Enzyme-induced carbonate precipitation(EICP)is an emanating,eco-friendly and potentially sound technique that has presented promise in various geotechnical applications.However,the durability and microscopic character...Enzyme-induced carbonate precipitation(EICP)is an emanating,eco-friendly and potentially sound technique that has presented promise in various geotechnical applications.However,the durability and microscopic characteristics of EICP-treated specimens against the impact of drying-wetting(D-W)cycles is under-explored yet.This study investigates the evolution of mechanical behavior and pore charac-teristics of EICP-treated sea sand subjected to D-W cycles.The uniaxial compressive strength(UCS)tests,synchrotron radiation micro-computed tomography(micro-CT),and three-dimensional(3D)recon-struction of CT images were performed to study the multiscale evolution characteristics of EICP-reinforced sea sand under the effect of D-W cycles.The potential correlations between microstructure characteristics and macro-mechanical property deterioration were investigated using gray relational analysis(GRA).Results showed that the UCS of EICP-treated specimens decreases by 63.7% after 15 D-W cycles.The proportion of mesopores gradually decreases whereas the proportion of macropores in-creases due to the exfoliated calcium carbonate with increasing number of D-W cycles.The micro-structure in EICP-reinforced sea sand was gradually disintegrated,resulting in increasing pore size and development of pore shape from ellipsoidal to columnar and branched.The gray relational degree suggested that the weight loss rate and UCS deterioration were attributed to the development of branched pores with a size of 100-1000 m m under the action of D-W cycles.Overall,the results in this study provide a useful guidancee for the long-term stability and evolution characteristics of EICP-reinforced sea sand under D-W weathering conditions.展开更多
Based on seawater immersion,drying-wetting cycles,carbonation and drying-wetting cycles for coral aggregate sea-water concrete(CASC)with different strength grades,the effect of carbonation and drying-wetting cycles on...Based on seawater immersion,drying-wetting cycles,carbonation and drying-wetting cycles for coral aggregate sea-water concrete(CASC)with different strength grades,the effect of carbonation and drying-wetting cycles on chloride diffusion be-havior of CASC is studied.The results show that the free surface chloride concentration(Cs),free chloride diffusion coefficient(Df)and time-dependent index(m)of CASC in the drying-wetting cycles is obviously higher than that in seawater immersion.The Df and m of CASC of carbonation and drying-wetting cycles is higher than that in the drying-wetting cycles.Carbonation increases the Df and m of CASC,which is against CASC to resist chloride corrosion.The corrosion possibility of CASC structures in different ex-posed areas is as follows:splash zone(carbonation and drying-wetting cycles)>tidal zone(drying-wetting cycles)>underwater zone(seawater immersion).Besides,the chloride diffusion rate of C65-CASC is 17.8%-63.4%higher than that of C65-ordinary aggre-gate concrete(OAC)in seawater immersion(underwater zone).Therefore,anti-corrosion measures should be adopted to improve the service life of CASC structure in the oceanic environment.展开更多
The chloride ion transmission model considering diffusion and convection was established respectively for different zones in concrete by analyzing chloride ion transmission mechanism under the dryingwetting cycles. Th...The chloride ion transmission model considering diffusion and convection was established respectively for different zones in concrete by analyzing chloride ion transmission mechanism under the dryingwetting cycles. The finite difference method was adopted to solve the model. The equation of chloride ion transmission model in the convection and diffusion zone of concrete was discreted by the group explicit scheme with right single point (GER method) and the equation in diffusion zone was discreted by FTCS difference scheme. According to relative humidity characteristics in concrete under drying-wetting cycles, the seepage velocity equation was formulated based on Kelvin Equation and Darcy's Law. The time-variant equations of chloride ion concentration of concrete surface and the boundary surface of the convection and diffusion zone were established. Based on the software MATLAB the numerical calculation was carried out by using the model and basic material parameters from the experiments. The calculation of chloride ion concentration distribution in concrete is in good agreement with the drying-wetting cycles experiments. It can be shown that the chloride ion transmission model and the seepage velocity equation are reasonable and practical. Studies have shown that the chloride ion transmission in concrete considering convection and diffusion under the drying-wetting cycles is the better correlation with the actual situation than that only considering the diffusion.展开更多
