2007 Vol. 24, No. 3
2007, 24(3): 1-6.
Abstract:
The center-cracked aluminum alloy plates were one-sidedly bonded with unidirectional carbon fiber/ epoxycomposite patches by the vacuum-bagging process. The tensile st rength of the bonded plate was measured , the crackpropagation , the interface disbond between the patch and the plate , and the residual tensile st rength of the bondedplates were also investigated. The result s show that both the tensile st rength and the stiffness of the center-crackedplates bonded with composite patches increase significantly. The crack propagation rate of the bonded plate is smaller than that of the cracked plate , and the fatigue life of the bonded plate is longer than that of the cracked plate.The tensile st rength and the fatigue life of the bonded plates are 364. 74 MPa and 77546 cycles , respectively , whilethose of the cracked plates are 311. 48 MPa and 32217 cycles , respectively. An elliptical debond area between thecomposite patches and cracked plate is found during the tension-tension fatigue testing. The interface debond area increases with increasing the fatigue cyclic number , and the magnitude of the increase is related with the fatigue cyclicnumber.
The center-cracked aluminum alloy plates were one-sidedly bonded with unidirectional carbon fiber/ epoxycomposite patches by the vacuum-bagging process. The tensile st rength of the bonded plate was measured , the crackpropagation , the interface disbond between the patch and the plate , and the residual tensile st rength of the bondedplates were also investigated. The result s show that both the tensile st rength and the stiffness of the center-crackedplates bonded with composite patches increase significantly. The crack propagation rate of the bonded plate is smaller than that of the cracked plate , and the fatigue life of the bonded plate is longer than that of the cracked plate.The tensile st rength and the fatigue life of the bonded plates are 364. 74 MPa and 77546 cycles , respectively , whilethose of the cracked plates are 311. 48 MPa and 32217 cycles , respectively. An elliptical debond area between thecomposite patches and cracked plate is found during the tension-tension fatigue testing. The interface debond area increases with increasing the fatigue cyclic number , and the magnitude of the increase is related with the fatigue cyclicnumber.
2007, 24(3): 7-12.
Abstract:
The Kevlar fibers were t reated by phosphorous acid ( PA) solutions of different concent rations. Thesurface properties of the t reated Kevlar fiber and the interfacial properties of the fiber/ epoxy resin composites wereinvestigated. The result s show that the amount of the oxygenous functional groups on the surface reaches a maximum af ter being t reated with 20 wt % PA solution. The amount of the oxygenous functional groups and the surfaceroughness decrease as the concent ration of PA solution increases , but the filament st rength rises. Af ter beingt reated with 20 wt % PA solution , the interlaminar shear st rength ( ILSS) of Kevlar fiber/ epoxy composites reaches62 MPa and the interfacial shear st rength ( IFSS) of Kevlar fiber/ epoxy composites increases by 18 %. The amount ofthe functional groups on the fiber surface and the surface roughness are the crucial factors to improve interfacialproperties of Kevlar fiber/ epoxy composites .
The Kevlar fibers were t reated by phosphorous acid ( PA) solutions of different concent rations. Thesurface properties of the t reated Kevlar fiber and the interfacial properties of the fiber/ epoxy resin composites wereinvestigated. The result s show that the amount of the oxygenous functional groups on the surface reaches a maximum af ter being t reated with 20 wt % PA solution. The amount of the oxygenous functional groups and the surfaceroughness decrease as the concent ration of PA solution increases , but the filament st rength rises. Af ter beingt reated with 20 wt % PA solution , the interlaminar shear st rength ( ILSS) of Kevlar fiber/ epoxy composites reaches62 MPa and the interfacial shear st rength ( IFSS) of Kevlar fiber/ epoxy composites increases by 18 %. The amount ofthe functional groups on the fiber surface and the surface roughness are the crucial factors to improve interfacialproperties of Kevlar fiber/ epoxy composites .
2007, 24(3): 13-17.
Abstract:
The surface properties of rectorite (REC) directly affect the dispersion of rectorite in the polymer mat rixand make a great cont ribution to the st ructure and mechanical properties of composite materials. The inverse gaschromatography ( IGC) was used to investigate the dispersive component of the surface energy (γds) and the surfaceacid-base properties of the native rectorite , organic-modified rectorite with dodecyl benzyl dimethyl ammonium bromide (12-OREC) , organic-modified rectorite with hexadecyl t rimethyl ammonium bromide (16-OREC) and thermoplastic polyurethane ( TPU) with non-polar and polar probes. The correlation of the surface properties of REC andTPU with the st ructure of the composites was analyzed. The result s indicate that the modification of REC lowers it ssurface energy and changes the surface f rom being acidic to being predominantly basic and hence improving the dispersibility of 12-OREC and 16-OREC in TPU ; 12-OREC can achieve the best dispersibility in TPU , because thedispersive energy and acid-base property are most comparable with those of the polymer mat rix.
The surface properties of rectorite (REC) directly affect the dispersion of rectorite in the polymer mat rixand make a great cont ribution to the st ructure and mechanical properties of composite materials. The inverse gaschromatography ( IGC) was used to investigate the dispersive component of the surface energy (γds) and the surfaceacid-base properties of the native rectorite , organic-modified rectorite with dodecyl benzyl dimethyl ammonium bromide (12-OREC) , organic-modified rectorite with hexadecyl t rimethyl ammonium bromide (16-OREC) and thermoplastic polyurethane ( TPU) with non-polar and polar probes. The correlation of the surface properties of REC andTPU with the st ructure of the composites was analyzed. The result s indicate that the modification of REC lowers it ssurface energy and changes the surface f rom being acidic to being predominantly basic and hence improving the dispersibility of 12-OREC and 16-OREC in TPU ; 12-OREC can achieve the best dispersibility in TPU , because thedispersive energy and acid-base property are most comparable with those of the polymer mat rix.
2007, 24(3): 18-22.
Abstract:
The accelerated salt-spray test was used to simulate a marine environment and determine the durability ofglass fiber reinforced polymer ( GFRP) composites in marine environment s. Aging behavior af ter exposure in saltspray environment was studied by changes in mass gain and mechanical properties including tension , compressionand interlaminar shearing st rength. The mass gain increases and the mechanical properties decrease with the agingtime. Curves of the compression and interlaminar shearing test show more plastic than the original ones. Mechanicalproperties decrease quickly in the initial period of moisture absorption. The longitude tensile st rength , transversetensile st rength , compression strength and interlaminar shearing strength decrease to 56. 1 %, 54. 7 %, 54. 0 %, 61. 0 %,respectively. The tensile strength is more steady and more suitable for evaluating the aging degree of the composites.
The accelerated salt-spray test was used to simulate a marine environment and determine the durability ofglass fiber reinforced polymer ( GFRP) composites in marine environment s. Aging behavior af ter exposure in saltspray environment was studied by changes in mass gain and mechanical properties including tension , compressionand interlaminar shearing st rength. The mass gain increases and the mechanical properties decrease with the agingtime. Curves of the compression and interlaminar shearing test show more plastic than the original ones. Mechanicalproperties decrease quickly in the initial period of moisture absorption. The longitude tensile st rength , transversetensile st rength , compression strength and interlaminar shearing strength decrease to 56. 1 %, 54. 7 %, 54. 0 %, 61. 0 %,respectively. The tensile strength is more steady and more suitable for evaluating the aging degree of the composites.
