2013 Vol. 30, No. 1
2013, 30(1): 1-13.
Abstract:
In this article, preparing technology and properties of the particulate reinforced metal matrix composites coatings are reviewed. Development history, current status, microstructures and mechanical properties of the composite coatings prepared by the electro-thermal explosion ultra-high speed spraying technology and the electro-brush plating technology are described in details. Finally, the engineering applications and the development prospects of those coatings are discussed.
In this article, preparing technology and properties of the particulate reinforced metal matrix composites coatings are reviewed. Development history, current status, microstructures and mechanical properties of the composite coatings prepared by the electro-thermal explosion ultra-high speed spraying technology and the electro-brush plating technology are described in details. Finally, the engineering applications and the development prospects of those coatings are discussed.
2013, 30(1): 14-21.
Abstract:
Graphene is a new found carbon material and has attracted great academic interests because of its perfect structure and excellent properties. The modification of graphene and/or graphene oxide and their utilization in the fabrication of nano filler/polymer composites with different polymer matrices have been explored by various methods and extensively studied. Compared with pure polymer matrix, the nano filler/polymer composites can become multifunctional with the adding of graphene. The resultant nano filler/polymer composites exhibit enhanced mechanical, electrical and thermal properties as well as improved processability, which can be applied in various fields. Herein, the preparation, structure and properties of graphene/polymer composites are summarized in general and the outlooks of future development were also discussed.
Graphene is a new found carbon material and has attracted great academic interests because of its perfect structure and excellent properties. The modification of graphene and/or graphene oxide and their utilization in the fabrication of nano filler/polymer composites with different polymer matrices have been explored by various methods and extensively studied. Compared with pure polymer matrix, the nano filler/polymer composites can become multifunctional with the adding of graphene. The resultant nano filler/polymer composites exhibit enhanced mechanical, electrical and thermal properties as well as improved processability, which can be applied in various fields. Herein, the preparation, structure and properties of graphene/polymer composites are summarized in general and the outlooks of future development were also discussed.
2013, 30(1): 22-26.
Abstract:
The electromagnetic interference(EMI) shielding effectiveness(SE) of the graphene sheets/polyaniline (GSs/PANI) composite in different contents of GSs was investigated. The high crystalline GSs were prepared by DC arc-discharge method. The GSs/PANI composites were synthesized by an alcohol-assisted dispersion and pressing process. Compared with the pure PANI materials’ Raman spectra, the GSs/PANI composites show the decrease of the characteristic peak intensity or a red shift of the peak, which is induced by the interaction between the GSs and PANI. The electrical conductivity of GSs/PANI composite increases with the increase of the GSs doping quantity and reaches to 19.4 S/cm at the mass fraction of 25%, which almost equals to that of pure GSs (20.1 S/cm). The EMI SE increases with the frequency and the GSs doping quantity. When the mass fraction of GSs is 25%, the EMI SE increases about 42%, from 19.8 dB to 34.2 dB in the range of 2~18 GHz. Besides, the absorption proportion increases from 66% to 81%, which indicates that the GSs/PANI composite is the absorption-dominated EMI shielding material. These also prove that GSs are excellent filler of the PANI because of their special structure and properties. There will be a wide application prospects in the field of EMI shielding and microwave absorption.
The electromagnetic interference(EMI) shielding effectiveness(SE) of the graphene sheets/polyaniline (GSs/PANI) composite in different contents of GSs was investigated. The high crystalline GSs were prepared by DC arc-discharge method. The GSs/PANI composites were synthesized by an alcohol-assisted dispersion and pressing process. Compared with the pure PANI materials’ Raman spectra, the GSs/PANI composites show the decrease of the characteristic peak intensity or a red shift of the peak, which is induced by the interaction between the GSs and PANI. The electrical conductivity of GSs/PANI composite increases with the increase of the GSs doping quantity and reaches to 19.4 S/cm at the mass fraction of 25%, which almost equals to that of pure GSs (20.1 S/cm). The EMI SE increases with the frequency and the GSs doping quantity. When the mass fraction of GSs is 25%, the EMI SE increases about 42%, from 19.8 dB to 34.2 dB in the range of 2~18 GHz. Besides, the absorption proportion increases from 66% to 81%, which indicates that the GSs/PANI composite is the absorption-dominated EMI shielding material. These also prove that GSs are excellent filler of the PANI because of their special structure and properties. There will be a wide application prospects in the field of EMI shielding and microwave absorption.
2013, 30(1): 27-31.
Abstract:
Graphene/polyaniline(RGO/PANI) conducting composites were synthesized using graphene oxide with 1 nm thickness, synthesized by ultrasound-assisted Hummers method, as the oxidant. AFM, SEM, FTIR and XRD were employed to characterize RGO/PANI composites. The results show that graphene oxide(GO) nanosheets can be readily reduced by aniline in an aqueous acid medium at the temperatures just above room temperature, while simultaneously aniline undergoes an oxidative polymerization by oxidability of oxygen functional groups on GO to produce RGO/PANI conducting composites. When the amounts of GO and aniline in the reaction are 0.1 g and 1 mL respectively, the best conductivity of the prepared RGO/PANI composites is 10 S/cm.
Graphene/polyaniline(RGO/PANI) conducting composites were synthesized using graphene oxide with 1 nm thickness, synthesized by ultrasound-assisted Hummers method, as the oxidant. AFM, SEM, FTIR and XRD were employed to characterize RGO/PANI composites. The results show that graphene oxide(GO) nanosheets can be readily reduced by aniline in an aqueous acid medium at the temperatures just above room temperature, while simultaneously aniline undergoes an oxidative polymerization by oxidability of oxygen functional groups on GO to produce RGO/PANI conducting composites. When the amounts of GO and aniline in the reaction are 0.1 g and 1 mL respectively, the best conductivity of the prepared RGO/PANI composites is 10 S/cm.
2013, 30(1): 32-38.
Abstract:
The silver/polyacrylonitrile(Ag/PAN) composite was synthesized by aqueous in situ precipitation polymerization. The influence of the reactant ratio on molecular mass of Ag/PAN was investigated by measuring its relative viscosity. The optimized synthetic condition of the as-prepared composite is that the concentrations of acrylonitrile(AN) monomer, AgNO3 and K2S2O8 are 10%, 0.6% and 2%, respectively. The nano-silver/cyclized polyacrylonitrile (Ag/C-PAN) composite was prepared by the preoxidation of resultant Ag/PAN. The components, and also the relative cyclization indexes of nano-Ag/C-PAN composite at different preoxidation temperatures and times were analyzed by FTIR spectrum. The microstructure of the as-prepared composites was characterized by TEM and XRD. The results show that silver nanoparticles with diameter about 10 nm and appeared as face-centered cubic crystal are homogeneously dispersed in the cyclized PAN matrix.
The silver/polyacrylonitrile(Ag/PAN) composite was synthesized by aqueous in situ precipitation polymerization. The influence of the reactant ratio on molecular mass of Ag/PAN was investigated by measuring its relative viscosity. The optimized synthetic condition of the as-prepared composite is that the concentrations of acrylonitrile(AN) monomer, AgNO3 and K2S2O8 are 10%, 0.6% and 2%, respectively. The nano-silver/cyclized polyacrylonitrile (Ag/C-PAN) composite was prepared by the preoxidation of resultant Ag/PAN. The components, and also the relative cyclization indexes of nano-Ag/C-PAN composite at different preoxidation temperatures and times were analyzed by FTIR spectrum. The microstructure of the as-prepared composites was characterized by TEM and XRD. The results show that silver nanoparticles with diameter about 10 nm and appeared as face-centered cubic crystal are homogeneously dispersed in the cyclized PAN matrix.
2013, 30(1): 39-44.
