Loess soil deposits are widely distributed in arid and semi-arid regions and constitute about 10% of land area of the world.These soils typically have a loose honeycomb-type meta-stable structure that is susceptible t...Loess soil deposits are widely distributed in arid and semi-arid regions and constitute about 10% of land area of the world.These soils typically have a loose honeycomb-type meta-stable structure that is susceptible to a large reduction in total volume or collapse upon wetting.Collapse characteristics contribute to various problems to infrastructures that are constructed on loess soils.For this reason,collapse triggering mechanism for loess soils has been of significant interest for researchers and practitioners all over the world.This paper aims at providing a state-of-the-art review on collapse mechanism with special reference to loess soil deposits.The collapse mechanism studies are summarized under three different categories,i.e.traditional approaches,microstructure approach,and soil mechanics-based approaches.The traditional and microstructure approaches for interpreting the collapse behavior are comprehensively summarized and critically reviewed based on the experimental results from the literature.The soil mechanics-based approaches proposed based on the experimental results of both compacted soils and natural loess soils are reviewed highlighting their strengths and limitations for estimating the collapse behavior.Simpler soil mechanics-based approaches with less parameters or parameters that are easy-to-determine from conventional tests are suggested for future research to better understand the collapse behavior of natural loess soils.Such studies would be more valuable for use in conventional geotechnical engineering practice applications.展开更多
A new roller compacted concrete dam of Fengman Hydropower Station is to be built in the toe of the old dam,which was identified as a dangerous dam.The new dam during construction would be influenced by the high-speed ...A new roller compacted concrete dam of Fengman Hydropower Station is to be built in the toe of the old dam,which was identified as a dangerous dam.The new dam during construction would be influenced by the high-speed flow discharged from the old dam,which is an important problem to be considered for the first time in China,and which would affect the construction of the whole project.Therefore,a series of erosion experiments were conducted in this article.A high-speed flow erosion test apparatus was developed for the erosion experiments of the new dam materials.The maximum jet velocity goes up to 40 m/s and the section area of the nozzle is 0.0025 m2.In the process of experiments,the equipment shows a good performance.Erosive wear tests for two types of materials used in the new dam,a roller compacted concrete and a distorted concrete with four kinds of ages were carried out with the flow velocity in the range of 30 m/s-35 m/s.Erosion parameters and erosion laws for the two types of concretes with different ages were determined,and a general relationship between the erosion rate and the flow velocity is obtained as：,with the velocity exponent between 3.33 and 3.93.It is concluded that the erosion resistance of the distorted concrete is better than that of the roller compacted concrete and the mechanical properties of the concretes of over 14 d age are influenced slightly by the water impact.The test results might serve as a practical technique guide for the safety of this project during its construction in the flood season.展开更多
The demands for improved fuel economy,performance and emissions continue to pose challenges for engine designers and the materials they choose. This is particularly true for modern diesel engines,where the primary pat...The demands for improved fuel economy,performance and emissions continue to pose challenges for engine designers and the materials they choose. This is particularly true for modern diesel engines,where the primary path to achieving improved engine performance and emissions is to increase the Peak Firing Pressure in the combustion chamber. The resulting increase in thermal and mechanical loading has required a change from conventional grey cast iron to Compacted Graphite Iron (CGI) in order to satisfy durability requirements without increasing the size or the weight of the engines. With at least 75% higher tensile strength,45% higher stiffness and approximately double the fatigue strength of conventional grey cast iron,CGI satisfies durability requirements and also provides the dimensional stability required to meet emissions legislation throughout the life of the engine. Currently,there are no CGI diesel engines running on the roads in North America. This is set to change considerably as new commercial vehicle and pick-up SUV diesel engines are launched with CGI cylinder blocks in 2008 and 2009. These initial programs will provide over 2 million CGI diesel engines when ramped to mature volume,potentially accounting for 10%-15% of the North American passenger vehicle fleet within the next four years.展开更多
In view of the diversity and complexity of mechanical parameters of roller compacted concrete dam(RCCD),the uniform design method,partial least-squares regression(PLS)and least squares support vector machine(LSSVM)wer...In view of the diversity and complexity of mechanical parameters of roller compacted concrete dam(RCCD),the uniform design method,partial least-squares regression(PLS)and least squares support vector machine(LSSVM)were applied to the back analysis of RCCD with the use of the complex nonlinear relationship between dam mechanical parameters and dam displacements.During the process of back analysis,the initial samples of parameters were designed with uniform design method.Then,a transversely isotropic model of RCCD was established by MSC.Marc software.Through this model,training samples of LSSVM model could be obtained.And then,the complex nonlinear relationship between relative values of hydraulic components of dam displacements and mechanical parameters was established.Finally,actual relative values of dam hydraulic components are isolated from the measured data of dam displacements by using PLS.By inputting the isolated relative values into LSSVM model,the back analysis values of RCCD mechanical parameters can be obtained.The example analysis showed that mechanical parameters obtained by the above-mentioned back analysis method are reasonable,and the back analysis method is feasible.展开更多
