2005 Vol. 22, No. 4
2005, 22(4): 1-5.
Abstract:
In order to eliminate the bubble during the autoclave curing of composites , the shape changing processof bubbles during t raversing through the monolayer fabric was studied preliminarily , and the driving force for themoving of bubbles was described based on the pressure. The effect s of the viscosity of resin , the size of the bubble ,the external pressure , the inter-space area as well as the number of layers on the t raversing behavior of bubbles werealso studied. The result s show that bubble t raverses through the layers by the flow of resin ; for a single void , thelower the viscosity of the resin is , the less the layers are , the larger the inter-space size is and the easier it is for thebubble to t raverse through the layers. Under the same condition it is easier for a large bubble to t raverse through thelayers than for a small one. These result s will provide the basis for establishing the bubble movement model in thehot-compaction process.
In order to eliminate the bubble during the autoclave curing of composites , the shape changing processof bubbles during t raversing through the monolayer fabric was studied preliminarily , and the driving force for themoving of bubbles was described based on the pressure. The effect s of the viscosity of resin , the size of the bubble ,the external pressure , the inter-space area as well as the number of layers on the t raversing behavior of bubbles werealso studied. The result s show that bubble t raverses through the layers by the flow of resin ; for a single void , thelower the viscosity of the resin is , the less the layers are , the larger the inter-space size is and the easier it is for thebubble to t raverse through the layers. Under the same condition it is easier for a large bubble to t raverse through thelayers than for a small one. These result s will provide the basis for establishing the bubble movement model in thehot-compaction process.
2005, 22(4): 6-10.
Abstract:
Edge effect is one of the common draping defect s of a fiber preform in liquid composite molding (LCM)processes. The unidirectional flow method was adopted to study the influences of the edge effect on the preform permeability and the mold filling. Based on the theoretic model of equivalent permeability , the edge effect s under theconditions of different fiber content s and gap widths were simulated and analyzed. A characterization factor for thest rength of the edge effect was also proposed. Furthermore , the on-line strategic cont rol and measurement for edgeeffect s were described taking the mold filling in a complex mold cavity for a case.
Edge effect is one of the common draping defect s of a fiber preform in liquid composite molding (LCM)processes. The unidirectional flow method was adopted to study the influences of the edge effect on the preform permeability and the mold filling. Based on the theoretic model of equivalent permeability , the edge effect s under theconditions of different fiber content s and gap widths were simulated and analyzed. A characterization factor for thest rength of the edge effect was also proposed. Furthermore , the on-line strategic cont rol and measurement for edgeeffect s were described taking the mold filling in a complex mold cavity for a case.
2005, 22(4): 11-16.
Abstract:
NANO-SiO2 particles were added in the bisphenol A epoxy resin. The curing characteristics of the NANO-SiO2 / epoxy resin system were researched. The effect s of NANO-SiO2 content on reaction temperature , gel fraction ,dimension of the cured area and dynamic mechanic performance of the elect ron beam ( EB) cured epoxy resin systemwere investigated. The result s show that the exothermal peak of the curing system decreases with the increasing ofNANO-SiO2 content , and a small amount of NANO-SiO2 particles cont ribute to increasing the dimension of the curedarea , gel f raction , glass temperature and high temperature modulus. The growth mechanism of the system withNANO-SiO2 particles is similar to that without NANO-SiO2 particles , although the propagation path of EB is changed byNANO-SiO2 particles.
NANO-SiO2 particles were added in the bisphenol A epoxy resin. The curing characteristics of the NANO-SiO2 / epoxy resin system were researched. The effect s of NANO-SiO2 content on reaction temperature , gel fraction ,dimension of the cured area and dynamic mechanic performance of the elect ron beam ( EB) cured epoxy resin systemwere investigated. The result s show that the exothermal peak of the curing system decreases with the increasing ofNANO-SiO2 content , and a small amount of NANO-SiO2 particles cont ribute to increasing the dimension of the curedarea , gel f raction , glass temperature and high temperature modulus. The growth mechanism of the system withNANO-SiO2 particles is similar to that without NANO-SiO2 particles , although the propagation path of EB is changed byNANO-SiO2 particles.
2005, 22(4): 17-22.
Abstract:
The compressive mechanical properties of epoxy syntactic foam reinforced with hollow glass microspheres are studied by quasi-static compression test s. Some predicting formulae of Young’s modulus and yieldst rength of syntactic foam are proposed based on the result s of composite mechanics. In addition , the failure mechanism of syntactic foam is investigated by macroscopic and microscopic observation of f ractured specimens. The result s show that the deformation characteristics of syntactic foams are very similar to those of plain foams duringcompression. The syntactic foam is yielded when the st rain reaches about 2 % and it is collap sed when the st rain islarger than 30 %. Furthermore , the Young’s modulus and yield st rength of syntactic foam are decreased with thedecrease of density of material , and the predicted result s of formulae are basically in agreement with the experimental data. The macroscopic and microscopic observation of f ractured specimens indicates that the main failure mode iselasto-plastic collap se caused by shear.
The compressive mechanical properties of epoxy syntactic foam reinforced with hollow glass microspheres are studied by quasi-static compression test s. Some predicting formulae of Young’s modulus and yieldst rength of syntactic foam are proposed based on the result s of composite mechanics. In addition , the failure mechanism of syntactic foam is investigated by macroscopic and microscopic observation of f ractured specimens. The result s show that the deformation characteristics of syntactic foams are very similar to those of plain foams duringcompression. The syntactic foam is yielded when the st rain reaches about 2 % and it is collap sed when the st rain islarger than 30 %. Furthermore , the Young’s modulus and yield st rength of syntactic foam are decreased with thedecrease of density of material , and the predicted result s of formulae are basically in agreement with the experimental data. The macroscopic and microscopic observation of f ractured specimens indicates that the main failure mode iselasto-plastic collap se caused by shear.
2005, 22(4): 23-29.
