2015 Vol. 32, No. 3
2015, 32(3): 617-624.
doi: 10.13801/j.cnki.fhclxb.20150128.002
Abstract:
Composites are multi-scale in nature. The multi-scale simulation stands among one of the most important methods for response analysis of composites, due to its ability to incorporate micro scale damage initiation, evolution and the corresponding effects in macro material property and mechanical behavior. The multi-scale asymptotic expansion theory was used to decompose macro and micro scale governing equation from the original elastic ones, from which the relationship between macro scale and micro scale response was established. Based on synergistic multi-scale computational technique, a multi-scale simulation framework was proposed, and development capability provided in commercial finite element software, including user subroutines and scripts were used to implement it. The developed framework can call micro scale model to carry out multi-scale progressive damage simulation during macro model calculation, and information exchange and feedback between macro and micro scale were realized. Micro scale damage model and macro scale phenomenological strength theory can be easily integrated into this multi-scale numerical simulation method with good generality. The tensile simulation example results of carbon/carbon composites shows good agreement with test results.
Composites are multi-scale in nature. The multi-scale simulation stands among one of the most important methods for response analysis of composites, due to its ability to incorporate micro scale damage initiation, evolution and the corresponding effects in macro material property and mechanical behavior. The multi-scale asymptotic expansion theory was used to decompose macro and micro scale governing equation from the original elastic ones, from which the relationship between macro scale and micro scale response was established. Based on synergistic multi-scale computational technique, a multi-scale simulation framework was proposed, and development capability provided in commercial finite element software, including user subroutines and scripts were used to implement it. The developed framework can call micro scale model to carry out multi-scale progressive damage simulation during macro model calculation, and information exchange and feedback between macro and micro scale were realized. Micro scale damage model and macro scale phenomenological strength theory can be easily integrated into this multi-scale numerical simulation method with good generality. The tensile simulation example results of carbon/carbon composites shows good agreement with test results.
2015, 32(3): 625-631.
doi: 10.13801/j.cnki.fhclxb.201503.001
Abstract:
Incorporating multi-functional nano-particles into natural fiber reinforced polymer composites can provide with the multi-functionality, making them possess sensor performance, which are capable of in-situ sensing the change of surrounding environment. However, it is realized by dispersing nano-particle into matrix, which normally leads to high viscosity of matrix, hindering its application and meanwhile high nano-particle loadings are needed to reach percolation threshold. Dip coating technology was used for the surface modification of sisal fibres (SF) with multi-walled carbon nanotubes (MWCNTs) dispersion as dye, the resulting MWCNTs modified sisal fibers (MWCNTs-SF) and their epoxy based composite (MWCNTs-SF/EP) sensors were prepared. A continuous and homogenous dispersed MWCNTs network coating forms on surface of MWCNTs-SF. The current versus voltage characteristic curve of MWCNTs-SF indicates the formation of ohmic contacts for MWCNTs-MWCNTs and MWCNTs-electrode. Both MWCNT-SF and MWCNTs-SF/EP are characterized by negative temperature coefficient thermistor. Under external strain-stress, the electrical resistance of MWCNTs-SF and MWCNTs-SF/EP exhibits nearly constant at very low strains, then increases linearly at intermediate strains, while an exponential correlation between electrical resistance and strain exists at higher strains. The different sensing characteristics for MWCNTs-SF and MWCNTs-SF/EP mostly relate to the MWCNTs network structure change during consolidation. The tensile strength of MWCNTs modified sisal fiber fabric reinforced epoxy based composite increases gradually from 37.6 MPa to 46.7 MPa with increasing surface modification time, elastic modulus also increases accordingly.
Incorporating multi-functional nano-particles into natural fiber reinforced polymer composites can provide with the multi-functionality, making them possess sensor performance, which are capable of in-situ sensing the change of surrounding environment. However, it is realized by dispersing nano-particle into matrix, which normally leads to high viscosity of matrix, hindering its application and meanwhile high nano-particle loadings are needed to reach percolation threshold. Dip coating technology was used for the surface modification of sisal fibres (SF) with multi-walled carbon nanotubes (MWCNTs) dispersion as dye, the resulting MWCNTs modified sisal fibers (MWCNTs-SF) and their epoxy based composite (MWCNTs-SF/EP) sensors were prepared. A continuous and homogenous dispersed MWCNTs network coating forms on surface of MWCNTs-SF. The current versus voltage characteristic curve of MWCNTs-SF indicates the formation of ohmic contacts for MWCNTs-MWCNTs and MWCNTs-electrode. Both MWCNT-SF and MWCNTs-SF/EP are characterized by negative temperature coefficient thermistor. Under external strain-stress, the electrical resistance of MWCNTs-SF and MWCNTs-SF/EP exhibits nearly constant at very low strains, then increases linearly at intermediate strains, while an exponential correlation between electrical resistance and strain exists at higher strains. The different sensing characteristics for MWCNTs-SF and MWCNTs-SF/EP mostly relate to the MWCNTs network structure change during consolidation. The tensile strength of MWCNTs modified sisal fiber fabric reinforced epoxy based composite increases gradually from 37.6 MPa to 46.7 MPa with increasing surface modification time, elastic modulus also increases accordingly.
2015, 32(3): 632-639.
doi: 10.13801/j.cnki.fhclxb.20140725.002
Abstract:
Chitosan/cellulose biomass foaming composites were successfully prepared by a freeze dry method using chitosan particles as reinforcement and ionic liquid as cellulose solvent. The microstructure, crystallization property and thermo-stability of porous composites were characterized by SEM, XRD and TGA, respectively. The porosity and water absorption ability were also analyzed. The results show that chitosan/cellulose porous composites exhibit 3-dimensional interconnected porous structure and chitosan particles facilitate the formation of pores. TGA demonstrates that the addition of chitosan particles improves the thermal stability of cellulose porous materials. XRD presents that the crystalline structure of cellulose is converted from cellulose I to cellulose II in original cellulose during dissolution and regeneration. When the cellulose content is relatively low (≤4wt%), the incorporation of 1wt% chitosan powders increases the porosity of the chitosan/cellulose porous composites. Mechanical properties of chitosan/cellulose porous composites increase with increasing cellulose contents, while water absorption ability decreases. The porosity of the chitosan/cellulose (mass ratio is 1:3) porous composites is 72.7%, the water absorption rate and relative retention rate are 28.0 g/g and 17.6 g/g, the breaking strength and breaking elongation are 0.32 MPa and 25.4%, receptively. This chitosan/cellulose porous composites as excellent absorption material can be used for medical dressing with high performances.
Chitosan/cellulose biomass foaming composites were successfully prepared by a freeze dry method using chitosan particles as reinforcement and ionic liquid as cellulose solvent. The microstructure, crystallization property and thermo-stability of porous composites were characterized by SEM, XRD and TGA, respectively. The porosity and water absorption ability were also analyzed. The results show that chitosan/cellulose porous composites exhibit 3-dimensional interconnected porous structure and chitosan particles facilitate the formation of pores. TGA demonstrates that the addition of chitosan particles improves the thermal stability of cellulose porous materials. XRD presents that the crystalline structure of cellulose is converted from cellulose I to cellulose II in original cellulose during dissolution and regeneration. When the cellulose content is relatively low (≤4wt%), the incorporation of 1wt% chitosan powders increases the porosity of the chitosan/cellulose porous composites. Mechanical properties of chitosan/cellulose porous composites increase with increasing cellulose contents, while water absorption ability decreases. The porosity of the chitosan/cellulose (mass ratio is 1:3) porous composites is 72.7%, the water absorption rate and relative retention rate are 28.0 g/g and 17.6 g/g, the breaking strength and breaking elongation are 0.32 MPa and 25.4%, receptively. This chitosan/cellulose porous composites as excellent absorption material can be used for medical dressing with high performances.
2015, 32(3): 640-648.
doi: 10.13801/j.cnki.fhclxb.20150601.001
Abstract:
In order to study the effects of adding different functionalized carbon nanotubes on mechanical properties of epoxy, multi-walled carbon nanotubes with reactive amino groups(MWCNTs-EDA) were prepared by chemical processing on MWCNTs-COOH. MWCNTs-COOH and MWCNTs-EDA were dispersed in epoxy. T700 carbon fiber prepreg which epoxy containing carbon nanotubes was successfully produced by hot-melt method and then the quasi isotropic composite laminates were prepared. The results confirm that MWCNTs-EDA has better dispersion than MWCNTs-COOH. MWCNTs-EDA itself has curing reaction activity and exhibites a little effect on crosslinking density of matrix. Compared with MWCNTs-COOH, MWCNTs-EDA is more effective in enhancing the mechanical performance of epoxy and carbon fiber/epoxy composites. When the content of MWCNTs-EDA is 1.0wt%, the compression properties, flexural properties and compression strength after impact (CAI) of quasi isotropic MWCNTs-carbon fiber/epoxy composite laminates can be increased by 14.7%, 40.9% and 20.6%, respectively.
In order to study the effects of adding different functionalized carbon nanotubes on mechanical properties of epoxy, multi-walled carbon nanotubes with reactive amino groups(MWCNTs-EDA) were prepared by chemical processing on MWCNTs-COOH. MWCNTs-COOH and MWCNTs-EDA were dispersed in epoxy. T700 carbon fiber prepreg which epoxy containing carbon nanotubes was successfully produced by hot-melt method and then the quasi isotropic composite laminates were prepared. The results confirm that MWCNTs-EDA has better dispersion than MWCNTs-COOH. MWCNTs-EDA itself has curing reaction activity and exhibites a little effect on crosslinking density of matrix. Compared with MWCNTs-COOH, MWCNTs-EDA is more effective in enhancing the mechanical performance of epoxy and carbon fiber/epoxy composites. When the content of MWCNTs-EDA is 1.0wt%, the compression properties, flexural properties and compression strength after impact (CAI) of quasi isotropic MWCNTs-carbon fiber/epoxy composite laminates can be increased by 14.7%, 40.9% and 20.6%, respectively.
2015, 32(3): 649-656.
doi: 10.13801/j.cnki.fhclxb.20140702.003
Abstract:
In order to obtain retardant ethylene-vinyl acetate (EVA) foam composites, two different compounded fire retardant consisting of expandable graphite-ammonium polyphosphate (EG-APP) and expandable graphite-ammonium polyphosphate-thermoplastic starch (EG-APP-TPS) were added to prepare alogen-free fire retardant EVA foam composites by process of molten blending and sulfuration foam. The EG-APP/EVA and EG-APP-TPS/EVA foam composites were characterized by limit oxygen index (LOI), vertical combustion (UL-94), thermal analysis mass spectrometry (TG-MASS) and scanning electron microscopy (SEM) test. The results demonstrate that the LOI of EG-APP/EVA foam composite is 28.1% and the flame retardant grade reaches to UL-94 V-1 at 30wt% total loading of EG and APP with mass ratio of 1:4.However, at 30wt% total loading of EG, APP and TPS with mass ratio of 1:4:1, LOI 29.3% and UL-94 V-0 rating are obtained. The results from TG-MASS and SEM tests show a good synergistic effect of EG, APP and TPS in solid and gas phase.
