2009 Vol. 26, No. 4
2009, 26(4): 1-7.
Abstract:
The curing properties and chemorheological behaviors of unsaturated polyester resin syste(Palatal1777-G-4) for vacuum infusion molding process (VIMP) were studied with DSC analysis and visco experiments. A modified dual Arrhenius rheological model and an engineering viscosity model were stablished simulate the rheological behavior of the resin system. The two rheological models were compared. The compa results indicate that the modified dual Arrhenius model can provide more accurate prediction of the viscosity be the gel point，while the engineering model is more accurate after the gel point. Combining the two models accurately predict the rheological behaviors of the resin system in the vacuum infusion molding process.simulated viscosity is in good agreement with that from the experiments. The processing window of the resin system for VIMP can be well determined based on the proposed models. The results show that the optimum process temperature of the Palatal1777-G-4 resin system for VIMP is 20～38℃，at which the resin can keep the viscoless than 300 mPa·s for 30 min at least. The developed model is important for processing simulation of resiparameter optimization and quality control of VIMP for high performance composites.
The curing properties and chemorheological behaviors of unsaturated polyester resin syste(Palatal1777-G-4) for vacuum infusion molding process (VIMP) were studied with DSC analysis and visco experiments. A modified dual Arrhenius rheological model and an engineering viscosity model were stablished simulate the rheological behavior of the resin system. The two rheological models were compared. The compa results indicate that the modified dual Arrhenius model can provide more accurate prediction of the viscosity be the gel point，while the engineering model is more accurate after the gel point. Combining the two models accurately predict the rheological behaviors of the resin system in the vacuum infusion molding process.simulated viscosity is in good agreement with that from the experiments. The processing window of the resin system for VIMP can be well determined based on the proposed models. The results show that the optimum process temperature of the Palatal1777-G-4 resin system for VIMP is 20～38℃，at which the resin can keep the viscoless than 300 mPa·s for 30 min at least. The developed model is important for processing simulation of resiparameter optimization and quality control of VIMP for high performance composites.
2009, 26(4): 8-14.
Abstract:
The structure and dynamic mechanical properties of unpressed and pressed composites consisting of carboxylated nit rile rubber (XNBR) and hindered phenol compound 2，2'-methylenebis-(6-tertbutyl-4-methyl-phenol) (AO-2246) were investigated respectively. The results show that the dispersion state of AO-2246 in the XNBR matrix has an important influence on the dynamic mechanical properties of the composites. In unpressed AO-2246/XNBR composites，most AO-2246 molecules exist in the form of crystalline particles，which leads to alower tanδ value than that of the pure XNBR matrix. On the contrary，in the pressed composites，all AO-2246 molecules are hybridized with XNBR during the hot-pressing and quenching process，so the tanδ value is increased remarkably and the damping property is improved significantly. DSC measurement and SEM observation show that in the AO-2246/XNBR hybrids with a larger AO-2246 mass fraction than 40%，AO-2246 molecules can be divided into three kinds：hybrid，microseparated，and crystal，which affect the dynamic mechanical properties of the composites together. The peak value of the tanδ peak of AO-2246/XNBR (50 wt%) hybrid reaches 3.5，meanwhile，its peak position also shifts to room temperature，demonst rating that AO-2246/XNBR composite is a promising high-performance damping material.
The structure and dynamic mechanical properties of unpressed and pressed composites consisting of carboxylated nit rile rubber (XNBR) and hindered phenol compound 2，2'-methylenebis-(6-tertbutyl-4-methyl-phenol) (AO-2246) were investigated respectively. The results show that the dispersion state of AO-2246 in the XNBR matrix has an important influence on the dynamic mechanical properties of the composites. In unpressed AO-2246/XNBR composites，most AO-2246 molecules exist in the form of crystalline particles，which leads to alower tanδ value than that of the pure XNBR matrix. On the contrary，in the pressed composites，all AO-2246 molecules are hybridized with XNBR during the hot-pressing and quenching process，so the tanδ value is increased remarkably and the damping property is improved significantly. DSC measurement and SEM observation show that in the AO-2246/XNBR hybrids with a larger AO-2246 mass fraction than 40%，AO-2246 molecules can be divided into three kinds：hybrid，microseparated，and crystal，which affect the dynamic mechanical properties of the composites together. The peak value of the tanδ peak of AO-2246/XNBR (50 wt%) hybrid reaches 3.5，meanwhile，its peak position also shifts to room temperature，demonst rating that AO-2246/XNBR composite is a promising high-performance damping material.
2009, 26(4): 15-21.
Abstract:
In order to improve the performance of unsaturated polyester resin (UPR)，the polyhedral oligomeric silsesquioxane containing vinyl group (V-POSS) was used to modify the unsaturated polyester resins. The curing kinetics and the relationship of apparent activation energy (Ea) with conversionαwere studied by non-isothermal DSC. The properties of mechanics and electricity for the fiberglass-reinforced laminate were determined. The results show that the Ea decreases with increase of conversion α. The curing reaction could be described by autocatalyticŠesták-Berggren (S-B) model and kinetic equations of curing reaction were obtained. The tensile strength of the fiberglass-reinforced laminate increases 17.6 MPa when the mass fraction of V-POSS is up to 5%. The impact strength is lower with V-POSS increase. The electric properties increase with increasing the content of V-POSS，while volume resistivity and surface resistivity rise by 1～2 orders of magnitude.
In order to improve the performance of unsaturated polyester resin (UPR)，the polyhedral oligomeric silsesquioxane containing vinyl group (V-POSS) was used to modify the unsaturated polyester resins. The curing kinetics and the relationship of apparent activation energy (Ea) with conversionαwere studied by non-isothermal DSC. The properties of mechanics and electricity for the fiberglass-reinforced laminate were determined. The results show that the Ea decreases with increase of conversion α. The curing reaction could be described by autocatalyticŠesták-Berggren (S-B) model and kinetic equations of curing reaction were obtained. The tensile strength of the fiberglass-reinforced laminate increases 17.6 MPa when the mass fraction of V-POSS is up to 5%. The impact strength is lower with V-POSS increase. The electric properties increase with increasing the content of V-POSS，while volume resistivity and surface resistivity rise by 1～2 orders of magnitude.
2009, 26(4): 22-28.
Abstract:
The hygrothermal stresses in the composite with fiber volume fraction of 30% were investigated by using micro Raman spectroscopy. The results show that the Raman wavenumber shift for carbon fibers can be caused by the hygrothermal stresses，which can be used to characterize the hygrothermal stress in the fibers. The appropriate selections of the tested points are the key to success in the hygrothermal stress test with Raman spect roscopy for the composites. The results also show that during the long-term moisture absorption process，the axial residual stresses within the fibers transform from thermal residual compressive stresses before absorption into hygrothermal tensile stresses after absorption. The axial stresses within the fibers induced purely by the absorption can be obtained by using the tensile stresses after absorption minus the compressive stresses before absorption，which is rather high (2272 MPa on average) and close to the tensile strength of 2800 MPa of the carbon fibers used in this paper. The suitable thermal residual stresses can reduce the moisture induced stresses to some extent.
