Considering the self-excited and forced vibrations in high-speed milling processes, a novel method for dynamic optimization of system stability is used to determine the cutting parameters and structural parameters by ...Considering the self-excited and forced vibrations in high-speed milling processes, a novel method for dynamic optimization of system stability is used to determine the cutting parameters and structural parameters by increasing the chatter free material removal rate （CF-MRR） and surface finish. The method is hased on the theory of the chatter stability and the semi-bandwidth of the resonant region. The objective function of the method is material removal rate（MRR）,the constraints are chatter stability and surface finish, and the optimizing variables are cutting and structural parameters. The optimization procedure is stated. The method is applied to a milling system and CF-MRR is increased 18.86%. It is shown that the influences of the chatter stability and the resonance are simultaneously considered in the dynamic optimization of the milling system for increasing CF-MRR and the surface finish.展开更多
Flow behavior and microstructure of a homogenized ZK60 magnesium alloy were investigated during compression in the temperature range of 250-400 ℃ and the strain rate range of 0.1-50 s^-1. The results showed that dyna...Flow behavior and microstructure of a homogenized ZK60 magnesium alloy were investigated during compression in the temperature range of 250-400 ℃ and the strain rate range of 0.1-50 s^-1. The results showed that dynamic recrystallization （DRX） developed mainly at grain boundaries at lower strain rate （0.1-1 s^-1）, while in the case of higher strain rate （10-50 s^-1）, DRX occurred extensively both at twins and grain boundaries at all temperature range, especially at temperature lower than 350 ℃, which resulted in a more homogeneous microstructure than that under other deformation conditions. The DRX extent determines the hot workability of the workpiece, therefore, hot deformation at the strain rate of 10-50 s^-1 and in the temperature range of 250-350 ℃ was desirable for ZK60 alloy. Twin induced DRX during high strain rate compression included three steps. Firstly, twins with high dislocation subdivided the initial grain, then dislocation arrays subdivided the twins into subgrains, and after that DRX took place with a further increase of strain.展开更多
The microstructure and texture evolutions in Mg-Zn-Er alloy during hot compression were investigated by using opticalmicroscope （OM）, field emission scanning electron microscope （EBSD） and transmission electron mi...The microstructure and texture evolutions in Mg-Zn-Er alloy during hot compression were investigated by using opticalmicroscope （OM）, field emission scanning electron microscope （EBSD） and transmission electron microscope （TEM）. The resultsindicate that the temperature plays an important role in dynamic recrystallization （DRX） mechanism. The twin dynamicrecrystallization （TDRX） is induced at a strain of 0.6 because of the activation of non-basal slip （a＋c ） dislocations at 200 ℃.Meanwhile, the continuous DRX （CDRX） occurs at 350℃, which is identified by the typical necklace-like structure around theresidual initial grains. The DRX contributes to the modification of texture significantly. The tension twins are responsible for theweak texture at 200 ℃. Meanwhile, the decrease in the basal texture is ascribed to the DRX sites which transfer from twinboundaries to initial grain boundaries as the temperature is increased from 200 to 350 ℃.展开更多
A Thermecmastor-Z hot deformation simulator,optical microscopy,XRD and TEM were employed to characterize the flow stress behavior and microstructure of twin roll cast ZK60 magnesium alloy during initial stage of hot c...A Thermecmastor-Z hot deformation simulator,optical microscopy,XRD and TEM were employed to characterize the flow stress behavior and microstructure of twin roll cast ZK60 magnesium alloy during initial stage of hot compression at elevated temperature of 300 ℃ and 400 ℃ and a given strain rate of 10-2s-1.The results suggest that flow stress drop during initial stage of hot compression at 300℃,generally led by dynamic recrystallization,is attributed to twinning,correspondingly to dynamic recrystallization as deformation temperature is raised to 400 ℃.展开更多
