2008 Vol. 25, No. 4
2008, 25(4): 1-6.
Abstract:
Calcium sulfate whiskers were used to modify the polyurethane-epoxy resin，and the influence of the pretreatment condition，the length and content of the whiskers on the adhesive properties of the polyurethane-epoxy resins was investigated. The modifying mechanism of calcium sulfate whiskers to the polyurethane-epoxy resin was discussed，too. The adhesive properties of the modified polyurethane-epoxy resin to aluminum alloy LY12 were improved when the shorter whisker pretreated with 1% KH-560 was added into the resins，whose RT peel strength rose by 27%，the 100℃ and -70℃ lap shear strength of the modified polyurethane-epoxy resins rose by 39% and 10%，respectively. The adhesive properties of the modified resins and the SEM images show that the modifying mechanism of the whiskers to the polyurethane-epoxy resin was crack deflexion.
Calcium sulfate whiskers were used to modify the polyurethane-epoxy resin，and the influence of the pretreatment condition，the length and content of the whiskers on the adhesive properties of the polyurethane-epoxy resins was investigated. The modifying mechanism of calcium sulfate whiskers to the polyurethane-epoxy resin was discussed，too. The adhesive properties of the modified polyurethane-epoxy resin to aluminum alloy LY12 were improved when the shorter whisker pretreated with 1% KH-560 was added into the resins，whose RT peel strength rose by 27%，the 100℃ and -70℃ lap shear strength of the modified polyurethane-epoxy resins rose by 39% and 10%，respectively. The adhesive properties of the modified resins and the SEM images show that the modifying mechanism of the whiskers to the polyurethane-epoxy resin was crack deflexion.
2008, 25(4): 7-12.
Abstract:
The mechanical properties，morphologies of the fractured surfaces and the glass transition temperature were investigated for the epoxy resins cured with a mixed curing agent (aromatic diamine DETD and amine-terminated polyether D-400). The results show that with the addition of 40% relative mass fraction of D-400，the epoxy resin at room temperature exhibits the highest tensile strength of 82.52 MPa and Young‘s modulus of 2.30 GPa. And the tensile strength of the composites is enhanced by 6.3% while Young’s modulus by 14.4%. In addition，the cryogenic impact strength is enhanced by 14% at this content. SEM analysis of tensile fracture surfaces shows that the fractography tends to be irregular with the increase of flexible amine content，indicating that the fracture resistance is increased. Thermal analysis of the specimens shows that the glass transition temperature decreases with increasing the relative content of D-400. Finally，the mechanism of toughened epoxy resins at cryogenic temperature is discussed.
The mechanical properties，morphologies of the fractured surfaces and the glass transition temperature were investigated for the epoxy resins cured with a mixed curing agent (aromatic diamine DETD and amine-terminated polyether D-400). The results show that with the addition of 40% relative mass fraction of D-400，the epoxy resin at room temperature exhibits the highest tensile strength of 82.52 MPa and Young‘s modulus of 2.30 GPa. And the tensile strength of the composites is enhanced by 6.3% while Young’s modulus by 14.4%. In addition，the cryogenic impact strength is enhanced by 14% at this content. SEM analysis of tensile fracture surfaces shows that the fractography tends to be irregular with the increase of flexible amine content，indicating that the fracture resistance is increased. Thermal analysis of the specimens shows that the glass transition temperature decreases with increasing the relative content of D-400. Finally，the mechanism of toughened epoxy resins at cryogenic temperature is discussed.
Effect of carbon black modification on the electrical reproducibility behavior of CB/HDPE composites
2008, 25(4): 13-17.
Abstract:
The carbon black (CB) or oxidative carbon black (CB-O) filled high-density polyethylene composites were prepared by melting blending. The influence of CB oxidation on the positive temperature coefficient (PTC) behavior，negative temperature coefficient (NTC) behavior and the electrical reproducibility of CB/HDPE and CB-O/HDPE composites were studied. It is shown that the NTC effect is decreased or even eliminated，the electrical reproducibility is improved and the PTC intensity is enhanced by CB oxidation. It is also revealed that the room temperature resistivity of CB-O/HDPE is increased by only 0.3 order compared with CB/HDPE，but is lower by one order than that of crosslinked CB/HDPE. The results are due to the increase of the polarity on the surface of CB-O，which is induced by the increase of the carboxyl and hydroxyl. Thus the agglomeration of CB-O at high temperature is restricted and the NTC effect of the composites is decreased. On the other hand，the reduction of the poor electrical conductive regions at boundaries of the crystallites on the surface of CB improves the electrical conductivity of the composites and the strong physical adsorption interaction between CB-O particles and HDPE improves the electrical reproducibility of the composites.
The carbon black (CB) or oxidative carbon black (CB-O) filled high-density polyethylene composites were prepared by melting blending. The influence of CB oxidation on the positive temperature coefficient (PTC) behavior，negative temperature coefficient (NTC) behavior and the electrical reproducibility of CB/HDPE and CB-O/HDPE composites were studied. It is shown that the NTC effect is decreased or even eliminated，the electrical reproducibility is improved and the PTC intensity is enhanced by CB oxidation. It is also revealed that the room temperature resistivity of CB-O/HDPE is increased by only 0.3 order compared with CB/HDPE，but is lower by one order than that of crosslinked CB/HDPE. The results are due to the increase of the polarity on the surface of CB-O，which is induced by the increase of the carboxyl and hydroxyl. Thus the agglomeration of CB-O at high temperature is restricted and the NTC effect of the composites is decreased. On the other hand，the reduction of the poor electrical conductive regions at boundaries of the crystallites on the surface of CB improves the electrical conductivity of the composites and the strong physical adsorption interaction between CB-O particles and HDPE improves the electrical reproducibility of the composites.
2008, 25(4): 18-23.
Abstract:
To predict the curing behavior theoretically, the isothermal differential scanning calorimetry (DSC) method was used to investigate the curing process of a hybrid epoxy resin system for resin film infusion (RFI) at 80，90，100，110 and 120℃，respectively. The curing system is composed of hybrid epoxy resin of E-44/E-21(6/4，mass ratio) with GA-327(GA-327/resin=40/100，mass ratio) as curing agent，and a uniform film can be formed at room temperature and cured at 70～80℃. The corresponding parameters of the n-order curing model，the autocatalytic model and the Kamal model were determined by fitting the experimental data using Matlab software，respectively. According to the values of R2 and the sum of square due to error (SSE) of the fitted data，a suitable curing reaction kinetic model was determined. It was found that the curing reaction of the hybrid epoxy resin system was of autocatalyzed and diffusion controlled characteristics，and the effect of the diffusion was much evident at a lower temperature. The data fitting results also indicate that the autocatalytic reaction kinetic model can be used to describe the cure kinetics of the curing system. The apparent activation energy Ea of the curing reactions is 56.7 kJ/mol and the pre-exponential factor A of the system is 1.18×107 s-1. The cure reaction order m and n are 0.529 and 1.561，respectively.
To predict the curing behavior theoretically, the isothermal differential scanning calorimetry (DSC) method was used to investigate the curing process of a hybrid epoxy resin system for resin film infusion (RFI) at 80，90，100，110 and 120℃，respectively. The curing system is composed of hybrid epoxy resin of E-44/E-21(6/4，mass ratio) with GA-327(GA-327/resin=40/100，mass ratio) as curing agent，and a uniform film can be formed at room temperature and cured at 70～80℃. The corresponding parameters of the n-order curing model，the autocatalytic model and the Kamal model were determined by fitting the experimental data using Matlab software，respectively. According to the values of R2 and the sum of square due to error (SSE) of the fitted data，a suitable curing reaction kinetic model was determined. It was found that the curing reaction of the hybrid epoxy resin system was of autocatalyzed and diffusion controlled characteristics，and the effect of the diffusion was much evident at a lower temperature. The data fitting results also indicate that the autocatalytic reaction kinetic model can be used to describe the cure kinetics of the curing system. The apparent activation energy Ea of the curing reactions is 56.7 kJ/mol and the pre-exponential factor A of the system is 1.18×107 s-1. The cure reaction order m and n are 0.529 and 1.561，respectively.
