2012 Vol. 29, No. 3
2012, (3): 1-8.
Abstract:
The ability and characteristic of each electrolyte to oxidize carbon fiber(CF) were investigated by multi-scan cyclic voltammetry. The effect of different electrolytes on mechanical performance of high strength and high modulus CF with anodic oxidation surface treatment were discussed. The suitable parameters of surface treatment for high strength and high modulus CF were proposed. The effect of electrochemical oxidation on the surface structure and mechanical performance of high strength and high modulus carbon fibers were discussed using laser Raman spectroscopy, XPS and SEM. Compared with NH4H2PO4 solution, the surfacial functional groups containing oxygen in the fiber significantly increases in the mixed electrolytes of NH4H2PO4 and CH3COONH4, and the relative content of sp2 hybrid carbon atom is higher. The interlaminar shear strength(ILSS) of CF/epoxy composite is improved and the mechanical performance of CF is kept at the same time. When the mole ratio of CH3COONH4 to NH4H2PO4 is 2∶1 in the mixed electrolytes, the ILSS of CF/epoxy composite increases by 168% and the tensile strength little decreases compared with untreated fiber. Therefore, it is a good electrolyte for surface treatment for high strength and high modulus CF.
The ability and characteristic of each electrolyte to oxidize carbon fiber(CF) were investigated by multi-scan cyclic voltammetry. The effect of different electrolytes on mechanical performance of high strength and high modulus CF with anodic oxidation surface treatment were discussed. The suitable parameters of surface treatment for high strength and high modulus CF were proposed. The effect of electrochemical oxidation on the surface structure and mechanical performance of high strength and high modulus carbon fibers were discussed using laser Raman spectroscopy, XPS and SEM. Compared with NH4H2PO4 solution, the surfacial functional groups containing oxygen in the fiber significantly increases in the mixed electrolytes of NH4H2PO4 and CH3COONH4, and the relative content of sp2 hybrid carbon atom is higher. The interlaminar shear strength(ILSS) of CF/epoxy composite is improved and the mechanical performance of CF is kept at the same time. When the mole ratio of CH3COONH4 to NH4H2PO4 is 2∶1 in the mixed electrolytes, the ILSS of CF/epoxy composite increases by 168% and the tensile strength little decreases compared with untreated fiber. Therefore, it is a good electrolyte for surface treatment for high strength and high modulus CF.
2012, (3): 9-15.
Abstract:
Ethyl acrylate(EA) and butyl acrylate(BA) were employed to modify the diglycidyl ether of bisphenol A (DGEBA)-methyltetrahydrophthalic anhydride (MeTHPA) epoxy system via in-situ polymerization. The "sea-island" structure is observed from the SEM micrographs of the DGEBA-MeTHPA system modified by polyacrylates. By the addition of 10% (mass fraction) EA and BA, the tensile strength of the epoxy system reduces by 9.51% and 4.00%, and the modulus reduces by 14.81% and 9.52%, respectively. The glass transition temperature is not obviously influenced by the addition of polyacrylates. By contrast, the impact strength dramatically increases by 26.5% and 31.0%, and the elongation increases by 22.03% and 30.07%, respectively, showing obvious toughening effects.
Ethyl acrylate(EA) and butyl acrylate(BA) were employed to modify the diglycidyl ether of bisphenol A (DGEBA)-methyltetrahydrophthalic anhydride (MeTHPA) epoxy system via in-situ polymerization. The "sea-island" structure is observed from the SEM micrographs of the DGEBA-MeTHPA system modified by polyacrylates. By the addition of 10% (mass fraction) EA and BA, the tensile strength of the epoxy system reduces by 9.51% and 4.00%, and the modulus reduces by 14.81% and 9.52%, respectively. The glass transition temperature is not obviously influenced by the addition of polyacrylates. By contrast, the impact strength dramatically increases by 26.5% and 31.0%, and the elongation increases by 22.03% and 30.07%, respectively, showing obvious toughening effects.
2012, (3): 16-22.
Abstract:
MWCNTs were functionalized with carboxyl and then mixed with epoxy TDE85. The obtained mixtures were used to impregnate the NCF laminates, stacking with a sequence of [0°/90°/+45°/-45°]S. Flexural properties, interlaminar shear strength (ILSS), and mode Ⅱ interlaminar fracture toughness (GⅡC), as well as the glass transition temperature (Tg) of the resulting laminates were characterized using three-point bending, short beam shear, end-notch flexure (ENF) specimens, and a dynamic mechanical analysis, respectively. SEM was used to analyze the fracture characteristics of the tested ENF specimens. The results show that there are reinforcing effects of the MWCNTs on the mechanical properties when the mass fraction of the MWCNTs varies from 0 to 2.0%. The flexural strength and modulus are improved by 26% and 6%, respectively, with 2.0% mass fraction of MWCNTs. The ILSS, GⅡC and Tg are enhanced by 14%, 27% and 14%, respectively when 0.5% mass fraction of MWCNTs is used.
MWCNTs were functionalized with carboxyl and then mixed with epoxy TDE85. The obtained mixtures were used to impregnate the NCF laminates, stacking with a sequence of [0°/90°/+45°/-45°]S. Flexural properties, interlaminar shear strength (ILSS), and mode Ⅱ interlaminar fracture toughness (GⅡC), as well as the glass transition temperature (Tg) of the resulting laminates were characterized using three-point bending, short beam shear, end-notch flexure (ENF) specimens, and a dynamic mechanical analysis, respectively. SEM was used to analyze the fracture characteristics of the tested ENF specimens. The results show that there are reinforcing effects of the MWCNTs on the mechanical properties when the mass fraction of the MWCNTs varies from 0 to 2.0%. The flexural strength and modulus are improved by 26% and 6%, respectively, with 2.0% mass fraction of MWCNTs. The ILSS, GⅡC and Tg are enhanced by 14%, 27% and 14%, respectively when 0.5% mass fraction of MWCNTs is used.
2012, (3): 23-29.
Abstract:
Multi-walled carbon nanotubes (MWCNTs)/poly(ether ether ketone) (PEEK) composite fibers containing 0.1% and 0.5% mass fraction of MWCNTs were melt-spun, respectively. The effects of heat-set temperature and cooling rates on the structures and properties of the composite fibers were studied in the process of tension heat-setting process. TEM, SEM, DSC, DMA, XRD and tensile tester were used to characterize the morphology, structures and properties of the fibers. The results show that, the heat-set temperature and cooling rates affect the Young's modulus, tensile strength and strain of the fibers. The heat-setting improves the orientation of MWCNTs in composite fibers. The tensile strength, Young's modulus and strain of the fiber heat-set at 280℃ and cooling rate of 1.5℃/min are 384MPa,0.62GPa and 28%, respectively. The tensile strength and Young's modulus are about 147% and 19% higher than that of the fiber heat-set at 130℃ and cooling rate of 1.5℃/min. Therefore, the optimized heat-set condition is obtained for the MWCNTs/PEEK composite fibers.
Multi-walled carbon nanotubes (MWCNTs)/poly(ether ether ketone) (PEEK) composite fibers containing 0.1% and 0.5% mass fraction of MWCNTs were melt-spun, respectively. The effects of heat-set temperature and cooling rates on the structures and properties of the composite fibers were studied in the process of tension heat-setting process. TEM, SEM, DSC, DMA, XRD and tensile tester were used to characterize the morphology, structures and properties of the fibers. The results show that, the heat-set temperature and cooling rates affect the Young's modulus, tensile strength and strain of the fibers. The heat-setting improves the orientation of MWCNTs in composite fibers. The tensile strength, Young's modulus and strain of the fiber heat-set at 280℃ and cooling rate of 1.5℃/min are 384MPa,0.62GPa and 28%, respectively. The tensile strength and Young's modulus are about 147% and 19% higher than that of the fiber heat-set at 130℃ and cooling rate of 1.5℃/min. Therefore, the optimized heat-set condition is obtained for the MWCNTs/PEEK composite fibers.
