2003 Vol. 20, No. 3
2003, 20(3): 1-6.
Abstract:
Based on the zig-zag deformation model, the first order shear strain effect laminated plate theory and the von Karman non-linearity assumption, a finite element method for fractural analysis of the debonded sandwich composites is developed. The total energy release rate can be estimated by a virtual crack closure technique (VCCT). The delamination fracture behavior of the sandwich plates containing an different shape interfacial crack under compression is studied. From some typical numerical examples and discussions, it can be seen that the magnitude and distribution of the energy release rate along the crack front are dependent on the crack area, shape and loading orientation.
Based on the zig-zag deformation model, the first order shear strain effect laminated plate theory and the von Karman non-linearity assumption, a finite element method for fractural analysis of the debonded sandwich composites is developed. The total energy release rate can be estimated by a virtual crack closure technique (VCCT). The delamination fracture behavior of the sandwich plates containing an different shape interfacial crack under compression is studied. From some typical numerical examples and discussions, it can be seen that the magnitude and distribution of the energy release rate along the crack front are dependent on the crack area, shape and loading orientation.
2003, 20(3): 7-12.
Abstract:
Starting from defining generalized stress, this paper presents a modified stiffness matrix method to overcome the thickness locking of solid shell elements and guarantee the continuous distribution of the transverse normal stress of composite laminate shell structures. By splitting the stress into lower order and higher order terms, a new nonlinear variational principle is developed and a 9-node solid shell element with 6 DOF per node is derived for geometrically nonlinear analysis of composite laminated shells. The higher order assumed stress modes are judiciously selected to vanish at the sampling points of the second order quadrature and their energy products with the displacement- derived covariant strain can be programmed without resorting to numerical integration. Accuracy of the present element is virtually identical to that of the uniformly reduced integration element(URI) yet with a little additional computational costs for the stabilization matrix. The stabilization matrix is of prime importance as the global tangential stiffness matrices resulting from the URI elements often become singular after a few iterations.
Starting from defining generalized stress, this paper presents a modified stiffness matrix method to overcome the thickness locking of solid shell elements and guarantee the continuous distribution of the transverse normal stress of composite laminate shell structures. By splitting the stress into lower order and higher order terms, a new nonlinear variational principle is developed and a 9-node solid shell element with 6 DOF per node is derived for geometrically nonlinear analysis of composite laminated shells. The higher order assumed stress modes are judiciously selected to vanish at the sampling points of the second order quadrature and their energy products with the displacement- derived covariant strain can be programmed without resorting to numerical integration. Accuracy of the present element is virtually identical to that of the uniformly reduced integration element(URI) yet with a little additional computational costs for the stabilization matrix. The stabilization matrix is of prime importance as the global tangential stiffness matrices resulting from the URI elements often become singular after a few iterations.
2003, 20(3): 13-16.
Abstract:
According to the physicochemical properties of C/C composites and TaC and the environment, in which C/TaC/C composites is ablated, the ablation mechanism of C/TaC/C composites is deduced. It is analyzed in detail for C/TaC/C composites how to resist erosion and denudation. Then, its ablative model is established on the basis of analyzing the ablation mechanism of C/TaC/C composites. The flow velocity of liquid TaC can be deduced by using Darcy's law. The mass ablative rate of C/TaC/C composites is ultimately derived from hydrokinetics and conservation of mass. All these make some helpful discussion for thermal protection materials in the field of astronautics.
According to the physicochemical properties of C/C composites and TaC and the environment, in which C/TaC/C composites is ablated, the ablation mechanism of C/TaC/C composites is deduced. It is analyzed in detail for C/TaC/C composites how to resist erosion and denudation. Then, its ablative model is established on the basis of analyzing the ablation mechanism of C/TaC/C composites. The flow velocity of liquid TaC can be deduced by using Darcy's law. The mass ablative rate of C/TaC/C composites is ultimately derived from hydrokinetics and conservation of mass. All these make some helpful discussion for thermal protection materials in the field of astronautics.
