2009 Vol. 26, No. 6
2009, 26(6): 1-7.
Abstract:
The quasi-static and dynamic compressive properties of glass-fiber polymer composites embedded with different mass fractions ZnO whiskers were investigated by an Instron testing machine and a split-Hopkinson pressure bar in the normal direction and the in-plane direction，respectively. In each direction，the stress-strain curve was obtained and the failure mechanism of materials was investigated by the macroscopic and microscopic observation of fractured specimens. The experimental results show that the materials have obvious non-linear constitutive relation and strain rate strengthening effects. The specimens have various failure modes，in each direction. The peak stress and failure strain of the specimens are both related with the mass fraction of ZnO whiskers.
The quasi-static and dynamic compressive properties of glass-fiber polymer composites embedded with different mass fractions ZnO whiskers were investigated by an Instron testing machine and a split-Hopkinson pressure bar in the normal direction and the in-plane direction，respectively. In each direction，the stress-strain curve was obtained and the failure mechanism of materials was investigated by the macroscopic and microscopic observation of fractured specimens. The experimental results show that the materials have obvious non-linear constitutive relation and strain rate strengthening effects. The specimens have various failure modes，in each direction. The peak stress and failure strain of the specimens are both related with the mass fraction of ZnO whiskers.
2009, 26(6): 8-17.
Abstract:
The sisal fiber (SF) reinforced polypropylene composites were manufactured by injection molding. The effects of fiber content，fiber length distribution，matrix types and compatibilizer types on the impact strength of the composites were studied. The distribution of individual fiber tensile strength was analyzed. The tensile strength of fibers at the critical fiber length was estimated by the modified Weibull distribution model. The impact strength of the composites was predicted. The results show that the impact strength increases with the fiber content. The matrix types have important influence on the impact strength. Owing to forming a rigid interfacial layer between the matrix and fiber，the MAPP compatibilizer has a negative influence on the impact strength，while the PP-g-GMA compatibilizer has a positive influence on the impact strength owing to forming a soft interfacial layer. The impact strength of the composite with PP-g-GMA is 21.7% higher than with MAPP at the same compatibilizer content. When the softer interfacial layer is introduced through the reactions of the natural fiber treated by KH550 silane with PP-g-GMA compatibilizer，the impact strength is 50.7% higher than that with MAPP. The predicted and the experimental values are reasonably well approximated considering the fiber orientation factor to the impact strength model.
The sisal fiber (SF) reinforced polypropylene composites were manufactured by injection molding. The effects of fiber content，fiber length distribution，matrix types and compatibilizer types on the impact strength of the composites were studied. The distribution of individual fiber tensile strength was analyzed. The tensile strength of fibers at the critical fiber length was estimated by the modified Weibull distribution model. The impact strength of the composites was predicted. The results show that the impact strength increases with the fiber content. The matrix types have important influence on the impact strength. Owing to forming a rigid interfacial layer between the matrix and fiber，the MAPP compatibilizer has a negative influence on the impact strength，while the PP-g-GMA compatibilizer has a positive influence on the impact strength owing to forming a soft interfacial layer. The impact strength of the composite with PP-g-GMA is 21.7% higher than with MAPP at the same compatibilizer content. When the softer interfacial layer is introduced through the reactions of the natural fiber treated by KH550 silane with PP-g-GMA compatibilizer，the impact strength is 50.7% higher than that with MAPP. The predicted and the experimental values are reasonably well approximated considering the fiber orientation factor to the impact strength model.
2009, 26(6): 18-24.
Abstract:
Hybrid composites reinforced with Fe-based amorphous ribbons and glass fibers were manufactured and mechanical properties were studied. Influences of surface treatment and heat treatment of ribbons on their properties were investigated. The failure mechanism of the hybrid composite was analyzed. The surface of the ribbon was roughened and its surface energy was increased，the bonding st rength between ribbon and different resins was increased by surface treatment，while axial tensile properties of the ribbon did not change a lot. The longitudinal elastic modulus obeys the rule of mixture while the transverse tensile strength and modulus are mainly contributed by amorphous ribbons. Delamination between fiber layer and ribbon layer as well as fracture of fiber in the compressed side was observed in the flexure and interlaminar shear specimens.
Hybrid composites reinforced with Fe-based amorphous ribbons and glass fibers were manufactured and mechanical properties were studied. Influences of surface treatment and heat treatment of ribbons on their properties were investigated. The failure mechanism of the hybrid composite was analyzed. The surface of the ribbon was roughened and its surface energy was increased，the bonding st rength between ribbon and different resins was increased by surface treatment，while axial tensile properties of the ribbon did not change a lot. The longitudinal elastic modulus obeys the rule of mixture while the transverse tensile strength and modulus are mainly contributed by amorphous ribbons. Delamination between fiber layer and ribbon layer as well as fracture of fiber in the compressed side was observed in the flexure and interlaminar shear specimens.
2009, 26(6): 25-30.
Abstract:
The isobutylene-isoprene rubber(IIR) composites were prepared by the melt blending method containing nanoparticle fillers with different morphologies and structures including organomontmorillonites (OMMT)，silica aerogel and precipitated silica. Microstructures of the IIR composites were characterized via SEM and XRD. Effects of nanofillers on the mechanical properties，mustard protection and flammability of the composites were also investigated. The results show that the IIR composites reinforced with 15 wt% nanometer silica aerogel have the best mechanical properties and the tensile strength and tear strength are 9 and 2.2 times greater than those of the pure IIR vulcanizate. The mustard protection of the composites has close relation to particle shapes of nanofillers. Compared with the composite reinforced with sphere like silica aerogel or precipitated silica，the plate-like OMMT/IIR composites show more out standing mustard protection and offer over 21 hours protection against mustard when 15 wt% OMMT is added. Unfortunately，nanofillers do not exhibit remarkable flame retardancy in experiments and oxygen indexes and oxidative decomposition temperatures of the composites only increase a little compared with the pure IIR vulcanizate.
The isobutylene-isoprene rubber(IIR) composites were prepared by the melt blending method containing nanoparticle fillers with different morphologies and structures including organomontmorillonites (OMMT)，silica aerogel and precipitated silica. Microstructures of the IIR composites were characterized via SEM and XRD. Effects of nanofillers on the mechanical properties，mustard protection and flammability of the composites were also investigated. The results show that the IIR composites reinforced with 15 wt% nanometer silica aerogel have the best mechanical properties and the tensile strength and tear strength are 9 and 2.2 times greater than those of the pure IIR vulcanizate. The mustard protection of the composites has close relation to particle shapes of nanofillers. Compared with the composite reinforced with sphere like silica aerogel or precipitated silica，the plate-like OMMT/IIR composites show more out standing mustard protection and offer over 21 hours protection against mustard when 15 wt% OMMT is added. Unfortunately，nanofillers do not exhibit remarkable flame retardancy in experiments and oxygen indexes and oxidative decomposition temperatures of the composites only increase a little compared with the pure IIR vulcanizate.
2009, 26(6): 31-36.
