2006 Vol. 23, No. 5
2006, 23(5): 1-6.
Abstract:
The pressure properties , Vickers hardness and sliding wear-resistance of 1. 5～5 vol % SiCP (130 nm) / Al(149～75μm) mat rix composites fabricated by powder metallurgy and hot ext rusion were investigated to research theeffect of submicrometer SiCP dispersed in alumina mat rix on the wear behaviour. The result s show that increase inthe volume f raction of SiCP causes Vickers hardness increasing. It s Vickers hardness is 28. 4 and 33. 3 when thevolume f raction of SiCP (130 nm) is 1. 5～5 vol %. The pressure properties of the material are 170 MPa and 186 MParespectively. Under the higher load , the sliding wear - property increases with increasing the volume f raction ofSiCP ; 1. 5 vol % and 5 vol % SiCP / Al composites have higher sliding wear-behavior than 61520. 4 bronze bearing material and Al. An excellent wear-resistance microst ructure consisting of aluminum mat rix and minute hole and homogeneous dist ribution SiCP is formed in the wear surface of SiCP / Al mat rix composites.
The pressure properties , Vickers hardness and sliding wear-resistance of 1. 5～5 vol % SiCP (130 nm) / Al(149～75μm) mat rix composites fabricated by powder metallurgy and hot ext rusion were investigated to research theeffect of submicrometer SiCP dispersed in alumina mat rix on the wear behaviour. The result s show that increase inthe volume f raction of SiCP causes Vickers hardness increasing. It s Vickers hardness is 28. 4 and 33. 3 when thevolume f raction of SiCP (130 nm) is 1. 5～5 vol %. The pressure properties of the material are 170 MPa and 186 MParespectively. Under the higher load , the sliding wear - property increases with increasing the volume f raction ofSiCP ; 1. 5 vol % and 5 vol % SiCP / Al composites have higher sliding wear-behavior than 61520. 4 bronze bearing material and Al. An excellent wear-resistance microst ructure consisting of aluminum mat rix and minute hole and homogeneous dist ribution SiCP is formed in the wear surface of SiCP / Al mat rix composites.
2006, 23(5): 7-11.
Abstract:
A model of the compressive st rength of metal mat rix composites reinforced by porous network st ructurehas been proposed and modified through the mixing rule and referring the Zum- Gahr model and Khruschov model.The composites with different volume f raction reinforcement s were fabricated via the method of infilt ration by pressure assisted and vacuum driven ( PVI) . Many test data of compressive st rength were obtained using YAW-1000pressure experiment machine and proved the correctness of the model. The model includes maximum limit and minimum limit , the maximum limit follows a linear rule while the minimum limit no longer does. The result s show thatthe compressive st rength of metal mat rix composites with interpenet rated and intertwisted st ructure is improved distinctly and increased with the increasing of volume f raction of the reinforcement . Specially , the compressive st rengthincreases greatly when the volume f raction exceeds 80 %.
A model of the compressive st rength of metal mat rix composites reinforced by porous network st ructurehas been proposed and modified through the mixing rule and referring the Zum- Gahr model and Khruschov model.The composites with different volume f raction reinforcement s were fabricated via the method of infilt ration by pressure assisted and vacuum driven ( PVI) . Many test data of compressive st rength were obtained using YAW-1000pressure experiment machine and proved the correctness of the model. The model includes maximum limit and minimum limit , the maximum limit follows a linear rule while the minimum limit no longer does. The result s show thatthe compressive st rength of metal mat rix composites with interpenet rated and intertwisted st ructure is improved distinctly and increased with the increasing of volume f raction of the reinforcement . Specially , the compressive st rengthincreases greatly when the volume f raction exceeds 80 %.
2006, 23(5): 12-16.
Abstract:
A new process of preparation of C/ SiC-Cu composite by copper dichloride saturated solution infilt rationand reduction was investigated. The conditions of reduction were studied primarily. The phase identification and microst ructure of the C/ SiC-Cu composite were analyzed by XRD , EDS and SEM. Mechanical properties were evaluated by the three-point flexural test . The results show that the main influencing factors of mass gain are porosityand repeat times. It has been observed that the particle-like or block-like Cu infiltrates into the pores among f iber bundles , also among the filaments. The infiltration of Cu hardly has any effect on the flexural strength of C/ SiC-Cu composite.
A new process of preparation of C/ SiC-Cu composite by copper dichloride saturated solution infilt rationand reduction was investigated. The conditions of reduction were studied primarily. The phase identification and microst ructure of the C/ SiC-Cu composite were analyzed by XRD , EDS and SEM. Mechanical properties were evaluated by the three-point flexural test . The results show that the main influencing factors of mass gain are porosityand repeat times. It has been observed that the particle-like or block-like Cu infiltrates into the pores among f iber bundles , also among the filaments. The infiltration of Cu hardly has any effect on the flexural strength of C/ SiC-Cu composite.
2006, 23(5): 17-23.
Abstract:
The Ni-P-carbon nanotubes (Ni-P-CNTs) composite elect roless deposit on the basis of copper foil wasprepared by means of composite elect roless plating. The optical microscope , scanning elect ronic microscope (SEM) ,microhardness tester and omnipotence tensile testing machine were used to study the Ni-P-CNTs composite elect roless plating samplespmicrost ructure and properties. The result s show that the grain size on the sample surface decreases and the hardness for composite plating increases with the increment of CNTs content in the elect roless plating solution. In addition , the maximum extensibility , the reduction of area and the crack density of the f racture sideof Ni-P-CNTs composite elect roless plating samples increase with the increment of CNTs content , while the tensilest rength , the f racture st rength and Youngps modulus decrease.
The Ni-P-carbon nanotubes (Ni-P-CNTs) composite elect roless deposit on the basis of copper foil wasprepared by means of composite elect roless plating. The optical microscope , scanning elect ronic microscope (SEM) ,microhardness tester and omnipotence tensile testing machine were used to study the Ni-P-CNTs composite elect roless plating samplespmicrost ructure and properties. The result s show that the grain size on the sample surface decreases and the hardness for composite plating increases with the increment of CNTs content in the elect roless plating solution. In addition , the maximum extensibility , the reduction of area and the crack density of the f racture sideof Ni-P-CNTs composite elect roless plating samples increase with the increment of CNTs content , while the tensilest rength , the f racture st rength and Youngps modulus decrease.
