2011 Vol. 28, No. 5
2011, 28(5): 1-11.
Abstract:
Because inorganic nanoparticles tend to agglomerate and their hydrophilic surface is nearly incompatible with hydrophobic polymers, they have to present themselves in the form of large agglomerates in the polymer composites, which results in poor properties of the composites. The fabrication of nanoparticles/polymer composites via conventional compounding should still be workable. The key issue lies in the effective dispersion and the application of the nanoparticles. The current paper reviews the recent achievements in surface modification of nanoparticles and processing aided dispersion techniques during blending with polymers.
Because inorganic nanoparticles tend to agglomerate and their hydrophilic surface is nearly incompatible with hydrophobic polymers, they have to present themselves in the form of large agglomerates in the polymer composites, which results in poor properties of the composites. The fabrication of nanoparticles/polymer composites via conventional compounding should still be workable. The key issue lies in the effective dispersion and the application of the nanoparticles. The current paper reviews the recent achievements in surface modification of nanoparticles and processing aided dispersion techniques during blending with polymers.
2011, 28(5): 12-19.
Abstract:
The effect of the particle spatial distribution on the thermal conductivity of composites and the essential condition of the formation of the effective thermal conductive pathways were investigated. In order to solve the modeling problem of the representative volume element (RVE) with any volume fraction and specified spatial configuration, the strategy to describe the objective spatial distribution configuration by the spatial distribution potential-energy function was employed, and a Monte Carlo controllable spatial distribution algorithm was designed, which can effectively create the RVE containing cluster and network configurations with any volume fraction. The simulated results show that, at the same volume fraction, the network configuration is easier to form the thermal conductive pathways and features higher thermal conductivity than the cluster one does; the volume fraction plays a key role in the formation of the effective thermal conductive pathways, which can occur only when the volume fraction is larger than 20% and the distance between the particles is short to some extent; with the increasing distance between the particles, the thermal conduction decreases in an exponent form. Therefore, a given amount of volume fraction and relative effective distribution of particles become two essential conditions of the formation of the effective thermal conductive pathways.
The effect of the particle spatial distribution on the thermal conductivity of composites and the essential condition of the formation of the effective thermal conductive pathways were investigated. In order to solve the modeling problem of the representative volume element (RVE) with any volume fraction and specified spatial configuration, the strategy to describe the objective spatial distribution configuration by the spatial distribution potential-energy function was employed, and a Monte Carlo controllable spatial distribution algorithm was designed, which can effectively create the RVE containing cluster and network configurations with any volume fraction. The simulated results show that, at the same volume fraction, the network configuration is easier to form the thermal conductive pathways and features higher thermal conductivity than the cluster one does; the volume fraction plays a key role in the formation of the effective thermal conductive pathways, which can occur only when the volume fraction is larger than 20% and the distance between the particles is short to some extent; with the increasing distance between the particles, the thermal conduction decreases in an exponent form. Therefore, a given amount of volume fraction and relative effective distribution of particles become two essential conditions of the formation of the effective thermal conductive pathways.
2011, 28(5): 20-26.
Abstract:
Three kinds of poly(lactide-co-glycolide)/chitosan microspheres (abbreviated as PLGA/chitosan microspheres) were prepared with multiple emulsion technique. PLGA microspheres were prepared with the double emulsion method (W/O/W) based on PLGA as the matrix and bovine serum albumin (BSA) as the model protein. The PLGA microspheres were re-emulsified with chitosan solution containing BSA followed by cross-linking with sodium tripolyphosphate (TPP). Three kinds of PLGA were used as the raw material of PLGA microspheres in order to modulate the release kinetics of the model protein. The microstructure, the size distribution and the physical chemical properties of the PLGA/chitosan microspheres were analyzed by scanning electron microscope (SEM), laser scattering particle analyzer and fourier transform infrared (FTIR), respectively. The release of BSA from PLGA/chitosan microspheres was monitored in PBS and compared with PLGA microspheres. Simultaneously, the pH changes of the PBS were measured during the incubation. The results show that PLGA/chitosan microspheres demonstrate a multinuclear and dual microsphere structure. The drug-loading rate and the mean size of the PLGA/chitosan microspheres were 6%~8% and 40~60 μm, respectively. The PLGA/chitosan microspheres have excellent release curves with a less burst release and a longer than 75 days release. The degradation of PLGA/chitosan microspheres does not induce acidic environment as indicated by a pH value of 7~8 throughout the degradation. The PLGA/chitosan microspheres are excellent vehicles suitable for the proteins.
Three kinds of poly(lactide-co-glycolide)/chitosan microspheres (abbreviated as PLGA/chitosan microspheres) were prepared with multiple emulsion technique. PLGA microspheres were prepared with the double emulsion method (W/O/W) based on PLGA as the matrix and bovine serum albumin (BSA) as the model protein. The PLGA microspheres were re-emulsified with chitosan solution containing BSA followed by cross-linking with sodium tripolyphosphate (TPP). Three kinds of PLGA were used as the raw material of PLGA microspheres in order to modulate the release kinetics of the model protein. The microstructure, the size distribution and the physical chemical properties of the PLGA/chitosan microspheres were analyzed by scanning electron microscope (SEM), laser scattering particle analyzer and fourier transform infrared (FTIR), respectively. The release of BSA from PLGA/chitosan microspheres was monitored in PBS and compared with PLGA microspheres. Simultaneously, the pH changes of the PBS were measured during the incubation. The results show that PLGA/chitosan microspheres demonstrate a multinuclear and dual microsphere structure. The drug-loading rate and the mean size of the PLGA/chitosan microspheres were 6%~8% and 40~60 μm, respectively. The PLGA/chitosan microspheres have excellent release curves with a less burst release and a longer than 75 days release. The degradation of PLGA/chitosan microspheres does not induce acidic environment as indicated by a pH value of 7~8 throughout the degradation. The PLGA/chitosan microspheres are excellent vehicles suitable for the proteins.
2011, 28(5): 27-33.
Abstract:
The multi-walled carbon nanotubes (MWCNTs) were modified by covalent, noncovalent, or hybrid functionalization respectively. By means of solution blending, three types of functionalized MWCNTs were incorporated into the epoxy resin (EP) with various mass fractions to prepare MWCNTs/EP composites. The effect of the content and functionalization method of MWCNTs on the mechanical and thermal properties of the composites was studied through tensile test and thermal gravimetric analysis. The fracture sections of the tensile specimen were examined by SEM. The results indicate that the hybrid functionalized composites (MWCNTs-Epon828-PPA/EP) exhibit the best mechanical and thermal properties comparing with covalent and noncovalent functionalized composites (MWCNTs-Epon828/EP, MWCNTs-PPA/EP). With 0.3% mass fraction of MWCNTs, the tensile strength, elastic modulus, and the elongation at break increase by 30%, 62%, and 26% compared with that of the pure EP, respectively.
The multi-walled carbon nanotubes (MWCNTs) were modified by covalent, noncovalent, or hybrid functionalization respectively. By means of solution blending, three types of functionalized MWCNTs were incorporated into the epoxy resin (EP) with various mass fractions to prepare MWCNTs/EP composites. The effect of the content and functionalization method of MWCNTs on the mechanical and thermal properties of the composites was studied through tensile test and thermal gravimetric analysis. The fracture sections of the tensile specimen were examined by SEM. The results indicate that the hybrid functionalized composites (MWCNTs-Epon828-PPA/EP) exhibit the best mechanical and thermal properties comparing with covalent and noncovalent functionalized composites (MWCNTs-Epon828/EP, MWCNTs-PPA/EP). With 0.3% mass fraction of MWCNTs, the tensile strength, elastic modulus, and the elongation at break increase by 30%, 62%, and 26% compared with that of the pure EP, respectively.
