Large size titanium alloy parts are widely used in aerospace.However,they are difficult to manufacture using mechanical cutting technology because of severe tool wear.Electrochemical jet machining is a promising techn...Large size titanium alloy parts are widely used in aerospace.However,they are difficult to manufacture using mechanical cutting technology because of severe tool wear.Electrochemical jet machining is a promising technology to achieve high efficiency,because it has high machining flexibility and no machining tool wear.However,reports on the macro electrochemical jet machining of large size titanium alloy parts are very scarce,because it is difficult to achieve effective constraint of the flow field in macro electrochemical jet machining.In addition,titanium alloy is very sensitive to fluctuation of the flow field,and a turbulent flow field would lead to serious stray corrosion.This paper reports a series of investigations of the electrochemical jet machining of titanium alloy parts.Based on the flow analysis and experiments,the machining flow field was effectively constrained.TB6 titanium alloy part with a perimeter of one meter was machined.The machined surface was smooth with no obvious machining defects.The machining process was particularly stable with no obvious spark discharge.The research provides a reference for the application of electrochemical jet machining technology to achieve large allowance material removal in the machining of large titanium alloy parts.展开更多
This paper briefs the developmental course, manufacturing and applications, as well as future prospect of excitation systems of large size turbogenerators in China, emphatically expounds the advantages of seif-excitat...This paper briefs the developmental course, manufacturing and applications, as well as future prospect of excitation systems of large size turbogenerators in China, emphatically expounds the advantages of seif-excitation systems with potential source reetifiers and matters needing to be noted during dissemination and application of them.展开更多
Large size vessels sailing in continuous level ice and broken ice of high concentration are mostly assisted by icebreakers.This is done in order to provide for fast transportation through the North Sea Route and safe ...Large size vessels sailing in continuous level ice and broken ice of high concentration are mostly assisted by icebreakers.This is done in order to provide for fast transportation through the North Sea Route and safe operation in extreme ice conditions.Currently,new large size gas and oil carriers and container ships are being designed and built with beams much greater than the beams of existing icebreakers.At the same time,no mathematical description exists for the breaking mechanism of ice channel edges,when such vessels move under icebreaker escort.This paper suggests a simple method for assessment of the ice resistance in the case of a large ship running in an icebreaker channel;the method is based on modification of well-known semi-empirical methods for calculation of the ice resistance to ships in level and broken ice.The main feature of the proposed calculation scheme consists in that different methods are applied to estimate the ice resistance in broken ice and due to breaking of level ice edges.The combination of these methods gives a deliverable ice resistance of a large size vessel moving under icebreaker assistance in a newly made ice channel.In general,proposed method allows to define the speed of a carrier moving in an ice channel behind a modern linear icebreaker and could be applied at the ship design stage and during development of the marine transportation system.The paper also discusses the ways for further refinement of the assessment procedure suggested.展开更多
The kinetics of austenite formation in the surface and center regions of a 40 t forged ingot of a high-strength medium- carbon low-alloy steel was studied using high-resolution dilatometry. The starting microstructure...The kinetics of austenite formation in the surface and center regions of a 40 t forged ingot of a high-strength medium- carbon low-alloy steel was studied using high-resolution dilatometry. The starting microstructures from the surface or center regions had different proportions of bainite and residual austenite as well as different prior austenite grain sizes. Two heating rates representing the actual heating rates in the surface （5℃ s -1） and center regions （0.5℃ s -1） of large size forged blocks were utilized. Dilatometric curves revealed only one transformation step of austenite formation at both heating rates independent of grain size or proportion of phases. Optical microscopy, field emission gun scanning electron microscopy and X-ray diffraction were used to study microstructure evolution and confirm the results obtained by dilatometry. The kinetic parameters for austenite formation were determined from the dilatometry data by Johnson-Mehl- Avrami-Kolmogorov （JMAK） equation. The JMAK coefficients were determined for each condition of the investigated steels. The calculations indicated that the nucleation and growth of austenite in the surface region were accelerated more than 10,000 times due to a significantly smaller average prior austenite grain size, stability of initial retained austenite, and accumulation of coarse carbides at the surface. The results were discussed in the framework of classical nucleation and growth theories using the kinetic parameters for austenite formation.展开更多
