A math formula about the relation between fluid pressure after overflowing and punch stroke that can be applied in general FEM software was proposed. It is proved that theoretical results keep coincident to experiment...A math formula about the relation between fluid pressure after overflowing and punch stroke that can be applied in general FEM software was proposed. It is proved that theoretical results keep coincident to experimental results and the method to simulate hydrodynamic deep drawing process that integrates general FEM software with mathematical description is feasible. [展开更多
Micro-arc oxidation (MAO) method was used for the surface modification of an Mg-5wt.%Li alloy. Ceramic coatings were in-situ fabricated on the Mg-Li alloy. The morphology feature,phase composition,and corrosion-resist...Micro-arc oxidation (MAO) method was used for the surface modification of an Mg-5wt.%Li alloy. Ceramic coatings were in-situ fabricated on the Mg-Li alloy. The morphology feature,phase composition,and corrosion-resistance of the formed ceramic coatings were studied by SEM,XRD,and electrochemical methods,respectively. The results showed that the coatings produced in a sodium silicate solution system were composed of MgO and Mg2SiO4. The ceramic coating became thicker and the content of Mg2SiO4 phase increase...展开更多
The contact reaction method was employed to prepare TiC p/2024Al composites and the semi solid extrusion was employed to manufacture composite rods. Through many experiments, suitable processing parameters were obtain...The contact reaction method was employed to prepare TiC p/2024Al composites and the semi solid extrusion was employed to manufacture composite rods. Through many experiments, suitable processing parameters were obtained, under which sound rods can be fabricated. It is found from the extrusion pressure—stroke curves of semi solid extrusion that the deformation force during semi solid extrusion is low and steady. The reason for lower extrusion pressure of semi solid extrusion was given. Some fabrication defects, such as break out and excessive extrusion force, owing to the inappropriate selection of processing parameters were also observed. The microstructures of TiCp/2024Al composites are characterized by well densified matrix, uniformly distributed TiC particles, some banded particle clusters and realignment of TiC particles along the extrusion direction, and no fracture of TiC particles. The mechanical properties of TiC p/2024Al composites are much higher than those of unreinforced alloy. In the meantime, the elongations of the composites are maintained at the level enough for practical applications.展开更多
Multiwalled carbon nanotubes (MWNTs) were treated with the reflux within the concentrated nitric acid for 0-25 h to purify and disperse the tangled MWNTs. The effect of reflux time on the morphology and the weight los...Multiwalled carbon nanotubes (MWNTs) were treated with the reflux within the concentrated nitric acid for 0-25 h to purify and disperse the tangled MWNTs. The effect of reflux time on the morphology and the weight loss of MWNTs were investigated. Meanwhile,the dispersion of MWNTs with 0-2.0 wt.% in 2024Al powders using mechanical stirring with an assisting ultrasonic shaker in ethanol was also studied. The results show that the reflux time markedly affects the morphology of MWNTs. The weight loss of MWNTs i...展开更多
In this paper, the scattering of harmonic antiplane shear waves bytwo finite cracks is studied using the non-local theory. The Fouriertransform is applied and a mixed boundary value prob- lem isformulated. Then a set ...In this paper, the scattering of harmonic antiplane shear waves bytwo finite cracks is studied using the non-local theory. The Fouriertransform is applied and a mixed boundary value prob- lem isformulated. Then a set of triple integral equations is solved using anew method, namely Schimidt's method. This method is more exact andmore reasonable than Erigen's for solving this Kind of problem. Theresult of the stress near the crack tip was obtained. Contrary to theclassical elas- Ticity solution, it is found that no stresssingularity is present at the crack tip, which can explain theProblem of macroscopic and microscopic mechanics.展开更多
