2009 Vol. 26, No. 2
2009, 26(2): 1-5.
Abstract:
30 vol%Al2O3P/Al-2.26Mg-0.63Si composite was fabricated by the Pressure Infiltration Method for investigating the aging behavior of the composites with sub-micron Al2O3 particles. The corresponding matrix alloy was obtained by tailoring the Mg and Si contents of 6061Al. The aging behaviors of the composites and the corresponding matrix alloy were investigated by means of Brinell hardness test，SEM and TEM. The results show that the aging behavior of the matrix alloy of Al-2.26Mg-0.63Si is visible and the peak-aging time is put ahead with the aging temperature rise. The aging softening phenomenon appears at 190℃. The addition of sub-micron Al2O3 particles rest rains strongly the precipitation process within the matrix. There are no obvious aging peaks to appear in the aging-hardening curves of the composites. TEM observation shows that a mass of MgAl2O4 spinel forms in the interfaces , and atoms cannot diffuse efficiently for little dislocations existing in the matrix alloy. Therefore，GP zone does not grow-up at over-aged course within the composites，and the aging precipitation is restrained.
30 vol%Al2O3P/Al-2.26Mg-0.63Si composite was fabricated by the Pressure Infiltration Method for investigating the aging behavior of the composites with sub-micron Al2O3 particles. The corresponding matrix alloy was obtained by tailoring the Mg and Si contents of 6061Al. The aging behaviors of the composites and the corresponding matrix alloy were investigated by means of Brinell hardness test，SEM and TEM. The results show that the aging behavior of the matrix alloy of Al-2.26Mg-0.63Si is visible and the peak-aging time is put ahead with the aging temperature rise. The aging softening phenomenon appears at 190℃. The addition of sub-micron Al2O3 particles rest rains strongly the precipitation process within the matrix. There are no obvious aging peaks to appear in the aging-hardening curves of the composites. TEM observation shows that a mass of MgAl2O4 spinel forms in the interfaces , and atoms cannot diffuse efficiently for little dislocations existing in the matrix alloy. Therefore，GP zone does not grow-up at over-aged course within the composites，and the aging precipitation is restrained.
2009, 26(2): 6-10.
Abstract:
YAl 2P/ Mg-Li-Al composite was prepared by stir-casting. The mechanisms of the crack forming and the
propagation were investigated during the dynamic tension under the static load by SEM. The result s show that the microcracks appear at the casting defect s , in the Mg-Li-Al mat rix and on the interface of YAl 2P/ Mg-Li-Al
composite. The microcracks propagated mainly in mat rix or along the particle/ mat rix interface. The dominant crack is mainly developed along the boundary between the particle-dense regions and particle2f ree regions , and the samples lose the stability and f racture rapidly af ter the cracks propagating to some extent . The mat rix failure may play a significant role in the failure mechanism of YAl 2P/ Mg-Li-Al composite.
YAl 2P/ Mg-Li-Al composite was prepared by stir-casting. The mechanisms of the crack forming and the
propagation were investigated during the dynamic tension under the static load by SEM. The result s show that the microcracks appear at the casting defect s , in the Mg-Li-Al mat rix and on the interface of YAl 2P/ Mg-Li-Al
composite. The microcracks propagated mainly in mat rix or along the particle/ mat rix interface. The dominant crack is mainly developed along the boundary between the particle-dense regions and particle2f ree regions , and the samples lose the stability and f racture rapidly af ter the cracks propagating to some extent . The mat rix failure may play a significant role in the failure mechanism of YAl 2P/ Mg-Li-Al composite.
2009, 26(2): 11-17.
Abstract:
The newly developed lead-free solders should have good mechanical properties，as well as excellent creep resistance in order to meet the needs of reliability required by electronic industries. Nano-sized polyhedral oligomeric silsesquioxane (POSS) reinforcement particles were incorporated into the promising lead-free solder，Sn-3. 5Ag，to improve the mechanical property of the lead-free solder. Experimental results show that the thickness of intermetallic compound (IMC) layer between solder and substrate Cu is restrained when the mass fraction of POSS is less than 2%. The composite solders contain different POSS reinforcement types and mass fractions，and their joints possess better mechanical properties. The creep rupture lives are enhanced in the composite solder joint at different temperatures and different stress combinations compared to the Sn-3.5Ag solder joint，especially at low temperatures.
The newly developed lead-free solders should have good mechanical properties，as well as excellent creep resistance in order to meet the needs of reliability required by electronic industries. Nano-sized polyhedral oligomeric silsesquioxane (POSS) reinforcement particles were incorporated into the promising lead-free solder，Sn-3. 5Ag，to improve the mechanical property of the lead-free solder. Experimental results show that the thickness of intermetallic compound (IMC) layer between solder and substrate Cu is restrained when the mass fraction of POSS is less than 2%. The composite solders contain different POSS reinforcement types and mass fractions，and their joints possess better mechanical properties. The creep rupture lives are enhanced in the composite solder joint at different temperatures and different stress combinations compared to the Sn-3.5Ag solder joint，especially at low temperatures.
2009, 26(2): 18-24.
Abstract:
Based on the mesoscopic finite element model of particle reinforced composites，the time-dependent ratcheting behavior of SiCP/6061Al composites was numerically analyzed at room and high temperatures by employing a three-dimensional (3D) multi-particulate unit cell and advanced cyclic visco-plastic constitutive model .In the simulation，the effects of the particulate arrangement and interfacial binding state on the ratcheting of the composites were discussed. Some microscopic deformation features in the matrix and the interface were also analyzed. The uniaxial time-dependent ratcheting of SiCP/6061Al composites was simulated by the finite element model with a suitable choice of the interfacial bonding parameters，and the predicting capability of the model was addressed by comparison with the experimental results. The results show that more microscopic details of the composites can be reflected by using the 3D multi-particulate unit cell，and the particulate arrangement influences the ratcheting of the composites significantly；the better the interfacial bonding，the smaller the ratcheting strain；the weak interface model with suitable interfacial parameters provides more reasonable simulation to the time-dependent ratcheting of the composites than the perfect interface model does.
Based on the mesoscopic finite element model of particle reinforced composites，the time-dependent ratcheting behavior of SiCP/6061Al composites was numerically analyzed at room and high temperatures by employing a three-dimensional (3D) multi-particulate unit cell and advanced cyclic visco-plastic constitutive model .In the simulation，the effects of the particulate arrangement and interfacial binding state on the ratcheting of the composites were discussed. Some microscopic deformation features in the matrix and the interface were also analyzed. The uniaxial time-dependent ratcheting of SiCP/6061Al composites was simulated by the finite element model with a suitable choice of the interfacial bonding parameters，and the predicting capability of the model was addressed by comparison with the experimental results. The results show that more microscopic details of the composites can be reflected by using the 3D multi-particulate unit cell，and the particulate arrangement influences the ratcheting of the composites significantly；the better the interfacial bonding，the smaller the ratcheting strain；the weak interface model with suitable interfacial parameters provides more reasonable simulation to the time-dependent ratcheting of the composites than the perfect interface model does.
2009, 26(2): 25-29.
Abstract:
Cu(NO3)2 was deposited into the nano-channels of mesoporous SBA-15 using the supercritical fluid deposition (SCFD) method at a pressure of about 20 MPa and a temperature of 50℃，where supercritical CO2 was employed as the solvent and ethanol as the cosolvent. The subsequent reduction of this composite (Cu(NO3)2/SBA-15) led to copper nanowires and/or nanoparticles dispersed in the channels of SBA-15. The resultant Cu/SBA-15 composites were characterized by means of TEM and XRD. The results showed that Cu nanowires with the mean diameter 6 nm grow and curve along the channels of SBA-15 and their lengths vary from several nanometers to several micrometers；while the Cu nanoparticles with sizes of ～ 3 nm are highly dispersed in the channels. Moreover，it is found that with proper cosolvent，inorganic metallic can be solved in supercritical CO2，and the morphology of copper can be controlled by changing the experimental conditions.
