Bulk flow model with perturbation simplification has been used to calculate rotordynamic coefficients in annular seals which have significant influences on the dynamic behavior of rotors in turbomachinery. In this wor...Bulk flow model with perturbation simplification has been used to calculate rotordynamic coefficients in annular seals which have significant influences on the dynamic behavior of rotors in turbomachinery. In this work, a transient bulk flow model with arbitrary rotor motion is developed, and the boundary conditions and friction factor in the model are calibrated with steady Computational Fluid Dynamics（CFD） analysis. The numerical solution scheme is developed based on the finite element method to obtain the transient reaction force in the seal clearance. With a periodic circular rotor orbit, the transient forces at multiple whirling frequencies are used to evaluate the rotordynamic coefficients. The leakage flowrate of CFD analysis has good agreement with experimental results and the calibrated parameters in bulk flow model are dependent on operating conditions. Although CFD calibration improves the accuracy of the perturbed bulk flow model, the direct damping is overestimated and the cross-coupled damping is underestimated. Compared with the perturbed model, the predictions of the transient bulk flow model are more agreeable with the experiment.展开更多
This paper, using the dataset of BBFs （bursty bulk flows） observed by two Cluster satellites C1 and C4, studies the difference between onset times of BBFs observed by C1 and C4. It is found that the onset time diffe...This paper, using the dataset of BBFs （bursty bulk flows） observed by two Cluster satellites C1 and C4, studies the difference between onset times of BBFs observed by C1 and C4. It is found that the onset time differences of most of BBFs observed by Cl and C4 are smaller than 60 s. The average onset time difference of BBFs of CI and C4 is 68.5 s. The probabilities of onset time difference of BBFs of C1 and C4 larger than 30, 60, 90 and 120 s are respectively 55%, 35%, 27% and 23%. The largest onset time difference of BBFs of C1 and C4 decreases with the increase of earthward component of maximum velocities of BBFs. The onset time difference of BBFs of C1 and C4 results from the velocity inhomogeneity inside the flow channel of BBF, which may be produced in propagation path and/or in source region of BBFs. Such a wide range of onset time difference of BBFs suggests that the velocity inhomogeneity inside the flow channel of BBF is various. These results are very important to the current study of substorm research based on THEMIS data because they indicate that it is impossible to determine the onset time of BBF with a single satellite.展开更多
The high temperature deformation behaviors and thermal workability of Cu_（43）Zr_（48）Al_9 and（Cu_（43）Zr_（48）Al_9）_（98）Y_2 bulk metallic glasses in the supercooled liquid region were investigated by the unia...The high temperature deformation behaviors and thermal workability of Cu_（43）Zr_（48）Al_9 and（Cu_（43）Zr_（48）Al_9）_（98）Y_2 bulk metallic glasses in the supercooled liquid region were investigated by the uniaxial compression tests. The results showed that the high temperature deformation behaviors were highly sensitive to strain rate and temperature, and the flow stress decreased with the increase of temperature, as well as with the decrease of strain rate. Additionally, the（Cu_（43）Zr_（48）Al_9）_（98）Y_2 bulk metallic glass displayed smaller flow stress under the same condition. The flow behavior changed from Newtonian to non-Newtonian with increase of the strain rate, as well as the decrease of temperature, which could be explained by the transition state theory. We found that（Cu_（43）Zr_（48）Al_9）_（98）Y_2 bulk metallic glass had better flow behavior than the Cu_（43）Zr_（48）Al_9 bulk metallic glass in the supercooled liquid region. In addition, the processing maps of the two bulk metallic glasses were constructed considering the power dissipation efficiency. The optimum domain for thermal workability of the bulk metallic glass was located using the processing map, where the power dissipation efficiency was larger than 0.8. It was shown that the（Cu_（43）Zr_（48）Al_9）_（98）Y_2 bulk metallic glass, which had larger area of optimum domain, had excellent thermoplastic forming.展开更多