2003, 20(3): 17-21.
Abstract:
A novel hybrid yarn manufacturing method, co-braiding, was introduced in this paper. A series of GF/PP co-braided yarns were prepared successfully by changing braiding parameters, bundle size and type of fibers, number of braiding yarns and axial yarns, etc. The composite panels were fabricated successfully from prepared GF/PP co-braided yarns. Influences of pressure, temperature and holding time during consolidation process on the impregnation and quality of composite laminates were investigated. Influences of type, bundle size and content of reinforcement on the void content in composites were also studied. A circular model was adopted to model the impregnation of GF in the GF/PP co-braided yarns.
A novel hybrid yarn manufacturing method, co-braiding, was introduced in this paper. A series of GF/PP co-braided yarns were prepared successfully by changing braiding parameters, bundle size and type of fibers, number of braiding yarns and axial yarns, etc. The composite panels were fabricated successfully from prepared GF/PP co-braided yarns. Influences of pressure, temperature and holding time during consolidation process on the impregnation and quality of composite laminates were investigated. Influences of type, bundle size and content of reinforcement on the void content in composites were also studied. A circular model was adopted to model the impregnation of GF in the GF/PP co-braided yarns.
2003, 20(3): 22-26.
Abstract:
The curing behaviors and kinetics analysis of polyethylene glycol modified unsaturated polyester for bulk moulding compounds (BMC) were examined by means of IR and DSC. The curing kinetic parameters of the modified systems were obtained by the Kissinger's equation and Crane's equation. It has shown that the reactive maleic anhydride terminated polyethylene glycol participated in the curing reaction of the unsaturated polyester, which lowered the curing temperature and accelerated the curing process of the system.
The curing behaviors and kinetics analysis of polyethylene glycol modified unsaturated polyester for bulk moulding compounds (BMC) were examined by means of IR and DSC. The curing kinetic parameters of the modified systems were obtained by the Kissinger's equation and Crane's equation. It has shown that the reactive maleic anhydride terminated polyethylene glycol participated in the curing reaction of the unsaturated polyester, which lowered the curing temperature and accelerated the curing process of the system.
2003, 20(3): 27-30.
Abstract:
The ultra-high temperature composite was fabricated based on polyimide containing biphenyl structure as the matrix resin and carbon fiber AS4. The rheology of polyimide precursor prepared by a modified polymerization of monomeric reactants approach (MPMR) was studied. The flexural strength and flexural modulus of the composite at RT and 371℃ are 1190 MPa,763 MPa and 121 GPa, 116 GPa, respectively. The shear strength of the composite at RT and 371℃ are 42 MPa and 26 MPa. The mechanical property of the composite can reach half of its mechanical property at room temperature. The glass transition temperature is up to 472℃ by DMA. The weight losses of the resin and composite at 371℃ for 100 h are 1.9 % and 2.0 %.
The ultra-high temperature composite was fabricated based on polyimide containing biphenyl structure as the matrix resin and carbon fiber AS4. The rheology of polyimide precursor prepared by a modified polymerization of monomeric reactants approach (MPMR) was studied. The flexural strength and flexural modulus of the composite at RT and 371℃ are 1190 MPa,763 MPa and 121 GPa, 116 GPa, respectively. The shear strength of the composite at RT and 371℃ are 42 MPa and 26 MPa. The mechanical property of the composite can reach half of its mechanical property at room temperature. The glass transition temperature is up to 472℃ by DMA. The weight losses of the resin and composite at 371℃ for 100 h are 1.9 % and 2.0 %.
2003, 20(3): 31-34.
Abstract:
The optimal parameter of the ultrasonic treatment is studied, emphasizing on the research of the effect of the ultrasonic treatment on the interfacial performance of RTM composites. In order to increase the resin impregnation for fiber mats the ultrasonic technique was used. The results show that the resin viscidities are decreased and its flow velocities at the flow front are increased when the ultrasonic irradiates on the mold during the process of RTM. Furthermore, air traps are very difficult to be formatted, and the impregnation is improved considerably. Hence, interfacial performances of the composites are enhanced.
