2012 Vol. 29, No. 6
2012, (6): 1-8.
Abstract:
The near space airship has widespread and uninterrupted ability of efficient information capturing and transmitting, which is the future information platform recently developed warmly in the world. The envelope materials are the chief materials of the near space airship, and regarded as the foundation of developing the near space airship, whose mass and performance determine the size, service life and cost of the airship. Aiming at several difficulties existing in the selection and application of the envelope materials for the near space airship, and based on the project requirements of the envelope materials, several aspects of the research progress in the envelope materials were reviewed in this paper, including the strength, weatherability, barrier property and test evaluation method, and the direction of future research on the high performance envelope materials for the near space airship were discussed.
The near space airship has widespread and uninterrupted ability of efficient information capturing and transmitting, which is the future information platform recently developed warmly in the world. The envelope materials are the chief materials of the near space airship, and regarded as the foundation of developing the near space airship, whose mass and performance determine the size, service life and cost of the airship. Aiming at several difficulties existing in the selection and application of the envelope materials for the near space airship, and based on the project requirements of the envelope materials, several aspects of the research progress in the envelope materials were reviewed in this paper, including the strength, weatherability, barrier property and test evaluation method, and the direction of future research on the high performance envelope materials for the near space airship were discussed.
2012, (6): 9-18.
Abstract:
Montmorillonite (MMT)/polystyrene (PS) composites were prepared by melt-compounding PS resin and different kinds of MMT. The structures of the composites were investigated by XRD and high resolution TEM. The pyrolytic charring behavior and fire performance of the composites were studied by means of SEM, X-ray energy dispersive spectrometry (EDX), XRD, oxygen index and cone calorimetry experiments. It is shown that the NaMMT/PS composite is a simple physical blend of PS and virgin MMT (NaMMT), while the organic montmorillonite(OMMT)/PS composite is an intercalated-partially exfoliated nanocomposite. When the mass ratio of MMT to PS is 6:100, the peak heat release rate(PHRR) and average heat release rate(AHRR) of the OMMT/PS composite are only 70.7% and 67.4% that of its NaMMT/PS counterpart, respectively. Meanwhile, the fire performance index (FPI) of the OMMT/PS composite is 1.2 times that of the NaMMT/PS composite, and the oxygen index value of the former is 1.0% higher than that of the latter. The content of carbon element in the residue surface of OMMT/PS composite is 2.5 times that of NaMMT/PS composite. A thick, compact and continuous carbon-containing silicate residue layer is formed on the surface of the OMMT/PS composite, which can effectively inhibit burning. The NaMMT/PS composite hardly has any charring ability. The residue of this composite derives from the pyrolysis of NaMMT completely and it exhibits very poor flame retardancy.
Montmorillonite (MMT)/polystyrene (PS) composites were prepared by melt-compounding PS resin and different kinds of MMT. The structures of the composites were investigated by XRD and high resolution TEM. The pyrolytic charring behavior and fire performance of the composites were studied by means of SEM, X-ray energy dispersive spectrometry (EDX), XRD, oxygen index and cone calorimetry experiments. It is shown that the NaMMT/PS composite is a simple physical blend of PS and virgin MMT (NaMMT), while the organic montmorillonite(OMMT)/PS composite is an intercalated-partially exfoliated nanocomposite. When the mass ratio of MMT to PS is 6:100, the peak heat release rate(PHRR) and average heat release rate(AHRR) of the OMMT/PS composite are only 70.7% and 67.4% that of its NaMMT/PS counterpart, respectively. Meanwhile, the fire performance index (FPI) of the OMMT/PS composite is 1.2 times that of the NaMMT/PS composite, and the oxygen index value of the former is 1.0% higher than that of the latter. The content of carbon element in the residue surface of OMMT/PS composite is 2.5 times that of NaMMT/PS composite. A thick, compact and continuous carbon-containing silicate residue layer is formed on the surface of the OMMT/PS composite, which can effectively inhibit burning. The NaMMT/PS composite hardly has any charring ability. The residue of this composite derives from the pyrolysis of NaMMT completely and it exhibits very poor flame retardancy.
2012, (6): 19-25.
Abstract:
Three types of nano-CaCO3 filled powdered rubber composite particles were prepared by coagulation method using nano-CaCO3 and latices as raw materials. The influence of the content of the composite particles on the mechanical properties of polyvinyl chloride (PVC) and their different reinforcing and toughening mechanisms were investigated. TEM micrographs show that the composite particles disperse well in the PVC matrix, where the nano-CaCO3 particles exist either uncovered or embedded in the rubber continuum. It was demonstrated that all three composite particles can dramatically increase the notched impact strength of PVC, among which nano-CaCO3 filled powdered acrylonitrile-butadiene rubber (CaCO3-NBR) can achieve high stiffness and toughness. While nano-CaCO3 filled powdered styrene-butadiene rubber (CaCO3-SBR) improves the impact resistance at the cost of decrease in stiffness, resulting in the significantly decreasing of flexural modulus and tensile strength. The modification effect of nano-CaCO3 filled powdered carboxylated styrene-butadiene rubber (CaCO3-X-SBR) is between CaCO3-NBR and CaCO3-SBR. The results also show that the compatibility between the composite particles and PVC is the key point for the reinforcing and toughening effect. The composite particles with good compatibility with PVC matrix demonstrate better synergistic reinforce and toughen effect than the ones with bad compatibility.
Three types of nano-CaCO3 filled powdered rubber composite particles were prepared by coagulation method using nano-CaCO3 and latices as raw materials. The influence of the content of the composite particles on the mechanical properties of polyvinyl chloride (PVC) and their different reinforcing and toughening mechanisms were investigated. TEM micrographs show that the composite particles disperse well in the PVC matrix, where the nano-CaCO3 particles exist either uncovered or embedded in the rubber continuum. It was demonstrated that all three composite particles can dramatically increase the notched impact strength of PVC, among which nano-CaCO3 filled powdered acrylonitrile-butadiene rubber (CaCO3-NBR) can achieve high stiffness and toughness. While nano-CaCO3 filled powdered styrene-butadiene rubber (CaCO3-SBR) improves the impact resistance at the cost of decrease in stiffness, resulting in the significantly decreasing of flexural modulus and tensile strength. The modification effect of nano-CaCO3 filled powdered carboxylated styrene-butadiene rubber (CaCO3-X-SBR) is between CaCO3-NBR and CaCO3-SBR. The results also show that the compatibility between the composite particles and PVC is the key point for the reinforcing and toughening effect. The composite particles with good compatibility with PVC matrix demonstrate better synergistic reinforce and toughen effect than the ones with bad compatibility.
2012, (6): 26-31.
Abstract:
Multiwall carbon nanotubes (MWCNTs) buckypaper was prepared using vacuum filtration method. The tensile properties and fracture morphology of buckypaper reinforced different kinds of epoxy resin composites were analyzed. The effects of the MWCNTs content, matrix tensile properties and interfacial adhesive effects between buckypaper and the resin matrix on the composites tensile properties were investigated. The results show that the tensile properties of composites increase considerably with increasing content of MWCNTs when the MWCNTs mass fraction is lower than 39.1%. The tensile properties of buckypaper/epoxy resin composites are also closely related to the properties of resin matrix, of which the toughness and brittleness have obvious effects on the tensile failure mode of the composites as well. Comparatively speaking, the influence of the adhesion work between the buckypaper and the resin matrix is not significant.
Multiwall carbon nanotubes (MWCNTs) buckypaper was prepared using vacuum filtration method. The tensile properties and fracture morphology of buckypaper reinforced different kinds of epoxy resin composites were analyzed. The effects of the MWCNTs content, matrix tensile properties and interfacial adhesive effects between buckypaper and the resin matrix on the composites tensile properties were investigated. The results show that the tensile properties of composites increase considerably with increasing content of MWCNTs when the MWCNTs mass fraction is lower than 39.1%. The tensile properties of buckypaper/epoxy resin composites are also closely related to the properties of resin matrix, of which the toughness and brittleness have obvious effects on the tensile failure mode of the composites as well. Comparatively speaking, the influence of the adhesion work between the buckypaper and the resin matrix is not significant.
2012, (6): 32-36.
Abstract:
As the surface modifier of carbon fiber, silica sol were prepared using silane coupling agent, tetraethoxysilane(TEOS) as the precursor and p-toluenesulfonic acid(PTSA) as the catalyst. The single fiber/epoxy composite were prepared using the treated carbon fiber as the reinforcement. The carbon fibers were characterized by examination of the morphology and mechanical properties using SEM, TEM and tensile testing. Interfacial shear strength (IFSS) of the composite was measured by single-fiber fragmentation testing. The results show that a layer of the membrane-grain structure on the surface of the carbon fiber is formed in situ after being treated by the silica sol. The tensile strength of a single fiber increases from 2.41 GPa to 3.00 GPa. The interfacial properties of the composite is greatly improved and the interfacial shear strength increases by 51.41%.
