2013 Vol. 30, No. 4
2013, 30(4): 1-6.
Abstract:
The dual matrix method in single fiber fragmentation test (SFFT) was established which made it possible to obtain the saturated breakpoints of the single fiber embedded in the inner layer brittle resin because of the protection of the outer layer ductile resin. The matrix with low elongation can be used in this method to obtain interfacial shear strength, where conventional SFFT can not work in this case. Interfacial shear strength and interfacial fracture energy were used to investigate carbon fiber/epoxy resin interfacial properties under dry and water aging conditions. Two kinds of T300 grade carbon fiber as well as two types of T800 grade carbon fiber were adopted. The interfacial fracture energies obtained from dual matrix sample and single matrix sample were compared. The results show that the qualitative changes of interfacial adhesion of carbon fiber/epoxy resin in the dual matrix method and single matrix method are similar. The interfacial fracture energy and interfacial shear strength of dual matrix sample can be used to evaluate the moisture resistance of interfacial property, and the changes of the two parameters are consistent. The interfacial adhesions of all studied carbon fiber/epoxy resin decrease after water aging, and the interfacial properties of imported carbon fiber systems are greater than those of national carbon fiber systems.
The dual matrix method in single fiber fragmentation test (SFFT) was established which made it possible to obtain the saturated breakpoints of the single fiber embedded in the inner layer brittle resin because of the protection of the outer layer ductile resin. The matrix with low elongation can be used in this method to obtain interfacial shear strength, where conventional SFFT can not work in this case. Interfacial shear strength and interfacial fracture energy were used to investigate carbon fiber/epoxy resin interfacial properties under dry and water aging conditions. Two kinds of T300 grade carbon fiber as well as two types of T800 grade carbon fiber were adopted. The interfacial fracture energies obtained from dual matrix sample and single matrix sample were compared. The results show that the qualitative changes of interfacial adhesion of carbon fiber/epoxy resin in the dual matrix method and single matrix method are similar. The interfacial fracture energy and interfacial shear strength of dual matrix sample can be used to evaluate the moisture resistance of interfacial property, and the changes of the two parameters are consistent. The interfacial adhesions of all studied carbon fiber/epoxy resin decrease after water aging, and the interfacial properties of imported carbon fiber systems are greater than those of national carbon fiber systems.
2013, 30(4): 7-12.
Abstract:
The multiwalled carbon nanotubes/polystyrene-polyvinyl chloride (MWNTs/PS-PVC) composites were prepared by solution blending, and the electrical property of composites was studied. Through the measurement of concentration of carriers, the mobility and the calculated conductivity activation energy, the influence factors on the composite material conductivity and the electrical conductivity mechanism of MWNTs/PS-PVC composites were analyzed. The results show that when the mass ratio of PS/PVC is 1:1, the sample is found which exhibits the lowest electrical percolation threshold in all the composites. MWNTs/PS-PVC composites with 1.5% mass fraction of MWNTs, the electrical property of the samples changes with the content of PS, the electrical conductivity of the samples containing 50% PS in PS-PVC is improved by 4 orders of magnitude compared with that of MWNTs/PVC composites. During the formation of conductive network, the n-i-p-i alternating structural units in the composite are similar to the super lattice structure of the inorganic compound, reducing the conductivity activation energy and increasing the carrier concentration, which causes the electrical conductivity of MWNTs/PS-PVC composites to improve significantly.
The multiwalled carbon nanotubes/polystyrene-polyvinyl chloride (MWNTs/PS-PVC) composites were prepared by solution blending, and the electrical property of composites was studied. Through the measurement of concentration of carriers, the mobility and the calculated conductivity activation energy, the influence factors on the composite material conductivity and the electrical conductivity mechanism of MWNTs/PS-PVC composites were analyzed. The results show that when the mass ratio of PS/PVC is 1:1, the sample is found which exhibits the lowest electrical percolation threshold in all the composites. MWNTs/PS-PVC composites with 1.5% mass fraction of MWNTs, the electrical property of the samples changes with the content of PS, the electrical conductivity of the samples containing 50% PS in PS-PVC is improved by 4 orders of magnitude compared with that of MWNTs/PVC composites. During the formation of conductive network, the n-i-p-i alternating structural units in the composite are similar to the super lattice structure of the inorganic compound, reducing the conductivity activation energy and increasing the carrier concentration, which causes the electrical conductivity of MWNTs/PS-PVC composites to improve significantly.
2013, 30(4): 13-21.
Abstract:
p-aminophenyl propargyl ether (APPE) was synthesized by amino-protection and deprotection process. Phenol, APPE and paraformaldehyde were used to prepare the propargyl ether-based monofunctional benzoxazine (P-APPE) by Mannich condensation. P-APPE, phenol/aniline-based benzoxazine (PAF) and silicon-containing arylacetylene (PSA) were blended to obtain the modified benzoxazines in solution. Differential scanning calorimeter, dynamic mechanical analysis, thermal gravimetric analysis and broadband dielectric spectrometer were used to study the thermal and dielectrical properties of the blend resins. The results show that the thermal properties of the benzoxazine blends are improved with addition of PSA, and the dielectrical constant and dissipation factor of the benzoxazine blends decrease with the increase of PSA content in the blends. With the addition of 14.3% mass fraction of PSA, the glass transition temperature and the temperature at 5% mass loss of the cured blend resin can increase from 195℃ to 235℃, and from 355℃ to 399℃, respectively. However, more than 50% of the inter-layer shear strength (ILSS) and bending strength of the glass fabric-reinforced composites decrease with the addition of 5.3% mass fraction of PSA in the blends.
p-aminophenyl propargyl ether (APPE) was synthesized by amino-protection and deprotection process. Phenol, APPE and paraformaldehyde were used to prepare the propargyl ether-based monofunctional benzoxazine (P-APPE) by Mannich condensation. P-APPE, phenol/aniline-based benzoxazine (PAF) and silicon-containing arylacetylene (PSA) were blended to obtain the modified benzoxazines in solution. Differential scanning calorimeter, dynamic mechanical analysis, thermal gravimetric analysis and broadband dielectric spectrometer were used to study the thermal and dielectrical properties of the blend resins. The results show that the thermal properties of the benzoxazine blends are improved with addition of PSA, and the dielectrical constant and dissipation factor of the benzoxazine blends decrease with the increase of PSA content in the blends. With the addition of 14.3% mass fraction of PSA, the glass transition temperature and the temperature at 5% mass loss of the cured blend resin can increase from 195℃ to 235℃, and from 355℃ to 399℃, respectively. However, more than 50% of the inter-layer shear strength (ILSS) and bending strength of the glass fabric-reinforced composites decrease with the addition of 5.3% mass fraction of PSA in the blends.
2013, 30(4): 22-28.
Abstract:
PA6 was modified by self-made modifier of phenolic-montmorillonite (PF-MMT) and γ-aminpropyltriethoxysilane-halloysite (KH550-HNTs). The effects of different compound proportion on PA6 crystallization, thermal stability, water absorption and mechanical properties were studied. The results show that PA6 matrix composite system, modified by PF-MMT compound KH550-HNTs, whose thermal stability and resistance of water absorption are improved, and Tg is changed little, while the crystallinity of PF-MMT compound KH550-HNTs/PA6 is decreased. The rigidity of the system is enhanced, while toughness decreased a little. The bending strength has a considerable improvement, compared to pure PA6.
PA6 was modified by self-made modifier of phenolic-montmorillonite (PF-MMT) and γ-aminpropyltriethoxysilane-halloysite (KH550-HNTs). The effects of different compound proportion on PA6 crystallization, thermal stability, water absorption and mechanical properties were studied. The results show that PA6 matrix composite system, modified by PF-MMT compound KH550-HNTs, whose thermal stability and resistance of water absorption are improved, and Tg is changed little, while the crystallinity of PF-MMT compound KH550-HNTs/PA6 is decreased. The rigidity of the system is enhanced, while toughness decreased a little. The bending strength has a considerable improvement, compared to pure PA6.
2013, 30(4): 29-34.
