2004 Vol. 21, No. 6
2004, 21(6): 1-8.
Abstract:
The effects of the drawing ratio and the addition of a compatibilizer on the morphology of dispersed thermotropic liquid crystalline polymer(TLCP) phase in the PP/TLCP in-situ composites were studied. The results show that a well-developed fibrils structure forms gradually with the increase of the drawing ratio after extrusion, and TLCP fibrils with large aspect ratios form in the composites at a relatively low drawing ratio with the introduction of PP-g-MAH as the compatibilizer. The obtained in-situ composites were further melt with glass fibers at 200℃ to be molded to a hybrid composite reinforced with glass fiber and TLCP fibrils. The microscopy investigation shows that the TLCP morphology is well maintained at this temperature. The typical skin-core structure of in-situ composites does not exist in the injected samples. The interfacial adhesion between glass fibers and PP matrix is enhanced by the addition of PP-g-MAH.
The effects of the drawing ratio and the addition of a compatibilizer on the morphology of dispersed thermotropic liquid crystalline polymer(TLCP) phase in the PP/TLCP in-situ composites were studied. The results show that a well-developed fibrils structure forms gradually with the increase of the drawing ratio after extrusion, and TLCP fibrils with large aspect ratios form in the composites at a relatively low drawing ratio with the introduction of PP-g-MAH as the compatibilizer. The obtained in-situ composites were further melt with glass fibers at 200℃ to be molded to a hybrid composite reinforced with glass fiber and TLCP fibrils. The microscopy investigation shows that the TLCP morphology is well maintained at this temperature. The typical skin-core structure of in-situ composites does not exist in the injected samples. The interfacial adhesion between glass fibers and PP matrix is enhanced by the addition of PP-g-MAH.
2004, 21(6): 9-13.
Abstract:
The tensile test and dynamic mechanical analysis (DMA) were conducted to investigate the mechanical properties of polypropylene/thermotropic liquid crystalline polymer/glass fiber (PP/TLCP/GF) hybrid composites with a good TLCP fibrils structure.The tensile test results show that the tensile strengths and moduli of hybrid composites increase with increasing drawing ratio after the extrusion of PP and TLCP.The hybrid composites compatibilized with PP-g-MAH have more excellent mechanical properties than the systems without the compatibilizer.The DMA results show that the dynamic storage moduli of hybrid composites increase with the increase of glass fiber content.The storage moduli, e.g.the rigidity of hybrid composites, increase further after the introduction of PP-g-MAH as the compatibilizer.Whether using PP-g-MAH as the compatibilizer or not, the increase of the storage moduli slows down after the glass fiber content reached 20% (mass fraction).The peak value of tanδ of the matrix decreases with increasing glass fiber content.The addition of PP-g-MAH as the compatibilizer also decreases this value after the modification of the interfacial adhesion between the matrix and reinforcing phase.
The tensile test and dynamic mechanical analysis (DMA) were conducted to investigate the mechanical properties of polypropylene/thermotropic liquid crystalline polymer/glass fiber (PP/TLCP/GF) hybrid composites with a good TLCP fibrils structure.The tensile test results show that the tensile strengths and moduli of hybrid composites increase with increasing drawing ratio after the extrusion of PP and TLCP.The hybrid composites compatibilized with PP-g-MAH have more excellent mechanical properties than the systems without the compatibilizer.The DMA results show that the dynamic storage moduli of hybrid composites increase with the increase of glass fiber content.The storage moduli, e.g.the rigidity of hybrid composites, increase further after the introduction of PP-g-MAH as the compatibilizer.Whether using PP-g-MAH as the compatibilizer or not, the increase of the storage moduli slows down after the glass fiber content reached 20% (mass fraction).The peak value of tanδ of the matrix decreases with increasing glass fiber content.The addition of PP-g-MAH as the compatibilizer also decreases this value after the modification of the interfacial adhesion between the matrix and reinforcing phase.
2004, 21(6): 14-20.
Abstract:
To improve unlubricated sliding wear properties of Epoxy, nano-SiC particles were incorporated as fillers to fabricate composites. Effects of surface modification via graft polymerization, content of the nanoparticles and wear conditions were studied. Based on the morphological observation of the worn surfaces and characterization of heat distortion and surface microhardness of the composites, the possible wear mechanism was discussed. The results indicate that the addition of low loading SiC nanoparticles can significantly decrease the specific wear rate and frictional coefficient of Epoxy resin. Much lower wear rate and frictional coefficient of the composites were observed when surface modified nanoparticles were used. The specific wear rate of the composites is 4 times lower than that of unfilled Epoxy and the frictional coefficient is decreased by 36%. It means that the grafting polymer (i.e. polyacrylamide) introduced onto the SiC nanoparticles enhanced the interfacial adhesion, leading to increase crack initiation resistance and improve tribological properties of the composites.
To improve unlubricated sliding wear properties of Epoxy, nano-SiC particles were incorporated as fillers to fabricate composites. Effects of surface modification via graft polymerization, content of the nanoparticles and wear conditions were studied. Based on the morphological observation of the worn surfaces and characterization of heat distortion and surface microhardness of the composites, the possible wear mechanism was discussed. The results indicate that the addition of low loading SiC nanoparticles can significantly decrease the specific wear rate and frictional coefficient of Epoxy resin. Much lower wear rate and frictional coefficient of the composites were observed when surface modified nanoparticles were used. The specific wear rate of the composites is 4 times lower than that of unfilled Epoxy and the frictional coefficient is decreased by 36%. It means that the grafting polymer (i.e. polyacrylamide) introduced onto the SiC nanoparticles enhanced the interfacial adhesion, leading to increase crack initiation resistance and improve tribological properties of the composites.
