastructures. The Latian Dam, located 35 km north east of Tehran （Iran）, is one of the cases which has encountered serious problems with instability of its rock abutments. This paper addresses the stability analysis of the right abutment of the Latian Dam using limit equilibrium and numerical methods. Geomechanical characteristics of the rock abutment were first estimated based on engineering classification of the rock mass. Different search methods were examined for locating the critical circular/non-circular slip surface in conjunction with the general limit equilibrium method. The effect of variabi]ity of rock mass properties, water table, and earthquake load on the factor of safety （FS） and probability of failure （PF） was studied. In the event of rapid drawdown in the reservoir, the limit equilibrium analysis calculated FS=1.067 and PF=21.1%, and the numerical analysis returned FS=1.01. The results of the analyses suggest that the right abutment of the Latian Dam is prone to slide and needs treatment. Investigations demonstrated that a slope reduction by 15° at the upper part of the abutment would meet stability conditions even in the worst-case scenario （FS=1.297 and PF=2.07%）.展开更多
Experimental and discrete element methods were used to investigate the failure behavior of room and pillar with different configura-tions under uniaxial loading.Concrete samples with dimension of 15 cm×15 cm×...Experimental and discrete element methods were used to investigate the failure behavior of room and pillar with different configura-tions under uniaxial loading.Concrete samples with dimension of 15 cm×15 cm×5 cm were prepared.Within the specimens,rooms and pillars with different configurations were provided.The room dimension was 1 cm×1 cm,and the pillar dimension was according to the room configuration.Twelve different configurations were chosen for rooms and pillars.The axial load was applied to the model by rate of 0.05 mm/min.The results show that the failure process was mostly governed by both the non-persistent joint angle and joint number.The compressive strength of the specimens was related to the fracture pattern and failure mechanism of the pillars.It was shown that the shear behaviour of pillars was related to the number of the induced tensile cracks,which increased by increasing the room angle.The compressive strength of samples increased with the increase of the room angle.The failure pattern and failure strength are similar in both methods,i.e.,the experimental testing and the numerical simulation.展开更多
In this study,the effect of hot deformation on martensitic stainless steel was carried out in temperatures between 950 to 1100℃ and strain rates of 0.001,0.01 and 0.1 s 1.Two important dynamic recrystallization param...In this study,the effect of hot deformation on martensitic stainless steel was carried out in temperatures between 950 to 1100℃ and strain rates of 0.001,0.01 and 0.1 s 1.Two important dynamic recrystallization parameters,the critical strain and the point of maximum dynamic softening,were derived from strain hardening rate vs stress curves.Then the calculated parameters were used to predict the dynamic recrystallized fraction.Our results show that critical stress and strain increase with decreasing deformation temperature and increasing strain rate.The hot deformation activation energy of the steel is also investigated in the present work with 413 kJ/mol.Our experimental flow curves are in fair agreement with the kinetics of dynamic recrystallization model.展开更多
The segregation behavior of a mixture of silica-coated titanium dioxide(TiO2)particles of three different sizes in a pseudo two-dimensional fluidized bed was studied experimentally by the freeze-sieving method and num...The segregation behavior of a mixture of silica-coated titanium dioxide(TiO2)particles of three different sizes in a pseudo two-dimensional fluidized bed was studied experimentally by the freeze-sieving method and numerically by the multi-fluid model(MFM).Three-dimensional computational fluid dynamics(CFD)simulations were carried out to evaluate the effects of the solid wall boundary conditions on particle segregation in terms of specularity and particle-wall restitution coefficients.The quantitative indexes of segregation tendency and segregation degree were used to determine the axial segregation of the mixture in triangular coordinates.The simulation results revealed that the axial segregation increased with the specularity coefficient,whereas the particle-wall restitution coefficient had a minor effect on axial segregation.Comparison of the simulation results with experimental data showed that the appropriate value of the specularity coefficient used in the CFD model depended on superficial gas velocity.The study of the effects of superficial gas velocity on segregation behavior demonstrated that the greatest segregation was obtained at minimum fluidization velocity and the segregation decreased as the gas velocity gradually increased.展开更多