2011, 28(5): 34-40.
Abstract:
A thermoset type isotropic conductive adhesive (ICA) was prepared by epoxy resin E-51 as the matrix, nanosized and microsized copper powder modified by silane coupling KH550 as the conductive fillers, polyamide resin with low molecular weight as the curing agent, and some other additives. A new liquid curing agent, polyamide resin with low molecular weight, was used which solved some difficult problems during the preparation of ICA, such as limit of quantity of conductive fillers. The effects of different factors such as curing agent, silane coupling agent, reducer, and conductive filler on the bonding performance and the conductivity for conductive adhesive were discussed by the orthogonal experiments. The preparation parameters of the conductive adhesive were optimized, and the optimal preparation parameters for the conductive adhesive was obtained. The results show that optimum conditions of conductive adhesive are composed of 65% of nano-and micro-copper powder with curing time for 4 hours at 60 ℃. The adhesion strength reaches 17.6 MPa and the bulk resistivity is 3.6×10-4 Ω·cm. The change rates of bulk resistivity are less than 10% at the high temperature (85 ℃) and the high humidity(RH 85%).
A thermoset type isotropic conductive adhesive (ICA) was prepared by epoxy resin E-51 as the matrix, nanosized and microsized copper powder modified by silane coupling KH550 as the conductive fillers, polyamide resin with low molecular weight as the curing agent, and some other additives. A new liquid curing agent, polyamide resin with low molecular weight, was used which solved some difficult problems during the preparation of ICA, such as limit of quantity of conductive fillers. The effects of different factors such as curing agent, silane coupling agent, reducer, and conductive filler on the bonding performance and the conductivity for conductive adhesive were discussed by the orthogonal experiments. The preparation parameters of the conductive adhesive were optimized, and the optimal preparation parameters for the conductive adhesive was obtained. The results show that optimum conditions of conductive adhesive are composed of 65% of nano-and micro-copper powder with curing time for 4 hours at 60 ℃. The adhesion strength reaches 17.6 MPa and the bulk resistivity is 3.6×10-4 Ω·cm. The change rates of bulk resistivity are less than 10% at the high temperature (85 ℃) and the high humidity(RH 85%).
2011, 28(5): 41-45.
Abstract:
Nano-SiC/Polyimide (n-SiC/PI) composite films were prepared by using in-situ dispersive polymerization. The surface morphology, thermal expansion, dielectric properties and thermal stability of n-SiC/PI were studied by SEM, thermal mechanical analysis (TMA), impedance analyzer and thermal gravimetric analysis (TG) respectively. The results show that n-SiC particles are dispersed in the PI matrix evenly by employing the in-situ polymerization. The coefficient of thermal expansion (CTE) of n-SiC/PI composite films decreases with the increasing of the SiC content, while the experimental data could be analyzed by Kerner model closely. The CTE of PI with n-SiC mass fraction of 15% decrease about 11% than that of the pure PI. The dielectric constant and dielectric loss of films vary with the content of n-SiC fillers, remaining in the lower range and stable in a wide frequency range.
Nano-SiC/Polyimide (n-SiC/PI) composite films were prepared by using in-situ dispersive polymerization. The surface morphology, thermal expansion, dielectric properties and thermal stability of n-SiC/PI were studied by SEM, thermal mechanical analysis (TMA), impedance analyzer and thermal gravimetric analysis (TG) respectively. The results show that n-SiC particles are dispersed in the PI matrix evenly by employing the in-situ polymerization. The coefficient of thermal expansion (CTE) of n-SiC/PI composite films decreases with the increasing of the SiC content, while the experimental data could be analyzed by Kerner model closely. The CTE of PI with n-SiC mass fraction of 15% decrease about 11% than that of the pure PI. The dielectric constant and dielectric loss of films vary with the content of n-SiC fillers, remaining in the lower range and stable in a wide frequency range.
2011, 28(5): 46-51.
Abstract:
PS-SiO2 composites and SiO2 hollow spheres were successfully prepared by using polystyrene (PS) particles as templates and tetraethoxysilane as precursors. The silica shells were coated on the surfaces of template via electrostatic interaction. Fourier transform-infrared spectroscopy, thermo-gravimetric analysis, transmission electron microscopy, and scanning electron microscope measurements were used to characterize these hollow silica spheres. Their tribological properties were also investigated. The results show that large quantity of monodispersed PS-SiO2 composites with a diameter of about 0.7 μm can be obtained in this process. After the calcination treatment, the templates were removed and SiO2 hollowspheres were perfectly retained. The friction experiment was made at UMT-2 (CETR) and it could be concluded that the base oil with 2 wt% prepared SiO2 nanostructures had better friction reduction than those with pure oil. The friction coefficient can be reduced to about 0.058 in low load.
PS-SiO2 composites and SiO2 hollow spheres were successfully prepared by using polystyrene (PS) particles as templates and tetraethoxysilane as precursors. The silica shells were coated on the surfaces of template via electrostatic interaction. Fourier transform-infrared spectroscopy, thermo-gravimetric analysis, transmission electron microscopy, and scanning electron microscope measurements were used to characterize these hollow silica spheres. Their tribological properties were also investigated. The results show that large quantity of monodispersed PS-SiO2 composites with a diameter of about 0.7 μm can be obtained in this process. After the calcination treatment, the templates were removed and SiO2 hollowspheres were perfectly retained. The friction experiment was made at UMT-2 (CETR) and it could be concluded that the base oil with 2 wt% prepared SiO2 nanostructures had better friction reduction than those with pure oil. The friction coefficient can be reduced to about 0.058 in low load.
2011, 28(5): 52-57.
Abstract:
Three kinds of non-crimp fabrics (NCF) of carbon fiber studied. The internal structures of each kind of fabrics is described together with bending tests to investigate the impact of knit pattern on mechanical properties of NCF composites. Biaxial fabric with chain stitch has better binding effect and smaller width of deformation induced by stitching yarns than biaxial fabric with tricot stitch. Biaxial fabric reinforced composites have relatively less resin-rich areas and voids, the bending strength and modulus are higher than that of the biaxial fabric reinforced composites. In contrast to biaxial warp knitted fabrics, unidirectional NCF reinforced composites have more accurate fibre orientation and less distortions or damages caused by the stitching yarns, thus higher bending strength and modulus.
Three kinds of non-crimp fabrics (NCF) of carbon fiber studied. The internal structures of each kind of fabrics is described together with bending tests to investigate the impact of knit pattern on mechanical properties of NCF composites. Biaxial fabric with chain stitch has better binding effect and smaller width of deformation induced by stitching yarns than biaxial fabric with tricot stitch. Biaxial fabric reinforced composites have relatively less resin-rich areas and voids, the bending strength and modulus are higher than that of the biaxial fabric reinforced composites. In contrast to biaxial warp knitted fabrics, unidirectional NCF reinforced composites have more accurate fibre orientation and less distortions or damages caused by the stitching yarns, thus higher bending strength and modulus.
2011, 28(5): 58-63.
Abstract:
The wave transmission property of the three-dimensional (3D) glass fiber spacer fabric/cyanate ester (CE) composite was investigated by comparison with the 3D spacer fabric/epoxy composite and the honeycomb sandwich composite. The results indicate that the 3D spacer fabric/CE composite shows better wave transmission property than that of both the spacer fabric/epoxy composite and the honeycomb sandwich composite. Moreover, the wave input angle has little influence on the wave transmission property of the 3D spacer fabric/CE composite, and the spacer fabric/CE composite reveals highest wave transmission property with the pile height of 8 mm. When the wave transmits parallel to the warp direction larger transmission property can be observed than that along the weft direction. And the wave transmission property in the range of 8~12 GHz is better than that of 12~18 GHz. Besides, the facesheet reinforcement decreases the wave transmission property due to the wave reflection.