2004, 21(6): 21-26.
Abstract:
The friction and wear behaviors of aluminum borate whiskers modified bismaleimide resin were investigated at different coupling agents and whisker contents. The results show that wear resistance can be improved by adding aluminum borate whiskers. Coupling agents have no marked influence on the friction and wear resistance, and the friction coefficient of the composite reveals increasing tendency with the prolonging frictional time. At a relatively lower whisker content, the wear of the composites is characteristic of adhesion and fatigue. When the whisker content is higher than 8%, it is dominated by fatigue, and accompanied by adhesion.
The friction and wear behaviors of aluminum borate whiskers modified bismaleimide resin were investigated at different coupling agents and whisker contents. The results show that wear resistance can be improved by adding aluminum borate whiskers. Coupling agents have no marked influence on the friction and wear resistance, and the friction coefficient of the composite reveals increasing tendency with the prolonging frictional time. At a relatively lower whisker content, the wear of the composites is characteristic of adhesion and fatigue. When the whisker content is higher than 8%, it is dominated by fatigue, and accompanied by adhesion.
2004, 21(6): 27-33.
Abstract:
The kinds of materials used in the circuit analogue, the size of the circuit analogue and the electromagnetic parameter influencing the properties of the microwave absorbing composite were studied for the microwave absorbing composite material systems in "trap" type and gradually changed resistance type. The research results show that the microwave absorbing property is improved by 3~5 dB in the frequency range of 8~18 GHz. The microwave absorbing property with the thickness of 4 mm is more than 12 dB in the frequency range of 8~18 GHz. The introduction of circuit analogue into the structural design of the microwave absorbing composite improves not only the wave absorbing properties, but also the mechanical properties. So it is feasible to apply circuit analogue in the design of microwave absorbing composites.
The kinds of materials used in the circuit analogue, the size of the circuit analogue and the electromagnetic parameter influencing the properties of the microwave absorbing composite were studied for the microwave absorbing composite material systems in "trap" type and gradually changed resistance type. The research results show that the microwave absorbing property is improved by 3~5 dB in the frequency range of 8~18 GHz. The microwave absorbing property with the thickness of 4 mm is more than 12 dB in the frequency range of 8~18 GHz. The introduction of circuit analogue into the structural design of the microwave absorbing composite improves not only the wave absorbing properties, but also the mechanical properties. So it is feasible to apply circuit analogue in the design of microwave absorbing composites.
2004, 21(6): 34-38.
Abstract:
In order to research new sensitive materials, a mathematic piezoresistivity model of the conductive composites filled by carbon black particles is presented on the basis of general effective medium (GEM) theory . The model quantitatively describes the effects of the carbon particles size, volume fraction and polymer's elastic modulus. Some experimental samples were fabricated by dispersing three carbon black particles with different sizes in silicone rubber and high density polyethylene matrix respectively. It is proved in experiments that the mathematic piezoresistivity model is consonant with the experimental results very well under three boundary conditions: The carbon particles are dispersed homogeneously, the volume fraction of carbon black is near by the critical threshold, and the applied pressure is not more than 2 MPa.
In order to research new sensitive materials, a mathematic piezoresistivity model of the conductive composites filled by carbon black particles is presented on the basis of general effective medium (GEM) theory . The model quantitatively describes the effects of the carbon particles size, volume fraction and polymer's elastic modulus. Some experimental samples were fabricated by dispersing three carbon black particles with different sizes in silicone rubber and high density polyethylene matrix respectively. It is proved in experiments that the mathematic piezoresistivity model is consonant with the experimental results very well under three boundary conditions: The carbon particles are dispersed homogeneously, the volume fraction of carbon black is near by the critical threshold, and the applied pressure is not more than 2 MPa.
2004, 21(6): 39-46.
Abstract:
Stress corrosion cracking of three kinds of oriented glass fibre reinforced plastics(GRP), including ±30°,±45°,±60°oriented GRP, were studied by fracture mechanics theory and compared with the stress corrosion cracking of unidirectional GRP. The results show that the fibre orientation affects on the stress corrosion cracking of GRP seriously. For the oriented GRP in this investigation, from better stress corrosion resistance to worse the order is ±30°,±45°,±60°oriented GRP. Compared with unidirectional GRP, oriented GRP demonstrate higher stress corrosion threshold loads, below which GRP can't fail in acceptable exposure time. Further discussions conform that fibre/matrix interface plays an important role in the stress corrosion cracking of oriented GRP and the crack growth mechanisms of oriented GRP and unidirectional GRP are different under different applied loads.
Stress corrosion cracking of three kinds of oriented glass fibre reinforced plastics(GRP), including ±30°,±45°,±60°oriented GRP, were studied by fracture mechanics theory and compared with the stress corrosion cracking of unidirectional GRP. The results show that the fibre orientation affects on the stress corrosion cracking of GRP seriously. For the oriented GRP in this investigation, from better stress corrosion resistance to worse the order is ±30°,±45°,±60°oriented GRP. Compared with unidirectional GRP, oriented GRP demonstrate higher stress corrosion threshold loads, below which GRP can't fail in acceptable exposure time. Further discussions conform that fibre/matrix interface plays an important role in the stress corrosion cracking of oriented GRP and the crack growth mechanisms of oriented GRP and unidirectional GRP are different under different applied loads.
2004, 21(6): 47-52.
