The frequency-dependent dynamic effective properties (phase velocity, attenuation and elastic modulus) of porous materials are studied numerically. The coherent plane longitudinal and shear wave equations, which are o...The frequency-dependent dynamic effective properties (phase velocity, attenuation and elastic modulus) of porous materials are studied numerically. The coherent plane longitudinal and shear wave equations, which are obtained by averaging on the multiple scattering fields, are used to evaluate the frequency-dependent dynamic effective properties of a porous material. It is found that the prediction of the dynamic effective properties includes the size effects of voids which are not included in most prediction of the traditional static effective properties. The prediction of the dynamic effective elastic modulus at a relatively low frequency range is compared with that of the traditional static effective elastic modulus, and the dynamic effective elastic modulus is found to be very close to the Hashin-Shtrikman upper bound.展开更多
The paper describes use of self-consistent finite element method (SCFEM) for predicting effective properties of fiber composite with partially debonded interface. The effective longitudinal Young's modulus and she...The paper describes use of self-consistent finite element method (SCFEM) for predicting effective properties of fiber composite with partially debonded interface. The effective longitudinal Young's modulus and shear modulus for unidirectional fiber reinforced composites with fiber-end cracks are calculated. Numerical results show that the effective properties are considerably influenced by the fiber-end cracks. The effects of microstructural parameters, such as fiber volume fraction, modulus ratio of the constituents and fiber aspect, on the effective properties of the composites were discussed.展开更多
Representative volume element （RVE） method and asymptotic homogenization （AH） method are two widely used methods in predicting effective properties of pe- riodic materials. This paper develops a novel implementa- ...Representative volume element （RVE） method and asymptotic homogenization （AH） method are two widely used methods in predicting effective properties of pe- riodic materials. This paper develops a novel implementa- tion of the AH method, which has rigorous mathematical foundation of the AH method, and also simplicity as the RVE method. This implementation can be easily realized using commercial software as a black box, and can use all kinds of elements available in commercial software to model unit cells with rather complicated microstructures, so the model may remain a fairly small scale. Several examples were car- fled out to demonstrate the simplicity and effectiveness of the new implementation.展开更多
The influences of interphase on dynamic effective properties of composites reinforced by randomly dispersed spherical particles were studied. A thin homogeneous elastic interphase with different shear and bulk moduli,...The influences of interphase on dynamic effective properties of composites reinforced by randomly dispersed spherical particles were studied. A thin homogeneous elastic interphase with different shear and bulk moduli, located between the reinforced particle and the host matrix, was introduced to model the interfacial bonding state. The effects of such an interphase on the coherent plane waves were studied numerically. Numerical simulations were carried out for SiC-Al composites with four typical cases of interphase. It was found that the property of interphase has significant influences on the effective propagation constants of coherent waves and the dynamic effective elastic moduli of the composites. The influences on the coherent longitudinal wave and the coherent shear waves were different and dependent upon the frequency range. Moreover, several imperfect interface models, i.e., the spring model, mass model, and spring-mass model, were studied numerically and compared with the interphase model, It was found that the spring model is a more suitable model than the mass model for the light and weak interphase whereas the mass model is a more suitable model than the spring model for the heavy and strong interphase.展开更多
The present study aims at developing a new method-RandomMicrostructure Finite Element Method (RMFEM) for the effectiveproperties of com- Posite materials. In this method, a randommicrostructure Model is used to simula...The present study aims at developing a new method-RandomMicrostructure Finite Element Method (RMFEM) for the effectiveproperties of com- Posite materials. In this method, a randommicrostructure Model is used to simulate the microstructure of thereal composite materials. The physical fields in such a randomMicrosturucture model under specified boundary and initial Conditionsare analyzed by finite element method.展开更多
This study focused on investigating the effects of various factors on the mechanical properties of superconducting matrix composites reinforced with ferromagnetic particles and interface phases when exposed to externa...This study focused on investigating the effects of various factors on the mechanical properties of superconducting matrix composites reinforced with ferromagnetic particles and interface phases when exposed to external magnetic fields.A micromechanical model was created by simplifying the basic properties and composition of the interface,utilizing principles such as Eshelby’s equivalent inclusion theory and Hooke’s law,as well as applying uniform stress boundary conditions.Through the development of equations,the study predicted changes in effective mechanical properties,highlighting the significant influence of parameters like the interface phase,inclusions,and magnetic field on the effective elastic modulus and magnetostriction of the composite material.By shedding light on these relationships,the research offers valuable insights for the manufacture and application of ferromagnetic particle-reinforced superconducting matrix composites with interface phases,providing a foundation for future research in this area.展开更多
