2015 Vol. 32, No. 4
Preparation and properties of low compression set conductive carbon black/silicone rubber composites
2015, 32(4): 925-932.
doi: 10.13801/j.cnki.fhclxb.20150522.003
Abstract:
In order to obtain a conductive and electromagnetic shielding silicone rubber sealing material with low compression set and high resilience, a kind of conductive carbon black/silicone rubber composite based on methyl vinyl silicone raw rubber were prepared by filling carbon black treated by coupling agent as reinforcing agent and conductive fillers. The mechanical properties, elasticity, dispersity and electrical conductivity of these conductive carbon black/silicone rubber composites with different carbon black contents were investigated. The distribution morphologies of conductive carbon in silicone rubber matrix were characterized by SEM and the conductive and shielding mechanism of conductive carbon black/silicone rubber composites were analyzed. The results show that with the increasing of carbon black content, the Shore A hardness of conductive carbon black/silicone rubber composites increases from 31 to 70, the tensile strength first increases from 3.31 MPa to 5.28 MPa then tends to be steady, the elongation ratio first increases from 198% to 297% then decreases to 210%, while the constant compression set amount decreases first then increases and the instant rebound ratio decreases gradually. The conductive properties and shielding efficiency of conductive carbon black/silicone rubber composites improve promptly when "carbon black cluster" and the conductive road are established.
In order to obtain a conductive and electromagnetic shielding silicone rubber sealing material with low compression set and high resilience, a kind of conductive carbon black/silicone rubber composite based on methyl vinyl silicone raw rubber were prepared by filling carbon black treated by coupling agent as reinforcing agent and conductive fillers. The mechanical properties, elasticity, dispersity and electrical conductivity of these conductive carbon black/silicone rubber composites with different carbon black contents were investigated. The distribution morphologies of conductive carbon in silicone rubber matrix were characterized by SEM and the conductive and shielding mechanism of conductive carbon black/silicone rubber composites were analyzed. The results show that with the increasing of carbon black content, the Shore A hardness of conductive carbon black/silicone rubber composites increases from 31 to 70, the tensile strength first increases from 3.31 MPa to 5.28 MPa then tends to be steady, the elongation ratio first increases from 198% to 297% then decreases to 210%, while the constant compression set amount decreases first then increases and the instant rebound ratio decreases gradually. The conductive properties and shielding efficiency of conductive carbon black/silicone rubber composites improve promptly when "carbon black cluster" and the conductive road are established.
2015, 32(4): 933-941.
doi: 10.13801/j.cnki.fhclxb.20141022.006
Abstract:
In order to make waste concrete and recycled rubber apply in concrete engineering in northern region, the effects of recycled coarse aggregates content, strengthening method of recycled coarse aggregates, content of steel fibers as well as content of rubber on compressive strength and frost resistance of steel fiber rubber recycled concrete (C45) were investigated by orthogonal design tests. Through the scanning electron microscopy and screw CT scanning technique, the macro and micro structure and their effect mechanisms on frost resistance of steel fiber rubber recycled concrete were analyzed. The results show that the content of rubber particles is a prominent factor affecting the gas content, compressive strength and relative dynamic elastic modulus of recycled concrete, and the content of recycled coarse aggregates is also an important factor affecting the relative dynamic elastic modulus and strength loss rate. In addition, the compressive strength of concrete increases slowly with the increase of steel fibers, and strengthening method of aggregates has almost no effect on the performance of concrete. The crack width between rubber particles and mortar interface falls into 5-55 μm. Compatibility between rubber particles and mortar interface is a little bad. When the content of rubber particles is above 20% (volume ratio between rubber particles and sands), the inner hole number of concrete will rise with the increase of rubber particle content. The compressive strength of steel fiber rubber recycled concrete will drop, and frost resistance will also decrease.
In order to make waste concrete and recycled rubber apply in concrete engineering in northern region, the effects of recycled coarse aggregates content, strengthening method of recycled coarse aggregates, content of steel fibers as well as content of rubber on compressive strength and frost resistance of steel fiber rubber recycled concrete (C45) were investigated by orthogonal design tests. Through the scanning electron microscopy and screw CT scanning technique, the macro and micro structure and their effect mechanisms on frost resistance of steel fiber rubber recycled concrete were analyzed. The results show that the content of rubber particles is a prominent factor affecting the gas content, compressive strength and relative dynamic elastic modulus of recycled concrete, and the content of recycled coarse aggregates is also an important factor affecting the relative dynamic elastic modulus and strength loss rate. In addition, the compressive strength of concrete increases slowly with the increase of steel fibers, and strengthening method of aggregates has almost no effect on the performance of concrete. The crack width between rubber particles and mortar interface falls into 5-55 μm. Compatibility between rubber particles and mortar interface is a little bad. When the content of rubber particles is above 20% (volume ratio between rubber particles and sands), the inner hole number of concrete will rise with the increase of rubber particle content. The compressive strength of steel fiber rubber recycled concrete will drop, and frost resistance will also decrease.
2015, 32(4): 942-947.
doi: 10.13801/j.cnki.fhclxb.20141204.001
Abstract:
In order to promote the compatibility between rubber graft and nylon 6 (PA6) and its toughening effect, the anhydride and p-phenylene diamine were used to compound a dicarboxylic acid containing an amide bond and named terephthalic diamide of maleic acid (modified maleic anhydride, MDMA).MDMA was grafted onto ethylene propylene diene monomer(EPDM) to prepare modified maleic anhydride grafted rubbers(EPDM-g-MDMA). EPDM-g-MDMA/PA6 blends containing different graft ratio grafts were prepared when mass ratio of EPDM-g-MDMA to nylon6 (PA6) is 30:70. MDMA was tested by NMR and FTIR for indicating the successful synthesis of the desired dicarboxylic acid. The results of compatibility test, DSC, melting index (MI) test, SEM, tensile and impact mechanical property tests of blends were preformed.Results show that with the graft ratio increasing, the melting peak temperature of the blend is slightly reduced, increasing the melt viscosity.The grafted rubber has good dispersion in PA6 matrix to make the impact strength of EPDM-g-MDMA/PA6 blends increased by 5.5 times, indicating EPDM-g-MDMA toughening PA6 effect is more obvious.
In order to promote the compatibility between rubber graft and nylon 6 (PA6) and its toughening effect, the anhydride and p-phenylene diamine were used to compound a dicarboxylic acid containing an amide bond and named terephthalic diamide of maleic acid (modified maleic anhydride, MDMA).MDMA was grafted onto ethylene propylene diene monomer(EPDM) to prepare modified maleic anhydride grafted rubbers(EPDM-g-MDMA). EPDM-g-MDMA/PA6 blends containing different graft ratio grafts were prepared when mass ratio of EPDM-g-MDMA to nylon6 (PA6) is 30:70. MDMA was tested by NMR and FTIR for indicating the successful synthesis of the desired dicarboxylic acid. The results of compatibility test, DSC, melting index (MI) test, SEM, tensile and impact mechanical property tests of blends were preformed.Results show that with the graft ratio increasing, the melting peak temperature of the blend is slightly reduced, increasing the melt viscosity.The grafted rubber has good dispersion in PA6 matrix to make the impact strength of EPDM-g-MDMA/PA6 blends increased by 5.5 times, indicating EPDM-g-MDMA toughening PA6 effect is more obvious.
2015, 32(4): 948-954.
doi: 10.13801/j.cnki.fhclxb.20140923.003
Abstract:
In order to obtain dispersed phase particles with good electrorheological property,γ-amino propyl triethoxy silane (APTES) was used to modify fly-ash floating beads. Polyaniline (PAn) was coupled with chemical bonds to form core-shell structural composites, with mod-FAFB as core and PAn as shell on the surfaces of decorated FAFB (mod-FAFB). The structure and performance of PAn@mod-FAFB composites were analyzed by FTIR, SEM, digital four point probe technique and LCR dielectric spectrometer. The effect of different contents of mod-FAFB on conductivity and dielectric properties of PAn@mod-FAFB composites were researched.The results show that PAn@mod-FAFB core-shell structural composites with chemical bond graft polymerization have a relatively high electrical conductivity, and the electrical conductivity decreases with the increasing content of mod-FAFB. The relative dielectric constant is higher at low alternating electric field frequency (100-2 000 kHz), and dielectric constant of PAn@mod-FAFB composites decreases obviously with the increasing of mod-FAFB content. The dielectric loss of PAn@mod-FAFB composites is relatively low, and decreases obviously with the increasing of mod-FAFB content.
In order to obtain dispersed phase particles with good electrorheological property,γ-amino propyl triethoxy silane (APTES) was used to modify fly-ash floating beads. Polyaniline (PAn) was coupled with chemical bonds to form core-shell structural composites, with mod-FAFB as core and PAn as shell on the surfaces of decorated FAFB (mod-FAFB). The structure and performance of PAn@mod-FAFB composites were analyzed by FTIR, SEM, digital four point probe technique and LCR dielectric spectrometer. The effect of different contents of mod-FAFB on conductivity and dielectric properties of PAn@mod-FAFB composites were researched.The results show that PAn@mod-FAFB core-shell structural composites with chemical bond graft polymerization have a relatively high electrical conductivity, and the electrical conductivity decreases with the increasing content of mod-FAFB. The relative dielectric constant is higher at low alternating electric field frequency (100-2 000 kHz), and dielectric constant of PAn@mod-FAFB composites decreases obviously with the increasing of mod-FAFB content. The dielectric loss of PAn@mod-FAFB composites is relatively low, and decreases obviously with the increasing of mod-FAFB content.
2015, 32(4): 955-961.
doi: 10.13801/j.cnki.fhclxb.20140919.002
Abstract:
To achieve the morphology-controllable synthesis of nano Fe3O4/polypyrrole(PPy) composites,nano Fe3O4/PPy composites were synthesized through emulsion polymerization method in the presence of sodium dodecyl benzene sulfonate (NaDBS) surfactant. The effects of usage of oil phase pyrrole and surfactant on surface morphology of nano Fe3O4/PPy composites were discussed. The relationship between morphology and conductive-magnetic properties of nano Fe3O4/PPy composites was analyzed.The results show that the morphology of nano Fe3O4/PPy composites can be changed from strawberry-like structure to core-shell structure through increasing the amount of pyrrole, and the amount of the micelles changes with the usage variation of the surfactant, according to which can achieve the controllable adjust of the quantity of cores to get the core-shell structure nano Fe3O4/PPy composites with single core or multiple cores.
To achieve the morphology-controllable synthesis of nano Fe3O4/polypyrrole(PPy) composites,nano Fe3O4/PPy composites were synthesized through emulsion polymerization method in the presence of sodium dodecyl benzene sulfonate (NaDBS) surfactant. The effects of usage of oil phase pyrrole and surfactant on surface morphology of nano Fe3O4/PPy composites were discussed. The relationship between morphology and conductive-magnetic properties of nano Fe3O4/PPy composites was analyzed.The results show that the morphology of nano Fe3O4/PPy composites can be changed from strawberry-like structure to core-shell structure through increasing the amount of pyrrole, and the amount of the micelles changes with the usage variation of the surfactant, according to which can achieve the controllable adjust of the quantity of cores to get the core-shell structure nano Fe3O4/PPy composites with single core or multiple cores.
