Compaction process simulation and residual stress prediction of green PM compact were carried out with elasto-plastic 3D FEA based on the modified Drueker-Prager Cap model in Abaqus. The model parameters of the invest...Compaction process simulation and residual stress prediction of green PM compact were carried out with elasto-plastic 3D FEA based on the modified Drueker-Prager Cap model in Abaqus. The model parameters of the investigated powder Distaloy AE were determined as functions of relative density through typical mechanical property tests of powder. The model was implemented as a user subroutine USDFLD. Single sided compaction of a d20 ram^5 mm disk green compact of Distaloy AE was simulated, and the residual stress of the disk after ejection was predicted with FEA. The FEA results of the compaction process and the residual stress of the disk show good agreement with compaction experiments and X-ray diffraction measurements, which validates the model and its parameters. The results indicate that the compressive residual stresses exist mainly in a thin layer on the side surface, but the residual stresses are very small on the top and bottom surfaces.展开更多
Porous sintered Ti-Ag compacts with different Ag content were fabricated by powder metallurgy. The associated hydrothermal treatment and the effect on the apatite formation were studied. The results suggested that TiO...Porous sintered Ti-Ag compacts with different Ag content were fabricated by powder metallurgy. The associated hydrothermal treatment and the effect on the apatite formation were studied. The results suggested that TiO was generated under the condition of low vacuum （1 ×10^-2 Pa） during the process of burning out the spacer-holding particles. After hydrothermal treatment, a sub-microscale porous layer was formed at the pore wall surface of the samples. The apatite-inducing ability of hydrothermal treated porous sintered Ti-Ag compacts with different Ag content was evaluated in modified simulated body fluid （SBF）. And the results proved that there is a clear correlation between the apatite-inducing ability and Ag content. The higher Ag content in porous leads to the decrease of Na＋ ions and basic hydroxyl （OH）b amount, resulting in the decline of apatite-inducing ability in the first stage. However, their apatite-inducing ability was not significantly different from that of Ti after two weeks SBF immersing. Hence, the ionic activity should restore with the processing of SBF soaking, as the saturation of Ag effect.展开更多
Practical experiences gained in the past several years show that the thermal residual stress(TRS)is a main cause leading polycrystalline diamond compacts(PDC)to premature failure.It is the very important to measure th...Practical experiences gained in the past several years show that the thermal residual stress(TRS)is a main cause leading polycrystalline diamond compacts(PDC)to premature failure.It is the very important to measure the TRS accurately for optimizing the interface and improving the service performance of PDC.In this paper,the TRS in 1913 flat-interface PDC was measured using improved stress-release method(ISRM).The TRS on the surface of polycrystalline diamond(PCD)table was obtained,which can be used to calculate the radial thermal residual stress(RTRS)at the interface of PCD table via a refutation process.The obtained results show that there are compressive residual stress at the PCD table interface and in the most region of PCD table surface.The exception occurs near the outer diameter of the PCD table,where the PDC begins to bend and put the PCD table surface into a tension state,an undesirable state for a brittle material.The ISRM has covered the shortage existing in traditional stress-release method,in which only finite points on the surface of PCD table can be tested for one specimen and one time.Simple as the experimental procedures are,the test results are also very accurate and reliable.This method provides the theoretical and experimental basis for testing TRS of PDC accurately.展开更多
Aluminium-alumina compacts with varying wt% of alumina were compacted in the pressure range of 115 - 290 MPa. Compacts prepared at 290 MPa pressure, were sintered in an argon atmosphere at 573, 673, 773 and 873 K for ...Aluminium-alumina compacts with varying wt% of alumina were compacted in the pressure range of 115 - 290 MPa. Compacts prepared at 290 MPa pressure, were sintered in an argon atmosphere at 573, 673, 773 and 873 K for 1 hour. The green density, % porosity, % spring back and hardness of the green compacts were determined. Scanning Electron Microscopy was carried out to observe the morphology of pores and alumina particles in green and sintered compacts. The present study indicates that, densification of the compact increases with increasing compacting pressure and decreases with increasing alumina content. Maximum density achieved is 93% for pure aluminium compacts and decreases to 85% for Al-20 wt% alumina compacts. Grain growth of aluminium particles is noticed in the compacts after sintering at 773 and 873 K. Dispersion of fine alumina particle in the aluminium matrix occurs predominantly in the compact when sintered at 773 K which results in increase in hardness value.展开更多