The movement mode of the atomizer is a very important parameter during spray deposition process,which has direct influence on the size and surface texture of the billets. To resolve the problem of manufacturing large ...The movement mode of the atomizer is a very important parameter during spray deposition process,which has direct influence on the size and surface texture of the billets. To resolve the problem of manufacturing large size billets,a method of spray deposition by the atomizer with off-center swing was put forward. The atomizer was driven by the alternating current servomotor to swing within 7° at varying speed. The influence of the atomizer parameters,such as translation of the atomizer,swing angle of the atomizer,substrate falling speed and spraying pressure,on the spray deposition was studied. The optimized parameters of the spray deposition process were obtained. The results show that the large size billets with uniform surface quality can be made through adjusting swing frequency and angle of the atomizer,offset distance of the atomizer and inclined angle of the substrate; the valid spray area will decrease and the dimension of top surface will reduce when pressure is less than 0.4 MPa within certain spray distance; meantime,the moving time and cooling time of the droplets are extended,which will lead to loose structure and bad densification. When the pressure,the swing angle and the eccentric offset of the atomization equal 0.5 MPa,7° and 60 mm,respectively,large size billets with fine texture and diameter of 500 mm can be produced.展开更多
LNA is a new laser crystal discovered several years ago.The investigations have confirmed interest in LNA as a new,high-power,high-efficiency,solid-state neodymium laser.One of the advantages of LNA is the ability to ...LNA is a new laser crystal discovered several years ago.The investigations have confirmed interest in LNA as a new,high-power,high-efficiency,solid-state neodymium laser.One of the advantages of LNA is the ability to achieve a high Nd content,six times as high as that in YAG(2×10^(20)ions cm^(-3))without severe concentration quenching of the fluorescence and strong segregation of the dopingion along the laser rod.展开更多
The primary concern in stealth aircraft design is the very large electrical size objects.However,the computational and storage requirements of these objects present significant obstacles for current highfidelity desig...The primary concern in stealth aircraft design is the very large electrical size objects.However,the computational and storage requirements of these objects present significant obstacles for current highfidelity design methods,particularly when addressing high-dimensional complex engineering design problems.To address these challenges,we developed a surface sensitivity technique based on the multilevel fast multipole algorithm(MLFMA).An access and storage of sparse partial derivative tensor was improved to significantly enhanced the computation performance.The far-field interactions of the surface sensitivity equation were realized by differential the multipole expansion.In addition,we proposed a fast far-field multiplication method to accelerate the multiplication process.The surface mesh derivative with respect to the design variables was calculated by analytical and complex variable methods,substantially improving computational efficiency.These advancements enabled the MLFMAbased surface sensitivity method to millions meshes and large-scale gradients,extending gradientbased optimization for very large electrical size problems.Test cases have verified the effectiveness of this method in optimizing very large electrical objects in terms of both accuracy and efficiency.展开更多
Based on the observation of a model test and in combination with some theoretical analysis, the researches of some basic hydrodynamics characteristics of cavity spiral flow in a large size level pipe with a shaft-inle...Based on the observation of a model test and in combination with some theoretical analysis, the researches of some basic hydrodynamics characteristics of cavity spiral flow in a large size level pipe with a shaft-inlet is presented in the paper, which include the basic flow pattern, formation condition of the cavity spiral flow, discharge Q, cavity diameter d0, wall pressure coefficient Cpw, velocity distribution, total energy dissipation rate η etc. The results show that the basic flow patterns can be divided into three zones according to the variations in amount of ventilation Ф, cavity diameter d0 and gas pressure p0 within cavity spiral flow when the upstream and downstream water level changes and that the basic hydrodynamics characteristics change with the flow pattern and have the different behaviour.展开更多
Ultra-large zirconia toughened alumina (ZTA,mass ratio of Al2O3 and ZrO2 is 78∶22) ceramics with eccentric circle shape were successfully sintered by microwave sintering with a multi-mode cavity at 2.45 GHz.The dimen...Ultra-large zirconia toughened alumina (ZTA,mass ratio of Al2O3 and ZrO2 is 78∶22) ceramics with eccentric circle shape were successfully sintered by microwave sintering with a multi-mode cavity at 2.45 GHz.The dimension of ZTA ceramics (green body) is 165 mm (outer diameter) × 25 mm (thickness).The optimized sintering temperature of microwave sintering is about 1500 ℃ for 30 min,and the total sintering time is about 4 h which is much shorter than that of conventional sintering.An auxiliary-heating insulation device was designed based on the principle of local caloric compensation to guarantee the intact sintered samples.With the increasing of sintering temperature,more and more microwave energy is absorbed within the entire sample,volumetric densification performs,and phases shift from m-ZrO2 phase to t-ZrO2 phase and cause Al2O3 grain growth.展开更多