2015, 32(4): 962-968.
doi: 10.13801/j.cnki.fhclxb.20141022.003
Abstract:
In order to investigate the influence of antimildew agent zinc borate on the fungus corrosion resistance of wheat straw/polypropylene (PP) composites, the fungus accelerating corrosion experiments of wheat straw/PP composites with different contents of zinc borate were conducted. The mechanical properties, color variation and water absorption of composites after corrosion were tested. And FTIR was used to analysis the changes of functional groups of composites. Also the surface mildew growth and microstructure of composites were observed by stereomicroscope. The results show that the zinc borate could improve the corrosion resistance of wheat straw/PP composites. The optimum additive amount of zinc borate is 2wt%, wheat straw/PP composites have little mildew on the surface and flexural strength, flexural elastic modulus, tensile strength and impact strength are increased by 6.5%, 50.2%, 6.8% and 11.1% respectively after corrosion compared with non-adding zinc borate composites. The water absorption rate and color difference value are decreased by 23.9% and 30.7%. The zinc borate could effectively prevent the mildew corrosion to the cellulose and hemicellulose of wheat straw in wheat straw/PP composites when the content of zinc borate is 2wt% and interface wheat straw fiber is easily corrodible by fungus when the content of zinc borate is more than 2wt% due to its effect on interface of composites.
In order to investigate the influence of antimildew agent zinc borate on the fungus corrosion resistance of wheat straw/polypropylene (PP) composites, the fungus accelerating corrosion experiments of wheat straw/PP composites with different contents of zinc borate were conducted. The mechanical properties, color variation and water absorption of composites after corrosion were tested. And FTIR was used to analysis the changes of functional groups of composites. Also the surface mildew growth and microstructure of composites were observed by stereomicroscope. The results show that the zinc borate could improve the corrosion resistance of wheat straw/PP composites. The optimum additive amount of zinc borate is 2wt%, wheat straw/PP composites have little mildew on the surface and flexural strength, flexural elastic modulus, tensile strength and impact strength are increased by 6.5%, 50.2%, 6.8% and 11.1% respectively after corrosion compared with non-adding zinc borate composites. The water absorption rate and color difference value are decreased by 23.9% and 30.7%. The zinc borate could effectively prevent the mildew corrosion to the cellulose and hemicellulose of wheat straw in wheat straw/PP composites when the content of zinc borate is 2wt% and interface wheat straw fiber is easily corrodible by fungus when the content of zinc borate is more than 2wt% due to its effect on interface of composites.
2015, 32(4): 969-976.
doi: 10.13801/j.cnki.fhclxb.20141021.004
Abstract:
To obtain good dispersion and interface properties of SiO2 in ethylene-propylene-diene monomer (EPDM) composites, a series of macromolecular coupling agents with different grafting ratios were synthesized by conventional free radical polymerization, that is EPDM, methyl methacrylate (MMA) and γ-methacryloxypropyltrimethoxy silane (KH-570) terpolymer. The macromolecular coupling agents with different grafting ratios were used to modify SiO2/EPDM composites. FTIR, 1H-NMR, TGA, DMA and SEM were used to characterize the structure of terpolymer and properties of SiO2/EPDM composites. The results show that the compatibility of SiO2/EPDM composites is improved significantly after SiO2 surface treated by macromolecular coupling agent. The tensile and tear strength of SiO2/EPDM composites is increased up to 109.4% and 44.0% respectively when comparing with the composites without coupling agent. The storage modulus and glass transition temperature of SiO2/EPDM composites have been increased after SiO2 surface treatment.
To obtain good dispersion and interface properties of SiO2 in ethylene-propylene-diene monomer (EPDM) composites, a series of macromolecular coupling agents with different grafting ratios were synthesized by conventional free radical polymerization, that is EPDM, methyl methacrylate (MMA) and γ-methacryloxypropyltrimethoxy silane (KH-570) terpolymer. The macromolecular coupling agents with different grafting ratios were used to modify SiO2/EPDM composites. FTIR, 1H-NMR, TGA, DMA and SEM were used to characterize the structure of terpolymer and properties of SiO2/EPDM composites. The results show that the compatibility of SiO2/EPDM composites is improved significantly after SiO2 surface treated by macromolecular coupling agent. The tensile and tear strength of SiO2/EPDM composites is increased up to 109.4% and 44.0% respectively when comparing with the composites without coupling agent. The storage modulus and glass transition temperature of SiO2/EPDM composites have been increased after SiO2 surface treatment.
2015, 32(4): 977-982.
doi: 10.13801/j.cnki.fhclxb.20141105.005
Abstract:
For preparing high-performance wood plastic composites and broading the application fields, the surface of bamboo flour was modified by A-171 silane coupling agent and an amount of bauxite was added into it. The bamboo flour/high density polyethylene (HDPE) composites were prepared by hot pressing technology. The influence of bauxite content on mechanical properties, heat resistance and tribological behavior of the bamboo flour/HDPE composites were investigated. The crystallization characteristics of bauxite were observed using XRD and their morphology of fracture surface and distribution of elements on the surface were analyzed by SEM and EDS. The results show that the mechanical strength, heat resistance and the wear resistance of bamboo flour/HDPE composites are improved by adding the appropriate content of bauxite. Bauxite can be evenly distributed in bamboo flour/HDPE composite matrix and bear the load effectively, and the crystallization properties of bamboo flour/HDPE composites are improved. The deformation and failure of bamboo flour/HDPE composites under exterior stress were reduced. However, when the content of bauxite is too high, the mechanical strength and the wear resistance decrease, and the coefficient of linear thermal expansion of bamboo flour/HDPE composites increases, because that the bauxite is unevenly distributed and formes agglomeration easily.
For preparing high-performance wood plastic composites and broading the application fields, the surface of bamboo flour was modified by A-171 silane coupling agent and an amount of bauxite was added into it. The bamboo flour/high density polyethylene (HDPE) composites were prepared by hot pressing technology. The influence of bauxite content on mechanical properties, heat resistance and tribological behavior of the bamboo flour/HDPE composites were investigated. The crystallization characteristics of bauxite were observed using XRD and their morphology of fracture surface and distribution of elements on the surface were analyzed by SEM and EDS. The results show that the mechanical strength, heat resistance and the wear resistance of bamboo flour/HDPE composites are improved by adding the appropriate content of bauxite. Bauxite can be evenly distributed in bamboo flour/HDPE composite matrix and bear the load effectively, and the crystallization properties of bamboo flour/HDPE composites are improved. The deformation and failure of bamboo flour/HDPE composites under exterior stress were reduced. However, when the content of bauxite is too high, the mechanical strength and the wear resistance decrease, and the coefficient of linear thermal expansion of bamboo flour/HDPE composites increases, because that the bauxite is unevenly distributed and formes agglomeration easily.
2015, 32(4): 983-988.
doi: 10.13801/j.cnki.fhclxb.20141118.005
Abstract:
Though the homemade impregnation mold, the effects of processing parameters such as roving pulling speed, melt temperature and number of pins on fiber fracture of continuous glass fiber reinforced thermalplastic composites were studied quantitatively in compound process. A fiber fracture mathematical model was developed for producing prepreg process to predict the fiber fracture rate and describe the experimental results. The results suggest that the model and experimental data are in good agreement. The model can provide guidance and reference for industrial production. The fiber fracture is mainly caused by viscous shear effect on fiber bundle when pulling the fiber bundle. Reducing the number of impregnation pins and using low-viscosity resin can significantly ease the fiber fracture, as well aspromote the process stability.
Though the homemade impregnation mold, the effects of processing parameters such as roving pulling speed, melt temperature and number of pins on fiber fracture of continuous glass fiber reinforced thermalplastic composites were studied quantitatively in compound process. A fiber fracture mathematical model was developed for producing prepreg process to predict the fiber fracture rate and describe the experimental results. The results suggest that the model and experimental data are in good agreement. The model can provide guidance and reference for industrial production. The fiber fracture is mainly caused by viscous shear effect on fiber bundle when pulling the fiber bundle. Reducing the number of impregnation pins and using low-viscosity resin can significantly ease the fiber fracture, as well aspromote the process stability.
2015, 32(4): 989-996.
doi: 10.13801/j.cnki.fhclxb.20141118.003
Abstract:
In order to improve the mechanical properties of glass fiber reinforced epoxy composites, multi-walled carbon nanotubes (MWCNTs) were attached to glass fiber fabrics surface using electrostatic flocking method to get modified glass fiber fabrics. The MWCNTs modified glass fiber fabrics/epoxy composite laminates were prepared using method of vacuum assisted resin infusion (VARI) with low-viscosity epoxy and the prepared modified fabrics. The mechanical properties of the laminates were characterized. The fracture surfaces of the MWCNTs modified glass fiber fabrics/epoxy composite specimens after mechanical experiments were observed by SEM and OPM. The results show that compared with the unmodified glass fiber fabrics/epoxy composite laminates without MWCNTs, the tensile strength of MWCNTs modified laminates decreases by 10.24%, flexural strength decreases by 13.90%, and compressive strength decreases by 17.33%. The tensile modulus and flexural modulus improve by 19.38% and 16.04% respectively, while compressive modulus increases by 13%. The bondings between MWCNTs and glass fiber fabrics are weak and there are debondings and delaminations between them under tensile loading. After the modified glass fiber fabrics treated by hot pressing at 200 ℃ for 2 h, the mechanical properties of MWCNTs modified glass fiber fabrics/epoxy composite laminates increase. The interface bondings between resin and glass fiber fabrics is improved after hot pressing treatment.
In order to improve the mechanical properties of glass fiber reinforced epoxy composites, multi-walled carbon nanotubes (MWCNTs) were attached to glass fiber fabrics surface using electrostatic flocking method to get modified glass fiber fabrics. The MWCNTs modified glass fiber fabrics/epoxy composite laminates were prepared using method of vacuum assisted resin infusion (VARI) with low-viscosity epoxy and the prepared modified fabrics. The mechanical properties of the laminates were characterized. The fracture surfaces of the MWCNTs modified glass fiber fabrics/epoxy composite specimens after mechanical experiments were observed by SEM and OPM. The results show that compared with the unmodified glass fiber fabrics/epoxy composite laminates without MWCNTs, the tensile strength of MWCNTs modified laminates decreases by 10.24%, flexural strength decreases by 13.90%, and compressive strength decreases by 17.33%. The tensile modulus and flexural modulus improve by 19.38% and 16.04% respectively, while compressive modulus increases by 13%. The bondings between MWCNTs and glass fiber fabrics are weak and there are debondings and delaminations between them under tensile loading. After the modified glass fiber fabrics treated by hot pressing at 200 ℃ for 2 h, the mechanical properties of MWCNTs modified glass fiber fabrics/epoxy composite laminates increase. The interface bondings between resin and glass fiber fabrics is improved after hot pressing treatment.