A simultaneous experimental and numerical study of shear fracture of concrete-like materials is carried out using Brazilian disc specimens with initial double edge cracks and fourpoint bending beam specimens with doub...A simultaneous experimental and numerical study of shear fracture of concrete-like materials is carried out using Brazilian disc specimens with initial double edge cracks and fourpoint bending beam specimens with double edge-notches.The interference effects of two cracks/notches are investigated through varied ligament angles and crack lengths.It is shown that shear fracturing paths change remarkably with the initial ligament angles and crack lengths.The cracked specimens are numerically simulated by an indirect boundary element method.A comparison between the numerical results and the experimental ones shows good agreement.展开更多
文摘This study investigated the effects of weathering depth and thickness on the failure mechanisms of rock samples through experimental and numerical methods.The first configuration involved conducting artificial weathering on limestone using the freezing and thawing(F-T)for 40 cycles.The mechanical parameters of the samples were measured at the end of the 40th cycle.In the second configuration,a series of specimens underwent salt crystallization(S-C)tests for 20 cycles.Experimental results were validated using discrete element method(DEM).Next,the weathered limestone model with dimensions of 108 mm54 mm were prepared.The weathering layers were tested at four different thicknesses(i.e.2.5 mm,5 mm,7.5 mm,and 10 mm)and three different positions(at the surface,5 mm under the rock surface,and 10 mm under the rock surface).According to the results,weathering depth and thickness have a considerable effect on the failure process.The results also showed a correlation between the values of compressive strength and failure mechanisms associated with the weathering layer.The numerical results revealed that the tension crack was the dominant factor.Additionally,with increasing weathering thickness,Young's modulus,crack initiation stress,and final strength decreased in constant weathering depth.The results also demonstrated that the failure progress of the numerical models was similar to that observed in the laboratory.
文摘The hot deformation characteristics of 1.4462 duplex stainless steel （DSS） were analyzed by considering strain partitioning between austenite and ferrite constituents. The individual behavior of ferrite and austenite in microstructure was studied in an iso-stress condition. Hot compression tests were performed at temperatures of 800-1100~C and strain rates of 0.001-1 s-1. The flow stress was modeled by a hyperbolic sine constitutive equation, the corresponding constants and apparent activation energies were determined for the studied alloys. The constitutive equation and law of mixture were used to measure the contribution factor of each phase at any given strain. It is found that the contribution factor of ferrite exponentially declines as the Zener-HoUomon parameter （Z） increases. On the contrary, the austenite contribution polynomially increases with the increase of Z. At low Z values below 2.6. x 1015 （lnZ---35.5）, a negative contribution factor is determined for austenite that is attributed to dynamic recrystallization. At high Z values, the contribution factor of austenite is about two orders of magnitude greater than that of ferrite, and therefore, austenite can accommodate more strain. Microstructural characterization via electron back-scattered diffraction （EBSD） confirms the mechanical results and shows that austenite recrystallization is possible only at high temperature and low strain rate.
文摘Dual equal channel lateral extrusion(DECLE)process with various passes followed by sheet extrusion process was performed to produce fine-grained ZK60 alloy sheets.The coarse grain structure of the annealed sample after applying sheet extrusion(size:68μm)changed to fine grains of 6.0 and 5.2μm after 3 and 5 passes of DECLE and following extrusion.The hot shear deformation behavior of samples was studied by developing constitutive equations based on shear punch test(SPT)results.SPT was carried out in the temperature range of 200−300℃ and strain rate range of 0.003−0.33 s^(–1).The activation energy of 125−139 kJ/mol and the stress exponent of 3.5−4.2 were calculated for all conditions,which indicated that dislocation creep,controlled by dislocation climb and solute drag mechanism,acted as the main hot deformation mechanism.It was concluded that material constants of n and Q are dependent on the microstructural factors such as grain size and second phase particle fraction,and the relationship of which was anticipated using a 3D surface curve.Moreover,the similar strong basal texture of extruded sheets gave rise to the same deformation mechanisms during SPT and similar n and Q values for ZK60 alloy.
