2011 Vol. 28, No. 1
2011, 28(1): 1-7.
Abstract:
Nano-SiO2/poly (glycerol-sebacate-citrate)(PGSC) bioelastomer composites were prepared by solvent assistant in-situ dispersion technique, and their structure and properties were characterized by FTIR, SEM, WXRD, DSC and tensile tests. Results demonstrate that nano-SiO2 is imbedded in the PGSC matrixes, and chemical bonding is formed between them. Nano-SiO2 presents finer and more homogeneous dispersion with the increasing of its mass fractions. The ordered structures of the matrixes are weakened after nano-SiO2 is added, but the ordered structures of the composites are intensified with the formation of inorganic filler networks. The glass transition temperature (Tg) of the matrix increases when the nano-SiO2 mass fraction is lower, while the Tg decreases when its mass fraction is higher. The composites possess excellent resilience, and their tensile strength and modulus rise with the increasing of nano-SiO2 mass fractions, separately rising by 602.20% and 258.21% at its mass fraction of 16.67% than those of the pure matrixes.
Nano-SiO2/poly (glycerol-sebacate-citrate)(PGSC) bioelastomer composites were prepared by solvent assistant in-situ dispersion technique, and their structure and properties were characterized by FTIR, SEM, WXRD, DSC and tensile tests. Results demonstrate that nano-SiO2 is imbedded in the PGSC matrixes, and chemical bonding is formed between them. Nano-SiO2 presents finer and more homogeneous dispersion with the increasing of its mass fractions. The ordered structures of the matrixes are weakened after nano-SiO2 is added, but the ordered structures of the composites are intensified with the formation of inorganic filler networks. The glass transition temperature (Tg) of the matrix increases when the nano-SiO2 mass fraction is lower, while the Tg decreases when its mass fraction is higher. The composites possess excellent resilience, and their tensile strength and modulus rise with the increasing of nano-SiO2 mass fractions, separately rising by 602.20% and 258.21% at its mass fraction of 16.67% than those of the pure matrixes.
2011, 28(1): 8-14.
Abstract:
A device for thermal insulation performance of high-temperature materials was designed and established to test light mass thermal insulation materials via a rapid and simple procedure. The thermal insulation performance of carbon fiber/phenolic composite and ZrO2 fiberboard were tested by this device when the temperature at the center point of hot face was 1600℃±10℃. The heat transport process of ZrO2 fiberboard was numerically simulated by finite-difference method, and the effective thermal conductivity was also predicted. The results show that thermal insulation performance of carbon fiber/phenolic composite is better than that of ZrO2 fiberboard from the beginning of test to 400s, while the thermal insulation performance of ZrO2 fiberboard is better from 400s to the end of test. Thermal insulation performance of ZrO2 fiberboard is affected by the bulk density, and the effective thermal conductivity of ZrO2 fiberboard increases nonlinearly with the elevated temperature.
A device for thermal insulation performance of high-temperature materials was designed and established to test light mass thermal insulation materials via a rapid and simple procedure. The thermal insulation performance of carbon fiber/phenolic composite and ZrO2 fiberboard were tested by this device when the temperature at the center point of hot face was 1600℃±10℃. The heat transport process of ZrO2 fiberboard was numerically simulated by finite-difference method, and the effective thermal conductivity was also predicted. The results show that thermal insulation performance of carbon fiber/phenolic composite is better than that of ZrO2 fiberboard from the beginning of test to 400s, while the thermal insulation performance of ZrO2 fiberboard is better from 400s to the end of test. Thermal insulation performance of ZrO2 fiberboard is affected by the bulk density, and the effective thermal conductivity of ZrO2 fiberboard increases nonlinearly with the elevated temperature.
2011, 28(1): 15-20.
Abstract:
A new high performance benzoxazine resin (BA21) for RTM technique was prepared. The processing property and cure schedule of BA21 resin, and mechanical properties of BA21 matrix composites using RTM were studied. The viscosity tests show that BA21 can meet to the require ments of RTM process. A chemorheology model based on the modified dual-Arrhenius equation was proposed . The model that agrees well with the experimental data can provide a theoretic support for t he mold-filling stage in the RTM process. The overall reaction orders of BA21 were estimated from the isothermal DSC tests based on a modified Kamal kinetics model, and 200 ℃ was chosen as the postcure temperature of the composites. The composites with high fiber contents were prepared by the RTM technique. The fl exure strength and modulus of these composites are up to 600 MPa and 30 GPa, respectively, and the impact strength is up to 200 kJ/ m2.
A new high performance benzoxazine resin (BA21) for RTM technique was prepared. The processing property and cure schedule of BA21 resin, and mechanical properties of BA21 matrix composites using RTM were studied. The viscosity tests show that BA21 can meet to the require ments of RTM process. A chemorheology model based on the modified dual-Arrhenius equation was proposed . The model that agrees well with the experimental data can provide a theoretic support for t he mold-filling stage in the RTM process. The overall reaction orders of BA21 were estimated from the isothermal DSC tests based on a modified Kamal kinetics model, and 200 ℃ was chosen as the postcure temperature of the composites. The composites with high fiber contents were prepared by the RTM technique. The fl exure strength and modulus of these composites are up to 600 MPa and 30 GPa, respectively, and the impact strength is up to 200 kJ/ m2.
2011, 28(1): 21-25.
Abstract:
To investigate the synergistic effect of the drug 5-fluorouracil(5-Fu) and indomethacin(IDMC), the microspheres of poly(L-lactide) with IDMC and 5-Fu were prepared by the technique of solution-enhanced dispersion by supercritical CO2 (SEDS), using dichloromethane/dimethyl sulfoxide as a cosolvent system. A single factor method was used to explore the best external conditions. The morphology, drug loading, particle size distribution and release profiles of 5-Fu-IDMC-PLLA microspheres were characterized, and the in vitro cell culture was designed and performed. The results indicate that 39℃, 14MPa is the preferable condition for the microspheres preparation when the ratio of the cosolvent is 30∶1. The microspheres exhibite a good spherical morphology, a particle size distribution between 0.5~ 5μm, which possess a sustained-release property and enhanced after composited with IDMC. The in vitro cell culture experiment show that the drug-loaded microspheres significantly inhibite the proliferation of A549 cell line, but the relative growth rate (RGR) of the two group of cells cultured with the microspheres before and after composition IDMC have no significant difference.
To investigate the synergistic effect of the drug 5-fluorouracil(5-Fu) and indomethacin(IDMC), the microspheres of poly(L-lactide) with IDMC and 5-Fu were prepared by the technique of solution-enhanced dispersion by supercritical CO2 (SEDS), using dichloromethane/dimethyl sulfoxide as a cosolvent system. A single factor method was used to explore the best external conditions. The morphology, drug loading, particle size distribution and release profiles of 5-Fu-IDMC-PLLA microspheres were characterized, and the in vitro cell culture was designed and performed. The results indicate that 39℃, 14MPa is the preferable condition for the microspheres preparation when the ratio of the cosolvent is 30∶1. The microspheres exhibite a good spherical morphology, a particle size distribution between 0.5~ 5μm, which possess a sustained-release property and enhanced after composited with IDMC. The in vitro cell culture experiment show that the drug-loaded microspheres significantly inhibite the proliferation of A549 cell line, but the relative growth rate (RGR) of the two group of cells cultured with the microspheres before and after composition IDMC have no significant difference.
2011, 28(1): 26-30.
Abstract:
Ring-opening polymerization of L-lactide was successfully used to prepare single-walled carbon nanotube/poly(L-lactide)(SWCNTs/PLA) composites, and its degradability and thermal stability were explored. Fourier transform infrared (FTIR) spectra, Raman spectra, thermogravimetric (TGA) analysis and scanning electron microscopy were used to characterize the products.The results show that ring-opening polymerization takes place between the functionalized SWCNTs and L-lactide , resulting in attachment of poly(L-lactide) (PLA) chains to SWCNTs, and the SWCNTs/PLA composites can be hydrolyzed under alkaline solution. The DSC study suggests that the presence of functionalized SWCNTs can enhance the glass transition temperature (Tg) of the composite campared with pure PLA.