The serrated plastic flow,microstructure and residual stress of a Zr_（55）Cu_（30）Ni_5Al_（10） bulk metallic glass（BMG）undergone surface mechanical attrition treatment（SMAT）have been investigated by a combinati...The serrated plastic flow,microstructure and residual stress of a Zr_（55）Cu_（30）Ni_5Al_（10） bulk metallic glass（BMG）undergone surface mechanical attrition treatment（SMAT）have been investigated by a combination of compression tests with scanning electron microscopy（SEM）,high resolution transmission electron microscopy（HRTEM）and the incremental hole-drilling strain-gage method.It is found that SMAT leads to various microstructural modifications and residual stress distribution in the surface layers of the Zrbased BMG due to the mechanically-induced nanocrystallization and generation of shear bands.As a result,the BMG alloy exhibits a remarkable work-hardening like behavior and significant increase of plastic strain from less than 1%to 15%,and its plastic deformation dynamics yields a power-law distribution of shear avalanches.Based upon the analysis of the experimental results,it is indicated that this can be connected to the SMAT-induced microstructural modifications and the resulting residual compressive stress in the Zr-based BMG.展开更多
The rate dependence of serrated flow and its effects on the stability of shear banding were systematically investigated in a prototypic bulk metallic glass.It was found that with the increase of external strain rate,t...The rate dependence of serrated flow and its effects on the stability of shear banding were systematically investigated in a prototypic bulk metallic glass.It was found that with the increase of external strain rate,the serrated flow is gradually suppressed and could completely disappear at a critical strain rate.The serration size,characterized by the mean stress drop amplitude,decreases inversely with the strain rate,while the waiting time for serration decreases with the strain rate in a power-law manner.The rate dependence of the serrated flow has important effects on the dynamics and stability of shear banding process,and leads to an optimal plasticity achieved around the critical strain rate for the disappearance of serrated flow.These results are discussed and interpreted in terms of the microscopic deformation theory and the stick-slip dynamics of shear banding for bulk metallic glasses.展开更多
La57.6Al17.5(Cu,Ni)24.9 and La64Al14(Cu,Ni)22 bulk metallic glasses (BMGs) were prepared by copper-mould casting method. Plastic deformation behavior of the two BMGs at various loading rates was studied by nanoindenta...La57.6Al17.5(Cu,Ni)24.9 and La64Al14(Cu,Ni)22 bulk metallic glasses (BMGs) were prepared by copper-mould casting method. Plastic deformation behavior of the two BMGs at various loading rates was studied by nanoindentation. The results showed that the La57.6Al17.5(Cu,Ni)24.9 BMG with a glass transition temperature of 423 K exhibited prominent serrated flow at low loading rates, whereas less pronounced serrated flow at high rates during nanoindentation. In contrast, the La64Al14(Cu,Ni)22 BMG with a glass transition temperature of 401 K exhibited prominent serrated flow at high loading rates. The different rate dependency of serrated flow in the two La-based BMGs is related to the different glass transition temperature, and consequently the degree of viscous flow during indentation at room temperature. A smoother flow occurs in the alloy with relatively lower glass transition temperature, due to the relaxation of stress concentration.展开更多
Research results on the viscous flow deformation behavior of bulk amorphous alloy in different systems are reviewed. The material exhibits an ideal Newtonian fluid at a high temperature. Analytical solution of lamella...Research results on the viscous flow deformation behavior of bulk amorphous alloy in different systems are reviewed. The material exhibits an ideal Newtonian fluid at a high temperature. Analytical solution of lamellar fluid flow behavior is used to discuss the viscous flow behavior of the bulk amorphous alloy in the supercooled liquid state. A material model, which describes such deformation behavior of Mg6oCusoYlo amorphous alloy, is introduced into the finite element method of microformin8 process. Surface feature size was investigated and found not sensitive to the micro formability. Bulk amorphous alloy may possibly be applied to microelectro-mechanical-systems （MEMS） fabrication.展开更多