Abstract:
The aminosilane coupling agent KH550 modified rectorite(REC) powder was prepared by the spray drying method, and the influence of the inlet air temperature on the surface characteristics, structure and morphology of the modified REC powder was examined. The modified REC/ styrene-butadiene rubber(SBR), REC/natural rubber(NR) and REC/nitrile-butadiene rubber(NBR) composites were prepared by the melt blending method. The dispersion of the modified REC powder in the rubber matrixes and its reinforcement effects on the matrixes were also investigated. The results show that raising the inlet air temperature increases the amount of KH550 in the modified REC, and then promotes the modification of REC. KH550 molecules intercalate into the intergallery of REC, resulting in smaller aggregates and more loosely packed structures in the modified REC powders. No intercalation of rubber macromolecules into the interlayer of REC occurs in all three modified REC/rubber composites. The modified REC layers aggregate locally in SBR, they are uniformly dispersed in NBR, and exhibit the best dispersion state in NR. Compared with the corresponding the pure rubbers, the mechanical properties of the modified REC powder filled SBR and NBR composites are comprehensively improved, regarding the modified REC/NR composite, the stress is enhanced, the tensile and tear strengths are kept unchanged, and the elongation at break is decreased compared with the pure NR.
The aminosilane coupling agent KH550 modified rectorite(REC) powder was prepared by the spray drying method, and the influence of the inlet air temperature on the surface characteristics, structure and morphology of the modified REC powder was examined. The modified REC/ styrene-butadiene rubber(SBR), REC/natural rubber(NR) and REC/nitrile-butadiene rubber(NBR) composites were prepared by the melt blending method. The dispersion of the modified REC powder in the rubber matrixes and its reinforcement effects on the matrixes were also investigated. The results show that raising the inlet air temperature increases the amount of KH550 in the modified REC, and then promotes the modification of REC. KH550 molecules intercalate into the intergallery of REC, resulting in smaller aggregates and more loosely packed structures in the modified REC powders. No intercalation of rubber macromolecules into the interlayer of REC occurs in all three modified REC/rubber composites. The modified REC layers aggregate locally in SBR, they are uniformly dispersed in NBR, and exhibit the best dispersion state in NR. Compared with the corresponding the pure rubbers, the mechanical properties of the modified REC powder filled SBR and NBR composites are comprehensively improved, regarding the modified REC/NR composite, the stress is enhanced, the tensile and tear strengths are kept unchanged, and the elongation at break is decreased compared with the pure NR.
2013, 30(1): 45-53.
Abstract:
Multi-walled carbon nanotubes(MWCNTs) were functionalized with 4-substituted benzoic acid via direct Friedel-Crafts acylation in a mild reaction medium of polyphosphoric acid(PPA)/pentoxide(P2O5). Functionalized multi-walled carbon nanotubes (F-MWCNTs)/polyamide 6(PA6) composite was prepared via in situ polymerization and the dried powders were melt-spun into fibers. The fibers were characterized using TEM, TG, DSC, SEM. MWCNTs inherently have functional groups on their surfaces as a result of the reaction. F-MWCNTs are homogeneously dispersed in PA6 matrix without any aggregation. The incorporation of F-MWCNTs into PA6 has no obvious effect on the melting point and the crystallinity of PA6, except increasing the crystallization temperature. With the content of F-MWCNTs increasing, thermal stability of the composite fibers is improved significantly. The tensile strength and Young’s modulus of the fibers are significantly improved with increasing the content of F-MWCNTs. The tensile strength and Young’s modulus of the fibers reach a maximum when the mass fraction of F-MWCNTs is 0.5%, which are improved by 45% and 208% respectively than PA6 fibers.
Multi-walled carbon nanotubes(MWCNTs) were functionalized with 4-substituted benzoic acid via direct Friedel-Crafts acylation in a mild reaction medium of polyphosphoric acid(PPA)/pentoxide(P2O5). Functionalized multi-walled carbon nanotubes (F-MWCNTs)/polyamide 6(PA6) composite was prepared via in situ polymerization and the dried powders were melt-spun into fibers. The fibers were characterized using TEM, TG, DSC, SEM. MWCNTs inherently have functional groups on their surfaces as a result of the reaction. F-MWCNTs are homogeneously dispersed in PA6 matrix without any aggregation. The incorporation of F-MWCNTs into PA6 has no obvious effect on the melting point and the crystallinity of PA6, except increasing the crystallization temperature. With the content of F-MWCNTs increasing, thermal stability of the composite fibers is improved significantly. The tensile strength and Young’s modulus of the fibers are significantly improved with increasing the content of F-MWCNTs. The tensile strength and Young’s modulus of the fibers reach a maximum when the mass fraction of F-MWCNTs is 0.5%, which are improved by 45% and 208% respectively than PA6 fibers.
2013, 30(1): 54-61.
Abstract:
To monitor the strains of the composite T-stiffened panels during its curing and compression after impact, the fiber Bragg grating(FBG) sensors were embedded in the triangle area of the composite T-stiffened panels(structure non-interference region). The reflection spectra obtained from the uncoated FBG sensors and the FBG sensors coated with UV-cured resin were compared, and the effect of thermal residual stress on the reflection spectrum was studied. It was indicated that the full width at half maximum(FWHM) value of the coated FBG sensor almost unchanged during the curing, and the thermal residual stress upon the reflection spectrum can be attenuated by coating UV-cured resin on the FBG sensors. Furthermore, the strain measured by the coated FBG sensor is correspondence to the results of the strain gauge on the composites surface. The validity of the strain measured by FBG sensors was verified during the curing and the compression after impact.
To monitor the strains of the composite T-stiffened panels during its curing and compression after impact, the fiber Bragg grating(FBG) sensors were embedded in the triangle area of the composite T-stiffened panels(structure non-interference region). The reflection spectra obtained from the uncoated FBG sensors and the FBG sensors coated with UV-cured resin were compared, and the effect of thermal residual stress on the reflection spectrum was studied. It was indicated that the full width at half maximum(FWHM) value of the coated FBG sensor almost unchanged during the curing, and the thermal residual stress upon the reflection spectrum can be attenuated by coating UV-cured resin on the FBG sensors. Furthermore, the strain measured by the coated FBG sensor is correspondence to the results of the strain gauge on the composites surface. The validity of the strain measured by FBG sensors was verified during the curing and the compression after impact.
2013, 30(1): 62-66.
Abstract:
Hybrid coating of epoxy acrylate(EA) and modified nano organic montmorillonite(OMMT) was prepared for optical fiber Bragg grating(FBG) sensors. Mechanical performance testing and heat performance testing were carried on the OMMT/EA hybrid coating. The results demonstrate that, the performance of OMMT/EA coating with 2% mass fraction of nano OMMT is the best. SEM photographs and XRD analysis show that thesingle-lamellar nano OMMT is even distribution in EA. The tensile property, adhesion force, pencil hardness and glass temperature of OMMT/EA coating can be improved by adding nano OMMT, while the linear thermal expansion coefficient is decreased. FBG sensors with OMMT/EA coating and EA were embedded in the composites which processed under certain temperature and pressure, respectively. Comparing two groups of data, the results show that the modified OMMT/EA coating could obviously decrease the hysteresis of FBG sensor signals.
Hybrid coating of epoxy acrylate(EA) and modified nano organic montmorillonite(OMMT) was prepared for optical fiber Bragg grating(FBG) sensors. Mechanical performance testing and heat performance testing were carried on the OMMT/EA hybrid coating. The results demonstrate that, the performance of OMMT/EA coating with 2% mass fraction of nano OMMT is the best. SEM photographs and XRD analysis show that thesingle-lamellar nano OMMT is even distribution in EA. The tensile property, adhesion force, pencil hardness and glass temperature of OMMT/EA coating can be improved by adding nano OMMT, while the linear thermal expansion coefficient is decreased. FBG sensors with OMMT/EA coating and EA were embedded in the composites which processed under certain temperature and pressure, respectively. Comparing two groups of data, the results show that the modified OMMT/EA coating could obviously decrease the hysteresis of FBG sensor signals.
2013, 30(1): 67-72.
Abstract:
Nickel films were deposited on the piezoelectric composites by the electroless Ni plating. The optimal process and formula conditions of pretreatment process, activation process and the electroless plating solution were obtained in combination with the orthogonal test and the practical production as follows, 350 g/L of mass concentration, 25 ℃ of roughening temperature, 25 min of roughening time; 0.4 g/L of PdCl2, 30 ℃ of activation temperature, 5 min of activation time; 38~43 ℃ of plating temperature, 8~10 min of plating time and pH value of 8.5~9.5. The deposit’s micro-morphology and compositions of piezoelectric composites were analyzed and compared by using SEM, EDS and XRD analysis. The results show that the deposit of the optimal conditions has well uniformity, and with good adhesion and corrosion resistance.