The optimal parameter of the ultrasonic treatment is studied, emphasizing on the research of the effect of the ultrasonic treatment on the interfacial performance of RTM composites. In order to increase the resin impregnation for fiber mats the ultrasonic technique was used. The results show that the resin viscidities are decreased and its flow velocities at the flow front are increased when the ultrasonic irradiates on the mold during the process of RTM. Furthermore, air traps are very difficult to be formatted, and the impregnation is improved considerably. Hence, interfacial performances of the composites are enhanced.
2003, 20(3): 35-40.
Abstract:
This paper studied the microstructure, graphitization degree, heat transfer coefficient, hardness, compression strength, bending strength, interlayer shear strength, friction and wear properties of different specimens from different producers such as Dunlop, B.F.Goodrich, Missier, Bendix and state key laboratory for powder metallurgy of CSU. The results show that as a superior braking material, carbon/carbon composites must have reasonable felt and proportional rough laminar structure, high graphitization degree, high heat transfer coefficient in the vertical direction of the carbon fibers in the composites as well. The results also show that China has got the ability to produce carbon /carbon composites for braking materials compared with the other companies that are very outstanding in this field.
This paper studied the microstructure, graphitization degree, heat transfer coefficient, hardness, compression strength, bending strength, interlayer shear strength, friction and wear properties of different specimens from different producers such as Dunlop, B.F.Goodrich, Missier, Bendix and state key laboratory for powder metallurgy of CSU. The results show that as a superior braking material, carbon/carbon composites must have reasonable felt and proportional rough laminar structure, high graphitization degree, high heat transfer coefficient in the vertical direction of the carbon fibers in the composites as well. The results also show that China has got the ability to produce carbon /carbon composites for braking materials compared with the other companies that are very outstanding in this field.
2003, 20(3): 41-46.
Abstract:
Frictional and wear behaviors of the C/C composite from a needled felt were investigated at different pressures and speeds by simulating the aircraft braking with pairs of circle samples. The rubbing surfaces were examined with SEM. The braking speeds increased from 0 in step of 5 m/s. The mechanisms of friction and wear depend on the wear debris film covered on the rubbing surfaces. At a low speed of 5 m/s or at static the friction coefficient is very low due to the lubricating of absorbed water vapor on the surface. When the speed increases to 10 m/s, the surface temperature will be high enough to absorb the absorbed water vapor by the frictional heating, so the friction coefficient can rapidly increase to the maximum. Then, with the further increasing of the braking speeds and the surface temperatures, the decrease of the inter-laminar shear strength of the wear debris film will result in the friction coefficient decreasing. But the friction coefficients will be high enough at high braking speeds, demonstrating its excellent high energy braking character.
Frictional and wear behaviors of the C/C composite from a needled felt were investigated at different pressures and speeds by simulating the aircraft braking with pairs of circle samples. The rubbing surfaces were examined with SEM. The braking speeds increased from 0 in step of 5 m/s. The mechanisms of friction and wear depend on the wear debris film covered on the rubbing surfaces. At a low speed of 5 m/s or at static the friction coefficient is very low due to the lubricating of absorbed water vapor on the surface. When the speed increases to 10 m/s, the surface temperature will be high enough to absorb the absorbed water vapor by the frictional heating, so the friction coefficient can rapidly increase to the maximum. Then, with the further increasing of the braking speeds and the surface temperatures, the decrease of the inter-laminar shear strength of the wear debris film will result in the friction coefficient decreasing. But the friction coefficients will be high enough at high braking speeds, demonstrating its excellent high energy braking character.
2003, 20(3): 47-51.