The pneumatic conveying system of coal particles can greatly reduce the dust and improve the environmental quality at underground mining workface and the surrounding of coal enterprises.The particle shape and the inte...The pneumatic conveying system of coal particles can greatly reduce the dust and improve the environmental quality at underground mining workface and the surrounding of coal enterprises.The particle shape and the interaction coefficients between particles and the contact surface play important roles in the pneumatic conveying and CFD-DEM simulation.In order to build the semblable shape models and obtain the accurate interaction coefficients of large coal particles,this article establishes the con tact model by the particle overlap method and describes the mathematical model of the shape characteristics for large coal particle.The particle models are simulated by adopting the multi-index mixed orthogonal experiments.The accumulation density,the porosity and the error between simulation and experiment are taken as the indexes,and the particle models and the particle contact coefficients are taken as the orthogonal test factors.As a result,three more accurate particle models and their interaction coefficients are obtained,which provide the model basis for the pneumatic conveying of large coal particles.展开更多
Traditional method to prevent stored grain from deterioration is to control grain temperature.A three dimensional(3-D)numerical model was established to study the temperature variation in outdoor squat silo and large ...Traditional method to prevent stored grain from deterioration is to control grain temperature.A three dimensional(3-D)numerical model was established to study the temperature variation in outdoor squat silo and large size horizontal warehouse at quasi-steady-state.In this research,porous media model and solar radiation model were adopted.Numerical and experimental results showed that grain temperature was influenced by temperature of wall,height of grain and the distance between grain and the wall.Temperature changes dramatically at the top layer of grain heap due to solar radiation and heat convection at air layer.Temperature of grain close to wall increased with the increasing of ambient temperature.The model established in this research is suitable for predicting grain temperature in outdoor squat silo and large size horizontal warehouse.展开更多
In order to effectively reduce energy consumption and increase range mile,new energy vehicles represented by Tesla have greatly aroused the application of integrated magnesium(Mg)alloy die casting technology in automo...In order to effectively reduce energy consumption and increase range mile,new energy vehicles represented by Tesla have greatly aroused the application of integrated magnesium(Mg)alloy die casting technology in automobiles.Previously,the application of Mg alloys in automobiles,especially in automotive cockpit components,is quite extensive,while it has almost disappeared for a period of time due to its relatively high cost,causing a certain degree of information loss in the application technology of Mg alloy parts in automobiles.The rapid development of automotive technology has led to a higher requirement for the automotive components compared with those traditional one.Therefore,whatever the components themselves,or the Mg alloy materials and die casting process have to face an increasing challenge,needing to be upgraded.In addition,owing to its high integration characteristics,the application of Mg alloy die casting technology in large-sized and thin-walled automotive parts has inherent advantages and needs to be expanded urgently.Indeed,it necessitates exploring advance Mg alloys and new product structures and optimizing die casting processes.This article summarizes and analyzes the development status of thin-walled and large-sized die casting Mg alloy parts in passenger car cockpit and corresponding material selection methods,die casting processes as well as mold design techniques.Furthermore,this work will aid researchers in establishing a comprehensive understanding of the manufacture of thin-walled and large-sized die casting Mg alloy parts in automobile cockpit.It will also assist them in developing new Mg alloys with improved comprehensive performance and new processes to meet the high requirements for die casting automotive components.展开更多
Mimicking the structure of natural bone collagen fibers/hydroxyapatite(HA)to synthesize large size of HA for accelerated bone repair remains a challenge.Herein,silicon nitride nanowires(SN)-graphene(GE)was designed by...Mimicking the structure of natural bone collagen fibers/hydroxyapatite(HA)to synthesize large size of HA for accelerated bone repair remains a challenge.Herein,silicon nitride nanowires(SN)-graphene(GE)was designed by the chemical vapor deposition,forming SN-GE(SG)similar to collagen fibers.Then,the large size HA was assembled onto SG by pulsed electrochemical deposition,the SG/HA(SGH)mimics the collagen fibers/HA structure of bone.The introduction of SG induces HA to large size grow in the form of coral-like.HA can be grown on a large size inextricably with the existence of GE modified layers.On the one hand,the upright GE sheets effectively increases the surface roughness which enhances the nucleation site of HA.On the other hand,the C=O provides chemical bonding and induces HA nucle-ation.Compared with SN/HA(SH),the porosity of SGH decreased by 71%.The average diameter of the SGH is(9.76±0.25)mm.Compared with SH,the diameter of SGH is 22 times larger than the diameter of SH.Indicating that SG induces large size growth of HA.Our work can provide a general strategy for the efficient preparation of biological scaffolds with large size HA that can be used in bone tissue engineering.展开更多