Carbon fibre reinforced carbon and SiC dual matrices composites （C/C-SiC） show superior tribological properties,high thermal shock resistance and good abrasive resistance,and they are promising candidates for advanc...Carbon fibre reinforced carbon and SiC dual matrices composites （C/C-SiC） show superior tribological properties,high thermal shock resistance and good abrasive resistance,and they are promising candidates for advanced brake and clutch systems.The microstructure,mechanical properties,friction and wear properties,and application of the C/C-SiC composites fabricated by warm compacted-in situ reaction were introduced.The results indicated that the composites were composed of 50-60 wt pct carbon,2-10 wt pct residual silicon and 30-40 wt pct silicon carbide.The C/C-SiC brake composites exhibited good mechanical properties.The value of flexural strength and compressive strength could reach 160 and 112 MPa,respectively.The impact strength was about 2.5 kJ·m-2.The C/C-SiC brake composites showed excellent tribological performance,including high coefficient of friction （0.38）,good abrasive resistance （1.10 μm/cycle） and brake steadily on dry condition.The tribological properties on wet condition could be mostly maintained.The silicon carbide matrix in C/C-SiC brake composites improved the wear resistance,and the graphite played the lubrication function,and right volume content of graphite was helpful to forming friction film to reduce the wear rate.These results showed that C/C-SiC composites fabricated by warm compacted-in situ reaction had excellent properties for use as brake materials.展开更多
The high compacted density LiNi<sub>0.5-x</sub>Co<sub>0.2</sub>Mn<sub>0.3</sub>Mg<sub>x</sub>O<sub>2</sub> cathode material for lithium-ion batteries was syn...The high compacted density LiNi<sub>0.5-x</sub>Co<sub>0.2</sub>Mn<sub>0.3</sub>Mg<sub>x</sub>O<sub>2</sub> cathode material for lithium-ion batteries was synthesized by high temperature solid-state method, taking the Mg element as a doping element and the spherical Ni<sub>0.5</sub>Co<sub>0.2</sub>Mn<sub>0.3</sub> (OH)<sub>2</sub>, Li<sub>2</sub>CO<sub>3</sub> as raw materials. The effects of calcination temperature on the structure and properties of the products were investigated. The structure and morphology of cathode materials powder were analyzed by X-ray diffraction spectroscopy (XRD) and scanning electronmicroscopy (SEM). The electrochemical properties of the cathode materials were studied by charge-discharge test and cyclic properties test. The results show that LiNi<sub>0.4985</sub>Co<sub>0.2</sub>Mn<sub>0.3</sub> Mg<sub>0.0015</sub>O<sub>2</sub> cathode material prepared at calcination temperature 930°C has a good layered structure, and the compacted density of the electrode sheet is above 3.68 g/cm<sup>3</sup>. The discharge capacity retention rate is more than 97.5% after 100 cycles at a charge-discharge rate of 1C, displaying a good cyclic performance.展开更多
The infl uence of Si, Sn, Mo and Ni on the ductility and thermal conductivity of compacted graphite iron(CGI) was investigated. Metallographic observation and Differential Scanning Calorimetry(DSC) experiments were ca...The infl uence of Si, Sn, Mo and Ni on the ductility and thermal conductivity of compacted graphite iron(CGI) was investigated. Metallographic observation and Differential Scanning Calorimetry(DSC) experiments were carried out to analyze the roles of various additions in the eutectoid reaction. The experimental results showed that the ductility of CGI is proportional to the ferrite fraction, so moderate Si content could dramatically improve the ductility by increasing the ferrite fraction. DSC measurements showed that Mo has moderate inhibition on eutectoid transformation during both the heating and cooling processes, while the sample without Sn obviously broadens the three-phase region. Vermicularity and ferrite are known to improve thermal conductivity, and the former plays a more important role. Besides, among the alloy elements investigated, Sn has the greatest negative effect on conductivity, followed by Ni and Mo having the smallest effects.展开更多
This paper gives a brief introduction to the four research methods for the study on thermal conductivity of cast irons,including experimental measurement,statistical analysis,effective medium theory and numerical simu...This paper gives a brief introduction to the four research methods for the study on thermal conductivity of cast irons,including experimental measurement,statistical analysis,effective medium theory and numerical simulation.Recent studies on the thermal conductivity of various cast irons are reviewed through the influence of alloying elements,structural constituents,and temperature.The addition of alloying elements is the main reason that restricts the thermal conductivity of cast irons,especially spheroidal graphite cast iron.The connectivity of graphite has a significant effect on the thermal conductivity of flake and compacted graphite cast irons,semiquantitative and quantitative analysis of this factor is a key and difficult point in the study of thermal conductivity of cast irons.The thermal conductivities of different types of cast irons show varying degrees of dependence on temperature.This phenomenon is the combination of graphite and matrix,rather than just depending on graphite morphology.The study of the relationship between individual phase and temperature is the focus of future research.These summaries and discussions may provide reference and guidance for the future research and development of high thermal conductivity cast irons.展开更多
Compacted graphite cast iron （CG1） has been the material for high-power diesel engines recently, but its increased strength causes poor machinability. In this study, coated and uncoated carbide tools were used in dr...Compacted graphite cast iron （CG1） has been the material for high-power diesel engines recently, but its increased strength causes poor machinability. In this study, coated and uncoated carbide tools were used in dry milling experiment and FEM simulation to study the machinability of CGI and wear behaviour of tools. The experimental and FEM simulation results show that coated tool has great advantage in dry milling of CGI. SEM and EDS analysis of tool wear indicate the wear morphology and wear mechanism. Adhesive wear is the main mechanism to cause un- coated tool wear, while abrasive wear and delamination wear are the main mechanism to cause coated tool wear. Stress and temperature distribution in FEM simulation help to understand the wear mechanism including the reason for coat- ing peeled off.展开更多