The hygrothermal stresses in the composite with fiber volume fraction of 30% were investigated by using micro Raman spectroscopy. The results show that the Raman wavenumber shift for carbon fibers can be caused by the hygrothermal stresses，which can be used to characterize the hygrothermal stress in the fibers. The appropriate selections of the tested points are the key to success in the hygrothermal stress test with Raman spect roscopy for the composites. The results also show that during the long-term moisture absorption process，the axial residual stresses within the fibers transform from thermal residual compressive stresses before absorption into hygrothermal tensile stresses after absorption. The axial stresses within the fibers induced purely by the absorption can be obtained by using the tensile stresses after absorption minus the compressive stresses before absorption，which is rather high (2272 MPa on average) and close to the tensile strength of 2800 MPa of the carbon fibers used in this paper. The suitable thermal residual stresses can reduce the moisture induced stresses to some extent.
2009, 26(4): 29-35.
Abstract:
By using glass fiber 120 twill fabric/epoxy 5224 as the panel and Nomex honeycomb as the core，the ability of resisting the lateral distortion of honeycomb cores was investigated. For cocuring process with the vacuum bag，a gas pressure measuring method was established and was used to study the influence factors of core internal pressure and the relationship between core internal pressure and core crush. It is found that the ability of the honeycomb core to avoid core crush is limited，especially for large core grid length and core thickness. Core internal pressure has close relation with the expansion of core gas and permeability of prepreg stack，so core internal pressure is affected significantly by the temperature cycle，the number of prepreg plies and adhesive film. Moreover，the core internal pressure plays an important role in avoiding core crush. Larger internal core pressure before prepreg gelation is helpful to preventing core crush.
By using glass fiber 120 twill fabric/epoxy 5224 as the panel and Nomex honeycomb as the core，the ability of resisting the lateral distortion of honeycomb cores was investigated. For cocuring process with the vacuum bag，a gas pressure measuring method was established and was used to study the influence factors of core internal pressure and the relationship between core internal pressure and core crush. It is found that the ability of the honeycomb core to avoid core crush is limited，especially for large core grid length and core thickness. Core internal pressure has close relation with the expansion of core gas and permeability of prepreg stack，so core internal pressure is affected significantly by the temperature cycle，the number of prepreg plies and adhesive film. Moreover，the core internal pressure plays an important role in avoiding core crush. Larger internal core pressure before prepreg gelation is helpful to preventing core crush.
2009, 26(4): 36-40.
Abstract:
Microcapsules with gelatin as wall material and silicone resin as core material were prepared by means of separation in water phase. Microcapsules-silicone coatings of atomic oxygen (AO) resistant was prepared by Czochralski method on the surface of Kapton. The erosion behaviors of Kapton without and with microcapsules-silicone coatings were studied during exposure in AO environment in ground-based simulation facilities. The result sindicate that the Kapton undergoes dramatical degradation with an obvious mass loss and change of surface morphologies. The optical properties of Kapton also significantly degenerate with a solar absorption rate changing of 0.272 before and after AO exposure. The microcapsules-silicone coatings posses a good performance on the AO resistant with less mass loss and erosion rate and theΔα is only 0.071. Specially，the mass loss of the coating，whose mass ratio of microcapsules to silicone is 1∶5，decreases to 2.3% of the uncoated Kapton.
Microcapsules with gelatin as wall material and silicone resin as core material were prepared by means of separation in water phase. Microcapsules-silicone coatings of atomic oxygen (AO) resistant was prepared by Czochralski method on the surface of Kapton. The erosion behaviors of Kapton without and with microcapsules-silicone coatings were studied during exposure in AO environment in ground-based simulation facilities. The result sindicate that the Kapton undergoes dramatical degradation with an obvious mass loss and change of surface morphologies. The optical properties of Kapton also significantly degenerate with a solar absorption rate changing of 0.272 before and after AO exposure. The microcapsules-silicone coatings posses a good performance on the AO resistant with less mass loss and erosion rate and theΔα is only 0.071. Specially，the mass loss of the coating，whose mass ratio of microcapsules to silicone is 1∶5，decreases to 2.3% of the uncoated Kapton.
2009, 26(4): 41-46.
Abstract:
As a kind of fibrillar conductive filler，multi-wall carbon nanotubes (CNTs) are int roduced into carbon black (CB)/polypropylene (PP) composites，so as to combine their different conductive mechanisms. The experimental results reveal that CNTs can form bridges between CB particles and result in a remarkable decrease of volume resistivity of CB/PP composites. CB∶CNTs=19∶1 is the optimum proportion for CB-CNTs/PP composites.The conductive percolation threshold of CB-CNTs (19∶1)/PP composite is much lower than that of CB/PP composite. When the total volume fraction of the conductive filler is 4.76%，due to the addition of CNTs，the volume resistivity of the composites can decrease from 109Ω·cm to 105Ω·cm，the positive temperature coefficient(PTC) intensity of CB/PP composites also decreases from 6.10 to 1.48，and the peak temperature of PTC transition increases from 166℃ to 174℃. The crystallizing point of PP rises by 12℃ even if at a very low CNTs content due to CNTs‘ higher nucleation than CB. The mechanical properties of the composites remarkably decrease with an increase of CB or CB-CNTs filler volume fraction. To reach the same volume resistivity，the conductive filler volume fraction of CB-CNTs/PP composite is much lower than that of CB/PP composite，so the higher mechanical properties of CB-CNTs/PP composite can be maintained by the addition of CNTs.
As a kind of fibrillar conductive filler，multi-wall carbon nanotubes (CNTs) are int roduced into carbon black (CB)/polypropylene (PP) composites，so as to combine their different conductive mechanisms. The experimental results reveal that CNTs can form bridges between CB particles and result in a remarkable decrease of volume resistivity of CB/PP composites. CB∶CNTs=19∶1 is the optimum proportion for CB-CNTs/PP composites.The conductive percolation threshold of CB-CNTs (19∶1)/PP composite is much lower than that of CB/PP composite. When the total volume fraction of the conductive filler is 4.76%，due to the addition of CNTs，the volume resistivity of the composites can decrease from 109Ω·cm to 105Ω·cm，the positive temperature coefficient(PTC) intensity of CB/PP composites also decreases from 6.10 to 1.48，and the peak temperature of PTC transition increases from 166℃ to 174℃. The crystallizing point of PP rises by 12℃ even if at a very low CNTs content due to CNTs‘ higher nucleation than CB. The mechanical properties of the composites remarkably decrease with an increase of CB or CB-CNTs filler volume fraction. To reach the same volume resistivity，the conductive filler volume fraction of CB-CNTs/PP composite is much lower than that of CB/PP composite，so the higher mechanical properties of CB-CNTs/PP composite can be maintained by the addition of CNTs.
2009, 26(4): 47-52.
Abstract:
A new kind of porous composite used as bone and cartilage tissue engineering scaffolds was prepared with chitosan，gelatin and 3-aminopropyltriethoxysilane modified bioglass (SBG) by the freeze-drying technique in order to improve the compatibility of BG and polymer. The porosity，bending strength and microstructure of the composite scaffolds were characterized. The effects of the concent ration of SBG and CS-Gel，the cross linking agent and the super-cooling temperature on the microstructure of the composite scaffolds were investigated，respectively. The results show that the composite scaffolds with 3D interconnective porous structure，high porosity (90%) and high mechanical strength could be prepared under 70 g·L-1 of SBG concentration and 40 g· L-1 of CS-Gel concentration，then crosslinked with EDC and NHS，frozen at -50℃ for 2h and -15℃ for 15h，and finally lyophilized.