Cu(NO3)2 was deposited into the nano-channels of mesoporous SBA-15 using the supercritical fluid deposition (SCFD) method at a pressure of about 20 MPa and a temperature of 50℃，where supercritical CO2 was employed as the solvent and ethanol as the cosolvent. The subsequent reduction of this composite (Cu(NO3)2/SBA-15) led to copper nanowires and/or nanoparticles dispersed in the channels of SBA-15. The resultant Cu/SBA-15 composites were characterized by means of TEM and XRD. The results showed that Cu nanowires with the mean diameter 6 nm grow and curve along the channels of SBA-15 and their lengths vary from several nanometers to several micrometers；while the Cu nanoparticles with sizes of ～ 3 nm are highly dispersed in the channels. Moreover，it is found that with proper cosolvent，inorganic metallic can be solved in supercritical CO2，and the morphology of copper can be controlled by changing the experimental conditions.
2009, 26(2): 30-36.
Abstract:
Fe/Si3N4 composite powder was synthesized by the heterogeneous precipitation-thermal reduction process，and then pressed into flakes under a pressure of 10 MPa. The flakes were sintered by pressureless and hot-pressing at 1873K in 0.1 MPaN2. The chemical composition，microstructure and phases of the composite powder and the sintered flakes were investigated by scanning electron microscopy (SEM)，transmission electron microscopy (TEM)，energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). It is proved that the structure of the composite powders is Si3N4 coated by nano Fe. The crystal phases of sintered flakes by pressureless are iron silicide，SiC andSi3N4. The crystal phases of the sintered samples by hot-pressing are Fe，iron silicide and Si3N4. It is found that the crystal phases flakes by pressureless and hot-pressing are very different.
Fe/Si3N4 composite powder was synthesized by the heterogeneous precipitation-thermal reduction process，and then pressed into flakes under a pressure of 10 MPa. The flakes were sintered by pressureless and hot-pressing at 1873K in 0.1 MPaN2. The chemical composition，microstructure and phases of the composite powder and the sintered flakes were investigated by scanning electron microscopy (SEM)，transmission electron microscopy (TEM)，energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). It is proved that the structure of the composite powders is Si3N4 coated by nano Fe. The crystal phases of sintered flakes by pressureless are iron silicide，SiC andSi3N4. The crystal phases of the sintered samples by hot-pressing are Fe，iron silicide and Si3N4. It is found that the crystal phases flakes by pressureless and hot-pressing are very different.
2009, 26(2): 37-40.
Abstract:
Nickel-silicone rubber polymer composites were prepared using silicone rubber and nickel powder at a ratio of 1∶2. The effect of pressure and the dielectric properties of the composite samples at room temperature were measured. The results show that the resistance of samples under modest compression can fall f rom about 1×1012Ω to <10Ω，a change of 11 orders of magnitude. A resistance creep has also been observed：the resistance of samples under constant st ress decreases with time. The permit tivity and dielectric loss of the composite at room temperature decrease with increasing frequency but increase with application of uniaxial stress. This is because the special microstructure of a capacitor network formed by the metallic filler particles and the insulating polymer materials of the composite. Under uniaxial pressure，the distance between metallic particles decreases，leading to an increase in capacitance and conductivity , which in turn results in an increase in dielectric loss.
Nickel-silicone rubber polymer composites were prepared using silicone rubber and nickel powder at a ratio of 1∶2. The effect of pressure and the dielectric properties of the composite samples at room temperature were measured. The results show that the resistance of samples under modest compression can fall f rom about 1×1012Ω to <10Ω，a change of 11 orders of magnitude. A resistance creep has also been observed：the resistance of samples under constant st ress decreases with time. The permit tivity and dielectric loss of the composite at room temperature decrease with increasing frequency but increase with application of uniaxial stress. This is because the special microstructure of a capacitor network formed by the metallic filler particles and the insulating polymer materials of the composite. Under uniaxial pressure，the distance between metallic particles decreases，leading to an increase in capacitance and conductivity , which in turn results in an increase in dielectric loss.
2009, 26(2): 41-46.
Abstract:
In order to meet the requirements of high temperature proton exchange membrane fuel cells，HPA/SPAEEKS composite proton exchange membranes were prepared by solvent casting film. FTIR spectra prove that the strong interaction between sulfonated acidic groups and HPA particles has been formed. The SEM pictures show that the solid HPA particles uniformly disperse in the composite membranes matrix. The thermo-stability of composite membrane is improved due to the introduction of HPA particle. The Tg and T5%of HPA30/SPAEEKS-0.8 reach 236℃and 299℃respectively. The proton conductivity of HPA30/SPAEEKS-1. 0 composite membrane at 80℃ exceeds that of Nafion 117 under the same measured condition and reaches 0.098S/cm at 120℃.
In order to meet the requirements of high temperature proton exchange membrane fuel cells，HPA/SPAEEKS composite proton exchange membranes were prepared by solvent casting film. FTIR spectra prove that the strong interaction between sulfonated acidic groups and HPA particles has been formed. The SEM pictures show that the solid HPA particles uniformly disperse in the composite membranes matrix. The thermo-stability of composite membrane is improved due to the introduction of HPA particle. The Tg and T5%of HPA30/SPAEEKS-0.8 reach 236℃and 299℃respectively. The proton conductivity of HPA30/SPAEEKS-1. 0 composite membrane at 80℃ exceeds that of Nafion 117 under the same measured condition and reaches 0.098S/cm at 120℃.
2009, 26(2): 47-53.
Abstract:
The liquid crystalline polymer/nylon 6 (LCP/PA6) blends with dispersed LCP microspheres were prepared. An ionomer (Zn-SPS) and a reactive copolymer (SMA) were used as compatibilizers to improve the interfacial adhesion. The effects of LCP microspheres on the strength and toughness of LCP/PA6 blends were investigated. The morphological observation of samples after tensile tests shows that the dispersed LCP microspheres are well embedded in the PA6 matrix. The holes deform to some degree after LCP microspheres are pulled out during the fracture of the samples. The mechanical tests show that the addition of LCP decreases the tensile strength of blends due to the poor adhesion between the two phases，while the compatibilizers enhanced the tensile strength. With LCP mass fraction of 10%，the tensile strength of the compatibilized system is similar to that of pure PA6. The tensile energy of compatibilized systems is higher than that of corresponding uncompatibilized systems. With LCP mass fraction of 4%，the tensile fracture energy of Zn-SPS compatibilized system increases by 12% and 62% compared to that of LCP/PA6 and pure PA6， respectively. With LCP mass fraction of 10%，the tensile energy of SMA compatibilized system increases by 46% and 55% compared to LCP/PA6 and pure PA6，respectively. The results indicate that LCP microspheres can increase the toughness of the blends while kept the tensile strength under proper conditions.
The liquid crystalline polymer/nylon 6 (LCP/PA6) blends with dispersed LCP microspheres were prepared. An ionomer (Zn-SPS) and a reactive copolymer (SMA) were used as compatibilizers to improve the interfacial adhesion. The effects of LCP microspheres on the strength and toughness of LCP/PA6 blends were investigated. The morphological observation of samples after tensile tests shows that the dispersed LCP microspheres are well embedded in the PA6 matrix. The holes deform to some degree after LCP microspheres are pulled out during the fracture of the samples. The mechanical tests show that the addition of LCP decreases the tensile strength of blends due to the poor adhesion between the two phases，while the compatibilizers enhanced the tensile strength. With LCP mass fraction of 10%，the tensile strength of the compatibilized system is similar to that of pure PA6. The tensile energy of compatibilized systems is higher than that of corresponding uncompatibilized systems. With LCP mass fraction of 4%，the tensile fracture energy of Zn-SPS compatibilized system increases by 12% and 62% compared to that of LCP/PA6 and pure PA6， respectively. With LCP mass fraction of 10%，the tensile energy of SMA compatibilized system increases by 46% and 55% compared to LCP/PA6 and pure PA6，respectively. The results indicate that LCP microspheres can increase the toughness of the blends while kept the tensile strength under proper conditions.