2007, 24(3): 23-27.
Abstract:
As a new kind of radar absorbing material , carbon nanotubes show an excellent wave absorbing propertyin a wide f requence range because of their special st ructures and elect romagnetic properties. Moreover , they haveother characteristics such as light weight and good stability , so they are considered to be promising. In this paper ,the radar absorbing property was studied for MWCNTs/ GF/ epoxy composites in millimeter wave (f rom 26. 5 to4010 GHz) with the same thickness and different content s of MWCNTs or different thickness and the same contentof MWCNTs. The result s show that the radar absorbing property of this kind of composites is improved withincreasing the content of MWCNTs. The out standing radar absorbing property of MWCNTs/ GF/ epoxy compositesis due to not only the radar absorbing property of MWCNTs , but also the resonant absorbing property of composites.The test result s calculated with elect romagnetic parameters such as relative dielect ric parameter and relative magneticconductive ratio of this kind of composites are in agreement with the absorbing theory.
As a new kind of radar absorbing material , carbon nanotubes show an excellent wave absorbing propertyin a wide f requence range because of their special st ructures and elect romagnetic properties. Moreover , they haveother characteristics such as light weight and good stability , so they are considered to be promising. In this paper ,the radar absorbing property was studied for MWCNTs/ GF/ epoxy composites in millimeter wave (f rom 26. 5 to4010 GHz) with the same thickness and different content s of MWCNTs or different thickness and the same contentof MWCNTs. The result s show that the radar absorbing property of this kind of composites is improved withincreasing the content of MWCNTs. The out standing radar absorbing property of MWCNTs/ GF/ epoxy compositesis due to not only the radar absorbing property of MWCNTs , but also the resonant absorbing property of composites.The test result s calculated with elect romagnetic parameters such as relative dielect ric parameter and relative magneticconductive ratio of this kind of composites are in agreement with the absorbing theory.
2007, 24(3): 28-34.
Abstract:
The biodegradable composites reinforced with kenaf fibers were prepared by press forming , and the flexural modulus of the composites was investigated in view of the effect of the fiber volume f raction , length and orientation dist ribution. Based on the COX shear-lag and the characteristic of the kenaf fiber compression , a modified modelwas put forward and the flexural modulus was predicted. The experimental result s show that the flexural modulusincreases with the increase of the fiber volume f raction , length and orientation factor. SEM observations reveal thatthe cellular st ructure of the raw kenaf fiber is compressed and becomes more rigid and denser af ter fabrication. Thiscould cont ribute to the improvement in the flexural modulus. With the modified shear-lag model incorporated withthe fiber compress ratio , the predicted result s agree well with the experimental values.
The biodegradable composites reinforced with kenaf fibers were prepared by press forming , and the flexural modulus of the composites was investigated in view of the effect of the fiber volume f raction , length and orientation dist ribution. Based on the COX shear-lag and the characteristic of the kenaf fiber compression , a modified modelwas put forward and the flexural modulus was predicted. The experimental result s show that the flexural modulusincreases with the increase of the fiber volume f raction , length and orientation factor. SEM observations reveal thatthe cellular st ructure of the raw kenaf fiber is compressed and becomes more rigid and denser af ter fabrication. Thiscould cont ribute to the improvement in the flexural modulus. With the modified shear-lag model incorporated withthe fiber compress ratio , the predicted result s agree well with the experimental values.
2007, 24(3): 35-39.
Abstract:
Nano- TiO2 / regenerated cellulose films with different titania content s were prepared by directly blendingtitania powder and cellulose (pulp) in 1-allyl-3-methylimidazolium chloride ionic liquid at room temperature. Thecellulose was regenerated by water and then dried by supercritical CO2 . The morphology , phase component s , st ructure and thermal property of the films were characterized by SEM , XRD and FTIR. The photocatalytic activities ofthe films were evaluated for decomposition of the methylene blue under UV light irradiation by PCC-2 photocatalysisevaluation checker. The influencing factors on photocatalytic activity of the films were discussed , such as the content of nano-TiO2 and the drying methods of supercritical CO2 . The result s show that , with the addition of titania ,the photocatalytic activity of the films t reated by supercritical CO2 medium is higher than that of films dried in vacuum. The photocatalytic activity of the films increases with the increasing of nano- TiO2 particles up to 5 % and thendecreases with the increasing of TiO2 content .
Nano- TiO2 / regenerated cellulose films with different titania content s were prepared by directly blendingtitania powder and cellulose (pulp) in 1-allyl-3-methylimidazolium chloride ionic liquid at room temperature. Thecellulose was regenerated by water and then dried by supercritical CO2 . The morphology , phase component s , st ructure and thermal property of the films were characterized by SEM , XRD and FTIR. The photocatalytic activities ofthe films were evaluated for decomposition of the methylene blue under UV light irradiation by PCC-2 photocatalysisevaluation checker. The influencing factors on photocatalytic activity of the films were discussed , such as the content of nano-TiO2 and the drying methods of supercritical CO2 . The result s show that , with the addition of titania ,the photocatalytic activity of the films t reated by supercritical CO2 medium is higher than that of films dried in vacuum. The photocatalytic activity of the films increases with the increasing of nano- TiO2 particles up to 5 % and thendecreases with the increasing of TiO2 content .
2007, 24(3): 40-44.
Abstract:
The poly( lactic acid) / ethyl cellulose composite films were prepared by a casting method using n-alkenylsuccinic anhydride( ASA) as novel plast icizer and chlor oform as co-solvent. Fourier transform infr ared spectroscopy( FTIR) and X-r ay diffraction (XRD) were used to analyze the morphological pr operties of the composit e films. Themechanical proper ties and water absor ption of the cast composite films were also measured. FTIR indicates thatther e are some strong inter action and good compatibility in the composite films. XRD shows that both poly( lact icacid) ( PLA) and ethyl cellulose ( EC) lose cr ystallinity after being plast icized, and the PLA/ EC composite filmsplast icized with n- ASA r esult in a markedly enhanced coalescence of the two polymers. The mechanical proper tieswer e t ested and n- ASA becomes an ideal plast icizer for EC based films. The PLA r esin has a reinforcing effect onPLA/ EC composite films when the mass f raction of PLA is less than 37%. The water absorption decreases withincr easing ASA content while it increases with incr easing PLA content in the PLA/ EC composite films. Thecomposite films can be used as a new kind of drug delivery materia l with a wide application pr ospect.
The poly( lactic acid) / ethyl cellulose composite films were prepared by a casting method using n-alkenylsuccinic anhydride( ASA) as novel plast icizer and chlor oform as co-solvent. Fourier transform infr ared spectroscopy( FTIR) and X-r ay diffraction (XRD) were used to analyze the morphological pr operties of the composit e films. Themechanical proper ties and water absor ption of the cast composite films were also measured. FTIR indicates thatther e are some strong inter action and good compatibility in the composite films. XRD shows that both poly( lact icacid) ( PLA) and ethyl cellulose ( EC) lose cr ystallinity after being plast icized, and the PLA/ EC composite filmsplast icized with n- ASA r esult in a markedly enhanced coalescence of the two polymers. The mechanical proper tieswer e t ested and n- ASA becomes an ideal plast icizer for EC based films. The PLA r esin has a reinforcing effect onPLA/ EC composite films when the mass f raction of PLA is less than 37%. The water absorption decreases withincr easing ASA content while it increases with incr easing PLA content in the PLA/ EC composite films. Thecomposite films can be used as a new kind of drug delivery materia l with a wide application pr ospect.