Abstract:
POSS/PS composite was synthesized through the condensation reaction of 3-chloropropylheptaisooctyl-POSS and functional PS. Sodium alkoxide group was attached to PS chain by three steps and the monofunctional POSS molecule containing one single 3-chloropropyl group was synthesized by the corner-capping method. The structures of all intermediates and the POSS/PS composite were well characterized by 1H NMR，FTIR and XRD. The results show that the condensation reaction of 3-chloropropylheptaisooctyl-POSS and functional PS is efficient，and POSS is well dispersed in the composite. The thermal properties were investigated by a differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA). The data indicate that the glass transition temperature (Tg) and the initial decomposition temperature (Tdec) of POSS/PS composite are 16℃ and 69℃ higher than those of the pure PS，respectively，which is mainly due to the incorporation of POSS unit.
POSS/PS composite was synthesized through the condensation reaction of 3-chloropropylheptaisooctyl-POSS and functional PS. Sodium alkoxide group was attached to PS chain by three steps and the monofunctional POSS molecule containing one single 3-chloropropyl group was synthesized by the corner-capping method. The structures of all intermediates and the POSS/PS composite were well characterized by 1H NMR，FTIR and XRD. The results show that the condensation reaction of 3-chloropropylheptaisooctyl-POSS and functional PS is efficient，and POSS is well dispersed in the composite. The thermal properties were investigated by a differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA). The data indicate that the glass transition temperature (Tg) and the initial decomposition temperature (Tdec) of POSS/PS composite are 16℃ and 69℃ higher than those of the pure PS，respectively，which is mainly due to the incorporation of POSS unit.
2009, 26(6): 37-41.
Abstract:
FEP-based composites filled with alumina platelets were prepared by the physical blending method. The thermal conductivity and elongation of the composites containing Al2O3 platelets were studied in comparison with Al2O3 particles as filler. The microstructure of the composites was also observed by SEM. The results show that the Al2O3 fillers with low mass fractions display an island distribution in the FEP matrix and cannot form the continuous thermal conduction chains. However，the thermal conductivities of the composites greatly increase compared with the single FEP. The tensile strength and the elongation at break of the composites decrease with the increase of the Al2O3 content . The increasing thermal conductivity of the composites containing fine alumina platelets is associated with the prolonged heat conducting path and the interface between the fillers and FEP.
FEP-based composites filled with alumina platelets were prepared by the physical blending method. The thermal conductivity and elongation of the composites containing Al2O3 platelets were studied in comparison with Al2O3 particles as filler. The microstructure of the composites was also observed by SEM. The results show that the Al2O3 fillers with low mass fractions display an island distribution in the FEP matrix and cannot form the continuous thermal conduction chains. However，the thermal conductivities of the composites greatly increase compared with the single FEP. The tensile strength and the elongation at break of the composites decrease with the increase of the Al2O3 content . The increasing thermal conductivity of the composites containing fine alumina platelets is associated with the prolonged heat conducting path and the interface between the fillers and FEP.
2009, 26(6): 42-47.
Abstract:
In order to further understand the stretching effect of polymer-based composites，the Ni/PVDF films were prepared using a simple physics blending and then stretched at 120℃ to improve the electronic properties. The results show that there is an abrupt increase of 17 times (12→220) in the dielectric constant of the stretched samples at the stretching ratio of 2.3 with Ni content less than the percolation threshold，which is similar to percolation and named stretching-induced percolation. Additionally，an insulation-conduction transition tends to occur with enhancement of 4～5 orders of magnitude in conductivity after stretching. The enhancement in the dielectric constant with increase of stretching ratio is attributed to the gradual formation of conductive networks induced by stretching，which consists of a great many nickel groups and micro-parallel-capacitors. The large increase in conductivity is in agreement with the percolation theory before and after stretching.
In order to further understand the stretching effect of polymer-based composites，the Ni/PVDF films were prepared using a simple physics blending and then stretched at 120℃ to improve the electronic properties. The results show that there is an abrupt increase of 17 times (12→220) in the dielectric constant of the stretched samples at the stretching ratio of 2.3 with Ni content less than the percolation threshold，which is similar to percolation and named stretching-induced percolation. Additionally，an insulation-conduction transition tends to occur with enhancement of 4～5 orders of magnitude in conductivity after stretching. The enhancement in the dielectric constant with increase of stretching ratio is attributed to the gradual formation of conductive networks induced by stretching，which consists of a great many nickel groups and micro-parallel-capacitors. The large increase in conductivity is in agreement with the percolation theory before and after stretching.
2009, 26(6): 48-53.
Abstract:
Pressure sensitive superconductor/polymer composites were prepared using silicone rubber and high temperature superconductor YBa2Cu3O7 +δ(YBCO) powder at different mass ratios. The piezoresistance and the dielectric properties of the composite samples at room temperature were measured. It was found that the resistance of all samples decreases exponentially with increasing pressure：application of different pressurees could result in a decease of 1～4 orders of magnitude in resistivity. Both resistivity and its sensitivity to external pressure vary with the superconductor filler content. The electrical resistivity was also measured as a function of temperature for samples from 300～50 K. The result shows that the change of resistivity is considerably larger. There are sharp decreases in the resistivity of superconductor/polymer composite samples below 90 K，but the sample of superconduction with zero resistivity was not found from 90～50 K. The dielectric content and dielectric loss of the composite at room temperature decrease with increasing frequency in the range from 1000 Hz to 5 MHz. It is found that both dielectric constant and dielectric loss are strongly dependent on the YBCO content. With increasing YBCO content，the dielectric constant and dielectric loss of all samples are larger.
Pressure sensitive superconductor/polymer composites were prepared using silicone rubber and high temperature superconductor YBa2Cu3O7 +δ(YBCO) powder at different mass ratios. The piezoresistance and the dielectric properties of the composite samples at room temperature were measured. It was found that the resistance of all samples decreases exponentially with increasing pressure：application of different pressurees could result in a decease of 1～4 orders of magnitude in resistivity. Both resistivity and its sensitivity to external pressure vary with the superconductor filler content. The electrical resistivity was also measured as a function of temperature for samples from 300～50 K. The result shows that the change of resistivity is considerably larger. There are sharp decreases in the resistivity of superconductor/polymer composite samples below 90 K，but the sample of superconduction with zero resistivity was not found from 90～50 K. The dielectric content and dielectric loss of the composite at room temperature decrease with increasing frequency in the range from 1000 Hz to 5 MHz. It is found that both dielectric constant and dielectric loss are strongly dependent on the YBCO content. With increasing YBCO content，the dielectric constant and dielectric loss of all samples are larger.
2009, 26(6): 54-60.
Abstract:
Montmorillonite was modified，and organo montmorillonite/poly(vinylidene) fluoride hexafluoropropylene composed polymer electrolyte was prepared. Its morphologies and properties were characterized by scanning electron micrograph and XRD. The electrochemical properties of polymer batteries were studied with the AC impedance and charging-discharging test. The results show that the composed polymer membrane has rich micro-pores and exhibits 1.51 mS/cm of ionic conductivity at room temperature，and its electrochemical stability window reaches 5.5 V. When discharging at 0.1 current rate，the capacity maintenance ratio of the polymer battery prepared by LiCoO2 cathode material is 95.3% after 50 cycles，and the polymer battery has excellent rate performance. By adding OMMT into polymer electrolyte，the interfacial impedance of polymer battery is stable，and its cycling performance is improved.
