The structure stiffness of presses has great effects on the forming precision of workpieces, especially in near-net or net shape forming. Conventionally the stiffness specification of presses is empirically determined...The structure stiffness of presses has great effects on the forming precision of workpieces, especially in near-net or net shape forming. Conventionally the stiffness specification of presses is empirically determined, resulting in poor designs with insufficient or over sufficient stiffness of press structures. In this paper, an approach for the structure design of hydraulic presses is proposed, which is forming-precision-driven and can make presses costeffective by lightweight optimization. The approach consists of five steps:(1)the determination of the press stiffness specification in terms of the forming precision requirement of workpieces;(2)the conceptual design of the press structures according to the stiffness and workspace specifications, and the structure configuration of the press;(3)the prototype design of the press structures by equivalently converting the conceptual design to prototypes;(4)the selection of key structure parameters by sensitivity analysis of the prototype design; and(5)the optimization of the prototype design. The approach is demonstrated and validated through a case study of the structure design of a 100 MN hydraulic press.展开更多
The mechanically bonded CRA-lined pipe is developed to meet the need forcorrosion-resistant alloy steel pipe. Residual contact pressure at the interface of lined pipe isimportant factor that governs the quality of lin...The mechanically bonded CRA-lined pipe is developed to meet the need forcorrosion-resistant alloy steel pipe. Residual contact pressure at the interface of lined pipe isimportant factor that governs the quality of lined pipe. A simplified theoretical method ispresented to predict the residual contact pressure created by hydraulic pressure. The calculatingequation related hydro-forming pressure to the residual contact pressure between two metal faces isderived. And the validation of the proposed equation is accomplished by comparing its result tothose obtained by experimental investigation.展开更多
Urban trees are sensitive to extreme weather events under climate change.Freeze-thaw induced hydraulic failure could induce urban tree dieback and nullify the services they provide.Plant height is a simple but signifi...Urban trees are sensitive to extreme weather events under climate change.Freeze-thaw induced hydraulic failure could induce urban tree dieback and nullify the services they provide.Plant height is a simple but significant trait for plant ecological strategies.Understanding how urban trees with different heights adapt to freeze-thaw stress is increasingly important under climate change.We investigated the relationship between tree height and stem hydraulic functional traits of six common urban tree species in North China to explore tree height-related hydraulic strategies to cope with freeze-thaw stress.Results showed that tall trees had wider vessels,higher hydraulic conductivity,more winter embolism,but lower vessel and wood densities.Positive relationships were found between tree height and vessel diameter,hydraulic conductivity,and freeze-thaw induced embolism,and negative relationships were found between tree height and vessel and wood densities,which implied that short trees employ more conservative ecological strategies than tall trees.Tall and short tree species were well separated by multiple stem hydraulic functional traits;this is consistent with the fact that tall and short trees occupy different niches and indicates that different hydraulic strategies for freeze-thaw stress exist between them.Tall trees might face more pressure to survive under extreme cold weather caused by climate change in the future.Therefore,more attention should be paid to tall urban tree management in North China to cope with extreme cold weather.展开更多
基金Supported by the National Natural Science Foundation of China(No.50805101 and No.51275347)the National Key S&T Special Projects of China on CNC Machine Tools and Fundamental Manufacturing Equipment(No.2010ZX04001-191 and No.2011ZX04002-032)the Science and Technology R&D Program of Tianjin(No.13JCZDJC35000 and No.12ZCDZGX45000)
文摘The structure stiffness of presses has great effects on the forming precision of workpieces, especially in near-net or net shape forming. Conventionally the stiffness specification of presses is empirically determined, resulting in poor designs with insufficient or over sufficient stiffness of press structures. In this paper, an approach for the structure design of hydraulic presses is proposed, which is forming-precision-driven and can make presses costeffective by lightweight optimization. The approach consists of five steps:(1)the determination of the press stiffness specification in terms of the forming precision requirement of workpieces;(2)the conceptual design of the press structures according to the stiffness and workspace specifications, and the structure configuration of the press;(3)the prototype design of the press structures by equivalently converting the conceptual design to prototypes;(4)the selection of key structure parameters by sensitivity analysis of the prototype design; and(5)the optimization of the prototype design. The approach is demonstrated and validated through a case study of the structure design of a 100 MN hydraulic press.
文摘The mechanically bonded CRA-lined pipe is developed to meet the need forcorrosion-resistant alloy steel pipe. Residual contact pressure at the interface of lined pipe isimportant factor that governs the quality of lined pipe. A simplified theoretical method ispresented to predict the residual contact pressure created by hydraulic pressure. The calculatingequation related hydro-forming pressure to the residual contact pressure between two metal faces isderived. And the validation of the proposed equation is accomplished by comparing its result tothose obtained by experimental investigation.
基金This work was financially supported by the National Natural Science Foundation of China(30900564,41877542)the Project of Henan Agricultural University Program for Fundamental Research(30900649).
文摘Urban trees are sensitive to extreme weather events under climate change.Freeze-thaw induced hydraulic failure could induce urban tree dieback and nullify the services they provide.Plant height is a simple but significant trait for plant ecological strategies.Understanding how urban trees with different heights adapt to freeze-thaw stress is increasingly important under climate change.We investigated the relationship between tree height and stem hydraulic functional traits of six common urban tree species in North China to explore tree height-related hydraulic strategies to cope with freeze-thaw stress.Results showed that tall trees had wider vessels,higher hydraulic conductivity,more winter embolism,but lower vessel and wood densities.Positive relationships were found between tree height and vessel diameter,hydraulic conductivity,and freeze-thaw induced embolism,and negative relationships were found between tree height and vessel and wood densities,which implied that short trees employ more conservative ecological strategies than tall trees.Tall and short tree species were well separated by multiple stem hydraulic functional traits;this is consistent with the fact that tall and short trees occupy different niches and indicates that different hydraulic strategies for freeze-thaw stress exist between them.Tall trees might face more pressure to survive under extreme cold weather caused by climate change in the future.Therefore,more attention should be paid to tall urban tree management in North China to cope with extreme cold weather.