Ring-opening polymerization of L-lactide was successfully used to prepare single-walled carbon nanotube/poly(L-lactide)(SWCNTs/PLA) composites, and its degradability and thermal stability were explored. Fourier transform infrared (FTIR) spectra, Raman spectra, thermogravimetric (TGA) analysis and scanning electron microscopy were used to characterize the products.The results show that ring-opening polymerization takes place between the functionalized SWCNTs and L-lactide , resulting in attachment of poly(L-lactide) (PLA) chains to SWCNTs, and the SWCNTs/PLA composites can be hydrolyzed under alkaline solution. The DSC study suggests that the presence of functionalized SWCNTs can enhance the glass transition temperature (Tg) of the composite campared with pure PLA.
2011, 28(1): 31-36.
Abstract:
The short glass fiber (SGF) reinforced composites were prepared by the injection molding using acrylonitrile-butadiene-styrene copolymer (ABS) and the short glass fibers as the raw materials, styrene-maleic anhydride copolymer (SMA) and epoxy resin(EP) as the compatibilizer. The effects of compatibilizer on the mechanical properties and interfacial adhesion of the composites were investigated using SEM, dynamic mechanical analysis (DMTA) and mechanical measurement. It was found that the mechanical properties of SGF/ABS composites could be improved by the incorporation of SMA or EP. Compared to the composites without compatibilizer, the tensile strength, flexural strength and impact strength could be improved by 56%, 42% and 79% respectively for SGF/EP-SMA-ABS composites with 30% mass fraction of short glass fibers . SEM and DMTA reveal that the incorporation of SMA and EP could introduce great improvement to the composites.
The short glass fiber (SGF) reinforced composites were prepared by the injection molding using acrylonitrile-butadiene-styrene copolymer (ABS) and the short glass fibers as the raw materials, styrene-maleic anhydride copolymer (SMA) and epoxy resin(EP) as the compatibilizer. The effects of compatibilizer on the mechanical properties and interfacial adhesion of the composites were investigated using SEM, dynamic mechanical analysis (DMTA) and mechanical measurement. It was found that the mechanical properties of SGF/ABS composites could be improved by the incorporation of SMA or EP. Compared to the composites without compatibilizer, the tensile strength, flexural strength and impact strength could be improved by 56%, 42% and 79% respectively for SGF/EP-SMA-ABS composites with 30% mass fraction of short glass fibers . SEM and DMTA reveal that the incorporation of SMA and EP could introduce great improvement to the composites.
2011, 28(1): 37-42.
Abstract:
In order to develop environment-friendly wood adhesive, the thermosetting process and the rheological properties of the blending adhesive consisted of konjac glucomannan (KGM), chitosan (CA) and polyvinyl alcohol (PVA) were investigated by DSC and rheometer. The results show that the rheological behavior of adhesives is significantly nonlinear. The relationship between the viscosity and the shear rate fit the Cross model well, while the dependence of the viscosity on the temperature can meet the Arrhenius equation well in which the pre-exponential factor is 1.25×10-6Pa·s and the flow activation enthalpy is 54.24kJ/mol. The fourth order polynomials can be used to fit the frequency curves which show that average molecular mass of adhesive decreases gradually with the temperature increase while wider molecular mass distribution of adhesive reverse. The gelling temperature, gel time, glass transition temperature and heating temperature are 110.4℃, 20.1min, 87.4℃ and 130℃ respectively according to the temperature and time curves.
In order to develop environment-friendly wood adhesive, the thermosetting process and the rheological properties of the blending adhesive consisted of konjac glucomannan (KGM), chitosan (CA) and polyvinyl alcohol (PVA) were investigated by DSC and rheometer. The results show that the rheological behavior of adhesives is significantly nonlinear. The relationship between the viscosity and the shear rate fit the Cross model well, while the dependence of the viscosity on the temperature can meet the Arrhenius equation well in which the pre-exponential factor is 1.25×10-6Pa·s and the flow activation enthalpy is 54.24kJ/mol. The fourth order polynomials can be used to fit the frequency curves which show that average molecular mass of adhesive decreases gradually with the temperature increase while wider molecular mass distribution of adhesive reverse. The gelling temperature, gel time, glass transition temperature and heating temperature are 110.4℃, 20.1min, 87.4℃ and 130℃ respectively according to the temperature and time curves.
2011, 28(1): 43-49.
Abstract:
Sm2O3/epoxy resin composite materials were prepared by the method of surface treatment. Polycyclic acid samarium(Sm(AA)3)/epoxy resin composite materials were prepared via the route of graft copolymerization. The composite materials microstructure was studied and compared by X-ray diffraction(XRD) and scanning electron microscope(SEM). The mechanical property of the materials was also tested and compared. Gamma energy spectrum system and Gamma vision software were used to measure and calculate their radiation shielding property. The results show that preparation of Sm(AA)3/epoxy resin composite is more complex and the element of Sm in it is more homogeneous. Its mechanical property is better than Sm2O3/epoxy resin composite . But the concentration of Sm in polyacrylic acid samarium/epoxy resin can only increase to 11%. For low energy photon, concentration of Sm is the key factor that can affect the shield capability of the composite while distribution of Sm is the key factor for high energy photon.
Sm2O3/epoxy resin composite materials were prepared by the method of surface treatment. Polycyclic acid samarium(Sm(AA)3)/epoxy resin composite materials were prepared via the route of graft copolymerization. The composite materials microstructure was studied and compared by X-ray diffraction(XRD) and scanning electron microscope(SEM). The mechanical property of the materials was also tested and compared. Gamma energy spectrum system and Gamma vision software were used to measure and calculate their radiation shielding property. The results show that preparation of Sm(AA)3/epoxy resin composite is more complex and the element of Sm in it is more homogeneous. Its mechanical property is better than Sm2O3/epoxy resin composite . But the concentration of Sm in polyacrylic acid samarium/epoxy resin can only increase to 11%. For low energy photon, concentration of Sm is the key factor that can affect the shield capability of the composite while distribution of Sm is the key factor for high energy photon.
2011, 28(1): 50-55.
Abstract:
The micro-morphologies of porous poly(vinyl alcohol) (PVA) hydrogel with different porous structures were observed. The digital speckle correlation method (DSCM) connected with mechanical properties test was used to investigate the deformation of porous hydrogel. The deformation of micro-fields, compressive modulus and Poisson’s ratio of porous hydrogel were compared under different compressive loads. The pore size and porosity of different structures significantly affect the distribution of iso-displacement lines. It is revealed that the iso-displacement lines are equality and approximately parallel in hydrogels with unconnected porous structure, but are tortuous and "S" like in hydrogels with connected porous structure. The field, in which the iso-displacement lines are intensive, is the area of stress concentration. The deformation is increased with adding porosity. The Poisson’s ratio of hydrogel is decreased with increasing of load and content of porogen. The compression modulus is increased with increasing of the strain.
The micro-morphologies of porous poly(vinyl alcohol) (PVA) hydrogel with different porous structures were observed. The digital speckle correlation method (DSCM) connected with mechanical properties test was used to investigate the deformation of porous hydrogel. The deformation of micro-fields, compressive modulus and Poisson’s ratio of porous hydrogel were compared under different compressive loads. The pore size and porosity of different structures significantly affect the distribution of iso-displacement lines. It is revealed that the iso-displacement lines are equality and approximately parallel in hydrogels with unconnected porous structure, but are tortuous and "S" like in hydrogels with connected porous structure. The field, in which the iso-displacement lines are intensive, is the area of stress concentration. The deformation is increased with adding porosity. The Poisson’s ratio of hydrogel is decreased with increasing of load and content of porogen. The compression modulus is increased with increasing of the strain.
2011, 28(1): 56-60.
Abstract:
The straw fibers were treated with different methods and modifiers, and blended with poly(butylene succinate)(PBS) to modify PBS. The straw fiber/PBS composites were prepared by hot-pressing. The effects of boiling processes and microwave treatment on the extraction of the straw fibers, as well as impacts of the type of modifiers and its addition on the straw fiber and properties of the straw fiber/PBS composites were studied. SEM was used to observe the surface morphology of the straw fibers before and after the treatment. The results show that straw fibers boiled for 30min twice, processed continuously by microwave for 15min, respectively get the best specimen. The straw fibers treated in the latter way have a looser property but larger specific surface than that processed the former, and the straw fiber/PBS composites have a better combination property and the best mechanical property under stearic acid condition of about 3.5%.