2009, 26(2): 54-58.
Abstract:
OMMT/EVA-g-PU nanocomposites were prepared through the method of melting graft and melting intercalation. The characterization of FTIR and 13C-NMR indicates that —NCO terminated polyether-polyurethane prepolymer is grafted on the EVAL main chain successfully. The dispersion state of OMMT in matrix was observed by XRD and TEM. The mechanical properties and storage modulus and thermal stability were studied by the microcomputer-cont rolled electronic tensile tester and DMA and TG. The results indicate that the chief dispersion state of OMMT in EVA-g-PU matrix is intercalated. When the mass fraction of OMMT is 3%，the tensile strength，Young‘s modulus and tear strength are 7.96 MPa，7.12 MPa and 49.97 MPa，respectively. The storage modulus of nanocomposites increase with the increase of OMMT amount . When the mass fraction of OMMT is 7%，the storage modulus of nanocomposites is 2 times than that of pure EVA. The thermal stability of OMMT/EVA-g-PU nanocomposites is far superior to that of pure EVA with the increase of OMMT amount .
OMMT/EVA-g-PU nanocomposites were prepared through the method of melting graft and melting intercalation. The characterization of FTIR and 13C-NMR indicates that —NCO terminated polyether-polyurethane prepolymer is grafted on the EVAL main chain successfully. The dispersion state of OMMT in matrix was observed by XRD and TEM. The mechanical properties and storage modulus and thermal stability were studied by the microcomputer-cont rolled electronic tensile tester and DMA and TG. The results indicate that the chief dispersion state of OMMT in EVA-g-PU matrix is intercalated. When the mass fraction of OMMT is 3%，the tensile strength，Young‘s modulus and tear strength are 7.96 MPa，7.12 MPa and 49.97 MPa，respectively. The storage modulus of nanocomposites increase with the increase of OMMT amount . When the mass fraction of OMMT is 7%，the storage modulus of nanocomposites is 2 times than that of pure EVA. The thermal stability of OMMT/EVA-g-PU nanocomposites is far superior to that of pure EVA with the increase of OMMT amount .
2009, 26(2): 59-66.
Abstract:
Polypropylene (PP) matrix composites，reinforced with nonmetals recycled from waste printed circuit boards and milled glass fibers，respectively，were prepared by the melt blending method. The effects of the two reinforcing materials and surface modification on the strengthening of PP matrix were investigated based on the results of mechanical properties and impact fracture surface morphologies of the composites，and on the surface morphologies of the two reinforcing materials. The results show that both strength and rigidity of the composites can be successfully reinforced by filling the two materials. The maximum increment of tensile strength，tensile modulus，flexural st rength and flexural modulus of the nonmetals/PP composites is 28%，41%，86% and 133%，respectively，but the toughness decreases. The surface modification of nonmetals has little effect on the mechanical properties of the composites，while the surface modification of the milled glass fibers has a great effect. The nonmetals recycled are more effective in improving the mechanical properties of the composites than the milled glass fibers，and can replace milled glass fibers as reinforcing fillers in the PP composites，which provides a promising way for resolving the environmental pollutions，recycling resources and reducing the composite materials cost.
Polypropylene (PP) matrix composites，reinforced with nonmetals recycled from waste printed circuit boards and milled glass fibers，respectively，were prepared by the melt blending method. The effects of the two reinforcing materials and surface modification on the strengthening of PP matrix were investigated based on the results of mechanical properties and impact fracture surface morphologies of the composites，and on the surface morphologies of the two reinforcing materials. The results show that both strength and rigidity of the composites can be successfully reinforced by filling the two materials. The maximum increment of tensile strength，tensile modulus，flexural st rength and flexural modulus of the nonmetals/PP composites is 28%，41%，86% and 133%，respectively，but the toughness decreases. The surface modification of nonmetals has little effect on the mechanical properties of the composites，while the surface modification of the milled glass fibers has a great effect. The nonmetals recycled are more effective in improving the mechanical properties of the composites than the milled glass fibers，and can replace milled glass fibers as reinforcing fillers in the PP composites，which provides a promising way for resolving the environmental pollutions，recycling resources and reducing the composite materials cost.
2009, 26(2): 67-71.
Abstract:
The composites of low molecular weight functionalized polyisobutene with montmorillonite were prepared as one of blend compatibilizers for improving the mechanical properties of polypropylene. The influences of active agent and blend temperature on the mechanical properties of the polyisobutene-montmorillonite/polypropylene composites were investigated. The SEM and TEM images of montmorillonite in the polypropylene matrix were observed. The results reveal that the montmorillonite disperses well in the polypropylene matrix because of the effect of the functionalized polyisobutene and the active agent. When 4wt% montmorillonite and 1wt% (of montmorillonite) active agent are used in the composites，the properties of polyisobutene-montmorillonite/polypropylene composite，such as modulus of 2280MPa，impact strength of 63J/m and recovery ratio of 0.5%，are obviously bet ter than those of the pure polypropylene. The size of montmorillonite dispersed in the polypropylene matrix is about 1μm.
The composites of low molecular weight functionalized polyisobutene with montmorillonite were prepared as one of blend compatibilizers for improving the mechanical properties of polypropylene. The influences of active agent and blend temperature on the mechanical properties of the polyisobutene-montmorillonite/polypropylene composites were investigated. The SEM and TEM images of montmorillonite in the polypropylene matrix were observed. The results reveal that the montmorillonite disperses well in the polypropylene matrix because of the effect of the functionalized polyisobutene and the active agent. When 4wt% montmorillonite and 1wt% (of montmorillonite) active agent are used in the composites，the properties of polyisobutene-montmorillonite/polypropylene composite，such as modulus of 2280MPa，impact strength of 63J/m and recovery ratio of 0.5%，are obviously bet ter than those of the pure polypropylene. The size of montmorillonite dispersed in the polypropylene matrix is about 1μm.
Relationship between the moisture absorption and properties of carbon fiber filament-wound NOL rings
2009, 26(2): 72-78.
Abstract:
An accelerated aging method to characterize the hygrothermal properties of carbon fiber (CF) filament-wound composite pressure vessels in storage and service process was presented based on filament-wound composite NOL rings. The hygrothermal aging behavior of the CF/epoxy NOL rings in distilled water at 35℃，55℃，65℃ and 75℃ was analyzed in terms of the absorption characteristics，static and dynamic mechanical properties. The CF/epoxy NOL rings display a three-stage absorption process，which is controlled in turn by diffusion in free volume，molecular relaxation and interface degradation. When the moisture content reaches about 1wt%，the ring shear strength and flexural strength decrease to 75% and 67%；meanwhile，the Tg decreases by 20℃. The results providea good basis for the prediction and estimation of the storage life of carbon fiber filament-wound composite pressure vessels.
An accelerated aging method to characterize the hygrothermal properties of carbon fiber (CF) filament-wound composite pressure vessels in storage and service process was presented based on filament-wound composite NOL rings. The hygrothermal aging behavior of the CF/epoxy NOL rings in distilled water at 35℃，55℃，65℃ and 75℃ was analyzed in terms of the absorption characteristics，static and dynamic mechanical properties. The CF/epoxy NOL rings display a three-stage absorption process，which is controlled in turn by diffusion in free volume，molecular relaxation and interface degradation. When the moisture content reaches about 1wt%，the ring shear strength and flexural strength decrease to 75% and 67%；meanwhile，the Tg decreases by 20℃. The results providea good basis for the prediction and estimation of the storage life of carbon fiber filament-wound composite pressure vessels.
2009, 26(2): 79-84.