Sn-36%Ni peritectie alloys were directionally solidified at different growth rates under a constant temperature gradient （20 K/mm）, the dependences of microstructural characteristic length scales on the growth rate ...Sn-36%Ni peritectie alloys were directionally solidified at different growth rates under a constant temperature gradient （20 K/mm）, the dependences of microstructural characteristic length scales on the growth rate were investigated. Experimental results are presented, including primary and higher order dendrite arm spacings 21, 22, 23 and dendrite tip radius R of primary NisSn2 phase. Comparisons between the theoretical predictions and the experimental results show that, for the primary dendrites, 21=335.882v-0.21, which is in agreement with the Kurz-Fisher model; for the secondary dendrites, λ2=44.957v-0.277, which is consistent with the Bouchard-Kirkaldy model; for the tertiary dendrites, λ3=40.512v-0.274; for the dendrite tip radius, R=22.7v-0.36. The experimental results also show that the 21/22 changes greatly with increasing growth rate while the 21/23 has no significant change, indicating that tertiary dendrite arms have a more similar growth characteristics to primary dendrites compared with secondary dendrites. The λ1/R ranges from 2 to 2.3 with the increase of growth rate. Key words： Sn-Ni alloy; directional solidification; dendrite arm spacing; dendrite tip radius展开更多
A comprehensive treatment of fracture of functionally gradedmaterials (FGMs) is provided. It is assumed that the materialproperties depend only on the coordinate perpendicular to the cracksurface And vary continuously...A comprehensive treatment of fracture of functionally gradedmaterials (FGMs) is provided. It is assumed that the materialproperties depend only on the coordinate perpendicular to the cracksurface And vary continuously along the crack faces. By using alaminated composite plate model to simulate the ma- Terialnon-homogeneity, an algorithm for solving the system based on Laplacetransform and Fourier transform Techniques is presented. Unlikeearlier studies that considered certain assumed propertydistributions and a Single crack problem, the current investigationstudies multiple crack problem in the FGMs with arbitrarily Varyingmaterial properties. Transient thermal stresses are presented.展开更多
Based on the theory of elastic dynamics, the scattering of elasticwaves and dynamic stress concentration of fiber-reinforced compositewith interfaces are studied. Analytical expressions of elastic wavesin different me...Based on the theory of elastic dynamics, the scattering of elasticwaves and dynamic stress concentration of fiber-reinforced compositewith interfaces are studied. Analytical expressions of elastic wavesin different medium areas are presented and an analytic method ofsolving this problem is established. The mode coefficients aredetermined by means of the continuous conditions of displacement andstress on the boundary of the interfaces. The influence of materialproperties and structural size on the dynamic stress con- centrationfactors near the interfaces is analyzed.展开更多
By using the complex variable method and conformal mapping, the diffraction of flexural waves and dynamic stress concentrations in thick plates with a cavity have been studied. A general solution of the stress problem...By using the complex variable method and conformal mapping, the diffraction of flexural waves and dynamic stress concentrations in thick plates with a cavity have been studied. A general solution of the stress problem of the thick plate satisfying the boundary conditions on the contour of an arbitrary cavity is obtained. By employing the orthogonal function expansion technique, the dynamic stress problem can be reduced to the solution of an infinite algebraic equation series. As an example, the numerical results for the dynamic stress concentration factor in thick plates with a circular, elliptic cavity are graphically presented. The numerical results are discussed.展开更多
This paper mainly discusses the constitutive laws of incompressible rubber-like materials and the associated finite element analysis method. By a multiplicative decomposition of the deformation gradient into distortio...This paper mainly discusses the constitutive laws of incompressible rubber-like materials and the associated finite element analysis method. By a multiplicative decomposition of the deformation gradient into distortional and dilatational parts, the YEOH mode type constitutive laws of rubber-like materials and their numerical implementation are presented. In order to deal with incompressible problems, a three-field variational principle is developed in which deformation, Jacobian and pressure field are treated independently. The connection between the three-field principle and the Hu-Wasizhu generalized variational principle is established. It is shown that the approach proposed can be degenerated to the B-bar method in the linear case. The derailed FE formulation is given in which deformation is ap proximated by isoparametric conforming element, and Jacobian and pressure by discontinuous approximation. Finally, two numerical examples are presented to show the effectiveness and reliability of the method proposed. The work in this paper provides a corner stone of FEA of this kind of problem. This paper features the combination of the multiplicative decomposition, the three-field principle and YEOH model of rubber-like materials, especially under Lagrangian description, giving an effective way for solving this kind of problems. The Lagrangian description is compatible with usually geometrically nonlinear FEM and the constitutive laws are expressed by the second Kirchhoff stress and the Green strain.展开更多
