The initial collision between Indian and Asian continents marked the starting point for transformation of land-sea thermal contrast,uplift of the Tibet-Himalaya orogen,and climate change in Asia.In this paper,we revie...The initial collision between Indian and Asian continents marked the starting point for transformation of land-sea thermal contrast,uplift of the Tibet-Himalaya orogen,and climate change in Asia.In this paper,we review the published literatures from the past 30 years in order to draw consensus on the processes of initial collision and suturing that took place between the Indian and Asian plates.Following a comparison of the different methods that have been used to constrain the initial timing of collision,we propose that the tectono-sedimentary response in the peripheral foreland basin provides the most sensitive index of this event,and that paleomagnetism presents independent evidence as an alternative,reliable,and quantitative research method.In contrast to previous studies that have suggested collision between India and Asia started in Pakistan between ca.55 Ma and50 Ma and progressively closed eastwards,more recent researches have indicated that this major event first occurred in the center of the Yarlung Tsangpo suture zone(YTSZ) between ca.65 Ma and 63 Ma and then spreading both eastwards and westwards.While continental collision is a complicated process,including the processes of deformation,sedimentation,metamorphism,and magmatism,different researchers have tended to define the nature of this event based on their own understanding,an intuitive bias that has meant that its initial timing has remained controversial for decades.Here,we recommend the use of reconstructions of each geological event within the orogenic evolution sequence as this will allow interpretation of collision timing on the basis of multidisciplinary methods.展开更多
Due to extensitve application of bridge structure on high speed railway line, it is necessary to consider comprehensively the common effect of the train, the track and the bridge. By forming an integrated large system...Due to extensitve application of bridge structure on high speed railway line, it is necessary to consider comprehensively the common effect of the train, the track and the bridge. By forming an integrated large system including the car and locomotive system, track system, bridge structure system and making use the interaction of the wheel/rail as the ″link″ between these systems, the study focuses on the coupling dynamic analysis of the train, the track and the bridge. Based on the summary and digestion of the predecessor′s research experiences, this article studies the coupling vibration of the train, the track and the bridge structure system on the high speed railway line. It covers the following: 1. Establishment of a more completed dynamic analysis model for cars and locomotives: the four axle car with two level suspension is used for the study and a space vibration analysis model constituting of such rigid bodies as carbody, bogie frame and wheelset is built. There are totally 31 degree of freedom, i e, 5 for the carbody and the front and rear bogie respectively, including horizontal movement, bounce, roll, pitch and yaw, 4 for each wheelset, including horizontal movement, bounce, roll and yaw. In the wheelset movement equation, the previous assumption that the wheelset always keep rigid contact with track in the car bridge coupling analysis has been corrected. The wheelset is allowed to leave the track, i e, ″jump on rail″. The degree of freedom of the wheelset has increased from horizontal movement and yaw, 2 in total, to horizontal movement, bounce, roll, and yaw, 4 in total. The degree of freedom for the car model has increased from 23 to 31. 2.Establishment of track structure dynamic analysis model of the multi layer supporting system aiming at ballasted track bridge of multiple spans for the first time: in accordance with the type and characteristics of different track structure and their models and aiming at the most common used ballasted track, the study selected the continuous elastic Eule展开更多
Extended digital image correlation(X-DIC) method is one novel test method in experimental mechanics.In this paper,the principle of the X-DIC method was introduced in detail.A selection scheme of the initial value of N...Extended digital image correlation(X-DIC) method is one novel test method in experimental mechanics.In this paper,the principle of the X-DIC method was introduced in detail.A selection scheme of the initial value of Newton iteration method was proposed when Newton iteration method was applied to solve the partial differential equations.This scheme could make the X-DIC method suitable for the large deformation measurement and avoid the non-convergence phenomenon effectively.The performance of the X-DIC method was verified by simulated images.Since the pixel point with the maximum absolute error occurred mainly at the corner or on the interface of the region of interest(ROI,region used for correlation calculation),measured deformation of the core area(area surrounding the center point of the ROI with a smaller size) was taken as the reliable measured value.The measurement accuracy of the X-DIC method could be improved greatly by using the core area.Combined with a long-distance microscope,the X-DIC method could be used in the deformation measurement of the micro-region.Zero deformation experiment was done to test the precision of the measurement system.Then,the X-DIC method was applied to measure the micro-region deformation of the specimen with a crack.Test value was proved to be in accordance with the actual deformation,showing that the X-DIC method is suitable for the research of microscale mechanical behavior of materials.展开更多
A new phenomenological and empirically-based constitutive model was proposed to modify the term in the original Johnson−Cook constitutive model.The new model can be used to describe and predict the flow stress of AA10...A new phenomenological and empirically-based constitutive model was proposed to modify the term in the original Johnson−Cook constitutive model.The new model can be used to describe and predict the flow stress of AA1070 aluminum with different initial grain sizes in the hot working process.This developed model considers thermal softening,strain-rate hardening,strain hardening,initial grain size,and interactions with each other and can correctly model the behavior of AA1070 at elevated temperature with different strains,strain rates,and initial grain sizes.The hot flow behavior of AA1070 was investigated through compression tests over wide ranges of temperature from 623 to 773 K,strain rate from 0.005 to 0.5 s−1 and initial grain size from 50 to 450μm.Results show that the initial grain size has a significant effect on the flow behavior of AA1070.Then,correlation coefficient(R),average absolute relative error(AARE),and relative error were examined for comparative predictability of the model.Results show that flow stresses for different initial grain sizes calculated by the new proposed model perfectly correlate with experimental ones,with a mean relative error of 1.19%,which confirms that the new modified Johnson−Cook relation can give a precise estimation of the hot flow stress of AA1070 aluminum by considering the initial grain size.展开更多
基金supported by the Chinese Academy of Sciences(Grant No.XDB03010401)the National Key Research and Development Plan(Grant No.2016YFC0600303)National Natural Science Foundation of China(Grant No.41490615)
文摘The initial collision between Indian and Asian continents marked the starting point for transformation of land-sea thermal contrast,uplift of the Tibet-Himalaya orogen,and climate change in Asia.In this paper,we review the published literatures from the past 30 years in order to draw consensus on the processes of initial collision and suturing that took place between the Indian and Asian plates.Following a comparison of the different methods that have been used to constrain the initial timing of collision,we propose that the tectono-sedimentary response in the peripheral foreland basin provides the most sensitive index of this event,and that paleomagnetism presents independent evidence as an alternative,reliable,and quantitative research method.In contrast to previous studies that have suggested collision between India and Asia started in Pakistan between ca.55 Ma and50 Ma and progressively closed eastwards,more recent researches have indicated that this major event first occurred in the center of the Yarlung Tsangpo suture zone(YTSZ) between ca.65 Ma and 63 Ma and then spreading both eastwards and westwards.While continental collision is a complicated process,including the processes of deformation,sedimentation,metamorphism,and magmatism,different researchers have tended to define the nature of this event based on their own understanding,an intuitive bias that has meant that its initial timing has remained controversial for decades.Here,we recommend the use of reconstructions of each geological event within the orogenic evolution sequence as this will allow interpretation of collision timing on the basis of multidisciplinary methods.