A new kind of porous composite used as bone and cartilage tissue engineering scaffolds was prepared with chitosan，gelatin and 3-aminopropyltriethoxysilane modified bioglass (SBG) by the freeze-drying technique in order to improve the compatibility of BG and polymer. The porosity，bending strength and microstructure of the composite scaffolds were characterized. The effects of the concent ration of SBG and CS-Gel，the cross linking agent and the super-cooling temperature on the microstructure of the composite scaffolds were investigated，respectively. The results show that the composite scaffolds with 3D interconnective porous structure，high porosity (90%) and high mechanical strength could be prepared under 70 g·L-1 of SBG concentration and 40 g· L-1 of CS-Gel concentration，then crosslinked with EDC and NHS，frozen at -50℃ for 2h and -15℃ for 15h，and finally lyophilized.
2009, 26(4): 53-58.
Abstract:
In order to solve the distribution of hydroxyapatite (HA) in the chitosan (CS) matrix，a novel route of in-situ hydrothermal precipitation was developed to fabricate the nano-HA/CS composites，based on the combination of the advantages of in-situ precipitation and hydrothermal synthesis. The effect of pH value on the structure of the HA/CS composites was studied. All the results show that the as-prepared composites are composed of CS crystals and nano-HA with lower crystallinity，and the growth of CS crystals and HA crystallites is towards the preferred orientation along the c-axis in the crystal structure. Moreover，there is an increase of the crystallinity of CS and HA with the increase of pH value in the composites. It was noticed that the crystallite size of HA and the degree of the ordered arrangement of CS molecules are increased with raising the pH value in the composites. The pH value of 12 is favorable to the formation of the α-CS crystals with higher crystallinity and nano-HA crystallites in these composites. When the composites were prepared at the pH value of 12，there is a more ordered arrangement in the α-CS crystals and the good interaction behavior is found between CS molecules and HA crystallites in the composites.
In order to solve the distribution of hydroxyapatite (HA) in the chitosan (CS) matrix，a novel route of in-situ hydrothermal precipitation was developed to fabricate the nano-HA/CS composites，based on the combination of the advantages of in-situ precipitation and hydrothermal synthesis. The effect of pH value on the structure of the HA/CS composites was studied. All the results show that the as-prepared composites are composed of CS crystals and nano-HA with lower crystallinity，and the growth of CS crystals and HA crystallites is towards the preferred orientation along the c-axis in the crystal structure. Moreover，there is an increase of the crystallinity of CS and HA with the increase of pH value in the composites. It was noticed that the crystallite size of HA and the degree of the ordered arrangement of CS molecules are increased with raising the pH value in the composites. The pH value of 12 is favorable to the formation of the α-CS crystals with higher crystallinity and nano-HA crystallites in these composites. When the composites were prepared at the pH value of 12，there is a more ordered arrangement in the α-CS crystals and the good interaction behavior is found between CS molecules and HA crystallites in the composites.
2009, 26(4): 59-62.
Abstract:
To investigate the cellular compatibility of β-calcium metaphosphate (β-CMP)/poly-L-lactide (PLLA) fracture innerfixation composites prepared by a two-step method，and to provide a biological evidence for the application of the composites，the osteoblasts proliferation and adhesion on β-CMP/PLLA composite were analyzedby methyl thiazolyl tetrazolium (MTT) and SEM，respectively. The cytology experiments show that β-CMP/PLLAcomposite can promote cells growth and osteoblasts adhered and spread well on the materials. The new fracture innerfixation material，β-CMP/PLLA composite，has good cytocompatibility in vitro.
To investigate the cellular compatibility of β-calcium metaphosphate (β-CMP)/poly-L-lactide (PLLA) fracture innerfixation composites prepared by a two-step method，and to provide a biological evidence for the application of the composites，the osteoblasts proliferation and adhesion on β-CMP/PLLA composite were analyzedby methyl thiazolyl tetrazolium (MTT) and SEM，respectively. The cytology experiments show that β-CMP/PLLAcomposite can promote cells growth and osteoblasts adhered and spread well on the materials. The new fracture innerfixation material，β-CMP/PLLA composite，has good cytocompatibility in vitro.
2009, 26(4): 63-67.
Abstract:
Lead zirconate titanate particles with different particle size contributions were obtained by mixing with different size PZT powders，which were employed to prepare PZT/PVDF composites by filling PZT particles in PVDF matrix. The dielectric and piezoelectric properties of composites were determined. The results show that the piezoelectric coefficient of composites with bimodal distribution can reach 75 pC·N-1 as the PZT volume fraction is up to 70%. It can be explained that the piezoelectric composites with bimodal distribution exhibit a better continuous distribution because of the micro-particles filling up among larger particles. This provides more paths for mechanical-electric coupling. All these make the PZT/PVDF composite show a satisfying piezoelectric property.
Lead zirconate titanate particles with different particle size contributions were obtained by mixing with different size PZT powders，which were employed to prepare PZT/PVDF composites by filling PZT particles in PVDF matrix. The dielectric and piezoelectric properties of composites were determined. The results show that the piezoelectric coefficient of composites with bimodal distribution can reach 75 pC·N-1 as the PZT volume fraction is up to 70%. It can be explained that the piezoelectric composites with bimodal distribution exhibit a better continuous distribution because of the micro-particles filling up among larger particles. This provides more paths for mechanical-electric coupling. All these make the PZT/PVDF composite show a satisfying piezoelectric property.
2009, 26(4): 68-73.
Abstract:
The polycarboxylate-nano Fe3O4 magnetic particles (PC-NMPs) were synthesized via suspension polymerization. The PC-NMPs were characterized by IR，EA，AAS，TGA，XRD，TEM and VSM. Their application to the adsorption of parabens from water was investigated. The results show that these PC-NMPs have an average size of 100～150 nm，with saturation magnetization intensity of 10.66 emu/g，and residual gnetization intensity of 0.61 emu/g and coercive force of 14.96 Oe，respectively. The adsorption capacities were vestigated by adsorbing 4 kinds of commonly used parabens from aqueous solution，which demonst rates an excellent adsorption capacity of 556 mg/g for methylparaben (MPB)，ethylparaben (EPB)，propyl paraben (PPB) and 588 mg/g for butyl paraben (BPB)，respectively. The isothermal adsorption curves mainly obey the Langmuir mode. The PC-NMPs can be used as the potential sorbents for the removal of parabens，the important kinds of environmental hormones from wastewater. Primary mechanism studies reveal that the adsorption process can be carried out quickly and efficiently，which may be due to the hydrogen bonds and π-π interactions between parabens and the PC-NMPs.
The polycarboxylate-nano Fe3O4 magnetic particles (PC-NMPs) were synthesized via suspension polymerization. The PC-NMPs were characterized by IR，EA，AAS，TGA，XRD，TEM and VSM. Their application to the adsorption of parabens from water was investigated. The results show that these PC-NMPs have an average size of 100～150 nm，with saturation magnetization intensity of 10.66 emu/g，and residual gnetization intensity of 0.61 emu/g and coercive force of 14.96 Oe，respectively. The adsorption capacities were vestigated by adsorbing 4 kinds of commonly used parabens from aqueous solution，which demonst rates an excellent adsorption capacity of 556 mg/g for methylparaben (MPB)，ethylparaben (EPB)，propyl paraben (PPB) and 588 mg/g for butyl paraben (BPB)，respectively. The isothermal adsorption curves mainly obey the Langmuir mode. The PC-NMPs can be used as the potential sorbents for the removal of parabens，the important kinds of environmental hormones from wastewater. Primary mechanism studies reveal that the adsorption process can be carried out quickly and efficiently，which may be due to the hydrogen bonds and π-π interactions between parabens and the PC-NMPs.