This paper provides a method for studying the penny-shaped cracksconfiguration in functionally graded material(FGM)structuressubjected to dynamic or steady loading. It is assumed that the FGMare transversely isotropic...This paper provides a method for studying the penny-shaped cracksconfiguration in functionally graded material(FGM)structuressubjected to dynamic or steady loading. It is assumed that the FGMare transversely isotropic and all the material properties onlydepend on the axial coordi- nate z. In the analysis, the elasticregion is treated as a number of layers. The material properties aretaken to be constants for each layer. By utilizing the Laplacetransform and Hankel transform tech- nique, the general solution forthe layers are derived.展开更多
In this paper, the interaction between two collinear cracks inpiezoelectric materials under anti-plane shear loading wasinvestigated for the impermeable crack face conditions. By using theFourier transform, the proble...In this paper, the interaction between two collinear cracks inpiezoelectric materials under anti-plane shear loading wasinvestigated for the impermeable crack face conditions. By using theFourier transform, the problem can be solved with two pairs of tripleintegral equations. These equations are solved using Schmidt'smethod. This process is quite different from that adopted previously.This makes it possible to understand the two collinear cracksinteraction in piezoelectric materials.展开更多
Hypo- and hyper-eutectic At-Si alloys were rapidly solidified from the tow or high temperature melt using water quenching and melt-spinning technique. The differences in microstructure of rapid solidification alloys w...Hypo- and hyper-eutectic At-Si alloys were rapidly solidified from the tow or high temperature melt using water quenching and melt-spinning technique. The differences in microstructure of rapid solidification alloys were studied by scanning and transmission electron microscopy, and X-ray diffraction methods. The primary silicon in the Al-22(wt pct)Si alloy quenched in room temperature water from high temperature melt was smaller than that quenched from low temperature melt. Compared with the ribbons spun from low temperature melt, the ribbons spun from high temperature melt had finer Al-rich and Si-rich phase particles in either Al-7(wt pct)Si or Al-18(wt pct)Si alloy. The mechanism was explained by the nature of the liquid structure.展开更多
The thermodynamics and kinetics of the internal oxidation in dilute Cu-Al alloy are investigated. The internal oxidation of copper alloy containing 0.2 similar to 1.2 wt pet Al is studied in the temperature range from...The thermodynamics and kinetics of the internal oxidation in dilute Cu-Al alloy are investigated. The internal oxidation of copper alloy containing 0.2 similar to 1.2 wt pet Al is studied in the temperature range from 1073 K to 1273 K. A related equilibrium diagram is drawn. A mathematic model of oxidation layer depth is developed on the base of the experimental results. The experiments and investigation show that the formation rate of the internal oxidation layer is mainly controlled by the diffusion of O in matrix, the O concentration on the surface and the Al concentration in the alloy.展开更多
Influence of Ti on MC carbide of M2 high speed steel was investigated by experimental observation, thermodynamic calculation and crystallographic calculation. With addition of Ti into M2 steel, large quantities of dis...Influence of Ti on MC carbide of M2 high speed steel was investigated by experimental observation, thermodynamic calculation and crystallographic calculation. With addition of Ti into M2 steel, large quantities of dispersed TiC particles formed in the steel melt at higher temperature than that of the formation of MC carbide. TiC can act as heterogeneous nuclei for the crystallization of MC carbide particles, and therefore promote the formation of blocky MC carbide.展开更多
Open-cell porous Al alloy was fabricated by pressure penetration method and the fabrication of preform was studied in detail. When forming temperature is about 700 degree C and binder content is about 10%, preform wi...Open-cell porous Al alloy was fabricated by pressure penetration method and the fabrication of preform was studied in detail. When forming temperature is about 700 degree C and binder content is about 10%, preform with high compressive strength was obtained. Good porous Al alloy with pore size 0.5-1.6 mm and porosity 60%-80% can be obtained under 100 degree C super-heating of liquid metal and about 1.0 MPa applied pressure. The size of the largest sample is up to 100 mm in diameter and 100 mm in height. With the help of SEM it was found that the obtained material is a three-dimensional open-cell porous structure with well-distributed and connected with each other pores. Finally, theoretical analysis was carried out to explain the effect of fabricating process. (Edited author abstract) 4 Refs.展开更多