In order to obtain retardant ethylene-vinyl acetate (EVA) foam composites, two different compounded fire retardant consisting of expandable graphite-ammonium polyphosphate (EG-APP) and expandable graphite-ammonium polyphosphate-thermoplastic starch (EG-APP-TPS) were added to prepare alogen-free fire retardant EVA foam composites by process of molten blending and sulfuration foam. The EG-APP/EVA and EG-APP-TPS/EVA foam composites were characterized by limit oxygen index (LOI), vertical combustion (UL-94), thermal analysis mass spectrometry (TG-MASS) and scanning electron microscopy (SEM) test. The results demonstrate that the LOI of EG-APP/EVA foam composite is 28.1% and the flame retardant grade reaches to UL-94 V-1 at 30wt% total loading of EG and APP with mass ratio of 1:4.However, at 30wt% total loading of EG, APP and TPS with mass ratio of 1:4:1, LOI 29.3% and UL-94 V-0 rating are obtained. The results from TG-MASS and SEM tests show a good synergistic effect of EG, APP and TPS in solid and gas phase.
2015, 32(3): 657-664.
doi: 10.13801/j.cnki.fhclxb.20140718.001
Abstract:
In order to investigate the feasibility of biomass resources improving the interface and comprehensive properties of bio-composites, the oxidation modification ammonium lignosulphonate (OMAL) was used to produce the environment friendly OMAL-polylactic acid (PLA)/wood fiber (WF) composites by the high speed mix-flat hot pressing process with WF as matrix and PLA as reinforcement. The influence of OMAL on mechanical and thermal properties of OMAL-PLA/WF composites was investigated. The results show that OMAL can improve the modulus of rupture, elastic modulus and internal bond strength of OMAL-PLA/WF composites with mass ratio 7:3 of WF to PLA, and the optimized mechanical properties are achieved with OMAL dosage of 15wt%-20wt%. When the OMAL dosage is 20wt%, the thermal decomposition initial temperature decreases 45 ℃, the characteristic peak of thermal decomposition rate arises 107 ℃ in advance, the residue quantity increases by 5.3%, the glass transition temperature, cold crystallization temperature and melting temperature shift to low temperature, the storage modulus and loss tangent increase with the temperature range of the platform stage increases about 20 ℃ compared to that of PLA/WF composites.
In order to investigate the feasibility of biomass resources improving the interface and comprehensive properties of bio-composites, the oxidation modification ammonium lignosulphonate (OMAL) was used to produce the environment friendly OMAL-polylactic acid (PLA)/wood fiber (WF) composites by the high speed mix-flat hot pressing process with WF as matrix and PLA as reinforcement. The influence of OMAL on mechanical and thermal properties of OMAL-PLA/WF composites was investigated. The results show that OMAL can improve the modulus of rupture, elastic modulus and internal bond strength of OMAL-PLA/WF composites with mass ratio 7:3 of WF to PLA, and the optimized mechanical properties are achieved with OMAL dosage of 15wt%-20wt%. When the OMAL dosage is 20wt%, the thermal decomposition initial temperature decreases 45 ℃, the characteristic peak of thermal decomposition rate arises 107 ℃ in advance, the residue quantity increases by 5.3%, the glass transition temperature, cold crystallization temperature and melting temperature shift to low temperature, the storage modulus and loss tangent increase with the temperature range of the platform stage increases about 20 ℃ compared to that of PLA/WF composites.
2015, 32(3): 665-672.
doi: 10.13801/j.cnki.fhclxb.20140721.003
Abstract:
Nano-Al2O3 was modified by supercritical ethanol (SCE-Al2O3) and the surface of SCE-Al2O3 was coated with active group. 4, 4'-diamino diphenyl methane bismaleimide (BMI) was used as matrix, 3, 3'-diallyl bisphenol A (BBA) and bisphenol-A diallyl ether (BBE) were used as reactive diluent, polyether sulfone (PES) as toughening agent and SCE-Al2O3 as modifier, SCE-Al2O3/PES-BMI-BBA-BBE composites were prepared through in-situ polymerization method. The toughening mechanisms of SCE-Al2O3nano particles and PES were observed and analyzed by SEM and FTIR. The results show that the processing time of SCE-Al2O3nano particles should not be too long(5 min is appropriate). FTIR shows that the characteristic peak of —OH at 3 457 cm-1 is enhanced and indicates that the surface of Al2O3 is coated with reactive group —OH. PES presentes as two-phase structure in BMI-BBA-BBE matrix, PES resin disperses in polymer matrix with "honeycomb" shape evenly and the size of "honeycomb" enlarges with the increasing of PES content (5wt% is appropriate). Results of heat resistance of composites show that the thermal decomposition temperature would decline when BMI-BBA-BBE matrix mixed with PES, and SCE-Al2O3 could enhance the thermal stability of composites. The thermal decomposition temperature of 4wt% SCE -Al2O3/PES-BMI-BBA-BBE is 444.41 ℃, which is 20.52 ℃ higher than that of matrix resin. Rate of residual mass at 600 ℃ is 47.64%, enhanced by 7.09%.
Nano-Al2O3 was modified by supercritical ethanol (SCE-Al2O3) and the surface of SCE-Al2O3 was coated with active group. 4, 4'-diamino diphenyl methane bismaleimide (BMI) was used as matrix, 3, 3'-diallyl bisphenol A (BBA) and bisphenol-A diallyl ether (BBE) were used as reactive diluent, polyether sulfone (PES) as toughening agent and SCE-Al2O3 as modifier, SCE-Al2O3/PES-BMI-BBA-BBE composites were prepared through in-situ polymerization method. The toughening mechanisms of SCE-Al2O3nano particles and PES were observed and analyzed by SEM and FTIR. The results show that the processing time of SCE-Al2O3nano particles should not be too long(5 min is appropriate). FTIR shows that the characteristic peak of —OH at 3 457 cm-1 is enhanced and indicates that the surface of Al2O3 is coated with reactive group —OH. PES presentes as two-phase structure in BMI-BBA-BBE matrix, PES resin disperses in polymer matrix with "honeycomb" shape evenly and the size of "honeycomb" enlarges with the increasing of PES content (5wt% is appropriate). Results of heat resistance of composites show that the thermal decomposition temperature would decline when BMI-BBA-BBE matrix mixed with PES, and SCE-Al2O3 could enhance the thermal stability of composites. The thermal decomposition temperature of 4wt% SCE -Al2O3/PES-BMI-BBA-BBE is 444.41 ℃, which is 20.52 ℃ higher than that of matrix resin. Rate of residual mass at 600 ℃ is 47.64%, enhanced by 7.09%.
2015, 32(3): 673-682.
doi: 10.13801/j.cnki.fhclxb.20140721.005
Abstract:
Three kinds of graphene oxide (GO) with different oxidation degrees were synthesized by Hummers method. The GO/polyurethane (PU) mixed matrix membranes were fabricated via in-situ polymerization of PU monomers (Methylene Diphenyl 4, 4'-Diisocyanate (MDI) and 1, 4-Butanediol (BDO)) with GO. The structure of GO was characterized by XRD, Raman, FTIR and TEM etc. The effects of GO filling content on the morphology and permeabilities of CO2 and N2 of GO/PU mixed matrix membranes were discussed. The results reveal that the three kinds of GO with different oxidation degrees present a state of complete stripping, and are translucent sheet structure, and with the increasing of oxidation degree, the relative intensities of D peak to G peak in Raman are 0.947, 1.103 and 1.245. The oxidation degree of GO has greater effects on the dispersibility of GO in solution and mixed matrix membrane, when the oxidation degree is higher, the dispersibility is better. The permeability coeffcients of CO2 and N2 and CO2/N2 permeation selectivity factor of GO/PU mixed matrix membrane increase firstly and then decrease with GO filling content increasing. When the mass ratio of middle oxidation degree GO (M-GO) to (MDI+BDO) reaches 1.0%, the CO2 permeability coefficient of M-GO/PU mixed matrix membrane is 63.6×10-13 cm3(STP)/(cm·Pa·s), STP represents for standard temperature and pressure, and the permeation selectivity factor of CO2/N2 reaches 48.5. The filling of appropriate amount of GO could significantly improve the permeability of CO2 and the CO2/N2 permeation selectivity of GO/PU mixed matrix membrane.
Three kinds of graphene oxide (GO) with different oxidation degrees were synthesized by Hummers method. The GO/polyurethane (PU) mixed matrix membranes were fabricated via in-situ polymerization of PU monomers (Methylene Diphenyl 4, 4'-Diisocyanate (MDI) and 1, 4-Butanediol (BDO)) with GO. The structure of GO was characterized by XRD, Raman, FTIR and TEM etc. The effects of GO filling content on the morphology and permeabilities of CO2 and N2 of GO/PU mixed matrix membranes were discussed. The results reveal that the three kinds of GO with different oxidation degrees present a state of complete stripping, and are translucent sheet structure, and with the increasing of oxidation degree, the relative intensities of D peak to G peak in Raman are 0.947, 1.103 and 1.245. The oxidation degree of GO has greater effects on the dispersibility of GO in solution and mixed matrix membrane, when the oxidation degree is higher, the dispersibility is better. The permeability coeffcients of CO2 and N2 and CO2/N2 permeation selectivity factor of GO/PU mixed matrix membrane increase firstly and then decrease with GO filling content increasing. When the mass ratio of middle oxidation degree GO (M-GO) to (MDI+BDO) reaches 1.0%, the CO2 permeability coefficient of M-GO/PU mixed matrix membrane is 63.6×10-13 cm3(STP)/(cm·Pa·s), STP represents for standard temperature and pressure, and the permeation selectivity factor of CO2/N2 reaches 48.5. The filling of appropriate amount of GO could significantly improve the permeability of CO2 and the CO2/N2 permeation selectivity of GO/PU mixed matrix membrane.
2015, 32(3): 683-690.
doi: 10.13801/j.cnki.fhclxb.20141105.003
Abstract:
In order to investigate the effect of bamboo fiber energy on adhesion work between fiber and resin and the interface of composites, the surface of bamboo fiber was modified by alkali treatment, then bamboo fiber reinforced polypropylene(PP) composites were prepared by means of compression molding technology. The effects of alkali treatment on properties of bamboo fiber, the adhesion work between bamboo fiber and PP and the mechanical properties of bamboo fiber/PP composites were studied. SEM was used to describe bamboo fiber surface morphology change after different concentration of alkali treatment. The results reveal that with the increase of the concentration of alkali, bamboo fiber strength shows some fluctuations, while at the alkali concentration of 1wt%, bamboo fiber strength reaches the maximum value. The adhesion work between bamboo fiber and PP is closely related to bamboo fiber polarity ratio. The smaller polarity ratio is, the bigger adhesion work becomes. With the increase of the concentration of alkali, the adhesion work between bamboo fiber and PP resin and shear properties of bamboo/PP composites show the same trend, and both of them attain optimal level at the alkali agent concentration of 20wt%. Compared with untreated bamboo fiber, the adhesion work between bamboo fiber and PP resin increases by 67.18%, while bamboo fiber/PP composite's shear properties increase by 23.29%. While at the alkali agent concentration of 5wt%, the flexural strength of the bamboo fiber/PP composites attains optimal level, which is 23.13% higher than that of untreated.