Abstract:
ZnSn(OH)6 (ZHS) nanocubes were synthesized using a chemical precipitation method. Then a novel composite flame retardant, ZHS-MF was prepared by means of coating melamine-formaldehyde resin (MF) on the surface of the ZHS. Study on fire-retardant mechanism of ZHS-MF filled with flexible poly(vinyl chloride) (PVC). According to XRD, TEM, FTIR, TG results, MF resins have been successfully coated on ZHS surface. The mass fraction of ZHS is about 35%. The limiting oxygen index (LOI) results show that LOI of flexible PVC increases from 23.8% to 29.6% with the increasing of ZHS-MF, which indicates ZHS-MF is a highly effective flame retardant for flexible PVC. In the meantime, the MF shell could increase the flame retarding efficiency of ZHS-MF and decrease the dosage of nano-ZHS under the same LOI condition. The smoke density rating (SDR) results show that the SDR values of the samples treated with ZHS-MF are lower than that for those treated with ZHS alone when the addition of flame retardant ZHS-MF is 15%, which indicates the shell of MF and the core of ZHS have synergistic smoke suppression.
ZnSn(OH)6 (ZHS) nanocubes were synthesized using a chemical precipitation method. Then a novel composite flame retardant, ZHS-MF was prepared by means of coating melamine-formaldehyde resin (MF) on the surface of the ZHS. Study on fire-retardant mechanism of ZHS-MF filled with flexible poly(vinyl chloride) (PVC). According to XRD, TEM, FTIR, TG results, MF resins have been successfully coated on ZHS surface. The mass fraction of ZHS is about 35%. The limiting oxygen index (LOI) results show that LOI of flexible PVC increases from 23.8% to 29.6% with the increasing of ZHS-MF, which indicates ZHS-MF is a highly effective flame retardant for flexible PVC. In the meantime, the MF shell could increase the flame retarding efficiency of ZHS-MF and decrease the dosage of nano-ZHS under the same LOI condition. The smoke density rating (SDR) results show that the SDR values of the samples treated with ZHS-MF are lower than that for those treated with ZHS alone when the addition of flame retardant ZHS-MF is 15%, which indicates the shell of MF and the core of ZHS have synergistic smoke suppression.
2013, 30(4): 35-43.
Abstract:
Using magnesium hydroxide (MH), aluminum trihydrate (ATH) and microencapsulated red phosphorus (MRP) as halogen-free flame retardants and high impact polystyrene (HIPS) as polymer matrix, a series of MH-ATH-MRP/HIPS composites were prepared by melt-compounding the flame retardants and HIPS. The flame retardancy of the composites was investigated by means of horizontal burning, vertical burning, oxygen index, cone calorimetry and high temperature pyrolysis experiments. It is shown that the composite containing both MH and ATH exhibits better flame retardancy than its counterpart containing only MH or ATH at the same flame retardant contents. When the mass ratio of MH-ATH/HIPS is 70:30:100, the horizontal burning rating of the obtained composite can reach FH-1 and its oxygen index is 25.2%, but its vertical burning cannot meet any rating. The introduction of a tiny amount of MRP, whose mass fraction is 2.9% of the composite, to the above composite can make the fire performance index of the composite increase by 85% and slow the heat release and mass loss upon combustion. Meanwhile, the charring ability of the composite is enhanced considerably and the vertical burning reaches FV-0 rating. The composite displays optimal fire retardancy when the mass ratio of MH-ATH-MRP/HIPS is 21:9:12:100, thus reducing the loading of flame retardant remarkably. There is very prominent synergistic flame retardant effect among MH, ATH and MRP to HIPS. The coexistence of MH and ATH can not only suppress the temperature rise and pyrolysis of HIPS in a much wider temperature range, it can also release water vapor one after another in a much wider temperature range, which dilutes the concentrations of both oxygen and combustible gases. Thus, they have a synergistic effect in HIPS composites. The charring ability of the composite is enhanced appreciably after the introduction of MRP, which has further improved the effect of condensed phase flame retardation. Consequently, the fire retardancy of the composites is increased considerably.
Using magnesium hydroxide (MH), aluminum trihydrate (ATH) and microencapsulated red phosphorus (MRP) as halogen-free flame retardants and high impact polystyrene (HIPS) as polymer matrix, a series of MH-ATH-MRP/HIPS composites were prepared by melt-compounding the flame retardants and HIPS. The flame retardancy of the composites was investigated by means of horizontal burning, vertical burning, oxygen index, cone calorimetry and high temperature pyrolysis experiments. It is shown that the composite containing both MH and ATH exhibits better flame retardancy than its counterpart containing only MH or ATH at the same flame retardant contents. When the mass ratio of MH-ATH/HIPS is 70:30:100, the horizontal burning rating of the obtained composite can reach FH-1 and its oxygen index is 25.2%, but its vertical burning cannot meet any rating. The introduction of a tiny amount of MRP, whose mass fraction is 2.9% of the composite, to the above composite can make the fire performance index of the composite increase by 85% and slow the heat release and mass loss upon combustion. Meanwhile, the charring ability of the composite is enhanced considerably and the vertical burning reaches FV-0 rating. The composite displays optimal fire retardancy when the mass ratio of MH-ATH-MRP/HIPS is 21:9:12:100, thus reducing the loading of flame retardant remarkably. There is very prominent synergistic flame retardant effect among MH, ATH and MRP to HIPS. The coexistence of MH and ATH can not only suppress the temperature rise and pyrolysis of HIPS in a much wider temperature range, it can also release water vapor one after another in a much wider temperature range, which dilutes the concentrations of both oxygen and combustible gases. Thus, they have a synergistic effect in HIPS composites. The charring ability of the composite is enhanced appreciably after the introduction of MRP, which has further improved the effect of condensed phase flame retardation. Consequently, the fire retardancy of the composites is increased considerably.
2013, 30(4): 44-52.
Abstract:
Microencapsulated red phosphorus (MRP) and poly(phenylene oxide) (PPO) were used to improve the flame retardancy of high impact polystyrene (HIPS). A series of MRP-PPO/HIPS composites with different compositions were prepared by melt-compounding. The flame retardancy of the composites was investigated by horizontal burning, vertical burning, oxygen index, cone calorimetry and high temperature pyrolysis experiments. It is indicated that the composite containing both MRP and PPO exhibits better fire retardancy than its counterpart containing only PPO or MRP at the same flame retardant contents. When the mass ratio of MRP-PPO/HIPS is 10:20:70, the oxygen index of the composite is 23.9% and the horizontal burning rating and vertical burning rating of the composite can reach FH-1 and FV-0, respectively. The composite with this composition displays the optimum flame retardancy. Excessive contents of MRP can decrease the fire retardancy of the composite. It is believed that there is strong synergistic effect between MRP and PPO on the flame retardancy of HIPS. The coexistence of MRP and PPO with suitable mass ratio can decrease the heat release rate and combustion heat of the composite considerably, which lowers the temperature in the gaseous combustion zone and leads to increased flame retardancy in the gas phase. Meanwhile, the composite can produce a continuous and compact charred residue layer during pyrolysis and combustion. This char layer suppresses heat transfer and mass exchange and improves the flame retardant effect in the condensed phase. As a result, the flame retardancy of the composite is improved considerably.
Microencapsulated red phosphorus (MRP) and poly(phenylene oxide) (PPO) were used to improve the flame retardancy of high impact polystyrene (HIPS). A series of MRP-PPO/HIPS composites with different compositions were prepared by melt-compounding. The flame retardancy of the composites was investigated by horizontal burning, vertical burning, oxygen index, cone calorimetry and high temperature pyrolysis experiments. It is indicated that the composite containing both MRP and PPO exhibits better fire retardancy than its counterpart containing only PPO or MRP at the same flame retardant contents. When the mass ratio of MRP-PPO/HIPS is 10:20:70, the oxygen index of the composite is 23.9% and the horizontal burning rating and vertical burning rating of the composite can reach FH-1 and FV-0, respectively. The composite with this composition displays the optimum flame retardancy. Excessive contents of MRP can decrease the fire retardancy of the composite. It is believed that there is strong synergistic effect between MRP and PPO on the flame retardancy of HIPS. The coexistence of MRP and PPO with suitable mass ratio can decrease the heat release rate and combustion heat of the composite considerably, which lowers the temperature in the gaseous combustion zone and leads to increased flame retardancy in the gas phase. Meanwhile, the composite can produce a continuous and compact charred residue layer during pyrolysis and combustion. This char layer suppresses heat transfer and mass exchange and improves the flame retardant effect in the condensed phase. As a result, the flame retardancy of the composite is improved considerably.
2013, 30(4): 53-58.