Compacted clay liners are an integral part of the waste landfills,which are provided to contain the leachate within the landfills and protect the surrounding environment.Generally,locally available natural soils are u...Compacted clay liners are an integral part of the waste landfills,which are provided to contain the leachate within the landfills and protect the surrounding environment.Generally,locally available natural soils are used for the construction of compacted clay liners if they satisfy the design criteria.However,not all soils in their natural state satisfy all the design criteria for the liner materials.Thus,there is a definite need to modify the locally available natural soils by blending with bentonite to meet the required design criteria for the liners.In view of this,the present study evaluates the suitability of an Indian red soil enhanced with bentonite as a liner material.To achieve this,a series of experiments were carried out using locally available red soil and bentonite.First,the suitability of the red soil was evaluated as a liner material.The experimental results showed that the red soil met all the selection criteria stipulated by the Environmental Protection Agencies(EPAs)for the liners except the hydraulic conductivity criterion.Therefore,the red soil was mixed with bentonite contents of 10%,20%and 30%,and the red soil-bentonite mixtures were evaluated for their suitability for liners in their compacted state.Further,as the liners in the arid and semi-arid regions are subjected to moisture variations due to seasonal moisture fluctuations and other factors,the red soil-bentonite mixtures were subjected to wetdry cycles,and their suitability was evaluated after wet-dry cycles.The experimental results revealed that all the red soil-bentonite mixtures met the stipulated EPA criteria for the liners in the as-compacted state.However,the red soil-bentonite mixtures with 20%and 30%bentonite contents only satisfied the hydraulic conductivity requirement even after wet-dry cycles.The experimental findings were supplemented with the microstructural insights captured through digital camera images,scanning electron microscopy(SEM),and mercury intrusion porosimetry(MIP)studies.展开更多
The increase in payload capacity of trucks has heightened the demand for cost-effective yet high performance brake discs.In this work,the thermal fatigue and wear of compacted graphite iron brake discs were investigat...The increase in payload capacity of trucks has heightened the demand for cost-effective yet high performance brake discs.In this work,the thermal fatigue and wear of compacted graphite iron brake discs were investigated,aiming to provide an experimental foundation for achieving a balance between their thermal and mechanical properties.Compacted graphite iron brake discs with different tensile strengths,macrohardnesses,specific heat capacities and thermal diffusion coefficients were produced by changing the proportion and strength of ferrite.The peak temperature,pressure load and friction coefficient of compacted graphite iron brake discs were analyzed through inertia friction tests.The morphology of thermal cracks and 3D profiles of the worn surfaces were also discussed.It is found that the thermal fatigue of compacted graphite iron discs is determined by their thermal properties.A compacted graphite iron with the highest specific heat capacity and thermal diffusion coefficient exhibits optimal thermal fatigue resistance.Oxidization of the matrix at low temperatures significantly weakens the function of alloy strengthening in hindering the propagation of thermal cracks.Despite the reduced hardness,increasing the ferrite proportion can mitigate wear loss resulting from low disc temperatures and the absence of abrasive wear.展开更多
Mountain excavation and city construction(MECC)projects being launched in the Loess Plateau in China involve the creation of large-scale artificial land.Understanding the subsurface evolution characteristics of the ar...Mountain excavation and city construction(MECC)projects being launched in the Loess Plateau in China involve the creation of large-scale artificial land.Understanding the subsurface evolution characteristics of the artificial land is essential,yet challenging.Here,we use an improved fiber-optic monitoring system for its subsurface multi-physical characterization.The system enables us to gather spatiotemporal distribution of various parameters,including strata deformation,temperature,and moisture.Yan’an New District was selected as a case study to conduct refined in-situ monitoring through a 77 m-deep borehole and a 30 m-long trench.Findings reveal that the ground settlement involves both the deformation of the filling loess and the underlying intact loess.Notably,the filling loess exhibits a stronger creep capability compared to underlying intact loess.The deformation along the profile is unevenly distributed,with a positive correlation with soil moisture.Water accumulation has been observed at the interface between the filling loess and the underlying intact loess,leading to a significant deformation.Moreover,the temperature and moisture in the filling loess have reached a new equilibrium state,with their depths influenced by atmospheric conditions measuring at 31 m and 26 m,respectively.The refined investigation allows us to identify critical layers that matter the sustainable development of newly created urban areas,and provide improved insights into the evolution mechanisms of land creation.展开更多
Thermal analysis plays a key role in the online inspection of molten iron quality.Different solidification process of molten iron can be reflected by thermal analysis curves,and silicon is one of important elements af...Thermal analysis plays a key role in the online inspection of molten iron quality.Different solidification process of molten iron can be reflected by thermal analysis curves,and silicon is one of important elements affecting the solidification of molten iron.In this study,FeSi75 was added in one chamber of the dual-chamber sample cup,and the influences of FeSi75 additive on the characteristic values of thermal analysis curves and vermiculating rate were investigated.The results show that with the increase of FeSi75,the start temperature of austenite formation TALfirstly decreases and then increases,but the start temperature of eutectic growth TSEF,the lowest eutectic temperature TEU,temperature at maximum eutectic reaction rate TEM,and highest eutectic temperature TERkeep always an increase.The temperature at final solidification point TEShas little change.The FeSi75 additive has different influences on the vermiculating rate of molten iron with different vermiculation,and the vermiculating rate increases for lower vermiculation molten iron while decreases for higher one.According to the thermal analysis curves obtained by a dual-chamber sample cup with 0.30wt.%FeSi75 additive in one chamber,the vermiculating rate of molten iron can be evaluated by comparing the characteristic values of these curves.The time differenceΔtERcorresponding to the highest eutectic temperature TERhas a closer relationship with the vermiculating rate,and a parabolic regression curve between the time differenceΔtERand vermiculating rateηhas been obtained within the range of 65%to 95%,which is suitable for the qualified melt.展开更多