As a widely-applied engineering material in cold regions, the frozen subgrade soils are usually subjected to seismic loading, which are also dramatically influenced by the freeze-thaw(F-T)cycles due to the varying tem...As a widely-applied engineering material in cold regions, the frozen subgrade soils are usually subjected to seismic loading, which are also dramatically influenced by the freeze-thaw(F-T)cycles due to the varying temperature. A series of dynamic cyclic triaxial experiments were conducted through a cryogenic triaxial apparatus for exploring the influences of F-T cycles on the dynamic mechanical properties of frozen subgrade clay.According to the experimental results of frozen clay at the temperature of-10℃, the dynamic responses and microstructure variation at different times of F-T cycles(0, 1, 5, and 20 cycles) were explored in detail.It is experimentally demonstrated that the dynamic stress-strain curves and dynamic volumetric strain curves of frozen clay are significantly sparse after 20F-T cycles. Meanwhile, the cyclic number at failure(Nf) of the frozen specimen reduces by 89% after 20freeze-thaw cycles at a low ratio of the dynamic stress amplitude. In addition, with the increasing F-T cycles,the axial accumulative strain, residual deformation,and the value of damage variable of frozen clay increase, while the dynamic resilient modulus and dynamic strength decrease. Finally, the influence of the F-T cycles on the failure mechanisms of frozen clay was discussed in terms of the microstructure variation. These studies contribute to a better understanding of the fundamental changes in the dynamic mechanical of frozen soils exposed to F-T cycles in cold and seismic regions.展开更多
In order to study the effect of PVA fiber on the dynamic and static mechanical properties of low-temperature freeze-thaw concrete under the saturated surface dry state,different contents of PVA fiber were added to pre...In order to study the effect of PVA fiber on the dynamic and static mechanical properties of low-temperature freeze-thaw concrete under the saturated surface dry state,different contents of PVA fiber were added to prepare concrete in this experiment.The concrete was subjected to compression,flexural and SHPB impact tests combined with scanning electron microscopy for microstructure analysis,after different times of freeze-thaw cycles in the temperature range of 20-70℃.The experimental results show that the compressive strength of the PVA fiber reinforced concrete first increases and then decreases after freeze and thaw cycles,and the compressive strength is positively correlated with the fiber content.The flexural strength gradually decreases with freeze-thaw cycles.The flexural strength of the concrete with 1.2 kg/m^(3) of PVA fiber presents the lowest strength loss after 45 freeze and thaw cycles,which is about 14%.The dynamic failure strength gradually decreases with the increase of freeze-thaw times,and the reduction amplitude decreases with the increase of PVA fiber content.The best impact resistance is achieved when the PVA fiber dosage is 1.2 kg/m^(3).展开更多
To investigate the stability of gravity anchors of suspension bridges,in-situ tests of the vertical bearing capacity of the bedrock,shear resistance of the anchor-rock interface,shear resistance of the bedrock were co...To investigate the stability of gravity anchors of suspension bridges,in-situ tests of the vertical bearing capacity of the bedrock,shear resistance of the anchor-rock interface,shear resistance of the bedrock were conducted in a suspension bridge project.Under dry-wet cycles,the deterioration law of the mechanical properties of argillaceous sandstone was identified in laboratory tests:the elastic modulus,cohesion and friction of the argillaceous sandstone deteriorated significantly at first few dry-wet cycles and then declined slowly after 10 cycles,ultimately these three mechanical parameters were reduced to about 1/3,1/3,2/3 of the initial value respectively.Moreover,numerical simulation was used to restore in-situ shear tests and a good agreement was obtained.Base on the results of in-situ and laboratory tests,the stability of the gravity anchor foundation under natural conditions and drywet cycles was calculated and its failure modes were analyzed.The results demonstrated that the dry-wet cycles caused uneven settlement of the anchor foundation,resulting in more serious stress concentration in the substrate.The dry-wet cycles remarkably reduced the stability coefficient of the anchor foundation,whose failure mode shifted from overturning failure under natural conditions to sliding failure.When there was weak interlayer in the rock layer,the anti-sliding stability of the anchor foundation was affected drastically.展开更多
To study the shear behavior of the ultrafine magnetite tailings subjected to freeze-thaw cycles,unconsolidated-undrained shear tests were conducted on ultrafine-grained tailings that were subjected to 1-11 cycles of f...To study the shear behavior of the ultrafine magnetite tailings subjected to freeze-thaw cycles,unconsolidated-undrained shear tests were conducted on ultrafine-grained tailings that were subjected to 1-11 cycles of freeze-thaw and defined as a type of clayey silt under confining pressures of 100,200,and 300 kPa.Taking the number of freeze-thaw cycles,cooling temperature,initial dry density,and moisture content as the four main influencing factors of shear behavior of the tailings samples,the shear stress-strain curve,compression modulus,failure strength,cohesion,and internal friction angle were measured.The results show that the freeze-thaw cycle has an obvious weakening effect on the shear behavior of the tailings material,and the shear mechanical parameters are affected by a combination of confining pressure,freeze-thaw cycle condition,and initial physical-mechanical properties of the tailings samples.Through the microstructural analysis of the tailings samples subjected to freeze-thaw cycles,it shows that the freeze-thaw cycle mainly affects the porosity,bound water,and arrangement of the tailings particles.Subsequently,the macroscopic changes in shear strength indexes emerge,and then the stability of the tailings dam will decrease.展开更多