Abstract:
Fiber orientation and distribution are the main factors affecting the mechanical properties of fiber reinforced PP composite. This paper presented an approach for predicting the number of fibers and each fiber's orientation. By introducing fiber orientation tensor, the average distribution of fibers in the glass fiber reinforced PP resin composite was acquired through injection molding simulation with Moldflow. Quantitative fiber distribution and orientation along thickness at specific spots were obtained by metallographic method. The proposed approached was demonstrated by a car instrument panel made from injection molding of thermoplastics with glass fibers. Tensile test samples were cut from the instrument panel with an angle of 0°, 45°, 90° to the fiber direction at sites where fibers were highly aligned. The tensile moduli were obtained through tensile tests. The fiber orientation distribution and its effect on the tensile modulus were investigated by the proposed method. It is shown that the car instrument panel is heterogeneous in mechanical properties. The fibers are roughly distributed into three layers along the thickness direction with each layer having aligned fibers.
Fiber orientation and distribution are the main factors affecting the mechanical properties of fiber reinforced PP composite. This paper presented an approach for predicting the number of fibers and each fiber's orientation. By introducing fiber orientation tensor, the average distribution of fibers in the glass fiber reinforced PP resin composite was acquired through injection molding simulation with Moldflow. Quantitative fiber distribution and orientation along thickness at specific spots were obtained by metallographic method. The proposed approached was demonstrated by a car instrument panel made from injection molding of thermoplastics with glass fibers. Tensile test samples were cut from the instrument panel with an angle of 0°, 45°, 90° to the fiber direction at sites where fibers were highly aligned. The tensile moduli were obtained through tensile tests. The fiber orientation distribution and its effect on the tensile modulus were investigated by the proposed method. It is shown that the car instrument panel is heterogeneous in mechanical properties. The fibers are roughly distributed into three layers along the thickness direction with each layer having aligned fibers.
2013, 30(4): 59-65.
Abstract:
Polyimide (PI) composites reinforced by cenosphere and carbon fiber (CF) were prepared by compression molding. The effects of load, sliding speed and content of cenosphere on tribological performances of the composites were evaluated on MRH-3 ring-on-block wear tester, and the wear morphology and mechanism were also analyzed. The results show that carbon fiber and cenosphere have the synergistic effect on the tribological properties of cenosphere-carbon fiber/polyimide composites; the tribological properties of the composite filled by cenosphere and carbon fiber were superior than those filled by single incorporation of cenosphere or carbon fiber. The content of cenosphere has little impact on the friction coefficient of cenosphere-carbon fiber/polyimide composites, but the wear rate declines with the increase of load and then improves. The 15% cenosphere-10% carbon fiber(mass fraction)/polyimide composite exhibits the lowest friction coefficient and wear rate. As an increase of the sliding speed, the friction coefficient of the composites decreases and the wear rate increases. The friction coefficient of the composite declines with the increase of load and then rises, but the wear rate increases with the increase of load. It is found that the main wear mechanism of the cenosphere-carbon fiber/polyimide is abrasive wear in the case of lower load, and shifts to the adhesive wear and abrasion while under higher load.
Polyimide (PI) composites reinforced by cenosphere and carbon fiber (CF) were prepared by compression molding. The effects of load, sliding speed and content of cenosphere on tribological performances of the composites were evaluated on MRH-3 ring-on-block wear tester, and the wear morphology and mechanism were also analyzed. The results show that carbon fiber and cenosphere have the synergistic effect on the tribological properties of cenosphere-carbon fiber/polyimide composites; the tribological properties of the composite filled by cenosphere and carbon fiber were superior than those filled by single incorporation of cenosphere or carbon fiber. The content of cenosphere has little impact on the friction coefficient of cenosphere-carbon fiber/polyimide composites, but the wear rate declines with the increase of load and then improves. The 15% cenosphere-10% carbon fiber(mass fraction)/polyimide composite exhibits the lowest friction coefficient and wear rate. As an increase of the sliding speed, the friction coefficient of the composites decreases and the wear rate increases. The friction coefficient of the composite declines with the increase of load and then rises, but the wear rate increases with the increase of load. It is found that the main wear mechanism of the cenosphere-carbon fiber/polyimide is abrasive wear in the case of lower load, and shifts to the adhesive wear and abrasion while under higher load.
2013, 30(4): 66-73.
Abstract:
The HGM/epoxy composites reinforced with modified hollow glass microbeads(HGM), and with foam aluminum are prepared. Their densities of the HGM/epoxy and foal aluminum-HGM/epoxy composites before and after natural aging indoor are studied. And their yield limits and effective elastic modulus are investigated by a series of quasi static compressive experiments. The relationship between damage morphologies and material structure is discussed. The change reasons of mechanical properties of them are analyzed. It is found that the yield limit of epoxy is a little decrease after natural aging. But the mechanical properties of syntactic foams are increase after natural aging. And the increase percentage increases firstly and then decreases with the increase of HGM volume ratio. The mechanical properties of foam aluminum/epoxy have a large decrease after aging. But the mechanical properties of foam aluminum-HGM/epoxy which HGM volume ratio greater than 20% are increased.
The HGM/epoxy composites reinforced with modified hollow glass microbeads(HGM), and with foam aluminum are prepared. Their densities of the HGM/epoxy and foal aluminum-HGM/epoxy composites before and after natural aging indoor are studied. And their yield limits and effective elastic modulus are investigated by a series of quasi static compressive experiments. The relationship between damage morphologies and material structure is discussed. The change reasons of mechanical properties of them are analyzed. It is found that the yield limit of epoxy is a little decrease after natural aging. But the mechanical properties of syntactic foams are increase after natural aging. And the increase percentage increases firstly and then decreases with the increase of HGM volume ratio. The mechanical properties of foam aluminum/epoxy have a large decrease after aging. But the mechanical properties of foam aluminum-HGM/epoxy which HGM volume ratio greater than 20% are increased.
2013, 30(4): 74-81.
Abstract:
Pure foam Al, foam Al-epoxy and three types of foam Al-hollow glass microbead (HGM)/epoxy foam interpenetrating phase composites (IPC) with different volume fractions of HGM were prepared. A series of quasi-static compressive experiments were conducted. Their deformation morphologies were observed. The relationship between volume fraction of HGM and their elastic modulus, yield limit, specific strength and specific stiffness were studied. Three point bending tests were carried out to investigate the load limit and flexural modulus. The relationship between fracture morphologies and structural behavior was discussed. It is found that the mechanical properties of these four IPC are better than pure foam Al. The mechanical properties of foam Al-epoxy is the best one. The mechanical properties of IPC decrease slowly with the increase of volume fraction of HGM.
Pure foam Al, foam Al-epoxy and three types of foam Al-hollow glass microbead (HGM)/epoxy foam interpenetrating phase composites (IPC) with different volume fractions of HGM were prepared. A series of quasi-static compressive experiments were conducted. Their deformation morphologies were observed. The relationship between volume fraction of HGM and their elastic modulus, yield limit, specific strength and specific stiffness were studied. Three point bending tests were carried out to investigate the load limit and flexural modulus. The relationship between fracture morphologies and structural behavior was discussed. It is found that the mechanical properties of these four IPC are better than pure foam Al. The mechanical properties of foam Al-epoxy is the best one. The mechanical properties of IPC decrease slowly with the increase of volume fraction of HGM.
2013, 30(4): 82-87.
Abstract:
In order to improve lower mechanical property, transparency, swelling ratio and biocompatibility of traditional chemical-cross-linked hydrogel, the temperature-sensitive and biocompatible nanocomposite hydrogel was prepared by in-situ free-radical polymerization by adopting lithium magnesium silicate hydrate (LMSH) as physical cross-linker, galactosylated acrylate (GAC) as biocompatible monomer, and isopropylacrylamide(NIPAM) as functional monomer. The results show that LMSH platelets were completely exfoliated and act as cross-linker. In comparison with traditional chemical cross-linked hydrogel, the resulting physical cross-linked nanocomposite hydrogel exhibits high swelling ratio, good temperature-sensitivity, and excellent impulse responsibility, but poor L929 cell viability on the surface of nanocomposite hydrogel. The volume phase transition temperature (VPTT) has little change by using LMSH as cross-linker and hydrophilic GAC, keeping still at 33℃.
In order to improve lower mechanical property, transparency, swelling ratio and biocompatibility of traditional chemical-cross-linked hydrogel, the temperature-sensitive and biocompatible nanocomposite hydrogel was prepared by in-situ free-radical polymerization by adopting lithium magnesium silicate hydrate (LMSH) as physical cross-linker, galactosylated acrylate (GAC) as biocompatible monomer, and isopropylacrylamide(NIPAM) as functional monomer. The results show that LMSH platelets were completely exfoliated and act as cross-linker. In comparison with traditional chemical cross-linked hydrogel, the resulting physical cross-linked nanocomposite hydrogel exhibits high swelling ratio, good temperature-sensitivity, and excellent impulse responsibility, but poor L929 cell viability on the surface of nanocomposite hydrogel. The volume phase transition temperature (VPTT) has little change by using LMSH as cross-linker and hydrophilic GAC, keeping still at 33℃.