In this paper, the phase characteristic disturbance model for baseband direct sequence spread spectrum (DSSS) signal in additive white Gaussian noise (AWGN) environment is established, and the probability density func...In this paper, the phase characteristic disturbance model for baseband direct sequence spread spectrum (DSSS) signal in additive white Gaussian noise (AWGN) environment is established, and the probability density function (PDF) of phase characteristic disturbance is obtained. Then a novel receiver model for baseband DSSS signal based on maximum likelihood (ML) criterion is proposed. The simulation results show that, comparing with correlation scheme, the performance of the proposed method for baseband DSSS signal is 1dB worse in AWGN environment. However, if there is narrow interference in the AWGN environment, the proposed method will show better performance up to 2.5dB, and it has good adaptive resistance to narrowband interference located in different frequency points. This method could be used as an alterative communication scheme for military circumstance when existing strong narrowband interference of various frequencies.展开更多
文摘A math formula about the relation between fluid pressure after overflowing and punch stroke that can be applied in general FEM software was proposed. It is proved that theoretical results keep coincident to experimental results and the method to simulate hydrodynamic deep drawing process that integrates general FEM software with mathematical description is feasible. [
文摘Micro-arc oxidation (MAO) method was used for the surface modification of an Mg-5wt.%Li alloy. Ceramic coatings were in-situ fabricated on the Mg-Li alloy. The morphology feature,phase composition,and corrosion-resistance of the formed ceramic coatings were studied by SEM,XRD,and electrochemical methods,respectively. The results showed that the coatings produced in a sodium silicate solution system were composed of MgO and Mg2SiO4. The ceramic coating became thicker and the content of Mg2SiO4 phase increase...
文摘The contact reaction method was employed to prepare TiC p/2024Al composites and the semi solid extrusion was employed to manufacture composite rods. Through many experiments, suitable processing parameters were obtained, under which sound rods can be fabricated. It is found from the extrusion pressure—stroke curves of semi solid extrusion that the deformation force during semi solid extrusion is low and steady. The reason for lower extrusion pressure of semi solid extrusion was given. Some fabrication defects, such as break out and excessive extrusion force, owing to the inappropriate selection of processing parameters were also observed. The microstructures of TiCp/2024Al composites are characterized by well densified matrix, uniformly distributed TiC particles, some banded particle clusters and realignment of TiC particles along the extrusion direction, and no fracture of TiC particles. The mechanical properties of TiC p/2024Al composites are much higher than those of unreinforced alloy. In the meantime, the elongations of the composites are maintained at the level enough for practical applications.
文摘Multiwalled carbon nanotubes (MWNTs) were treated with the reflux within the concentrated nitric acid for 0-25 h to purify and disperse the tangled MWNTs. The effect of reflux time on the morphology and the weight loss of MWNTs were investigated. Meanwhile,the dispersion of MWNTs with 0-2.0 wt.% in 2024Al powders using mechanical stirring with an assisting ultrasonic shaker in ethanol was also studied. The results show that the reflux time markedly affects the morphology of MWNTs. The weight loss of MWNTs i...
文摘In this paper, the scattering of harmonic antiplane shear waves bytwo finite cracks is studied using the non-local theory. The Fouriertransform is applied and a mixed boundary value prob- lem isformulated. Then a set of triple integral equations is solved using anew method, namely Schimidt's method. This method is more exact andmore reasonable than Erigen's for solving this Kind of problem. Theresult of the stress near the crack tip was obtained. Contrary to theclassical elas- Ticity solution, it is found that no stresssingularity is present at the crack tip, which can explain theProblem of macroscopic and microscopic mechanics.