Nickel films were deposited on the piezoelectric composites by the electroless Ni plating. The optimal process and formula conditions of pretreatment process, activation process and the electroless plating solution were obtained in combination with the orthogonal test and the practical production as follows, 350 g/L of mass concentration, 25 ℃ of roughening temperature, 25 min of roughening time; 0.4 g/L of PdCl2, 30 ℃ of activation temperature, 5 min of activation time; 38~43 ℃ of plating temperature, 8~10 min of plating time and pH value of 8.5~9.5. The deposit’s micro-morphology and compositions of piezoelectric composites were analyzed and compared by using SEM, EDS and XRD analysis. The results show that the deposit of the optimal conditions has well uniformity, and with good adhesion and corrosion resistance.
2013, 30(1): 73-82.
Abstract:
Two methods, i.e. laying resin bonding film at the face-core interface and using foams with well-arranged holes, were proposed aiming to improve the face-core interface properties of sandwich panels fabricated by vacuum assisted resin infusion(VARI) process. The possibility and benefits of these methods were investigated. Moreover, the influence of the existence of resin film and its thickness and density of holes in the foam core were investigated by non-destructive test, three-point bending test, computer simulation and interface microstructure observations. The analysis results indicate that sandwich structures without resin film achieve the highest face-core interface strength, while with 0.5 mm resin film show the fewest defects in non-destructive testing(NDT). When the film is as thick as 2 mm, the interface properties will deteriorate. Well-arranged holes in the foam core can promote infiltration process through the whole thickness of the sandwich construction, resulting in good interfacial and high stiffness.
Two methods, i.e. laying resin bonding film at the face-core interface and using foams with well-arranged holes, were proposed aiming to improve the face-core interface properties of sandwich panels fabricated by vacuum assisted resin infusion(VARI) process. The possibility and benefits of these methods were investigated. Moreover, the influence of the existence of resin film and its thickness and density of holes in the foam core were investigated by non-destructive test, three-point bending test, computer simulation and interface microstructure observations. The analysis results indicate that sandwich structures without resin film achieve the highest face-core interface strength, while with 0.5 mm resin film show the fewest defects in non-destructive testing(NDT). When the film is as thick as 2 mm, the interface properties will deteriorate. Well-arranged holes in the foam core can promote infiltration process through the whole thickness of the sandwich construction, resulting in good interfacial and high stiffness.
2013, 30(1): 83-89.
Abstract:
Polypropylene(PP) was flame retarded with an intumescent flame retardant(IFR) system containing 1, 2, 3-tri(5, 5-dibromomethyl-1, 3-dioxaphosphorinanyl-2-oxy)benzene(FR), polyphosphate(APP ) and melamine(MEL).The effect of content on flame retarding properties such as limited oxygen index(LOI)measurements, thermal gravimetric analysis(TGA), UL-94 and cone tests was studied. The results demonstrate that IFR is effective on improving the flame retardancy of polypropylene. The limited oxygen index value could reach 36.2% for the sample containing 30% IFR(FR∶APP∶MEL, 4∶8∶3, mass ratio). The cone experimental results show that the peak heat release rate(pk-HRR), average heat release rate(av-HRR), average effective heat of combustion(av-EHC), average specific extinction area(av-SEA), average mass loss rate(av-MLR) and average CO release rate(av-CO) of the PP are reduced 75.9%, 71.7%, 76.4% , 74.6%, 58.3% and 50.0% respectively than those of the pure PP. The release rate of soot and poisonous gas are reduced, which reaches to about zero at burning time of 300 s. In addition, SEM observation reveales that the IFR can promote the formation of strong charred layers in the early stage of burning of the composite.
Polypropylene(PP) was flame retarded with an intumescent flame retardant(IFR) system containing 1, 2, 3-tri(5, 5-dibromomethyl-1, 3-dioxaphosphorinanyl-2-oxy)benzene(FR), polyphosphate(APP ) and melamine(MEL).The effect of content on flame retarding properties such as limited oxygen index(LOI)measurements, thermal gravimetric analysis(TGA), UL-94 and cone tests was studied. The results demonstrate that IFR is effective on improving the flame retardancy of polypropylene. The limited oxygen index value could reach 36.2% for the sample containing 30% IFR(FR∶APP∶MEL, 4∶8∶3, mass ratio). The cone experimental results show that the peak heat release rate(pk-HRR), average heat release rate(av-HRR), average effective heat of combustion(av-EHC), average specific extinction area(av-SEA), average mass loss rate(av-MLR) and average CO release rate(av-CO) of the PP are reduced 75.9%, 71.7%, 76.4% , 74.6%, 58.3% and 50.0% respectively than those of the pure PP. The release rate of soot and poisonous gas are reduced, which reaches to about zero at burning time of 300 s. In addition, SEM observation reveales that the IFR can promote the formation of strong charred layers in the early stage of burning of the composite.
2013, 30(1): 90-95.
Abstract:
According to wind turbine blade worked in sandy environment, high winds can carry abrasive particles disrupting the blade and reducing its aerodynamic efficiency, the behaviors of sand erosion were investigated. In this paper, three different samples: the pure epoxy (EPIKOTETM RIM 135, EPIKURETM RIM H 137 especially for wind turbine blade), the conventional glass fiber reinforced composite and the carbon nano-fiber paper-glass fiber/epoxy composite were compared in terms of wear loss, surface profile, glass transition temperature and water contact angle. For the erosion testing, the mass loss of the traditional composite is larger than that of pure epoxy resin, and that of carbon nano-fiber paper-glass fiber/epoxy composite. Compared with traditional composite, carbon nano-fiber paper-glass fiber/epoxy composite shows a higher glass transition temperature (from 55 ℃ increased to 63 ℃) and a larger contact angle (from 104° increased to 131°, more hydrophobic), which can improve the heat-resistance performance and the anti-ice properties. This novel carbon nano-fiber paper-glass fiber/epoxy composite has a great potential as a coating materials for wind turbine blade, providing erosion resistance, preventing ice-buildup, and reducing the energy loss.
According to wind turbine blade worked in sandy environment, high winds can carry abrasive particles disrupting the blade and reducing its aerodynamic efficiency, the behaviors of sand erosion were investigated. In this paper, three different samples: the pure epoxy (EPIKOTETM RIM 135, EPIKURETM RIM H 137 especially for wind turbine blade), the conventional glass fiber reinforced composite and the carbon nano-fiber paper-glass fiber/epoxy composite were compared in terms of wear loss, surface profile, glass transition temperature and water contact angle. For the erosion testing, the mass loss of the traditional composite is larger than that of pure epoxy resin, and that of carbon nano-fiber paper-glass fiber/epoxy composite. Compared with traditional composite, carbon nano-fiber paper-glass fiber/epoxy composite shows a higher glass transition temperature (from 55 ℃ increased to 63 ℃) and a larger contact angle (from 104° increased to 131°, more hydrophobic), which can improve the heat-resistance performance and the anti-ice properties. This novel carbon nano-fiber paper-glass fiber/epoxy composite has a great potential as a coating materials for wind turbine blade, providing erosion resistance, preventing ice-buildup, and reducing the energy loss.
2013, 30(1): 96-102.
Abstract:
A new kind of injectable composite of nano hydroxyapatite/aspartic acid-glutamic acid copolymer/calcium sulfate(nano HA/PAG/CS) was prepared by using polymerization in situ. The composition, structure, surface morphology and mechanical strength of the composite were characterized by FTIR, XRD and SEM etc, and its degradability was investigated in simulated body liquid(SBF). The results show that the interaction appear between the inorganic and organic phase of the composite. The composite exhibits good compressive strength and degrads totally after soaking in SBF for 7 weeks with surface degradation methods. In the degradation process, the pH of SBF solution changes from 6.4 to 7.4. The composite has good bioactivity because the apatite can be formed on its surfaces after soaking into SBF, which is very useful for the formation of interface combination between implant and tissue.