Seismic prediction of cracks is of great significance in many disciplines,for which the rock physics model is indispensable.However,up to now,multitudinous analytical models focus primarily on the cracked rock with th...Seismic prediction of cracks is of great significance in many disciplines,for which the rock physics model is indispensable.However,up to now,multitudinous analytical models focus primarily on the cracked rock with the isotropic background,while the explicit model for the cracked rock with the anisotropic background is rarely investigated in spite of such case being often encountered in the earth.Hence,we first studied dependences of the crack opening displacement tensors on the crack dip angle in the coordinate systems formed by symmetry planes of the crack and the background anisotropy,respectively,by forty groups of numerical experiments.Based on the conclusion from the experiments,the analytical solution was derived for the effective elastic properties of the rock with the inclined penny-shaped cracks in the transversely isotropic background.Further,we comprehensively analyzed,according to the developed model,effects of the crack dip angle,background anisotropy,filling fluid and crack density on the effective elastic properties of the cracked rock.The analysis results indicate that the dip angle and background anisotropy can significantly either enhance or weaken the anisotropy degrees of the P-and SH-wave velocities,whereas they have relatively small effects on the SV-wave velocity anisotropy.Moreover,the filling fluid can increase the stiffness coefficients related to the compressional modulus by reducing crack compliance parameters,while its effects on shear coefficients depend on the crack dip angle.The increasing crack density reduces velocities of the dry rock,and decreasing rates of the velocities are affected by the crack dip angle.By comparing with exact numerical results and experimental data,it was demonstrated that the proposed model can achieve high-precision estimations of stiffness coefficients.Moreover,the assumption of the weakly anisotropic background results in the consistency between the proposed model and Hudson's published theory for the orthorhombic rock.展开更多
A homogenization theory is developed to predict the influence of spherical inclusions on the effective thermoelectric properties of thermoelectric composite materials based on the general principles of thermodynamics ...A homogenization theory is developed to predict the influence of spherical inclusions on the effective thermoelectric properties of thermoelectric composite materials based on the general principles of thermodynamics and Mori-Tanaka method.The closed-form solutions of effective Seebeck coefficient,electric conductivity,heat conductivity,and figure of merit for such thermoelectric materials are obtained by solving the nonlinear coupled transport equations of electricity and heat.It is found that the effective figure of merit of thermoelectric material containing spherical inclusions can be higher than that of each constituent in the absence of size effect and interface effect.Some interesting examples of actual thermoelectric composites with spherical inclusions,such as insulated cavities,inclusions subjected to conductive electric and heat exchange and thermoelectric inclusions,are considered,and the numerical results lead to the conclusion that considerable enhancement of the effective figure of merit is achievable by introducing inclusions.In this paper,we provide a theoretical foundation for analytically and computationally treating the thermoelectric composites with more complicated inclusion structures,and thus pointing out a new route to their design and optimization.展开更多
This paper presents a numerical homogenization analysis of a porous piezoelectric composite with a partially metalized pore surface.The metal layers can be added to the pore surfaces to improve the mechanical and elec...This paper presents a numerical homogenization analysis of a porous piezoelectric composite with a partially metalized pore surface.The metal layers can be added to the pore surfaces to improve the mechanical and electromechanical properties of ordinary porous piezocomposites.Physically,constructing that composite with completely metalized pore surfaces is a challenging process,and imperfect metallization is more expected.Here,we investigate the effects of possible incomplete metallization of pore surfaces on the composite’s equivalent properties.We applied the effective moduli theory,which was developed for the piezoelectric medium based on the Hill-Mandel principle,and the finite element method to compute the effective moduli of the considered composites.Using specific algorithms and programs in the ANSYS APDL programming language,we constructed the representative unit cell element models and performed various computational experiments.Due to the presence of metal inclusion,we found that the dielectric and piezoelectric properties of the considered composites differ dramatically from the corresponding properties of the ordinary porous piezocomposites.The results of this work showed that piezocomposites with partially metallized pore surfaces can have a higher anisotropy,compared to the pure piezoceramic matrix,due to the defects in metal coatings.展开更多