Abstract:
The magnetoresistance of C/C composite was studied in different measuring orientation. The magnetoresistance varies with the measuring orientation; the maximal magnetoresistance was found in different orientation for the materials that have different structures and different technics. Graphitized materials have positive magnetoresistance, and non-graphitized materials have negative magnetoresistance, but both of its absolute value increase with temperature rising. Magnetoresistance-temperature is a linear function in every measuring orientation. When the temperature is high enough, some materials' magnetoresistance will keep unchanged. By regressing the magnetoresistance-temperature curves, the slopes of the obtained equations are equal but the intercept is unequal. The magnetoresistance of every orientation is ranged, and dissimilar orientation serials are found for different materials. When the intensity of the magnetic field changes, the value of magnetoresistance changes, but the orientation serial does not change.
The magnetoresistance of C/C composite was studied in different measuring orientation. The magnetoresistance varies with the measuring orientation; the maximal magnetoresistance was found in different orientation for the materials that have different structures and different technics. Graphitized materials have positive magnetoresistance, and non-graphitized materials have negative magnetoresistance, but both of its absolute value increase with temperature rising. Magnetoresistance-temperature is a linear function in every measuring orientation. When the temperature is high enough, some materials' magnetoresistance will keep unchanged. By regressing the magnetoresistance-temperature curves, the slopes of the obtained equations are equal but the intercept is unequal. The magnetoresistance of every orientation is ranged, and dissimilar orientation serials are found for different materials. When the intensity of the magnetic field changes, the value of magnetoresistance changes, but the orientation serial does not change.
2003, 20(3): 52-56.
Abstract:
The phenolic resin synthesized from phenol and formaldehyde in the presence of a tertiary amine catalyst was chemically modified with a small amount of aniline derivative to produce a higher molecular weight,modified phenolic resin.The resulting resin was used as the curing agent of epoxy resin to produce the epoxide woven glass fabric laminated sheet.The insulation resistance after immersion in water of the laminated sheet is greater than 1011Ω,and other properties are similar to those of EP GC201(IEC 893-3-2).Molecular weight distribution and structural feature of the modified phenolic resin were studied by means of gel permeation chromatography(GPC),infrared spectroscopy(IR)and proton magnetic resonance(1H-NMR)analytical techniques.
The phenolic resin synthesized from phenol and formaldehyde in the presence of a tertiary amine catalyst was chemically modified with a small amount of aniline derivative to produce a higher molecular weight,modified phenolic resin.The resulting resin was used as the curing agent of epoxy resin to produce the epoxide woven glass fabric laminated sheet.The insulation resistance after immersion in water of the laminated sheet is greater than 1011Ω,and other properties are similar to those of EP GC201(IEC 893-3-2).Molecular weight distribution and structural feature of the modified phenolic resin were studied by means of gel permeation chromatography(GPC),infrared spectroscopy(IR)and proton magnetic resonance(1H-NMR)analytical techniques.
2003, 20(3): 57-63.
Abstract:
The void formation during RTM processing seems to be inevitable and the presence of voids has a deleterious effect on the mechanical properties of textile composites. The purpose of this study is to investigate the mechanism of void formation in multi-layer woven fabrics. Two unit cell models were suggested to represent the cross sections of multi-layer woven fabrics with two typical layering patterns. Based on these two geometrical models, an analytical model was developed to describe the mechanism of void formation during RTM processing. The flow fronts and void formation in these two cells were also numerically simulated using a control-volume method. The simulated results agree well with those predicted by the analytical model. The results show that, for a given fiber preform, the ratio of the weft axial permeability Kab to the warp transverse permeability Ktb is responsible for the size of the void.
The void formation during RTM processing seems to be inevitable and the presence of voids has a deleterious effect on the mechanical properties of textile composites. The purpose of this study is to investigate the mechanism of void formation in multi-layer woven fabrics. Two unit cell models were suggested to represent the cross sections of multi-layer woven fabrics with two typical layering patterns. Based on these two geometrical models, an analytical model was developed to describe the mechanism of void formation during RTM processing. The flow fronts and void formation in these two cells were also numerically simulated using a control-volume method. The simulated results agree well with those predicted by the analytical model. The results show that, for a given fiber preform, the ratio of the weft axial permeability Kab to the warp transverse permeability Ktb is responsible for the size of the void.