In order to investigate the effect of bamboo fiber energy on adhesion work between fiber and resin and the interface of composites, the surface of bamboo fiber was modified by alkali treatment, then bamboo fiber reinforced polypropylene(PP) composites were prepared by means of compression molding technology. The effects of alkali treatment on properties of bamboo fiber, the adhesion work between bamboo fiber and PP and the mechanical properties of bamboo fiber/PP composites were studied. SEM was used to describe bamboo fiber surface morphology change after different concentration of alkali treatment. The results reveal that with the increase of the concentration of alkali, bamboo fiber strength shows some fluctuations, while at the alkali concentration of 1wt%, bamboo fiber strength reaches the maximum value. The adhesion work between bamboo fiber and PP is closely related to bamboo fiber polarity ratio. The smaller polarity ratio is, the bigger adhesion work becomes. With the increase of the concentration of alkali, the adhesion work between bamboo fiber and PP resin and shear properties of bamboo/PP composites show the same trend, and both of them attain optimal level at the alkali agent concentration of 20wt%. Compared with untreated bamboo fiber, the adhesion work between bamboo fiber and PP resin increases by 67.18%, while bamboo fiber/PP composite's shear properties increase by 23.29%. While at the alkali agent concentration of 5wt%, the flexural strength of the bamboo fiber/PP composites attains optimal level, which is 23.13% higher than that of untreated.
2015, 32(3): 691-698.
doi: 10.13801/j.cnki.fhclxb.20140611.002
Abstract:
To study the effect of glass fiber (GF) surface modified by nano-SiO2 on mechanical properties of GF reinforced matrix composites, vacuum-assisted mold pressing (VAMP) technology was adopted to prepare polymerized poly(cyclic butylene terephthalate)(PCBT)-based composites reinforced by GF modified by various nano-SiO2 on the surface. The effect of GF surface modification on mechanical properties of the obtained GF/PCBT composites was investigated and the hygrothermal aging resistance of GF/PCBT composites with modified GF was further studied. The fiber pull-out test results show that the interface shear strength of GF/PCBT composites enhances by 1.16 times after nano modification on fiber surface. With nano-SiO2 content of 0.5wt%, 2wt% (mass ratio of nano-SiO2 to PCBT), the three-point flexural strength of GF/PCBT composites increases by 1.5 times and 1.67 times, flexural modulus increases by 1.03 times and 1.17 times, respectively. Observations by SEM show that the damaged fibers are covered tightly by PCBT resin when nano-SiO2 content is 2wt%, which is an indication of good bonding properties between the matrix and fibers. Under hygrothermal conditions, hydrone diffusion along the interphase region is hindered and results in the enhancement of the anti-aging performance of the modified GF/PCBT composites, due to the existence of nano-SiO2 particles.
To study the effect of glass fiber (GF) surface modified by nano-SiO2 on mechanical properties of GF reinforced matrix composites, vacuum-assisted mold pressing (VAMP) technology was adopted to prepare polymerized poly(cyclic butylene terephthalate)(PCBT)-based composites reinforced by GF modified by various nano-SiO2 on the surface. The effect of GF surface modification on mechanical properties of the obtained GF/PCBT composites was investigated and the hygrothermal aging resistance of GF/PCBT composites with modified GF was further studied. The fiber pull-out test results show that the interface shear strength of GF/PCBT composites enhances by 1.16 times after nano modification on fiber surface. With nano-SiO2 content of 0.5wt%, 2wt% (mass ratio of nano-SiO2 to PCBT), the three-point flexural strength of GF/PCBT composites increases by 1.5 times and 1.67 times, flexural modulus increases by 1.03 times and 1.17 times, respectively. Observations by SEM show that the damaged fibers are covered tightly by PCBT resin when nano-SiO2 content is 2wt%, which is an indication of good bonding properties between the matrix and fibers. Under hygrothermal conditions, hydrone diffusion along the interphase region is hindered and results in the enhancement of the anti-aging performance of the modified GF/PCBT composites, due to the existence of nano-SiO2 particles.
2015, 32(3): 699-704.
doi: 10.13801/j.cnki.fhclxb.20141021.003
Abstract:
In order to improve the breakdown strength of BaTiO3/PVDF composites, first, dopamine was used to functionalize the surface of BaTiO3, and dopamine modified BaTiO3 (DoPa@BaTiO3) was obtained. Then, it was compounded with polyvinylidene fluoride (PVDF), and Dopa@BaTiO3/PVDF composites were prepared via solution casting method. Finally, breakdown strength and dielectric properties of Dopa@BaTiO3/PVDF composites with different Dopa@BaTiO3 addition were measured. The results show that compared with BaTiO3/PVDF composites before modification, the breakdown strength of Dopa@BaTiO3/PVDF composites improves significantly, while the dielectric constant is almost unchanged. When Dopa@BaTiO3 addition is 3vol%, the breakdown strength is 210 kV/mm, which improves by 78% compared with the composites before modification; when Dopa@BaTiO3 addition is 10vol%, the breakdown strength is 180 kV/mm, which improves by 88% compared with the composites before modification. The research solves the problem of low breakdown strength of BaTiO3/PVDF composites, and can provide references to improve the dielectric constant and breakdown strength of composites at the same time.
In order to improve the breakdown strength of BaTiO3/PVDF composites, first, dopamine was used to functionalize the surface of BaTiO3, and dopamine modified BaTiO3 (DoPa@BaTiO3) was obtained. Then, it was compounded with polyvinylidene fluoride (PVDF), and Dopa@BaTiO3/PVDF composites were prepared via solution casting method. Finally, breakdown strength and dielectric properties of Dopa@BaTiO3/PVDF composites with different Dopa@BaTiO3 addition were measured. The results show that compared with BaTiO3/PVDF composites before modification, the breakdown strength of Dopa@BaTiO3/PVDF composites improves significantly, while the dielectric constant is almost unchanged. When Dopa@BaTiO3 addition is 3vol%, the breakdown strength is 210 kV/mm, which improves by 78% compared with the composites before modification; when Dopa@BaTiO3 addition is 10vol%, the breakdown strength is 180 kV/mm, which improves by 88% compared with the composites before modification. The research solves the problem of low breakdown strength of BaTiO3/PVDF composites, and can provide references to improve the dielectric constant and breakdown strength of composites at the same time.
2015, 32(3): 705-711.
doi: 10.13801/j.cnki.fhclxb.20140725.003
Abstract:
In order to improve the barrier properties of thermoplastic polyurethane (TPU), first, functional graphene oxide (IP-GO)/TPU composite films were prepared by solution casting method on the coating machine. Then, the morphologies and properties of IP-GO/TPU composite films were investigated by FTIR, XPS, XRD, FE-SEM, atomic force microscope and oxygen transmission rate tester. The results indicate that the layer spacing of IP-GO increases of 0.696 nm compared with the primitive flake graphite and the thickness of sheets is about 1.2 nm. IP-GO evenly dispersed in TPU matrix by form of fold layers, and coated on the fracture surfaces of composite films. When the contnent of IP-GO is 3wt%, the oxygen transmission rate of IP-GO/TPU composite film is 84.325 cm3/(m2·d·Pa), compared with the pure TPU film's value which is 280.973 cm3/(m2·d·Pa) decreases by 70%, reveals that the barrier property is improved significantly. The research solves the problem of poor barrier performance of TPU films, and provides a thought and a method for the preparation of high barrier polymers.
In order to improve the barrier properties of thermoplastic polyurethane (TPU), first, functional graphene oxide (IP-GO)/TPU composite films were prepared by solution casting method on the coating machine. Then, the morphologies and properties of IP-GO/TPU composite films were investigated by FTIR, XPS, XRD, FE-SEM, atomic force microscope and oxygen transmission rate tester. The results indicate that the layer spacing of IP-GO increases of 0.696 nm compared with the primitive flake graphite and the thickness of sheets is about 1.2 nm. IP-GO evenly dispersed in TPU matrix by form of fold layers, and coated on the fracture surfaces of composite films. When the contnent of IP-GO is 3wt%, the oxygen transmission rate of IP-GO/TPU composite film is 84.325 cm3/(m2·d·Pa), compared with the pure TPU film's value which is 280.973 cm3/(m2·d·Pa) decreases by 70%, reveals that the barrier property is improved significantly. The research solves the problem of poor barrier performance of TPU films, and provides a thought and a method for the preparation of high barrier polymers.
2015, 32(3): 712-720.
doi: 10.13801/j.cnki.fhclxb.201503.005
Abstract:
In order to improve the flame retardant of glass fiber (GF) reinforced polypropylene (PP) composites (GF/PP), by means of melamine cyanurate (MCA) molecular self-assembly in montmorillonite (MMT) suspension, a new synergistic charring agent MCA-MMT was prepared. FTIR, XRD, SEM and TGA were utilized to characterize the structure and thermal properties of MCA-MMT. Flame retardant composites MCA-MMT/(GF/PP) were prepared by melt blending of MCA-MMT, halogen-free intumescent flame retardant and GF/PP. The flame retardant efficiency and flame retardant mechanism of MCA-MMT toward GF/PP were investigated by limiting oxygen index (LOI) test, vertical burning test and cone calorimeter test. The mechanical properties of composites were also tested. The results indicate that the addition of MMT affects the hydrogen-bond interaction between cyanuric acid and melamine in the synthetic process of MCA, interrupts and inhibits the formation of large planar hydrogen bonding network, and reduces the molecular volume of MCA hydrogen bonding composite which makes the particles smaller. The UL-94 fire rating of MCA-MMT/(GF/PP) reaches V-0, the LOI is 31.3%. The flame retardant efficiency of MCA-MMT is higher than that of traditional MCA, it can reduce the heat release degree and total smoke released, and improves the flame retardant propertier of composites. The mechanism is the MMT with sheet-like structure can improve the char residue amount of MCA, makes the MCA-MMT/(GF/PP) after combustion forms the compact and dense char residue. The tensile and impact strength of MCA-MMT/(GF/PP) do not decrease comparing with those of MCA/(GF/PP).
