2010 Vol. 27, No. 5
2010, 27(5): 1-6.
Abstract:
In the single fiber composite fragmentation test （SFCFT）, the fiber fragmented randomly with the load increasing and the number of fiber fragments saturated under some load （The number of fiber fragments didn’t increase）. This test was commonly used to characterize the interfacial property between fiber and matrix. For this test, the stress transfer analysis was done with the elastic-plastic shear-lag theory under the consideration of the real performance of component materials (elastic-plastic of the matrix). So the more true form of stress distribution in the fiber axial direction and at the interface between fiber/matrix could be obtained. The heterogeneity of fiber strength distribution was considered also and the random fragmentation process in the test was simulated with the method of Monte Carlo based on the analysis of stress transfer. The relationship between load and the number of fiber fragments is forecasted. The anastomosis of result between simulation and test is achieved. So it is manifested that the stress analysis and simulation method are valid.
In the single fiber composite fragmentation test （SFCFT）, the fiber fragmented randomly with the load increasing and the number of fiber fragments saturated under some load （The number of fiber fragments didn’t increase）. This test was commonly used to characterize the interfacial property between fiber and matrix. For this test, the stress transfer analysis was done with the elastic-plastic shear-lag theory under the consideration of the real performance of component materials (elastic-plastic of the matrix). So the more true form of stress distribution in the fiber axial direction and at the interface between fiber/matrix could be obtained. The heterogeneity of fiber strength distribution was considered also and the random fragmentation process in the test was simulated with the method of Monte Carlo based on the analysis of stress transfer. The relationship between load and the number of fiber fragments is forecasted. The anastomosis of result between simulation and test is achieved. So it is manifested that the stress analysis and simulation method are valid.
2010, 27(5): 7-12.
Abstract:
In order to prepare a polymer reinforced wood---based composite with excellent properties, a fast---growing wood, Populus ussuriensis Kom, and glycidyl methacrylate (GMA) as a difunctional monomer and methyl methacrylate (MMA) as an acrylate monomer were selected, and the monomers were impregnated into the porous structure of wood and further initiated by a catalyst---thermal treatment for their in situ polymerization. The composite’s structure was characterized by SEM, FTIR and XRD, and its corresponding properties were also tested. The results show that the contact between polymers and wood cell walls is tight, and the interfacial interaction is strengthened after adding GMA. GMA fully reacts with the hydroxyl group on wood cell walls by its epoxy group, and reacts with MMA in a free radical copolymerization form by its double bond. The copolymer, P(GMAcoMMA) is finally grafted onto wood cell walls in an amorphous form. The testing results of its properties show that the modulus of rupture (MOR), the dimensional stability, the decay resistance and the thermal stability of P(GMAcoMMA)/wood are increased by 90.53%, 54.05%, 92.85% and 31℃ compared with those of untreated wood, respectively.
In order to prepare a polymer reinforced wood---based composite with excellent properties, a fast---growing wood, Populus ussuriensis Kom, and glycidyl methacrylate (GMA) as a difunctional monomer and methyl methacrylate (MMA) as an acrylate monomer were selected, and the monomers were impregnated into the porous structure of wood and further initiated by a catalyst---thermal treatment for their in situ polymerization. The composite’s structure was characterized by SEM, FTIR and XRD, and its corresponding properties were also tested. The results show that the contact between polymers and wood cell walls is tight, and the interfacial interaction is strengthened after adding GMA. GMA fully reacts with the hydroxyl group on wood cell walls by its epoxy group, and reacts with MMA in a free radical copolymerization form by its double bond. The copolymer, P(GMAcoMMA) is finally grafted onto wood cell walls in an amorphous form. The testing results of its properties show that the modulus of rupture (MOR), the dimensional stability, the decay resistance and the thermal stability of P(GMAcoMMA)/wood are increased by 90.53%, 54.05%, 92.85% and 31℃ compared with those of untreated wood, respectively.
2010, 27(5): 13-18.
Abstract:
Nisilicone rubber composites were prepared with the metal (Ni) and silicone rubber (110) by a mass ratio of 2.7∶1 using a room-temperature twice cure method. At the room temperature, the sample’s piezoresistive and dielectric properties were measured before and after applying a 0.024 T magnetic field. The results show that when the uniaxial force increases from 3.75kPa to 312.5kPa, the sample’s resistivity decreases 8 orders of magnitude. Compared with the values measured before applying the magnetic field, the AC conductivity at low frequencies(40~104Hz) increases 2.46 times, the dielectric constant increases 20% and the dielectric loss increases 2 times by the action of a 0.024T magnetic field. This is mainly caused by the composite’s tunneling-magnetoresistance and magnetoelectric coupling effect. After taking away the magnetic field, conductivity, dielectric constant and dielectric loss could not go back to the initial values, which has something to do with the ferromagnetism of Ni powders. Ni-silicone rubber pressure-sensitive composites have potential applications in magnetic sensors and information storage with the properties of piezoresistive, TMR and magnetoelectric coupling effects.
