The asphalt pavement longitudinal crack is a common distress in cold regions,resulting from uneven deformation of the subgrade.Analysis of the correlation law between uneven deformation and crack distress is of positi...The asphalt pavement longitudinal crack is a common distress in cold regions,resulting from uneven deformation of the subgrade.Analysis of the correlation law between uneven deformation and crack distress is of positive significance for understanding the mechanism of crack initiation,and putting forward treatment measures.In view of the complexity of longitudinal crack inducement and road surface deformation,the grey relational method was used to analyze this relationship.Through long-term monitoring of the vertical deformation data of typical road sections,the vertical deformation law of the pavement surface and its deformation characteristics under the action of temperature field are analyzed.Parameters such as vertical relative deformation,vertical relative deformation rate and vertical differential deformation VDSr were constructed to describe vertical deformation characteristics.Typical distribution characteristics of longitudinal fractures and their length and distribution characteristics are also described.The grey correlation analysis theory was utilized to analyze the relationship between deformation characteristics of sections,cross sections and monitoring points and longitudinal crack characteristics(length and location).The analysis reveals a linear positive correlation or a high correlation between several indicators.This study can provide a deeper understanding of the occurrence and development mechanism of longitudinal cracks in asphalt pavement of cold areas,and give references for the research of road engineering structure,materials and distress prevention.展开更多
Deformation behavior of slab at the straightening stage during continuous casting was simulated by the explicit dynamic finite element method,and the stress distribution along the width direction of the slab and its c...Deformation behavior of slab at the straightening stage during continuous casting was simulated by the explicit dynamic finite element method,and the stress distribution along the width direction of the slab and its change regularity at slab center during continuous casting were obtained.The influence of distribution and change of stress on the propagation of longitudinal cracks on slab surface was discussed.The results show that the tensional stress appears on slab surface at the inner arc side and the compressive stress appears on slab surface at the outer arc side at stages 6-8 in straightening zone during continuous casting.Longitudinal cracks generally appear on slab top surface and do not appear on slab bottom surface,which are also observed in industry.展开更多
In the continuous casting production of medium carbon steel (whose mass fraction of carbon is 0.09 % to 0.16 %) and high strength low alloy steel (whose mass fraction of Mn is 0.90 % to 1.40 %), flecks occurring the m...In the continuous casting production of medium carbon steel (whose mass fraction of carbon is 0.09 % to 0.16 %) and high strength low alloy steel (whose mass fraction of Mn is 0.90 % to 1.40 %), flecks occurring the most often are usually longitudinal and star cracks. In additional to the employment of a galvanized plate mould, two kinds of fluxes with special properties were studied and used to harmonize the conflicts between the function of heat transfer and lubrication. An industrial application revealed that the crystallizing temperature (Tc) and crystal ratio (R) of fluxes have a crucible effect on impeding the occurrence of above defects on a slab surface. In the case of slab section (180 to 240) mm(1000 to 1400) mm and casting speed Vc of (0.7 to 1.2) m/min, the optimized parameters of fluxes are Tc of (1170 to 1190) ℃, R of 80 % to 95 % for medium carbon steel, and Tc of (1100 to 1150) ℃, plus R of 40 % to 60 % for high strength low alloy steel.展开更多
The fact that the amount of the mold flux components differs at different locations on the cracking surface indicates that the longitudinal surface cracks are initially formed in the mold and are enlarged in the secon...The fact that the amount of the mold flux components differs at different locations on the cracking surface indicates that the longitudinal surface cracks are initially formed in the mold and are enlarged in the secondary cooling zone. Based on the hot ductility measurement of two typical container used steels, it is known that the steels are in severe embrittlement state in the temperature range of 825-775℃. By means of increasing Cr/Ni plating thickness on the upper part of the mold, reducing mold heat flux, adopting new secondary cooling pattern, etc., the occurrence of the surface longitudinal cracks on the steel CC (continuous casting) slabs has been significantly reduced.展开更多