2012, (3): 30-35.
Abstract:
A formula of positive temperature coefficient of resistance (PTCR) of conductive rubber filled by carbon black (CB) used for temperature sensor was given by general effective media theory. The sensitive coefficient was analyzed by the equation of sensitive coefficient deduced from the formula of PTCR and the impact of the strain and resistivity on PTCR effect. The formula of PTCR is constant in the experiment when the CB is homogeneously dispersed and the volume fraction of CB is close to the critical threshold. A dilution of the volume fraction of CB due to the volume expansion of the composites has a significant influence on PTCR effect. When the volume fraction of CB is within the percolation zone, the sensitive coefficient is from 280 to 420, and it is from 32.5 to 62.0 when the volume fraction of CB is within the conductive zone. PTCR effect is a complex process of the heat-deformation and the deformation-conductivity. Due to the low coefficient of cubical expansion, the conductive carbon black/rubber has high sensitive coefficient, but the value of PTCR is low.
A formula of positive temperature coefficient of resistance (PTCR) of conductive rubber filled by carbon black (CB) used for temperature sensor was given by general effective media theory. The sensitive coefficient was analyzed by the equation of sensitive coefficient deduced from the formula of PTCR and the impact of the strain and resistivity on PTCR effect. The formula of PTCR is constant in the experiment when the CB is homogeneously dispersed and the volume fraction of CB is close to the critical threshold. A dilution of the volume fraction of CB due to the volume expansion of the composites has a significant influence on PTCR effect. When the volume fraction of CB is within the percolation zone, the sensitive coefficient is from 280 to 420, and it is from 32.5 to 62.0 when the volume fraction of CB is within the conductive zone. PTCR effect is a complex process of the heat-deformation and the deformation-conductivity. Due to the low coefficient of cubical expansion, the conductive carbon black/rubber has high sensitive coefficient, but the value of PTCR is low.
2012, (3): 36-41.
Abstract:
Intumescently flame retardant polylactide (SPBDM-OMMT/PLA) nanocomposites were prepared by melt-extruding polylactide(PLA)with spirocyclic pentaerythritol bisphosphorate disphosphoryl melamine (SPBDM) and organo-modified montmorillonite (OMMT). The internal structure of the composites was probed established by XRD and TEM. The SPBDM-OMMT/PLA nanocomposites were also evaluated by thermal gravimetric analysis(TGA), limiting oxygen index(LOI) measurements and UL-94 tests. The results reveal that the uniformly dispersed OMMT clay exfoliates or intercalates in PLA matrix. The thermal stability and char yield of these nanocomposites are greatly enhanced at high temperature, and the maximum degradation temperature increases compared with those of pure PLA. The LOI value of 32% and V-0 level are achieved when 10.0% of SPBDM and 1.0% of OMMT (mass fraction) are added.
Intumescently flame retardant polylactide (SPBDM-OMMT/PLA) nanocomposites were prepared by melt-extruding polylactide(PLA)with spirocyclic pentaerythritol bisphosphorate disphosphoryl melamine (SPBDM) and organo-modified montmorillonite (OMMT). The internal structure of the composites was probed established by XRD and TEM. The SPBDM-OMMT/PLA nanocomposites were also evaluated by thermal gravimetric analysis(TGA), limiting oxygen index(LOI) measurements and UL-94 tests. The results reveal that the uniformly dispersed OMMT clay exfoliates or intercalates in PLA matrix. The thermal stability and char yield of these nanocomposites are greatly enhanced at high temperature, and the maximum degradation temperature increases compared with those of pure PLA. The LOI value of 32% and V-0 level are achieved when 10.0% of SPBDM and 1.0% of OMMT (mass fraction) are added.
2012, (3): 42-48.
Abstract:
In order to choose the best parameters of tackifier in vacuum assisted resin infusion(VARI) processing, the effects of tackifier on perform permeability, fiber compression and mechanical performance were addressed. The component of tackifier and its melting characteristics were ananlyzed by DSC and IR. The perform permeability, fiber compression characteristics and mechanical performance at different temperatures were examined. It is shown that the tackfier is a kind of polymer with epoxide group and low melting point. For the same tackifier concentration, the perform permeability and compressed thickness decrease as the temperature increasing below 100℃, but between 100℃ and 140℃, the compressed thickness keeps constant and the permeability increases as the temperature increasing. The temperature has no significant effect on the mechanical properties.
In order to choose the best parameters of tackifier in vacuum assisted resin infusion(VARI) processing, the effects of tackifier on perform permeability, fiber compression and mechanical performance were addressed. The component of tackifier and its melting characteristics were ananlyzed by DSC and IR. The perform permeability, fiber compression characteristics and mechanical performance at different temperatures were examined. It is shown that the tackfier is a kind of polymer with epoxide group and low melting point. For the same tackifier concentration, the perform permeability and compressed thickness decrease as the temperature increasing below 100℃, but between 100℃ and 140℃, the compressed thickness keeps constant and the permeability increases as the temperature increasing. The temperature has no significant effect on the mechanical properties.
2012, (3): 49-53.
Abstract:
By the analysis of automated tape laying (ATL) process, the viscosity-temperature relationship of the composite prepregs was investigated. By the research on hot-air temperature and placement rate, which are two main factors on the prepregs temperature, the theoretic relationship between hot-air temperature and placement rate was examined, and then the controlling method of prepregs temperature was proposed to guide the ATL manufacturing. Finally, according to the viscosity-temperature curve of the bismaleimide resin prepregs, the experiments were conducted under different hot-air temperatures and placement rates. The results show that the viscosity of the prepregs agrees with the processing demand when the hot-air temperature is set at 90℃ and the placement rate is about 10-20m/min. The research work indicates the influence on the composites structure, caused by prepregs hot-air temperature and placement rate, which will be helpful for the ATL process.
By the analysis of automated tape laying (ATL) process, the viscosity-temperature relationship of the composite prepregs was investigated. By the research on hot-air temperature and placement rate, which are two main factors on the prepregs temperature, the theoretic relationship between hot-air temperature and placement rate was examined, and then the controlling method of prepregs temperature was proposed to guide the ATL manufacturing. Finally, according to the viscosity-temperature curve of the bismaleimide resin prepregs, the experiments were conducted under different hot-air temperatures and placement rates. The results show that the viscosity of the prepregs agrees with the processing demand when the hot-air temperature is set at 90℃ and the placement rate is about 10-20m/min. The research work indicates the influence on the composites structure, caused by prepregs hot-air temperature and placement rate, which will be helpful for the ATL process.
2012, (3): 54-58.
Abstract:
Nano-silver/poly(2-acrylamido-2-methylpropanesulfonate sodium (PAMPS)) composite was synthesized in situ by microwave radiation without addition of any reducer. The composite was analyzed and characterized by UV-Vis, XRD, FTIR, TEM and XPS. The results show that nano-silver is homogeneously dispersed in PAMPS matrix and possesses face-centered cubic structure. The morphology of nano-silver was not affected by microwave radiation time. It is also found that interactions exist between nano-Ag and nitrogen and carbonyl oxygen atoms in PAMPS, and the thermal stability of PAMPS decreases with nano-Ag dispersion in the composite.