Abstract:
The elect ospinning technique was used to produce multi-walled nanotubes (MWNTs) and polyurethane (PU) compound ultrafine fibers. Thermal stability and dynamic mechanical properties of MWNTs/PU non-wovens were examined by the thermogravimetric analysis and dynamic mechanical analysis. The relationship between the direct current electrical conductivity and the mass fraction of the MWNTs was tested. The dynamic electrical conductivity in the range from 40 Hz to 110 MHz was measured by a dielectric spectroscopy using an Agilent 4294A impedance analyzer. The results show that the thermal stability is improved significantly with increasing the content 10 of MWNTs in the compound ultrafine fibers. The electrical conductivity of the membranes is improved 10 times compared with that of the pure PU when the mass fraction of MWNTs is 40 %.
The elect ospinning technique was used to produce multi-walled nanotubes (MWNTs) and polyurethane (PU) compound ultrafine fibers. Thermal stability and dynamic mechanical properties of MWNTs/PU non-wovens were examined by the thermogravimetric analysis and dynamic mechanical analysis. The relationship between the direct current electrical conductivity and the mass fraction of the MWNTs was tested. The dynamic electrical conductivity in the range from 40 Hz to 110 MHz was measured by a dielectric spectroscopy using an Agilent 4294A impedance analyzer. The results show that the thermal stability is improved significantly with increasing the content 10 of MWNTs in the compound ultrafine fibers. The electrical conductivity of the membranes is improved 10 times compared with that of the pure PU when the mass fraction of MWNTs is 40 %.
2009, 26(2): 85-89.
Abstract:
The chemo-rheological behavior of low temperature curing bisphenol- F epoxy resin for vacuum assisted resin transfer molding was studied by means of viscosity experiments. An engineering viscosity model was established and used to simulate the rheological behavior of the epoxy resin system. The estimated viscosity values of the established model are in good agreement with the experimental ones. The glass transition temperature，tensile strength and bending strength of the epoxy resin reach 111.9℃，78.5 MPa and 106 MPa，respectively. The engineering model can be used to predict the processing windows of different processing parameters of VARTM process，which is critical for the simulation and optimization of composite manufacturing processes.
The chemo-rheological behavior of low temperature curing bisphenol- F epoxy resin for vacuum assisted resin transfer molding was studied by means of viscosity experiments. An engineering viscosity model was established and used to simulate the rheological behavior of the epoxy resin system. The estimated viscosity values of the established model are in good agreement with the experimental ones. The glass transition temperature，tensile strength and bending strength of the epoxy resin reach 111.9℃，78.5 MPa and 106 MPa，respectively. The engineering model can be used to predict the processing windows of different processing parameters of VARTM process，which is critical for the simulation and optimization of composite manufacturing processes.
2009, 26(2): 90-93.
Abstract:
A mesostructures model of the plain weave fabric was set up. The homogenization method was introduced to predict the permeability of the plain fabric preform. The results of the permeability obtained by the approach were compared with the experimental results in the literature，and it shows good agreement. The influence of the mesostructures parameters on the permeability was discussed. The permeabilities of three kinds of plain glass fabrics were measured and the results were compared with the predicttion. It shows that the permeability obtained by the present method is at the same order of magnitude as the experimental results.
A mesostructures model of the plain weave fabric was set up. The homogenization method was introduced to predict the permeability of the plain fabric preform. The results of the permeability obtained by the approach were compared with the experimental results in the literature，and it shows good agreement. The influence of the mesostructures parameters on the permeability was discussed. The permeabilities of three kinds of plain glass fabrics were measured and the results were compared with the predicttion. It shows that the permeability obtained by the present method is at the same order of magnitude as the experimental results.
2009, 26(2): 94-100.
Abstract:
In order to study microwave absorbing properties of composites reinforced by irregular carbon fiber , the surface topography，microstructure and chemical composition of irregular carbon fiber (ICF) and T300 were investigated by scanning electron microscopy (SEM)，X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The results indicate that the cross-section of the irregular carbon fiber is approximately regular triangle，the degree of profile is 13.16 %，and the interaction with resin matrix is strong. The mechanical property of ICF is comparative to that of T300，and ICF can be used as structural materials. The electromagnetic property and microwave absorbing property of the composites reinforced by ICF and T300 were also analyzed by four-probe measurement，mesh method and radar cross section (RCS). The results show that the resistivity of the composites reinforced by ICF is larger than that of composites reinforced by T300. For high frequency electromagnetic wave，both the imaginary part of permittivity (ε″) and loss tangent (tanδ) of the composites reinforced by ICF are higher than those of composites reinforced by T300. For electromagnetic wave with frequency about 16 GHz，the reflectivity of the composites reinforced by ICF is - 8dB. According to the test results，the composites reinforced by ICF have both the function of load bearing and the electromagnetic energy absorbing capability，and the composites as radar absorbing structure (RAS) will become a promising material .
In order to study microwave absorbing properties of composites reinforced by irregular carbon fiber , the surface topography，microstructure and chemical composition of irregular carbon fiber (ICF) and T300 were investigated by scanning electron microscopy (SEM)，X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The results indicate that the cross-section of the irregular carbon fiber is approximately regular triangle，the degree of profile is 13.16 %，and the interaction with resin matrix is strong. The mechanical property of ICF is comparative to that of T300，and ICF can be used as structural materials. The electromagnetic property and microwave absorbing property of the composites reinforced by ICF and T300 were also analyzed by four-probe measurement，mesh method and radar cross section (RCS). The results show that the resistivity of the composites reinforced by ICF is larger than that of composites reinforced by T300. For high frequency electromagnetic wave，both the imaginary part of permittivity (ε″) and loss tangent (tanδ) of the composites reinforced by ICF are higher than those of composites reinforced by T300. For electromagnetic wave with frequency about 16 GHz，the reflectivity of the composites reinforced by ICF is - 8dB. According to the test results，the composites reinforced by ICF have both the function of load bearing and the electromagnetic energy absorbing capability，and the composites as radar absorbing structure (RAS) will become a promising material .
2009, 26(2): 101-106.
Abstract:
After melt-spinning by adding hexamethylenetetramine and the curing treatment，carbon fibers were prepared from the phenolated Chinese fir (Cunninghamia lanceolata) by using the direct carbonization method. The structure characterization of carbon fibers was studied by SEM，FTIR，Raman spectroscopy and elemental analysis.The results show that with carbonization temperature rising，the Raman spectra of carbon fibers from the phenolated Chinese fir have the D peak at 1360 cm -1 and the G peak at 1595 cm-1 that are similar to other graphitoidal materials. At the same time，the value of the disordering R decreases and the crystallite sizes La increases with the rise of carbonization temperature. It is found that the microstructure of the carbon fibers becomes more and more ordered. The carbon fibers at 1000℃ have smooth surface and an ellipse cross-section，and the elemental mass fractions of the carbon fibers are 94.04% for C，4.26% for O and 0.5% for H，respectively.
After melt-spinning by adding hexamethylenetetramine and the curing treatment，carbon fibers were prepared from the phenolated Chinese fir (Cunninghamia lanceolata) by using the direct carbonization method. The structure characterization of carbon fibers was studied by SEM，FTIR，Raman spectroscopy and elemental analysis.The results show that with carbonization temperature rising，the Raman spectra of carbon fibers from the phenolated Chinese fir have the D peak at 1360 cm -1 and the G peak at 1595 cm-1 that are similar to other graphitoidal materials. At the same time，the value of the disordering R decreases and the crystallite sizes La increases with the rise of carbonization temperature. It is found that the microstructure of the carbon fibers becomes more and more ordered. The carbon fibers at 1000℃ have smooth surface and an ellipse cross-section，and the elemental mass fractions of the carbon fibers are 94.04% for C，4.26% for O and 0.5% for H，respectively.
2009, 26(2): 107-112.
Abstract:
An ultraviolet aging test of ARMOS fiber was carried out with the irradiation of xenon lamp，in which the effects of ultraviolet aging on ARMOS fiber were studied by single fiber tension，FTIR，SEM and XRD. The results show that the tensile strength of ARMOS fiber increases 13.7% after UV irradiation for 6 h and decreases 2.1% after 36 h. The C—N in amide of the ARMOS fiber is broken；hydrogen bond combination ability and crystallinity increase；grooves appear on the surface of ARMOS fiber；the tensile failure mode changes from fibril splitting to brittle fracture by FTIR，SEM and XRD. It could，therefore，be concluded that short time UV irradiation can cause two contradictory effects on the ARMOS fiber.