2015, 32(4): 997-1006.
doi: 10.13801/j.cnki.fhclxb.20140925.002
Abstract:
In order to improve the properties of sodium alginate and gelatin respectively, sodium alginate and gelatin were used as raw materials, genipin and CaCl2 were used as the cross-linkers, and the gelatin/sodium alginate interpenetrating polymeric network films were prepared by step-by-step crosslinking method firstly. Then, the gelatin/sodium alginate interpenetrating polymeric network formation was characterized and analyzed by FTIR, and the formation mechanisms of interpenetrating polymeric network were speculated by FTIR results. Finally, the effects of the additive amount of genipin and the mass ratio of gelatin to genipin on the mechanical properties and crosslinking degree of interpenetrating polymeric network films, and the mass ratio of sodium alginate to gelatin on the mechanical properties, fracture morphologies, thermal stabilities, water absorption and retaining properties of interpenetrating polymeric network films were discussed. The results show that when the mass ratio of gelatin to genipin is 200:1 and the mass ratio of sodium alginate to gelatin is 2:1, the mechanical properties, water absorption and retaining properties and compatibility of interpenetrating polymeric network films reach the best. In addition, the mechanical properties of interpenetrating polymeric network films are also superior to that of pure sodium alginate film and pure gelatin film. The addition of gelatin improves the thermal stabilities of interpenetrating polymeric network films at lower temperature zone, while decreases the thermal stabilities at higher temperature zone. Sodium alginate and gelatin interact each other by intermolecular forces, hydrogen bonding, ionic bond and so on, which improves the initial decomposition temperatures and the maximum-rate thermal decomposition temperatures of the two components. The research solves the problem of the poor mechanical properties of sodium alginate and gelatin, and provides a reference for the application of sodium alginate used in medical fields.
In order to improve the properties of sodium alginate and gelatin respectively, sodium alginate and gelatin were used as raw materials, genipin and CaCl2 were used as the cross-linkers, and the gelatin/sodium alginate interpenetrating polymeric network films were prepared by step-by-step crosslinking method firstly. Then, the gelatin/sodium alginate interpenetrating polymeric network formation was characterized and analyzed by FTIR, and the formation mechanisms of interpenetrating polymeric network were speculated by FTIR results. Finally, the effects of the additive amount of genipin and the mass ratio of gelatin to genipin on the mechanical properties and crosslinking degree of interpenetrating polymeric network films, and the mass ratio of sodium alginate to gelatin on the mechanical properties, fracture morphologies, thermal stabilities, water absorption and retaining properties of interpenetrating polymeric network films were discussed. The results show that when the mass ratio of gelatin to genipin is 200:1 and the mass ratio of sodium alginate to gelatin is 2:1, the mechanical properties, water absorption and retaining properties and compatibility of interpenetrating polymeric network films reach the best. In addition, the mechanical properties of interpenetrating polymeric network films are also superior to that of pure sodium alginate film and pure gelatin film. The addition of gelatin improves the thermal stabilities of interpenetrating polymeric network films at lower temperature zone, while decreases the thermal stabilities at higher temperature zone. Sodium alginate and gelatin interact each other by intermolecular forces, hydrogen bonding, ionic bond and so on, which improves the initial decomposition temperatures and the maximum-rate thermal decomposition temperatures of the two components. The research solves the problem of the poor mechanical properties of sodium alginate and gelatin, and provides a reference for the application of sodium alginate used in medical fields.
2015, 32(4): 1007-1016.
doi: 10.13801/j.cnki.fhclxb.20141103.001
Abstract:
In order to investigate the effects of carbon black on the hyper-elastic mechanical behaviors of rubber composites, first, by employing the quasi-static mechanical test data of carbon black reinforced rubber composites with different filling volume fractions, the finite deformation characterizing abilities of existing "deformation amplification" micromechanics models which based on homogenization method were evaluated. Then, a new "1st invariant amplification" relationship was proposed on the basis, and rational prediction results were obtained. Finally, by using the random sequential absorption algorithm, the spherical particulate filling numerical models which were approximate to the real microstructures of materials were established, and 3D numerical simulations under finite deformation situation were conducted. In order to investigate the influences of particle clustering effect, two forms which were particles regular random dispersion and agglomerate random dispersion were designed. The comparison between computational results and test data indicates that the proposed 3D micromechanics numerical modes are able to predict the finite deformation macroscopic mechanical behavior of filled rubbers to some extent, and the prediction abilities of particles agglomerate random dispersion models are better. The test results confirm the reliability of proposed models, and the proposed models provide some references to the further related research.
In order to investigate the effects of carbon black on the hyper-elastic mechanical behaviors of rubber composites, first, by employing the quasi-static mechanical test data of carbon black reinforced rubber composites with different filling volume fractions, the finite deformation characterizing abilities of existing "deformation amplification" micromechanics models which based on homogenization method were evaluated. Then, a new "1st invariant amplification" relationship was proposed on the basis, and rational prediction results were obtained. Finally, by using the random sequential absorption algorithm, the spherical particulate filling numerical models which were approximate to the real microstructures of materials were established, and 3D numerical simulations under finite deformation situation were conducted. In order to investigate the influences of particle clustering effect, two forms which were particles regular random dispersion and agglomerate random dispersion were designed. The comparison between computational results and test data indicates that the proposed 3D micromechanics numerical modes are able to predict the finite deformation macroscopic mechanical behavior of filled rubbers to some extent, and the prediction abilities of particles agglomerate random dispersion models are better. The test results confirm the reliability of proposed models, and the proposed models provide some references to the further related research.
2015, 32(4): 1017-1024.
doi: 10.13801/j.cnki.fhclxb.20141118.002
Abstract:
In order to enhance the anti-corrosion performances of epoxy coatings, first, graphene oxide (GO) was prepared by modified Hummers method. Then, by loading 3-aminopropyltriethoxysilane (KH550) modified nano-TiO2 on the surface of GO, composite particles of modified nano-TiO2 and GO (TiO2-GO) were prepared, and TiO2-GO were characterized by FTIR, XRD and SEM. Finally, the TiO2-GO were dispersed in epoxy, and TiO2-GO/epoxy coatings whose TiO2-GO contents were 1wt%, 2wt% and 3wt% and pure epoxy coatings were fabricated, respectively. The fracture surface morphologies of coatings were observed by SEM, and the anti-corrosion performances of coatings were characterized by electrochemical workstation and high temperature and high pressure corrosion test. The results demonstrate that nano-TiO2 connects with GO by chemical bond, and dispersing TiO2-GO in epoxy coating can evidently enhance the anti-corrosion performances of epoxy coatings. The research provides references for improving the anti-corrosion performances of epoxy coatings by means of adding GO.
In order to enhance the anti-corrosion performances of epoxy coatings, first, graphene oxide (GO) was prepared by modified Hummers method. Then, by loading 3-aminopropyltriethoxysilane (KH550) modified nano-TiO2 on the surface of GO, composite particles of modified nano-TiO2 and GO (TiO2-GO) were prepared, and TiO2-GO were characterized by FTIR, XRD and SEM. Finally, the TiO2-GO were dispersed in epoxy, and TiO2-GO/epoxy coatings whose TiO2-GO contents were 1wt%, 2wt% and 3wt% and pure epoxy coatings were fabricated, respectively. The fracture surface morphologies of coatings were observed by SEM, and the anti-corrosion performances of coatings were characterized by electrochemical workstation and high temperature and high pressure corrosion test. The results demonstrate that nano-TiO2 connects with GO by chemical bond, and dispersing TiO2-GO in epoxy coating can evidently enhance the anti-corrosion performances of epoxy coatings. The research provides references for improving the anti-corrosion performances of epoxy coatings by means of adding GO.
2015, 32(4): 1025-1031.
doi: 10.13801/j.cnki.fhclxb.20141118.007
Abstract:
In order to provide the theoretical basis for the process and performance optimization of nano-ZnO/ethylene-vinyl acetate copolymer (EVA) composites, nano-ZnO/EVA composites were prepared by melt blending method. The melting and crystallization behaviors of the composites were studied by DSC. The influence of the mass fraction and surface-modification by coupling agent of nano-ZnO on dynamic rheological behavior of the composite system was analyzed by rotational rheometer. The results show that both of the crystallization temperature and melting temperature of nano-ZnO/EVA composites increase firstly, and then decrease with the nano-ZnO mass fraction increasing, while the modified nano-ZnO mass fraction has little effect on melting temperature and crystallization temperature of modified nano-ZnO/EVA composites. The complex viscosity of nano-ZnO/EVA system changes suddenly when the mass fraction of nano-ZnO is greater than 20%, and the storage modulus-angular frequency curve shows the second plateau at low frequency region which corresponding to the two section of linear viscoelastic regions at strain scanning curves, and indicate that local ordered percolation network structure is formed due to the correlation, glomeration between nano-ZnO particles and the interaction between particles and matrix. While after the surface-modification of nano-ZnO by coupling agent, the complex viscosity of system decreases and the plateau of storage modulus-angular frequency curve does not appear, which indicates that the modified nano-ZnO particles are dispersed more homogeneously in the composite system. The research shows that surface-modification of nano-ZnO by coupling agent improves the dispersibility of nano-ZnO in EVA.
In order to provide the theoretical basis for the process and performance optimization of nano-ZnO/ethylene-vinyl acetate copolymer (EVA) composites, nano-ZnO/EVA composites were prepared by melt blending method. The melting and crystallization behaviors of the composites were studied by DSC. The influence of the mass fraction and surface-modification by coupling agent of nano-ZnO on dynamic rheological behavior of the composite system was analyzed by rotational rheometer. The results show that both of the crystallization temperature and melting temperature of nano-ZnO/EVA composites increase firstly, and then decrease with the nano-ZnO mass fraction increasing, while the modified nano-ZnO mass fraction has little effect on melting temperature and crystallization temperature of modified nano-ZnO/EVA composites. The complex viscosity of nano-ZnO/EVA system changes suddenly when the mass fraction of nano-ZnO is greater than 20%, and the storage modulus-angular frequency curve shows the second plateau at low frequency region which corresponding to the two section of linear viscoelastic regions at strain scanning curves, and indicate that local ordered percolation network structure is formed due to the correlation, glomeration between nano-ZnO particles and the interaction between particles and matrix. While after the surface-modification of nano-ZnO by coupling agent, the complex viscosity of system decreases and the plateau of storage modulus-angular frequency curve does not appear, which indicates that the modified nano-ZnO particles are dispersed more homogeneously in the composite system. The research shows that surface-modification of nano-ZnO by coupling agent improves the dispersibility of nano-ZnO in EVA.
2015, 32(4): 1032-1041.
doi: 10.13801/j.cnki.fhclxb.20141031.001
Abstract:
First, in order to investigate the evolution characteristics of matrix cracks in composite laminates under quasi-static loading, a synergistic damage evolving model based on energy was proposed. Then, the damage was analyzed in multi-scale through the model: in micro-level, crack surface displacements were calculated by three-dimensional finite element method; in macro-level, the energy released rates of matrix crack initiation were obtained with the crack surface displacements. Finally, the evolving process of matrix cracks was predicted by the crack initiation criterion. The model had taken the damage interaction, residual stress, nonlinearity of matrix, material initial damage distribution and inhomogeneity of damage evolving in evolutionary process into consideration. According to the evolutionary analysis process, matrix crack evolution process in glass fiber composites with the configuration of [±θ/904]s was analyzed. The results show that the model is capable to predict the damage evolution laws of matrix cracks of composite laminates under quasi-static loading.