Nisilicone rubber composites were prepared with the metal (Ni) and silicone rubber (110) by a mass ratio of 2.7∶1 using a room-temperature twice cure method. At the room temperature, the sample’s piezoresistive and dielectric properties were measured before and after applying a 0.024 T magnetic field. The results show that when the uniaxial force increases from 3.75kPa to 312.5kPa, the sample’s resistivity decreases 8 orders of magnitude. Compared with the values measured before applying the magnetic field, the AC conductivity at low frequencies(40~104Hz) increases 2.46 times, the dielectric constant increases 20% and the dielectric loss increases 2 times by the action of a 0.024T magnetic field. This is mainly caused by the composite’s tunneling-magnetoresistance and magnetoelectric coupling effect. After taking away the magnetic field, conductivity, dielectric constant and dielectric loss could not go back to the initial values, which has something to do with the ferromagnetism of Ni powders. Ni-silicone rubber pressure-sensitive composites have potential applications in magnetic sensors and information storage with the properties of piezoresistive, TMR and magnetoelectric coupling effects.
2010, 27(5): 19-23.
Abstract:
In order to improve the process of nickel-plated carbon fiber production efficiency as well as filled composite electromagnetic shielding materials development, nickel-coated carbon fiber (NiCF) was prepared by continuous plating process, and used for the preparation of NiCF reinforced acrylonitrilebutadienestyrene (ABS) composites (NiCF/ABS). Mechanical properties, electromagnetic shielding performance and their controlling factors of the composites were investigated. The results reveal that coupling treatment can improve the mechanical properties of the composite. Tensile strength and bending strength of composites have reached 41 MPa and 61.4 MPa respectively. The composites achieve excellent electromagnetic shielding effectiveness with a carbon fiber mass fraction (Wf) of 12%.
In order to improve the process of nickel-plated carbon fiber production efficiency as well as filled composite electromagnetic shielding materials development, nickel-coated carbon fiber (NiCF) was prepared by continuous plating process, and used for the preparation of NiCF reinforced acrylonitrilebutadienestyrene (ABS) composites (NiCF/ABS). Mechanical properties, electromagnetic shielding performance and their controlling factors of the composites were investigated. The results reveal that coupling treatment can improve the mechanical properties of the composite. Tensile strength and bending strength of composites have reached 41 MPa and 61.4 MPa respectively. The composites achieve excellent electromagnetic shielding effectiveness with a carbon fiber mass fraction (Wf) of 12%.
2010, 27(5): 24-28.
Abstract:
In order to improve the mechanical properties of electrospun silk fibroin (SF) ultrafine fibrous membranes, SF and poly(butylene succinate) (PBS) were dissolved in 1, 1, 1, 3, 3, 3hexafluoro2propanol (HFIP) to fabricate SF/PBS composite ultrafine fibrous membranes by electrospinning. After the composite ultrafine fibrous membranes prepared by using different mass ratios of SF to PBS were treated by methanol, the morphology, structure, and mechanical properties of membranes were characterized by means of FESEM, FTIR, XRD, DSC and Instron 5543 tensile tester respectively. The results show that the average diameter of composite ultrafine fibers increases from 289nm to 425nm and the crystallinity of composite ultrafine fibers increases with the adding of PBS. Especially the mechanical properties are improved. The tensile failure stress of composite ultrafine fibrous membranes first decreases and then increases with the adding of PBS, and the failure strain gradually increases. When the blend mass ratio is 50/50, failure stress is close to 16 MPa and failure strain is up to 50%. The morphology and mechanical properties of ultrafine fibrous membranes can be adjusted and controlled effectively by adding PBS.
In order to improve the mechanical properties of electrospun silk fibroin (SF) ultrafine fibrous membranes, SF and poly(butylene succinate) (PBS) were dissolved in 1, 1, 1, 3, 3, 3hexafluoro2propanol (HFIP) to fabricate SF/PBS composite ultrafine fibrous membranes by electrospinning. After the composite ultrafine fibrous membranes prepared by using different mass ratios of SF to PBS were treated by methanol, the morphology, structure, and mechanical properties of membranes were characterized by means of FESEM, FTIR, XRD, DSC and Instron 5543 tensile tester respectively. The results show that the average diameter of composite ultrafine fibers increases from 289nm to 425nm and the crystallinity of composite ultrafine fibers increases with the adding of PBS. Especially the mechanical properties are improved. The tensile failure stress of composite ultrafine fibrous membranes first decreases and then increases with the adding of PBS, and the failure strain gradually increases. When the blend mass ratio is 50/50, failure stress is close to 16 MPa and failure strain is up to 50%. The morphology and mechanical properties of ultrafine fibrous membranes can be adjusted and controlled effectively by adding PBS.
2010, 27(5): 29-35.