Abstract:
The temperature characterizations of epoxy resin systems during electron-beam curing were measured by using automatic testing and collection systems. The effects of different factors, such as the chemical structures, the molecular weights of epoxy resins and the concentration of resins in the mixture with dilution were investigated. The properties of cured resins were evaluated by the gel mass fraction and the dynamic mechanical analysis. The data indicate that the rising of temperature in resins mainly results from the electron energy absorbance by the epoxy resins, in the process of EB curing, and the absorbency of resin systems depends on its chemical structures rather than the molecular weight of the epoxy oligomer. The addition of diluting agent would change the temperature characterization of resin systems and it was found that the more the concentration of the diluting agent, the higher the peak of temperature curves.
The temperature characterizations of epoxy resin systems during electron-beam curing were measured by using automatic testing and collection systems. The effects of different factors, such as the chemical structures, the molecular weights of epoxy resins and the concentration of resins in the mixture with dilution were investigated. The properties of cured resins were evaluated by the gel mass fraction and the dynamic mechanical analysis. The data indicate that the rising of temperature in resins mainly results from the electron energy absorbance by the epoxy resins, in the process of EB curing, and the absorbency of resin systems depends on its chemical structures rather than the molecular weight of the epoxy oligomer. The addition of diluting agent would change the temperature characterization of resin systems and it was found that the more the concentration of the diluting agent, the higher the peak of temperature curves.
2004, 21(6): 53-57.
Abstract:
Curing reaction of the matrix resin (MR) developed by the authors of this paper was studied for the composites structural repair application through in-situ FTIR. Conversions of the epoxy radical at different curing temperatures were calculated and were compared with the gelation time of the MR system. Conversions of the epoxy radical were also compared with the viscosity changes vs. time at the same temperatures. When the curing temperature reaches the onset curing temperature (108℃) on DSC trace of MR, the conversion curve from in-situ FTIR tallied with the gelation time and the curve of viscosity vs. time by means of macroscopical methods. When the curing temperature is below 108℃, the conversion curve from in-situ FTIR will deviate from the curing degrees concluded from the gelation time and the curve of viscosity vs. time at the corresponding temperature. The main causes of the deviation were analyzed.
Curing reaction of the matrix resin (MR) developed by the authors of this paper was studied for the composites structural repair application through in-situ FTIR. Conversions of the epoxy radical at different curing temperatures were calculated and were compared with the gelation time of the MR system. Conversions of the epoxy radical were also compared with the viscosity changes vs. time at the same temperatures. When the curing temperature reaches the onset curing temperature (108℃) on DSC trace of MR, the conversion curve from in-situ FTIR tallied with the gelation time and the curve of viscosity vs. time by means of macroscopical methods. When the curing temperature is below 108℃, the conversion curve from in-situ FTIR will deviate from the curing degrees concluded from the gelation time and the curve of viscosity vs. time at the corresponding temperature. The main causes of the deviation were analyzed.
2004, 21(6): 58-62.
Abstract:
Glass fiber reinforced plastics (GFRP)laminates containing the extrinsic fabry-perot interferometr (EFPI) sensor in its middle plane were made for experiments. Three-point bending tests of the laminate were performed to obtain the relationship between the bending moment and the strain output from the sensor. Microscopic examination of the cross section containing the sensor was carried out. Finite element method (FEM) strain analysis was also performed to obtain the strain of the sensor embedded at the off-center position obtained from the microscopic observation. From these results,it is found that the strain output from the EFPI sensor is larger than that calculated for the off-center sensor. This discrepancy shows that the bending moment affects the measuring ability of the sensor.
Glass fiber reinforced plastics (GFRP)laminates containing the extrinsic fabry-perot interferometr (EFPI) sensor in its middle plane were made for experiments. Three-point bending tests of the laminate were performed to obtain the relationship between the bending moment and the strain output from the sensor. Microscopic examination of the cross section containing the sensor was carried out. Finite element method (FEM) strain analysis was also performed to obtain the strain of the sensor embedded at the off-center position obtained from the microscopic observation. From these results,it is found that the strain output from the EFPI sensor is larger than that calculated for the off-center sensor. This discrepancy shows that the bending moment affects the measuring ability of the sensor.
2004, 21(6): 63-69.
Abstract:
FRTP composites were manufactured from a kind of GF/PP warp-knitting fabrics by means of hot-mold compression moulding.The effects of processing conditions in terms of pressure and holding time on microstructure of the materials were studied with SEM,and the impregnation mechanism was proposed based on the SEM photos.The cause of defects in the materials was also investigated. The experiment result that a good quality of impregnation and fiber dispersion could be achieved under appropriate processing conditions indicates the feasibility of warp-knitting fabrics to manufacture FRTP composites.
FRTP composites were manufactured from a kind of GF/PP warp-knitting fabrics by means of hot-mold compression moulding.The effects of processing conditions in terms of pressure and holding time on microstructure of the materials were studied with SEM,and the impregnation mechanism was proposed based on the SEM photos.The cause of defects in the materials was also investigated. The experiment result that a good quality of impregnation and fiber dispersion could be achieved under appropriate processing conditions indicates the feasibility of warp-knitting fabrics to manufacture FRTP composites.
2004, 21(6): 70-74.
Abstract:
A developed computer code and a FEM/CV analysis software can combine to model any complex 3D composite parts and simulate the RTM mold-filling process. The simulation and experiments of I-shaped 2D plane with different processing parameters were investigated, and the results show that the mold-filling time is inverse proportion to pressure and penetrability, and direct proportion to resin viscosity. The experimental data are in good agreement with the numerical data, which validates that the simulation software is reliable to predict resin flow patterns and processing efficiency. The results can be further utilized to find the optimal processing conditions for RTM parts.