To successfully employ powder injection molding (PIM) as a manufacturing technique, the function of the component, design of the part, material and process should be optimized for overall processing ability of the PIM...To successfully employ powder injection molding (PIM) as a manufacturing technique, the function of the component, design of the part, material and process should be optimized for overall processing ability of the PIM process. A comparison between the requirements of flowability and moldability and the compacts shape retention has been made in this work. There is often a contradiction between the requirements of flowability and the compacts shape retention. Many works have been done to attain good molding conditions. However, they fail to take into account the effect of some factors that satisfies good molding conditions on the compacts shape retention during debinding. This paper studies the effect of the powder-binder mixture characteristics and the molding conditions on the flowability and moldability and the shape retention of PIM compacts during debinding process so as to attain the benefits of each.展开更多
Thermal residual stresses in polycrystalline diamond compact(PDC)cutter arising from the difference in thermal expansion between the polycrystalline diamond(PCD)and the supporting tungsten carbide substrate after sint...Thermal residual stresses in polycrystalline diamond compact(PDC)cutter arising from the difference in thermal expansion between the polycrystalline diamond(PCD)and the supporting tungsten carbide substrate after sintering at high pressure and high temperature were investigated using finite element simulation,laboratory tests and theoretical analysis.The obtained results show that although compressive residual stresses exist both in the interface of PCD table and in the most region of PCD table surface, the tensile residual stress,which is a fatal shortage to PDC,can also occur near the outer diameter area of PCD table,and the maximum value is 690 MPa.Distribution of tensile stress in the PCD table is given through experimental results,which is well consistent with the numerical results.This finding may be significant in designing new PDC cutters with lower residual stress and high cutting behavior.展开更多
In this work, a kind of new vitrified bond based on Li2O-Al2O3-SiO2 glass ceramics was used to bond the diamond grains, which is made into grinding wheel and the cylindrical grinding process of polycrystalline diamond...In this work, a kind of new vitrified bond based on Li2O-Al2O3-SiO2 glass ceramics was used to bond the diamond grains, which is made into grinding wheel and the cylindrical grinding process of polycrystalline diamond compacts （PDCs） by using the new vitrified bond diamond grinding wheel was discussed. Several factors which influence the properties of grinding wheel such as amount of vitrified bond and the kinds and amount of stuff in grinding wheel were also investigated. It was found that the new vitrified bond can firmly combine diamond grains, when there are only diamonds and vitrified bond in the structure of grinding wheel, the longevity of the grinding wheel is about 2.5-3 times as that of resin bond grinding wheel for processing PDCs. The grinding size precision of PDCs can be improved from 4-0.03 mm to 4-0.01 mm because of larger Young＇s modulus of vitrified bond than resin bond. The grinding time of a PDC product can be 1.75-2.0 min from 3.25-3.5 min, so this kind of grinding wheel can save much time for processing PDCs. Also, there is hardly noise when using this new vitrified bond diamond grinding wheel to process PDCs. The amount of vitrified bond in grinding wheel influences the longevity of grinding wheel. When the size of diamond grains is 90-107 μm, the optimal amount of vitrified bond in grinding wheel is 21% （wt pct）. When the amount of vitrified bond exceeds 21%, there are many pores in grinding block, which will decrease the longevity of grinding wheel. The existence of addition stuff such as Al2O3 or SiC can reduce the longevity of grinding wheel.展开更多
The effects of temperature （0-500°C） on the compressive strength,hardness,average relative density,and microstructure of Ti6Al4V powder green compacts prepared by magnetic pulse compaction were investigated.The...The effects of temperature （0-500°C） on the compressive strength,hardness,average relative density,and microstructure of Ti6Al4V powder green compacts prepared by magnetic pulse compaction were investigated.The results show that with increasing heating temperature,the compressive strength first increases and then decreases with the maximum value of 976.74 MPa at 400°C.The average relative density and hardness constantly increase,and their values reach 96.11% and HRA 69.8 at 500°C,respectively.The increase of partial welding is found among the junctions of particles inside the compacts; there is no obvious grain growth inside the compacts within the temperature range.展开更多
Ti6Al4V powder compaction was performed by using magnetic pulse compaction in air at 200℃.Effects of process parameters such as voltage,capacitance,discharge times on the microstructure,compressive strength,hardness ...Ti6Al4V powder compaction was performed by using magnetic pulse compaction in air at 200℃.Effects of process parameters such as voltage,capacitance,discharge times on the microstructure,compressive strength,hardness and relative density of compacts were investigated.The experimental results show that the relative density,hardness and compressive strength of compacted specimens increase with increasing voltage.In addition,the relative density and compressive strength of compacted specimens increase with the augmentation of capacitance in the range investigated.The relative density increases,the hardness firstly increases and then tends to be a fixed value;and the compressive strength firstly increases and then decreases from one to five times compaction.Both values of the hardness and compressive strength reach the maxima of HRA 69.1 and 1 062.31 MPa,at three times compaction,respectively.There are pores in and between particles.展开更多