In order to improve the flame retardant of glass fiber (GF) reinforced polypropylene (PP) composites (GF/PP), by means of melamine cyanurate (MCA) molecular self-assembly in montmorillonite (MMT) suspension, a new synergistic charring agent MCA-MMT was prepared. FTIR, XRD, SEM and TGA were utilized to characterize the structure and thermal properties of MCA-MMT. Flame retardant composites MCA-MMT/(GF/PP) were prepared by melt blending of MCA-MMT, halogen-free intumescent flame retardant and GF/PP. The flame retardant efficiency and flame retardant mechanism of MCA-MMT toward GF/PP were investigated by limiting oxygen index (LOI) test, vertical burning test and cone calorimeter test. The mechanical properties of composites were also tested. The results indicate that the addition of MMT affects the hydrogen-bond interaction between cyanuric acid and melamine in the synthetic process of MCA, interrupts and inhibits the formation of large planar hydrogen bonding network, and reduces the molecular volume of MCA hydrogen bonding composite which makes the particles smaller. The UL-94 fire rating of MCA-MMT/(GF/PP) reaches V-0, the LOI is 31.3%. The flame retardant efficiency of MCA-MMT is higher than that of traditional MCA, it can reduce the heat release degree and total smoke released, and improves the flame retardant propertier of composites. The mechanism is the MMT with sheet-like structure can improve the char residue amount of MCA, makes the MCA-MMT/(GF/PP) after combustion forms the compact and dense char residue. The tensile and impact strength of MCA-MMT/(GF/PP) do not decrease comparing with those of MCA/(GF/PP).
2015, 32(3): 721-727.
doi: 10.13801/j.cnki.fhclxb.201503.006
Abstract:
In order to improve the surface wettability of carbon fiber/resin composites, the surfaces of composites were treated by plasma directly. By means of contact angle measurement, tensile test, metallographic microscopic analysis and infrared spectruma nalysis, the best treating technology of carbon fiber/resin composites treated by plasma,mechanical properties and surface functional group changes of carbon fiber/resin composites before and after treatment were investigated. The results indicate that the current, pressure and treating time all have significant influence on the surface wettability of carbon fiber/resin composites, when current is 1.0 A, pressure is 1.0 Pa and treating time is 10 min, the surface wettability is optimal. The tensile strength of carbon fiber/resin composites does not decrease after treatment, while goes up of 8%. Infrared spectrum analysis shows that the ester group chain on treated carbon fiber/resin composite surface breaks and the quantity of eater group decreases. Accordingly, more ketone group, carboxyl group and alcoholic hydroxyl group are formed. The surface polarity is enhanced and wettability is improved significantly.The research solves the problem that the carbon fiber/resin composite surface is unreactiveness, and establishes the foundation for the surface function coating preparation.
In order to improve the surface wettability of carbon fiber/resin composites, the surfaces of composites were treated by plasma directly. By means of contact angle measurement, tensile test, metallographic microscopic analysis and infrared spectruma nalysis, the best treating technology of carbon fiber/resin composites treated by plasma,mechanical properties and surface functional group changes of carbon fiber/resin composites before and after treatment were investigated. The results indicate that the current, pressure and treating time all have significant influence on the surface wettability of carbon fiber/resin composites, when current is 1.0 A, pressure is 1.0 Pa and treating time is 10 min, the surface wettability is optimal. The tensile strength of carbon fiber/resin composites does not decrease after treatment, while goes up of 8%. Infrared spectrum analysis shows that the ester group chain on treated carbon fiber/resin composite surface breaks and the quantity of eater group decreases. Accordingly, more ketone group, carboxyl group and alcoholic hydroxyl group are formed. The surface polarity is enhanced and wettability is improved significantly.The research solves the problem that the carbon fiber/resin composite surface is unreactiveness, and establishes the foundation for the surface function coating preparation.
2015, 32(3): 728-736.
doi: 10.13801/j.cnki.fhclxb.201503.007
Abstract:
In order to study the flame retardant effects of epoxy resin coated ammonium polyphosphate (EP@APP) microcapsules on polypropylene (PP), firstly, EP was used as the shell to coat APP by in situ polymerization method, then the EP@APP microcapsules were prepared, and it was compound with PP to prepare the EP@APP/PP composites. Secondly, solubility of EP@APP microcapsules was tested to explore the effects of process parameters on solubility. The water resistance was also investigated. With infrared spectroscopy, surface functional groups of EP@APP microcapsules were analyzed. Finally, limited oxygen index, tensile strength and thermogravimetric curves were tested and the thermal degradation kinetics of PP composites was analyzed. The results show that when the addition of EP is 10wt% of APP, and curing agent addition is 15wt% of EP, the completely coated EP@APP microcapsules were prepared by step heating method of maintaining 40 ℃ for 1 h, followed by maintaining 70 ℃ for 1 h. The solubility of the microcapsules in water is lower and the water resistance is good. After adding EP@APP microcapsules into PP, the limited oxygen index of PP composites is 35.5% and reaches V-0 burning class, the mass of residual char after burning increases, and the carbonize effect is better than that of PP composites which adding APP directly. Comparing with APP, the destructiveness of EP@APP microcapsules toward tensile strength of PP reduces obviously. The addition of EP@APP microcapsules makes the apparent activation energy of PP composites increases from 100.8 kJ/mol to 127.5 kJ/mol, and changes the thermal degradation oxidation process of PP composites, and a stable protecting carbon layer is formed by the generated residual char. The research results show that EP@APP microcapsules can improve the flame retardancy of PP composites effectively.
In order to study the flame retardant effects of epoxy resin coated ammonium polyphosphate (EP@APP) microcapsules on polypropylene (PP), firstly, EP was used as the shell to coat APP by in situ polymerization method, then the EP@APP microcapsules were prepared, and it was compound with PP to prepare the EP@APP/PP composites. Secondly, solubility of EP@APP microcapsules was tested to explore the effects of process parameters on solubility. The water resistance was also investigated. With infrared spectroscopy, surface functional groups of EP@APP microcapsules were analyzed. Finally, limited oxygen index, tensile strength and thermogravimetric curves were tested and the thermal degradation kinetics of PP composites was analyzed. The results show that when the addition of EP is 10wt% of APP, and curing agent addition is 15wt% of EP, the completely coated EP@APP microcapsules were prepared by step heating method of maintaining 40 ℃ for 1 h, followed by maintaining 70 ℃ for 1 h. The solubility of the microcapsules in water is lower and the water resistance is good. After adding EP@APP microcapsules into PP, the limited oxygen index of PP composites is 35.5% and reaches V-0 burning class, the mass of residual char after burning increases, and the carbonize effect is better than that of PP composites which adding APP directly. Comparing with APP, the destructiveness of EP@APP microcapsules toward tensile strength of PP reduces obviously. The addition of EP@APP microcapsules makes the apparent activation energy of PP composites increases from 100.8 kJ/mol to 127.5 kJ/mol, and changes the thermal degradation oxidation process of PP composites, and a stable protecting carbon layer is formed by the generated residual char. The research results show that EP@APP microcapsules can improve the flame retardancy of PP composites effectively.
2015, 32(3): 737-743.
doi: 10.13801/j.cnki.fhclxb.201503.004
Abstract:
In order to investigate the effects of multi-walled carbon nanotubes (MWNTs) on the cold crystallization kinetics and spherulitic morphologies of polylactide (PLA), PLA and nano-SiO2 modified MWNTs (SiO2-MWNTs) which was surface-coated with nano-SiO2 and grafted with silane couple agent were selected as matrix and modifying agent respectively to prepare SiO2-MWNTs/PLA composites via solution blended process. DSC, polarized optical microscope, Jeziorny model and Johnson-Mehl-Avrami model were used to investigate the non-isothermal cold crystallization kinetics and spherulitic morphologies of composites. The results indicate that SiO2-MWNTs can act as heterogeneous nucleating agent which decreases the cold crystallization temperature, increases the nucleation rate and the activation energy of crystal growth of SiO2-MWNTs/PLA composites effectively. Cold crystallization process of SiO2-MWNTs/PLA composites is mainly dominated by nucleation, and the addition of SiO2-MWNTs can improve crystallization rate and crystallinity of the composites simultaneously. The spherulitic size of PLA which is cold crystallized is smaller than that of melt cooling crystallized. The influence of SiO2-MWNTs content on cold crystallization spherulitic size is much smaller than that of it on melt cooling crystallization spherulitic size. The conclusions have guiding significance for optimizing the crystal structure and properties of PLA and preparing high-performance PLA composites.
In order to investigate the effects of multi-walled carbon nanotubes (MWNTs) on the cold crystallization kinetics and spherulitic morphologies of polylactide (PLA), PLA and nano-SiO2 modified MWNTs (SiO2-MWNTs) which was surface-coated with nano-SiO2 and grafted with silane couple agent were selected as matrix and modifying agent respectively to prepare SiO2-MWNTs/PLA composites via solution blended process. DSC, polarized optical microscope, Jeziorny model and Johnson-Mehl-Avrami model were used to investigate the non-isothermal cold crystallization kinetics and spherulitic morphologies of composites. The results indicate that SiO2-MWNTs can act as heterogeneous nucleating agent which decreases the cold crystallization temperature, increases the nucleation rate and the activation energy of crystal growth of SiO2-MWNTs/PLA composites effectively. Cold crystallization process of SiO2-MWNTs/PLA composites is mainly dominated by nucleation, and the addition of SiO2-MWNTs can improve crystallization rate and crystallinity of the composites simultaneously. The spherulitic size of PLA which is cold crystallized is smaller than that of melt cooling crystallized. The influence of SiO2-MWNTs content on cold crystallization spherulitic size is much smaller than that of it on melt cooling crystallization spherulitic size. The conclusions have guiding significance for optimizing the crystal structure and properties of PLA and preparing high-performance PLA composites.
2015, 32(3): 744-755.
doi: 10.13801/j.cnki.fhclxb.201503.008
Abstract:
Bipolar plate is an important part of proton exchange membrane fuel cell. The composite bipolar plate of graphite and polymer is the main direction of research. With phenolic resin as binder, natural flake graphite as conductive aggregate, carbon black as additive, the composite bipolar plate for proton exchange membrane fuel cell was prepared by using the molding and thermosetting two-step method. The effects of graphite species on conductive properties and flexural strength of graphite/phenolic resin composites were investigated and analyzed systematically. The results show that there will be the best performance when the natural flake graphite is used as conductive raw material. The electrical conductivity of the graphite/phenolic resin composites can be effectively improved if conductive carbon black is added. By adding 4wt% carbon fiber into composites, the flexural strength of the carbon fiber-graphite/phenolic resin composites is improved by 29%. The liquid phase oxidation processing of carbon fiber surface can effectively improve the bonding strength between the fibers and matrix. With the extending of processing time and elevating of processing temperature, electrical conductivity and flexural strength of carbon fiber-graphite/phenolic resin composites are greatly improved. The final curing temperature mainly affects the cross-linking degree of phenolic resins. With the increase of final curing temperature, the crosslinking degree of phenolic resin gets increased, and the electrical conductivity increases while flexural strength decreases to a certain extent.
Bipolar plate is an important part of proton exchange membrane fuel cell. The composite bipolar plate of graphite and polymer is the main direction of research. With phenolic resin as binder, natural flake graphite as conductive aggregate, carbon black as additive, the composite bipolar plate for proton exchange membrane fuel cell was prepared by using the molding and thermosetting two-step method. The effects of graphite species on conductive properties and flexural strength of graphite/phenolic resin composites were investigated and analyzed systematically. The results show that there will be the best performance when the natural flake graphite is used as conductive raw material. The electrical conductivity of the graphite/phenolic resin composites can be effectively improved if conductive carbon black is added. By adding 4wt% carbon fiber into composites, the flexural strength of the carbon fiber-graphite/phenolic resin composites is improved by 29%. The liquid phase oxidation processing of carbon fiber surface can effectively improve the bonding strength between the fibers and matrix. With the extending of processing time and elevating of processing temperature, electrical conductivity and flexural strength of carbon fiber-graphite/phenolic resin composites are greatly improved. The final curing temperature mainly affects the cross-linking degree of phenolic resins. With the increase of final curing temperature, the crosslinking degree of phenolic resin gets increased, and the electrical conductivity increases while flexural strength decreases to a certain extent.