An ultraviolet aging test of ARMOS fiber was carried out with the irradiation of xenon lamp，in which the effects of ultraviolet aging on ARMOS fiber were studied by single fiber tension，FTIR，SEM and XRD. The results show that the tensile strength of ARMOS fiber increases 13.7% after UV irradiation for 6 h and decreases 2.1% after 36 h. The C—N in amide of the ARMOS fiber is broken；hydrogen bond combination ability and crystallinity increase；grooves appear on the surface of ARMOS fiber；the tensile failure mode changes from fibril splitting to brittle fracture by FTIR，SEM and XRD. It could，therefore，be concluded that short time UV irradiation can cause two contradictory effects on the ARMOS fiber.
2009, 26(2): 113-119.
Abstract:
The Co doped ATO (Antimony (Sb) doped tin oxide (SnO2) composite films were successfully synthesized by using sol-gel combined with dip-coating methods and originating from the primary materials of SnCl2·2H2O，SbCl3 and Co(NO3)2· 9H2O. The structures and properties of Co/ATO composite films were characterized by X-ray diffraction (XRD)，scanning electron microscope (SEM)，four-probe method，ultraviolet visible near-infrared spectrophotometer and vibrating sample magnetometer (VSM). The results indicate that a tetragonal rutile structure is retained by a little Co doped ATO，and the nano-particles are well distributed in the thin films and their size can be controlled in the range of 4～7 nm. With increasing the Co content，the resistivity of the composite films decreases and then increases，and it presents a very low value at 0.5 mol% Co. In the range of 400～700 nm visible region，the transmit tance values are up to 90 %，also the transmit tance in the visible region and the optical band gap trends to decrease with increasing the Co content. The room temperature ferromagnetism of the composite film has a coercive force of about 100 Oe when the Co-doped is 3.0 mol%，and it is mainly originated from the interaction of magnetic atoms and the body carrying ions.
The Co doped ATO (Antimony (Sb) doped tin oxide (SnO2) composite films were successfully synthesized by using sol-gel combined with dip-coating methods and originating from the primary materials of SnCl2·2H2O，SbCl3 and Co(NO3)2· 9H2O. The structures and properties of Co/ATO composite films were characterized by X-ray diffraction (XRD)，scanning electron microscope (SEM)，four-probe method，ultraviolet visible near-infrared spectrophotometer and vibrating sample magnetometer (VSM). The results indicate that a tetragonal rutile structure is retained by a little Co doped ATO，and the nano-particles are well distributed in the thin films and their size can be controlled in the range of 4～7 nm. With increasing the Co content，the resistivity of the composite films decreases and then increases，and it presents a very low value at 0.5 mol% Co. In the range of 400～700 nm visible region，the transmit tance values are up to 90 %，also the transmit tance in the visible region and the optical band gap trends to decrease with increasing the Co content. The room temperature ferromagnetism of the composite film has a coercive force of about 100 Oe when the Co-doped is 3.0 mol%，and it is mainly originated from the interaction of magnetic atoms and the body carrying ions.
2009, 26(2): 120-124.
Abstract:
The new ceramic composites of BaWO4/(B a，Sr)TiO3 were successfully fabricated by a standard ceramic
processing. The sintering properties，microstructure and the dielectric properties of BaWO4/(Ba，Sr )TiO3 were systemically studied by means of XRD，SEM and property measurement. The results show that BaWO4/(Ba，Sr)TiO3 could be well sintered at 1250～1350℃ without chemical reaction between perovskite and scheelite phases. With the BaWO4 mass fraction increasing，the density of the ceramic composites increases apparently，the dielectric permit tivity and tunability decrease gradually，and the dielectric loss has a slight change at the grade of 10-3. Typically，for the sample with 60% BaWO4 and 40% Ba 0.5Sr 0.5TiO3(mass fraction)，the tunability under external DC field of 2 V·μm-1 is 14.7%，and the dielectric constant and dielectric loss are 182.7 and 0.0024 separately，which presents excellent properties and can basically meet the requirements of phased array applications.
The new ceramic composites of BaWO4/(B a，Sr)TiO3 were successfully fabricated by a standard ceramic
processing. The sintering properties，microstructure and the dielectric properties of BaWO4/(Ba，Sr )TiO3 were systemically studied by means of XRD，SEM and property measurement. The results show that BaWO4/(Ba，Sr)TiO3 could be well sintered at 1250～1350℃ without chemical reaction between perovskite and scheelite phases. With the BaWO4 mass fraction increasing，the density of the ceramic composites increases apparently，the dielectric permit tivity and tunability decrease gradually，and the dielectric loss has a slight change at the grade of 10-3. Typically，for the sample with 60% BaWO4 and 40% Ba 0.5Sr 0.5TiO3(mass fraction)，the tunability under external DC field of 2 V·μm-1 is 14.7%，and the dielectric constant and dielectric loss are 182.7 and 0.0024 separately，which presents excellent properties and can basically meet the requirements of phased array applications.
2009, 26(2): 125-130.
Abstract:
The superconductor Bi2Sr2CaCu2Ox (Bi2212) samples were synthesized by the solid-state reaction method，and the tribological properties were investigated on the friction and wear tester from ambient temperature to liquid nitrogen temperature. The results indicate that the friction coefficient of the Bi2212 against stainless steel is about 0.35 at ambient temperature and abruptly decreases when the temperature is cooled below superconducting transition temperature of the Bi2212，as low as 0. 11. Ag/Bi2212 composites were prepared by sintering Bi2212 with Ag at different mass fractions to improve the tribological properties of Bi2212 at ambient temperature. The structure and morphology were investigated by means of XRD，SEM，and the elemental compositions of the worn surfaces of Ag/Bi2212 composites were determined using energy dispersive X-ray analysis (EDS). The results show that the Ag particles distribute in the Bi2212 matrix，improving the density，flexibility and toughness of Ag/Bi2212 composites，and a soft metallic Ag film forms on the surface of Ag/Bi2212 composite during f riction process and lowers the friction coefficient. The friction coefficient of 10%Ag/Bi2212 against stainless steel shows a lower value (0.2)，and the wear rate of 15%Ag/Bi2212 is minimum 9.5×10-5 mm3 (N·m)-1 at ambient temperature. Ag/Bi2212 composites show improved tribological properties.
The superconductor Bi2Sr2CaCu2Ox (Bi2212) samples were synthesized by the solid-state reaction method，and the tribological properties were investigated on the friction and wear tester from ambient temperature to liquid nitrogen temperature. The results indicate that the friction coefficient of the Bi2212 against stainless steel is about 0.35 at ambient temperature and abruptly decreases when the temperature is cooled below superconducting transition temperature of the Bi2212，as low as 0. 11. Ag/Bi2212 composites were prepared by sintering Bi2212 with Ag at different mass fractions to improve the tribological properties of Bi2212 at ambient temperature. The structure and morphology were investigated by means of XRD，SEM，and the elemental compositions of the worn surfaces of Ag/Bi2212 composites were determined using energy dispersive X-ray analysis (EDS). The results show that the Ag particles distribute in the Bi2212 matrix，improving the density，flexibility and toughness of Ag/Bi2212 composites，and a soft metallic Ag film forms on the surface of Ag/Bi2212 composite during f riction process and lowers the friction coefficient. The friction coefficient of 10%Ag/Bi2212 against stainless steel shows a lower value (0.2)，and the wear rate of 15%Ag/Bi2212 is minimum 9.5×10-5 mm3 (N·m)-1 at ambient temperature. Ag/Bi2212 composites show improved tribological properties.
2009, 26(2): 131-137.