The strength and thermal conductivity of compacted graphite iron(CGI)are crucial performance indicators in its engineering application.The presence of graphite in CGI significantly influences the two properties.In the...The strength and thermal conductivity of compacted graphite iron(CGI)are crucial performance indicators in its engineering application.The presence of graphite in CGI significantly influences the two properties.In the previous studies,graphite in CGI was often described using two-dimensional(2D)morphology.In this study,the three-dimensional(3D)size,shape,and distribution of graphite in CGI were analyzed using X-ray tomography.Based on this,a new method is introduced to calculate the 3D vermicularity and compare it with the 2D vermicularity in terms of tensile properties and thermal conductivity.The results demonstrate that vermicular graphite exhibits greater connectivity in 3D observation compared to 2D observation.Therefore,the calculation method of 3D vermicularity is determined by considering the surface area and volume of the connected graphite.Then a linear relationship between 3 and 2D vermicularity has been observed.By comparing the correlation coefficient,it has been found that the 3D vermicularity offers a more accurate method to establish the relationship among graphite morphology,thermal conductivity and tensile property of CGI.展开更多
This study focuses on the saturated anisotropic hydraulic conductivity of a compacted lateritic clayey sandy soil. The effects of the molding water content and the confining stress on the anisotropic hydraulic conduct...This study focuses on the saturated anisotropic hydraulic conductivity of a compacted lateritic clayey sandy soil. The effects of the molding water content and the confining stress on the anisotropic hydraulic conductivity are investigated. The hydraulic conductivity is measured with a flexible-wall permeameter. Samples are dynamically compacted into the three compaction states of a standard Proctor compaction curve： the dry branch, optimum water content and wet branch. Depending on the molding water content and confining stress, the hydraulic conductivity may increase or decrease. In addition, the results indicate that, when the samples are compacted to the optimum water content, lower hydraulic conductivity is obtained, except at a confining stress equal to 50 kPa. The increase of the confining stress decreases the hydraulic conductivity for each of the evaluated compaction states. In the wet branch, horizontal hy- draulic conductivity is about 8 times higher than the vertical value. The anisotropic hydraulic conduc- tivities of the dry and wet branches decrease when the confining stress increases, and the opposite is observed in the optimum water content state.展开更多
The tribological behaviors of Cu-15Ni-8Sn/graphite composites with the graphite content of 38 vol.%against AISI321 stainless steel under dry-sliding,deionized water and sea water were investigated on a block-on-ring c...The tribological behaviors of Cu-15Ni-8Sn/graphite composites with the graphite content of 38 vol.%against AISI321 stainless steel under dry-sliding,deionized water and sea water were investigated on a block-on-ring configuration.The results indicated that the friction coefficient was the lowest under dry-sliding,and the highest in deionized water.The wear rate decreased to reach the minimum value of 1.39×10-15 m3/(N·m)in sea water and in deionized water,it increased to the maximum value of 5.56×10-15 m3/(N·m).The deionized water hindered the formation of tribo-oxide layer and lubricating film,which resulted in the largest friction coefficient and wear rate.In sea water,however,the corrosion products comprised of oxides,hydroxides and chlorides were found on the worn surface,and the compacted layer composed of corrosion products and graphite played an important role in keeping the excellent wear resistance.It was elucidated that the tribological behaviors of Cu-15Ni-8Sn/graphite composite were powerful influenced by the friction environments.展开更多
The characteristics of diffusion are essential to the transport of radionuclides through buffer/backfill materials, such as bentonite, which are commonly found in waste repositories. This study used through-diffusion ...The characteristics of diffusion are essential to the transport of radionuclides through buffer/backfill materials, such as bentonite, which are commonly found in waste repositories. This study used through-diffusion techniques to investigate the diffusion behavior of HTO and ^(99)TcO_4^- on GMZ bentonite of various densities. Diffusion rates were calculated by measuring the diffusion coefficients(De, Da), plotting breakthrough curves and interpreting experiment data. The apparent and effective diffusion coefficients of HTO ranged from(1.68 ± 0.40) 9 × 10^(-11) to(2.80 ± 0.62) 9 × 10^(-11) m^2/s and from(4.61 ±1.28) 9 × 10^(-12) to (16.2 ± 2.50) 9 × 10^(-12) m^2/s, respectively.The apparent and effective diffusion coefficients of^(99)TcO_4^-ranged from(5.26 ± 0.16) 9 × 10^-12to(7.78 ± 0.43) 9× 10^-12m^2/s and from(1.49 ± 0.002) 9 × 10^(-12) to(4.16 ±0.07) 9 × 10^(-12) m^2/s, respectively. The distribution coefficients of HTO and^(99)TcO_4^-ranged from(0.70 ± 0.12) 9× 10^(-2) to(1.36 ± 0.53) 9 × 10^(-2) mL/g and from(1.12 ±0.06) 9 × 10^(-2) to(5.79 ± 2.22) 9 × 10^(-2) mL/g, respectively.The Deand Kdvalues were shown to decrease with an increase in the bulk dry density of compacted bentonite. Our results show that HTO and ^(99)Tc could be considered nonsorbent radionuclides. The data obtained in this studyprovide a valuable reference for the safety assessment of waste repositories.展开更多
Thermal conductivity, water retention curve and swelling behavior of two MX80 bentonite samples were studied in the present work. The difference obtained from these two MX80 bentonite samples was then analyzed in term...Thermal conductivity, water retention curve and swelling behavior of two MX80 bentonite samples were studied in the present work. The difference obtained from these two MX80 bentonite samples was then analyzed in terms of mineralogical effects （effects of the proportion of quartz and montmorillonite）. It was concluded that the mineralogical effect was significant on the thermal conductivity and the swelling capacity; on the contrary, it was negligible on the water retention property.展开更多