Due to the large quasi-piezoelectric d33 coefficient in the film thickness direction, cellular piezoelectret has emerged as a new kind of compliant electromechanical transducer materials. The macroscopic piezoelectric...Due to the large quasi-piezoelectric d33 coefficient in the film thickness direction, cellular piezoelectret has emerged as a new kind of compliant electromechanical transducer materials. The macroscopic piezoelectric effect of cellular piezoelectret is closely related to the void microstructures as well as the material constants of host polymer. Complex void microstmctures are usually encountered in the optimum design of cellular piezoelectret polymer film with ad- vanced piezoelectric properties. Analysis of the effective electromechanical properties is generally needed. This article presents an overview of the recent progress on theoretical models and numerical simulation for the effective electromechanical properties of cellular piezoelectret. Emphasis is placed on our own works of cellular piezoelectret published in past several years.展开更多
The closed-form solutions of the dynamic problem of heterogeneous piezoelectric materials are formulated by introducing polarizations into a reference medium and using the generalized reciprocity theorem.These solutio...The closed-form solutions of the dynamic problem of heterogeneous piezoelectric materials are formulated by introducing polarizations into a reference medium and using the generalized reciprocity theorem.These solutions can be reduced to the ones of an elastodynamic problem.Based on the effective medium method,these closedform solutions can be used to establish the self-consistent equations about the frequencydependent effective parameters,which can be numerically solved by iteration.Theoretical predictions are compared with the experimental results,and good agreement can be found.Furthermore,the analyses on the effects of microstructure and wavelength on the effective properties,resonance frequencies,and attenuation are also presented,which may provide some guidance for the microstructure design and analysis of piezoelectric composites.展开更多
Some theoretical methods have been reported to deal with nonlinear problems of composite materials but the accuracy is not so good. In the meantime, a lot of linear problems are difficult to be managed by the theoreti...Some theoretical methods have been reported to deal with nonlinear problems of composite materials but the accuracy is not so good. In the meantime, a lot of linear problems are difficult to be managed by the theoretical methods. The present study aims to use the developed method, the random microstructure finite element method, to deal with these nonlinear problems. In this paper, the random microstructure finite element method is used to deal with all three kinds of nonlinear property problems of composite materials. The analyzed results suggest the influences of the nonlinear phenomena on the effective properties of composite materials are significant and the random microstructure finite element method is an effective tool to investigate the nonlinear problems.展开更多
The rate of hydrothermal reaction of SiO_2 and/or A1_2O_3 in the system of CaO-Al_2O_3-SiO_2-H_2O at 200℃ and the factors which influence the reactions are investigated by determining the reaction ratio.The rate of r...The rate of hydrothermal reaction of SiO_2 and/or A1_2O_3 in the system of CaO-Al_2O_3-SiO_2-H_2O at 200℃ and the factors which influence the reactions are investigated by determining the reaction ratio.The rate of reactions depends on the reactive activities of raw materials, initial composition of mixture and relative activity of SiO_2 and A12O3. The hydrothermal reaction can be accelerated by sodium hydroxide,in the case of silica,which has low activity, this is quite obvious.展开更多
We utilize the effective field theory approach to study the properties of the axion. In particular, with s as well as u and d quarks regarded to be relatively light we derive a formula for the mass of the axion; a rou...We utilize the effective field theory approach to study the properties of the axion. In particular, with s as well as u and d quarks regarded to be relatively light we derive a formula for the mass of the axion; a rough estimate of the rate for its dominant decay mode at low energy is also carried out.展开更多
In this paper, the techniques to manage and control the flow over airfoils by using the external unsteady excitations are investigated. The mechanisms of these excitation effects are also explored. The principal goal ...In this paper, the techniques to manage and control the flow over airfoils by using the external unsteady excitations are investigated. The mechanisms of these excitation effects are also explored. The principal goal of this study is to gain a better understanding and to find the possible ways for enhancing the aerodynamic efficients. The experimental investigations are carried out in two low-speed wind tunnels. The test models are two dimensional airfoils with different section geometries. Four means of excitations have been used in these experiments. (1) The pitch oscillation of the airfoil high-angle-of-attack situation. (2) The moving surface effects of the airfoil with a leading edge rotating cylinder. (3) Oscillating leading edge flaperon. (4) Small oscillating spoiler located near the leading edge of the airfoil. The lift, drag and pitch moment coefficients are measured in these experiments. But, we will put the emphasis only on the 'dynamic amplifying effects' on aerodynamic lift in this paper. Results obtained indicate that the beneficial aerodynamic effects of section lift increase can be obtained at the high angle of attack near stall regime, as long as the frequency and amplitute of the excitation are appropriately selected.展开更多
Ultrahigh-molecular-weight polyethylene(UtlMWPE) has been irradiated (0-40 Mrad) with a Co^(60) source at room temperature under vacuum. Their crystallinity has been investigated by DSC and SAXS A significant increase...Ultrahigh-molecular-weight polyethylene(UtlMWPE) has been irradiated (0-40 Mrad) with a Co^(60) source at room temperature under vacuum. Their crystallinity has been investigated by DSC and SAXS A significant increase of heat of fusion can be seen at low irradiation doses, which is attributed to crystallization caused by chain scission during the process of irradiation. It is also observed that thickness of lamellae changes with irradiation dose. Young's modulus has been improved significantly after irradiation at low doses.展开更多