First, in order to investigate the evolution characteristics of matrix cracks in composite laminates under quasi-static loading, a synergistic damage evolving model based on energy was proposed. Then, the damage was analyzed in multi-scale through the model: in micro-level, crack surface displacements were calculated by three-dimensional finite element method; in macro-level, the energy released rates of matrix crack initiation were obtained with the crack surface displacements. Finally, the evolving process of matrix cracks was predicted by the crack initiation criterion. The model had taken the damage interaction, residual stress, nonlinearity of matrix, material initial damage distribution and inhomogeneity of damage evolving in evolutionary process into consideration. According to the evolutionary analysis process, matrix crack evolution process in glass fiber composites with the configuration of [±θ/904]s was analyzed. The results show that the model is capable to predict the damage evolution laws of matrix cracks of composite laminates under quasi-static loading.
2015, 32(4): 1042-1052.
doi: 10.13801/j.cnki.fhclxb.20141204.003
Abstract:
In order to develop the application of natural cellulose material, based on the domestic and international relative research of natural cellulose materials, nanomaterials and antibacterial materials, LiCl/N, N-dimethylacetamide (DMAC) solvent system was used to prepare the natural cellulose/polyacrylonitrile spinning solutions with different blending proportions, and cellulose/polyacrylonitrile nanofibers were prepared by electrospinning technique firstly. Then, copper ammonia solution was used to prepare the fibrous assemblies with anti-bacterial function at a certain extend through antibacterial treatment of nanofibers. Finally, the morphology of nanofibers with different blending ratios was characterized by SEM; the thermal properties were characterized by TG and DSC; the changes of chemical compositions and hydrophilicity of nanofibers after blending were determined by FTIR and optical contact angle measuring instrument; antibacterial properties of the nanofibers were detected by oscillation technique. The results indicate that the cellulose/polyacrylonitrile nanofibers with diameter ranges from 200-400 nm can be prepared by electrospinning technology. With the increasing of cellulose content, the surfaces of nanofibers tend to be more rough, the adhesion becomes serious, and the discrete degree of diameter also increases. When the blending mass ratio of cellulose to polyacrylonitrile exceeds 75:25, the standard deviation of diameter increases from less than 100 nm of pure polyacrylonitrile fiber to more than 150 nm. The cellulose/polyacrylonitrile nanofibers have good thermal performance, the thermostability has a certain improvement comparing with pure cellulose nanofibers. When the blending mass ratio of cellulose to polyacrylonitrile is 25:75, the thermostability achieves the best. The hydrophily of cellulose/polyacrylonitrile nanofibers is better than that of ordinary medical gauze. The nanofibers after antibacterial treatment using copper ammonia solution have good antibacterial abilities, and the bacteriostasis rates of staphylococcus aureus and E. coli are 82% and 75%, respectively.
In order to develop the application of natural cellulose material, based on the domestic and international relative research of natural cellulose materials, nanomaterials and antibacterial materials, LiCl/N, N-dimethylacetamide (DMAC) solvent system was used to prepare the natural cellulose/polyacrylonitrile spinning solutions with different blending proportions, and cellulose/polyacrylonitrile nanofibers were prepared by electrospinning technique firstly. Then, copper ammonia solution was used to prepare the fibrous assemblies with anti-bacterial function at a certain extend through antibacterial treatment of nanofibers. Finally, the morphology of nanofibers with different blending ratios was characterized by SEM; the thermal properties were characterized by TG and DSC; the changes of chemical compositions and hydrophilicity of nanofibers after blending were determined by FTIR and optical contact angle measuring instrument; antibacterial properties of the nanofibers were detected by oscillation technique. The results indicate that the cellulose/polyacrylonitrile nanofibers with diameter ranges from 200-400 nm can be prepared by electrospinning technology. With the increasing of cellulose content, the surfaces of nanofibers tend to be more rough, the adhesion becomes serious, and the discrete degree of diameter also increases. When the blending mass ratio of cellulose to polyacrylonitrile exceeds 75:25, the standard deviation of diameter increases from less than 100 nm of pure polyacrylonitrile fiber to more than 150 nm. The cellulose/polyacrylonitrile nanofibers have good thermal performance, the thermostability has a certain improvement comparing with pure cellulose nanofibers. When the blending mass ratio of cellulose to polyacrylonitrile is 25:75, the thermostability achieves the best. The hydrophily of cellulose/polyacrylonitrile nanofibers is better than that of ordinary medical gauze. The nanofibers after antibacterial treatment using copper ammonia solution have good antibacterial abilities, and the bacteriostasis rates of staphylococcus aureus and E. coli are 82% and 75%, respectively.
2015, 32(4): 1053-1060.
doi: 10.13801/j.cnki.fhclxb.20140917.004
Abstract:
Ti3SiC2/MgAl2O4 composites were fabricated by reactive hot pressing method. The effects of the content of MgAl2O4 and hot pressing temperature on the phase constituent, mechanical properties and oxidation resistance of composites were investigated.The results show that hot pressing temperature affects the phase composition of Ti3SiC2/MgAl2O4 composites and it can get good properties of Ti3SiC2/MgAl2O4 composite materials in 1 450 ℃. MgAl2O4 by introducing the appropriate content has the effect of dispersion strengthening and contributes to improving the mechanical properties of composite materials. When the addition amount is 20wt%, bending strength is 527.6 MPa and fracture toughness is 7.09 MPa·m1/2. The oxidation resistance of Ti3SiC2/MgAl2O4 sample is better than pure Ti3SiC2. The oxidation layers of Ti3SiC2/MgAl2O4 composites are composed of two layer at 1 400 ℃, the outer consists of Mg0.6Al0.8Ti1.6O5 solid solution and rutile of TiO2, and the inner is a mixture of TiO2, cristobalite and a small amount of unoxidized matrix.
Ti3SiC2/MgAl2O4 composites were fabricated by reactive hot pressing method. The effects of the content of MgAl2O4 and hot pressing temperature on the phase constituent, mechanical properties and oxidation resistance of composites were investigated.The results show that hot pressing temperature affects the phase composition of Ti3SiC2/MgAl2O4 composites and it can get good properties of Ti3SiC2/MgAl2O4 composite materials in 1 450 ℃. MgAl2O4 by introducing the appropriate content has the effect of dispersion strengthening and contributes to improving the mechanical properties of composite materials. When the addition amount is 20wt%, bending strength is 527.6 MPa and fracture toughness is 7.09 MPa·m1/2. The oxidation resistance of Ti3SiC2/MgAl2O4 sample is better than pure Ti3SiC2. The oxidation layers of Ti3SiC2/MgAl2O4 composites are composed of two layer at 1 400 ℃, the outer consists of Mg0.6Al0.8Ti1.6O5 solid solution and rutile of TiO2, and the inner is a mixture of TiO2, cristobalite and a small amount of unoxidized matrix.
2015, 32(4): 1061-1066.
doi: 10.13801/j.cnki.fhclxb.20141209.001
Abstract:
The graphene/nano-Ag(RGO/Ag) composite was prepared by a simple one-step chemical method, in which the hydrazine hydrate was used as a reductant. The microstructure and the components of the RGO/Ag composite were characterized by UV-vis, XRD, FTIR, SEM. Through analyzing heat flow and structure change, the influence of material structure and heat treatment on electrical conductivity of RGO/Ag composite was investigated. The results indicate that similar spherical Ag can be successfully synthesised companying with the reduction of silver nitrate and thus the RGO/Ag composite is prepared. The conductivity of the RGO/Ag composite increases significantly through adjusting Ag addition and heat treatment, when the loading amount of GO is below 50 wt%. The sheet resistance of RGO/Ag composite can be reached to 8 mΩ/□, when the loading amount of GO is 16 wt%. However, Ag content and heat treatment have much less effect on the conductivity of the resulting composite, when the loading amount of GO is more than 50 wt%.
The graphene/nano-Ag(RGO/Ag) composite was prepared by a simple one-step chemical method, in which the hydrazine hydrate was used as a reductant. The microstructure and the components of the RGO/Ag composite were characterized by UV-vis, XRD, FTIR, SEM. Through analyzing heat flow and structure change, the influence of material structure and heat treatment on electrical conductivity of RGO/Ag composite was investigated. The results indicate that similar spherical Ag can be successfully synthesised companying with the reduction of silver nitrate and thus the RGO/Ag composite is prepared. The conductivity of the RGO/Ag composite increases significantly through adjusting Ag addition and heat treatment, when the loading amount of GO is below 50 wt%. The sheet resistance of RGO/Ag composite can be reached to 8 mΩ/□, when the loading amount of GO is 16 wt%. However, Ag content and heat treatment have much less effect on the conductivity of the resulting composite, when the loading amount of GO is more than 50 wt%.
2015, 32(4): 1067-1074.
doi: 10.13801/j.cnki.fhclxb.20141031.002
Abstract:
The water/cement ratios of 0.2, 0.4, and 0.65 were selected to form three types of polyvinyl alcohol (PVA) fiber reinforced cementitious composites. Three-point bending test was implemented to evaluate the effects of water/cement ratio on properties based on crack patterns and PVA fibers morphology in cracks; SEM micrographs of PVA fiber side surface, fibers' embedded and ruptured or pullouted ends in fracture surface were investigated to analyze PVA fiber-matrix interface microstructure at the micro level. Bending test results show that the number of cracks near mid-span site and that of pullouted PVA fibers in cracks increase significantly. Meanwhile, bending toughness value and the rate of improvement from crack strength to bending strength are improved with increasing water/cement ratio. Interface microstructure finds out that matrix structure becomes looser and interface bonding ability becomes lower with increasing water/cement ratio. Meanwhile, the PVA fibers morphology of bridging cracks changes from PVA fiber instant breakage to pullouted and slipped with slight abrasion surface, which significantly improve the rate of fiber reinforced and fiber toughening.
The water/cement ratios of 0.2, 0.4, and 0.65 were selected to form three types of polyvinyl alcohol (PVA) fiber reinforced cementitious composites. Three-point bending test was implemented to evaluate the effects of water/cement ratio on properties based on crack patterns and PVA fibers morphology in cracks; SEM micrographs of PVA fiber side surface, fibers' embedded and ruptured or pullouted ends in fracture surface were investigated to analyze PVA fiber-matrix interface microstructure at the micro level. Bending test results show that the number of cracks near mid-span site and that of pullouted PVA fibers in cracks increase significantly. Meanwhile, bending toughness value and the rate of improvement from crack strength to bending strength are improved with increasing water/cement ratio. Interface microstructure finds out that matrix structure becomes looser and interface bonding ability becomes lower with increasing water/cement ratio. Meanwhile, the PVA fibers morphology of bridging cracks changes from PVA fiber instant breakage to pullouted and slipped with slight abrasion surface, which significantly improve the rate of fiber reinforced and fiber toughening.