In order to obtain high property powder metallurgy products, at present rotary forging process has often been used to further densify the sintered powder compact, but the densification law and property analysis have v...In order to obtain high property powder metallurgy products, at present rotary forging process has often been used to further densify the sintered powder compact, but the densification law and property analysis have very rarely been studied, therefore the densification laws of sintered powder compacts being composed of Fe 0.8%C 4.0%Cu 0.2% zinc stearate and formed as cylindrical shape by double action pressing, and then further densified as well in a rotary forging process was studied by orthogonal experiment and regression analysis. The experimental results show that the H / D ratio and the rotary forging force are major factors affecting the density of the sintered powder compacts in the rotary forging process. The effect of the H / D ratio and the rotary forging force on the density were discovered. By determining both the density and the hardness of compacts, it was found that the density distributions show no difference from the hardness distributions and that the gradients of the density and the hardness in the axial direction are larger than those in the radial direction.展开更多
Observations of microstructure of explosive compacts made of Al or Al-Li alloy powders by atomization with water,nitrogen or ultrasoic Ar gas were carried out under optical and scanning electron microscopes.The rsults...Observations of microstructure of explosive compacts made of Al or Al-Li alloy powders by atomization with water,nitrogen or ultrasoic Ar gas were carried out under optical and scanning electron microscopes.The rsults indicate that super quality explosive compact can only be obtained by powders of which the thickness of the oxide layer is less than 30 nm.展开更多
Soil compaction often imposes stress on root development and plant survival.However,root anatomical responses that enable persistent root growth and functioning under soil compaction remain unclear.We grew 10 herbaceo...Soil compaction often imposes stress on root development and plant survival.However,root anatomical responses that enable persistent root growth and functioning under soil compaction remain unclear.We grew 10 herbaceous species differing substantially in lateral root diameter,in soils with low(1.0 g cm^(-3))and high(1.4 g cm^(-3))bulk density,and assessed root traits including root biomass,anatomical structures,and respiration rates.Greater root thickening upon soil compaction was found in species with thicker first-order lateral roots,mainly due to larger cortical cell size.Both xylem vessel diameter and wall thickness increased more in compacted soils in these species.Despite these anatomical shifts,root respiration rate responded little to soil compaction across most species,likely due to the opposite investment in cortical cells and xylem vessels.Notably,root biomass,independent of root respiration rate and anatomical structures,determined whole-plant growth under soil compaction.Our study reveals two independent strategies of root response to soil compaction:anatomical remodeling for mechanical and metabolic maintenance,and root biomass investment for resource acquisition.These findings offer new insights for breeding and selecting species tolerant to soil compaction and highlight multidimensional strategies of plant adaptation to physical stress.展开更多
Laser-assisted drilling combined with full-size polycrystalline diamond compact(PDC)bit is considered a feasible solution to enhance the drilling performance of engineering machinery.In this method,determining the opt...Laser-assisted drilling combined with full-size polycrystalline diamond compact(PDC)bit is considered a feasible solution to enhance the drilling performance of engineering machinery.In this method,determining the optimal collaborative control parameters that support rapid drilling is crucial for improving the combined performance.This study used average drilling speed,average torque,and total specificenergy for quantitative analysis to characterize the efficiencyand economy of combined rock breaking.Given the advantage of the response surface methodology in providing high-precision predictions with limited experimental data,regression models of the average drilling speed,average torque,and total specificenergy were established.The results showed that as the laser power and irradiation time increased,the average drilling speed firstincreased rapidly and then leveled off,while the average torque decreased sharply before decelerating.The total specificenergy initially decreased and then increased,with the combined drilling outperforming conventional mechanical drilling within specific parameter ranges.As the weight on bit increased,both the average torque and total specificenergy first decreased and then increased.With rising rotating speed,the average torque exhibited a trend of initial increase,then decrease,and finalincrease,whereas the total specificenergy increased slowly at firstand then sharply.Both parameters exhibited optimal values at which the average torque and total specific energy remained at minimal levels.For granite combined drilling,the optimal performance was achieved at a laser power of 3000 W,irradiation time of 31 s,the weight on bit of 2.4 kN,and the rotating speed of 97 r/min.展开更多