Nano-silver/poly(2-acrylamido-2-methylpropanesulfonate sodium (PAMPS)) composite was synthesized in situ by microwave radiation without addition of any reducer. The composite was analyzed and characterized by UV-Vis, XRD, FTIR, TEM and XPS. The results show that nano-silver is homogeneously dispersed in PAMPS matrix and possesses face-centered cubic structure. The morphology of nano-silver was not affected by microwave radiation time. It is also found that interactions exist between nano-Ag and nitrogen and carbonyl oxygen atoms in PAMPS, and the thermal stability of PAMPS decreases with nano-Ag dispersion in the composite.
2012, (3): 59-64.
Abstract:
3D carbon/carbon (C/C) composite materials with different porosities and bulk densities were fabricated by repeated precursor infiltration and pyrolysis (PIP) process, and the electromagnetic interference shielding (EMI) effectiveness of C/C composites at 8.2-12.4GHz (X band) with different porosities were studied. The results indicate that both EMI absorption shielding effectiveness and the total EMI shielding effectiveness of C/C composites could be improved by reducing the porosity appropriately. When the open porosity is 33.4%, the C/C composite material shows a maximum shielding effectiveness of 40dB, and the EIM apsorption shielding effectiveness(30dB) is much higher than EMI reflection shielding effectiveness(12dB)). Porous C/C composite is one kind of excellent EMI shielding materials with high absorption and low reflection.
3D carbon/carbon (C/C) composite materials with different porosities and bulk densities were fabricated by repeated precursor infiltration and pyrolysis (PIP) process, and the electromagnetic interference shielding (EMI) effectiveness of C/C composites at 8.2-12.4GHz (X band) with different porosities were studied. The results indicate that both EMI absorption shielding effectiveness and the total EMI shielding effectiveness of C/C composites could be improved by reducing the porosity appropriately. When the open porosity is 33.4%, the C/C composite material shows a maximum shielding effectiveness of 40dB, and the EIM apsorption shielding effectiveness(30dB) is much higher than EMI reflection shielding effectiveness(12dB)). Porous C/C composite is one kind of excellent EMI shielding materials with high absorption and low reflection.
2012, (3): 65-71.
Abstract:
The flame-retardant polycarbonates (PC) were prepared by mixing the PC with different compounded flame retardants which were obtained by separately mixing the polyborosiloxane (PB) with three types of organophosphate (OPP). The synergistic effect of PB on OPP/PC system was evaluated using limited oxygen index (LOI) and cone calorimeter analysis. The results show that, at 5% mass fraction of total flame retardant addition, the compounded flame retardant with above 1.25% mass fraction of PB can improve the LOI of the PB-OPP/PC system. PB flame retardant promotes the char formation during the combustion of the PB-OPP/PC, which reduces the emission of the smoke, heat and CO. The total smoke release decreases by 31.8% to 51.0% when each of the three compounded flame retardants is added into PC. The combustion process is moderated and the hazard of fire is reduced. It is also found that the moderate addition of PB improves the tensile strength, flexural strength, vicat temperature and the transparency of PB-OPP/PC.
The flame-retardant polycarbonates (PC) were prepared by mixing the PC with different compounded flame retardants which were obtained by separately mixing the polyborosiloxane (PB) with three types of organophosphate (OPP). The synergistic effect of PB on OPP/PC system was evaluated using limited oxygen index (LOI) and cone calorimeter analysis. The results show that, at 5% mass fraction of total flame retardant addition, the compounded flame retardant with above 1.25% mass fraction of PB can improve the LOI of the PB-OPP/PC system. PB flame retardant promotes the char formation during the combustion of the PB-OPP/PC, which reduces the emission of the smoke, heat and CO. The total smoke release decreases by 31.8% to 51.0% when each of the three compounded flame retardants is added into PC. The combustion process is moderated and the hazard of fire is reduced. It is also found that the moderate addition of PB improves the tensile strength, flexural strength, vicat temperature and the transparency of PB-OPP/PC.
2012, (3): 72-78.
Abstract:
The defense performance of sandwich structure of steel plate-fiber composite material plate-steel plate structure against fragment was investigated. By the experiment on the fragment simulation projectile (FSP), impacted to different kinds of sandwich plate with high velocity, the ballistic limits of fragment pierced 16 kinds of sandwich plates were obtained, and the influence of structure characteristic on the specific energy absorption of the sandwich plate was analyzed. The results show that the specific energy absorption of laminated sandwich structure on aramid and glass fiber is 8.31% and 16.09% higher than that of a single-layer structure, respectively.The specific energy absorption of the sandwich structure with 8 mm front +8mm core +6 mm back on aramid and glass fiber is 37.72% and 25.35% higher than the one with 4 mm front +8 mm core +10 mm back, respectively. The specific energy absorption of sandwich plate exponentially increases with the thickness of fiber composite sandwich. The tensile properties of middle layer plate is an important factor on the specific energy absorption of the sandwich plate. At the same areal density, the specific energy absorption of the sandwich plate can be significantly improved by adopting thicker faceplate, thinner backboard and laminated structure for middle layer.
The defense performance of sandwich structure of steel plate-fiber composite material plate-steel plate structure against fragment was investigated. By the experiment on the fragment simulation projectile (FSP), impacted to different kinds of sandwich plate with high velocity, the ballistic limits of fragment pierced 16 kinds of sandwich plates were obtained, and the influence of structure characteristic on the specific energy absorption of the sandwich plate was analyzed. The results show that the specific energy absorption of laminated sandwich structure on aramid and glass fiber is 8.31% and 16.09% higher than that of a single-layer structure, respectively.The specific energy absorption of the sandwich structure with 8 mm front +8mm core +6 mm back on aramid and glass fiber is 37.72% and 25.35% higher than the one with 4 mm front +8 mm core +10 mm back, respectively. The specific energy absorption of sandwich plate exponentially increases with the thickness of fiber composite sandwich. The tensile properties of middle layer plate is an important factor on the specific energy absorption of the sandwich plate. At the same areal density, the specific energy absorption of the sandwich plate can be significantly improved by adopting thicker faceplate, thinner backboard and laminated structure for middle layer.
2012, (3): 79-84.
Abstract:
icrocapsules containing paraffin as core and SiO2 as shell were synthesized in-situ in polyvinyl alcohol (PVA) spinning solution. Thus energy storage paraffin/PVA fibre was prepared via wet-spinning process. To get the optimum conditions for the synthesis of microcapsules, the orthogonal experimental design was used together with the particle size analysis software to analyze relevant factors of particle size. Chemical structures and morphologies of the microcapsules and the fibres were characterized by FTIR-ATR, SEM, EDS and TEM. DSC and TGA were adopted to determine the coated rate of microcapsules, the latent heat storage and thermal stability of the fibre. The results indicate that energy storage microcapsules are successfully synthesized in PVA spinning solution with a paraffin encapsulated ratio as high as 94.72%, and the average particle size of 1.39 μm is suitable for wet-spinning. The paraffin/PVA fibre shows a relatively good thermal stability with a high latent heat of 45.39 J/g.
icrocapsules containing paraffin as core and SiO2 as shell were synthesized in-situ in polyvinyl alcohol (PVA) spinning solution. Thus energy storage paraffin/PVA fibre was prepared via wet-spinning process. To get the optimum conditions for the synthesis of microcapsules, the orthogonal experimental design was used together with the particle size analysis software to analyze relevant factors of particle size. Chemical structures and morphologies of the microcapsules and the fibres were characterized by FTIR-ATR, SEM, EDS and TEM. DSC and TGA were adopted to determine the coated rate of microcapsules, the latent heat storage and thermal stability of the fibre. The results indicate that energy storage microcapsules are successfully synthesized in PVA spinning solution with a paraffin encapsulated ratio as high as 94.72%, and the average particle size of 1.39 μm is suitable for wet-spinning. The paraffin/PVA fibre shows a relatively good thermal stability with a high latent heat of 45.39 J/g.
