The mechanical properties of rock deteriorate under repeated wet-dry(WD)cycles,causing the deformation and failure of the rock mass.A reasonable damage constitutive model can truly reflect the whole process of rock de...The mechanical properties of rock deteriorate under repeated wet-dry(WD)cycles,causing the deformation and failure of the rock mass.A reasonable damage constitutive model can truly reflect the whole process of rock deformation and failure.Therefore,it is of great significance to study the damage characteristics and constitutive behaviour of rock subjected to numerous WD cycles.First,sandstone from Tingliang tunnel was sampled for the WD cycle experiment,and uniaxial and triaxial tests were carried out on the rock samples after various numbers of WD cycles to analyze their macroscale damage characteristics.Then,the damage mechanisms of the rock samples under the action of WD cycling were identified by X-ray diffraction(XRD)and scanning electron microscopy(SEM).Finally,based on the test data,the WD cycle-induced damage variable,Weibull distribution function,damage threshold,Drucker-Prager(D-P)yield criterion and residual strength correction coefficient were introduced,a wet-dry loading(WDL)constitutive damage model that considers the cracking stress of rock masses was established,and the expressions of the corresponding parameters were given.The results show that an increasing number of WD cycles induces considerable variations in the macroscopic physical and mechanical parameters(such as the rock sample mass,saturated water content,longitudinal-wave velocity,compressive strength and elastic modulus),and the rate of change presents two stages,the inflection point of their rate of change is the 15th WD cycle.Microscopically,the rock sample structure changes from intact and dense to fragmented and unconsolidated;additionally,the surface roughness increases,and the mineral composition changes.The established constitutive damage model exhibited good agreement with the experimental data;thus,this model can reflect the deformation and failure of rocks under WDL conditions,and the physical meaning of each parameter is clear.展开更多
The uniform settle caused by the permafrost creep is still the primary problem of engineering construction in cold region.To investigate the creep characteristics of frozen soils mixed with silty clay and coarse-grain...The uniform settle caused by the permafrost creep is still the primary problem of engineering construction in cold region.To investigate the creep characteristics of frozen soils mixed with silty clay and coarse-grained sand,several triaxial creep tests of frozen mixed soils under different conditions(temperature,confining pressure,coarse-grained particle content) were performed,and the effects of the temperature,confining pressure and coarse particle content on the creep characteristics of frozen mixed soils were also analyzed.The results of the experiments indicated that when the confining pressure was low,the specimen exhibited an attenuation creep under a low-stress level(0.4-0.7) and a non-attenuation creep under a high-stress level(0.7-0.9).In contrast,when the confining pressure was high,the specimen had both initial and stable creep stages,but no the accelerated creep stage.The higher the content of coarse grains,the shorter the stable creep stage,and the easier to enter the accelerated creep stage for the specimen.Further,the long-term strength of frozen soils decreased with an increase in the content of coarse grains.Finally,a newly improved Nishihara model was proposed to consider both the hardening effect and damage effect by introducing both the hardening and damage variables,which can model the entire creep process of frozen soils modeled relatively easily.It was found that with the increasing content of coarse particle,both the strengthening and damaged effects in the creep process are reduced。展开更多
Healthy full life cycle has become an important national strategy,which indicates that attention needs to be given to human health throughout the life course.The full life cycle includes the whole process of conceptio...Healthy full life cycle has become an important national strategy,which indicates that attention needs to be given to human health throughout the life course.The full life cycle includes the whole process of conception and birth,development,growth,aging,and death,which has been recorded in Yellow Emperor's Canon of Medicine.From the perspective of traditional Chinese medicine (TCM) constitution theory,the TCM constitution focuses on the life process in a continuous evolution based on individual development at different phases or stages from infancy to senility.The development of TCM constitution is beneficial in accumulating the theoretical and practical experience for promoting the application of TCM constitution health service into the full life cycle,and providing theory,technique and method for TCM health service in the full life cycle,as well.Through this review,we've found that TCM constitution has being widely used for clinical practice,but still needs further improvement.展开更多
