Based on microstructure analysis of the new Ti-A1 intermetallic compound porous material, a micromechanics model of heterogeneous Plateau porous structure was established and calculation formulas of elastic constants ...Based on microstructure analysis of the new Ti-A1 intermetallic compound porous material, a micromechanics model of heterogeneous Plateau porous structure was established and calculation formulas of elastic constants （including effective elastic modulus, effective shear elastic modulus and effective Poisson ratio） were derived by the energy method for this porous material. Calculation results show that both the effective elastic modulus and effective shear elastic modulus increase with the increase of the relative density while the effective Poisson ratio decreases. Compared with the currently-existing hexagonal honeycomb model and micromechanics model of composite materials, the micromechanics model of heterogeneous Plateau porous structure in this study is more suitable for characterizing the medium-density porous material and more accurate for predicting the effective elastic constants of the medium-density porous material. Moreover, the obtained explicit expressions of the effective elastic constants in term of the relative density rather than the microstructural parameters for the uniform and regular Plateau porous structure are more convenient to engineering application.展开更多
With the wide demands of cellular materials applications in aerospace and civil engineering,research effort sacrificed for this type of materials attains nowadays a higher level than ever before.This paper is focused ...With the wide demands of cellular materials applications in aerospace and civil engineering,research effort sacrificed for this type of materials attains nowadays a higher level than ever before.This paper is focused on the prediction methods of effective Young's modulus for periodical cellular materials.Based on comprehensive studies of the existing homogenization method(HM),the G-A meso-mechanics method(G-A MMM) and the stretching energy method(SEM) that are unable to reflect the size effect,we propose the bending energy method(BEM) for the first time,and a comparative study of these four methods is further made to show the generality and the capability of capturing the size effect of the BEM method.Meanwhile,the underlying characteristics of each method and their relations are clarified.To do this,the detailed finite element computing and existing experimental results of hexagonal honeycombs from the literature are adopted as the standard of comparison for the above four methods.Stretch and bending models of periodical cellular materials are taken into account,respectively for the comparison of stretch and flexural displacements resulting from the above methods.We conclude that the BEM has the strong ability of both predicting the effective Young's modulus and revealing the size effect.Such a method is also able to predict well the variations of structural displacements in terms of the cell size under stretching and bending loads including the non-monotonous variations for the hexagonal cell.On the contrary,other three methods can only predict the limited results whenever the cell size tends to be infinitely small.展开更多
This paper presents a direct Mori-Tanaka approach to calculate the effective moduli of particle-reinforced composites and fiber-reinforced composites with spring-like imperfect interfaces. By a comparison between thes...This paper presents a direct Mori-Tanaka approach to calculate the effective moduli of particle-reinforced composites and fiber-reinforced composites with spring-like imperfect interfaces. By a comparison between these results and those obtained from the approximate Mori-Tanaka method developed by Qu for composites with slightly weakened interface, the validity of the Qu's method is revealed.展开更多
This paper concerns the homogenization problems for porous piezocomposites with infinitely thin metalized pore surfaces.To determine the effective properties,we used the effective moduli method and the finite element ...This paper concerns the homogenization problems for porous piezocomposites with infinitely thin metalized pore surfaces.To determine the effective properties,we used the effective moduli method and the finite element approaches,realized in the ANSYS package.As a simple model of the representative volume,we applied a unit cell of porous piezoceramic material in the form of a cube with one spherical pore.We modeled metallization by introducing an additional layer of material with very large permittivity coefficients along the pore boundary.Then we simulated the nonuniform polarization field around the pore.For taking this effect into account,we previously solved the electrostatic problem for a porous dielectric material with the same geometric structure.From this problem,we obtained the polarization field in the porous piezomaterial;after that,we modified the material properties of the finite elements from dielectric to piezoelectric with element coordinate systems whose corresponding axes rotated along the polarization vectors.As a result,we obtained the porous unit cell of an inhomogeneously polarized piezoceramic matrix.From the solutions of these homogenization problems,we observed that the examined porous piezoceramics composite with metalized pore boundaries has more extensive effective transverse and shear piezomoduli,and effective dielectric constants compared to the conventional porous piezoceramics.The analysis also showed that the effect of the polarization field inhomogeneity is insignificant on the ordinary porous piezoceramics;however,it is more significant on the porous piezoceramics with metalized pore surfaces.展开更多