2003, 20(3): 64-68.
Abstract:
A Ti-C-Fe preform was pre-placed in a mould cavity and then was directly ignited to bring about the self-propagating high-temperature synthesis (SHS) reaction by the temperature of pouring liquid carbon steel. As a result, a TiC-Fe cermet coating with a thickness of 10 mm was simultaneously synthesized on the steel substrate during its casting. The phase constituents of the synthesized coating were inspected by X-ray diffraction (XRD), and the microstructure of the coating, especially its interfacial structure with the substrate, was analyzed with optical microscopy (OM), scanning electron microscopy (SEM) and electron probe microanalyzer (EPMA). The experimental results show that the coating, except for its outside layer with about 2 mm thickness, has dense microstructure. The amount and size of the synthesized TiC particles in the coating decrease gradually in the thickness direction, so that a graded composite interface is formed between the coating and the substrate. It is considered that the infiltrations of the poured liquid steel into the preform and the fusion of Fe powders in the preform may make a contribution to the formation of the graded composite coating.
A Ti-C-Fe preform was pre-placed in a mould cavity and then was directly ignited to bring about the self-propagating high-temperature synthesis (SHS) reaction by the temperature of pouring liquid carbon steel. As a result, a TiC-Fe cermet coating with a thickness of 10 mm was simultaneously synthesized on the steel substrate during its casting. The phase constituents of the synthesized coating were inspected by X-ray diffraction (XRD), and the microstructure of the coating, especially its interfacial structure with the substrate, was analyzed with optical microscopy (OM), scanning electron microscopy (SEM) and electron probe microanalyzer (EPMA). The experimental results show that the coating, except for its outside layer with about 2 mm thickness, has dense microstructure. The amount and size of the synthesized TiC particles in the coating decrease gradually in the thickness direction, so that a graded composite interface is formed between the coating and the substrate. It is considered that the infiltrations of the poured liquid steel into the preform and the fusion of Fe powders in the preform may make a contribution to the formation of the graded composite coating.
2003, 20(3): 69-73.
Abstract:
A deformable SiCP/Al composite was fabricated by squeeze casting technique using an SiC particle preform with a controllable volume fraction which was made by adding aluminum powder into the preform. The deformability of the SiCP/Al composite was studied by hot extrusion and the effect of the hot extrusion on microstructure and properties of the composite was investigated. The results show that the 25vol% SiCP/Al composite fabricated by the modified squeeze casting method could be extruded successfully by an extrusion ratio of 25∶1, and the strength, modulus and tensile elongation were improved by the hot extrusion.
A deformable SiCP/Al composite was fabricated by squeeze casting technique using an SiC particle preform with a controllable volume fraction which was made by adding aluminum powder into the preform. The deformability of the SiCP/Al composite was studied by hot extrusion and the effect of the hot extrusion on microstructure and properties of the composite was investigated. The results show that the 25vol% SiCP/Al composite fabricated by the modified squeeze casting method could be extruded successfully by an extrusion ratio of 25∶1, and the strength, modulus and tensile elongation were improved by the hot extrusion.
2003, 20(3): 74-78.
Abstract:
The effect of five typical heat treatment technologies on the damping properties and the damping peak of the SiCP/6061Al MMC, fabricated by spray atomization and deposition, was studied. The results show that the internal friction spectra of various heat treated samples exhibit the internal friction peak versus temperature between 150℃ and 200℃. Furthermore, the peak temperature and the peak height increase with increasing frequencies. By Arrhenius equation we can get the active energy of the damping peak, which is above 1 eV. On the other hand, different quenching treatments affect the damping peak remarkably; when the rate of cooling is above water quenching, the damping peak will shift to a higher temperature while enhancing the cooling speed.