The straw fibers were treated with different methods and modifiers, and blended with poly(butylene succinate)(PBS) to modify PBS. The straw fiber/PBS composites were prepared by hot-pressing. The effects of boiling processes and microwave treatment on the extraction of the straw fibers, as well as impacts of the type of modifiers and its addition on the straw fiber and properties of the straw fiber/PBS composites were studied. SEM was used to observe the surface morphology of the straw fibers before and after the treatment. The results show that straw fibers boiled for 30min twice, processed continuously by microwave for 15min, respectively get the best specimen. The straw fibers treated in the latter way have a looser property but larger specific surface than that processed the former, and the straw fiber/PBS composites have a better combination property and the best mechanical property under stearic acid condition of about 3.5%.
2011, 28(1): 61-67.
Abstract:
Poly(N-isopropylacrylamide-co-acrylic amide) superporous hydrogels were prepared by dispersion polymerization in foam state using N-isopropylacrylamide (NIPA) and acrylic amide (AM) as monomers, ammonium persulfate (APS) as initiator, N, N’-Methylene-bis-acrylamide (BIS) as crosslink agent . Its swelling ratio and deswelling ratio were measured when the molar content of AM, the dosages of initiator or crosslink agent or HCI or NaHCO3 were changed. The structure of SPH was characterized by DSC, FTIR and SEM. The results show that lower critical solution temperature(LCST) of P(NIPA-co-AM) gels is improved with the increasing molar content of AM. The hydrogel prepared at condition of x(AM)=20%, ρ(APS)=20g/L, ρ(BIS)=3.5g/L, c(HCI)= 0. 55mol/L, ρ(NaHCO3)= 5.0×102g/L, is more superporous which has higher swelling ratio and deswelling ratio, and good temperature sensitive properties, which makes it possible to load and release with macromolecular drugs.
Poly(N-isopropylacrylamide-co-acrylic amide) superporous hydrogels were prepared by dispersion polymerization in foam state using N-isopropylacrylamide (NIPA) and acrylic amide (AM) as monomers, ammonium persulfate (APS) as initiator, N, N’-Methylene-bis-acrylamide (BIS) as crosslink agent . Its swelling ratio and deswelling ratio were measured when the molar content of AM, the dosages of initiator or crosslink agent or HCI or NaHCO3 were changed. The structure of SPH was characterized by DSC, FTIR and SEM. The results show that lower critical solution temperature(LCST) of P(NIPA-co-AM) gels is improved with the increasing molar content of AM. The hydrogel prepared at condition of x(AM)=20%, ρ(APS)=20g/L, ρ(BIS)=3.5g/L, c(HCI)= 0. 55mol/L, ρ(NaHCO3)= 5.0×102g/L, is more superporous which has higher swelling ratio and deswelling ratio, and good temperature sensitive properties, which makes it possible to load and release with macromolecular drugs.
2011, 28(1): 68-71.
Abstract:
Polyhedal oligomeric silsequioxane (POSS)/ethylene-propylene-diene-monomer rubber (EPDM) hybrid materials were prepared by twin roller mixing with octaphenylsilsequioxane (OVP), EPDM and vulcanizing agent.The mechanical properties and the flame retardcy of the hybrid materials were studied.The thermal stability and heat release rate (HRR) of the hybrid materials were investigated with thermo gravimetric analyzer and cone calorimeter.Comparing with the pure EPDM, the limited oxygen index (LOI) and thermal stability of POSS/EPDM with OVP are increased dramatically, the p-HRR of POSS/EPDM with OVP is decreased remarkably.The LOI is increased by 11.8%, the temperature of degradation is increased by 51℃, the HRR is decreased by 25.8%, the content of residue is 1.58 times as that of pure EPDM when 0.88% mass fraction OVP is added.The results show that OVP has great application value.
Polyhedal oligomeric silsequioxane (POSS)/ethylene-propylene-diene-monomer rubber (EPDM) hybrid materials were prepared by twin roller mixing with octaphenylsilsequioxane (OVP), EPDM and vulcanizing agent.The mechanical properties and the flame retardcy of the hybrid materials were studied.The thermal stability and heat release rate (HRR) of the hybrid materials were investigated with thermo gravimetric analyzer and cone calorimeter.Comparing with the pure EPDM, the limited oxygen index (LOI) and thermal stability of POSS/EPDM with OVP are increased dramatically, the p-HRR of POSS/EPDM with OVP is decreased remarkably.The LOI is increased by 11.8%, the temperature of degradation is increased by 51℃, the HRR is decreased by 25.8%, the content of residue is 1.58 times as that of pure EPDM when 0.88% mass fraction OVP is added.The results show that OVP has great application value.
Synthesis and magnetic properties of magnetic-improved SBA 15 mesoporous composites by nanoparticles
2011, 28(1): 72-76.
Abstract:
The nano-Co3O4 and nano-CoFe2O4 modified SBA-15 magnetic mesoporous, Co3O4 /SBA-15 and CoFe2O4/SBA-15 composites were prepared by immersion method. The microstructure and magnetic properties of the composites were analyzed by X-ray diffraction (XRD), transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM) and vibrating sample magnetometer (VSM). All results indicate that Co3O4 and CoFe2O4 nanoparticles exist in the mesopores of SBA-15, which can improve the magnetic properties of the SBA-15 nanocomposites. The study reveals that the magnetic properties of SBA-15 nanocomposites are attributed to the doped magnetic nanoparticles. And the magnetic properties are improved with the content of Co3O4 and CoFe2O4 nanoparticles, in which the coercivity reaches the maximum of 400 Oe and the saturation magnetization is 9emu/g.
The nano-Co3O4 and nano-CoFe2O4 modified SBA-15 magnetic mesoporous, Co3O4 /SBA-15 and CoFe2O4/SBA-15 composites were prepared by immersion method. The microstructure and magnetic properties of the composites were analyzed by X-ray diffraction (XRD), transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM) and vibrating sample magnetometer (VSM). All results indicate that Co3O4 and CoFe2O4 nanoparticles exist in the mesopores of SBA-15, which can improve the magnetic properties of the SBA-15 nanocomposites. The study reveals that the magnetic properties of SBA-15 nanocomposites are attributed to the doped magnetic nanoparticles. And the magnetic properties are improved with the content of Co3O4 and CoFe2O4 nanoparticles, in which the coercivity reaches the maximum of 400 Oe and the saturation magnetization is 9emu/g.
2011, 28(1): 77-81.
Abstract:
CaO stabilized ZrO2 powders were calcined with certain content of SiO2 at 1400℃, the obtained powders were used to fabricate coatings with different Ca2SiO4 contents (mass fraction: 20％, 40％, 60％) by atmospheric plasma spraying technology. The morphology and phase composition of the ZrO2 modified CaO-SiO2 coatings were characterized by X-ray diffraction (XRD), electronic probe microanalyzer (EPMA) and energy dispersive spectrometry (EDS). The composite coatings were immersed in simulated body fluid (SBF) and Tris-HCl buffer solution for the in vitro appraisement of bioactivity and stability. The results show that the formation ability of apatite on the surface of the coatings is related with Ca2SiO4 content in the coatings. The apatite precipitation becomes difficult on the coating’s surface with Ca2SiO4 content lower than 40％. The dissolution rate of the coatings in Tris-HCl solution increases with increase of Ca2SiO4 content.
CaO stabilized ZrO2 powders were calcined with certain content of SiO2 at 1400℃, the obtained powders were used to fabricate coatings with different Ca2SiO4 contents (mass fraction: 20％, 40％, 60％) by atmospheric plasma spraying technology. The morphology and phase composition of the ZrO2 modified CaO-SiO2 coatings were characterized by X-ray diffraction (XRD), electronic probe microanalyzer (EPMA) and energy dispersive spectrometry (EDS). The composite coatings were immersed in simulated body fluid (SBF) and Tris-HCl buffer solution for the in vitro appraisement of bioactivity and stability. The results show that the formation ability of apatite on the surface of the coatings is related with Ca2SiO4 content in the coatings. The apatite precipitation becomes difficult on the coating’s surface with Ca2SiO4 content lower than 40％. The dissolution rate of the coatings in Tris-HCl solution increases with increase of Ca2SiO4 content.
2011, 28(1): 82-87.