文摘This paper proposes a novel adaptive sliding mode control(SMC) method for synchronization of non-identical fractional-order(FO) chaotic and hyper-chaotic systems. Under the existence of system uncertainties and external disturbances,finite-time synchronization between two FO chaotic and hyperchaotic systems is achieved by introducing a novel adaptive sliding mode controller(ASMC). Here in this paper, a fractional sliding surface is proposed. A stability criterion for FO nonlinear dynamic systems is introduced. Sufficient conditions to guarantee stable synchronization are given in the sense of the Lyapunov stability theorem. To tackle the uncertainties and external disturbances, appropriate adaptation laws are introduced. Particle swarm optimization(PSO) is used for estimating the controller parameters. Finally, finite-time synchronization of the FO chaotic and hyper-chaotic systems is applied to secure communication.
文摘In order to analyze the flow behavior and workability of Ni-42Cu in cast and wrought conditions, hot deformation tests were performed at temperatures and strain rates within the ranges of 900-1150 ℃ and 0.001-1 s^-1, respectively. Tensile tests showed a “hot ductility trough” at 950 ℃ for both alloys. The drop in hot ductility was more considerable in the cast alloy because of the sluggish dynamic recrystallization. The hot ductility drop and grain boundary cracking, particularly in the cast alloy, were attributed to the segregation of detrimental atoms to the boundaries. It was shown that the hot ductility of the wrought alloy could be improved with increasing strain rate. It was associated with increasing the fraction of dynamic recrystallization at higher strain rates. This finding corroborated the change in the mechanism of dynamic recrystallization with strain rate. The strain rate sensitivity and instability parameters calculated for the wrought alloy showed that the material is prone to strain localization at low temperatures, i.e., 950-1050 ℃, and high strain rates of 0.1 and 1 s-1. Based on the tensile and compression tests, the best temperature range for a desirable hot workability was introduced as 1050-1150 ℃.
文摘Hot compression tests were carried out on a Fe-29Ni-17Co alloy in the temperature range of 900 ℃ to 1200 ℃ and at strain rates of 0.001-1 s-1. Dynamic recrystallization was found responsible for flow softening during hot compression. The flow behavior was successfully analyzed by the hyperbolic sine equation and the corresponding material constants A, n and αwere determined. The value of apparent activation energy was determined as 423 kJ/mol. The peak and steady state strains showed simple power-law dependence on the Zener-Hollomon parameter. The dynamic recrystallization kinetics was analyzed using Avrami equation and the corresponding exponent was determined to be about 2.7. This value, higher than 2 reported in the literatures, is associated with the mechanism of continuous dynamic recrystallization in the studied alloy. The flow curve up to the peak was modeled by the Cingara equation and the strain exponent, c, was determined about 0.85. The higher value of c compared with the value of 0.2 which has been reported for some stainless steels fortified the idea of extended dynamic recovery or continuous dynamic recrystallization in the studied alloy.
文摘The underground or open-pit methods are used for the extraction of mineral resources,each of which is divided into different categories.Coal is one of the mineral resources,which is exploited either by the surface or the underground methods.The long-wall mining is one of the methods for the underground coal mining.In this method,which is a mechanized one,some machines such as the shearer or plow are used for the mining.The coal mine in Parvadeh,Tabas is a mechanized mine that is extracted by the long-wall mining.The modeling with particle flow code software was used in this mine for the evaluation of plow performance using the coal specifications.In this regard,the sample was first calibrated by sampling from the Parvadeh coal mine and performing the uniaxial and Brazilian tests on the model.Then,the modeling was done by constructing the model and using the variables such as the clearance angle and the linear velocity of the plow.After making 28 models for the plow,the best model of the plow was selected based on the maximum force applied to the machine in the X direction.Finally,the results of this study showed that the best plow performance is for a model with the clearance angle of zero and the linear velocity of 9 mm/min,and the maximum force applied to this model is equal to 39,000 kN in the X direction.