Abstract:
Three different POSS (4-(2-Ferrocenylethenyl)-phenyl-heptacyclopentyl-POSS(POSS1), acryloisobutyl-POSS(POSS2), aminopropylcyclopentyl-POSS(POSS3)) were respectively added into styrene and POSS/polystyrene composites were prepared by bulk free radical polymerization. The dispersion quality of POSS in the matrix of polystyrene was characterized by XRD and TEM. The results indicate that some POSS1 particles in the POSS1/PS are presented in stripe figure. POSS2 is completely dispersed at molecular level in PS matrix, while aggregated POSS3 particles can be seen in POSS3/PS. TGA data indicate that the thermal stabilities of three POSS/PS composites are obviously improved compared to neat PS, and that of POSS1/PS composites are prior to the others. Glass transition temperatures (Tg) of POSS1/PS and POSS2/PS composites are respectively increased by 10℃ and 8℃ in comparison with the neat PS.
Three different POSS (4-(2-Ferrocenylethenyl)-phenyl-heptacyclopentyl-POSS(POSS1), acryloisobutyl-POSS(POSS2), aminopropylcyclopentyl-POSS(POSS3)) were respectively added into styrene and POSS/polystyrene composites were prepared by bulk free radical polymerization. The dispersion quality of POSS in the matrix of polystyrene was characterized by XRD and TEM. The results indicate that some POSS1 particles in the POSS1/PS are presented in stripe figure. POSS2 is completely dispersed at molecular level in PS matrix, while aggregated POSS3 particles can be seen in POSS3/PS. TGA data indicate that the thermal stabilities of three POSS/PS composites are obviously improved compared to neat PS, and that of POSS1/PS composites are prior to the others. Glass transition temperatures (Tg) of POSS1/PS and POSS2/PS composites are respectively increased by 10℃ and 8℃ in comparison with the neat PS.
2010, 27(5): 36-40.
Abstract:
In order to accurately measure the topography and dimension of the interphase structure in carbon fiber reinforced resin matrix composites, a quantitative, in-situ nanomechanical imaging technique was used to map the dynamic mechanical properties of carbon fiber reinforced thermoset resin matrix composites. This technique for interphase structure testing was analyzed including parameter setting, data processing and its applicability. The results indicate that the nanoscale lateral resolution of the method can resolve the width and topography of the interphase in carbon fiber composites. For the carbon fiber/epoxy resin and carbon fiber/bismaleimide resin systems, the storage modulus presents the gradient change in the interphase region. The average interphase width is about 100 nm obtained by statistical analysis on the storage modulus image, and the morphology of interphase on the cross section is “river-like”, which is similar to the surface topography of carbon fibers.
In order to accurately measure the topography and dimension of the interphase structure in carbon fiber reinforced resin matrix composites, a quantitative, in-situ nanomechanical imaging technique was used to map the dynamic mechanical properties of carbon fiber reinforced thermoset resin matrix composites. This technique for interphase structure testing was analyzed including parameter setting, data processing and its applicability. The results indicate that the nanoscale lateral resolution of the method can resolve the width and topography of the interphase in carbon fiber composites. For the carbon fiber/epoxy resin and carbon fiber/bismaleimide resin systems, the storage modulus presents the gradient change in the interphase region. The average interphase width is about 100 nm obtained by statistical analysis on the storage modulus image, and the morphology of interphase on the cross section is “river-like”, which is similar to the surface topography of carbon fibers.
2010, 27(5): 41-46.
Abstract:
This article was aimed at physicochemical interaction between epoxy resin and carbon fiber under composite processing conditions. The influences of temperature on surface tension of E51 resin, E51/DDS and E51/imidazole systems, contact angle between E51 resin and T700 fiber, and the initial apparent contact angle between E51 resin and T700 fiber bundle were studied first; and then the contact angle between E51/DDS and T700 fiber was investigated, based on what the thermodynamic work of adhesion was calculated. The results indicated that wetting between epoxy resin and fiber can be improved by increasing the temperature and lowering the viscosity of resin, of which the effect of the latter is more significant. Before chemical reaction of the epoxy system started, improvement of adhesion between fiber and resin was not significant by increasing the temperature.
This article was aimed at physicochemical interaction between epoxy resin and carbon fiber under composite processing conditions. The influences of temperature on surface tension of E51 resin, E51/DDS and E51/imidazole systems, contact angle between E51 resin and T700 fiber, and the initial apparent contact angle between E51 resin and T700 fiber bundle were studied first; and then the contact angle between E51/DDS and T700 fiber was investigated, based on what the thermodynamic work of adhesion was calculated. The results indicated that wetting between epoxy resin and fiber can be improved by increasing the temperature and lowering the viscosity of resin, of which the effect of the latter is more significant. Before chemical reaction of the epoxy system started, improvement of adhesion between fiber and resin was not significant by increasing the temperature.
2010, 27(5): 47-54.
Abstract:
The anti-scaling performance of 304 stainless steel pipe, epoxy-silicone coating, polyphenylene sulfide (PPS) coating and polytetrafluoroethylene (PTFE)/PPS coating was studied by the methods of image binarization processing, scanning electron microscopy, energy dispersion spectrometry, electrochemical test and so on. The results indicate that the scale formed on the different coatings consisted of a needle-like substance and its main components are CaCO3. The surface energy of PTFE/PPS coating is lower than that of PPS coating, which could restrain effectively the scaling nucleus to form on the sample surface and affect the growth way of nucleus. After the samples were immersed in the static simulated geothermal water for 10 days, the mass of scaling on the PTFE/PPS coating surface was equal to 37.3% with respect to that on the 304 stainless steel. Furthermore, PTFE/PPS coating has a better anti-corrosion performance in the simulated geothermal water.