2009, 26(4): 74-78.
Abstract:
Copper powder (Cu) pigment was modified with silane coupling agent (KH550) as modifying agent.The effect and mechanism of Cu pigment modified with different coupling agent concent rations on mechanical property，infrared emissivity and corrosion resistance property of 50% Cu/polyurethane (PU) composite coatings were investigated in detail. The results indicate that the Cu pigment is modified by silane coupling agent successfully. Compared to that of Cu pigment without modification，low inf rared emissivity 50% Cu/PU composite coatings treated with a suitable coupling agent concent ration still keep the low value of 0.1 in 8～14μm. However，the adhesion of the coatings is improved from grade 2 to grade 1；the hardness is increased f rom 4H to 6H. The anti-alkaline，anti-acid and anti-salt times are improved from 1h to 90h，50h to 60h，10h to 50h before the emissivity of the coatings is increased，respectively. The modification of Cu improves the interfacial compliance between Cu and PU，and results in higher compactness of the coating.
Copper powder (Cu) pigment was modified with silane coupling agent (KH550) as modifying agent.The effect and mechanism of Cu pigment modified with different coupling agent concent rations on mechanical property，infrared emissivity and corrosion resistance property of 50% Cu/polyurethane (PU) composite coatings were investigated in detail. The results indicate that the Cu pigment is modified by silane coupling agent successfully. Compared to that of Cu pigment without modification，low inf rared emissivity 50% Cu/PU composite coatings treated with a suitable coupling agent concent ration still keep the low value of 0.1 in 8～14μm. However，the adhesion of the coatings is improved from grade 2 to grade 1；the hardness is increased f rom 4H to 6H. The anti-alkaline，anti-acid and anti-salt times are improved from 1h to 90h，50h to 60h，10h to 50h before the emissivity of the coatings is increased，respectively. The modification of Cu improves the interfacial compliance between Cu and PU，and results in higher compactness of the coating.
2009, 26(4): 79-82.
Abstract:
To understand deeply the active characters of groups in the binder of Hydroxyl terminated polybutadiene (HTPB) propellants，in which the groups react easily with other materials in the store period，and to find a method to decrease the aging of propellants and extend the store life of rocket motor，the chemical reactiveness of the functional groups in tolylene diisocyanate (TDI)/HTPB binder was studied by means of quantum chemical calculations and IR spectrum analysis. The effect of the active group aging on the mechanical property of HTPB propellant was also investigated. The quantum chemical calculations show that the active groups in the dhesive matrix are C=C bonds and urethane groups. IR spectrum analysis confirms that the aging the binder mainly concerns the oxidation of C=C bonds，which contributes to the destruction of the adhesive matrix and then results in decreasing the mechanical properties of HTPB propellant during the storing.
To understand deeply the active characters of groups in the binder of Hydroxyl terminated polybutadiene (HTPB) propellants，in which the groups react easily with other materials in the store period，and to find a method to decrease the aging of propellants and extend the store life of rocket motor，the chemical reactiveness of the functional groups in tolylene diisocyanate (TDI)/HTPB binder was studied by means of quantum chemical calculations and IR spectrum analysis. The effect of the active group aging on the mechanical property of HTPB propellant was also investigated. The quantum chemical calculations show that the active groups in the dhesive matrix are C=C bonds and urethane groups. IR spectrum analysis confirms that the aging the binder mainly concerns the oxidation of C=C bonds，which contributes to the destruction of the adhesive matrix and then results in decreasing the mechanical properties of HTPB propellant during the storing.
2009, 26(4): 83-88.
Abstract:
he experimental study was performed on tensile strength of high volume fraction SiCP/Al composites. The results show that the loading and unloading processes have little effect on the tensile strength of high volume fraction SiCP/Al composites. An FEM model was established to simulate the tensile properties of SiCP/Al composites. The simulated results show that low volume fraction SiCP/Al composites mainly represent plastic mechanical properties. On the contrary，high volume fraction SiCP/Al composites mainly represent the brittle mechanical properties. The errors of the tensile strength got from the model are little compared with the testing results. Breakage of matrix is the main factor of high volume fraction SiCP/Al composites tensile failure.
he experimental study was performed on tensile strength of high volume fraction SiCP/Al composites. The results show that the loading and unloading processes have little effect on the tensile strength of high volume fraction SiCP/Al composites. An FEM model was established to simulate the tensile properties of SiCP/Al composites. The simulated results show that low volume fraction SiCP/Al composites mainly represent plastic mechanical properties. On the contrary，high volume fraction SiCP/Al composites mainly represent the brittle mechanical properties. The errors of the tensile strength got from the model are little compared with the testing results. Breakage of matrix is the main factor of high volume fraction SiCP/Al composites tensile failure.
2009, 26(4): 89-94.
Abstract:
The effect of the addition of reinforcing particles on the casting properties of metal matrix composites was studied by numerical simulation. A database of ProCAST was developed based on the function equation between the volume fraction of reinforcing particles and physical property parameters. Gravity die casting of motorcycle wheels was taken as an example to study the casting property of the 5% Al2O3 particle reinforced aluminum matrix composites. The calculated results indicate that the fluidity of the aluminum matrix composites tends to decrease because of the addition of the particles. Melt viscosity of the composite is higher than A356.2. Shrinkage porosity defect appears both in the spoke and rim of the wheel. The mass fraction of silicon is enhanced by 7.5% in the allowed range. The temperature interval from pouring temperature to liquidus temperature can be increased and the crystallization temperature interval can be reduced synchronously. The latent heat of fusion is increased，so as to shorten the solid-liquid coexistence time，enhancing the fluidity of melt and feeding capacity. The shrinkage porosity defect in the spoke and rim of the wheel is decreased and eliminated.
The effect of the addition of reinforcing particles on the casting properties of metal matrix composites was studied by numerical simulation. A database of ProCAST was developed based on the function equation between the volume fraction of reinforcing particles and physical property parameters. Gravity die casting of motorcycle wheels was taken as an example to study the casting property of the 5% Al2O3 particle reinforced aluminum matrix composites. The calculated results indicate that the fluidity of the aluminum matrix composites tends to decrease because of the addition of the particles. Melt viscosity of the composite is higher than A356.2. Shrinkage porosity defect appears both in the spoke and rim of the wheel. The mass fraction of silicon is enhanced by 7.5% in the allowed range. The temperature interval from pouring temperature to liquidus temperature can be increased and the crystallization temperature interval can be reduced synchronously. The latent heat of fusion is increased，so as to shorten the solid-liquid coexistence time，enhancing the fluidity of melt and feeding capacity. The shrinkage porosity defect in the spoke and rim of the wheel is decreased and eliminated.
2009, 26(4): 95-101.