A developed computer code and a FEM/CV analysis software can combine to model any complex 3D composite parts and simulate the RTM mold-filling process. The simulation and experiments of I-shaped 2D plane with different processing parameters were investigated, and the results show that the mold-filling time is inverse proportion to pressure and penetrability, and direct proportion to resin viscosity. The experimental data are in good agreement with the numerical data, which validates that the simulation software is reliable to predict resin flow patterns and processing efficiency. The results can be further utilized to find the optimal processing conditions for RTM parts.
2004, 21(6): 75-81.
Abstract:
The internal strain of composite laminates during a constant stress amplitude fatigue testing process was monitored with fiber Bragg gratings (FBGs) as a fatigue indicator to reveal Young's modulus decrease of the specimen, which is a direct index of damage. It is demonstrated that FBGs can not only be embedded in composite structures to detect fatigue damage during fatigue process, but also with excellent durability compared with other sensors such as foil gauges, which is most frequently used in strain measurement. After 1 million cycles, the FBGs can still keep good sensibility. It can be concluded that it is a novel way to monitor, evaluate and give crash alert for the health state of composite structures during their whole service life with FBGs as a fatigue indicator.
The internal strain of composite laminates during a constant stress amplitude fatigue testing process was monitored with fiber Bragg gratings (FBGs) as a fatigue indicator to reveal Young's modulus decrease of the specimen, which is a direct index of damage. It is demonstrated that FBGs can not only be embedded in composite structures to detect fatigue damage during fatigue process, but also with excellent durability compared with other sensors such as foil gauges, which is most frequently used in strain measurement. After 1 million cycles, the FBGs can still keep good sensibility. It can be concluded that it is a novel way to monitor, evaluate and give crash alert for the health state of composite structures during their whole service life with FBGs as a fatigue indicator.
2004, 21(6): 87-92.
Abstract:
Using nitrogen, hydrogen respectively as the carrier gas, the C/C composite was fabricated by the thermal gradient CVI process under the condition of 1000℃,0.5 kPa propylene partial pressure. The influence of the carrier gas especially hydrogen on the structure of pyrocarbon was researched. Extinction angles of CVI pyrocarbon at different areas of the samples were tested by polarized light microscopy, which were used to analyze the alteration of the microstructure of pyrocarbon. The results show that the addition of nitrogen can not change the microstructure of pyrocarbon which plays an inert role. And the addition of hydrogen has more advantage to obtain rough laminar microstructure pyrocarbon by changing components of the micro-environment during CVI process. The influence of density addition on residence time of the reactants leads to an abrupt change of pyrocarbon microstructure. The better control of the structure of the pyrocarbon in the C/C composite can be achieved by adding hydrogen.
Using nitrogen, hydrogen respectively as the carrier gas, the C/C composite was fabricated by the thermal gradient CVI process under the condition of 1000℃,0.5 kPa propylene partial pressure. The influence of the carrier gas especially hydrogen on the structure of pyrocarbon was researched. Extinction angles of CVI pyrocarbon at different areas of the samples were tested by polarized light microscopy, which were used to analyze the alteration of the microstructure of pyrocarbon. The results show that the addition of nitrogen can not change the microstructure of pyrocarbon which plays an inert role. And the addition of hydrogen has more advantage to obtain rough laminar microstructure pyrocarbon by changing components of the micro-environment during CVI process. The influence of density addition on residence time of the reactants leads to an abrupt change of pyrocarbon microstructure. The better control of the structure of the pyrocarbon in the C/C composite can be achieved by adding hydrogen.
2004, 21(6): 93-97.
Abstract:
Using the M-2000 tribology machine, without lubrication, the tribology properties of two kinds of graphite and two kinds of C/C composites were studied with GCr15 steel as couple. The results show that C/C composites own the lower friction coefficient and bulk worn loss than the graphite. Both the friction coefficient and bulk worn loss of C/C composites with the smooth lamination(SL) carbon matrix structure are lower than the two of C/C composites with rough lamination (RL) structure. The low density graphite gets higher friction coefficient and bulk worn loss than the high density graphite. With time prolonging, the friction coefficient of RL C/C composites increased under 60 N,80 N and 200 N while others decreased. But the friction coefficient of SL C/C composites decreased except 60 N and changed a little, and that of two kinds of graphite increased. The SEM show that the friction film of RL C/C composites becomes more integrate with increasing load, while that changes only a little of SL C/C composites. The friction film of high density graphite is more integrate than the low density graphite. C/C composites have advantage over graphite used as the seal ring of the main axis of turbine engine for airplane.
Using the M-2000 tribology machine, without lubrication, the tribology properties of two kinds of graphite and two kinds of C/C composites were studied with GCr15 steel as couple. The results show that C/C composites own the lower friction coefficient and bulk worn loss than the graphite. Both the friction coefficient and bulk worn loss of C/C composites with the smooth lamination(SL) carbon matrix structure are lower than the two of C/C composites with rough lamination (RL) structure. The low density graphite gets higher friction coefficient and bulk worn loss than the high density graphite. With time prolonging, the friction coefficient of RL C/C composites increased under 60 N,80 N and 200 N while others decreased. But the friction coefficient of SL C/C composites decreased except 60 N and changed a little, and that of two kinds of graphite increased. The SEM show that the friction film of RL C/C composites becomes more integrate with increasing load, while that changes only a little of SL C/C composites. The friction film of high density graphite is more integrate than the low density graphite. C/C composites have advantage over graphite used as the seal ring of the main axis of turbine engine for airplane.