The anti-scaling performance of 304 stainless steel pipe, epoxy-silicone coating, polyphenylene sulfide (PPS) coating and polytetrafluoroethylene (PTFE)/PPS coating was studied by the methods of image binarization processing, scanning electron microscopy, energy dispersion spectrometry, electrochemical test and so on. The results indicate that the scale formed on the different coatings consisted of a needle-like substance and its main components are CaCO3. The surface energy of PTFE/PPS coating is lower than that of PPS coating, which could restrain effectively the scaling nucleus to form on the sample surface and affect the growth way of nucleus. After the samples were immersed in the static simulated geothermal water for 10 days, the mass of scaling on the PTFE/PPS coating surface was equal to 37.3% with respect to that on the 304 stainless steel. Furthermore, PTFE/PPS coating has a better anti-corrosion performance in the simulated geothermal water.
2010, 27(5): 55-61.
Abstract:
With FactSage thermodynamic software, the thermodynamic equilibrium yields figure and deposition diagram of methyltrichlorosilane (MTS), boron trichloride and hydrogen system at high temperatures (900~1100 ℃) and low pressures (2 kPa, 5 kPa, 12 kPa) were calculated. The effects of total pressure, deposition temperature and ratio of precursor on equilibrium yields were discussed. The results show that temperature, total pressure and ratio of precursor have little effect on yield of SiC, but significant effect on yield of B4C. Ratio of precursor has an influence on yield of C, but other parameters have little effect. The changes of parameter also influence the yields of main vapors (BHx, CxHy, SiClx etc) in a certain degree. The increase of partial pressure of diluent gas is beneficial to formation of B-rich phase, and the increase of partial pressure of MTS favors SiC formation.
With FactSage thermodynamic software, the thermodynamic equilibrium yields figure and deposition diagram of methyltrichlorosilane (MTS), boron trichloride and hydrogen system at high temperatures (900~1100 ℃) and low pressures (2 kPa, 5 kPa, 12 kPa) were calculated. The effects of total pressure, deposition temperature and ratio of precursor on equilibrium yields were discussed. The results show that temperature, total pressure and ratio of precursor have little effect on yield of SiC, but significant effect on yield of B4C. Ratio of precursor has an influence on yield of C, but other parameters have little effect. The changes of parameter also influence the yields of main vapors (BHx, CxHy, SiClx etc) in a certain degree. The increase of partial pressure of diluent gas is beneficial to formation of B-rich phase, and the increase of partial pressure of MTS favors SiC formation.
2010, 27(5): 62-67.
Abstract:
ZrC coatings were prepared by chemical vapor deposition （CVD） using the ZrCl4-Ar-CH4-H2system. The effects of the substrate species, deposition temperature and input concentration ratio of CH4 to ZrCl4 (C/Zr) on the morphology, composition and phase of the coatings as well as the deposition mechanism of ZrC were studied. The experimental results show that the morphology of the ZrC coatings is insensitive to the substrate species. The morphologies and compositions of the ZrC coatings are significantly influenced by the deposition temperature and the input C/Zr ratio. The morphology of ZrC coating changes from a platelet structure to a fine-grained polycrystalline structure as the temperature increases from 1100℃ to 1350℃. As the input C/Zr ratio decreases from 8.5 to 3.5, the coatings morphology changes from a porous structure to a cauliflower structure and then to a glassy structure. The carbon content of the ZrC coatings increases with the temperature and the input C/Zr ratio.
ZrC coatings were prepared by chemical vapor deposition （CVD） using the ZrCl4-Ar-CH4-H2system. The effects of the substrate species, deposition temperature and input concentration ratio of CH4 to ZrCl4 (C/Zr) on the morphology, composition and phase of the coatings as well as the deposition mechanism of ZrC were studied. The experimental results show that the morphology of the ZrC coatings is insensitive to the substrate species. The morphologies and compositions of the ZrC coatings are significantly influenced by the deposition temperature and the input C/Zr ratio. The morphology of ZrC coating changes from a platelet structure to a fine-grained polycrystalline structure as the temperature increases from 1100℃ to 1350℃. As the input C/Zr ratio decreases from 8.5 to 3.5, the coatings morphology changes from a porous structure to a cauliflower structure and then to a glassy structure. The carbon content of the ZrC coatings increases with the temperature and the input C/Zr ratio.
2010, 27(5): 68-72.
Abstract:
Chitosan/hydroxyapatite (CS/HA) composite coating was fabricated on pure titanium substrate surface by the electrophoretic deposition, and porous HA coating was obtained by sintering treatment process. The surface morphology and phase composition of the porous HA coating were characterized by SEM and XRD, respectively. The bonding strength between the coating and the substrate was measured by a shear strength test, while the bioactivity of the coating was determined by immersion in simulated body fluid (SBF). The results show that the porous HA coating can be obtained by sintering at 700℃ from the CS/HA composite coating fabricated in CS/HA suspension with 1∶1 mass ratio of CS/HA, with macro-pore diameter about 10~25 μm and bonding strength up to 19.5 MPa. The coating surface is covered totally by carbonate-apatite after immersion in 1.5 times ion concentration of SBF (1.5SBF) for 5 days, indicating that the coating has a good bioactivity on its surface.
