Bedding structural planes significantly influence the mechanical properties and stability of engineering rock masses.This study conducts uniaxial compression tests on layered sandstone with various bedding angles(0...Bedding structural planes significantly influence the mechanical properties and stability of engineering rock masses.This study conducts uniaxial compression tests on layered sandstone with various bedding angles(0°,15°,30°,45°,60°,75°and 90°)to explore the impact of bedding angle on the deformational mechanical response,failure mode,and damage evolution processes of rocks.It develops a damage model based on the Logistic equation derived from the modulus’s degradation considering the combined effect of the sandstone bedding dip angle and load.This model is employed to study the damage accumulation state and its evolution within the layered rock mass.This research also introduces a piecewise constitutive model that considers the initial compaction characteristics to simulate the whole deformation process of layered sandstone under uniaxial compression.The results revealed that as the bedding angle increases from 0°to 90°,the uniaxial compressive strength and elastic modulus of layered sandstone significantly decrease,slightly increase,and then decline again.The corresponding failure modes transition from splitting tensile failure to slipping shear failure and back to splitting tensile failure.As indicated by the modulus’s degradation,the damage characteristics can be categorized into four stages:initial no damage,damage initiation,damage acceleration,and damage deceleration termination.The theoretical damage model based on the Logistic equation effectively simulates and predicts the entire damage evolution process.Moreover,the theoretical constitutive model curves closely align with the actual stress−strain curves of layered sandstone under uniaxial compression.The introduced constitutive model is concise,with fewer parameters,a straightforward parameter determination process,and a clear physical interpretation.This study offers valuable insights into the theory of layered rock mechanics and holds implications for ensuring the safety of rock engineering.展开更多
Cable-stayed bridges have been widely used in high-speed railway infrastructure.The accurate determination of cable’s representative temperatures is vital during the intricate processes of design,construction,and mai...Cable-stayed bridges have been widely used in high-speed railway infrastructure.The accurate determination of cable’s representative temperatures is vital during the intricate processes of design,construction,and maintenance of cable-stayed bridges.However,the representative temperatures of stayed cables are not specified in the existing design codes.To address this issue,this study investigates the distribution of the cable temperature and determinates its representative temperature.First,an experimental investigation,spanning over a period of one year,was carried out near the bridge site to obtain the temperature data.According to the statistical analysis of the measured data,it reveals that the temperature distribution is generally uniform along the cable cross-section without significant temperature gradient.Then,based on the limited data,the Monte Carlo,the gradient boosted regression trees(GBRT),and univariate linear regression(ULR)methods are employed to predict the cable’s representative temperature throughout the service life.These methods effectively overcome the limitations of insufficient monitoring data and accurately predict the representative temperature of the cables.However,each method has its own advantages and limitations in terms of applicability and accuracy.A comprehensive evaluation of the performance of these methods is conducted,and practical recommendations are provided for their application.The proposed methods and representative temperatures provide a good basis for the operation and maintenance of in-service long-span cable-stayed bridges.展开更多
The observation of geomagnetic field variations is an important approach to studying earthquake precursors.Since 1987,the China Earthquake Administration has explored this seismomagnetic relationship.In particular,the...The observation of geomagnetic field variations is an important approach to studying earthquake precursors.Since 1987,the China Earthquake Administration has explored this seismomagnetic relationship.In particular,they studied local magnetic field anomalies over the Chinese mainland for earthquake prediction.Owing to the years of research on the seismomagnetic relationship,earthquake prediction experts have concluded that the compressive magnetic effect,tectonic magnetic effect,electric magnetic fluid effect,and other factors contribute to preearthquake magnetic anomalies.However,this involves a small magnitude of magnetic field changes.It is difficult to relate them to the abnormal changes of the extremely large magnetic field in regions with extreme earthquakes owing to the high cost of professional geomagnetic equipment,thereby limiting large-scale deployment.Moreover,it is difficult to obtain strong magnetic field changes before an earthquake.The Tianjin Earthquake Agency has developed low-cost geomagnetic field observation equipment through the Beijing–Tianjin–Hebei geomagnetic equipment test project.The new system was used to test the availability of equipment and determine the findings based on big data..展开更多