A new kind of injectable composite of nano hydroxyapatite/aspartic acid-glutamic acid copolymer/calcium sulfate(nano HA/PAG/CS) was prepared by using polymerization in situ. The composition, structure, surface morphology and mechanical strength of the composite were characterized by FTIR, XRD and SEM etc, and its degradability was investigated in simulated body liquid(SBF). The results show that the interaction appear between the inorganic and organic phase of the composite. The composite exhibits good compressive strength and degrads totally after soaking in SBF for 7 weeks with surface degradation methods. In the degradation process, the pH of SBF solution changes from 6.4 to 7.4. The composite has good bioactivity because the apatite can be formed on its surfaces after soaking into SBF, which is very useful for the formation of interface combination between implant and tissue.
2013, 30(1): 103-111.
Abstract:
Hdroxyapatite(HA) was prepared using porcine trabecular bone after being degreased, deproteined, calcined and ball milling. HA/chitosan(CS) composite membranes were prepared by blending and drying HA and CS solution. The effect of milling conditions on the HA particle size was inspected by the orthogonal design. MC3T3-E1 preosteoblasts were seeded on the surface of the composite membranes, and then cell morphology and proliferation were detected by SEM and 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl tetrazolium bromide(MTT) methods. The results show that the prepared HA is relatively homogeneous micrometer-scale spherical particle with median diameter(D50) in 1.21~1.67 μm range, and HA particles are distributed uniformly in the matrix, HA particle and CS combined closely. Composite membrane has good mechanical properties, MC3T3-E1 cells can adhere and grow well on the surface of composite membrane. The cell proliferation results show that composite membrane under the preparation conditions: calcination temperature 1000 ℃, the milling ball propotion 4∶4∶2, milling rate 230 r·min-1, milling time 2.5 h, HA∶CS =5∶5 (mass ratio) is the most beneficial for cell proliferation.
Hdroxyapatite(HA) was prepared using porcine trabecular bone after being degreased, deproteined, calcined and ball milling. HA/chitosan(CS) composite membranes were prepared by blending and drying HA and CS solution. The effect of milling conditions on the HA particle size was inspected by the orthogonal design. MC3T3-E1 preosteoblasts were seeded on the surface of the composite membranes, and then cell morphology and proliferation were detected by SEM and 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl tetrazolium bromide(MTT) methods. The results show that the prepared HA is relatively homogeneous micrometer-scale spherical particle with median diameter(D50) in 1.21~1.67 μm range, and HA particles are distributed uniformly in the matrix, HA particle and CS combined closely. Composite membrane has good mechanical properties, MC3T3-E1 cells can adhere and grow well on the surface of composite membrane. The cell proliferation results show that composite membrane under the preparation conditions: calcination temperature 1000 ℃, the milling ball propotion 4∶4∶2, milling rate 230 r·min-1, milling time 2.5 h, HA∶CS =5∶5 (mass ratio) is the most beneficial for cell proliferation.
2013, 30(1): 112-118.
Abstract:
The carboxylic waterborne polyurethane was synthesized with isophorone diisocyanate(IPDI), polyether glycol(N210) and 2,2-bis(hydroxymethyl) propionic acid(DMPA) as the major materials, and terminated by C=C from β-hydroxyethyl methacrylate(HEMA). SiO2-PMMA composite microspheres were prepared with different types of initiators by double in situ miniemulsion polymerization, in which the waterborne polyurethane was used as a polymerizable surfactant. The prepared products were characterized by TEM, FTIR and TGA, respectively. The results indicate that morphologies of the SiO2-PMMA composite microsphere prepared by waterborne polyurethane surfactant(PUS) are different from those prepared by conventional micromolecule surfactants. The type of initiators affects significantly on the morphologies of the SiO2-PMMA.
The carboxylic waterborne polyurethane was synthesized with isophorone diisocyanate(IPDI), polyether glycol(N210) and 2,2-bis(hydroxymethyl) propionic acid(DMPA) as the major materials, and terminated by C=C from β-hydroxyethyl methacrylate(HEMA). SiO2-PMMA composite microspheres were prepared with different types of initiators by double in situ miniemulsion polymerization, in which the waterborne polyurethane was used as a polymerizable surfactant. The prepared products were characterized by TEM, FTIR and TGA, respectively. The results indicate that morphologies of the SiO2-PMMA composite microsphere prepared by waterborne polyurethane surfactant(PUS) are different from those prepared by conventional micromolecule surfactants. The type of initiators affects significantly on the morphologies of the SiO2-PMMA.
2013, 30(1): 119-124.
Abstract:
The vitrified bonds with different molar ratios about MgO∶Li2O( M ) and cBN wheels were prepared at the base of ZnO-Na2O-SiO2-Al2O3-B2O3 ceramic system. X-diffraction analysis, SEM and thermal expansion coefficient tests were used to study the influence of M and sintering temperature on the properties of vitrified bonds and cBN wheels.The results show that with the M value increasing, the soften temperature, refractoriness and chemical stability of the bond increase, while the thermal expansion coefficient increases and then decreases. When the M value is 0.67, the increasing of the temperature restrains the quartz crystal separating. Meanwhile, the content of Mg(Zn)Al2O4 crystalline phase increases, and the size decreases at first and then increases. Moreover, when the temperature reaches 870 ℃, the grain size is the minimum about 2 μm, and the most compact microstructure is obtained. At the same time, the bending strength of the bond reaches the maximum value of 136.28 MPa. As the sintering temperature increasing, the porosity and water absorption of cBN wheel decrease at the beginning and then increase. However, its bulk density, hardness, bending strength, abrasion and grinding efficiency exhibit contrary trend. When the temperature is 890 ℃, the abrasion and grinding efficiency reache the maximum values of 98.72% and 1.3675 g·min-1 respectively.
The vitrified bonds with different molar ratios about MgO∶Li2O( M ) and cBN wheels were prepared at the base of ZnO-Na2O-SiO2-Al2O3-B2O3 ceramic system. X-diffraction analysis, SEM and thermal expansion coefficient tests were used to study the influence of M and sintering temperature on the properties of vitrified bonds and cBN wheels.The results show that with the M value increasing, the soften temperature, refractoriness and chemical stability of the bond increase, while the thermal expansion coefficient increases and then decreases. When the M value is 0.67, the increasing of the temperature restrains the quartz crystal separating. Meanwhile, the content of Mg(Zn)Al2O4 crystalline phase increases, and the size decreases at first and then increases. Moreover, when the temperature reaches 870 ℃, the grain size is the minimum about 2 μm, and the most compact microstructure is obtained. At the same time, the bending strength of the bond reaches the maximum value of 136.28 MPa. As the sintering temperature increasing, the porosity and water absorption of cBN wheel decrease at the beginning and then increase. However, its bulk density, hardness, bending strength, abrasion and grinding efficiency exhibit contrary trend. When the temperature is 890 ℃, the abrasion and grinding efficiency reache the maximum values of 98.72% and 1.3675 g·min-1 respectively.
2013, 30(1): 125-129.
Abstract:
Porous BN/Si3N4 ceramics with high strength and low dielectric constant were prepared by tert-butyl alcohol (TBA)-based gel-casting method and pressureless sintering process at 1750 ℃ for 1.5 h in flowing nitrogen. At a fixed solid loading (15%, volume fraction) of the initial slurry, the influence of boron nitride content on the porosity, phase and microstructure was discussed. The relationships among flexural strength, dielectric constant and microstructure were also discussed. The results show that porous BN/Si3N4 composite ceramics with high porosity ranging from 55.1% to 66.2% are prepared by adjusting the content of BN. Dielectric constant of porous BN/Si3N4 composite ceramics is between 3.39 and 2.25, which shows a decreased trend with the content of BN increasing. Flexural strength decreases with BN content increasing, flexural strength reaches the maximum value (74.8±4.25) MPa, when the mass fraction of BN is 2.5%.