Rock creep properties can be used to predict the long-term stability in rock engineering.In reservoir bank slopes,sandstones which are frequently used in the bank slope undergoing longterm effects of dry-wet(DW) cycle...Rock creep properties can be used to predict the long-term stability in rock engineering.In reservoir bank slopes,sandstones which are frequently used in the bank slope undergoing longterm effects of dry-wet(DW) cycles due to periodic water inundation and drainage may gradually accumulate creep deformation,resulting in rock structure’s damage or even geological hazards such as landslides.To fully investigate the effect of DW cycles on the creep damage properties of sandstone,triaxial creep tests were conducted on saturated sandstone with different DW cycles by using a triaxial rheometer apparatus.The experimental results show that both the instantaneous strain and the stabilized strain increase with the DW cycles.In addition,using the Burgers model,four kinds of functions including an exponentially decreasing function,a linearly decreasing function,a linearly increasing function and an exponentially increasing function were proposed to express the relationships between the shear modulus,viscoelastic parameters of the Burgers model and the deviatoric stress under different DW cycles.Through comparative analysis,it is found that the theoretical curves generated using proposed four kinds of functions are in good agreement with the experimental data.Furthermore,macromorphological and microstructural observations were performed on specimens after various triaxial rheological tests.For samples with small number of DW cycles,approximately X-shaped fracture surfaces were observed in shear failure zones,whereas several shear fractures including obvious axial and horizontal tensile cracks,and flaws were found for samples with relatively large DW cycles due to long-term propagation and evolution of micro-fissures and micro-pores.Furthermore,as the DW cycles increases,the variation in micro-structure of samples after creep failure was summarized into three stages,namely,a stage with good and dense structure,a stage with pore and fissure propagation,and a stage with extensive increase of pores,fissures and loose particles.It is concluded that the combination effect of permeation of water molecules through pores and fissures within sandstone,and the propagation of preexisting pores and fissures owing to the dissolution of mineral particles leads to further deterioration of the mechanical properties of sandstone as the number of DW cycles increases.This study provides a fundamental basis for evaluating the long-term stability of reservoir bank slopes under cyclic fluctuations of water level.展开更多
Low average temperature, large temperature difference and continual freeze-thaw (F-T) cycles have significant impacts on mechanical property of asphalt pavement. F-T cycles test was applied to illustrate the mixture...Low average temperature, large temperature difference and continual freeze-thaw (F-T) cycles have significant impacts on mechanical property of asphalt pavement. F-T cycles test was applied to illustrate the mixtures' compressive characteristics. Exponential model was applied to analyze the variation of compressive characteristics with F-T cycles; Loss ratio model and Logistic model were used to present the deterioration trend with the increase of F-T cycles. ANOVA was applied to show the significant impact of F-T cycles and asphalt- aggregate ratio. The experiment results show that the compressive strength and resilient modulus decline with increasing F-T cycles; the degradation is sharp during the initial F-T cycles, after 8 F-T cycles it turns to gentle. ANOVA results show that F-T cycles, and asphalt-aggregate ratio have significant influence on the compressive characteristics. Exponential model, Loss ratio model and Logistic model are significantly fitting the test data from statistics view. These models well reflect the compressive characteristics of asphalt mixture degradation trend with increasing F-T cycles.展开更多
The problem of sequential fault diagnosis is to construct a diagnosis tree that can isolate the failure sources with minimal test cost. Pervious sequential fault diagnosis strategy generating algorithms only consider ...The problem of sequential fault diagnosis is to construct a diagnosis tree that can isolate the failure sources with minimal test cost. Pervious sequential fault diagnosis strategy generating algorithms only consider the execution cost at application stage, which may result in a solution with poor quality from the view of life cycle cost. Furthermore, due to the fact that uncertain information exists extensively in the real-world systems, the tests are always imperfect. In order to reduce the cost of fault diagnosis in the realistic systems, the sequential fault diagnosis problem with imperfect tests considering life cycle cost is presented and formulated in this work, which is an intractable NP-hard AND/OR decision tree construction problem. An algorithm based on AND/OR graph search is proposed to solve this problem. Heuristic search based on information theory is applied to generate the sub-tree in the algorithm. Some practical issues such as the method to improve the computational efficiency and the diagnosis strategy with multi-outcome tests are discussed. The algorithm is tested and compared with previous algorithms on the simulated systems with different scales and uncertainty. Application on a wheel momentum system of a spacecraft is studied in detail. Both the simulation and application results suggest that the cost of the diagnosis strategy can be reduced significantly by using the proposed algorithm, especially when the placement cost of the tests constitutes a large part of the total cost.展开更多