The Yangtze River estuary is the main production area of Anguilla japonica in China,as well as the only existing fishery area for adult eels.Japanese eels are distributed in the main rivers and many tributaries from t...The Yangtze River estuary is the main production area of Anguilla japonica in China,as well as the only existing fishery area for adult eels.Japanese eels are distributed in the main rivers and many tributaries from the Yangtze River estuary to the upper Jinsha River,which extend to nearly 3 000 km.However,their migration behaviors remain relatively unknown.We analyzed the biological characteristics of 153 specimens of silver eels collected from the Jingjiang section of Yangtze River（31o30＇N,120o42＇E） between September and November,2008,and tested the sagittal Sr/Ca ratios of 27 specimens.Among the 153 specimens examined,85 were female and 68 were male,which translated to a female-male ratio of 1：0.8.The ages of the female specimens ranged from 3 to 7 a（average 5.52） with an average total length（TL） of（669±80） mm,average body weight（BW） of（555±229）g,average condition factor of 1.77±0.22,and average gonad somatic index（GSI） of 1.32±0.31.The ages of the males ranged from 3 to 5 a（average：4.38） with an average TL of（518±51） mm,average BW of（234±76） g,average condition factor of 1.62±0.18,and average GSI of 0.21±0.11.All biological parameters of females were significantly larger than those of the male specimens（P0.05）.According to the average Sr/Ca ratio（7.99±1.05） ×10-3 of the elver mark of sagitta,17 individuals（62.96%） were river eels and 10 individuals（37.04%） were estuarine eels.Of 16 females,13 individuals（81.25%） were river eels and 3 were estuarine eels,while of 11 males,36.36% were river eels and 63.64% were estuarine eels.The analysis on Sr/Ca ratios for every growth layer group（GLG） indicated there were no significant differences between second-age males and females.However,significant differences were observed between the third-age,fourth-age,and migration-age male and female specimens.This was likely related to the fact that second-age eels of both sexes stay in the same inhabitation waters;however,as they grow older,they move to different areas.展开更多
An ontology and metadata for online learning resource repository management is constructed. First, based on the analysis of the use-case diagram, the upper ontology is illustrated which includes resource library ontol...An ontology and metadata for online learning resource repository management is constructed. First, based on the analysis of the use-case diagram, the upper ontology is illustrated which includes resource library ontology and user ontology, and evaluated from its function and implementation; then the corresponding class diagram, resource description framework （RDF） schema and extensible markup language （XML） schema are given. Secondly, the metadata for online learning resource repository management is proposed based on the Dublin Core Metadata Initiative and the IEEE Learning Technologies Standards Committee Learning Object Metadata Working Group. Finally, the inference instance is shown, which proves the validity of ontology and metadata in online learning resource repository management.展开更多
The material of nickel aluminum bronze (NAB) presents superior properties such as high strength, excellent wear resistance and stress corrosion resistance and is extensively used for marine propellers. In order to est...The material of nickel aluminum bronze (NAB) presents superior properties such as high strength, excellent wear resistance and stress corrosion resistance and is extensively used for marine propellers. In order to establish the constitutive relation of NAB under high strain rate condition, a new methodology was proposed to accurately identify the constitutive parameters of Johnson?Cook model in machining, combining SHPB tests, predictive cutting force model and orthogonal cutting experiment. Firstly, SHPB tests were carried out to obtain the true stress?strain curves at various temperatures and strain rates. Then, an objective function of the predictive and experimental flow stresses was set up, which put the identified parameters of SHPB tests as the initial value, and utilized the PSO algorithm to identify the constitutive parameters of NAB in machining. Finally, the identified parameters were verified to be sufficiently accurate by comparing the values of cutting forces calculated from the predictive model and FEM simulation.展开更多