Porous BN/Si3N4 ceramics with high strength and low dielectric constant were prepared by tert-butyl alcohol (TBA)-based gel-casting method and pressureless sintering process at 1750 ℃ for 1.5 h in flowing nitrogen. At a fixed solid loading (15%, volume fraction) of the initial slurry, the influence of boron nitride content on the porosity, phase and microstructure was discussed. The relationships among flexural strength, dielectric constant and microstructure were also discussed. The results show that porous BN/Si3N4 composite ceramics with high porosity ranging from 55.1% to 66.2% are prepared by adjusting the content of BN. Dielectric constant of porous BN/Si3N4 composite ceramics is between 3.39 and 2.25, which shows a decreased trend with the content of BN increasing. Flexural strength decreases with BN content increasing, flexural strength reaches the maximum value (74.8±4.25) MPa, when the mass fraction of BN is 2.5%.
2013, 30(1): 130-134.
Abstract:
The superparamagnetic nano-Fe3O4 was prepared by coprecipitation method. Then wave-absorbing composite material Fe3O4-SrFe12O19 was prepared. The crystal phase, microstructure, magnetic property and wave-absorbing property of the sample were characterized by XRD, TEM, VSM and PNA. The results show that, when the mass ratio of Fe3O4 to SrFe12O19 is 1∶0.3, the saturation magnetization, coercive field and residual magnetization of Fe3O4-SrFe12O19 are 11.1 emu·g-1, 0.86 Oe and 0.08 emu·g-1 respectively. It has the best wave-absorbing property, which of the maximum absorption can reach-17.7 dB and the-5 dB bandwidth is 1.3 GHz. Compared with Fe3O4 and SrFe12O19, the maximum absorption respectively increases by 247% and 185%, the frequency band widens 1.12 GHz and 0.40 GHz respectively.
The superparamagnetic nano-Fe3O4 was prepared by coprecipitation method. Then wave-absorbing composite material Fe3O4-SrFe12O19 was prepared. The crystal phase, microstructure, magnetic property and wave-absorbing property of the sample were characterized by XRD, TEM, VSM and PNA. The results show that, when the mass ratio of Fe3O4 to SrFe12O19 is 1∶0.3, the saturation magnetization, coercive field and residual magnetization of Fe3O4-SrFe12O19 are 11.1 emu·g-1, 0.86 Oe and 0.08 emu·g-1 respectively. It has the best wave-absorbing property, which of the maximum absorption can reach-17.7 dB and the-5 dB bandwidth is 1.3 GHz. Compared with Fe3O4 and SrFe12O19, the maximum absorption respectively increases by 247% and 185%, the frequency band widens 1.12 GHz and 0.40 GHz respectively.
2013, 30(1): 135-140.
Abstract:
The nano-LiFePO4/C composites were prepared by means of wet grinding and following high temperature solid-state reaction using water-soluble phenolic resin, Li2CO3, and nano-FePO4 as precursors. The composites were characterized by XRD, SEM, TEM, TG and Raman spectroscopy and their electrochemical performances were studied. The results show that the as-prepared LiFePO4/C nano-composites are spherical-like particles which consist of a carbon shell with a thickness of about 5 nm and the LiFePO4 core, and show excellent high-rate performance and cycling performance as the cathode for lithium ion batteries. The initial discharge capacities at rates of 0.2 C (1 C=170 mAh·g-1), 0.5 C、1 C、2 C、5 C and 10 C are 151 mAh·g-1, 150 mAh·g-1, 146 mAh·g-1, 142 mAh·g-1, 132 mAh·g-1 and 119 mAh·g-1, respectively. The material still shows initial discharge capacity of 105 mAh·g-1 even at 20 C and its capacity doesn’t decay after 50 cycles.
The nano-LiFePO4/C composites were prepared by means of wet grinding and following high temperature solid-state reaction using water-soluble phenolic resin, Li2CO3, and nano-FePO4 as precursors. The composites were characterized by XRD, SEM, TEM, TG and Raman spectroscopy and their electrochemical performances were studied. The results show that the as-prepared LiFePO4/C nano-composites are spherical-like particles which consist of a carbon shell with a thickness of about 5 nm and the LiFePO4 core, and show excellent high-rate performance and cycling performance as the cathode for lithium ion batteries. The initial discharge capacities at rates of 0.2 C (1 C=170 mAh·g-1), 0.5 C、1 C、2 C、5 C and 10 C are 151 mAh·g-1, 150 mAh·g-1, 146 mAh·g-1, 142 mAh·g-1, 132 mAh·g-1 and 119 mAh·g-1, respectively. The material still shows initial discharge capacity of 105 mAh·g-1 even at 20 C and its capacity doesn’t decay after 50 cycles.
2013, 30(1): 141-146.
Abstract:
NiTi metal matrix in-situ composite was prepared by directional solidification in-situ method, adding a small amount of Al, Nb, Hf. The directionally solidified bars were homogenized at 950 ℃ for 12 h, 50 h and 100 h, respectively, and the tensile strength was tested at room temperature. The results indicate that a vimineous, acicular cellular structure that grow along the [001] orientation is achieved after the directional solidification. The β-Nb and Ti2Ni reinforcement particles distribute along the [001] orientation in the intercellular regions. The cellular structure becomes coarser with the increase of the homogenizing time, and the two reinforcement particles are more dispersed and distributed more homogeneously. After heat treatment, the highest tensile strength reaches to 1972 MPa, exceeding that of the 4130 and 8640 ultrahigh-strength steel, being almost equal to 4140 and 4340 ultrahigh-strength steel, and reaching or surpassing many kinds of ultrahigh-strength titanium alloy.
NiTi metal matrix in-situ composite was prepared by directional solidification in-situ method, adding a small amount of Al, Nb, Hf. The directionally solidified bars were homogenized at 950 ℃ for 12 h, 50 h and 100 h, respectively, and the tensile strength was tested at room temperature. The results indicate that a vimineous, acicular cellular structure that grow along the [001] orientation is achieved after the directional solidification. The β-Nb and Ti2Ni reinforcement particles distribute along the [001] orientation in the intercellular regions. The cellular structure becomes coarser with the increase of the homogenizing time, and the two reinforcement particles are more dispersed and distributed more homogeneously. After heat treatment, the highest tensile strength reaches to 1972 MPa, exceeding that of the 4130 and 8640 ultrahigh-strength steel, being almost equal to 4140 and 4340 ultrahigh-strength steel, and reaching or surpassing many kinds of ultrahigh-strength titanium alloy.
2013, 30(1): 147-154.
Abstract:
Composite solders were prepared through mechanical dispersing and the effects of nano-sized Ag reinforced particulates on In-3Ag solder matrix and interfacial IMC(intermetallic compound) layer after multiple reflows were studied. The microstructures of the solder matrix and IMC layer were investigated using SEM, HRTEM, Energy Dispersive Spectrometer(EDS) and Electron probe Micro-Analysis(EPMA). The results indicate that Ag nanoparticulates nucleate grains and the fine AgIn2 particles in composite solder matrix do not coarsen after multiple reflows. Due to the diffusion path blocking and surface absorption effect, the growth of the interfacial IMC layer is significantly suppressed by Ag nanoparticulates addition. The solder joint with 0.5%(mass fraction) Ag particulates added shows the best mechanical properties. Adding 1% Ag particulates, the particles tend to agglomerate leading to the formation of spherical particles at the interface, which decreases the mechanical properties of solder joint.
Composite solders were prepared through mechanical dispersing and the effects of nano-sized Ag reinforced particulates on In-3Ag solder matrix and interfacial IMC(intermetallic compound) layer after multiple reflows were studied. The microstructures of the solder matrix and IMC layer were investigated using SEM, HRTEM, Energy Dispersive Spectrometer(EDS) and Electron probe Micro-Analysis(EPMA). The results indicate that Ag nanoparticulates nucleate grains and the fine AgIn2 particles in composite solder matrix do not coarsen after multiple reflows. Due to the diffusion path blocking and surface absorption effect, the growth of the interfacial IMC layer is significantly suppressed by Ag nanoparticulates addition. The solder joint with 0.5%(mass fraction) Ag particulates added shows the best mechanical properties. Adding 1% Ag particulates, the particles tend to agglomerate leading to the formation of spherical particles at the interface, which decreases the mechanical properties of solder joint.
2013, 30(1): 155-164.