2007, 24(3): 45-51.
Abstract:
Nanocomposites consisting of polypropylene homopolymer filled with in-situ graf ted nano-silica wereprepared by a conventional melt compounding technique. The influence of processing conditions on the mechanicalproperties of the nanocomposites was discussed. The mechanical performance , crystallization behaviors , morphologyand dynamic mechanical behaviors of the nanocomposites were studied. It can be concluded f rom the result s that thenotched Charpy impact st rength is significantly increased and a toughening effect can be attained by adding low loading (volume f raction ≤1.36 %) of the in-situ graf ted nanoparticles. Meanwhile , the tensile st rength can also beincreased. The reasonable processing conditions of the mixer can be set as 180 ℃for 10 min with the rotation speedof 60 r/ min. Studies of the crystalline characteristics indicate that addition of nanoparticles increases the rate of crystallization of PP. Filler/ mat rix interaction is enhanced due to interdiffusion and entanglement between the graftingpolymer and the mat rix , which is also emphasized by studies of the dynamic viscoelastic behavior and elucidates thetoughening and reinforcing mechanism of nanoparticles.
Nanocomposites consisting of polypropylene homopolymer filled with in-situ graf ted nano-silica wereprepared by a conventional melt compounding technique. The influence of processing conditions on the mechanicalproperties of the nanocomposites was discussed. The mechanical performance , crystallization behaviors , morphologyand dynamic mechanical behaviors of the nanocomposites were studied. It can be concluded f rom the result s that thenotched Charpy impact st rength is significantly increased and a toughening effect can be attained by adding low loading (volume f raction ≤1.36 %) of the in-situ graf ted nanoparticles. Meanwhile , the tensile st rength can also beincreased. The reasonable processing conditions of the mixer can be set as 180 ℃for 10 min with the rotation speedof 60 r/ min. Studies of the crystalline characteristics indicate that addition of nanoparticles increases the rate of crystallization of PP. Filler/ mat rix interaction is enhanced due to interdiffusion and entanglement between the graftingpolymer and the mat rix , which is also emphasized by studies of the dynamic viscoelastic behavior and elucidates thetoughening and reinforcing mechanism of nanoparticles.
2007, 24(3): 52-58.
Abstract:
Knit ted GF/ PP composites were produced by hot-pressing knitted GF/ PP preforms made of GF/ PPcommingled yarns. Four groups of GF/ PP composites with different cooling histories were prepared by changing thecooling method used in the cooling stage. The crystal st ructure of the mat rix of GF/ PP composites with differentcooling histories was studied using X- ray diff raction method. It is found that the cooling conditions studied in thepaper have no effect on the crystal types of the PP mat rix. However , the crystal degree and the sizes of the microliteand the spherulite vary with the cooling conditions. They all tend to increase with the decrease of cooling speed andthe prolongation of the cooling time.
Knit ted GF/ PP composites were produced by hot-pressing knitted GF/ PP preforms made of GF/ PPcommingled yarns. Four groups of GF/ PP composites with different cooling histories were prepared by changing thecooling method used in the cooling stage. The crystal st ructure of the mat rix of GF/ PP composites with differentcooling histories was studied using X- ray diff raction method. It is found that the cooling conditions studied in thepaper have no effect on the crystal types of the PP mat rix. However , the crystal degree and the sizes of the microliteand the spherulite vary with the cooling conditions. They all tend to increase with the decrease of cooling speed andthe prolongation of the cooling time.
2007, 24(3): 59-62.
Abstract:
Zirconia fiber reinforced polymethyl methacrylate polymethyl acrylate ( PMMA-PMA) mat rix composites were prepared using a suspension polymerization process. The influences of monomer ratio , initiator dosage andfiber content on the mechanical properties of the composites were particularly investigated. The flexural st rength andmicrost ructure of the composites were characterized by the universal testing machine , SEM and XRD analyses. Theresult s show that the flexural st rength of the composites reaches the optimum value when the volume ratio of methylmethacrylate and methyl acrylate (MMA/ MA) is 9∶1. With the increase of benzoyl peroxide (BPO) content , theflexural st rength of ZrO2 (f) / PMMA-PMA composites increases to a maximum and then decreases. With the increaseof ZrO2 fiber content , the morphologies of the fractured surfaces change from smooth to crapy , indicating that thetoughness of the composites is improved.
Zirconia fiber reinforced polymethyl methacrylate polymethyl acrylate ( PMMA-PMA) mat rix composites were prepared using a suspension polymerization process. The influences of monomer ratio , initiator dosage andfiber content on the mechanical properties of the composites were particularly investigated. The flexural st rength andmicrost ructure of the composites were characterized by the universal testing machine , SEM and XRD analyses. Theresult s show that the flexural st rength of the composites reaches the optimum value when the volume ratio of methylmethacrylate and methyl acrylate (MMA/ MA) is 9∶1. With the increase of benzoyl peroxide (BPO) content , theflexural st rength of ZrO2 (f) / PMMA-PMA composites increases to a maximum and then decreases. With the increaseof ZrO2 fiber content , the morphologies of the fractured surfaces change from smooth to crapy , indicating that thetoughness of the composites is improved.
2007, 24(3): 63-71.
Abstract:
The surfaces of intercalated montmorillonite (OMMT) and wood flour (WF) were modified by silanecoupling agent Ti-14. They were melt-blended and ext ruded into wood plastic composites samples. The effect s ofthe content s of OMMT and WF on the composites mechanical properties were investigated. The intercalation anddispersion of OMMT were observed by XRD , TEM and SEM. FTIR and XPS were used to analyze the silane modification effect s. The reaction mechanisms were proposed. The graf ting improves the interfacial compliance betweencomponent s and result s in higher properties of the composites. Adding OMMT can reinforce further the composites.However , a thicker interfacial layer which is weak will form and the st ress-concent ration will impair the compositesproperties when the content s of OMMT or coupling agent are higher.
The surfaces of intercalated montmorillonite (OMMT) and wood flour (WF) were modified by silanecoupling agent Ti-14. They were melt-blended and ext ruded into wood plastic composites samples. The effect s ofthe content s of OMMT and WF on the composites mechanical properties were investigated. The intercalation anddispersion of OMMT were observed by XRD , TEM and SEM. FTIR and XPS were used to analyze the silane modification effect s. The reaction mechanisms were proposed. The graf ting improves the interfacial compliance betweencomponent s and result s in higher properties of the composites. Adding OMMT can reinforce further the composites.However , a thicker interfacial layer which is weak will form and the st ress-concent ration will impair the compositesproperties when the content s of OMMT or coupling agent are higher.
2007, 24(3): 72-77.