基金Financial support for the study was provided by the Natural Sciences Foundation Committee of China(Grant No.41472254Jinming Xu,http://www.nsfc.gov.cn)and the Science and Technology Research-development Program of China Railway Construction Corporation Limited(Grant No.17-C13,Jinming Xu and Chuanjiang Zhong,http://www.crcc.cn).These supports are gratefully acknowledged.
文摘Granite is generally composed of quartz,biotite,feldspar,and cracks.The changes in digital parameters of these compositions reflect the detail of the deformation process of the rock.Therefore,the estimation of the changes in digital parameters of the compositions is much helpful to understand the deformation and failure stages of the rock.In the current study,after dividing the frames in the video images photographed during the axial compression test into four parts(or,the upper left,upper right,lower left,and lower right ones),the digital parameters of various compositions in each part were then extracted.Using these parameters as input dataset,a long short-term memory(LSTM)based neural network was then established for exploring the changes of various compositions.After dividing the deformation process into four stages based on the stress-strain curve and using the digital parameters of various compositions as the dataset,the LSTM-based neural network for estimating the rock deformation stage was also established.The root mean squared error(RMSE)and goodness of fit(R2)and the average accuracy(ACC)were used to evaluate the efficiencies of these two LSTM-based neural networks.The influences of variables(such as the number of hidden layers,maximum epoch,learning rate,minimum batch size and train ratio)on efficiencies of the LSTM-based neural networks were thereafter explored.It shows that the super parameters have a great influence on the efficiency of the established LSTM-based neural network for estimating digital parameter changes of various compositions;the estimations were relatively good if the number of hidden layers,maximum epoch,learning ratio,minimum batch size,and train ratio is 2,150,0.005,10,and 0.8,respectively;the compositions with the greater percentage have a greater accuracy using the neural network;the great-small sequence of ACC is biotite,feldspar,crack,and quartz,if the LSTM-based architecture for estimating deformation stages was used.These results may be referable both for investigating the availably of the established LSTM-based architectures and for exploring the deformation process of the rock materials.
文摘Single-and two-step hot compression experiments were carried out on 16Cr25Ni6Mo superaustenitic stainless steel in the temperature range from 950 to 1150°C and at a strain rate of 0.1 s^（-1）. In the two-step tests, the first pass was interrupted at a strain of 0.2; after an interpass time of 5, 20, 40, 60, or 80 s, the test was resumed. The progress of dynamic recrystallization at the interruption strain was less than 10%. The static softening in the interpass period increased with increasing deformation temperature and increasing interpass time. The static recrystallization was found to be responsible for fast static softening in the temperature range from 950 to 1050°C. However, the gentle static softening at 1100 and 1150°C was attributed to the combination of static and metadynamic recrystallizations. The correlation between calculated fractional softening and microstructural observations showed that approximately 30% of interpass softening could be attributed to the static recovery. The microstructural observations illustrated the formation of fine recrystallized grains at the grain boundaries at longer interpass time. The Avrami kinetics equation was used to establish a relationship between the fractional softening and the interpass period. The activation energy for static softening was determined as 276 kJ/mol.
