The temperature and density of plasma jets were estimated with a Boltzmann plot and Stark broadening of Ar I(696.54 nm) lines by optical emission spectroscopy(OES) in the process of plasma plastic, and the morphology ...The temperature and density of plasma jets were estimated with a Boltzmann plot and Stark broadening of Ar I(696.54 nm) lines by optical emission spectroscopy(OES) in the process of plasma plastic, and the morphology and microstructure of tungsten(W) powders were investigated by scanning electron microscope(SEM) and x-ray Diffraction(XRD), respectively.The results show that the assumption of local thermodynamic equilibrium(LTE) was invalid at the end of the plasma jets, and earlier than this after the injection of tungsten powder. The temperature and electron density of the plasma jets were up to about T?=?6797 K with Qc?=?50 slpm and ne?=?1.05?×?1016 cm-3 with Qs?=?115 slpm at Z?=?60 mm, respectively, and both dropped rapidly with the injected tungsten powders of 20 μm. After the plasma plastic process,the spherical tungsten powders were prepared and there were some satellite particles on the surface of the spherical products. The tungsten powders were both composed of a single equilibrium α-W phase with a body centered cubic(bbc) crystal structure before and after plasma treatment.展开更多
The powders of the AA 7075-ZRO2 were mixed by mechanical milling, but it was found that the system presents a few disadvantages when processed by conventional sintering and hot extrusion, since intermetallic phases be...The powders of the AA 7075-ZRO2 were mixed by mechanical milling, but it was found that the system presents a few disadvantages when processed by conventional sintering and hot extrusion, since intermetallic phases between ZrO2 particles and alloying elements were formed. Equal channel angular pressing （ECAP） processing was proposed as an alternative method to consolidate the composite where there is no intermetallic formation. The analysis of the ECAP process showed that the intermediate temperature （220℃） produced a higher consolidation level than conventional sintering and hot extrusion （400 and 500℃, respectively）. This fact was supported by relative density analysis. In the case of the sintered and hot-extruded sample, the relative density exhibited a value of 0.95, while ECAP sample showed a value of 0.98. Hardness values show that microstructural refinement obtained during mechanical milling was preserved during ECAP processing even when it was carded out at 220℃.展开更多
A simple gravity drop experiment was run to investigate plastic deformation of powder aggregrate sprayed on a hard ball under impact of another free falling hard ball and measure coefficient of restitution and plastic...A simple gravity drop experiment was run to investigate plastic deformation of powder aggregrate sprayed on a hard ball under impact of another free falling hard ball and measure coefficient of restitution and plastic strain of powder aggregate. Experimental results show that coefficient of restitution and plastic strain of powder aggregate increase as the velocity of ball increases and initial height (h 0) of powder aggregate has great effects on plastic deformation of powder aggregate. At a higher initial height (h 0), much of kinetic energy is dissipated is interparticle frictional work and coefficient of restitution is very small. Plastic strain of powder aggregate first increases as h 0 increases until a maximum value and then decreases as h 0 increases.展开更多
This article deals with the influence of the partial substitution of bitumen by a mixture of sulphur and tyre and plastic bottle powders on the characterization of asphalt concrete. The approach adopted was to subject...This article deals with the influence of the partial substitution of bitumen by a mixture of sulphur and tyre and plastic bottle powders on the characterization of asphalt concrete. The approach adopted was to subject a control asphalt concrete to level 2 formulation tests as well as those modified at 10%, 20%, 30% and 40% by substituting bitumen with a mixture of tyre powder, plastic bottle powder and sulphur at 40%, 28% and 32% respectively. The results of the PCG, Duriez and rutting tests carried out on the control and modified bituminous concretes (manufactured using the wet process) revealed three (03) major findings, in particular with regard to workability, resistance to simple compression and rutting. The experimental results show an increasing trend in the essential parameters. At 40% substitution, there was a 22.73% increase in compactness, reflecting a significant improvement in the material’s workability. With regard to simple compressive strength, the increase is 34.02% at 40% substitution, highlighting the limitation of crack formation and propagation under heavy precipitation. With regard to rutting, the 16% drop in susceptibility at 40% substitution reflects a significant improvement in the behaviour of the material under dynamic mechanical stresses in heavy precipitation. The improvement in these behaviours results from the insertion of the plastic bottle powder into the interstices of the granular skeleton, thus reducing its cellular structure, and also from the interactions between the sulphur with the tyre powder and the sulphur with the plastic bottle powder, i.e. cross-linking or vulcanisation.展开更多