Montmorillonite was modified，and organo montmorillonite/poly(vinylidene) fluoride hexafluoropropylene composed polymer electrolyte was prepared. Its morphologies and properties were characterized by scanning electron micrograph and XRD. The electrochemical properties of polymer batteries were studied with the AC impedance and charging-discharging test. The results show that the composed polymer membrane has rich micro-pores and exhibits 1.51 mS/cm of ionic conductivity at room temperature，and its electrochemical stability window reaches 5.5 V. When discharging at 0.1 current rate，the capacity maintenance ratio of the polymer battery prepared by LiCoO2 cathode material is 95.3% after 50 cycles，and the polymer battery has excellent rate performance. By adding OMMT into polymer electrolyte，the interfacial impedance of polymer battery is stable，and its cycling performance is improved.
2009, 26(6): 61-65.
Abstract:
The hollow glass microspheres were coated with Al by DC magnetron sputtering. XRD and SEM were used to investigate the structure and morphology of the microspheres coated with Al，respectively. The hollow glass microspheres coated and uncoated with Al，as well as the polymer binder were used to prepare the artificial dielectric materials，and the dielectric properties at 8.2~12.4 GHz were measured with a network vector analyzer. The results show that the hollow glass microspheres could be coated with Al film by a magnetron sputtering，and the Al films are combined well with the microsphere substrates. At the same addition amount of the microspheres coated with Al，the dielectric constant of the artificial dielectric materials increases with the thickness of Al film. Meanwhile，keeping the thickness of Al film constant，the dielectric constant of the artificial dielectric materials increases with the addition amount of microspheres coated with Al. The artificial dielectric material has a low dielectric loss of less 3 than 0.02 and a low density of no greater than 0.8g/cm.
The hollow glass microspheres were coated with Al by DC magnetron sputtering. XRD and SEM were used to investigate the structure and morphology of the microspheres coated with Al，respectively. The hollow glass microspheres coated and uncoated with Al，as well as the polymer binder were used to prepare the artificial dielectric materials，and the dielectric properties at 8.2~12.4 GHz were measured with a network vector analyzer. The results show that the hollow glass microspheres could be coated with Al film by a magnetron sputtering，and the Al films are combined well with the microsphere substrates. At the same addition amount of the microspheres coated with Al，the dielectric constant of the artificial dielectric materials increases with the thickness of Al film. Meanwhile，keeping the thickness of Al film constant，the dielectric constant of the artificial dielectric materials increases with the addition amount of microspheres coated with Al. The artificial dielectric material has a low dielectric loss of less 3 than 0.02 and a low density of no greater than 0.8g/cm.
2009, 26(6): 66-71.
Abstract:
T-stiffened skins widely used in aircraft industry nowadays were fabricated by integral molding technology of co-bonding in autoclave. A method of self-designed solid pressure testing was introduced to measure the pressure distribution in the T-stiffeners during fabrication. The resin flow and fiber compaction of T-stiffened skins were investigated by analyzing the bleeding quantity and stiffener thickness. The results indicate that the presence of significant resin flow in plane is induced by pressure difference distributing in the various zones of the stiffeners，which results in some manufacturing defects of rich resin and non-uniform thickness in the corner section of stiffeners. Theratios of the thickness of the corner to the web and to the flange are almost in the range of 1.1~1.4. Moreover，the resin flow and fiber compaction are remarkably influenced by tool assembly schemes，curvature radii and fillers.
T-stiffened skins widely used in aircraft industry nowadays were fabricated by integral molding technology of co-bonding in autoclave. A method of self-designed solid pressure testing was introduced to measure the pressure distribution in the T-stiffeners during fabrication. The resin flow and fiber compaction of T-stiffened skins were investigated by analyzing the bleeding quantity and stiffener thickness. The results indicate that the presence of significant resin flow in plane is induced by pressure difference distributing in the various zones of the stiffeners，which results in some manufacturing defects of rich resin and non-uniform thickness in the corner section of stiffeners. Theratios of the thickness of the corner to the web and to the flange are almost in the range of 1.1~1.4. Moreover，the resin flow and fiber compaction are remarkably influenced by tool assembly schemes，curvature radii and fillers.
2009, 26(6): 72-77.
Abstract:
An apparatus was designed and constructed capable of measuring the permeability of unidirectional fiber bundles. In order to analyse the axial permeation，saturated and unsaturated permeabilities were compared，and the influences of pressure type，fiber volume fraction and types of liquid on the unsaturated permeability were investigated. It is found that the saturated permeability is bigger than unsaturated permeability under the same test condition，and the influence of capillary force on unsaturated permeability reduces with increasing the external pressure. Besides，as the fiber volume fraction increases，the permeability declines and the permeability from the vacuum drive test is larger than that from the air drive test under the same pressure.
An apparatus was designed and constructed capable of measuring the permeability of unidirectional fiber bundles. In order to analyse the axial permeation，saturated and unsaturated permeabilities were compared，and the influences of pressure type，fiber volume fraction and types of liquid on the unsaturated permeability were investigated. It is found that the saturated permeability is bigger than unsaturated permeability under the same test condition，and the influence of capillary force on unsaturated permeability reduces with increasing the external pressure. Besides，as the fiber volume fraction increases，the permeability declines and the permeability from the vacuum drive test is larger than that from the air drive test under the same pressure.
2009, 26(6): 78-84.
Abstract:
Dynamic mechanical analysis (DMA) is an important method to study the cure process of prepregs. It was used to investigate the isothermal curing of the 648 epoxy prepreg. Based on the relative conversion definition of the increase in storage modulus E′，the evolution of E′ at different isothermal temperatures was studied. It was found that the increase of E′ during isothermal cure process at high temperatures is different from the one at low temperatures. The low temperature conversion curve includes a transitional stage which was not observed in the high temperature curves，and this transitional stage is found to be strongly frequency-dependent. Hsich‘s non-equilibrium thermodynamic fluctuation theory and Avrami equation are fitted to the conversion curves of E′，and can describe the evolution of E′ by two separate stages. The value and evolution of activation energy calculated by Avrami equation and the isoconversional methods are different in different temperature regions.
Dynamic mechanical analysis (DMA) is an important method to study the cure process of prepregs. It was used to investigate the isothermal curing of the 648 epoxy prepreg. Based on the relative conversion definition of the increase in storage modulus E′，the evolution of E′ at different isothermal temperatures was studied. It was found that the increase of E′ during isothermal cure process at high temperatures is different from the one at low temperatures. The low temperature conversion curve includes a transitional stage which was not observed in the high temperature curves，and this transitional stage is found to be strongly frequency-dependent. Hsich‘s non-equilibrium thermodynamic fluctuation theory and Avrami equation are fitted to the conversion curves of E′，and can describe the evolution of E′ by two separate stages. The value and evolution of activation energy calculated by Avrami equation and the isoconversional methods are different in different temperature regions.
2009, 26(6): 85-90.