As the surface modifier of carbon fiber, silica sol were prepared using silane coupling agent, tetraethoxysilane(TEOS) as the precursor and p-toluenesulfonic acid(PTSA) as the catalyst. The single fiber/epoxy composite were prepared using the treated carbon fiber as the reinforcement. The carbon fibers were characterized by examination of the morphology and mechanical properties using SEM, TEM and tensile testing. Interfacial shear strength (IFSS) of the composite was measured by single-fiber fragmentation testing. The results show that a layer of the membrane-grain structure on the surface of the carbon fiber is formed in situ after being treated by the silica sol. The tensile strength of a single fiber increases from 2.41 GPa to 3.00 GPa. The interfacial properties of the composite is greatly improved and the interfacial shear strength increases by 51.41%.
2012, (6): 37-41.
Abstract:
The rheological behaves of polyether-ether ketone (PEKC)-bismaleimide (BMI) system during isothermal curing was studied by in-situ rheology. The time and temperature dependence were discussed in detail. The influence of PEKC contents on the viscosity of the PEKC-BMI blends was investigated. The results show that the gel point of BMI resin is of the frequency dependence, while tanδ is frequency independent. The viscosity increase of PEKC-BMI resin system is caused by PEKC dissolving in BMI and BMI curing with the increasing temperature. Comparison of 110℃ with 130℃ shows that, at higher temperature, the viscosity increase of the composite resin system is mainly caused by BMI resin curing. As the temperature increase, the gel time with increasing PEKC content shortens more rapidly, while the gel modulus increment becomes less. However, at lower temperature, the gel modulus increment becomes more with increasing PEKC content. With PEKC content of the resin system increasing, the apparent activation energy of gelation reaction increases from 4.9 kJ/mol to 65.9 kJ/mol. It is indicated that the temperature sensitivity of gelation behavior increases.
The rheological behaves of polyether-ether ketone (PEKC)-bismaleimide (BMI) system during isothermal curing was studied by in-situ rheology. The time and temperature dependence were discussed in detail. The influence of PEKC contents on the viscosity of the PEKC-BMI blends was investigated. The results show that the gel point of BMI resin is of the frequency dependence, while tanδ is frequency independent. The viscosity increase of PEKC-BMI resin system is caused by PEKC dissolving in BMI and BMI curing with the increasing temperature. Comparison of 110℃ with 130℃ shows that, at higher temperature, the viscosity increase of the composite resin system is mainly caused by BMI resin curing. As the temperature increase, the gel time with increasing PEKC content shortens more rapidly, while the gel modulus increment becomes less. However, at lower temperature, the gel modulus increment becomes more with increasing PEKC content. With PEKC content of the resin system increasing, the apparent activation energy of gelation reaction increases from 4.9 kJ/mol to 65.9 kJ/mol. It is indicated that the temperature sensitivity of gelation behavior increases.
2012, (6): 42-49.
Abstract:
Nanoparticles of AgCl were synthesized in W/O reverse microemulsion using ionic liquid 1-dodecyl-3-methyl imidazoium chloride(C12mimCl) as surfactant, methyl methacrylate(MMA)-acrylamide(AM) mixture as oil phase. And then AgCl/poly(MMA-co-AM) hybrid membranes were prepared by microemulsion polymerization for separation of benzene-cyclohexane(mass fraction 50%) mixture by pervaporation at 30℃. The effect of concentration of surfactant (cC12mimCl) and salt (cAgNO3) on formation and morphology of AgCl nanoparticles were studied by ultraviolet-visible spectrum and transmission electron microscopy(TEM). The structures of hybrid membranes were characterized by XRD and SEM. The pervaporation performance of the hybrid membranes was studied. The results show that the number and average size of AgCl nanoparticles increase significantly with the increase of c AgNO3, and the number of AgCl nanoparticles increases but the average sizes decreases with the increase of cC12mimCl. AgCl nanoparticles maintain well dispersion with small size in AgCl/poly(MMA-co-AM) hybrid membranes. With the increase of cAgNO3, the flux of the hybrid membranes increases significantly, and the separation factor of hybrid membranes for benzene-cyclohexane mixtures increases first and then decreases. When cC12mimCl rising, the separation factor increases continuously, and the flux increases first and then decreases. The maximum separation factor of hybrid membrane for benzene-cyclohexane mixtures reaches 5.0 and the flux of the hybrid membrane is 490 g·m-2·h-1, which demonstrates good separation property.
Nanoparticles of AgCl were synthesized in W/O reverse microemulsion using ionic liquid 1-dodecyl-3-methyl imidazoium chloride(C12mimCl) as surfactant, methyl methacrylate(MMA)-acrylamide(AM) mixture as oil phase. And then AgCl/poly(MMA-co-AM) hybrid membranes were prepared by microemulsion polymerization for separation of benzene-cyclohexane(mass fraction 50%) mixture by pervaporation at 30℃. The effect of concentration of surfactant (cC12mimCl) and salt (cAgNO3) on formation and morphology of AgCl nanoparticles were studied by ultraviolet-visible spectrum and transmission electron microscopy(TEM). The structures of hybrid membranes were characterized by XRD and SEM. The pervaporation performance of the hybrid membranes was studied. The results show that the number and average size of AgCl nanoparticles increase significantly with the increase of c AgNO3, and the number of AgCl nanoparticles increases but the average sizes decreases with the increase of cC12mimCl. AgCl nanoparticles maintain well dispersion with small size in AgCl/poly(MMA-co-AM) hybrid membranes. With the increase of cAgNO3, the flux of the hybrid membranes increases significantly, and the separation factor of hybrid membranes for benzene-cyclohexane mixtures increases first and then decreases. When cC12mimCl rising, the separation factor increases continuously, and the flux increases first and then decreases. The maximum separation factor of hybrid membrane for benzene-cyclohexane mixtures reaches 5.0 and the flux of the hybrid membrane is 490 g·m-2·h-1, which demonstrates good separation property.
2012, (6): 50-54.
Abstract:
CNTs/PLA composites were prepared by solution blending method in the presence of pristine carbon nanotubes(MWCNTs)and carboxylated carbon nanotubes(MWCNTCOOH). The dispersity of CNTs, crystallization morphology, electric conductivity and degradation were studied. The results show that MWCNTCOOH are dispersed more homogeneously in PLA than the pristine MWCNTs by SEM. POM(Polarizing Optical Microscope) results shows that the MWCNTs act as effective nucleating agents and decrease the crystal size. With the addition of a little MWCNTCOOH, the volume resistivity of the nanocomposite decreases by 7 orders of magnitude, and the degradation also increases by MWCNTCOOH.
CNTs/PLA composites were prepared by solution blending method in the presence of pristine carbon nanotubes(MWCNTs)and carboxylated carbon nanotubes(MWCNTCOOH). The dispersity of CNTs, crystallization morphology, electric conductivity and degradation were studied. The results show that MWCNTCOOH are dispersed more homogeneously in PLA than the pristine MWCNTs by SEM. POM(Polarizing Optical Microscope) results shows that the MWCNTs act as effective nucleating agents and decrease the crystal size. With the addition of a little MWCNTCOOH, the volume resistivity of the nanocomposite decreases by 7 orders of magnitude, and the degradation also increases by MWCNTCOOH.
2012, (6): 55-59.
Abstract:
The polylactide(PLA) and thermoplastic acetylated starch(TPAS) composities were prepared by molten blending method, and the mechanical properties, thermal properties and morphology of TPAS/PLA composites were investigated. TPAS was prepared with acetylated starch as matrix and glycerol as plasticizer. The experimental results show that the toughness of TPAS/PLA composite was significantly improved with the increase of TPAS. The elongation at break of TPAS/PLA improves by four times as much as pure PLA with TPAS mass fraction of 40%. In addition, TPAS has little effect on the thermal stability of PLA/ATPS composites. DSC, dynamic mechanical analysis and SEM results indicate that PLA and ATPS are immiscible.