Abstract:
The Al-xSi-yMg composites containing various contents of Si and Mg were fabricated by centrifugal casting. The macrostructures and microstructures, and wear resistance of all the castings were examined. The relation of the Si/Mg contents and the formation of primary particles was analyzed. It shows that except the Al-15Si-5Mg, a reinforcement layer containing primary Si or Mg2Si particles in the inner layer, and the un-reinforcement layer having no particles in the outer layer of the other castings are formed. The castings fabricated with various compositions have different kinds of primary particles, different relative thicknesses of reinforcement layer(k), and different particle volume fractions. The wear resistance of the Al-xSi-yMg composites is improved with the increasing particle volume fraction. The calculation results indicate that the primary Si and Mg2Si are formed on the condition of x≥12.8＋0.49y, y≥5(15≤x≤30, y≤8); only primary Mg2Si particles are formed on the condition of x<12.8＋0.49y, y≥5; only primary Si particles are formed on the condition of x≥12.8＋0.49y, y<5; and no particle is formed on the condition of x<12.8＋0.49y, y<5.
The Al-xSi-yMg composites containing various contents of Si and Mg were fabricated by centrifugal casting. The macrostructures and microstructures, and wear resistance of all the castings were examined. The relation of the Si/Mg contents and the formation of primary particles was analyzed. It shows that except the Al-15Si-5Mg, a reinforcement layer containing primary Si or Mg2Si particles in the inner layer, and the un-reinforcement layer having no particles in the outer layer of the other castings are formed. The castings fabricated with various compositions have different kinds of primary particles, different relative thicknesses of reinforcement layer(k), and different particle volume fractions. The wear resistance of the Al-xSi-yMg composites is improved with the increasing particle volume fraction. The calculation results indicate that the primary Si and Mg2Si are formed on the condition of x≥12.8＋0.49y, y≥5(15≤x≤30, y≤8); only primary Mg2Si particles are formed on the condition of x<12.8＋0.49y, y≥5; only primary Si particles are formed on the condition of x≥12.8＋0.49y, y<5; and no particle is formed on the condition of x<12.8＋0.49y, y<5.
2013, 30(1): 165-171.
Abstract:
Based on the fundamental mechanical tests of 2D woven C/SiC composite material, a macroscopic orthotropic non-linear damage constitutive model was established. In this model, the detectable strains were chosen as variables, and functions in simple form were used to demonstrate the stress-strain relationship of the material under damage evolution caused by uniaxial tension and shear loads, and besides the rule of stiffness change in unloading state respectively. Meanwhile, the unilateral effect and damage-deactivation behavior were also considered. The constitutive model was implemented into UMAT in ABAQUS finite element software, and it could describe the material’s non-linear and linear property of stress-strain relationship in loading and unloading state respectively, and also its load history. Through modeling the open hole plates in tension, strain distribution besides the hole agrees well with the experiment result, which proves the availability of the proposed constitutive model.
Based on the fundamental mechanical tests of 2D woven C/SiC composite material, a macroscopic orthotropic non-linear damage constitutive model was established. In this model, the detectable strains were chosen as variables, and functions in simple form were used to demonstrate the stress-strain relationship of the material under damage evolution caused by uniaxial tension and shear loads, and besides the rule of stiffness change in unloading state respectively. Meanwhile, the unilateral effect and damage-deactivation behavior were also considered. The constitutive model was implemented into UMAT in ABAQUS finite element software, and it could describe the material’s non-linear and linear property of stress-strain relationship in loading and unloading state respectively, and also its load history. Through modeling the open hole plates in tension, strain distribution besides the hole agrees well with the experiment result, which proves the availability of the proposed constitutive model.
2013, 30(1): 172-179.
Abstract:
An approach to predict the elastic modulus of unidirectional C/SiC composites at 400~900 ℃ oxidation environments was developed. The approach combined the mass loss rate model with the mixed rule formulation. The elastic modulus of C/SiC composites at 400~700 ℃ and 700~900 ℃ air environment which represents two different kinds of oxidation model was predicted. The influence of oxidation temperature, oxidation time and fiber volume fraction on composites elastic modulus was analyzed. The experiments of C/SiC composites at 650 ℃ and 800 ℃ air environment with non-stress have been performed, the relationship between mass loss rate and oxidation time has been established, and the tensile stress-strain curves have been obtained. Besides, the theoretical results have been compared with the experimental data. It is found that the predicted results agree well with the experimental ones. And it is verified that the approach developed in this paper can predict the elastic modulus of ceramic matrix composites under non-stress oxidation efficiently.
An approach to predict the elastic modulus of unidirectional C/SiC composites at 400~900 ℃ oxidation environments was developed. The approach combined the mass loss rate model with the mixed rule formulation. The elastic modulus of C/SiC composites at 400~700 ℃ and 700~900 ℃ air environment which represents two different kinds of oxidation model was predicted. The influence of oxidation temperature, oxidation time and fiber volume fraction on composites elastic modulus was analyzed. The experiments of C/SiC composites at 650 ℃ and 800 ℃ air environment with non-stress have been performed, the relationship between mass loss rate and oxidation time has been established, and the tensile stress-strain curves have been obtained. Besides, the theoretical results have been compared with the experimental data. It is found that the predicted results agree well with the experimental ones. And it is verified that the approach developed in this paper can predict the elastic modulus of ceramic matrix composites under non-stress oxidation efficiently.
2013, 30(1): 180-186.
Abstract:
The same size specimens strengthened by FRP(CFRP/GFRP) sheets with different wrapping modes were studied experimentally by quasi-static test system for the purpose of investigating the mechanical property of concrete filled GFRP-steel tube structure under combined seismic loading and comparing it with concrete filled CFRP steel tube. Combined loads including axial pressure and bending were applied to simulate the complex seismic loadings. The test results indicate that the strengthening of FRP(CFRP/GFRP) is potential and effective for significant improvements in dynamic bending resistance of the structures. Concrete filled GFRP-steel tube equips higher ductility, comparing with concrete filled steel tube, energy dissipation coefficient of the components with circumferential, longitudinal and bi-directional GFRP improve 2.0%, 7.0% and 12.7% respectively, while components with circumferential, longitudinal and bi-directional CFRP get improvement of 2.0%, 5.8% and 6.7% respectively.
The same size specimens strengthened by FRP(CFRP/GFRP) sheets with different wrapping modes were studied experimentally by quasi-static test system for the purpose of investigating the mechanical property of concrete filled GFRP-steel tube structure under combined seismic loading and comparing it with concrete filled CFRP steel tube. Combined loads including axial pressure and bending were applied to simulate the complex seismic loadings. The test results indicate that the strengthening of FRP(CFRP/GFRP) is potential and effective for significant improvements in dynamic bending resistance of the structures. Concrete filled GFRP-steel tube equips higher ductility, comparing with concrete filled steel tube, energy dissipation coefficient of the components with circumferential, longitudinal and bi-directional GFRP improve 2.0%, 7.0% and 12.7% respectively, while components with circumferential, longitudinal and bi-directional CFRP get improvement of 2.0%, 5.8% and 6.7% respectively.
2013, 30(1): 187-193.
Abstract:
Through the experiments on the specimens after being heated to certain temperatures, the exterior appearance, thermal spalling, mass loss and mechanical properties of high strength concrete(HSC) and polypropylene fiber-steel fiber reinforced high strength concrete(hybrid fiber/HSC) were studied. The results show that the HSC specimen spalls after being exposed to 600 ℃, while hybrid fiber/HSC specimen does not spall until being exposed to 800 ℃, which results from the action of hybrid fibers. The mass loss of hybrid fiber/HSC increases with the increasing of temperature. The compressive strength and modulus of rupture of HFRC decrease with the increasing of temperature, especially after being heated to the temperature of 400 ℃. For the same exposure temperature of specimens, the hybrid fibers improve the HSC strength. Based on the statistical analysis of the experimental results, the relational expressions of mass loss, compressive strength, and modulus of rupture with temperature were established, respectively.
