To develop suitable grouting materials for water conveyance tunnels in cold regions,firstly,this study investigated the performance evolution of ferrite-rich sulfoaluminate-based composite cement(FSAC grouting materia...To develop suitable grouting materials for water conveyance tunnels in cold regions,firstly,this study investigated the performance evolution of ferrite-rich sulfoaluminate-based composite cement(FSAC grouting material)at 20 and 3℃.The results show that low temperature only delays the strength development of FSAC grouting material within the first 3 d.Then,the effect of four typical early strength synergists on the early properties of FSAC grouting material was evaluated to optimize the early(£1 d)strength at 3℃.The most effective synergist,Ca(HCOO)_(2),which enhances the low-temperature early strength without compromising fluidity was selected based on strength and fluidity tests.Its micro-mechanism was analyzed by XRD,TG,and SEM methods.The results reveal that the most suitable dosage range is 0.3 wt%−0.5 wt%.Proper addition of Ca(HCOO)_(2)changed the crystal morphology of the hydration products,decreased the pore size and formed more compact hydration products by interlocking and overlapping.However,excessive addition of Ca(HCOO)_(2)inhibited the hydration reaction,resulting in a simple and loose structure of the hydration products.The research results have reference value for controlling surrounding rock deformation and preventing water and mud inrushes during the excavation in cold region tunnels.展开更多
The effects of Ag on the microstructure and mechanical properties of 2519 aluminum alloy were investigated by means of tensile test, micro-hardness test, transmission electron microscope and scanning electron microsco...The effects of Ag on the microstructure and mechanical properties of 2519 aluminum alloy were investigated by means of tensile test, micro-hardness test, transmission electron microscope and scanning electron microscope. The results show that the addition of 0.3% (mass fraction) Ag accelerates 2519 aluminum alloy’s age-hardening, increases its peak hardness and reduces 4h of peak aged time at 180℃. The addition of 0.3%(mass fraction) Ag increses the tensile strength at room temperature and elevated temperature. This increment at room temperature and 200℃ is 24MPa and 78MPa, respectively. In contrast, the elongation of 2519 aluminum alloy is decreased with Ag addition. The increase of tensile strength of 2519 aluminum alloy with Ag addition is attributed to the high volume fraction of Ω phase.展开更多
The effects of heat treatment on the microstructure and mechanical properties of two alloys, namely Al-12.2%Zn-2.48%Cu-2.0%Mg-0.15%Zr-0.166%Ag（alloy 1）, and Al-9.99%Zn-1.72%Cu-2.5%Mg- 0.13%Zr （alloy 2） were invest...The effects of heat treatment on the microstructure and mechanical properties of two alloys, namely Al-12.2%Zn-2.48%Cu-2.0%Mg-0.15%Zr-0.166%Ag（alloy 1）, and Al-9.99%Zn-1.72%Cu-2.5%Mg- 0.13%Zr （alloy 2） were investigated. The results show that low temperature aging after promotive solution treatment can increase elongation without the loss of strength for the studied alloys. The optimum aging treatment （T6） for alloy 1 and alloy 2 is 100℃/80h and 100℃/48h, respectively. Compared with other heat treatment alloys, alloy 1 and alloy 2 show super-high tensile strength up to 753MPa and 788MPa, remaining 9.3% and 9.7% elongation under T6 condition, respectively. During aging, trace addition of Ag enhances the formations of GP zone and metastable phase, and stabilizes GP zone and metastable phase to a higher temperature. Trace addition of Ag prolongs the aging time of reaching the peak strength and delays over-aging condition of the alloy. However, trace addition of Ag promotes the formation of coarse constituent in the alloy and consumes hardening alloying elements of Zn and Mg. Moreover, the addition of the transition element Zr in 7000 series super-high alloy forms incoherent Al3Zr dispersoid which can serve as nucleation sites for nonuniform precipitation of η phase during aging process. The higher the aging temperature, the greater the tendency for nonuniform precipitation of η phase.展开更多