The experimental tests of tensile for lead-flee solder Sn-3.5Ag were performed for the general work temperatures range from 11 to 90 ℃ and strain rate range from 5 × 10^-5 to 2 × 10^-2s^-1, and its stress--...The experimental tests of tensile for lead-flee solder Sn-3.5Ag were performed for the general work temperatures range from 11 to 90 ℃ and strain rate range from 5 × 10^-5 to 2 × 10^-2s^-1, and its stress--strain curves were compared to those of solder Sn-37Pb. The parameters in Anand model for solder Sn-3.5Ag were fitted based on experimental data and nonlinear fitting method, and its validity was checked by means of experimental data. Furthermore, the Anand model was used in the FEM analysis to evaluate solder joint thermal cycle reliability. The results show that solder Sn-3.5Ag has a better creep resistance than solder Sn-37Pb. The maximum stress is located at the upper right comer of the outmost solder joint from the symmetric center, and thermal fatigue life is predicted to be 3.796 × 10^4 cycles under the calculated conditions.展开更多
The mechanical behaviors of the interface between coarse-grained soil and concrete were investigated by simple shear tests under condition of mixed soil slurry (bentonite mixed with cement grout).For comparison,the in...The mechanical behaviors of the interface between coarse-grained soil and concrete were investigated by simple shear tests under condition of mixed soil slurry (bentonite mixed with cement grout).For comparison,the interfaces both without slurry and with bentonite slurry were analyzed.The experimental results show that different slurries exert much influence on the strength and deformation of soil/structure interface.Under mixed soil slurry,strain softening and shear dilatation are observed,while shear dilatation appears under the small normal stress of the interface without slurry,and shear contraction is significant under the condition of the bentonite slurry.The thickness of the interface was determined by analyzing the disturbed height of the sample with both simple shear test and particle flow code (PFC).An elasto-plastic constitutive model incorporating strain softening and dilatancy for thin layer element of interface was formulated in the framework of generalized potential theory.The relation curves of shear stress and shear strain,as well as the relation curves of normal strain and shear strain,were fitted by a piecewise function composed by hyperbolic functions and resembling normal functions.The entire model parameters can be identified by tests.The new model is verified by comparing the measured data of indoor cut-off wall model tests with the predictions from finite element method (FEM).The FEM results indicate that the stress of wall calculated by using Goodman element is too large,and the maximum deviation between the test data and prediction is about 45%.While the prediction from the proposed model is close to the measured data,and the error is generally less than 10%.展开更多
The constitutive equation under the low-cycle fatigue (LCF) was discussed, and a two-dimensional (2-D) model for simulating fatigue crack extension was put forward in order to propose a new cyclic J-integral. The ...The constitutive equation under the low-cycle fatigue (LCF) was discussed, and a two-dimensional (2-D) model for simulating fatigue crack extension was put forward in order to propose a new cyclic J-integral. The definition, primary characteristics, physical interpretations and numerical evaluation of the new parameter were investigated in detail. Moreover, the new cyclic J-integral for LCF behaviors was validated by the compact tension (CT) specimens. Results show that the calculated values of the new parameter can correlate well with LCF crack growth rate, during constant-amplitude loading. In addition, the phenomenon of fatigue retardation was explained through the viewpoint of energy based on the concept of the new parameter.展开更多
基金supported by the National Natural Science Foundation of China(Grant No.52108367)Guangxi University Young and middle-aged teachers’basic scientific research ability improvement project(2020ky01011)。
文摘The mechanical properties of rock deteriorate under repeated wet-dry(WD)cycles,causing the deformation and failure of the rock mass.A reasonable damage constitutive model can truly reflect the whole process of rock deformation and failure.Therefore,it is of great significance to study the damage characteristics and constitutive behaviour of rock subjected to numerous WD cycles.First,sandstone from Tingliang tunnel was sampled for the WD cycle experiment,and uniaxial and triaxial tests were carried out on the rock samples after various numbers of WD cycles to analyze their macroscale damage characteristics.Then,the damage mechanisms of the rock samples under the action of WD cycling were identified by X-ray diffraction(XRD)and scanning electron microscopy(SEM).Finally,based on the test data,the WD cycle-induced damage variable,Weibull distribution function,damage threshold,Drucker-Prager(D-P)yield criterion and residual strength correction coefficient were introduced,a wet-dry loading(WDL)constitutive damage model that considers the cracking stress of rock masses was established,and the expressions of the corresponding parameters were given.The results show that an increasing number of WD cycles induces considerable variations in the macroscopic physical and mechanical parameters(such as the rock sample mass,saturated water content,longitudinal-wave velocity,compressive strength and elastic modulus),and the rate of change presents two stages,the inflection point of their rate of change is the 15th WD cycle.Microscopically,the rock sample structure changes from intact and dense to fragmented and unconsolidated;additionally,the surface roughness increases,and the mineral composition changes.The established constitutive damage model exhibited good agreement with the experimental data;thus,this model can reflect the deformation and failure of rocks under WDL conditions,and the physical meaning of each parameter is clear.