2013, 30(4): 88-92.
Abstract:
To obtain antibacterial chitosan with improved dynamic mechanic properties, the Ag-MMT was dispersed in chitosan solution dissolving in acetic acid to obtain nano Ag-MMT/CS composite via solution intercalation. The Ag+ ion can be released steady and slowly from Ag-MMT/CS in vitro release test in simulated fluid. The bacterial inhibition zone diameter of Ag-MMT/CS is 9.2 mm, which is 50.6% larger than that of CS, the result shows Ag-MMT/CS's good antibacterial activity against Staphylococcus aureus. And the inhibition ratio test result suggests the significant surface area and adsorption capacities of MMT help a lot to immobilize more bacteria on the surface and improve the antibacterial activity of Ag-MMT/CS. In the dynamic thermomechanical analysis (DMA) test, the storage modulus of Ag-MMT/CS is 3261 MPa, which exhibits remarkable increase (195% larger than CS) in mechanic property.
To obtain antibacterial chitosan with improved dynamic mechanic properties, the Ag-MMT was dispersed in chitosan solution dissolving in acetic acid to obtain nano Ag-MMT/CS composite via solution intercalation. The Ag+ ion can be released steady and slowly from Ag-MMT/CS in vitro release test in simulated fluid. The bacterial inhibition zone diameter of Ag-MMT/CS is 9.2 mm, which is 50.6% larger than that of CS, the result shows Ag-MMT/CS's good antibacterial activity against Staphylococcus aureus. And the inhibition ratio test result suggests the significant surface area and adsorption capacities of MMT help a lot to immobilize more bacteria on the surface and improve the antibacterial activity of Ag-MMT/CS. In the dynamic thermomechanical analysis (DMA) test, the storage modulus of Ag-MMT/CS is 3261 MPa, which exhibits remarkable increase (195% larger than CS) in mechanic property.
2013, 30(4): 93-100.
Abstract:
The effect of oxidation on internal friction behavior of C/SiC composites was investigated to lay foundation for evaluating the oxidation behavior using the internal friction, by analyzing the change of the porosity, mass, flexural strength, phase, microstructure and also measuring the internal friction by thermal mechanical analyzer during oxidation at elevated temperature (1250, 1300 and 1350℃) in air. The relationship between oxidation and internal friction for SiC ceramics was also studied at 1300℃ in air, to clarify the affect of oxidation of each component in C/SiC on the internal friction behavior. The results show that the effect of oxidation on internal friction for SiC is irregular and weak; the internal friction behavior of C/SiC is controlled obviously by the oxidation of carbon phase and the peak value of internal friction retention at 1250, 1300 and 1350℃ is 6.65, 3.48 and 1.59, respectively.
The effect of oxidation on internal friction behavior of C/SiC composites was investigated to lay foundation for evaluating the oxidation behavior using the internal friction, by analyzing the change of the porosity, mass, flexural strength, phase, microstructure and also measuring the internal friction by thermal mechanical analyzer during oxidation at elevated temperature (1250, 1300 and 1350℃) in air. The relationship between oxidation and internal friction for SiC ceramics was also studied at 1300℃ in air, to clarify the affect of oxidation of each component in C/SiC on the internal friction behavior. The results show that the effect of oxidation on internal friction for SiC is irregular and weak; the internal friction behavior of C/SiC is controlled obviously by the oxidation of carbon phase and the peak value of internal friction retention at 1250, 1300 and 1350℃ is 6.65, 3.48 and 1.59, respectively.
2013, 30(4): 101-107.
Abstract:
An interfacial friction model has been presented to analysis the mechanical behavior of unidirectional fiber reinforced ceramic matrix composites. The matrix crack spacing was determined by means of the critical matrix strain energy criterion; the percentage of fractured fibers was determined via a unique Weibull failure distribution; the extent of interface wear has been estimated as a function of the relative displacement between fiber and matrix, τi=τi (Δδ). The stress-strain responses under quasi-static and cyclic loading obtained from the present analytical model are in a good agreement with their experimental counterparts. The interface slip distribution under a random load course has been discussed.
An interfacial friction model has been presented to analysis the mechanical behavior of unidirectional fiber reinforced ceramic matrix composites. The matrix crack spacing was determined by means of the critical matrix strain energy criterion; the percentage of fractured fibers was determined via a unique Weibull failure distribution; the extent of interface wear has been estimated as a function of the relative displacement between fiber and matrix, τi=τi (Δδ). The stress-strain responses under quasi-static and cyclic loading obtained from the present analytical model are in a good agreement with their experimental counterparts. The interface slip distribution under a random load course has been discussed.
2013, 30(4): 108-115.
Abstract:
The expanded graphite-based C/C composites were prepared by vacuum impregnation while expanded graphite (EG), sucrose and phosphoric acid solution were selected as starting materials. The effect of phosphoric acid/sucrose mass ratio (Xp), sucrose concentration on pore structure and specific surface area surface area of the composites was investigated by SEM, nitrogen adsorption/desorption techniques, TG and TEM. The surface chemical functional groups of composite material were characterized by FTIR and Boehm titration method. And the formaldehyde adsorption ability was investigated. The results indicate that there are a lot of micropores, a certain amount of meso-and macropores. The abandant oxygen-containing functional groups on the surface of the composites are benefit to the adsorption of formaldehyde. Under the condition of Xp=1.0, 30% sucrose concentration(mass fraction), the C/C composite is obtained with the highest surface area of 2112 m2/g and total pore volume of 1.08 mL/g. The formaldehyde removal capabilities of expanded graphite-based C/C composites are 26.9% higher than that of activated carbons which were prepared under the same condition.
The expanded graphite-based C/C composites were prepared by vacuum impregnation while expanded graphite (EG), sucrose and phosphoric acid solution were selected as starting materials. The effect of phosphoric acid/sucrose mass ratio (Xp), sucrose concentration on pore structure and specific surface area surface area of the composites was investigated by SEM, nitrogen adsorption/desorption techniques, TG and TEM. The surface chemical functional groups of composite material were characterized by FTIR and Boehm titration method. And the formaldehyde adsorption ability was investigated. The results indicate that there are a lot of micropores, a certain amount of meso-and macropores. The abandant oxygen-containing functional groups on the surface of the composites are benefit to the adsorption of formaldehyde. Under the condition of Xp=1.0, 30% sucrose concentration(mass fraction), the C/C composite is obtained with the highest surface area of 2112 m2/g and total pore volume of 1.08 mL/g. The formaldehyde removal capabilities of expanded graphite-based C/C composites are 26.9% higher than that of activated carbons which were prepared under the same condition.
2013, 30(4): 116-120.
Abstract:
To improve the compatibility of carbon nanotubes(CNTs) and the metal matrix by reducing the surface activation energy, the CNTs with Ni coatings were obtained by an electroless deposition process. The effects of the plating time and the concentration of plating solution on the thickness of the Ni coatings were studied. The results show that as the plating time is prolonged, the depositional particles become larger and the thickness of coatings increases. Moreover, the numbers of depositional particles increase and the coatings gradually become densified with the increase of concentration of the plating solution. The CNTs coated with a dense Ni layer can be successfully prepared with the plating solution concentration of 0.08 mol/L Ni2+ and the plating time of 30 min in this experiment, and the Ni layer possesses well interfacial interaction with CNTs and has a thickness of 10 nm. Heat treatment can effectively relive the stress between Ni layer and CNTs and increase interfacial interaction.
To improve the compatibility of carbon nanotubes(CNTs) and the metal matrix by reducing the surface activation energy, the CNTs with Ni coatings were obtained by an electroless deposition process. The effects of the plating time and the concentration of plating solution on the thickness of the Ni coatings were studied. The results show that as the plating time is prolonged, the depositional particles become larger and the thickness of coatings increases. Moreover, the numbers of depositional particles increase and the coatings gradually become densified with the increase of concentration of the plating solution. The CNTs coated with a dense Ni layer can be successfully prepared with the plating solution concentration of 0.08 mol/L Ni2+ and the plating time of 30 min in this experiment, and the Ni layer possesses well interfacial interaction with CNTs and has a thickness of 10 nm. Heat treatment can effectively relive the stress between Ni layer and CNTs and increase interfacial interaction.