Abstract:
Glass fibers were surface treated with polymethylmethacrylate (PMMA) acetone solutions of various concent rations. The amount of PMMA on glass fiber，surface nature of glass fibers and the interfacial and mechanical properties of the treated glass fiber/dental resin composites were investigated. The results show that PMMA polymer adhered to the glass fiber surface and the amount of PMMA on the glass fiber surface increases with increasing concentration of PMMA solution. By controlling the mass fraction of PMMA on the glass fiber surface about 1%，a perfect semi-interpenet rating polymer network interface is formed between glass fiber and dental resin matrix. The flexural strength and flexural modulus of the treated glass fiber/dental resin composites increase by 29.6% and 30% after being treated with 5% PMMA solution，which could be used as a new bio-composite for dental restoration.
Glass fibers were surface treated with polymethylmethacrylate (PMMA) acetone solutions of various concent rations. The amount of PMMA on glass fiber，surface nature of glass fibers and the interfacial and mechanical properties of the treated glass fiber/dental resin composites were investigated. The results show that PMMA polymer adhered to the glass fiber surface and the amount of PMMA on the glass fiber surface increases with increasing concentration of PMMA solution. By controlling the mass fraction of PMMA on the glass fiber surface about 1%，a perfect semi-interpenet rating polymer network interface is formed between glass fiber and dental resin matrix. The flexural strength and flexural modulus of the treated glass fiber/dental resin composites increase by 29.6% and 30% after being treated with 5% PMMA solution，which could be used as a new bio-composite for dental restoration.
2009, 26(6): 91-96.
Abstract:
By means of scanning electronic microscope (SEM)，laser scanning confocal microscope (LSCM) and mechanical properties measuring，the microstructure morphology and the compressive mechanical properties of the 3D C/C composite along x，y and z directions were studied. The results show that there are obvious defects，and there is weak adhesion in the fiber/matrix interface of the 3D C/C composite. The compressive strength and fracture strain along z direction are all much greater than those along x direction and y direction. The compressive fracture mechanism of 3D C/C composite was also investigated based on the macro-pictures of the fracture surface of specimens. The results show that the compressive stress-strain curves exhibit the almost linear characteristics at the beginning，and show nonlinear characteristics with the time. Failure models of the samples under compressive load along x，y and z directions present shear fracture. The fiber/matrix interfacial strength has a great effect on the compressive failure mechanism.
By means of scanning electronic microscope (SEM)，laser scanning confocal microscope (LSCM) and mechanical properties measuring，the microstructure morphology and the compressive mechanical properties of the 3D C/C composite along x，y and z directions were studied. The results show that there are obvious defects，and there is weak adhesion in the fiber/matrix interface of the 3D C/C composite. The compressive strength and fracture strain along z direction are all much greater than those along x direction and y direction. The compressive fracture mechanism of 3D C/C composite was also investigated based on the macro-pictures of the fracture surface of specimens. The results show that the compressive stress-strain curves exhibit the almost linear characteristics at the beginning，and show nonlinear characteristics with the time. Failure models of the samples under compressive load along x，y and z directions present shear fracture. The fiber/matrix interfacial strength has a great effect on the compressive failure mechanism.
2009, 26(6): 97-102.
Abstract:
A novel C/C/Cu composite with excellent wear resistance was fabricated by pressureless infiltration. The tribological behavior of the composite was evaluated using UMT-3 test system，and compared with C/Cu composite prepared by traditional powder metallurgy process. C/C/Cu composite has better electrical conductivity and mechanical performance compared to C/Cu composite，which may be attributed to the 3D net-like interconnected structure. The friction coefficients of both composites are similar. The wear rates of both the composites and corresponding counterparts increase with the rising load. C/C/Cu composite shows a significantly better wear resistance and causes small damage to the counterpart，especially under a load of 70N. The interconnected structure and a continuous debris layer are main causes for favorable tribological characteristics of C/C/Cu composite.
A novel C/C/Cu composite with excellent wear resistance was fabricated by pressureless infiltration. The tribological behavior of the composite was evaluated using UMT-3 test system，and compared with C/Cu composite prepared by traditional powder metallurgy process. C/C/Cu composite has better electrical conductivity and mechanical performance compared to C/Cu composite，which may be attributed to the 3D net-like interconnected structure. The friction coefficients of both composites are similar. The wear rates of both the composites and corresponding counterparts increase with the rising load. C/C/Cu composite shows a significantly better wear resistance and causes small damage to the counterpart，especially under a load of 70N. The interconnected structure and a continuous debris layer are main causes for favorable tribological characteristics of C/C/Cu composite.
2009, 26(6): 103-108.
Abstract:
The corrosion behavior of SiCP/Al composites with different SiCP sizes (220，140，90，70μm) and different SiCP volume fractions (42%，49%，55%) was investigated by the alternate immersion test. Mass loss was used to evaluate the corrosion rate. The microstructure of composites was observed by the optical microscope (OM). The phase and surface photography of corrosion products were analyzed by the X-ray diffraction (XRD) and scanning electron microscope (SEM) . Experimental results show that the corrosion resistance of the SiCP/Al composites decreases with decreasing the particle size in the initial stage of corrosion，but increases with decreasing the particle size in the corrosion latter stage. SiCP accelerates the nucleation of pit，also interrupts the continuity of the matrix channels，alters the growth way and suppresses the further expansion. The corrosion resistance of the SiCP/Al composites decreases with the increasing the particle content，of which the main corrosion products are Al2O3 and AlxSO4y OHz.
The corrosion behavior of SiCP/Al composites with different SiCP sizes (220，140，90，70μm) and different SiCP volume fractions (42%，49%，55%) was investigated by the alternate immersion test. Mass loss was used to evaluate the corrosion rate. The microstructure of composites was observed by the optical microscope (OM). The phase and surface photography of corrosion products were analyzed by the X-ray diffraction (XRD) and scanning electron microscope (SEM) . Experimental results show that the corrosion resistance of the SiCP/Al composites decreases with decreasing the particle size in the initial stage of corrosion，but increases with decreasing the particle size in the corrosion latter stage. SiCP accelerates the nucleation of pit，also interrupts the continuity of the matrix channels，alters the growth way and suppresses the further expansion. The corrosion resistance of the SiCP/Al composites decreases with the increasing the particle content，of which the main corrosion products are Al2O3 and AlxSO4y OHz.
2009, 26(6): 109-115.
Abstract:
Taking the mixture powders of Cu-Ni-Y2O3 MoS2 Graphite as the matrix，and adding nano-Al2O3 mass fraction of 0%，1%，2%，3% and 4% as the particle ment reinforce phase，Cu- based self-lubricating composite was prepared by powder metallurgy technology. The results show that the density of the samples decreases with increasing the content of nano-Al2O3，but the hardness and crushing strength of the samples increase firstly，then decrease. The hardness increas from HV 23.7 to HV 35.1 and the crushing strength increases from 189 to 276 MPa with the increasing mass frautions of nano-Al2O3 from 0% to 2%. Friction coefficient of the materials with the mixture of graphite and MoS2 is about 0.12. The least wear loss is 1/7~1/8 by contrasting the sample with non-nano-Al2O3. The copper-based self-lubricating composites reinforced with Ni and nano-Al2O3 by dispersion strengthening，and added with graphite and MoS2 as solid lubricant，have definite self-lubricating property.