2012, (3): 85-89.
Abstract:
Carbon nanotubes (CNTs) were prepared by chemical vapor deposition (CVD) method using Co-containing mesoporous molecular sieve as catalyst and ethanol as carbon source. A series of carbon nanotubes/hydroxyapatite (CNTs/HA) composites with different amounts of CNTs were synthesized by using an in-situ method. The structure, morphology, crystal phase and the surface area of the as-synthesized CNTs/HA composites were characterized by XRD, FTIR, TEM, N2 physical adsorption-desorption and Raman spectroscopy. At the same time, the effect of CNTs on the morphology of the CNTs/HA composites was also investigated. XRD and Raman results show that CNTs/HA composites exhibit two kinds of crystal phases including CNTs and HA with good quality and crystallinity. TEM results reveal that the surface of CNTs was uniformly wrapped by nano-sized and needle-liked HA particles, and the good interfacial bonding exists between CNTs and HA. The optimal combination can be achieved between HA and CNTs when the mass ratio of CNTs to HA is 3:17. N2 adsorption-desorption results indicate that CNTs/HA composites have high specific surface area as compared with HA.
Carbon nanotubes (CNTs) were prepared by chemical vapor deposition (CVD) method using Co-containing mesoporous molecular sieve as catalyst and ethanol as carbon source. A series of carbon nanotubes/hydroxyapatite (CNTs/HA) composites with different amounts of CNTs were synthesized by using an in-situ method. The structure, morphology, crystal phase and the surface area of the as-synthesized CNTs/HA composites were characterized by XRD, FTIR, TEM, N2 physical adsorption-desorption and Raman spectroscopy. At the same time, the effect of CNTs on the morphology of the CNTs/HA composites was also investigated. XRD and Raman results show that CNTs/HA composites exhibit two kinds of crystal phases including CNTs and HA with good quality and crystallinity. TEM results reveal that the surface of CNTs was uniformly wrapped by nano-sized and needle-liked HA particles, and the good interfacial bonding exists between CNTs and HA. The optimal combination can be achieved between HA and CNTs when the mass ratio of CNTs to HA is 3:17. N2 adsorption-desorption results indicate that CNTs/HA composites have high specific surface area as compared with HA.
2012, (3): 90-97.
Abstract:
In order to improve the dispersion of ethylidene-2-norbornene (ENB) based self–healing microcapsules in the epoxy, KH560 coupling agent was chosen to modify the surface of ENB microcapsules. The dispersion of KH560-ENB microcapsules and their influence on tensile property of KH560-ENB/Epoxy composites were studied. The results show that, the tensile fracture strength, tensile modulus and elongation at break of ENB/Epoxy composites, decrease when the mass ratio of ENB microcapsules to epoxy increases to no more than 5%. The falling slopes of those three tensile properties vary with pre-curing temperature for ENB/Epoxy composites. The linear coefficient of cumulative distribution of KH560-ENB microcapsule in epoxy is 0.9945, nearly to 1, showing better dispersion. Furthermore, tensile fracture strength and tensile modulus of KH560-ENB/Epoxy composites increase by 19.1% and 6.6%, respectively. According to SEM observations of KH560-ENB/Epoxy cross section, the interface between KH560-ENB microcapsules and epoxy is well bonded.
In order to improve the dispersion of ethylidene-2-norbornene (ENB) based self–healing microcapsules in the epoxy, KH560 coupling agent was chosen to modify the surface of ENB microcapsules. The dispersion of KH560-ENB microcapsules and their influence on tensile property of KH560-ENB/Epoxy composites were studied. The results show that, the tensile fracture strength, tensile modulus and elongation at break of ENB/Epoxy composites, decrease when the mass ratio of ENB microcapsules to epoxy increases to no more than 5%. The falling slopes of those three tensile properties vary with pre-curing temperature for ENB/Epoxy composites. The linear coefficient of cumulative distribution of KH560-ENB microcapsule in epoxy is 0.9945, nearly to 1, showing better dispersion. Furthermore, tensile fracture strength and tensile modulus of KH560-ENB/Epoxy composites increase by 19.1% and 6.6%, respectively. According to SEM observations of KH560-ENB/Epoxy cross section, the interface between KH560-ENB microcapsules and epoxy is well bonded.
2012, (3): 98-104.
Abstract:
A new kind of biocomposite of dicalcium phosphate (DCP)/four element poly (amino acid) copolymer (PAA) was prepared by using polymerization in situ for bone repair, and its composition and structure were characterized by XRD and IR. The in vitro bioactivity and degradability of DCP/PAA composite were determined by using simulated body liquid (SBF) and Tris-HCl solution, respectively. The results show that the interactions exist between the inorganic and organic phase of the DCP/PAA composite. The polymerized reaction time has significant effects on the mechanical strength of PAA and DCP/PAA composite, and the viscosities of PAA increases with the increase of the reaction time, so the compressive strength is improved. The DCP/PAA composite has good bioactivity because the apatite could be formed on its surfaces after soaking into SBF, and the newly formed apatite is calcium deficient apatite with the Ca/P atom ratio of 1.59. The DCP/PAA composite could be degradable in the Tris-HCl solution, and intrinsic viscosities of PAA have effects on the degradation of the biocomposite. The pH value of the solution decreases slightly after the composite soaking into Tris-HCl solution at initial stages, but it is stable around 7.0~7.2 after 4 weeks later.
A new kind of biocomposite of dicalcium phosphate (DCP)/four element poly (amino acid) copolymer (PAA) was prepared by using polymerization in situ for bone repair, and its composition and structure were characterized by XRD and IR. The in vitro bioactivity and degradability of DCP/PAA composite were determined by using simulated body liquid (SBF) and Tris-HCl solution, respectively. The results show that the interactions exist between the inorganic and organic phase of the DCP/PAA composite. The polymerized reaction time has significant effects on the mechanical strength of PAA and DCP/PAA composite, and the viscosities of PAA increases with the increase of the reaction time, so the compressive strength is improved. The DCP/PAA composite has good bioactivity because the apatite could be formed on its surfaces after soaking into SBF, and the newly formed apatite is calcium deficient apatite with the Ca/P atom ratio of 1.59. The DCP/PAA composite could be degradable in the Tris-HCl solution, and intrinsic viscosities of PAA have effects on the degradation of the biocomposite. The pH value of the solution decreases slightly after the composite soaking into Tris-HCl solution at initial stages, but it is stable around 7.0~7.2 after 4 weeks later.
2012, (3): 105-110.
Abstract:
The poly(N-isopropylacrylamide)(polyNIPAM) hydrogels with various silk sericin (SS) content were successfully prepared by semi-interpenetrating network (semi-IPN) method. The structure, compatibility and thermal stability of hydrogel, including the internal pore shape and volume phase transition behavior of hydrogels, were investigated by XRD, SEM, DSC and TGA-DTG. The results show that hydrogen bond acting force can be found between silk sericin polypeptide chains and polyNIPAM molecular chains. With increasing mass faction of silk sericin from 0 to 20%, the interior pore size of PNIPAM hydrogel increases by one or two times and presents honeycomb patterned structure. The SS chains homodisperse into the hydrogel matrix without any phase separation. In comparison with volume phase transition temperature(VPTT) value of pure polyNIPAM hydrogel, the introduction of silk sericin molecular chains leads to temperature enhancement of 0.2-0.3℃. The maximum thermal decomposition temperature and DTG decomposition temperature increase gradually.