2006, 23(5): 24-28.
Abstract:
With the nanoporous templates formed by the cont rolled hydrolysis and condensation of butyl titanate( Ti (OC4H9)4 ) , silver (Ag) nanowires with a slenderness ratio of 50～60 were prepared by using silver nit rate (AgNO3 ) as precursor. The prepared Ag nanowires were characterized by X-ray diff raction (XRD) and t ransmissionelect ro microscopy ( TEM) . A new kind of isot ropical conductive adhesive ( ICA) was developed by using these Agnanowires as conductive filler. The bulk resistivity and shear st rength testing results show that the novel ICA filledwith Ag nanowires (mass f raction 56 %) has bulk resistivity (1. 2 ×10-4Ω·cm) 6 times lower than that of ICA filledwith Ag particles (mass f raction 75 %) . For the lower filler content , the ICA filled with Ag nanowires exhibit shigher shear st rength (17. 6 MPa on Al subst rate) than the ICA filled with micrometer-sized Ag particles or nanometer-sized Ag particles cloes.
With the nanoporous templates formed by the cont rolled hydrolysis and condensation of butyl titanate( Ti (OC4H9)4 ) , silver (Ag) nanowires with a slenderness ratio of 50～60 were prepared by using silver nit rate (AgNO3 ) as precursor. The prepared Ag nanowires were characterized by X-ray diff raction (XRD) and t ransmissionelect ro microscopy ( TEM) . A new kind of isot ropical conductive adhesive ( ICA) was developed by using these Agnanowires as conductive filler. The bulk resistivity and shear st rength testing results show that the novel ICA filledwith Ag nanowires (mass f raction 56 %) has bulk resistivity (1. 2 ×10-4Ω·cm) 6 times lower than that of ICA filledwith Ag particles (mass f raction 75 %) . For the lower filler content , the ICA filled with Ag nanowires exhibit shigher shear st rength (17. 6 MPa on Al subst rate) than the ICA filled with micrometer-sized Ag particles or nanometer-sized Ag particles cloes.
2006, 23(5): 29-33.
Abstract:
In order to disperse the carbon nanotubes (CNTs) equably in the composite and develop the interconnection between CNTs and the copper mat rix , composite elect roplating with the aid of ult rasonic agitation was employed to prepare the copper/ CNTs composite coatings. SEM was used to observe their morphology. It was verifiedthat the surface of the composite is quite smooth ; CNTs are equably dispersed throughout the mat rix , and in addition , the interfacial binding between CNTs and copper was well. In these cases , a brief understanding of the effectof the ult rasonic agitation on the codeposition was ascertained.
In order to disperse the carbon nanotubes (CNTs) equably in the composite and develop the interconnection between CNTs and the copper mat rix , composite elect roplating with the aid of ult rasonic agitation was employed to prepare the copper/ CNTs composite coatings. SEM was used to observe their morphology. It was verifiedthat the surface of the composite is quite smooth ; CNTs are equably dispersed throughout the mat rix , and in addition , the interfacial binding between CNTs and copper was well. In these cases , a brief understanding of the effectof the ult rasonic agitation on the codeposition was ascertained.
2006, 23(5): 34-38.
Abstract:
C/ C-SiC composites were fabricated by molten silicon infilt ration (MSI) to C/ C preforms prepared bychemical vapor infilt ration (CVI) . The influences of adding Al in molten Si infilt rating agent on the microst ructureand mechanical properties of the composites was studied. The result s show that the composites fabricated by infiltrating Si into C/ C preforms contain SiC , C and residual Si phases. With the increasing of the amount of adding Al inthe agent , the amount of Al phase in the composites increases and the amount s of other phases such as SiC and Siphase decrease. SiC phase dist ributes around the carbon f iber , and Si phase exist s far away from the carbon f iberwhere there is nearly no Al phase. The bending st rength and the f racture toughness increase with the increase of theamount of adding Al. When the amount of Al increases from 0 to 10 % , the bending st rength increases from 116. 7MPa to 175. 4 MPa and the f racture toughness from 5. 8 MPa·m1/2 to 8. 6 MPa·m1/2 , that is , by 50. 3 % and 48. 2 %respectively. The Al phase makes the f racture mechanism of the composite become toughness f racture.
C/ C-SiC composites were fabricated by molten silicon infilt ration (MSI) to C/ C preforms prepared bychemical vapor infilt ration (CVI) . The influences of adding Al in molten Si infilt rating agent on the microst ructureand mechanical properties of the composites was studied. The result s show that the composites fabricated by infiltrating Si into C/ C preforms contain SiC , C and residual Si phases. With the increasing of the amount of adding Al inthe agent , the amount of Al phase in the composites increases and the amount s of other phases such as SiC and Siphase decrease. SiC phase dist ributes around the carbon f iber , and Si phase exist s far away from the carbon f iberwhere there is nearly no Al phase. The bending st rength and the f racture toughness increase with the increase of theamount of adding Al. When the amount of Al increases from 0 to 10 % , the bending st rength increases from 116. 7MPa to 175. 4 MPa and the f racture toughness from 5. 8 MPa·m1/2 to 8. 6 MPa·m1/2 , that is , by 50. 3 % and 48. 2 %respectively. The Al phase makes the f racture mechanism of the composite become toughness f racture.
2006, 23(5): 39-43.
Abstract:
In order to obtain a low resistivity and high PTC effect , the Ni/ Mn/ BaTiO3 composite was prepared bythe t raditional solid-crystal sintering method. The effect s of metal content s (Ni , Mn) and heat t reatment techniqueson positive temperature coefficient resistor ( PTCR) ceramic properties were studied. The very weak PTC effect ofthe composite sintered in deoxidizing atmosphere (1250 ℃, 20 min) was renewed effectively by heat-t reatment in air(780 ℃, 60 min) . The Ni/ Mn/ BaTiO3 composite has the low room-temperature resistivity (ρ25 ℃ = 10. 2Ω·cm) andan obvious PTC effect (ρmax /ρmin = 1. 42 ×103 ) .