基金the funding of the Autonomous Research Topic of the State Key Laboratory of Frozen Soil Engineering,Chinese Academy of Sciences (Nos.Y951061401)the Science and Technology Project of Yalong River Hydropower Development Company (YLLHK-LHA-2019006)the National Natural Science Foundation of China (NSFC) (Grant number 41771066)。
文摘The uniform settle caused by the permafrost creep is still the primary problem of engineering construction in cold region.To investigate the creep characteristics of frozen soils mixed with silty clay and coarse-grained sand,several triaxial creep tests of frozen mixed soils under different conditions(temperature,confining pressure,coarse-grained particle content) were performed,and the effects of the temperature,confining pressure and coarse particle content on the creep characteristics of frozen mixed soils were also analyzed.The results of the experiments indicated that when the confining pressure was low,the specimen exhibited an attenuation creep under a low-stress level(0.4-0.7) and a non-attenuation creep under a high-stress level(0.7-0.9).In contrast,when the confining pressure was high,the specimen had both initial and stable creep stages,but no the accelerated creep stage.The higher the content of coarse grains,the shorter the stable creep stage,and the easier to enter the accelerated creep stage for the specimen.Further,the long-term strength of frozen soils decreased with an increase in the content of coarse grains.Finally,a newly improved Nishihara model was proposed to consider both the hardening effect and damage effect by introducing both the hardening and damage variables,which can model the entire creep process of frozen soils modeled relatively easily.It was found that with the increasing content of coarse particle,both the strengthening and damaged effects in the creep process are reduced。
基金The paper was supported by the Key Project of National Natural Science Foundation of China(8173000574).
文摘Healthy full life cycle has become an important national strategy,which indicates that attention needs to be given to human health throughout the life course.The full life cycle includes the whole process of conception and birth,development,growth,aging,and death,which has been recorded in Yellow Emperor's Canon of Medicine.From the perspective of traditional Chinese medicine (TCM) constitution theory,the TCM constitution focuses on the life process in a continuous evolution based on individual development at different phases or stages from infancy to senility.The development of TCM constitution is beneficial in accumulating the theoretical and practical experience for promoting the application of TCM constitution health service into the full life cycle,and providing theory,technique and method for TCM health service in the full life cycle,as well.Through this review,we've found that TCM constitution has being widely used for clinical practice,but still needs further improvement.
基金Project(50376076) supported by the National Natural Science Foundation of China
文摘The experimental tests of tensile for lead-flee solder Sn-3.5Ag were performed for the general work temperatures range from 11 to 90 ℃ and strain rate range from 5 × 10^-5 to 2 × 10^-2s^-1, and its stress--strain curves were compared to those of solder Sn-37Pb. The parameters in Anand model for solder Sn-3.5Ag were fitted based on experimental data and nonlinear fitting method, and its validity was checked by means of experimental data. Furthermore, the Anand model was used in the FEM analysis to evaluate solder joint thermal cycle reliability. The results show that solder Sn-3.5Ag has a better creep resistance than solder Sn-37Pb. The maximum stress is located at the upper right comer of the outmost solder joint from the symmetric center, and thermal fatigue life is predicted to be 3.796 × 10^4 cycles under the calculated conditions.
基金Project(20110094110002) supported by the Specialized Research Fund for the Doctoral Program of Higher Education of ChinaProject(200801014) supported by the Ministry of Water Resources of ChinaProject(50825901) supported by the National Natural Science Foundation of China
文摘The mechanical behaviors of the interface between coarse-grained soil and concrete were investigated by simple shear tests under condition of mixed soil slurry (bentonite mixed with cement grout).For comparison,the interfaces both without slurry and with bentonite slurry were analyzed.The experimental results show that different slurries exert much influence on the strength and deformation of soil/structure interface.Under mixed soil slurry,strain softening and shear dilatation are observed,while shear dilatation appears under the small normal stress of the interface without slurry,and shear contraction is significant under the condition of the bentonite slurry.The thickness of the interface was determined by analyzing the disturbed height of the sample with both simple shear test and particle flow code (PFC).An elasto-plastic constitutive model incorporating strain softening and dilatancy for thin layer element of interface was formulated in the framework of generalized potential theory.The relation curves of shear stress and shear strain,as well as the relation curves of normal strain and shear strain,were fitted by a piecewise function composed by hyperbolic functions and resembling normal functions.The entire model parameters can be identified by tests.The new model is verified by comparing the measured data of indoor cut-off wall model tests with the predictions from finite element method (FEM).The FEM results indicate that the stress of wall calculated by using Goodman element is too large,and the maximum deviation between the test data and prediction is about 45%.While the prediction from the proposed model is close to the measured data,and the error is generally less than 10%.
基金Project supported by the Municipal Key Subject Program of Shanghai (No.Y0103)
文摘The constitutive equation under the low-cycle fatigue (LCF) was discussed, and a two-dimensional (2-D) model for simulating fatigue crack extension was put forward in order to propose a new cyclic J-integral. The definition, primary characteristics, physical interpretations and numerical evaluation of the new parameter were investigated in detail. Moreover, the new cyclic J-integral for LCF behaviors was validated by the compact tension (CT) specimens. Results show that the calculated values of the new parameter can correlate well with LCF crack growth rate, during constant-amplitude loading. In addition, the phenomenon of fatigue retardation was explained through the viewpoint of energy based on the concept of the new parameter.
基金Project(52275371) supported by the National Natural Science Foundation of ChinaProject(2020YFA0714900) supported by the National Key R&D Program of China。