The poly(N-isopropylacrylamide)(polyNIPAM) hydrogels with various silk sericin (SS) content were successfully prepared by semi-interpenetrating network (semi-IPN) method. The structure, compatibility and thermal stability of hydrogel, including the internal pore shape and volume phase transition behavior of hydrogels, were investigated by XRD, SEM, DSC and TGA-DTG. The results show that hydrogen bond acting force can be found between silk sericin polypeptide chains and polyNIPAM molecular chains. With increasing mass faction of silk sericin from 0 to 20%, the interior pore size of PNIPAM hydrogel increases by one or two times and presents honeycomb patterned structure. The SS chains homodisperse into the hydrogel matrix without any phase separation. In comparison with volume phase transition temperature(VPTT) value of pure polyNIPAM hydrogel, the introduction of silk sericin molecular chains leads to temperature enhancement of 0.2-0.3℃. The maximum thermal decomposition temperature and DTG decomposition temperature increase gradually.
2012, (3): 111-116.
Abstract:
Composite conductive fibers with high conductivity, good mechanical properties and well-behaved spinnability were obtained by the wet spinning based on poly(3,4-ethylenedioxythiophene)-polystyrene sulfonic acid (PEDOT-PSS) blended with polyvinyl alcohol(PVA). The effect of draw ratios on the conductivity, structure, thermostability and mechanical properties of the fibers was investigated. The results show that the number of microfibers on the surface of PEDOT-PSS/PVA composite fiber increases, and its crystallization, thermal stability and mechanical properties are all improved with the increase of the draw ratio. When the draw ratio of PEDOT-PSS/PVA composite fiber is 4.0, its breaking strength, tensile stretch and initial modulus are 6.74 cN/ dtex, 5.95% and 42.43 cN/dtex, respectively, and its conductivity reaches 34.5 S/cm, which presents a good utility.
Composite conductive fibers with high conductivity, good mechanical properties and well-behaved spinnability were obtained by the wet spinning based on poly(3,4-ethylenedioxythiophene)-polystyrene sulfonic acid (PEDOT-PSS) blended with polyvinyl alcohol(PVA). The effect of draw ratios on the conductivity, structure, thermostability and mechanical properties of the fibers was investigated. The results show that the number of microfibers on the surface of PEDOT-PSS/PVA composite fiber increases, and its crystallization, thermal stability and mechanical properties are all improved with the increase of the draw ratio. When the draw ratio of PEDOT-PSS/PVA composite fiber is 4.0, its breaking strength, tensile stretch and initial modulus are 6.74 cN/ dtex, 5.95% and 42.43 cN/dtex, respectively, and its conductivity reaches 34.5 S/cm, which presents a good utility.
2012, (3): 117-121.
Abstract:
A kind of biomimetic amphoteric polymer, phosphatidylcholine (PC), was used as surfactant to produce water soluble and biocompatible magnetic carbon nanotubes (Fe3O4/CNTs), which was prepared by solvothermal method. Fe3O4/CNTs was facilely dispersed in aqueous media by ultrasonication with the help of PC, with the long hydrophobic segment and the hydrophilic group as controls. The biological properties of the PC modified Fe3O4/CNTs (Fe3O4/CNTs-PC) were evaluated using protein adsorption assay and recalcification time. The results indicate that the adsorption capacity of bovine serum albumin (BSA) is 0.1368 mg/mg, and the recalcification time is 324 s. These experimental results suggest that Fe3O4/CNTs-PC has good outstanding biocompatibility.
A kind of biomimetic amphoteric polymer, phosphatidylcholine (PC), was used as surfactant to produce water soluble and biocompatible magnetic carbon nanotubes (Fe3O4/CNTs), which was prepared by solvothermal method. Fe3O4/CNTs was facilely dispersed in aqueous media by ultrasonication with the help of PC, with the long hydrophobic segment and the hydrophilic group as controls. The biological properties of the PC modified Fe3O4/CNTs (Fe3O4/CNTs-PC) were evaluated using protein adsorption assay and recalcification time. The results indicate that the adsorption capacity of bovine serum albumin (BSA) is 0.1368 mg/mg, and the recalcification time is 324 s. These experimental results suggest that Fe3O4/CNTs-PC has good outstanding biocompatibility.
2012, (3): 122-126.
Abstract:
Centrifugal gel forming was applied to the molding of 316L-TiC composite powders. The effect of the solids loading on the rheological behavior of 316L-TiC composite powders slurry was investigated, and the effect of the amount of initiator on the solidification time was also studied.Moreover, the relationship between the rotation speed and the density and strength of green body by centrifugal gel forming was analyzed. The results show that, using oleic acid as dispersion, slurry with good flowability and good stability has been prepared, at which a maximum solids volume fraction of 55% and the amount of initiator of 0.7%(mass fraction in the premix) can be obtained. Using the device made by ourselves and choosing the optimum rotation speed 3000 r/min, the green body with high density and no residue stomatal has been prepared, while the relative density and strength is 64.3% and 26.3 MPa, respectively. 316L-TiC alloy pipe is achieved by sintered at 1380℃ for 1 h in vacuum, which has a uniform shrinkage without deformation and the homogeneous distribution of the TiC particles.
Centrifugal gel forming was applied to the molding of 316L-TiC composite powders. The effect of the solids loading on the rheological behavior of 316L-TiC composite powders slurry was investigated, and the effect of the amount of initiator on the solidification time was also studied.Moreover, the relationship between the rotation speed and the density and strength of green body by centrifugal gel forming was analyzed. The results show that, using oleic acid as dispersion, slurry with good flowability and good stability has been prepared, at which a maximum solids volume fraction of 55% and the amount of initiator of 0.7%(mass fraction in the premix) can be obtained. Using the device made by ourselves and choosing the optimum rotation speed 3000 r/min, the green body with high density and no residue stomatal has been prepared, while the relative density and strength is 64.3% and 26.3 MPa, respectively. 316L-TiC alloy pipe is achieved by sintered at 1380℃ for 1 h in vacuum, which has a uniform shrinkage without deformation and the homogeneous distribution of the TiC particles.
2012, (3): 127-133.
Abstract:
Monolithic TiO2 aerogels have been prepared by sol-gel method and subsequent process such as solvent replacement with ambient pressure drying using titanate tetrabutoxide, formamide and acetic acid as raw material. The influences of organic ligand on the structure of aerogels were investigated. The microstructure and properties of samples were characterized by means of XRD, BET, SEM, EDS and DSC-TG. The results indicate that when the mole ratio of organic ligand to titanate tetrabutoxide is 0.9, the property of prepared TiO2 aerogel is the best, with the apparent density of 0.25 g·cm-3, the specific surface area of 716.5 m2·g-1, and the average pore size of 19.1 nm. After calcined at 850℃ for 2 h in air, the sample has high photocatalytic activity, while it's specific surface area reduces to 122.4 m2·g-1 and average pore size increases to 23.4 nm. After calcined at 1000℃, anatase is still the main crystalling phase, and shows low photocatalytic activity. The apparent density of TiO2 aerogel (not using organic ligand) is 0.57 g·cm-3, and it's specific surface area is 482.2 m2·g-1. TiO2 aerogels prepared using organic ligand present less dense and higher specific surface area.