In this paper, we review the magnetic properties and magnetocaloric effects（MCE） of binary R–T（R = Pr, Gd, Tb,Dy, Ho, Er, Tm; T = Ga, Ni, Co, Cu） intermetallic compounds（including RGa series, RNi series, R_（12...In this paper, we review the magnetic properties and magnetocaloric effects（MCE） of binary R–T（R = Pr, Gd, Tb,Dy, Ho, Er, Tm; T = Ga, Ni, Co, Cu） intermetallic compounds（including RGa series, RNi series, R_（12）Co_7 series, R_3 Co series and RCu_2series）, which have been investigated in detail in the past several years. The R–T compounds are studied by means of magnetic measurements, heat capacity measurements, magnetoresistance measurements and neutron powder diffraction measurements. The R–T compounds show complex magnetic transitions and interesting magnetic properties.The types of magnetic transitions are investigated and confirmed in detail by multiple approaches. Especially, most of the R–T compounds undergo more than one magnetic transition, which has significant impact on the magnetocaloric effect of R–T compounds. The MCE of R–T compounds are calculated by different ways and the special shapes of MCE peaks for different compounds are investigated and discussed in detail. To improve the MCE performance of R–T compounds,atoms with large spin（S） and atoms with large total angular momentum（J） are introduced to substitute the related rare earth atoms. With the atom substitution, the maximum of magnetic entropy change（？SM）, refrigerant temperature width（Twidth）or refrigerant capacity（RC） is enlarged for some R–T compounds. In the low temperature range, binary R–T（R = Pr, Gd,Tb, Dy, Ho, Er, Tm; T = Ga, Ni, Co, Cu） intermetallic compounds（including RGa series, RNi series,R_（12）Co_7 series, R_3 Co series and RCu_2series） show excellent performance of MCE, indicating the potential application for gas liquefaction in the future.展开更多
The transformation behavior, microstructural evolution and mechanical properties were compared in a coldrolled Nb–Mo microalloyed 6.5Mn alloy after intercritical annealing（IA） and quenching and partitioning（Q ＆ P...The transformation behavior, microstructural evolution and mechanical properties were compared in a coldrolled Nb–Mo microalloyed 6.5Mn alloy after intercritical annealing（IA） and quenching and partitioning（Q ＆ P）,respectively. The thermodynamic calculation and theoretical analysis were used to determine the optimal heat treatment parameters. The Q ＆ P samples exhibited relatively higher strength with relatively low ductility, mainly due to the hard martensite matrix, which resulted in continuous yielding behavior upon loading, whereas the IA samples showed the significantly improved ductility, which benefited from the more sufficient transformation-induced plasticity（TRIP） effects and the softer ultrafine ferrite matrix. The dependence of yield point elongation（YPE） of IA samples on grain size demonstrated that the YPE value was in the reverse proportional relationship to the average grain size, which agreed well with theoretical analysis.展开更多
The effect of excitation current intensity on the mechanical properties of ZL205 A castings solidified under a traveling magnetic field was studied. The results of the experiment indicate that the excitation current i...The effect of excitation current intensity on the mechanical properties of ZL205 A castings solidified under a traveling magnetic field was studied. The results of the experiment indicate that the excitation current intensity of the traveling magnetic field has a great influence on the mechanical properties of the ZL205 A castings. When the excitation current intensity is 15 A, the tensile strength and elongation of ZL205 A alloy castings increase 27.2% and 67.7%, respectively, compared with those of the same alloy solidified under gravity. The improvement of mechanical properties is attributed to the decrease of micro-porosity in the alloy. Under the traveling magnetic field, the feeding pressure in the alloy melt before solidification can be enhanced due to the electromagnetic force. Moreover, the melt flow induced by the traveling magnetic field can decrease the temperature gradient. The feeding resistance will be increased because the temperature gradient decrease. So traveling magnetic field has an optimum effect on feeding.展开更多
The therapeutic actions of Qing Luo Yin (QLY清络饮) with heat property and Wen Luo Yin (WLY温络饮) with cold property on pain, swelling of the ankle, arthritis index and ultrastructures of synoviocytes were compared i...The therapeutic actions of Qing Luo Yin (QLY清络饮) with heat property and Wen Luo Yin (WLY温络饮) with cold property on pain, swelling of the ankle, arthritis index and ultrastructures of synoviocytes were compared in rats of type II collagen-induced arthritis (CIA), with tripterygium glycosidorum (TG) used as control. The results indicated that both QLY and WLY could reduce pain, swelling of the ankle and the arthritis index of CIA, and QLY had better effects in reducing the swelling of the ankle and controlling the secondary pathological lesions as compared with WLY. Investigation on the ultrastructures of synoviocytes indicated that both QLY and WLY could reduce the number of Golgi apparatus, rough surface endoplasmic reticulum, dense bodies, matrix filaments and vacuoles so as to suppress the excessive secretion of synoviocytes in rats of CIA.展开更多
基金This work was financially supported by the National Natural Science Foundation of China (No.10272003, No. 10032010, and No. 10372004) the Talent Foundation of the University of Sciences and Technology Beijing.