Abstract:
The crystallization behavior of n-HA/ PA66 biocomposite at different processing pressures and annealingtemperatures was investigated by XRD and DSC. The result s show that the crystalline intensities of pure PA66 andit s composite decrease with the increase of the annealing temperature. For n-HA/ PA66 composites , the peaks ofα1crystals of PA66 disappear , only those ofα2 crystals exist , and with the increase of injection pressure and annealingtemperature , the crystalline intensity of PA66 decreases. The degree of crystallinity of PA66 in composites increaseswith the increase of the injection pressure ; however , the annealing temperature has no obvious effect s on the crystalline degree. The mechanical properties have a close relationship with the crystallization behavior of the materials.
The crystallization behavior of n-HA/ PA66 biocomposite at different processing pressures and annealingtemperatures was investigated by XRD and DSC. The result s show that the crystalline intensities of pure PA66 andit s composite decrease with the increase of the annealing temperature. For n-HA/ PA66 composites , the peaks ofα1crystals of PA66 disappear , only those ofα2 crystals exist , and with the increase of injection pressure and annealingtemperature , the crystalline intensity of PA66 decreases. The degree of crystallinity of PA66 in composites increaseswith the increase of the injection pressure ; however , the annealing temperature has no obvious effect s on the crystalline degree. The mechanical properties have a close relationship with the crystallization behavior of the materials.
2007, 24(3): 78-83.
Abstract:
The conductive composites based on conductive carbon black (CB) , polypropylene ( PP) and poly (ethylene-co-acrylate) ( EAA) were prepared via the melt blending. The dispersion of CB in the two-phase mat rix and theeffect of crystallinity of PP on the conductivity of the composites were discussed. SEM observation indicates that theCB particles were selectively located in the polar EAA resin , which formed a continuous network st ructure in the PPmat rix , resulting in a great decrease of the conductive percolation threshold of the composites. The elect rical testingresult s indicate that compared to the CB/ PP system , the volume resistivity of CB/ PP-EAA composites decreases by7～8 orders of magnitude at the same filler content . PP with higher crystallinity is more favorable for decreasing thevolume resistivity of the composites. Furthermore , the tensile st rength of CB/ PP-EAA composite decreases somewhat compared to the CB/ PP system , while the elongation at break increases.
The conductive composites based on conductive carbon black (CB) , polypropylene ( PP) and poly (ethylene-co-acrylate) ( EAA) were prepared via the melt blending. The dispersion of CB in the two-phase mat rix and theeffect of crystallinity of PP on the conductivity of the composites were discussed. SEM observation indicates that theCB particles were selectively located in the polar EAA resin , which formed a continuous network st ructure in the PPmat rix , resulting in a great decrease of the conductive percolation threshold of the composites. The elect rical testingresult s indicate that compared to the CB/ PP system , the volume resistivity of CB/ PP-EAA composites decreases by7～8 orders of magnitude at the same filler content . PP with higher crystallinity is more favorable for decreasing thevolume resistivity of the composites. Furthermore , the tensile st rength of CB/ PP-EAA composite decreases somewhat compared to the CB/ PP system , while the elongation at break increases.
2007, 24(3): 84-88.
Abstract:
SiO2 / wood hybrid materials were prepared by the method of sol gel using TEOS as inorganic mediumand china fir as raw materials , according to the principle of solvothermal method. The st ructure and property of thehybrid materials were analyzed by FTIR , XRD , TGA and SEM. The result s show that the WPG (weight percentgain) of the wood get s a marked improvement and the hydroxyl groups f rom the hydrolysis of TEOS reacted withthe hydroxyl groups of the wood. In SEM analysis , the network whose size is in nanoscale is found , which resultedf rom the coagulation of Si —O —C network. And in XRD analysis , the crystalline phase of lignocellulose has beendest royed. Meanwhile , the crystallinity decreases from 75. 37 % for pure wood powder to 32. 42 % for 78 % WPGhybrid material. TGA shows that the hybrid materials has a better thermostability. The characteristic degradationtemperature at 10 % mass loss is evidently increased from 270 ℃for pure wood powder to 409 ℃for 78 % WPGhybrid materials.
SiO2 / wood hybrid materials were prepared by the method of sol gel using TEOS as inorganic mediumand china fir as raw materials , according to the principle of solvothermal method. The st ructure and property of thehybrid materials were analyzed by FTIR , XRD , TGA and SEM. The result s show that the WPG (weight percentgain) of the wood get s a marked improvement and the hydroxyl groups f rom the hydrolysis of TEOS reacted withthe hydroxyl groups of the wood. In SEM analysis , the network whose size is in nanoscale is found , which resultedf rom the coagulation of Si —O —C network. And in XRD analysis , the crystalline phase of lignocellulose has beendest royed. Meanwhile , the crystallinity decreases from 75. 37 % for pure wood powder to 32. 42 % for 78 % WPGhybrid material. TGA shows that the hybrid materials has a better thermostability. The characteristic degradationtemperature at 10 % mass loss is evidently increased from 270 ℃for pure wood powder to 409 ℃for 78 % WPGhybrid materials.
2007, 24(3): 89-93.
Abstract:
The compressive yield st ress and modulus of the two natural foam cores of kaoliang stem and corn stemwere tested. Their st ructures and morphologies were determined by scanning elect ron microscope. The differentcompressive deformation mechanics of the foams were discussed. A compound st ructure model made up of hexangular prisms and tubular cells was established f rom the observation on scanning elect ron microscope photographs. Theeffect s of the compound st ructure of the foams on their mechanical properties were studied on the basis of the model.The result s show that the compressive yield st ress and modulus of the two natural foam cores in the axial directionare more than 4 times of those in the radial direction. The compound st ructure of the foams reinforced by the tubularcells has more significant effect s on the corresponding mechanical properties of the foams. The axial compressivemodulus of a tubular cell is 105 times that of an abnormal hexangular prism cell.
The compressive yield st ress and modulus of the two natural foam cores of kaoliang stem and corn stemwere tested. Their st ructures and morphologies were determined by scanning elect ron microscope. The differentcompressive deformation mechanics of the foams were discussed. A compound st ructure model made up of hexangular prisms and tubular cells was established f rom the observation on scanning elect ron microscope photographs. Theeffect s of the compound st ructure of the foams on their mechanical properties were studied on the basis of the model.The result s show that the compressive yield st ress and modulus of the two natural foam cores in the axial directionare more than 4 times of those in the radial direction. The compound st ructure of the foams reinforced by the tubularcells has more significant effect s on the corresponding mechanical properties of the foams. The axial compressivemodulus of a tubular cell is 105 times that of an abnormal hexangular prism cell.
2007, 24(3): 94-99.
Abstract:
The elect ron beam ( EB) curing characterizations of bisphenol A epoxy resins and phenolic aldehyde epoxy resins with different diluent s were investigated. The effect s of the kind and content of diluent s on the gel massf raction , curing uniformity , cure dimension , glass t ransition temperature ( Tg ) and dynamic modulus for differentsamples were analyzed. It can be found that the use of diluent s in the epoxy resin systems will reduce the gel massf raction , Tg and storage modulus of EB cured epoxy resins , while it will improve the curing uniformity. The curedthickness of the epoxy resin with diluent is smaller than that of the resin without diluent , while the cure diameter ofepoxy resin with diluent is larger. With the increasing diluent content , the gel mass f raction decreases gradually , thecure thickness increases , and the cure diameter increases at first and then decreases.