One of the biggest challenges in the biocompatibility of implantable metals is the prevention of the stress shielding effect,which is related to the coupling of the bone-metal mechanical properties.This stress shieldi...One of the biggest challenges in the biocompatibility of implantable metals is the prevention of the stress shielding effect,which is related to the coupling of the bone-metal mechanical properties.This stress shielding phenomenon provokes bone resorption and the consequent adverse effects on prosthesis fixation.However,it can be inhibited by adapting the stiffness of the implant material.Since the use of titanium(Ti)porous structures is a great alternative not only to inhibit this effect but also to improve the osteointegration of orthopedic and dental implants,a brief description of the techniques used for their manufacturing and a review of the current commercialized implants produced from porous Ti assemblies are compiled in this work.As powder metallurgy(PM)with space holder(SH)is a powerful technology used to produce porous Ti structures,it is here discussed its potential for the fabrication of medical devices from the perspectives of both design and manufacture.The most important parameters of the technique such as the size and shape of the initial metallic particles,the SH and binder type of materials,the compaction pressure of the green form,and in the sintering stage,the temperature,atmosphere,and time are reviewed according to the bibliography reported.Furthermore,the importance of the porosity and its types together with the influence of the mentioned parameters in the final porosity and,consequently,in the ultimate mechanical properties of the structure are discussed.Finally,a few examples of the PM-SH application for the manufacturing of orthopedic implants are presented.展开更多
基金Project(50825102) supported by the National Natural Science Funds for Distinguished Young Scholar,ChinaProject(2009CB623406) supported by the National Basic Research Program of China
文摘Based on microstructure analysis of the new Ti-A1 intermetallic compound porous material, a micromechanics model of heterogeneous Plateau porous structure was established and calculation formulas of elastic constants （including effective elastic modulus, effective shear elastic modulus and effective Poisson ratio） were derived by the energy method for this porous material. Calculation results show that both the effective elastic modulus and effective shear elastic modulus increase with the increase of the relative density while the effective Poisson ratio decreases. Compared with the currently-existing hexagonal honeycomb model and micromechanics model of composite materials, the micromechanics model of heterogeneous Plateau porous structure in this study is more suitable for characterizing the medium-density porous material and more accurate for predicting the effective elastic constants of the medium-density porous material. Moreover, the obtained explicit expressions of the effective elastic constants in term of the relative density rather than the microstructural parameters for the uniform and regular Plateau porous structure are more convenient to engineering application.
基金Supported by the National Natural Science Foundation of China (Grant No. 50775184)the National Basic Research Program of China (Grant No. 2006CB601-205)+2 种基金the Aeronautical Science Foundation (Grant No. 2008ZA53007)the Doctorate Foundation of Northwestern Polytechnical University (Grant No. CX200610)the State Key Laboratory of Advanced Design and Manufacturing for Vehicle Body, Hunan University (Grant No. 30715003)
文摘With the wide demands of cellular materials applications in aerospace and civil engineering,research effort sacrificed for this type of materials attains nowadays a higher level than ever before.This paper is focused on the prediction methods of effective Young's modulus for periodical cellular materials.Based on comprehensive studies of the existing homogenization method(HM),the G-A meso-mechanics method(G-A MMM) and the stretching energy method(SEM) that are unable to reflect the size effect,we propose the bending energy method(BEM) for the first time,and a comparative study of these four methods is further made to show the generality and the capability of capturing the size effect of the BEM method.Meanwhile,the underlying characteristics of each method and their relations are clarified.To do this,the detailed finite element computing and existing experimental results of hexagonal honeycombs from the literature are adopted as the standard of comparison for the above four methods.Stretch and bending models of periodical cellular materials are taken into account,respectively for the comparison of stretch and flexural displacements resulting from the above methods.We conclude that the BEM has the strong ability of both predicting the effective Young's modulus and revealing the size effect.Such a method is also able to predict well the variations of structural displacements in terms of the cell size under stretching and bending loads including the non-monotonous variations for the hexagonal cell.On the contrary,other three methods can only predict the limited results whenever the cell size tends to be infinitely small.