Abstract:
The RTM filling process of a wind turbine blade was simulated in 3D using the RTM simulation systemto optimize it s RTM process. The simulation result s of two different injection ways are compared and analyzed tofind the optimal injection means. As a result , line injection on the side of the blade is the better way. 8 simulationsare carried out for different injection locations on the side to find the optimal injection location and reasonable outletlocations are ensured. Finally , The optimal process is applied successfully to manufacture the blade. Using the system of RTM simulation to optimize the process is cost-effective and the optimal process for blade manufacture is ofgreat reference value for other shape-similar component s.
The RTM filling process of a wind turbine blade was simulated in 3D using the RTM simulation systemto optimize it s RTM process. The simulation result s of two different injection ways are compared and analyzed tofind the optimal injection means. As a result , line injection on the side of the blade is the better way. 8 simulationsare carried out for different injection locations on the side to find the optimal injection location and reasonable outletlocations are ensured. Finally , The optimal process is applied successfully to manufacture the blade. Using the system of RTM simulation to optimize the process is cost-effective and the optimal process for blade manufacture is ofgreat reference value for other shape-similar component s.
2005, 22(4): 30-34.
Abstract:
Surface silvered (Ag) polyimide films containing different silver mass f raction f rom 9 % to 15 % basedmainly on 3 , 3’- 4 ,4’- benzophenonetet racarboxylic acid dianhydride (BTDA) , 4 , 4’- oxydianiline (ODA) and t rifluoroacetylacetone (AgTFA) were fabricated by an in si tu single-stage self-metallization process , factors influencingthe film properties were investigated , meanwhile , highly conductive (Surface resistance is about 1Ω) and highly reflective (Absolute reflectivity is 65.3 %) surface silvered polyimide films were obtained. Additionally , the relationship s between the submicron morphology and properties of the films are observed and the dynamic equation betweenreflectivity and cure time is explored for the first time.
Surface silvered (Ag) polyimide films containing different silver mass f raction f rom 9 % to 15 % basedmainly on 3 , 3’- 4 ,4’- benzophenonetet racarboxylic acid dianhydride (BTDA) , 4 , 4’- oxydianiline (ODA) and t rifluoroacetylacetone (AgTFA) were fabricated by an in si tu single-stage self-metallization process , factors influencingthe film properties were investigated , meanwhile , highly conductive (Surface resistance is about 1Ω) and highly reflective (Absolute reflectivity is 65.3 %) surface silvered polyimide films were obtained. Additionally , the relationship s between the submicron morphology and properties of the films are observed and the dynamic equation betweenreflectivity and cure time is explored for the first time.
2005, 22(4): 35-39.
Abstract:
The joining of Cf / SiC composites with preceramic silicone resin (SR) at high temperature was studied.The influences of the curing and pyrolysis process of silicone resin and those of the inert and active fillers were especially discussed. The result s show that the curing process of SR was accomplished by Si —OH. An appropriateamount of inert filler SiC (5 % , mass f raction) or active filler nano-Al/ Si powder is good for the joining of Cf / SiCcomposites.
The joining of Cf / SiC composites with preceramic silicone resin (SR) at high temperature was studied.The influences of the curing and pyrolysis process of silicone resin and those of the inert and active fillers were especially discussed. The result s show that the curing process of SR was accomplished by Si —OH. An appropriateamount of inert filler SiC (5 % , mass f raction) or active filler nano-Al/ Si powder is good for the joining of Cf / SiCcomposites.
2005, 22(4): 40-46.
Abstract:
The pressure sensitive behaviors of carbon fiber-reinforced cement-mat rix composites with differentmoisture content s were studied. The result s show that the relative change in resistanceΔR/ R0 varies with the moisture content of the composites. With higher moisture content , the relative change in resistanceΔR/ R0 increases withthe increase of compressive st ress , and decreases during unloading , demonst rating the positive pressure sensitivity.However , when the moisture content is reduced af ter specimens’being oven-dried , the relative change in resistanceΔR/ R0 decreases monotonically with the increase of compressive st ress , and increases monotonically during unloading , showing the negative pressure sensitivity. The mechanism for these phenomena is discussed.
The pressure sensitive behaviors of carbon fiber-reinforced cement-mat rix composites with differentmoisture content s were studied. The result s show that the relative change in resistanceΔR/ R0 varies with the moisture content of the composites. With higher moisture content , the relative change in resistanceΔR/ R0 increases withthe increase of compressive st ress , and decreases during unloading , demonst rating the positive pressure sensitivity.However , when the moisture content is reduced af ter specimens’being oven-dried , the relative change in resistanceΔR/ R0 decreases monotonically with the increase of compressive st ress , and increases monotonically during unloading , showing the negative pressure sensitivity. The mechanism for these phenomena is discussed.
2005, 22(4): 47-52.
Abstract:
Installing special elect ric layer in preforms of carbon felt , C/ C composites were fabricated by chemicalvapor infilt ration (CVI) with multi-factor coupling physical fields , and the infilt ration conditions were optimized.The textures of pyrolytic carbons were observed using polarized light microscopy ( PLM) , and the graphitization degree of these C/ C composites was analyzed by XRD ; The effect of elect romagnetic field on the CVI and dynamicprocess of dual convective heat of outer thermogenesis and inner thermogenesis and mass rest rainning of consumingt ransfer , and three of deposition models were discussed. The result s show that the rate of deposition of pyrolyticcarbon is improved with multi-factor coupling physical fields , and the porous carbon-carbon preforms (260 mm ×60 mm ×20 mm) can be densified in one-cycle. C/ C composites with density of more than 1.7 g/ cm3 are obtainedwithin 20 h. Though optimizing the infilt ration conditions , some kinds of microst ructure of pyrolytic carbons can beobtained , ranging f rom rough laminar , smooth laminar , isot ropic and banded st ructure. Under the infilt ration conditions of 960 ℃and 0.1 kPa , the rough laminar of higher texture can be obtained.