The wave transmission property of the three-dimensional (3D) glass fiber spacer fabric/cyanate ester (CE) composite was investigated by comparison with the 3D spacer fabric/epoxy composite and the honeycomb sandwich composite. The results indicate that the 3D spacer fabric/CE composite shows better wave transmission property than that of both the spacer fabric/epoxy composite and the honeycomb sandwich composite. Moreover, the wave input angle has little influence on the wave transmission property of the 3D spacer fabric/CE composite, and the spacer fabric/CE composite reveals highest wave transmission property with the pile height of 8 mm. When the wave transmits parallel to the warp direction larger transmission property can be observed than that along the weft direction. And the wave transmission property in the range of 8~12 GHz is better than that of 12~18 GHz. Besides, the facesheet reinforcement decreases the wave transmission property due to the wave reflection.
2011, 28(5): 64-69.
Abstract:
Liquid crystal polyurethans (HBLCP) containing imide units were synthesized by polyaddition reaction of N, N'-bis(2-hydroxyhexyl)-dicarboxyimide (BHDI) with 2, 4-toluenediisocyanate (2, 4-TDI) and hydroquinone dibenzoate ester (HQB) through changing the molar ratio of BHDI and HQB, and blending HBLCP with epoxy resin (E-51), to prepare HBLCP/E-51 composites. The structure and liquid crystalline phase behavior of HBLCP were characteristied by using FTIR, DSC, polarized light microscopy (POM), X-ray diffraction (WAXD), and the fracture structure of the HBLCP/E-51 composites was investigated by SEM, and the toughening mechanism was also explored. Experimental results reveale that the impact strength of the epoxy resin modified with 3 wt% HBLCP is 2.3 times higher than that of unmodified epoxy resin, and the tensile strength as well as the bending strength is also improved, present the typical ductile fracture. The thermal decomposition temperature of HBLCP/E-51 composites is also 12~20 ℃ higher than that of the pure epoxy resin, and the temperature for the maximum decomposition rate of composites is 12~15 ℃ higher than that of the pure epoxy resin.
Liquid crystal polyurethans (HBLCP) containing imide units were synthesized by polyaddition reaction of N, N'-bis(2-hydroxyhexyl)-dicarboxyimide (BHDI) with 2, 4-toluenediisocyanate (2, 4-TDI) and hydroquinone dibenzoate ester (HQB) through changing the molar ratio of BHDI and HQB, and blending HBLCP with epoxy resin (E-51), to prepare HBLCP/E-51 composites. The structure and liquid crystalline phase behavior of HBLCP were characteristied by using FTIR, DSC, polarized light microscopy (POM), X-ray diffraction (WAXD), and the fracture structure of the HBLCP/E-51 composites was investigated by SEM, and the toughening mechanism was also explored. Experimental results reveale that the impact strength of the epoxy resin modified with 3 wt% HBLCP is 2.3 times higher than that of unmodified epoxy resin, and the tensile strength as well as the bending strength is also improved, present the typical ductile fracture. The thermal decomposition temperature of HBLCP/E-51 composites is also 12~20 ℃ higher than that of the pure epoxy resin, and the temperature for the maximum decomposition rate of composites is 12~15 ℃ higher than that of the pure epoxy resin.
2011, 28(5): 70-76.
Abstract:
A unit cell of the non-crimped fabrics' geometrical structure was established, and the meso-level resin flow behavior within it was simulated by coupling the inter-tow and intra-tow flows. According to the Darcy's law, the equivalent in-plane permeability was calculated. And then this method was verified. Based on the above work, the relationship between the in-plane permeability of the unit cell and the meso-level structural parameters, such as the distance between fiber bundles, the fiber bundle's height and permeability, was investigated. The results show that the in-plane permeability of the unit cell increases with the increase of the distance between fiber bundles, and a positive linear relationship exists between the logarithms of their reciprocals; the height of fiber bundles has the similar effect on the permeability as the distance between fiber bundles does; the in-plane permeability of the unit cell increases linearly with the increase of the permeability of fiber bundles.
A unit cell of the non-crimped fabrics' geometrical structure was established, and the meso-level resin flow behavior within it was simulated by coupling the inter-tow and intra-tow flows. According to the Darcy's law, the equivalent in-plane permeability was calculated. And then this method was verified. Based on the above work, the relationship between the in-plane permeability of the unit cell and the meso-level structural parameters, such as the distance between fiber bundles, the fiber bundle's height and permeability, was investigated. The results show that the in-plane permeability of the unit cell increases with the increase of the distance between fiber bundles, and a positive linear relationship exists between the logarithms of their reciprocals; the height of fiber bundles has the similar effect on the permeability as the distance between fiber bundles does; the in-plane permeability of the unit cell increases linearly with the increase of the permeability of fiber bundles.
2011, 28(5): 77-82.
Abstract:
The cyclic moisture absorption and desorption behavior of CCF300 carbon fiber/5405 bismaleimid composites immersed in 71 ℃ distilled water were investigated. After three cycles of moisture absorption-desorption process, moisture diffusion coefficient and moisture uptake of CCF300/5405 composites in different cycles were studied. Using SEM, the change mechanism of absorption behavior of composites in the hygrothermal condition was discussed. The results show that the moisture absorption behavior of CCF300/5405 composites basically conforms the Fick's second law. After 14 days of moisture absorption, the composites reach to the saturated moisture level, and saturated moisture uptake is about 0.66%. Additionally, after cycles of moisture absorption process, the interface between fiber and matrix is damaged by moisture, which leads to a large number of voids and cracks. As a result, water diffusion coefficient increases significantly and saturated moisture uptake rises slightly. Furthermore, the damage is irreversible even after the moisture desorpion.
The cyclic moisture absorption and desorption behavior of CCF300 carbon fiber/5405 bismaleimid composites immersed in 71 ℃ distilled water were investigated. After three cycles of moisture absorption-desorption process, moisture diffusion coefficient and moisture uptake of CCF300/5405 composites in different cycles were studied. Using SEM, the change mechanism of absorption behavior of composites in the hygrothermal condition was discussed. The results show that the moisture absorption behavior of CCF300/5405 composites basically conforms the Fick's second law. After 14 days of moisture absorption, the composites reach to the saturated moisture level, and saturated moisture uptake is about 0.66%. Additionally, after cycles of moisture absorption process, the interface between fiber and matrix is damaged by moisture, which leads to a large number of voids and cracks. As a result, water diffusion coefficient increases significantly and saturated moisture uptake rises slightly. Furthermore, the damage is irreversible even after the moisture desorpion.
2011, 28(5): 83-88.
Abstract:
Using homogenization and unit cell finite element method (FEM), 3D material constitutive model of twill-weave carbon fabric/epoxy composites was studied and applied on the light-weight structure of electric vehicles (EV). The micro-geometric structure parameters were obtained by observing the internal microstructure of twill-weave T300 carbon fabric/epoxy composites with the help of optical microscope, then the geometric and FEM of representative volume element of composites laminate were established; The material parameters of 3D material constitutive model was studied using the cell FEM based on the laminate theory, and the predicted values were compared with uniaxial tension and three point bending test values. Through the second development, the 3D material parameters were used on the light-weight electric vehicle structure design, the EV safety was inspected according to federal motor vehicle safety standard (FMVSS571.216). The result indicates that 3D material constitutive model developed is in agreement with tension and bending experiment results, whose relative errors are 4.04% and 7.79%. The weight of EV developed by using the twill-weave carbon fabric/epoxy composites is 12% lighter than that of the traditional vehicle under the same safety condition.