Abstract:
SiC/ZrB2 composites reinforced by SiC nanowhiskers (SiCW ) and SiC particles (SiCP) were prepared by a hot-pressing process at 1950℃ under 20 MPa in a flow argon atmosphere. The effects of SiCW and SiCP on microstructures，mechanical properties of SiC/ZrB2 composites were investigated. The results showed that the fracture toughnesses of SiC/ZrB2 composites with 15 vol% of SiC Wand with 15 vol% of SiCP were 8.08 MPa· m1/2 and 8.515 MPa·m1/2，respectively. The fracture toughness of the SiC/ZrB-composites with both 15 vol% of SiCW and 15 vol% of SiCP reached 9.03 MPa·m1/2. SiCW and SiCP effectively improved the densification of SiC/ZrB2 composites,and limited the coarsening of ZrB2 grains，which was in favor of improving the bending strength and fracture toughness of the SiC/ZrB2 composites. Furthermore，the synergistic effect of SiCW and SiCP favored the increase of the toughness.
SiC/ZrB2 composites reinforced by SiC nanowhiskers (SiCW ) and SiC particles (SiCP) were prepared by a hot-pressing process at 1950℃ under 20 MPa in a flow argon atmosphere. The effects of SiCW and SiCP on microstructures，mechanical properties of SiC/ZrB2 composites were investigated. The results showed that the fracture toughnesses of SiC/ZrB2 composites with 15 vol% of SiC Wand with 15 vol% of SiCP were 8.08 MPa· m1/2 and 8.515 MPa·m1/2，respectively. The fracture toughness of the SiC/ZrB-composites with both 15 vol% of SiCW and 15 vol% of SiCP reached 9.03 MPa·m1/2. SiCW and SiCP effectively improved the densification of SiC/ZrB2 composites,and limited the coarsening of ZrB2 grains，which was in favor of improving the bending strength and fracture toughness of the SiC/ZrB2 composites. Furthermore，the synergistic effect of SiCW and SiCP favored the increase of the toughness.
2009, 26(4): 102-106.
Abstract:
B4C based composites toughened by TiB2 were fabricated by in situ reaction sintering with the original microcrystalline powders B4C，TiO2 and glucose. The influences of sintering temperature and additive on the sintering behavior and mechanical properties were investigated. TiB2/B4C composites with relative density of 97.7% were obtained by in situ reaction hot-pressing at 1950℃. The composites exhibit improved fracture toughness of 5.3 MPa·m1/2. (TiB2，Al2O3)/B4C and (TiB2，SiC)/B4C composites with almost full densification were fabricated by using additives of Al2O3 and Si powders and sintering at 1950℃ and 1900℃; the fracture toughness of composites reaches 7.09 and 6.35 MPa·m1/2 respectively. The analysis of microstructure shows that the main toughening mechanism is the crack deflection due to the existence of residual stress.
B4C based composites toughened by TiB2 were fabricated by in situ reaction sintering with the original microcrystalline powders B4C，TiO2 and glucose. The influences of sintering temperature and additive on the sintering behavior and mechanical properties were investigated. TiB2/B4C composites with relative density of 97.7% were obtained by in situ reaction hot-pressing at 1950℃. The composites exhibit improved fracture toughness of 5.3 MPa·m1/2. (TiB2，Al2O3)/B4C and (TiB2，SiC)/B4C composites with almost full densification were fabricated by using additives of Al2O3 and Si powders and sintering at 1950℃ and 1900℃; the fracture toughness of composites reaches 7.09 and 6.35 MPa·m1/2 respectively. The analysis of microstructure shows that the main toughening mechanism is the crack deflection due to the existence of residual stress.
2009, 26(4): 107-110.
Abstract:
In order to investigate the effects of the plate graphite content and its preferred orientation on the structure and property of graphite/ceramic composites，graphite/ceramic conductive composites were prepared from the ceramic matrix (albite，diopside，quartz) and graphite by wet-mixing，drying，granulating，and rapid sintering processes. The electric resistance along directions perpendicular and parallel to the molding pressure was accurately measured. The grain phases and the fracture surface micrograph were analyzed with XRD and SEM. The results show that the ceramic matrix reacts hardly with the graphite in the sintering process and no new phase is found. The plate graphite of the graphite/ceramic conductive composites is oriented，and the c-axis of graphite inclines to be parallel to the direction of the molding pressure. The resistivity of graphite/ceramic conductive composites is anisotropic. With the increase of the graphite content，the resistivity of composites rapidly decreases. However，it decreases very slowly when the graphite content exceeds 15 wt%.
In order to investigate the effects of the plate graphite content and its preferred orientation on the structure and property of graphite/ceramic composites，graphite/ceramic conductive composites were prepared from the ceramic matrix (albite，diopside，quartz) and graphite by wet-mixing，drying，granulating，and rapid sintering processes. The electric resistance along directions perpendicular and parallel to the molding pressure was accurately measured. The grain phases and the fracture surface micrograph were analyzed with XRD and SEM. The results show that the ceramic matrix reacts hardly with the graphite in the sintering process and no new phase is found. The plate graphite of the graphite/ceramic conductive composites is oriented，and the c-axis of graphite inclines to be parallel to the direction of the molding pressure. The resistivity of graphite/ceramic conductive composites is anisotropic. With the increase of the graphite content，the resistivity of composites rapidly decreases. However，it decreases very slowly when the graphite content exceeds 15 wt%.
2009, 26(4): 111-118.
Abstract:
The microstructures,surface morphology and composition of nanocrystalline Ni-Co alloy and nano SiC/Ni-Co composite coating prepared by pulse electrodeposition were studied by XRD，SEM and EDS. The corrosion characteristics of nanocrystalline Ni-Co alloy and nano SiC/Ni-Co composite coating were comparatively tested by the soak method and the electrochemical polarization method，respectively. The experimental results indicate that typical nanocrystalline Ni-Co alloy and nano SiC/Ni-Co composite coatings can be synthesized by pulse electrodeposition，and with the increasing of the nano SiC particles，the grain size of nano SiC/ Ni-Co composite coating is diminished while the microhardness is increased. The nano SiC/ Ni-Co composite coating has better dispersion and it exhibits better corrosion resistance in 3.5 wt% NaCl and 5 wt% HCl solution than the nanocrystalline Ni-Co alloy. The surface morphology of all samples after corrosion in 3.5 wt% NaCl solution shows good corrosion resistance,while the samples show spot corrosion in 5 wt% HCl solution.
The microstructures,surface morphology and composition of nanocrystalline Ni-Co alloy and nano SiC/Ni-Co composite coating prepared by pulse electrodeposition were studied by XRD，SEM and EDS. The corrosion characteristics of nanocrystalline Ni-Co alloy and nano SiC/Ni-Co composite coating were comparatively tested by the soak method and the electrochemical polarization method，respectively. The experimental results indicate that typical nanocrystalline Ni-Co alloy and nano SiC/Ni-Co composite coatings can be synthesized by pulse electrodeposition，and with the increasing of the nano SiC particles，the grain size of nano SiC/ Ni-Co composite coating is diminished while the microhardness is increased. The nano SiC/ Ni-Co composite coating has better dispersion and it exhibits better corrosion resistance in 3.5 wt% NaCl and 5 wt% HCl solution than the nanocrystalline Ni-Co alloy. The surface morphology of all samples after corrosion in 3.5 wt% NaCl solution shows good corrosion resistance,while the samples show spot corrosion in 5 wt% HCl solution.