Abstract:
The nHA/Mg-2.5Zn-0.5Zr(mass fraction, %)composites, prepared by melting method in an argon gas atmosphere and electromagnetic stirring, were cultured with rat osteoblasts to investigate the biocompatibility in vitro compared to magnesium-matrix material. The results both of the two groups show no obvious cytotoxicity, while the cellular morphology is better and the cell density is higher in the nHA/Mg-2.5Zn-0.5Zr group than in the magnesium-matrix group. The cell growth curve shows osteoblast proliferation is greater on the nHA/Mg-2.5Zn-0.5Zr composites than on the magnesium-matrix material during the prescribed time periods, meanwhile, there are statistical differences between the two groups after 3 and 5 days of culture. Under the SEM observation, the cell responses to the samples were different, the osteoblasts attached very well to the composites with the shape of shuttle and/or triangular, and the cells were in a close contact with each other. The cells in the magnesium-matrix control group appeared with a spindle-shape, which indicated a weak adhesion to the material.
The nHA/Mg-2.5Zn-0.5Zr(mass fraction, %)composites, prepared by melting method in an argon gas atmosphere and electromagnetic stirring, were cultured with rat osteoblasts to investigate the biocompatibility in vitro compared to magnesium-matrix material. The results both of the two groups show no obvious cytotoxicity, while the cellular morphology is better and the cell density is higher in the nHA/Mg-2.5Zn-0.5Zr group than in the magnesium-matrix group. The cell growth curve shows osteoblast proliferation is greater on the nHA/Mg-2.5Zn-0.5Zr composites than on the magnesium-matrix material during the prescribed time periods, meanwhile, there are statistical differences between the two groups after 3 and 5 days of culture. Under the SEM observation, the cell responses to the samples were different, the osteoblasts attached very well to the composites with the shape of shuttle and/or triangular, and the cells were in a close contact with each other. The cells in the magnesium-matrix control group appeared with a spindle-shape, which indicated a weak adhesion to the material.
2011, 28(1): 88-93.
Abstract:
Joining of pressureless sintered SiC was carried out by the reaction joining process using the mixture of hydrogen-containing polysiloxane and vinyl-containing polysiloxane (denoted by HPSO-VPSO) with additive Al-Si powders as joining materials. The pyrolysis of HPSO-VPSO with Al-Si powders was studied by thermogravimetry, differential scanning calorimetry and X-ray diffraction. The effects of the joining temperature, the content of Al-Si powders and the heating rate on the joining strength of joints were investigated. The microstructure and composition of interfacial area were analyzed by scanning electron microscopy and energy dispersive spectrometry. The results show that the additive Al-Si powders promote the pyrolysis of HPSO-VPSO and lead to the increase of the ceramic yield per unit HPSO-VPSO. The maximum shearing strength of the joints is obtained to be 93MPa at the joining pressure of 50kPa, the joining temperature of 900℃, the holding time of 30min, the heating rate of 4℃/min and the Al-Si powders mass fraction of 50%. Microstructure study reveals that the thickness of the interlayer is about 75μm, and the contact at the interfaces is intact without obvious pores and cracks. The interdiffusion of Al and Si takes place at the interfacial area, which contributes to the interfacial bonding, resulting in the increase of the joining strength of the joints.
Joining of pressureless sintered SiC was carried out by the reaction joining process using the mixture of hydrogen-containing polysiloxane and vinyl-containing polysiloxane (denoted by HPSO-VPSO) with additive Al-Si powders as joining materials. The pyrolysis of HPSO-VPSO with Al-Si powders was studied by thermogravimetry, differential scanning calorimetry and X-ray diffraction. The effects of the joining temperature, the content of Al-Si powders and the heating rate on the joining strength of joints were investigated. The microstructure and composition of interfacial area were analyzed by scanning electron microscopy and energy dispersive spectrometry. The results show that the additive Al-Si powders promote the pyrolysis of HPSO-VPSO and lead to the increase of the ceramic yield per unit HPSO-VPSO. The maximum shearing strength of the joints is obtained to be 93MPa at the joining pressure of 50kPa, the joining temperature of 900℃, the holding time of 30min, the heating rate of 4℃/min and the Al-Si powders mass fraction of 50%. Microstructure study reveals that the thickness of the interlayer is about 75μm, and the contact at the interfaces is intact without obvious pores and cracks. The interdiffusion of Al and Si takes place at the interfacial area, which contributes to the interfacial bonding, resulting in the increase of the joining strength of the joints.
2011, 28(1): 94-98.
Abstract:
The Mg4Nb2O9-CaTiO3 composite ceramics were synthesised by the conventional solid-state reaction. The effects of Li2CO3-V2O5 (LV) addition on the sintering behavior, microstructure and microwave dielectric properties of Mg4Nb2O9/CaTiO3 ceramics were investigated. It is found that an amount LV co-doped can effectively low the desification sintering temperature to 1200℃ of Mg4Nb2O9/CaTiO3 ceramics. Two-phase system was confirmed by the XRD and EDX spectrum analysis. A near zero temperature coefficient of resonant frequency was obtained. Inparticular, a new Mg4Nb2O9-CaTiO3 ceramics with 1.5% mass fraction of LV doped sintered at 1200℃ for 5h exhibited excellent microwave dieletric properties of ε=23.29, Qf=23460GHz and τf=1.0×10-6℃-1. It is proposed as a candidate subatrate material for GPS microstrip antenna.
The Mg4Nb2O9-CaTiO3 composite ceramics were synthesised by the conventional solid-state reaction. The effects of Li2CO3-V2O5 (LV) addition on the sintering behavior, microstructure and microwave dielectric properties of Mg4Nb2O9/CaTiO3 ceramics were investigated. It is found that an amount LV co-doped can effectively low the desification sintering temperature to 1200℃ of Mg4Nb2O9/CaTiO3 ceramics. Two-phase system was confirmed by the XRD and EDX spectrum analysis. A near zero temperature coefficient of resonant frequency was obtained. Inparticular, a new Mg4Nb2O9-CaTiO3 ceramics with 1.5% mass fraction of LV doped sintered at 1200℃ for 5h exhibited excellent microwave dieletric properties of ε=23.29, Qf=23460GHz and τf=1.0×10-6℃-1. It is proposed as a candidate subatrate material for GPS microstrip antenna.
2011, 28(1): 99-103.
Abstract:
A novel biodegradable scaffold was prepared by utilizing polymer microspheres as the building blocks for scaffold formation. This saffold can be used for cartilage and bone repair. Optical microscope, SEM method were used to investigate the inside and the surface characteristics of the scaffold.The mechanical performance and the porosity of the scaffold were also tested. Results show that this scaffold consists of two distinct yet continuous phases, one is composed by poly(L, D-lactic-co-glycolic acid) (PLGA) microspheres, the other is composed by PLGA/Bioglass(BG) microspheres; the composite scaffolds have 3-D interconnective porous structure. The data of porosity also indicate that the porosity is independent of microsphere diameter in the range of diameters examined. Porosity is (53.37±4.39)% when the size of microspheres is between 150μm and 200μm and the compressive stress is 0.9MPa when compressive strain is 10%. With the decrease of the microspheres size, the porosity of the scaffold gradually increases.This scaffold shows potential as polymeric substitutes for bone and cartilage repair.
A novel biodegradable scaffold was prepared by utilizing polymer microspheres as the building blocks for scaffold formation. This saffold can be used for cartilage and bone repair. Optical microscope, SEM method were used to investigate the inside and the surface characteristics of the scaffold.The mechanical performance and the porosity of the scaffold were also tested. Results show that this scaffold consists of two distinct yet continuous phases, one is composed by poly(L, D-lactic-co-glycolic acid) (PLGA) microspheres, the other is composed by PLGA/Bioglass(BG) microspheres; the composite scaffolds have 3-D interconnective porous structure. The data of porosity also indicate that the porosity is independent of microsphere diameter in the range of diameters examined. Porosity is (53.37±4.39)% when the size of microspheres is between 150μm and 200μm and the compressive stress is 0.9MPa when compressive strain is 10%. With the decrease of the microspheres size, the porosity of the scaffold gradually increases.This scaffold shows potential as polymeric substitutes for bone and cartilage repair.
2011, 28(1): 104-108.