In order to obtain a low resistivity and high PTC effect , the Ni/ Mn/ BaTiO3 composite was prepared bythe t raditional solid-crystal sintering method. The effect s of metal content s (Ni , Mn) and heat t reatment techniqueson positive temperature coefficient resistor ( PTCR) ceramic properties were studied. The very weak PTC effect ofthe composite sintered in deoxidizing atmosphere (1250 ℃, 20 min) was renewed effectively by heat-t reatment in air(780 ℃, 60 min) . The Ni/ Mn/ BaTiO3 composite has the low room-temperature resistivity (ρ25 ℃ = 10. 2Ω·cm) andan obvious PTC effect (ρmax /ρmin = 1. 42 ×103 ) .
2006, 23(5): 44-50.
Abstract:
Microst ructural characteristics and thermal shock resistance of nano-powder reinforcing Ti (C ,N) basedcermet s were investigated in order to efficiently improve the mechanical properties of Ti (C ,N) based cermet s and thehigh-speed cutting behaviors of cermet s cutters. SEM and TEM analyses show that the coarser ceramic particles exhibit a typical core-rim st ructure (core is usually referred to as TiC or Ti (C ,N) and rim is virtually a ( Ti ,Mo ,W)(C ,N) solid solution) . The nano-powder reinforcing mechanisms can be summarized as grain fining st rengthening ,dispersion st rengthening and solid solution st rengthening. The thermal shock test s on nano - powder reinforcingcermet s and conventional cermet s show that the quantity and size of the voids plus the size of micro-cracks in bothcermet s increase and other phenomena such as surface oxidation , cracks growth , cracks deflection and cracks bridging are found to become increasingly apparent with thermal shock cycles , and the nano-powder reinforcing cermet spossess a better thermal shock resistance in comparison with conventional cermet s.
Microst ructural characteristics and thermal shock resistance of nano-powder reinforcing Ti (C ,N) basedcermet s were investigated in order to efficiently improve the mechanical properties of Ti (C ,N) based cermet s and thehigh-speed cutting behaviors of cermet s cutters. SEM and TEM analyses show that the coarser ceramic particles exhibit a typical core-rim st ructure (core is usually referred to as TiC or Ti (C ,N) and rim is virtually a ( Ti ,Mo ,W)(C ,N) solid solution) . The nano-powder reinforcing mechanisms can be summarized as grain fining st rengthening ,dispersion st rengthening and solid solution st rengthening. The thermal shock test s on nano - powder reinforcingcermet s and conventional cermet s show that the quantity and size of the voids plus the size of micro-cracks in bothcermet s increase and other phenomena such as surface oxidation , cracks growth , cracks deflection and cracks bridging are found to become increasingly apparent with thermal shock cycles , and the nano-powder reinforcing cermet spossess a better thermal shock resistance in comparison with conventional cermet s.
2006, 23(5): 51-57.
Abstract:
A series of microcapsules were prepared by in-si tu polymerization with poly (urea-formaldehyde) as theshell material and the mixture of epoxy resin E-51 and butyl glycidyl ether (501 # ) as the core material. The effect sof the processing parameters , including the mass ratio of core material to shell material , final p H value , agitationrate , acidification time and heating rate , on the state of microencapsulation , the microcapsule size and it s dist ribution were discussed by L16 (45 ) orthogonal experiment . The physical properties of microcap sules were investigatedusing scanning elect ron microscopy (SEM) and optical-photographic microscopy (OM) . The state of microencapsulation is dramatically dependent on the mass ratio of core material to shell material and final p H value. Themicrocapsule surface morphologies are better when the acidification time and heating rate are properly increased.The microcap sule size decreases and it s dist ribution narrows with the increasing of agitation rate. The optimum conditions are as follows : the mass ratio of core material to shell material is 0. 8∶1 , final p H value is 2. 0～4. 0 , acidification time is 2. 0～3. 0 h , heating rate is 0. 17～0. 25 ℃·min-1 , and agitation rate is 325～350 r·min -1 .
A series of microcapsules were prepared by in-si tu polymerization with poly (urea-formaldehyde) as theshell material and the mixture of epoxy resin E-51 and butyl glycidyl ether (501 # ) as the core material. The effect sof the processing parameters , including the mass ratio of core material to shell material , final p H value , agitationrate , acidification time and heating rate , on the state of microencapsulation , the microcapsule size and it s dist ribution were discussed by L16 (45 ) orthogonal experiment . The physical properties of microcap sules were investigatedusing scanning elect ron microscopy (SEM) and optical-photographic microscopy (OM) . The state of microencapsulation is dramatically dependent on the mass ratio of core material to shell material and final p H value. Themicrocapsule surface morphologies are better when the acidification time and heating rate are properly increased.The microcap sule size decreases and it s dist ribution narrows with the increasing of agitation rate. The optimum conditions are as follows : the mass ratio of core material to shell material is 0. 8∶1 , final p H value is 2. 0～4. 0 , acidification time is 2. 0～3. 0 h , heating rate is 0. 17～0. 25 ℃·min-1 , and agitation rate is 325～350 r·min -1 .
2006, 23(5): 58-62.
Abstract:
The composites of polypyrrole ( PPy) and vanadium pentoxide (V2O5 ) were synthesized by chemicaloxidative polymerization. By using different methods of adding oxidant , different st ructure composites wereobtained. The conductivities of the composites were measured by a four-probe instrument . The composites were investigated and characterized by BET , XRD and SEM. The result s show that the composites obtained by using differentmethods of adding the oxidant have different st ructures and morphologies. When the oxidant is added into the reaction vessel first , polypyrrole intercalates into the sandwich of V2O5 . When the pyrrole is added into the reaction vessel first , PPy deposit s preferentially on the V2O5 particle surface. To study the elect rochemical performance of composites , button-type lithium secondary batteries were fabricated with the composites as anodes. The elect rochemicalproperties as anodes were investigated with galvanostatic charge-discharge test and A. C. impedance spect roscopy.It was found that the V2O5 / PPy composite obtained by adding oxidant first possessed excellent elect rochemical performance. The highest discharge capacity of V2O5 / PPy anode reached 230 mAh/ g.