Multicomponent alloys with high entropy of mixing,e.g.,high entropy alloys（HEAs）and/or multiprincipal-element alloys（MEAs）,are attracting increasing attentions,because the materials with novel properties are being...Multicomponent alloys with high entropy of mixing,e.g.,high entropy alloys（HEAs）and/or multiprincipal-element alloys（MEAs）,are attracting increasing attentions,because the materials with novel properties are being developed,based on the design strategy of the equiatomic ratio,multicomponent,and high entropy of mixing in their liquid or random solution state.Recently,HEAs with the ultrahigh strength and fracture toughness,excellent magnetic properties,high fatigue,wear and corrosion resistance,great phase stability/high resistance to heat-softening behavior,sluggish diffusion effects,and potential superconductivity,etc.,were developed.The HEAs can even have very high irradiation resistance and may have some self-healing effects,and can potentially be used as the first wall and nuclear fuel cladding materials.Serration behaviors and flow units are powerful methods to understand the plastic deformation or fracture of materials.The methods have been successfully used to study the plasticity of amorphous alloys（also bulk metallic glasses,BMGs）.The flow units are proposed as：free volumes,shear transition zones（STZs）,tension-transition zones（TTZs）,liquid-like regions,soft regions or soft spots,etc.The flow units in the crystalline alloys are usually dislocations,which may interact with the solute atoms,interstitial types,or substitution types.Moreover,the flow units often change with the testing temperatures and loading strain rates,e.g.,at the low temperature and high strain rate,plastic deformation will be carried out by the flow unit of twinning,and at high temperatures,the grain boundary will be the weak area,and play as the flow unit.The serration shapes are related to the types of flow units,and the serration behavior can be analyzed using the power law and modified power law.展开更多
Sheet bulk metal forming is widely used for medium thick metal plate due to its convenience in the manu- facture of accurately finished 3D functional components. To obtain precise anisotropy and flow curve of metal pl...Sheet bulk metal forming is widely used for medium thick metal plate due to its convenience in the manu- facture of accurately finished 3D functional components. To obtain precise anisotropy and flow curve of metal plate is a prerequisite for correct simulation of sheet bulk metal forming processes. Inverse analysis of compression test was introduced here to evaluate the sensitivity of different flow curve models and geometric influence of compression test specimen. Besides, a methodology was proposed to compute plastic anisotropic coefficients of Hill quadratic yield cri- terion, which is based on the ratios of flow curves obtained by inverse analysis of compression tests using specimens cut in six directions on the medium-thick metal plate. The obtained flow curves and anisotropic coefficients were compared with those calculated from tensile tests. Flow curves based on inverse analysis of compression tests cover the curves of the tensile tests well, while the anisotropic coefficients are different, especially for the coefficient relat- ed to the RT45 direction. To estimate the effectiveness of the proposed method, the calculated material properties and those based on the traditional tensile tests were applied in a rim-hole process simulation. The simulation results based on the material properties from inverse analysis of compression tests accorded with the tested properties better.展开更多
In this study,hot compression tests of (Cu_(43)Zr_(48)Al_9)_(98)Y_2 bulk metallic glasses (BMGs) were performed,and their micro structure and thermal properties after the deformation were studied to explore the approp...In this study,hot compression tests of (Cu_(43)Zr_(48)Al_9)_(98)Y_2 bulk metallic glasses (BMGs) were performed,and their micro structure and thermal properties after the deformation were studied to explore the appropriate range of their optimum processing parameters. The experimental results show that the superplastic deformation of (Cu_(43)Zr_(48)Al_9)_(98)Y_2 bulk metallic glasses depends mainly on the temperature and strain rate. It is suitable for superplastic processing when the alloys are in the state of Newtonian flow and do not crystallise. The appropriate processing parameters of (Cu_(43)Zr_(48)Al_9)_(98)Y_2 BMGs are the temperatures and strain rates, which are below the "dividing line". And when the temperature is above733 K, the strain rate must be>1×10^(-3) s^(-1).展开更多