Compaction processes are one the most important par ts of powder forming technology. The main applications are focused on pieces for a utomotive, aeronautic, electric and electronic industries. The main goals of the c...Compaction processes are one the most important par ts of powder forming technology. The main applications are focused on pieces for a utomotive, aeronautic, electric and electronic industries. The main goals of the compaction processes are to obtain a compact with the geometrical requirements, without cracks, and with a uniform distribution of density. Design of such proc esses consist, essentially, in determine the sequence and relative displacements of die and punches in order to achieve such goals. A.B. Khoei presented a gener al framework for the finite element simulation of powder forming processes based on the following aspects; a large displacement formulation, centred on a total and updated Lagrangian formulation; an adaptive finite element strategy based on error estimates and automatic remeshing techniques; a cap model based on a hard ening rule in modelling of the highly non-linear behaviour of material; and the use of an efficient contact algorithm in the context of an interface element fo rmulation. In these references, the non-linear behaviour of powder was adequately desc ribed by the cap plasticity model. However, it suffers from a serious deficiency when the stress-point reaches a yield surface. In the flow theory of plasticit y, the transition from an elastic state to an elasto-plastic state appears more or less abruptly. For powder material it is very difficult to define the locati on of yield surface, because there is no distinct transition from elastic to ela stic-plastic behaviour. Results of experimental test on some hard met al powder show that the plastic effects were begun immediately upon loading. In such mater ials the domain of the yield surface would collapse to a point, so making the di rection of plastic increment indeterminate, because all directions are normal to a point. Thus, the classical plasticity theory cannot deal with such materials and an advanced constitutive theory is necessary. In the present paper, the constitutive equations of powder materials will be discussed via an endochronic theory of plasticity. This theory provides a unifi ed point of view to describe the elastic-plastic behaviour of material since it places no requirement for a yield surface and a ’loading function’ to disting uish between loading an unloading. Endochronic theory of plasticity has been app lied to a number of metallic materials, concrete and sand, but to the knowledge of authors, no numerical scheme of the model has been applied to powder material . In the present paper, a new approach is developed based on an endochronic rate independent, density-dependent plasticity model for describing the isothermal deformation behavior of metal powder at low homologous temperature. Although the concept of yield surface has not been explicitly assumed in endochronic theory, it is shown that the cone-cap plasticity yield surface (Fig.1), which is the m ost commonly used plasticity models for describing the behavior of powder materi al can be easily derived as a special case of the proposed endochronic theory. Fig.1 Trace of cone-cap yield function on the meridian pl ane for different relative density As large deformation is observed in powder compaction process, a hypoelastic-pl astic formulation is developed in the context of finite deformation plasticity. Constitutive equations are stated in unrotated frame of reference that greatly s implifies endochronic constitutive relation in finite plasticity. Constitutive e quations of the endochronic theory and their numerical integration are establish ed and procedures for determining material parameters of the model are demonstra ted. Finally, the numerical schemes are examined for efficiency in the model ling of a tip shaped component, as shown in Fig.2. Fig.2 A shaped tip component. a) Geometry, boundary conditio n and finite element mesh; b) density distribution at final stage of展开更多
To study the plastic properties of reactive powder concrete continuous beams reinforced with GFRP bars,the calculation programs for moment redistribution coefficients are prepared by using nonlinear analysis methods s...To study the plastic properties of reactive powder concrete continuous beams reinforced with GFRP bars,the calculation programs for moment redistribution coefficients are prepared by using nonlinear analysis methods such as moment-curvature,conjugate beam method and so on. By comparing the test results of existed FRP bars reinforced concrete continuous beams with simulation results,the accuracy of the calculation program is verified. Then 18 simulated GFRP bars reinforced reactive powder concrete continuous beams are selected whose change parameters are reinforcement ratio of mid-span and middle support. Through the nonlinear analysis of simulated beams,moment redistribution coefficients under mid-span concentrated loads,one-third point loads and uniformly distributed loads are obtained respectively. Thus the formula of moment redistribution coefficients is obtained by fitting moment redistribution coefficients and factors. The results show that the reactive powder concrete continuous beams reinforced with GFRP bars have good plastic properties.展开更多