The battery test methods are the key issues to investigate the energy-storage characteristics and dynamic characteristics of electric vehicle(EV) batteries.In this paper,the research advances of existing battery test ...The battery test methods are the key issues to investigate the energy-storage characteristics and dynamic characteristics of electric vehicle(EV) batteries.In this paper,the research advances of existing battery test methods as well as driving cycles are reviewed.An electric vehicle model that consists of EV dynamics model,battery model and electric motor model is built.The dynamic characteristics of the battery in frequency domain are analyzed.Based on the EV model and the frequency domain characteristics of the battery,a driving cycle test procedure of EV battery is proposed.The battery test procedure is able to reflect the real-world characteristics of EV batteries,and can be used as a universal EV battery test method.展开更多
The insulated gate bipolar transistor(IGBT)module is one of the most age-affected components in the switch power supply, and its reliability prediction is conducive to timely troubleshooting and reduction in safety ri...The insulated gate bipolar transistor(IGBT)module is one of the most age-affected components in the switch power supply, and its reliability prediction is conducive to timely troubleshooting and reduction in safety risks and unnecessary costs. The pulsed current pattern of the accelerator power supply is different from other converter applications;therefore, this study proposed a lifetime estimation method for IGBT modules in pulsed power supplies for accelerator magnets. The proposed methodology was based on junction temperature calculations using square-wave loss discretization and thermal modeling.Comparison results showed that the junction temperature error between the simulation and IR measurements was less than 3%. An AC power cycling test under real pulsed power supply applications was performed via offline wearout monitoring of the tested power IGBT module. After combining the IGBT4 PC curve and fitting the test results,a simple corrected lifetime model was developed to quantitatively evaluate the lifetime of the IGBT module,which can be employed for the accelerator pulsed power supply in engineering. This method can be applied to other IGBT modules and pulsed power supplies.展开更多
Aiming at the complex corrosion degradation factors of reinforced concrete and clearing the deterioration mechanism in the constant stress state,a new type of constant current accelerated corrosion method in the salin...Aiming at the complex corrosion degradation factors of reinforced concrete and clearing the deterioration mechanism in the constant stress state,a new type of constant current accelerated corrosion method in the saline soil environment was developed.The three-dimensional paraffin isolation specimens and the three-dimensional penetration specimens were taken as the research objects,and the Cl−content and AC impedance Bode diagram were measured.The macro morphology and micro analysis were also used to evaluate the corrosion degradation laws of the two groups of specimens.A constant current three-factor system accelerated model was established for the current acceleration factor,chloride ion,and sulfate ion acceleration factor.The experimental results show that,in the constant stress test of the saline soil environmental conditions,the paraffin isolation layer can effectively isolate corrosive chloride ions,which is a brand-new research method of single factor variable control in the constant stress test.According to the basic corrosion data,the law of constant current acceleration test is summarized and divided into five corrosion degradation stages,and each stage has significant changes in the accelerated corrosion efficiency.The corrosion degradation of a constant stress test is the combined effect of constant current,positive and negative penetration of chloride ions and sulfate ions.展开更多
WMTC,which means a worldwide motorcycle testing cycle,is now regarded as the most possible choice for the global motorcycle emission testing cycle,but whether or not it can be used in China is still unknown.In this st...WMTC,which means a worldwide motorcycle testing cycle,is now regarded as the most possible choice for the global motorcycle emission testing cycle,but whether or not it can be used in China is still unknown.In this study,a large number of data on the speed-time trace of motorcycles were sampled from various kinds of roads in 5 cities in China.Based on a series of criterion numbers defined,the driving character of motorcycles in the real-road conditions of China was obtained.With the aid of a specially designed program,an emission testing cycle that can indicate the driving characteristics of motorcycle in the real-road conditions was synthesized,and the exhaust emission tests of 20 motorcycles under the synchronized cycle and WMTC were carried out based on a CVS system and a motorcycle chassis dynamometer.The results show that although there do exist differences in some criterion numbers between the real-road condition and WMTC,such as proportion of idling mode,mean speed,mean running speed and the average acceleration and deceleration rates,the driving behaviors are similar.The results of exhaust emission tests indicate that the emission values of motorcycles under the synchronized cycle and WMTC have a relatively strong correlation.This means that WMTC can be introduced as a standard motorcycle emission test regulation into China.展开更多
基金The authors gratefully acknowledge the financial support of National NaturalScience Foundation of China(Grant No.41972276)Natural Science Foundation of Fujian Province,China(Grant No.2020J06013)"Foal Eagle Program"Youth Top-notch Talent Project of Fujian Province,China(Grant No.00387088).