A new scheduling model for the bulk ore blending process in iron-making industry is presented , by converting the process into an assembly flow shop scheduling problem with sequence-depended setup time and limited int...A new scheduling model for the bulk ore blending process in iron-making industry is presented , by converting the process into an assembly flow shop scheduling problem with sequence-depended setup time and limited intermediate buffer , and it facilitates the scheduling optimization for this process.To find out the optimal solution of the scheduling problem , an improved genetic algorithm hybridized with problem knowledge-based heuristics is also proposed , which provides high-quality initial solutions and fast searching speed.The efficiency of the algorithm is verified by the computational experiments.展开更多
基金supported by the National Natural Science Foundation of China(No.11176010)
文摘Bulk flow model with perturbation simplification has been used to calculate rotordynamic coefficients in annular seals which have significant influences on the dynamic behavior of rotors in turbomachinery. In this work, a transient bulk flow model with arbitrary rotor motion is developed, and the boundary conditions and friction factor in the model are calibrated with steady Computational Fluid Dynamics（CFD） analysis. The numerical solution scheme is developed based on the finite element method to obtain the transient reaction force in the seal clearance. With a periodic circular rotor orbit, the transient forces at multiple whirling frequencies are used to evaluate the rotordynamic coefficients. The leakage flowrate of CFD analysis has good agreement with experimental results and the calibrated parameters in bulk flow model are dependent on operating conditions. Although CFD calibration improves the accuracy of the perturbed bulk flow model, the direct damping is overestimated and the cross-coupled damping is underestimated. Compared with the perturbed model, the predictions of the transient bulk flow model are more agreeable with the experiment.
基金supported by the National Natural Science Foundation of China (Grant Nos. 40931054 and 41174141)National Basic Research Program of China ("973" Program) (Grant No. 2011CB811404)
文摘This paper, using the dataset of BBFs （bursty bulk flows） observed by two Cluster satellites C1 and C4, studies the difference between onset times of BBFs observed by C1 and C4. It is found that the onset time differences of most of BBFs observed by Cl and C4 are smaller than 60 s. The average onset time difference of BBFs of CI and C4 is 68.5 s. The probabilities of onset time difference of BBFs of C1 and C4 larger than 30, 60, 90 and 120 s are respectively 55%, 35%, 27% and 23%. The largest onset time difference of BBFs of C1 and C4 decreases with the increase of earthward component of maximum velocities of BBFs. The onset time difference of BBFs of C1 and C4 results from the velocity inhomogeneity inside the flow channel of BBF, which may be produced in propagation path and/or in source region of BBFs. Such a wide range of onset time difference of BBFs suggests that the velocity inhomogeneity inside the flow channel of BBF is various. These results are very important to the current study of substorm research based on THEMIS data because they indicate that it is impossible to determine the onset time of BBF with a single satellite.
基金supported by the Education Department of Shaanxi Province(14JK1351)the Principal Fund of Xi’an Technological University(0852-302021407)
文摘The high temperature deformation behaviors and thermal workability of Cu_（43）Zr_（48）Al_9 and（Cu_（43）Zr_（48）Al_9）_（98）Y_2 bulk metallic glasses in the supercooled liquid region were investigated by the uniaxial compression tests. The results showed that the high temperature deformation behaviors were highly sensitive to strain rate and temperature, and the flow stress decreased with the increase of temperature, as well as with the decrease of strain rate. Additionally, the（Cu_（43）Zr_（48）Al_9）_（98）Y_2 bulk metallic glass displayed smaller flow stress under the same condition. The flow behavior changed from Newtonian to non-Newtonian with increase of the strain rate, as well as the decrease of temperature, which could be explained by the transition state theory. We found that（Cu_（43）Zr_（48）Al_9）_（98）Y_2 bulk metallic glass had better flow behavior than the Cu_（43）Zr_（48）Al_9 bulk metallic glass in the supercooled liquid region. In addition, the processing maps of the two bulk metallic glasses were constructed considering the power dissipation efficiency. The optimum domain for thermal workability of the bulk metallic glass was located using the processing map, where the power dissipation efficiency was larger than 0.8. It was shown that the（Cu_（43）Zr_（48）Al_9）_（98）Y_2 bulk metallic glass, which had larger area of optimum domain, had excellent thermoplastic forming.