2004, 21(6): 98-103.
Abstract:
The effects of nano Al2O3 particle content in the electrolyte on the nanoparticle content, microstructure, hardness and wear resistance of the composite coating were studied. The results show that the microstructure and hardness of the composite coating are improved with the increase of the nano-particles in the electrolyte， and the wear resistance of nanocomposite coating is 80% higher than that of high speed nickel coating. The nano-composite coating has the best wear resistance when the nano-particle content in the electrolyte is 20 g/L, above which the wear resistance decreases.
The effects of nano Al2O3 particle content in the electrolyte on the nanoparticle content, microstructure, hardness and wear resistance of the composite coating were studied. The results show that the microstructure and hardness of the composite coating are improved with the increase of the nano-particles in the electrolyte， and the wear resistance of nanocomposite coating is 80% higher than that of high speed nickel coating. The nano-composite coating has the best wear resistance when the nano-particle content in the electrolyte is 20 g/L, above which the wear resistance decreases.
2004, 21(6): 104-107.
Abstract:
Automotive friction materials were prepared with different kinds of resins and different resin contents. The effects of resin on mechanical and friction properties of automotive friction materials were studied. The results show that friction materials with YSM modified phenolic resin have better mechanical and friction properties than those with pure phenolic resin. Friction materials by Resin-NBR mixing modification have good mechanical properties, wear-resistance and smooth coefficient. With the increase of resin content, the mechanical properties of friction materials are improved. With the resin content of 9%~12%, the materials have excellent friction and wear properties. When the resin content is less than 6%, the friction coefficient of materials is low and unstable. And when more than 15%, the friction materials begin to decay at high temperatures.
Automotive friction materials were prepared with different kinds of resins and different resin contents. The effects of resin on mechanical and friction properties of automotive friction materials were studied. The results show that friction materials with YSM modified phenolic resin have better mechanical and friction properties than those with pure phenolic resin. Friction materials by Resin-NBR mixing modification have good mechanical properties, wear-resistance and smooth coefficient. With the increase of resin content, the mechanical properties of friction materials are improved. With the resin content of 9%~12%, the materials have excellent friction and wear properties. When the resin content is less than 6%, the friction coefficient of materials is low and unstable. And when more than 15%, the friction materials begin to decay at high temperatures.
2004, 21(6): 108-113.
Abstract:
The vacuum thermo-cycling tests (93~413 K, 10-5Pa) were carried out on the unidirectional M40J/5228A composite. The mass loss and linear expansion coefficient of the specimens were measured after vacuum thermo-cycling of different cycles. The effect of vacuum thermal cycles on the linear expansion coefficient profile was analyzed using a proposed two-dimensional model of micro-damage. The results show that the mass loss rate increases with increasing the vacuum thermal cycles, and becomes flat after 48 cycles; the transverse expansion coefficient linearly increases with increasing temperature, and is not affected by vacuum thermal cycles. The longitudinal expansion coefficient linearly decreases with increasing temperature under the original state, while it exhibits a non-linear characteristic of decreasing firstly and then increasing with temperature after 113 cycles. The effect of vacuum thermal cycles on the longitudinal linear expansion coefficient closely depends on the breaking extent of the binding interface and the relief of residual stress.
The vacuum thermo-cycling tests (93~413 K, 10-5Pa) were carried out on the unidirectional M40J/5228A composite. The mass loss and linear expansion coefficient of the specimens were measured after vacuum thermo-cycling of different cycles. The effect of vacuum thermal cycles on the linear expansion coefficient profile was analyzed using a proposed two-dimensional model of micro-damage. The results show that the mass loss rate increases with increasing the vacuum thermal cycles, and becomes flat after 48 cycles; the transverse expansion coefficient linearly increases with increasing temperature, and is not affected by vacuum thermal cycles. The longitudinal expansion coefficient linearly decreases with increasing temperature under the original state, while it exhibits a non-linear characteristic of decreasing firstly and then increasing with temperature after 113 cycles. The effect of vacuum thermal cycles on the longitudinal linear expansion coefficient closely depends on the breaking extent of the binding interface and the relief of residual stress.
2004, 21(6): 108-113.
Abstract:
The vacuum thermo-cycling tests (93~413 K, 10-5Pa) were carried out on the unidirectional M40J/5228A composite. The mass loss and linear expansion coefficient of the specimens were measured after vacuum thermo-cycling of different cycles. The effect of vacuum thermal cycles on the linear expansion coefficient profile was analyzed using a proposed two-dimensional model of micro-damage. The results show that the mass loss rate increases with increasing the vacuum thermal cycles, and becomes flat after 48 cycles; the transverse expansion coefficient linearly increases with increasing temperature, and is not affected by vacuum thermal cycles. The longitudinal expansion coefficient linearly decreases with increasing temperature under the original state, while it exhibits a non-linear characteristic of decreasing firstly and then increasing with temperature after 113 cycles. The effect of vacuum thermal cycles on the longitudinal linear expansion coefficient closely depends on the breaking extent of the binding interface and the relief of residual stress.