2015, 32(3): 756-761.
doi: 10.13801/j.cnki.fhclxb.20140402.002
Abstract:
In order to prepare polymer piezoresistive materials with good flexibility, carbon black/polypropylene-poly(styrene-ethylene/butylene-styrene) (CB/PP-SEBS) composites were fabricated through melt blending method. The effects of CB content on the dielectric properties and piezoresistive properties of CB/PP-SEBS composites were investigated. The results indicate that the dielectric constant, dielectric loss and electrical conductivity of CB/PP-SEBS composites are all enhanced with the increasing of CB content. The electrical conductivity percolation of CB/PP-SEBS composites occurs when the CB content is 12.2wt%. Owing to the external force destruction of conductive network of CB, the electrical resistivity of CB/PP-SEBS composites increases with the strain increasing during the elastic deformation process of CB/PP-SEBS composites. The periodic piezoresistive measurement results indicate that the electrical resistivity of CB/PP-SEBS composites varies periodically with strain in the elastic deformation region. The results could give some experience for the preparation of polymer piezoresistive materials with stable resistance variation.
In order to prepare polymer piezoresistive materials with good flexibility, carbon black/polypropylene-poly(styrene-ethylene/butylene-styrene) (CB/PP-SEBS) composites were fabricated through melt blending method. The effects of CB content on the dielectric properties and piezoresistive properties of CB/PP-SEBS composites were investigated. The results indicate that the dielectric constant, dielectric loss and electrical conductivity of CB/PP-SEBS composites are all enhanced with the increasing of CB content. The electrical conductivity percolation of CB/PP-SEBS composites occurs when the CB content is 12.2wt%. Owing to the external force destruction of conductive network of CB, the electrical resistivity of CB/PP-SEBS composites increases with the strain increasing during the elastic deformation process of CB/PP-SEBS composites. The periodic piezoresistive measurement results indicate that the electrical resistivity of CB/PP-SEBS composites varies periodically with strain in the elastic deformation region. The results could give some experience for the preparation of polymer piezoresistive materials with stable resistance variation.
2015, 32(3): 762-768.
doi: 10.13801/j.cnki.fhclxb.20140917.003
Abstract:
To enhance the hardness of ZrO2 matrix composites, TiC0.7N0.3/ZrO2 composites were fabricated by hot pressing method, and the effects of TiC0.7N0.3 particle reinforcing phase on the phase composition, microstructure and mechanical properties of the composites were investigated. The results show that the addition of TiC0.7N0.3 has the effect to stabilize tetragonal ZrO2 (t-ZrO2), and can improve the t-ZrO2 content in TiC0.7N0.3/ZrO2 composites, thus improve the fracture toughness. With the hot pressing temperature and TiC0.7N0.3 content increasing, the hardness of composites increases. When hot pressing at 1 400 ℃, TiC0.7N0.3 decomposes partially, and the released N can react with reduced ZrO2 to form ZrN, which increases the hardness of composites. The relative density of 35wt% TiC0.7N0.3/ZrO2 composites after hot pressing at 1 400 ℃ exceeds 99.9% and Vickers hardness reaches 17 GPa. While the fracture toughness of composites is higher after hot pressing at 1 300 ℃, which is 6.48 MPa·m1/2. The conclusions provide references for microstructure controlling and improvement TiC0.7N0.3/ZrO2 composite properties.
To enhance the hardness of ZrO2 matrix composites, TiC0.7N0.3/ZrO2 composites were fabricated by hot pressing method, and the effects of TiC0.7N0.3 particle reinforcing phase on the phase composition, microstructure and mechanical properties of the composites were investigated. The results show that the addition of TiC0.7N0.3 has the effect to stabilize tetragonal ZrO2 (t-ZrO2), and can improve the t-ZrO2 content in TiC0.7N0.3/ZrO2 composites, thus improve the fracture toughness. With the hot pressing temperature and TiC0.7N0.3 content increasing, the hardness of composites increases. When hot pressing at 1 400 ℃, TiC0.7N0.3 decomposes partially, and the released N can react with reduced ZrO2 to form ZrN, which increases the hardness of composites. The relative density of 35wt% TiC0.7N0.3/ZrO2 composites after hot pressing at 1 400 ℃ exceeds 99.9% and Vickers hardness reaches 17 GPa. While the fracture toughness of composites is higher after hot pressing at 1 300 ℃, which is 6.48 MPa·m1/2. The conclusions provide references for microstructure controlling and improvement TiC0.7N0.3/ZrO2 composite properties.
2015, 32(3): 769-775.
doi: 10.13801/j.cnki.fhclxb.20141118.006
Abstract:
In order to prepare a new composite of water treatment adsorbent, modified bentonite was prepared under microwave radiation by using doped Al-TiO2 as modifier. The best condition of microwave radiation was investigated. The samples were characterized by EDS, SEM, FTIR, XRD, N2 adsorption-desorption, differential scanning calorimetry and thermal gravity analysis (DSC-TGA). The results show that the best condition of microwave radiation are microwave power 260 W and microwave time 8 min. The modifier enters into the interlayer of bentonite and Ti—O—Si bond is formed between the framework of bentonite in the modified bentonite. The interlayer spacing increases from 1.280 nm to 1.533 nm, the surface area increases from 39.66 m2·g-1 to 72.05 m2·g-1, the pore volume increases from 0.103 4 cm3·g-1 to 0.140 5 cm3·g-1, while the saturated adsorption capacity of methylene blue increases from 32.56 g/100 g to 57.96 g/100 g, and the thermal stability is evidently improved by modification.
In order to prepare a new composite of water treatment adsorbent, modified bentonite was prepared under microwave radiation by using doped Al-TiO2 as modifier. The best condition of microwave radiation was investigated. The samples were characterized by EDS, SEM, FTIR, XRD, N2 adsorption-desorption, differential scanning calorimetry and thermal gravity analysis (DSC-TGA). The results show that the best condition of microwave radiation are microwave power 260 W and microwave time 8 min. The modifier enters into the interlayer of bentonite and Ti—O—Si bond is formed between the framework of bentonite in the modified bentonite. The interlayer spacing increases from 1.280 nm to 1.533 nm, the surface area increases from 39.66 m2·g-1 to 72.05 m2·g-1, the pore volume increases from 0.103 4 cm3·g-1 to 0.140 5 cm3·g-1, while the saturated adsorption capacity of methylene blue increases from 32.56 g/100 g to 57.96 g/100 g, and the thermal stability is evidently improved by modification.
2015, 32(3): 776-781.
doi: 10.13801/j.cnki.fhclxb.20140620.001
Abstract:
Mechanical properties and toughening mechanisms of three ceramics, 99.5vol% Al2O3 (AD995) ceramic, ZrO2(15vol%)/Al2O3 ceramic and ZrO2(25vol%)/Al2O3 ceramic prepared by hot pressing sintering were investigated by experimental and theoretical research. Based on the micro-mechanics theory of composites, a micromechanical constitution model was developed to describe mechanical properties of ZrO2/Al2O3 considering phase transformation of ZrO2. The results show that the grain size of Al2O3 matrix decreases and densification is improved with addition of ZrO2. The failure of three ceramic specimens show characteristic of small deformation to brittle failure. The compression stress-strain curves show an approximately linear relationship. The fracture toughness of AD995 ceramic is 5.65 MPa·m1/2, while ZrO2(25vol%)/Al2O3 is 8.42 MPa·m1/2, approximately 50% improvement.With toughening phase ZrO2 content increasing, elastic modulus of ZrO2/Al2O3 decreases and fracture toughness increases, which are consistent with experimental results.
Mechanical properties and toughening mechanisms of three ceramics, 99.5vol% Al2O3 (AD995) ceramic, ZrO2(15vol%)/Al2O3 ceramic and ZrO2(25vol%)/Al2O3 ceramic prepared by hot pressing sintering were investigated by experimental and theoretical research. Based on the micro-mechanics theory of composites, a micromechanical constitution model was developed to describe mechanical properties of ZrO2/Al2O3 considering phase transformation of ZrO2. The results show that the grain size of Al2O3 matrix decreases and densification is improved with addition of ZrO2. The failure of three ceramic specimens show characteristic of small deformation to brittle failure. The compression stress-strain curves show an approximately linear relationship. The fracture toughness of AD995 ceramic is 5.65 MPa·m1/2, while ZrO2(25vol%)/Al2O3 is 8.42 MPa·m1/2, approximately 50% improvement.With toughening phase ZrO2 content increasing, elastic modulus of ZrO2/Al2O3 decreases and fracture toughness increases, which are consistent with experimental results.
2015, 32(3): 782-788.
doi: 10.13801/j.cnki.fhclxb.20141010.002
Abstract:
Oil well cement composites are apt to embrittlement crack downhole, and that will lead to the failure of interlaminar packers of oil well, then effect the exploitation of oil well. In order to solve this problem, it is necessary to reduce the brittleness and increase the toughness of oil well cement composites. Firstly, the dispersancy effectiveness of methylcellulose and carboxymethylcellulose toward carbon fibers were investigated. Then, the effects of carbon fibers on the compressive strength, flexible strength and splitting tensile strength of oil well cement composites were investigated, and the uniaxial and triaxial stress-strain curves of cement composites were measured under the simulated downhole environment. Finally, the microtopographies of carbon fiber reinforced oil well cement composites were observed by scanning electron microscope and the toughening mechanism of carbon fibers toward cement composites was discussed. The results demonstrate that 0.2wt% carboxymethylcellulose solution can disperse carbon fibers effectively. After cured for 28 d, the compressive strength, flexible strength and splitting tensile strength of 0.3wt% carbon fiber reinforced cement composites increase by 8.6%, 31.5% and 52.4%, respectively, under the condition of triaxial direct loading, the elastic modulus reduces by 49.5% comparing with the pure cement composites. The dispersed carbon fibers distribute in cement composites disorderly, form the three-dimensional network structures and toughing cement composites by the energy-dissipation effects of bridging, peel and pulling-out. The conclusions provide theoretical reference to solve the problem of brittleness of oil well cement composites.