Using homogenization and unit cell finite element method (FEM), 3D material constitutive model of twill-weave carbon fabric/epoxy composites was studied and applied on the light-weight structure of electric vehicles (EV). The micro-geometric structure parameters were obtained by observing the internal microstructure of twill-weave T300 carbon fabric/epoxy composites with the help of optical microscope, then the geometric and FEM of representative volume element of composites laminate were established; The material parameters of 3D material constitutive model was studied using the cell FEM based on the laminate theory, and the predicted values were compared with uniaxial tension and three point bending test values. Through the second development, the 3D material parameters were used on the light-weight electric vehicle structure design, the EV safety was inspected according to federal motor vehicle safety standard (FMVSS571.216). The result indicates that 3D material constitutive model developed is in agreement with tension and bending experiment results, whose relative errors are 4.04% and 7.79%. The weight of EV developed by using the twill-weave carbon fabric/epoxy composites is 12% lighter than that of the traditional vehicle under the same safety condition.
2011, 28(5): 89-95.
Abstract:
The curing kinetics, curing mechanism and pyrolysis of boron-modified phenolic resin were investigated by means of non-isothermal DSC technique, Ozawa method, solid-state 13C nuclear magnetic resonance (NMR), infrared spectrum (IR), pyrolysis-gas chromatography (Py-GC)and XRD. The results show that the approximate theoretical temperatures of gel, cure and post-treatment are 350.0 K, 386.2 K and 433.3 K, respectively. Its apparent activation energy at exothermic peak is 152.4 kJ/mol. The curing process involves the reactions of PhCH2—OH to itself, PhCH2—OH to B—OH, PhCH2—OH to H of phenol ring as well as disproportionation of ether link. The mass loss at the range of 500 ℃ to 800 ℃ in the pyrolysis is 14.9%, and the pyrolysis products are mainly volatile compounds, such as CO, CO2, H2O, benzene and toluene. The residual carbon value at 1000 ℃ is 67.2%. The boron-modified phenolic resin is pyrolyzed into glass carbon after the heat-treatment at 1000 ℃ for 30 min.
The curing kinetics, curing mechanism and pyrolysis of boron-modified phenolic resin were investigated by means of non-isothermal DSC technique, Ozawa method, solid-state 13C nuclear magnetic resonance (NMR), infrared spectrum (IR), pyrolysis-gas chromatography (Py-GC)and XRD. The results show that the approximate theoretical temperatures of gel, cure and post-treatment are 350.0 K, 386.2 K and 433.3 K, respectively. Its apparent activation energy at exothermic peak is 152.4 kJ/mol. The curing process involves the reactions of PhCH2—OH to itself, PhCH2—OH to B—OH, PhCH2—OH to H of phenol ring as well as disproportionation of ether link. The mass loss at the range of 500 ℃ to 800 ℃ in the pyrolysis is 14.9%, and the pyrolysis products are mainly volatile compounds, such as CO, CO2, H2O, benzene and toluene. The residual carbon value at 1000 ℃ is 67.2%. The boron-modified phenolic resin is pyrolyzed into glass carbon after the heat-treatment at 1000 ℃ for 30 min.
2011, 28(5): 96-99.
Abstract:
The degradable performance and bio-mineralization function of bioglass/poly(lactic acid) tissue engineering scaffolds were systematically studied in the simulated body fluid (SBF) by measuring pH value of SBF, the loss mass rate of the scaffolds and analyzing SEM pictures, XRD and FTIR spectra of scaffolds' surface. It was found that in SBF, the pH value of SBF with bioglass/poly(lactic acid) tissue engineering scaffolds and the mass of bioglass/poly(lactic acid) scaffolds decreases with the prolongation of time. SEM pictures and XRD, FTIR spectra showed that there appears the deposition of carbonate hydroxyl apatite on the surface of the bioglass/poly(lactic acid) tissue engineering scaffolds. The result shows that the bioglass/poly(lactic acid) tissue engineering scaffolds have good bio-mineralization function.
The degradable performance and bio-mineralization function of bioglass/poly(lactic acid) tissue engineering scaffolds were systematically studied in the simulated body fluid (SBF) by measuring pH value of SBF, the loss mass rate of the scaffolds and analyzing SEM pictures, XRD and FTIR spectra of scaffolds' surface. It was found that in SBF, the pH value of SBF with bioglass/poly(lactic acid) tissue engineering scaffolds and the mass of bioglass/poly(lactic acid) scaffolds decreases with the prolongation of time. SEM pictures and XRD, FTIR spectra showed that there appears the deposition of carbonate hydroxyl apatite on the surface of the bioglass/poly(lactic acid) tissue engineering scaffolds. The result shows that the bioglass/poly(lactic acid) tissue engineering scaffolds have good bio-mineralization function.
2011, 28(5): 100-105.
Abstract:
Hydroxyapatite/thermotropic liquid crystal polymer (HA/Vectra A950) composites were processed with optimized parameters. When the HA/Vectra A950 mass ratio is less than 10/100, the composite exhibits a core-shell structure. The HA particles are mainly dispersed in the core part, while the skin layer is composed of highly oriented Vectra A950 microfibrils. The tensile modulus and strength of the composite are comparable or even higher than those of natural bone. With the increase of HA content, the core-shell structure disappears gradually, but the defects increase. With the increase of HA/Vectra A950 mass ratio to 20/100, the composite mechanical properties, fracture strain in particular, significantly decrease. This is attributed to the interface adhesion between HA particles and Vectra A950 matrix is poor. To ensure the bioactivity, HA content of the bone mimicking composite needs to be close to that of natural bone. Therefore, the interface of HA/Vectra A950 needs to be modified to improve their adhesion.
Hydroxyapatite/thermotropic liquid crystal polymer (HA/Vectra A950) composites were processed with optimized parameters. When the HA/Vectra A950 mass ratio is less than 10/100, the composite exhibits a core-shell structure. The HA particles are mainly dispersed in the core part, while the skin layer is composed of highly oriented Vectra A950 microfibrils. The tensile modulus and strength of the composite are comparable or even higher than those of natural bone. With the increase of HA content, the core-shell structure disappears gradually, but the defects increase. With the increase of HA/Vectra A950 mass ratio to 20/100, the composite mechanical properties, fracture strain in particular, significantly decrease. This is attributed to the interface adhesion between HA particles and Vectra A950 matrix is poor. To ensure the bioactivity, HA content of the bone mimicking composite needs to be close to that of natural bone. Therefore, the interface of HA/Vectra A950 needs to be modified to improve their adhesion.
2011, 28(5): 106-111.
Abstract:
The Ca-Alg (Sodium Alginate) beads with smooth surface, good sphericity and dispersivity, and average size of 210 μm were prepared by the electronic droplet generator, and Alg and chitosan (Chi) were used as wall materials. Then embolic Ca-Alg/Chi microcapsules loading CAP (Capecitabine) were prepared by one-step method and two-step method. Effect of CAP concentrations on drug-loading and drug-release of the microcapsules were investigated. The results show that the drug-loading increases with the CAP concentrations, but the encapsulation efficiency decreases. The cumulative amount of CAP released from the microcapsules is lower than 20% in 0.5 h, which indicate that there is no initial burst release. The embolic microcapsules are likely to be a new dosage form of embolic anti-tumor drugs.
The Ca-Alg (Sodium Alginate) beads with smooth surface, good sphericity and dispersivity, and average size of 210 μm were prepared by the electronic droplet generator, and Alg and chitosan (Chi) were used as wall materials. Then embolic Ca-Alg/Chi microcapsules loading CAP (Capecitabine) were prepared by one-step method and two-step method. Effect of CAP concentrations on drug-loading and drug-release of the microcapsules were investigated. The results show that the drug-loading increases with the CAP concentrations, but the encapsulation efficiency decreases. The cumulative amount of CAP released from the microcapsules is lower than 20% in 0.5 h, which indicate that there is no initial burst release. The embolic microcapsules are likely to be a new dosage form of embolic anti-tumor drugs.