Based on a series of related investigations,a mechanism for the formation of longitudinal surface cracks on a continuous casting slab of high-carbon steel was investigated. High-temperature tensile tests performed on ...Based on a series of related investigations,a mechanism for the formation of longitudinal surface cracks on a continuous casting slab of high-carbon steel was investigated. High-temperature tensile tests performed on slab samples,metallographic and scanning electron microscopy studies,as well as heat flux and shell thickness in continuous casting predicted on the basis of a mathematical model were conducted. The results showed that highcarbon steel exhibited a much lower liquidus temperature and a wider brittle temperature range immediately after solidification compared with those of low-carbon steel. Concentrations of elements K and Na,which are contained in the mold fluxes,were not observed in the cracks during this study. The calculated results showed that the heat flux and the shell thickness were uneven along the mold width and that the shell was thinner and close to the center line of the slab surface. The longitudinal cracks were observed in situ using confocal laser scanning microscopy,to first occur close to the solidification front,where the ductility was extremely low;in addition,the shell growth was slower than in other regions,which led to a thinner shell and depressed shrinkage owing to a lack of lubrication by the mold fluxes below the meniscus. Furthermore,the pouring temperature of high-carbon steel is ~ 100 ℃ lower than that of low-carbon steel,so the formation of a stable liquid flux near the meniscus within a short time at the beginning of casting is difficult. The amounts of liquid slag film and crystalline slag film were insufficient to provide adequate lubrication between the shell and the mold,which resulted in greater friction force that induced or aggravated cracks. Therefore,the homogeneity of mold fluxes and initial solidification in the mold should be improved to reduce the concentration of slab surface defects.展开更多
At present,embankment longitudinal cracks are a major problem in highways through permafrost regions,and seriously affect traffic safety and the normal operations of the highway.In the past,roadbed height in permafros...At present,embankment longitudinal cracks are a major problem in highways through permafrost regions,and seriously affect traffic safety and the normal operations of the highway.In the past,roadbed height in permafrost regions was relatively low,and embankment cracks were rare and did not affect traffic safety.Thus,highway designers and researchers paid little attention to this problem,and they knew very little about distribution laws and mechanism of embankment longitudinal cracks.Due to this lack of knowledge,there is no uniform opinion on this problem,making it difficult to find measures that will mediate the impact of longitudinal cracks.Temperature is a major factor that affects and controls embankment stability in permafrost regions,especially in ice-rich and high-temperature regions,and solar radiation is the principal factor that determines surface temperatures.Under higher embankment,the difference of temperature will be larger between a sunny slope and a shady slope.Hence,the probability for longitudinal cracks generation is higher.In this paper,a survey and analysis of longitudinal cracks along the Qinghai-Tibet Highway were carried out.The longitudinal cracks are found to be related to the road strikes.Solar radiation is considered to play an important role in the generation of longitudinal cracks.展开更多
基金funded by Key Scientific Research Project of Heilongjiang Provincial Department of Transportation(Grant number MH20200828)National Natural Science Foundation of China joint fund for regional innovation and development(Grant number U20A20315)。
文摘The asphalt pavement longitudinal crack is a common distress in cold regions,resulting from uneven deformation of the subgrade.Analysis of the correlation law between uneven deformation and crack distress is of positive significance for understanding the mechanism of crack initiation,and putting forward treatment measures.In view of the complexity of longitudinal crack inducement and road surface deformation,the grey relational method was used to analyze this relationship.Through long-term monitoring of the vertical deformation data of typical road sections,the vertical deformation law of the pavement surface and its deformation characteristics under the action of temperature field are analyzed.Parameters such as vertical relative deformation,vertical relative deformation rate and vertical differential deformation VDSr were constructed to describe vertical deformation characteristics.Typical distribution characteristics of longitudinal fractures and their length and distribution characteristics are also described.The grey correlation analysis theory was utilized to analyze the relationship between deformation characteristics of sections,cross sections and monitoring points and longitudinal crack characteristics(length and location).The analysis reveals a linear positive correlation or a high correlation between several indicators.This study can provide a deeper understanding of the occurrence and development mechanism of longitudinal cracks in asphalt pavement of cold areas,and give references for the research of road engineering structure,materials and distress prevention.
基金Project(50634030) supported by the National Natural Science Foundation of ChinaProject(20090042120005) supported by the Doctorate Foundation of the Ministry of Education of ChinaProject(2006CB605208-1) supported by the State Basic Research Program of China
文摘Deformation behavior of slab at the straightening stage during continuous casting was simulated by the explicit dynamic finite element method,and the stress distribution along the width direction of the slab and its change regularity at slab center during continuous casting were obtained.The influence of distribution and change of stress on the propagation of longitudinal cracks on slab surface was discussed.The results show that the tensional stress appears on slab surface at the inner arc side and the compressive stress appears on slab surface at the outer arc side at stages 6-8 in straightening zone during continuous casting.Longitudinal cracks generally appear on slab top surface and do not appear on slab bottom surface,which are also observed in industry.