2015, 32(4): 1075-1082.
doi: 10.13801/j.cnki.fhclxb.20141031.003
Abstract:
The method of micromechanics was used to study the matrix failure mechanism of UD-C/SiC ceramic matrix composites (CMCs). Shear-lag theory model and critical matrix strain energy (CMSE) were employed to forecast the tensile process, and the stress-strain curves of UD-C/SiC CMCs matrix cracking and failure were obtained. Extended finite element method (XFEM) was also utilized to simulate this process and the relative stress-strain curves were obtained. It is indicated that the calculation results of the two different methods are in accordance with that of the experiment. And it is proved that both of the two methods are valuable to forecast the matrix failure property of the UD-C/SiC CMCs.
The method of micromechanics was used to study the matrix failure mechanism of UD-C/SiC ceramic matrix composites (CMCs). Shear-lag theory model and critical matrix strain energy (CMSE) were employed to forecast the tensile process, and the stress-strain curves of UD-C/SiC CMCs matrix cracking and failure were obtained. Extended finite element method (XFEM) was also utilized to simulate this process and the relative stress-strain curves were obtained. It is indicated that the calculation results of the two different methods are in accordance with that of the experiment. And it is proved that both of the two methods are valuable to forecast the matrix failure property of the UD-C/SiC CMCs.
2015, 32(4): 1083-1091.
doi: 10.13801/j.cnki.fhclxb.20150428.001
Abstract:
In order to satisfy the urgent demand to test the mechanics/thermal/oxidization key performance parameters for new ultra-high temperature structures of hypersonic flight vehicles, a self-designed radiation type thermal-mechanical joint test system that can perform fracture property test of structures under extremely high-temperature/oxidization environment up to 1 500 ℃ was established. By using this system, key performance parameters, such as fracture strength and fracture time, for C/SiC high-temperature-resistant composite material were tested in high-temperature/oxidization environments up to 1 500 ℃. The results show that the C/SiC specimen's fracture load decreases 47.5% when the temperature rises from 1 000 ℃ to 1 500 ℃, and the time to failure reduces to 50.1% of that at 1 000 ℃. This extreme high-temperature experimental system provides important test method for thermal-mechanical research on thermal strength of structures in oxidization environments. In this thermal-mechanical test, the phenomenon that the preloading process in high temperatures can increase the fracture strength obviously for C/SiC composite structure is observed, and the fracture strength increases by 38% and the time to failure increases by 61.1%. The results provide important basis for the safety and reliability design as well as improvements of material strength properties of composite structures for hypersonic flight vehicles under extreme thermal environments.
In order to satisfy the urgent demand to test the mechanics/thermal/oxidization key performance parameters for new ultra-high temperature structures of hypersonic flight vehicles, a self-designed radiation type thermal-mechanical joint test system that can perform fracture property test of structures under extremely high-temperature/oxidization environment up to 1 500 ℃ was established. By using this system, key performance parameters, such as fracture strength and fracture time, for C/SiC high-temperature-resistant composite material were tested in high-temperature/oxidization environments up to 1 500 ℃. The results show that the C/SiC specimen's fracture load decreases 47.5% when the temperature rises from 1 000 ℃ to 1 500 ℃, and the time to failure reduces to 50.1% of that at 1 000 ℃. This extreme high-temperature experimental system provides important test method for thermal-mechanical research on thermal strength of structures in oxidization environments. In this thermal-mechanical test, the phenomenon that the preloading process in high temperatures can increase the fracture strength obviously for C/SiC composite structure is observed, and the fracture strength increases by 38% and the time to failure increases by 61.1%. The results provide important basis for the safety and reliability design as well as improvements of material strength properties of composite structures for hypersonic flight vehicles under extreme thermal environments.
2015, 32(4): 1092-1098.
doi: 10.13801/j.cnki.fhclxb.20140919.003
Abstract:
The manufacturing tolerance, which leads to different fit clearances between bolts and composite plate holes, is ineluctable in the manufacture process. Thus diversified pin load distribution of composite bolted joint is present and further results in the strength scatter of the joints. Taking a double-lap four-bolt composite joint with high locked bolts as an example, the influence of the fit clearance on the pin load distribution was investigated by a clearance-based direct stiffness method. Furthermore, the strength scatters of the four-bolt joint stemmed from the manufacturing tolerance have been predicted by a modified characteristic curve method, a modified strength envelope method and a progressive damage model with the dispersion intervals being [-3.87%, 2.16%], [-4.01%, 3.95%] and [-3.16%, 5.14%], respectively, which shows the effect range of the manufacturing tolerance on the strength of the joint is less than 6%, if the fasteners and holes both meet the manufacturing criterion.
The manufacturing tolerance, which leads to different fit clearances between bolts and composite plate holes, is ineluctable in the manufacture process. Thus diversified pin load distribution of composite bolted joint is present and further results in the strength scatter of the joints. Taking a double-lap four-bolt composite joint with high locked bolts as an example, the influence of the fit clearance on the pin load distribution was investigated by a clearance-based direct stiffness method. Furthermore, the strength scatters of the four-bolt joint stemmed from the manufacturing tolerance have been predicted by a modified characteristic curve method, a modified strength envelope method and a progressive damage model with the dispersion intervals being [-3.87%, 2.16%], [-4.01%, 3.95%] and [-3.16%, 5.14%], respectively, which shows the effect range of the manufacturing tolerance on the strength of the joint is less than 6%, if the fasteners and holes both meet the manufacturing criterion.
2015, 32(4): 1099-1106.
doi: 10.13801/j.cnki.fhclxb.20141022.001
Abstract:
To simulate fracture problems that might occur during the engineering service of functionally graded material (FGM) and calculate the corresponding crack initiation loads, graded extended finite element was embedded into ABAQUS software by user-defined subroutine UEL, and physical fields in functionally graded materials were simulated by finite element method. Mixed-mode stress intensity factors (SIFs) were calculated by interactive energy integral post-processing subroutine. Maximum hoop stress criterion was adopted in subroutines to calculate crack deflection angles, and to predict crack propagation paths and crack initiation loads in functionally graded materials were both predicted. Influences of material gradient parameters on cracking propagation paths and crack initiation loads were discussed. The improvement of fracture characteristics in graded composites was validated by comparing with homogeneous materials. The results show that the initial crack perpendicular to the gradient direction tends to propagate towards the part exhibiting lower equivalent elastic modulus, and the crack deflection angle peaks at linear gradient index, and increases with the elastic modulus ratio of constitutes. When the applied load and the initial crack are both parallel to the gradient direction, an increase in the equivalent elastic modulus and fracture toughness or a decrease in the gradient index all lead to an enhanced crack initiation load.
To simulate fracture problems that might occur during the engineering service of functionally graded material (FGM) and calculate the corresponding crack initiation loads, graded extended finite element was embedded into ABAQUS software by user-defined subroutine UEL, and physical fields in functionally graded materials were simulated by finite element method. Mixed-mode stress intensity factors (SIFs) were calculated by interactive energy integral post-processing subroutine. Maximum hoop stress criterion was adopted in subroutines to calculate crack deflection angles, and to predict crack propagation paths and crack initiation loads in functionally graded materials were both predicted. Influences of material gradient parameters on cracking propagation paths and crack initiation loads were discussed. The improvement of fracture characteristics in graded composites was validated by comparing with homogeneous materials. The results show that the initial crack perpendicular to the gradient direction tends to propagate towards the part exhibiting lower equivalent elastic modulus, and the crack deflection angle peaks at linear gradient index, and increases with the elastic modulus ratio of constitutes. When the applied load and the initial crack are both parallel to the gradient direction, an increase in the equivalent elastic modulus and fracture toughness or a decrease in the gradient index all lead to an enhanced crack initiation load.
2015, 32(4): 1107-1117.
doi: 10.13801/j.cnki.fhclxb.20150623.003
Abstract:
This paper aims at effectively simulating the influence of microscopic heterogeneous properties of functionally graded material (FGM) to the overall thermomechanics performances. The two-dimensional microstructures of FGM were generated based on the random morphology description functions (RMDF) method and exponential function distribution of volume fraction, and then the coupling extended multiscale finite element method (CEMsFEM) was developed for the thermal stress analysis of FGM. Based on the basic idea of extended multiscale finite element method (EMsFEM), two sets of numerical base functions of temperature and displacement were constructed to bring the microscopic heterogeneous properties to the macroscopic response. The additional coupling items for base functions of displacement were added to consider the coupling effects caused by the Poisson's ratio. The mapping relationship between the element information on macroscale and microscale was then constructed by the base functions, thus the equivalent equations were solved on macroscale and the computational complexity can be greatly reduced. To better consider the influence of microscopic load, the actual response of the structure was decomposed into macroscopic response and microscopic perturbation and then the modified macroscopic load vectors were derived. Finally the thermal stress analysis of FGM examples in different load cases was presented and demonstrates the accuracy and efficiency of the proposed method. The size effect of microscopic structure to the structural thermo-mechanical response was also discussed.
This paper aims at effectively simulating the influence of microscopic heterogeneous properties of functionally graded material (FGM) to the overall thermomechanics performances. The two-dimensional microstructures of FGM were generated based on the random morphology description functions (RMDF) method and exponential function distribution of volume fraction, and then the coupling extended multiscale finite element method (CEMsFEM) was developed for the thermal stress analysis of FGM. Based on the basic idea of extended multiscale finite element method (EMsFEM), two sets of numerical base functions of temperature and displacement were constructed to bring the microscopic heterogeneous properties to the macroscopic response. The additional coupling items for base functions of displacement were added to consider the coupling effects caused by the Poisson's ratio. The mapping relationship between the element information on macroscale and microscale was then constructed by the base functions, thus the equivalent equations were solved on macroscale and the computational complexity can be greatly reduced. To better consider the influence of microscopic load, the actual response of the structure was decomposed into macroscopic response and microscopic perturbation and then the modified macroscopic load vectors were derived. Finally the thermal stress analysis of FGM examples in different load cases was presented and demonstrates the accuracy and efficiency of the proposed method. The size effect of microscopic structure to the structural thermo-mechanical response was also discussed.
2015, 32(4): 1118-1124.
doi: 10.13801/j.cnki.fhclxb.20140923.002
Abstract:
In order to study the biaxial shear mechanical performance of the polyester fabric-polyvinyl chloride-polyvinylidene fluoride (P-PVC-PVDF) membrane, the calculation formula for engineering shear strain, the modified formula for shear stress, and the method for stress loading were given. The biaxial shear test of P-PVC-PVDF membrane was then carried out using a self-developed biaxial tensile tester. The shear stress-strain curves, shear modulus and hysteresis loop area were obtained. The analysis results show that the mechanical parameters are different when the direction of shear stress is changed. However, all the mechanical parameters turn stable after the first loading cycle. The range of stable shear modulus is 11-13 kN/m when the up and lower limit of shear stress is set to be ±2 kN/m. The change of the angle between the principle axial and the direction of loading has little influence on the calculation result. These results can be useful for the analysis and design of membrane structures.