The composites of polypyrrole ( PPy) and vanadium pentoxide (V2O5 ) were synthesized by chemicaloxidative polymerization. By using different methods of adding oxidant , different st ructure composites wereobtained. The conductivities of the composites were measured by a four-probe instrument . The composites were investigated and characterized by BET , XRD and SEM. The result s show that the composites obtained by using differentmethods of adding the oxidant have different st ructures and morphologies. When the oxidant is added into the reaction vessel first , polypyrrole intercalates into the sandwich of V2O5 . When the pyrrole is added into the reaction vessel first , PPy deposit s preferentially on the V2O5 particle surface. To study the elect rochemical performance of composites , button-type lithium secondary batteries were fabricated with the composites as anodes. The elect rochemicalproperties as anodes were investigated with galvanostatic charge-discharge test and A. C. impedance spect roscopy.It was found that the V2O5 / PPy composite obtained by adding oxidant first possessed excellent elect rochemical performance. The highest discharge capacity of V2O5 / PPy anode reached 230 mAh/ g.
Pretreatment of jute f iber and the mechanical properties ofjute f iber mat reinforced polypropylene
2006, 23(5): 63-69.
Abstract:
A new method of pret reatment of jute f iber is put forward , where MPP emulsion was used in the pret reatment . Several issues were studied including the effect s of pret reatment of jute f iber with alkali solution on themoisture and thermal stability as well as the effect s of pret reatment of jute f iber with alkali solution and combinationof alkali solution and MPP emulsion on the mechanical properties of the jute f iber mat reinforced polypropylene. Theresult s show that the moisture and thermal stability of the jute f iber are improved and the mechanical properties ofjute f iber mat reinforced polypropylene are obviously increased af ter t reating with alkali solution. The mechanicalproperties of the composites are even better af ter t reating with combination of alkali solution and MPP emulsion.
A new method of pret reatment of jute f iber is put forward , where MPP emulsion was used in the pret reatment . Several issues were studied including the effect s of pret reatment of jute f iber with alkali solution on themoisture and thermal stability as well as the effect s of pret reatment of jute f iber with alkali solution and combinationof alkali solution and MPP emulsion on the mechanical properties of the jute f iber mat reinforced polypropylene. Theresult s show that the moisture and thermal stability of the jute f iber are improved and the mechanical properties ofjute f iber mat reinforced polypropylene are obviously increased af ter t reating with alkali solution. The mechanicalproperties of the composites are even better af ter t reating with combination of alkali solution and MPP emulsion.
2006, 23(5): 70-74.
Abstract:
Polyphenylacetylene ( PPA) was prepared with anhydrous AlCl3 as catalyst , and sulfonated by concent rated H2SO4 . The conductivities were studied for carbon nanotubes (CNT) / PPA and sulfonated CNT/ PPA composite , which were prepared by mixing CNT with polymer in tet rahydrofuran under sonication. The room temperature conductivity of the two kinds of composites increases with increasing the ratio of CNT. The estimated percolation threshold of sulfonated CNT/ PPA is 1 % less than that of CNT/ PPA and the amount of CNT added to PPA forobtaining the maximum conductivity is 10 % of that of the sulfonated PPA. And the factors that affect the conductivity of the composites were analyzed when the temperature changes. The XRD shows that the sulfonated PPA hascreated a new crystal st ructure on the interface of CNT.
Polyphenylacetylene ( PPA) was prepared with anhydrous AlCl3 as catalyst , and sulfonated by concent rated H2SO4 . The conductivities were studied for carbon nanotubes (CNT) / PPA and sulfonated CNT/ PPA composite , which were prepared by mixing CNT with polymer in tet rahydrofuran under sonication. The room temperature conductivity of the two kinds of composites increases with increasing the ratio of CNT. The estimated percolation threshold of sulfonated CNT/ PPA is 1 % less than that of CNT/ PPA and the amount of CNT added to PPA forobtaining the maximum conductivity is 10 % of that of the sulfonated PPA. And the factors that affect the conductivity of the composites were analyzed when the temperature changes. The XRD shows that the sulfonated PPA hascreated a new crystal st ructure on the interface of CNT.
2006, 23(5): 75-78.
Abstract:
TiO2 / ( PEO)8LiClO4 composite polymer elect rolyte films were prepared by a solution cast method. TiO2particles were in2si tu formed in ( PEO)8LiClO4 mat rix by simply mixing PEO , LiClO4 and tet rabutyl titanate andthen drying. The morphology , thermal performance and conductivity of the films were studied using SEM , DSC andelect rical impedance spect roscopy , respectively. The result s show that the in-situ formed TiO2 particles are founduniformly dispersed in PEO mat rix. The glass t ransition temperature and crystallinity of the films are lowered due tothe presence of TiO2 . The conductive behaviour of the films follows an Arrhenius type relation. A maximal conductivity 5. 5 ×10 - 5 S/ cm at 20 ℃of the TiO2 / ( PEO)8LiClO4 film was obtained at 5 % mass f raction of TiO2 . Thepolymer lithium ion battery with the elect rolyte films exhibit s stable discharge voltage. The discharge specificcapacity could still retain 107 mAh/ g af ter 20 cycles.
TiO2 / ( PEO)8LiClO4 composite polymer elect rolyte films were prepared by a solution cast method. TiO2particles were in2si tu formed in ( PEO)8LiClO4 mat rix by simply mixing PEO , LiClO4 and tet rabutyl titanate andthen drying. The morphology , thermal performance and conductivity of the films were studied using SEM , DSC andelect rical impedance spect roscopy , respectively. The result s show that the in-situ formed TiO2 particles are founduniformly dispersed in PEO mat rix. The glass t ransition temperature and crystallinity of the films are lowered due tothe presence of TiO2 . The conductive behaviour of the films follows an Arrhenius type relation. A maximal conductivity 5. 5 ×10 - 5 S/ cm at 20 ℃of the TiO2 / ( PEO)8LiClO4 film was obtained at 5 % mass f raction of TiO2 . Thepolymer lithium ion battery with the elect rolyte films exhibit s stable discharge voltage. The discharge specificcapacity could still retain 107 mAh/ g af ter 20 cycles.
2006, 23(5): 79-83.
Abstract:
The short quartz f iber reinforced polyimide composites (SQF/ PI) were prepared by thermal curing of B-stagedmolding powders , which were obtained by impregnating of short quartz f ibers with PMR monomer solution in ethyl alcoholfollowed by thermal baking up to 220 ℃. The experimental results demonstrate that the fully-cured SQF/ PI composites exhibit high thermal stability and good mechanical properties , and the f iber content has little influence on the thermal propertybut great influence on the mechanical property. The SQF/ PI composites show an excellent dielectric property , stabledielect ric constant and dissipation factor in the broad f requency range from 1 kHz to 18 GHz.