Abstract:
The chitosan/polycaprolactone(CS/PCL) vascular scaffolds were prepared by electrospinning in order to combine the advantage of chitosan(CS) and polycaprolactone(PCL) into the vascular scaffolds. The obtained CS/PCL vascular scaffolds were characterized by SEM and electronic universal testing machine. The endothelial progenitor cells(EPCs) were implanted in the scaffolds with various mass ratios of CS to PCL. The vascular scaffolds were examined by adhesion rate in different culturing times and the cells breeding was observed. The obtained CS/PCL vascular scaffolds show porous, nano-structured surfaces, similar to the natural extracellular matrix. When the mass ratio of CS to PCL is 0.5, the breaking elongation of CS/PCL vascular scaffolds reaches 31.64%, and the curves of stress-strain indicate that the obtained vascular scaffolds possess good elastic deformation. The adhesion rate of EPCs on CS/PCL vascular scaffolds is 95.1%, the observation of EPCs labeled with CM-DiI(chlormethylbenzamido-1, 1 dioctadecy l-3, 3, 3', 3'-tetramethylindocarbocyamine)after culturing 72 h by fluorescence microscopy also illustrates that CS/PCL vascular scaffolds are beneficial to cell growth and cell adhesion.
The chitosan/polycaprolactone(CS/PCL) vascular scaffolds were prepared by electrospinning in order to combine the advantage of chitosan(CS) and polycaprolactone(PCL) into the vascular scaffolds. The obtained CS/PCL vascular scaffolds were characterized by SEM and electronic universal testing machine. The endothelial progenitor cells(EPCs) were implanted in the scaffolds with various mass ratios of CS to PCL. The vascular scaffolds were examined by adhesion rate in different culturing times and the cells breeding was observed. The obtained CS/PCL vascular scaffolds show porous, nano-structured surfaces, similar to the natural extracellular matrix. When the mass ratio of CS to PCL is 0.5, the breaking elongation of CS/PCL vascular scaffolds reaches 31.64%, and the curves of stress-strain indicate that the obtained vascular scaffolds possess good elastic deformation. The adhesion rate of EPCs on CS/PCL vascular scaffolds is 95.1%, the observation of EPCs labeled with CM-DiI(chlormethylbenzamido-1, 1 dioctadecy l-3, 3, 3', 3'-tetramethylindocarbocyamine)after culturing 72 h by fluorescence microscopy also illustrates that CS/PCL vascular scaffolds are beneficial to cell growth and cell adhesion.
2011, 28(1): 109-113.
Abstract:
In this paper, nanoscale bioactive glass particles with different morphologies were prepared through adding citric acid in a sol-gel process. The structure of as-prepared samples was characterized using specific surface area analysis apparatus、 SEM and TEM. The results indicate that just using citric acid as hydrolysis catalyst can easily control the nanostructure and morphology of bioactive glass and is in favor of preparing the bioactive glass with smaller particle size, larger specific surface area and pore volume. This procedure can serve a simple mean with low cost to produce nanoscale bioactive glass and control its morphology.
In this paper, nanoscale bioactive glass particles with different morphologies were prepared through adding citric acid in a sol-gel process. The structure of as-prepared samples was characterized using specific surface area analysis apparatus、 SEM and TEM. The results indicate that just using citric acid as hydrolysis catalyst can easily control the nanostructure and morphology of bioactive glass and is in favor of preparing the bioactive glass with smaller particle size, larger specific surface area and pore volume. This procedure can serve a simple mean with low cost to produce nanoscale bioactive glass and control its morphology.
2011, 28(1): 114-118.
Abstract:
The silane coupling agent was used to modify the inorganic bioactive glass (BG) surface aiming at improving affinity with polymer. BG was prepared by sol-gel method, then 3-aminopropyltriethoxysilane (APTES) was grafted onto BG surface. FTIR, TG and laser particle size analyzer were adopted to characterize BG before and after modification, and the cell biocompatibility of the material was studied preliminarily through cell culture. The results show that stretching vibration attributed to saturated C—H appears in FTIR spectrum of modified BG, and remarkable mass loss resulted from combustion of organic group is observed in DTG curve, which suggest that APTES has been bonded onto BG surface. The MC-3T3 cell proliferation measurement and SEM photos show that the modified BG is in favor of the cell growth and proliferation compared with unmodified BG.
The silane coupling agent was used to modify the inorganic bioactive glass (BG) surface aiming at improving affinity with polymer. BG was prepared by sol-gel method, then 3-aminopropyltriethoxysilane (APTES) was grafted onto BG surface. FTIR, TG and laser particle size analyzer were adopted to characterize BG before and after modification, and the cell biocompatibility of the material was studied preliminarily through cell culture. The results show that stretching vibration attributed to saturated C—H appears in FTIR spectrum of modified BG, and remarkable mass loss resulted from combustion of organic group is observed in DTG curve, which suggest that APTES has been bonded onto BG surface. The MC-3T3 cell proliferation measurement and SEM photos show that the modified BG is in favor of the cell growth and proliferation compared with unmodified BG.
2011, 28(1): 119-123.
Abstract:
The composites of bis(8-hydroxyquinoline) zinc (Znq2) and carbon microspheres (CMSs) were synthesized by rheological phase reaction. Their structure and photoluminescence property were characterized by the field emission scanning electron microscopy, X-ray diffraction, thermogravimetry, X-ray photoelectron spectroscopy, Fourier transformation infrared absorption spectrometry and fluorospectrophotometer. The results show that Znq2 is loaded on the surfaces of uniform CMSs with 300~400 nm in diameters in the form of non-covalent bond and the peak wavelength of the composite is 540 nm in photoluminescence spectra. It is expected to apply in the field of organic electroluminescence for Znq2/CMSs composite.
The composites of bis(8-hydroxyquinoline) zinc (Znq2) and carbon microspheres (CMSs) were synthesized by rheological phase reaction. Their structure and photoluminescence property were characterized by the field emission scanning electron microscopy, X-ray diffraction, thermogravimetry, X-ray photoelectron spectroscopy, Fourier transformation infrared absorption spectrometry and fluorospectrophotometer. The results show that Znq2 is loaded on the surfaces of uniform CMSs with 300~400 nm in diameters in the form of non-covalent bond and the peak wavelength of the composite is 540 nm in photoluminescence spectra. It is expected to apply in the field of organic electroluminescence for Znq2/CMSs composite.
2011, 28(1): 124-131.
Abstract:
The strength of a thick-walled vessel with alternate-ply filament winding(FW) outside an isotropic liner under internal and external pressure was investigated by three-dimensional (3D) orthotropic stress-strain relation and axisymmetric thick-walled cylinder theory. The stresses of the liner and the fiber layer, as well as longitudinal stress along the fiber direction, transverse stresses perpendicular to the fiber direction and shear stress were obtained analytically. Using Hoffman failure criteria and Tsai-Wu 3D failure criteria, the strength of the filament layer of FW cylinder with respect to thickness and winding angle was investigated by the thin-walled theory and 3D theory, respectively. The strength of FW vessel with a liner with respect to winding angle was compared numerically with FW vessel without a liner. Numeric results of finite element (FE) model were presented in ANSYS software by layered element SOLID191, and perfect agreement of stresses in fiber directions and strength ratio between FEA and the theory was achieved. It is found that the laminate theory gives imprecise two dimensional fiber stresses, in which transverse stresses lead to lower strength estimation. The influence of the thickness-radius ratio to strength ratio is different for different filament types and winding angles, and the strength ratio given by 3D stress analysis under external pressure is far beyond the thin-walled theory. The comparison shows that the strength ratio of FW vessel without a liner is more sensitive to winding angle than the vessel with a liner.
The strength of a thick-walled vessel with alternate-ply filament winding(FW) outside an isotropic liner under internal and external pressure was investigated by three-dimensional (3D) orthotropic stress-strain relation and axisymmetric thick-walled cylinder theory. The stresses of the liner and the fiber layer, as well as longitudinal stress along the fiber direction, transverse stresses perpendicular to the fiber direction and shear stress were obtained analytically. Using Hoffman failure criteria and Tsai-Wu 3D failure criteria, the strength of the filament layer of FW cylinder with respect to thickness and winding angle was investigated by the thin-walled theory and 3D theory, respectively. The strength of FW vessel with a liner with respect to winding angle was compared numerically with FW vessel without a liner. Numeric results of finite element (FE) model were presented in ANSYS software by layered element SOLID191, and perfect agreement of stresses in fiber directions and strength ratio between FEA and the theory was achieved. It is found that the laminate theory gives imprecise two dimensional fiber stresses, in which transverse stresses lead to lower strength estimation. The influence of the thickness-radius ratio to strength ratio is different for different filament types and winding angles, and the strength ratio given by 3D stress analysis under external pressure is far beyond the thin-walled theory. The comparison shows that the strength ratio of FW vessel without a liner is more sensitive to winding angle than the vessel with a liner.
2011, 28(1): 132-137.