2013, 30(4): 121-127.
Abstract:
Different mass fractions of NbSe2/Cu composite were made from NbSe2 sheets by repressing and resintering process of powder metallurgy. Physical and tribological property and microstructure of NbSe2/Cu composites were investigated. The results show that the friction coefficient and wear rate are greatly reduced by the addition of the NbSe2 sheets. This is due to the enrichment of NbSe2 in the surface of the composite and the forming of a solid lubricating film by the combined effect of frictional heat and extrusion. When the NbSe2 sheets are coated with copper, the interfacial combination between NbSe2 and Cu-matrix is improved and thus the composite will have better physical and tribological property.
Different mass fractions of NbSe2/Cu composite were made from NbSe2 sheets by repressing and resintering process of powder metallurgy. Physical and tribological property and microstructure of NbSe2/Cu composites were investigated. The results show that the friction coefficient and wear rate are greatly reduced by the addition of the NbSe2 sheets. This is due to the enrichment of NbSe2 in the surface of the composite and the forming of a solid lubricating film by the combined effect of frictional heat and extrusion. When the NbSe2 sheets are coated with copper, the interfacial combination between NbSe2 and Cu-matrix is improved and thus the composite will have better physical and tribological property.
2013, 30(4): 128-135.
Abstract:
The friction and wear behaviors of spheroidal-graphite iron and its composites reinforced with 3D-meshy Al2O3 were investigated on an optimal SRV(Schwinggung Reibungund Verschleiss) testing machine. The friction coefficients and wear rates of the alloy and the iron reinforced by Al2O3 were measured at various friction frequencies and loads. The worn surface morphologies of the composites were observed with SEM and the effect of the 3D-meshy Al2O3 on the wear mechanisms were discussed accordingly. As the results, the composites with good interfacial bonding between ceramic and metal matrix have stable friction coefficients and much better wear-resistance than that of the spheroidal-graphite iron with increasing normal load. It is supposed that the continuous 3D interconnected ceramic/metal networks and good interfacial bonding provide the Al2O3/iron composites with a capability of load transfer. And due to the lubrication action, the spheroidal-graphite in the metal matrix could keep the friction coefficients stability. In addition, the 3D-meshy Al2O3 is able to support the load applied onto the sliding surface and to restrict the plastic deformation and high-temperature softening of the iron matrix.
The friction and wear behaviors of spheroidal-graphite iron and its composites reinforced with 3D-meshy Al2O3 were investigated on an optimal SRV(Schwinggung Reibungund Verschleiss) testing machine. The friction coefficients and wear rates of the alloy and the iron reinforced by Al2O3 were measured at various friction frequencies and loads. The worn surface morphologies of the composites were observed with SEM and the effect of the 3D-meshy Al2O3 on the wear mechanisms were discussed accordingly. As the results, the composites with good interfacial bonding between ceramic and metal matrix have stable friction coefficients and much better wear-resistance than that of the spheroidal-graphite iron with increasing normal load. It is supposed that the continuous 3D interconnected ceramic/metal networks and good interfacial bonding provide the Al2O3/iron composites with a capability of load transfer. And due to the lubrication action, the spheroidal-graphite in the metal matrix could keep the friction coefficients stability. In addition, the 3D-meshy Al2O3 is able to support the load applied onto the sliding surface and to restrict the plastic deformation and high-temperature softening of the iron matrix.
2013, 30(4): 136-141.
Abstract:
The adiabatic temperature of CuO-Al thermit adding W particles was calculated and analyzed. Thermit compact of CuO-Al with 20% mass fraction of W particles addition was ignited in the ultra-gravity field, through which the W-Cu composites was obtained. The results of microstructure inspection indicate that the low mass fraction of W displays inhomogeneous distribution. Along with the centrifugal direction, the compact of pure W particles is put under the compact of CuO-Al-W which can be ignited in the ultra-gravity field then the liquid Cu production with high temperature will infiltrate into the W compact. The inspection results of bulk W-Cu composites alloy indicate that the W mass fraction continuously gradient changes like: 60%-65% in the bottom, 80%-89% in the medium and low at the top(<40%), for inhomogeneous distribution with chains and clumps characteristic structure on the top. The hardness measurement and XRD inspection further verify the conclusion. The formation mechanism is also primarily analyzed and discussed, which indicates that W mass fraction continuously gradient variation is resulted in the characteristic aspects of the ultra-gravity SHS infiltration technique.
The adiabatic temperature of CuO-Al thermit adding W particles was calculated and analyzed. Thermit compact of CuO-Al with 20% mass fraction of W particles addition was ignited in the ultra-gravity field, through which the W-Cu composites was obtained. The results of microstructure inspection indicate that the low mass fraction of W displays inhomogeneous distribution. Along with the centrifugal direction, the compact of pure W particles is put under the compact of CuO-Al-W which can be ignited in the ultra-gravity field then the liquid Cu production with high temperature will infiltrate into the W compact. The inspection results of bulk W-Cu composites alloy indicate that the W mass fraction continuously gradient changes like: 60%-65% in the bottom, 80%-89% in the medium and low at the top(<40%), for inhomogeneous distribution with chains and clumps characteristic structure on the top. The hardness measurement and XRD inspection further verify the conclusion. The formation mechanism is also primarily analyzed and discussed, which indicates that W mass fraction continuously gradient variation is resulted in the characteristic aspects of the ultra-gravity SHS infiltration technique.
2013, 30(4): 142-147.
Abstract:
Lecithin/zinc-pectin composite microspheres were designed and developed as colon-specific carrier. The novel complex hydrogel microspheres were prepared from polymers: pectin, a carbohydrate from plants, and lecithin(PC), a phospholipid from soybean. Indomethacin (IDM) was chosen as model drug and sapond saponified high-methylated apple pectin as framework material. Intermolecular cross-links were formed between the negatively charged carboxyl groups and the positively charged zinc ions, and gel microspheres were produced. Effect of parameters on size, mass, encapsulation efficiency, drug loading, and drug release pattern of the microspheres were investigated. It is found that formulations were spherical with diameter of 1.13-1.42 mm, mass of 1.13-2.32 mg, encapsulation efficiency of 70.72%-94.76%, and drug loading of 5.84%-13.54%. It is also found that the morphology of microspheres and their loading/releasing capacity are significantly influenced by the lecithin concentration, the degree of saponification, and the mass ratio of indomethacin to pectin. The experiment results show that the lecithin has greatly improved the property of drug load and drug release of the gel microspheres in simulated intestinal fluid. With the mass ratio of PC to pectin 5:4, concentration of NaOH 30 g/L, mass ratio of IDM to pectin 1:4, drug release in simulated intestines is only 8.93% in 8 h. According to stability experiment, microspheres with lecithin were more stable at 60℃ or exposing to sunlight than that without lecithin. Observations from the present study reveals that optimized pectin-Zn-lecithin beads composited with lecithin can efficiently encapsulate indomethacin and have potential for colon-specific delivery to the lower gastrointestinal tract.
Lecithin/zinc-pectin composite microspheres were designed and developed as colon-specific carrier. The novel complex hydrogel microspheres were prepared from polymers: pectin, a carbohydrate from plants, and lecithin(PC), a phospholipid from soybean. Indomethacin (IDM) was chosen as model drug and sapond saponified high-methylated apple pectin as framework material. Intermolecular cross-links were formed between the negatively charged carboxyl groups and the positively charged zinc ions, and gel microspheres were produced. Effect of parameters on size, mass, encapsulation efficiency, drug loading, and drug release pattern of the microspheres were investigated. It is found that formulations were spherical with diameter of 1.13-1.42 mm, mass of 1.13-2.32 mg, encapsulation efficiency of 70.72%-94.76%, and drug loading of 5.84%-13.54%. It is also found that the morphology of microspheres and their loading/releasing capacity are significantly influenced by the lecithin concentration, the degree of saponification, and the mass ratio of indomethacin to pectin. The experiment results show that the lecithin has greatly improved the property of drug load and drug release of the gel microspheres in simulated intestinal fluid. With the mass ratio of PC to pectin 5:4, concentration of NaOH 30 g/L, mass ratio of IDM to pectin 1:4, drug release in simulated intestines is only 8.93% in 8 h. According to stability experiment, microspheres with lecithin were more stable at 60℃ or exposing to sunlight than that without lecithin. Observations from the present study reveals that optimized pectin-Zn-lecithin beads composited with lecithin can efficiently encapsulate indomethacin and have potential for colon-specific delivery to the lower gastrointestinal tract.