2009, 26(4): 119-125.
Abstract:
To improve the anti-oxidation property of graphite at high temperature，an Mo5Si3-MoSi2/SiC multi-coating was prepared by the chemical vapor reaction (CVR) and slurry method. The structure of the ulti-coating was studied by XRD，SEM and EDS analysis，and the oxidation behavior of the multi-coating at high emperature was investigated by the isothermal oxidation test and thermodynamics calculation. The results show that the Mo5Si3 and MoSi2 phases in the multi-coating are prone to produce the reactions of forming the MoO3 gas in air at 1823 K and result in the mass loss，while the mass gain in the initial oxidation stage (0～6 h) is primarily attributed to the dominating passive oxidation of SiC. As the main phases of the multi-coating can oxidize and form the SiO2 glass at high temperature，it enables the coating to have the excellent anti-oxidation ability and thermal shock resistance. After oxidation in air at 1823 K for 20 h and thermal cycling between 1823 K and room temperature 16 times，the mass loss of the coated sample is only 3.78%.
To improve the anti-oxidation property of graphite at high temperature，an Mo5Si3-MoSi2/SiC multi-coating was prepared by the chemical vapor reaction (CVR) and slurry method. The structure of the ulti-coating was studied by XRD，SEM and EDS analysis，and the oxidation behavior of the multi-coating at high emperature was investigated by the isothermal oxidation test and thermodynamics calculation. The results show that the Mo5Si3 and MoSi2 phases in the multi-coating are prone to produce the reactions of forming the MoO3 gas in air at 1823 K and result in the mass loss，while the mass gain in the initial oxidation stage (0～6 h) is primarily attributed to the dominating passive oxidation of SiC. As the main phases of the multi-coating can oxidize and form the SiO2 glass at high temperature，it enables the coating to have the excellent anti-oxidation ability and thermal shock resistance. After oxidation in air at 1823 K for 20 h and thermal cycling between 1823 K and room temperature 16 times，the mass loss of the coated sample is only 3.78%.
2009, 26(4): 126-129.
Abstract:
Cu doped ZnO powder was prepared by the sol-gel method in order to study the origin of room temperature ferromagnetism of ZnO-based diluted magnetic semiconductors. X-ray diffraction spectra show that the solid solubility of Cu in ZnO was 0.08 (mole ratio)；TEM indicate that the Cu/ZnO particles are crystalline and uniform in size. The vibrating sample magnetometer measurements show that the Cu/ZnO powders are of room temperature ferromagnetism. As Cu itself does not have any magnetic properties，the origin of the observed room temperature ferromagnetism of Cu/ZnO could only be attributed to the exchange interaction between the defects of zinc oxide and the doped Cu ions.
Cu doped ZnO powder was prepared by the sol-gel method in order to study the origin of room temperature ferromagnetism of ZnO-based diluted magnetic semiconductors. X-ray diffraction spectra show that the solid solubility of Cu in ZnO was 0.08 (mole ratio)；TEM indicate that the Cu/ZnO particles are crystalline and uniform in size. The vibrating sample magnetometer measurements show that the Cu/ZnO powders are of room temperature ferromagnetism. As Cu itself does not have any magnetic properties，the origin of the observed room temperature ferromagnetism of Cu/ZnO could only be attributed to the exchange interaction between the defects of zinc oxide and the doped Cu ions.
2009, 26(4): 130-135.
Abstract:
The matrix random cracking of ceramic matrix composite was simulated by Monte Carlo model. The shear lag model was used to analyze the micro stress field of the damaged composites. The process of matrix random cracking was simulated by using computer，the effect of some model parameters on matrix cracking was analyzed，and the simulating results were compared with those of Curtin model. The results show that the final nominal crack space is between 1～2 debonded length，the final nominal crack space decreases with the increase of the minimum cracking stress，and increases with the increase of the thermal residual stress. The simulating length has little effect on the matrix crack evolution. Monte Carlo model can simulate the matrix random cracking efficiently.
The matrix random cracking of ceramic matrix composite was simulated by Monte Carlo model. The shear lag model was used to analyze the micro stress field of the damaged composites. The process of matrix random cracking was simulated by using computer，the effect of some model parameters on matrix cracking was analyzed，and the simulating results were compared with those of Curtin model. The results show that the final nominal crack space is between 1～2 debonded length，the final nominal crack space decreases with the increase of the minimum cracking stress，and increases with the increase of the thermal residual stress. The simulating length has little effect on the matrix crack evolution. Monte Carlo model can simulate the matrix random cracking efficiently.
2009, 26(4): 136-140.
Abstract:
Based on the half-cylinder oxidation regime，a model was developed to simulate the fatigue behavior of the SiC coated C/C composite in wet oxygen atmosphere. Under the current experimental conditions，the fatigue failure of the C/C composite was primarily controlled by the oxidation depth，which is mostly affected by the crack width of the coating. The effects of temperature and the applied stress were discussed. Modulus reduction effect on the crack width，which caused by fatigue，is also considered. The composite mean lives under 90，105，120，135 and 150 MPa are 48660，32645，22078，12332 and 4786 cycles，respectively. Comparisons are conducted between the experimental and simulation data. The experimental and simulative results agree fairly well. Besides，the calculation is close to the practical results when the applied stress is sufficiently high and the test time is short.
Based on the half-cylinder oxidation regime，a model was developed to simulate the fatigue behavior of the SiC coated C/C composite in wet oxygen atmosphere. Under the current experimental conditions，the fatigue failure of the C/C composite was primarily controlled by the oxidation depth，which is mostly affected by the crack width of the coating. The effects of temperature and the applied stress were discussed. Modulus reduction effect on the crack width，which caused by fatigue，is also considered. The composite mean lives under 90，105，120，135 and 150 MPa are 48660，32645，22078，12332 and 4786 cycles，respectively. Comparisons are conducted between the experimental and simulation data. The experimental and simulative results agree fairly well. Besides，the calculation is close to the practical results when the applied stress is sufficiently high and the test time is short.
2009, 26(4): 141-145.
Abstract:
The object translation often occurs between the serial images，which are captured at different analyzer positions in the polarized light microscopy for determining the extinction angle (Ae) of pyrocarbon in C/C composites. The translation results in the incorrect Ae value. An image registration algorithm based on structure features was proposed for translation correction. A circular template was used in the algorithm to detect the centre of the same fiber circular section in each image as a matching point. The image registration was realized through coordinate transform. The proposed algorithm has been applied to the Ae measurement of pyrocarbon. The experiment result shows that the image registration can avoid the wrong sampling data caused by object translation and assure Ae measurement accuracy.
The object translation often occurs between the serial images，which are captured at different analyzer positions in the polarized light microscopy for determining the extinction angle (Ae) of pyrocarbon in C/C composites. The translation results in the incorrect Ae value. An image registration algorithm based on structure features was proposed for translation correction. A circular template was used in the algorithm to detect the centre of the same fiber circular section in each image as a matching point. The image registration was realized through coordinate transform. The proposed algorithm has been applied to the Ae measurement of pyrocarbon. The experiment result shows that the image registration can avoid the wrong sampling data caused by object translation and assure Ae measurement accuracy.
2009, 26(4): 146-150.