文摘Enzyme-induced carbonate precipitation(EICP)is an emanating,eco-friendly and potentially sound technique that has presented promise in various geotechnical applications.However,the durability and microscopic characteristics of EICP-treated specimens against the impact of drying-wetting(D-W)cycles is under-explored yet.This study investigates the evolution of mechanical behavior and pore charac-teristics of EICP-treated sea sand subjected to D-W cycles.The uniaxial compressive strength(UCS)tests,synchrotron radiation micro-computed tomography(micro-CT),and three-dimensional(3D)recon-struction of CT images were performed to study the multiscale evolution characteristics of EICP-reinforced sea sand under the effect of D-W cycles.The potential correlations between microstructure characteristics and macro-mechanical property deterioration were investigated using gray relational analysis(GRA).Results showed that the UCS of EICP-treated specimens decreases by 63.7% after 15 D-W cycles.The proportion of mesopores gradually decreases whereas the proportion of macropores in-creases due to the exfoliated calcium carbonate with increasing number of D-W cycles.The micro-structure in EICP-reinforced sea sand was gradually disintegrated,resulting in increasing pore size and development of pore shape from ellipsoidal to columnar and branched.The gray relational degree suggested that the weight loss rate and UCS deterioration were attributed to the development of branched pores with a size of 100-1000 m m under the action of D-W cycles.Overall,the results in this study provide a useful guidancee for the long-term stability and evolution characteristics of EICP-reinforced sea sand under D-W weathering conditions.
基金sup-ports from the National Natural Science Foundation of China(Nos.11832013 and 51878350)the Fundamental Research Funds for the Central Universities(No.B210202023)+5 种基金the Young Scientific and Technological Talents to Support Project of Jiangsu Association for Science and Technology(No.027)the Water Conservancy Science and Technology Project of Jiangsu Province(No.2020017)the Postdoctoral Research Funding Program of Ji-angsu Province(No.2021K133B)the Ningbo Science and Technology Innovation Project(No.2020Z040)the Nantong Science and Technology Plan Project(No.JC 2020120)the Open Research Fund of Changjiang River Research Institute of Changjiang Water Resources Com-mittee(No.CKWV2021879/KY).
文摘Based on seawater immersion,drying-wetting cycles,carbonation and drying-wetting cycles for coral aggregate sea-water concrete(CASC)with different strength grades,the effect of carbonation and drying-wetting cycles on chloride diffusion be-havior of CASC is studied.The results show that the free surface chloride concentration(Cs),free chloride diffusion coefficient(Df)and time-dependent index(m)of CASC in the drying-wetting cycles is obviously higher than that in seawater immersion.The Df and m of CASC of carbonation and drying-wetting cycles is higher than that in the drying-wetting cycles.Carbonation increases the Df and m of CASC,which is against CASC to resist chloride corrosion.The corrosion possibility of CASC structures in different ex-posed areas is as follows:splash zone(carbonation and drying-wetting cycles)>tidal zone(drying-wetting cycles)>underwater zone(seawater immersion).Besides,the chloride diffusion rate of C65-CASC is 17.8%-63.4%higher than that of C65-ordinary aggre-gate concrete(OAC)in seawater immersion(underwater zone).Therefore,anti-corrosion measures should be adopted to improve the service life of CASC structure in the oceanic environment.
基金Funded by the National Natural Science Foundation of China(Nos.51278495,51174291)the Open Fund of Nation Engineering Laboratory for High Speed Railway Construction(No.HSR2013011)
文摘The chloride ion transmission model considering diffusion and convection was established respectively for different zones in concrete by analyzing chloride ion transmission mechanism under the dryingwetting cycles. The finite difference method was adopted to solve the model. The equation of chloride ion transmission model in the convection and diffusion zone of concrete was discreted by the group explicit scheme with right single point (GER method) and the equation in diffusion zone was discreted by FTCS difference scheme. According to relative humidity characteristics in concrete under drying-wetting cycles, the seepage velocity equation was formulated based on Kelvin Equation and Darcy's Law. The time-variant equations of chloride ion concentration of concrete surface and the boundary surface of the convection and diffusion zone were established. Based on the software MATLAB the numerical calculation was carried out by using the model and basic material parameters from the experiments. The calculation of chloride ion concentration distribution in concrete is in good agreement with the drying-wetting cycles experiments. It can be shown that the chloride ion transmission model and the seepage velocity equation are reasonable and practical. Studies have shown that the chloride ion transmission in concrete considering convection and diffusion under the drying-wetting cycles is the better correlation with the actual situation than that only considering the diffusion.