The models constructed by particle flow simulation method can effectively simulate the heterogeneous substance characteristics and failure behaviors of rocks.However,existing contact models overlook the rock cracks,an...The models constructed by particle flow simulation method can effectively simulate the heterogeneous substance characteristics and failure behaviors of rocks.However,existing contact models overlook the rock cracks,and the various simulation methods that do consider cracks still exhibit certain limitations.In this paper,based on Flat-Joint model and Linear Parallel Bond model,a crack contact model considering linked substance in the crack is proposed by splitting the crack contact into two portions:linked portion and unlinked portion for calculation.The new contact model considers the influence of crack closure on the contact force-displacement law.And a better compressive tensile strength ratio(UCS/T)was obtained by limiting the failure of the contact bond to be solely controlled by the contact force and moment of the linked portion.Then,by employing the FISH Model tool within the Particle Flow Code,the contact model was constructed and verified through contact force–displacement experiments and loading-unloading tests with cracked model.Finally,the contact model was tested through simulations of rock mechanics experiments.The results indicate that the contact model can effectively simulate the axial and lateral strain laws of rocks simultaneously and has a relatively good reproduction of the bi-modularity of rocks.展开更多
Real-time assessment of subgrade compaction quality poses a significant challenge in the implementation of intelligent compaction(IC).Current compaction evaluation models are confined to specific scenarios and lack ro...Real-time assessment of subgrade compaction quality poses a significant challenge in the implementation of intelligent compaction(IC).Current compaction evaluation models are confined to specific scenarios and lack robustness.This study proposes a subgrade compaction strategy that utilizes a heterogeneous dataset to estimate compaction quality across diverse scenarios while maintaining model accuracy.Field compaction tests are conducted in four distinct scenarios,considering various construction parameters.Compaction models are developed using several machine learning algorithms.The datasets are thoroughly assessed in terms of quality,diversity and similarity.The proposed model exhibits good performance in new scenarios by incorporating an additional 5%e8%of new data for retraining.The model's generalization capability is enhanced by conducting a limited number of field tests,which are labor-saving and time-efficient.The model's accuracy consistently improves across diverse scenarios and optimal algorithms.The proposed compaction strategy adopts a physics-and-data dual-driven approach,aimed at practical engineering applications and guiding the compaction procedure.展开更多
In this paper,the authors study the fractional Calderon type commutator T_(Ω,α)^(A)and its maximal operator M_(Ω,α)^(A)with kernels having some kinds of Log-type Dini-condition and obtain the compactness on Morrey...In this paper,the authors study the fractional Calderon type commutator T_(Ω,α)^(A)and its maximal operator M_(Ω,α)^(A)with kernels having some kinds of Log-type Dini-condition and obtain the compactness on Morrey spaces L^(p,λ)(R^(n)).展开更多
Purpose-The indoor vibration compaction test(IVCT)was a key step in controlling the compaction quality for high-speed railway graded aggregate(HRGA),which currently had a research gap on the assessment indicators and ...Purpose-The indoor vibration compaction test(IVCT)was a key step in controlling the compaction quality for high-speed railway graded aggregate(HRGA),which currently had a research gap on the assessment indicators and compaction parameters.Design/methodology/approach-To address these issues,a novel multi-indicator IVCT method was proposed,including physical indicator dry density(ρd)and mechanical indicators dynamic stiffness(Krb)and bearing capacity coefficient(K20).Then,a series of IVCTs on HRGA under different compaction parameters were conducted with an improved vibration compactor,which could monitor the physical-mechanical indicators in real-time.Finally,the optimal vibration compaction parameters,including the moisture content(ω),the diameter-to-maximum particle size ratio(Rd),the thickness-to-maximum particle size ratio(Rh),the vibration frequency(f),the vibration mass(Mc)and the eccentric distance(re),were determined based on the evolution characteristics for the physical-mechanical indicators during compaction.Findings-All results indicated that theρd gradually increased and then stabilized,and the Krb initially increased and then decreased.Moreover,the inflection time of the Krb was present as the optimal compaction time(Tlp)during compaction.Additionally,optimal compaction was achieved whenωwas the water-holding content after mud pumping,Rd was 3.4,Rh was 3.5,f was the resonance frequency,and the ratio between the excitation force and the Mc was 1.8.Originality/value-The findings of this paper were significant for the quality control of HRGA compaction.展开更多
基金Project(2009ZX04004-031-04) supported by the National Science and Technology Major Project of the Ministry of Science and Technology of China
文摘Compaction process simulation and residual stress prediction of green PM compact were carried out with elasto-plastic 3D FEA based on the modified Drueker-Prager Cap model in Abaqus. The model parameters of the investigated powder Distaloy AE were determined as functions of relative density through typical mechanical property tests of powder. The model was implemented as a user subroutine USDFLD. Single sided compaction of a d20 ram^5 mm disk green compact of Distaloy AE was simulated, and the residual stress of the disk after ejection was predicted with FEA. The FEA results of the compaction process and the residual stress of the disk show good agreement with compaction experiments and X-ray diffraction measurements, which validates the model and its parameters. The results indicate that the compressive residual stresses exist mainly in a thin layer on the side surface, but the residual stresses are very small on the top and bottom surfaces.