Abstract:
The modern RTM process is actually a non-isothermal process due to the high speed of the filling mold and the short curing period. By analyzing the process and investigating related problems，a mathematical model was founded considering energy conservation equation and curing equation by using CV/FEM and upwind scheme. The differential equations were also discretized and integrated. The control equations fitting for numerical simulation are produced and the code is developed，and the calculation results are in agreement with those of the correlative literature.
The modern RTM process is actually a non-isothermal process due to the high speed of the filling mold and the short curing period. By analyzing the process and investigating related problems，a mathematical model was founded considering energy conservation equation and curing equation by using CV/FEM and upwind scheme. The differential equations were also discretized and integrated. The control equations fitting for numerical simulation are produced and the code is developed，and the calculation results are in agreement with those of the correlative literature.
2009, 26(4): 151-155.
Abstract:
The thermal conductivities of fiber reinforced composites with an inhomogeneous interphase are studied.The inhomogeneous interphase with continuously varied thermal conductivity can be modeled by a multi-layer concentric cylindrical homogeneous shell. The generalized self-consistent method and complex variable technology are applied to obtain an analytical recurrence formula of the effective conductivity. In the cases of the idealized zero thickness interface and homogeneous interphase，the closed form solutions are given by the recurrence formulae. The former has been given by previous researchers. When the volume fraction of fibers is small，the predictions by both models of the idealized zero thickness interface and inhomogeneous interphase and the experiment results are in good agreement，but when the volume fraction of fiber gets large，only the model of inhomogeneous interphase leads to good predictions. The present recurrence formula can also be used to analyze the thermal conductivity of a composite with multi-coating fibers.
The thermal conductivities of fiber reinforced composites with an inhomogeneous interphase are studied.The inhomogeneous interphase with continuously varied thermal conductivity can be modeled by a multi-layer concentric cylindrical homogeneous shell. The generalized self-consistent method and complex variable technology are applied to obtain an analytical recurrence formula of the effective conductivity. In the cases of the idealized zero thickness interface and homogeneous interphase，the closed form solutions are given by the recurrence formulae. The former has been given by previous researchers. When the volume fraction of fibers is small，the predictions by both models of the idealized zero thickness interface and inhomogeneous interphase and the experiment results are in good agreement，but when the volume fraction of fiber gets large，only the model of inhomogeneous interphase leads to good predictions. The present recurrence formula can also be used to analyze the thermal conductivity of a composite with multi-coating fibers.
2009, 26(4): 156-162.
Abstract:
In order to study the nonlinear mechanical properties of concrete beams with carbon fiber reinforced composite (CFRP) rebars，a finite element analytical model of the beam with CFRP rebars was set up combined with corresponding nonlinear theories. The nonlinear whole course of four beams with prest ressed CFRP rebars was analyzed and the regularities of the stresses of CFRP rebars，GFRP rebars and common steels were studied. Compared with the experiment results，the calculations are in good agreements with the test results. The result shows that the nonlinear properties of the concrete are properly considered on the basis of the smearing crack model，Owen yielding criterion and Hinton crushing theory. The prestressed CFRP rebars are efficiently modeled by combined elements and the corresponding computational procedure for nonlinear whole course analysis is of satisfying correctness. CFRP rebars are still in an elastic status when the beam reaches the ultimate loads because of high strength property. Compared with the specimens which have common steels in the bottom，GFRP rebars are always in the elastic status during the whole course.
In order to study the nonlinear mechanical properties of concrete beams with carbon fiber reinforced composite (CFRP) rebars，a finite element analytical model of the beam with CFRP rebars was set up combined with corresponding nonlinear theories. The nonlinear whole course of four beams with prest ressed CFRP rebars was analyzed and the regularities of the stresses of CFRP rebars，GFRP rebars and common steels were studied. Compared with the experiment results，the calculations are in good agreements with the test results. The result shows that the nonlinear properties of the concrete are properly considered on the basis of the smearing crack model，Owen yielding criterion and Hinton crushing theory. The prestressed CFRP rebars are efficiently modeled by combined elements and the corresponding computational procedure for nonlinear whole course analysis is of satisfying correctness. CFRP rebars are still in an elastic status when the beam reaches the ultimate loads because of high strength property. Compared with the specimens which have common steels in the bottom，GFRP rebars are always in the elastic status during the whole course.
2009, 26(4): 163-168.
Abstract:
The modeⅠfracture toughness of Z-pin reinforced double cantilever beam configuration laminates was studied based on mesomechanics and virtual crack closure technique (VCCT). A finite element model was built using solid elements to model the composite laminates and non-linear combined elements to simulate the Z -pin reinforcement. The numerical results of the strain energy release rate were compared between the fracture toughness of the modeⅠcomposite laminate reinforced with the Z-pin and that of the modeⅠcomposite laminate without the Z-pin. The study demonst rates that Z-pin reinforcement can increase the composite delaminated resistance and reinforce the fracture toughness of the modeⅠcomposite laminate aggressively. The influence of design parameters such as the number of Z-pin in the bridging area，the Z-pin density and some other parameters on the toughness enhancement of Z-pinned laminates was investigated.
The modeⅠfracture toughness of Z-pin reinforced double cantilever beam configuration laminates was studied based on mesomechanics and virtual crack closure technique (VCCT). A finite element model was built using solid elements to model the composite laminates and non-linear combined elements to simulate the Z -pin reinforcement. The numerical results of the strain energy release rate were compared between the fracture toughness of the modeⅠcomposite laminate reinforced with the Z-pin and that of the modeⅠcomposite laminate without the Z-pin. The study demonst rates that Z-pin reinforcement can increase the composite delaminated resistance and reinforce the fracture toughness of the modeⅠcomposite laminate aggressively. The influence of design parameters such as the number of Z-pin in the bridging area，the Z-pin density and some other parameters on the toughness enhancement of Z-pinned laminates was investigated.
2009, 26(4): 169-175.
Abstract:
A warp skeleton method was proposed to solve the descriptive issue of arbitrary 3D woven composite architecture，with the unit cell being decomposed into subcells/grids. The subcell vector concept was introduced to digitalize the 3D architecture，in order to use the 2D database table to store it. An initial rupture model was built by the digitalized data and the classical cross-section hypothesis，an iterative algorithm was used to optimize the model，amied at approaching the real world model，and thus the 3D solid model and mesh generation were completed. The results show that the iterative method can naturalize the tow pattern，with the model approaching the physical composite. The numeric analysis results show that the rate of astringency of the iterative algorithm is optimized when the proportion for moving warp and weft was situated between 0.6～0.7.
A warp skeleton method was proposed to solve the descriptive issue of arbitrary 3D woven composite architecture，with the unit cell being decomposed into subcells/grids. The subcell vector concept was introduced to digitalize the 3D architecture，in order to use the 2D database table to store it. An initial rupture model was built by the digitalized data and the classical cross-section hypothesis，an iterative algorithm was used to optimize the model，amied at approaching the real world model，and thus the 3D solid model and mesh generation were completed. The results show that the iterative method can naturalize the tow pattern，with the model approaching the physical composite. The numeric analysis results show that the rate of astringency of the iterative algorithm is optimized when the proportion for moving warp and weft was situated between 0.6～0.7.
2009, 26(4): 176-180.