Installing special elect ric layer in preforms of carbon felt , C/ C composites were fabricated by chemicalvapor infilt ration (CVI) with multi-factor coupling physical fields , and the infilt ration conditions were optimized.The textures of pyrolytic carbons were observed using polarized light microscopy ( PLM) , and the graphitization degree of these C/ C composites was analyzed by XRD ; The effect of elect romagnetic field on the CVI and dynamicprocess of dual convective heat of outer thermogenesis and inner thermogenesis and mass rest rainning of consumingt ransfer , and three of deposition models were discussed. The result s show that the rate of deposition of pyrolyticcarbon is improved with multi-factor coupling physical fields , and the porous carbon-carbon preforms (260 mm ×60 mm ×20 mm) can be densified in one-cycle. C/ C composites with density of more than 1.7 g/ cm3 are obtainedwithin 20 h. Though optimizing the infilt ration conditions , some kinds of microst ructure of pyrolytic carbons can beobtained , ranging f rom rough laminar , smooth laminar , isot ropic and banded st ructure. Under the infilt ration conditions of 960 ℃and 0.1 kPa , the rough laminar of higher texture can be obtained.
2005, 22(4): 53-57.
Abstract:
A Cr3C2-Ni2Al welding wire was produced by pressureless sintering process in vacuum. When thewelding wires were welded on the surface of carbon steel , carbide particles reinforced Ni3Al base composite wasformed due to the physical heat of arc and Ni-Al exothermic reaction. XRD shows that Ni react s with Al to formNi3Al and Cr3C2 is dissolved during welding. Most of [Cr ] and [C] react to form Cr7C3 phase except that a few dissolve into Ni3Al mat rix. The size of Cr7C3 particles mainly depends on the cooling rate of different welding regions.In addition , as the solid solubility of Cr in Ni3Al is much larger than that of C and Cr3C2 changes to Cr7C3 duringwelding , some graphites are formed in welding layers. The graphites mainly segregate on welding outer layers dueto it s low density and high melting point . The room and high temperature hardness of Cr7C3 / Ni3Al composite ismuch higher than that of stellite alloys. It is predicted that Cr7C3 / Ni3Al composite may become an att ractive potential candidate for high2temperature surface wear-resistant material.
A Cr3C2-Ni2Al welding wire was produced by pressureless sintering process in vacuum. When thewelding wires were welded on the surface of carbon steel , carbide particles reinforced Ni3Al base composite wasformed due to the physical heat of arc and Ni-Al exothermic reaction. XRD shows that Ni react s with Al to formNi3Al and Cr3C2 is dissolved during welding. Most of [Cr ] and [C] react to form Cr7C3 phase except that a few dissolve into Ni3Al mat rix. The size of Cr7C3 particles mainly depends on the cooling rate of different welding regions.In addition , as the solid solubility of Cr in Ni3Al is much larger than that of C and Cr3C2 changes to Cr7C3 duringwelding , some graphites are formed in welding layers. The graphites mainly segregate on welding outer layers dueto it s low density and high melting point . The room and high temperature hardness of Cr7C3 / Ni3Al composite ismuch higher than that of stellite alloys. It is predicted that Cr7C3 / Ni3Al composite may become an att ractive potential candidate for high2temperature surface wear-resistant material.
2005, 22(4): 58-67.
Abstract:
The dynamic response of functionally graded plates was simulated under impulsive load. These platesare supposed to be metal mat rix composites (MMC) made f rom aluminum alloy reinforced by ceramic particles. Thereinforcement volume f raction varies continuously along thickness following a power law. The reinforcement volumef raction reaches it s maximum at both f ront surface and back surface with the symmet ric dist ribution. The result sshow that the st ress wave propagations in such gradient st ructures are very complex. The elastic and viscoplasticwaves are coupled together and the amplitude of reflected tension wave and the unloading wave have very close relation with the gradient dist ribution of the composition. The dist ributions of equivalent plastic st rain , dissipated , kinetic and elastic st rain energies are all dependent on the gradient dist ribution of the composition. All these play avery important role in optimum design of the functionally graded st ructures under the impact load.
The dynamic response of functionally graded plates was simulated under impulsive load. These platesare supposed to be metal mat rix composites (MMC) made f rom aluminum alloy reinforced by ceramic particles. Thereinforcement volume f raction varies continuously along thickness following a power law. The reinforcement volumef raction reaches it s maximum at both f ront surface and back surface with the symmet ric dist ribution. The result sshow that the st ress wave propagations in such gradient st ructures are very complex. The elastic and viscoplasticwaves are coupled together and the amplitude of reflected tension wave and the unloading wave have very close relation with the gradient dist ribution of the composition. The dist ributions of equivalent plastic st rain , dissipated , kinetic and elastic st rain energies are all dependent on the gradient dist ribution of the composition. All these play avery important role in optimum design of the functionally graded st ructures under the impact load.
2005, 22(4): 68-74.
Abstract:
Superplasticity of the pulse elect rodeposited SiCP / Ni nanocomposite was investigated by tensile test s.St rain rates range f rom 8.3 ×10 -4 to 5 ×10 -2 s -1 , and the selected temperatures are 410 ℃and 450 ℃. A maximumelongation of 836 % was obtained at the st rain rate of 1.67 ×10 -2 s -1 and temperature of 450 ℃. Surface morphology , f racture surfaces and deformed microst ructure were observed by SEM and TEM. The deformation mechanismwas analyzed. SiC has a favorable effect on the superplasticity of the material by enhancing the microst ructural stability. A low volume f raction of cavity was helpful to obtain high elongation. The main deformation mechanisms aredislocation accommodated grain boundary sliding and dislocation slip plasticity when the grains grow to micro size.
Superplasticity of the pulse elect rodeposited SiCP / Ni nanocomposite was investigated by tensile test s.St rain rates range f rom 8.3 ×10 -4 to 5 ×10 -2 s -1 , and the selected temperatures are 410 ℃and 450 ℃. A maximumelongation of 836 % was obtained at the st rain rate of 1.67 ×10 -2 s -1 and temperature of 450 ℃. Surface morphology , f racture surfaces and deformed microst ructure were observed by SEM and TEM. The deformation mechanismwas analyzed. SiC has a favorable effect on the superplasticity of the material by enhancing the microst ructural stability. A low volume f raction of cavity was helpful to obtain high elongation. The main deformation mechanisms aredislocation accommodated grain boundary sliding and dislocation slip plasticity when the grains grow to micro size.
2005, 22(4): 75-80.