2011, 28(5): 112-118.
Abstract:
In order to explore the feasibility for testing and evaluating oxidative damages in 2D C/SiC composite by thermography, the oxidative damages of 2D C/SiC samples with a blind hole without SiC coatings and three point bending 2D C/SiC samples with SiC coatings were investigated by means of thermography. The relationship between the thermography signal and the oxidative damage was analyzed, and the relationship between the thermal diffusivity and the density as well as the relationship between the thermal diffusivity and the bending strength were established. The results show that the oxidative damage can be visually recognized by thermography. The density of C/SiC logarithmically reduces with the decrease of the thermal diffusivity, and the bending strength parabolically decrease with the decrease of thermal diffusivity. The thermal diffusivity can measure the degree of oxidative damages of the ceramic matrix composite and thermography is an effective method of non-destructive testing of oxidation damage in the ceramic matrix composite.
In order to explore the feasibility for testing and evaluating oxidative damages in 2D C/SiC composite by thermography, the oxidative damages of 2D C/SiC samples with a blind hole without SiC coatings and three point bending 2D C/SiC samples with SiC coatings were investigated by means of thermography. The relationship between the thermography signal and the oxidative damage was analyzed, and the relationship between the thermal diffusivity and the density as well as the relationship between the thermal diffusivity and the bending strength were established. The results show that the oxidative damage can be visually recognized by thermography. The density of C/SiC logarithmically reduces with the decrease of the thermal diffusivity, and the bending strength parabolically decrease with the decrease of thermal diffusivity. The thermal diffusivity can measure the degree of oxidative damages of the ceramic matrix composite and thermography is an effective method of non-destructive testing of oxidation damage in the ceramic matrix composite.
2011, 28(5): 119-125.
Abstract:
Polyacrylonitrile(PAN)/SiO2 composites were prepared by using large-sized macroporous silica as template, in which acrylonitrile solution was filled to perform in-situ polymerization followed by solvent evaporation. The PAN/SiO2 composites were carbonized in vacuum at 800 ℃ to obtain C/SiO2 composites. The samples were characterized by SEM, FTIR, XPS and XRD. The results show that the silica template has a strong capillarity effect, which makes PAN coated on the 3D silica layer as thin films. The thickness of the PAN film can be adjusted by changing the concentration of acrylonitrile in the polymerizing solution or the repeating times of the coating. The dependence of conductivity on the thickness of carbon film has also been observed. When the silica template is coated twice by a solution containing 33% mass fraction of acrylonitrile, the obtained C/SiO2 composites exhibit the volume resistance of 16 Ω·cm, and the average thickness of carbon film is 16 nm, while the BET surface area is 93 m2·g-1.
Polyacrylonitrile(PAN)/SiO2 composites were prepared by using large-sized macroporous silica as template, in which acrylonitrile solution was filled to perform in-situ polymerization followed by solvent evaporation. The PAN/SiO2 composites were carbonized in vacuum at 800 ℃ to obtain C/SiO2 composites. The samples were characterized by SEM, FTIR, XPS and XRD. The results show that the silica template has a strong capillarity effect, which makes PAN coated on the 3D silica layer as thin films. The thickness of the PAN film can be adjusted by changing the concentration of acrylonitrile in the polymerizing solution or the repeating times of the coating. The dependence of conductivity on the thickness of carbon film has also been observed. When the silica template is coated twice by a solution containing 33% mass fraction of acrylonitrile, the obtained C/SiO2 composites exhibit the volume resistance of 16 Ω·cm, and the average thickness of carbon film is 16 nm, while the BET surface area is 93 m2·g-1.
2011, 28(5): 126-132.
Abstract:
The SiC coatings on the surface of C/SiC composites which were annealed in the dry and wet oxidizing environment at 1300 ℃ for 60 h were examined nondestructively using X-ray microtomography (Micro CT). The oxidation morphology along the coating surface and depth direction was investigated by reconstructing images of different depth SiC coatings assisted with SEM, EDS and XRD. The results demonstrate that Micro CT is applicable to distinguish the oxidation products of SiO2 in the SiC coating and the oxidation depth. Oxidation products SiO2 along the SiC coating surface and depth direction is non-uniform distribution. With increasing depth of the coating, the oxidized area percentage of the coating decreases in the dry oxidizing environment; and first increases and then decreases in the wet oxidizing environment. The different oxidation mechanisms of SiC coatings in the dry and wet oxidizing environment are confirmed by Micro CT.
The SiC coatings on the surface of C/SiC composites which were annealed in the dry and wet oxidizing environment at 1300 ℃ for 60 h were examined nondestructively using X-ray microtomography (Micro CT). The oxidation morphology along the coating surface and depth direction was investigated by reconstructing images of different depth SiC coatings assisted with SEM, EDS and XRD. The results demonstrate that Micro CT is applicable to distinguish the oxidation products of SiO2 in the SiC coating and the oxidation depth. Oxidation products SiO2 along the SiC coating surface and depth direction is non-uniform distribution. With increasing depth of the coating, the oxidized area percentage of the coating decreases in the dry oxidizing environment; and first increases and then decreases in the wet oxidizing environment. The different oxidation mechanisms of SiC coatings in the dry and wet oxidizing environment are confirmed by Micro CT.
2011, 28(5): 133-138.
Abstract:
The master alloy ingot with the nominal composition of Nb-16Si-22Ti-2Hf-2Cr-2Al was prepared by vacuum non-consumable arc-melting and then vacuum induction melting. The melt was poured in a ceramic mould (Y2O3) with the temperature gradient of about 4 ℃/mm. The ingot with the dimension of Φ 60 mm×170 mm was fabricated. Heat treatment was conducted at 1500 ℃ for 100 h. The microstructure, room temperature tensile strength, as well as compression strength at 1250 ℃ of the heat treated ingot were described. Relationship between the microstructure and mechanical properties was also investigated. The results reveal that microstructure of the heat treated ingot is composed of NbSS dendrites, Nb5Si3 particles or lamellae and remaining Nb3Si blocks. Room temperature tensile strength is in the range of 208 to 355 MPa. Both Nb3Si and HfO2 have detrimental effects on the tensile strength. The volume fraction of silicides is in proportion to the high temperature compression strength at 1250 ℃.
The master alloy ingot with the nominal composition of Nb-16Si-22Ti-2Hf-2Cr-2Al was prepared by vacuum non-consumable arc-melting and then vacuum induction melting. The melt was poured in a ceramic mould (Y2O3) with the temperature gradient of about 4 ℃/mm. The ingot with the dimension of Φ 60 mm×170 mm was fabricated. Heat treatment was conducted at 1500 ℃ for 100 h. The microstructure, room temperature tensile strength, as well as compression strength at 1250 ℃ of the heat treated ingot were described. Relationship between the microstructure and mechanical properties was also investigated. The results reveal that microstructure of the heat treated ingot is composed of NbSS dendrites, Nb5Si3 particles or lamellae and remaining Nb3Si blocks. Room temperature tensile strength is in the range of 208 to 355 MPa. Both Nb3Si and HfO2 have detrimental effects on the tensile strength. The volume fraction of silicides is in proportion to the high temperature compression strength at 1250 ℃.
2011, 28(5): 139-144.
Abstract:
Field-activated pressure-assisted synthesis (FAPAS) combining in-situ synthesis method was used to prepare TiB2-TiC-Ni/TiAl/Ti functionally graded materials. Interfacial microstructure and bonding strength of materials have been mainly investigated. The microstructure and distribution of element of interface was analyzed. The shear strength and micro-hardness were also tested. The results show that the grains of TiB2-TiC composite ceramics prepared by FAPAS are fine and homogeneous distribution. The interface forms closely combination and the elements appear mutual diffusion, which forms good metallurgical bonding and the maximum shear strength of joint reaches 85.878 MPa. The micro-hardness of the sample changes gradually from titanium substrate to the cermet, and the maximum hardness of the surface up to HV2760.