Abstract:
Nano-hydroxyapatite/polyamide 66(n-2HA/PA66) and Ag loaded hydroxyapatite/titania/polyamide 66 (Ag-HA-TiO2/PA66) composite membranes for guided bone regeneration (GBR) were prepared by the phase inversion method. Biocompatibility of the two kinds membranes was assessed via 32(4，52dimethylthiazol222yl)22，52 diphenyl-tetrazolium-bromide assay (MTT) and flow cytometry (FCM) test. The fabricated membranes have asymmetric porous structure. SEM analysis reveals that pores less than 10μm and pores with a size ranging from 30μm to 200μm distribute in the micropore layer and the spongy structure layer，respectively. MTT and FCM results indicate that the two kinds membranes have good cell affinity，while Ag-HA-TiO2/PA66 membrane can promote cell apopotosis to some extent. The structure and biocompatibility of the fabricated membranes can meet the requirements of GBR.
Nano-hydroxyapatite/polyamide 66(n-2HA/PA66) and Ag loaded hydroxyapatite/titania/polyamide 66 (Ag-HA-TiO2/PA66) composite membranes for guided bone regeneration (GBR) were prepared by the phase inversion method. Biocompatibility of the two kinds membranes was assessed via 32(4，52dimethylthiazol222yl)22，52 diphenyl-tetrazolium-bromide assay (MTT) and flow cytometry (FCM) test. The fabricated membranes have asymmetric porous structure. SEM analysis reveals that pores less than 10μm and pores with a size ranging from 30μm to 200μm distribute in the micropore layer and the spongy structure layer，respectively. MTT and FCM results indicate that the two kinds membranes have good cell affinity，while Ag-HA-TiO2/PA66 membrane can promote cell apopotosis to some extent. The structure and biocompatibility of the fabricated membranes can meet the requirements of GBR.
2009, 26(2): 138-142.
Abstract:
The short carbon fiber (Cf) reinforced hydroxyapatite (HA)/poly (methyl methacrylate) (PMMA) bio-composites were prepared by an in-situ processing and solution co-mixing process. The structures and fracture surface morphologies of as-used materials were characterized using XRD，FTIR spectra，SEM and EDS analysis.The mechanical properties of the Cf-HA/ PMMA composites were tested by a universal testing machine. The results reveal that short Cf and HA nano-particles are uniformly dispersed in the PMMA matrix. The as-prepared Cf-HA/PMMA composites have excellent mechanical properties. With the increase of the content，the flexural strength and flexural modulus of Cf-HA/PMMA composites firstly increase to the maximum and then decrease. When Cf and HA mass fractions are 4% and 2%，respectively，the flexural strength and modulus reach the maximum values of 97.41MPa and 3.06 GPa. The SEM fracture morphologies of Cf-HA/ PMMA composites indicate that with the increase of Cf mass fraction to 6%，the aggregation of Cf in the PMMA matrix is found.
The short carbon fiber (Cf) reinforced hydroxyapatite (HA)/poly (methyl methacrylate) (PMMA) bio-composites were prepared by an in-situ processing and solution co-mixing process. The structures and fracture surface morphologies of as-used materials were characterized using XRD，FTIR spectra，SEM and EDS analysis.The mechanical properties of the Cf-HA/ PMMA composites were tested by a universal testing machine. The results reveal that short Cf and HA nano-particles are uniformly dispersed in the PMMA matrix. The as-prepared Cf-HA/PMMA composites have excellent mechanical properties. With the increase of the content，the flexural strength and flexural modulus of Cf-HA/PMMA composites firstly increase to the maximum and then decrease. When Cf and HA mass fractions are 4% and 2%，respectively，the flexural strength and modulus reach the maximum values of 97.41MPa and 3.06 GPa. The SEM fracture morphologies of Cf-HA/ PMMA composites indicate that with the increase of Cf mass fraction to 6%，the aggregation of Cf in the PMMA matrix is found.
2009, 26(2): 143-148.
Abstract:
Chitosan microspheres (CMs) loaded with bovine serum albumin (BSA) were prepared by an emulsion-ionic crosslinking method in the presence of tripolyphosphate (TPP). Porous CMs/nano-hydroxyapatite/collagen/polylactide (CMs/nHAC/PLA) composite was developed by thermally induced phase separation. The properties of the CMs and composite were investigated by SEM，laser particle size analyzer，mercury porosimeter and universal testing machine. The results indicate that the CMs are spherical in shape，with a regular surface. The diameters of the CMs are in the range of 20～50μm. With the increase of initial BSA dosage，the loading capacity is also increased from 0.78% to 2.74%，whereas the encap sulation efficiency is decreased from 86.9% to 78.4%.Controlling the CMs dosage to be not higher than 30% on a PLA weight basis，the CMs can distribute perfectly in the whole CMs/nHAC/PLA composite. The total porosity of the porous composite is over 83.1%. The pore diameter is about 100～200μm，and the compressive strength is about 1～2 MPa. This porous composite is a promising material for non-loaded bone implants and tissue engineering scaffolds.
Chitosan microspheres (CMs) loaded with bovine serum albumin (BSA) were prepared by an emulsion-ionic crosslinking method in the presence of tripolyphosphate (TPP). Porous CMs/nano-hydroxyapatite/collagen/polylactide (CMs/nHAC/PLA) composite was developed by thermally induced phase separation. The properties of the CMs and composite were investigated by SEM，laser particle size analyzer，mercury porosimeter and universal testing machine. The results indicate that the CMs are spherical in shape，with a regular surface. The diameters of the CMs are in the range of 20～50μm. With the increase of initial BSA dosage，the loading capacity is also increased from 0.78% to 2.74%，whereas the encap sulation efficiency is decreased from 86.9% to 78.4%.Controlling the CMs dosage to be not higher than 30% on a PLA weight basis，the CMs can distribute perfectly in the whole CMs/nHAC/PLA composite. The total porosity of the porous composite is over 83.1%. The pore diameter is about 100～200μm，and the compressive strength is about 1～2 MPa. This porous composite is a promising material for non-loaded bone implants and tissue engineering scaffolds.
2009, 26(2): 149-154.
Abstract:
The characterization and mechanism of the adsorption of human serum albumin (HSA) on silicon-substituted hydroxyapatite (Si-HA) were studied. A Langmuir adsorption isotherm and the apparent activation energy were obtained by analyzing the kinetic properties of the adsorptive reactions. The results show that the apparent activation energy of the adsorption of HSA on Si-HA and HA is 21. 28 kJ· mol-1 and 35. 57 kJ· mol-1 respectively and the rate constant of adsorption reaction is 1.48 and 1.34 min-1 respectively at 20℃. The adsorptive capacity of HSA on Si-HA is stronger than that on HA. The adsorptive mechanism was also investigated by XRD，FTIR and fluorescence spectrum. The results indicate that the adsorptive action is mainly the chemical adsorption including physical adsorption. The adsorption differences are presented by analyzing the molecular structure of Si-HA and HA，which may pave the way for the study on biocompatibility of Si-HA and HA.
The characterization and mechanism of the adsorption of human serum albumin (HSA) on silicon-substituted hydroxyapatite (Si-HA) were studied. A Langmuir adsorption isotherm and the apparent activation energy were obtained by analyzing the kinetic properties of the adsorptive reactions. The results show that the apparent activation energy of the adsorption of HSA on Si-HA and HA is 21. 28 kJ· mol-1 and 35. 57 kJ· mol-1 respectively and the rate constant of adsorption reaction is 1.48 and 1.34 min-1 respectively at 20℃. The adsorptive capacity of HSA on Si-HA is stronger than that on HA. The adsorptive mechanism was also investigated by XRD，FTIR and fluorescence spectrum. The results indicate that the adsorptive action is mainly the chemical adsorption including physical adsorption. The adsorption differences are presented by analyzing the molecular structure of Si-HA and HA，which may pave the way for the study on biocompatibility of Si-HA and HA.
2009, 26(2): 155-159.