Abstract:
Considering the layer thicknesses, fiber angles and materials properties as random variables, the variation of buckling strengths for composite sandwich plates was analyzed. With the stochastic finite element method (SFEM) based on high-order shear deformation theory (HSDT), the influences of fiber angles and side-to-thickness ratios on the coefficient of variance (COV) of buckling strengths for composite sandwich plates with different stacking sequences were studied. The sensitivity degrees of COV indicate the main effect factors for buckling strengths variances of sandwich plates, and the results are meaningful for material manufacture processes improvement for increasing the buckling reliability of composite sandwich plates.
Considering the layer thicknesses, fiber angles and materials properties as random variables, the variation of buckling strengths for composite sandwich plates was analyzed. With the stochastic finite element method (SFEM) based on high-order shear deformation theory (HSDT), the influences of fiber angles and side-to-thickness ratios on the coefficient of variance (COV) of buckling strengths for composite sandwich plates with different stacking sequences were studied. The sensitivity degrees of COV indicate the main effect factors for buckling strengths variances of sandwich plates, and the results are meaningful for material manufacture processes improvement for increasing the buckling reliability of composite sandwich plates.
2011, 28(1): 138-142.
Abstract:
The elastic properties of three-dimensional woven carbon fiber reinforced C-SiC binary matrix(3D woven C/C-SiC) composite were studied. Based on the scanning electron micrographs (SEM) of 3D woven C/C-SiC composite, the micro-structure was analyzed, a series of assumptions were proposed, and the micro-mechanical model was founded. The elastic properties of 3D woven C/C-SiC composite are evaluated with homogenization method. The variable regularity of elastic modulus is also studied as the warp angle increases. The results of the numerical calculation agree with the experiments very well, and the method of numerical calculation is proved to be accurate; as the warp angle increases, the elastic modulus in the warp direction decreases and the elastic moduli in other directions increase, but the in-plane shear modulus and the elastic modulus in thickness direction increase a little.
The elastic properties of three-dimensional woven carbon fiber reinforced C-SiC binary matrix(3D woven C/C-SiC) composite were studied. Based on the scanning electron micrographs (SEM) of 3D woven C/C-SiC composite, the micro-structure was analyzed, a series of assumptions were proposed, and the micro-mechanical model was founded. The elastic properties of 3D woven C/C-SiC composite are evaluated with homogenization method. The variable regularity of elastic modulus is also studied as the warp angle increases. The results of the numerical calculation agree with the experiments very well, and the method of numerical calculation is proved to be accurate; as the warp angle increases, the elastic modulus in the warp direction decreases and the elastic moduli in other directions increase, but the in-plane shear modulus and the elastic modulus in thickness direction increase a little.
2011, 28(1): 143-150.
Abstract:
Finite element model of a helicopter whole rotor blade was established through ANSYS software. The relation between vibration characteristics and damage position was obtained by simulating perforation damage at different locations in the blade spanwise and chordwise directions. And comparison was carried out with that of the undamaged blade. The effect of different perforation locations on vibration performance was analyzed. The results show that damage cannot induce the change of vibration generally but affects vibration frequencies. The effect on vibration frequencies not only relates with the damage locations but also with the damage degree of major structures. The damage at blade root influences the whole vibration frequencies obviously, while the damage in the leading and trailing edge affect lag frequencies greatest. The damage in the wing box has maximum affect on the twist frequencies. The larger the damage in the trailing-edge strip and the main beam is, the greater the effect of lag frequencies is. The relation between twist wrap, spar and inner twist wrap in the main beam with the twist frequencies is the same with the lag vibration.
Finite element model of a helicopter whole rotor blade was established through ANSYS software. The relation between vibration characteristics and damage position was obtained by simulating perforation damage at different locations in the blade spanwise and chordwise directions. And comparison was carried out with that of the undamaged blade. The effect of different perforation locations on vibration performance was analyzed. The results show that damage cannot induce the change of vibration generally but affects vibration frequencies. The effect on vibration frequencies not only relates with the damage locations but also with the damage degree of major structures. The damage at blade root influences the whole vibration frequencies obviously, while the damage in the leading and trailing edge affect lag frequencies greatest. The damage in the wing box has maximum affect on the twist frequencies. The larger the damage in the trailing-edge strip and the main beam is, the greater the effect of lag frequencies is. The relation between twist wrap, spar and inner twist wrap in the main beam with the twist frequencies is the same with the lag vibration.
2011, 28(1): 151-155.
Abstract:
The finite element model of the whole rotor blade was established to study the effect of perforation damage size and direction on vibration performance.For the rectangular section of blade root at z=50mm and the leading edge section of its midst at z=835mm, the relation between vibration performance and size of perforation damage was obtained by simulating different holes of perforation damage in the leading edge, wing box and trailing edge respectively.And the relation between vibration performance and perforation damage direction was also obtained by means of changing perforation damage direction of the leading edge.It shows that the damage cannot induce the change of vibration modality but affects vibration frequency.As the perforation hole is increased, the vibration frequencies go down wholly.When the damage arose in the leading and trailing edge, lag frequencies go down great, and lowing twist frequency mostly occurred in the wing box area.The effect of perforation on vibration frequency is concerned with not only the perforation location and structure, but also with the geometry of perforation section.When the perforation direction is at the angle with 75° and 105° to the blade chordwise in the root rectangular section, lag frequency is influenced maximum.While in the midst airfoil section, as the angle approaching to 0°(180°), twist frequency is effected greatest.
The finite element model of the whole rotor blade was established to study the effect of perforation damage size and direction on vibration performance.For the rectangular section of blade root at z=50mm and the leading edge section of its midst at z=835mm, the relation between vibration performance and size of perforation damage was obtained by simulating different holes of perforation damage in the leading edge, wing box and trailing edge respectively.And the relation between vibration performance and perforation damage direction was also obtained by means of changing perforation damage direction of the leading edge.It shows that the damage cannot induce the change of vibration modality but affects vibration frequency.As the perforation hole is increased, the vibration frequencies go down wholly.When the damage arose in the leading and trailing edge, lag frequencies go down great, and lowing twist frequency mostly occurred in the wing box area.The effect of perforation on vibration frequency is concerned with not only the perforation location and structure, but also with the geometry of perforation section.When the perforation direction is at the angle with 75° and 105° to the blade chordwise in the root rectangular section, lag frequency is influenced maximum.While in the midst airfoil section, as the angle approaching to 0°(180°), twist frequency is effected greatest.
2011, 28(1): 156-160.
Abstract:
A non-orthogonal constitutive model, previously developed by the authors to characterize the anisotropic material behavior of woven composite fabrics under large deformation, which results from the angle change between warp and weft yarns, was validated by a hemispherical stamping simulation of a square plain woven composite fabric at room temperature. As a comparison, the forming is simulated by using a corresponding orthotropic constitutive model. The simulation results show that the non-orthogonal constitutive model brings out almost the same boundary profile as that in the experiment and shear angles are in the experimental standard deviation range. While quite large discrepancy is found in the case with orthogonal constitutive model. The proposed non-orthogonal model is better than the orthogonal model in characterizing the anisotropic material behavior of woven composites under large shear deformation.
A non-orthogonal constitutive model, previously developed by the authors to characterize the anisotropic material behavior of woven composite fabrics under large deformation, which results from the angle change between warp and weft yarns, was validated by a hemispherical stamping simulation of a square plain woven composite fabric at room temperature. As a comparison, the forming is simulated by using a corresponding orthotropic constitutive model. The simulation results show that the non-orthogonal constitutive model brings out almost the same boundary profile as that in the experiment and shear angles are in the experimental standard deviation range. While quite large discrepancy is found in the case with orthogonal constitutive model. The proposed non-orthogonal model is better than the orthogonal model in characterizing the anisotropic material behavior of woven composites under large shear deformation.
2011, 28(1): 161-165.
Abstract:
The effects of fiber angel orientation and mixed-mode ratio of interlaminar fracture on the properties of delamination were experimentally studied in the laminate propogates. The results show that 0°ply is able to stop delaminating from jumping into adjacent plies in mode Ⅰ interlaminar fracture; fracture toughness of unidirectional laminate at all mixed-mode ratios could be regarded as the conservative value; the curve of mixed-mode fracture toughness resembles sine as the mixed-mode ratio varies.