Crystalline rare-earth(RE)carbonates having large particle size were prepared from the lixivium of weathered crust elution-deposited rare-earth ores using the precipitation method with ammonium bicarbonate as the prec...Crystalline rare-earth(RE)carbonates having large particle size were prepared from the lixivium of weathered crust elution-deposited rare-earth ores using the precipitation method with ammonium bicarbonate as the precipitant.Their chemical composition was studied using elemental and thermogravimetric analyses(TGA),and their structure and morphology were characterized using Fourier transform infrared(FTIR)spectroscopy,X-ray diffraction(XRD),and scanning electron microscopy(SEM).The results demonstrate that the crystalline rareearth carbonate is a hydrated basic carbonate or oxycarbonate and not astable intermediate carbonate in the process of thermal decomposition.The particle size of crystalline rare-earth carbonates with large particle size is in the range of 50–200μm.With an RE2O3 content of up to 95wt%,the quality of crystalline rare-earth carbonates is higher compared to the Chinese National Standard(GB/T 28882–2012).The quality of the product is superior to the Chinese National Standard.展开更多
After finishing 102 replicate constant amplitude crack initiation and growth tests on Ly12-CZ aluminum alloy plate, a statistical investigation of the fatigue crack initiation and growth process is conducted in this p...After finishing 102 replicate constant amplitude crack initiation and growth tests on Ly12-CZ aluminum alloy plate, a statistical investigation of the fatigue crack initiation and growth process is conducted in this paper. According to the post-mortem fractographic examination by scanning electron microscopy (SEM), some qualitative observations of the spacial correlation among fatigue striations are developed to reveal the statistical nature of material intrinsic inhomogeneity during the crack growth process. From the test data, an engineering division between crack initiation and growth is defined as the upper limit of small crack. The distributions of crack initiation life N-i, growth life N, and the statistical characteristics of crack growth rate da/dN are also investigated. It is hoped that the work will provide a solid test basis for the study of probabilistic fatigue, probabilistic fracture mechanics, fatigue reliability and its engineering applications.展开更多
The largest movable mold EMS developed by POSCO in collaboration with Daineli-Rotelec for improving internal quality of a large CC bloom is being used at a large size bloom caster of POSCO since 2011.Internal quality ...The largest movable mold EMS developed by POSCO in collaboration with Daineli-Rotelec for improving internal quality of a large CC bloom is being used at a large size bloom caster of POSCO since 2011.Internal quality of carbon steel CC bloom of 700×700 mm~2 section size with the mold EMS was much improved compared with without the mold EMS.Equiaxed zone ratio increased from 50%to 100%and the grain of equiaxed structure became globular and fine.Top shrinkage was also much reduced by applying the movable mold EMS.展开更多
Thermal performance was the most important factor in the development of borehole heat exchanger utilizing geothermal energy. The thermal performance was affected by many different design parameters, such as configurat...Thermal performance was the most important factor in the development of borehole heat exchanger utilizing geothermal energy. The thermal performance was affected by many different design parameters, such as configuration type and borehole size of geothermal heat exchanger. These eventually determined the operation and cost efficiency of the geothermal heat exchanger system. The main purpose of this work was to assess the thermal performance of geother^nal heat exchanger with variation of borehole sizes and numbers of U-tubes inside a borehole. For this, a thermal response test rig was established with line-source theory. The thermal response test was performed with in-line variable input heat source. Effective thermal conductivity and thermal resistance were obtained from the measured data. From the measurement, the effective thermal conductivity is found to have similar values for two- pair type （4 U-tubes） and three-pair type （6 U-tubes） borehole heat exchanger systems indicating similar heat transfer ability. Meanwhile, the thermal resistance shows lower value for the three-pair type compared to the two-pair type. Measured data based resistance have lower value compared to computed result from design programs. Overall comparison finds better thermal performance for the three-pair type, however, fluctuating temperature variation indicates complex flow behavior inside the borehole and requires further study on flow characteristics.展开更多