文摘The frequency-dependent dynamic effective properties (phase velocity, attenuation and elastic modulus) of porous materials are studied numerically. The coherent plane longitudinal and shear wave equations, which are obtained by averaging on the multiple scattering fields, are used to evaluate the frequency-dependent dynamic effective properties of a porous material. It is found that the prediction of the dynamic effective properties includes the size effects of voids which are not included in most prediction of the traditional static effective properties. The prediction of the dynamic effective elastic modulus at a relatively low frequency range is compared with that of the traditional static effective elastic modulus, and the dynamic effective elastic modulus is found to be very close to the Hashin-Shtrikman upper bound.
基金The project supported by the National Natural Science Foundation of China
文摘The paper describes use of self-consistent finite element method (SCFEM) for predicting effective properties of fiber composite with partially debonded interface. The effective longitudinal Young's modulus and shear modulus for unidirectional fiber reinforced composites with fiber-end cracks are calculated. Numerical results show that the effective properties are considerably influenced by the fiber-end cracks. The effects of microstructural parameters, such as fiber volume fraction, modulus ratio of the constituents and fiber aspect, on the effective properties of the composites were discussed.
基金supported by the National Natural Science Foundation of China(91216201)
文摘Representative volume element （RVE） method and asymptotic homogenization （AH） method are two widely used methods in predicting effective properties of pe- riodic materials. This paper develops a novel implementa- tion of the AH method, which has rigorous mathematical foundation of the AH method, and also simplicity as the RVE method. This implementation can be easily realized using commercial software as a black box, and can use all kinds of elements available in commercial software to model unit cells with rather complicated microstructures, so the model may remain a fairly small scale. Several examples were car- fled out to demonstrate the simplicity and effectiveness of the new implementation.
基金This work was financially supported by the National Natural Science Foundation of China (No.10272003) and the Talent Foundationof University of Science & Technology Beijing.
文摘The influences of interphase on dynamic effective properties of composites reinforced by randomly dispersed spherical particles were studied. A thin homogeneous elastic interphase with different shear and bulk moduli, located between the reinforced particle and the host matrix, was introduced to model the interfacial bonding state. The effects of such an interphase on the coherent plane waves were studied numerically. Numerical simulations were carried out for SiC-Al composites with four typical cases of interphase. It was found that the property of interphase has significant influences on the effective propagation constants of coherent waves and the dynamic effective elastic moduli of the composites. The influences on the coherent longitudinal wave and the coherent shear waves were different and dependent upon the frequency range. Moreover, several imperfect interface models, i.e., the spring model, mass model, and spring-mass model, were studied numerically and compared with the interphase model, It was found that the spring model is a more suitable model than the mass model for the light and weak interphase whereas the mass model is a more suitable model than the spring model for the heavy and strong interphase.
基金the National Science Foundation of China under the Grant 19772037 and 19902014
文摘The present study aims at developing a new method-RandomMicrostructure Finite Element Method (RMFEM) for the effectiveproperties of com- Posite materials. In this method, a randommicrostructure Model is used to simulate the microstructure of thereal composite materials. The physical fields in such a randomMicrosturucture model under specified boundary and initial Conditionsare analyzed by finite element method.
基金supported by the National Natural Science Foundation of China(No.12262020).
文摘This study focused on investigating the effects of various factors on the mechanical properties of superconducting matrix composites reinforced with ferromagnetic particles and interface phases when exposed to external magnetic fields.A micromechanical model was created by simplifying the basic properties and composition of the interface,utilizing principles such as Eshelby’s equivalent inclusion theory and Hooke’s law,as well as applying uniform stress boundary conditions.Through the development of equations,the study predicted changes in effective mechanical properties,highlighting the significant influence of parameters like the interface phase,inclusions,and magnetic field on the effective elastic modulus and magnetostriction of the composite material.By shedding light on these relationships,the research offers valuable insights for the manufacture and application of ferromagnetic particle-reinforced superconducting matrix composites with interface phases,providing a foundation for future research in this area.