2008, 25(4): 24-28.
Abstract:
The nano-SiO2/cellulose composites were successfully synthesized by a sol-gel method using tetraethylorthosilicate (TEOS) as the silica precursor and cellulose in heterogeneous ethanol solution. The morphology，structure and thermal stability of the composite materials were characterized by TEM，FTIR and TGA. The influence of SiO2 content on the mechanical properties of composites was discussed. The effect of basic catalyst ammonia on the content of silica in cellulose was studied.The results indicate that the elastic modulus of the composites increases with the increasing of SiO2 mass fraction until 3.1% and then decreases，and the same is true of tensile strength when SiO2 mass fraction is 10.6%. SiO2 is incorporated into cellulose most effectively when the dosage of ammonia is 3.70×10-4 mol/L.The hydrophobicity，thermal stability and mechanical properties of nano-SiO2/cellulose composites in the heterogeneous system are also higher than those of the cellulosic materials.
The nano-SiO2/cellulose composites were successfully synthesized by a sol-gel method using tetraethylorthosilicate (TEOS) as the silica precursor and cellulose in heterogeneous ethanol solution. The morphology，structure and thermal stability of the composite materials were characterized by TEM，FTIR and TGA. The influence of SiO2 content on the mechanical properties of composites was discussed. The effect of basic catalyst ammonia on the content of silica in cellulose was studied.The results indicate that the elastic modulus of the composites increases with the increasing of SiO2 mass fraction until 3.1% and then decreases，and the same is true of tensile strength when SiO2 mass fraction is 10.6%. SiO2 is incorporated into cellulose most effectively when the dosage of ammonia is 3.70×10-4 mol/L.The hydrophobicity，thermal stability and mechanical properties of nano-SiO2/cellulose composites in the heterogeneous system are also higher than those of the cellulosic materials.
2008, 25(4): 29-34.
Abstract:
Chopped glass fiber and waste printed wiring board powder reinforced composites were prepared by compression molding. Effects of the shape，content and size of waste powders on the mechanical property of waste filler reinforced composites were studied，and the application of waste composite was discussed. The results show that the mechanical property of composite reinforced by chopped glass fiber and waste printed wiring board powder is better than that of waste powder reinforced composite. Effects of large powders (1～3 mm) on composite properties were better than of small powders (0.25 mm). Large powder mass fraction can reach 65%，and a mixed reinforced composite with flexural strength of 150 MPa and impact strength of 18 kJ/m2 can be developed.
Chopped glass fiber and waste printed wiring board powder reinforced composites were prepared by compression molding. Effects of the shape，content and size of waste powders on the mechanical property of waste filler reinforced composites were studied，and the application of waste composite was discussed. The results show that the mechanical property of composite reinforced by chopped glass fiber and waste printed wiring board powder is better than that of waste powder reinforced composite. Effects of large powders (1～3 mm) on composite properties were better than of small powders (0.25 mm). Large powder mass fraction can reach 65%，and a mixed reinforced composite with flexural strength of 150 MPa and impact strength of 18 kJ/m2 can be developed.
2008, 25(4): 35-39.
Abstract:
The conductive poly-aniline (PANI) was synthesized by the chemical oxidation method，and the composite absorbents
of carbonyl iron powder/polymethacrylate (CIP/PMMA) with core-shell structure and carbonyl iron powder/polymethacrylate/poly-aniline (CIP/PMMA/PANI) with two-coating structure were prepared by in-situ composite technique，using aniline，carbonyl iron powder and methacrylate. The structure and morphology of three absorbents were characterized by XRD，SEM and TEM. The electromagnetic parameters of them were measured by using vector network analyzer，and the results show that the CIP/PMMA/PANI composite absorbent has both electric losses and magnetic losses. When the thickness of the material is 1.0 mm，its least reflectivity of computing is -11.26 dB in 2～18 GHz frequency range，and the bandwidths for-10 dB and for -8 dB are respectively 9.2 GHz and 14 GHz. The computing results show that the composite absorbent has a better broad-frequency absorbing property.
The conductive poly-aniline (PANI) was synthesized by the chemical oxidation method，and the composite absorbents
of carbonyl iron powder/polymethacrylate (CIP/PMMA) with core-shell structure and carbonyl iron powder/polymethacrylate/poly-aniline (CIP/PMMA/PANI) with two-coating structure were prepared by in-situ composite technique，using aniline，carbonyl iron powder and methacrylate. The structure and morphology of three absorbents were characterized by XRD，SEM and TEM. The electromagnetic parameters of them were measured by using vector network analyzer，and the results show that the CIP/PMMA/PANI composite absorbent has both electric losses and magnetic losses. When the thickness of the material is 1.0 mm，its least reflectivity of computing is -11.26 dB in 2～18 GHz frequency range，and the bandwidths for-10 dB and for -8 dB are respectively 9.2 GHz and 14 GHz. The computing results show that the composite absorbent has a better broad-frequency absorbing property.
2008, 25(4): 40-44.
Abstract:
With in-situ bending various contents of multi-wall carbon nanotubes (MWNTs) were introduced into the solution polymerization system of poly (p-phenylene benzobisoxazole) (PBO)，and the blends were spun into high performance fibers via liquid crystal spinning. Under the observation with a polarized optical microscope，it is found that the pre-diffusion in poly(phosphoric acid) (PPA) instead of direct adding MWNTs will promise better dispersion in PBO. The mechanical and thermal properties of PBO and MWNTs/PBO fibers were tested by a tensile strength tester and thermogravimetric analyzer. The results show that the tensile strength and modulus of the blend fiber containing 2% MWNTs are 4.69 GPa and 128.8 GPa respectively，which are approximately 24% and 23.5% higher than of the pure PBO fibers. The decomposition temperature of the composites is also improved from 668.9℃ to 700.8℃. When the mass fraction increases to 5%，MWNTs aggregate seriously，giving a negative influence on the spinnability of MWNTs/PBO blend and the mechanical properties of the blend fibers.
With in-situ bending various contents of multi-wall carbon nanotubes (MWNTs) were introduced into the solution polymerization system of poly (p-phenylene benzobisoxazole) (PBO)，and the blends were spun into high performance fibers via liquid crystal spinning. Under the observation with a polarized optical microscope，it is found that the pre-diffusion in poly(phosphoric acid) (PPA) instead of direct adding MWNTs will promise better dispersion in PBO. The mechanical and thermal properties of PBO and MWNTs/PBO fibers were tested by a tensile strength tester and thermogravimetric analyzer. The results show that the tensile strength and modulus of the blend fiber containing 2% MWNTs are 4.69 GPa and 128.8 GPa respectively，which are approximately 24% and 23.5% higher than of the pure PBO fibers. The decomposition temperature of the composites is also improved from 668.9℃ to 700.8℃. When the mass fraction increases to 5%，MWNTs aggregate seriously，giving a negative influence on the spinnability of MWNTs/PBO blend and the mechanical properties of the blend fibers.
2008, 25(4): 45-50.