The effects of fiber angel orientation and mixed-mode ratio of interlaminar fracture on the properties of delamination were experimentally studied in the laminate propogates. The results show that 0°ply is able to stop delaminating from jumping into adjacent plies in mode Ⅰ interlaminar fracture; fracture toughness of unidirectional laminate at all mixed-mode ratios could be regarded as the conservative value; the curve of mixed-mode fracture toughness resembles sine as the mixed-mode ratio varies.
2011, 28(1): 166-171.
Abstract:
In order to explore the influence of Ni-coating thickness on the thermal residual stress in AZ91D magnesium matrix composite reinforced with Ni coated carbon nanotubes(Ni-CNTs/AZ91D), the distribution of the thermal residual stresses in Ni-CNTs/AZ91D composite was simulated by using finite element method(FEM)based on some experiments. The results indicate that plating Ni on CNTs’surface can greatly reduce the thermal residual stress of Ni-CNTs/AZ91D. For the Ni-CNTs/AZ91D composite materials, the thermal residual stress achieves the minimum at the thickness of Ni-coating is 6nm. While the thickness of Ni-coating is varying from 2nm to 6nm, the thermal residual stress is diminished with the increase of the thickness of Ni-coating. Once the thickness of Ni-coating is larger than 6nm, the thermal residual stress increases with increasing the thickness of Ni-coating. Moreover, the location of thermal residual stress’s maximum moves toward the interface of Ni-coating and substrate with increasing of the thickness of Ni-coating.
In order to explore the influence of Ni-coating thickness on the thermal residual stress in AZ91D magnesium matrix composite reinforced with Ni coated carbon nanotubes(Ni-CNTs/AZ91D), the distribution of the thermal residual stresses in Ni-CNTs/AZ91D composite was simulated by using finite element method(FEM)based on some experiments. The results indicate that plating Ni on CNTs’surface can greatly reduce the thermal residual stress of Ni-CNTs/AZ91D. For the Ni-CNTs/AZ91D composite materials, the thermal residual stress achieves the minimum at the thickness of Ni-coating is 6nm. While the thickness of Ni-coating is varying from 2nm to 6nm, the thermal residual stress is diminished with the increase of the thickness of Ni-coating. Once the thickness of Ni-coating is larger than 6nm, the thermal residual stress increases with increasing the thickness of Ni-coating. Moreover, the location of thermal residual stress’s maximum moves toward the interface of Ni-coating and substrate with increasing of the thickness of Ni-coating.
2011, 28(1): 172-177.
Abstract:
The interfacial reinforcement mechanism of composite sandwich beams has been studied by experiment and numerical method. The sandwich beam specimens were manufactured by the vacuum assisted resin injection process and an experimental investigation was also performed to determine interfacial fracture toughness for the sandwich specimens with and without chopped fiber reinforcement. A meso-mechanical model considering energy dissipation was adopted to describe the process of single fiber peeling and pull-out as the crack extended. And a stochastic uniform distribution model was established to characterize the energy dissipation of overall chopped fibers per unit area. A finite element model was used to simulate the process of interfacial crack growth for a double cantilever beam. A nonlinear spring element was employed to account for bridging stress caused by the chopped fiber and the energy release rate was calculated by the virtual crack closure technique. Some numerical results and discussions were given for verifying the validity of the meso-mechanical model with stochastic distribution provided. The experimental and numerical investigation indicates that the chopped fiber reinforcement was an effective technique to improve the load capacity and interfacial toughness of the sandwich structures.
The interfacial reinforcement mechanism of composite sandwich beams has been studied by experiment and numerical method. The sandwich beam specimens were manufactured by the vacuum assisted resin injection process and an experimental investigation was also performed to determine interfacial fracture toughness for the sandwich specimens with and without chopped fiber reinforcement. A meso-mechanical model considering energy dissipation was adopted to describe the process of single fiber peeling and pull-out as the crack extended. And a stochastic uniform distribution model was established to characterize the energy dissipation of overall chopped fibers per unit area. A finite element model was used to simulate the process of interfacial crack growth for a double cantilever beam. A nonlinear spring element was employed to account for bridging stress caused by the chopped fiber and the energy release rate was calculated by the virtual crack closure technique. Some numerical results and discussions were given for verifying the validity of the meso-mechanical model with stochastic distribution provided. The experimental and numerical investigation indicates that the chopped fiber reinforcement was an effective technique to improve the load capacity and interfacial toughness of the sandwich structures.
2011, 28(1): 178-185.
Abstract:
The uniaxial tensile stress-strain behavior of cross-ply ceramic matrix composites has been investigated using a micro-mechanical approach. The shear-lag model was adopted to obtain the micro stress field of the damaged composites. The fracture mechanics approach, critical matrix strain energy criterion, strain energy release rate criterion and Curtin’s statistical approaches were used to determine transverse crack space of 90° ply, matrix crack space of 0° ply, fiber/matrix interface debonded length and fiber failure volume fraction. By combining the shear-lag model with the failure criterion, the tensile stress-strain curve of each damage stage was modeled, and the exact model of predicting the toughness and strength of the composite was established. The uniaxial tensile stress-strain curve of cross-ply ceramic matrix composite at room temperature was compared with the present analysis. The stress-strain curve of each damage stage, the failure strength and failure strain agree well with the experimental data. The effects of fracture energy of 90° ply, fiber/matrix interface shear stress, interface debonded energy, and fiber Weibull modulus on the damage of the composite and the stress-strain curve were also investigated.
The uniaxial tensile stress-strain behavior of cross-ply ceramic matrix composites has been investigated using a micro-mechanical approach. The shear-lag model was adopted to obtain the micro stress field of the damaged composites. The fracture mechanics approach, critical matrix strain energy criterion, strain energy release rate criterion and Curtin’s statistical approaches were used to determine transverse crack space of 90° ply, matrix crack space of 0° ply, fiber/matrix interface debonded length and fiber failure volume fraction. By combining the shear-lag model with the failure criterion, the tensile stress-strain curve of each damage stage was modeled, and the exact model of predicting the toughness and strength of the composite was established. The uniaxial tensile stress-strain curve of cross-ply ceramic matrix composite at room temperature was compared with the present analysis. The stress-strain curve of each damage stage, the failure strength and failure strain agree well with the experimental data. The effects of fracture energy of 90° ply, fiber/matrix interface shear stress, interface debonded energy, and fiber Weibull modulus on the damage of the composite and the stress-strain curve were also investigated.
2011, 28(1): 186-193.
Abstract:
To overcome the problem of frequency dispersion, multi-mode and mode convention of Lamb wave signal propagation on composite structures, a spatial filter based strunctural damage imaging method improved by Hilbert transform was proposed. The principle of signal synthesis and imaging based on spatial filter was analyzed. Based on the principle, Hilbert transform was adopted to construct analytic signals of time domain response signals of sensors to participate in the process of signals synthesis and imaging. Imaging of simulating acoustic source was done to validate the feasibility of this method, and then imaging of excitation source and damage on plate-like structures of carbon fiber composite materials was performed to validate the function of this method. The research shows that this method can recognize the angle of damage and the time-of-arrival of damage scattering signals relative to the piezoelectric transducers array efficiently.
To overcome the problem of frequency dispersion, multi-mode and mode convention of Lamb wave signal propagation on composite structures, a spatial filter based strunctural damage imaging method improved by Hilbert transform was proposed. The principle of signal synthesis and imaging based on spatial filter was analyzed. Based on the principle, Hilbert transform was adopted to construct analytic signals of time domain response signals of sensors to participate in the process of signals synthesis and imaging. Imaging of simulating acoustic source was done to validate the feasibility of this method, and then imaging of excitation source and damage on plate-like structures of carbon fiber composite materials was performed to validate the function of this method. The research shows that this method can recognize the angle of damage and the time-of-arrival of damage scattering signals relative to the piezoelectric transducers array efficiently.
2011, 28(1): 194-198.
Abstract:
A linearly orthotropic constitutive model with maximum tensile stress failure criterion was developed by secondary development kit of LS-DYNA, and was coupled with Gruneison equation of state to describe the mechanic behaviors of Nomex-Kevlar plain woven fabric under the hypervelocity impact condition. A 3D numerical analysis model was created using LS-DYNA to simulate Al-2017-T4 spherical projectiles impacting Nomex-Kevlar plain woven fabric at 6.84km/s, 30° obliquity, which condition is as same as the test’s condition of NASA. Compared simulation results to test results, it shows that the developed material constitutive model and the numerical analysis model are suitable to describe the hypervelocity impact behaviors of Nomex-Kevlar plain woven fabric.