基金supported by the National Basic Research Program of China("973 Program",Nos.2012CB619102 and 2012CB619100)National Science Fund for Distinguished Young Scholars(Grant No.51225101)+1 种基金the Fundamental Research Funds for the Central Universities(Nos.HEUCFZ1017 and HEUCFR1020)the Natural Science Foundation of Heilongjiang Province,China(No.ZD201012)
文摘Porous sintered Ti-Ag compacts with different Ag content were fabricated by powder metallurgy. The associated hydrothermal treatment and the effect on the apatite formation were studied. The results suggested that TiO was generated under the condition of low vacuum （1 ×10^-2 Pa） during the process of burning out the spacer-holding particles. After hydrothermal treatment, a sub-microscale porous layer was formed at the pore wall surface of the samples. The apatite-inducing ability of hydrothermal treated porous sintered Ti-Ag compacts with different Ag content was evaluated in modified simulated body fluid （SBF）. And the results proved that there is a clear correlation between the apatite-inducing ability and Ag content. The higher Ag content in porous leads to the decrease of Na＋ ions and basic hydroxyl （OH）b amount, resulting in the decline of apatite-inducing ability in the first stage. However, their apatite-inducing ability was not significantly different from that of Ti after two weeks SBF immersing. Hence, the ionic activity should restore with the processing of SBF soaking, as the saturation of Ag effect.
基金supported by the Natural Science of Hunan(06JJ4062)
文摘Practical experiences gained in the past several years show that the thermal residual stress(TRS)is a main cause leading polycrystalline diamond compacts(PDC)to premature failure.It is the very important to measure the TRS accurately for optimizing the interface and improving the service performance of PDC.In this paper,the TRS in 1913 flat-interface PDC was measured using improved stress-release method(ISRM).The TRS on the surface of polycrystalline diamond(PCD)table was obtained,which can be used to calculate the radial thermal residual stress(RTRS)at the interface of PCD table via a refutation process.The obtained results show that there are compressive residual stress at the PCD table interface and in the most region of PCD table surface.The exception occurs near the outer diameter of the PCD table,where the PDC begins to bend and put the PCD table surface into a tension state,an undesirable state for a brittle material.The ISRM has covered the shortage existing in traditional stress-release method,in which only finite points on the surface of PCD table can be tested for one specimen and one time.Simple as the experimental procedures are,the test results are also very accurate and reliable.This method provides the theoretical and experimental basis for testing TRS of PDC accurately.
文摘Aluminium-alumina compacts with varying wt% of alumina were compacted in the pressure range of 115 - 290 MPa. Compacts prepared at 290 MPa pressure, were sintered in an argon atmosphere at 573, 673, 773 and 873 K for 1 hour. The green density, % porosity, % spring back and hardness of the green compacts were determined. Scanning Electron Microscopy was carried out to observe the morphology of pores and alumina particles in green and sintered compacts. The present study indicates that, densification of the compact increases with increasing compacting pressure and decreases with increasing alumina content. Maximum density achieved is 93% for pure aluminium compacts and decreases to 85% for Al-20 wt% alumina compacts. Grain growth of aluminium particles is noticed in the compacts after sintering at 773 and 873 K. Dispersion of fine alumina particle in the aluminium matrix occurs predominantly in the compact when sintered at 773 K which results in increase in hardness value.