2013, 30(4): 148-155.
Abstract:
Cordierite was prepared by solid reaction of raw materials including decomposed magnesite, industrial Al2O3 and SiO2 powder. Adding different mass fractions of Eu2O3, Dy2O3 and Er2O3 as additive, the effect of Eu3+, Dy3+ and Er3+ on the composition, grain size, lattice parameters, crystallinity and microstructure of crystalline phases was studied and compared. The crystalline phases and microstructure were determined by XRD and SEM respectively. The lattice parameters and crystallinity of the crystalline phases were estimated by X'Pert plus software. The phase composition was evaluated by semi-quantification method, and the grain size was calculated by Scherrer formula. The results show that the mullite phase is observed in the sintered samples because of the addtion of Eu2O3, Dy2O3 and Er2O3. Due to the substitution of Eu3+, Dy3+ and Er3+ for Mg2+, the lattice parameters and lattice volume of cordierite are changed. The liquid phase and density for room temperature increase, while relative crystallinity and grain size of cordierite decrease with addtives increasing. Comprehensive analysis shows that the effect of Eu2O3 on the phasetransition is the weakest, while the effect of Eu2O3 is the strongest among the three additives. The effect of Eu2O3 on sintering property and thermal shock resistance is the best of three additives.
Cordierite was prepared by solid reaction of raw materials including decomposed magnesite, industrial Al2O3 and SiO2 powder. Adding different mass fractions of Eu2O3, Dy2O3 and Er2O3 as additive, the effect of Eu3+, Dy3+ and Er3+ on the composition, grain size, lattice parameters, crystallinity and microstructure of crystalline phases was studied and compared. The crystalline phases and microstructure were determined by XRD and SEM respectively. The lattice parameters and crystallinity of the crystalline phases were estimated by X'Pert plus software. The phase composition was evaluated by semi-quantification method, and the grain size was calculated by Scherrer formula. The results show that the mullite phase is observed in the sintered samples because of the addtion of Eu2O3, Dy2O3 and Er2O3. Due to the substitution of Eu3+, Dy3+ and Er3+ for Mg2+, the lattice parameters and lattice volume of cordierite are changed. The liquid phase and density for room temperature increase, while relative crystallinity and grain size of cordierite decrease with addtives increasing. Comprehensive analysis shows that the effect of Eu2O3 on the phasetransition is the weakest, while the effect of Eu2O3 is the strongest among the three additives. The effect of Eu2O3 on sintering property and thermal shock resistance is the best of three additives.
2013, 30(4): 156-162.
Abstract:
Nomex honeycomb and smart self-adhesive prepreg were used to manufacture honeycomb sandwich panels with uniform platen by co-curing process in autoclave. Climbing drum peel test was used to measure their peel strength, and scanning electron microscope was used to observe micromorphology of bonding interface of skin-honeycomb, and the structure of the skin surface after peel and cellular wall ends. Moreover, thickness of cellular wall and composition of impregnated resin were also measured. Combined with the above test results, effects of processing parameters and character of cellular wall ends on the peel strength of honeycomb sandwich panels were studied and types of the adhesive bonding between skin and core were also investigated. It is found that the bond strength increases with the decrease of the temperature ramp rate within a certain range during the co-curing process with uniform platen. However, the pressure-applied moment has no significant effect on bond strength between the skin and core. The honeycomb sandwich panel has higher bond strength when the cellular wall end is rougher or the thickness of the resin layer on the cellular wall is smaller.
Nomex honeycomb and smart self-adhesive prepreg were used to manufacture honeycomb sandwich panels with uniform platen by co-curing process in autoclave. Climbing drum peel test was used to measure their peel strength, and scanning electron microscope was used to observe micromorphology of bonding interface of skin-honeycomb, and the structure of the skin surface after peel and cellular wall ends. Moreover, thickness of cellular wall and composition of impregnated resin were also measured. Combined with the above test results, effects of processing parameters and character of cellular wall ends on the peel strength of honeycomb sandwich panels were studied and types of the adhesive bonding between skin and core were also investigated. It is found that the bond strength increases with the decrease of the temperature ramp rate within a certain range during the co-curing process with uniform platen. However, the pressure-applied moment has no significant effect on bond strength between the skin and core. The honeycomb sandwich panel has higher bond strength when the cellular wall end is rougher or the thickness of the resin layer on the cellular wall is smaller.
2013, 30(4): 163-169.
Abstract:
TiO2/nanocrystalline cellulose composite solution was prepared via blending nano TiO2 powder and nanocrystalline cellulose solution, which was produced by dissolving microcrystalline cellulose(MCC) in low temperature NaOH-ureal aqueous solution, and then regeneration in water bath. The composite solution was coated on glass to form TiO2/nanocrystalline cellulose composite film by adding a little tetrabutyl orthotitanate as cross-linking agent. The morphology and structure of the composite films were characterized by using SEM and XRD. The photocatalytic activitives of the composite films were evaluated by decomposition of the methyl orange under UV-light irradiation. The mass fraction of the TiO2 in the film, and the repeatability of photocatalytic activity of the films were discussed, and also the degradation kinetics was analyzed. The results show that photocatalytic activity of the films is comparable to the pure TiO2 powder, up to 90%.When the films are repeated three times, it still keeps the same photocatalytic activity. The dynamic kinetics of the photodegradation is first order process. When the mass fraction of TiO2 is up to 33.3%, the film possesses the better photocatalytic activity and higher dynamic rate constant with 0.035 min-1.
TiO2/nanocrystalline cellulose composite solution was prepared via blending nano TiO2 powder and nanocrystalline cellulose solution, which was produced by dissolving microcrystalline cellulose(MCC) in low temperature NaOH-ureal aqueous solution, and then regeneration in water bath. The composite solution was coated on glass to form TiO2/nanocrystalline cellulose composite film by adding a little tetrabutyl orthotitanate as cross-linking agent. The morphology and structure of the composite films were characterized by using SEM and XRD. The photocatalytic activitives of the composite films were evaluated by decomposition of the methyl orange under UV-light irradiation. The mass fraction of the TiO2 in the film, and the repeatability of photocatalytic activity of the films were discussed, and also the degradation kinetics was analyzed. The results show that photocatalytic activity of the films is comparable to the pure TiO2 powder, up to 90%.When the films are repeated three times, it still keeps the same photocatalytic activity. The dynamic kinetics of the photodegradation is first order process. When the mass fraction of TiO2 is up to 33.3%, the film possesses the better photocatalytic activity and higher dynamic rate constant with 0.035 min-1.
2013, 30(4): 170-176.
Abstract:
To determine the model parameters of functionally graded material(FGM), an inverse analysis procedure based on genetic algorithm and response surface interpolation was introduced, in which the experimental records obtained from instrumented micro-indentation and their finite element analysis results were utilized. With an uncoupled manner, the finite element simulation of indentation was first conducted followed by the construction of a set of load-displacement response surfaces by a cubic Lagrange interpolation function, and then transferred to genetic algorithm for material parameter identification. This study shows that this approach inherits high accuracy from the general method based on genetic algorithm; however its solution efficiency is much higher since the large amounts of finite element calculations are substituted by interpolation on response surfaces. Numerical investigation also discloses that a double-indenter test mode can obtain a more reasonable result in comparison with the single-indenter mode for parameter identification of FGM.
To determine the model parameters of functionally graded material(FGM), an inverse analysis procedure based on genetic algorithm and response surface interpolation was introduced, in which the experimental records obtained from instrumented micro-indentation and their finite element analysis results were utilized. With an uncoupled manner, the finite element simulation of indentation was first conducted followed by the construction of a set of load-displacement response surfaces by a cubic Lagrange interpolation function, and then transferred to genetic algorithm for material parameter identification. This study shows that this approach inherits high accuracy from the general method based on genetic algorithm; however its solution efficiency is much higher since the large amounts of finite element calculations are substituted by interpolation on response surfaces. Numerical investigation also discloses that a double-indenter test mode can obtain a more reasonable result in comparison with the single-indenter mode for parameter identification of FGM.
2013, 30(4): 177-184.