A linearly orthotropic constitutive model with maximum tensile stress failure criterion was developed by secondary development kit of LS-DYNA, and was coupled with Gruneison equation of state to describe the mechanic behaviors of Nomex-Kevlar plain woven fabric under the hypervelocity impact condition. A 3D numerical analysis model was created using LS-DYNA to simulate Al-2017-T4 spherical projectiles impacting Nomex-Kevlar plain woven fabric at 6.84km/s, 30° obliquity, which condition is as same as the test’s condition of NASA. Compared simulation results to test results, it shows that the developed material constitutive model and the numerical analysis model are suitable to describe the hypervelocity impact behaviors of Nomex-Kevlar plain woven fabric.
2011, 28(1): 199-205.
Abstract:
Based on infrared lock-in thermography technology, the nondestructive testing of composite grid stiffened structures with typical defects was carried out.The result was also analyzed using infrared lock-in thermography system developed by Cedip in France.The effects of loading frequency and output voltage offset to the testing result were discussed.The result shows that there are more information of phase figures than that of amplitude figures. Different frequencies will lead to different results and the loading frequency is the key to the success.Increasing the output voltage offset will make a useful contribution for better testing.This method is feasible to inspect the unknown defect of composite materials.
Based on infrared lock-in thermography technology, the nondestructive testing of composite grid stiffened structures with typical defects was carried out.The result was also analyzed using infrared lock-in thermography system developed by Cedip in France.The effects of loading frequency and output voltage offset to the testing result were discussed.The result shows that there are more information of phase figures than that of amplitude figures. Different frequencies will lead to different results and the loading frequency is the key to the success.Increasing the output voltage offset will make a useful contribution for better testing.This method is feasible to inspect the unknown defect of composite materials.
2011, 28(1): 206-210.
Abstract:
The compressive properties of one-third composite cylindrical shells were tested and theoretical analyzed. The test results show that the cylindrical shells failure in buckling. The finite element method was used to establish an analysis model of the shell. The model was used for the further static strength and buckling analysis. The results show that the static strength is much higher than the buckling strength. So the shell should fail in buckling at first. This is coordinate with the test result. And the buckling strength of this model also agrees with the test results well. This model can be used to analyze the compression behavior of the integrated composite cylindrical shell and the results would provide reference for cylindrical shell structure design. Comparing the strains of the model with that of the specimen at the corresponding points under a certain compressive load, it shows that the strains match each other and indicates the efficiency of the model.
The compressive properties of one-third composite cylindrical shells were tested and theoretical analyzed. The test results show that the cylindrical shells failure in buckling. The finite element method was used to establish an analysis model of the shell. The model was used for the further static strength and buckling analysis. The results show that the static strength is much higher than the buckling strength. So the shell should fail in buckling at first. This is coordinate with the test result. And the buckling strength of this model also agrees with the test results well. This model can be used to analyze the compression behavior of the integrated composite cylindrical shell and the results would provide reference for cylindrical shell structure design. Comparing the strains of the model with that of the specimen at the corresponding points under a certain compressive load, it shows that the strains match each other and indicates the efficiency of the model.
2011, 28(1): 211-217.
Abstract:
Based on the variational asymptotic method (VAM), an engineering model for piezoelectric composite shell under mechanical and electronic loads was established in order to efficient analyze the nonlinear, one-way coupled piezoelectric problem. The 3D energy expressions based on the decomposition of rotation tensor (DRT) were deduced. The 3D shell model was decomposed into a 2D, nonlinear shell analysis and a linear analysis through the normal direction based on VAM. The approximate energy after dimensionality reduction was deduced and converted to a form of Reissner-Mindlin model. The 3D field recovery relations were provided to obtain accurate stress distribution through the thickness. The cylindrical bending example of 4-layer piezoelectric composite shell shows that the 3D stress field recovered by the variational asymptotic plate and shell analysis program (VAPAS) based on this theory agrees better with the exact results than those of first-order shear deformation theory (FOSDT) and classic laminated theory (CLT), indicating the validity of this model.
Based on the variational asymptotic method (VAM), an engineering model for piezoelectric composite shell under mechanical and electronic loads was established in order to efficient analyze the nonlinear, one-way coupled piezoelectric problem. The 3D energy expressions based on the decomposition of rotation tensor (DRT) were deduced. The 3D shell model was decomposed into a 2D, nonlinear shell analysis and a linear analysis through the normal direction based on VAM. The approximate energy after dimensionality reduction was deduced and converted to a form of Reissner-Mindlin model. The 3D field recovery relations were provided to obtain accurate stress distribution through the thickness. The cylindrical bending example of 4-layer piezoelectric composite shell shows that the 3D stress field recovered by the variational asymptotic plate and shell analysis program (VAPAS) based on this theory agrees better with the exact results than those of first-order shear deformation theory (FOSDT) and classic laminated theory (CLT), indicating the validity of this model.
2011, 28(1): 218-222.
Abstract:
By means of the asymptotic method, the two-order two-scale asymptotic expansions coupled with boundary layer of the electrical potential and the displacement were built for the structures of general periodic composites under piezoelectric condition, the coupled relation between the displacement field and the electric field within basic cell is given, and the finite element method and the algorithm of two-scale coupled with boundary layer of the displacement and the electrical potential are presented. The effectiveness and high efficiency is shown by some simple numerical examples.
By means of the asymptotic method, the two-order two-scale asymptotic expansions coupled with boundary layer of the electrical potential and the displacement were built for the structures of general periodic composites under piezoelectric condition, the coupled relation between the displacement field and the electric field within basic cell is given, and the finite element method and the algorithm of two-scale coupled with boundary layer of the displacement and the electrical potential are presented. The effectiveness and high efficiency is shown by some simple numerical examples.
2011, 28(1): 223-229.
Abstract:
Damage analysis of axial tension specimen was implemented by stochastic progressive failure analysis and acoustic emission (AE) monitoring.The results show that the stochastic progressive failure analysis characteres failure of composite materials well. In the early load stage, the stochastic character of composite failure is apparent, and the failure occurs in the whole specimen. With the load increasing, damage accumulates, "stochastical critical nuclei" emerges and the composite fails completely and quickly.Once there is failure happens, fiber breakage number is positive correlative with AE events.The effect of matrix crack and interface debonding on the composites was also compared and it is found that interface debonding affects tensile strength drop of the composite more severely than matrix crack, if matrix crack and interface debonding are not taken into consideration, clustering characteristics of fiber fracture appears and the composite fails in brittle manner.
Damage analysis of axial tension specimen was implemented by stochastic progressive failure analysis and acoustic emission (AE) monitoring.The results show that the stochastic progressive failure analysis characteres failure of composite materials well. In the early load stage, the stochastic character of composite failure is apparent, and the failure occurs in the whole specimen. With the load increasing, damage accumulates, "stochastical critical nuclei" emerges and the composite fails completely and quickly.Once there is failure happens, fiber breakage number is positive correlative with AE events.The effect of matrix crack and interface debonding on the composites was also compared and it is found that interface debonding affects tensile strength drop of the composite more severely than matrix crack, if matrix crack and interface debonding are not taken into consideration, clustering characteristics of fiber fracture appears and the composite fails in brittle manner.
2011, 28(1): 230-234.
Abstract:
A new structual model was developed for the compressive analysis of 3D integrated sandwich composites by using the finite element software ANSYS. The influence of pile height, pile density and material elastic modulus of the 3D composites on the compressive properties was studied in detail, and the influence characterizations were analyzed and discussed too. The results show that the maximum value of the stress appears in the interface between pile and face-sheet when the 3D composites are subject under compressive loads, in which the composites damage easily. The compressive properties of the 3D composites increase with the increase of the pile density, material elastic molulus, and decrease with that of the pile height. The results provide reference for the structure optimum of the 3D composites.
A new structual model was developed for the compressive analysis of 3D integrated sandwich composites by using the finite element software ANSYS. The influence of pile height, pile density and material elastic modulus of the 3D composites on the compressive properties was studied in detail, and the influence characterizations were analyzed and discussed too. The results show that the maximum value of the stress appears in the interface between pile and face-sheet when the 3D composites are subject under compressive loads, in which the composites damage easily. The compressive properties of the 3D composites increase with the increase of the pile density, material elastic molulus, and decrease with that of the pile height. The results provide reference for the structure optimum of the 3D composites.