基金the National Natural Science Foundation of China (NSFC)(Grant Nos.U22A20596 and 41771066)the Science and Technology Project of Qinghai-Tibet Railway Company (QZ2021-G03)。
文摘As a widely-applied engineering material in cold regions, the frozen subgrade soils are usually subjected to seismic loading, which are also dramatically influenced by the freeze-thaw(F-T)cycles due to the varying temperature. A series of dynamic cyclic triaxial experiments were conducted through a cryogenic triaxial apparatus for exploring the influences of F-T cycles on the dynamic mechanical properties of frozen subgrade clay.According to the experimental results of frozen clay at the temperature of-10℃, the dynamic responses and microstructure variation at different times of F-T cycles(0, 1, 5, and 20 cycles) were explored in detail.It is experimentally demonstrated that the dynamic stress-strain curves and dynamic volumetric strain curves of frozen clay are significantly sparse after 20F-T cycles. Meanwhile, the cyclic number at failure(Nf) of the frozen specimen reduces by 89% after 20freeze-thaw cycles at a low ratio of the dynamic stress amplitude. In addition, with the increasing F-T cycles,the axial accumulative strain, residual deformation,and the value of damage variable of frozen clay increase, while the dynamic resilient modulus and dynamic strength decrease. Finally, the influence of the F-T cycles on the failure mechanisms of frozen clay was discussed in terms of the microstructure variation. These studies contribute to a better understanding of the fundamental changes in the dynamic mechanical of frozen soils exposed to F-T cycles in cold and seismic regions.
基金Funded by the National Natural Science Foundation of China (No.51972214)the Innovation Team of Higher Education Institutions in Liaoning Province (No.LT2019012)。
文摘In order to study the effect of PVA fiber on the dynamic and static mechanical properties of low-temperature freeze-thaw concrete under the saturated surface dry state,different contents of PVA fiber were added to prepare concrete in this experiment.The concrete was subjected to compression,flexural and SHPB impact tests combined with scanning electron microscopy for microstructure analysis,after different times of freeze-thaw cycles in the temperature range of 20-70℃.The experimental results show that the compressive strength of the PVA fiber reinforced concrete first increases and then decreases after freeze and thaw cycles,and the compressive strength is positively correlated with the fiber content.The flexural strength gradually decreases with freeze-thaw cycles.The flexural strength of the concrete with 1.2 kg/m^(3) of PVA fiber presents the lowest strength loss after 45 freeze and thaw cycles,which is about 14%.The dynamic failure strength gradually decreases with the increase of freeze-thaw times,and the reduction amplitude decreases with the increase of PVA fiber content.The best impact resistance is achieved when the PVA fiber dosage is 1.2 kg/m^(3).
基金supported by the National Science Foundation of China(Grant No.52278469)the Natural Science Foundation of Hunan Province(Grant No.2022JJ30715)。
文摘To investigate the stability of gravity anchors of suspension bridges,in-situ tests of the vertical bearing capacity of the bedrock,shear resistance of the anchor-rock interface,shear resistance of the bedrock were conducted in a suspension bridge project.Under dry-wet cycles,the deterioration law of the mechanical properties of argillaceous sandstone was identified in laboratory tests:the elastic modulus,cohesion and friction of the argillaceous sandstone deteriorated significantly at first few dry-wet cycles and then declined slowly after 10 cycles,ultimately these three mechanical parameters were reduced to about 1/3,1/3,2/3 of the initial value respectively.Moreover,numerical simulation was used to restore in-situ shear tests and a good agreement was obtained.Base on the results of in-situ and laboratory tests,the stability of the gravity anchor foundation under natural conditions and drywet cycles was calculated and its failure modes were analyzed.The results demonstrated that the dry-wet cycles caused uneven settlement of the anchor foundation,resulting in more serious stress concentration in the substrate.The dry-wet cycles remarkably reduced the stability coefficient of the anchor foundation,whose failure mode shifted from overturning failure under natural conditions to sliding failure.When there was weak interlayer in the rock layer,the anti-sliding stability of the anchor foundation was affected drastically.
文摘To study the shear behavior of the ultrafine magnetite tailings subjected to freeze-thaw cycles,unconsolidated-undrained shear tests were conducted on ultrafine-grained tailings that were subjected to 1-11 cycles of freeze-thaw and defined as a type of clayey silt under confining pressures of 100,200,and 300 kPa.Taking the number of freeze-thaw cycles,cooling temperature,initial dry density,and moisture content as the four main influencing factors of shear behavior of the tailings samples,the shear stress-strain curve,compression modulus,failure strength,cohesion,and internal friction angle were measured.The results show that the freeze-thaw cycle has an obvious weakening effect on the shear behavior of the tailings material,and the shear mechanical parameters are affected by a combination of confining pressure,freeze-thaw cycle condition,and initial physical-mechanical properties of the tailings samples.Through the microstructural analysis of the tailings samples subjected to freeze-thaw cycles,it shows that the freeze-thaw cycle mainly affects the porosity,bound water,and arrangement of the tailings particles.Subsequently,the macroscopic changes in shear strength indexes emerge,and then the stability of the tailings dam will decrease.