基金the Chinese Scholarship Council,which funded her Joint Ph D research programthe support from Natural Sciences and Engineering Research Council of Canada(NSERC)for his research programsthe Chinese Ministry of Science and Technology for supporting his research program(grant No.2014CB744701)
文摘Loess soil deposits are widely distributed in arid and semi-arid regions and constitute about 10% of land area of the world.These soils typically have a loose honeycomb-type meta-stable structure that is susceptible to a large reduction in total volume or collapse upon wetting.Collapse characteristics contribute to various problems to infrastructures that are constructed on loess soils.For this reason,collapse triggering mechanism for loess soils has been of significant interest for researchers and practitioners all over the world.This paper aims at providing a state-of-the-art review on collapse mechanism with special reference to loess soil deposits.The collapse mechanism studies are summarized under three different categories,i.e.traditional approaches,microstructure approach,and soil mechanics-based approaches.The traditional and microstructure approaches for interpreting the collapse behavior are comprehensively summarized and critically reviewed based on the experimental results from the literature.The soil mechanics-based approaches proposed based on the experimental results of both compacted soils and natural loess soils are reviewed highlighting their strengths and limitations for estimating the collapse behavior.Simpler soil mechanics-based approaches with less parameters or parameters that are easy-to-determine from conventional tests are suggested for future research to better understand the collapse behavior of natural loess soils.Such studies would be more valuable for use in conventional geotechnical engineering practice applications.
基金supported by the National Natural Science Foundation of China(Grant No.51109143)the 11th Five Year Plan National Key Programs for Science and Technology Development of China(Grant No.2009BAK56B04)the Natural Science Foundation of Jiangsu Province(Grant No.BK2011109).
文摘A new roller compacted concrete dam of Fengman Hydropower Station is to be built in the toe of the old dam,which was identified as a dangerous dam.The new dam during construction would be influenced by the high-speed flow discharged from the old dam,which is an important problem to be considered for the first time in China,and which would affect the construction of the whole project.Therefore,a series of erosion experiments were conducted in this article.A high-speed flow erosion test apparatus was developed for the erosion experiments of the new dam materials.The maximum jet velocity goes up to 40 m/s and the section area of the nozzle is 0.0025 m2.In the process of experiments,the equipment shows a good performance.Erosive wear tests for two types of materials used in the new dam,a roller compacted concrete and a distorted concrete with four kinds of ages were carried out with the flow velocity in the range of 30 m/s-35 m/s.Erosion parameters and erosion laws for the two types of concretes with different ages were determined,and a general relationship between the erosion rate and the flow velocity is obtained as：,with the velocity exponent between 3.33 and 3.93.It is concluded that the erosion resistance of the distorted concrete is better than that of the roller compacted concrete and the mechanical properties of the concretes of over 14 d age are influenced slightly by the water impact.The test results might serve as a practical technique guide for the safety of this project during its construction in the flood season.
文摘The demands for improved fuel economy,performance and emissions continue to pose challenges for engine designers and the materials they choose. This is particularly true for modern diesel engines,where the primary path to achieving improved engine performance and emissions is to increase the Peak Firing Pressure in the combustion chamber. The resulting increase in thermal and mechanical loading has required a change from conventional grey cast iron to Compacted Graphite Iron (CGI) in order to satisfy durability requirements without increasing the size or the weight of the engines. With at least 75% higher tensile strength,45% higher stiffness and approximately double the fatigue strength of conventional grey cast iron,CGI satisfies durability requirements and also provides the dimensional stability required to meet emissions legislation throughout the life of the engine. Currently,there are no CGI diesel engines running on the roads in North America. This is set to change considerably as new commercial vehicle and pick-up SUV diesel engines are launched with CGI cylinder blocks in 2008 and 2009. These initial programs will provide over 2 million CGI diesel engines when ramped to mature volume,potentially accounting for 10%-15% of the North American passenger vehicle fleet within the next four years.
基金supported by the National Natural Science Foundation of China(Grant Nos.50909041,50539110,50809025 and 50879024)National Science and Technology Support Plan(Grant Nos.2008BAB29B03 and 2008BAB29B06)+2 种基金China Hydropower Engineering Consulting Group Co.Science and Technology Support Project(Grant No.CHC-KJ-2007-02)Jiangsu Province"333 High-Level Personnel Training Project"(Grant No.2017-B08037)Science Foundation for The Excellent Youth Scholars of Ministry of Education of China(Grant No.20070294023)
文摘In view of the diversity and complexity of mechanical parameters of roller compacted concrete dam(RCCD),the uniform design method,partial least-squares regression(PLS)and least squares support vector machine(LSSVM)were applied to the back analysis of RCCD with the use of the complex nonlinear relationship between dam mechanical parameters and dam displacements.During the process of back analysis,the initial samples of parameters were designed with uniform design method.Then,a transversely isotropic model of RCCD was established by MSC.Marc software.Through this model,training samples of LSSVM model could be obtained.And then,the complex nonlinear relationship between relative values of hydraulic components of dam displacements and mechanical parameters was established.Finally,actual relative values of dam hydraulic components are isolated from the measured data of dam displacements by using PLS.By inputting the isolated relative values into LSSVM model,the back analysis values of RCCD mechanical parameters can be obtained.The example analysis showed that mechanical parameters obtained by the above-mentioned back analysis method are reasonable,and the back analysis method is feasible.