Chinese forest resources have become very scarce in the face of rapid economic growth demand, while the reform of collective forest right system is in full swing across the country. It will directly affect the regener...Chinese forest resources have become very scarce in the face of rapid economic growth demand, while the reform of collective forest right system is in full swing across the country. It will directly affect the regeneration level of forest resources and the diverse ecological value functions. In this article, the mainstream model paradigm of forest economics, that is, the basic framework of the Faustmann model and its evolution process are made in a more detailed explanation, especially the extended model including considered silvicultural effort, tax subsidies, risk dynamic management, and forest regeneration factors are made in more detailed explanations. This article concludes with the future further research directions of forest economics, including the design of dynamic models that includes considered uneven-aged forest management, non-timber goods and services, dynamic forest models. The research reflects the general trend of interdisciplinary and cross-border.展开更多
A fluctuating flow was used to investigate the thermo-fluid characteristic of a regenerative heat exchanger assembly designed, modelled, built and constructed for the used in Stifling engines applications. Vibration o...A fluctuating flow was used to investigate the thermo-fluid characteristic of a regenerative heat exchanger assembly designed, modelled, built and constructed for the used in Stifling engines applications. Vibration of the regenerative heat exchanger assembly was a problem to deal with during the experimental investigation. Hence, a dynamic analysis of the regenerative heat exchanger assembly was undertaken. The main sources of excitation in vibrations of the regenerative heat exchanger assembly were investigated and calculated based initially on the empirical correlations provided in the literature. Thereafter, a mathematical model of the regenerative heat exchanger assembly was developed based on the energy equations for each moving part of the assembly. The kinetic and potential energy equations were formulated for each moving part of the regenerative heat exchanger assembly. From the kinetic and potential equations, the Lag, range operator was defined, and then the Lagrange formulations were used to derive the differential equations representing the dynamic behavior of each moving part of the assembly. The differential equations were integrated to determine the system natural frequencies. These were then compared to the frequency on excitation in vibrations in order to predict the regenerative heat exchanger working conditions despite the existence of vibration in the system.展开更多
基金Supported by the National Key Basic Research Program of China("973"Project)(2009CB724401)the China Postdoctoral Science Foundation(20070420208)the Postdoctoral Innovation Foundation of Shandong Province(200702023)~~
文摘Considering the self-excited and forced vibrations in high-speed milling processes, a novel method for dynamic optimization of system stability is used to determine the cutting parameters and structural parameters by increasing the chatter free material removal rate （CF-MRR） and surface finish. The method is hased on the theory of the chatter stability and the semi-bandwidth of the resonant region. The objective function of the method is material removal rate（MRR）,the constraints are chatter stability and surface finish, and the optimizing variables are cutting and structural parameters. The optimization procedure is stated. The method is applied to a milling system and CF-MRR is increased 18.86%. It is shown that the influences of the chatter stability and the resonance are simultaneously considered in the dynamic optimization of the milling system for increasing CF-MRR and the surface finish.
基金Project (14JJ6047) supported by the Natural Science Foundation of Hunan Province,ChinaProject (51274092) supported by the National Natural Science Foundation of ChinaProject (20120161110040) supported by the Doctoral Program of Higher Education ofChina
文摘Flow behavior and microstructure of a homogenized ZK60 magnesium alloy were investigated during compression in the temperature range of 250-400 ℃ and the strain rate range of 0.1-50 s^-1. The results showed that dynamic recrystallization （DRX） developed mainly at grain boundaries at lower strain rate （0.1-1 s^-1）, while in the case of higher strain rate （10-50 s^-1）, DRX occurred extensively both at twins and grain boundaries at all temperature range, especially at temperature lower than 350 ℃, which resulted in a more homogeneous microstructure than that under other deformation conditions. The DRX extent determines the hot workability of the workpiece, therefore, hot deformation at the strain rate of 10-50 s^-1 and in the temperature range of 250-350 ℃ was desirable for ZK60 alloy. Twin induced DRX during high strain rate compression included three steps. Firstly, twins with high dislocation subdivided the initial grain, then dislocation arrays subdivided the twins into subgrains, and after that DRX took place with a further increase of strain.