Chitosan/hydroxyapatite (CS/HA) composite coating was fabricated on pure titanium substrate surface by the electrophoretic deposition, and porous HA coating was obtained by sintering treatment process. The surface morphology and phase composition of the porous HA coating were characterized by SEM and XRD, respectively. The bonding strength between the coating and the substrate was measured by a shear strength test, while the bioactivity of the coating was determined by immersion in simulated body fluid (SBF). The results show that the porous HA coating can be obtained by sintering at 700℃ from the CS/HA composite coating fabricated in CS/HA suspension with 1∶1 mass ratio of CS/HA, with macro-pore diameter about 10~25 μm and bonding strength up to 19.5 MPa. The coating surface is covered totally by carbonate-apatite after immersion in 1.5 times ion concentration of SBF (1.5SBF) for 5 days, indicating that the coating has a good bioactivity on its surface.
Electromagnetic wave absorption properties of ferrite and graphite cement-based composite materials
2010, 27(5): 73-78.
Abstract:
Electromagnetic wave absorption properties of cement-based composite material doped with ferrite and graphite (F/G/C) were investigated. The analysis focused on the main impacting factors of absorption performance and explored the mechanism of its influence by changing ferrite and graphite ratio. The results show that 20vol% graphite causes percolation effect and has great loss tangent. The main influence factor of absorbing depth is graphite, while the main factor impacting absorption width is ferrite. 20wt% 60μm ferrite, 10wt% 250μm ferrite and 30vol% graphtite is the best level combination and its reflectivity reached -32dB, which is obviously better than single form compound. Additionally, graphite doping improved space wave impedance,but the main absorption mechanism is still magnetic loss.
Electromagnetic wave absorption properties of cement-based composite material doped with ferrite and graphite (F/G/C) were investigated. The analysis focused on the main impacting factors of absorption performance and explored the mechanism of its influence by changing ferrite and graphite ratio. The results show that 20vol% graphite causes percolation effect and has great loss tangent. The main influence factor of absorbing depth is graphite, while the main factor impacting absorption width is ferrite. 20wt% 60μm ferrite, 10wt% 250μm ferrite and 30vol% graphtite is the best level combination and its reflectivity reached -32dB, which is obviously better than single form compound. Additionally, graphite doping improved space wave impedance,but the main absorption mechanism is still magnetic loss.
2010, 27(5): 79-85.
Abstract:
The glass fiber, copper fiber, mineral fiber, Kevlar, potassium titanate whisker and vermiculite were used to prepare the multi-reinforced non-asbestos organic (NAO) automotive friction materials. The multi-reinforced materials have the various characters of micro and nano sized structures, one and two dimensions, inorganic and organic natures. The mechanical and friction properties of the automotive friction material were investigated to optimize the experimental condition. The reinforcing mechanism was discussed based on the environment scanning electron microscopy observation. The research results show that the multi-reinforced NAO automotive friction material under the optimized condition possesses higher impact strength (0.54J/cm2), better wear resistance (total wear： 1.35×10-7cm3/(N·m)) and friction stability (coefficient of variation： 5.86%), resulting from the mix and synergistic effect of various reinforced materials.
The glass fiber, copper fiber, mineral fiber, Kevlar, potassium titanate whisker and vermiculite were used to prepare the multi-reinforced non-asbestos organic (NAO) automotive friction materials. The multi-reinforced materials have the various characters of micro and nano sized structures, one and two dimensions, inorganic and organic natures. The mechanical and friction properties of the automotive friction material were investigated to optimize the experimental condition. The reinforcing mechanism was discussed based on the environment scanning electron microscopy observation. The research results show that the multi-reinforced NAO automotive friction material under the optimized condition possesses higher impact strength (0.54J/cm2), better wear resistance (total wear： 1.35×10-7cm3/(N·m)) and friction stability (coefficient of variation： 5.86%), resulting from the mix and synergistic effect of various reinforced materials.
2010, 27(5): 86-92.
Abstract:
Based on the unit cell analytic model, a method to predict the strength of unidirectional composites is developed from the micro component of composites. The micromacro correlation matrix is presented according to the continuum mechanics and homogenization method. The elastic and damage properties of the component phases are passed to unidirectional composites by the micromacro correlation matrix. Considering the micro damage of component phases, failure arises in the fiber and matrix, when the strength criteria are satisfied. Once the component phases have failed, the stiffness is degraded by the failure factor. On this basis, the simulation of unidirectional composites in the longitudinal and transverse tensilon is achieved to predict the tensile strength of unidirectional composites by combining with finite element analysis. Numerical results show that the predicted modulus and strength of the method in this paper are well fit with experimental results and the strength prediction method for composites is of validity and efficiency.