The elect ron beam ( EB) curing characterizations of bisphenol A epoxy resins and phenolic aldehyde epoxy resins with different diluent s were investigated. The effect s of the kind and content of diluent s on the gel massf raction , curing uniformity , cure dimension , glass t ransition temperature ( Tg ) and dynamic modulus for differentsamples were analyzed. It can be found that the use of diluent s in the epoxy resin systems will reduce the gel massf raction , Tg and storage modulus of EB cured epoxy resins , while it will improve the curing uniformity. The curedthickness of the epoxy resin with diluent is smaller than that of the resin without diluent , while the cure diameter ofepoxy resin with diluent is larger. With the increasing diluent content , the gel mass f raction decreases gradually , thecure thickness increases , and the cure diameter increases at first and then decreases.
2007, 24(3): 100-104.
Abstract:
The kinetics of the cure reaction for a system of 840S epoxy resin was monitored by the differentail scanning calorimet ry (DSC) and investigated by the constant heating methods. According to the DSC graphs , the curingprocess temperatures such as gelation temperature ( Tgel ) , peak temperature ( Tp ) and t reat temperature ( Ttreat ) wereacquired using T βgraph ext rapolation , and these temperatures play an important role in confirming the technicalparameters of the molding process of the resin system. The kinetic parameters of the curing reaction of 840S epoxyresin such as the overall activation energy Ea , the f requency factor A and the value of reaction order n wereobtained , and the kinetic model of the curing process based on n order reaction equation was set up using Kissingerand Crane equation. The characteristics of the curing reaction under dynamic and isothermal conditions is great useful for determining reasonable curing process parameters of the 840S epoxy resin system.
The kinetics of the cure reaction for a system of 840S epoxy resin was monitored by the differentail scanning calorimet ry (DSC) and investigated by the constant heating methods. According to the DSC graphs , the curingprocess temperatures such as gelation temperature ( Tgel ) , peak temperature ( Tp ) and t reat temperature ( Ttreat ) wereacquired using T βgraph ext rapolation , and these temperatures play an important role in confirming the technicalparameters of the molding process of the resin system. The kinetic parameters of the curing reaction of 840S epoxyresin such as the overall activation energy Ea , the f requency factor A and the value of reaction order n wereobtained , and the kinetic model of the curing process based on n order reaction equation was set up using Kissingerand Crane equation. The characteristics of the curing reaction under dynamic and isothermal conditions is great useful for determining reasonable curing process parameters of the 840S epoxy resin system.
2007, 24(3): 105-108.
Abstract:
RTM; filling time ; low viscosity platform time ; resin injection temperature ; optimization
RTM; filling time ; low viscosity platform time ; resin injection temperature ; optimization
2007, 24(3): 109-115.
Abstract:
The overall heat t ransfer coefficients of the sandwich panels with two-dimensional metal cores were analyzed using the effective medium model’. Based on the multifunctional demand for the effective heat t ransfer performance ata specified pumping power and st ructural stiffness , the thermo-mechanical performance of Kagome cells wasstudied in comparison with the t raditional regular t riangle , square and hexagon cells with low relative density. Thein-plane shear stiffness is taken as a relevant measure of the st ructural utility in the work. The analytic result s indicate that Kagome cells provide not only higher levels of heat dissipation performance but also the most optimum multifunctional performances at a specified st ructural weight by optimizing the relative density and the size of the cells.
The overall heat t ransfer coefficients of the sandwich panels with two-dimensional metal cores were analyzed using the effective medium model’. Based on the multifunctional demand for the effective heat t ransfer performance ata specified pumping power and st ructural stiffness , the thermo-mechanical performance of Kagome cells wasstudied in comparison with the t raditional regular t riangle , square and hexagon cells with low relative density. Thein-plane shear stiffness is taken as a relevant measure of the st ructural utility in the work. The analytic result s indicate that Kagome cells provide not only higher levels of heat dissipation performance but also the most optimum multifunctional performances at a specified st ructural weight by optimizing the relative density and the size of the cells.
2007, 24(3): 116-120.
Abstract:
The saturated and unsaturated permeabilities of the 3D braided preform were measured by unidirectionalflow. The capillary pressure was determined through the permeabilities experiment s. The influences of the fibervolume f raction on the saturated and unsaturated permeabilities were studied. The effect s of braiding parameter andinjection pressures on permeability were analyzed. A plot of different injection pressures against the square distanceof the flow f ront was fitted with a st raight line for a certain period of time. The capillary pressure was determined asthe horizontal axis intercept value. The experimental result s show that saturated and unsaturated permeabilitiesdecrease with increasing the fiber volume f ractions. The saturated permeability is larger than the unsaturated permeability. The braiding st ructure influences the permeability. The unsaturated permeability decreases with increasing the braiding angle. The accurate permeability does not depend on the injection pressure and it denotes a decreasing behavior until it reaches a stabilized value.
The saturated and unsaturated permeabilities of the 3D braided preform were measured by unidirectionalflow. The capillary pressure was determined through the permeabilities experiment s. The influences of the fibervolume f raction on the saturated and unsaturated permeabilities were studied. The effect s of braiding parameter andinjection pressures on permeability were analyzed. A plot of different injection pressures against the square distanceof the flow f ront was fitted with a st raight line for a certain period of time. The capillary pressure was determined asthe horizontal axis intercept value. The experimental result s show that saturated and unsaturated permeabilitiesdecrease with increasing the fiber volume f ractions. The saturated permeability is larger than the unsaturated permeability. The braiding st ructure influences the permeability. The unsaturated permeability decreases with increasing the braiding angle. The accurate permeability does not depend on the injection pressure and it denotes a decreasing behavior until it reaches a stabilized value.
2007, 24(3): 121-125.
Abstract:
The ult ra-thin films of pyrrole and polystyrene were deposited on the surfaces of the multi-wall carbonnanotubes (MWNTs) using a plasma polymerization method. The high resolution t ransmission elect ron microscopy( HRTEM) images show a 7 nm thickness polymer layer has been uniformly deposited on the outer surface of theMWNTs , while an only 1～3 nm polymer layer was deposited on the inner surface. MWNTs coated with polystyrene and uncoated were added into the polystyrene mat rix , respectively. Transmission elect ron microscopy ( TEM)analysis reveals that the MWNTs coated with the polystyrene are well-dispersed in the polystyrene mat rix. The mechanical test s result s show that the well-dispersed MWNTs can effectively enhance the tensile st rength and modulusof the composites.
The ult ra-thin films of pyrrole and polystyrene were deposited on the surfaces of the multi-wall carbonnanotubes (MWNTs) using a plasma polymerization method. The high resolution t ransmission elect ron microscopy( HRTEM) images show a 7 nm thickness polymer layer has been uniformly deposited on the outer surface of theMWNTs , while an only 1～3 nm polymer layer was deposited on the inner surface. MWNTs coated with polystyrene and uncoated were added into the polystyrene mat rix , respectively. Transmission elect ron microscopy ( TEM)analysis reveals that the MWNTs coated with the polystyrene are well-dispersed in the polystyrene mat rix. The mechanical test s result s show that the well-dispersed MWNTs can effectively enhance the tensile st rength and modulusof the composites.
2007, 24(3): 126-130.