The local and global mechanical responses of gas tungsten arc welds（GTAW） of a 2219-T87 aluminum alloy were investigated with experiment and numerical simulation.Digital image correlation（DIC） was used to access t...The local and global mechanical responses of gas tungsten arc welds（GTAW） of a 2219-T87 aluminum alloy were investigated with experiment and numerical simulation.Digital image correlation（DIC） was used to access the local strain fields in transversely loaded welds and to determine the local stress-strain curves of various regions in the joint.The results show that the DIC method is efficient to acquire the local stress-strain curves but the curves of harder regions are incomplete because the stress and strain ranges are limited by the weakest region.With appropriate extrapolation,the complete local stress-strain curves were acquired and proved to be effective to predict the tensile behavior of the welded joint.During the tensile process,the fracture initiates from the weld toes owing to their plastic strain concentrations and then propagates along the fusion line,finally propagates into the partially melted zone（PMZ）.展开更多
To study the capacity of artificial neural network (ANN) applying to battlefield target classification and result of classification, according to the characteristics of battlefield target acoustic and seismic sign...To study the capacity of artificial neural network (ANN) applying to battlefield target classification and result of classification, according to the characteristics of battlefield target acoustic and seismic signals, an on the spot experiment was carried out to derive acoustic and seismic signals of a tank and jeep by special experiment system. Experiment data processed by fast Fourier transform(FFT) were used to train the ANN to distinguish the two battlefield targets. The ANN classifier was performed by the special program based on the modified back propagation (BP) algorithm. The ANN classifier has high correct identification rates for acoustic and seismic signals of battlefield targets, and is suitable for the classification of battlefield targets. The modified BP algorithm eliminates oscillations and local minimum of the standard BP algorithm, and enhances the convergence rate of the ANN.展开更多
Numerical control（NC） warm bending is a proven strategy to form the large diameter thin-walled（LDTW） Ti-6 Al-4 V tubes, which are typical light-weight and high-performance structural components urgently required i...Numerical control（NC） warm bending is a proven strategy to form the large diameter thin-walled（LDTW） Ti-6 Al-4 V tubes, which are typical light-weight and high-performance structural components urgently required in many industries. In virtue of unveiling the thermo-mechanical coupled deformation behaviors, uniaxial tensile tests were conducted on Ti-6 Al-4 V tube within wide ranges of temperatures（25-600 ℃） and strain rates（0.00067-0.1 s～（-1））. Moreover, a modified Johnson-Cook（JC） model is proposed with a consideration of nonlinear strain rate hardening and the interaction between strain hardening and thermal softening. Resultantly, the present model gives more accurate predictions for flow stress over the entire deformation ranges and the maximum error decreases by about 90%. By employing proposed model to NC warm bending, preferable precision is obtained in predicting forming defects including fracture, wrinkling and over thinning. The present work lays foundation for the forming limit prediction and process optimization in NC warm bending of LDTW Ti-6 Al-4 V tubes.展开更多
Effects of initial δ phase（Ni_3Nb） on the hot tensile deformation behaviors and material constants of a Ni-based superalloy were investigated over wide ranges of strain rate and deformation temperature. It is found...Effects of initial δ phase（Ni_3Nb） on the hot tensile deformation behaviors and material constants of a Ni-based superalloy were investigated over wide ranges of strain rate and deformation temperature. It is found that the true stress-true strain curves exhibit peak stress at a small strain, and the peak stress increases with the increase of initial δ phase. After the peak stress, initial δ phase promotes the dynamic softening behaviors, resulting in the decreased flow stress. An improved Arrhenius constitutive model is proposed to consider the synthetical effects of initial δ phase, deformation temperature, strain rate, and strain on hot deformation behaviors. In the improved model, material constants are expressed as the functions of the content of initial δ phase and strain. A good agreement between the predicted and measured results indicates that the improved Arrhenius constitutive model can well describe hot deformation behaviors of the studied Ni-based superalloy.展开更多
基金Projects(52074299,41941018)supported by the National Natural Science Foundation of ChinaProject(2023JCCXSB02)supported by the Fundamental Research Funds for the Central Universities,China。