Abstract:
Manufacturing cost evaluation is required in the preliminary design stage for composite wings. A cost model for the composite wings was developed based on the manufacturing process cost models. A model generator，which was implemented using CATIA software API，was used to generate the parametric CAD model of wings and provided the geometric attribute for the cost model. The seamless linkage was established automatically between the CAD model and the cost model. The steps of the implementation procedure were presented. The composite wings of an unmanned aircraft were used to test the method. It is concluded that the procedure is able to rapidly evaluate the costs for the wings with different external shapes and different structural layouts. The results indicate that the total cost of the composite wing increases by 2.5% when one more spar is added and four ribs are moved away for the structural layout. The aspect ratio and taper of the wing do not have considerable influence on the total cost of the wing if the wing structural layout is unchanged.
Manufacturing cost evaluation is required in the preliminary design stage for composite wings. A cost model for the composite wings was developed based on the manufacturing process cost models. A model generator，which was implemented using CATIA software API，was used to generate the parametric CAD model of wings and provided the geometric attribute for the cost model. The seamless linkage was established automatically between the CAD model and the cost model. The steps of the implementation procedure were presented. The composite wings of an unmanned aircraft were used to test the method. It is concluded that the procedure is able to rapidly evaluate the costs for the wings with different external shapes and different structural layouts. The results indicate that the total cost of the composite wing increases by 2.5% when one more spar is added and four ribs are moved away for the structural layout. The aspect ratio and taper of the wing do not have considerable influence on the total cost of the wing if the wing structural layout is unchanged.
2009, 26(4): 181-185.
Abstract:
Considering the structure characteristics of 3D orthogonal woven composite (3D-OWC)，a cell model composed of three orthogonal bundles of fibers and matrix was proposed based on the assumption that the fiber bundle has the rectangular cross section. According to the cell model，an equation relating the fiber volume fraction and the woven parameters (such as the fiber roughness，weaving density and so on) was obtained. The relatively simple formulas of Young‘s modulus of 3D-OWC were developed by the assumption that both the fiber and matrix are elastic. With the new formulas，three dimensional orthogonal composite’s Young's modulus can be got by the fiber modulus，matrix modulus and fiber volume fraction. The fiber volume fraction and elastic modulus calculated by the equations are in good agreement with the experiments. It is concluded that the proposed cell model is effective and valuable，and it will be useful in the study of 3D-OWC mechanical properties.
Considering the structure characteristics of 3D orthogonal woven composite (3D-OWC)，a cell model composed of three orthogonal bundles of fibers and matrix was proposed based on the assumption that the fiber bundle has the rectangular cross section. According to the cell model，an equation relating the fiber volume fraction and the woven parameters (such as the fiber roughness，weaving density and so on) was obtained. The relatively simple formulas of Young‘s modulus of 3D-OWC were developed by the assumption that both the fiber and matrix are elastic. With the new formulas，three dimensional orthogonal composite’s Young's modulus can be got by the fiber modulus，matrix modulus and fiber volume fraction. The fiber volume fraction and elastic modulus calculated by the equations are in good agreement with the experiments. It is concluded that the proposed cell model is effective and valuable，and it will be useful in the study of 3D-OWC mechanical properties.
2009, 26(4): 186-190.
Abstract:
Based on the first-order shear deformation theory and the lamination model of MSC Patran，an FEA model for plain woven fabric single ply plates was established，and an FEA model for the plain woven fabric laminates with multiple elliptical embedded delaminations was developed. A linearity contact model was used to simulate the interaction between the upper and lower sub-laminates along the delaminated region during the vibration process. From some typical examples，the effects of the elliptical angle of long axis and lengthways embedded delaminations of specimens on the vibration characteristic were discussed. The results show that the distinction of the effect on frequency between surface and inner embedded delaminations was not evident. With the increasing of the elliptical angle of the long axis and lengthways embedded delaminations of the specimens，the influence on the vibration characteristic is increasing.
Based on the first-order shear deformation theory and the lamination model of MSC Patran，an FEA model for plain woven fabric single ply plates was established，and an FEA model for the plain woven fabric laminates with multiple elliptical embedded delaminations was developed. A linearity contact model was used to simulate the interaction between the upper and lower sub-laminates along the delaminated region during the vibration process. From some typical examples，the effects of the elliptical angle of long axis and lengthways embedded delaminations of specimens on the vibration characteristic were discussed. The results show that the distinction of the effect on frequency between surface and inner embedded delaminations was not evident. With the increasing of the elliptical angle of the long axis and lengthways embedded delaminations of the specimens，the influence on the vibration characteristic is increasing.
2009, 26(4): 191-196.
Abstract:
The free vibration characteristic was studied for plain woven fabric laminates with multiple delaminations around a central hole. Finite elements analysis models were established by MSC. Nastran/Patran for plain woven fabric laminates with elliptical multiple delaminations around an elliptical central hole. From some typical examples，the effects of the holes' size，multiple delaminations' size and damage's location on the vibration characteristic were discussed. The results show that the effect of small-sized hole and delaminations is not great. On the natural frequencies，the effect of transverse elliptical multiple delaminations around an elliptical central hole is more serious than that of lengthways elliptical multiple delaminations around an elliptical central hole；the natural frequencies are very sensitive to damages location，and less sensitive to multiple delaminations' size and the holes' size.
The free vibration characteristic was studied for plain woven fabric laminates with multiple delaminations around a central hole. Finite elements analysis models were established by MSC. Nastran/Patran for plain woven fabric laminates with elliptical multiple delaminations around an elliptical central hole. From some typical examples，the effects of the holes' size，multiple delaminations' size and damage's location on the vibration characteristic were discussed. The results show that the effect of small-sized hole and delaminations is not great. On the natural frequencies，the effect of transverse elliptical multiple delaminations around an elliptical central hole is more serious than that of lengthways elliptical multiple delaminations around an elliptical central hole；the natural frequencies are very sensitive to damages location，and less sensitive to multiple delaminations' size and the holes' size.
2009, 26(4): 197-202.
Abstract:
Based on the computing platform of the finite element method commercial software ABAQUS，a parameter identification method was developed for orthotropic composite structures. The material parameter identification problem was formulated as the problem of minimizing the objective function defined as a square sum of differences between the measured and calculated data on displacements. Levenberg-Marquardt method，in which the sensitivity analysis was based on the differentiation of the discretized algebraic finite element matrix equations with respect to material parameter，was used to solve the minimization problem. Numerical example shows that the proposed method for parameter identification is feasible and effective. The initial values and upper and lower bounds of parameters identified play an important role in the parameter identification process. Therefore，a priori information of parameters should be used as much as possible. ABAQUS is effective and reliable commercial software for the finite element method，and hence the proposed method based on such a kind of software has strong practicability.
Based on the computing platform of the finite element method commercial software ABAQUS，a parameter identification method was developed for orthotropic composite structures. The material parameter identification problem was formulated as the problem of minimizing the objective function defined as a square sum of differences between the measured and calculated data on displacements. Levenberg-Marquardt method，in which the sensitivity analysis was based on the differentiation of the discretized algebraic finite element matrix equations with respect to material parameter，was used to solve the minimization problem. Numerical example shows that the proposed method for parameter identification is feasible and effective. The initial values and upper and lower bounds of parameters identified play an important role in the parameter identification process. Therefore，a priori information of parameters should be used as much as possible. ABAQUS is effective and reliable commercial software for the finite element method，and hence the proposed method based on such a kind of software has strong practicability.