Through the experiments on the specimens after being heated to certain temperatures, the exterior appearance, thermal spalling, mass loss and mechanical properties of high strength concrete(HSC) and polypropylene fiber-steel fiber reinforced high strength concrete(hybrid fiber/HSC) were studied. The results show that the HSC specimen spalls after being exposed to 600 ℃, while hybrid fiber/HSC specimen does not spall until being exposed to 800 ℃, which results from the action of hybrid fibers. The mass loss of hybrid fiber/HSC increases with the increasing of temperature. The compressive strength and modulus of rupture of HFRC decrease with the increasing of temperature, especially after being heated to the temperature of 400 ℃. For the same exposure temperature of specimens, the hybrid fibers improve the HSC strength. Based on the statistical analysis of the experimental results, the relational expressions of mass loss, compressive strength, and modulus of rupture with temperature were established, respectively.
2013, 30(1): 194-200.
Abstract:
Based on the random field theory, the random field was discreted by local average method with the material properties of fibers and matrix and the fiber volume fraction as variables. The Monte-Carlo simulation of the critical buckling load discrepancy for composite laminates was performed combining MATLAB and PDS module of ANSYS, and the influences of the discrepancy features of various random field variables, the correlation distance, the symmetry characteristic as well as the boundary condition were analyzed on the discrepancy of the critical buckling load. The results show that various random field variables have different influences on the critical buckling load discrepancy for composite laminates, among which the fiber volume fraction being the strongest factor and fiber and matrix properties being the next. The coefficient of variance(COV) for the critical buckling load has size effect and it reduces individually with the plate size increases. Reducing the correlation length can effectively incline the discrepancy of critical buckling load. The COV for the critical buckling load for symmetric laminates is slightly bigger than that for antisymmetric laminates. The COV for simply-supported laminates is generally less than that for two corresponding sides fixed-supported laminates.
Based on the random field theory, the random field was discreted by local average method with the material properties of fibers and matrix and the fiber volume fraction as variables. The Monte-Carlo simulation of the critical buckling load discrepancy for composite laminates was performed combining MATLAB and PDS module of ANSYS, and the influences of the discrepancy features of various random field variables, the correlation distance, the symmetry characteristic as well as the boundary condition were analyzed on the discrepancy of the critical buckling load. The results show that various random field variables have different influences on the critical buckling load discrepancy for composite laminates, among which the fiber volume fraction being the strongest factor and fiber and matrix properties being the next. The coefficient of variance(COV) for the critical buckling load has size effect and it reduces individually with the plate size increases. Reducing the correlation length can effectively incline the discrepancy of critical buckling load. The COV for the critical buckling load for symmetric laminates is slightly bigger than that for antisymmetric laminates. The COV for simply-supported laminates is generally less than that for two corresponding sides fixed-supported laminates.
Prediction for failure envelopes of composite laminates based on refined generalized method of cells
2013, 30(1): 201-209.
Abstract:
The generalized method of cells is often used in micromechanical analysis of composites. Large number of unknowns and lower computational efficiency are the shortcomings of original generalized method of cells. Here, the original method is improved by refined generalized method of cells of which unknowns are tractions of subcells in this paper. The micro-components such as fiber, matrix and interface can be modeled fully by the presented method. The macro-micro multi-scale mechanical analysis of unidirectional composite laminates can be achieved by the presented model. A prediction method combined the classical lamination theory and failure criteria of micro-components is presented. A quantitative assessment of failure envelopes is developed to evaluate the performance of failure criteria. The higher computational accuracy and universality have been demonstrated in comparison with other methods and experimental data provided by World-Wide Failure Exercise.
The generalized method of cells is often used in micromechanical analysis of composites. Large number of unknowns and lower computational efficiency are the shortcomings of original generalized method of cells. Here, the original method is improved by refined generalized method of cells of which unknowns are tractions of subcells in this paper. The micro-components such as fiber, matrix and interface can be modeled fully by the presented method. The macro-micro multi-scale mechanical analysis of unidirectional composite laminates can be achieved by the presented model. A prediction method combined the classical lamination theory and failure criteria of micro-components is presented. A quantitative assessment of failure envelopes is developed to evaluate the performance of failure criteria. The higher computational accuracy and universality have been demonstrated in comparison with other methods and experimental data provided by World-Wide Failure Exercise.
2013, 30(1): 210-217.
Abstract:
Test and finite element analysis were carried out to characterize the pin-load distribution of multiple-bolted metal-to-composite fastener joints. The specimens are the single-lap and double-lap joints with an array of three bolts and subjected to tension loading. The surface strains at certain cross-sections of the metallic plates were measured using the strain gage technique. The pin-load fractions of the multiple bolts were then estimated indirectly using the measured strains. Two-and-three dimensional finite element models were also constructed to calculate those strains and the pin-loads. The calculated strains agree well with the measurement, whereas significant difference is observed between the pin-load fraction results of both methods. The investigation reveals that the way to determine the pin-load distributions ratios according to the plate surface strains is not able to account for the built-in effects of additional bending moment concurrently with the tension loading. The authors believe that the numerical calculation to estimate the pin-load fractions, based on finite element modeling which has been validated by the surface strain measurement, is a technically feasible approach. The two-dimensional models formed by beam and shell elements are of satisfied accuracy to determine the pin-load distributions.
Test and finite element analysis were carried out to characterize the pin-load distribution of multiple-bolted metal-to-composite fastener joints. The specimens are the single-lap and double-lap joints with an array of three bolts and subjected to tension loading. The surface strains at certain cross-sections of the metallic plates were measured using the strain gage technique. The pin-load fractions of the multiple bolts were then estimated indirectly using the measured strains. Two-and-three dimensional finite element models were also constructed to calculate those strains and the pin-loads. The calculated strains agree well with the measurement, whereas significant difference is observed between the pin-load fraction results of both methods. The investigation reveals that the way to determine the pin-load distributions ratios according to the plate surface strains is not able to account for the built-in effects of additional bending moment concurrently with the tension loading. The authors believe that the numerical calculation to estimate the pin-load fractions, based on finite element modeling which has been validated by the surface strain measurement, is a technically feasible approach. The two-dimensional models formed by beam and shell elements are of satisfied accuracy to determine the pin-load distributions.
2013, 30(1): 218-222.
Abstract:
The viscoelastic behavior of glass microsphere reinforced rigid polyurethane syntactic foams(glass microsphere/RPUF) under different temperatures and humidities was investigated. The experimental results show that temperature and humidity have an obvious effect on viscoelastic behavior of glass microsphere/RPUF. With increasing the relative humidity, the loss factors value increases while the storage modulus decreases. Under the same temperature, the creep compliance increases as humidity increasing. Using the time-humidity super-position principle, each master curve can be shifted to collapse into the reference master curve by introducing shift factors for humidity, and the master curves of creep compliance at reference temperature(60 ℃) and humidity(50%RH) are put forward.
The viscoelastic behavior of glass microsphere reinforced rigid polyurethane syntactic foams(glass microsphere/RPUF) under different temperatures and humidities was investigated. The experimental results show that temperature and humidity have an obvious effect on viscoelastic behavior of glass microsphere/RPUF. With increasing the relative humidity, the loss factors value increases while the storage modulus decreases. Under the same temperature, the creep compliance increases as humidity increasing. Using the time-humidity super-position principle, each master curve can be shifted to collapse into the reference master curve by introducing shift factors for humidity, and the master curves of creep compliance at reference temperature(60 ℃) and humidity(50%RH) are put forward.
2013, 30(1): 223-229.
Abstract:
Experimental study on tensile behavior of hybrid plain woven fabric laminate repaired by scarfing method was conducted. The results show under the same initial damage dimension, the specimen with scarf ratio of 1∶30 has the highest tensile strength which can reach 97.8% of the intact laminate strength and the failure mode changes upon the scarf ratio. Besides, when the scarf ratio is fixed, extending the dimension of initial damage can decrease the tensile strength of specimen. Based on test results, a finite element model is adopted to research tensile strength and progressive damage process of repaired specimen. The calculated strength and failure mode are in good agreement with test results.
Experimental study on tensile behavior of hybrid plain woven fabric laminate repaired by scarfing method was conducted. The results show under the same initial damage dimension, the specimen with scarf ratio of 1∶30 has the highest tensile strength which can reach 97.8% of the intact laminate strength and the failure mode changes upon the scarf ratio. Besides, when the scarf ratio is fixed, extending the dimension of initial damage can decrease the tensile strength of specimen. Based on test results, a finite element model is adopted to research tensile strength and progressive damage process of repaired specimen. The calculated strength and failure mode are in good agreement with test results.