Abstract:
The wettability of a ( Ti , Me) (C , N) / Ni system was studied by using the sessile drop method. Thevalence elect ron st ructure (VES) of ceramic multiphase in cermets was calculated by using EET theory and relationship s among chemical compositions , valence elect ron st ructure and contact angle were established by means of regression. Wetting test s reveal that the contact angle (θ) reduces continuously with the increase of temperature andholding time and decreases definitely with the increase of carbides content , while the impact order of the carbides onθis Mo2C > TaC > WC > VC > NbC. It can be deduced f rom EET calculations that the covalent elect rons on thest rongest bond in ceramic phases ( nA ) increase with the content of carbides , and the impact order is VC > Mo2C >NbC > WC > TaC.
The wettability of a ( Ti , Me) (C , N) / Ni system was studied by using the sessile drop method. Thevalence elect ron st ructure (VES) of ceramic multiphase in cermets was calculated by using EET theory and relationship s among chemical compositions , valence elect ron st ructure and contact angle were established by means of regression. Wetting test s reveal that the contact angle (θ) reduces continuously with the increase of temperature andholding time and decreases definitely with the increase of carbides content , while the impact order of the carbides onθis Mo2C > TaC > WC > VC > NbC. It can be deduced f rom EET calculations that the covalent elect rons on thest rongest bond in ceramic phases ( nA ) increase with the content of carbides , and the impact order is VC > Mo2C >NbC > WC > TaC.
2005, 22(4): 81-85.
Abstract:
The macro-mechanical behavior of 2D-woven C/ SiC composites produced with CVI technique was investigated by loading and unloading uniaxial tensile and compress test s. The changes in elastic modulus , residualst rain , and Poisson ratio were studied for further characterization of mechanical properties of the CMCs in complexst ress states. Failure mode and damage mechanisms were analyzed by SEM and optical microscope. The tensile test sshow that damage begins at a very low tensile st ress level of about 40 MPa , and that the unloading modules andPoisson ratio decrease linearly as the tensile st ress increases , while the residual st rain increases. Fractography analysis shows that mat rix cracks around the 0°fiber bundles and interlaminar cracks are the main damage mechanisms.The compress behavior is almost linear to failure. The compress modulus and Poisson ratio remain constant . Thetensile specimens break in a ductile manner , because of delamination , longitudinal bundles failure and pull out . Theglobal compress failure in a plane orient s about 13°to the loading direction , and because of cracks between bundlesand within the 90°bundles , the 0°bundles are sheared to failure.
The macro-mechanical behavior of 2D-woven C/ SiC composites produced with CVI technique was investigated by loading and unloading uniaxial tensile and compress test s. The changes in elastic modulus , residualst rain , and Poisson ratio were studied for further characterization of mechanical properties of the CMCs in complexst ress states. Failure mode and damage mechanisms were analyzed by SEM and optical microscope. The tensile test sshow that damage begins at a very low tensile st ress level of about 40 MPa , and that the unloading modules andPoisson ratio decrease linearly as the tensile st ress increases , while the residual st rain increases. Fractography analysis shows that mat rix cracks around the 0°fiber bundles and interlaminar cracks are the main damage mechanisms.The compress behavior is almost linear to failure. The compress modulus and Poisson ratio remain constant . Thetensile specimens break in a ductile manner , because of delamination , longitudinal bundles failure and pull out . Theglobal compress failure in a plane orient s about 13°to the loading direction , and because of cracks between bundlesand within the 90°bundles , the 0°bundles are sheared to failure.
2005, 22(4): 86-90.
Abstract:
The combustion synthesis reaction with reductive process was used to produce ZrB2 / Al2O3 compositepowders f rom B2O3-ZrO2-Al system. The phases , chemical compositions and interfaces of the composite powderswere characterized and analysed by X-ray diff raction (XRD) , X-ray photoelect ron spect roscope (XPS) , t ransmissionelect ron microscope ( TEM) and high resolution elect ron microscope ( HRTEM) . The result s show that Zr , B , Aland O element s exist in composite powders as ZrB2 and Al2O3 . The ZrB2 and Al2O3 are the primary phase in thecomposite powders. The presence of a very small amount of ZrO2 is considered to be unreacted zirconium oxide powders. TEM and HRTEM observations of interface of the composite powders indicate that the good interfacial bonding states are formed between the ZrB2 and Al2O3particle. It can be suggested to be related to the crystallizationprocess of the ZrB2 particles.
The combustion synthesis reaction with reductive process was used to produce ZrB2 / Al2O3 compositepowders f rom B2O3-ZrO2-Al system. The phases , chemical compositions and interfaces of the composite powderswere characterized and analysed by X-ray diff raction (XRD) , X-ray photoelect ron spect roscope (XPS) , t ransmissionelect ron microscope ( TEM) and high resolution elect ron microscope ( HRTEM) . The result s show that Zr , B , Aland O element s exist in composite powders as ZrB2 and Al2O3 . The ZrB2 and Al2O3 are the primary phase in thecomposite powders. The presence of a very small amount of ZrO2 is considered to be unreacted zirconium oxide powders. TEM and HRTEM observations of interface of the composite powders indicate that the good interfacial bonding states are formed between the ZrB2 and Al2O3particle. It can be suggested to be related to the crystallizationprocess of the ZrB2 particles.
2005, 22(4): 91-95.
Abstract:
A novel nano-doping process was int roduced for the preparation of Ba TiO3-based ult rafine nonreducibledielect rics for multilayer ceramic capacitance (MLCC) . According to TG-DTA , XRD and TEM analysis , the nano-dopant prepared by the water-based sol-gel method was well dispersive and active. The nano-doping mechanism wasinvestigated based on comparing conventional process with nano-doping process. It indicated that due to the specialnano-effect , the modification effect of foreign atom was improved effectively and the microst ructure and macro dielect ric characteristics of so acquired ceramics were improved consequently. The result s show that high performancedielect rics are obtained , with permittivity more than 2800 , dielect ric loss lower than 110 % and average grain size about 0.3μm , which satisfies the requirement s of EIA X7R/ X8R specifications.