Abstract:
The interfacial structure and properties of the carbon fiber reinforced poly phthalazinone-ether-ketone (CF/PPEK) composites were studied. The interfacial structure of CF/PPEK composite was characterized by XPS and Raman spectrum. And the interfacial properties were discussed through microdebonding experiments. The results show that PPEK resin can form strong interaction with treated carbon fiber at interface，which assures the stress transfer between the matrix and fiber. As a result，CF/PPEK composites have good heat-stability and mechanical properties. A mesomechanical model was presented based on the hypothesis of periodicity in microstructure with continuous and periodic boundary conditions carried out. The interfacial strength of CF/PPEK was analyzed and calculated according to the shear-lag theory and nonlinear FEM method. The results well correspond with the experiments.
The interfacial structure and properties of the carbon fiber reinforced poly phthalazinone-ether-ketone (CF/PPEK) composites were studied. The interfacial structure of CF/PPEK composite was characterized by XPS and Raman spectrum. And the interfacial properties were discussed through microdebonding experiments. The results show that PPEK resin can form strong interaction with treated carbon fiber at interface，which assures the stress transfer between the matrix and fiber. As a result，CF/PPEK composites have good heat-stability and mechanical properties. A mesomechanical model was presented based on the hypothesis of periodicity in microstructure with continuous and periodic boundary conditions carried out. The interfacial strength of CF/PPEK was analyzed and calculated according to the shear-lag theory and nonlinear FEM method. The results well correspond with the experiments.
2008, 25(4): 51-55.
Abstract:
The in-situ sol-gel method was employed to prepare nano-alumina/PI hybrid composite. The chemical structure，morphology，the corona-resistant lifespan and thermal property were characterized by the method of Fourier transform infrared spectroscopy (FTIR)，atomic force microscope (AFM)，scan electric microscope (SEM) and thermogravimetric analysis (TGA). The micrographs of AFM and SEM indicate that nano-alumina particles are finely dispersed in the polymer resin. The sizes of alumina particles are 40～100 nm. The solid content of nano-alumina influences the corona-resistant lifespan and thermal-resistance. The corona-resistant lifespan and thermal decomposition temperature are increased with increasing the solid content. When the mass fraction of nano-alumina is 16% Al2O3/PI， the width of sample is 25 μm and breakdown strength is 60 kV/mm, its corona-resistant lifespan is 130 h，rising 11 times，its thermal decomposition temperature is 498.63℃，rising 20℃，and the shear strength is a little lower than that of the pure material.
The in-situ sol-gel method was employed to prepare nano-alumina/PI hybrid composite. The chemical structure，morphology，the corona-resistant lifespan and thermal property were characterized by the method of Fourier transform infrared spectroscopy (FTIR)，atomic force microscope (AFM)，scan electric microscope (SEM) and thermogravimetric analysis (TGA). The micrographs of AFM and SEM indicate that nano-alumina particles are finely dispersed in the polymer resin. The sizes of alumina particles are 40～100 nm. The solid content of nano-alumina influences the corona-resistant lifespan and thermal-resistance. The corona-resistant lifespan and thermal decomposition temperature are increased with increasing the solid content. When the mass fraction of nano-alumina is 16% Al2O3/PI， the width of sample is 25 μm and breakdown strength is 60 kV/mm, its corona-resistant lifespan is 130 h，rising 11 times，its thermal decomposition temperature is 498.63℃，rising 20℃，and the shear strength is a little lower than that of the pure material.
2008, 25(4): 56-61.
Abstract:
The PA66-based nano-composites containing nano-SiO2 were prepared in a twin-screw extruder by melt compounding，and the mechanical and thermal properties of the nano-composites were investigated. The results of mechanical testing show that the tensile strength and Young's modulus of the nano-composites are all reinforced with the addition of silica nano-particles. The tensile strength reaches a maximum at 3% mass fraction，which is 11.2% higher than that of the pure PA66. And the Young's modulus reaches a maximum at 5% mass fraction，which is 30.1% higher than that of the pure PA66. The storage modulus and glass transition temperature of the composites obviously increase compared with those of the pure PA66. The differential scanning calorimetry (DSC) indicates that the incorporation of nano-SiO2，on the one hand，can hinder the crystallization process of PA66. On the other hand，it can act as a nucleation agent and increase the nucleation site and nucleation rate of PA66.
The PA66-based nano-composites containing nano-SiO2 were prepared in a twin-screw extruder by melt compounding，and the mechanical and thermal properties of the nano-composites were investigated. The results of mechanical testing show that the tensile strength and Young's modulus of the nano-composites are all reinforced with the addition of silica nano-particles. The tensile strength reaches a maximum at 3% mass fraction，which is 11.2% higher than that of the pure PA66. And the Young's modulus reaches a maximum at 5% mass fraction，which is 30.1% higher than that of the pure PA66. The storage modulus and glass transition temperature of the composites obviously increase compared with those of the pure PA66. The differential scanning calorimetry (DSC) indicates that the incorporation of nano-SiO2，on the one hand，can hinder the crystallization process of PA66. On the other hand，it can act as a nucleation agent and increase the nucleation site and nucleation rate of PA66.
2008, 25(4): 62-67.
Abstract:
The surface contact angles of several meta-aramid fibers and meta-aramid pulps as well as their sheets were measured，and the surface energy of aramid fiber，aramid pulp and sheet was determined according to the harmonic mean-based Wu equation. The relationship between the surface energy and sheet properties in sheet processing was discussed according to the surface energy as well as the interfacial tension and work of adhesion of aramid fibers and pulps. The results show that the surface energy of aramid fibers and pulps is in the range of 35～45 mJ·m-2，the surface energy of fibers is slightly higher than that of pulps，the polar component of surface energy is larger than the dispersion one，and the wettability and work of adhesion are enhanced with increase of the surface energy of aramid fibers and pulps，when water and glycol are employed as the testing liquids. The surface energy of aramid sheet decreases during hot-press process，and compared to Nomex sheet，the surface energy of self-made aramid sheet decreases sharply after hot-press process. The better the matching of polar component with dispersion component，the smaller the difference of surface energy and the smaller the interfacial tension，the stronger the adhesion between fibers and pulp with the improved strength of aramid sheet.
The surface contact angles of several meta-aramid fibers and meta-aramid pulps as well as their sheets were measured，and the surface energy of aramid fiber，aramid pulp and sheet was determined according to the harmonic mean-based Wu equation. The relationship between the surface energy and sheet properties in sheet processing was discussed according to the surface energy as well as the interfacial tension and work of adhesion of aramid fibers and pulps. The results show that the surface energy of aramid fibers and pulps is in the range of 35～45 mJ·m-2，the surface energy of fibers is slightly higher than that of pulps，the polar component of surface energy is larger than the dispersion one，and the wettability and work of adhesion are enhanced with increase of the surface energy of aramid fibers and pulps，when water and glycol are employed as the testing liquids. The surface energy of aramid sheet decreases during hot-press process，and compared to Nomex sheet，the surface energy of self-made aramid sheet decreases sharply after hot-press process. The better the matching of polar component with dispersion component，the smaller the difference of surface energy and the smaller the interfacial tension，the stronger the adhesion between fibers and pulp with the improved strength of aramid sheet.
2008, 25(4): 68-72.
Abstract:
0-3（PZT，KTN）/P（VDF-TrFE）triphase ferroelectric composite was prepared when potassium tantalate niobate (KTN) particles and lead zirconate titanate (PZT) particles were embedded into the polyvinylidene fluoride trifluoroethylene (P(VDF-TrFE)) copolymer. The microstructure and distributions of PZT phase and KTN phase were analyzed using SEM and EDAX technique. The electric properties were measured for the ferroelectric composite with different volume fractions of KTN phase. The results indicate that PZT and KTN particles are distributed uniformly although a few of clusters occur. With increasing the KTN volume fraction，the poling current I，dielectric constant εr and dielectric loss tanδ increase，piezoelectric coefficients d33 and pyroelectric coefficients p3 increase firstly and then reduce，but both d33 and p3 are higher than those of PZT/P(VDF-TrFE) composite with the same PZT volume fraction.