Oil well cement composites are apt to embrittlement crack downhole, and that will lead to the failure of interlaminar packers of oil well, then effect the exploitation of oil well. In order to solve this problem, it is necessary to reduce the brittleness and increase the toughness of oil well cement composites. Firstly, the dispersancy effectiveness of methylcellulose and carboxymethylcellulose toward carbon fibers were investigated. Then, the effects of carbon fibers on the compressive strength, flexible strength and splitting tensile strength of oil well cement composites were investigated, and the uniaxial and triaxial stress-strain curves of cement composites were measured under the simulated downhole environment. Finally, the microtopographies of carbon fiber reinforced oil well cement composites were observed by scanning electron microscope and the toughening mechanism of carbon fibers toward cement composites was discussed. The results demonstrate that 0.2wt% carboxymethylcellulose solution can disperse carbon fibers effectively. After cured for 28 d, the compressive strength, flexible strength and splitting tensile strength of 0.3wt% carbon fiber reinforced cement composites increase by 8.6%, 31.5% and 52.4%, respectively, under the condition of triaxial direct loading, the elastic modulus reduces by 49.5% comparing with the pure cement composites. The dispersed carbon fibers distribute in cement composites disorderly, form the three-dimensional network structures and toughing cement composites by the energy-dissipation effects of bridging, peel and pulling-out. The conclusions provide theoretical reference to solve the problem of brittleness of oil well cement composites.
2015, 32(3): 789-796.
doi: 10.13801/j.cnki.fhclxb.20140725.001
Abstract:
In filament wound thick-walled cylindrical pipe or vessel, the winding tension makes stress state of fiber layer change, which forms a non-uniform structure through thickness. According to the analysis of stress state and constitutive relation of fiber bundle in winding process, the relationship between the fiber volume content and the stress state was obtained. Based on the orthotropic constitutive relations and discrete superposition method of a double layered cylinder model, a calculation method to determine the residual tension for given winding tension in filament wound thick-walled cylindrical structure was established, where the distribution of fiber volume content through wall thickness was calculated for a constant winding tension. Using Tsai-Wu failure criteria, the strength of filament layer was investigated in thick-walled cylindrical structure with non-uniform fiber volume content. It is found that winding process makes the fiber volume content and strength of inner layer higher than those of the outer layer, where the influence of non-unform material property should be considered in analyzing and designing of filament wound thick-walled cylindrical structure. Uniform distribution of strength through thickness can be achieved by design of variational winding tension.
In filament wound thick-walled cylindrical pipe or vessel, the winding tension makes stress state of fiber layer change, which forms a non-uniform structure through thickness. According to the analysis of stress state and constitutive relation of fiber bundle in winding process, the relationship between the fiber volume content and the stress state was obtained. Based on the orthotropic constitutive relations and discrete superposition method of a double layered cylinder model, a calculation method to determine the residual tension for given winding tension in filament wound thick-walled cylindrical structure was established, where the distribution of fiber volume content through wall thickness was calculated for a constant winding tension. Using Tsai-Wu failure criteria, the strength of filament layer was investigated in thick-walled cylindrical structure with non-uniform fiber volume content. It is found that winding process makes the fiber volume content and strength of inner layer higher than those of the outer layer, where the influence of non-unform material property should be considered in analyzing and designing of filament wound thick-walled cylindrical structure. Uniform distribution of strength through thickness can be achieved by design of variational winding tension.
2015, 32(3): 797-804.
doi: 10.13801/j.cnki.fhclxb.20140918.003
Abstract:
This dissertation focus on the optimization method for composite stiffened panel structure. Due to the high number and different type (discrete and continuous) of design variable, hierarchy optimization is introduced in this method.The mass of structure was fixed to be constant, while the locations of reinforced beams, cross-sectional dimensions, number of piles and stacking sequences were optimized to improve the buckling performance of overall structure. Artificial plies were introduced so that the optimization of the other variables can be done without considering the stacking sequence. Then design of factorial experiment was conducted to define the primary and secondary variables that influence the structure buckling load in the remaining variables. Level 1 and Level 2 optimizations were conducted independently to obtain the optimums for two types of design variables. For computing efficiency improvement, according to the type of variables and value range in the process of optimization, radial basis agent model was set up for some variables.Genetic algorithm was implemented in Level 3 optimization to search for the best stacking sequence.Optimization results show that the resultant buckling load is 3.21 times higher than that of the original one.
This dissertation focus on the optimization method for composite stiffened panel structure. Due to the high number and different type (discrete and continuous) of design variable, hierarchy optimization is introduced in this method.The mass of structure was fixed to be constant, while the locations of reinforced beams, cross-sectional dimensions, number of piles and stacking sequences were optimized to improve the buckling performance of overall structure. Artificial plies were introduced so that the optimization of the other variables can be done without considering the stacking sequence. Then design of factorial experiment was conducted to define the primary and secondary variables that influence the structure buckling load in the remaining variables. Level 1 and Level 2 optimizations were conducted independently to obtain the optimums for two types of design variables. For computing efficiency improvement, according to the type of variables and value range in the process of optimization, radial basis agent model was set up for some variables.Genetic algorithm was implemented in Level 3 optimization to search for the best stacking sequence.Optimization results show that the resultant buckling load is 3.21 times higher than that of the original one.
2015, 32(3): 805-814.
doi: 10.13801/j.cnki.fhclxb.20141021.005
Abstract:
Test and numerical simulations were adopted to study buckling properties of 2D textile composite curved panels. In order to study the influence of curvature radius, length and arc length on buckling properties of 2D textile composite curved panels, four groups of specimens with different curvature radius, length and arc length have been designed to conduct buckling test. Comparing the buckling load and buckling mode of four different groups of curved panels, the influences of different geometric parameters on buckling properties have been acquired. The buckling load rises by 26.85% as the curvature radius decreases 25%, which exert the most important influence. As with the 26.32% increase of arc length, the buckling load per area keeps equal generally and buckling load increases 23.783%. The buckling load increases by 24.41%, while the length decreases by 42.25%. As to buckling mode, length affects most, arc length ranks second, and curvature radius follows. A standard test referring to ASTM was designed to acquire material stiffness coefficient. As the arc sides of curved plates were quite constrained as a result of fixing and friction in aerocraft structure and test, buckling finite element analysis under two types of boundary conditions, with and without constraints were conducted. Through the comparison of test and finite element result, simulated load under two boundary conditions can determine the scope of the test buckling load.
Test and numerical simulations were adopted to study buckling properties of 2D textile composite curved panels. In order to study the influence of curvature radius, length and arc length on buckling properties of 2D textile composite curved panels, four groups of specimens with different curvature radius, length and arc length have been designed to conduct buckling test. Comparing the buckling load and buckling mode of four different groups of curved panels, the influences of different geometric parameters on buckling properties have been acquired. The buckling load rises by 26.85% as the curvature radius decreases 25%, which exert the most important influence. As with the 26.32% increase of arc length, the buckling load per area keeps equal generally and buckling load increases 23.783%. The buckling load increases by 24.41%, while the length decreases by 42.25%. As to buckling mode, length affects most, arc length ranks second, and curvature radius follows. A standard test referring to ASTM was designed to acquire material stiffness coefficient. As the arc sides of curved plates were quite constrained as a result of fixing and friction in aerocraft structure and test, buckling finite element analysis under two types of boundary conditions, with and without constraints were conducted. Through the comparison of test and finite element result, simulated load under two boundary conditions can determine the scope of the test buckling load.
Trapezoidal cellular support structure applied to flexible telescopic sandwich skin of morphing wing
2015, 32(3): 815-822.
doi: 10.13801/j.cnki.fhclxb.20140917.001
Abstract:
An in-plane corrugated trapezoidal cellular supporting structure applied to flexible telescopic sandwich skin of morphing wing was proposed. By analyzing the in-plane scaling properties of the supporting structure, the relationship between the in-plane transverse dimensionless equivalent elastic modulus and the three parameters (shape coefficient k, width coefficient t and height coefficient h) was obtained.The equivalent elastic modulus decreases with the increase of k or h, and increases with the increase of t. Finite element analysis were carried out with ANSYS software, and the in-palne mechanical characteristics were demonstrated through experiment. The results show that the theoretical analysis and finite element analysis was basically consistent with the experimental results. By selecting appropriate structure parameters, the in-plane transverse equivalent elastic modulus can be as low as 10-4 of the raw material, smaller than the accordion cellular supporting structure with the same parameters, which means that the trapezoidal cellular has stronger ability of transformation. Compared with traditional support structures, this structure may reduce the driving force required and energy consumed during morphing, and improve the morphing efficiency of the flexible skin.
An in-plane corrugated trapezoidal cellular supporting structure applied to flexible telescopic sandwich skin of morphing wing was proposed. By analyzing the in-plane scaling properties of the supporting structure, the relationship between the in-plane transverse dimensionless equivalent elastic modulus and the three parameters (shape coefficient k, width coefficient t and height coefficient h) was obtained.The equivalent elastic modulus decreases with the increase of k or h, and increases with the increase of t. Finite element analysis were carried out with ANSYS software, and the in-palne mechanical characteristics were demonstrated through experiment. The results show that the theoretical analysis and finite element analysis was basically consistent with the experimental results. By selecting appropriate structure parameters, the in-plane transverse equivalent elastic modulus can be as low as 10-4 of the raw material, smaller than the accordion cellular supporting structure with the same parameters, which means that the trapezoidal cellular has stronger ability of transformation. Compared with traditional support structures, this structure may reduce the driving force required and energy consumed during morphing, and improve the morphing efficiency of the flexible skin.
2015, 32(3): 823-830.
doi: 10.13801/j.cnki.fhclxb.20150609.001
Abstract:
Considering the present situation that the foundation data for a new T800 composite system adopted in civil aircraft industries are extremely scarce, a progressive damage method (PDA) substituting the tests can reduce the research period and cost significantly. In conjunction with the progressive damage method and the engineering algorithm, a numerical strategy for the strength prediction of multi-bolt joints is presented. In this strategy, the progressive damage analyses of the samples for determine stress concentration relief factors (SCRFs) were carried out to substitute the physical tests. And the strength envelope was constructed. In order to verify the feasibility of the proposed numerical strategy, a bypass-load modified strength envelope method was adopted. The progressive damage analyses of typical ply for stress concentration relief factors were performed and the predictive value of strength was obtained to calculate the stress concentration relief factors. Modified strength envelope of bolted joints bypass-load for typical ply composite was plotted. The failure load of bolted joints was predicted and compared with test results. It can be found that the strength envelope and the ultimate failure loads as well as failure modes of multi-bolt joints based on the numerical strategy agree well with the test results, which provide evidence for the feasibility of the proposed numerical strategy.
Considering the present situation that the foundation data for a new T800 composite system adopted in civil aircraft industries are extremely scarce, a progressive damage method (PDA) substituting the tests can reduce the research period and cost significantly. In conjunction with the progressive damage method and the engineering algorithm, a numerical strategy for the strength prediction of multi-bolt joints is presented. In this strategy, the progressive damage analyses of the samples for determine stress concentration relief factors (SCRFs) were carried out to substitute the physical tests. And the strength envelope was constructed. In order to verify the feasibility of the proposed numerical strategy, a bypass-load modified strength envelope method was adopted. The progressive damage analyses of typical ply for stress concentration relief factors were performed and the predictive value of strength was obtained to calculate the stress concentration relief factors. Modified strength envelope of bolted joints bypass-load for typical ply composite was plotted. The failure load of bolted joints was predicted and compared with test results. It can be found that the strength envelope and the ultimate failure loads as well as failure modes of multi-bolt joints based on the numerical strategy agree well with the test results, which provide evidence for the feasibility of the proposed numerical strategy.