基金Project(2172013)supported by the Natural Science Foundation of Beijing,ChinaProject(2016YFB0301101)supported by the National Key Research and Development Program,ChinaProject(KZ201810005005)supported by Key Science and Technology Program of Beijing Municipal Commission of Education,China
文摘The microstructure and texture evolutions in Mg-Zn-Er alloy during hot compression were investigated by using opticalmicroscope （OM）, field emission scanning electron microscope （EBSD） and transmission electron microscope （TEM）. The resultsindicate that the temperature plays an important role in dynamic recrystallization （DRX） mechanism. The twin dynamicrecrystallization （TDRX） is induced at a strain of 0.6 because of the activation of non-basal slip （a＋c ） dislocations at 200 ℃.Meanwhile, the continuous DRX （CDRX） occurs at 350℃, which is identified by the typical necklace-like structure around theresidual initial grains. The DRX contributes to the modification of texture significantly. The tension twins are responsible for theweak texture at 200 ℃. Meanwhile, the decrease in the basal texture is ascribed to the DRX sites which transfer from twinboundaries to initial grain boundaries as the temperature is increased from 200 to 350 ℃.
基金Project(10020072) supported by Brain Pool Program of Korea Government and Core Technology R & D Program for the Development of High Performance Eco-friendly Structural Materials of the Korean Ministry of Commerce, Industry and Energy
文摘A Thermecmastor-Z hot deformation simulator,optical microscopy,XRD and TEM were employed to characterize the flow stress behavior and microstructure of twin roll cast ZK60 magnesium alloy during initial stage of hot compression at elevated temperature of 300 ℃ and 400 ℃ and a given strain rate of 10-2s-1.The results suggest that flow stress drop during initial stage of hot compression at 300℃,generally led by dynamic recrystallization,is attributed to twinning,correspondingly to dynamic recrystallization as deformation temperature is raised to 400 ℃.
基金funded by the Humanities and So-cial Sciences Youth Fund Program under Ministry of Education and the program name is "The research about risk avoidance behavior in the production process of Chinese farmers" (Grant no.09YJC790214)
文摘Chinese forest resources have become very scarce in the face of rapid economic growth demand, while the reform of collective forest right system is in full swing across the country. It will directly affect the regeneration level of forest resources and the diverse ecological value functions. In this article, the mainstream model paradigm of forest economics, that is, the basic framework of the Faustmann model and its evolution process are made in a more detailed explanation, especially the extended model including considered silvicultural effort, tax subsidies, risk dynamic management, and forest regeneration factors are made in more detailed explanations. This article concludes with the future further research directions of forest economics, including the design of dynamic models that includes considered uneven-aged forest management, non-timber goods and services, dynamic forest models. The research reflects the general trend of interdisciplinary and cross-border.
文摘A fluctuating flow was used to investigate the thermo-fluid characteristic of a regenerative heat exchanger assembly designed, modelled, built and constructed for the used in Stifling engines applications. Vibration of the regenerative heat exchanger assembly was a problem to deal with during the experimental investigation. Hence, a dynamic analysis of the regenerative heat exchanger assembly was undertaken. The main sources of excitation in vibrations of the regenerative heat exchanger assembly were investigated and calculated based initially on the empirical correlations provided in the literature. Thereafter, a mathematical model of the regenerative heat exchanger assembly was developed based on the energy equations for each moving part of the assembly. The kinetic and potential energy equations were formulated for each moving part of the regenerative heat exchanger assembly. From the kinetic and potential equations, the Lag, range operator was defined, and then the Lagrange formulations were used to derive the differential equations representing the dynamic behavior of each moving part of the assembly. The differential equations were integrated to determine the system natural frequencies. These were then compared to the frequency on excitation in vibrations in order to predict the regenerative heat exchanger working conditions despite the existence of vibration in the system.