基金supported by the National Natural Science Foundation of China (No. 41902268)the Systematic Project of Guangxi Key Laboratory of Disaster Prevention and Structural Safety (No. 2019ZDK030)+1 种基金the Opening fund of State Key Laboratory of Geohazard Prevention and Geoenvironment Protection (Chengdu University of Technology) (No. SKLGP2020K016)the China Postdoctoral Science Foundation (No. 2019T120871)。
文摘Rock creep properties can be used to predict the long-term stability in rock engineering.In reservoir bank slopes,sandstones which are frequently used in the bank slope undergoing longterm effects of dry-wet(DW) cycles due to periodic water inundation and drainage may gradually accumulate creep deformation,resulting in rock structure’s damage or even geological hazards such as landslides.To fully investigate the effect of DW cycles on the creep damage properties of sandstone,triaxial creep tests were conducted on saturated sandstone with different DW cycles by using a triaxial rheometer apparatus.The experimental results show that both the instantaneous strain and the stabilized strain increase with the DW cycles.In addition,using the Burgers model,four kinds of functions including an exponentially decreasing function,a linearly decreasing function,a linearly increasing function and an exponentially increasing function were proposed to express the relationships between the shear modulus,viscoelastic parameters of the Burgers model and the deviatoric stress under different DW cycles.Through comparative analysis,it is found that the theoretical curves generated using proposed four kinds of functions are in good agreement with the experimental data.Furthermore,macromorphological and microstructural observations were performed on specimens after various triaxial rheological tests.For samples with small number of DW cycles,approximately X-shaped fracture surfaces were observed in shear failure zones,whereas several shear fractures including obvious axial and horizontal tensile cracks,and flaws were found for samples with relatively large DW cycles due to long-term propagation and evolution of micro-fissures and micro-pores.Furthermore,as the DW cycles increases,the variation in micro-structure of samples after creep failure was summarized into three stages,namely,a stage with good and dense structure,a stage with pore and fissure propagation,and a stage with extensive increase of pores,fissures and loose particles.It is concluded that the combination effect of permeation of water molecules through pores and fissures within sandstone,and the propagation of preexisting pores and fissures owing to the dissolution of mineral particles leads to further deterioration of the mechanical properties of sandstone as the number of DW cycles increases.This study provides a fundamental basis for evaluating the long-term stability of reservoir bank slopes under cyclic fluctuations of water level.
基金Funded by the National Science&Technology Support Program during the 12th Five-year Plan Period(No.2014BAG05B04)the Construction and Science Project of the Ministry of Transport of China(No.2013 318 490 010)the Doctor Postgraduate Technical Project of Chang’an University(No.2014G5210002)
文摘Low average temperature, large temperature difference and continual freeze-thaw (F-T) cycles have significant impacts on mechanical property of asphalt pavement. F-T cycles test was applied to illustrate the mixtures' compressive characteristics. Exponential model was applied to analyze the variation of compressive characteristics with F-T cycles; Loss ratio model and Logistic model were used to present the deterioration trend with the increase of F-T cycles. ANOVA was applied to show the significant impact of F-T cycles and asphalt- aggregate ratio. The experiment results show that the compressive strength and resilient modulus decline with increasing F-T cycles; the degradation is sharp during the initial F-T cycles, after 8 F-T cycles it turns to gentle. ANOVA results show that F-T cycles, and asphalt-aggregate ratio have significant influence on the compressive characteristics. Exponential model, Loss ratio model and Logistic model are significantly fitting the test data from statistics view. These models well reflect the compressive characteristics of asphalt mixture degradation trend with increasing F-T cycles.
基金Project(C1320063131)supported by China Civil Space Foundation
文摘The problem of sequential fault diagnosis is to construct a diagnosis tree that can isolate the failure sources with minimal test cost. Pervious sequential fault diagnosis strategy generating algorithms only consider the execution cost at application stage, which may result in a solution with poor quality from the view of life cycle cost. Furthermore, due to the fact that uncertain information exists extensively in the real-world systems, the tests are always imperfect. In order to reduce the cost of fault diagnosis in the realistic systems, the sequential fault diagnosis problem with imperfect tests considering life cycle cost is presented and formulated in this work, which is an intractable NP-hard AND/OR decision tree construction problem. An algorithm based on AND/OR graph search is proposed to solve this problem. Heuristic search based on information theory is applied to generate the sub-tree in the algorithm. Some practical issues such as the method to improve the computational efficiency and the diagnosis strategy with multi-outcome tests are discussed. The algorithm is tested and compared with previous algorithms on the simulated systems with different scales and uncertainty. Application on a wheel momentum system of a spacecraft is studied in detail. Both the simulation and application results suggest that the cost of the diagnosis strategy can be reduced significantly by using the proposed algorithm, especially when the placement cost of the tests constitutes a large part of the total cost.