A waterproof nanocrystalline soft magnetic alloy core with a size of O.D.850 mm×I.D.316 mm×H.25 mm for radio frequency acceleration was successfully developed by winding 18μm 1k107b MA ribbons.Theμ'_(p...A waterproof nanocrystalline soft magnetic alloy core with a size of O.D.850 mm×I.D.316 mm×H.25 mm for radio frequency acceleration was successfully developed by winding 18μm 1k107b MA ribbons.Theμ'_(p)Qf products reached 7.5,10,and 12 GHz at 1,3,and 5 MHz,respectively.Theμ'_(p)Qf products of the MA core(O.D.250 mm×I.D.100 mm×H.25 mm)manufactured using a 13μm MA ribbon further increased by 30%.Detailed improvements on the MA core manufacture process are discussed herein.Continuous high-power tests on the new MA cores demonstrated its good performance of waterproofness,particularly its stability of highμ'_(p)Qf products.The MA core with highμ'pQf product and large size can operate under a high average RF power,high electric field,and in deionized water,which will be used in the China Spallation Neutron Source PhaseⅡ(CSNS-Ⅱ).展开更多
基金the National Natural Science Foundation of China(No.52205468)China Postdoctoral Science Foundation(No.2022M710061 and No.2023T160277)Natural Science Foundation of Jiangsu Province(No.BK20210755)。
文摘Large size titanium alloy parts are widely used in aerospace.However,they are difficult to manufacture using mechanical cutting technology because of severe tool wear.Electrochemical jet machining is a promising technology to achieve high efficiency,because it has high machining flexibility and no machining tool wear.However,reports on the macro electrochemical jet machining of large size titanium alloy parts are very scarce,because it is difficult to achieve effective constraint of the flow field in macro electrochemical jet machining.In addition,titanium alloy is very sensitive to fluctuation of the flow field,and a turbulent flow field would lead to serious stray corrosion.This paper reports a series of investigations of the electrochemical jet machining of titanium alloy parts.Based on the flow analysis and experiments,the machining flow field was effectively constrained.TB6 titanium alloy part with a perimeter of one meter was machined.The machined surface was smooth with no obvious machining defects.The machining process was particularly stable with no obvious spark discharge.The research provides a reference for the application of electrochemical jet machining technology to achieve large allowance material removal in the machining of large titanium alloy parts.
文摘This paper briefs the developmental course, manufacturing and applications, as well as future prospect of excitation systems of large size turbogenerators in China, emphatically expounds the advantages of seif-excitation systems with potential source reetifiers and matters needing to be noted during dissemination and application of them.
基金This work was funded by the Russian Science Foundation(Grant No.17-79-20162-П).
文摘Large size vessels sailing in continuous level ice and broken ice of high concentration are mostly assisted by icebreakers.This is done in order to provide for fast transportation through the North Sea Route and safe operation in extreme ice conditions.Currently,new large size gas and oil carriers and container ships are being designed and built with beams much greater than the beams of existing icebreakers.At the same time,no mathematical description exists for the breaking mechanism of ice channel edges,when such vessels move under icebreaker escort.This paper suggests a simple method for assessment of the ice resistance in the case of a large ship running in an icebreaker channel;the method is based on modification of well-known semi-empirical methods for calculation of the ice resistance to ships in level and broken ice.The main feature of the proposed calculation scheme consists in that different methods are applied to estimate the ice resistance in broken ice and due to breaking of level ice edges.The combination of these methods gives a deliverable ice resistance of a large size vessel moving under icebreaker assistance in a newly made ice channel.In general,proposed method allows to define the speed of a carrier moving in an ice channel behind a modern linear icebreaker and could be applied at the ship design stage and during development of the marine transportation system.The paper also discusses the ways for further refinement of the assessment procedure suggested.
文摘The kinetics of austenite formation in the surface and center regions of a 40 t forged ingot of a high-strength medium- carbon low-alloy steel was studied using high-resolution dilatometry. The starting microstructures from the surface or center regions had different proportions of bainite and residual austenite as well as different prior austenite grain sizes. Two heating rates representing the actual heating rates in the surface （5℃ s -1） and center regions （0.5℃ s -1） of large size forged blocks were utilized. Dilatometric curves revealed only one transformation step of austenite formation at both heating rates independent of grain size or proportion of phases. Optical microscopy, field emission gun scanning electron microscopy and X-ray diffraction were used to study microstructure evolution and confirm the results obtained by dilatometry. The kinetic parameters for austenite formation were determined from the dilatometry data by Johnson-Mehl- Avrami-Kolmogorov （JMAK） equation. The JMAK coefficients were determined for each condition of the investigated steels. The calculations indicated that the nucleation and growth of austenite in the surface region were accelerated more than 10,000 times due to a significantly smaller average prior austenite grain size, stability of initial retained austenite, and accumulation of coarse carbides at the surface. The results were discussed in the framework of classical nucleation and growth theories using the kinetic parameters for austenite formation.