The polylactide(PLA) and thermoplastic acetylated starch(TPAS) composities were prepared by molten blending method, and the mechanical properties, thermal properties and morphology of TPAS/PLA composites were investigated. TPAS was prepared with acetylated starch as matrix and glycerol as plasticizer. The experimental results show that the toughness of TPAS/PLA composite was significantly improved with the increase of TPAS. The elongation at break of TPAS/PLA improves by four times as much as pure PLA with TPAS mass fraction of 40%. In addition, TPAS has little effect on the thermal stability of PLA/ATPS composites. DSC, dynamic mechanical analysis and SEM results indicate that PLA and ATPS are immiscible.
2012, (6): 60-65.
Abstract:
The silane coupling agent and alkaline solution were used for surface treatment on the bagasse fiber (BF), and the influence of surface treatment methods on the mechanical property of BF/PLA composite were investigated. The morphology of the impact section of BF/PLA composite was observed by SEM. The results show that surface treatment on BF can improve the interface compatibility between BF and PLA matrix and enhance the mechanical strength of BF/PLA composite to some extent. Among the three surface treatments investigated, the silane coupling agent treatment after being treated by alkaline solution on BF performs the best effect on improving the mechanical property of BF/PLA composite, and the mechanical strength of BF/PLA composite can keep 85.42% tensile strength and 59.74% impact strength of neat PLA after treated by alkaline solution combined with silane coupling agent even the mass fraction of BF reaches 40%. Moreover, the surface of BF turns rough, specific surface area grows larger, length-diameter ratio increases and the interfacial adhesion enhances after being treated by alkaline, which result in the effective improvement of the machanical property.
The silane coupling agent and alkaline solution were used for surface treatment on the bagasse fiber (BF), and the influence of surface treatment methods on the mechanical property of BF/PLA composite were investigated. The morphology of the impact section of BF/PLA composite was observed by SEM. The results show that surface treatment on BF can improve the interface compatibility between BF and PLA matrix and enhance the mechanical strength of BF/PLA composite to some extent. Among the three surface treatments investigated, the silane coupling agent treatment after being treated by alkaline solution on BF performs the best effect on improving the mechanical property of BF/PLA composite, and the mechanical strength of BF/PLA composite can keep 85.42% tensile strength and 59.74% impact strength of neat PLA after treated by alkaline solution combined with silane coupling agent even the mass fraction of BF reaches 40%. Moreover, the surface of BF turns rough, specific surface area grows larger, length-diameter ratio increases and the interfacial adhesion enhances after being treated by alkaline, which result in the effective improvement of the machanical property.
2012, (6): 66-72.
Abstract:
Based on depth of penetration (DOP) experiments, a series of anti-penetration experiments were conducted in Glass, Carbon, Kevlar-49 and PBO plain weave fabric reinforced rubber composite targets subjected to shaped charge jet penetration. The residual penetration depths for four types of composites plate in validating targets were obtained. Deformations of F-plate and damage characteristics of weave fabric were analyzed. The space efficiency factor and the differential efficiency factor of four types of plain weave fabric composite plate were calculated. Results show that deformations of F-plate has an important impact on the fragmentation and scattering of the jet. The longer interaction regions between jet and F-plate, the more obvious of jet were disturbed. The protection ability of Kevlar-49 and PBO plain weave fabric reinforced rubber composite targets are better than the other two types of composites targets.
Based on depth of penetration (DOP) experiments, a series of anti-penetration experiments were conducted in Glass, Carbon, Kevlar-49 and PBO plain weave fabric reinforced rubber composite targets subjected to shaped charge jet penetration. The residual penetration depths for four types of composites plate in validating targets were obtained. Deformations of F-plate and damage characteristics of weave fabric were analyzed. The space efficiency factor and the differential efficiency factor of four types of plain weave fabric composite plate were calculated. Results show that deformations of F-plate has an important impact on the fragmentation and scattering of the jet. The longer interaction regions between jet and F-plate, the more obvious of jet were disturbed. The protection ability of Kevlar-49 and PBO plain weave fabric reinforced rubber composite targets are better than the other two types of composites targets.
2012, (6): 73-77.
Abstract:
Under the condition of tensile stress, dielectric strengths of resin and unique directional glass fiber reinforced resin composites were tested, and a relationship between dielectric strength and tensile stress of the resin and glass fiber/resin composites was studied. A negative exponential equation for expressing the relationship between dielectric strength and tensile stress for the resin was proposed and then was experimental proved. It has been found that the interface of the fiber and the resin plays a dominant role on the dielectric strength of composites.
Under the condition of tensile stress, dielectric strengths of resin and unique directional glass fiber reinforced resin composites were tested, and a relationship between dielectric strength and tensile stress of the resin and glass fiber/resin composites was studied. A negative exponential equation for expressing the relationship between dielectric strength and tensile stress for the resin was proposed and then was experimental proved. It has been found that the interface of the fiber and the resin plays a dominant role on the dielectric strength of composites.
2012, (6): 78-82,96.
Abstract:
In order to reduce the content of residual Si generated in the process of liquid silicon infiltration, B12(C, Si, B)3 modified C/C-SiC composite was prepared by a joint process of slurry impregnation and liquid silicon infiltration. By analyzing the products of B4C-Si system with different B4C/Si molar ratios after sintered at different temperatures, the formation condition of B12(C, Si, B)3 was studied. The results indicate that B4C starts to react with Si at 1300℃, leading to the formation of a small amount of B12(C, Si, B)3 and SiC. The amount of B12(C, Si, B)3 generated in the reaction increases with increasing sintering temperature. The sintering product of B4C-Si system with a B4C/Si molar ratio of 3:1 at 1500℃ is composed of B12 (C, Si, B)3 and SiC. The C/C-SiC composite fabricated by liquid silicon infiltration is composed of amorphous C, β-SiC and B12(C,Si,B)3, and no residual Si is detected.
In order to reduce the content of residual Si generated in the process of liquid silicon infiltration, B12(C, Si, B)3 modified C/C-SiC composite was prepared by a joint process of slurry impregnation and liquid silicon infiltration. By analyzing the products of B4C-Si system with different B4C/Si molar ratios after sintered at different temperatures, the formation condition of B12(C, Si, B)3 was studied. The results indicate that B4C starts to react with Si at 1300℃, leading to the formation of a small amount of B12(C, Si, B)3 and SiC. The amount of B12(C, Si, B)3 generated in the reaction increases with increasing sintering temperature. The sintering product of B4C-Si system with a B4C/Si molar ratio of 3:1 at 1500℃ is composed of B12 (C, Si, B)3 and SiC. The C/C-SiC composite fabricated by liquid silicon infiltration is composed of amorphous C, β-SiC and B12(C,Si,B)3, and no residual Si is detected.
2012, (6): 83-89.
Abstract:
CeO2-La2O3/attapulgite(CeO2-La2O3/ATP) nanocomposites with different molar ratios of Ce4+ to La3+ were prepared by homogeneous precipitation method using ATP as support, cerium nitrate hexahydrate and lanthanum nitrate hexahydrate as raw materials, and hexamethylene tetramine as precipitant, respectively. TG-DSC, TEM, XRD and FTIR were adopted to characterize the microstructure and composition of the prepared products. Effects of molar ratios of Ce4+ to La3+ and the dosage of H2O2 as oxidant on the decolorization of acid fuchsin were investigated. Results indicate that the solid solution particles with a size of 5-10 nm are uniformly dispersed on the surface of ATP when the molar ratio of Ce4+ to La3+ is 5:5. With the increase of the molar ratio of Ce4+ to La3+, the decoloring rate tends to increase first and then decrease. The decoloring rate can reach 82% after 300 min, when the concentration of acid fuchsin is 100 mg/L, the molar ratio of Ce4+ to La3+ is 5:5 and the dosage of H2O2 is 10 mL.
CeO2-La2O3/attapulgite(CeO2-La2O3/ATP) nanocomposites with different molar ratios of Ce4+ to La3+ were prepared by homogeneous precipitation method using ATP as support, cerium nitrate hexahydrate and lanthanum nitrate hexahydrate as raw materials, and hexamethylene tetramine as precipitant, respectively. TG-DSC, TEM, XRD and FTIR were adopted to characterize the microstructure and composition of the prepared products. Effects of molar ratios of Ce4+ to La3+ and the dosage of H2O2 as oxidant on the decolorization of acid fuchsin were investigated. Results indicate that the solid solution particles with a size of 5-10 nm are uniformly dispersed on the surface of ATP when the molar ratio of Ce4+ to La3+ is 5:5. With the increase of the molar ratio of Ce4+ to La3+, the decoloring rate tends to increase first and then decrease. The decoloring rate can reach 82% after 300 min, when the concentration of acid fuchsin is 100 mg/L, the molar ratio of Ce4+ to La3+ is 5:5 and the dosage of H2O2 is 10 mL.