基金This work was supported by the National Natural Science Foundation of Chira(project No.50044012)the Natural Science Foundation of Hunan Provience(project No.99JJYY20048).
文摘To successfully employ powder injection molding (PIM) as a manufacturing technique, the function of the component, design of the part, material and process should be optimized for overall processing ability of the PIM process. A comparison between the requirements of flowability and moldability and the compacts shape retention has been made in this work. There is often a contradiction between the requirements of flowability and the compacts shape retention. Many works have been done to attain good molding conditions. However, they fail to take into account the effect of some factors that satisfies good molding conditions on the compacts shape retention during debinding. This paper studies the effect of the powder-binder mixture characteristics and the molding conditions on the flowability and moldability and the shape retention of PIM compacts during debinding process so as to attain the benefits of each.
基金Project(20070533113)supported by the Doctoral Foundation of Ministry of Education of China
文摘Thermal residual stresses in polycrystalline diamond compact(PDC)cutter arising from the difference in thermal expansion between the polycrystalline diamond(PCD)and the supporting tungsten carbide substrate after sintering at high pressure and high temperature were investigated using finite element simulation,laboratory tests and theoretical analysis.The obtained results show that although compressive residual stresses exist both in the interface of PCD table and in the most region of PCD table surface, the tensile residual stress,which is a fatal shortage to PDC,can also occur near the outer diameter area of PCD table,and the maximum value is 690 MPa.Distribution of tensile stress in the PCD table is given through experimental results,which is well consistent with the numerical results.This finding may be significant in designing new PDC cutters with lower residual stress and high cutting behavior.
文摘In this work, a kind of new vitrified bond based on Li2O-Al2O3-SiO2 glass ceramics was used to bond the diamond grains, which is made into grinding wheel and the cylindrical grinding process of polycrystalline diamond compacts （PDCs） by using the new vitrified bond diamond grinding wheel was discussed. Several factors which influence the properties of grinding wheel such as amount of vitrified bond and the kinds and amount of stuff in grinding wheel were also investigated. It was found that the new vitrified bond can firmly combine diamond grains, when there are only diamonds and vitrified bond in the structure of grinding wheel, the longevity of the grinding wheel is about 2.5-3 times as that of resin bond grinding wheel for processing PDCs. The grinding size precision of PDCs can be improved from 4-0.03 mm to 4-0.01 mm because of larger Young＇s modulus of vitrified bond than resin bond. The grinding time of a PDC product can be 1.75-2.0 min from 3.25-3.5 min, so this kind of grinding wheel can save much time for processing PDCs. Also, there is hardly noise when using this new vitrified bond diamond grinding wheel to process PDCs. The amount of vitrified bond in grinding wheel influences the longevity of grinding wheel. When the size of diamond grains is 90-107 μm, the optimal amount of vitrified bond in grinding wheel is 21% （wt pct）. When the amount of vitrified bond exceeds 21%, there are many pores in grinding block, which will decrease the longevity of grinding wheel. The existence of addition stuff such as Al2O3 or SiC can reduce the longevity of grinding wheel.
文摘The effects of temperature （0-500°C） on the compressive strength,hardness,average relative density,and microstructure of Ti6Al4V powder green compacts prepared by magnetic pulse compaction were investigated.The results show that with increasing heating temperature,the compressive strength first increases and then decreases with the maximum value of 976.74 MPa at 400°C.The average relative density and hardness constantly increase,and their values reach 96.11% and HRA 69.8 at 500°C,respectively.The increase of partial welding is found among the junctions of particles inside the compacts; there is no obvious grain growth inside the compacts within the temperature range.
文摘Ti6Al4V powder compaction was performed by using magnetic pulse compaction in air at 200℃.Effects of process parameters such as voltage,capacitance,discharge times on the microstructure,compressive strength,hardness and relative density of compacts were investigated.The experimental results show that the relative density,hardness and compressive strength of compacted specimens increase with increasing voltage.In addition,the relative density and compressive strength of compacted specimens increase with the augmentation of capacitance in the range investigated.The relative density increases,the hardness firstly increases and then tends to be a fixed value;and the compressive strength firstly increases and then decreases from one to five times compaction.Both values of the hardness and compressive strength reach the maxima of HRA 69.1 and 1 062.31 MPa,at three times compaction,respectively.There are pores in and between particles.