The short quartz f iber reinforced polyimide composites (SQF/ PI) were prepared by thermal curing of B-stagedmolding powders , which were obtained by impregnating of short quartz f ibers with PMR monomer solution in ethyl alcoholfollowed by thermal baking up to 220 ℃. The experimental results demonstrate that the fully-cured SQF/ PI composites exhibit high thermal stability and good mechanical properties , and the f iber content has little influence on the thermal propertybut great influence on the mechanical property. The SQF/ PI composites show an excellent dielectric property , stabledielect ric constant and dissipation factor in the broad f requency range from 1 kHz to 18 GHz.
2006, 23(5): 84-88.
Abstract:
In order to study the effect of laser parameters on the mass ablative rate of the carbon f iber reinforcedsilicone modified epoxy resin composite , laser irradiation experiment s of the composite were carried out by a highpower CO2 laser with different laser parameters. The effect of the irradiation time , laser intensity and spot diameteron the mass ablative rate of carbon f iber reinforced silicone modified epoxy resin composite was analyzed respectively. The result s indicate that the mass ablative rate of the composite is not greatly affected by the laser irradiationtime , but affected by the laser intensity and spot diameter. The mass ablative rate of the composite increases whenthe laser intensity and spot diameter are increased.
In order to study the effect of laser parameters on the mass ablative rate of the carbon f iber reinforcedsilicone modified epoxy resin composite , laser irradiation experiment s of the composite were carried out by a highpower CO2 laser with different laser parameters. The effect of the irradiation time , laser intensity and spot diameteron the mass ablative rate of carbon f iber reinforced silicone modified epoxy resin composite was analyzed respectively. The result s indicate that the mass ablative rate of the composite is not greatly affected by the laser irradiationtime , but affected by the laser intensity and spot diameter. The mass ablative rate of the composite increases whenthe laser intensity and spot diameter are increased.
2006, 23(5): 89-95.
Abstract:
A real time monitoring system for Liquid Composites Molding (LCM) process based on the direct current principle was established to improve quality stability of products and make the process cost-efficient . The experiments indicate that the monitoring system can precisely reflect the resin flow f ront arrival and curing course of resinon the inspecting spot . The main process factorsp effect s on the monitoring signal were studied. The experimentalresult s show that different resin systems have distinct responses to the monitoring signal. The monitoring saturationvalue increases with the increase of temperature and the brass wirespbare length respectively. The f iber volume fraction and laying angle of f ibers have neglectable effects on the monitoring signal .
A real time monitoring system for Liquid Composites Molding (LCM) process based on the direct current principle was established to improve quality stability of products and make the process cost-efficient . The experiments indicate that the monitoring system can precisely reflect the resin flow f ront arrival and curing course of resinon the inspecting spot . The main process factorsp effect s on the monitoring signal were studied. The experimentalresult s show that different resin systems have distinct responses to the monitoring signal. The monitoring saturationvalue increases with the increase of temperature and the brass wirespbare length respectively. The f iber volume fraction and laying angle of f ibers have neglectable effects on the monitoring signal .
2006, 23(5): 96-100.
Abstract:
Through radical copolymerization , modified waterborne poly methacrylic acid (MPMA) with hydrophilicand hydrophobic group s was prepared by reacting ally poly (ehtenoxy ether) , methacrylic acid and methyl methacrylate. Using MPMA as ceramic dispersant , the effect s of MPMA concent ration on the rheological behavior of Diamond/ Feldspar/ Clay compound slurry and ceramic breaking st rength were studied , and simultaneously the reasonsand dispersive mechanism were analyzed. The result s show that MPMA can improve the slurryps rheological properties and the ceramic st rength. The optimum MPMA concent ration is 0. 57 wt % (based on the absolute dry slurry)with p H ranging from 9 to 10. When adding 0. 57 wt % MPMA , the slurryps negative Zeta potential increases from28. 5 mV to 65. 5 mV , and it s zero shear viscosity decreases from 690. 9 mPa·s to 81. 6 mPa·s. At the same time , it sthixot ropy area reaches the minimum , and the slurry exhibit s Newton flow behavior. Compared with ceramic withinorganic dispersant addition , the ceramic with MPMA addition owns higher breaking st rength , which is increasedfrom 160 MPa to 268 MPa.
Through radical copolymerization , modified waterborne poly methacrylic acid (MPMA) with hydrophilicand hydrophobic group s was prepared by reacting ally poly (ehtenoxy ether) , methacrylic acid and methyl methacrylate. Using MPMA as ceramic dispersant , the effect s of MPMA concent ration on the rheological behavior of Diamond/ Feldspar/ Clay compound slurry and ceramic breaking st rength were studied , and simultaneously the reasonsand dispersive mechanism were analyzed. The result s show that MPMA can improve the slurryps rheological properties and the ceramic st rength. The optimum MPMA concent ration is 0. 57 wt % (based on the absolute dry slurry)with p H ranging from 9 to 10. When adding 0. 57 wt % MPMA , the slurryps negative Zeta potential increases from28. 5 mV to 65. 5 mV , and it s zero shear viscosity decreases from 690. 9 mPa·s to 81. 6 mPa·s. At the same time , it sthixot ropy area reaches the minimum , and the slurry exhibit s Newton flow behavior. Compared with ceramic withinorganic dispersant addition , the ceramic with MPMA addition owns higher breaking st rength , which is increasedfrom 160 MPa to 268 MPa.
2006, 23(5): 101-106.
Abstract:
Silicon nit ride materials doped with 6 wt % ytterbium oxide and 2 wt % alumina were prepared by nit rogen gas pressure sintering. The high temperature dynamic fatigue behavior of the Si3N4 composites was investigatedin terms of the loading rate dependence of fatigue st rength at high temperatures. The specimens were pre-cracked byVickers indentation to avoid creep and to ensure slow crack growth dominating in fatigue damage. The tests wereperformed in the four-point bending mode in air at the temperature of 1000 ℃, 1200 ℃, 1300 ℃and 1400 ℃respectively. The cross head speeds were chosen of 1 , 0. 5 , 011 and 0. 01 mm/ min at each temperature. By plotting fatiguest rength against cross-head speed in double logarithm coordinates , the highest slow crack exponent number N wasfound in the test at 1200 ℃, indicating that the critical crack growth was the slowest at this temperature. X-raydiff raction and t ransmission elect ron microscopy show that the grain boundary crystallization and crack healinginhibit the crack growth thus increasing the slow crack growth exponent number. Energy dispersive spect rumreveals that the crack surface oxidation may benefit the crystallization at 1200 ℃, while slow crack growth may bepromoted at higher temperatures because of over-oxidation.