2012, (6): 90-96.
Abstract:
The laminated structure of the Ti/C composite materials with the sheet of Ti and C as raw materials was prepared by spark plasma sintering (SPS) technology. Microstructure and room temperature mechanical properties of laminated material were studied at different sintering temperatures. The results show that the layer thickness increases with the sintering temperature. When the sintering temperature reaches 1500℃, the layer thickness is up to 32.6 μm. Ti will be partially melted when the sintering temperature is higher than 1500℃ and the Ti/C laminated composite material can’t be obtained. When the sintering temperature reaches 1500℃ and 1510℃, the laminated composite bending strength and fracture power reach the maximum value of 1571.51 MPa and 215.09×103 J/m2, respectively. The crack propagation of Ti/C laminated material includes the crack deflection, crack parallel expansion and bifurcation of the crack tip passive, and these expansion pathes are the main toughening mechanism.
The laminated structure of the Ti/C composite materials with the sheet of Ti and C as raw materials was prepared by spark plasma sintering (SPS) technology. Microstructure and room temperature mechanical properties of laminated material were studied at different sintering temperatures. The results show that the layer thickness increases with the sintering temperature. When the sintering temperature reaches 1500℃, the layer thickness is up to 32.6 μm. Ti will be partially melted when the sintering temperature is higher than 1500℃ and the Ti/C laminated composite material can’t be obtained. When the sintering temperature reaches 1500℃ and 1510℃, the laminated composite bending strength and fracture power reach the maximum value of 1571.51 MPa and 215.09×103 J/m2, respectively. The crack propagation of Ti/C laminated material includes the crack deflection, crack parallel expansion and bifurcation of the crack tip passive, and these expansion pathes are the main toughening mechanism.
2012, (6): 97-101.
Abstract:
Pure nano TiO2 and La3+-Pr3+ co-doped nano-TiO2(La3+-Pr3+/TiO2) catalyst were prepared by a sol-gel method with TBT and distilled water as forerunner body, ethanol as solvent and glacial acetic acid as inhibitor. The prepared samples were characterized by XRD, TEM and UV-Vis. The UV-light photocatalytic performance of the obtained materials was evaluated by methylene orange decomposition. The results show that the prepared samples are all pure anatase phase nano-TiO2 and their diffraction peak broadens obviously after La3+-Pr3+ co-doped. Compared with pure TiO2, the particle sizes of La3+-Pr3+ co-doped TiO2 are smaller, its specific surface area is larger, and its absorption edge shifts more remarkably towards longer wavelength. The photocatalytic activity of La3+-Pr3+ co-doped TiO2 is higher than that of TiO2 or La3+(Pr3+)-doped TiO2, which is enhanced with the La3+ and Pr3+ contents, reaching the maximum at the La3+/TiO2 and Pr3+/TiO2 molar ratios of 1.0% and 0.2%, respectively. The enhanced visible photocatalytic performance is attributed to the synergetic effect of La3+ and Pr3+ co-doped.
Pure nano TiO2 and La3+-Pr3+ co-doped nano-TiO2(La3+-Pr3+/TiO2) catalyst were prepared by a sol-gel method with TBT and distilled water as forerunner body, ethanol as solvent and glacial acetic acid as inhibitor. The prepared samples were characterized by XRD, TEM and UV-Vis. The UV-light photocatalytic performance of the obtained materials was evaluated by methylene orange decomposition. The results show that the prepared samples are all pure anatase phase nano-TiO2 and their diffraction peak broadens obviously after La3+-Pr3+ co-doped. Compared with pure TiO2, the particle sizes of La3+-Pr3+ co-doped TiO2 are smaller, its specific surface area is larger, and its absorption edge shifts more remarkably towards longer wavelength. The photocatalytic activity of La3+-Pr3+ co-doped TiO2 is higher than that of TiO2 or La3+(Pr3+)-doped TiO2, which is enhanced with the La3+ and Pr3+ contents, reaching the maximum at the La3+/TiO2 and Pr3+/TiO2 molar ratios of 1.0% and 0.2%, respectively. The enhanced visible photocatalytic performance is attributed to the synergetic effect of La3+ and Pr3+ co-doped.
2012, (6): 102-107.
Abstract:
TiO2/AC composites were prepared via the sol-gel method from a carrier of activated carbon (AC) and Ti(OBu)4. Photocatalysts were characterized by TGA-DSC, SEM, XRD, diffuse reflectance spectroscopy (DRS) and FTIR. The ultrasound-TiO2 photocatalytic reduction removal rate by determination concentration of chrome(Ⅵ) and copper (Ⅱ) was also studied by atomic absorption spectrophotometer (AAS). The results show that TiO2/AC prepared by sol-gel method transforms from rutile into anatase at the temperature of 290℃ and shows the highest catalytic activity at 500℃. TiO2/AC composites which formed C—O—Ti between the AC bulk and TiO2 has good dispersion, low agglomeration and high surface area. The mechanism of photocatalytic reduction and adsorption follows the first order kinetics equation ln(c0/c)=kt and Langmuir-Hinshelwood adsorption. Compared with the no-ultrasound, the reductive removal rate of Cr(Ⅵ) and Cu(Ⅱ) can be improved by 39.32% and 52.95% using ultrasound-photocatalytic technology. Cr(Ⅵ) and Cu(Ⅱ) removal rate is 70.61% and 75.30% even when the catalysts are recycled three times.
TiO2/AC composites were prepared via the sol-gel method from a carrier of activated carbon (AC) and Ti(OBu)4. Photocatalysts were characterized by TGA-DSC, SEM, XRD, diffuse reflectance spectroscopy (DRS) and FTIR. The ultrasound-TiO2 photocatalytic reduction removal rate by determination concentration of chrome(Ⅵ) and copper (Ⅱ) was also studied by atomic absorption spectrophotometer (AAS). The results show that TiO2/AC prepared by sol-gel method transforms from rutile into anatase at the temperature of 290℃ and shows the highest catalytic activity at 500℃. TiO2/AC composites which formed C—O—Ti between the AC bulk and TiO2 has good dispersion, low agglomeration and high surface area. The mechanism of photocatalytic reduction and adsorption follows the first order kinetics equation ln(c0/c)=kt and Langmuir-Hinshelwood adsorption. Compared with the no-ultrasound, the reductive removal rate of Cr(Ⅵ) and Cu(Ⅱ) can be improved by 39.32% and 52.95% using ultrasound-photocatalytic technology. Cr(Ⅵ) and Cu(Ⅱ) removal rate is 70.61% and 75.30% even when the catalysts are recycled three times.
2012, (6): 108-112.
Abstract:
A non-crystal nanometer titanium oxide film was fabricated on the glass substrate with a method of sol-gel, SEM, XPS, XRD and contact angle meter were employed to characterize its surface morphologies, elements contained, crystal structure and wettability, respectively. The wettability of the film was discussed on the basis of Wenzel’ s and Cassie’ s theory. The results show that the film changes from superhydrophobicity to superhydrophilicity with a static contact angle of 0° after being irradiated under ultraviolet light for about 16 hours. The superhydrophobic properties are caused by the cooperation effect of appropriate surface roughness and surface modification of low surface energy material.
A non-crystal nanometer titanium oxide film was fabricated on the glass substrate with a method of sol-gel, SEM, XPS, XRD and contact angle meter were employed to characterize its surface morphologies, elements contained, crystal structure and wettability, respectively. The wettability of the film was discussed on the basis of Wenzel’ s and Cassie’ s theory. The results show that the film changes from superhydrophobicity to superhydrophilicity with a static contact angle of 0° after being irradiated under ultraviolet light for about 16 hours. The superhydrophobic properties are caused by the cooperation effect of appropriate surface roughness and surface modification of low surface energy material.
2012, (6): 113-119.
Abstract:
Ion-exchange polymer metal composites with Ag as electrodes (Ag-IPMC) samples were manufactured by the chemical deposition method at the reaction temperature of 23℃ and 10℃. As shown from the morphologies of samples observed by SEM and EDAX, the samples manufactured at reaction temperature of 10℃ possess better electrode deposition effects than those manufactured at 23℃, and the thicknesses of surface and interlocked electrodes increase by 25% and 34%, respectively, and cracking and spalling on surface electrodes are suppressed. Sensing characteristics of samples with thickness of 0.2 mm, 0.4 mm and 0.8 mm at reaction temperature of 10℃ were tested and analyzed. The results indicate that samples voltage output and sensitivity obviously increase with increasing sample thickness. All samples are sensitive to low frequency excitation, especially within the range of 0.3-0.8 Hz. As the excitation frequency is 0.65 Hz, the sensing voltage and sensitivity of sample in thickness of 0.8 mm are 17.82 mV and 1030.06 mV/mm, respectively.