Field-activated pressure-assisted synthesis (FAPAS) combining in-situ synthesis method was used to prepare TiB2-TiC-Ni/TiAl/Ti functionally graded materials. Interfacial microstructure and bonding strength of materials have been mainly investigated. The microstructure and distribution of element of interface was analyzed. The shear strength and micro-hardness were also tested. The results show that the grains of TiB2-TiC composite ceramics prepared by FAPAS are fine and homogeneous distribution. The interface forms closely combination and the elements appear mutual diffusion, which forms good metallurgical bonding and the maximum shear strength of joint reaches 85.878 MPa. The micro-hardness of the sample changes gradually from titanium substrate to the cermet, and the maximum hardness of the surface up to HV2760.
2011, 28(5): 145-149.
Abstract:
Al2O3 materials with MgO and La2O3 as additives were prepared by hot-pressing. The density, microstructure and phase composition of the samples were studied by the Archimedes method, SEM and XRD. The mechanical properties were studied by the three-point bending test. The dielectric properties and gas tightness were studied by the resistance meter and helium mass spectrometer leak detector. The results show that the average grain size of the sample sintered at 1500 ℃ is less than 1 μm. The bending strength of samples is more than 600 MPa. The dielectric loss is 4.00 × 10-4 and the leak rate is 2.2×10-9 Pa·m3·s-1 for the sample with 2% La2O3.
Al2O3 materials with MgO and La2O3 as additives were prepared by hot-pressing. The density, microstructure and phase composition of the samples were studied by the Archimedes method, SEM and XRD. The mechanical properties were studied by the three-point bending test. The dielectric properties and gas tightness were studied by the resistance meter and helium mass spectrometer leak detector. The results show that the average grain size of the sample sintered at 1500 ℃ is less than 1 μm. The bending strength of samples is more than 600 MPa. The dielectric loss is 4.00 × 10-4 and the leak rate is 2.2×10-9 Pa·m3·s-1 for the sample with 2% La2O3.
2011, 28(5): 150-155.
Abstract:
In order to investigate the diffusion and transition mechanism for Ag in Ag-Al supersaturated solid under oxygen atmosphere, the diffusion rate, temperature and process for Ag-Al-O phase transition were calculated by the molecular dynamics simulation. The calculated results show that there are conflict between precipitation of Ag and formation of compact alumina film during oxidation process, Ag precipitates quickly at 600 K in oxygen atmosphere, associated with the formation of the Ag2Al phase in Al-Ag solution. The model and calculation result were proved to be reasonable through experiment, Ag in nano scale could be controlled through the short path diffusion of Ag and formation of compact alumina film under reaction temperature。
In order to investigate the diffusion and transition mechanism for Ag in Ag-Al supersaturated solid under oxygen atmosphere, the diffusion rate, temperature and process for Ag-Al-O phase transition were calculated by the molecular dynamics simulation. The calculated results show that there are conflict between precipitation of Ag and formation of compact alumina film during oxidation process, Ag precipitates quickly at 600 K in oxygen atmosphere, associated with the formation of the Ag2Al phase in Al-Ag solution. The model and calculation result were proved to be reasonable through experiment, Ag in nano scale could be controlled through the short path diffusion of Ag and formation of compact alumina film under reaction temperature。
2011, 28(5): 156-161.
Abstract:
The expanded vermiculite (EV)-gypsum thermal insulation composites were manufactured by compression moulding. The effects of flake diameter and preparation methods of expanded EV, mass ratio of EV to gypsum (Rm) on the thermal and mechanical properties of EV-gypsum composites were investigated. The results indicate that the thermal conductivity (λ) and compressive strength of the samples decrease with the increase of EV flake size, and increase as a quadratic function of rising Rm. The samples containing EV expanded by microwave chemical method present a better thermal insulation property (λ=0.082 W(m·K)-1) than that of the ones filled with microwave exfoliated EV (λ=0.097 W(m·K)-1). The EV-gypsum composites can play an important role in the fields of heat insulation, acoustic isolation and moisture adjustment.
The expanded vermiculite (EV)-gypsum thermal insulation composites were manufactured by compression moulding. The effects of flake diameter and preparation methods of expanded EV, mass ratio of EV to gypsum (Rm) on the thermal and mechanical properties of EV-gypsum composites were investigated. The results indicate that the thermal conductivity (λ) and compressive strength of the samples decrease with the increase of EV flake size, and increase as a quadratic function of rising Rm. The samples containing EV expanded by microwave chemical method present a better thermal insulation property (λ=0.082 W(m·K)-1) than that of the ones filled with microwave exfoliated EV (λ=0.097 W(m·K)-1). The EV-gypsum composites can play an important role in the fields of heat insulation, acoustic isolation and moisture adjustment.
2011, 28(5): 162-167.
Abstract:
The relationship between the content of basalt fiber (BF) and the mechanical properties of basalt fiber reinforced wood plastic composites (BF/WPC) was studied. The reinforcement mechanism of the materials was also discussed. The results show that except a little decline of elongation, the tensile strength, impact strength and bending strength of BF/WPC are enhanced and the maximum of them increases about 30%, compared with pure WPC, when the content of BF is between 15%~30%, 15%~25% and 20%~30%, respectively. Therefore, a qualitative hypothesis that the end cross section of BF is the "weak link" is proposed, which could explain the maximum range between the strength index and the mass fraction of fiber.
The relationship between the content of basalt fiber (BF) and the mechanical properties of basalt fiber reinforced wood plastic composites (BF/WPC) was studied. The reinforcement mechanism of the materials was also discussed. The results show that except a little decline of elongation, the tensile strength, impact strength and bending strength of BF/WPC are enhanced and the maximum of them increases about 30%, compared with pure WPC, when the content of BF is between 15%~30%, 15%~25% and 20%~30%, respectively. Therefore, a qualitative hypothesis that the end cross section of BF is the "weak link" is proposed, which could explain the maximum range between the strength index and the mass fraction of fiber.
2011, 28(5): 168-173.
Abstract:
Based on the improved straight chain plastic hinge model proposed by authors recently, the effects of two foam deformation modes on the compressive properties of foam-filled circular tubes were investigated. Considering the average crushing forces as the sum of average force of non-filled column, uniaxial resistance of foam, and the interaction between tube and foam, the analytical expressions of the optimal buckling half-wavelength and the average crushing force were obtained. The results show that the average crushing force under the foam deformation mode Ⅰ is a little higher than that of under the foam deformation mode Ⅱ , and the foam deformation modes greatly affect the optimal buckling half-wavelength. Compared with reference [14], the theoretical predictions of average crushing forces derived in this paper agree better with the experimental results.
Based on the improved straight chain plastic hinge model proposed by authors recently, the effects of two foam deformation modes on the compressive properties of foam-filled circular tubes were investigated. Considering the average crushing forces as the sum of average force of non-filled column, uniaxial resistance of foam, and the interaction between tube and foam, the analytical expressions of the optimal buckling half-wavelength and the average crushing force were obtained. The results show that the average crushing force under the foam deformation mode Ⅰ is a little higher than that of under the foam deformation mode Ⅱ , and the foam deformation modes greatly affect the optimal buckling half-wavelength. Compared with reference [14], the theoretical predictions of average crushing forces derived in this paper agree better with the experimental results.
2011, 28(5): 174-180.