Abstract:
Based on the elect romagnetic-wave penet ration method , the elect romagnetic-wave attenuation abilities ofsix kinds of carbon nanotubes (CNTs) were studied in experiment at 8～12 GHz , whose diameters were 30 nm ,60 nm and 100 nm , and lengths were 2μm and 15μm. The results show that with the same diameter of 30 nm , theelect romagnetic2wave attenuation ability of CNTs with the length of 15μm is better than that with the length of2μm. With the same diameter of 60 nm , the absorption ability of CNTs with the length of 2μm is bet ter than thatwith the length of 15μm. With the same diameter of 100 nm , the elect romagnetic2wave attenuation ability of CNTswith the length of 2μm is better than that with the length of 15μm. The order of elect romagnetic2wave at tenuationabilities of CNTs with the same length is that Ф60 nm > Ф100 nm > Ф30 nm. At 8～12 GHz , the elect romagnetic2wave attenuation order of the 6 kinds of CNTs is Ф60 nm ×2μm > Ф60 nm ×15μm > Ф100 nm ×2μm > Ф100 nm ×15μm > Ф30 nm ×15μm > Ф30 nm ×2μm. Based on the experiment s , the elect romagnetic-wave at tenuation abilityof CNTs with smaller slenderness ratio is better than that with larger slenderness ratio. However , liner relationshipdoesnpt exist between the absorption ability and slenderness ratio for CNTs.
Based on the elect romagnetic-wave penet ration method , the elect romagnetic-wave attenuation abilities ofsix kinds of carbon nanotubes (CNTs) were studied in experiment at 8～12 GHz , whose diameters were 30 nm ,60 nm and 100 nm , and lengths were 2μm and 15μm. The results show that with the same diameter of 30 nm , theelect romagnetic2wave attenuation ability of CNTs with the length of 15μm is better than that with the length of2μm. With the same diameter of 60 nm , the absorption ability of CNTs with the length of 2μm is bet ter than thatwith the length of 15μm. With the same diameter of 100 nm , the elect romagnetic2wave attenuation ability of CNTswith the length of 2μm is better than that with the length of 15μm. The order of elect romagnetic2wave at tenuationabilities of CNTs with the same length is that Ф60 nm > Ф100 nm > Ф30 nm. At 8～12 GHz , the elect romagnetic2wave attenuation order of the 6 kinds of CNTs is Ф60 nm ×2μm > Ф60 nm ×15μm > Ф100 nm ×2μm > Ф100 nm ×15μm > Ф30 nm ×15μm > Ф30 nm ×2μm. Based on the experiment s , the elect romagnetic-wave at tenuation abilityof CNTs with smaller slenderness ratio is better than that with larger slenderness ratio. However , liner relationshipdoesnpt exist between the absorption ability and slenderness ratio for CNTs.
2007, 24(3): 131-135.
Abstract:
Magnetic Ni nanoparticles coated with silica were successfully synthesized via the liquid deposition methodusing Na2SiO3 as the main raw material , and their st ructures and properties were studied by X-ray diff raction(XRD) , Fourier t ransform inf rared spect rometer ( FTIR) , t ransmission elect ron microscopy ( TEM) , thermogravimet ric analysis ( TGA) , differential scanning calorimet ry (DSC) and vibrating sample magnetometer (VSM) . XRD ,FTIR and TEM result s show that there is noncrystal silica on the surface of Ni nanoparticles and it prevents the nanoparticles f rom agglomerating. The oxidation resistance of SiO2 / Ni nanoparticles is improved because of the protection of the silica coating. Magnetic properties show that Ni and SiO2 / Ni are ferromagnetic materials. The hysteresisloop of Ni has an excursion because of the anti-ferromagnetic NiO. The silica coating reduces the saturation magnetization and improves the coercivity.
Magnetic Ni nanoparticles coated with silica were successfully synthesized via the liquid deposition methodusing Na2SiO3 as the main raw material , and their st ructures and properties were studied by X-ray diff raction(XRD) , Fourier t ransform inf rared spect rometer ( FTIR) , t ransmission elect ron microscopy ( TEM) , thermogravimet ric analysis ( TGA) , differential scanning calorimet ry (DSC) and vibrating sample magnetometer (VSM) . XRD ,FTIR and TEM result s show that there is noncrystal silica on the surface of Ni nanoparticles and it prevents the nanoparticles f rom agglomerating. The oxidation resistance of SiO2 / Ni nanoparticles is improved because of the protection of the silica coating. Magnetic properties show that Ni and SiO2 / Ni are ferromagnetic materials. The hysteresisloop of Ni has an excursion because of the anti-ferromagnetic NiO. The silica coating reduces the saturation magnetization and improves the coercivity.
2007, 24(3): 136-140.
Abstract:
The anatase TiO2 / MnFe2O4 composite nanoparticles with a core-shell structure have been obtained. Thecore MnFe2O4 nanoparticles were synthesized by the co-precipitation method , and the shell TiO2 nanocrystals werederived using the sol-gel technology followed by a heat-t reatment at 450 ℃. The TiO2 / MnFe2O4 samples were characterized by X-ray diff raction (XRD) and t ransmission elect ron microscopy ( TEM) . The TiO2 / MnFe2O4 compositeparticles can be used as a magnetic photocatalyst , which can be fluidized and recovered by an applied magnetic fieldenhancing both the separation and mixing efficiency for recyclable fluids. When the mass f raction of TiO2 is 30 % andthere is enough UV illumination (4 h in our experiment s) , the photodegradation ratio of Rhodamine B by the composite of TiO2 / MnFe2O4 is 100 % , similar to that of the pure TiO2 .
The anatase TiO2 / MnFe2O4 composite nanoparticles with a core-shell structure have been obtained. Thecore MnFe2O4 nanoparticles were synthesized by the co-precipitation method , and the shell TiO2 nanocrystals werederived using the sol-gel technology followed by a heat-t reatment at 450 ℃. The TiO2 / MnFe2O4 samples were characterized by X-ray diff raction (XRD) and t ransmission elect ron microscopy ( TEM) . The TiO2 / MnFe2O4 compositeparticles can be used as a magnetic photocatalyst , which can be fluidized and recovered by an applied magnetic fieldenhancing both the separation and mixing efficiency for recyclable fluids. When the mass f raction of TiO2 is 30 % andthere is enough UV illumination (4 h in our experiment s) , the photodegradation ratio of Rhodamine B by the composite of TiO2 / MnFe2O4 is 100 % , similar to that of the pure TiO2 .
2007, 24(3): 141-146.
Abstract:
In order to improve hydroxyapatite ( HAP) brittleness and osteo -inductivity , HAP was prepared usingthe co-precipitation method. Silk-fibroin (SF) was obtained by salt-resolving. The SF/ HAP composite was derivedby mixing HAP sols with SF sols. The phase composition and morphology of HAP and SF/ HAP composites wereinvestigated using X-ray diff raction (XRD) , scanning elect ron microscopy (SEM) and Fourier inf rared spect roscopy( FIR) . The compressive st rength of the SF/ HAP composites was also measured. The biological activity of the SF/HAP composites was observed while thermostatic held in simulated body fluid (SBF) . The result s show that HAPmixes with SF in the SF/ HAP composites at the nano-scale. The SF in the SF/ HAP composites mainly has the typical silk Ⅱconformation (β-sheet) . The pect ral peak of acyl Ⅴofβ-sheet conformation disappears and the positionsof the other spect ral peaks ofβ-sheet conformation in the SF/ HAP composites are changed , which indicates that thechemical bonds are formed between SF and HAP granules. When the SF/ HAP composite is dipped in SBF for eighteen days , the needle-like HAP sheet is formed on the surface. The compressive st rength of the SF/ HAP compositesreaches 63 MPa. It is clear that the SF/ HAP composite is a desirable biomedical material for the repairing of bonedefect s with an excellent bioactivity , osteo-inductivity and high mechanical st rength.