文摘The buckling resisting brace(BRB)is an efficient system against lateral loads that enjoy high seismic energy absorption capacity.Although desirable behavior of BRBs has been confirmed,the stiffness of the system is not desirable that it can be compensated by changing the configuration of BRB braces.In so doing,the configuration in the form of double K(DK)is investigated to achieve more favorable behavior.Also,the required mathematical formulas were proposed to design the system.Comparison of DK system with other conventional BRB showed that the DK system has a better structural performance and is more economical(due to needing less core area)than other conventional BRB.Numerical results indicated that the DK system increases the lateral ultimate strength,lateral nonlinear stiffness,and energy absorption.Besides,the DK configuration reduces the axial forces created in columns in the nonlinear zone.Reducing material demand,created forces in the main frame,and also increasing of nonlinear stiffens by DK improve the structure’s safety.
基金supported by the General Project of China Postdoctoral Science Foundation(2023M742141)the Open Fund of State Key Laboratory of Mining Response and Disaster Prevention and Control in Deep Coal Mine(SKLMRDPC23KF06)the Talent Introduction Project of Shandong University of Science and Technology(0104060540171).
文摘The blast-induced vibration during excavation by drilling and blasting method has an important impact on thesurrounding structures. In particular, with the development of tunnel engineering, the impact of blasting vibrationon tunnel construction has attracted extensive attention. In this paper, the propagation attenuation characteristicsof blast-induced vibration (PPV, peak particle velocity) on different tunnel structures were systematically studiedbased on the field monitoring data. Initially, the attenuation characteristics of blasting vibration PPV on the lowerbench surface, the side wall of the excavated tunnel and the closely spaced adjacent tunnel were investigated.Subsequently, the capacity of several widely utilized empirical prediction equations to estimate the PPV on tunnelstructures was examined, along with a comparative analysis of their prediction accuracy. The research findingsindicate that it is feasible to predict the PPV on the tunnel structures using empirical equations. The attenuationcharacteristics of blasting vibration PPV are different in different structures and directions. The prediction accuracy of the empirical equations varies, while the discrepancies are minimal. The principal variation amongthese equations lies in the site-specific coefficients k, β, λ, highlighting the differential impact of structural anddirectional considerations on the predictive efficacy. Based on the empirical equation and safe PPV provided bythe blasting vibration safe standards on tunnels of China (GB6722-2014), and considering the influence of allstructures and directions, it is determined that the safe distance of blasting vibration in the tested tunnel projectshould be larger than 20.28–18.31 m, 18.31–16.16 m, and 16.16–13.75 m for blasting vibration frequency locatedin 10 Hz, 10–50 Hz, and >50 Hz.
基金the financial support from Hamedan University of Technology(No.16.91.294)
文摘Dynamic recrystallization and precipitation in a high manganese austenitic stainless steel were investigated by hot compression tests over temperatures of 950-1150~C at strain rates of 0.001 s-1-1 s-1. All the flow curves within the studied deformation regimes were typ- ical of dynamic recrystallization. A window was constructed to determine the value of apparent activation energy as a function of strain rate and deformation temperature. The kinetics of dynamic recrystallization was analyzed using the Avrami kinetics equation. A range of apparent activation energy for hot deformation from 303 kJ/mol to 477 kJ/mol is obtained at different deformation regimes. Microscopic characterization confirms that under a certain deformation condition （medium Zener-Hollomon parameter （Z） values）, dynamic recrystalliza- tion appears at first, but large particles can not inhibit the recrystallization. At low or high Z values, dynamic recrystallization may occur be- fore dynamic precipitation and proceeds faster. In both cases, secondary phase precipitation is observed along prior austenite grain bounda- ries. Stress relaxation tests at the same deformation temperatures also confirm the possibility of dynamic precipitation. Unexpectedly, the Avrami＇s exponent value increases with the increase of Z value. It is associated with the priority of dynamic recrystallization to dynamic precipitation at higher Z values.