基金Project(G1999064900) supported by the National Key Fundamental Research and Development Program of China
文摘The movement mode of the atomizer is a very important parameter during spray deposition process,which has direct influence on the size and surface texture of the billets. To resolve the problem of manufacturing large size billets,a method of spray deposition by the atomizer with off-center swing was put forward. The atomizer was driven by the alternating current servomotor to swing within 7° at varying speed. The influence of the atomizer parameters,such as translation of the atomizer,swing angle of the atomizer,substrate falling speed and spraying pressure,on the spray deposition was studied. The optimized parameters of the spray deposition process were obtained. The results show that the large size billets with uniform surface quality can be made through adjusting swing frequency and angle of the atomizer,offset distance of the atomizer and inclined angle of the substrate; the valid spray area will decrease and the dimension of top surface will reduce when pressure is less than 0.4 MPa within certain spray distance; meantime,the moving time and cooling time of the droplets are extended,which will lead to loose structure and bad densification. When the pressure,the swing angle and the eccentric offset of the atomization equal 0.5 MPa,7° and 60 mm,respectively,large size billets with fine texture and diameter of 500 mm can be produced.
文摘LNA is a new laser crystal discovered several years ago.The investigations have confirmed interest in LNA as a new,high-power,high-efficiency,solid-state neodymium laser.One of the advantages of LNA is the ability to achieve a high Nd content,six times as high as that in YAG(2×10^(20)ions cm^(-3))without severe concentration quenching of the fluorescence and strong segregation of the dopingion along the laser rod.
基金supported by the National Key Research and Development Program of China(Grant No.2023YFB3002800).
文摘The primary concern in stealth aircraft design is the very large electrical size objects.However,the computational and storage requirements of these objects present significant obstacles for current highfidelity design methods,particularly when addressing high-dimensional complex engineering design problems.To address these challenges,we developed a surface sensitivity technique based on the multilevel fast multipole algorithm(MLFMA).An access and storage of sparse partial derivative tensor was improved to significantly enhanced the computation performance.The far-field interactions of the surface sensitivity equation were realized by differential the multipole expansion.In addition,we proposed a fast far-field multiplication method to accelerate the multiplication process.The surface mesh derivative with respect to the design variables was calculated by analytical and complex variable methods,substantially improving computational efficiency.These advancements enabled the MLFMAbased surface sensitivity method to millions meshes and large-scale gradients,extending gradientbased optimization for very large electrical size problems.Test cases have verified the effectiveness of this method in optimizing very large electrical objects in terms of both accuracy and efficiency.
文摘Based on the observation of a model test and in combination with some theoretical analysis, the researches of some basic hydrodynamics characteristics of cavity spiral flow in a large size level pipe with a shaft-inlet is presented in the paper, which include the basic flow pattern, formation condition of the cavity spiral flow, discharge Q, cavity diameter d0, wall pressure coefficient Cpw, velocity distribution, total energy dissipation rate η etc. The results show that the basic flow patterns can be divided into three zones according to the variations in amount of ventilation Ф, cavity diameter d0 and gas pressure p0 within cavity spiral flow when the upstream and downstream water level changes and that the basic hydrodynamics characteristics change with the flow pattern and have the different behaviour.
基金This work was sponsored by the National Natural Science Foundation of China
文摘Ultra-large zirconia toughened alumina (ZTA,mass ratio of Al2O3 and ZrO2 is 78∶22) ceramics with eccentric circle shape were successfully sintered by microwave sintering with a multi-mode cavity at 2.45 GHz.The dimension of ZTA ceramics (green body) is 165 mm (outer diameter) × 25 mm (thickness).The optimized sintering temperature of microwave sintering is about 1500 ℃ for 30 min,and the total sintering time is about 4 h which is much shorter than that of conventional sintering.An auxiliary-heating insulation device was designed based on the principle of local caloric compensation to guarantee the intact sintered samples.With the increasing of sintering temperature,more and more microwave energy is absorbed within the entire sample,volumetric densification performs,and phases shift from m-ZrO2 phase to t-ZrO2 phase and cause Al2O3 grain growth.
基金the Natural Science Foundation ofjiangsu Province(BK20170241)the National Natural Science Foundation of China(51705222 and 51675521)supported by the State Key Laboratory of Process Automation in Mining&Metallurgy and the Beijing Key Laboratory of Process Automation in Mining&Metallurgy(BGRIMM-KZSKL-2019-07).
文摘The pneumatic conveying system of coal particles can greatly reduce the dust and improve the environmental quality at underground mining workface and the surrounding of coal enterprises.The particle shape and the interaction coefficients between particles and the contact surface play important roles in the pneumatic conveying and CFD-DEM simulation.In order to build the semblable shape models and obtain the accurate interaction coefficients of large coal particles,this article establishes the con tact model by the particle overlap method and describes the mathematical model of the shape characteristics for large coal particle.The particle models are simulated by adopting the multi-index mixed orthogonal experiments.The accumulation density,the porosity and the error between simulation and experiment are taken as the indexes,and the particle models and the particle contact coefficients are taken as the orthogonal test factors.As a result,three more accurate particle models and their interaction coefficients are obtained,which provide the model basis for the pneumatic conveying of large coal particles.
