A new generation of fluid pressure forming technology has been developed for the three typical structures of tubes,sheets,and shells,and hard-to-deform material components that are urgently needed for aerospace,aircra...A new generation of fluid pressure forming technology has been developed for the three typical structures of tubes,sheets,and shells,and hard-to-deform material components that are urgently needed for aerospace,aircraft,automobile,and high-speed train industries.in this paper,an over all review is introduced on the state of the art in fundamentals and processes for lower-pressure hydroforming of tubular components,double-sided pressure hydroforming of sheet components,die-less hydroforming of ellipsoidai shells,and dual hardening hot medium forming af hard-to-deform materiais Particular attention is paid to deformation behavior,stress state adjustment,defect prevention,and typical applications.In addition,future development directions of fluid pressure forming technology are discussed,including hyper lower-loading forming for ultra-large non-uniform components,precision for ming for intermetallic compound and high-entropy alloy components,intelligent process and equipment,and precise finite element simulation of inhomogeneous and strong anisotropic thin shells.展开更多
Wave reflection and refraction in layered media is a topic closely related to seismology,acoustics,geophysics and earthquake engineering.Analytical solutions for wave reflection and refraction coefficients in multi-la...Wave reflection and refraction in layered media is a topic closely related to seismology,acoustics,geophysics and earthquake engineering.Analytical solutions for wave reflection and refraction coefficients in multi-layered media subjected to P wave incidence from the elastic half-space are derived in terms of displacement potentials.The system is composed of ideal fluid,porous medium,and underlying elastic solid.By numerical examples,the effects of porous medium and the incident wave angle on the dynamic pressures of ideal fluid are analyzed.The results show that the existence of the porous medium,especially in the partially saturated case,may significantly affect the dynamic pressures of the overlying fluid.展开更多
Vapor pressure deficit(VPD)plays a crucial role in determining plant physiological functions and exerts a substantial influence on vegetation,second only to carbon dioxide(CO_(2)).As a robust indicator of atmospheric ...Vapor pressure deficit(VPD)plays a crucial role in determining plant physiological functions and exerts a substantial influence on vegetation,second only to carbon dioxide(CO_(2)).As a robust indicator of atmospheric water demand,VPD has implications for global water resources,and its significance extends to the structure and functioning of ecosystems.However,the influence of VPD on vegetation growth under climate change remains unclear in China.This study employed empirical equations to estimate the VPD in China from 2000 to 2020 based on meteorological reanalysis data of the Climatic Research Unit(CRU)Time-Series version 4.06(TS4.06)and European Centre for Medium-Range Weather Forecasts(ECMWF)Reanalysis 5(ERA-5).Vegetation growth status was characterized using three vegetation indices,namely gross primary productivity(GPP),leaf area index(LAI),and near-infrared reflectance of vegetation(NIRv).The spatiotemporal dynamics of VPD and vegetation indices were analyzed using the Theil-Sen median trend analysis and Mann-Kendall test.Furthermore,the influence of VPD on vegetation growth and its relative contribution were assessed using a multiple linear regression model.The results indicated an overall negative correlation between VPD and vegetation indices.Three VPD intervals for the correlations between VPD and vegetation indices were identified:a significant positive correlation at VPD below 4.820 hPa,a significant negative correlation at VPD within 4.820–9.000 hPa,and a notable weakening of negative correlation at VPD above 9.000 hPa.VPD exhibited a pronounced negative impact on vegetation growth,surpassing those of temperature,precipitation,and solar radiation in absolute magnitude.CO_(2) contributed most positively to vegetation growth,with VPD offsetting approximately 30.00%of the positive effect of CO_(2).As the rise of VPD decelerated,its relative contribution to vegetation growth diminished.Additionally,the intensification of spatial variations in temperature and precipitation accentuated the spatial hetero展开更多
In order to investigate the relationship between bar diameter and loading rate of the split Hopkinson pressure bar(SHPB) setup under the failure of rock specimen and realize the medium strain rate loading of specimen,...In order to investigate the relationship between bar diameter and loading rate of the split Hopkinson pressure bar(SHPB) setup under the failure of rock specimen and realize the medium strain rate loading of specimen,new SHPB setups with different elastic bar's diameters of 22,36,50 and 75 mm were constructed.The tests were carried out on these setups at different loading rates,and the specimens had the same diameter of elastic bars and same ratio of length to diameter.The test results show that the larger the elastic bar's diameter is,the less the loading rate is needed to cause specimen failure,they show good power relationship,and that under the same strain rate loading,specimens are broken more seriously with larger diameter SHPB setup than with smaller one.展开更多
基金supported by the National Science Fund for Distinguished Young Scholars(50525516)the National Natural Science Foundation of China(U1637209,51175111,50375036,and 59975021).