文摘Due to extensitve application of bridge structure on high speed railway line, it is necessary to consider comprehensively the common effect of the train, the track and the bridge. By forming an integrated large system including the car and locomotive system, track system, bridge structure system and making use the interaction of the wheel/rail as the ″link″ between these systems, the study focuses on the coupling dynamic analysis of the train, the track and the bridge. Based on the summary and digestion of the predecessor′s research experiences, this article studies the coupling vibration of the train, the track and the bridge structure system on the high speed railway line. It covers the following: 1. Establishment of a more completed dynamic analysis model for cars and locomotives: the four axle car with two level suspension is used for the study and a space vibration analysis model constituting of such rigid bodies as carbody, bogie frame and wheelset is built. There are totally 31 degree of freedom, i e, 5 for the carbody and the front and rear bogie respectively, including horizontal movement, bounce, roll, pitch and yaw, 4 for each wheelset, including horizontal movement, bounce, roll and yaw. In the wheelset movement equation, the previous assumption that the wheelset always keep rigid contact with track in the car bridge coupling analysis has been corrected. The wheelset is allowed to leave the track, i e, ″jump on rail″. The degree of freedom of the wheelset has increased from horizontal movement and yaw, 2 in total, to horizontal movement, bounce, roll, and yaw, 4 in total. The degree of freedom for the car model has increased from 23 to 31. 2.Establishment of track structure dynamic analysis model of the multi layer supporting system aiming at ballasted track bridge of multiple spans for the first time: in accordance with the type and characteristics of different track structure and their models and aiming at the most common used ballasted track, the study selected the continuous elastic Eule
基金supported by the National Natural Science Foundation of China (Grant Nos. 10772133 and 11072172)the Doctoral Fund of Ministry of Education of China (Grant No. 20090032110006)
文摘Extended digital image correlation(X-DIC) method is one novel test method in experimental mechanics.In this paper,the principle of the X-DIC method was introduced in detail.A selection scheme of the initial value of Newton iteration method was proposed when Newton iteration method was applied to solve the partial differential equations.This scheme could make the X-DIC method suitable for the large deformation measurement and avoid the non-convergence phenomenon effectively.The performance of the X-DIC method was verified by simulated images.Since the pixel point with the maximum absolute error occurred mainly at the corner or on the interface of the region of interest(ROI,region used for correlation calculation),measured deformation of the core area(area surrounding the center point of the ROI with a smaller size) was taken as the reliable measured value.The measurement accuracy of the X-DIC method could be improved greatly by using the core area.Combined with a long-distance microscope,the X-DIC method could be used in the deformation measurement of the micro-region.Zero deformation experiment was done to test the precision of the measurement system.Then,the X-DIC method was applied to measure the micro-region deformation of the specimen with a crack.Test value was proved to be in accordance with the actual deformation,showing that the X-DIC method is suitable for the research of microscale mechanical behavior of materials.
文摘A new phenomenological and empirically-based constitutive model was proposed to modify the term in the original Johnson−Cook constitutive model.The new model can be used to describe and predict the flow stress of AA1070 aluminum with different initial grain sizes in the hot working process.This developed model considers thermal softening,strain-rate hardening,strain hardening,initial grain size,and interactions with each other and can correctly model the behavior of AA1070 at elevated temperature with different strains,strain rates,and initial grain sizes.The hot flow behavior of AA1070 was investigated through compression tests over wide ranges of temperature from 623 to 773 K,strain rate from 0.005 to 0.5 s−1 and initial grain size from 50 to 450μm.Results show that the initial grain size has a significant effect on the flow behavior of AA1070.Then,correlation coefficient(R),average absolute relative error(AARE),and relative error were examined for comparative predictability of the model.Results show that flow stresses for different initial grain sizes calculated by the new proposed model perfectly correlate with experimental ones,with a mean relative error of 1.19%,which confirms that the new modified Johnson−Cook relation can give a precise estimation of the hot flow stress of AA1070 aluminum by considering the initial grain size.