Silicon nit ride materials doped with 6 wt % ytterbium oxide and 2 wt % alumina were prepared by nit rogen gas pressure sintering. The high temperature dynamic fatigue behavior of the Si3N4 composites was investigatedin terms of the loading rate dependence of fatigue st rength at high temperatures. The specimens were pre-cracked byVickers indentation to avoid creep and to ensure slow crack growth dominating in fatigue damage. The tests wereperformed in the four-point bending mode in air at the temperature of 1000 ℃, 1200 ℃, 1300 ℃and 1400 ℃respectively. The cross head speeds were chosen of 1 , 0. 5 , 011 and 0. 01 mm/ min at each temperature. By plotting fatiguest rength against cross-head speed in double logarithm coordinates , the highest slow crack exponent number N wasfound in the test at 1200 ℃, indicating that the critical crack growth was the slowest at this temperature. X-raydiff raction and t ransmission elect ron microscopy show that the grain boundary crystallization and crack healinginhibit the crack growth thus increasing the slow crack growth exponent number. Energy dispersive spect rumreveals that the crack surface oxidation may benefit the crystallization at 1200 ℃, while slow crack growth may bepromoted at higher temperatures because of over-oxidation.
2006, 23(5): 107-110.
Abstract:
Perhydropolysilazane ( PHPS) and polyhydridomethylsilazane ( PHMS) were used as preceramic polymers , respectively , to prepare three-dimensional silica f iber reinforced silicon nit ride composites through repeatedinfilt ration and pyrolysis at a low temperature (600 ℃) , and the mechanical properties and microst ructures of thecomposites were investigated through comparison. The composite prepared with PHPS , with density of 1. 83 g/cm3 , porosity of 10 % , and flexural st rength of 45. 4 MPa , shows a smooth f racture surface and st rong f iber/ mat rixbonding , while the composite prepared with PHMS exhibit s a rough f racture surface and moderate interfacialadhesion , lower density of 1. 66 g/ cm3 , higher porosity of 16 % , but higher flexural st rength of 56. 3 MPa. Thedifferent activities of the precursors result in different interfacial microst ructures and mechanical properties of thecomposites.
Perhydropolysilazane ( PHPS) and polyhydridomethylsilazane ( PHMS) were used as preceramic polymers , respectively , to prepare three-dimensional silica f iber reinforced silicon nit ride composites through repeatedinfilt ration and pyrolysis at a low temperature (600 ℃) , and the mechanical properties and microst ructures of thecomposites were investigated through comparison. The composite prepared with PHPS , with density of 1. 83 g/cm3 , porosity of 10 % , and flexural st rength of 45. 4 MPa , shows a smooth f racture surface and st rong f iber/ mat rixbonding , while the composite prepared with PHMS exhibit s a rough f racture surface and moderate interfacialadhesion , lower density of 1. 66 g/ cm3 , higher porosity of 16 % , but higher flexural st rength of 56. 3 MPa. Thedifferent activities of the precursors result in different interfacial microst ructures and mechanical properties of thecomposites.
2006, 23(5): 111-115.
Abstract:
A mathematical model according to st ructural feature of Si3N4 particle reinforcement and process characteristic of isothermal chemical vapor infilt ration ( ICVI) was proposed to numerically simulate the densification behaviors of Si3N4 particle reinforced Si3N4 composites. The ball-like pore model is developed to depict the st ructure ofSi3N4 particle reinforcement and the mass t ransfer equation of reagent s is used to characterize the concent ration profile in the preform. The corresponding experiment was done in order to testify the mathematical model . The calculated result s represent the same densification regularity as the experimental data does , and the curves of calculatedinfilt ration time and porosity are in agreement with the experimental ones , which indicates that the model developedhere is reasonable to characterize the ICVI process of Si3N4P / Si3N4 composites.
A mathematical model according to st ructural feature of Si3N4 particle reinforcement and process characteristic of isothermal chemical vapor infilt ration ( ICVI) was proposed to numerically simulate the densification behaviors of Si3N4 particle reinforced Si3N4 composites. The ball-like pore model is developed to depict the st ructure ofSi3N4 particle reinforcement and the mass t ransfer equation of reagent s is used to characterize the concent ration profile in the preform. The corresponding experiment was done in order to testify the mathematical model . The calculated result s represent the same densification regularity as the experimental data does , and the curves of calculatedinfilt ration time and porosity are in agreement with the experimental ones , which indicates that the model developedhere is reasonable to characterize the ICVI process of Si3N4P / Si3N4 composites.
2006, 23(5): 116-120.
Abstract:
A two-dimensional axisymmet ric model for the densification behavior of C/ SiC composites in isothermalchemical vapor infilt ration was developed according to the st ructural feature of C/ SiC composites and the physicochemical phenomena of the isothermal chemical vapor infilt ration process. A mathematical model was proposed tocharacterize the densification behavior of a small scale thruster liner component of C/ SiC composites for a rocket engine by the finite element method. The density was measured and X-ray CT was inspected in order to validate the model.The analogical regularities represented by the calculation results and the experimental data show that the model developed inthis article is reasonable and feasible to characterize the densification behavior of C/ SiC composites in ICVI process. Thecalculated results , such as distribution and evolution of porosity and density of thruster liner component , lay the foundationof further research and optimization of ICVI process for fabrication of C/ SiC composites components.
A two-dimensional axisymmet ric model for the densification behavior of C/ SiC composites in isothermalchemical vapor infilt ration was developed according to the st ructural feature of C/ SiC composites and the physicochemical phenomena of the isothermal chemical vapor infilt ration process. A mathematical model was proposed tocharacterize the densification behavior of a small scale thruster liner component of C/ SiC composites for a rocket engine by the finite element method. The density was measured and X-ray CT was inspected in order to validate the model.The analogical regularities represented by the calculation results and the experimental data show that the model developed inthis article is reasonable and feasible to characterize the densification behavior of C/ SiC composites in ICVI process. Thecalculated results , such as distribution and evolution of porosity and density of thruster liner component , lay the foundationof further research and optimization of ICVI process for fabrication of C/ SiC composites components.