基金supported by the National Hi-Tech Research Development Program of China (No.2006AA03Z560)Excellent Youth of Hunan Province,China (No. 06JJ1007)
文摘Carbon fibre reinforced carbon and SiC dual matrices composites （C/C-SiC） show superior tribological properties,high thermal shock resistance and good abrasive resistance,and they are promising candidates for advanced brake and clutch systems.The microstructure,mechanical properties,friction and wear properties,and application of the C/C-SiC composites fabricated by warm compacted-in situ reaction were introduced.The results indicated that the composites were composed of 50-60 wt pct carbon,2-10 wt pct residual silicon and 30-40 wt pct silicon carbide.The C/C-SiC brake composites exhibited good mechanical properties.The value of flexural strength and compressive strength could reach 160 and 112 MPa,respectively.The impact strength was about 2.5 kJ·m-2.The C/C-SiC brake composites showed excellent tribological performance,including high coefficient of friction （0.38）,good abrasive resistance （1.10 μm/cycle） and brake steadily on dry condition.The tribological properties on wet condition could be mostly maintained.The silicon carbide matrix in C/C-SiC brake composites improved the wear resistance,and the graphite played the lubrication function,and right volume content of graphite was helpful to forming friction film to reduce the wear rate.These results showed that C/C-SiC composites fabricated by warm compacted-in situ reaction had excellent properties for use as brake materials.
文摘The high compacted density LiNi<sub>0.5-x</sub>Co<sub>0.2</sub>Mn<sub>0.3</sub>Mg<sub>x</sub>O<sub>2</sub> cathode material for lithium-ion batteries was synthesized by high temperature solid-state method, taking the Mg element as a doping element and the spherical Ni<sub>0.5</sub>Co<sub>0.2</sub>Mn<sub>0.3</sub> (OH)<sub>2</sub>, Li<sub>2</sub>CO<sub>3</sub> as raw materials. The effects of calcination temperature on the structure and properties of the products were investigated. The structure and morphology of cathode materials powder were analyzed by X-ray diffraction spectroscopy (XRD) and scanning electronmicroscopy (SEM). The electrochemical properties of the cathode materials were studied by charge-discharge test and cyclic properties test. The results show that LiNi<sub>0.4985</sub>Co<sub>0.2</sub>Mn<sub>0.3</sub> Mg<sub>0.0015</sub>O<sub>2</sub> cathode material prepared at calcination temperature 930°C has a good layered structure, and the compacted density of the electrode sheet is above 3.68 g/cm<sup>3</sup>. The discharge capacity retention rate is more than 97.5% after 100 cycles at a charge-discharge rate of 1C, displaying a good cyclic performance.
文摘The infl uence of Si, Sn, Mo and Ni on the ductility and thermal conductivity of compacted graphite iron(CGI) was investigated. Metallographic observation and Differential Scanning Calorimetry(DSC) experiments were carried out to analyze the roles of various additions in the eutectoid reaction. The experimental results showed that the ductility of CGI is proportional to the ferrite fraction, so moderate Si content could dramatically improve the ductility by increasing the ferrite fraction. DSC measurements showed that Mo has moderate inhibition on eutectoid transformation during both the heating and cooling processes, while the sample without Sn obviously broadens the three-phase region. Vermicularity and ferrite are known to improve thermal conductivity, and the former plays a more important role. Besides, among the alloy elements investigated, Sn has the greatest negative effect on conductivity, followed by Ni and Mo having the smallest effects.
基金financial support by the National Natural Science Foundationof China(Grant No.51371104)。
文摘This paper gives a brief introduction to the four research methods for the study on thermal conductivity of cast irons,including experimental measurement,statistical analysis,effective medium theory and numerical simulation.Recent studies on the thermal conductivity of various cast irons are reviewed through the influence of alloying elements,structural constituents,and temperature.The addition of alloying elements is the main reason that restricts the thermal conductivity of cast irons,especially spheroidal graphite cast iron.The connectivity of graphite has a significant effect on the thermal conductivity of flake and compacted graphite cast irons,semiquantitative and quantitative analysis of this factor is a key and difficult point in the study of thermal conductivity of cast irons.The thermal conductivities of different types of cast irons show varying degrees of dependence on temperature.This phenomenon is the combination of graphite and matrix,rather than just depending on graphite morphology.The study of the relationship between individual phase and temperature is the focus of future research.These summaries and discussions may provide reference and guidance for the future research and development of high thermal conductivity cast irons.
基金Supported by National Natural Science Foundation of China (No. 50935001 and No. U0734007)Important National Science and Technology Specific Projects of China (No.,20011ZX04015-031)+1 种基金National High Technology Research and Development Program of China("863"Program, No. 2009AA04Z150)Major State Basic Research Development Program of China ("973"Program, No. 2010CB731703 and No. 2011CB706804)
文摘Compacted graphite cast iron （CG1） has been the material for high-power diesel engines recently, but its increased strength causes poor machinability. In this study, coated and uncoated carbide tools were used in dry milling experiment and FEM simulation to study the machinability of CGI and wear behaviour of tools. The experimental and FEM simulation results show that coated tool has great advantage in dry milling of CGI. SEM and EDS analysis of tool wear indicate the wear morphology and wear mechanism. Adhesive wear is the main mechanism to cause un- coated tool wear, while abrasive wear and delamination wear are the main mechanism to cause coated tool wear. Stress and temperature distribution in FEM simulation help to understand the wear mechanism including the reason for coat- ing peeled off.