基金Supported by National Science Foundationthe National Lab of MMC at Shanghai Jiaotong University.
文摘This paper presents a direct Mori-Tanaka approach to calculate the effective moduli of particle-reinforced composites and fiber-reinforced composites with spring-like imperfect interfaces. By a comparison between these results and those obtained from the approximate Mori-Tanaka method developed by Qu for composites with slightly weakened interface, the validity of the Qu's method is revealed.
基金the framework of the RFBR project 16-58-48009 IND omi and DST.
文摘This paper concerns the homogenization problems for porous piezocomposites with infinitely thin metalized pore surfaces.To determine the effective properties,we used the effective moduli method and the finite element approaches,realized in the ANSYS package.As a simple model of the representative volume,we applied a unit cell of porous piezoceramic material in the form of a cube with one spherical pore.We modeled metallization by introducing an additional layer of material with very large permittivity coefficients along the pore boundary.Then we simulated the nonuniform polarization field around the pore.For taking this effect into account,we previously solved the electrostatic problem for a porous dielectric material with the same geometric structure.From this problem,we obtained the polarization field in the porous piezomaterial;after that,we modified the material properties of the finite elements from dielectric to piezoelectric with element coordinate systems whose corresponding axes rotated along the polarization vectors.As a result,we obtained the porous unit cell of an inhomogeneously polarized piezoceramic matrix.From the solutions of these homogenization problems,we observed that the examined porous piezoceramics composite with metalized pore boundaries has more extensive effective transverse and shear piezomoduli,and effective dielectric constants compared to the conventional porous piezoceramics.The analysis also showed that the effect of the polarization field inhomogeneity is insignificant on the ordinary porous piezoceramics;however,it is more significant on the porous piezoceramics with metalized pore surfaces.
基金the Ministry of Science and Innovation of Spain for financial support(Nos.RTI2018098075-B-C21 and RTI2018-098075-B-C22)the EU through the European Regional Development Funds(No.MINECO-FEDER,EU)+1 种基金Generalitat de Catalunya(No.2017SGR-1165)the KTT Excellence Program,funded by the European Union through the European Regional Development Fund(EDF),the Government of Catalonia and the UPC。
文摘One of the biggest challenges in the biocompatibility of implantable metals is the prevention of the stress shielding effect,which is related to the coupling of the bone-metal mechanical properties.This stress shielding phenomenon provokes bone resorption and the consequent adverse effects on prosthesis fixation.However,it can be inhibited by adapting the stiffness of the implant material.Since the use of titanium(Ti)porous structures is a great alternative not only to inhibit this effect but also to improve the osteointegration of orthopedic and dental implants,a brief description of the techniques used for their manufacturing and a review of the current commercialized implants produced from porous Ti assemblies are compiled in this work.As powder metallurgy(PM)with space holder(SH)is a powerful technology used to produce porous Ti structures,it is here discussed its potential for the fabrication of medical devices from the perspectives of both design and manufacture.The most important parameters of the technique such as the size and shape of the initial metallic particles,the SH and binder type of materials,the compaction pressure of the green form,and in the sintering stage,the temperature,atmosphere,and time are reviewed according to the bibliography reported.Furthermore,the importance of the porosity and its types together with the influence of the mentioned parameters in the final porosity and,consequently,in the ultimate mechanical properties of the structure are discussed.Finally,a few examples of the PM-SH application for the manufacturing of orthopedic implants are presented.