2006, 23(5): 121-125.
Abstract:
Based on the conductive mechanism of the carbon f iber reinforced cement (CFRC) composite , a mathematic model was set up to describe the conductivity of CFRC. By using the model , the relationships between the elect ric conductivity and the microst ructure parameters as well as the motion parameters of carriers within the CFRCcomposites were obtained. Moreover , the load sensitivity of CFRC composites was analyzed in terms of the conductivity model. The theoretical deductions obtained from the model were in good agreement with the experimental results , which proved the rationality of the conductivity model of CFRC.
Based on the conductive mechanism of the carbon f iber reinforced cement (CFRC) composite , a mathematic model was set up to describe the conductivity of CFRC. By using the model , the relationships between the elect ric conductivity and the microst ructure parameters as well as the motion parameters of carriers within the CFRCcomposites were obtained. Moreover , the load sensitivity of CFRC composites was analyzed in terms of the conductivity model. The theoretical deductions obtained from the model were in good agreement with the experimental results , which proved the rationality of the conductivity model of CFRC.
2006, 23(5): 126-131.
Abstract:
To investigate the size effect of effective elastic properties for a nearly lamellar γ- TiAl based alloy , amicromechanical method was developed based on the micropolar theory. The emphasis was placed on proposing ananalytical-micromechanical model. In cont rast to the classical micromechanics theory , the model was const ructed byusing the orientational average over all PST ( Polysynthetically twinned crystal ) grain orientations and extendingMori- Tanakaps method to micropolar mediums. The computed result s show that the size dependence is morepronounced when the PST particleps size a approaches the mat rix characteristic length lm , and with decreasing thediameter of PST particles , the effective elastic moduli of γ- TiAl based alloy increase. The classical prediction ofeffective elastic properties for Cauchy mediums is recovered when the PST particleps diameter tends to infinitycompared to the characteristic length of the micropolar mat rix.
To investigate the size effect of effective elastic properties for a nearly lamellar γ- TiAl based alloy , amicromechanical method was developed based on the micropolar theory. The emphasis was placed on proposing ananalytical-micromechanical model. In cont rast to the classical micromechanics theory , the model was const ructed byusing the orientational average over all PST ( Polysynthetically twinned crystal ) grain orientations and extendingMori- Tanakaps method to micropolar mediums. The computed result s show that the size dependence is morepronounced when the PST particleps size a approaches the mat rix characteristic length lm , and with decreasing thediameter of PST particles , the effective elastic moduli of γ- TiAl based alloy increase. The classical prediction ofeffective elastic properties for Cauchy mediums is recovered when the PST particleps diameter tends to infinitycompared to the characteristic length of the micropolar mat rix.
2006, 23(5): 132-136.
Abstract:
This paper studies the sensitivity of eigenvalues to ply angles for composite plates. Based on the classicaltheory of the laminated composite plate , the mass mat rix and stiffness mat rix were obtained by using thefinite-element-method and principle of virtual work. The equation between ply angles and stiffness mat rix was determined and by using the perturbation method in dynamic equation , the sensitivities of the eigenvalues to the ply angles were obtained explicitly. Through the numerical example given in the paper , the conclusion was demonst ratedthat the present method has superiority in accuracy compared with the finite difference method.
This paper studies the sensitivity of eigenvalues to ply angles for composite plates. Based on the classicaltheory of the laminated composite plate , the mass mat rix and stiffness mat rix were obtained by using thefinite-element-method and principle of virtual work. The equation between ply angles and stiffness mat rix was determined and by using the perturbation method in dynamic equation , the sensitivities of the eigenvalues to the ply angles were obtained explicitly. Through the numerical example given in the paper , the conclusion was demonst ratedthat the present method has superiority in accuracy compared with the finite difference method.
2006, 23(5): 137-142.
Abstract:
The theoretical formulas are worked out to predict the effective bulk moduli , shear moduli and Young’smoduli of the composite reinforced by hollow coating spheres using the developed five phase spherical model. Therelations of the effective moduli of the composite , the thickness of the hollow sphere wall , volume f raction of thefiller , and thickness of the coating were investigated. In order to illust rate the validity of the present result s , thefive phase model can be reduced to the case of hollow noncoating spheres filled into the mat rix , and the reducedresult s were compared with the experimental data. The calculating example shows that the greater filler volumef raction and relatively thicker wall lead to the bigger elastic moduli , and the smallest elastic moduli appear in the caseof the greatest filler volume f raction and the relative thinnest wall when the thickness of the coating is very thin.
The theoretical formulas are worked out to predict the effective bulk moduli , shear moduli and Young’smoduli of the composite reinforced by hollow coating spheres using the developed five phase spherical model. Therelations of the effective moduli of the composite , the thickness of the hollow sphere wall , volume f raction of thefiller , and thickness of the coating were investigated. In order to illust rate the validity of the present result s , thefive phase model can be reduced to the case of hollow noncoating spheres filled into the mat rix , and the reducedresult s were compared with the experimental data. The calculating example shows that the greater filler volumef raction and relatively thicker wall lead to the bigger elastic moduli , and the smallest elastic moduli appear in the caseof the greatest filler volume f raction and the relative thinnest wall when the thickness of the coating is very thin.
2006, 23(5): 143-148.
Abstract:
The mass loss of thermal protection material under the condition of high temperatures , enthalpies andpressures is caused by physical , chemical and mechanical factors and the change of material thermomechanical properties and thermophysical properties at high temperatures is irreversible , showing complex nonlinear characteristics.The present paper is devoted to the development and establishment of corresponding thermochemical and thermomechanical ablative models by analyzing flow and C/ C composite materials ablative mechanism. With the help of theconservation law of mass and energy and thermochemical equilibrium of system chemical reaction , the thermal conduct equation is presented based on a moving boundary caused by linear ablation ; the mathematical equation is solvednumerically by a nonlinear coupling scheme , while the changes of material properties with temperature are considered. The calculated result s characterize the dynamic thermomechanical behavior of the material in special environments such as high temperature. This analysis accords well with experimental data. The analysis realizes instantane2ous simulation of ablation effected by complex coupling factors of high temperature and load.