文摘Compacted clay liners are an integral part of the waste landfills,which are provided to contain the leachate within the landfills and protect the surrounding environment.Generally,locally available natural soils are used for the construction of compacted clay liners if they satisfy the design criteria.However,not all soils in their natural state satisfy all the design criteria for the liner materials.Thus,there is a definite need to modify the locally available natural soils by blending with bentonite to meet the required design criteria for the liners.In view of this,the present study evaluates the suitability of an Indian red soil enhanced with bentonite as a liner material.To achieve this,a series of experiments were carried out using locally available red soil and bentonite.First,the suitability of the red soil was evaluated as a liner material.The experimental results showed that the red soil met all the selection criteria stipulated by the Environmental Protection Agencies(EPAs)for the liners except the hydraulic conductivity criterion.Therefore,the red soil was mixed with bentonite contents of 10%,20%and 30%,and the red soil-bentonite mixtures were evaluated for their suitability for liners in their compacted state.Further,as the liners in the arid and semi-arid regions are subjected to moisture variations due to seasonal moisture fluctuations and other factors,the red soil-bentonite mixtures were subjected to wetdry cycles,and their suitability was evaluated after wet-dry cycles.The experimental results revealed that all the red soil-bentonite mixtures met the stipulated EPA criteria for the liners in the as-compacted state.However,the red soil-bentonite mixtures with 20%and 30%bentonite contents only satisfied the hydraulic conductivity requirement even after wet-dry cycles.The experimental findings were supplemented with the microstructural insights captured through digital camera images,scanning electron microscopy(SEM),and mercury intrusion porosimetry(MIP)studies.
基金supported by the Science and Technology Innovation Development Project of Yantai(No.2023ZDX016)。
文摘The increase in payload capacity of trucks has heightened the demand for cost-effective yet high performance brake discs.In this work,the thermal fatigue and wear of compacted graphite iron brake discs were investigated,aiming to provide an experimental foundation for achieving a balance between their thermal and mechanical properties.Compacted graphite iron brake discs with different tensile strengths,macrohardnesses,specific heat capacities and thermal diffusion coefficients were produced by changing the proportion and strength of ferrite.The peak temperature,pressure load and friction coefficient of compacted graphite iron brake discs were analyzed through inertia friction tests.The morphology of thermal cracks and 3D profiles of the worn surfaces were also discussed.It is found that the thermal fatigue of compacted graphite iron discs is determined by their thermal properties.A compacted graphite iron with the highest specific heat capacity and thermal diffusion coefficient exhibits optimal thermal fatigue resistance.Oxidization of the matrix at low temperatures significantly weakens the function of alloy strengthening in hindering the propagation of thermal cracks.Despite the reduced hardness,increasing the ferrite proportion can mitigate wear loss resulting from low disc temperatures and the absence of abrasive wear.
基金supported by National Natural Science Foundation of China(Grant Nos.4203070 and 41977217)the Key Research&Development Program of Shaanxi Province(Grant No.2020ZDLSF06-03).
文摘Mountain excavation and city construction(MECC)projects being launched in the Loess Plateau in China involve the creation of large-scale artificial land.Understanding the subsurface evolution characteristics of the artificial land is essential,yet challenging.Here,we use an improved fiber-optic monitoring system for its subsurface multi-physical characterization.The system enables us to gather spatiotemporal distribution of various parameters,including strata deformation,temperature,and moisture.Yan’an New District was selected as a case study to conduct refined in-situ monitoring through a 77 m-deep borehole and a 30 m-long trench.Findings reveal that the ground settlement involves both the deformation of the filling loess and the underlying intact loess.Notably,the filling loess exhibits a stronger creep capability compared to underlying intact loess.The deformation along the profile is unevenly distributed,with a positive correlation with soil moisture.Water accumulation has been observed at the interface between the filling loess and the underlying intact loess,leading to a significant deformation.Moreover,the temperature and moisture in the filling loess have reached a new equilibrium state,with their depths influenced by atmospheric conditions measuring at 31 m and 26 m,respectively.The refined investigation allows us to identify critical layers that matter the sustainable development of newly created urban areas,and provide improved insights into the evolution mechanisms of land creation.
基金the financial support of the State Key Laboratory of Engine Reliability(skler-202105)。
文摘Thermal analysis plays a key role in the online inspection of molten iron quality.Different solidification process of molten iron can be reflected by thermal analysis curves,and silicon is one of important elements affecting the solidification of molten iron.In this study,FeSi75 was added in one chamber of the dual-chamber sample cup,and the influences of FeSi75 additive on the characteristic values of thermal analysis curves and vermiculating rate were investigated.The results show that with the increase of FeSi75,the start temperature of austenite formation TALfirstly decreases and then increases,but the start temperature of eutectic growth TSEF,the lowest eutectic temperature TEU,temperature at maximum eutectic reaction rate TEM,and highest eutectic temperature TERkeep always an increase.The temperature at final solidification point TEShas little change.The FeSi75 additive has different influences on the vermiculating rate of molten iron with different vermiculation,and the vermiculating rate increases for lower vermiculation molten iron while decreases for higher one.According to the thermal analysis curves obtained by a dual-chamber sample cup with 0.30wt.%FeSi75 additive in one chamber,the vermiculating rate of molten iron can be evaluated by comparing the characteristic values of these curves.The time differenceΔtERcorresponding to the highest eutectic temperature TERhas a closer relationship with the vermiculating rate,and a parabolic regression curve between the time differenceΔtERand vermiculating rateηhas been obtained within the range of 65%to 95%,which is suitable for the qualified melt.