Abstract:
The propagation of Lamb wave in a composite panel was modeled based on the spectral finite element (SFE). Combined with Gabor wavelet analysis, the simulated results obtained by the SFE and by the classical finite element method (FEM) were compared to the theoretical result. The scanning process of the Phased Array damage detection was simulated by the SFE, and the propagation and scanning images of Lamb wave were presented. The results show that besides getting more accurate results, the SFE is able to immensely save computing time compared with the classical FEM. Thus, the advantage of the SFE in modeling the Lamb wave propagation in composite panels is verified. The results also show that the SFE method can accurately simulate the scanning process of the Phased Array damage detection. The coincidence of the simulated results with the actual situation verifies the feasibility and veracity of the present modeling method.
The propagation of Lamb wave in a composite panel was modeled based on the spectral finite element (SFE). Combined with Gabor wavelet analysis, the simulated results obtained by the SFE and by the classical finite element method (FEM) were compared to the theoretical result. The scanning process of the Phased Array damage detection was simulated by the SFE, and the propagation and scanning images of Lamb wave were presented. The results show that besides getting more accurate results, the SFE is able to immensely save computing time compared with the classical FEM. Thus, the advantage of the SFE in modeling the Lamb wave propagation in composite panels is verified. The results also show that the SFE method can accurately simulate the scanning process of the Phased Array damage detection. The coincidence of the simulated results with the actual situation verifies the feasibility and veracity of the present modeling method.
2011, 28(5): 181-185.
Abstract:
The mechanical properties of elytra without epicuticle and sections of Cybister' s elytra were studied. The hardness and elastic modulus of elytra without epicuticle were obtained from the nano-indenter tests and the values are (0.065±0.007) GPa and (0.704±0.013) GPa, which are much smaller than the values of elytra with epicuticle. The mechanical properties of elytra sections follow some rules: On the transverse section, the hardness and elastic modulus in the coupling zone are slightly larger than those in the central and outer zone; and on the longitudeinal section, the hardness and elastic modulus in the central zone are apparently larger than those in the cephalosome and empennage zone.
The mechanical properties of elytra without epicuticle and sections of Cybister' s elytra were studied. The hardness and elastic modulus of elytra without epicuticle were obtained from the nano-indenter tests and the values are (0.065±0.007) GPa and (0.704±0.013) GPa, which are much smaller than the values of elytra with epicuticle. The mechanical properties of elytra sections follow some rules: On the transverse section, the hardness and elastic modulus in the coupling zone are slightly larger than those in the central and outer zone; and on the longitudeinal section, the hardness and elastic modulus in the central zone are apparently larger than those in the cephalosome and empennage zone.
2011, 28(5): 186-191.
Abstract:
p-Aminobenzoic acid was controlled intercalated into magnesium aluminum layered double hydroxides (LDHs) by using co-precipitation, ion-exchange and calcine-recovering. Supramolecular structure of the p-aminobenzoic acid pillared hydrotalcite was characterized by XRD, FTIR, TG-DSC, SEM. Experimental results show that interlayer spacings of p-aminobenzoic acid-LDHs are respectively 0.81 nm、0.79 nm、1.45 nm. The property of UV-absorb is related with the interlayer spacings of p-aminobenzoic acid pillared hydrotalcite. It suggests that p-aminobenzoic acid pillared hydroxides may have the application as a novel UV-absorbing reagent in cosmetics field.
p-Aminobenzoic acid was controlled intercalated into magnesium aluminum layered double hydroxides (LDHs) by using co-precipitation, ion-exchange and calcine-recovering. Supramolecular structure of the p-aminobenzoic acid pillared hydrotalcite was characterized by XRD, FTIR, TG-DSC, SEM. Experimental results show that interlayer spacings of p-aminobenzoic acid-LDHs are respectively 0.81 nm、0.79 nm、1.45 nm. The property of UV-absorb is related with the interlayer spacings of p-aminobenzoic acid pillared hydrotalcite. It suggests that p-aminobenzoic acid pillared hydroxides may have the application as a novel UV-absorbing reagent in cosmetics field.
2011, 28(5): 192-196.
Abstract:
Strain invariant failure theory (SIFT) is a novel micromechanics-based failure criteria for composites, which could be applied to all composite failure analysis. The micromechanics model was built to obtain the mechanical and residual thermal strain aplification factors of fiber and resin. Tensile properties of the domestic composites CCF300/5228、CCF300/5428 and T700/5428 in various unidirectional laminate configurations were measured. Test results were used to obtain SIFT invariant properties. The effect of the component of composites on the SIFT invariant properties was investigated. The results show that the critical first strain invariant and von-mises strain of matrix are dependent on resins, while critical von-mises strain of fiber depends on fibers. SIFT can be used for the failure analysis of domestic composites.
Strain invariant failure theory (SIFT) is a novel micromechanics-based failure criteria for composites, which could be applied to all composite failure analysis. The micromechanics model was built to obtain the mechanical and residual thermal strain aplification factors of fiber and resin. Tensile properties of the domestic composites CCF300/5228、CCF300/5428 and T700/5428 in various unidirectional laminate configurations were measured. Test results were used to obtain SIFT invariant properties. The effect of the component of composites on the SIFT invariant properties was investigated. The results show that the critical first strain invariant and von-mises strain of matrix are dependent on resins, while critical von-mises strain of fiber depends on fibers. SIFT can be used for the failure analysis of domestic composites.
2011, 28(5): 197-205.
Abstract:
Dynamics of drop spreading for water and ethanol absolute on polypropylene (840A) and terylene (728) was investigated using a CCD camera to deal with the problems caused by material and water distribution of wet electrostatic precipitator (ESP). The results show that the contact angles for water on 728 and 840A were 52.5° and 136.2°, respectively, and the contact angles for ethanol absolute on 728 and 840A were 46.5° and 41.9°, respectively. It was observed that the overall duration of the spreading process can be divided into two stages, namely initial stage and later stage. The following rules of drop spreading for water and ethanol absolute on 728 were ExpAssoc and Hill, and the diffusion shapes were elliptical. The shapes for water and ethanol absolute on 840A were circular and elliptical, respectively. The following rule of drop spreading for ethanol absolute on 840A was Hill. The effects of several parameters on drop spreading were obvious, such as the assemblages into strands of fabrics, the properties and size of drop, the thickness of fabrics and the surface free energy of material.
Dynamics of drop spreading for water and ethanol absolute on polypropylene (840A) and terylene (728) was investigated using a CCD camera to deal with the problems caused by material and water distribution of wet electrostatic precipitator (ESP). The results show that the contact angles for water on 728 and 840A were 52.5° and 136.2°, respectively, and the contact angles for ethanol absolute on 728 and 840A were 46.5° and 41.9°, respectively. It was observed that the overall duration of the spreading process can be divided into two stages, namely initial stage and later stage. The following rules of drop spreading for water and ethanol absolute on 728 were ExpAssoc and Hill, and the diffusion shapes were elliptical. The shapes for water and ethanol absolute on 840A were circular and elliptical, respectively. The following rule of drop spreading for ethanol absolute on 840A was Hill. The effects of several parameters on drop spreading were obvious, such as the assemblages into strands of fabrics, the properties and size of drop, the thickness of fabrics and the surface free energy of material.
2011, 28(5): 206-213.
Abstract:
Uniaxial tensile experiments of textile reinforced concrete (TRC) plates and the results were detailed presented in this paper. Then the mechanical properties of textile reinforced concrete and its main influence factors on ultimate loading capacity were studied. And the concept of critical textile ratio was proposed. The mechanical properties of textile reinforced concrete plate were discussed at low textile ratios. When textile ratio was larger than the critical textile ratio, the ultimate bearing capacity exceeds the cracking load, and there was no sudden drop during the loading process. With the increase of textile ratio, the efficiency of fibers decreases in a linear way. And strength of fibers was not fully utilized. Moreover, the crack form was also investigated on different textile ratios. With the increase of textile ratio, cracking space reduces and cracking width decreases as well. Finally, according to the mixture law and ACK model, the stress-strain curve of TRC plates is simplified as a trilinear model. The calculation formula was proposed taking the textile ratio into consideration to forecast the ultimate bearing capacity of TRC plates.