A novel nano-doping process was int roduced for the preparation of Ba TiO3-based ult rafine nonreducibledielect rics for multilayer ceramic capacitance (MLCC) . According to TG-DTA , XRD and TEM analysis , the nano-dopant prepared by the water-based sol-gel method was well dispersive and active. The nano-doping mechanism wasinvestigated based on comparing conventional process with nano-doping process. It indicated that due to the specialnano-effect , the modification effect of foreign atom was improved effectively and the microst ructure and macro dielect ric characteristics of so acquired ceramics were improved consequently. The result s show that high performancedielect rics are obtained , with permittivity more than 2800 , dielect ric loss lower than 110 % and average grain size about 0.3μm , which satisfies the requirement s of EIA X7R/ X8R specifications.
2005, 22(4): 96-99.
Abstract:
The influences of two kinds of bonding layer materials and different thicknesses at two locations on theinternal f riction characteristics of the seven layer anisot ropic laminated damped st ructures were investigated by dynamic mechanical analyzer (DMA Q800) . The experimental result s show that the temperature characteristics of thest ructural internal f riction with pressure sensitive adhesive as bonding materials are better than with epoxy resinwhile the experimental temperature is lower than the Tg of the damping material. The influences of different thicknesses at different locations on the temperature and f requency characteristics of internal f riction are different , andthe st ructural frequency characteristics keep close relation to the materials and the thicknesses , and the thicker thelayer , the better the st ructural temperature characteristics.
The influences of two kinds of bonding layer materials and different thicknesses at two locations on theinternal f riction characteristics of the seven layer anisot ropic laminated damped st ructures were investigated by dynamic mechanical analyzer (DMA Q800) . The experimental result s show that the temperature characteristics of thest ructural internal f riction with pressure sensitive adhesive as bonding materials are better than with epoxy resinwhile the experimental temperature is lower than the Tg of the damping material. The influences of different thicknesses at different locations on the temperature and f requency characteristics of internal f riction are different , andthe st ructural frequency characteristics keep close relation to the materials and the thicknesses , and the thicker thelayer , the better the st ructural temperature characteristics.
2005, 22(4): 100-107.
Abstract:
The SPACE system integrated with the dynamic mixing algorithm provided an opportunity to generate amodel concrete with high volume f raction of aggregate. In this cont ribution , influences of fineness and volume f raction (φ= 40 %～70 %) of aggregates were studied on the nearest surface spacing dist ribution between neighboringaggregate grains in model mortar for three types of aggregate size dist ributions (one with the size range of 0.125～1.34 mm , the other two with 0.25～5.00 mm) . The modeling result s demonst rate that increase in volume f ractionof aggregate or in fineness of aggregate has the same effect , i1 e. , the curve of the nearest surface spacing dist ribution moves toward the smaller surface spacing ; the value of maximum possible nearest surface spacing where peakprobability occurs also decreases. Furthermore , the result of interval cumulative probability of the nearest surfacespacing shows that more than 57 % of the nearest surface spacing probability is smaller than 10μm. Finally , the analysis of the mean value of the nearest surface spacing reveals that the mean value of the nearest surface spacing isbetween 54.6～1.1μm if the volume f raction of aggregate varied f rom 40 % to 70 %. And when the volume fractionof aggregate is kept in the range of 50 %～70 % , the linear relationship may be built between the mean value of thenearest surface spacing and the volume f raction of aggregate. The surface area of aggregate per unit volume of mortar does have influence on the mean value of the nearest surface spacing , but the ratio between them is not constant .
The SPACE system integrated with the dynamic mixing algorithm provided an opportunity to generate amodel concrete with high volume f raction of aggregate. In this cont ribution , influences of fineness and volume f raction (φ= 40 %～70 %) of aggregates were studied on the nearest surface spacing dist ribution between neighboringaggregate grains in model mortar for three types of aggregate size dist ributions (one with the size range of 0.125～1.34 mm , the other two with 0.25～5.00 mm) . The modeling result s demonst rate that increase in volume f ractionof aggregate or in fineness of aggregate has the same effect , i1 e. , the curve of the nearest surface spacing dist ribution moves toward the smaller surface spacing ; the value of maximum possible nearest surface spacing where peakprobability occurs also decreases. Furthermore , the result of interval cumulative probability of the nearest surfacespacing shows that more than 57 % of the nearest surface spacing probability is smaller than 10μm. Finally , the analysis of the mean value of the nearest surface spacing reveals that the mean value of the nearest surface spacing isbetween 54.6～1.1μm if the volume f raction of aggregate varied f rom 40 % to 70 %. And when the volume fractionof aggregate is kept in the range of 50 %～70 % , the linear relationship may be built between the mean value of thenearest surface spacing and the volume f raction of aggregate. The surface area of aggregate per unit volume of mortar does have influence on the mean value of the nearest surface spacing , but the ratio between them is not constant .
2005, 22(4): 108-111.
Abstract:
To study the open-hole tensile properties of stitched laminates , the open-hole tensile test s were carriedout with uniweave T300/ Q Y9512 laminates , and a finite element method was developed to calculate the open-holetensile properties of stitched laminates. The result s show that stitching has no significant effect on the open-holetensile properties , and the stitching direction does not alter the open-hole tensile st rength.
To study the open-hole tensile properties of stitched laminates , the open-hole tensile test s were carriedout with uniweave T300/ Q Y9512 laminates , and a finite element method was developed to calculate the open-holetensile properties of stitched laminates. The result s show that stitching has no significant effect on the open-holetensile properties , and the stitching direction does not alter the open-hole tensile st rength.
2005, 22(4): 112-117.
Abstract:
Based on the plane st ress full-elastic model and 3D numerical model , 2D and 3D methods of calculatingthe failure rotating speed of the composite flywheel were established. In these methods , the maximal tension st resscriterion of orthot ropic material was adopted. Two st rength criteria were adopted in the 3D method , namely averagevalue criterion and maximal value criterion. High speed rotating and failure experiment was developed on three flywheels and the failure occurred at the interface between mandrel and flywheel. The test result s show that the actualfailure speed is very close to the theoretical failure speed and the 2D and 3D methods are reliable. The theoreticalfailure speed calculated by the 2D method is comparatively higher. And the actual failure speed is in between of thetheoretical failure speed calculated by the 3D method. It shows that the 3D method is more accurate.