VAlN coating is of particular interest for dry cutting applications owing to its low-friction and excellent abrasiveness.Nano-multilayer structure is designed to tailor the properties of VAlN coating.In this work,a se...VAlN coating is of particular interest for dry cutting applications owing to its low-friction and excellent abrasiveness.Nano-multilayer structure is designed to tailor the properties of VAlN coating.In this work,a series of VAlN/Si_(3)N_(4) nano-multilayer coatings with varied Si_(3)N_(4) layer thicknesses were prepared by reactive sputtering method.The microstructure and mechanical properties of the coatings were both investigated.It is revealed that Si_(3)N_(4) with a shallow thickness(~0.4 nm)was crystallized and grown coherently with VAlN,showing a remarkable increase in hardness compared to VAlN monolayer coating.The hardness of coherently VAlN/Si_(3)N_(4) nano-multilayer coatings reached to 48.7 GPa.With further increase of Si_(3)N_(4) layer thickness,the coherent growth of nano-multilayers was terminated,showing amorphous structure formed in nano-multilayers and the hardness was declined.On the other hand,when Si_(3)N_(4) layer thickness was 0.4 nm,the friction coefficient of VAlN/Si_(3)N_(4) nano-multilayer coating was almost equal to that of VAlN monolayer coating,which was attributed to the crystallization of Si_(3)N_(4) and the produced coherent interfaces between VAlN and Si_(3)N_(4) for the hardening effect of nano-multilayer coatings.Upon further increase of Si_(3)N_(4) layer thickness,pronounced improvement of friction coefficient in VAlN/Si_(3)N_(4) nano-multilayer coating was observed.展开更多
Natural ventilation is driven by either buoyancy forces or wind pressure forces or their combinations that inherit stochastic variation into ventilation rates. Since the ventilation rate is a nonlinear function of mul...Natural ventilation is driven by either buoyancy forces or wind pressure forces or their combinations that inherit stochastic variation into ventilation rates. Since the ventilation rate is a nonlinear function of multiple variable factors including wind speed, wind direction, internal heat source and building structural thermal mass, the conventional methods for quantifying ventilation rate simply using dominant wind direction and average wind speed may not accurately describe the characteristic performance of natural ventilation. From a new point of view, the natural ventilation performance of a single room building under fluctuating wind speed condition using the Monte-Carlo simulation approach was investigated by incorporating building facade thermal mass effect. Given a same hourly turbulence intensity distribution, the wind speeds with 1 rain frequency fluctuations were generated using a stochastic model, the modified GARCH model. Comparisons of natural ventilation profiles, effective ventilation rates, and air conditioning electricity use for a three-month period show statistically significant differences （for 80% confidence interval） between the new calculations and the traditional methods based on hourly average wind speed.展开更多
Poly （vinyl butyral） （PVB） hollow fiber membranes were fabricated via thermally induced phase separation （TIPS）. The effects of coagulation bath temperature （CBT） on the structure and performance of membranes ...Poly （vinyl butyral） （PVB） hollow fiber membranes were fabricated via thermally induced phase separation （TIPS）. The effects of coagulation bath temperature （CBT） on the structure and performance of membranes were investigated in detail. The morphologies of the membranes were studied by scanning electron microscopy （SEM）, the performances of water permeability, rejection, breaking strength and elongation were measured, respectively. The results indicate that all the membranes have the asymmetric morphology and the thickness of the skin layer decreases and the pore size of the outer layer increases with the increase of CBT. The permeability of membranes prepared at air gap 1.0 cm and take-up speed 0.253 m/s increases from 1.047×10-7 to 5.909×10-7 m3/（m2·s-kPa） with the CBT increasing from 20 ℃ to 40℃, and sharply increases to 35.226×10 7 m3/（m2.s.kPa）once the CBT arrives at 50 ℃. While the carbonic ink rejections have no significant decrease, totally exceed 98%, but that of acid-maleic acid copolymer greatly decreases with the increase of CBT. Both the breaking strength and elongation decrease with the increase of CBT.展开更多