Abstract:
The mechanical strengths and deformation behaviors of roller-compacted rubberized concrete (RCR) were studied by keeping compressive strengths of all specimens at 40 MPa. The rubber particles were incorporated by replacing an equal volume of sand，and the rubber volume fractions were 5%，10% and 12%，respectively. The test results show that the rigid behavior of roller compacted concrete (RCC) is improved by the addition of rubber particles，and the specimens containing tire rubber exhibit ductile characteristic during the compressive test. The relations among cubic compressive strength，axial compressive strength，tensile strength and flexural strength of RCR are similar to those of the normal cement concrete. In comparison with control concrete，the tensile strength，flexural strength and ultimate tensile elongation of RCR increase with the increase of the rubber content while their compressive strengths are kept at the same level. Unfortunately，no improvement is observed for the shrinkage behavior. On the contrary，a little increase is found in both of shrinkage velocity and total shrinkage for the specimen containing tire rubber .
The mechanical strengths and deformation behaviors of roller-compacted rubberized concrete (RCR) were studied by keeping compressive strengths of all specimens at 40 MPa. The rubber particles were incorporated by replacing an equal volume of sand，and the rubber volume fractions were 5%，10% and 12%，respectively. The test results show that the rigid behavior of roller compacted concrete (RCC) is improved by the addition of rubber particles，and the specimens containing tire rubber exhibit ductile characteristic during the compressive test. The relations among cubic compressive strength，axial compressive strength，tensile strength and flexural strength of RCR are similar to those of the normal cement concrete. In comparison with control concrete，the tensile strength，flexural strength and ultimate tensile elongation of RCR increase with the increase of the rubber content while their compressive strengths are kept at the same level. Unfortunately，no improvement is observed for the shrinkage behavior. On the contrary，a little increase is found in both of shrinkage velocity and total shrinkage for the specimen containing tire rubber .
2009, 26(2): 160-164.
Abstract:
The high-strain-rate mechanical behavior of the basalt fiber reinforced geopolymeric concrete (BFRGC)，including compressive strength，deformation and energy absorption capacities，was investigated using a 100mm-diameter split Hopkinson pressure bar (SHPB). The experimental results show that the highst-rain-rate behavior of geopolymeric concrete materials exhibits strong strain rate dependency. The addition of short basalt fibers can significantly improve the deformation and energy absorption capacities of the geopolymeric concrete (GC)，while there is no notable improvement in the compressive strength.
The high-strain-rate mechanical behavior of the basalt fiber reinforced geopolymeric concrete (BFRGC)，including compressive strength，deformation and energy absorption capacities，was investigated using a 100mm-diameter split Hopkinson pressure bar (SHPB). The experimental results show that the highst-rain-rate behavior of geopolymeric concrete materials exhibits strong strain rate dependency. The addition of short basalt fibers can significantly improve the deformation and energy absorption capacities of the geopolymeric concrete (GC)，while there is no notable improvement in the compressive strength.
2009, 26(2): 165-170.
Abstract:
Different size distributions determine different packing densities. A formula of packing density with continuous grain size distribution for cement pastes was developed. Based on measuring the water requirements of the cement-slag powder system with different size distributions in the same fluidity degree，the packing density of the different size distributions of the slag and their water requirements were calculated by the formula，and the results agree well with the testing ones. The difference among the water demands of 15 samples used in the experiment is 4% to 10%. In addition，the validity of the method was verified through experiment. The formula could simulate the packing density of the blend materials such as cement，fine-slag，and fly ashes.
Different size distributions determine different packing densities. A formula of packing density with continuous grain size distribution for cement pastes was developed. Based on measuring the water requirements of the cement-slag powder system with different size distributions in the same fluidity degree，the packing density of the different size distributions of the slag and their water requirements were calculated by the formula，and the results agree well with the testing ones. The difference among the water demands of 15 samples used in the experiment is 4% to 10%. In addition，the validity of the method was verified through experiment. The formula could simulate the packing density of the blend materials such as cement，fine-slag，and fly ashes.
2009, 26(2): 171-175.
Abstract:
The high strain rate compressive properties of 3D orthogonal glass fiber woven composite were tested in through-thickness and in-plane directions by a Split Hopkinson Pressure Bar (SHPB). And the relevant quasi-static compressions were carried out in the material universal testing machine. The stress-strain plots at 3 high strain rates and quasi-static were obtained，and the fractures of the samples were observed. The results indicate that the 3D orthogonal woven composite is strain rate sensitive material：its peak stress and compression modulus increase with the increase of strain rate. The 3D orthogonal woven structure makes the composite show anisotropy：the values of peak stress and failure strain in the out-of-plane direction are higher，but its compression modulus reaches a higher value，and tends to be more sensitive to the change of strain rate in the in-plane direction. Comparing the performances in the warp and weft directions reveals that the composite has higher peak stress in the weft direction.
The high strain rate compressive properties of 3D orthogonal glass fiber woven composite were tested in through-thickness and in-plane directions by a Split Hopkinson Pressure Bar (SHPB). And the relevant quasi-static compressions were carried out in the material universal testing machine. The stress-strain plots at 3 high strain rates and quasi-static were obtained，and the fractures of the samples were observed. The results indicate that the 3D orthogonal woven composite is strain rate sensitive material：its peak stress and compression modulus increase with the increase of strain rate. The 3D orthogonal woven structure makes the composite show anisotropy：the values of peak stress and failure strain in the out-of-plane direction are higher，but its compression modulus reaches a higher value，and tends to be more sensitive to the change of strain rate in the in-plane direction. Comparing the performances in the warp and weft directions reveals that the composite has higher peak stress in the weft direction.
2009, 26(2): 176-180.
Abstract:
Eight carbon fiber reinforced plastics (CFRP) pressure vessels were manufactured according to GJB 1878-94 and experiments were conducted to obtain the probabilistic dist ribution of design variables，such as the fiber strength，winding angle，geometric size，burst strength and so on. The reliability design for solid rocket motor vessels based on the experimental data was compared with the traditional safety factor design. The results show that the reliability design of CFRP solid rocket motor vessel effectively unitized the safety and requirements of composite vessel design. The variance level of burst strength of CFRP solid rocket motor vessel is influenced by the variance level of some variables，such as fiber strength，winding angle，geometric size. And not only the variance level of winding angle，but also the mean value of the winding angle influence the variance level of the burst strength.
Eight carbon fiber reinforced plastics (CFRP) pressure vessels were manufactured according to GJB 1878-94 and experiments were conducted to obtain the probabilistic dist ribution of design variables，such as the fiber strength，winding angle，geometric size，burst strength and so on. The reliability design for solid rocket motor vessels based on the experimental data was compared with the traditional safety factor design. The results show that the reliability design of CFRP solid rocket motor vessel effectively unitized the safety and requirements of composite vessel design. The variance level of burst strength of CFRP solid rocket motor vessel is influenced by the variance level of some variables，such as fiber strength，winding angle，geometric size. And not only the variance level of winding angle，but also the mean value of the winding angle influence the variance level of the burst strength.
2009, 26(2): 181-186.
Abstract:
The mechanical behaviour of compositeπjoints under out-of-plane tensile load was investigated by the experimental and numerical simulation method. The tests were operated on the Instron 8803. During the experiments，the onset of the damage initiation，the failure process and their corresponding load were tested. The experimental results show that the fillers on the joint connection represent a potential zone of weakness and it is essential that their mechanical behaviour is well characterized. To simulate the mechanical behaviour of the weakness，basic assumptions and simulated method were presented. Based on the general FEM sof tware，the stress distribution of each composite lamina and filler was investigated with a 3D FE model and the estimated damage load was obtained by the modified maximum stress criteria. The filler as a critical component of the joint is pointed numerically，which is consistent with the experimental phenomena. At the same time，the predicted load of the onset of the damage has good agreement with the mean value of experimental data. These agreements verify the feasibility of the numerical analysis.