Based on the plane st ress full-elastic model and 3D numerical model , 2D and 3D methods of calculatingthe failure rotating speed of the composite flywheel were established. In these methods , the maximal tension st resscriterion of orthot ropic material was adopted. Two st rength criteria were adopted in the 3D method , namely averagevalue criterion and maximal value criterion. High speed rotating and failure experiment was developed on three flywheels and the failure occurred at the interface between mandrel and flywheel. The test result s show that the actualfailure speed is very close to the theoretical failure speed and the 2D and 3D methods are reliable. The theoreticalfailure speed calculated by the 2D method is comparatively higher. And the actual failure speed is in between of thetheoretical failure speed calculated by the 3D method. It shows that the 3D method is more accurate.
2005, 22(4): 118-124.
Abstract:
The curing process of the filament wound pressure vessel with metal liner is simulated. A methodologyis proposed for predicting the evolution of the dist ributions of temperature and process-induced st ress fields duringthe whole curing process. Based on cure kinetic , t ransit heat conductive and composite laminated st ress analysis theories , the corresponding formulas of the finite element method are briefly int roduced. A typical numerical example ispresented to illust rate it . The result s show that the temperature and process-induced thermo-st ress fields involvecomplex variations during the curing process , and the peak values for all st ress component s tend to occur simultaneously at the beginning cooling down stage , whose magnitudes are related to the variations of the temperature in theautoclave during the curing process. The numerical simulation method and conclusions could be of great value to engineers of the composite st ructures.
The curing process of the filament wound pressure vessel with metal liner is simulated. A methodologyis proposed for predicting the evolution of the dist ributions of temperature and process-induced st ress fields duringthe whole curing process. Based on cure kinetic , t ransit heat conductive and composite laminated st ress analysis theories , the corresponding formulas of the finite element method are briefly int roduced. A typical numerical example ispresented to illust rate it . The result s show that the temperature and process-induced thermo-st ress fields involvecomplex variations during the curing process , and the peak values for all st ress component s tend to occur simultaneously at the beginning cooling down stage , whose magnitudes are related to the variations of the temperature in theautoclave during the curing process. The numerical simulation method and conclusions could be of great value to engineers of the composite st ructures.
2005, 22(4): 125-130.
Abstract:
A micro-mechanical elastic analysis of composites reinforced by a large volume fraction of particles ispursued. A simplified microst ructure model has been suggested. The particles are assumed to be spheres linked byshort cylinders of mat rix material. The displacement component s are assumed to be linearly dist ributed along the axial direction of mat rix cylinders. Micro st resses and micro elastic constant s of a two-particle combination are first deduced for tensile and shear loading cases. Macro elastic constant s for the composite are then obtained by averagingthe micro elastic constant s in various special directions. Thus a relation between micro and macro analyses is const ructed. The model is applied to a metal mat rix composite with two different particle volume f ractions. The predicted elastic properties agree well with the experiment result s. The analysis also reveals that the effect of the particlepacking pattern on the macro elastic properties is t rivial ; however , the dist ribution of micro st resses in differentpacking patterns varies significantly.
A micro-mechanical elastic analysis of composites reinforced by a large volume fraction of particles ispursued. A simplified microst ructure model has been suggested. The particles are assumed to be spheres linked byshort cylinders of mat rix material. The displacement component s are assumed to be linearly dist ributed along the axial direction of mat rix cylinders. Micro st resses and micro elastic constant s of a two-particle combination are first deduced for tensile and shear loading cases. Macro elastic constant s for the composite are then obtained by averagingthe micro elastic constant s in various special directions. Thus a relation between micro and macro analyses is const ructed. The model is applied to a metal mat rix composite with two different particle volume f ractions. The predicted elastic properties agree well with the experiment result s. The analysis also reveals that the effect of the particlepacking pattern on the macro elastic properties is t rivial ; however , the dist ribution of micro st resses in differentpacking patterns varies significantly.
2005, 22(4): 131-135.
Abstract:
Based on the micro-mechanical model , micro elastic-plastic and micro damage analyses are further carried out . The mat rix is assumed to be Von Mises elastic-perfect-plastic material. The average st ress over the entirelength of the mat rix cylinder is used to predict the yield of the mat rix material. The plastic zone is simplified to expand axi-symmet rically under plastic loading1 A unified damage criterion is proposed for both mat rix damage andparticle/ mat rix interface failure , considering the short length of the mat rix cylinder in the micro model for composites with high volume f ractions of particles1 The effect s of principal st rain and t ri-axial st ress state are also considered in the damage criterion. A decreased macro modulus is obtained by averaging spatial dist ributions of microyielding and damage. Uniaxial tensile and compressive behaviors of a particle reinforced metal mat rix composite aresimulated by using the proposed method1 The simulations are in good agreement with experimental data.
Based on the micro-mechanical model , micro elastic-plastic and micro damage analyses are further carried out . The mat rix is assumed to be Von Mises elastic-perfect-plastic material. The average st ress over the entirelength of the mat rix cylinder is used to predict the yield of the mat rix material. The plastic zone is simplified to expand axi-symmet rically under plastic loading1 A unified damage criterion is proposed for both mat rix damage andparticle/ mat rix interface failure , considering the short length of the mat rix cylinder in the micro model for composites with high volume f ractions of particles1 The effect s of principal st rain and t ri-axial st ress state are also considered in the damage criterion. A decreased macro modulus is obtained by averaging spatial dist ributions of microyielding and damage. Uniaxial tensile and compressive behaviors of a particle reinforced metal mat rix composite aresimulated by using the proposed method1 The simulations are in good agreement with experimental data.
2005, 22(4): 136-141.
Abstract:
A finite element method was developed for the numerical analysis of advanced grid stiffened st ructure(AGS) , and the stability problem of AGS with an embedded delamination was investigated. Based on the Mindlinfirst-order shear deformation theory , a composite laminates element and a beam element were adopted to model theskin and the stiffener , respectively. The corresponding formulae for finite element analysis were deduced. By coordinate t ransformation and the geomet ry continuum condition of the skin and the stiffener , the element stiffness mat rices and geomet rical stiffness mat rices for the AGS were deduced. The governing equation for the stability problem ofthe composite grid stiffened plate and shell was established. The effect s of configuration , size , and location of thedelamination , and the height , the width , the dist ribution of the stiffeners on the stability characteristics of the AGSsubjected to a compressive load are discussed. The numerical investigation indicates that the buckling behavior of theAGS is much more complicated. The buckling load and modes relate to the configuration , size , and location of thedelamination , and the height , the width , the dist ribution of the stiffeners closely.