Taking the mixture powders of Cu-Ni-Y2O3 MoS2 Graphite as the matrix，and adding nano-Al2O3 mass fraction of 0%，1%，2%，3% and 4% as the particle ment reinforce phase，Cu- based self-lubricating composite was prepared by powder metallurgy technology. The results show that the density of the samples decreases with increasing the content of nano-Al2O3，but the hardness and crushing strength of the samples increase firstly，then decrease. The hardness increas from HV 23.7 to HV 35.1 and the crushing strength increases from 189 to 276 MPa with the increasing mass frautions of nano-Al2O3 from 0% to 2%. Friction coefficient of the materials with the mixture of graphite and MoS2 is about 0.12. The least wear loss is 1/7~1/8 by contrasting the sample with non-nano-Al2O3. The copper-based self-lubricating composites reinforced with Ni and nano-Al2O3 by dispersion strengthening，and added with graphite and MoS2 as solid lubricant，have definite self-lubricating property.
2009, 26(6): 116-120.
Abstract:
A new technology，thixo-die-forging of composite in pseudo-semi-solid state was proposed based on powder metallurgy technology combing with semi-solid metal process，and the cup shell with Al/Al2O3 composite was prepared successfully. The metallographic analysis and performance test show that the microstructure of Al/Al2O3 is dense and mechanical properties are excellent. The bend strength and fracture toughness of the composite are about 430~690 MPa and 8.5~16.8 MPa·m1/2 respectively，in which the volume fraction of Al is 37% under different pressures. Comparing with reaction in situ and high temperature oxidation technologies，the bending strength and fracture toughness improve greatly. At the same time it shows that the technology parameters have great influences on the properties，for example，forming temperature，pressure，etc. All the results prove that this new technology is feasible for the metal/ceramics composites.
A new technology，thixo-die-forging of composite in pseudo-semi-solid state was proposed based on powder metallurgy technology combing with semi-solid metal process，and the cup shell with Al/Al2O3 composite was prepared successfully. The metallographic analysis and performance test show that the microstructure of Al/Al2O3 is dense and mechanical properties are excellent. The bend strength and fracture toughness of the composite are about 430~690 MPa and 8.5~16.8 MPa·m1/2 respectively，in which the volume fraction of Al is 37% under different pressures. Comparing with reaction in situ and high temperature oxidation technologies，the bending strength and fracture toughness improve greatly. At the same time it shows that the technology parameters have great influences on the properties，for example，forming temperature，pressure，etc. All the results prove that this new technology is feasible for the metal/ceramics composites.
2009, 26(6): 121-127.
Abstract:
The superconducting Bi1.6Pb0.4Sr2Ca2Cu3O10-x samples were prepared by the solid-state synthesis method. The tribological properties were measured on the friction and wear tester from ambient temperature to liquid nitrogen temperature. The results indicate that the friction coefficient of Bi1.6Pb0.4Sr2Ca2Cu3O10-x against stainless steel is about 0.35 at the ambient temperature and decreases abruptly to half of the normal state value when the temperature is below the superconducting transition temperature of Bi1.6Pb0.4Sr2Ca2Cu3O10-x. The measurements prove directly the effect of electronic excitation on friction. Moreover，the Ag/Bi1.6Pb0.4Sr2Ca2Cu3O10-x composite samples were prepared by sintering Bi1.6Pb0.4Sr2Ca2Cu3O10-x with Ag at different mass fractions to improve the tribological properties of Bi1.6Pb0.4Sr2Ca2Cu3O10-x at room temperature. The experimental results show that the friction coefficient of 10 wt%Ag/Bi1.6Pb0.4Sr2Ca2Cu3O10-x is about 0.2~0.3 and the wear rate is 4.57 ×10-4 mm3·(N·m)-1，and the superconductivity of 10 wt% Ag/Bi1.6Pb0.4Sr2Ca2Cu3O10-x is not degenerated.
The superconducting Bi1.6Pb0.4Sr2Ca2Cu3O10-x samples were prepared by the solid-state synthesis method. The tribological properties were measured on the friction and wear tester from ambient temperature to liquid nitrogen temperature. The results indicate that the friction coefficient of Bi1.6Pb0.4Sr2Ca2Cu3O10-x against stainless steel is about 0.35 at the ambient temperature and decreases abruptly to half of the normal state value when the temperature is below the superconducting transition temperature of Bi1.6Pb0.4Sr2Ca2Cu3O10-x. The measurements prove directly the effect of electronic excitation on friction. Moreover，the Ag/Bi1.6Pb0.4Sr2Ca2Cu3O10-x composite samples were prepared by sintering Bi1.6Pb0.4Sr2Ca2Cu3O10-x with Ag at different mass fractions to improve the tribological properties of Bi1.6Pb0.4Sr2Ca2Cu3O10-x at room temperature. The experimental results show that the friction coefficient of 10 wt%Ag/Bi1.6Pb0.4Sr2Ca2Cu3O10-x is about 0.2~0.3 and the wear rate is 4.57 ×10-4 mm3·(N·m)-1，and the superconductivity of 10 wt% Ag/Bi1.6Pb0.4Sr2Ca2Cu3O10-x is not degenerated.
2009, 26(6): 128-132.
Abstract:
Nano FeCo/Al2O3 composites were synthesized using a sol-gel technique combined with H-reduction method. The microstructure and magnetic properties of the samples were characterized by X-ray diffraction，transmission electron microscopy，vibrating sample magnetometer and Mssbauer spectroscopy. The results show that nano FeCo in FeCo/Al2O3 composites presents bcc structure. With the increasing of reducing temperature，the grain size of FeCo increases，while glomeration and growth of α-FeCo are rest ricted effectively due to the existence of Al2O3. With the increasing of the grain size of FeCo，the saturation magnetization of the samples increases，but the coercivity of the samples increases firstly then decreases. The maximum values of saturation magnetization and coercivity are 62.41 emu·g-1 and 208.99 Oe respectively；FeCo/Al2O3 transforms from a mixed state containing superparamagnetism and magnetic-order to a complete magnetic-order state. The change of coercivity results from the transformation of magnetic structure from single-domain to multi-domain.
Nano FeCo/Al2O3 composites were synthesized using a sol-gel technique combined with H-reduction method. The microstructure and magnetic properties of the samples were characterized by X-ray diffraction，transmission electron microscopy，vibrating sample magnetometer and Mssbauer spectroscopy. The results show that nano FeCo in FeCo/Al2O3 composites presents bcc structure. With the increasing of reducing temperature，the grain size of FeCo increases，while glomeration and growth of α-FeCo are rest ricted effectively due to the existence of Al2O3. With the increasing of the grain size of FeCo，the saturation magnetization of the samples increases，but the coercivity of the samples increases firstly then decreases. The maximum values of saturation magnetization and coercivity are 62.41 emu·g-1 and 208.99 Oe respectively；FeCo/Al2O3 transforms from a mixed state containing superparamagnetism and magnetic-order to a complete magnetic-order state. The change of coercivity results from the transformation of magnetic structure from single-domain to multi-domain.
2009, 26(6): 133-137.