2015, 32(3): 831-839.
doi: 10.13801/j.cnki.fhdxb.20150609.003
Abstract:
The theoretical analysis of intimate contact and autohesion in molding process was carried out based on the research of composite winding process. The key process parameters affecting the quality of winding product, such as winding temperature, pressure and tension, were proposed. Based on Box-Behnken Design (BBD) theory of response surface methodology, the regression model of process parameters coupling on shear strength was established to optimize the interlaminar shear strength (ILSS). The reliability and effectiveness of regression model were verified through the test analysis such as residual, analysis of variance (ANVOA) and predicted versus actual. Furthermore, the optimal process parameters of winding process were obtained. Results illustrate that the winding products employing the optimum parameters bond in the highest strength with the interlaminar shear strength of 22.9 MPa.
The theoretical analysis of intimate contact and autohesion in molding process was carried out based on the research of composite winding process. The key process parameters affecting the quality of winding product, such as winding temperature, pressure and tension, were proposed. Based on Box-Behnken Design (BBD) theory of response surface methodology, the regression model of process parameters coupling on shear strength was established to optimize the interlaminar shear strength (ILSS). The reliability and effectiveness of regression model were verified through the test analysis such as residual, analysis of variance (ANVOA) and predicted versus actual. Furthermore, the optimal process parameters of winding process were obtained. Results illustrate that the winding products employing the optimum parameters bond in the highest strength with the interlaminar shear strength of 22.9 MPa.
2015, 32(3): 840-847.
doi: 10.13801/j.cnki.fhclxb.201503.009
Abstract:
Mathematical models that objectify both resin meso flow between adjacent yarns themselves and micro flow in yarns were established for textile preform unit cell. Based on the principle of minimum potential energy, geometric model of unit cell in slack state was built. Meanwhile, the deformation of unit cells influenced by mold compression was analyzed, and the geometric models of different compressed states were established. According to the mathematical model solution of resin flowing in unit cell, fields of flow velocity and pressure were obtained. Forecasts of the preform permeability were then conducted. Permeability of a group of unit cell was predicted.The effects of compression deformation of preform on permeability were studied. Results show that with the increase of deformation amount, the permeability gradually decreases. Through the experimental results and data analysis, the correctness of models and the forecast method were verified.
Mathematical models that objectify both resin meso flow between adjacent yarns themselves and micro flow in yarns were established for textile preform unit cell. Based on the principle of minimum potential energy, geometric model of unit cell in slack state was built. Meanwhile, the deformation of unit cells influenced by mold compression was analyzed, and the geometric models of different compressed states were established. According to the mathematical model solution of resin flowing in unit cell, fields of flow velocity and pressure were obtained. Forecasts of the preform permeability were then conducted. Permeability of a group of unit cell was predicted.The effects of compression deformation of preform on permeability were studied. Results show that with the increase of deformation amount, the permeability gradually decreases. Through the experimental results and data analysis, the correctness of models and the forecast method were verified.
2015, 32(3): 848-855.
doi: 10.13801/j.cnki.fhclxb.20140916.001
Abstract:
In order to design and develop lightweight bionic composites, the microstructure of Cybister's elytra cross section was analyzed. It was found that the inside hollow structure of Cybister's elytra is non-connected spherical lumens. Inspired by the unique structures of Cybister's elytra, a lightweight bionic structure was designed. Some spherical lumens were distributed by regular hexagon form in the structure. In order to investigate the mechanical characteristics of the bionic structure, two kinds of common hollow structures were brought in. By using the finite element analysis software ANSYS, the compression, tension and bending properties of the bionic structure and the other two kinds of common hollow structures were finite element analyzed and comparatively studied. The result shows that the bionic structure has much stronger anti-pressure ability and tensile resistance, as well as far higher yield strength, than the other two kinds of common hollow structures, the mechanical properties are excellent. This bionic structure could provide bionics references for developing novel biomimetic composites in the aspect of material structures.
In order to design and develop lightweight bionic composites, the microstructure of Cybister's elytra cross section was analyzed. It was found that the inside hollow structure of Cybister's elytra is non-connected spherical lumens. Inspired by the unique structures of Cybister's elytra, a lightweight bionic structure was designed. Some spherical lumens were distributed by regular hexagon form in the structure. In order to investigate the mechanical characteristics of the bionic structure, two kinds of common hollow structures were brought in. By using the finite element analysis software ANSYS, the compression, tension and bending properties of the bionic structure and the other two kinds of common hollow structures were finite element analyzed and comparatively studied. The result shows that the bionic structure has much stronger anti-pressure ability and tensile resistance, as well as far higher yield strength, than the other two kinds of common hollow structures, the mechanical properties are excellent. This bionic structure could provide bionics references for developing novel biomimetic composites in the aspect of material structures.
2015, 32(3): 856-863.
doi: 10.13801/j.cnki.fhclxb.20140918.002
Abstract:
In order to develop novel lightweight structure, based on the observation of the cross-sectional microstructure of beetle's elytra, the morphological features of beetle's elytra were analyzed, hereby a bio-inspired lightweight structure made by carbon fiber/epoxy composites was designed. The quasi-static compression test was carried out on bio-inspired lightweight structure, and finite element method was used at the same time to analyse the compressive ability of bio-inspired lightweight structure. The analytical results and the test results were compared, which proved the correctness and effectiveness of the finite element analysis. In addition, the optimum design of parameters of the bio-inspired lightweight structure was conducted by response surface method. The results reveal the maximum bearing capacity of bio-inspired lightweight structure under compressive load reaches 18 455.00 N, which increased by 26.4% compared with the structure before optimization, and its specific compressive strength reaches 47.43 MPa/(g·cm-3), the optimal effect is remarkable.
In order to develop novel lightweight structure, based on the observation of the cross-sectional microstructure of beetle's elytra, the morphological features of beetle's elytra were analyzed, hereby a bio-inspired lightweight structure made by carbon fiber/epoxy composites was designed. The quasi-static compression test was carried out on bio-inspired lightweight structure, and finite element method was used at the same time to analyse the compressive ability of bio-inspired lightweight structure. The analytical results and the test results were compared, which proved the correctness and effectiveness of the finite element analysis. In addition, the optimum design of parameters of the bio-inspired lightweight structure was conducted by response surface method. The results reveal the maximum bearing capacity of bio-inspired lightweight structure under compressive load reaches 18 455.00 N, which increased by 26.4% compared with the structure before optimization, and its specific compressive strength reaches 47.43 MPa/(g·cm-3), the optimal effect is remarkable.
2015, 32(3): 864-873.
doi: 10.13801/j.cnki.fhclxb.20140925.001
Abstract:
Macroscopic strength criteria for composites were summarized and reviewed. The prediction abilities of five of the most representative strength criteria were analyzed comprehensively. Firstly, the theoretical failure envelopes of AS4/3501-6 material under different plane stress states were established based on each strength criterion, which were used to show the physical significance of each strength criterion. Then, considering the dispersity of strength, probabilistic failure envelops and strength scattering zones for four kinds of materials were set up based on each of the strength criterion with the Monte-Carlo method. Finally, several groups of experiment data were adopted to evaluate the prediction abilities of each strength criterion objectively. The evaluation results show that prediction results of every strength criterion are impossible to match all of the test results perfectly. Compared to the Max-Stress criterion, Hashin criterion and Tsai-Wu criterion, the prediction abilities of Puck criterion and LaRC03 criterion are relatively better, and have more reasonable explanation for damage mechanisms of composites.
Macroscopic strength criteria for composites were summarized and reviewed. The prediction abilities of five of the most representative strength criteria were analyzed comprehensively. Firstly, the theoretical failure envelopes of AS4/3501-6 material under different plane stress states were established based on each strength criterion, which were used to show the physical significance of each strength criterion. Then, considering the dispersity of strength, probabilistic failure envelops and strength scattering zones for four kinds of materials were set up based on each of the strength criterion with the Monte-Carlo method. Finally, several groups of experiment data were adopted to evaluate the prediction abilities of each strength criterion objectively. The evaluation results show that prediction results of every strength criterion are impossible to match all of the test results perfectly. Compared to the Max-Stress criterion, Hashin criterion and Tsai-Wu criterion, the prediction abilities of Puck criterion and LaRC03 criterion are relatively better, and have more reasonable explanation for damage mechanisms of composites.
2015, 32(3): 874-880.
doi: 10.13801/j.cnki.fhclxb.20141028.004
Abstract:
In order to investigate the curing deformation process of resin matrix composite curved structure, first, the evolutions of physical properties such as density, modulus, thermal expansion coefficient, specific heat capacity and thermal conductivity et al during the curing process of carbon fiber reinforced resin matrix composites were analyzed, and those evolutions were introduced into the numerical simulation. Second, the new approach of constructing the curvilinear coordinate system by streamline equation of steady flow was proposed for the composite complex curved structure. Third, the distribution of internal temperature, curing degree and internal stresses, and evolution situations of material physical properties along with curing degree during the curing process of the skin plate of a light aircraft wing were calculated by finite-element method based on the curvilinear coordinate system constructed. Finally, the deformations of the structure caused by the uneven distributions of internal temperature field and cure degree field, anisotropy of thermal expansion coefficient and volumetric shrinkage of resin result from curing were calculated. The results show that the numerical simulation of curing process will be more reasonable and the simulation results will be more accurate when the evolutions of material physical properties are adopted, and the curvilinear coordinate system constructed by streamline equation of steady flow is applicable to the finite element analysis of composite curved structure.The conclusions have instruction significance to the research of curing deformation process of resin matrix composites and the establishment of three dimensional solid model of composite complex curved structure which is anisotropic.
In order to investigate the curing deformation process of resin matrix composite curved structure, first, the evolutions of physical properties such as density, modulus, thermal expansion coefficient, specific heat capacity and thermal conductivity et al during the curing process of carbon fiber reinforced resin matrix composites were analyzed, and those evolutions were introduced into the numerical simulation. Second, the new approach of constructing the curvilinear coordinate system by streamline equation of steady flow was proposed for the composite complex curved structure. Third, the distribution of internal temperature, curing degree and internal stresses, and evolution situations of material physical properties along with curing degree during the curing process of the skin plate of a light aircraft wing were calculated by finite-element method based on the curvilinear coordinate system constructed. Finally, the deformations of the structure caused by the uneven distributions of internal temperature field and cure degree field, anisotropy of thermal expansion coefficient and volumetric shrinkage of resin result from curing were calculated. The results show that the numerical simulation of curing process will be more reasonable and the simulation results will be more accurate when the evolutions of material physical properties are adopted, and the curvilinear coordinate system constructed by streamline equation of steady flow is applicable to the finite element analysis of composite curved structure.The conclusions have instruction significance to the research of curing deformation process of resin matrix composites and the establishment of three dimensional solid model of composite complex curved structure which is anisotropic.