2013, 30(1): 230-235.
Abstract:
Multi-scale approach has been developed for evaluating the damage resistance of sandwich structures composed of stitched foam-core and woven face sheets subjected to low-velocity impact. Simplified model of stitched foam-core was established. The classical theory of homogenization was adapted and used by treating the foam strengthened by the glass fiber resin column as orthotropic equivalent core material which elastic properties depended on each component and their volume participation. And finite element model of sandwich structure was established. Interface elements were added between panels and foam-core to simulate the initiation and propagation of adhesive disbond damage. Impact behaviors of the stitched foam-core sandwich composites were calculated with GENOA progressive failure analysis commercial software and compared with those in experimental. Good agreements between numerical and experimental were found, which demonstrates the validity of the multi-scale progressive failure analysis method. The analysis shows that the damage in upper panel and delamination between panels and foam-core reduce effectively when the sandwich composites stitched. However, stitches brought initial damage to the structure; higher stitch density increased the foam-core stiffness, as a result, reduced energy absorption capability of sandwich structures.
Multi-scale approach has been developed for evaluating the damage resistance of sandwich structures composed of stitched foam-core and woven face sheets subjected to low-velocity impact. Simplified model of stitched foam-core was established. The classical theory of homogenization was adapted and used by treating the foam strengthened by the glass fiber resin column as orthotropic equivalent core material which elastic properties depended on each component and their volume participation. And finite element model of sandwich structure was established. Interface elements were added between panels and foam-core to simulate the initiation and propagation of adhesive disbond damage. Impact behaviors of the stitched foam-core sandwich composites were calculated with GENOA progressive failure analysis commercial software and compared with those in experimental. Good agreements between numerical and experimental were found, which demonstrates the validity of the multi-scale progressive failure analysis method. The analysis shows that the damage in upper panel and delamination between panels and foam-core reduce effectively when the sandwich composites stitched. However, stitches brought initial damage to the structure; higher stitch density increased the foam-core stiffness, as a result, reduced energy absorption capability of sandwich structures.
2013, 30(1): 236-243.
Abstract:
An algorithm for the automatic generation of 2D representative volume element (RVE) of nano-particle reinforced composites is developed by using Monte-Carlo method. The bilinear cohesive zone model was adopted to evaluate the weak interface traction and separation distance. The macroscopic mechanical behavior of nano TiO2 particle reinforced epoxy composite was simulated by using ABAQUS software, and the validity of model is demonstrated by comparison of test results and simulation results. The effects of TiO2 particle mass fraction and particle size on composite macroscopic effective modulus, and the progressive damage process of composites, were discussed under weak interface condition. The results show that the Young’s modulus and fracture elongation of composite increase gradually with the increasing of mass fraction of TiO2 particle, while the yield strength decreases. Under the same mass fraction of particulate, the total length of interfacial unit between particulates and matrix, and the fracture elongation of composite, were gradually reduced with the increasing of TiO2 particle size.
An algorithm for the automatic generation of 2D representative volume element (RVE) of nano-particle reinforced composites is developed by using Monte-Carlo method. The bilinear cohesive zone model was adopted to evaluate the weak interface traction and separation distance. The macroscopic mechanical behavior of nano TiO2 particle reinforced epoxy composite was simulated by using ABAQUS software, and the validity of model is demonstrated by comparison of test results and simulation results. The effects of TiO2 particle mass fraction and particle size on composite macroscopic effective modulus, and the progressive damage process of composites, were discussed under weak interface condition. The results show that the Young’s modulus and fracture elongation of composite increase gradually with the increasing of mass fraction of TiO2 particle, while the yield strength decreases. Under the same mass fraction of particulate, the total length of interfacial unit between particulates and matrix, and the fracture elongation of composite, were gradually reduced with the increasing of TiO2 particle size.
2013, 30(1): 244-251.
Abstract:
The micro-mechanics of failure(MMF) is a micromechanics-based failure criterion for composites, which can be applied to design composite accurately and reliably. The strength and mechanical properties of unidirectional laminate of UTS50/E51 were measured by the static tensile loading and compressive loading tests as well as three points bending test. The micro-mechanics model was built to obtain the mechanical and residual thermal stress amplification factors for the key points in the fiber and matrix. The MMF parameters were characterized by using the stress amplification factors and the measured strengths of unidirectional laminate. The failure envelopes were made based on the MMF theory, and compared with that based on Tsai-Wu failure criterion. The carbon fiber reinforced plastic UTS50/E51 is used to demonstrate the application of MMF theory.
The micro-mechanics of failure(MMF) is a micromechanics-based failure criterion for composites, which can be applied to design composite accurately and reliably. The strength and mechanical properties of unidirectional laminate of UTS50/E51 were measured by the static tensile loading and compressive loading tests as well as three points bending test. The micro-mechanics model was built to obtain the mechanical and residual thermal stress amplification factors for the key points in the fiber and matrix. The MMF parameters were characterized by using the stress amplification factors and the measured strengths of unidirectional laminate. The failure envelopes were made based on the MMF theory, and compared with that based on Tsai-Wu failure criterion. The carbon fiber reinforced plastic UTS50/E51 is used to demonstrate the application of MMF theory.
2013, 30(1): 252-256.
Abstract:
Starting from the indentation damage mechanics, a numerical model of laminated composites subjected to quasi-static indentation was established on the basis of progressive damage mechanics. The different kinds of composite damages and their progressive processes were quantitatively analyzed. Furthermore, under the condition of same laminates thickness, the effect of single ply thickness on the indentation damage was discussed. The results show that the increase of single ply thickness can enlarge the matrix damage and the delamination degree, whereas it can restrain the development of fiber fracture.
Starting from the indentation damage mechanics, a numerical model of laminated composites subjected to quasi-static indentation was established on the basis of progressive damage mechanics. The different kinds of composite damages and their progressive processes were quantitatively analyzed. Furthermore, under the condition of same laminates thickness, the effect of single ply thickness on the indentation damage was discussed. The results show that the increase of single ply thickness can enlarge the matrix damage and the delamination degree, whereas it can restrain the development of fiber fracture.
2013, 30(1): 257-262.
Abstract:
The micro-structure of elytra was observed by SEM. The nano-mechanical property of elytra was tested and analyzed with a nano-indentation machine. SEM images indicate that the elytra of Allomyrina dichotoma are lightweight biological composites with a hollow structure like as arch shape. The duty ratio of cross-section is 26.36%. The elytra are composed of epicuticle(EPI) and exocuticle(EXO). The exocuticle consists of 11~12 fiber layers, laying in quadrature manner with a ply angle 45? plus lots of fibrils braiding across, which form a laminated plate structure. The hardness, modulus and contact stiffness of epicuticle in elytra acquired with nano-indentation testing are (0.28?0.13) GPa,(5.62?1.21) GPa and (1.67?0.14)?104 N/m, respectively. The nano-mechanical properties of elytra present a topological distribution characteristic, namely is a gradually incremental tendency from the cephalosome zone to the empennage zone. The results may provide biological template and biomimetic theory to design a new lightweight bionic structure inspired by the elytra in beetle Allomyrina dichotoma for the further researches.
The micro-structure of elytra was observed by SEM. The nano-mechanical property of elytra was tested and analyzed with a nano-indentation machine. SEM images indicate that the elytra of Allomyrina dichotoma are lightweight biological composites with a hollow structure like as arch shape. The duty ratio of cross-section is 26.36%. The elytra are composed of epicuticle(EPI) and exocuticle(EXO). The exocuticle consists of 11~12 fiber layers, laying in quadrature manner with a ply angle 45? plus lots of fibrils braiding across, which form a laminated plate structure. The hardness, modulus and contact stiffness of epicuticle in elytra acquired with nano-indentation testing are (0.28?0.13) GPa,(5.62?1.21) GPa and (1.67?0.14)?104 N/m, respectively. The nano-mechanical properties of elytra present a topological distribution characteristic, namely is a gradually incremental tendency from the cephalosome zone to the empennage zone. The results may provide biological template and biomimetic theory to design a new lightweight bionic structure inspired by the elytra in beetle Allomyrina dichotoma for the further researches.