基金National Natural Science Foundation of China(31271972)University Science and Technology Innovation Team Support Plan of Henan Province,China in 2016(16IRTSTHN009).
文摘Traditional method to prevent stored grain from deterioration is to control grain temperature.A three dimensional(3-D)numerical model was established to study the temperature variation in outdoor squat silo and large size horizontal warehouse at quasi-steady-state.In this research,porous media model and solar radiation model were adopted.Numerical and experimental results showed that grain temperature was influenced by temperature of wall,height of grain and the distance between grain and the wall.Temperature changes dramatically at the top layer of grain heap due to solar radiation and heat convection at air layer.Temperature of grain close to wall increased with the increasing of ambient temperature.The model established in this research is suitable for predicting grain temperature in outdoor squat silo and large size horizontal warehouse.
基金supported by the foundation of“Cold area new energy service engineering laboratory battery pack comprehensive test system”from Jilin Provincial Development and Reform Commission(2020C021-6)the National Natural Science Foundation of China(NNSFC,No.52371109).
文摘In order to effectively reduce energy consumption and increase range mile,new energy vehicles represented by Tesla have greatly aroused the application of integrated magnesium(Mg)alloy die casting technology in automobiles.Previously,the application of Mg alloys in automobiles,especially in automotive cockpit components,is quite extensive,while it has almost disappeared for a period of time due to its relatively high cost,causing a certain degree of information loss in the application technology of Mg alloy parts in automobiles.The rapid development of automotive technology has led to a higher requirement for the automotive components compared with those traditional one.Therefore,whatever the components themselves,or the Mg alloy materials and die casting process have to face an increasing challenge,needing to be upgraded.In addition,owing to its high integration characteristics,the application of Mg alloy die casting technology in large-sized and thin-walled automotive parts has inherent advantages and needs to be expanded urgently.Indeed,it necessitates exploring advance Mg alloys and new product structures and optimizing die casting processes.This article summarizes and analyzes the development status of thin-walled and large-sized die casting Mg alloy parts in passenger car cockpit and corresponding material selection methods,die casting processes as well as mold design techniques.Furthermore,this work will aid researchers in establishing a comprehensive understanding of the manufacture of thin-walled and large-sized die casting Mg alloy parts in automobile cockpit.It will also assist them in developing new Mg alloys with improved comprehensive performance and new processes to meet the high requirements for die casting automotive components.
基金supported by the National Natural Science Foundation of China under Grant Nos.51872232the Research Fund of the State Key Laboratory of Solidification Processing(NWPU),China(Grant No.136-QP-2015)and“111”project of China(B08040)+2 种基金The Key Scientific and Technological Innovation Research Team of Shaanxi Province(2022TD-31)Project supported by the Joint Funds of the National Natural Science Foundation of China(Grant No.U21B2067)The Key R&D Program of Shaanxi Province(2021ZDLGY14-04).
文摘Mimicking the structure of natural bone collagen fibers/hydroxyapatite(HA)to synthesize large size of HA for accelerated bone repair remains a challenge.Herein,silicon nitride nanowires(SN)-graphene(GE)was designed by the chemical vapor deposition,forming SN-GE(SG)similar to collagen fibers.Then,the large size HA was assembled onto SG by pulsed electrochemical deposition,the SG/HA(SGH)mimics the collagen fibers/HA structure of bone.The introduction of SG induces HA to large size grow in the form of coral-like.HA can be grown on a large size inextricably with the existence of GE modified layers.On the one hand,the upright GE sheets effectively increases the surface roughness which enhances the nucleation site of HA.On the other hand,the C=O provides chemical bonding and induces HA nucle-ation.Compared with SN/HA(SH),the porosity of SGH decreased by 71%.The average diameter of the SGH is(9.76±0.25)mm.Compared with SH,the diameter of SGH is 22 times larger than the diameter of SH.Indicating that SG induces large size growth of HA.Our work can provide a general strategy for the efficient preparation of biological scaffolds with large size HA that can be used in bone tissue engineering.
基金This work was financially supported by the National Natural Science Foundation of China(Nos.51964021 and 51774156)the Jiangxi Province Nature Science Foundation,China(No.20181BAB206020)and China’s National Key R&D Plan Project(No.2019YFC0605000).