Based on the unit cell analytic model, a method to predict the strength of unidirectional composites is developed from the micro component of composites. The micromacro correlation matrix is presented according to the continuum mechanics and homogenization method. The elastic and damage properties of the component phases are passed to unidirectional composites by the micromacro correlation matrix. Considering the micro damage of component phases, failure arises in the fiber and matrix, when the strength criteria are satisfied. Once the component phases have failed, the stiffness is degraded by the failure factor. On this basis, the simulation of unidirectional composites in the longitudinal and transverse tensilon is achieved to predict the tensile strength of unidirectional composites by combining with finite element analysis. Numerical results show that the predicted modulus and strength of the method in this paper are well fit with experimental results and the strength prediction method for composites is of validity and efficiency.
2010, 27(5): 93-100.
Abstract:
A finite element model of C/C-SiC microstructure characterizing different scale parameters was established for the woven C/C-SiC composites. The strain energy method was used to study the effects of relevant parameters of the microstructure on the macroscopic performances of C/C-SiC composites. The numerical computing results were compared for many cases of C/C-SiC composites with different scale parameters. It is shown that the elastic properties of C/C-SiC composites are associated with the scale parameters identified in the C/C-SiC composites. The effective moduli agree reasonably with the experimental ones.
A finite element model of C/C-SiC microstructure characterizing different scale parameters was established for the woven C/C-SiC composites. The strain energy method was used to study the effects of relevant parameters of the microstructure on the macroscopic performances of C/C-SiC composites. The numerical computing results were compared for many cases of C/C-SiC composites with different scale parameters. It is shown that the elastic properties of C/C-SiC composites are associated with the scale parameters identified in the C/C-SiC composites. The effective moduli agree reasonably with the experimental ones.
2010, 27(5): 101-107.
Abstract:
A stiffness prediction model was established for stitched foam-core sandwich composites based on the microstructure, and the equivalent stiffness was also achieved by experiments. Considering different sizes of representative volume element (RVE) and resin enriched zone caused by different stitching angles, a modified fiber waviness model was developed to evaluate the stiffness of stitching laminated face-panels, and the effect of thickness variation of the face panels after stitching was also included. The stitched foam core, stiffened by the resin cylinder, was simplified as a unidirectional composite, and its stiffness was estimated by a mixed series parallel model. Stiffness experiments of stitched foam-core sandwich composite panels were performed. The predicted equivalent moduli of the stitched face panel and the stitched foam-core sandwich panels show good agreement with the experimental data. The effects of stitching parameters and structural parameters on the stiffness were discussed.
A stiffness prediction model was established for stitched foam-core sandwich composites based on the microstructure, and the equivalent stiffness was also achieved by experiments. Considering different sizes of representative volume element (RVE) and resin enriched zone caused by different stitching angles, a modified fiber waviness model was developed to evaluate the stiffness of stitching laminated face-panels, and the effect of thickness variation of the face panels after stitching was also included. The stitched foam core, stiffened by the resin cylinder, was simplified as a unidirectional composite, and its stiffness was estimated by a mixed series parallel model. Stiffness experiments of stitched foam-core sandwich composite panels were performed. The predicted equivalent moduli of the stitched face panel and the stitched foam-core sandwich panels show good agreement with the experimental data. The effects of stitching parameters and structural parameters on the stiffness were discussed.
2010, 27(5): 108-115.
Abstract:
基于经典层板理论和细观力学桥联模型, 提出了缝纫泡沫夹芯复合材料失效强度的理论预测方法, 并进行了失效强度的相关试验验证。其中, 将缝纫复合材料面板看作单层组成的准层状结构, 采用经典层板理论进行逐层失效分析, 并同时考虑了局部皱曲的面板失效模式; 而对缝纫泡沫夹芯, 引入桥联模型计算其各组分材料中的应力, 并通过对各组分材料选取适当失效准则来建立失效判据; 对于缝纫泡沫夹芯复合材料采取逐级加载方式, 当面板或者夹芯失效时, 则认为其发生整体失效, 由此可以确定其在不同载荷形式下的失效强度。此外, 通过试验得到了缝纫泡沫夹芯复合材料板试件在平压、 侧压、 横向剪切及三点弯曲载荷形式下的失效模式及其失效强度, 并利用本文方法对缝纫泡沫夹芯复合材料的失效强度进行了理论预测, 所得结果与试验吻合, 证明了本文方法的有效性。
基于经典层板理论和细观力学桥联模型, 提出了缝纫泡沫夹芯复合材料失效强度的理论预测方法, 并进行了失效强度的相关试验验证。其中, 将缝纫复合材料面板看作单层组成的准层状结构, 采用经典层板理论进行逐层失效分析, 并同时考虑了局部皱曲的面板失效模式; 而对缝纫泡沫夹芯, 引入桥联模型计算其各组分材料中的应力, 并通过对各组分材料选取适当失效准则来建立失效判据; 对于缝纫泡沫夹芯复合材料采取逐级加载方式, 当面板或者夹芯失效时, 则认为其发生整体失效, 由此可以确定其在不同载荷形式下的失效强度。此外, 通过试验得到了缝纫泡沫夹芯复合材料板试件在平压、 侧压、 横向剪切及三点弯曲载荷形式下的失效模式及其失效强度, 并利用本文方法对缝纫泡沫夹芯复合材料的失效强度进行了理论预测, 所得结果与试验吻合, 证明了本文方法的有效性。
2010, 27(5): 116-121.