In order to improve hydroxyapatite ( HAP) brittleness and osteo -inductivity , HAP was prepared usingthe co-precipitation method. Silk-fibroin (SF) was obtained by salt-resolving. The SF/ HAP composite was derivedby mixing HAP sols with SF sols. The phase composition and morphology of HAP and SF/ HAP composites wereinvestigated using X-ray diff raction (XRD) , scanning elect ron microscopy (SEM) and Fourier inf rared spect roscopy( FIR) . The compressive st rength of the SF/ HAP composites was also measured. The biological activity of the SF/HAP composites was observed while thermostatic held in simulated body fluid (SBF) . The result s show that HAPmixes with SF in the SF/ HAP composites at the nano-scale. The SF in the SF/ HAP composites mainly has the typical silk Ⅱconformation (β-sheet) . The pect ral peak of acyl Ⅴofβ-sheet conformation disappears and the positionsof the other spect ral peaks ofβ-sheet conformation in the SF/ HAP composites are changed , which indicates that thechemical bonds are formed between SF and HAP granules. When the SF/ HAP composite is dipped in SBF for eighteen days , the needle-like HAP sheet is formed on the surface. The compressive st rength of the SF/ HAP compositesreaches 63 MPa. It is clear that the SF/ HAP composite is a desirable biomedical material for the repairing of bonedefect s with an excellent bioactivity , osteo-inductivity and high mechanical st rength.
2007, 24(3): 147-153.
Abstract:
ZrW2O8 which exhibit s excellent isot ropic negative thermal expansion was synthesized using the step bystep solid state reaction. The ZrW2O8 / ZrO2 composites with cont rollable thermal expansion coefficient were prepared by mixing ZrW2O8 and ZrO2 at different volume ratios and sintered at 1200 ℃for 24 h. The thermal expansioncoefficient of ZrW2O8 / ZrO2 composites can be cont rolled , being negative , positive or even zero , by adjusting the volume fraction of ZrW2O8 . The ZrW2O8 / ZrO2 composites show almost zero thermal expansion when the volume f rac2tion of ZrW2O8 is 37 %. In order to obtain dense and tough ZrW2O8 / ZrO2 ceramic , Al2O3 was adopted as an additive. The result s reveal that it is effective to improve the density of the composites. 0. 35 wt % Al2O3 additive canincrease the density of the composites rapidly with slight effect s on the thermal expansion property.
ZrW2O8 which exhibit s excellent isot ropic negative thermal expansion was synthesized using the step bystep solid state reaction. The ZrW2O8 / ZrO2 composites with cont rollable thermal expansion coefficient were prepared by mixing ZrW2O8 and ZrO2 at different volume ratios and sintered at 1200 ℃for 24 h. The thermal expansioncoefficient of ZrW2O8 / ZrO2 composites can be cont rolled , being negative , positive or even zero , by adjusting the volume fraction of ZrW2O8 . The ZrW2O8 / ZrO2 composites show almost zero thermal expansion when the volume f rac2tion of ZrW2O8 is 37 %. In order to obtain dense and tough ZrW2O8 / ZrO2 ceramic , Al2O3 was adopted as an additive. The result s reveal that it is effective to improve the density of the composites. 0. 35 wt % Al2O3 additive canincrease the density of the composites rapidly with slight effect s on the thermal expansion property.
2007, 24(3): 154-159.
Abstract:
The quasi 2 static indentation (QSI) damage resistance of composite laminates was tested. Ult rasonicC2scan and SEM were conducted on QSI specimens under two given loads and the damage process was analyzed.The damage resistance of composite laminates was discussed through the initial delamination contact force f1 and themaximal contact force f2 . The repetitive characteristic of f2 was confirmed by testing two kinds of materials systems. Moreover , the effect s of the test conditions ( specimens dimension and clamp hole diameter) and materialsproperties (the size of fiber , resin mat rix and plying pattern) on the maximal contact force were studied. The testresults indicate that the effect of the specimens dimension and clamp hole diameter on the maximal contact force is neglectable , materials components properties (fiber characteristic , resin characteristic and plying ways) could influence the maximalcontact force and the dent depth d2 corresponding with f2 is principally decided by the st rength and elongation of the fiber.
The quasi 2 static indentation (QSI) damage resistance of composite laminates was tested. Ult rasonicC2scan and SEM were conducted on QSI specimens under two given loads and the damage process was analyzed.The damage resistance of composite laminates was discussed through the initial delamination contact force f1 and themaximal contact force f2 . The repetitive characteristic of f2 was confirmed by testing two kinds of materials systems. Moreover , the effect s of the test conditions ( specimens dimension and clamp hole diameter) and materialsproperties (the size of fiber , resin mat rix and plying pattern) on the maximal contact force were studied. The testresults indicate that the effect of the specimens dimension and clamp hole diameter on the maximal contact force is neglectable , materials components properties (fiber characteristic , resin characteristic and plying ways) could influence the maximalcontact force and the dent depth d2 corresponding with f2 is principally decided by the st rength and elongation of the fiber.
2007, 24(3): 160-167.
Abstract:
With less than 5 % volume f raction of through2thickness Z-pins insertion , the delamination toughness ofZ-pinned laminates can be improved significantly and the delamination area induced by low-energy impact can also bereduced greatly. Based on the currently available Z-pin micro-model , a Z-pin element was developed and a beam element model for Z-pinned double cantilever beam (DCB) specimens was proposed in this paper to study the effect ofZ-pins dist ribution on the mode Ⅰdelamination toughness of Z-pinned DCB specimens. A contact element is also int roduced to the proposed model to avoid the unrealistic penet ration of the two subst rate beams at the delaminationcrack tip. The numerical results show that the Z-pin distribution has an insignificant effect on the mode Ⅰdelaminationtoughness of the Z-pinned laminated DCB specimens.
With less than 5 % volume f raction of through2thickness Z-pins insertion , the delamination toughness ofZ-pinned laminates can be improved significantly and the delamination area induced by low-energy impact can also bereduced greatly. Based on the currently available Z-pin micro-model , a Z-pin element was developed and a beam element model for Z-pinned double cantilever beam (DCB) specimens was proposed in this paper to study the effect ofZ-pins dist ribution on the mode Ⅰdelamination toughness of Z-pinned DCB specimens. A contact element is also int roduced to the proposed model to avoid the unrealistic penet ration of the two subst rate beams at the delaminationcrack tip. The numerical results show that the Z-pin distribution has an insignificant effect on the mode Ⅰdelaminationtoughness of the Z-pinned laminated DCB specimens.
2007, 24(3): 167-172.