基金We would like to acknowledge all the reviewers and editors and the sponsorship of National Natural Science Foundation of China(42030103)the Marine S&T Fund of Shandong Province for Pilot National Laboratory for Marine Science and Technology(Qingdao)(2021QNLM020001-6)the Laoshan National Laboratory of Science and Technology Foundation(LSKJ202203400).
文摘Seismic prediction of cracks is of great significance in many disciplines,for which the rock physics model is indispensable.However,up to now,multitudinous analytical models focus primarily on the cracked rock with the isotropic background,while the explicit model for the cracked rock with the anisotropic background is rarely investigated in spite of such case being often encountered in the earth.Hence,we first studied dependences of the crack opening displacement tensors on the crack dip angle in the coordinate systems formed by symmetry planes of the crack and the background anisotropy,respectively,by forty groups of numerical experiments.Based on the conclusion from the experiments,the analytical solution was derived for the effective elastic properties of the rock with the inclined penny-shaped cracks in the transversely isotropic background.Further,we comprehensively analyzed,according to the developed model,effects of the crack dip angle,background anisotropy,filling fluid and crack density on the effective elastic properties of the cracked rock.The analysis results indicate that the dip angle and background anisotropy can significantly either enhance or weaken the anisotropy degrees of the P-and SH-wave velocities,whereas they have relatively small effects on the SV-wave velocity anisotropy.Moreover,the filling fluid can increase the stiffness coefficients related to the compressional modulus by reducing crack compliance parameters,while its effects on shear coefficients depend on the crack dip angle.The increasing crack density reduces velocities of the dry rock,and decreasing rates of the velocities are affected by the crack dip angle.By comparing with exact numerical results and experimental data,it was demonstrated that the proposed model can achieve high-precision estimations of stiffness coefficients.Moreover,the assumption of the weakly anisotropic background results in the consistency between the proposed model and Hudson's published theory for the orthorhombic rock.
基金Project supported by the Ningbo Natural Science Foundation,China(Grant Nos.2019A610151 and 2018A610081)the Natural Science Foundation of Zhejiang Province,China(Grant Nos.LY17A020001 and LY20A020002)+1 种基金the National Natural Science Foundation of China(Grant No.11402063)the K C Wong Magna Fund in Ningbo University,China.
文摘A homogenization theory is developed to predict the influence of spherical inclusions on the effective thermoelectric properties of thermoelectric composite materials based on the general principles of thermodynamics and Mori-Tanaka method.The closed-form solutions of effective Seebeck coefficient,electric conductivity,heat conductivity,and figure of merit for such thermoelectric materials are obtained by solving the nonlinear coupled transport equations of electricity and heat.It is found that the effective figure of merit of thermoelectric material containing spherical inclusions can be higher than that of each constituent in the absence of size effect and interface effect.Some interesting examples of actual thermoelectric composites with spherical inclusions,such as insulated cavities,inclusions subjected to conductive electric and heat exchange and thermoelectric inclusions,are considered,and the numerical results lead to the conclusion that considerable enhancement of the effective figure of merit is achievable by introducing inclusions.In this paper,we provide a theoretical foundation for analytically and computationally treating the thermoelectric composites with more complicated inclusion structures,and thus pointing out a new route to their design and optimization.
基金This research was done in the framework of the RFBR project 20-31-90102.
文摘This paper presents a numerical homogenization analysis of a porous piezoelectric composite with a partially metalized pore surface.The metal layers can be added to the pore surfaces to improve the mechanical and electromechanical properties of ordinary porous piezocomposites.Physically,constructing that composite with completely metalized pore surfaces is a challenging process,and imperfect metallization is more expected.Here,we investigate the effects of possible incomplete metallization of pore surfaces on the composite’s equivalent properties.We applied the effective moduli theory,which was developed for the piezoelectric medium based on the Hill-Mandel principle,and the finite element method to compute the effective moduli of the considered composites.Using specific algorithms and programs in the ANSYS APDL programming language,we constructed the representative unit cell element models and performed various computational experiments.Due to the presence of metal inclusion,we found that the dielectric and piezoelectric properties of the considered composites differ dramatically from the corresponding properties of the ordinary porous piezocomposites.The results of this work showed that piezocomposites with partially metallized pore surfaces can have a higher anisotropy,compared to the pure piezoceramic matrix,due to the defects in metal coatings.