Abstract:
This research aims to establish a method to predict the dome thickness of composite pressure vessels. According to the dome shape of cured composite pressure vessels, a cubic spline function was presented to predict the dome thickness based on the volume of all fiber tows being constant. Using this method, the dome thickness of an arbitrary composite pressure vessel with different geometrical parameters and process parameters was forecasted. The predictive results were compared with the traditional methods and actual measured thickness. The results show that dome thickness obtained from the cubic spline function could reflect actual measured thickness better than the other methods and it could provide more accurate thickness parameters for the finite element modeling.
This research aims to establish a method to predict the dome thickness of composite pressure vessels. According to the dome shape of cured composite pressure vessels, a cubic spline function was presented to predict the dome thickness based on the volume of all fiber tows being constant. Using this method, the dome thickness of an arbitrary composite pressure vessel with different geometrical parameters and process parameters was forecasted. The predictive results were compared with the traditional methods and actual measured thickness. The results show that dome thickness obtained from the cubic spline function could reflect actual measured thickness better than the other methods and it could provide more accurate thickness parameters for the finite element modeling.
2010, 27(5): 122-128.
Abstract:
A multi-scale coupled numerical model was developed to investigate the mechanical behaviors of 3D woven composite pipes. Micro-and meso-scale unit cells were built to represent the inhomogeneity of fiber tow and weave structure of a 3D woven composite pipe, respectively. The periodic boundary condition of the camber shape meso-scale unit cell was specified. The macro-scale stiffness of the 3D woven composite pipe was obtained by averaging the stiffness on unit cells from micro-scale to meso-scale. The stiffness prediction is in good agreement with experimental results. On the other hand, using the multi-scale unit cells, the converse stress analysis process under multi-axial loads was carried out, i.e. to transfer stresses from macro-scale to meso-scale and finally to micro-scale. A model of embedding the meso-unit cell into a homogenous ring was suggested for meso-scale stress analysis in case of applied loads without periodicity in the annular direction.
A multi-scale coupled numerical model was developed to investigate the mechanical behaviors of 3D woven composite pipes. Micro-and meso-scale unit cells were built to represent the inhomogeneity of fiber tow and weave structure of a 3D woven composite pipe, respectively. The periodic boundary condition of the camber shape meso-scale unit cell was specified. The macro-scale stiffness of the 3D woven composite pipe was obtained by averaging the stiffness on unit cells from micro-scale to meso-scale. The stiffness prediction is in good agreement with experimental results. On the other hand, using the multi-scale unit cells, the converse stress analysis process under multi-axial loads was carried out, i.e. to transfer stresses from macro-scale to meso-scale and finally to micro-scale. A model of embedding the meso-unit cell into a homogenous ring was suggested for meso-scale stress analysis in case of applied loads without periodicity in the annular direction.
2010, 27(5): 129-135.
Abstract:
A geometrical model for 2D 1×1 and 2×2 biaxial braided composites was proposed. The jamming condition and the cross-sectional variation of the yarns were considered. Based on the microstructure and volume-averaged method, an analytical model was established to predict the elastic properties of 2D biaxial braided composites. Numerical results show good agreement with the experiment data, which validated the effectiveness of the model. The influences of various parameters such as braid angle, fiber volume fraction and cross-sectional shape of yarns on the effective elastic constants were also studied. The results indicate that the braid angle has a complimentary effect on the elastic constant; the effective modulus is in proportion to fiber volume fraction; cross-sectional shapes of yarns have slight effects on the elastic constant.
A geometrical model for 2D 1×1 and 2×2 biaxial braided composites was proposed. The jamming condition and the cross-sectional variation of the yarns were considered. Based on the microstructure and volume-averaged method, an analytical model was established to predict the elastic properties of 2D biaxial braided composites. Numerical results show good agreement with the experiment data, which validated the effectiveness of the model. The influences of various parameters such as braid angle, fiber volume fraction and cross-sectional shape of yarns on the effective elastic constants were also studied. The results indicate that the braid angle has a complimentary effect on the elastic constant; the effective modulus is in proportion to fiber volume fraction; cross-sectional shapes of yarns have slight effects on the elastic constant.
2010, 27(5): 136-141.
Abstract:
In order to investigate the mechanism for Cu-FeS composite (the mass fraction for reinforced FeS phase is 15%) thermal conductivity and the internal structure, the thermal conductivity for composite and reinforced phase were calculated by the molecular dynamics simulation model of FeS particle in the copper matrix and model of interface thermal barrier resistance. The calculated results show that： the structure of FeS changes in 600K and 900K; the interface thermal barrier tends to a constant when the size of particle is over 100nm. The difference between test and simulation for thermal conductivity is caused by the ignoring of imperfection and destruction of interface during heating, matrix defection, and the different particle sizes. The HasselmanJohnson model is suitable for the thermal conductivity prediction.