Ion-exchange polymer metal composites with Ag as electrodes (Ag-IPMC) samples were manufactured by the chemical deposition method at the reaction temperature of 23℃ and 10℃. As shown from the morphologies of samples observed by SEM and EDAX, the samples manufactured at reaction temperature of 10℃ possess better electrode deposition effects than those manufactured at 23℃, and the thicknesses of surface and interlocked electrodes increase by 25% and 34%, respectively, and cracking and spalling on surface electrodes are suppressed. Sensing characteristics of samples with thickness of 0.2 mm, 0.4 mm and 0.8 mm at reaction temperature of 10℃ were tested and analyzed. The results indicate that samples voltage output and sensitivity obviously increase with increasing sample thickness. All samples are sensitive to low frequency excitation, especially within the range of 0.3-0.8 Hz. As the excitation frequency is 0.65 Hz, the sensing voltage and sensitivity of sample in thickness of 0.8 mm are 17.82 mV and 1030.06 mV/mm, respectively.
2012, (6): 120-123.
Abstract:
A series of Ti-Zr-Nb-Cu-Be metallic glass matrix composites with β-Ti(Zr, Nb) dendrites were synthesized by the copper-mold injection casting. The effects of the components on the size and volume fraction of dendrites were studied, and the mechanical properties of the samples were also investigated. The results show that Ti48Zr20Nb12Cu5Be15 performs good mechanical properties with compressive strength of 2061 MPa and plasticity up to 22.5%. The plasticity of metallic glass matrix composites is not only determined by the volume fraction of dendries, but also by the size of dendrites. The larger the dendrites, the more obvious for the resistance of moving shear bands, and the much higher plasticity of the alloy.
A series of Ti-Zr-Nb-Cu-Be metallic glass matrix composites with β-Ti(Zr, Nb) dendrites were synthesized by the copper-mold injection casting. The effects of the components on the size and volume fraction of dendrites were studied, and the mechanical properties of the samples were also investigated. The results show that Ti48Zr20Nb12Cu5Be15 performs good mechanical properties with compressive strength of 2061 MPa and plasticity up to 22.5%. The plasticity of metallic glass matrix composites is not only determined by the volume fraction of dendries, but also by the size of dendrites. The larger the dendrites, the more obvious for the resistance of moving shear bands, and the much higher plasticity of the alloy.
2012, (6): 124-128.
Abstract:
Ni nanoparticles filled carbon nanotubes were successfully prepared by the anodic arc discharging plasma utilizing self-designed and fabricated experimental apparatus. The composition, morphology, microstructure and magnetic properties of the products by this process were investigated via the high-resolution transmission electron microscopy (HRTEM), XRD, TEM, X-ray energy dispersive spectrometry (XEDS) and vibration sample magnetmeter (VSM). The experiment results show that most of the products are filled with the metallic nanoparticles, while the particles inside are face centered cubic(FCC) structure Ni, and the outside are well-graphitized nanotubes. The diameter of carbon nanotubes ranges from 30 nm to 40 nm, with the wall thickness approximately 5-8 nm. The particles encapsulated in carbon nanotubes are scattered and noncontinuous homogeneously in spherical or ellipsoidal shapes. Magnetic property tests show that the products is super paramagnetic, with the coercivities of 78 Oe and the saturation magnetization of 33 emu/g.
Ni nanoparticles filled carbon nanotubes were successfully prepared by the anodic arc discharging plasma utilizing self-designed and fabricated experimental apparatus. The composition, morphology, microstructure and magnetic properties of the products by this process were investigated via the high-resolution transmission electron microscopy (HRTEM), XRD, TEM, X-ray energy dispersive spectrometry (XEDS) and vibration sample magnetmeter (VSM). The experiment results show that most of the products are filled with the metallic nanoparticles, while the particles inside are face centered cubic(FCC) structure Ni, and the outside are well-graphitized nanotubes. The diameter of carbon nanotubes ranges from 30 nm to 40 nm, with the wall thickness approximately 5-8 nm. The particles encapsulated in carbon nanotubes are scattered and noncontinuous homogeneously in spherical or ellipsoidal shapes. Magnetic property tests show that the products is super paramagnetic, with the coercivities of 78 Oe and the saturation magnetization of 33 emu/g.
2012, (6): 129-134.
Abstract:
The structure and properties of of the Ti-Al composite electrode materials prepared by the hot-pressing diffusion bonding method was analyzed by SEM, EDS, four-probe method and electrochemical workstation. The results show that the metallurgical bonding of Ti and Al can be achieved by the method of hot-pressing diffusion sintering with static pressure of 6 MPa, bonding temperature of 550℃ and holding time in Ar higher than 90 min. Change process of the diffusion reactive layer with temperature is TiAl→TiAl2→TiAl3. The electrochemical properties of the composite electrode materials is also much better than pure Ti anode, and the effects of preparation conditions and the resistivity on electrochemical properties are consistent. Under the same condition, the polarization potential of composite materials will fall by 37-54 mV in polarization potential of pure Ti, and the current density can be increased by more than 59.29%, while the resistivity is only 1/10 of pure Ti.
The structure and properties of of the Ti-Al composite electrode materials prepared by the hot-pressing diffusion bonding method was analyzed by SEM, EDS, four-probe method and electrochemical workstation. The results show that the metallurgical bonding of Ti and Al can be achieved by the method of hot-pressing diffusion sintering with static pressure of 6 MPa, bonding temperature of 550℃ and holding time in Ar higher than 90 min. Change process of the diffusion reactive layer with temperature is TiAl→TiAl2→TiAl3. The electrochemical properties of the composite electrode materials is also much better than pure Ti anode, and the effects of preparation conditions and the resistivity on electrochemical properties are consistent. Under the same condition, the polarization potential of composite materials will fall by 37-54 mV in polarization potential of pure Ti, and the current density can be increased by more than 59.29%, while the resistivity is only 1/10 of pure Ti.
2012, (6): 135-143.
Abstract:
The radio frequency identification technology was introduced into the area of structure health monitoring, and a new wireless monitoring method for SMA reinforced epoxy composite laminates was proposed by using sensor-tags and reader. Using the SMA wires as the capacitor electrodes and the sample matrix as the dielectric, the capacitance signals were measured and packaged with the current time and address information by sensor-tags, then transmitted to the monitoring station by reader networks. For two kinds of NiTi reinforced composite laminated board, the tensile test, bending test and impact experiment were conducted in universal material testing machine and impact testing machine, respectively. The results show that the system can monitor the outputs by embedded hyperelastic wires in composite structures, and it has the characteristics of good expansibility, simple routing and easy positioning.
The radio frequency identification technology was introduced into the area of structure health monitoring, and a new wireless monitoring method for SMA reinforced epoxy composite laminates was proposed by using sensor-tags and reader. Using the SMA wires as the capacitor electrodes and the sample matrix as the dielectric, the capacitance signals were measured and packaged with the current time and address information by sensor-tags, then transmitted to the monitoring station by reader networks. For two kinds of NiTi reinforced composite laminated board, the tensile test, bending test and impact experiment were conducted in universal material testing machine and impact testing machine, respectively. The results show that the system can monitor the outputs by embedded hyperelastic wires in composite structures, and it has the characteristics of good expansibility, simple routing and easy positioning.
2012, (6): 144-151.
Abstract:
To study the distribution regularity of nano particles in matrix material theoretically, SiC/PTFE(Poly Tetra Fluoro Ethylene) composites with SiC mass fraction of 3%, 5%, 7% and 9% were used as examples. According to the radius (25 nm), the density (3.2 g/cm3), mass fraction of SiC particles and the density of PTFE matrix material(2.2 g/cm3), 3D simulation models of uniform/deviation distributed nano particles in matrix material were established with 10-12 g for quality unit and to 25 nm:1 pixel for the scale. Based on box dimensions, dispersions of various cluster/deviation nano particles were characterized quantitatively and verified by mechanical experiment. Experimental results indicate that the box dimension of SiC particles decreases gradually in uniform distribution with the continuous increment of their radius, or the decrement of their volume fractions, and fractal characteristics doesn’t exist in the case of their radius above 100 nm. In another hand, the box dimension of SiC particles (50 nm for radius) decreases gradually in deviation distribution with the continuous increment of their span, or the decrement of their volume fractions, or varying of their distribution from layer and line to reunion, which is less than that in uniform distribution with the same volume fraction, and fractal characteristics doesn’t exist in the case of their span beyond 450 nm. Linear correlations (|R|>0.9) are observed between test results of mechanical properties of SiC/PTFE composites and box dimensions of their 3D simulation models in uniform distribution. Dispersions of nano particles can be characterized quantitatively using box dimension, which can be used to predict macroscopic properties of composites.