基金supported by the National Natural Science Foundation of China(NSFC)under Grant.Nos.51871224 and 52130002the Guangdong Basic and Applied Basic Research Foundation(2021A1515010890).
文摘The strength and thermal conductivity of compacted graphite iron(CGI)are crucial performance indicators in its engineering application.The presence of graphite in CGI significantly influences the two properties.In the previous studies,graphite in CGI was often described using two-dimensional(2D)morphology.In this study,the three-dimensional(3D)size,shape,and distribution of graphite in CGI were analyzed using X-ray tomography.Based on this,a new method is introduced to calculate the 3D vermicularity and compare it with the 2D vermicularity in terms of tensile properties and thermal conductivity.The results demonstrate that vermicular graphite exhibits greater connectivity in 3D observation compared to 2D observation.Therefore,the calculation method of 3D vermicularity is determined by considering the surface area and volume of the connected graphite.Then a linear relationship between 3 and 2D vermicularity has been observed.By comparing the correlation coefficient,it has been found that the 3D vermicularity offers a more accurate method to establish the relationship among graphite morphology,thermal conductivity and tensile property of CGI.
文摘This study focuses on the saturated anisotropic hydraulic conductivity of a compacted lateritic clayey sandy soil. The effects of the molding water content and the confining stress on the anisotropic hydraulic conductivity are investigated. The hydraulic conductivity is measured with a flexible-wall permeameter. Samples are dynamically compacted into the three compaction states of a standard Proctor compaction curve： the dry branch, optimum water content and wet branch. Depending on the molding water content and confining stress, the hydraulic conductivity may increase or decrease. In addition, the results indicate that, when the samples are compacted to the optimum water content, lower hydraulic conductivity is obtained, except at a confining stress equal to 50 kPa. The increase of the confining stress decreases the hydraulic conductivity for each of the evaluated compaction states. In the wet branch, horizontal hy- draulic conductivity is about 8 times higher than the vertical value. The anisotropic hydraulic conduc- tivities of the dry and wet branches decrease when the confining stress increases, and the opposite is observed in the optimum water content state.
基金Project(51674304) supported by the National Natural Science Foundation of ChinaProject(19B430013) supported by the Key Scientific Research Projects of Higher Education Institutions in Henan Province,ChinaProject(2017BSJJ013) supported by the Doctor Research Foundation of Zhengzhou University of Light Industry,China
文摘The tribological behaviors of Cu-15Ni-8Sn/graphite composites with the graphite content of 38 vol.%against AISI321 stainless steel under dry-sliding,deionized water and sea water were investigated on a block-on-ring configuration.The results indicated that the friction coefficient was the lowest under dry-sliding,and the highest in deionized water.The wear rate decreased to reach the minimum value of 1.39×10-15 m3/(N·m)in sea water and in deionized water,it increased to the maximum value of 5.56×10-15 m3/(N·m).The deionized water hindered the formation of tribo-oxide layer and lubricating film,which resulted in the largest friction coefficient and wear rate.In sea water,however,the corrosion products comprised of oxides,hydroxides and chlorides were found on the worn surface,and the compacted layer composed of corrosion products and graphite played an important role in keeping the excellent wear resistance.It was elucidated that the tribological behaviors of Cu-15Ni-8Sn/graphite composite were powerful influenced by the friction environments.
基金the Nuclear Backend Management Department at Taiwan Power Company for financially supporting this research
文摘The characteristics of diffusion are essential to the transport of radionuclides through buffer/backfill materials, such as bentonite, which are commonly found in waste repositories. This study used through-diffusion techniques to investigate the diffusion behavior of HTO and ^(99)TcO_4^- on GMZ bentonite of various densities. Diffusion rates were calculated by measuring the diffusion coefficients(De, Da), plotting breakthrough curves and interpreting experiment data. The apparent and effective diffusion coefficients of HTO ranged from(1.68 ± 0.40) 9 × 10^(-11) to(2.80 ± 0.62) 9 × 10^(-11) m^2/s and from(4.61 ±1.28) 9 × 10^(-12) to (16.2 ± 2.50) 9 × 10^(-12) m^2/s, respectively.The apparent and effective diffusion coefficients of^(99)TcO_4^-ranged from(5.26 ± 0.16) 9 × 10^-12to(7.78 ± 0.43) 9× 10^-12m^2/s and from(1.49 ± 0.002) 9 × 10^(-12) to(4.16 ±0.07) 9 × 10^(-12) m^2/s, respectively. The distribution coefficients of HTO and^(99)TcO_4^-ranged from(0.70 ± 0.12) 9× 10^(-2) to(1.36 ± 0.53) 9 × 10^(-2) mL/g and from(1.12 ±0.06) 9 × 10^(-2) to(5.79 ± 2.22) 9 × 10^(-2) mL/g, respectively.The Deand Kdvalues were shown to decrease with an increase in the bulk dry density of compacted bentonite. Our results show that HTO and ^(99)Tc could be considered nonsorbent radionuclides. The data obtained in this studyprovide a valuable reference for the safety assessment of waste repositories.
文摘Thermal conductivity, water retention curve and swelling behavior of two MX80 bentonite samples were studied in the present work. The difference obtained from these two MX80 bentonite samples was then analyzed in terms of mineralogical effects （effects of the proportion of quartz and montmorillonite）. It was concluded that the mineralogical effect was significant on the thermal conductivity and the swelling capacity; on the contrary, it was negligible on the water retention property.