Abstract:
Piezoelectric ceramic (lead niobium lithium zirconate titanate，P(LN)ZT)，sulphoaluminate cement and polymer were used to fabricate polymer modified cement piezoelectric composites by the cut filling technique. The influence of P(LN)ZT volume fraction on the piezoelectric and dielectric properties of composites was investigated.The results show that as the P(LN)ZT volume fraction increases，the piezoelectric strain factor d33，relative dielectric factor εr and the acoustic impedance Z increase evidently，while the piezoelectric voltage factor g33 and the dielectric loss tanδdecrease. Compared with P(LN)ZT，the vibration at thickness mode of 1-3 type piezoelectric composite is strengthened，however the electromechanical quality factor is reduced. When P(LN)ZT volume fraction is 30.86 %，the acoustic impedance value is 8.24 ×106 N·s/m3，which is close to that of the concrete (9.0 ×106 N·s/m3) and suitable for fabricating transducers for non destructive inspection.
Piezoelectric ceramic (lead niobium lithium zirconate titanate，P(LN)ZT)，sulphoaluminate cement and polymer were used to fabricate polymer modified cement piezoelectric composites by the cut filling technique. The influence of P(LN)ZT volume fraction on the piezoelectric and dielectric properties of composites was investigated.The results show that as the P(LN)ZT volume fraction increases，the piezoelectric strain factor d33，relative dielectric factor εr and the acoustic impedance Z increase evidently，while the piezoelectric voltage factor g33 and the dielectric loss tanδdecrease. Compared with P(LN)ZT，the vibration at thickness mode of 1-3 type piezoelectric composite is strengthened，however the electromechanical quality factor is reduced. When P(LN)ZT volume fraction is 30.86 %，the acoustic impedance value is 8.24 ×106 N·s/m3，which is close to that of the concrete (9.0 ×106 N·s/m3) and suitable for fabricating transducers for non destructive inspection.
2009, 26(6): 138-142.
Abstract:
The electrical conductivity and pressure-sensitivity of carbon fiber (1% mass fraction of cement) graphite (0% 50% mass fraction of cement) cement-based composites samples (40 mm×40 mm×40 mm) containing CCCW (cementitious capillary crystalline waterproofing materials，4% mass fraction of cement) were measured by the four-probe method and Instron 5882 system. The variation trend of volume resistivity with graphite contents and pressure sensitivity at different mixing amounts of the graphite were discussed. The results show that the resistivity of carbon fiber graphite cement-based composites containing CCCW versus the concent ration of graphite curves has typical features of percolation phenomena. The percolation threshold is 20% (mass fraction of cement). The corresponding relationship between stress and resistance exists with different contents of graphite under the action of cyclic loading，and it comes to the conclusion that when the content of graphite is up to 20%～30% mass fraction of cement，the pressure sensitivity is the best.
The electrical conductivity and pressure-sensitivity of carbon fiber (1% mass fraction of cement) graphite (0% 50% mass fraction of cement) cement-based composites samples (40 mm×40 mm×40 mm) containing CCCW (cementitious capillary crystalline waterproofing materials，4% mass fraction of cement) were measured by the four-probe method and Instron 5882 system. The variation trend of volume resistivity with graphite contents and pressure sensitivity at different mixing amounts of the graphite were discussed. The results show that the resistivity of carbon fiber graphite cement-based composites containing CCCW versus the concent ration of graphite curves has typical features of percolation phenomena. The percolation threshold is 20% (mass fraction of cement). The corresponding relationship between stress and resistance exists with different contents of graphite under the action of cyclic loading，and it comes to the conclusion that when the content of graphite is up to 20%～30% mass fraction of cement，the pressure sensitivity is the best.
2009, 26(6): 143-149.
Abstract:
Tensile tests were carried out on two kinds of carbon fiber/epoxy laminates specimen ( [(45/-45)4]S and [(0/45/90/-45)2]S) at quasi-static (strain rate 10-5~10-4 s-1)，intermediate (strain rate 10-1~101 s-1) and high strain rate (strain rate 102~104 s-1) using the MTS material machine and tensile split Hopkinson bar. A damage constitutive model based on the damage energy release rate was derived within a thermodynamic framework to analyze the dynamic failure of carbon fiber/epoxy. Three damage evolution laws associated with three damage mechanisms (fiber breakage，matrix cracking and shear in plane) were proposed. A procedure resembling the regularization used in viscoplasticity was adopted to take the strain rate into account on damage evolution. The model was coded and implemented into finite element software. The tests were simulated using the model，and the results verify that the model can simulate the dynamic tensile failure well for carbon fiber/epoxy laminates.
Tensile tests were carried out on two kinds of carbon fiber/epoxy laminates specimen ( [(45/-45)4]S and [(0/45/90/-45)2]S) at quasi-static (strain rate 10-5~10-4 s-1)，intermediate (strain rate 10-1~101 s-1) and high strain rate (strain rate 102~104 s-1) using the MTS material machine and tensile split Hopkinson bar. A damage constitutive model based on the damage energy release rate was derived within a thermodynamic framework to analyze the dynamic failure of carbon fiber/epoxy. Three damage evolution laws associated with three damage mechanisms (fiber breakage，matrix cracking and shear in plane) were proposed. A procedure resembling the regularization used in viscoplasticity was adopted to take the strain rate into account on damage evolution. The model was coded and implemented into finite element software. The tests were simulated using the model，and the results verify that the model can simulate the dynamic tensile failure well for carbon fiber/epoxy laminates.
2009, 26(6): 150-154.
Abstract:
The NiCr/ZrO2 functionally graded materials (FGMs) were fabricated by the powder metallurgy. To study the effect of material gradient on the mixed-mode crack initiation，two types of fracture samples were prepared：FGM-A corresponding to the specimen with the crack situated on the stiffer side and FGM-B corresponding to the specimen with the crack situated on the compliant side. The quasi-static fracture tests were conducted under the unsymmetrical loading conditions，and the full-field digital image correlation (DIC) was used to obtain the stress intensity factors KⅠand KⅡ. The experimental results show that the kinking angle of FGM-A is less than the one of FGM-B；the crack of FGM-A is shielded by the elastic gradient and the mixed-mode crack initiation is influenced by the elastic gradient and the local fracture toughness.
The NiCr/ZrO2 functionally graded materials (FGMs) were fabricated by the powder metallurgy. To study the effect of material gradient on the mixed-mode crack initiation，two types of fracture samples were prepared：FGM-A corresponding to the specimen with the crack situated on the stiffer side and FGM-B corresponding to the specimen with the crack situated on the compliant side. The quasi-static fracture tests were conducted under the unsymmetrical loading conditions，and the full-field digital image correlation (DIC) was used to obtain the stress intensity factors KⅠand KⅡ. The experimental results show that the kinking angle of FGM-A is less than the one of FGM-B；the crack of FGM-A is shielded by the elastic gradient and the mixed-mode crack initiation is influenced by the elastic gradient and the local fracture toughness.
2009, 26(6): 155-160.
Abstract:
The uniaxial ratcheting of short glass fiber reinforced polyester resin matrix composites was studied experimentally at room temperature. The ratcheting behaviors of the composites were discussed under different conditions. It is shown that the ratcheting behavior of the composites is similar to that of the un-reinforced matrix in macro-scale，namely，the ratcheting also occurs in the composites under asymmetrical stress cycling，and the ratcheting strain increases as the stress amplitude and mean stress increase；the ratcheting has great time-dependence，i.e.，the ratcheting strain depends on the stress rate and peak stress hold time. It is concluded that the viscous deformation of the matrix should be involved in constructing a constitutive model for the ratcheting of the composites.