0-3（PZT，KTN）/P（VDF-TrFE）triphase ferroelectric composite was prepared when potassium tantalate niobate (KTN) particles and lead zirconate titanate (PZT) particles were embedded into the polyvinylidene fluoride trifluoroethylene (P(VDF-TrFE)) copolymer. The microstructure and distributions of PZT phase and KTN phase were analyzed using SEM and EDAX technique. The electric properties were measured for the ferroelectric composite with different volume fractions of KTN phase. The results indicate that PZT and KTN particles are distributed uniformly although a few of clusters occur. With increasing the KTN volume fraction，the poling current I，dielectric constant εr and dielectric loss tanδ increase，piezoelectric coefficients d33 and pyroelectric coefficients p3 increase firstly and then reduce，but both d33 and p3 are higher than those of PZT/P(VDF-TrFE) composite with the same PZT volume fraction.
2008, 25(4): 73-77.
Abstract:
Polymer-matrix Re-Fe giant magnetostrictive composites were prepared by combining 0-3 type magnetostrictive alloy (Tb0.3 Dy0.7 Fe1.95) and epoxy (E-44). The magnetostriction and high frequency magnetic properties of the composites were studied by using the standard strain gauge technique and Agilent 4294A impedance analyzer. The dependence of permeability，cut-off frequency properties on the frequency and the volume fraction of E-44 was investigated in detail. The results show that the composites have both good dynamic response with a high frequency and magnetostriction properties. The cut-off frequency of composites is higher than 30 MHz，and their magnetostriction is 808×10-6 and 821×10-6 when the volume fraction of E-44 is 20% and 30%. The magnetostriction of the composite still keeps to be 592×10-6 when the volume fraction of E-44 is 50%. The high frequency response mechanism of the magnetostrictive composite was analyzed.
Polymer-matrix Re-Fe giant magnetostrictive composites were prepared by combining 0-3 type magnetostrictive alloy (Tb0.3 Dy0.7 Fe1.95) and epoxy (E-44). The magnetostriction and high frequency magnetic properties of the composites were studied by using the standard strain gauge technique and Agilent 4294A impedance analyzer. The dependence of permeability，cut-off frequency properties on the frequency and the volume fraction of E-44 was investigated in detail. The results show that the composites have both good dynamic response with a high frequency and magnetostriction properties. The cut-off frequency of composites is higher than 30 MHz，and their magnetostriction is 808×10-6 and 821×10-6 when the volume fraction of E-44 is 20% and 30%. The magnetostriction of the composite still keeps to be 592×10-6 when the volume fraction of E-44 is 50%. The high frequency response mechanism of the magnetostrictive composite was analyzed.
2008, 25(4): 78-83.
Abstract:
The unique structure of carbon nanotubes (CNTs) has prompted intensive study for special electromagnetic properties. For the multiwalled carbon nanotubes(MWCNTs)，the research work on electromagnetic properties is seldom reported. In this work，MWCNTs/glass fabrics (GF)/epoxy (EP) composites were produced by selecting the glass fabric as carriers to help MWCNTs to disperse. Then the permittivity，magnetic conductivity，reflection loss，electrical conductivity and morphology of the composites with different contents of MWCNTs in the wave band from 26.5 to 40 GHz were researched respectively. It is found that the real part and imaginary part of permittivity increase with the content of MWCNTs. Especially for the dielectric loss tangent，it has been increased by four times. However，the magnetic conductivity stays around the level of one (μ=1) and the composites present less magnetic properties. Moreover，the MWCNTs/GF/EP composite can be changed from the insulator to the semiconductor along with increasing the content of MWCNTs. In the electromagnetic wave band (26.5～40 GHz)，the effect of absorbing is not satisfying for the MWCNTs/GF/EP composites.
The unique structure of carbon nanotubes (CNTs) has prompted intensive study for special electromagnetic properties. For the multiwalled carbon nanotubes(MWCNTs)，the research work on electromagnetic properties is seldom reported. In this work，MWCNTs/glass fabrics (GF)/epoxy (EP) composites were produced by selecting the glass fabric as carriers to help MWCNTs to disperse. Then the permittivity，magnetic conductivity，reflection loss，electrical conductivity and morphology of the composites with different contents of MWCNTs in the wave band from 26.5 to 40 GHz were researched respectively. It is found that the real part and imaginary part of permittivity increase with the content of MWCNTs. Especially for the dielectric loss tangent，it has been increased by four times. However，the magnetic conductivity stays around the level of one (μ=1) and the composites present less magnetic properties. Moreover，the MWCNTs/GF/EP composite can be changed from the insulator to the semiconductor along with increasing the content of MWCNTs. In the electromagnetic wave band (26.5～40 GHz)，the effect of absorbing is not satisfying for the MWCNTs/GF/EP composites.
2008, 25(4): 84-89.
Abstract:
A nano-alumina/organic fluorine composite emulsion was prepared via in-situ polymerization using organic monomer and self-synthesized nano-alumina as raw materials. The nano-alumina was modified firstly by coupling agent to endow active groups onto the nano-particle surface. The structure and morphology of the modified and unmodified nano-alumina and the as-synthesized composite emulsion were characterized by different methods. The waterproof and oil-repellency properties of the composite emulsion were tested through treating the polyester fabric. The results show that the nano-alumina modified by coupling agent KH-570 could be perfectly dispersed in the organic monomer emulsion and the composite emulsion synthesized through in-situ polymerization. The waterproof and oil-repellency properties of the as-synthesized composition emulsion using coral nano-alumina as the raw material were proved to be stronger than using the sphere nano-alumina as the raw material. Moreover，the as-synthesized composite emulsion using coral nano-alumina as the raw material has many advantages such as small dosage，low baking temperature and permanent function compared with the conventional organic fluorine emulsions.
A nano-alumina/organic fluorine composite emulsion was prepared via in-situ polymerization using organic monomer and self-synthesized nano-alumina as raw materials. The nano-alumina was modified firstly by coupling agent to endow active groups onto the nano-particle surface. The structure and morphology of the modified and unmodified nano-alumina and the as-synthesized composite emulsion were characterized by different methods. The waterproof and oil-repellency properties of the composite emulsion were tested through treating the polyester fabric. The results show that the nano-alumina modified by coupling agent KH-570 could be perfectly dispersed in the organic monomer emulsion and the composite emulsion synthesized through in-situ polymerization. The waterproof and oil-repellency properties of the as-synthesized composition emulsion using coral nano-alumina as the raw material were proved to be stronger than using the sphere nano-alumina as the raw material. Moreover，the as-synthesized composite emulsion using coral nano-alumina as the raw material has many advantages such as small dosage，low baking temperature and permanent function compared with the conventional organic fluorine emulsions.
2008, 25(4): 90-95.
Abstract:
Using natural sericite mineral as raw material，through crashing and surface chemical modification，the ultrafine sericite powders were obtained. The excellent liquid silicone rubber reinforced by ultrafine sericite was；prepared through solution polymerization.The microstructures and properties of composities were investigated by SEMbecause the surface of sericite particles was modified with organic functional groups，they can disperse in the silicone rubber perfectly. The mechanical properties of composites，such as tensile strength and hardness(Shore A)are improved prominently. Compared to silicone rubber unreinforced，when the mass fraction of ultrafine sericite was 8%，tensile strength and hardness(Shore A ) have improved 197.62% and 48.78%. The result of TGA shows that the thermal stability was superior to that of silicone rubber without any fillers. The interaction between ultrafine sericite and silicone rubber was characterized by the Kraus equation. The Kraus curve shows that there is interaction between ultrafine sericite and silicone rubber.