In order to study the biaxial shear mechanical performance of the polyester fabric-polyvinyl chloride-polyvinylidene fluoride (P-PVC-PVDF) membrane, the calculation formula for engineering shear strain, the modified formula for shear stress, and the method for stress loading were given. The biaxial shear test of P-PVC-PVDF membrane was then carried out using a self-developed biaxial tensile tester. The shear stress-strain curves, shear modulus and hysteresis loop area were obtained. The analysis results show that the mechanical parameters are different when the direction of shear stress is changed. However, all the mechanical parameters turn stable after the first loading cycle. The range of stable shear modulus is 11-13 kN/m when the up and lower limit of shear stress is set to be ±2 kN/m. The change of the angle between the principle axial and the direction of loading has little influence on the calculation result. These results can be useful for the analysis and design of membrane structures.
2015, 32(4): 1125-1131.
doi: 10.13801/j.cnki.fhclxb.20141021.002
Abstract:
The core-shell structured hybrid particles with polystyrene (PS) as the core and SiO2 nanoparticle as the shell were synthesized via electrostatic interaction based on the opposite charges. The SiO2 shell thickness of the obtained hybrid particles could be tuned by varying the concentration of tetraethylorthosilicate. The atomic force microscope (AFM) was employed to probe the mechanical properties of the as-prepared samples. The compressive elastic modulus of the sample was measured by analyzing the force curves captured on the particle samples according to the Hertz contact model and Sneddon contact model. As confirmed by scanning electronic microscopy (SEM) and transmission electron microscope (TEM), the size of the PS core is (197±9) nm and the SiO2 shell which is 11-16 nm in thickness in the test is composed of a lot of tiny particles. Under the condition of Hertz contact model, the elastic modulus of the PS microspheres is (2.2±0.5) GPa. The modulus of the PS-SiO2 hybrid particle increases with the increase of the thickness of SiO2 shell. When the shell thickness increases from 11 nm to 16 nm, the elastic modulus of the composite grows from (4.4±0.6) GPa to (10.2±1.1) GPa. The elastic modulus of the composite is much lower than that of the silica, and is more close to the modulus of the PS core.
The core-shell structured hybrid particles with polystyrene (PS) as the core and SiO2 nanoparticle as the shell were synthesized via electrostatic interaction based on the opposite charges. The SiO2 shell thickness of the obtained hybrid particles could be tuned by varying the concentration of tetraethylorthosilicate. The atomic force microscope (AFM) was employed to probe the mechanical properties of the as-prepared samples. The compressive elastic modulus of the sample was measured by analyzing the force curves captured on the particle samples according to the Hertz contact model and Sneddon contact model. As confirmed by scanning electronic microscopy (SEM) and transmission electron microscope (TEM), the size of the PS core is (197±9) nm and the SiO2 shell which is 11-16 nm in thickness in the test is composed of a lot of tiny particles. Under the condition of Hertz contact model, the elastic modulus of the PS microspheres is (2.2±0.5) GPa. The modulus of the PS-SiO2 hybrid particle increases with the increase of the thickness of SiO2 shell. When the shell thickness increases from 11 nm to 16 nm, the elastic modulus of the composite grows from (4.4±0.6) GPa to (10.2±1.1) GPa. The elastic modulus of the composite is much lower than that of the silica, and is more close to the modulus of the PS core.
2015, 32(4): 1132-1137.
doi: 10.13801/j.cnki.fhclxb.20141028.001
Abstract:
This article studies the debond and crack propagation of carbon fiber reinforced plastic (CFRP) T-joints under tensile load. The numerical model for the T-joints provided the sensitive areas on which fiber Bragg grating (FBG) sensors could be fixed. FBG sensors along with a high speed camera were used to monitor the appearance and propagation of debond. The results show that the damage initiates at the T-joints filling area. The cracks propagate along two directions: the horizontal direction, i.e., the glue layers between the L prepreg and the skin and the vertical direction, i.e., the glue layers between two L prepregs. The propagation of cracks ultimately causes the structure failure. The changes of the FBG central wavelengths succeed in recording the appearance, accumulation and propagation of damage under non-visual conditions, which can help alarm the inner damage of the structure and indicate the crack propagation paths.
This article studies the debond and crack propagation of carbon fiber reinforced plastic (CFRP) T-joints under tensile load. The numerical model for the T-joints provided the sensitive areas on which fiber Bragg grating (FBG) sensors could be fixed. FBG sensors along with a high speed camera were used to monitor the appearance and propagation of debond. The results show that the damage initiates at the T-joints filling area. The cracks propagate along two directions: the horizontal direction, i.e., the glue layers between the L prepreg and the skin and the vertical direction, i.e., the glue layers between two L prepregs. The propagation of cracks ultimately causes the structure failure. The changes of the FBG central wavelengths succeed in recording the appearance, accumulation and propagation of damage under non-visual conditions, which can help alarm the inner damage of the structure and indicate the crack propagation paths.
2015, 32(4): 1138-1144.
doi: 10.13801/j.cnki.fhclxb.20141022.004
Abstract:
Based on the features of composite cruciform specimens under biaxial tensile loading, we analyzed the rules of how stress concentration factors and loading coefficients of the central testing zone in the cruciform specimens of different geometric shapes, change with different thickness ratios and load ratio conditions. The biaxial tensile tests with different load ratios were implemented for verification. The results show that the coefficients of the central testing zone have nothing to do with the loading magnitude, but are related to geometric shapes, thickness ratios and loading ratios. Smaller width of equal-width loading arms and larger thickness ratio contribute to smaller stress concentration factors, and different load ratios mean different stress concentration factors. Generally, the loading coefficients increase along with the increase of thickness ratios. The x-axis loading coefficient βx rises nonlinearly while the y-axis coefficient βy decreases linearly with the increase of load ratios. In addition, for the D-shaped cruciform specimen under biaxial tensile loading, the y-axis stress component of the central testing zone is negative when the load ratio f=4/1, and the central area shows a state of compressive stress.
Based on the features of composite cruciform specimens under biaxial tensile loading, we analyzed the rules of how stress concentration factors and loading coefficients of the central testing zone in the cruciform specimens of different geometric shapes, change with different thickness ratios and load ratio conditions. The biaxial tensile tests with different load ratios were implemented for verification. The results show that the coefficients of the central testing zone have nothing to do with the loading magnitude, but are related to geometric shapes, thickness ratios and loading ratios. Smaller width of equal-width loading arms and larger thickness ratio contribute to smaller stress concentration factors, and different load ratios mean different stress concentration factors. Generally, the loading coefficients increase along with the increase of thickness ratios. The x-axis loading coefficient βx rises nonlinearly while the y-axis coefficient βy decreases linearly with the increase of load ratios. In addition, for the D-shaped cruciform specimen under biaxial tensile loading, the y-axis stress component of the central testing zone is negative when the load ratio f=4/1, and the central area shows a state of compressive stress.
2015, 32(4): 1145-1152.
doi: 10.13801/j.cnki.fhclxb.20141105.004
Abstract:
With suitable fiber path, variable angle tow (VAT) laminate is superior to traditional straight fiber laminate in buckling resistance. The aim of this paper is to trace the influence of fiber path characteristic distance and directional coordinate rotation on buckling property of VAT laminates. The original method for linear vibration of fiber angle was improved, and a method for describing the piecewise linear variation of fiber angle was proposed, which is able to extend the design space of fiber path. A series of VAT laminates were fabricated utilizing the improved method. Based on the finite element method, the buckling properties of VAT laminates under different load cases were traced and discussed from the perspective of the stress resultant distribution. The numerical results show that under the axial compression condition, the fiber path with the characteristic distance being half of the edge length and the coordinate rotation being 90°, makes laminates of the highest stability; under the biaxial compression condition, the characteristic distance and directional coordinate rotation should be treated as extra design variables, and the optimal fiber path should be obtained through optimization.
With suitable fiber path, variable angle tow (VAT) laminate is superior to traditional straight fiber laminate in buckling resistance. The aim of this paper is to trace the influence of fiber path characteristic distance and directional coordinate rotation on buckling property of VAT laminates. The original method for linear vibration of fiber angle was improved, and a method for describing the piecewise linear variation of fiber angle was proposed, which is able to extend the design space of fiber path. A series of VAT laminates were fabricated utilizing the improved method. Based on the finite element method, the buckling properties of VAT laminates under different load cases were traced and discussed from the perspective of the stress resultant distribution. The numerical results show that under the axial compression condition, the fiber path with the characteristic distance being half of the edge length and the coordinate rotation being 90°, makes laminates of the highest stability; under the biaxial compression condition, the characteristic distance and directional coordinate rotation should be treated as extra design variables, and the optimal fiber path should be obtained through optimization.
2015, 32(4): 1153-1158.
doi: 10.13801/j.cnki.fhclxb.20141103.002
Abstract:
Based on homogenization method, a representative volume element (RVE) of discontinuous long glass fiber reinforced composites was constructed according to the microstructure of the composites. The equivalent elastic mechanical properties of the composites were obtained based on a numerical simulation on the RVE, and were then compared with the experimental data of the tensile properties of injected spline. Numerical results show that it is more reasonable based on the new finite element model built by adding polypropylene(PP) at both ends of glass fiber than on the traditional one which applied on continuous fiber reinforced composites. Glass fiber reinforced polypropylene is transversely isotropic when glass fibers are unidirectional. In addition, the equivalent elastic modulus in the tensile direction first decreases slightly, then drops rapidly, and then turns stable with the increase of the angle between fiber orientation and tensile direction. In conclusion, homogenization theory is very useful for the prediction of the equivalent elastic mechanical properties of discontinuous glass fiber reinforced moldings in engineering, and is significant to provide the scientific evidence for the analysis of structure service performance of the moldings.
Based on homogenization method, a representative volume element (RVE) of discontinuous long glass fiber reinforced composites was constructed according to the microstructure of the composites. The equivalent elastic mechanical properties of the composites were obtained based on a numerical simulation on the RVE, and were then compared with the experimental data of the tensile properties of injected spline. Numerical results show that it is more reasonable based on the new finite element model built by adding polypropylene(PP) at both ends of glass fiber than on the traditional one which applied on continuous fiber reinforced composites. Glass fiber reinforced polypropylene is transversely isotropic when glass fibers are unidirectional. In addition, the equivalent elastic modulus in the tensile direction first decreases slightly, then drops rapidly, and then turns stable with the increase of the angle between fiber orientation and tensile direction. In conclusion, homogenization theory is very useful for the prediction of the equivalent elastic mechanical properties of discontinuous glass fiber reinforced moldings in engineering, and is significant to provide the scientific evidence for the analysis of structure service performance of the moldings.
2015, 32(4): 1159-1165.
doi: 10.13801/j.cnki.fhclxb.20141022.002
Abstract:
After the 7.9 m/s vertical drop anti-crash simulation of a full scale composite fuselage structure with energy-absorbing subfloor, the corresponding dynamic impact parameters of the average acceleration, velocity and impact force of the structure were obtained. Different assessment methods were considered to evaluate the crashworthiness characteristics of the structure. The full scale composite fuselage structure was divided into different sections in the design, and the energy-absorbing foam was added into the bottom structure of the fuselage section. The calculated results indicate that the crashworthiness design can meet the corresponding specifications. The impact simulation was carried out using the professional nonlinear explicit transient dynamic finite element software. Compared with the test results, the calculated average acceleration does not exceed 13g, with the relative error being less than 11%. The maximum vertical impact load is less than 6 kN, and the persistent time of the average minus acceleration of crash is not more than 0.03 s. All these results are reasonable. The model can be used for the anti-crash design of the helicopter.