基金the financial supports provided by National Natural Science Foundation of China(Grant Nos.51171099,50871063)the MOST 973 Program of China(Grant Nos.2015CB856800 and 2012CB932203)
文摘The serrated plastic flow,microstructure and residual stress of a Zr_（55）Cu_（30）Ni_5Al_（10） bulk metallic glass（BMG）undergone surface mechanical attrition treatment（SMAT）have been investigated by a combination of compression tests with scanning electron microscopy（SEM）,high resolution transmission electron microscopy（HRTEM）and the incremental hole-drilling strain-gage method.It is found that SMAT leads to various microstructural modifications and residual stress distribution in the surface layers of the Zrbased BMG due to the mechanically-induced nanocrystallization and generation of shear bands.As a result,the BMG alloy exhibits a remarkable work-hardening like behavior and significant increase of plastic strain from less than 1%to 15%,and its plastic deformation dynamics yields a power-law distribution of shear avalanches.Based upon the analysis of the experimental results,it is indicated that this can be connected to the SMAT-induced microstructural modifications and the resulting residual compressive stress in the Zr-based BMG.
基金Item Sponsored by the Hong Kong Research Grant Council(RGC)of China(U102013,9042066,9054013)
文摘The rate dependence of serrated flow and its effects on the stability of shear banding were systematically investigated in a prototypic bulk metallic glass.It was found that with the increase of external strain rate,the serrated flow is gradually suppressed and could completely disappear at a critical strain rate.The serration size,characterized by the mean stress drop amplitude,decreases inversely with the strain rate,while the waiting time for serration decreases with the strain rate in a power-law manner.The rate dependence of the serrated flow has important effects on the dynamics and stability of shear banding process,and leads to an optimal plasticity achieved around the critical strain rate for the disappearance of serrated flow.These results are discussed and interpreted in terms of the microscopic deformation theory and the stick-slip dynamics of shear banding for bulk metallic glasses.
基金This work was financially supported by the National Natural Science Foundation of China (No.50571109, 10572142 and 10432050)the Knowledge Innovation Program of the Chinese Academy of Sciences.
文摘La57.6Al17.5(Cu,Ni)24.9 and La64Al14(Cu,Ni)22 bulk metallic glasses (BMGs) were prepared by copper-mould casting method. Plastic deformation behavior of the two BMGs at various loading rates was studied by nanoindentation. The results showed that the La57.6Al17.5(Cu,Ni)24.9 BMG with a glass transition temperature of 423 K exhibited prominent serrated flow at low loading rates, whereas less pronounced serrated flow at high rates during nanoindentation. In contrast, the La64Al14(Cu,Ni)22 BMG with a glass transition temperature of 401 K exhibited prominent serrated flow at high loading rates. The different rate dependency of serrated flow in the two La-based BMGs is related to the different glass transition temperature, and consequently the degree of viscous flow during indentation at room temperature. A smoother flow occurs in the alloy with relatively lower glass transition temperature, due to the relaxation of stress concentration.
基金supported by the National Natural Sci-ence Foundation of China under grant No. 50705092.
文摘Research results on the viscous flow deformation behavior of bulk amorphous alloy in different systems are reviewed. The material exhibits an ideal Newtonian fluid at a high temperature. Analytical solution of lamellar fluid flow behavior is used to discuss the viscous flow behavior of the bulk amorphous alloy in the supercooled liquid state. A material model, which describes such deformation behavior of Mg6oCusoYlo amorphous alloy, is introduced into the finite element method of microformin8 process. Surface feature size was investigated and found not sensitive to the micro formability. Bulk amorphous alloy may possibly be applied to microelectro-mechanical-systems （MEMS） fabrication.