The vacuum thermo-cycling tests (93~413 K, 10-5Pa) were carried out on the unidirectional M40J/5228A composite. The mass loss and linear expansion coefficient of the specimens were measured after vacuum thermo-cycling of different cycles. The effect of vacuum thermal cycles on the linear expansion coefficient profile was analyzed using a proposed two-dimensional model of micro-damage. The results show that the mass loss rate increases with increasing the vacuum thermal cycles, and becomes flat after 48 cycles; the transverse expansion coefficient linearly increases with increasing temperature, and is not affected by vacuum thermal cycles. The longitudinal expansion coefficient linearly decreases with increasing temperature under the original state, while it exhibits a non-linear characteristic of decreasing firstly and then increasing with temperature after 113 cycles. The effect of vacuum thermal cycles on the longitudinal linear expansion coefficient closely depends on the breaking extent of the binding interface and the relief of residual stress.
2004, 21(6): 114-118.
Abstract:
The phenolic resin(PF) modified by nano-copper, used in friction materials, was successfully prepared by in situ producing method invented newly. The prepared resin was characterized by XRD and TEM. The results show that the nano-copper particles are well dispersed in PF in diameter of 10~40 nm, and in spherical geometry. The results of TGA, impacting tests and friction and wear experiments indicate that the heat-resistance of the modified PF can be greatly raised. Compared with those of the pure PF, the initial decomposing and the half decomposing temperature rise by 31℃and 46℃, respectively; The toughness and tribological properties of the modified PF could be distinctly improved. Compared with those of the pure PF, the impact strength increases by 44%, the heat-fade rate and wear rate reduce by 50% and 2/3, respectively. The interfacial model of the phenolic resin / nano-copper composite was proposed. The mechanisms were discussed, that the properties of phenolic resin and friction materials are improved by nano-copper.
The phenolic resin(PF) modified by nano-copper, used in friction materials, was successfully prepared by in situ producing method invented newly. The prepared resin was characterized by XRD and TEM. The results show that the nano-copper particles are well dispersed in PF in diameter of 10~40 nm, and in spherical geometry. The results of TGA, impacting tests and friction and wear experiments indicate that the heat-resistance of the modified PF can be greatly raised. Compared with those of the pure PF, the initial decomposing and the half decomposing temperature rise by 31℃and 46℃, respectively; The toughness and tribological properties of the modified PF could be distinctly improved. Compared with those of the pure PF, the impact strength increases by 44%, the heat-fade rate and wear rate reduce by 50% and 2/3, respectively. The interfacial model of the phenolic resin / nano-copper composite was proposed. The mechanisms were discussed, that the properties of phenolic resin and friction materials are improved by nano-copper.
2004, 21(6): 119-124.
Abstract:
For the 3D five-direction tubular preform produced by four-step braiding, the yarn geometric topologies in the interior and the surface regions were studied, and a unit-cell structure model was presented on the basis of tubular braiding process and principles. Under these conditions, the yarn trajectory projection was simulated as the Archimedean screw in the interior region or the circular arc in the surface region and characterized with a corresponding mathematical formula. On the other hand, the fiber volume fraction of different zones in the fabric's cross-section was computed in terms of the unit-cell's geometric feature. Then the preform's architecture and the fiber volume fraction in a cross-section were simulated by building the yarn's data structure and using the computer visualization techniques, which may have a great meaning to characterize the structure of the 3D five-direction tubular preform and optimize the braiding parameters.
For the 3D five-direction tubular preform produced by four-step braiding, the yarn geometric topologies in the interior and the surface regions were studied, and a unit-cell structure model was presented on the basis of tubular braiding process and principles. Under these conditions, the yarn trajectory projection was simulated as the Archimedean screw in the interior region or the circular arc in the surface region and characterized with a corresponding mathematical formula. On the other hand, the fiber volume fraction of different zones in the fabric's cross-section was computed in terms of the unit-cell's geometric feature. Then the preform's architecture and the fiber volume fraction in a cross-section were simulated by building the yarn's data structure and using the computer visualization techniques, which may have a great meaning to characterize the structure of the 3D five-direction tubular preform and optimize the braiding parameters.
2004, 21(6): 125-129.
Abstract:
The effects of pH value, the amount of dispersant, ZrO2(3Y) content and solid volume fraction on viscosity of ZTA ceramic slurries were discussed. The mechanical properties and microstructure of sintered ZTA samples by gelcasting were investigated. The results show that low viscosity ZTA ( 20% ZrO2) suspension with 55% solid volume fraction is obtained at pH 8.5 and 0.9% dispersant. The sintered sample prepared with high solid volume fraction of the suspension has the advantages of compact structure, uniformity distribution of ZrO2 particles and higher content of t-ZrO2 phase. Its bending strength and fracture toughness are 631.5 MPa and 7.64 MPa · m1/2 under the test condition, respectively.
The effects of pH value, the amount of dispersant, ZrO2(3Y) content and solid volume fraction on viscosity of ZTA ceramic slurries were discussed. The mechanical properties and microstructure of sintered ZTA samples by gelcasting were investigated. The results show that low viscosity ZTA ( 20% ZrO2) suspension with 55% solid volume fraction is obtained at pH 8.5 and 0.9% dispersant. The sintered sample prepared with high solid volume fraction of the suspension has the advantages of compact structure, uniformity distribution of ZrO2 particles and higher content of t-ZrO2 phase. Its bending strength and fracture toughness are 631.5 MPa and 7.64 MPa · m1/2 under the test condition, respectively.
2004, 21(6): 130-136.