文摘Bedding structural planes significantly influence the mechanical properties and stability of engineering rock masses.This study conducts uniaxial compression tests on layered sandstone with various bedding angles(0°,15°,30°,45°,60°,75°and 90°)to explore the impact of bedding angle on the deformational mechanical response,failure mode,and damage evolution processes of rocks.It develops a damage model based on the Logistic equation derived from the modulus’s degradation considering the combined effect of the sandstone bedding dip angle and load.This model is employed to study the damage accumulation state and its evolution within the layered rock mass.This research also introduces a piecewise constitutive model that considers the initial compaction characteristics to simulate the whole deformation process of layered sandstone under uniaxial compression.The results revealed that as the bedding angle increases from 0°to 90°,the uniaxial compressive strength and elastic modulus of layered sandstone significantly decrease,slightly increase,and then decline again.The corresponding failure modes transition from splitting tensile failure to slipping shear failure and back to splitting tensile failure.As indicated by the modulus’s degradation,the damage characteristics can be categorized into four stages:initial no damage,damage initiation,damage acceleration,and damage deceleration termination.The theoretical damage model based on the Logistic equation effectively simulates and predicts the entire damage evolution process.Moreover,the theoretical constitutive model curves closely align with the actual stress−strain curves of layered sandstone under uniaxial compression.The introduced constitutive model is concise,with fewer parameters,a straightforward parameter determination process,and a clear physical interpretation.This study offers valuable insights into the theory of layered rock mechanics and holds implications for ensuring the safety of rock engineering.
基金Project(2017G006-N)supported by the Project of Science and Technology Research and Development Program of China Railway Corporation。
文摘Cable-stayed bridges have been widely used in high-speed railway infrastructure.The accurate determination of cable’s representative temperatures is vital during the intricate processes of design,construction,and maintenance of cable-stayed bridges.However,the representative temperatures of stayed cables are not specified in the existing design codes.To address this issue,this study investigates the distribution of the cable temperature and determinates its representative temperature.First,an experimental investigation,spanning over a period of one year,was carried out near the bridge site to obtain the temperature data.According to the statistical analysis of the measured data,it reveals that the temperature distribution is generally uniform along the cable cross-section without significant temperature gradient.Then,based on the limited data,the Monte Carlo,the gradient boosted regression trees(GBRT),and univariate linear regression(ULR)methods are employed to predict the cable’s representative temperature throughout the service life.These methods effectively overcome the limitations of insufficient monitoring data and accurately predict the representative temperature of the cables.However,each method has its own advantages and limitations in terms of applicability and accuracy.A comprehensive evaluation of the performance of these methods is conducted,and practical recommendations are provided for their application.The proposed methods and representative temperatures provide a good basis for the operation and maintenance of in-service long-span cable-stayed bridges.
基金supported by the Spark Program of Earthquake Science and Technology(No.XH23003C).
文摘The observation of geomagnetic field variations is an important approach to studying earthquake precursors.Since 1987,the China Earthquake Administration has explored this seismomagnetic relationship.In particular,they studied local magnetic field anomalies over the Chinese mainland for earthquake prediction.Owing to the years of research on the seismomagnetic relationship,earthquake prediction experts have concluded that the compressive magnetic effect,tectonic magnetic effect,electric magnetic fluid effect,and other factors contribute to preearthquake magnetic anomalies.However,this involves a small magnitude of magnetic field changes.It is difficult to relate them to the abnormal changes of the extremely large magnetic field in regions with extreme earthquakes owing to the high cost of professional geomagnetic equipment,thereby limiting large-scale deployment.Moreover,it is difficult to obtain strong magnetic field changes before an earthquake.The Tianjin Earthquake Agency has developed low-cost geomagnetic field observation equipment through the Beijing–Tianjin–Hebei geomagnetic equipment test project.The new system was used to test the availability of equipment and determine the findings based on big data..