To study the distribution regularity of nano particles in matrix material theoretically, SiC/PTFE(Poly Tetra Fluoro Ethylene) composites with SiC mass fraction of 3%, 5%, 7% and 9% were used as examples. According to the radius (25 nm), the density (3.2 g/cm3), mass fraction of SiC particles and the density of PTFE matrix material(2.2 g/cm3), 3D simulation models of uniform/deviation distributed nano particles in matrix material were established with 10-12 g for quality unit and to 25 nm:1 pixel for the scale. Based on box dimensions, dispersions of various cluster/deviation nano particles were characterized quantitatively and verified by mechanical experiment. Experimental results indicate that the box dimension of SiC particles decreases gradually in uniform distribution with the continuous increment of their radius, or the decrement of their volume fractions, and fractal characteristics doesn’t exist in the case of their radius above 100 nm. In another hand, the box dimension of SiC particles (50 nm for radius) decreases gradually in deviation distribution with the continuous increment of their span, or the decrement of their volume fractions, or varying of their distribution from layer and line to reunion, which is less than that in uniform distribution with the same volume fraction, and fractal characteristics doesn’t exist in the case of their span beyond 450 nm. Linear correlations (|R|>0.9) are observed between test results of mechanical properties of SiC/PTFE composites and box dimensions of their 3D simulation models in uniform distribution. Dispersions of nano particles can be characterized quantitatively using box dimension, which can be used to predict macroscopic properties of composites.
2012, (6): 152-158.
Abstract:
BNNT/Si3N4 composites were prepared with Si3N4 ceramics enhanced by BN nanotubes (BNNT). Bending strength and fracture toughness of BNNT/Si3N4 composites were tested by three point bending strength and SENB method. BNNT/Si3N4 composite microstructures were observed by SEM. The mathematical model of the crack propagation resistance of Si3N4 ceramics crack shielding region enhanced by BNNT was constructed, which was based on the crack propagation resistance formula of BNNT reinforcing Si3N4 ceramics. The calculated results used this model were compared with crack propagation resistance of Si3N4 ceramics. The results show that bending strength and fracture toughness of BNNT/Si3N4 composites are obviously higher than those of pure Si3N4 ceramics and BNNT increases the crack propagation resistance of Si3N4 ceramics. It can be seen that the friction resistance to pull out is the main reason of reducing the Si3N4 ceramics crack propagation capability and that Si3N4 ceramics added BNNT has clear appreciation of the resistance curve behavior. The finite element simulation results on the crack tip stress indicate that BNNT makes maximum stress of the crack tip to deflect nanotubes and reduce stress of the Si3N4 ceramics crack tip, which can improve the crack propagation resistance behavior of Si3N4 ceramics.
BNNT/Si3N4 composites were prepared with Si3N4 ceramics enhanced by BN nanotubes (BNNT). Bending strength and fracture toughness of BNNT/Si3N4 composites were tested by three point bending strength and SENB method. BNNT/Si3N4 composite microstructures were observed by SEM. The mathematical model of the crack propagation resistance of Si3N4 ceramics crack shielding region enhanced by BNNT was constructed, which was based on the crack propagation resistance formula of BNNT reinforcing Si3N4 ceramics. The calculated results used this model were compared with crack propagation resistance of Si3N4 ceramics. The results show that bending strength and fracture toughness of BNNT/Si3N4 composites are obviously higher than those of pure Si3N4 ceramics and BNNT increases the crack propagation resistance of Si3N4 ceramics. It can be seen that the friction resistance to pull out is the main reason of reducing the Si3N4 ceramics crack propagation capability and that Si3N4 ceramics added BNNT has clear appreciation of the resistance curve behavior. The finite element simulation results on the crack tip stress indicate that BNNT makes maximum stress of the crack tip to deflect nanotubes and reduce stress of the Si3N4 ceramics crack tip, which can improve the crack propagation resistance behavior of Si3N4 ceramics.
2012, (6): 159-163.
Abstract:
The cooling process of SiC/Ti-6Al-4V composites and the transverse tensile test were simulated by finite element method. The cruciform specimen was selected to conduct the transverse tensile test of SiC/Ti-6Al-4V composites. In finite element analysis, the plain stress finite element model was used to analyze the interface stress distribution and failure mechanism of the cruciform specimen under the transverse tensile stress. The axisymmetric finite element model was adopted to analyze the interface debonding process and the effects of residual stress on the radial stress distribution at the interface. The results show that under the transverse tensile stress, the interface failure of the cruciform specimen is only resulted from the radial stress. The interface failure mode is the normal failure not the tangential failure. The interface debonding of the cruciform specimen appears in the middle of the interface. With the increasing of the transverse tensile stress, the interface debonding of the cruciform specimen symmetrically extends to both sides. Radial stresses at the interface increase with the decreasing thermal residual stresses.
The cooling process of SiC/Ti-6Al-4V composites and the transverse tensile test were simulated by finite element method. The cruciform specimen was selected to conduct the transverse tensile test of SiC/Ti-6Al-4V composites. In finite element analysis, the plain stress finite element model was used to analyze the interface stress distribution and failure mechanism of the cruciform specimen under the transverse tensile stress. The axisymmetric finite element model was adopted to analyze the interface debonding process and the effects of residual stress on the radial stress distribution at the interface. The results show that under the transverse tensile stress, the interface failure of the cruciform specimen is only resulted from the radial stress. The interface failure mode is the normal failure not the tangential failure. The interface debonding of the cruciform specimen appears in the middle of the interface. With the increasing of the transverse tensile stress, the interface debonding of the cruciform specimen symmetrically extends to both sides. Radial stresses at the interface increase with the decreasing thermal residual stresses.
2012, (6): 164-169.
Abstract:
A three-dimensional(3D) FEM was proposed for the progressive damage analysis(PDA) of the stepped-patch bonding repaired composite laminate. Both of the composite laminate and adhesive damage progressing and acting on each other during the process of failure were taken into account. The laminate was modeled with the constitutive equations of continuum damage mechanics(CDM) in an orthotropic damage with a second-order tensor as the internal state variables to describe the damage status of material points. The adhesive layer was modeled with the constitutive equation of CDM in an isotropic damage with a constant internal state variable. The good agreement between the results of the proposed FEM and the experiments shows that the proposed FEM could well predict the tensile strength of laminates repaired with bonded stepped-patch and the whole process of repaired laminates failure.
A three-dimensional(3D) FEM was proposed for the progressive damage analysis(PDA) of the stepped-patch bonding repaired composite laminate. Both of the composite laminate and adhesive damage progressing and acting on each other during the process of failure were taken into account. The laminate was modeled with the constitutive equations of continuum damage mechanics(CDM) in an orthotropic damage with a second-order tensor as the internal state variables to describe the damage status of material points. The adhesive layer was modeled with the constitutive equation of CDM in an isotropic damage with a constant internal state variable. The good agreement between the results of the proposed FEM and the experiments shows that the proposed FEM could well predict the tensile strength of laminates repaired with bonded stepped-patch and the whole process of repaired laminates failure.
2012, (6): 170-178.
Abstract:
To predict the mechanical behaviors of non-crimp fabric reinforced composites, hexagonal unit cell (UC) and rectangular UC were developed to represent the fiber tow and composite, respectively. The equation boundary condition of the fiber tow UC was derived in detail. The macro-scale effective stiffness and strength of a non-crimp carbon fabric reinforced epoxy composite was obtained by calculating the effective elastic constants of the two UCs at different length scales. Finite element damage analyses were performed to study the progressive failure of the composite in tension. Results show that the initial damage occurs in either the resin pockets or the transverse tows. Damage develops within the resin pockets and transverse tows, and progresses into the longitudinal tows and causes the composite failure very quickly. The predicted value of tensile modulus of the non-crimp fabric reinforced composite is very close to experimental value, and the calculated value of tensile strength is slightly less than that of experimental value.