Abstract:
The synthesized process and thermodynamic mechanisms of high-quality SiAlON dispersed phase, effect of sintering additive on the properties of composite and microstructural characterizations were investigated to obtain high performance and inexpensive SiAlON/Al2O3 matrix composites. Thermodynamics reactions were given in the carbothermal reduction nitridation at 1400~1700℃ which possibly occurred in the system, and finally confirmed by specific cited test(XRD). Characterizations of the microstructural observation and the resultant identified by electron diffraction pattern, would supply significant evidence for advanced composites designed and fabricated with a variety of improving mechanisms, which primarily contained suitable doping of rare metal oxide, in situ strengthening of elongated SiAlON grain and high bonding of interfacial layer.
The synthesized process and thermodynamic mechanisms of high-quality SiAlON dispersed phase, effect of sintering additive on the properties of composite and microstructural characterizations were investigated to obtain high performance and inexpensive SiAlON/Al2O3 matrix composites. Thermodynamics reactions were given in the carbothermal reduction nitridation at 1400~1700℃ which possibly occurred in the system, and finally confirmed by specific cited test(XRD). Characterizations of the microstructural observation and the resultant identified by electron diffraction pattern, would supply significant evidence for advanced composites designed and fabricated with a variety of improving mechanisms, which primarily contained suitable doping of rare metal oxide, in situ strengthening of elongated SiAlON grain and high bonding of interfacial layer.
2004, 21(6): 137-142.
Abstract:
On the basis of comparability of structure and constitute about sepiolite and basalt fibers, basalt was mixed with sepiolite in different proportions. Modified basalt fibers were made by melting,drawing the mixture and other processes using the ACC- Ⅱ high-temperature pot resistance furnace. The microstructure, morphology and characteristic of modified basalt fibers with basalt fibers were investigated by using Scanning Electron Microscopy(SEM).The influence of sepiolite on performance of basalt fibers was studied. The possible mechanism of the modification was discussed. The results show that a kind of modified basalt composites with new network structure can be produced by melting the mixture of sepiolite in the mass fraction of 10%~20% sepiolite. It was found that sepiolite can change the structure,constitute and performances of basalt fibers and improve the chemical permanence, flexibility and heat-resistant performance of basalt fibers.
On the basis of comparability of structure and constitute about sepiolite and basalt fibers, basalt was mixed with sepiolite in different proportions. Modified basalt fibers were made by melting,drawing the mixture and other processes using the ACC- Ⅱ high-temperature pot resistance furnace. The microstructure, morphology and characteristic of modified basalt fibers with basalt fibers were investigated by using Scanning Electron Microscopy(SEM).The influence of sepiolite on performance of basalt fibers was studied. The possible mechanism of the modification was discussed. The results show that a kind of modified basalt composites with new network structure can be produced by melting the mixture of sepiolite in the mass fraction of 10%~20% sepiolite. It was found that sepiolite can change the structure,constitute and performances of basalt fibers and improve the chemical permanence, flexibility and heat-resistant performance of basalt fibers.
2004, 21(6): 143-148.
Abstract:
A spatial and temporal multiple scale method is studied to simulate the phenomenon of non-Fourier heat conduction in periodic heterogeneous materials . The model is derived from the higher-order homogenization theory with multiple spatial and temporal scales. Amplified spatial and reduced temporal scales are respectively introduced to account for fluctuations of non-Fourier heat conduction due to material heterogeneity and nonlocal effect of the homogenized solution. By combining various orders of homogenized non-Fourier heat conduction equations, the reduced time dependence is eliminated and the fourth-order differential equations are derived. To avoid the necessity of C1- continuity in finite element implementation, the C0-continuous mixed finite element approximation of the resulting nonlocal equations of non-Fourier heat conduction is put forward. Numerical examples are computed to demonstrate the efficiency and validity of the theories and model developed.
A spatial and temporal multiple scale method is studied to simulate the phenomenon of non-Fourier heat conduction in periodic heterogeneous materials . The model is derived from the higher-order homogenization theory with multiple spatial and temporal scales. Amplified spatial and reduced temporal scales are respectively introduced to account for fluctuations of non-Fourier heat conduction due to material heterogeneity and nonlocal effect of the homogenized solution. By combining various orders of homogenized non-Fourier heat conduction equations, the reduced time dependence is eliminated and the fourth-order differential equations are derived. To avoid the necessity of C1- continuity in finite element implementation, the C0-continuous mixed finite element approximation of the resulting nonlocal equations of non-Fourier heat conduction is put forward. Numerical examples are computed to demonstrate the efficiency and validity of the theories and model developed.
2004, 21(6): 149-154.
Abstract:
An analytical method is proposed to predict the nonlinear susceptibility of general composite materials. The method was based on the secant permittivities of each phase, and a nonlinear problem was transformed into a series of linear problems. The method is applied to any anisotropic composite and the nonlinearity of the constituents, contrary to the Stroud and Hui method, which is valid for isotropic composites and weak nonlinearity. As for the nonlinear mechanical behavior, it is shown that the proposed method is identical to the Ponte Castaneda variational method when the same method is used for the linear comparison composite. Some numerical computations are provided to illustrate the influence of the microstructure on the overall nonlinear relation between the electric displacement and the electric field.
An analytical method is proposed to predict the nonlinear susceptibility of general composite materials. The method was based on the secant permittivities of each phase, and a nonlinear problem was transformed into a series of linear problems. The method is applied to any anisotropic composite and the nonlinearity of the constituents, contrary to the Stroud and Hui method, which is valid for isotropic composites and weak nonlinearity. As for the nonlinear mechanical behavior, it is shown that the proposed method is identical to the Ponte Castaneda variational method when the same method is used for the linear comparison composite. Some numerical computations are provided to illustrate the influence of the microstructure on the overall nonlinear relation between the electric displacement and the electric field.