基金supported by the Chinese National Science Foundation under the Grant(30771650)the Key Programs of Science and Technology Commission Foundation of Shanghai(08391910200)+3 种基金Special Fund for Agroscientific Research in the Public Interest(201203065)Research Fund for the Doctoral Program of Higher Education of China(20070264001)E-class Programs of Shanghai Municipal Education Commission(E03009)the Key Subject Construction of Shanghai(S30701)
文摘The Yangtze River estuary is the main production area of Anguilla japonica in China,as well as the only existing fishery area for adult eels.Japanese eels are distributed in the main rivers and many tributaries from the Yangtze River estuary to the upper Jinsha River,which extend to nearly 3 000 km.However,their migration behaviors remain relatively unknown.We analyzed the biological characteristics of 153 specimens of silver eels collected from the Jingjiang section of Yangtze River（31o30＇N,120o42＇E） between September and November,2008,and tested the sagittal Sr/Ca ratios of 27 specimens.Among the 153 specimens examined,85 were female and 68 were male,which translated to a female-male ratio of 1：0.8.The ages of the female specimens ranged from 3 to 7 a（average 5.52） with an average total length（TL） of（669±80） mm,average body weight（BW） of（555±229）g,average condition factor of 1.77±0.22,and average gonad somatic index（GSI） of 1.32±0.31.The ages of the males ranged from 3 to 5 a（average：4.38） with an average TL of（518±51） mm,average BW of（234±76） g,average condition factor of 1.62±0.18,and average GSI of 0.21±0.11.All biological parameters of females were significantly larger than those of the male specimens（P0.05）.According to the average Sr/Ca ratio（7.99±1.05） ×10-3 of the elver mark of sagitta,17 individuals（62.96%） were river eels and 10 individuals（37.04%） were estuarine eels.Of 16 females,13 individuals（81.25%） were river eels and 3 were estuarine eels,while of 11 males,36.36% were river eels and 63.64% were estuarine eels.The analysis on Sr/Ca ratios for every growth layer group（GLG） indicated there were no significant differences between second-age males and females.However,significant differences were observed between the third-age,fourth-age,and migration-age male and female specimens.This was likely related to the fact that second-age eels of both sexes stay in the same inhabitation waters;however,as they grow older,they move to different areas.
基金The Advanced University Action Plan of the Minis-try of Education of China (2004XD-03).
文摘An ontology and metadata for online learning resource repository management is constructed. First, based on the analysis of the use-case diagram, the upper ontology is illustrated which includes resource library ontology and user ontology, and evaluated from its function and implementation; then the corresponding class diagram, resource description framework （RDF） schema and extensible markup language （XML） schema are given. Secondly, the metadata for online learning resource repository management is proposed based on the Dublin Core Metadata Initiative and the IEEE Learning Technologies Standards Committee Learning Object Metadata Working Group. Finally, the inference instance is shown, which proves the validity of ontology and metadata in online learning resource repository management.
基金Project(2014CB046704)supported by the National Basic Research Program of ChinaProject(2014BAB13B01)supported by the National Science and Technology Pillar Program of China
文摘The material of nickel aluminum bronze (NAB) presents superior properties such as high strength, excellent wear resistance and stress corrosion resistance and is extensively used for marine propellers. In order to establish the constitutive relation of NAB under high strain rate condition, a new methodology was proposed to accurately identify the constitutive parameters of Johnson?Cook model in machining, combining SHPB tests, predictive cutting force model and orthogonal cutting experiment. Firstly, SHPB tests were carried out to obtain the true stress?strain curves at various temperatures and strain rates. Then, an objective function of the predictive and experimental flow stresses was set up, which put the identified parameters of SHPB tests as the initial value, and utilized the PSO algorithm to identify the constitutive parameters of NAB in machining. Finally, the identified parameters were verified to be sufficiently accurate by comparing the values of cutting forces calculated from the predictive model and FEM simulation.