To predict the mechanical behaviors of non-crimp fabric reinforced composites, hexagonal unit cell (UC) and rectangular UC were developed to represent the fiber tow and composite, respectively. The equation boundary condition of the fiber tow UC was derived in detail. The macro-scale effective stiffness and strength of a non-crimp carbon fabric reinforced epoxy composite was obtained by calculating the effective elastic constants of the two UCs at different length scales. Finite element damage analyses were performed to study the progressive failure of the composite in tension. Results show that the initial damage occurs in either the resin pockets or the transverse tows. Damage develops within the resin pockets and transverse tows, and progresses into the longitudinal tows and causes the composite failure very quickly. The predicted value of tensile modulus of the non-crimp fabric reinforced composite is very close to experimental value, and the calculated value of tensile strength is slightly less than that of experimental value.
2012, (6): 179-186.
Abstract:
Nonlinear dynamics characteristics of symmetric rectangular honeycomb sandwich panels with completed clamped supported boundaries in primary resonance case were investigated using the homotopy analysis method(HAM). The honeycomb core of aluminum matrix was equivalent to a thick layer of orthotropic material whose equivalent elastic constants were calculated by the modified Gibson’s formula. Based on the classical laminated plate theory(CPT) and geometric large deformation theory, the forced vibration differential equations under transverse exciting force were derived. By means of vibration mode orthogonalization, the differential equations were simplified into dynamic control equations with dual-mode, and the average equations of primary resonance was obtained. Then the influences of different structural parameters on dynamic characteristics were studied. Numerical results show that the amplitude-frequency curves of honeycomb sandwich panels correspond to the response curves of Duffing equation with single degree. With the increase of the structural parameters, the obvious enhancement of the hard characteristic, and the remarkable decrease of the peak value of amplitude were observed. The conclusion can be applied to designing honeycomb sandwich panels and provide a theoretical basis for practical applications.
Nonlinear dynamics characteristics of symmetric rectangular honeycomb sandwich panels with completed clamped supported boundaries in primary resonance case were investigated using the homotopy analysis method(HAM). The honeycomb core of aluminum matrix was equivalent to a thick layer of orthotropic material whose equivalent elastic constants were calculated by the modified Gibson’s formula. Based on the classical laminated plate theory(CPT) and geometric large deformation theory, the forced vibration differential equations under transverse exciting force were derived. By means of vibration mode orthogonalization, the differential equations were simplified into dynamic control equations with dual-mode, and the average equations of primary resonance was obtained. Then the influences of different structural parameters on dynamic characteristics were studied. Numerical results show that the amplitude-frequency curves of honeycomb sandwich panels correspond to the response curves of Duffing equation with single degree. With the increase of the structural parameters, the obvious enhancement of the hard characteristic, and the remarkable decrease of the peak value of amplitude were observed. The conclusion can be applied to designing honeycomb sandwich panels and provide a theoretical basis for practical applications.
2012, (6): 187-196.
Abstract:
Based on the existing experiment observation and theoretical research, the spatial configuration of interior yarns was analyzed in detail, a new microstructure model of 3D braided composites was established and the mathematical relationship between technics parameters and microstructure model parameters was obtained. The new model truly reflects the jamming pattern between yarns and its cross-section variation along the axial of the yarns coinciding with the actual configuration of the 3D and four-directional braided composites. A model to predict stiffness was then established based on the stiffness volume average method and flexibility volume average method. The calculated simulation values of the geometric characteristics and elastic constants of braided composites well agree with the measured values, which prove the effectiveness of the model. The present model has presented a foundation for the strength prediction and failure mechanism of the 3D braided composites.
Based on the existing experiment observation and theoretical research, the spatial configuration of interior yarns was analyzed in detail, a new microstructure model of 3D braided composites was established and the mathematical relationship between technics parameters and microstructure model parameters was obtained. The new model truly reflects the jamming pattern between yarns and its cross-section variation along the axial of the yarns coinciding with the actual configuration of the 3D and four-directional braided composites. A model to predict stiffness was then established based on the stiffness volume average method and flexibility volume average method. The calculated simulation values of the geometric characteristics and elastic constants of braided composites well agree with the measured values, which prove the effectiveness of the model. The present model has presented a foundation for the strength prediction and failure mechanism of the 3D braided composites.
2012, (6): 197-205.
Abstract:
The domain decomposition method was proposed for the study of mechanical properties of 2D woven fabric composite (WFC) based on mesh superposition method. The domain decomposition method was different from traditional represent volume element method. Instead of modeling the fibre and matrix explicitly in traditional represent volume element method, domain decomposition method separately models the global domain and fibre domain, which can be easily discretized using the traditional solid element. Global domain was superimposed by fiber domain and matrix domain. The two domains were superimposed by coupling with multi-point constraints from commercial finite element package MSC. Nastran. The displacement function was established to simulate coupling between fibre domain and global domain by multi-point constraints. Domain decomposition method is easier to set up models of WFC than traditional represent volume element method. Numerical simulations show that the results predicted by domain decomposition method correlate very well with the experimental data. Otherwise, the tendency of mechanical properties under different fiber volume fraction of WFC was also investigated. With the increasing of fiber volume fraction, the moduli of WFC increases, while Poisson’s ratios decreases.
The domain decomposition method was proposed for the study of mechanical properties of 2D woven fabric composite (WFC) based on mesh superposition method. The domain decomposition method was different from traditional represent volume element method. Instead of modeling the fibre and matrix explicitly in traditional represent volume element method, domain decomposition method separately models the global domain and fibre domain, which can be easily discretized using the traditional solid element. Global domain was superimposed by fiber domain and matrix domain. The two domains were superimposed by coupling with multi-point constraints from commercial finite element package MSC. Nastran. The displacement function was established to simulate coupling between fibre domain and global domain by multi-point constraints. Domain decomposition method is easier to set up models of WFC than traditional represent volume element method. Numerical simulations show that the results predicted by domain decomposition method correlate very well with the experimental data. Otherwise, the tendency of mechanical properties under different fiber volume fraction of WFC was also investigated. With the increasing of fiber volume fraction, the moduli of WFC increases, while Poisson’s ratios decreases.
2012, (6): 206-211.
Abstract:
Based on the mesoscopic structure of the three-dimensional woven carbon/carbon (3D C/C) composite materials, a kind of flat cross-shaped specimen was designed followed by the test on biaxial mechanical testing machine under uniaxial and biaxial compression as well. Comparative analysis was carried out for the mechanical behavior of the 3D C/C composite materials under biaxial compression loading. The results show that the 3D C/C composite materials represent the non-linear compression behavior and brittle fracture. The nonlinear characteristics under biaxial loading are more significant, and the compression modulus increases along with the increase of stress. The strength and modulus of 3D C/C composites increase sharply under biaxial loading compared with the uniaxial results, and the enhanced effect of the material is remarkable. In addition, the fracture doesn’t appear in the central area of the specimen, but in the loading ends or the branch of the cross-shaped specimen. The main damages are matrix cracking, fiber breakage and interlaminar debonding. The compressive strength is affected directly by the carbon fiber cloth and the interlaminar shear strength of the material.
Based on the mesoscopic structure of the three-dimensional woven carbon/carbon (3D C/C) composite materials, a kind of flat cross-shaped specimen was designed followed by the test on biaxial mechanical testing machine under uniaxial and biaxial compression as well. Comparative analysis was carried out for the mechanical behavior of the 3D C/C composite materials under biaxial compression loading. The results show that the 3D C/C composite materials represent the non-linear compression behavior and brittle fracture. The nonlinear characteristics under biaxial loading are more significant, and the compression modulus increases along with the increase of stress. The strength and modulus of 3D C/C composites increase sharply under biaxial loading compared with the uniaxial results, and the enhanced effect of the material is remarkable. In addition, the fracture doesn’t appear in the central area of the specimen, but in the loading ends or the branch of the cross-shaped specimen. The main damages are matrix cracking, fiber breakage and interlaminar debonding. The compressive strength is affected directly by the carbon fiber cloth and the interlaminar shear strength of the material.
2012, (6): 212-218.
Abstract:
In an aircraft structure, it is often necessary to runout some of the stiffeners to satisfy detailed design requirements. Depending on the structural design, stiffeners for a wing structure may terminate at a chord-wise splice, at the forward or rear spar, at a rib, or at a structural discontinuity, such as an access hole. But an abrupt stiffener termination can cause highly localized bending gradients due to stiffness discontinuities and load-path centricities. In this paper, both experiment tests and FEM models relating to three different stiffener runout specimens were presented and the failure modes of these specimens were discussed in detail. In tension, the failure is deduced by peel stress and interlaminar shear stress. In compression, the failure is deduced by interlaminar shear stress only.