Using natural sericite mineral as raw material，through crashing and surface chemical modification，the ultrafine sericite powders were obtained. The excellent liquid silicone rubber reinforced by ultrafine sericite was；prepared through solution polymerization.The microstructures and properties of composities were investigated by SEMbecause the surface of sericite particles was modified with organic functional groups，they can disperse in the silicone rubber perfectly. The mechanical properties of composites，such as tensile strength and hardness(Shore A)are improved prominently. Compared to silicone rubber unreinforced，when the mass fraction of ultrafine sericite was 8%，tensile strength and hardness(Shore A ) have improved 197.62% and 48.78%. The result of TGA shows that the thermal stability was superior to that of silicone rubber without any fillers. The interaction between ultrafine sericite and silicone rubber was characterized by the Kraus equation. The Kraus curve shows that there is interaction between ultrafine sericite and silicone rubber.
2008, 25(4): 96-100.
Abstract:
In order to study the effect of the content of the short carbon fiber and the temperature on the percolation behavior of conducting composite，the equations relating the composite conductivity with the filler's volume fraction and the temperature were deduced via the Landau phase transition theory. And the percolation transition and PTC behavior in the short carbon fiber/vinyl resin composite were analyzed by these equations. The results show that the percolation threshold of composite increases with temperature as well as the PTC temperature increasing with the content of carbon fiber. The theoretical values of the percolation threshold in composite increase from 1.06% to 1.60% as the temperature from 24.6℃ to 108.4℃. And the ones of PTC temperature increase from 120℃ to 170℃ as the volume fraction of carbon fiber from 3.1% to 4.6%. The theoretical values of the percolation threshold and PTC temperature in composite fit well with the experimental data.
In order to study the effect of the content of the short carbon fiber and the temperature on the percolation behavior of conducting composite，the equations relating the composite conductivity with the filler's volume fraction and the temperature were deduced via the Landau phase transition theory. And the percolation transition and PTC behavior in the short carbon fiber/vinyl resin composite were analyzed by these equations. The results show that the percolation threshold of composite increases with temperature as well as the PTC temperature increasing with the content of carbon fiber. The theoretical values of the percolation threshold in composite increase from 1.06% to 1.60% as the temperature from 24.6℃ to 108.4℃. And the ones of PTC temperature increase from 120℃ to 170℃ as the volume fraction of carbon fiber from 3.1% to 4.6%. The theoretical values of the percolation threshold and PTC temperature in composite fit well with the experimental data.
2008, 25(4): 101-105.
Abstract:
In order to decrease the manufacturing time and improve the properties of the C/C brake discs，a new process of rapid densification to manufacture C/C brake discs was developed. This process is a method of the isothermal pressure gradient CVI whose precursors are CH4 and C3H8. The CVI (chemical vapor infiltration) time of the discs manufactured by the new process is a half of the CVI time of the discs manufactured by the conventional process whose precursor is C3H6. In addition, the thermal conductivity of the discs produced by the new process has increased by more than 5%，the mechanical properties including tensile strength，compressing strength，bending strength and shearing strength have increased by more than 10%，and the properties of friction and wear have been raised by more than 20%.
In order to decrease the manufacturing time and improve the properties of the C/C brake discs，a new process of rapid densification to manufacture C/C brake discs was developed. This process is a method of the isothermal pressure gradient CVI whose precursors are CH4 and C3H8. The CVI (chemical vapor infiltration) time of the discs manufactured by the new process is a half of the CVI time of the discs manufactured by the conventional process whose precursor is C3H6. In addition, the thermal conductivity of the discs produced by the new process has increased by more than 5%，the mechanical properties including tensile strength，compressing strength，bending strength and shearing strength have increased by more than 10%，and the properties of friction and wear have been raised by more than 20%.
2008, 25(4): 106-112.
Abstract:
CeO2-SiO2/Ni-W-P nano-composite films were prepared on the carbon steel surface by pulse co-deposition of Ni，W，P，nano-CeO2 and nano-SiO2 particles，the influence of Na2WO4 and NaH2PO2 concentrations in electrolyte on microstructures and properties of the nano-composite films was researched，and the characteristics were assessed by chemical composition, deposition rate, microhardness and surface morphologies. The results show that when the Na2WO4 and NaH2PO2 concentrations in electrolyte are controlled at 100 and 4 g/L respectively, the deposition rate of 25.03 μm/h and the microhardness of HV649 of the nano-composite films are obtained. The increase of the Na2WO4 concentration leads to refinement in the grain structure of the nano-composite films. When improved at 160 g/L，the nano-composite films possess a clear outline of the spherical matrix metal crystallite，fine crystal size, compact microstructure and uniform and dispersive distribution of nano-CeO2 and nano-SiO2 particles within the Ni-W-P matrix metal. The increase of the NaH2PO2 concentration in electrolyte has a little effect on the surface morphologies，but it results in a microhardness decrease of the nano-composite films.
CeO2-SiO2/Ni-W-P nano-composite films were prepared on the carbon steel surface by pulse co-deposition of Ni，W，P，nano-CeO2 and nano-SiO2 particles，the influence of Na2WO4 and NaH2PO2 concentrations in electrolyte on microstructures and properties of the nano-composite films was researched，and the characteristics were assessed by chemical composition, deposition rate, microhardness and surface morphologies. The results show that when the Na2WO4 and NaH2PO2 concentrations in electrolyte are controlled at 100 and 4 g/L respectively, the deposition rate of 25.03 μm/h and the microhardness of HV649 of the nano-composite films are obtained. The increase of the Na2WO4 concentration leads to refinement in the grain structure of the nano-composite films. When improved at 160 g/L，the nano-composite films possess a clear outline of the spherical matrix metal crystallite，fine crystal size, compact microstructure and uniform and dispersive distribution of nano-CeO2 and nano-SiO2 particles within the Ni-W-P matrix metal. The increase of the NaH2PO2 concentration in electrolyte has a little effect on the surface morphologies，but it results in a microhardness decrease of the nano-composite films.
2008, 25(4): 113-118.
Abstract:
(TiB+TiC)/TA15 in situ titanium matrix composites with 9%，11%，22% and 57% volume fractions of TiB+TiC reinforcements, respectively were fabricated by the laser melting deposition manufacturing process. The morphology of TiB changes from plate-like to prismatic while the morphology of TiC evolves from particle-like to dendritic with the increasing volume fraction of the reinforcements. The Rockwell hardness and elastic modulus of the composites increase and the ductility decreases with the increasing volume fraction of TiB+TiC reinforcements. The composite with a reinforcement volume fraction of 9% exhibits the optimum mechanical properties，while the tensile strength of the composites decreases abruptly when the reinforcement volume fraction is up to approximately 11%. The yield strength (935 MPa) and ultimate tensile strength (1040 MPa) of the laser melting deposited in situ (TiB+TiC)/TA15 composite containing 9% volume fraction of TiB+TiC reinforcements are both enhanced by 12% compared to the as-laser deposited titanium alloy TA15.
(TiB+TiC)/TA15 in situ titanium matrix composites with 9%，11%，22% and 57% volume fractions of TiB+TiC reinforcements, respectively were fabricated by the laser melting deposition manufacturing process. The morphology of TiB changes from plate-like to prismatic while the morphology of TiC evolves from particle-like to dendritic with the increasing volume fraction of the reinforcements. The Rockwell hardness and elastic modulus of the composites increase and the ductility decreases with the increasing volume fraction of TiB+TiC reinforcements. The composite with a reinforcement volume fraction of 9% exhibits the optimum mechanical properties，while the tensile strength of the composites decreases abruptly when the reinforcement volume fraction is up to approximately 11%. The yield strength (935 MPa) and ultimate tensile strength (1040 MPa) of the laser melting deposited in situ (TiB+TiC)/TA15 composite containing 9% volume fraction of TiB+TiC reinforcements are both enhanced by 12% compared to the as-laser deposited titanium alloy TA15.