Based on the characteristic of high energy milling and the micromechanics of composite material, a plastic constitutive equation is implemented for milled composite powders. To check the equation, the extrusion of Ti/...Based on the characteristic of high energy milling and the micromechanics of composite material, a plastic constitutive equation is implemented for milled composite powders. To check the equation, the extrusion of Ti/Al composite powders prepared by high energy milling was simulated. It was from the numerical analysis that the predicted extrusion pressure mounted up with milling time and extrusion ratio increasing, which was perfect agreement with experimental results.展开更多
The gas in plastics mould has great influence on performance, appearance and lifespan of the injection molded parts. Venting channel and its appendix system should be used for gas exhausting in general. However, the d...The gas in plastics mould has great influence on performance, appearance and lifespan of the injection molded parts. Venting channel and its appendix system should be used for gas exhausting in general. However, the dependence on the venting system complicates the mould design. Furthermore in certain condition, it is difficult to integrate the venting system into the mould. Currently a kind of mold material which has gas permeability has been developed in abroad, but the applications of this mold material were restricted by its higher cost and smaller size. In this research, a porous material which was made by powder metallurgy was applied to plastic mould to replace the venting system. Permeability of the steel with different secondary processing was tested and compared with a special apparatus. The metallographic samples of the steel with different secondary processing were prepared and investigated. Finally an actual injection set was established to investigate the applications of permeable steel. The metallographies indicate that the micro-holes inside permeable steel were interconnected. Moulds made of permeable steel exhibit good permeability in the plastic-injection experiments and gas generated in the mould cavity was smoothly exhausted. The melted plastic did not penetrate into the mould or block in the micro-holes. After several times of plastic-injection experiments, the mould still retained good permeability. The strength of this permeable steel is between 200–250 MPa and suitable for industrial applications. The venting systems simplified by permeable steel in plastic-injection have simple structures, which can be applied into any place that requires gas exhausting.展开更多
In order to study mechanical behaviors of corn stalk powder during the compaction, the yield criterion for corn stalk powder is proposed with a plasticity theory. From the stress-strain curves of uni-axial compaction ...In order to study mechanical behaviors of corn stalk powder during the compaction, the yield criterion for corn stalk powder is proposed with a plasticity theory. From the stress-strain curves of uni-axial compaction test for corn stalk powder, the constitutive model, in which the equations are modified by experiments on corn stalk powder, is adopted to describe plastic behaviors of powder, and is discussed based on the incremental theory and deformation theory. The numerical results agree well with the experimental ones.展开更多
基金supported by National Natural Science Foundation of China (Nos. 11805058, 11535003)Sichuan Science and Technology Program (No. 19ZDYF0012)
文摘The temperature and density of plasma jets were estimated with a Boltzmann plot and Stark broadening of Ar I(696.54 nm) lines by optical emission spectroscopy(OES) in the process of plasma plastic, and the morphology and microstructure of tungsten(W) powders were investigated by scanning electron microscope(SEM) and x-ray Diffraction(XRD), respectively.The results show that the assumption of local thermodynamic equilibrium(LTE) was invalid at the end of the plasma jets, and earlier than this after the injection of tungsten powder. The temperature and electron density of the plasma jets were up to about T?=?6797 K with Qc?=?50 slpm and ne?=?1.05?×?1016 cm-3 with Qs?=?115 slpm at Z?=?60 mm, respectively, and both dropped rapidly with the injected tungsten powders of 20 μm. After the plasma plastic process,the spherical tungsten powders were prepared and there were some satellite particles on the surface of the spherical products. The tungsten powders were both composed of a single equilibrium α-W phase with a body centered cubic(bbc) crystal structure before and after plasma treatment.
基金supported by Universidad Autónoma de San Luis Potosi, Centro de Investigación en Materiales Avanzados Unidad Chihuahua and Universitat Politècnica de CatalunyaFinancial support by CONACYT is appreciatedfinancial support from FAI-UASLP under the project CI5-FAI-04-45.45
文摘The powders of the AA 7075-ZRO2 were mixed by mechanical milling, but it was found that the system presents a few disadvantages when processed by conventional sintering and hot extrusion, since intermetallic phases between ZrO2 particles and alloying elements were formed. Equal channel angular pressing （ECAP） processing was proposed as an alternative method to consolidate the composite where there is no intermetallic formation. The analysis of the ECAP process showed that the intermediate temperature （220℃） produced a higher consolidation level than conventional sintering and hot extrusion （400 and 500℃, respectively）. This fact was supported by relative density analysis. In the case of the sintered and hot-extruded sample, the relative density exhibited a value of 0.95, while ECAP sample showed a value of 0.98. Hardness values show that microstructural refinement obtained during mechanical milling was preserved during ECAP processing even when it was carded out at 220℃.