基金Project(2012 2X04012-011)supported by the Innovation Platform for Process Modeling and Simulation of Advanced Materials Processing Technologies,China
文摘The local and global mechanical responses of gas tungsten arc welds（GTAW） of a 2219-T87 aluminum alloy were investigated with experiment and numerical simulation.Digital image correlation（DIC） was used to access the local strain fields in transversely loaded welds and to determine the local stress-strain curves of various regions in the joint.The results show that the DIC method is efficient to acquire the local stress-strain curves but the curves of harder regions are incomplete because the stress and strain ranges are limited by the weakest region.With appropriate extrapolation,the complete local stress-strain curves were acquired and proved to be effective to predict the tensile behavior of the welded joint.During the tensile process,the fracture initiates from the weld toes owing to their plastic strain concentrations and then propagates along the fusion line,finally propagates into the partially melted zone（PMZ）.
文摘To study the capacity of artificial neural network (ANN) applying to battlefield target classification and result of classification, according to the characteristics of battlefield target acoustic and seismic signals, an on the spot experiment was carried out to derive acoustic and seismic signals of a tank and jeep by special experiment system. Experiment data processed by fast Fourier transform(FFT) were used to train the ANN to distinguish the two battlefield targets. The ANN classifier was performed by the special program based on the modified back propagation (BP) algorithm. The ANN classifier has high correct identification rates for acoustic and seismic signals of battlefield targets, and is suitable for the classification of battlefield targets. The modified BP algorithm eliminates oscillations and local minimum of the standard BP algorithm, and enhances the convergence rate of the ANN.
基金Projects(50905144,51275415)supported by the National Natural Science Foundation of ChinaProject supported by the Program for New Century Excellent Talents in University,China+1 种基金Project(3102014KYJD001)supported by Fundamental Research Funds for the Central Universities,ChinaProject(B08040)supported by Program of Introducing Talents of Discipline to Universities("111"Project),China
文摘Numerical control（NC） warm bending is a proven strategy to form the large diameter thin-walled（LDTW） Ti-6 Al-4 V tubes, which are typical light-weight and high-performance structural components urgently required in many industries. In virtue of unveiling the thermo-mechanical coupled deformation behaviors, uniaxial tensile tests were conducted on Ti-6 Al-4 V tube within wide ranges of temperatures（25-600 ℃） and strain rates（0.00067-0.1 s～（-1））. Moreover, a modified Johnson-Cook（JC） model is proposed with a consideration of nonlinear strain rate hardening and the interaction between strain hardening and thermal softening. Resultantly, the present model gives more accurate predictions for flow stress over the entire deformation ranges and the maximum error decreases by about 90%. By employing proposed model to NC warm bending, preferable precision is obtained in predicting forming defects including fracture, wrinkling and over thinning. The present work lays foundation for the forming limit prediction and process optimization in NC warm bending of LDTW Ti-6 Al-4 V tubes.
基金Projects(5137550251305466) supported by the National Natural Science Foundation of China+2 种基金Project(2015CX002) supported by the Innovation-driven Plan in Central South University,ChinaProject(2013CB035801) supported by the National Basic Research Program of ChinaProject(2015NGQ001) supported by Key Laboratory of Efficient&Clean Energy Utilization,College of Hunan Province,China
文摘Effects of initial δ phase（Ni_3Nb） on the hot tensile deformation behaviors and material constants of a Ni-based superalloy were investigated over wide ranges of strain rate and deformation temperature. It is found that the true stress-true strain curves exhibit peak stress at a small strain, and the peak stress increases with the increase of initial δ phase. After the peak stress, initial δ phase promotes the dynamic softening behaviors, resulting in the decreased flow stress. An improved Arrhenius constitutive model is proposed to consider the synthetical effects of initial δ phase, deformation temperature, strain rate, and strain on hot deformation behaviors. In the improved model, material constants are expressed as the functions of the content of initial δ phase and strain. A good agreement between the predicted and measured results indicates that the improved Arrhenius constitutive model can well describe hot deformation behaviors of the studied Ni-based superalloy.