Application of composite material 3D damage model in strength prediction of large opening structures
2015, 32(3): 881-887.
doi: 10.13801/j.cnki.fhclxb.20140919.001
Abstract:
In order to predict the strength and damage revolution situation of large opening composite structures, the applied research of the three kinds of different composite material 3D damage degradation models (sudden degradation model, progressive damage model and continuum damage model) used in the prediction of the strength of large opening composite structures were conducted. In-plane pure shear test of large opening composite structure with frame reinforcer was carried out, and the three kinds of damage degradation models were used to numerically simulate the calculation examples of test specimen and relative reference. The comparison between numerical simulation results and experiment results shows that each of the three damage degradation models can predict the ultimate strength of large opening composite structures relatively accurately. Continuum damage model has the highest accuracy, best universality and lowest mesh dependency comparing to other models. The research results could provide theoretical guidance for the investigation of mechanical properties of large opening composite structures.
In order to predict the strength and damage revolution situation of large opening composite structures, the applied research of the three kinds of different composite material 3D damage degradation models (sudden degradation model, progressive damage model and continuum damage model) used in the prediction of the strength of large opening composite structures were conducted. In-plane pure shear test of large opening composite structure with frame reinforcer was carried out, and the three kinds of damage degradation models were used to numerically simulate the calculation examples of test specimen and relative reference. The comparison between numerical simulation results and experiment results shows that each of the three damage degradation models can predict the ultimate strength of large opening composite structures relatively accurately. Continuum damage model has the highest accuracy, best universality and lowest mesh dependency comparing to other models. The research results could provide theoretical guidance for the investigation of mechanical properties of large opening composite structures.
2015, 32(3): 888-895.
doi: 10.13801/j.cnki.fhclxb.20150303.001
Abstract:
The crack in strip is often used in fracture mechanics as research model. There is a magnetoelectroelastic elastomer which contains infinite collinear cracks, when crack surface on the left side near crack tip is under the electromagnetic force load and anti-plane shear stress along the crack surface, elastomer tends to produce dynamic fracture. By using arch transform formula of complex variable function method, the analytic solutions of the dynamic stress intensity factors and the mechanical strain energy release rate were presented with the boundary conditions that the surface of the crack was electrically and magnetically impermeable. When the movement velocity tends to zero, the analytic solutions is degraded to stationary state solution. Through numerical example, the fracture mechanism was analyzed, the influence of the geometry size of strip and crack, external force, electric field and magnetic field on energy release rate respectively under static state were discussed to help the design and manufacture of related devices.
The crack in strip is often used in fracture mechanics as research model. There is a magnetoelectroelastic elastomer which contains infinite collinear cracks, when crack surface on the left side near crack tip is under the electromagnetic force load and anti-plane shear stress along the crack surface, elastomer tends to produce dynamic fracture. By using arch transform formula of complex variable function method, the analytic solutions of the dynamic stress intensity factors and the mechanical strain energy release rate were presented with the boundary conditions that the surface of the crack was electrically and magnetically impermeable. When the movement velocity tends to zero, the analytic solutions is degraded to stationary state solution. Through numerical example, the fracture mechanism was analyzed, the influence of the geometry size of strip and crack, external force, electric field and magnetic field on energy release rate respectively under static state were discussed to help the design and manufacture of related devices.
2015, 32(3): 896-901.
doi: 10.13801/j.cnki.fhclxb.20140702.001
Abstract:
According to the topological optimization idea, an artificial material hypothesis was proposed, the topological optimization mathematical model of damping materials distribution was constructed. Based on the optimization distribution of damping material, the vibration and acoustic radiation were reduced, in which the mass of the damping material was defined as a constrain condition. By introducing genetic algorithm, the optimization problems were solved, and the structural material conversion between damping material and artificial material was carried out, and the topology optimization of damping material distribution was achieved. Numerical results show that the proposed optimization approach for reducing vibration and acoustic radiation is effective and feasible. The results turn out to have good practicable value in engineering. An feasible and effective method to solve the problem for damping material distribution was provided.
According to the topological optimization idea, an artificial material hypothesis was proposed, the topological optimization mathematical model of damping materials distribution was constructed. Based on the optimization distribution of damping material, the vibration and acoustic radiation were reduced, in which the mass of the damping material was defined as a constrain condition. By introducing genetic algorithm, the optimization problems were solved, and the structural material conversion between damping material and artificial material was carried out, and the topology optimization of damping material distribution was achieved. Numerical results show that the proposed optimization approach for reducing vibration and acoustic radiation is effective and feasible. The results turn out to have good practicable value in engineering. An feasible and effective method to solve the problem for damping material distribution was provided.
2015, 32(3): 902-910.
doi: 10.13801/j.cnki.fhclxb.201503.002
Abstract:
An improved adaptive simulated annealing(SA) algorithm, which combined with the feasibility based rule and direct search simulated annealing, was proposed to optimize the frequency characteristics of composite laminates. The optimization goals of laminates are fundamental frequency, frequency band gap and laminate thickness of band gap constraint. The discrete design variables include fiber orientation angles and the layer number. A new point generation mechanism with the dynamic variation search radius improves the drawback of the direction simulated annealing (DSA) algorithm easy to fall into local minima. Introducing the feasibility based rule into SA enhances the efficiency and simplicity of solving constrained problem. Accounting for bending-twisting coupling effects, the Ritz method was employed to calculate the laminate frequency response. Three types of examples of design symmetrically composite laminates with various layer numbers, angle increment and aspect ratios were conducted. Numerical results indicate that the present improved simulated annealing algorithm can effectively solve laminates frequency optimization and provide with more or better global optimum solutions for the stacking sequence.
An improved adaptive simulated annealing(SA) algorithm, which combined with the feasibility based rule and direct search simulated annealing, was proposed to optimize the frequency characteristics of composite laminates. The optimization goals of laminates are fundamental frequency, frequency band gap and laminate thickness of band gap constraint. The discrete design variables include fiber orientation angles and the layer number. A new point generation mechanism with the dynamic variation search radius improves the drawback of the direction simulated annealing (DSA) algorithm easy to fall into local minima. Introducing the feasibility based rule into SA enhances the efficiency and simplicity of solving constrained problem. Accounting for bending-twisting coupling effects, the Ritz method was employed to calculate the laminate frequency response. Three types of examples of design symmetrically composite laminates with various layer numbers, angle increment and aspect ratios were conducted. Numerical results indicate that the present improved simulated annealing algorithm can effectively solve laminates frequency optimization and provide with more or better global optimum solutions for the stacking sequence.
2015, 32(3): 911-917.
doi: 10.13801/j.cnki.fhclxb.201503.003
Abstract:
In order to deal with the problems that TiO2 nanoparticles were difficult to be separated and the supported catalysts were difficult to be recycled, first, TiO2 and sodium alginate were blended together to prepare the casting solution, and then outspread on a glass plate. TiO2-calcium alginate (T-CA) composite films were prepared by cross-linking with calcium ion. Second, the T-CA composite films were characterized by SEM and XRD. The photocatalytic degradation of T-CA composite films for dyes was also investigated. Finally, T-CA composite films were taken out from degradation liquid of dyes, and soaked in sodium citrate aqueous solution. The binding force of citrate towards calcium ion was stronger, thus made the alginate hydrogel dissolved. After centrifugal separation of TiO2 nanoparticles, cleaning and drying, the recycled TiO2 was obtained. SEM, TEM, FTIR and XRD were used to characterize the recycled TiO2. The results show that the degradation ratio of T-CA composite films for methyl orange reaches 82.37%. The recycled TiO2 are almost exactly the same as the original TiO2, which can be used again and the catalytic ability almost constant. So the method is an environmental-friendly, convenient and efficient method for recycling TiO2 nanoparticle from supporters.
In order to deal with the problems that TiO2 nanoparticles were difficult to be separated and the supported catalysts were difficult to be recycled, first, TiO2 and sodium alginate were blended together to prepare the casting solution, and then outspread on a glass plate. TiO2-calcium alginate (T-CA) composite films were prepared by cross-linking with calcium ion. Second, the T-CA composite films were characterized by SEM and XRD. The photocatalytic degradation of T-CA composite films for dyes was also investigated. Finally, T-CA composite films were taken out from degradation liquid of dyes, and soaked in sodium citrate aqueous solution. The binding force of citrate towards calcium ion was stronger, thus made the alginate hydrogel dissolved. After centrifugal separation of TiO2 nanoparticles, cleaning and drying, the recycled TiO2 was obtained. SEM, TEM, FTIR and XRD were used to characterize the recycled TiO2. The results show that the degradation ratio of T-CA composite films for methyl orange reaches 82.37%. The recycled TiO2 are almost exactly the same as the original TiO2, which can be used again and the catalytic ability almost constant. So the method is an environmental-friendly, convenient and efficient method for recycling TiO2 nanoparticle from supporters.
2015, 32(3): 918-923.
doi: 10.13801/j.cnki.fhclxb.20140917.002
Abstract:
In order to improve the visible-light photocatalytic property of TiO2, micrometer polystyrene microspheres were used as template, tetrabutyl titanate was used as precursor, and triethylamine was used as nitrogen source, electrostatic adsorption self-assembly method was applied to prepare the nitrogen-doped TiO2 hollow composite microspheres with good spherical morphologies whose particle size was 1.20 μm and shell thickness was about 30 nm. The structure and photocatalytic properties were investigated with SEM, XPS, XRD and ultraviolet-visible spectrophotometer. The results show that the entrance of nitrogen into the TiO2 lattice replaces parts of O and changes the chemical states of Ti and O in the lattice, but has no obvious effect on the crystal structure of TiO2. The band gap of TiO2 hollow composite microspheres after nitrogen-doping decreases, nitrogen-doped TiO2 hollow composite microspheres not only have stronger light absorption ability in ultraviolet region, but also have stronger light response in visible region, the photocatalytic degradation rate of methyl orange is enhanced obviously compared with Degussa P25 nanometer TiO2. The conclusion has theoretical guiding significance for the application of TiO2 in photocatalysis research.
In order to improve the visible-light photocatalytic property of TiO2, micrometer polystyrene microspheres were used as template, tetrabutyl titanate was used as precursor, and triethylamine was used as nitrogen source, electrostatic adsorption self-assembly method was applied to prepare the nitrogen-doped TiO2 hollow composite microspheres with good spherical morphologies whose particle size was 1.20 μm and shell thickness was about 30 nm. The structure and photocatalytic properties were investigated with SEM, XPS, XRD and ultraviolet-visible spectrophotometer. The results show that the entrance of nitrogen into the TiO2 lattice replaces parts of O and changes the chemical states of Ti and O in the lattice, but has no obvious effect on the crystal structure of TiO2. The band gap of TiO2 hollow composite microspheres after nitrogen-doping decreases, nitrogen-doped TiO2 hollow composite microspheres not only have stronger light absorption ability in ultraviolet region, but also have stronger light response in visible region, the photocatalytic degradation rate of methyl orange is enhanced obviously compared with Degussa P25 nanometer TiO2. The conclusion has theoretical guiding significance for the application of TiO2 in photocatalysis research.