基金Item Sponsored by National Natural Science Foundation of China(51471025,51210105006,51371122)
文摘Multicomponent alloys with high entropy of mixing,e.g.,high entropy alloys（HEAs）and/or multiprincipal-element alloys（MEAs）,are attracting increasing attentions,because the materials with novel properties are being developed,based on the design strategy of the equiatomic ratio,multicomponent,and high entropy of mixing in their liquid or random solution state.Recently,HEAs with the ultrahigh strength and fracture toughness,excellent magnetic properties,high fatigue,wear and corrosion resistance,great phase stability/high resistance to heat-softening behavior,sluggish diffusion effects,and potential superconductivity,etc.,were developed.The HEAs can even have very high irradiation resistance and may have some self-healing effects,and can potentially be used as the first wall and nuclear fuel cladding materials.Serration behaviors and flow units are powerful methods to understand the plastic deformation or fracture of materials.The methods have been successfully used to study the plasticity of amorphous alloys（also bulk metallic glasses,BMGs）.The flow units are proposed as：free volumes,shear transition zones（STZs）,tension-transition zones（TTZs）,liquid-like regions,soft regions or soft spots,etc.The flow units in the crystalline alloys are usually dislocations,which may interact with the solute atoms,interstitial types,or substitution types.Moreover,the flow units often change with the testing temperatures and loading strain rates,e.g.,at the low temperature and high strain rate,plastic deformation will be carried out by the flow unit of twinning,and at high temperatures,the grain boundary will be the weak area,and play as the flow unit.The serration shapes are related to the types of flow units,and the serration behavior can be analyzed using the power law and modified power law.
基金Sponsored by National Natural Science Foundation of China(51105250)National Science and Technology Specific Projects of China(2011ZX04016-051)
文摘Sheet bulk metal forming is widely used for medium thick metal plate due to its convenience in the manu- facture of accurately finished 3D functional components. To obtain precise anisotropy and flow curve of metal plate is a prerequisite for correct simulation of sheet bulk metal forming processes. Inverse analysis of compression test was introduced here to evaluate the sensitivity of different flow curve models and geometric influence of compression test specimen. Besides, a methodology was proposed to compute plastic anisotropic coefficients of Hill quadratic yield cri- terion, which is based on the ratios of flow curves obtained by inverse analysis of compression tests using specimens cut in six directions on the medium-thick metal plate. The obtained flow curves and anisotropic coefficients were compared with those calculated from tensile tests. Flow curves based on inverse analysis of compression tests cover the curves of the tensile tests well, while the anisotropic coefficients are different, especially for the coefficient relat- ed to the RT45 direction. To estimate the effectiveness of the proposed method, the calculated material properties and those based on the traditional tensile tests were applied in a rim-hole process simulation. The simulation results based on the material properties from inverse analysis of compression tests accorded with the tested properties better.
基金supported by the Principal Fund of Xi'an Technological University(0852-302021407)
文摘In this study,hot compression tests of (Cu_(43)Zr_(48)Al_9)_(98)Y_2 bulk metallic glasses (BMGs) were performed,and their micro structure and thermal properties after the deformation were studied to explore the appropriate range of their optimum processing parameters. The experimental results show that the superplastic deformation of (Cu_(43)Zr_(48)Al_9)_(98)Y_2 bulk metallic glasses depends mainly on the temperature and strain rate. It is suitable for superplastic processing when the alloys are in the state of Newtonian flow and do not crystallise. The appropriate processing parameters of (Cu_(43)Zr_(48)Al_9)_(98)Y_2 BMGs are the temperatures and strain rates, which are below the "dividing line". And when the temperature is above733 K, the strain rate must be>1×10^(-3) s^(-1).
基金Item Sponsored by National Key Technology Research and Development Program in 11th Five-Year Plan of China ( 2006AA04Z184 )National Natural Science Foundation of China ( 60974023 )
文摘A new scheduling model for the bulk ore blending process in iron-making industry is presented , by converting the process into an assembly flow shop scheduling problem with sequence-depended setup time and limited intermediate buffer , and it facilitates the scheduling optimization for this process.To find out the optimal solution of the scheduling problem , an improved genetic algorithm hybridized with problem knowledge-based heuristics is also proposed , which provides high-quality initial solutions and fast searching speed.The efficiency of the algorithm is verified by the computational experiments.