The uniaxial ratcheting of short glass fiber reinforced polyester resin matrix composites was studied experimentally at room temperature. The ratcheting behaviors of the composites were discussed under different conditions. It is shown that the ratcheting behavior of the composites is similar to that of the un-reinforced matrix in macro-scale，namely，the ratcheting also occurs in the composites under asymmetrical stress cycling，and the ratcheting strain increases as the stress amplitude and mean stress increase；the ratcheting has great time-dependence，i.e.，the ratcheting strain depends on the stress rate and peak stress hold time. It is concluded that the viscous deformation of the matrix should be involved in constructing a constitutive model for the ratcheting of the composites.
2009, 26(6): 161-166.
Abstract:
The uniaxial time-dependent ratcheting of continuous glass fiber reinforced polymer resin matrix composites (40%，50% glass fiber volume fractions) was experimentally observed at room temperature under the uniaxial stress-controlled cyclic loading，and the evolution features of the ratcheting of the composites presented under different cyclic loading conditions were discussed. The results show that the ratcheting occurs in the composites during the asymmetrical uniaxial stress-controlled cyclic loading (i.e.，the applied mean stress is not zero)，and the ratcheting strain increases as the applied stress amplitude and mean stress increase；however，the addition of continuous glass fibers into the polymer matrix increases the resistance of the composites to the ratcheting deformation，and the ratcheting strain produced in the cyclic loading decreases with the increase of glass fiber volume fraction；the ratcheting of the composites also presents apparent time-dependence，even at room temperature，i.e.，the ratcheting depends upon the stress loading rate and hold time at the peak stress，and the value of ratcheting strain increases apparently with the decrease of stress loading rate and increase of hold time at peak stress during the uniaxial stress-controlled cyclic loading.
The uniaxial time-dependent ratcheting of continuous glass fiber reinforced polymer resin matrix composites (40%，50% glass fiber volume fractions) was experimentally observed at room temperature under the uniaxial stress-controlled cyclic loading，and the evolution features of the ratcheting of the composites presented under different cyclic loading conditions were discussed. The results show that the ratcheting occurs in the composites during the asymmetrical uniaxial stress-controlled cyclic loading (i.e.，the applied mean stress is not zero)，and the ratcheting strain increases as the applied stress amplitude and mean stress increase；however，the addition of continuous glass fibers into the polymer matrix increases the resistance of the composites to the ratcheting deformation，and the ratcheting strain produced in the cyclic loading decreases with the increase of glass fiber volume fraction；the ratcheting of the composites also presents apparent time-dependence，even at room temperature，i.e.，the ratcheting depends upon the stress loading rate and hold time at the peak stress，and the value of ratcheting strain increases apparently with the decrease of stress loading rate and increase of hold time at peak stress during the uniaxial stress-controlled cyclic loading.
2009, 26(6): 167-172.
Abstract:
A three dimensional interfacial fatigue damage model was proposed. Mixed mode delamination of laminated composites caused by both monotonic and fatigue loads can be represented by this model. The maximum jumping displacement of interface experienced in the history was adopted as the damage indicator. For fatigue load，damage accumulation in one unloading and reloading cycle was taken into account. Damage thresholds and nointerface interpenetration conditions were considered in this model. A three-dimensional eight-node isoparametric interfacial element without initial thickness was constructed to model the constitutive law of the interface. A damage accelerating arithmetic was introduced to reduce the computing time. In this arithmetic damage accumulation in several real loading cycles was represented by damage increment in one computing cycle. This element was used to simulate the initiation and growth of fatigue delamination in a laminated composite rotating component . The interfacial damage near the interface crack tip and the development of delamination in the component were obtained. The predicted a-log N curves and residual stiffness agree well with the experimental data.
A three dimensional interfacial fatigue damage model was proposed. Mixed mode delamination of laminated composites caused by both monotonic and fatigue loads can be represented by this model. The maximum jumping displacement of interface experienced in the history was adopted as the damage indicator. For fatigue load，damage accumulation in one unloading and reloading cycle was taken into account. Damage thresholds and nointerface interpenetration conditions were considered in this model. A three-dimensional eight-node isoparametric interfacial element without initial thickness was constructed to model the constitutive law of the interface. A damage accelerating arithmetic was introduced to reduce the computing time. In this arithmetic damage accumulation in several real loading cycles was represented by damage increment in one computing cycle. This element was used to simulate the initiation and growth of fatigue delamination in a laminated composite rotating component . The interfacial damage near the interface crack tip and the development of delamination in the component were obtained. The predicted a-log N curves and residual stiffness agree well with the experimental data.
2009, 26(6): 173-176.
Abstract:
A nonlinear dynamic model of the composite rotor blade with piezoelectric fibers was developed. The effect of the piezoelectric fibers on the frequencies and torsional damping of a composite rotor blade was investigated.The numerical results show that the change of the twist angle increases with the applied voltage increasing. When the applied voltage is equal to 1000 V，the increment of the twist angle is about 2°. Change in blade frequencies is very little with the layup of the piezoelectric fibers. When the piezoelectric fibers are arranged at 45° to the length of blade，it has a powerful effect on the damping of the torsion with the controlled voltage applied to piezoelectric fibers.
A nonlinear dynamic model of the composite rotor blade with piezoelectric fibers was developed. The effect of the piezoelectric fibers on the frequencies and torsional damping of a composite rotor blade was investigated.The numerical results show that the change of the twist angle increases with the applied voltage increasing. When the applied voltage is equal to 1000 V，the increment of the twist angle is about 2°. Change in blade frequencies is very little with the layup of the piezoelectric fibers. When the piezoelectric fibers are arranged at 45° to the length of blade，it has a powerful effect on the damping of the torsion with the controlled voltage applied to piezoelectric fibers.
2009, 26(6): 177-181.
Abstract:
Finite element methods are employed to analyze the effects of layer angle，thickness，sequence and symmetry on torsion-properties of carbon fiber composite drive shafts. The analysis results show that the anti-torsion section coefficient is higher with the layer angles of near 0°，45° and near 90°，and increases with increasing the ply thickness；the better torsional stiffness can be obtained when the angle is between 40° and 70°. The anti-torsion property is improved by inserting a ply with an angle of 45° between the layers near 0° and near 90°，and it is better to be tacked in symmetric schemes than in anti-symmetric ones. The optimized ply stacking scheme has been used in the design of a certain type fan drive shaft and the torsion test indicates that this scheme satisfies the requirements for use and saves material .
Finite element methods are employed to analyze the effects of layer angle，thickness，sequence and symmetry on torsion-properties of carbon fiber composite drive shafts. The analysis results show that the anti-torsion section coefficient is higher with the layer angles of near 0°，45° and near 90°，and increases with increasing the ply thickness；the better torsional stiffness can be obtained when the angle is between 40° and 70°. The anti-torsion property is improved by inserting a ply with an angle of 45° between the layers near 0° and near 90°，and it is better to be tacked in symmetric schemes than in anti-symmetric ones. The optimized ply stacking scheme has been used in the design of a certain type fan drive shaft and the torsion test indicates that this scheme satisfies the requirements for use and saves material .