Abstract:
A finite element model for two steel pipes connected by a composite pipe joint was developed with ANSYS sof tware. With the functional module of contact element in ANSYS , the st ress dist ributions in the compositepipe joint under different contact conditions to the steel pipes ( bending , compression and torsion) were obtained ,and the load bearing capability of the composite pipe joint was further studied. The studies are focused on the effect sof the f riction coefficient on the friction st ress on the contact surfaces between the steel pipe and on the compositepipe joint , and on the effect s of the friction st ress on the load bearing capability of the composite pipe joint . The results show that , with the increasing of the friction coefficient , the maximum contact pressure between the compositepipe joint and the steel pipe decreases and the maximum friction st ress increases ; the load bearing capability of thecomposite pipe joint is st rengthened under the bending.
A finite element model for two steel pipes connected by a composite pipe joint was developed with ANSYS sof tware. With the functional module of contact element in ANSYS , the st ress dist ributions in the compositepipe joint under different contact conditions to the steel pipes ( bending , compression and torsion) were obtained ,and the load bearing capability of the composite pipe joint was further studied. The studies are focused on the effect sof the f riction coefficient on the friction st ress on the contact surfaces between the steel pipe and on the compositepipe joint , and on the effect s of the friction st ress on the load bearing capability of the composite pipe joint . The results show that , with the increasing of the friction coefficient , the maximum contact pressure between the compositepipe joint and the steel pipe decreases and the maximum friction st ress increases ; the load bearing capability of thecomposite pipe joint is st rengthened under the bending.
2007, 24(3): 173-177.
Abstract:
With the asymptotic homogenization theory , a novel digitized cell- based finite element method (DCB-FEA) is presented to simulate the constitutive properties of composite materials. In this method , a three-dimensional (3D) unit cell model to represent the actual geomet ry of the microst ructure is converted into a raster graphic by3D scan-conversion algorithms , and then directly interpreted to be a finite element model. Since all the elementshave the regular shape and the same size , the number of element stiffness mat rices actually needed is reduced to thenumber of materials. Furthermore , only the material IDps of each element s need to be stored ; the other geomet ry information of the FE mesh , e. g. , the number of nodes and elements , element connectivities , and node coordinatevalues , can be automatically evaluated only if necessary in the computation. Otherwise , even the periodic boundarycondition can be easily determined because the position of each boundary node is fixed. In the DCB-FE modeling ,much more element s than usual are used with an improved resolution , especially for 3D cell models. This leads tohuge memory required to store the result . So the element-by-element FEM with a preconditioned conjugate gradientmethod is utilized to avoid const ructing the global stiffness mat rix. Finally , numerical test s of 3D composite st ructure were conducted , and more accurate result s of the effective modulus were obtained.
With the asymptotic homogenization theory , a novel digitized cell- based finite element method (DCB-FEA) is presented to simulate the constitutive properties of composite materials. In this method , a three-dimensional (3D) unit cell model to represent the actual geomet ry of the microst ructure is converted into a raster graphic by3D scan-conversion algorithms , and then directly interpreted to be a finite element model. Since all the elementshave the regular shape and the same size , the number of element stiffness mat rices actually needed is reduced to thenumber of materials. Furthermore , only the material IDps of each element s need to be stored ; the other geomet ry information of the FE mesh , e. g. , the number of nodes and elements , element connectivities , and node coordinatevalues , can be automatically evaluated only if necessary in the computation. Otherwise , even the periodic boundarycondition can be easily determined because the position of each boundary node is fixed. In the DCB-FE modeling ,much more element s than usual are used with an improved resolution , especially for 3D cell models. This leads tohuge memory required to store the result . So the element-by-element FEM with a preconditioned conjugate gradientmethod is utilized to avoid const ructing the global stiffness mat rix. Finally , numerical test s of 3D composite st ructure were conducted , and more accurate result s of the effective modulus were obtained.
2007, 24(3): 178-185.
Abstract:
Based on the microst ructure model established by the authors , coinciding with the actual configuration ofbraided composites , a model to predict the elastic properties was proposed by using the 3D FEM , coupled with theperiodical boundary conditions. The calculated values by the model well agree with the measured values. Numericalresult s verify the effectiveness of the model. The st ress and st rain fields of the model under such typical load casesas tension and shear were analyzed in detail , respectively. The result s indicate that the application of the periodicalboundary conditions guarantees the continuities of the t raction and displacement on the parallel boundary surfaces ofthe cubic model. Therefore , the st ress field and the st rain field obtained by the model are more reasonable than bythe existing FEM models.
Based on the microst ructure model established by the authors , coinciding with the actual configuration ofbraided composites , a model to predict the elastic properties was proposed by using the 3D FEM , coupled with theperiodical boundary conditions. The calculated values by the model well agree with the measured values. Numericalresult s verify the effectiveness of the model. The st ress and st rain fields of the model under such typical load casesas tension and shear were analyzed in detail , respectively. The result s indicate that the application of the periodicalboundary conditions guarantees the continuities of the t raction and displacement on the parallel boundary surfaces ofthe cubic model. Therefore , the st ress field and the st rain field obtained by the model are more reasonable than bythe existing FEM models.
2007, 24(3): 186-192.
Abstract:
The st ress dist ribution of non-continuous carbon nanotubes (CNTs) / polymer composites was analyzedusing the homogenization method with exact periodic boundary conditions , and the numerical calculations for regularand stagger array models were performed by the macro-microscopic finite element method ( FEM) . In order to utilizethe t raditional continuous mechanics approaches to determine the mechanical properties of CNTs composites , thecarbon nanotubes here were simplified as the effective fiber models which were obtained f rom the molecular dynamicssimulation. The result s obtained f rom regular array model were compared with those f rom Coxp shear-lag model ,Lauke and Fu theories , which show that the st resses t ransfer in CNTs composites are not only related to the aspectratio and volume f raction of CNTs as described in the above theories , but also sensitive to CNTs arrays and CNTspgeomet rical configuration within the selected representative volume element (RVE) . A better st ress t ransfer efficiency is obtained f rom stagger array , and the distance between two CNTs (2Tf ) has a great influence on the stressdist ribution. The result s show that there are some special characteristics for CNTs as the reinforcement phase ofcomposites , and they also prove that the homogenization method with multi-CNTs is efficient to analyze the st resst ransfer in CNTs composites.
The st ress dist ribution of non-continuous carbon nanotubes (CNTs) / polymer composites was analyzedusing the homogenization method with exact periodic boundary conditions , and the numerical calculations for regularand stagger array models were performed by the macro-microscopic finite element method ( FEM) . In order to utilizethe t raditional continuous mechanics approaches to determine the mechanical properties of CNTs composites , thecarbon nanotubes here were simplified as the effective fiber models which were obtained f rom the molecular dynamicssimulation. The result s obtained f rom regular array model were compared with those f rom Coxp shear-lag model ,Lauke and Fu theories , which show that the st resses t ransfer in CNTs composites are not only related to the aspectratio and volume f raction of CNTs as described in the above theories , but also sensitive to CNTs arrays and CNTspgeomet rical configuration within the selected representative volume element (RVE) . A better st ress t ransfer efficiency is obtained f rom stagger array , and the distance between two CNTs (2Tf ) has a great influence on the stressdist ribution. The result s show that there are some special characteristics for CNTs as the reinforcement phase ofcomposites , and they also prove that the homogenization method with multi-CNTs is efficient to analyze the st resst ransfer in CNTs composites.