The mechanical behaviour of compositeπjoints under out-of-plane tensile load was investigated by the experimental and numerical simulation method. The tests were operated on the Instron 8803. During the experiments，the onset of the damage initiation，the failure process and their corresponding load were tested. The experimental results show that the fillers on the joint connection represent a potential zone of weakness and it is essential that their mechanical behaviour is well characterized. To simulate the mechanical behaviour of the weakness，basic assumptions and simulated method were presented. Based on the general FEM sof tware，the stress distribution of each composite lamina and filler was investigated with a 3D FE model and the estimated damage load was obtained by the modified maximum stress criteria. The filler as a critical component of the joint is pointed numerically，which is consistent with the experimental phenomena. At the same time，the predicted load of the onset of the damage has good agreement with the mean value of experimental data. These agreements verify the feasibility of the numerical analysis.
2009, 26(2): 187-194.
Abstract:
A method of estimating the manufacturing cost for composite stiffened panels was proposed on the basis of co-curing process. Considering cost as a major design parameter，an approach to optimize the configuration that minimizes the cost and weight of composite stiffened panels under compression and shear was presented，under structural requirements and manufacturing const raints. Based on the case of panel with T stiffener，the objective function of cost and weight was minimized respectively to verify the cost estimation model. The results estimated are in good agreement with practical process time of lay up. In addition，the stiffened panel cost and weight were discussed for seven stiffener cross-sectional shapes. It is found that T stiffener gives the lowest time configuration while its weight is only 0.5% more than that of the J stiffener，while J is of the lowest weight among seven stiffeners. The optimization conclusion can be applied to guide design of composite stiffened panel.
A method of estimating the manufacturing cost for composite stiffened panels was proposed on the basis of co-curing process. Considering cost as a major design parameter，an approach to optimize the configuration that minimizes the cost and weight of composite stiffened panels under compression and shear was presented，under structural requirements and manufacturing const raints. Based on the case of panel with T stiffener，the objective function of cost and weight was minimized respectively to verify the cost estimation model. The results estimated are in good agreement with practical process time of lay up. In addition，the stiffened panel cost and weight were discussed for seven stiffener cross-sectional shapes. It is found that T stiffener gives the lowest time configuration while its weight is only 0.5% more than that of the J stiffener，while J is of the lowest weight among seven stiffeners. The optimization conclusion can be applied to guide design of composite stiffened panel.
2009, 26(2): 195-199.
Abstract:
A three-dimensional bending analysis was presented for an orthotropic functionally graded plate. Assuming that material properties have the same variations along the plate-thickness direction，Peano-Baker series solution was obtained for the elastic fields of the simply supported functionally graded plate under the mechanical loads on its upper and lower surfaces by means of the state space method. The correctness of the obtained series solution was validated through numerical examples. The different graded parameters toward the influence of the structural response of the plate were also studied when the material properties were of cosine function dependence on the thickness-coordinate. The numerical results show that the series solution has good convergence.
A three-dimensional bending analysis was presented for an orthotropic functionally graded plate. Assuming that material properties have the same variations along the plate-thickness direction，Peano-Baker series solution was obtained for the elastic fields of the simply supported functionally graded plate under the mechanical loads on its upper and lower surfaces by means of the state space method. The correctness of the obtained series solution was validated through numerical examples. The different graded parameters toward the influence of the structural response of the plate were also studied when the material properties were of cosine function dependence on the thickness-coordinate. The numerical results show that the series solution has good convergence.
2009, 26(2): 200-205.
Abstract:
Combining the local load sharing principle，a perfect process of the random crack core evolvement was proposed for unidirectional composites with fibers dist ributed in hexagonal arrays. Based on the perfect process，the probability arithmetic of the random crack core evolvement was deduced，and examples of the random crack core with broken fibers from one to more were carried out. Compared with Markov process，the probability arithmetic of the random crack core evolvement based on the perfect process is accurate enough. Because this arithmetic changes megillah into simpleness，it becomes possible to consider some fiber breaks at the same time in the crack core evolvement process. The result shows that the probability arithmetic of the random crack core evolvement without considering some simultaneous fiber breaks brings marked errors，and computational precisions of the random crack core evolvement probability and composite strength could be enhanced with considering some fiber breaks at the same time.
Combining the local load sharing principle，a perfect process of the random crack core evolvement was proposed for unidirectional composites with fibers dist ributed in hexagonal arrays. Based on the perfect process，the probability arithmetic of the random crack core evolvement was deduced，and examples of the random crack core with broken fibers from one to more were carried out. Compared with Markov process，the probability arithmetic of the random crack core evolvement based on the perfect process is accurate enough. Because this arithmetic changes megillah into simpleness，it becomes possible to consider some fiber breaks at the same time in the crack core evolvement process. The result shows that the probability arithmetic of the random crack core evolvement without considering some simultaneous fiber breaks brings marked errors，and computational precisions of the random crack core evolvement probability and composite strength could be enhanced with considering some fiber breaks at the same time.
2009, 26(2): 206-209.
Abstract:
The linear bending of symmet ric laminates was analysed，which are composed of unidirectional materials and interleaved viscoelastic damping layer. The viscoelastic layer was treated as isotropic materials. The strain energy stored in in-plane as well as in transverse shear was considered. The Ritz method was employed to research the strain energy of individual stress components. As an example，for a square plate with the boundary condition of four edges clamped，the individual stress components and their strain energy of the unidirectional materials and the viscoelastic layers as well as the loss factor of the composite structures were discussed. The results show that the total energy is mainly composed of the in-plane strain energy in the composites and the shear strain energy in xz and yz directions in the viscoelastic damping layer. The disparity in Young‘s modulus between the viscoelastic damping layer and the unidirectional materials momentously impact the loss factor of the composite structures.
The linear bending of symmet ric laminates was analysed，which are composed of unidirectional materials and interleaved viscoelastic damping layer. The viscoelastic layer was treated as isotropic materials. The strain energy stored in in-plane as well as in transverse shear was considered. The Ritz method was employed to research the strain energy of individual stress components. As an example，for a square plate with the boundary condition of four edges clamped，the individual stress components and their strain energy of the unidirectional materials and the viscoelastic layers as well as the loss factor of the composite structures were discussed. The results show that the total energy is mainly composed of the in-plane strain energy in the composites and the shear strain energy in xz and yz directions in the viscoelastic damping layer. The disparity in Young‘s modulus between the viscoelastic damping layer and the unidirectional materials momentously impact the loss factor of the composite structures.
2009, 26(2): 210-216.
Abstract:
A three-dimensional (3D) finite element (FE) model for calculating the strain energy release rate (SERR) at the crack tip of composite laminates was built up based on the virtual crack closure technique (VCCT). The model involved effects on SERR computation by large rotation of the crack tip and variety of discrete element shapes. The method of SERR calculation at the crack tip was modified. When crack lengths were 15 mm and 35 mm，the SERRs of pure modeⅠand modeⅡwere computed with this model. The SERRs of pure modeⅠare 207 J/m2 and 253 J/m2，and the SERRs of pure mode Ⅱare 758 J/m2 and 1040 J/m2. The predicted values agree with experimental data. At the same time，the mixed-mode SERRs of varied ratios R = (GⅡ/GⅠ+GⅡ) with large cracks were also computed. The error range between predicted SERRs and experimental date is 0. 4 % to 11. 4 %. This model can exactly calculate SERRs at the crack tip.
A three-dimensional (3D) finite element (FE) model for calculating the strain energy release rate (SERR) at the crack tip of composite laminates was built up based on the virtual crack closure technique (VCCT). The model involved effects on SERR computation by large rotation of the crack tip and variety of discrete element shapes. The method of SERR calculation at the crack tip was modified. When crack lengths were 15 mm and 35 mm，the SERRs of pure modeⅠand modeⅡwere computed with this model. The SERRs of pure modeⅠare 207 J/m2 and 253 J/m2，and the SERRs of pure mode Ⅱare 758 J/m2 and 1040 J/m2. The predicted values agree with experimental data. At the same time，the mixed-mode SERRs of varied ratios R = (GⅡ/GⅠ+GⅡ) with large cracks were also computed. The error range between predicted SERRs and experimental date is 0. 4 % to 11. 4 %. This model can exactly calculate SERRs at the crack tip.