In an aircraft structure, it is often necessary to runout some of the stiffeners to satisfy detailed design requirements. Depending on the structural design, stiffeners for a wing structure may terminate at a chord-wise splice, at the forward or rear spar, at a rib, or at a structural discontinuity, such as an access hole. But an abrupt stiffener termination can cause highly localized bending gradients due to stiffness discontinuities and load-path centricities. In this paper, both experiment tests and FEM models relating to three different stiffener runout specimens were presented and the failure modes of these specimens were discussed in detail. In tension, the failure is deduced by peel stress and interlaminar shear stress. In compression, the failure is deduced by interlaminar shear stress only.
2012, (6): 219-224.
Abstract:
Based on the continuum damage theory, the stress-strain relationship for orthotropic materials with damage cracks was derived. A representative volume unit cell for 3D five-directional braided composites was constructed, in which the debonding on the interface was considered. The sizes of the finite element mesh and the crack were considered in the damage evolution equation. The Hashin and von-Mises criteria were used for prediction of the initial damage of yarns and matrix, and the Eshelby-Mori-Tanaka method was applied to calculate the stiffness reduction factor. The progressive damage behaviors were simulated by ANSYS, and the stress-strain curve and the critical strength under uniaxial tensile loading were obtained. It is shown that the main failure mode of the composites with a low braiding angle is yarn cracking with serious damage on the interface. The results from the simulation agree well with the experiments in the existing literature.
Based on the continuum damage theory, the stress-strain relationship for orthotropic materials with damage cracks was derived. A representative volume unit cell for 3D five-directional braided composites was constructed, in which the debonding on the interface was considered. The sizes of the finite element mesh and the crack were considered in the damage evolution equation. The Hashin and von-Mises criteria were used for prediction of the initial damage of yarns and matrix, and the Eshelby-Mori-Tanaka method was applied to calculate the stiffness reduction factor. The progressive damage behaviors were simulated by ANSYS, and the stress-strain curve and the critical strength under uniaxial tensile loading were obtained. It is shown that the main failure mode of the composites with a low braiding angle is yarn cracking with serious damage on the interface. The results from the simulation agree well with the experiments in the existing literature.
2012, (6): 225-229.
Abstract:
The upper bound theory was applied to analysis the bearing strength of single-bolted double-lapped joints in composite laminate. The displacement rate of the composite laminate was divided into moving zone(the composite laminate) and the static zone(the fastener). The failure occurred in the discontinuous region of the moving zone and the static zone, which were the bearing zone of the bolted-hole. Because of the different distribution of stress in each layer near the bearing hole, the failure regions and failure modes were also different. The failure regions and failure modes around the pin-loaded hole were studied, and an engineering approach was presented for the bearing strength of single-bolted double-lapped joints in composite laminate with the upper bound theory. Compared with the results of the single bolt-joint test, the new engineering formula could estimate the bearing strength of the single-bolted double-lapped joints in composite laminate suitably.
The upper bound theory was applied to analysis the bearing strength of single-bolted double-lapped joints in composite laminate. The displacement rate of the composite laminate was divided into moving zone(the composite laminate) and the static zone(the fastener). The failure occurred in the discontinuous region of the moving zone and the static zone, which were the bearing zone of the bolted-hole. Because of the different distribution of stress in each layer near the bearing hole, the failure regions and failure modes were also different. The failure regions and failure modes around the pin-loaded hole were studied, and an engineering approach was presented for the bearing strength of single-bolted double-lapped joints in composite laminate with the upper bound theory. Compared with the results of the single bolt-joint test, the new engineering formula could estimate the bearing strength of the single-bolted double-lapped joints in composite laminate suitably.
2012, (6): 230-236.
Abstract:
K-cor structure was successfully fabricated by inserting angle 70? Z-pin in Rohacell-51WF foam, using NHZP-1 and 5429/HT7 bismaleimides as pultrusion resin and preimpregnated medium, respectively. The corresponding investigation on mechanical tests were carried out. A structural model based on different binding styles between Z-pin and panel in K-and X-cor was established. In order to qualitatively describe the failure mode and strengthening mechanism, the critical stress of Z-pin in the compressive test was evaluated and compared by using Euler column buckling modes. The experimental results show that 62.74% curing degree of Z-pin in K-cor structure can make tensile strength and modulus reach 1.55 MPa and 88.56 MPa as well as 3.61 MPa and 128.84 MPa, respectively, in the compressive test, which is much higher than that of X-cor structure and blank foam matrix.
K-cor structure was successfully fabricated by inserting angle 70? Z-pin in Rohacell-51WF foam, using NHZP-1 and 5429/HT7 bismaleimides as pultrusion resin and preimpregnated medium, respectively. The corresponding investigation on mechanical tests were carried out. A structural model based on different binding styles between Z-pin and panel in K-and X-cor was established. In order to qualitatively describe the failure mode and strengthening mechanism, the critical stress of Z-pin in the compressive test was evaluated and compared by using Euler column buckling modes. The experimental results show that 62.74% curing degree of Z-pin in K-cor structure can make tensile strength and modulus reach 1.55 MPa and 88.56 MPa as well as 3.61 MPa and 128.84 MPa, respectively, in the compressive test, which is much higher than that of X-cor structure and blank foam matrix.
2012, (6): 237-242.
Abstract:
The signal features of CFRP T-joint disbond under static extension testing were investigated by piezoelectric sensors and active Lamb wave monitoring technology, and disbond damages were identified with improved BP artificial neural networks. The experimental results show that interfacial disbond appears firstly in T-joint triangle filling area and then extend to flanges. Both of the signal energy and least square peak factor linearly decrease with time before failure, which can be used to describe disbond extension of T-joint. The network training data improved by adaptive particle swarm optimization algorithm are corresponded to experimental results with error range of 3.8%~4.7%.
The signal features of CFRP T-joint disbond under static extension testing were investigated by piezoelectric sensors and active Lamb wave monitoring technology, and disbond damages were identified with improved BP artificial neural networks. The experimental results show that interfacial disbond appears firstly in T-joint triangle filling area and then extend to flanges. Both of the signal energy and least square peak factor linearly decrease with time before failure, which can be used to describe disbond extension of T-joint. The network training data improved by adaptive particle swarm optimization algorithm are corresponded to experimental results with error range of 3.8%~4.7%.
2012, (6): 243-248.
Abstract:
Experiments and finite-element-method(FEM) analysis have been conducted to investigate the effect of a large size elliptical cutout on the stress/strain concentration and buckling, post-buckling behaviour of a square composite laminate under in-plane shear load. It is observed that the stress/strain concentration near the vicinity of cutout is considerable and the stability of the laminate declines remarkably due to the large cutout. The post-buckling loading capacity of laminate structure with a cutout is specific high. The failure modes of the test panel evaluated by experiments show that the high inter-laminar stress induced by the bending of laminate leads to the local damage of delamination companied by the fibre matrix shear-out. And with the structure’s horizontal deflection increasing, the fibre in the stress/strain concentration area is stretched to fracture resulting in the whole laminate collapsed instantaneously. The FEM analysis results agree well with the experimental results.
Experiments and finite-element-method(FEM) analysis have been conducted to investigate the effect of a large size elliptical cutout on the stress/strain concentration and buckling, post-buckling behaviour of a square composite laminate under in-plane shear load. It is observed that the stress/strain concentration near the vicinity of cutout is considerable and the stability of the laminate declines remarkably due to the large cutout. The post-buckling loading capacity of laminate structure with a cutout is specific high. The failure modes of the test panel evaluated by experiments show that the high inter-laminar stress induced by the bending of laminate leads to the local damage of delamination companied by the fibre matrix shear-out. And with the structure’s horizontal deflection increasing, the fibre in the stress/strain concentration area is stretched to fracture resulting in the whole laminate collapsed instantaneously. The FEM analysis results agree well with the experimental results.
2012, (6): 249-256.
Abstract:
Based on the bend/twist coupling characteristics of composite materials, the design and process technology of unbalanced composite material laminating have been studied to achieve the design requirements of wingtip twist angle increment and improve the aero-elastic characteristics of aircraft. An engineering solution was developed to design the twist coupling characteristics for composite wing structure, and contrast experiments have been carried out. The test results show that the effectiveness of wash-out of the wing box is considerable after tailoring design and the twist angle increment of wingtip decreases by 10%-45% under different loadings.
Based on the bend/twist coupling characteristics of composite materials, the design and process technology of unbalanced composite material laminating have been studied to achieve the design requirements of wingtip twist angle increment and improve the aero-elastic characteristics of aircraft. An engineering solution was developed to design the twist coupling characteristics for composite wing structure, and contrast experiments have been carried out. The test results show that the effectiveness of wash-out of the wing box is considerable after tailoring design and the twist angle increment of wingtip decreases by 10%-45% under different loadings.