In order to investigate the mechanism for Cu-FeS composite (the mass fraction for reinforced FeS phase is 15%) thermal conductivity and the internal structure, the thermal conductivity for composite and reinforced phase were calculated by the molecular dynamics simulation model of FeS particle in the copper matrix and model of interface thermal barrier resistance. The calculated results show that： the structure of FeS changes in 600K and 900K; the interface thermal barrier tends to a constant when the size of particle is over 100nm. The difference between test and simulation for thermal conductivity is caused by the ignoring of imperfection and destruction of interface during heating, matrix defection, and the different particle sizes. The HasselmanJohnson model is suitable for the thermal conductivity prediction.
2010, 27(5): 142-149.
Abstract:
The load transfer mechanisms at the post-buckling stage were studied for an integrated stiffened composite panel subjected to uniaxial compression. An FEM model was created for the panel by using the commercial software ABAQUS. The post-buckling process of the panel was simulated under uniaxial compression. The internal resultant forces and the load transfer mechanisms were discussed in detail at different stages (i.e., the local and global post-buckling). The distributions for resultant forces and moments at nodal and anti-nodal lines were obtained. The simulations agree well with experimental data. Finally it is indicated that the nodal and anti-nodal lines are possibly the first debonding locations of the flange/skin interface at the post-buckling stage and the forces crucial for failure are identified as Mxy和My.
The load transfer mechanisms at the post-buckling stage were studied for an integrated stiffened composite panel subjected to uniaxial compression. An FEM model was created for the panel by using the commercial software ABAQUS. The post-buckling process of the panel was simulated under uniaxial compression. The internal resultant forces and the load transfer mechanisms were discussed in detail at different stages (i.e., the local and global post-buckling). The distributions for resultant forces and moments at nodal and anti-nodal lines were obtained. The simulations agree well with experimental data. Finally it is indicated that the nodal and anti-nodal lines are possibly the first debonding locations of the flange/skin interface at the post-buckling stage and the forces crucial for failure are identified as Mxy和My.
2010, 27(5): 150-155.
Abstract:
The post-buckling induced failure process was simulated by using the cohesive element in the commercial software ABAQUS. The internal forces on the flange/skin interface were extracted from FEM results, and then their features were studied. The flange thickness was considered as a parameter to build a parameterized model for studying the effect of stiffness ratios of the flange to the skin on the interface debonding. The relationship among each component of the internal forces was also investigated. Failure criteria and failure envelops were developed for the flange/skin interface debonding. Finally the design parameters of the thickness ratio and the stiffness ratio between the flange and the skin were suggested for the design.
The post-buckling induced failure process was simulated by using the cohesive element in the commercial software ABAQUS. The internal forces on the flange/skin interface were extracted from FEM results, and then their features were studied. The flange thickness was considered as a parameter to build a parameterized model for studying the effect of stiffness ratios of the flange to the skin on the interface debonding. The relationship among each component of the internal forces was also investigated. Failure criteria and failure envelops were developed for the flange/skin interface debonding. Finally the design parameters of the thickness ratio and the stiffness ratio between the flange and the skin were suggested for the design.
2010, 27(5): 156-164.
Abstract:
A study was performed on the nonlinear bending behavior of unidirectional fiber-reinforced elastic memory composite (EMC) laminates above the glass transition temperature of its resin (Tg). A series of multi-constraint bending experiments about EMC laminates were firstly introduced. According to the experimental results, the shape function of microbuckled fibers was proposed. Different strain energies of EMC laminate under bending were then analyzed. Finally, the bending moment as functions of curvature and equivalent bending strain was deduced based on the principl of virtual work. The results show that the neutral strain surface of EMC laminates rapidly approaches the outer surface during the bending process. The neutral strain surface location and bending behaviour of EMC laminates are very sensitive to the in-plane shear modulus. At the initial stage, the traditional linear elastic plate theory can describe the deformation response. However, with further increase of the bending curvature, the nonlinear model presented in this study must be considered. The theoretical predictions are agreeable with experimental results of EMC laminates under four-point pure bending.
A study was performed on the nonlinear bending behavior of unidirectional fiber-reinforced elastic memory composite (EMC) laminates above the glass transition temperature of its resin (Tg). A series of multi-constraint bending experiments about EMC laminates were firstly introduced. According to the experimental results, the shape function of microbuckled fibers was proposed. Different strain energies of EMC laminate under bending were then analyzed. Finally, the bending moment as functions of curvature and equivalent bending strain was deduced based on the principl of virtual work. The results show that the neutral strain surface of EMC laminates rapidly approaches the outer surface during the bending process. The neutral strain surface location and bending behaviour of EMC laminates are very sensitive to the in-plane shear modulus. At the initial stage, the traditional linear elastic plate theory can describe the deformation response. However, with further increase of the bending curvature, the nonlinear model presented in this study must be considered. The theoretical predictions are agreeable with experimental results of EMC laminates under four-point pure bending.