The mass loss of thermal protection material under the condition of high temperatures , enthalpies andpressures is caused by physical , chemical and mechanical factors and the change of material thermomechanical properties and thermophysical properties at high temperatures is irreversible , showing complex nonlinear characteristics.The present paper is devoted to the development and establishment of corresponding thermochemical and thermomechanical ablative models by analyzing flow and C/ C composite materials ablative mechanism. With the help of theconservation law of mass and energy and thermochemical equilibrium of system chemical reaction , the thermal conduct equation is presented based on a moving boundary caused by linear ablation ; the mathematical equation is solvednumerically by a nonlinear coupling scheme , while the changes of material properties with temperature are considered. The calculated result s characterize the dynamic thermomechanical behavior of the material in special environments such as high temperature. This analysis accords well with experimental data. The analysis realizes instantane2ous simulation of ablation effected by complex coupling factors of high temperature and load.
2006, 23(5): 149-153.
Abstract:
The properties of plain carbon fabric prepreg were researched using a picture f rame shear rig which isinstalled on a mechanical test machine. The result shows that the shear properties of the fabric prepreg were similarto those of the pure fabric , which has different properties during different shear stages. According to the experimentdata , two-dimensional shear models were set up in two different shear stages. At the beginning of the shear stage ,a torsion spring was used to simulate the friction of the cross point of the warp and the wef t in the prepreg fabric.The torsion stiffness coefficient of the torsion spring was determined on experiment . In the second shear stage , therelationship of shear angle and load was given. It is proved that the torsion spring can simulate the shear f rictionwell in the first shear stage.
The properties of plain carbon fabric prepreg were researched using a picture f rame shear rig which isinstalled on a mechanical test machine. The result shows that the shear properties of the fabric prepreg were similarto those of the pure fabric , which has different properties during different shear stages. According to the experimentdata , two-dimensional shear models were set up in two different shear stages. At the beginning of the shear stage ,a torsion spring was used to simulate the friction of the cross point of the warp and the wef t in the prepreg fabric.The torsion stiffness coefficient of the torsion spring was determined on experiment . In the second shear stage , therelationship of shear angle and load was given. It is proved that the torsion spring can simulate the shear f rictionwell in the first shear stage.
2006, 23(5): 154-160.
Abstract:
Based on the existing experiment observation and the movement t races of yarn carriers on the braidingmachine bed , a microst ructure model of 4-step three-dimensional rectangular braided composites is established bythe analytical approach. Especially , the spatial configuration of interior yarns was analyzed in detail , and the distortion of the cross-section of interior yarns caused by mutual contact and jamming was considered in the model. As thejamming conditions in different regions were not uniform , the yarn packing factor of interior yarns was differentfrom that of surface yarns and corner yarns in the model. Then a new unit-cell partition scheme that can overcomethe shortcomings of the existing 45°partition schemes was proposed to make the directions of all the unit-cells parallel with the edges of the cross-section of the composites. Then the microst ructure unit-cell models for the three regions of the composites , the interior , surface and corner were established , which were expediently utilized to establish the prediction models of mechanical properties. By using the unit cell models , the st ructural geometry of thecomposites was analyzed , and the mathematical relation between technics parameters and microst ructure of the unitcells was obtained. The calculated values of the geometric characteristics of braided composites specimens by themodel well agree with the measured values. The numerical results indicate the effectiveness of the model , and thepresent model has presented a foundation for the mechanical performance prediction of the composites.
Based on the existing experiment observation and the movement t races of yarn carriers on the braidingmachine bed , a microst ructure model of 4-step three-dimensional rectangular braided composites is established bythe analytical approach. Especially , the spatial configuration of interior yarns was analyzed in detail , and the distortion of the cross-section of interior yarns caused by mutual contact and jamming was considered in the model. As thejamming conditions in different regions were not uniform , the yarn packing factor of interior yarns was differentfrom that of surface yarns and corner yarns in the model. Then a new unit-cell partition scheme that can overcomethe shortcomings of the existing 45°partition schemes was proposed to make the directions of all the unit-cells parallel with the edges of the cross-section of the composites. Then the microst ructure unit-cell models for the three regions of the composites , the interior , surface and corner were established , which were expediently utilized to establish the prediction models of mechanical properties. By using the unit cell models , the st ructural geometry of thecomposites was analyzed , and the mathematical relation between technics parameters and microst ructure of the unitcells was obtained. The calculated values of the geometric characteristics of braided composites specimens by themodel well agree with the measured values. The numerical results indicate the effectiveness of the model , and thepresent model has presented a foundation for the mechanical performance prediction of the composites.
2006, 23(5): 161-167.
Abstract:
A new microelement method for the analysis of functionally graded st ructures was suggested , and themethod model , basic computational equations , features and functions were given in this paper. In order to reflect thegraded change of the material component , the dense microelement s were set up in the normal finite element of thest ructure , and the degrees of f reedom of all microelementps nodes were t ranslated into the ones of the same normalfinite element by the compatibility conditions , which were calculated by the computer. This microelement methodcan fully realize the transition from material micro-constitution to macroresponse of the st ructure , and it s computational element s and degrees of f reedom are the same as those of the normal finite element method. Therefore , thismethod is an effective means for the scale-span analysis of the functionally graded st ructures. In this paper , themacro-response can be immediately calculated by the material component dist ribution determined in the process ofthe material production. The three-dimensional dist ributions of mechanical quantities of the functionally gradedplates with different holes are given in this paper.
A new microelement method for the analysis of functionally graded st ructures was suggested , and themethod model , basic computational equations , features and functions were given in this paper. In order to reflect thegraded change of the material component , the dense microelement s were set up in the normal finite element of thest ructure , and the degrees of f reedom of all microelementps nodes were t ranslated into the ones of the same normalfinite element by the compatibility conditions , which were calculated by the computer. This microelement methodcan fully realize the transition from material micro-constitution to macroresponse of the st ructure , and it s computational element s and degrees of f reedom are the same as those of the normal finite element method. Therefore , thismethod is an effective means for the scale-span analysis of the functionally graded st ructures. In this paper , themacro-response can be immediately calculated by the material component dist ribution determined in the process ofthe material production. The three-dimensional dist ributions of mechanical quantities of the functionally gradedplates with different holes are given in this paper.