基金Projcet(52279119)supported by the National Natural Science Foundation of ChinaProject(XZ202201ZY0021G)supported by the Science and Technology Planning Project of Xizang Autonomous Region,China+1 种基金Project(2019QZKK0904)supported by the Second Xizang Plateau Scientific Expedition and Research Program of ChinaProject(51922104)supported by the National Natural Science Foundation for Distinguished Young Scholars of China。
文摘To develop suitable grouting materials for water conveyance tunnels in cold regions,firstly,this study investigated the performance evolution of ferrite-rich sulfoaluminate-based composite cement(FSAC grouting material)at 20 and 3℃.The results show that low temperature only delays the strength development of FSAC grouting material within the first 3 d.Then,the effect of four typical early strength synergists on the early properties of FSAC grouting material was evaluated to optimize the early(£1 d)strength at 3℃.The most effective synergist,Ca(HCOO)_(2),which enhances the low-temperature early strength without compromising fluidity was selected based on strength and fluidity tests.Its micro-mechanism was analyzed by XRD,TG,and SEM methods.The results reveal that the most suitable dosage range is 0.3 wt%−0.5 wt%.Proper addition of Ca(HCOO)_(2)changed the crystal morphology of the hydration products,decreased the pore size and formed more compact hydration products by interlocking and overlapping.However,excessive addition of Ca(HCOO)_(2)inhibited the hydration reaction,resulting in a simple and loose structure of the hydration products.The research results have reference value for controlling surrounding rock deformation and preventing water and mud inrushes during the excavation in cold region tunnels.
基金Project(2005CB623706)supported by the State Key Fundamental Research and Development Programof China
文摘The effects of Ag on the microstructure and mechanical properties of 2519 aluminum alloy were investigated by means of tensile test, micro-hardness test, transmission electron microscope and scanning electron microscope. The results show that the addition of 0.3% (mass fraction) Ag accelerates 2519 aluminum alloy’s age-hardening, increases its peak hardness and reduces 4h of peak aged time at 180℃. The addition of 0.3%(mass fraction) Ag increses the tensile strength at room temperature and elevated temperature. This increment at room temperature and 200℃ is 24MPa and 78MPa, respectively. In contrast, the elongation of 2519 aluminum alloy is decreased with Ag addition. The increase of tensile strength of 2519 aluminum alloy with Ag addition is attributed to the high volume fraction of Ω phase.
基金Project (2001AA332030) supported by the National High Technology Research and Development Programof China
文摘The effects of heat treatment on the microstructure and mechanical properties of two alloys, namely Al-12.2%Zn-2.48%Cu-2.0%Mg-0.15%Zr-0.166%Ag（alloy 1）, and Al-9.99%Zn-1.72%Cu-2.5%Mg- 0.13%Zr （alloy 2） were investigated. The results show that low temperature aging after promotive solution treatment can increase elongation without the loss of strength for the studied alloys. The optimum aging treatment （T6） for alloy 1 and alloy 2 is 100℃/80h and 100℃/48h, respectively. Compared with other heat treatment alloys, alloy 1 and alloy 2 show super-high tensile strength up to 753MPa and 788MPa, remaining 9.3% and 9.7% elongation under T6 condition, respectively. During aging, trace addition of Ag enhances the formations of GP zone and metastable phase, and stabilizes GP zone and metastable phase to a higher temperature. Trace addition of Ag prolongs the aging time of reaching the peak strength and delays over-aging condition of the alloy. However, trace addition of Ag promotes the formation of coarse constituent in the alloy and consumes hardening alloying elements of Zn and Mg. Moreover, the addition of the transition element Zr in 7000 series super-high alloy forms incoherent Al3Zr dispersoid which can serve as nucleation sites for nonuniform precipitation of η phase during aging process. The higher the aging temperature, the greater the tendency for nonuniform precipitation of η phase.