After the 7.9 m/s vertical drop anti-crash simulation of a full scale composite fuselage structure with energy-absorbing subfloor, the corresponding dynamic impact parameters of the average acceleration, velocity and impact force of the structure were obtained. Different assessment methods were considered to evaluate the crashworthiness characteristics of the structure. The full scale composite fuselage structure was divided into different sections in the design, and the energy-absorbing foam was added into the bottom structure of the fuselage section. The calculated results indicate that the crashworthiness design can meet the corresponding specifications. The impact simulation was carried out using the professional nonlinear explicit transient dynamic finite element software. Compared with the test results, the calculated average acceleration does not exceed 13g, with the relative error being less than 11%. The maximum vertical impact load is less than 6 kN, and the persistent time of the average minus acceleration of crash is not more than 0.03 s. All these results are reasonable. The model can be used for the anti-crash design of the helicopter.
2015, 32(4): 1166-1172.
doi: 10.13801/j.cnki.fhclxb.20150508.002
Abstract:
Biological surfaces endow a multi-gradient collaborative effect from nano-/micro-levels for people, displaying the unique ability to control the dynamic wettability and fluid transport. Based on the multi-gradient mechanism, we designed various kinds of bioinspired or biomimetic structures, and developed the new technology and methods. We introduced the bioinspired concept into the fabrication of materials. By being used the universal polymers, response polymer, organic-inorganic composite materials, the novel bioinspired micro-interface/nano-interface materials in one-or two-dimensions can be controllably fabricated. These novel bioinspired materials display excellent fluid-controlling functions from micro-/nano-levels and macro-level, e.g., driving of droplet, water collection and anti-icing functions, which will bring important application prospect and reference value to micro-fluidics, fresh water acquirement, fog-water engineering, energy transform, dust filter and so on.
Biological surfaces endow a multi-gradient collaborative effect from nano-/micro-levels for people, displaying the unique ability to control the dynamic wettability and fluid transport. Based on the multi-gradient mechanism, we designed various kinds of bioinspired or biomimetic structures, and developed the new technology and methods. We introduced the bioinspired concept into the fabrication of materials. By being used the universal polymers, response polymer, organic-inorganic composite materials, the novel bioinspired micro-interface/nano-interface materials in one-or two-dimensions can be controllably fabricated. These novel bioinspired materials display excellent fluid-controlling functions from micro-/nano-levels and macro-level, e.g., driving of droplet, water collection and anti-icing functions, which will bring important application prospect and reference value to micro-fluidics, fresh water acquirement, fog-water engineering, energy transform, dust filter and so on.
2015, 32(4): 1173-1178.
doi: 10.13801/j.cnki.fhclxb.20141010.001
Abstract:
A new micromechanics model was developed to accurately predict the effective thermal conductivity and local distribution of temperature field of heterogeneous composites using the variational asymptotic method for unit cell homogenization. Starting from a variational statement of the thermal conductivity problem of the heterogeneous continuum, the micromechanics model was formulated as a constrained minimization problem using the variational asymptotic method. The finite element method (FEM) was then used to solve the minimize solving process of energy functional with discrete form. To handle realistic microstructures in engineering applications, this new model was implemented using the FEM. The local fields within unit cell were recovered in terms of the macroscopic behavior including the global temperature and the corresponding gradient, and the fluctuation function. For validation, several binary composites examples were used to demonstrate the effectiveness and accuracy of the proposed theory.
A new micromechanics model was developed to accurately predict the effective thermal conductivity and local distribution of temperature field of heterogeneous composites using the variational asymptotic method for unit cell homogenization. Starting from a variational statement of the thermal conductivity problem of the heterogeneous continuum, the micromechanics model was formulated as a constrained minimization problem using the variational asymptotic method. The finite element method (FEM) was then used to solve the minimize solving process of energy functional with discrete form. To handle realistic microstructures in engineering applications, this new model was implemented using the FEM. The local fields within unit cell were recovered in terms of the macroscopic behavior including the global temperature and the corresponding gradient, and the fluctuation function. For validation, several binary composites examples were used to demonstrate the effectiveness and accuracy of the proposed theory.
2015, 32(4): 1179-1186.
doi: 10.13801/j.cnki.fhclxb.20141016.002
Abstract:
The polycaprolactone-polyethylene glycol-polycaprolactone triblock polymer (PCEC) and the PCEC end caped with triethoxysilane were synthesized for the organic-inorganic hybrid materials fabrication. The characteristic absorption bands at 3 440, 1 732, 1 242 and 1 106 cm-1 assigned to PCEC, as well as absorption bands at 3 350 cm-1 and 1 531 cm-1 assigned to the urethane bond of the end caped PCEC were revealed by the FTIR spectra. The hybrid PCEC-CaO-SiO2-P2O5 material was synthesized by the end caped PCEC with tetraethyl orthosilicate, calcium nitrate tetrahydrate and triethyl phosphate via a sol-gel method. The bioactivity of the PCEC-CaO-SiO2-P2O5 hybrid material was assessed using simulated body fluid. SEM pictures display that precipitate with the calcium phosphate was presented on the surface after soaking for 24 h. XRD results show that the diffraction peaks of precipitate have the characteristic of hydroxyapatite. It is also revealed that the polymer hydrophobicity would influence the precipitate formation on the hybrid material surface. The mechanics performance test shows that with the increase of PEG content in the polymer, the compression modulus increases from 6.9 MPa to 65 MPa. The cell viability experiments show that PCEC-CaO-SiO2-P2O5 hybrid material has no significant cytotoxic.
The polycaprolactone-polyethylene glycol-polycaprolactone triblock polymer (PCEC) and the PCEC end caped with triethoxysilane were synthesized for the organic-inorganic hybrid materials fabrication. The characteristic absorption bands at 3 440, 1 732, 1 242 and 1 106 cm-1 assigned to PCEC, as well as absorption bands at 3 350 cm-1 and 1 531 cm-1 assigned to the urethane bond of the end caped PCEC were revealed by the FTIR spectra. The hybrid PCEC-CaO-SiO2-P2O5 material was synthesized by the end caped PCEC with tetraethyl orthosilicate, calcium nitrate tetrahydrate and triethyl phosphate via a sol-gel method. The bioactivity of the PCEC-CaO-SiO2-P2O5 hybrid material was assessed using simulated body fluid. SEM pictures display that precipitate with the calcium phosphate was presented on the surface after soaking for 24 h. XRD results show that the diffraction peaks of precipitate have the characteristic of hydroxyapatite. It is also revealed that the polymer hydrophobicity would influence the precipitate formation on the hybrid material surface. The mechanics performance test shows that with the increase of PEG content in the polymer, the compression modulus increases from 6.9 MPa to 65 MPa. The cell viability experiments show that PCEC-CaO-SiO2-P2O5 hybrid material has no significant cytotoxic.
2015, 32(4): 1187-1193.
doi: 10.13801/j.cnki.fhclxb.20140918.001
Abstract:
Flower sphere-like Bi2WO6 and mesoporous carbon CMK-3/Bi2WO6 photocatalysts were synthesized by hydrothermal method, and then Ag/Bi2WO6 and Ag/CMK-3/Bi2WO6 were prepared via a photoreduction process in order to obtain the photocatalysts with high visible light activities. The as-prepared samples were characterized by ultraviolet-visible diffuse reflectance spectroscopy (UV-Vis DRS), X-ray diffraction (XRD), transmission electron microscope(TEM), high resolution transmission electron microscope (HR-TEM) and scanning electron microscope (SEM). The photocatalytic activities of the samples were evaluated by the photodegradation of methylene blue (MB) under visible light irradiation. The mechanism for the enhancement of the photocatalytic activity of CMK-3 and Ag-loaded Bi2WO6 was also investigated. The results show that CMK-3 or Ag loading greatly improves the photocatalytic activity of Bi2WO6, the photocatalytic activity of Ag/CMK-3/Bi2WO6 photocatalyst is superior to the activities of CMK-3/Bi2WO6 and Ag/Bi2WO6 photocatalysts.
Flower sphere-like Bi2WO6 and mesoporous carbon CMK-3/Bi2WO6 photocatalysts were synthesized by hydrothermal method, and then Ag/Bi2WO6 and Ag/CMK-3/Bi2WO6 were prepared via a photoreduction process in order to obtain the photocatalysts with high visible light activities. The as-prepared samples were characterized by ultraviolet-visible diffuse reflectance spectroscopy (UV-Vis DRS), X-ray diffraction (XRD), transmission electron microscope(TEM), high resolution transmission electron microscope (HR-TEM) and scanning electron microscope (SEM). The photocatalytic activities of the samples were evaluated by the photodegradation of methylene blue (MB) under visible light irradiation. The mechanism for the enhancement of the photocatalytic activity of CMK-3 and Ag-loaded Bi2WO6 was also investigated. The results show that CMK-3 or Ag loading greatly improves the photocatalytic activity of Bi2WO6, the photocatalytic activity of Ag/CMK-3/Bi2WO6 photocatalyst is superior to the activities of CMK-3/Bi2WO6 and Ag/Bi2WO6 photocatalysts.
2015, 32(4): 1194-1200.
doi: 10.13801/j.cnki.fhclxb.20150619.001
Abstract:
According to the requirments of liquid composite moulding, the compaction behaviors of two types of "ex-situ" toughened preforms were investigated. The preforms were fabricated by interleaving such "ex-situ" toughening layers as the porous film or the non-woven fabric between the carbon fabrics. The thickness of the preforms under different pressure was measured by the mechanical testing machine. The results show that the "ex-situ" toughening layers decreses the fiber volume fraction of the preforms under a certain pressure, and the compaction behaviors of the preforms,under different pressures, depend on the micro-structure of the toughening layers. Additionally, the thickness of the preforms was predicted by adopting a compaction constitutive model for the fabric. It is shown that the calculated results are in good agreement with the experimental results when the empirical coefficient k=2.
According to the requirments of liquid composite moulding, the compaction behaviors of two types of "ex-situ" toughened preforms were investigated. The preforms were fabricated by interleaving such "ex-situ" toughening layers as the porous film or the non-woven fabric between the carbon fabrics. The thickness of the preforms under different pressure was measured by the mechanical testing machine. The results show that the "ex-situ" toughening layers decreses the fiber volume fraction of the preforms under a certain pressure, and the compaction behaviors of the preforms,under different pressures, depend on the micro-structure of the toughening layers. Additionally, the thickness of the preforms was predicted by adopting a compaction constitutive model for the fabric. It is shown that the calculated results are in good agreement with the experimental results when the empirical coefficient k=2.