基金supported by National Natural Science Foundation of China (11072179,11090334)Shanghai Leading Academic Discipline Project (B302)
文摘Due to the large quasi-piezoelectric d33 coefficient in the film thickness direction, cellular piezoelectret has emerged as a new kind of compliant electromechanical transducer materials. The macroscopic piezoelectric effect of cellular piezoelectret is closely related to the void microstructures as well as the material constants of host polymer. Complex void microstmctures are usually encountered in the optimum design of cellular piezoelectret polymer film with ad- vanced piezoelectric properties. Analysis of the effective electromechanical properties is generally needed. This article presents an overview of the recent progress on theoretical models and numerical simulation for the effective electromechanical properties of cellular piezoelectret. Emphasis is placed on our own works of cellular piezoelectret published in past several years.
基金Project supported by the National Natural Science Foundation of China(No.12072240)。
文摘The closed-form solutions of the dynamic problem of heterogeneous piezoelectric materials are formulated by introducing polarizations into a reference medium and using the generalized reciprocity theorem.These solutions can be reduced to the ones of an elastodynamic problem.Based on the effective medium method,these closedform solutions can be used to establish the self-consistent equations about the frequencydependent effective parameters,which can be numerically solved by iteration.Theoretical predictions are compared with the experimental results,and good agreement can be found.Furthermore,the analyses on the effects of microstructure and wavelength on the effective properties,resonance frequencies,and attenuation are also presented,which may provide some guidance for the microstructure design and analysis of piezoelectric composites.
基金This work is supported by the National Natural Science Foundation of China under the Grant 19772037 and 19902014
文摘Some theoretical methods have been reported to deal with nonlinear problems of composite materials but the accuracy is not so good. In the meantime, a lot of linear problems are difficult to be managed by the theoretical methods. The present study aims to use the developed method, the random microstructure finite element method, to deal with these nonlinear problems. In this paper, the random microstructure finite element method is used to deal with all three kinds of nonlinear property problems of composite materials. The analyzed results suggest the influences of the nonlinear phenomena on the effective properties of composite materials are significant and the random microstructure finite element method is an effective tool to investigate the nonlinear problems.
基金National H-Tech Program under contract 863-7152101
文摘The rate of hydrothermal reaction of SiO_2 and/or A1_2O_3 in the system of CaO-Al_2O_3-SiO_2-H_2O at 200℃ and the factors which influence the reactions are investigated by determining the reaction ratio.The rate of reactions depends on the reactive activities of raw materials, initial composition of mixture and relative activity of SiO_2 and A12O3. The hydrothermal reaction can be accelerated by sodium hydroxide,in the case of silica,which has low activity, this is quite obvious.
基金Supported by the National Natural Science Foundation of China under Grant No 11175088
文摘We utilize the effective field theory approach to study the properties of the axion. In particular, with s as well as u and d quarks regarded to be relatively light we derive a formula for the mass of the axion; a rough estimate of the rate for its dominant decay mode at low energy is also carried out.
文摘In this paper, the techniques to manage and control the flow over airfoils by using the external unsteady excitations are investigated. The mechanisms of these excitation effects are also explored. The principal goal of this study is to gain a better understanding and to find the possible ways for enhancing the aerodynamic efficients. The experimental investigations are carried out in two low-speed wind tunnels. The test models are two dimensional airfoils with different section geometries. Four means of excitations have been used in these experiments. (1) The pitch oscillation of the airfoil high-angle-of-attack situation. (2) The moving surface effects of the airfoil with a leading edge rotating cylinder. (3) Oscillating leading edge flaperon. (4) Small oscillating spoiler located near the leading edge of the airfoil. The lift, drag and pitch moment coefficients are measured in these experiments. But, we will put the emphasis only on the 'dynamic amplifying effects' on aerodynamic lift in this paper. Results obtained indicate that the beneficial aerodynamic effects of section lift increase can be obtained at the high angle of attack near stall regime, as long as the frequency and amplitute of the excitation are appropriately selected.