Abstract:
The uncertainties in all-composite lattice truss core sandwich structure by integral forming process were quantified by an interval vector and the interval analysis model of flat crush resistance of lattice truss core sandwich structure was established. Considering the fuzziness in failure criterion of the structure, analysis and optimization models of fuzzy reliability containing interval parameters were constructed in two different cases: one was with the consideration of design tolerance induced by the production process and the other not. The results show that uncertainties in materials and structures, especially design tolerance, had great impact on the flat crush resistance of all-composite lattice truss core sandwich structure. Not only uncertainties in materials and external loads, but also design tolerance ignored in conventional uncertain design methods, should be considered fully in optimization of lattice truss core sandwich structure. The organic combination of the theoretical result and engineering application achieved in this paper presents an effective method for the analysis and optimization of flat crush resistance of all-composite lattice truss core sandwich structure in engineering.
The uncertainties in all-composite lattice truss core sandwich structure by integral forming process were quantified by an interval vector and the interval analysis model of flat crush resistance of lattice truss core sandwich structure was established. Considering the fuzziness in failure criterion of the structure, analysis and optimization models of fuzzy reliability containing interval parameters were constructed in two different cases: one was with the consideration of design tolerance induced by the production process and the other not. The results show that uncertainties in materials and structures, especially design tolerance, had great impact on the flat crush resistance of all-composite lattice truss core sandwich structure. Not only uncertainties in materials and external loads, but also design tolerance ignored in conventional uncertain design methods, should be considered fully in optimization of lattice truss core sandwich structure. The organic combination of the theoretical result and engineering application achieved in this paper presents an effective method for the analysis and optimization of flat crush resistance of all-composite lattice truss core sandwich structure in engineering.
2013, 30(4): 185-191.
Abstract:
A viscoelastic material meeting the manufacture process requirements of the embedded high-temperature co-cured composite damping structure was studied by using orthogonal experiment method, and the brush coating process is proposed to replace the membrane forming process in manufacturing the viscoelastic material film. The embedded co-cured composite(T300/QY8911) damping specimens are manufactured by employing these two processes respectively. And then the interlamination shear was measured for each specimen. The relationship of the interlamination shear property with viscoelastic film thickness was obtained by the experimental study. The experimental data indicate that the brush coating process can improve the interlaminar bonding force of the embedded co-cured composite damping structure by more than 10%, the thicker the damping film is, and the higher the bonding force increases. The failure surfaces show that the brush coating process makes the interface forming interpenetrating polymer network structures between viscoelastic film and composite.
A viscoelastic material meeting the manufacture process requirements of the embedded high-temperature co-cured composite damping structure was studied by using orthogonal experiment method, and the brush coating process is proposed to replace the membrane forming process in manufacturing the viscoelastic material film. The embedded co-cured composite(T300/QY8911) damping specimens are manufactured by employing these two processes respectively. And then the interlamination shear was measured for each specimen. The relationship of the interlamination shear property with viscoelastic film thickness was obtained by the experimental study. The experimental data indicate that the brush coating process can improve the interlaminar bonding force of the embedded co-cured composite damping structure by more than 10%, the thicker the damping film is, and the higher the bonding force increases. The failure surfaces show that the brush coating process makes the interface forming interpenetrating polymer network structures between viscoelastic film and composite.
2013, 30(4): 192-197.
Abstract:
By introducing an appropriate conformal mapping and using the complex variable function method, the fracture behavior of a semi-infinite crack in a magnetoelectroelastic strip was studied under the anti-plane shear stress and in-plane electric and magnetic loads. The analytical solutions of the field intensity factors and the energy release rate were presented with the assumption that the surface of the crack was electrically and magnetically impermeable. When the height of the strip tends to infinity, the analytical solutions of an infinitely large magnetoelectroelastic solid with a semi-infinite crack were obtained. Moreover, the present results can be reduced to the well-known solutions for a purely elastic material in the absence of electric and magnetic loadings. In addition, some numerical examples were conducted to analyze the influences of loaded crack length, the height of the strip and applied mechanical, electric and magnetic loads on the energy release rate.
By introducing an appropriate conformal mapping and using the complex variable function method, the fracture behavior of a semi-infinite crack in a magnetoelectroelastic strip was studied under the anti-plane shear stress and in-plane electric and magnetic loads. The analytical solutions of the field intensity factors and the energy release rate were presented with the assumption that the surface of the crack was electrically and magnetically impermeable. When the height of the strip tends to infinity, the analytical solutions of an infinitely large magnetoelectroelastic solid with a semi-infinite crack were obtained. Moreover, the present results can be reduced to the well-known solutions for a purely elastic material in the absence of electric and magnetic loadings. In addition, some numerical examples were conducted to analyze the influences of loaded crack length, the height of the strip and applied mechanical, electric and magnetic loads on the energy release rate.
2013, 30(4): 198-205.
Abstract:
A method was proposed for the global strain prediction of the composite laminate with special delaminations when the local buckling occurs. It was presented that the critical force of delamination buckling is determined by the maximum flexural stiffness of the sub-laminates in the delaminated region, so if two delaminations of same size have the same maximum sub-laminate flexural stiffness, their critical buckling force must be equal to each other. With the critical buckling force of a certain sub-laminate known, the loads on the debonded layer and intact layers were calculated using their axial stiffness. With the total load the global strain of the laminate was obtained when the local buckling occurs. Then, the three dimension finite element (FE) models of composite laminate with delamination of different area, depth and location were developed with ABAQUS, which are employed to simulate local buckling under quasi-static loading. The obtained delamination buckling loads compliance with above assumption. The proposed method was used to prediction global strain when the delamination buckling occurs, which agrees with those of FE well. Hence this method can be used to set up the samples for delamination depth detection.
A method was proposed for the global strain prediction of the composite laminate with special delaminations when the local buckling occurs. It was presented that the critical force of delamination buckling is determined by the maximum flexural stiffness of the sub-laminates in the delaminated region, so if two delaminations of same size have the same maximum sub-laminate flexural stiffness, their critical buckling force must be equal to each other. With the critical buckling force of a certain sub-laminate known, the loads on the debonded layer and intact layers were calculated using their axial stiffness. With the total load the global strain of the laminate was obtained when the local buckling occurs. Then, the three dimension finite element (FE) models of composite laminate with delamination of different area, depth and location were developed with ABAQUS, which are employed to simulate local buckling under quasi-static loading. The obtained delamination buckling loads compliance with above assumption. The proposed method was used to prediction global strain when the delamination buckling occurs, which agrees with those of FE well. Hence this method can be used to set up the samples for delamination depth detection.
2013, 30(4): 206-210.
Abstract:
Experiments with fibre Bragg grating were done to study the residual stresses distribution in composites structure during the autoclave curing process. From results of experiments, residual stresses development and distribution in thickness direction and planar have been obtained. And then the mechanism and influence of residual stresses on cure-induced deformation for composites structure were studied. The results show that the mismatch between composites and mold induce the strain gradient in thickness direction. The strain close to the mold is more than that away from the mold. And then the strain will cause deformation of composites structure after curing process, and the deformation in fibre direction is dominating.
Experiments with fibre Bragg grating were done to study the residual stresses distribution in composites structure during the autoclave curing process. From results of experiments, residual stresses development and distribution in thickness direction and planar have been obtained. And then the mechanism and influence of residual stresses on cure-induced deformation for composites structure were studied. The results show that the mismatch between composites and mold induce the strain gradient in thickness direction. The strain close to the mold is more than that away from the mold. And then the strain will cause deformation of composites structure after curing process, and the deformation in fibre direction is dominating.
2013, 30(4): 211-218.
Abstract:
A progressive damage finite element model was established for the analysis of stiffened composite panels under transversely low velocity impact. Five typical damage modes including fiber tensile failure, matrix crushing and delamination were considered in the model. Strain-based failure criteria coupled with corresponding stiffness degradation technologies were used to predict the type and evolution of intralaminar damage modes by VUMAT user-defined subroutine. Cohesive elements were adopted in interlaminar zones and zones between stiffener and laminates to simulate the initiation and evolution of delamination through stress-based failure criteria and facture-mechanics-based failure criterion. The reasonability and effectiveness were validated by the comparison between numerical simulation results and experimental data. Finally, the influence of impact position, impact energy and initial damage (delamination) on the low-velocity impact damage of stiffened composite panels was discussed in detail.