文摘In order to obtain high property powder metallurgy products, at present rotary forging process has often been used to further densify the sintered powder compact, but the densification law and property analysis have very rarely been studied, therefore the densification laws of sintered powder compacts being composed of Fe 0.8%C 4.0%Cu 0.2% zinc stearate and formed as cylindrical shape by double action pressing, and then further densified as well in a rotary forging process was studied by orthogonal experiment and regression analysis. The experimental results show that the H / D ratio and the rotary forging force are major factors affecting the density of the sintered powder compacts in the rotary forging process. The effect of the H / D ratio and the rotary forging force on the density were discovered. By determining both the density and the hardness of compacts, it was found that the density distributions show no difference from the hardness distributions and that the gradients of the density and the hardness in the axial direction are larger than those in the radial direction.
文摘Observations of microstructure of explosive compacts made of Al or Al-Li alloy powders by atomization with water,nitrogen or ultrasoic Ar gas were carried out under optical and scanning electron microscopes.The rsults indicate that super quality explosive compact can only be obtained by powders of which the thickness of the oxide layer is less than 30 nm.
基金funded by the National Natural Science Foundation of China(32471824,32171746,31870522,42477227,and 32560282)the leading talents of basic research in Henan Province(24XM0375)+6 种基金Excellent Youth Creative Research Group Project in Henan Province(252300421002)Foreign Scientists Studio in Henan Province(GZS2025011)MOHRSS National Foreign Expert Individual Projectsand(110000264820258001)Natural Science Foundation of Henan(242300420604)supported by the Guangdong Provincial Key Laboratory of Soil and Groundwater Pollution Control(2023B1212060002)the High-level University Special Fund(G03050K001)the China Postdoctoral Science Foundation(No.2021M690922).
文摘Soil compaction often imposes stress on root development and plant survival.However,root anatomical responses that enable persistent root growth and functioning under soil compaction remain unclear.We grew 10 herbaceous species differing substantially in lateral root diameter,in soils with low(1.0 g cm^(-3))and high(1.4 g cm^(-3))bulk density,and assessed root traits including root biomass,anatomical structures,and respiration rates.Greater root thickening upon soil compaction was found in species with thicker first-order lateral roots,mainly due to larger cortical cell size.Both xylem vessel diameter and wall thickness increased more in compacted soils in these species.Despite these anatomical shifts,root respiration rate responded little to soil compaction across most species,likely due to the opposite investment in cortical cells and xylem vessels.Notably,root biomass,independent of root respiration rate and anatomical structures,determined whole-plant growth under soil compaction.Our study reveals two independent strategies of root response to soil compaction:anatomical remodeling for mechanical and metabolic maintenance,and root biomass investment for resource acquisition.These findings offer new insights for breeding and selecting species tolerant to soil compaction and highlight multidimensional strategies of plant adaptation to physical stress.
基金funded by the National Natural Science Foundation of China(Grand No.52325904)National Key Research and Development Program of China(Grant No.2023YFB2390200)the National Natural Science Foundation of China(Grant No.52309134).
文摘Laser-assisted drilling combined with full-size polycrystalline diamond compact(PDC)bit is considered a feasible solution to enhance the drilling performance of engineering machinery.In this method,determining the optimal collaborative control parameters that support rapid drilling is crucial for improving the combined performance.This study used average drilling speed,average torque,and total specificenergy for quantitative analysis to characterize the efficiencyand economy of combined rock breaking.Given the advantage of the response surface methodology in providing high-precision predictions with limited experimental data,regression models of the average drilling speed,average torque,and total specificenergy were established.The results showed that as the laser power and irradiation time increased,the average drilling speed firstincreased rapidly and then leveled off,while the average torque decreased sharply before decelerating.The total specificenergy initially decreased and then increased,with the combined drilling outperforming conventional mechanical drilling within specific parameter ranges.As the weight on bit increased,both the average torque and total specificenergy first decreased and then increased.With rising rotating speed,the average torque exhibited a trend of initial increase,then decrease,and finalincrease,whereas the total specificenergy increased slowly at firstand then sharply.Both parameters exhibited optimal values at which the average torque and total specific energy remained at minimal levels.For granite combined drilling,the optimal performance was achieved at a laser power of 3000 W,irradiation time of 31 s,the weight on bit of 2.4 kN,and the rotating speed of 97 r/min.