文摘A reservoir landslide not only reduces the water storage capacity, but also causes extensive damages to the dam body, power/water transmission lines, roads, and other infrastructures. The Latian Dam, located 35 km north east of Tehran （Iran）, is one of the cases which has encountered serious problems with instability of its rock abutments. This paper addresses the stability analysis of the right abutment of the Latian Dam using limit equilibrium and numerical methods. Geomechanical characteristics of the rock abutment were first estimated based on engineering classification of the rock mass. Different search methods were examined for locating the critical circular/non-circular slip surface in conjunction with the general limit equilibrium method. The effect of variabi]ity of rock mass properties, water table, and earthquake load on the factor of safety （FS） and probability of failure （PF） was studied. In the event of rapid drawdown in the reservoir, the limit equilibrium analysis calculated FS=1.067 and PF=21.1%, and the numerical analysis returned FS=1.01. The results of the analyses suggest that the right abutment of the Latian Dam is prone to slide and needs treatment. Investigations demonstrated that a slope reduction by 15° at the upper part of the abutment would meet stability conditions even in the worst-case scenario （FS=1.297 and PF=2.07%）.
文摘Experimental and discrete element methods were used to investigate the failure behavior of room and pillar with different configura-tions under uniaxial loading.Concrete samples with dimension of 15 cm×15 cm×5 cm were prepared.Within the specimens,rooms and pillars with different configurations were provided.The room dimension was 1 cm×1 cm,and the pillar dimension was according to the room configuration.Twelve different configurations were chosen for rooms and pillars.The axial load was applied to the model by rate of 0.05 mm/min.The results show that the failure process was mostly governed by both the non-persistent joint angle and joint number.The compressive strength of the specimens was related to the fracture pattern and failure mechanism of the pillars.It was shown that the shear behaviour of pillars was related to the number of the induced tensile cracks,which increased by increasing the room angle.The compressive strength of samples increased with the increase of the room angle.The failure pattern and failure strength are similar in both methods,i.e.,the experimental testing and the numerical simulation.
文摘In this study,the effect of hot deformation on martensitic stainless steel was carried out in temperatures between 950 to 1100℃ and strain rates of 0.001,0.01 and 0.1 s 1.Two important dynamic recrystallization parameters,the critical strain and the point of maximum dynamic softening,were derived from strain hardening rate vs stress curves.Then the calculated parameters were used to predict the dynamic recrystallized fraction.Our results show that critical stress and strain increase with decreasing deformation temperature and increasing strain rate.The hot deformation activation energy of the steel is also investigated in the present work with 413 kJ/mol.Our experimental flow curves are in fair agreement with the kinetics of dynamic recrystallization model.
文摘The segregation behavior of a mixture of silica-coated titanium dioxide(TiO2)particles of three different sizes in a pseudo two-dimensional fluidized bed was studied experimentally by the freeze-sieving method and numerically by the multi-fluid model(MFM).Three-dimensional computational fluid dynamics(CFD)simulations were carried out to evaluate the effects of the solid wall boundary conditions on particle segregation in terms of specularity and particle-wall restitution coefficients.The quantitative indexes of segregation tendency and segregation degree were used to determine the axial segregation of the mixture in triangular coordinates.The simulation results revealed that the axial segregation increased with the specularity coefficient,whereas the particle-wall restitution coefficient had a minor effect on axial segregation.Comparison of the simulation results with experimental data showed that the appropriate value of the specularity coefficient used in the CFD model depended on superficial gas velocity.The study of the effects of superficial gas velocity on segregation behavior demonstrated that the greatest segregation was obtained at minimum fluidization velocity and the segregation decreased as the gas velocity gradually increased.
基金Project supported by Iran's National Elites Foundation(INEF)Partial supports of center of excellent for structures and earthquake engineering at Sharif University of technology
文摘A simultaneous experimental and numerical study of shear fracture of concrete-like materials is carried out using Brazilian disc specimens with initial double edge cracks and fourpoint bending beam specimens with double edge-notches.The interference effects of two cracks/notches are investigated through varied ligament angles and crack lengths.It is shown that shear fracturing paths change remarkably with the initial ligament angles and crack lengths.The cracked specimens are numerically simulated by an indirect boundary element method.A comparison between the numerical results and the experimental ones shows good agreement.