文摘In the continuous casting production of medium carbon steel (whose mass fraction of carbon is 0.09 % to 0.16 %) and high strength low alloy steel (whose mass fraction of Mn is 0.90 % to 1.40 %), flecks occurring the most often are usually longitudinal and star cracks. In additional to the employment of a galvanized plate mould, two kinds of fluxes with special properties were studied and used to harmonize the conflicts between the function of heat transfer and lubrication. An industrial application revealed that the crystallizing temperature (Tc) and crystal ratio (R) of fluxes have a crucible effect on impeding the occurrence of above defects on a slab surface. In the case of slab section (180 to 240) mm(1000 to 1400) mm and casting speed Vc of (0.7 to 1.2) m/min, the optimized parameters of fluxes are Tc of (1170 to 1190) ℃, R of 80 % to 95 % for medium carbon steel, and Tc of (1100 to 1150) ℃, plus R of 40 % to 60 % for high strength low alloy steel.
文摘The fact that the amount of the mold flux components differs at different locations on the cracking surface indicates that the longitudinal surface cracks are initially formed in the mold and are enlarged in the secondary cooling zone. Based on the hot ductility measurement of two typical container used steels, it is known that the steels are in severe embrittlement state in the temperature range of 825-775℃. By means of increasing Cr/Ni plating thickness on the upper part of the mold, reducing mold heat flux, adopting new secondary cooling pattern, etc., the occurrence of the surface longitudinal cracks on the steel CC (continuous casting) slabs has been significantly reduced.
文摘Based on a series of related investigations,a mechanism for the formation of longitudinal surface cracks on a continuous casting slab of high-carbon steel was investigated. High-temperature tensile tests performed on slab samples,metallographic and scanning electron microscopy studies,as well as heat flux and shell thickness in continuous casting predicted on the basis of a mathematical model were conducted. The results showed that highcarbon steel exhibited a much lower liquidus temperature and a wider brittle temperature range immediately after solidification compared with those of low-carbon steel. Concentrations of elements K and Na,which are contained in the mold fluxes,were not observed in the cracks during this study. The calculated results showed that the heat flux and the shell thickness were uneven along the mold width and that the shell was thinner and close to the center line of the slab surface. The longitudinal cracks were observed in situ using confocal laser scanning microscopy,to first occur close to the solidification front,where the ductility was extremely low;in addition,the shell growth was slower than in other regions,which led to a thinner shell and depressed shrinkage owing to a lack of lubrication by the mold fluxes below the meniscus. Furthermore,the pouring temperature of high-carbon steel is ~ 100 ℃ lower than that of low-carbon steel,so the formation of a stable liquid flux near the meniscus within a short time at the beginning of casting is difficult. The amounts of liquid slag film and crystalline slag film were insufficient to provide adequate lubrication between the shell and the mold,which resulted in greater friction force that induced or aggravated cracks. Therefore,the homogeneity of mold fluxes and initial solidification in the mold should be improved to reduce the concentration of slab surface defects.
基金funded by the Transportation Construction Projects from the Ministry of Transport of the People's Republic of China (Contract No.:2002 318 795 02)
文摘At present,embankment longitudinal cracks are a major problem in highways through permafrost regions,and seriously affect traffic safety and the normal operations of the highway.In the past,roadbed height in permafrost regions was relatively low,and embankment cracks were rare and did not affect traffic safety.Thus,highway designers and researchers paid little attention to this problem,and they knew very little about distribution laws and mechanism of embankment longitudinal cracks.Due to this lack of knowledge,there is no uniform opinion on this problem,making it difficult to find measures that will mediate the impact of longitudinal cracks.Temperature is a major factor that affects and controls embankment stability in permafrost regions,especially in ice-rich and high-temperature regions,and solar radiation is the principal factor that determines surface temperatures.Under higher embankment,the difference of temperature will be larger between a sunny slope and a shady slope.Hence,the probability for longitudinal cracks generation is higher.In this paper,a survey and analysis of longitudinal cracks along the Qinghai-Tibet Highway were carried out.The longitudinal cracks are found to be related to the road strikes.Solar radiation is considered to play an important role in the generation of longitudinal cracks.