基金Projects （51071062, 51271068, 51274077） supported by the National Natural Science Foundation of China Project （2011 -P03） supported by Open Fund of State Key Laboratory of Mold and Die Technology of Huazhong University of Science and Technology, China+1 种基金 Project （HIT. NSRIF. 2013002） supported by the Fundamental Research Funds for the Central Universities, China Project （2011CB610406） supported by the National Basic Research Program of China
文摘Sn-36%Ni peritectie alloys were directionally solidified at different growth rates under a constant temperature gradient （20 K/mm）, the dependences of microstructural characteristic length scales on the growth rate were investigated. Experimental results are presented, including primary and higher order dendrite arm spacings 21, 22, 23 and dendrite tip radius R of primary NisSn2 phase. Comparisons between the theoretical predictions and the experimental results show that, for the primary dendrites, 21=335.882v-0.21, which is in agreement with the Kurz-Fisher model; for the secondary dendrites, λ2=44.957v-0.277, which is consistent with the Bouchard-Kirkaldy model; for the tertiary dendrites, λ3=40.512v-0.274; for the dendrite tip radius, R=22.7v-0.36. The experimental results also show that the 21/22 changes greatly with increasing growth rate while the 21/23 has no significant change, indicating that tertiary dendrite arms have a more similar growth characteristics to primary dendrites compared with secondary dendrites. The λ1/R ranges from 2 to 2.3 with the increase of growth rate. Key words： Sn-Ni alloy; directional solidification; dendrite arm spacing; dendrite tip radius
基金the National Natural Science Foundation of China (Nos.10102004 and 19902003).
文摘A comprehensive treatment of fracture of functionally gradedmaterials (FGMs) is provided. It is assumed that the materialproperties depend only on the coordinate perpendicular to the cracksurface And vary continuously along the crack faces. By using alaminated composite plate model to simulate the ma- Terialnon-homogeneity, an algorithm for solving the system based on Laplacetransform and Fourier transform Techniques is presented. Unlikeearlier studies that considered certain assumed propertydistributions and a Single crack problem, the current investigationstudies multiple crack problem in the FGMs with arbitrarily Varyingmaterial properties. Transient thermal stresses are presented.
基金the National Natural Science Foundation of China(No.19972018)
文摘Based on the theory of elastic dynamics, the scattering of elasticwaves and dynamic stress concentration of fiber-reinforced compositewith interfaces are studied. Analytical expressions of elastic wavesin different medium areas are presented and an analytic method ofsolving this problem is established. The mode coefficients aredetermined by means of the continuous conditions of displacement andstress on the boundary of the interfaces. The influence of materialproperties and structural size on the dynamic stress con- centrationfactors near the interfaces is analyzed.
文摘By using the complex variable method and conformal mapping, the diffraction of flexural waves and dynamic stress concentrations in thick plates with a cavity have been studied. A general solution of the stress problem of the thick plate satisfying the boundary conditions on the contour of an arbitrary cavity is obtained. By employing the orthogonal function expansion technique, the dynamic stress problem can be reduced to the solution of an infinite algebraic equation series. As an example, the numerical results for the dynamic stress concentration factor in thick plates with a circular, elliptic cavity are graphically presented. The numerical results are discussed.
基金the National Natural Science Foundation of China(No.19632030)
文摘This paper mainly discusses the constitutive laws of incompressible rubber-like materials and the associated finite element analysis method. By a multiplicative decomposition of the deformation gradient into distortional and dilatational parts, the YEOH mode type constitutive laws of rubber-like materials and their numerical implementation are presented. In order to deal with incompressible problems, a three-field variational principle is developed in which deformation, Jacobian and pressure field are treated independently. The connection between the three-field principle and the Hu-Wasizhu generalized variational principle is established. It is shown that the approach proposed can be degenerated to the B-bar method in the linear case. The derailed FE formulation is given in which deformation is ap proximated by isoparametric conforming element, and Jacobian and pressure by discontinuous approximation. Finally, two numerical examples are presented to show the effectiveness and reliability of the method proposed. The work in this paper provides a corner stone of FEA of this kind of problem. This paper features the combination of the multiplicative decomposition, the three-field principle and YEOH model of rubber-like materials, especially under Lagrangian description, giving an effective way for solving this kind of problems. The Lagrangian description is compatible with usually geometrically nonlinear FEM and the constitutive laws are expressed by the second Kirchhoff stress and the Green strain.