文摘A simple gravity drop experiment was run to investigate plastic deformation of powder aggregrate sprayed on a hard ball under impact of another free falling hard ball and measure coefficient of restitution and plastic strain of powder aggregate. Experimental results show that coefficient of restitution and plastic strain of powder aggregate increase as the velocity of ball increases and initial height (h 0) of powder aggregate has great effects on plastic deformation of powder aggregate. At a higher initial height (h 0), much of kinetic energy is dissipated is interparticle frictional work and coefficient of restitution is very small. Plastic strain of powder aggregate first increases as h 0 increases until a maximum value and then decreases as h 0 increases.
文摘This article deals with the influence of the partial substitution of bitumen by a mixture of sulphur and tyre and plastic bottle powders on the characterization of asphalt concrete. The approach adopted was to subject a control asphalt concrete to level 2 formulation tests as well as those modified at 10%, 20%, 30% and 40% by substituting bitumen with a mixture of tyre powder, plastic bottle powder and sulphur at 40%, 28% and 32% respectively. The results of the PCG, Duriez and rutting tests carried out on the control and modified bituminous concretes (manufactured using the wet process) revealed three (03) major findings, in particular with regard to workability, resistance to simple compression and rutting. The experimental results show an increasing trend in the essential parameters. At 40% substitution, there was a 22.73% increase in compactness, reflecting a significant improvement in the material’s workability. With regard to simple compressive strength, the increase is 34.02% at 40% substitution, highlighting the limitation of crack formation and propagation under heavy precipitation. With regard to rutting, the 16% drop in susceptibility at 40% substitution reflects a significant improvement in the behaviour of the material under dynamic mechanical stresses in heavy precipitation. The improvement in these behaviours results from the insertion of the plastic bottle powder into the interstices of the granular skeleton, thus reducing its cellular structure, and also from the interactions between the sulphur with the tyre powder and the sulphur with the plastic bottle powder, i.e. cross-linking or vulcanisation.
文摘Compaction processes are one the most important par ts of powder forming technology. The main applications are focused on pieces for a utomotive, aeronautic, electric and electronic industries. The main goals of the compaction processes are to obtain a compact with the geometrical requirements, without cracks, and with a uniform distribution of density. Design of such proc esses consist, essentially, in determine the sequence and relative displacements of die and punches in order to achieve such goals. A.B. Khoei presented a gener al framework for the finite element simulation of powder forming processes based on the following aspects; a large displacement formulation, centred on a total and updated Lagrangian formulation; an adaptive finite element strategy based on error estimates and automatic remeshing techniques; a cap model based on a hard ening rule in modelling of the highly non-linear behaviour of material; and the use of an efficient contact algorithm in the context of an interface element fo rmulation. In these references, the non-linear behaviour of powder was adequately desc ribed by the cap plasticity model. However, it suffers from a serious deficiency when the stress-point reaches a yield surface. In the flow theory of plasticit y, the transition from an elastic state to an elasto-plastic state appears more or less abruptly. For powder material it is very difficult to define the locati on of yield surface, because there is no distinct transition from elastic to ela stic-plastic behaviour. Results of experimental test on some hard met al powder show that the plastic effects were begun immediately upon loading. In such mater ials the domain of the yield surface would collapse to a point, so making the di rection of plastic increment indeterminate, because all directions are normal to a point. Thus, the classical plasticity theory cannot deal with such materials and an advanced constitutive theory is necessary. In the present paper, the constitutive equations of powder materials will be discussed via an endochronic theory of plasticity. This theory provides a unifi ed point of view to describe the elastic-plastic behaviour of material since it places no requirement for a yield surface and a ’loading function’ to disting uish between loading an unloading. Endochronic theory of plasticity has been app lied to a number of metallic materials, concrete and sand, but to the knowledge of authors, no numerical scheme of the model has been applied to powder material . In the present paper, a new approach is developed based on an endochronic rate independent, density-dependent plasticity model for describing the isothermal deformation behavior of metal powder at low homologous temperature. Although the concept of yield surface has not been explicitly assumed in endochronic theory, it