A progressive damage finite element model was established for the analysis of stiffened composite panels under transversely low velocity impact. Five typical damage modes including fiber tensile failure, matrix crushing and delamination were considered in the model. Strain-based failure criteria coupled with corresponding stiffness degradation technologies were used to predict the type and evolution of intralaminar damage modes by VUMAT user-defined subroutine. Cohesive elements were adopted in interlaminar zones and zones between stiffener and laminates to simulate the initiation and evolution of delamination through stress-based failure criteria and facture-mechanics-based failure criterion. The reasonability and effectiveness were validated by the comparison between numerical simulation results and experimental data. Finally, the influence of impact position, impact energy and initial damage (delamination) on the low-velocity impact damage of stiffened composite panels was discussed in detail.
2013, 30(4): 219-224.
Abstract:
A composite cylinder structure consists of aluminum alloy cylinder structure wall winded by T700 carbon fiber composite. The failure data still cannot be obtained sufficiently by the accelerated life test due to the time limitation in engineering, and the most of the data is a mixture of high censored ratio data in high stress level and zero-failure data in low stress level. To the problem of low confidence level for rupture life evaluation by the current method, the equivalency of acceleration and consistency of failure mechanism for carbon fiber and cylinder were analyzed firstly, and then the statistical test was made and the information was fused for the part covariance matrix of accelerated model parameters. At last, a rupture life evaluation method was established for the cylinder with fusion the carbon fiber data. It can improve the evaluation accuracy of the cylinder by using the similar information. The proposed method is proved effectively by the test data, and it makes the evaluation accuracy of the cylinder increase 35%.
A composite cylinder structure consists of aluminum alloy cylinder structure wall winded by T700 carbon fiber composite. The failure data still cannot be obtained sufficiently by the accelerated life test due to the time limitation in engineering, and the most of the data is a mixture of high censored ratio data in high stress level and zero-failure data in low stress level. To the problem of low confidence level for rupture life evaluation by the current method, the equivalency of acceleration and consistency of failure mechanism for carbon fiber and cylinder were analyzed firstly, and then the statistical test was made and the information was fused for the part covariance matrix of accelerated model parameters. At last, a rupture life evaluation method was established for the cylinder with fusion the carbon fiber data. It can improve the evaluation accuracy of the cylinder by using the similar information. The proposed method is proved effectively by the test data, and it makes the evaluation accuracy of the cylinder increase 35%.
2013, 30(4): 225-230.
Abstract:
Compression and creep tests were carried out at room and high temperatures under the characteristic load of thermal protection system. Results show that the compression curve of the aerogel composite can be divided into three stages: linear stage, yielding stage and densification stage. The composite performs higher strength and fracture strain comparing with pure SiO2 aerogel. There is obvious creep deformation at room and high temperatures. The room temperature creep history in 240 h can be divided into three stages, in the third of which (i.e. after 168 h) the creep strain does not increase. The microstructures of specimens before creep, after heated and after creep were compared. It is found that the densification of aerogel matrix is the main reason for the sample shrinkage, as well as the creep behavior.
Compression and creep tests were carried out at room and high temperatures under the characteristic load of thermal protection system. Results show that the compression curve of the aerogel composite can be divided into three stages: linear stage, yielding stage and densification stage. The composite performs higher strength and fracture strain comparing with pure SiO2 aerogel. There is obvious creep deformation at room and high temperatures. The room temperature creep history in 240 h can be divided into three stages, in the third of which (i.e. after 168 h) the creep strain does not increase. The microstructures of specimens before creep, after heated and after creep were compared. It is found that the densification of aerogel matrix is the main reason for the sample shrinkage, as well as the creep behavior.
Experimental study and analysis on probability of detection forimpact damage of composite structures
2013, 30(4): 231-237.
Abstract:
Impact damage was the key damage type encountered by composite structures in service, which can produce permanent dents. In order to obtain the probability of detection(POD)of dents, the maximum likelihood method was used to calculate parameters of two POD models (the cumulative lognormal model and the log odds model) for general visual inspection (GVI) and detailed visual inspection (DET). Experimental DET study was performed and POD models were verified by test data. The results indicate that the cumulative lognormal model is fit for the POD of dents. Compare with black boards, the dents on green boards can be detected easier, and with the increase of inspection angle, the dents are more likely to be detected. Barely visible impact damage (BVID) thresholds are between 0.35 mm and 0.8 mm.
Impact damage was the key damage type encountered by composite structures in service, which can produce permanent dents. In order to obtain the probability of detection(POD)of dents, the maximum likelihood method was used to calculate parameters of two POD models (the cumulative lognormal model and the log odds model) for general visual inspection (GVI) and detailed visual inspection (DET). Experimental DET study was performed and POD models were verified by test data. The results indicate that the cumulative lognormal model is fit for the POD of dents. Compare with black boards, the dents on green boards can be detected easier, and with the increase of inspection angle, the dents are more likely to be detected. Barely visible impact damage (BVID) thresholds are between 0.35 mm and 0.8 mm.
2013, 30(4): 238-244.
Abstract:
With benzoyl peroxide (BPO) as initiator, the surface of polypropylene (PP) fibers was modified with acrylic acid by two step-chemical grafting methods. The effects of initiation temperature, concentration of BPO, grafting temperature, grafting time and concentration of AA on the grafting degree of PP fibers were studied with orthogonal analysis method, and the interfacial bonding between cement matrix and PP fibers before and after modification was evaluated. The results show that the influence of above factors on grafting degree of PP fibers in order is initiation temperature>concentration of BPO> grafting time > grafting temperature > concentration of AA. The optimum reaction conditions are as follows: initiation temperature is 90℃, concentration of BPO 4.50×10-2 mol/L, grafting time 60 min, grafting temperature 75℃ and concentration of AA 1.4 mol/L. Under this condition, the grafting degree of PP fibers is 13.12%. Though two step-chemical grafting modifications, the surface hydrophilicity and roughness of PP fibers are increased, so that the interfacial bonding between PP fibers and cement matrix is enhanced. When the volume fraction of modified PP fibers is 0.05%, the cracking-resistance ratio of PP fibers reinforced cement mortar increase by 26.6%, which indicate its plastic shrinkage cracking resistance is significantly enhanced.
With benzoyl peroxide (BPO) as initiator, the surface of polypropylene (PP) fibers was modified with acrylic acid by two step-chemical grafting methods. The effects of initiation temperature, concentration of BPO, grafting temperature, grafting time and concentration of AA on the grafting degree of PP fibers were studied with orthogonal analysis method, and the interfacial bonding between cement matrix and PP fibers before and after modification was evaluated. The results show that the influence of above factors on grafting degree of PP fibers in order is initiation temperature>concentration of BPO> grafting time > grafting temperature > concentration of AA. The optimum reaction conditions are as follows: initiation temperature is 90℃, concentration of BPO 4.50×10-2 mol/L, grafting time 60 min, grafting temperature 75℃ and concentration of AA 1.4 mol/L. Under this condition, the grafting degree of PP fibers is 13.12%. Though two step-chemical grafting modifications, the surface hydrophilicity and roughness of PP fibers are increased, so that the interfacial bonding between PP fibers and cement matrix is enhanced. When the volume fraction of modified PP fibers is 0.05%, the cracking-resistance ratio of PP fibers reinforced cement mortar increase by 26.6%, which indicate its plastic shrinkage cracking resistance is significantly enhanced.
2013, 30(4): 245-249.
Abstract:
Through changing the number of glass fiber mat layers to control the porosity, the saturated permeability of WindstandTM glass fiber in-plane and trans directions(x, y and z)was measured by the unidirectional saturated flow method. The influence of porosity, mold dimension and fibers direction (parallel and vertical 2% extra fibers tows) which affect the permeability were investigated. The results indicate that with the decrease of porosity, the permeability drops sharply. The effect of mold dimension has little influence of y direction permeability when porosity between 34.6%-54.7%. Changing 2% extra fibers tows direction (from parallel to vertical), has an effect on permeability when the porosity between 34.6%-54.7%. When porosity range is 45%-55%, the permeability in-plane direction is about 3-7 times as high as that in transone.
Through changing the number of glass fiber mat layers to control the porosity, the saturated permeability of WindstandTM glass fiber in-plane and trans directions(x, y and z)was measured by the unidirectional saturated flow method. The influence of porosity, mold dimension and fibers direction (parallel and vertical 2% extra fibers tows) which affect the permeability were investigated. The results indicate that with the decrease of porosity, the permeability drops sharply. The effect of mold dimension has little influence of y direction permeability when porosity between 34.6%-54.7%. Changing 2% extra fibers tows direction (from parallel to vertical), has an effect on permeability when the porosity between 34.6%-54.7%. When porosity range is 45%-55%, the permeability in-plane direction is about 3-7 times as high as that in transone.