基金Failure Mechanics Laboratory of State Education Commissionthe Post-doctor Research Fund of China
文摘This paper provides a method for studying the penny-shaped cracksconfiguration in functionally graded material(FGM)structuressubjected to dynamic or steady loading. It is assumed that the FGMare transversely isotropic and all the material properties onlydepend on the axial coordi- nate z. In the analysis, the elasticregion is treated as a number of layers. The material properties aretaken to be constants for each layer. By utilizing the Laplacetransform and Hankel transform tech- nique, the general solution forthe layers are derived.
基金the Post-Doctoral Science Foundationthe Natural Science Foundation of Heilongjiang Province
文摘In this paper, the interaction between two collinear cracks inpiezoelectric materials under anti-plane shear loading wasinvestigated for the impermeable crack face conditions. By using theFourier transform, the problem can be solved with two pairs of tripleintegral equations. These equations are solved using Schmidt'smethod. This process is quite different from that adopted previously.This makes it possible to understand the two collinear cracksinteraction in piezoelectric materials.
文摘Hypo- and hyper-eutectic At-Si alloys were rapidly solidified from the tow or high temperature melt using water quenching and melt-spinning technique. The differences in microstructure of rapid solidification alloys were studied by scanning and transmission electron microscopy, and X-ray diffraction methods. The primary silicon in the Al-22(wt pct)Si alloy quenched in room temperature water from high temperature melt was smaller than that quenched from low temperature melt. Compared with the ribbons spun from low temperature melt, the ribbons spun from high temperature melt had finer Al-rich and Si-rich phase particles in either Al-7(wt pct)Si or Al-18(wt pct)Si alloy. The mechanism was explained by the nature of the liquid structure.
文摘The thermodynamics and kinetics of the internal oxidation in dilute Cu-Al alloy are investigated. The internal oxidation of copper alloy containing 0.2 similar to 1.2 wt pet Al is studied in the temperature range from 1073 K to 1273 K. A related equilibrium diagram is drawn. A mathematic model of oxidation layer depth is developed on the base of the experimental results. The experiments and investigation show that the formation rate of the internal oxidation layer is mainly controlled by the diffusion of O in matrix, the O concentration on the surface and the Al concentration in the alloy.
文摘Influence of Ti on MC carbide of M2 high speed steel was investigated by experimental observation, thermodynamic calculation and crystallographic calculation. With addition of Ti into M2 steel, large quantities of dispersed TiC particles formed in the steel melt at higher temperature than that of the formation of MC carbide. TiC can act as heterogeneous nuclei for the crystallization of MC carbide particles, and therefore promote the formation of blocky MC carbide.
文摘Open-cell porous Al alloy was fabricated by pressure penetration method and the fabrication of preform was studied in detail. When forming temperature is about 700 degree C and binder content is about 10%, preform with high compressive strength was obtained. Good porous Al alloy with pore size 0.5-1.6 mm and porosity 60%-80% can be obtained under 100 degree C super-heating of liquid metal and about 1.0 MPa applied pressure. The size of the largest sample is up to 100 mm in diameter and 100 mm in height. With the help of SEM it was found that the obtained material is a three-dimensional open-cell porous structure with well-distributed and connected with each other pores. Finally, theoretical analysis was carried out to explain the effect of fabricating process. (Edited author abstract) 4 Refs.
基金supported by the National Basic Research Program (973 Program) of China under Grant No.2007CB310606National Key Technologies R&D Program under Grant No.2009ZX03004-001
文摘In this paper, the phase characteristic disturbance model for baseband direct sequence spread spectrum (DSSS) signal in additive white Gaussian noise (AWGN) environment is established, and the probability density function (PDF) of phase characteristic disturbance is obtained. Then a novel receiver model for baseband DSSS signal based on maximum likelihood (ML) criterion is proposed. The simulation results show that, comparing with correlation scheme, the performance of the proposed method for baseband DSSS signal is 1dB worse in AWGN environment. However, if there is narrow interference in the AWGN environment, the proposed method will show better performance up to 2.5dB, and it has good adaptive resistance to narrowband interference located in different frequency points. This method could be used as an alterative communication scheme for military circumstance when existing strong narrowband interference of various frequencies.