Monolithic TiO2 aerogels have been prepared by sol-gel method and subsequent process such as solvent replacement with ambient pressure drying using titanate tetrabutoxide, formamide and acetic acid as raw material. The influences of organic ligand on the structure of aerogels were investigated. The microstructure and properties of samples were characterized by means of XRD, BET, SEM, EDS and DSC-TG. The results indicate that when the mole ratio of organic ligand to titanate tetrabutoxide is 0.9, the property of prepared TiO2 aerogel is the best, with the apparent density of 0.25 g·cm-3, the specific surface area of 716.5 m2·g-1, and the average pore size of 19.1 nm. After calcined at 850℃ for 2 h in air, the sample has high photocatalytic activity, while it's specific surface area reduces to 122.4 m2·g-1 and average pore size increases to 23.4 nm. After calcined at 1000℃, anatase is still the main crystalling phase, and shows low photocatalytic activity. The apparent density of TiO2 aerogel (not using organic ligand) is 0.57 g·cm-3, and it's specific surface area is 482.2 m2·g-1. TiO2 aerogels prepared using organic ligand present less dense and higher specific surface area.
2012, (3): 134-139.
Abstract:
Using liquid epoxy resin as the bond, diamond as the abrasive and nano-SiO2 as the reinforcement, diamond whetstones were prepared by casting process, and the properties were studied. The results show that with the addition of 0.25% mass ratio of accelerant to molding compound, whetstones can be cured at 130℃/4 h+160℃/2 h. As diamond modified by silane coupling agent and Ni-coated, the wear resistance of whetstone is improved by 15.0% and 32.5%, respectively. Nano-SiO2 modified by silane coupling agent is homodispersed in the whetstone, and the bend strength of whetstone can be improved. While the mass fraction of nano-SiO2 is 4%, the flexural strength and Rockwell hardness reach the maximum, i. e. 106 MPa and HRB 56, respectively.
Using liquid epoxy resin as the bond, diamond as the abrasive and nano-SiO2 as the reinforcement, diamond whetstones were prepared by casting process, and the properties were studied. The results show that with the addition of 0.25% mass ratio of accelerant to molding compound, whetstones can be cured at 130℃/4 h+160℃/2 h. As diamond modified by silane coupling agent and Ni-coated, the wear resistance of whetstone is improved by 15.0% and 32.5%, respectively. Nano-SiO2 modified by silane coupling agent is homodispersed in the whetstone, and the bend strength of whetstone can be improved. While the mass fraction of nano-SiO2 is 4%, the flexural strength and Rockwell hardness reach the maximum, i. e. 106 MPa and HRB 56, respectively.
2012, (3): 140-144.
Abstract:
Deformation-processed Cu-11Cr-0.07Ag in situ composite was prepared by the cast and the thermo-mechanical treatment process. The microstructure, mechanical and electrical properties were investigated by scanning electronic microscope, tensile-testing machine and microhmmeter. The results indicate that, with increasing cold deformation strain, the initially randomly distributed Cr dendrites in the as-cast Cu-11Cr-0.07Ag alloy transform into Cr fibres of the deformation-processed in situ composite aligned parallel to the drawing axis, and the tensile strength increases, while the conductivity decreases. The good combination of strength and conductivity of the deformation-processed Cu-11Cr-0.07Ag in situ composite is achieved by using the proper cold deformation and heat treatment. The composite achieves a tensile strength of 851 MPa and a conductivity of 73.9% IACS when the cold deformation strain is 8.
Deformation-processed Cu-11Cr-0.07Ag in situ composite was prepared by the cast and the thermo-mechanical treatment process. The microstructure, mechanical and electrical properties were investigated by scanning electronic microscope, tensile-testing machine and microhmmeter. The results indicate that, with increasing cold deformation strain, the initially randomly distributed Cr dendrites in the as-cast Cu-11Cr-0.07Ag alloy transform into Cr fibres of the deformation-processed in situ composite aligned parallel to the drawing axis, and the tensile strength increases, while the conductivity decreases. The good combination of strength and conductivity of the deformation-processed Cu-11Cr-0.07Ag in situ composite is achieved by using the proper cold deformation and heat treatment. The composite achieves a tensile strength of 851 MPa and a conductivity of 73.9% IACS when the cold deformation strain is 8.
2012, (3): 145-149.
Abstract:
Sc2W3O12, which exhibits excellent anisotropic negative thermal expansion was synthesized using solid-state reaction. Sc2W3O12/ZrO2 composites were prepared by mixing ZrO2 and Sc2W3O12 at different volume ratios and sintered at 1200 ℃ for 10 h. The crystal structure, fracture surface morphology and thermal expansion properties of the synthesized samples were characterized by XRD, SEM, EDS and dilatometer. The results indicate that the obtained samples contain only orthorhombic Sc2W3O12 and monoclinic ZrO2 phase. All the thermal expansion properties of Sc2W3O12/ZrO2 composites are linear from 30 ℃ to 600 ℃, and their thermal expansion coefficients can be controlled as positive, negative or even zero by adjusting the volume fraction of Sc2W3O12. 60%Sc2W3O12/ZrO2 composite shows almost zero thermal expansion, and its average thermal expansion coefficient is 0.026×10-6 ℃-1 from 30 ℃ to 600 ℃.
Sc2W3O12, which exhibits excellent anisotropic negative thermal expansion was synthesized using solid-state reaction. Sc2W3O12/ZrO2 composites were prepared by mixing ZrO2 and Sc2W3O12 at different volume ratios and sintered at 1200 ℃ for 10 h. The crystal structure, fracture surface morphology and thermal expansion properties of the synthesized samples were characterized by XRD, SEM, EDS and dilatometer. The results indicate that the obtained samples contain only orthorhombic Sc2W3O12 and monoclinic ZrO2 phase. All the thermal expansion properties of Sc2W3O12/ZrO2 composites are linear from 30 ℃ to 600 ℃, and their thermal expansion coefficients can be controlled as positive, negative or even zero by adjusting the volume fraction of Sc2W3O12. 60%Sc2W3O12/ZrO2 composite shows almost zero thermal expansion, and its average thermal expansion coefficient is 0.026×10-6 ℃-1 from 30 ℃ to 600 ℃.
2012, (3): 150-157.
Abstract:
Chitosan (CS) was modified with nano-Pt/TiO2 semiconductor photocatalyst (CS-Pt/TiO2) which was prepared by doping Pt on TiO2 in advance. CMC-Pt/TiO2-CS bipolar membrane was then prepared using carboxymethyl cellulose(CMC)and CS-Pt/TiO2 which were cross-linked by FeCl3 and glutaraldehyde, respectively. Sandwich-typed CMC-Pt/TiO2-CS bipolar membrane, the composite membrane with fine protons and hydroxyl ion-permeability, was then applied as the septum of the electrolytic cell in the degradation of phenol. Nano-Pt/TiO2 semiconductor photocatalyst can not only generate hydroxyl radicals (·OH) which can directly degrade phenol into the small inorganic molecules, but also promote water splitting at the intermediate layer of CMC-Pt/TiO2-CS bipolar membrane and greatly reduce the impedance and resistance(IR) of bipolar membrane. Compared CMC-Pt/TiO2-CS bipolar membrane with CMC-TiO2-CS bipolar membrane under UV irradiation, the degradation rate of the former is 12.7% higher than that of the latter after 80 min electrolysis at the current density of 16.7 mA·cm-2, while IR drop of CMC-Pt/TiO2-CS is as low as 0.9 V.