The effect of five typical heat treatment technologies on the damping properties and the damping peak of the SiCP/6061Al MMC, fabricated by spray atomization and deposition, was studied. The results show that the internal friction spectra of various heat treated samples exhibit the internal friction peak versus temperature between 150℃ and 200℃. Furthermore, the peak temperature and the peak height increase with increasing frequencies. By Arrhenius equation we can get the active energy of the damping peak, which is above 1 eV. On the other hand, different quenching treatments affect the damping peak remarkably; when the rate of cooling is above water quenching, the damping peak will shift to a higher temperature while enhancing the cooling speed.
2003, 20(3): 79-84.
Abstract:
An Al2O3f+Cf/ZL109 short fibers reinforced hybrid metal matrix composite was fabricated by squeeze casting.By means of the statistical research method,the effects of heat-treatment on the dry sliding friction and wear properties of the hybrid composites were investigated under the condition of 196 N load and velocity of 0.837 m/s.The results show that the wear rate and friction coefficient of both as cast and as heat-treated hybrid composite accord with normal distribution of probability density.The normal distribution functions of the wear rate and friction coefficient are of identical variance,but the average values of the wear rate and friction coefficient of as cast hybrid composite are greater than those of as heat-treated hybrid composite.Heat-treatment is beneficial to improving the dry sliding friction and wear property of the composite.The dominant wear mechanism of as cast hybrid composite is plough and delamination.Heat-treatment can improve the resistivity of delamination of composite.The dominant wear mechanism of as heat-treated hybrid composite is slight plough.
An Al2O3f+Cf/ZL109 short fibers reinforced hybrid metal matrix composite was fabricated by squeeze casting.By means of the statistical research method,the effects of heat-treatment on the dry sliding friction and wear properties of the hybrid composites were investigated under the condition of 196 N load and velocity of 0.837 m/s.The results show that the wear rate and friction coefficient of both as cast and as heat-treated hybrid composite accord with normal distribution of probability density.The normal distribution functions of the wear rate and friction coefficient are of identical variance,but the average values of the wear rate and friction coefficient of as cast hybrid composite are greater than those of as heat-treated hybrid composite.Heat-treatment is beneficial to improving the dry sliding friction and wear property of the composite.The dominant wear mechanism of as cast hybrid composite is plough and delamination.Heat-treatment can improve the resistivity of delamination of composite.The dominant wear mechanism of as heat-treated hybrid composite is slight plough.
2003, 20(3): 85-88.
Abstract:
The work of adhesion for reactive metal/ceramic systems was investigated on the basis of a detailed description of the surface thermodynamics. A method to estimate the work of adhesion was developed. The calculated results from the method are approximately in agreement with experimental values. The results show that the work of adhesion depends on both the reactivity in a system and the detailed chemistry and structure of the reaction products.
The work of adhesion for reactive metal/ceramic systems was investigated on the basis of a detailed description of the surface thermodynamics. A method to estimate the work of adhesion was developed. The calculated results from the method are approximately in agreement with experimental values. The results show that the work of adhesion depends on both the reactivity in a system and the detailed chemistry and structure of the reaction products.
2003, 20(3): 89-92.
Abstract:
A Zr-based amorphous composite coating was produced by laser cladding of metal powder on a Ti substrate. The microstructure of the coating was studied using XRD, SEM, EDX and TEM. The coating consists of a mixture of intermetallic compounds, including a nanocrystal and an amorphous phase. The bonding zone between the substrate and the coating is composed of columnar crystalline α-type solid solution α-Ti/Zr.
A Zr-based amorphous composite coating was produced by laser cladding of metal powder on a Ti substrate. The microstructure of the coating was studied using XRD, SEM, EDX and TEM. The coating consists of a mixture of intermetallic compounds, including a nanocrystal and an amorphous phase. The bonding zone between the substrate and the coating is composed of columnar crystalline α-type solid solution α-Ti/Zr.
2003, 20(3): 93-97.