A finite element method was developed for the numerical analysis of advanced grid stiffened st ructure(AGS) , and the stability problem of AGS with an embedded delamination was investigated. Based on the Mindlinfirst-order shear deformation theory , a composite laminates element and a beam element were adopted to model theskin and the stiffener , respectively. The corresponding formulae for finite element analysis were deduced. By coordinate t ransformation and the geomet ry continuum condition of the skin and the stiffener , the element stiffness mat rices and geomet rical stiffness mat rices for the AGS were deduced. The governing equation for the stability problem ofthe composite grid stiffened plate and shell was established. The effect s of configuration , size , and location of thedelamination , and the height , the width , the dist ribution of the stiffeners on the stability characteristics of the AGSsubjected to a compressive load are discussed. The numerical investigation indicates that the buckling behavior of theAGS is much more complicated. The buckling load and modes relate to the configuration , size , and location of thedelamination , and the height , the width , the dist ribution of the stiffeners closely.
2005, 22(4): 142-148.
Abstract:
The methods for determining the fiber volume fraction in carbon fabric reinforced composite laminateswere developed by using the processing and analyzing techniques of section images of laminates , which are sampledby the use of CCD camera and A/ D device. Special measuring step s were designed according to the principles of determining the fiber volume f raction , using the geomet rical method and threshold method. The captured images weremanipulated and analyzed using Photoshop sof tware. The result s are in agreement with the values offered by thecomposites maker. Therefore the methods are considered feasible.
The methods for determining the fiber volume fraction in carbon fabric reinforced composite laminateswere developed by using the processing and analyzing techniques of section images of laminates , which are sampledby the use of CCD camera and A/ D device. Special measuring step s were designed according to the principles of determining the fiber volume f raction , using the geomet rical method and threshold method. The captured images weremanipulated and analyzed using Photoshop sof tware. The result s are in agreement with the values offered by thecomposites maker. Therefore the methods are considered feasible.
2005, 22(4): 149-155.
Abstract:
A 3D initial st ress analysis model of composite flywheel fabricated by filament tension winding was putforward by using the idea of the former plane st ress full elastic model. Based on the arithmetic of face to face contact , a 3D numerical method of calculating the initial st ress was proposed for composite in tension winding. The result s show that the numerical values of hoop initial st ress and radial initial st ress calculated by the 3D model are allsmaller than those obtained with the plane st ress model , and the difference increases slowly with the increase of theaxial length of the flywheel. The 3D analysis confirms that the plane st ress full elastic model has enough calculationprecision. The characterization and calculation method of the axial length effect of the 3D model is established.
A 3D initial st ress analysis model of composite flywheel fabricated by filament tension winding was putforward by using the idea of the former plane st ress full elastic model. Based on the arithmetic of face to face contact , a 3D numerical method of calculating the initial st ress was proposed for composite in tension winding. The result s show that the numerical values of hoop initial st ress and radial initial st ress calculated by the 3D model are allsmaller than those obtained with the plane st ress model , and the difference increases slowly with the increase of theaxial length of the flywheel. The 3D analysis confirms that the plane st ress full elastic model has enough calculationprecision. The characterization and calculation method of the axial length effect of the 3D model is established.
2005, 22(4): 156-164.
Abstract:
In order to build a uniform evaluating means of seismic ret rofitting performance of reinforced concretecolumns with CFRP sheet s , analytical models are studied through two-dimensional finite element analysis ( 2D-FEA) . Based on the paramet ric simulation of three RC columns st rengthened with CFRP sheet s , the applicabilityand availability of crack models , constitutive relationships on cracks and concrete compressive models are investigated. The result s show that Darwin-Pecknold’s equivalent uniaxial st rain model can be used to simulate the nonlinearbehavior and st rengthen effect of RC columns through comparing with test result s. The modified Kent-Park’s confinement model can be used to evaluate the influences on capacity of confinement effect s f rom hoop steels and CFRPsheet s , and Darwin’s failure criteria can be used to evaluate the concrete failure in a biaxial st ress state. Seismic retrofit ting performances of RC columns st rengthened with CFRP sheet s are verified by analyzing load2deformation relations and the processes of st ress-st rain at the inflection point and the foot of the columns.
In order to build a uniform evaluating means of seismic ret rofitting performance of reinforced concretecolumns with CFRP sheet s , analytical models are studied through two-dimensional finite element analysis ( 2D-FEA) . Based on the paramet ric simulation of three RC columns st rengthened with CFRP sheet s , the applicabilityand availability of crack models , constitutive relationships on cracks and concrete compressive models are investigated. The result s show that Darwin-Pecknold’s equivalent uniaxial st rain model can be used to simulate the nonlinearbehavior and st rengthen effect of RC columns through comparing with test result s. The modified Kent-Park’s confinement model can be used to evaluate the influences on capacity of confinement effect s f rom hoop steels and CFRPsheet s , and Darwin’s failure criteria can be used to evaluate the concrete failure in a biaxial st ress state. Seismic retrofit ting performances of RC columns st rengthened with CFRP sheet s are verified by analyzing load2deformation relations and the processes of st ress-st rain at the inflection point and the foot of the columns.
2005, 22(4): 165-171.
Abstract:
Based on the shear-lag theory , a layering shear-lag model taking into account the interfacial damage wasproposed and the st ress redist ributions for notched cross-ply laminates under tension were analyzed , f rom whichboth the length of the interfacial damage area and st ress concent ration factors in intact fibers at root of the notchwere obtained. On the basis of the knowledge of these st ress redist ributions , the tensile failure mechanism andst rengths of notched cross-ply laminates were studied by using a micro-statistical f racture theory. Consequently , therelation between residual tensile st rength and interfacial shear st rength was obtained quantitatively. The present result s are in good agreement with the existing experiment and show that both the st ress concent ration and st rengthare related to the interfacial shear st rength and the residual tensile st rength is relatively high when the interfacial cohesion is appropriate.