基金Project(51201187)supported by the National Natural Science Foundation of China。
文摘VAlN coating is of particular interest for dry cutting applications owing to its low-friction and excellent abrasiveness.Nano-multilayer structure is designed to tailor the properties of VAlN coating.In this work,a series of VAlN/Si_(3)N_(4) nano-multilayer coatings with varied Si_(3)N_(4) layer thicknesses were prepared by reactive sputtering method.The microstructure and mechanical properties of the coatings were both investigated.It is revealed that Si_(3)N_(4) with a shallow thickness(~0.4 nm)was crystallized and grown coherently with VAlN,showing a remarkable increase in hardness compared to VAlN monolayer coating.The hardness of coherently VAlN/Si_(3)N_(4) nano-multilayer coatings reached to 48.7 GPa.With further increase of Si_(3)N_(4) layer thickness,the coherent growth of nano-multilayers was terminated,showing amorphous structure formed in nano-multilayers and the hardness was declined.On the other hand,when Si_(3)N_(4) layer thickness was 0.4 nm,the friction coefficient of VAlN/Si_(3)N_(4) nano-multilayer coating was almost equal to that of VAlN monolayer coating,which was attributed to the crystallization of Si_(3)N_(4) and the produced coherent interfaces between VAlN and Si_(3)N_(4) for the hardening effect of nano-multilayer coatings.Upon further increase of Si_(3)N_(4) layer thickness,pronounced improvement of friction coefficient in VAlN/Si_(3)N_(4) nano-multilayer coating was observed.
文摘Natural ventilation is driven by either buoyancy forces or wind pressure forces or their combinations that inherit stochastic variation into ventilation rates. Since the ventilation rate is a nonlinear function of multiple variable factors including wind speed, wind direction, internal heat source and building structural thermal mass, the conventional methods for quantifying ventilation rate simply using dominant wind direction and average wind speed may not accurately describe the characteristic performance of natural ventilation. From a new point of view, the natural ventilation performance of a single room building under fluctuating wind speed condition using the Monte-Carlo simulation approach was investigated by incorporating building facade thermal mass effect. Given a same hourly turbulence intensity distribution, the wind speeds with 1 rain frequency fluctuations were generated using a stochastic model, the modified GARCH model. Comparisons of natural ventilation profiles, effective ventilation rates, and air conditioning electricity use for a three-month period show statistically significant differences （for 80% confidence interval） between the new calculations and the traditional methods based on hourly average wind speed.
基金Project(21176264)supported by the National Natural Science Foundation of ChinaProject(11JJ2010)supported by the Hunan Provincial Natural Science Foundation of China
文摘Poly （vinyl butyral） （PVB） hollow fiber membranes were fabricated via thermally induced phase separation （TIPS）. The effects of coagulation bath temperature （CBT） on the structure and performance of membranes were investigated in detail. The morphologies of the membranes were studied by scanning electron microscopy （SEM）, the performances of water permeability, rejection, breaking strength and elongation were measured, respectively. The results indicate that all the membranes have the asymmetric morphology and the thickness of the skin layer decreases and the pore size of the outer layer increases with the increase of CBT. The permeability of membranes prepared at air gap 1.0 cm and take-up speed 0.253 m/s increases from 1.047×10-7 to 5.909×10-7 m3/（m2·s-kPa） with the CBT increasing from 20 ℃ to 40℃, and sharply increases to 35.226×10 7 m3/（m2.s.kPa）once the CBT arrives at 50 ℃. While the carbonic ink rejections have no significant decrease, totally exceed 98%, but that of acid-maleic acid copolymer greatly decreases with the increase of CBT. Both the breaking strength and elongation decrease with the increase of CBT.