2008, 25(4): 119-125.
Abstract:
Based on the mesoscopic unit cell of particulate reinforced composites，the monotonic tension and ratcheting behaviors of SiCp/6061Al composite were simulated by the finite element method. In the simulation，the effects of the coupled boundary condition and the interfacial binding state on the ratcheting of the composite were discussed. Some microscopic deformation features in the matrix and the interface，and their evolution rules were analyzed. The ratcheting of SiCp/6061Al composite was simulated with a suitable choice of interfacial bonding parameters，and the predicting capability of the finite element model was discussed by comparing the simulations with the experimental results. The results show that considering the coupled boundary condition improves the simulated results greatly；the better the interfacial bonding is，i.e.，the higher Young's modulus，yield strength and hardening modulus are，the smaller the ratcheting strain；the weak interface model with suitable interfacial parameters provides more reasonable simulation to the ratcheting of the composite than the perfect interface model does.
Based on the mesoscopic unit cell of particulate reinforced composites，the monotonic tension and ratcheting behaviors of SiCp/6061Al composite were simulated by the finite element method. In the simulation，the effects of the coupled boundary condition and the interfacial binding state on the ratcheting of the composite were discussed. Some microscopic deformation features in the matrix and the interface，and their evolution rules were analyzed. The ratcheting of SiCp/6061Al composite was simulated with a suitable choice of interfacial bonding parameters，and the predicting capability of the finite element model was discussed by comparing the simulations with the experimental results. The results show that considering the coupled boundary condition improves the simulated results greatly；the better the interfacial bonding is，i.e.，the higher Young's modulus，yield strength and hardening modulus are，the smaller the ratcheting strain；the weak interface model with suitable interfacial parameters provides more reasonable simulation to the ratcheting of the composite than the perfect interface model does.
2008, 25(4): 126-130.
Abstract:
A new kind of Co-based alloy coating powder containing certain amount of nano-Al powder was designed. The ceramic phases in the coating were produced by YAG pulse laser inducing in-situ synthesis. The microstructure morphology and the forming mechanism of the coating were studied by means of scan electronic microscope，optical micrograph analysis techniques and micro-hardness tester. By the pulse laser inducing in-situ synthesis，the interfaces of the thin coatings are metallurgically combined and the ceramic particles are well dispersed. The micro-hardness of the Co-based composite alloy coating is promoted from HV87 to HV426. The added nano-Al supplies the interior heatfountain，which compensates for the energy loss caused by the quick heat transmission of Cu-based alloy. The added nano-Al can fully induce the interior chemical reaction，which improves the composite coating forming easily. Ceramic particles are less than 2.0 μm in diameter and dispersed in the strengthened coating.
A new kind of Co-based alloy coating powder containing certain amount of nano-Al powder was designed. The ceramic phases in the coating were produced by YAG pulse laser inducing in-situ synthesis. The microstructure morphology and the forming mechanism of the coating were studied by means of scan electronic microscope，optical micrograph analysis techniques and micro-hardness tester. By the pulse laser inducing in-situ synthesis，the interfaces of the thin coatings are metallurgically combined and the ceramic particles are well dispersed. The micro-hardness of the Co-based composite alloy coating is promoted from HV87 to HV426. The added nano-Al supplies the interior heatfountain，which compensates for the energy loss caused by the quick heat transmission of Cu-based alloy. The added nano-Al can fully induce the interior chemical reaction，which improves the composite coating forming easily. Ceramic particles are less than 2.0 μm in diameter and dispersed in the strengthened coating.
2008, 25(4): 131-136.
Abstract:
In order to develop a high performance self-lubricating material for bearing inner rings，a kind of stainless steel back tin-bronze gradient self-lubricating composites made of tin-bronze，316L stainless steel and MoS2 powders was prepared by the multi-billet extrusion method and sintering densification process. This material is composed of supporting layer made of 316L stainless steel powders，solid-lubricating layer mixed with tin-bronze and MoS2 powders，and transitional layer mixed with the powders of two front layers. The microstructure was characterized by OM and SEM. The wear and physics mechanical properties were investigated by the MTS and friction-wear tester. The results show that the structure of composites is compact，the interface of each layer transits gently under the process of 1050℃ and the holding time 2 h. The hardness and coefficient of friction gradually increase from the solid-lubricating layer to the supporting layer. The measured average density of sintered composites is 8.35 g·cm-3，and the relative density is 96.8%. The radial crushing strength is 950 MPa. The friction coefficient of working surface of the self-lubricating layer is about 0.30. The micro Vickers hardness of it is 1.44 GPa，and the wear rate is 5.2×10-9 m·N-1·m-1. Compared with other solid-lubricating materials，the mechanical properties and wear resistance capability of stainless steel back tin-bronze gradient self-lubricating composites are greatly improved.
In order to develop a high performance self-lubricating material for bearing inner rings，a kind of stainless steel back tin-bronze gradient self-lubricating composites made of tin-bronze，316L stainless steel and MoS2 powders was prepared by the multi-billet extrusion method and sintering densification process. This material is composed of supporting layer made of 316L stainless steel powders，solid-lubricating layer mixed with tin-bronze and MoS2 powders，and transitional layer mixed with the powders of two front layers. The microstructure was characterized by OM and SEM. The wear and physics mechanical properties were investigated by the MTS and friction-wear tester. The results show that the structure of composites is compact，the interface of each layer transits gently under the process of 1050℃ and the holding time 2 h. The hardness and coefficient of friction gradually increase from the solid-lubricating layer to the supporting layer. The measured average density of sintered composites is 8.35 g·cm-3，and the relative density is 96.8%. The radial crushing strength is 950 MPa. The friction coefficient of working surface of the self-lubricating layer is about 0.30. The micro Vickers hardness of it is 1.44 GPa，and the wear rate is 5.2×10-9 m·N-1·m-1. Compared with other solid-lubricating materials，the mechanical properties and wear resistance capability of stainless steel back tin-bronze gradient self-lubricating composites are greatly improved.
2008, 25(4): 137-142.
Abstract:
ZrW2O8/ZrO2 composites were prepared by calcining the precursor synthesized by the chemical co-precipitation method at 1150℃ for 3.5 h. The precursor of ZrW2O8/ZrO2 was studied by Fourier transform infrared spectroscopy(FTIR) and thermogravimetric and differential scanning calorimetry(TG-DSC). The crystal structure，section morphology and thermal expansion properties of the synthesized composites were investigated by X-ray diffraction (XRD)，scanning electron microscopy (SEM)，energy dispersive spectrometer(EDS) and dilatometry. The results indicate that the obtained composites contain only α-ZrW2O8 phase and m-ZrO2 phase without other phases，which have good chemical uniform and sintering ability. The average thermal expansion coefficient of ZrW2O8/ZrO2 composites decreases with the increase of mass fraction ofZrW2O8. Among all the samples，26%ZrW2O8/ZrO2 composites exhibit nearly zero thermal expansion，and the average thermal expansion coefficient is -0.5649 10-6K-1 from 30℃ to 600℃.