文摘Crystalline rare-earth(RE)carbonates having large particle size were prepared from the lixivium of weathered crust elution-deposited rare-earth ores using the precipitation method with ammonium bicarbonate as the precipitant.Their chemical composition was studied using elemental and thermogravimetric analyses(TGA),and their structure and morphology were characterized using Fourier transform infrared(FTIR)spectroscopy,X-ray diffraction(XRD),and scanning electron microscopy(SEM).The results demonstrate that the crystalline rareearth carbonate is a hydrated basic carbonate or oxycarbonate and not astable intermediate carbonate in the process of thermal decomposition.The particle size of crystalline rare-earth carbonates with large particle size is in the range of 50–200μm.With an RE2O3 content of up to 95wt%,the quality of crystalline rare-earth carbonates is higher compared to the Chinese National Standard(GB/T 28882–2012).The quality of the product is superior to the Chinese National Standard.
基金The project is supported by the Aeronautic Science Foundation,China
文摘After finishing 102 replicate constant amplitude crack initiation and growth tests on Ly12-CZ aluminum alloy plate, a statistical investigation of the fatigue crack initiation and growth process is conducted in this paper. According to the post-mortem fractographic examination by scanning electron microscopy (SEM), some qualitative observations of the spacial correlation among fatigue striations are developed to reveal the statistical nature of material intrinsic inhomogeneity during the crack growth process. From the test data, an engineering division between crack initiation and growth is defined as the upper limit of small crack. The distributions of crack initiation life N-i, growth life N, and the statistical characteristics of crack growth rate da/dN are also investigated. It is hoped that the work will provide a solid test basis for the study of probabilistic fatigue, probabilistic fracture mechanics, fatigue reliability and its engineering applications.
文摘The largest movable mold EMS developed by POSCO in collaboration with Daineli-Rotelec for improving internal quality of a large CC bloom is being used at a large size bloom caster of POSCO since 2011.Internal quality of carbon steel CC bloom of 700×700 mm~2 section size with the mold EMS was much improved compared with without the mold EMS.Equiaxed zone ratio increased from 50%to 100%and the grain of equiaxed structure became globular and fine.Top shrinkage was also much reduced by applying the movable mold EMS.
基金Project financially supported by the Second Stage of Brain Korea 21 Projects and Changwon National University,Korea
文摘Thermal performance was the most important factor in the development of borehole heat exchanger utilizing geothermal energy. The thermal performance was affected by many different design parameters, such as configuration type and borehole size of geothermal heat exchanger. These eventually determined the operation and cost efficiency of the geothermal heat exchanger system. The main purpose of this work was to assess the thermal performance of geother^nal heat exchanger with variation of borehole sizes and numbers of U-tubes inside a borehole. For this, a thermal response test rig was established with line-source theory. The thermal response test was performed with in-line variable input heat source. Effective thermal conductivity and thermal resistance were obtained from the measured data. From the measurement, the effective thermal conductivity is found to have similar values for two- pair type （4 U-tubes） and three-pair type （6 U-tubes） borehole heat exchanger systems indicating similar heat transfer ability. Meanwhile, the thermal resistance shows lower value for the three-pair type compared to the two-pair type. Measured data based resistance have lower value compared to computed result from design programs. Overall comparison finds better thermal performance for the three-pair type, however, fluctuating temperature variation indicates complex flow behavior inside the borehole and requires further study on flow characteristics.
基金supported by the funds of the National Natural Science Foundation of China (Nos. 11175194, 11875270, and U1832210)Youth Innovation Promotion Association CAS (No. 2018015)Guangdong Basic and Applied Basic Research Foundation (No.2019B1515120046)
文摘A waterproof nanocrystalline soft magnetic alloy core with a size of O.D.850 mm×I.D.316 mm×H.25 mm for radio frequency acceleration was successfully developed by winding 18μm 1k107b MA ribbons.Theμ'_(p)Qf products reached 7.5,10,and 12 GHz at 1,3,and 5 MHz,respectively.Theμ'_(p)Qf products of the MA core(O.D.250 mm×I.D.100 mm×H.25 mm)manufactured using a 13μm MA ribbon further increased by 30%.Detailed improvements on the MA core manufacture process are discussed herein.Continuous high-power tests on the new MA cores demonstrated its good performance of waterproofness,particularly its stability of highμ'_(p)Qf products.The MA core with highμ'pQf product and large size can operate under a high average RF power,high electric field,and in deionized water,which will be used in the China Spallation Neutron Source PhaseⅡ(CSNS-Ⅱ).