2004, 21(6): 155-160.
Abstract:
A micro beam model was developed to predict the deformation and micro stress distribution of fiber yarns and matrix in three dimensionally woven composites. The shear deformation in the interlayer matrix between adjunct fiber yarns caused by yarn bending was taken into account. In this model,the fiber yarn is modeled by beams in series, therefore its tension and bending deformations are coupled. To a typical three dimensionally woven composite material the method of determining microstructure by woven parameters is discussed. An analytical cell is adopted which is constructed by a least periodic section of yarn and interlayer matrix. Micro stresses of the cell were studied by this beam model. The macro modulus of this material was obtained by averaging micro stresses of the cell. The predictions agree well with those from material test and micro brick finite element method. Analysis reveals that the micro stress caused by the tensile/bending coupling effect is not ignorable.
A micro beam model was developed to predict the deformation and micro stress distribution of fiber yarns and matrix in three dimensionally woven composites. The shear deformation in the interlayer matrix between adjunct fiber yarns caused by yarn bending was taken into account. In this model,the fiber yarn is modeled by beams in series, therefore its tension and bending deformations are coupled. To a typical three dimensionally woven composite material the method of determining microstructure by woven parameters is discussed. An analytical cell is adopted which is constructed by a least periodic section of yarn and interlayer matrix. Micro stresses of the cell were studied by this beam model. The macro modulus of this material was obtained by averaging micro stresses of the cell. The predictions agree well with those from material test and micro brick finite element method. Analysis reveals that the micro stress caused by the tensile/bending coupling effect is not ignorable.
2004, 21(6): 161-166.
Abstract:
An impact damage tolerance reliability analysis method was discussed for composite structures by introducing an impact threat concept. The method was applied to the damage tolerance reliability evaluations of domestically produced composite laminates and stiffened panels such as T300/5405, T300/QY8911, T300S/9511, T800/9511 and T300/9512. The example reliability calculations indicate that the damage tolerance capability of composite structures could be taken fully since the impact threat distributions are considered in the present method.
An impact damage tolerance reliability analysis method was discussed for composite structures by introducing an impact threat concept. The method was applied to the damage tolerance reliability evaluations of domestically produced composite laminates and stiffened panels such as T300/5405, T300/QY8911, T300S/9511, T800/9511 and T300/9512. The example reliability calculations indicate that the damage tolerance capability of composite structures could be taken fully since the impact threat distributions are considered in the present method.
2004, 21(6): 167-172.
Abstract:
Mathematic models were established to represent the curing step of thermoset composites, a finite element formulation for three-dimensional transient cure simulation of composite structures was introduced and a simulation code CURESIM was developed based on the formulation. The simulated results match the experimental results well, which demonstrates the mathematic models and numerical algorithm are of high reliability. The temperature and degree of cure distribution can be obtained at any time by the simulated code. The numerical simulation method can be used to optimize the curing temperature cycle, which can improve the quality of composite products.
Mathematic models were established to represent the curing step of thermoset composites, a finite element formulation for three-dimensional transient cure simulation of composite structures was introduced and a simulation code CURESIM was developed based on the formulation. The simulated results match the experimental results well, which demonstrates the mathematic models and numerical algorithm are of high reliability. The temperature and degree of cure distribution can be obtained at any time by the simulated code. The numerical simulation method can be used to optimize the curing temperature cycle, which can improve the quality of composite products.
2004, 21(6): 173-178.
Abstract:
A micromechanical model was developed to study the mechanical behavior of a composite system consisting of aligned shape memory alloy (SMA) short fiber in elastoplastic matrix in the uniform thermal field. The analytical model was based on the Eshelby's equivalent inclusion method and the Mori-Tanaka scheme. The numerical example illustrates the mechanical response of SMA short fiber composite under isothermal longitudinal cycle loading. The effects of temperature, fiber volume fraction and fiber aspect ratio on the residual stress and residual strain of the composite were discussed, which is helpful to design the intelligent composites.
A micromechanical model was developed to study the mechanical behavior of a composite system consisting of aligned shape memory alloy (SMA) short fiber in elastoplastic matrix in the uniform thermal field. The analytical model was based on the Eshelby's equivalent inclusion method and the Mori-Tanaka scheme. The numerical example illustrates the mechanical response of SMA short fiber composite under isothermal longitudinal cycle loading. The effects of temperature, fiber volume fraction and fiber aspect ratio on the residual stress and residual strain of the composite were discussed, which is helpful to design the intelligent composites.
2004, 21(6): 179-183.
Abstract:
Models estimating stiffness and strength of stitched composites were established based on BP algorithm of neural network, and the longitudinal stiffness and strength networks were trained according to experimental data. The nonlinear relationship between input parameters and output parameters was determined and the analysis software of stitched laminates was completed. The longitudinal stiffness and strength of stitched laminates with new stitching parameters and new equivalent unstitched laminate performance parameters were predicted using the software. The results of the prediction and the test data are in good agreement. A very effective approach to estimate the stiffness and strength of stitched composites has been found.
Models estimating stiffness and strength of stitched composites were established based on BP algorithm of neural network, and the longitudinal stiffness and strength networks were trained according to experimental data. The nonlinear relationship between input parameters and output parameters was determined and the analysis software of stitched laminates was completed. The longitudinal stiffness and strength of stitched laminates with new stitching parameters and new equivalent unstitched laminate performance parameters were predicted using the software. The results of the prediction and the test data are in good agreement. A very effective approach to estimate the stiffness and strength of stitched composites has been found.