ZrW2O8/ZrO2 composites were prepared by calcining the precursor synthesized by the chemical co-precipitation method at 1150℃ for 3.5 h. The precursor of ZrW2O8/ZrO2 was studied by Fourier transform infrared spectroscopy(FTIR) and thermogravimetric and differential scanning calorimetry(TG-DSC). The crystal structure，section morphology and thermal expansion properties of the synthesized composites were investigated by X-ray diffraction (XRD)，scanning electron microscopy (SEM)，energy dispersive spectrometer(EDS) and dilatometry. The results indicate that the obtained composites contain only α-ZrW2O8 phase and m-ZrO2 phase without other phases，which have good chemical uniform and sintering ability. The average thermal expansion coefficient of ZrW2O8/ZrO2 composites decreases with the increase of mass fraction ofZrW2O8. Among all the samples，26%ZrW2O8/ZrO2 composites exhibit nearly zero thermal expansion，and the average thermal expansion coefficient is -0.5649 10-6K-1 from 30℃ to 600℃.
2008, 25(4): 143-148.
Abstract:
The superconducting material YBa2Cu3O7-δ samples were prepared by the sol-gel method. The tribological properties were measured on a friction and wear tester from ambient temperature to liquid nitrogen temperature. The results indicate that the friction coefficient of YBa2Cu3O7-δ against steeliness is about 0.5 at ambient temperature and decreases abruptly to half of the normal state value when the temperature is below the superconducting transition temperature of the YBa2Cu3O7-δ. The measurements prove directly the effect of electronic excitation on friction. Moreover，PbO/YBa2Cu3O7-δ composite samples were prepared by sintering YBa2Cu3O7-δ with PbO at different mass fractions to improve the tribological properties of YBa2Cu3O7-δ at room temperature. The experimental results show that the friction coefficient of 15%PbO/YBa2Cu3O7-δ is about 0.2~0.3 and the wear rate is 4.35×10-4 mm3·（N·m）-1，and the superconductivity of 15% PbO/YBa2Cu3O7-δ is not degenerated. Finally，the anti-friction and anti-wear mechanism of PbO/YBa2Cu3O7-δ is discussed.
The superconducting material YBa2Cu3O7-δ samples were prepared by the sol-gel method. The tribological properties were measured on a friction and wear tester from ambient temperature to liquid nitrogen temperature. The results indicate that the friction coefficient of YBa2Cu3O7-δ against steeliness is about 0.5 at ambient temperature and decreases abruptly to half of the normal state value when the temperature is below the superconducting transition temperature of the YBa2Cu3O7-δ. The measurements prove directly the effect of electronic excitation on friction. Moreover，PbO/YBa2Cu3O7-δ composite samples were prepared by sintering YBa2Cu3O7-δ with PbO at different mass fractions to improve the tribological properties of YBa2Cu3O7-δ at room temperature. The experimental results show that the friction coefficient of 15%PbO/YBa2Cu3O7-δ is about 0.2~0.3 and the wear rate is 4.35×10-4 mm3·（N·m）-1，and the superconductivity of 15% PbO/YBa2Cu3O7-δ is not degenerated. Finally，the anti-friction and anti-wear mechanism of PbO/YBa2Cu3O7-δ is discussed.
2008, 25(4): 149-153.
Abstract:
The composites of porous SiC ceramics coated with NiFe2O4 (NFPC) were prepared using the polyacrylamide gel method. The structural characteristics，morphology and electromagnetic properties of the composites were analyzed by X-ray diffraction (XRD)，scanning electron microscope (SEM) and HP8510 network analyzer. The results indicate that a pure spinel structure of NiFe2O4 forms on the porous ceramics (PC) at 600℃. The uniformity and consistency of the nickel ferrite coatings on porous ceramics increase with the increase of the layer number of coatings. NFPC exhibits lower dielectric loss tanδε and higher magnetic loss tanδμ compared with the porous ceramics matrix. Its tanδμ rises up to 0.45，which shows a better magnetic loss property. The tanδμ of NFPC decreases with the frequency in X band.
The composites of porous SiC ceramics coated with NiFe2O4 (NFPC) were prepared using the polyacrylamide gel method. The structural characteristics，morphology and electromagnetic properties of the composites were analyzed by X-ray diffraction (XRD)，scanning electron microscope (SEM) and HP8510 network analyzer. The results indicate that a pure spinel structure of NiFe2O4 forms on the porous ceramics (PC) at 600℃. The uniformity and consistency of the nickel ferrite coatings on porous ceramics increase with the increase of the layer number of coatings. NFPC exhibits lower dielectric loss tanδε and higher magnetic loss tanδμ compared with the porous ceramics matrix. Its tanδμ rises up to 0.45，which shows a better magnetic loss property. The tanδμ of NFPC decreases with the frequency in X band.
2008, 25(4): 154-160.
Abstract:
The uniaxial tensile stress-strain behavior of unidirectional fiber reinforced ceramic matrix composites was studied using a micromechanical approach. The Budiansky-Hutchinson-Evans (BHE) shear lag model was used to analyze the micro stress field of the damaged composites. The critical matrix strain energy criterion，strain energy release rate criterion and Curtin's statistical failure criterion were used to describe the matrix cracking，interface debonding and fiber failure，and to determine the matrix cracking space，the interface debonding length and the percentage of the fracture fibers. By combining the shear lag model and three damage models，the stress-strain curve of each damage stage was modeled，and the exact model of predicting the toughness and the strength of the composites was established. The influences of the interface parameter and fiber Weibull modulus on the damage of the composite and the stress-strain curve were discussed. The uniaxial tensile experimental data of ceramic matrix composites at room temperature was compared with the present analysis. The stress-strain curve of each damage stage，the failure strength and strain agreed well with the experimental data.
The uniaxial tensile stress-strain behavior of unidirectional fiber reinforced ceramic matrix composites was studied using a micromechanical approach. The Budiansky-Hutchinson-Evans (BHE) shear lag model was used to analyze the micro stress field of the damaged composites. The critical matrix strain energy criterion，strain energy release rate criterion and Curtin's statistical failure criterion were used to describe the matrix cracking，interface debonding and fiber failure，and to determine the matrix cracking space，the interface debonding length and the percentage of the fracture fibers. By combining the shear lag model and three damage models，the stress-strain curve of each damage stage was modeled，and the exact model of predicting the toughness and the strength of the composites was established. The influences of the interface parameter and fiber Weibull modulus on the damage of the composite and the stress-strain curve were discussed. The uniaxial tensile experimental data of ceramic matrix composites at room temperature was compared with the present analysis. The stress-strain curve of each damage stage，the failure strength and strain agreed well with the experimental data.
2008, 25(4): 161-167.
Abstract:
The primary objective of this paper is to develop the cost estimation software for composite fabrication based on the existing cost models. On the basis of the manufacturing process-based cost modeling，a cost estimation code was developed by using software Delphi and SQL server. The fundamental features，time scaling laws and complexity scaling of the cost modeling were discussed in detail. Moreover，the product complexity scaling factor defined by previous researchers was improved to characterize the complexity of products by introducing a curvature entropy concept. The whole scheme and flow of the cost estimation code were proposed，and the cost database management was established. The cost of a simple curved composite part was evaluated using the developed code. The costs of two kinds of ailerons manufactured with advanced composite and traditional metal materials were also estimated. The results indicate that the manufacturing cost of the composite aileron is lower than that of the metal aileron because of using the low-cost process and integrated design concept.
The primary objective of this paper is to develop the cost estimation software for composite fabrication based on the existing cost models. On the basis of the manufacturing process-based cost modeling，a cost estimation code was developed by using software Delphi and SQL server. The fundamental features，time scaling laws and complexity scaling of the cost modeling were discussed in detail. Moreover，the product complexity scaling factor defined by previous researchers was improved to characterize the complexity of products by introducing a curvature entropy concept. The whole scheme and flow of the cost estimation code were proposed，and the cost database management was established. The cost of a simple curved composite part was evaluated using the developed code. The costs of two kinds of ailerons manufactured with advanced composite and traditional metal materials were also estimated. The results indicate that the manufacturing cost of the composite aileron is lower than that of the metal aileron because of using the low-cost process and integrated design concept.