2015, 32(4): 1201-1210.
doi: 10.13801/j.cnki.fhclxb.20141118.004
Abstract:
In order to realize selective adsorption and removal of 2, 4, 6-trichlorophenol (2, 4, 6-TCP) in seawater, a 2, 4, 6-trichlorophenol-imprinted amino-functionalized nano-Fe3O4-polymer magnetic composite (nFe3O4@MIPNH2-polymer) was synthesized via ultrasonic assisted suspension polymerization. The composition, structure, morphology and magnetism of nFe3O4@MIPNH2-polymer were characterized by means of Elemental Analysis (EA), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, transmission electron microscopy (TEM) and vibrating sample magnetometer (VSM). The application for its adsorption and removal properties on 2, 4, 6-TCP pollutant from seawater was investigated. The results show that the nFe3O4@MIPNH2-polymer has an average size of around 800 nm, with the saturation magnetization intensity of 32.6 emu·g-1. Adsorption isotherm of 2, 4, 6-TCP onto nFe3O4@MIPNH2-polymer accords with Langmuir model, which demonstrate an excellent adsorption capacity with the maximum adsorption capacity at 105.26 mg·g-1, much higher than that of none-molecular imprinted amino-functionalized nano-Fe3O4-polymer magnetic material (nFe3O4@NH2-polymer, with the maximum adsorption capacity at 76.92 mg·g-1). The isothermal adsorption curve mainly obeys the Langmuir mode. The adsorption thermodynamic studies suggest that the adsorption processes of the 2, 4, 6-TCP by the nFe3O4@MIPNH2-polymer are endothermic, entropy favored, and spontaneous in nature, and the adsorption processes reach the equilibrium within 5 min and the kinetic data are well fitted to the pseudo-second-order model. The activation energy for the 2, 4, 6-TCP removal is 78.0 kJ·mol-1. There is almost no interference by the coexisting components in seawater for the adsorption of 2, 4, 6-TCP. The nFe3O4@MIPNH2-polymer can be reused at least 5 times after elusion. The 2, 4, 6-TCP in seawater can be selectively and effectively removed by the nFe3O4@MIPNH2-polymer.
In order to realize selective adsorption and removal of 2, 4, 6-trichlorophenol (2, 4, 6-TCP) in seawater, a 2, 4, 6-trichlorophenol-imprinted amino-functionalized nano-Fe3O4-polymer magnetic composite (nFe3O4@MIPNH2-polymer) was synthesized via ultrasonic assisted suspension polymerization. The composition, structure, morphology and magnetism of nFe3O4@MIPNH2-polymer were characterized by means of Elemental Analysis (EA), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, transmission electron microscopy (TEM) and vibrating sample magnetometer (VSM). The application for its adsorption and removal properties on 2, 4, 6-TCP pollutant from seawater was investigated. The results show that the nFe3O4@MIPNH2-polymer has an average size of around 800 nm, with the saturation magnetization intensity of 32.6 emu·g-1. Adsorption isotherm of 2, 4, 6-TCP onto nFe3O4@MIPNH2-polymer accords with Langmuir model, which demonstrate an excellent adsorption capacity with the maximum adsorption capacity at 105.26 mg·g-1, much higher than that of none-molecular imprinted amino-functionalized nano-Fe3O4-polymer magnetic material (nFe3O4@NH2-polymer, with the maximum adsorption capacity at 76.92 mg·g-1). The isothermal adsorption curve mainly obeys the Langmuir mode. The adsorption thermodynamic studies suggest that the adsorption processes of the 2, 4, 6-TCP by the nFe3O4@MIPNH2-polymer are endothermic, entropy favored, and spontaneous in nature, and the adsorption processes reach the equilibrium within 5 min and the kinetic data are well fitted to the pseudo-second-order model. The activation energy for the 2, 4, 6-TCP removal is 78.0 kJ·mol-1. There is almost no interference by the coexisting components in seawater for the adsorption of 2, 4, 6-TCP. The nFe3O4@MIPNH2-polymer can be reused at least 5 times after elusion. The 2, 4, 6-TCP in seawater can be selectively and effectively removed by the nFe3O4@MIPNH2-polymer.
2015, 32(4): 1211-1217.
doi: 10.13801/j.cnki.fhclxb.20141028.003
Abstract:
Residual stress problem in fiber reinforced resin matrix composite structures is a key issue to restrict their large-scale applications in aerospace, automobile and architecture fields. Non-uniformity of temperature and curing degree fields during curing process of composites is an important factor in causing residual thermal stress and curing shrinkage stress. In view of investigating the sensitive degree of curing process temperature, thermal conductivity coefficient, convective heat transfer coefficient and thickness of structure to curing uniformity during curing process of fiber composite structures, the influence rule of the four key parameters on uniformity of temperature and curing degree fields was analyzed by numerical simulation. The simulation results show that the non-uniformity of the temperature field of composites increases and the non-uniformity of the curing degree field decreases when raising the curing process temperature; the non-uniformity of the temperature and curing degree fields both decrease when increasing convective heat transfer coefficient and thermal conductivity coefficient; the non-uniformity of the temperature and curing degree fields increase when increasing the thickness of composite structure. On these basis, the influence degree of the four key parameters on curing uniformity of composites was quantized by Morris global sensitivity analysis method. The sensitive degree order of curing uniformity corresponding to the four key parameters from high to low is as follows: thickness of structure, thermal conductivity coefficient, curing process temperature, convective heat transfer coefficient.
Residual stress problem in fiber reinforced resin matrix composite structures is a key issue to restrict their large-scale applications in aerospace, automobile and architecture fields. Non-uniformity of temperature and curing degree fields during curing process of composites is an important factor in causing residual thermal stress and curing shrinkage stress. In view of investigating the sensitive degree of curing process temperature, thermal conductivity coefficient, convective heat transfer coefficient and thickness of structure to curing uniformity during curing process of fiber composite structures, the influence rule of the four key parameters on uniformity of temperature and curing degree fields was analyzed by numerical simulation. The simulation results show that the non-uniformity of the temperature field of composites increases and the non-uniformity of the curing degree field decreases when raising the curing process temperature; the non-uniformity of the temperature and curing degree fields both decrease when increasing convective heat transfer coefficient and thermal conductivity coefficient; the non-uniformity of the temperature and curing degree fields increase when increasing the thickness of composite structure. On these basis, the influence degree of the four key parameters on curing uniformity of composites was quantized by Morris global sensitivity analysis method. The sensitive degree order of curing uniformity corresponding to the four key parameters from high to low is as follows: thickness of structure, thermal conductivity coefficient, curing process temperature, convective heat transfer coefficient.
2015, 32(4): 1218-1224.
doi: 10.13801/j.cnki.fhclxb.20141204.002
Abstract:
By regulating spinning process of polyacrylonitrile (PAN) precursor, PAN based carbon fibers (CF) with rough surface and CF with smooth surface were produced, both of which share the same chemical structure as well as similar mechanical property to simulate the influence of surface morphology on the electrochemical oxidation behaviors. Under the same oxidized condition, CF with smooth surface shows a higher morphology resistance, and the O to C ratio is much more than that on CF with rough surface, indicating a higher oxidation degree of the former. XPS spectra reveals that the difference of O to C ratio is probably due to the changes of the relative amount of carbonyl groups on carbon fiber surface. The tensile strength and tensile modulus of CF with rough surface could be improved, however, the tensile strength could be obviously improved to a maximum of 17.3% at the initial stage of electrochemical oxidation. The interlaminar shear strength (ILSS) of carbon fiber reinforced epoxy composite was measured by a fragmentation test, and it is suggested that a better interfacial adhesion could be obtained from rough-surface carbon fiber reinforced epoxy composite, indicating the reinforced mechanism between carbon fiber and epoxy matrix is prone to be anchor force rather than chemical interaction.
By regulating spinning process of polyacrylonitrile (PAN) precursor, PAN based carbon fibers (CF) with rough surface and CF with smooth surface were produced, both of which share the same chemical structure as well as similar mechanical property to simulate the influence of surface morphology on the electrochemical oxidation behaviors. Under the same oxidized condition, CF with smooth surface shows a higher morphology resistance, and the O to C ratio is much more than that on CF with rough surface, indicating a higher oxidation degree of the former. XPS spectra reveals that the difference of O to C ratio is probably due to the changes of the relative amount of carbonyl groups on carbon fiber surface. The tensile strength and tensile modulus of CF with rough surface could be improved, however, the tensile strength could be obviously improved to a maximum of 17.3% at the initial stage of electrochemical oxidation. The interlaminar shear strength (ILSS) of carbon fiber reinforced epoxy composite was measured by a fragmentation test, and it is suggested that a better interfacial adhesion could be obtained from rough-surface carbon fiber reinforced epoxy composite, indicating the reinforced mechanism between carbon fiber and epoxy matrix is prone to be anchor force rather than chemical interaction.
2015, 32(4): 1225-1232.
doi: 10.13801/j.cnki.fhclxb.20141107.001
Abstract:
Aiming to solve the difficult manufacture of high strength and large size fiber reinforced thermoplastic composite components using high viscosity thermoplastic resins, combined vacuum assisted resin transfer molding(VARTM) technology with hot-pressing technology, continuous glass fiber (GF) reinforced poly (cyclic butylene terephthalate)(PCBT) composite laminates and fusion joints with 70% fiber volume fraction were prepared with PCBT as matrix via polymerization of cyclic butylene terephthalate (CBT) under the action of catalyst. And the mechanical parameters were measured. The carrying capacity and failure mode of three different schemes of GF/PCBT composite fusion joints with 1, 2, 3 layers of connection interfaces (A, B, C type) were predicted by numerical simulation method. The results show that different structure design schemes have a great impact on properties of GF/PCBT composite joints. When connection length is within a certain range, the interface delamination failure is the main failure mode of bonding region and the warping of composites in joint area is the main factor accelerating the expansion of interface crack. Compared with joint A, the structure carrying capacity of joint C is obviously improved and it has been increased with the increase of the connection length of joint C until the interface delamination at joint, fiber and matrix failure occur at the same time. Continue to increase the connection length, the fiber and matrix failure will become the main failure mode of bonding region and the carrying capacity has no obvious improvement.
Aiming to solve the difficult manufacture of high strength and large size fiber reinforced thermoplastic composite components using high viscosity thermoplastic resins, combined vacuum assisted resin transfer molding(VARTM) technology with hot-pressing technology, continuous glass fiber (GF) reinforced poly (cyclic butylene terephthalate)(PCBT) composite laminates and fusion joints with 70% fiber volume fraction were prepared with PCBT as matrix via polymerization of cyclic butylene terephthalate (CBT) under the action of catalyst. And the mechanical parameters were measured. The carrying capacity and failure mode of three different schemes of GF/PCBT composite fusion joints with 1, 2, 3 layers of connection interfaces (A, B, C type) were predicted by numerical simulation method. The results show that different structure design schemes have a great impact on properties of GF/PCBT composite joints. When connection length is within a certain range, the interface delamination failure is the main failure mode of bonding region and the warping of composites in joint area is the main factor accelerating the expansion of interface crack. Compared with joint A, the structure carrying capacity of joint C is obviously improved and it has been increased with the increase of the connection length of joint C until the interface delamination at joint, fiber and matrix failure occur at the same time. Continue to increase the connection length, the fiber and matrix failure will become the main failure mode of bonding region and the carrying capacity has no obvious improvement.