2009, 26(6): 182-188.
Abstract:
Toughening from interlaminar short fibers is one of the effective ways of interlaminar toughening in composite laminates. In order to study the effects of interlaminar short fibers on the delamination growth in composite laminates，the delamination growth in composite laminates with interlaminar short fibers was studied by 3D geometrically nonlinear and contact FEM. The FEM was improved with the virtual crack closure technique to calculate the energy release rate，and the current fracture criterion in mixed mode was used as the criterion for crack propagation. The crack propagation was simulated by node coupling/partition and the technology of element living and death. The effect of interlaminar short fibers was simulated by spring elements，and the bridging force of short fibers was modified by changing the spring stiffness. The GAP element method was used to deal with contact problems. The influence of interlaminar bridging stress on delamination front stresses，displacement and its growth was studied. Compared with delamination growth in composite panels without interlaminar short fibers，the results show that interlaminar short fibers can effectively reduce the delamination growth and enhance the interlaminar toughness.
Toughening from interlaminar short fibers is one of the effective ways of interlaminar toughening in composite laminates. In order to study the effects of interlaminar short fibers on the delamination growth in composite laminates，the delamination growth in composite laminates with interlaminar short fibers was studied by 3D geometrically nonlinear and contact FEM. The FEM was improved with the virtual crack closure technique to calculate the energy release rate，and the current fracture criterion in mixed mode was used as the criterion for crack propagation. The crack propagation was simulated by node coupling/partition and the technology of element living and death. The effect of interlaminar short fibers was simulated by spring elements，and the bridging force of short fibers was modified by changing the spring stiffness. The GAP element method was used to deal with contact problems. The influence of interlaminar bridging stress on delamination front stresses，displacement and its growth was studied. Compared with delamination growth in composite panels without interlaminar short fibers，the results show that interlaminar short fibers can effectively reduce the delamination growth and enhance the interlaminar toughness.
2009, 26(6): 189-193.
Abstract:
An improved model of lamination theory was used to forecast the mechanical properties of ionic polymer metal composite (IPMC). The outer layer doped with saturated metallic atoms was used as the exterior plating layer，the pure polymer was used as the middle layer，and the material between the two layers，in which the metal content gradually varied，was a gradient layer. Because of Pt content in thickness of Pt-IPMC was detected using EDS method，the rationality of the model was proved. The tensile and bending modulus were tested by the ASTM standards. The elasticity properties of the outer and the gradient layers were predicted by Mori-Tanaka method，and the properties of IPMC were obtained by using gradient mechanics. The tensile performance of IPMC under normal and saturation conditions was estimated and compared with the experiment results，the error of tensile module under normal and swelling conditions is 0.69% and -2.05% respectively，while the error of apparent bending module under normal conditions is -0.99%.
An improved model of lamination theory was used to forecast the mechanical properties of ionic polymer metal composite (IPMC). The outer layer doped with saturated metallic atoms was used as the exterior plating layer，the pure polymer was used as the middle layer，and the material between the two layers，in which the metal content gradually varied，was a gradient layer. Because of Pt content in thickness of Pt-IPMC was detected using EDS method，the rationality of the model was proved. The tensile and bending modulus were tested by the ASTM standards. The elasticity properties of the outer and the gradient layers were predicted by Mori-Tanaka method，and the properties of IPMC were obtained by using gradient mechanics. The tensile performance of IPMC under normal and saturation conditions was estimated and compared with the experiment results，the error of tensile module under normal and swelling conditions is 0.69% and -2.05% respectively，while the error of apparent bending module under normal conditions is -0.99%.
2009, 26(6): 194-200.
Abstract:
An eigenvalue method was proposed to study the singular stress field at the axisymmetric interface wedge of the fiber reinforced composites. Based on the fundamental equations of the spacial axisymmetric problem of the transversely isotropic materials and the first-order approximation assumption，a discrete characteristic equation was derived by using the displacement functions with separated variables and the meshless method. The eigenvalue was related to the order of stress singularity，and the associated eigenvector was with respect to the stress angular variations. The fiber/matrix axisymmetric interface wedge model was used to verify the validity of the proposed eigenvalue method. The order of stress singularity，the associated displacement and stress angular variations obtained by this eigenvalue method are in good agreement with those by the finite element method (FEM). Based on the order of stress singularity and the associated stress angular variations determined by the eigenvalue analysis，as well as the numerical results of singular stress fields by FEM，the stress intensity coefficient was also obtained in terms of the linear extropolation. The singular stress field around the axisymmetric interface wedge can be completely determined by the developed eigenvalue method coupling with the FEM analysis.
An eigenvalue method was proposed to study the singular stress field at the axisymmetric interface wedge of the fiber reinforced composites. Based on the fundamental equations of the spacial axisymmetric problem of the transversely isotropic materials and the first-order approximation assumption，a discrete characteristic equation was derived by using the displacement functions with separated variables and the meshless method. The eigenvalue was related to the order of stress singularity，and the associated eigenvector was with respect to the stress angular variations. The fiber/matrix axisymmetric interface wedge model was used to verify the validity of the proposed eigenvalue method. The order of stress singularity，the associated displacement and stress angular variations obtained by this eigenvalue method are in good agreement with those by the finite element method (FEM). Based on the order of stress singularity and the associated stress angular variations determined by the eigenvalue analysis，as well as the numerical results of singular stress fields by FEM，the stress intensity coefficient was also obtained in terms of the linear extropolation. The singular stress field around the axisymmetric interface wedge can be completely determined by the developed eigenvalue method coupling with the FEM analysis.
2009, 26(6): 201-209.
Abstract:
This paper introduces an extended Voronoi cell finite element model (X-VCFEM) proposed by Ghosh for modeling the propagation of interfacial debonding and matrix cracking in fiber reinforced composite materials. A series of criteria based on the theory of interface and fracture mechanics were proposed for assessing the damage development，which includes the interfacial debonding，the direction of damage at the interface and the crack propagation in the matrix. With a re-mesh strategy，comparisons of X-VEFEM simulations of one Voronoi element with reference results of traditional finite element method validate the effectiveness of X-VCFEM model .Meanwhile，the initiation and propagation of interfacial debonding and matrix cracking in fiber reinforced composite materials of random distributed fibers were simulated. The results show that this model for modeling the initiation and propagation of interfacial debonding and matrix cracking in complex fiber reinforced composite materials has the advantages of fast speed and high precision.
This paper introduces an extended Voronoi cell finite element model (X-VCFEM) proposed by Ghosh for modeling the propagation of interfacial debonding and matrix cracking in fiber reinforced composite materials. A series of criteria based on the theory of interface and fracture mechanics were proposed for assessing the damage development，which includes the interfacial debonding，the direction of damage at the interface and the crack propagation in the matrix. With a re-mesh strategy，comparisons of X-VEFEM simulations of one Voronoi element with reference results of traditional finite element method validate the effectiveness of X-VCFEM model .Meanwhile，the initiation and propagation of interfacial debonding and matrix cracking in fiber reinforced composite materials of random distributed fibers were simulated. The results show that this model for modeling the initiation and propagation of interfacial debonding and matrix cracking in complex fiber reinforced composite materials has the advantages of fast speed and high precision.