Chitosan (CS) was modified with nano-Pt/TiO2 semiconductor photocatalyst (CS-Pt/TiO2) which was prepared by doping Pt on TiO2 in advance. CMC-Pt/TiO2-CS bipolar membrane was then prepared using carboxymethyl cellulose(CMC)and CS-Pt/TiO2 which were cross-linked by FeCl3 and glutaraldehyde, respectively. Sandwich-typed CMC-Pt/TiO2-CS bipolar membrane, the composite membrane with fine protons and hydroxyl ion-permeability, was then applied as the septum of the electrolytic cell in the degradation of phenol. Nano-Pt/TiO2 semiconductor photocatalyst can not only generate hydroxyl radicals (·OH) which can directly degrade phenol into the small inorganic molecules, but also promote water splitting at the intermediate layer of CMC-Pt/TiO2-CS bipolar membrane and greatly reduce the impedance and resistance(IR) of bipolar membrane. Compared CMC-Pt/TiO2-CS bipolar membrane with CMC-TiO2-CS bipolar membrane under UV irradiation, the degradation rate of the former is 12.7% higher than that of the latter after 80 min electrolysis at the current density of 16.7 mA·cm-2, while IR drop of CMC-Pt/TiO2-CS is as low as 0.9 V.
2012, (3): 158-166.
Abstract:
Based on water-soluble mandrel, the integrated composite wing box was fabricated via resin transfer molding (RTM). The test of natural modal of wing box was conducted. The finite element (FE) models for modal and buckling analysis of wing box were generated by using 3D shell element to investigate the stacking sequence effect on the natural modal and bucking properties. The calculations of natural modal are consistent well with the experiments, validiting the FE model proposed in the paper. The FE model was applied to simulate the natural modal and stability of wing box with four different layups. The results show that symmetrical layers of the skin have significant beneficial effects on natural frequency and buckling loads of wing box under axial compression and torsion, in contrast, have distinct adverse effects on those under the bending and combination of bending and torsion. In addition, the rigidity of web has an apparent beneficial effect on the buckling load and natural frequency of wing box, whereas the increasing of 45? plies or the decreasing of the thickness of web would reduce buckling load and natural frequency.
Based on water-soluble mandrel, the integrated composite wing box was fabricated via resin transfer molding (RTM). The test of natural modal of wing box was conducted. The finite element (FE) models for modal and buckling analysis of wing box were generated by using 3D shell element to investigate the stacking sequence effect on the natural modal and bucking properties. The calculations of natural modal are consistent well with the experiments, validiting the FE model proposed in the paper. The FE model was applied to simulate the natural modal and stability of wing box with four different layups. The results show that symmetrical layers of the skin have significant beneficial effects on natural frequency and buckling loads of wing box under axial compression and torsion, in contrast, have distinct adverse effects on those under the bending and combination of bending and torsion. In addition, the rigidity of web has an apparent beneficial effect on the buckling load and natural frequency of wing box, whereas the increasing of 45? plies or the decreasing of the thickness of web would reduce buckling load and natural frequency.
2012, (3): 167-172.
Abstract:
A model for the damage analysis of the open-hole compression composite laminates was developed. The model divided the failure modes of composite laminates into intra-laminar and inter-laminar damage. The failure modes and failure loads of different laminates were predicted and compared with the experimental results based on progressive failure analysis methodology. The results show that the model can simulate damage initiation, damage progression, final damage and predicted failure mode and failure load of laminates with central circular holes subjected to compression load, then predict the failure mode and failure load of open-hole compression laminates.
A model for the damage analysis of the open-hole compression composite laminates was developed. The model divided the failure modes of composite laminates into intra-laminar and inter-laminar damage. The failure modes and failure loads of different laminates were predicted and compared with the experimental results based on progressive failure analysis methodology. The results show that the model can simulate damage initiation, damage progression, final damage and predicted failure mode and failure load of laminates with central circular holes subjected to compression load, then predict the failure mode and failure load of open-hole compression laminates.
2012, (3): 173-178.
Abstract:
A three dimensional microscopic model of the reticulate carbon nanotube/epoxy (R-CNT/EP) composites was established according to its structural characteristics based on the assumption of the uniform distribution of R-CNT. The effective stiffness coefficients and Young's modulus of the R-CNT/EP composite were calculated by two-scale expansion method. It is shown that the mechanical properties of the R-CNT/EP composite are anisotropic and the strength along the direction of the vapor flow is much higher than that in other directions. The shape of the R-CNT plays an important role on the mechanical properties of the R-CNT/EP composite, and the effective stiffnesses and Young's modulus of the R-CNT/EP composites are the highest when the angles of the Y-junctions are equal. All of the effective stiffnesses and Young's modulus of the R-CNT/EP composites are enhanced with the increase of volume fraction of R-CNT, but the influence degrees are different.
A three dimensional microscopic model of the reticulate carbon nanotube/epoxy (R-CNT/EP) composites was established according to its structural characteristics based on the assumption of the uniform distribution of R-CNT. The effective stiffness coefficients and Young's modulus of the R-CNT/EP composite were calculated by two-scale expansion method. It is shown that the mechanical properties of the R-CNT/EP composite are anisotropic and the strength along the direction of the vapor flow is much higher than that in other directions. The shape of the R-CNT plays an important role on the mechanical properties of the R-CNT/EP composite, and the effective stiffnesses and Young's modulus of the R-CNT/EP composites are the highest when the angles of the Y-junctions are equal. All of the effective stiffnesses and Young's modulus of the R-CNT/EP composites are enhanced with the increase of volume fraction of R-CNT, but the influence degrees are different.
2012, (3): 184-190.
Abstract:
The buckling factors of honeycomb sandwich structures with fixed size core were obtained with different faceplate thicknesses using homogenization core models. The solutions obtained with the finite element analysis approach were compared with the results from the conventional analytical formulas. The results obtained by two kinds of methods are basically consistent. The finite element models were used in the progress of structural stability analysis, considering the geometry characteristics of the core, and the effect of the core's geometry characteristics on the stability problem was discussed. A local instability phenomenon, called cell-wall buckling, was introduced. A prediction analytical approach for the phenomenon was presented, and the results were compared with that of the finite element analysis to validate the proposed approach. The stability problem of satellite sandwich bearing cylinder under the multi-axis inertial loads was studied by the finite element method. The results were obtained with different faceplate thicknesses and different ratios of vertical and horizontal inertial load. The related analysis equation for the multi-axis inertial loads was given.
The buckling factors of honeycomb sandwich structures with fixed size core were obtained with different faceplate thicknesses using homogenization core models. The solutions obtained with the finite element analysis approach were compared with the results from the conventional analytical formulas. The results obtained by two kinds of methods are basically consistent. The finite element models were used in the progress of structural stability analysis, considering the geometry characteristics of the core, and the effect of the core's geometry characteristics on the stability problem was discussed. A local instability phenomenon, called cell-wall buckling, was introduced. A prediction analytical approach for the phenomenon was presented, and the results were compared with that of the finite element analysis to validate the proposed approach. The stability problem of satellite sandwich bearing cylinder under the multi-axis inertial loads was studied by the finite element method. The results were obtained with different faceplate thicknesses and different ratios of vertical and horizontal inertial load. The related analysis equation for the multi-axis inertial loads was given.
2012, (3): 191-196.
Abstract:
Based on the stable winding condition of the general surface, a method for measuring the slippage coefficient was established. A special mandrel was proposed, which has a designed meridian profile that enables a linearly proportional relation between the cross-sectional radius and the measured values of the slippage coefficient. With the special mandrel, the slippage coefficient between carbon fiber/glass fiber and aluminum mandrel surface was obtained under several different typical filament-winding process parameters, such as winding speed, winding tension, resin viscosity, and so on. The experimental results show that this method can obtain the slippage coefficient easily and provide a reference for non-geodesic fiber path design.