文摘A new generation of fluid pressure forming technology has been developed for the three typical structures of tubes,sheets,and shells,and hard-to-deform material components that are urgently needed for aerospace,aircraft,automobile,and high-speed train industries.in this paper,an over all review is introduced on the state of the art in fundamentals and processes for lower-pressure hydroforming of tubular components,double-sided pressure hydroforming of sheet components,die-less hydroforming of ellipsoidai shells,and dual hardening hot medium forming af hard-to-deform materiais Particular attention is paid to deformation behavior,stress state adjustment,defect prevention,and typical applications.In addition,future development directions of fluid pressure forming technology are discussed,including hyper lower-loading forming for ultra-large non-uniform components,precision for ming for intermetallic compound and high-entropy alloy components,intelligent process and equipment,and precise finite element simulation of inhomogeneous and strong anisotropic thin shells.
基金National Natural Science Foundation of China Under Grant No.50309005National Key Basic Research and Development Program Under Grant No.2002CB412709
文摘Wave reflection and refraction in layered media is a topic closely related to seismology,acoustics,geophysics and earthquake engineering.Analytical solutions for wave reflection and refraction coefficients in multi-layered media subjected to P wave incidence from the elastic half-space are derived in terms of displacement potentials.The system is composed of ideal fluid,porous medium,and underlying elastic solid.By numerical examples,the effects of porous medium and the incident wave angle on the dynamic pressures of ideal fluid are analyzed.The results show that the existence of the porous medium,especially in the partially saturated case,may significantly affect the dynamic pressures of the overlying fluid.
基金This research was supported by the National Natural Science Foundation of China(42161058).
文摘Vapor pressure deficit(VPD)plays a crucial role in determining plant physiological functions and exerts a substantial influence on vegetation,second only to carbon dioxide(CO_(2)).As a robust indicator of atmospheric water demand,VPD has implications for global water resources,and its significance extends to the structure and functioning of ecosystems.However,the influence of VPD on vegetation growth under climate change remains unclear in China.This study employed empirical equations to estimate the VPD in China from 2000 to 2020 based on meteorological reanalysis data of the Climatic Research Unit(CRU)Time-Series version 4.06(TS4.06)and European Centre for Medium-Range Weather Forecasts(ECMWF)Reanalysis 5(ERA-5).Vegetation growth status was characterized using three vegetation indices,namely gross primary productivity(GPP),leaf area index(LAI),and near-infrared reflectance of vegetation(NIRv).The spatiotemporal dynamics of VPD and vegetation indices were analyzed using the Theil-Sen median trend analysis and Mann-Kendall test.Furthermore,the influence of VPD on vegetation growth and its relative contribution were assessed using a multiple linear regression model.The results indicated an overall negative correlation between VPD and vegetation indices.Three VPD intervals for the correlations between VPD and vegetation indices were identified:a significant positive correlation at VPD below 4.820 hPa,a significant negative correlation at VPD within 4.820–9.000 hPa,and a notable weakening of negative correlation at VPD above 9.000 hPa.VPD exhibited a pronounced negative impact on vegetation growth,surpassing those of temperature,precipitation,and solar radiation in absolute magnitude.CO_(2) contributed most positively to vegetation growth,with VPD offsetting approximately 30.00%of the positive effect of CO_(2).As the rise of VPD decelerated,its relative contribution to vegetation growth diminished.Additionally,the intensification of spatial variations in temperature and precipitation accentuated the spatial hetero
基金Project(10472134) supported by the National Natural Science Foundation of China
文摘In order to investigate the relationship between bar diameter and loading rate of the split Hopkinson pressure bar(SHPB) setup under the failure of rock specimen and realize the medium strain rate loading of specimen,new SHPB setups with different elastic bar's diameters of 22,36,50 and 75 mm were constructed.The tests were carried out on these setups at different loading rates,and the specimens had the same diameter of elastic bars and same ratio of length to diameter.The test results show that the larger the elastic bar's diameter is,the less the loading rate is needed to cause specimen failure,they show good power relationship,and that under the same strain rate loading,specimens are broken more seriously with larger diameter SHPB setup than with smaller one.