2008, 25(4): 168-173.
Abstract:
A new hybrid method by conjunction of the smearing model with the stiffened model is formulated to analyze the composite advanced grid stiffened structures (AGS). The smearing model is homogenizing the stiffness of stiffeners based on the structural mechanics theory and the grid panel therefore can be equivalent to a plate. The stiffened element model is an exact method，which can provide the compatibility between stiffeners and plate. In addition，the numbers and orientation of the stiffeners of the element can be defined randomly by users. The numerical results indicate that the hybrid method is effective and accurate. It is also known that the smearing model is remarkably affected by the distance and height of the ribs. The limitation of the hybrid method is investigated by simulating the grid-stiffened plate with a central circular cutout.
A new hybrid method by conjunction of the smearing model with the stiffened model is formulated to analyze the composite advanced grid stiffened structures (AGS). The smearing model is homogenizing the stiffness of stiffeners based on the structural mechanics theory and the grid panel therefore can be equivalent to a plate. The stiffened element model is an exact method，which can provide the compatibility between stiffeners and plate. In addition，the numbers and orientation of the stiffeners of the element can be defined randomly by users. The numerical results indicate that the hybrid method is effective and accurate. It is also known that the smearing model is remarkably affected by the distance and height of the ribs. The limitation of the hybrid method is investigated by simulating the grid-stiffened plate with a central circular cutout.
2008, 25(4): 174-180.
Abstract:
Considering the contribution of out-of-plane stresses and strains to laminate structural modal damping in FEM with fewer elements in the thickness direction，a composite structural modal damping prediction theory is presented based on the 3-D effective damping matrix. The composite structure was divided into several sub laminates along the thickness，and each sub laminate contains many laminas. These sub laminates'stiffness matrices，compliance matrices and 3-D effective damping matrices were calculated by the synthesizing theory. The finite elements were generated with these sub laminates，and a structural modal analysis was executed. Combining the 3-D effective damping matrices and the results of the modal analysis，specific damping capacities for each modal were calculated. The presented method is validated by the calculations for structural specific damping capacities of unidirectional laminates，symmetrical laminates and thick laminates. This method combines the accuracy and efficiency with the consideration of the contribution of out-of-plane stresses and strains.
Considering the contribution of out-of-plane stresses and strains to laminate structural modal damping in FEM with fewer elements in the thickness direction，a composite structural modal damping prediction theory is presented based on the 3-D effective damping matrix. The composite structure was divided into several sub laminates along the thickness，and each sub laminate contains many laminas. These sub laminates'stiffness matrices，compliance matrices and 3-D effective damping matrices were calculated by the synthesizing theory. The finite elements were generated with these sub laminates，and a structural modal analysis was executed. Combining the 3-D effective damping matrices and the results of the modal analysis，specific damping capacities for each modal were calculated. The presented method is validated by the calculations for structural specific damping capacities of unidirectional laminates，symmetrical laminates and thick laminates. This method combines the accuracy and efficiency with the consideration of the contribution of out-of-plane stresses and strains.
2008, 25(4): 181-186.
Abstract:
The paper tensile experiment and FEA methods were used to study the damage propagation and failure properties of stiffened composite panels with discrete-source damage. The research results indicate that a notched composite panel is suitable to simulate the discrete-source damage of the stiffened composite panels with discrete-source damage，and there is high strain concentration at the notch end. Break-through of the stringer made the load path changed. Based on the Hashin failure criterion，the FEA method with progressive failure procedure can be used to simulate the notched stiffened composite panels'damage progression and failure procedure effectively. The analytical results have a good correlation with the experimental data.
The paper tensile experiment and FEA methods were used to study the damage propagation and failure properties of stiffened composite panels with discrete-source damage. The research results indicate that a notched composite panel is suitable to simulate the discrete-source damage of the stiffened composite panels with discrete-source damage，and there is high strain concentration at the notch end. Break-through of the stringer made the load path changed. Based on the Hashin failure criterion，the FEA method with progressive failure procedure can be used to simulate the notched stiffened composite panels'damage progression and failure procedure effectively. The analytical results have a good correlation with the experimental data.
2008, 25(4): 187-192.
Abstract:
The interfacial shear stress of a three dimensional freezing slice of single-fiber pullout resin matrix composites under the combined effect of pullout loading and thermal residual stress was studied using the three dimensional photo-elasticity and the finite element method. The results show that the value of the interfacial thermal residual stress reaches its peaks near the ends of the embedded fiber in the interface of the single-fiber and the matrix. The interfacial shear stress presents a parabolic distribution，and the transferring area mainly focuses on the region of the embedded top of the fiber where the stress reaches the critical point first，causing the debonding of the interface，and then the shear stress transfers along the embedded fiber. The effect of interfacial thermal residual stress on the interfacial shear stress reduces the stress concentration near the end of the embedded fiber，making the maximum of the interfacial shear stress increase.
The interfacial shear stress of a three dimensional freezing slice of single-fiber pullout resin matrix composites under the combined effect of pullout loading and thermal residual stress was studied using the three dimensional photo-elasticity and the finite element method. The results show that the value of the interfacial thermal residual stress reaches its peaks near the ends of the embedded fiber in the interface of the single-fiber and the matrix. The interfacial shear stress presents a parabolic distribution，and the transferring area mainly focuses on the region of the embedded top of the fiber where the stress reaches the critical point first，causing the debonding of the interface，and then the shear stress transfers along the embedded fiber. The effect of interfacial thermal residual stress on the interfacial shear stress reduces the stress concentration near the end of the embedded fiber，making the maximum of the interfacial shear stress increase.
2008, 25(4): 193-197.
Abstract:
A winding mode on the elbow mandrel was designed. The differential equation of the cord thread winding locus on the elbow mandrel was derived and solved numerically by means of fourth-order Runge-Kutta numerical procedure with the self-adapting step length. The theoretical and experimental results indicate that the winding angle of the cord on the straight part of the elbow mandrel is constant if the axis of mandrel coincides with the rotating center of the yarn tray. If the axis of mandrel departs from the rotating center of the yarn tray，the winding angle is variable. When the cord thread winds on the curved part of the elbow mandrel，the winding angle is always variable and reaches its extreme value on its both sides，which is consistent with experimental results.
A winding mode on the elbow mandrel was designed. The differential equation of the cord thread winding locus on the elbow mandrel was derived and solved numerically by means of fourth-order Runge-Kutta numerical procedure with the self-adapting step length. The theoretical and experimental results indicate that the winding angle of the cord on the straight part of the elbow mandrel is constant if the axis of mandrel coincides with the rotating center of the yarn tray. If the axis of mandrel departs from the rotating center of the yarn tray，the winding angle is variable. When the cord thread winds on the curved part of the elbow mandrel，the winding angle is always variable and reaches its extreme value on its both sides，which is consistent with experimental results.
2008, 25(4): 198-204.
Abstract:
Based on the classical lenticular model，with a positive-negative-pre-overlap method，combined with visualization technology，the cross-section deformation rule is studied in this paper. “Concave convex alternate model” is presented and its mathematical function is deduced. The research shows that the tow‘s concave cross-section alternates with the convex one periodically in length. The classical “invariant cross-section assumption” is amended，which has dominated the academic world for many years. A breakthrough has been made in the cross-section research.
Based on the classical lenticular model，with a positive-negative-pre-overlap method，combined with visualization technology，the cross-section deformation rule is studied in this paper. “Concave convex alternate model” is presented and its mathematical function is deduced. The research shows that the tow‘s concave cross-section alternates with the convex one periodically in length. The classical “invariant cross-section assumption” is amended，which has dominated the academic world for many years. A breakthrough has been made in the cross-section research.