基金supported by the Natural Science Foundation of Heilongjiang Province(No.ZD2021E006)the National Natural Science Foundation of China(Nos.52174075 and 52074110).
文摘The models constructed by particle flow simulation method can effectively simulate the heterogeneous substance characteristics and failure behaviors of rocks.However,existing contact models overlook the rock cracks,and the various simulation methods that do consider cracks still exhibit certain limitations.In this paper,based on Flat-Joint model and Linear Parallel Bond model,a crack contact model considering linked substance in the crack is proposed by splitting the crack contact into two portions:linked portion and unlinked portion for calculation.The new contact model considers the influence of crack closure on the contact force-displacement law.And a better compressive tensile strength ratio(UCS/T)was obtained by limiting the failure of the contact bond to be solely controlled by the contact force and moment of the linked portion.Then,by employing the FISH Model tool within the Particle Flow Code,the contact model was constructed and verified through contact force–displacement experiments and loading-unloading tests with cracked model.Finally,the contact model was tested through simulations of rock mechanics experiments.The results indicate that the contact model can effectively simulate the axial and lateral strain laws of rocks simultaneously and has a relatively good reproduction of the bi-modularity of rocks.
基金supported by the National Natural Science Foundation of China(Grant Nos.52038005 and 52278342)the Natural Science Foundation of Tianjin Municipal(Grant No.23JCJQJC00160).
文摘Real-time assessment of subgrade compaction quality poses a significant challenge in the implementation of intelligent compaction(IC).Current compaction evaluation models are confined to specific scenarios and lack robustness.This study proposes a subgrade compaction strategy that utilizes a heterogeneous dataset to estimate compaction quality across diverse scenarios while maintaining model accuracy.Field compaction tests are conducted in four distinct scenarios,considering various construction parameters.Compaction models are developed using several machine learning algorithms.The datasets are thoroughly assessed in terms of quality,diversity and similarity.The proposed model exhibits good performance in new scenarios by incorporating an additional 5%e8%of new data for retraining.The model's generalization capability is enhanced by conducting a limited number of field tests,which are labor-saving and time-efficient.The model's accuracy consistently improves across diverse scenarios and optimal algorithms.The proposed compaction strategy adopts a physics-and-data dual-driven approach,aimed at practical engineering applications and guiding the compaction procedure.
文摘A survey of recent progress on the multiplicity and stability problems for closed characteristics on compact convex hypersurfaces in R^(2n) is given.
文摘In this paper,the authors study the fractional Calderon type commutator T_(Ω,α)^(A)and its maximal operator M_(Ω,α)^(A)with kernels having some kinds of Log-type Dini-condition and obtain the compactness on Morrey spaces L^(p,λ)(R^(n)).
基金funded by the National Key R&D Program“Transportation Infrastructure”project(No.2022YFB2603400)the Technology Research and Development Plan Program of China State Railway Group Co.,Ltd.(No.Q2024T001)the National project pre research project of Suzhou City University(No.2023SGY019).
文摘Purpose-The indoor vibration compaction test(IVCT)was a key step in controlling the compaction quality for high-speed railway graded aggregate(HRGA),which currently had a research gap on the assessment indicators and compaction parameters.Design/methodology/approach-To address these issues,a novel multi-indicator IVCT method was proposed,including physical indicator dry density(ρd)and mechanical indicators dynamic stiffness(Krb)and bearing capacity coefficient(K20).Then,a series of IVCTs on HRGA under different compaction parameters were conducted with an improved vibration compactor,which could monitor the physical-mechanical indicators in real-time.Finally,the optimal vibration compaction parameters,including the moisture content(ω),the diameter-to-maximum particle size ratio(Rd),the thickness-to-maximum particle size ratio(Rh),the vibration frequency(f),the vibration mass(Mc)and the eccentric distance(re),were determined based on the evolution characteristics for the physical-mechanical indicators during compaction.Findings-All results indicated that theρd gradually increased and then stabilized,and the Krb initially increased and then decreased.Moreover,the inflection time of the Krb was present as the optimal compaction time(Tlp)during compaction.Additionally,optimal compaction was achieved whenωwas the water-holding content after mud pumping,Rd was 3.4,Rh was 3.5,f was the resonance frequency,and the ratio between the excitation force and the Mc was 1.8.Originality/value-The findings of this paper were significant for the quality control of HRGA compaction.