Based on the shear-lag theory , a layering shear-lag model taking into account the interfacial damage wasproposed and the st ress redist ributions for notched cross-ply laminates under tension were analyzed , f rom whichboth the length of the interfacial damage area and st ress concent ration factors in intact fibers at root of the notchwere obtained. On the basis of the knowledge of these st ress redist ributions , the tensile failure mechanism andst rengths of notched cross-ply laminates were studied by using a micro-statistical f racture theory. Consequently , therelation between residual tensile st rength and interfacial shear st rength was obtained quantitatively. The present result s are in good agreement with the existing experiment and show that both the st ress concent ration and st rengthare related to the interfacial shear st rength and the residual tensile st rength is relatively high when the interfacial cohesion is appropriate.
2005, 22(4): 172-176.
Abstract:
The dynamic mechanical properties ———fatigue properties and the effect of braiding st ructures on the fatigue properties of three dimensional braiding composites were studied. Tensile-tensile fatigue test s were carried outat different maximum stress ratios . All the tests were run at a stress ratio R(σmin /σmax ) = 0.1. The fatigue f requency was 10 Hz. The result s show that the fatigue st rength of three dimensional braiding composites is 60 %～80 % ofit s static strength , which is higher than that of metal material. The braiding angles have a great influence on the fatigue properties of 3-D braiding composites. The fatigue damage will be easy and the hysteresis heat will occur forthe large braiding angle composites. The st rain-st ress curves of the specimens with large braiding angles are non-linear , and the modulus is increasing with the testing time increasing. The variational rule of fatigue properties of threedimensional composites cont rasted with the metal’s rules. After one million times of fatigue test s , the residualst rength of the specimens is higher than the static test st rength , which is due to fiber bundles being reoriented to alower angle toward the tensile loading direction af ter the fatigue test .
The dynamic mechanical properties ———fatigue properties and the effect of braiding st ructures on the fatigue properties of three dimensional braiding composites were studied. Tensile-tensile fatigue test s were carried outat different maximum stress ratios . All the tests were run at a stress ratio R(σmin /σmax ) = 0.1. The fatigue f requency was 10 Hz. The result s show that the fatigue st rength of three dimensional braiding composites is 60 %～80 % ofit s static strength , which is higher than that of metal material. The braiding angles have a great influence on the fatigue properties of 3-D braiding composites. The fatigue damage will be easy and the hysteresis heat will occur forthe large braiding angle composites. The st rain-st ress curves of the specimens with large braiding angles are non-linear , and the modulus is increasing with the testing time increasing. The variational rule of fatigue properties of threedimensional composites cont rasted with the metal’s rules. After one million times of fatigue test s , the residualst rength of the specimens is higher than the static test st rength , which is due to fiber bundles being reoriented to alower angle toward the tensile loading direction af ter the fatigue test .
2005, 22(4): 177-182.
Abstract:
Based on the 2D model , the user subroutine USFLD has been programmed for ABAQUS to simulatethe damage evaluation in the composite laminate. The numerical result s show that the present method can predict thebear st rength and demonst rate the failure mode of the bolt-loaded laminate very well. Af ter analyzing the result s , asfor the cross-ply laminate , the shear non-linearity effect is not evident , both the non-linear analysis and the linear analysis can be applied to predict the st rength and the failure mode of the cross-ply laminate , but as for the angle-plylaminate , the difference between the above two methods is very large , and the non-linear analysis is more fit forthis laminate. The clearance between the bolt and the hole affect s the ultimate st rength of the laminate to a great extent . The bear st rength decreases with the clearance increasing. At the same time , the clearance can affect the dist ribution and degree of damage in the bolt-loaded laminate.
Based on the 2D model , the user subroutine USFLD has been programmed for ABAQUS to simulatethe damage evaluation in the composite laminate. The numerical result s show that the present method can predict thebear st rength and demonst rate the failure mode of the bolt-loaded laminate very well. Af ter analyzing the result s , asfor the cross-ply laminate , the shear non-linearity effect is not evident , both the non-linear analysis and the linear analysis can be applied to predict the st rength and the failure mode of the cross-ply laminate , but as for the angle-plylaminate , the difference between the above two methods is very large , and the non-linear analysis is more fit forthis laminate. The clearance between the bolt and the hole affect s the ultimate st rength of the laminate to a great extent . The bear st rength decreases with the clearance increasing. At the same time , the clearance can affect the dist ribution and degree of damage in the bolt-loaded laminate.
2005, 22(4): 183-187.
Abstract:
Based on the st raight warp and wef t threads , combined sine and st raight line of the binder yarn , a geomet ric model of 3D orthogonal fabric st ructure was established. According to the yarn cross-area confined by thebinder , non-linear equations that include fabric structural parameters as unknown quantities were set up . The approximate values were calculated and the unknown quantity in the binder yarn model was determined by a numericalmethod. Two pieces of glass fiber three-dimensional orthogonal fabrics were woven and consolidated withunsaturated polyester. The shape of the binder yarn in the manufactured composites was tested. The observed shapeof the binder yarn is in accordance with the model result . Furthermore , the binder yarn crimp factor , the fiber volume f raction of tested values and modeled ones are also compared. The results show that the established fabric geomet ric model can be used to represent the practical 3D orthogonal woven fabric structures.
Based on the st raight warp and wef t threads , combined sine and st raight line of the binder yarn , a geomet ric model of 3D orthogonal fabric st ructure was established. According to the yarn cross-area confined by thebinder , non-linear equations that include fabric structural parameters as unknown quantities were set up . The approximate values were calculated and the unknown quantity in the binder yarn model was determined by a numericalmethod. Two pieces of glass fiber three-dimensional orthogonal fabrics were woven and consolidated withunsaturated polyester. The shape of the binder yarn in the manufactured composites was tested. The observed shapeof the binder yarn is in accordance with the model result . Furthermore , the binder yarn crimp factor , the fiber volume f raction of tested values and modeled ones are also compared. The results show that the established fabric geomet ric model can be used to represent the practical 3D orthogonal woven fabric structures.