Based on the stable winding condition of the general surface, a method for measuring the slippage coefficient was established. A special mandrel was proposed, which has a designed meridian profile that enables a linearly proportional relation between the cross-sectional radius and the measured values of the slippage coefficient. With the special mandrel, the slippage coefficient between carbon fiber/glass fiber and aluminum mandrel surface was obtained under several different typical filament-winding process parameters, such as winding speed, winding tension, resin viscosity, and so on. The experimental results show that this method can obtain the slippage coefficient easily and provide a reference for non-geodesic fiber path design.
2012, (3): 197-202.
Abstract:
The compressive failure mechanism of low-velocity-impacted composite laminates was studied by means of delamination configuration obtained by ultrasonic C-scan, strain field by strain gauges, and damage process by acoustic emission. The results show that serious stress concentration appears leading to subsequent fiber breakage and triggering catastrophic failure of the laminate because of unsymmetrical delamination distribution within the laminate. The key factor in compressive failure mechanism of impacted composite laminates was fiber breakage rather than delamination propagation.
The compressive failure mechanism of low-velocity-impacted composite laminates was studied by means of delamination configuration obtained by ultrasonic C-scan, strain field by strain gauges, and damage process by acoustic emission. The results show that serious stress concentration appears leading to subsequent fiber breakage and triggering catastrophic failure of the laminate because of unsymmetrical delamination distribution within the laminate. The key factor in compressive failure mechanism of impacted composite laminates was fiber breakage rather than delamination propagation.
2012, (3): 203-207.
Abstract:
The problems of composite laminated plate's structural vibration and acoustic radiation under external loading were investigated. The structural-acoustic optimization model of composite structure was presented. The stacking sequence problem of symmetric composite laminate and structural-acoustic radiation optimization were caried out using the genetic algorithm. The example shows that the vibration and acoustic radiation of composite laminated can be reduced by optimizing the stacking sequence parameters, such as layers number, layers thickness and layers angle. The calculation results has validited the optimized method.
The problems of composite laminated plate's structural vibration and acoustic radiation under external loading were investigated. The structural-acoustic optimization model of composite structure was presented. The stacking sequence problem of symmetric composite laminate and structural-acoustic radiation optimization were caried out using the genetic algorithm. The example shows that the vibration and acoustic radiation of composite laminated can be reduced by optimizing the stacking sequence parameters, such as layers number, layers thickness and layers angle. The calculation results has validited the optimized method.
2012, (3): 208-213.
Abstract:
The improved warp skeleton method was used to describe 3D woven composites architecture, and unit cell was decomposed into subcells/grids. The concept of crimp pattern code was put forward, and the yarn centerline could be fitted based on the information contained in the codes. With "mutual imitation method"of tows, cross-section contour line was fitted by sectioned spline curves. Merging centerlines and contour lines could derive yarns'curved surfaces, which were used to create geometric model of a preform. The obtained cross-section shape makes quite good agreement with SEM photoes. The results show that the sectioned spline curves can be used to describe the yarn pattern, and the efficiency of mutual imitation method is significantly higher than that of iteration one under the same precision.
The improved warp skeleton method was used to describe 3D woven composites architecture, and unit cell was decomposed into subcells/grids. The concept of crimp pattern code was put forward, and the yarn centerline could be fitted based on the information contained in the codes. With "mutual imitation method"of tows, cross-section contour line was fitted by sectioned spline curves. Merging centerlines and contour lines could derive yarns'curved surfaces, which were used to create geometric model of a preform. The obtained cross-section shape makes quite good agreement with SEM photoes. The results show that the sectioned spline curves can be used to describe the yarn pattern, and the efficiency of mutual imitation method is significantly higher than that of iteration one under the same precision.
2012, (3): 214-218.
Abstract:
The electro-elastic coupling interactions between a piezoelectric screw dislocation, which located in the matrix, and an elliptical inhomogeneity containing an electrically conductive confocal elliptical rigid core in piezoelectric composite material was studied. Based on the complex variable method, the analytical solutions of the complex potentials in the matrix and the inclusion regions were obtained explicitly in the series form. The image force acting on the piezoelectric screw dislocation was calculated using the generalized Peach-Koehler formula. The effects of the elliptical rigid core and the electro-elastic properties of the piezoelectric materials on the image force and the equilibrium position of the dislocation were discussed. In addition, piezoelectric inclusion and elastic matrix composites was studied in this paper. The main results show that, the elliptical rigid core has a significant repelling action, which enhances the repulsive force acting on the dislocation produced by the stiff inhomogeneity and weakens the attractive force produced by the soft inhomogeneity. For the soft inhomogeneity, there is an unstable equilibrium position near the interface. The image force increases rapidly near the interface of the matrix and the inhomogeneity. There is no equilibrium position of the dislocation near the interface when the shear modulus of the inhomogeneity is much smaller than that of the matrix.
The electro-elastic coupling interactions between a piezoelectric screw dislocation, which located in the matrix, and an elliptical inhomogeneity containing an electrically conductive confocal elliptical rigid core in piezoelectric composite material was studied. Based on the complex variable method, the analytical solutions of the complex potentials in the matrix and the inclusion regions were obtained explicitly in the series form. The image force acting on the piezoelectric screw dislocation was calculated using the generalized Peach-Koehler formula. The effects of the elliptical rigid core and the electro-elastic properties of the piezoelectric materials on the image force and the equilibrium position of the dislocation were discussed. In addition, piezoelectric inclusion and elastic matrix composites was studied in this paper. The main results show that, the elliptical rigid core has a significant repelling action, which enhances the repulsive force acting on the dislocation produced by the stiff inhomogeneity and weakens the attractive force produced by the soft inhomogeneity. For the soft inhomogeneity, there is an unstable equilibrium position near the interface. The image force increases rapidly near the interface of the matrix and the inhomogeneity. There is no equilibrium position of the dislocation near the interface when the shear modulus of the inhomogeneity is much smaller than that of the matrix.
2012, (3): 219-225.
Abstract:
Based on the theory of small deflection of thin plate and the constitutive description of Kelvin-Viogt viscoelastic material, the controlling equation which dominates the transverse vibration of the axially moving viscoelastic sandwich plate was established, followed by the study of the transverse vibration characteristic. One-mode and two-mode eigenequation were obtained by using 1-term and 2-term Galerkin truncation. The influence of the ratio of the core and axially moving velocity on the transverse vibration characteristic was discussed. It is found that both 1-term and 2-term Galerkin truncation results fit well when the axially moving velocity doesn't exceed the critical velocity. However, 1-term Galerkin truncation will not suit any more when the axially moving velocity exceeds the critical velocity. For simply supported plate at four sides, the critical velocity and coupled mode flutter velocity increase with the decrease of ratio of core.
Based on the theory of small deflection of thin plate and the constitutive description of Kelvin-Viogt viscoelastic material, the controlling equation which dominates the transverse vibration of the axially moving viscoelastic sandwich plate was established, followed by the study of the transverse vibration characteristic. One-mode and two-mode eigenequation were obtained by using 1-term and 2-term Galerkin truncation. The influence of the ratio of the core and axially moving velocity on the transverse vibration characteristic was discussed. It is found that both 1-term and 2-term Galerkin truncation results fit well when the axially moving velocity doesn't exceed the critical velocity. However, 1-term Galerkin truncation will not suit any more when the axially moving velocity exceeds the critical velocity. For simply supported plate at four sides, the critical velocity and coupled mode flutter velocity increase with the decrease of ratio of core.