文摘Ultrahigh-molecular-weight polyethylene(UtlMWPE) has been irradiated (0-40 Mrad) with a Co^(60) source at room temperature under vacuum. Their crystallinity has been investigated by DSC and SAXS A significant increase of heat of fusion can be seen at low irradiation doses, which is attributed to crystallization caused by chain scission during the process of irradiation. It is also observed that thickness of lamellae changes with irradiation dose. Young's modulus has been improved significantly after irradiation at low doses.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11274357,51501005,51590880,and 11674008)the Fundamental Research Funds for the Central Universities,China(Grant No.FRF-TP-15-010A1)+1 种基金the China Postdoctoral Science Foundation(Grant No.2016M591071)the Key Research Program of the Chinese Academy of Sciences(Grant No.KJZD-EW-M05)
文摘In this paper, we review the magnetic properties and magnetocaloric effects（MCE） of binary R–T（R = Pr, Gd, Tb,Dy, Ho, Er, Tm; T = Ga, Ni, Co, Cu） intermetallic compounds（including RGa series, RNi series, R_（12）Co_7 series, R_3 Co series and RCu_2series）, which have been investigated in detail in the past several years. The R–T compounds are studied by means of magnetic measurements, heat capacity measurements, magnetoresistance measurements and neutron powder diffraction measurements. The R–T compounds show complex magnetic transitions and interesting magnetic properties.The types of magnetic transitions are investigated and confirmed in detail by multiple approaches. Especially, most of the R–T compounds undergo more than one magnetic transition, which has significant impact on the magnetocaloric effect of R–T compounds. The MCE of R–T compounds are calculated by different ways and the special shapes of MCE peaks for different compounds are investigated and discussed in detail. To improve the MCE performance of R–T compounds,atoms with large spin（S） and atoms with large total angular momentum（J） are introduced to substitute the related rare earth atoms. With the atom substitution, the maximum of magnetic entropy change（？SM）, refrigerant temperature width（Twidth）or refrigerant capacity（RC） is enlarged for some R–T compounds. In the low temperature range, binary R–T（R = Pr, Gd,Tb, Dy, Ho, Er, Tm; T = Ga, Ni, Co, Cu） intermetallic compounds（including RGa series, RNi series,R_（12）Co_7 series, R_3 Co series and RCu_2series） show excellent performance of MCE, indicating the potential application for gas liquefaction in the future.
基金financially supported by the National Natural Science Foundation of China(No.51401050)the Fundamental Research Funding for the Central Universities(No.N160204001)supported by the Australian Research Council(ARC)Laureate Fellowship(Prof.Hodgson)
文摘The transformation behavior, microstructural evolution and mechanical properties were compared in a coldrolled Nb–Mo microalloyed 6.5Mn alloy after intercritical annealing（IA） and quenching and partitioning（Q ＆ P）,respectively. The thermodynamic calculation and theoretical analysis were used to determine the optimal heat treatment parameters. The Q ＆ P samples exhibited relatively higher strength with relatively low ductility, mainly due to the hard martensite matrix, which resulted in continuous yielding behavior upon loading, whereas the IA samples showed the significantly improved ductility, which benefited from the more sufficient transformation-induced plasticity（TRIP） effects and the softer ultrafine ferrite matrix. The dependence of yield point elongation（YPE） of IA samples on grain size demonstrated that the YPE value was in the reverse proportional relationship to the average grain size, which agreed well with theoretical analysis.
基金financially supported by the National Basic Research Program of China(2011CB610406)the Natural Science Foundation of Hei Longjiang Province(JC201209)the National Natural Science Foundation of China(51425402)
文摘The effect of excitation current intensity on the mechanical properties of ZL205 A castings solidified under a traveling magnetic field was studied. The results of the experiment indicate that the excitation current intensity of the traveling magnetic field has a great influence on the mechanical properties of the ZL205 A castings. When the excitation current intensity is 15 A, the tensile strength and elongation of ZL205 A alloy castings increase 27.2% and 67.7%, respectively, compared with those of the same alloy solidified under gravity. The improvement of mechanical properties is attributed to the decrease of micro-porosity in the alloy. Under the traveling magnetic field, the feeding pressure in the alloy melt before solidification can be enhanced due to the electromagnetic force. Moreover, the melt flow induced by the traveling magnetic field can decrease the temperature gradient. The feeding resistance will be increased because the temperature gradient decrease. So traveling magnetic field has an optimum effect on feeding.
文摘The therapeutic actions of Qing Luo Yin (QLY清络饮) with heat property and Wen Luo Yin (WLY温络饮) with cold property on pain, swelling of the ankle, arthritis index and ultrastructures of synoviocytes were compared in rats of type II collagen-induced arthritis (CIA), with tripterygium glycosidorum (TG) used as control. The results indicated that both QLY and WLY could reduce pain, swelling of the ankle and the arthritis index of CIA, and QLY had better effects in reducing the swelling of the ankle and controlling the secondary pathological lesions as compared with WLY. Investigation on the ultrastructures of synoviocytes indicated that both QLY and WLY could reduce the number of Golgi apparatus, rough surface endoplasmic reticulum, dense bodies, matrix filaments and vacuoles so as to suppress the excessive secretion of synoviocytes in rats of CIA.