Uniaxial tensile experiments of textile reinforced concrete (TRC) plates and the results were detailed presented in this paper. Then the mechanical properties of textile reinforced concrete and its main influence factors on ultimate loading capacity were studied. And the concept of critical textile ratio was proposed. The mechanical properties of textile reinforced concrete plate were discussed at low textile ratios. When textile ratio was larger than the critical textile ratio, the ultimate bearing capacity exceeds the cracking load, and there was no sudden drop during the loading process. With the increase of textile ratio, the efficiency of fibers decreases in a linear way. And strength of fibers was not fully utilized. Moreover, the crack form was also investigated on different textile ratios. With the increase of textile ratio, cracking space reduces and cracking width decreases as well. Finally, according to the mixture law and ACK model, the stress-strain curve of TRC plates is simplified as a trilinear model. The calculation formula was proposed taking the textile ratio into consideration to forecast the ultimate bearing capacity of TRC plates.
2011, 28(5): 214-219.
Abstract:
The piezoresistivity of short carbon fiber reinforced cement-matrix composites (CFRC) was experimentally studied. The whole process of transition from positive to negative piezoresistivity was observed. The results show that under continuously drying and uniaxially cyclic loading, both positive and negative piezoresistivity occur in CFRC due to the variation of moisture content in the composites. For most cases the electrical resistivity of the composites decreases monotonically upon longitudinal compression, and piezoresistivity tends to be positive. However, its magnitude varies. Lower moisture content leads to stronger piezoresistivity. When moisture content reduces to about 3.19%~4.04%, the electrical resistivity of the composites increases monotonically upon compressive strain, and piezoresistivity tends to be negative. This effect is much stronger than that of positive piezoresistivity. It is proposed that the occurrence of these phenomena is attributable to both the tunneling effect between fibers and decreasing in pore network connectivity during compression.
The piezoresistivity of short carbon fiber reinforced cement-matrix composites (CFRC) was experimentally studied. The whole process of transition from positive to negative piezoresistivity was observed. The results show that under continuously drying and uniaxially cyclic loading, both positive and negative piezoresistivity occur in CFRC due to the variation of moisture content in the composites. For most cases the electrical resistivity of the composites decreases monotonically upon longitudinal compression, and piezoresistivity tends to be positive. However, its magnitude varies. Lower moisture content leads to stronger piezoresistivity. When moisture content reduces to about 3.19%~4.04%, the electrical resistivity of the composites increases monotonically upon compressive strain, and piezoresistivity tends to be negative. This effect is much stronger than that of positive piezoresistivity. It is proposed that the occurrence of these phenomena is attributable to both the tunneling effect between fibers and decreasing in pore network connectivity during compression.
2011, 28(5): 220-227.
Abstract:
The equivalent panel theory was employed to calculate the equivalent parameters of the honeycomb sandwich panel to constitute the benchmark FEM, and the perturbations were added to the equivalent parameters to constitute the non-updated FEM. The equivalent parameters are divided into different groups to get the corresponding modal frequencies, and the Linear-Gaussian RBF response surface model is set up, which is updated by the particle swarm optimization algorithm with mutation operator, the updated parameters is introduced into the non-updated model and the updated model is attained. By comparing the similarity of the structure parameters and the modal frequencies of the benchmark model and the non-updated as well as the updated models, the validity of the updated model is proved.
The equivalent panel theory was employed to calculate the equivalent parameters of the honeycomb sandwich panel to constitute the benchmark FEM, and the perturbations were added to the equivalent parameters to constitute the non-updated FEM. The equivalent parameters are divided into different groups to get the corresponding modal frequencies, and the Linear-Gaussian RBF response surface model is set up, which is updated by the particle swarm optimization algorithm with mutation operator, the updated parameters is introduced into the non-updated model and the updated model is attained. By comparing the similarity of the structure parameters and the modal frequencies of the benchmark model and the non-updated as well as the updated models, the validity of the updated model is proved.
2011, 28(5): 228-233.
Abstract:
The interlaminar stresses of a carbon fiber-reinforced laminated plate with a hole were analyzed using three-dimensional finite element numerical simulation. This laminated plate was subjected to uniaxial forces and composed of layers with typical ply angles . The effects of the ply parameters on the interlaminar stress distribution were investigated; in the meantime, the maximum value and detailed distribution of interlaminar stresses in different typical interfaces were presented. The results show that the location of interfaces along thickness only affects the magnitudes of interlaminar stresses but not the trend of distribution, and the stacking sequence ( or ) affects neither the magnitudes of interlaminar stresses nor the trend of distribution. Furthermore, the maximum normal stress of interface occurs between layers at 90° from the loading axis with its value reaching 51% of the value of applied stress, the maximum interlaminar shearing stress occurs between layers: the maximum circle shearing stress occurs at 74° with its value reaching 64% of the value of applied stress, and the maximum radial shearing stress occurs at 66° with its value reaching 25% of the value of applied stress.
The interlaminar stresses of a carbon fiber-reinforced laminated plate with a hole were analyzed using three-dimensional finite element numerical simulation. This laminated plate was subjected to uniaxial forces and composed of layers with typical ply angles . The effects of the ply parameters on the interlaminar stress distribution were investigated; in the meantime, the maximum value and detailed distribution of interlaminar stresses in different typical interfaces were presented. The results show that the location of interfaces along thickness only affects the magnitudes of interlaminar stresses but not the trend of distribution, and the stacking sequence ( or ) affects neither the magnitudes of interlaminar stresses nor the trend of distribution. Furthermore, the maximum normal stress of interface occurs between layers at 90° from the loading axis with its value reaching 51% of the value of applied stress, the maximum interlaminar shearing stress occurs between layers: the maximum circle shearing stress occurs at 74° with its value reaching 64% of the value of applied stress, and the maximum radial shearing stress occurs at 66° with its value reaching 25% of the value of applied stress.
2011, 28(5): 234-240.
Abstract:
The experimental investigation on mechanical properties of the glass fiber laminates was carried out. The major parameters of mechanical properties were obtained, and the influence of the fiber direction in the fabric, the testing direction and the prescription factors on the mechanical properties was analyzed. According to the BS EN ISO standard, tensile, compression and shear destructive experiments on the glass fiber laminates were executed by using the PC controlling testing machine and the strain instrument. The mechanical properties of the laminates, such as tensile, compressive, shear strength, elasticity modulus and Poisson's ratio, were gained. The mechanical properties of the laminates in different prescriptions and the failure modes in different loading styles were compared and analyzed. The results show that the glass fiber laminates have obvious anisotropy and the high strength appears in the fiber direction; the prescription exerts a certain influence on the mechanical properties; the failure modes are in close relations with the fiber direction and the testing direction, but basically have nothing to do with the prescription.
The experimental investigation on mechanical properties of the glass fiber laminates was carried out. The major parameters of mechanical properties were obtained, and the influence of the fiber direction in the fabric, the testing direction and the prescription factors on the mechanical properties was analyzed. According to the BS EN ISO standard, tensile, compression and shear destructive experiments on the glass fiber laminates were executed by using the PC controlling testing machine and the strain instrument. The mechanical properties of the laminates, such as tensile, compressive, shear strength, elasticity modulus and Poisson's ratio, were gained. The mechanical properties of the laminates in different prescriptions and the failure modes in different loading styles were compared and analyzed. The results show that the glass fiber laminates have obvious anisotropy and the high strength appears in the fiber direction; the prescription exerts a certain influence on the mechanical properties; the failure modes are in close relations with the fiber direction and the testing direction, but basically have nothing to do with the prescription.