基金Supported by the National High Technology Research and Development Programme of China(No.2011AA05A109,2008AA11A104)International S&T Cooperation Program of China(ISTCP)(No.2011DFA70570,2010DFA72760)
文摘The battery test methods are the key issues to investigate the energy-storage characteristics and dynamic characteristics of electric vehicle(EV) batteries.In this paper,the research advances of existing battery test methods as well as driving cycles are reviewed.An electric vehicle model that consists of EV dynamics model,battery model and electric motor model is built.The dynamic characteristics of the battery in frequency domain are analyzed.Based on the EV model and the frequency domain characteristics of the battery,a driving cycle test procedure of EV battery is proposed.The battery test procedure is able to reflect the real-world characteristics of EV batteries,and can be used as a universal EV battery test method.
基金supported by the National Key Research and Development Program of China (No. 2019YFA0405402)。
文摘The insulated gate bipolar transistor(IGBT)module is one of the most age-affected components in the switch power supply, and its reliability prediction is conducive to timely troubleshooting and reduction in safety risks and unnecessary costs. The pulsed current pattern of the accelerator power supply is different from other converter applications;therefore, this study proposed a lifetime estimation method for IGBT modules in pulsed power supplies for accelerator magnets. The proposed methodology was based on junction temperature calculations using square-wave loss discretization and thermal modeling.Comparison results showed that the junction temperature error between the simulation and IR measurements was less than 3%. An AC power cycling test under real pulsed power supply applications was performed via offline wearout monitoring of the tested power IGBT module. After combining the IGBT4 PC curve and fitting the test results,a simple corrected lifetime model was developed to quantitatively evaluate the lifetime of the IGBT module,which can be employed for the accelerator pulsed power supply in engineering. This method can be applied to other IGBT modules and pulsed power supplies.
基金Funded by the National Natural Science Foundation of China (U21A20150,52208249,51878153,52008196,and 52178216)the National Natural Science Foundation of China Youth Science (52108219)+3 种基金the Deterioration Characteristics and Mechanisms of Cement Concrete with CWPM under Coupled Thermo-Hydro-Chemical Effect,the Youth Science and Technology Foundation of Gansu Province (22JR5RA288)the Research and Demonstration of Key Technologies of Green and Smart Highways in Gansu Province (21ZD3GA002)the Natural Science Innovation Foundation of Gansu Higher Education Institutions (2022CYZC-25)the Support from Research on Key Technologies of Durability Repair of Highway Concrete Bridges,Key Projects of Chongqing Science and Technology Bureau (cstc2021jscx-jbgs0029)。
文摘Aiming at the complex corrosion degradation factors of reinforced concrete and clearing the deterioration mechanism in the constant stress state,a new type of constant current accelerated corrosion method in the saline soil environment was developed.The three-dimensional paraffin isolation specimens and the three-dimensional penetration specimens were taken as the research objects,and the Cl−content and AC impedance Bode diagram were measured.The macro morphology and micro analysis were also used to evaluate the corrosion degradation laws of the two groups of specimens.A constant current three-factor system accelerated model was established for the current acceleration factor,chloride ion,and sulfate ion acceleration factor.The experimental results show that,in the constant stress test of the saline soil environmental conditions,the paraffin isolation layer can effectively isolate corrosive chloride ions,which is a brand-new research method of single factor variable control in the constant stress test.According to the basic corrosion data,the law of constant current acceleration test is summarized and divided into five corrosion degradation stages,and each stage has significant changes in the accelerated corrosion efficiency.The corrosion degradation of a constant stress test is the combined effect of constant current,positive and negative penetration of chloride ions and sulfate ions.
基金Supported by Tianjin Municipal Science and Technology Commission(No.05YFJMJC11100and No.07JCYBJC03900)Ministry of Education of China(No.20020056046).
文摘WMTC,which means a worldwide motorcycle testing cycle,is now regarded as the most possible choice for the global motorcycle emission testing cycle,but whether or not it can be used in China is still unknown.In this study,a large number of data on the speed-time trace of motorcycles were sampled from various kinds of roads in 5 cities in China.Based on a series of criterion numbers defined,the driving character of motorcycles in the real-road conditions of China was obtained.With the aid of a specially designed program,an emission testing cycle that can indicate the driving characteristics of motorcycle in the real-road conditions was synthesized,and the exhaust emission tests of 20 motorcycles under the synchronized cycle and WMTC were carried out based on a CVS system and a motorcycle chassis dynamometer.The results show that although there do exist differences in some criterion numbers between the real-road condition and WMTC,such as proportion of idling mode,mean speed,mean running speed and the average acceleration and deceleration rates,the driving behaviors are similar.The results of exhaust emission tests indicate that the emission values of motorcycles under the synchronized cycle and WMTC have a relatively strong correlation.This means that WMTC can be introduced as a standard motorcycle emission test regulation into China.