is shown that the cone-cap plasticity yield surface (Fig.1), which is the m ost commonly used plasticity models for describing the behavior of powder materi al can be easily derived as a special case of the proposed endochronic theory. Fig.1 Trace of cone-cap yield function on the meridian pl ane for different relative density As large deformation is observed in powder compaction process, a hypoelastic-pl astic formulation is developed in the context of finite deformation plasticity. Constitutive equations are stated in unrotated frame of reference that greatly s implifies endochronic constitutive relation in finite plasticity. Constitutive e quations of the endochronic theory and their numerical integration are establish ed and procedures for determining material parameters of the model are demonstra ted. Finally, the numerical schemes are examined for efficiency in the model ling of a tip shaped component, as shown in Fig.2. Fig.2 A shaped tip component. a) Geometry, boundary conditio n and finite element mesh; b) density distribution at final stage of
基金Sponsored by Changjiang Scholars Program of China (Grant No 2009-37)New Century Talent Support Program Project of Ministry of Education (Secretary for Education account2005290)
文摘To study the plastic properties of reactive powder concrete continuous beams reinforced with GFRP bars,the calculation programs for moment redistribution coefficients are prepared by using nonlinear analysis methods such as moment-curvature,conjugate beam method and so on. By comparing the test results of existed FRP bars reinforced concrete continuous beams with simulation results,the accuracy of the calculation program is verified. Then 18 simulated GFRP bars reinforced reactive powder concrete continuous beams are selected whose change parameters are reinforcement ratio of mid-span and middle support. Through the nonlinear analysis of simulated beams,moment redistribution coefficients under mid-span concentrated loads,one-third point loads and uniformly distributed loads are obtained respectively. Thus the formula of moment redistribution coefficients is obtained by fitting moment redistribution coefficients and factors. The results show that the reactive powder concrete continuous beams reinforced with GFRP bars have good plastic properties.
文摘Based on the characteristic of high energy milling and the micromechanics of composite material, a plastic constitutive equation is implemented for milled composite powders. To check the equation, the extrusion of Ti/Al composite powders prepared by high energy milling was simulated. It was from the numerical analysis that the predicted extrusion pressure mounted up with milling time and extrusion ratio increasing, which was perfect agreement with experimental results.
基金supported by Guangdong-Hong Kong Key Project of China (Grant No. 2007Z010)National Basic Research Program of China (973 Program, Grant No. 2007CB616905)
文摘The gas in plastics mould has great influence on performance, appearance and lifespan of the injection molded parts. Venting channel and its appendix system should be used for gas exhausting in general. However, the dependence on the venting system complicates the mould design. Furthermore in certain condition, it is difficult to integrate the venting system into the mould. Currently a kind of mold material which has gas permeability has been developed in abroad, but the applications of this mold material were restricted by its higher cost and smaller size. In this research, a porous material which was made by powder metallurgy was applied to plastic mould to replace the venting system. Permeability of the steel with different secondary processing was tested and compared with a special apparatus. The metallographic samples of the steel with different secondary processing were prepared and investigated. Finally an actual injection set was established to investigate the applications of permeable steel. The metallographies indicate that the micro-holes inside permeable steel were interconnected. Moulds made of permeable steel exhibit good permeability in the plastic-injection experiments and gas generated in the mould cavity was smoothly exhausted. The melted plastic did not penetrate into the mould or block in the micro-holes. After several times of plastic-injection experiments, the mould still retained good permeability. The strength of this permeable steel is between 200–250 MPa and suitable for industrial applications. The venting systems simplified by permeable steel in plastic-injection have simple structures, which can be applied into any place that requires gas exhausting.
基金Supported by the Fork Ying Tong Education Foundation (Grant No. 81029)
文摘In order to study mechanical behaviors of corn stalk powder during the compaction, the yield criterion for corn stalk powder is proposed with a plasticity theory. From the stress-strain curves of uni-axial compaction test for corn stalk powder, the constitutive model, in which the equations are modified by experiments on corn stalk powder, is adopted to describe plastic behaviors of powder, and is discussed based on the incremental theory and deformation theory. The numerical results agree well with the experimental ones.