Abstract:
A Cu-Al2O3(1.5wt% or so) composite was successfully prepared by using a new approach, which includes high energy milling of Cu and Al powder to produce Cu-Al alloy powder, high energy milling of the Cu-Al alloy powder together with Cu2O powder, and preparing Al2O3/Cu composite through conducting oxidation and sintering synchronously in vacuum. The peculiarities of this approach are that the reduction of superfluous Cu2O is left out, and the period of reacting and sintering is only 1 hour. It was observed that the Al2O3 particles uniformly dispersed in the copper matrix with an average size of 250nm in diameter and particles space between 500 nm. The properties of Al2O3/Cu composite are close to those of SCM products after cold working. The Al2O3/Cu composite possesses excellent thermal stability since there are no cracks observed after exposing to 800℃ and then cold quenching, which is cycled 20 times. The intenerating temperature of Al2O3/Cu composite is about 700℃.
A Cu-Al2O3(1.5wt% or so) composite was successfully prepared by using a new approach, which includes high energy milling of Cu and Al powder to produce Cu-Al alloy powder, high energy milling of the Cu-Al alloy powder together with Cu2O powder, and preparing Al2O3/Cu composite through conducting oxidation and sintering synchronously in vacuum. The peculiarities of this approach are that the reduction of superfluous Cu2O is left out, and the period of reacting and sintering is only 1 hour. It was observed that the Al2O3 particles uniformly dispersed in the copper matrix with an average size of 250nm in diameter and particles space between 500 nm. The properties of Al2O3/Cu composite are close to those of SCM products after cold working. The Al2O3/Cu composite possesses excellent thermal stability since there are no cracks observed after exposing to 800℃ and then cold quenching, which is cycled 20 times. The intenerating temperature of Al2O3/Cu composite is about 700℃.
2003, 20(3): 98-101.
Abstract:
The nano SiC(N) powder was synthesized by laser-induced gas-phase reaction. SiC(N)/LAS nano-composite was prepared from LAS glass powder and as-formed nano SiC(N) powder by the hot-pressing method. The microwave dielectric properties of the nano-composite in a frequency range of 8.2~12.4 GHz were studied. The results show that the permittivity of the nano-composite is related closely to the contents of nano SiC(N) and influenced fairly by sintering temperatures. Compared with the mixture of nano SiC(N) and paraffin, the sintering process improved the nano-composite's dissipation to electromagnetic wave. This amelioration is ascribed to the formation of carbon interface between nano SiC(N) and LAS matrix.
The nano SiC(N) powder was synthesized by laser-induced gas-phase reaction. SiC(N)/LAS nano-composite was prepared from LAS glass powder and as-formed nano SiC(N) powder by the hot-pressing method. The microwave dielectric properties of the nano-composite in a frequency range of 8.2~12.4 GHz were studied. The results show that the permittivity of the nano-composite is related closely to the contents of nano SiC(N) and influenced fairly by sintering temperatures. Compared with the mixture of nano SiC(N) and paraffin, the sintering process improved the nano-composite's dissipation to electromagnetic wave. This amelioration is ascribed to the formation of carbon interface between nano SiC(N) and LAS matrix.
2003, 20(3): 102-107.
Abstract:
In this paper, the modification of plasma treatment on PBO (poly(p-phenylene benzobisoxazole)) fiber surface was studied. AFM and XPS were used to analyze the influences of treating time on the morphology and surface compositions of PBO fiber respectively. The changes of fiber surface wettability and surface groups were determined by dynamic wettability test equipment and IR spectrum. The interfacial shear strength (IFSS) between fibers and resin was measured by the microbond test. The broken composites were analyzed by SEM. The results show that the wettability of the fiber surface after plasma treatment is improved and that many hydroxy groups are introduced to benzene rings on the fiber surface. Under the optimum parameters of 170 W and 10 min,the IFSS is improved by 64.7 %. The surface rough degree and oxygen content are the greatest. The ratio of oxygen to carbon is improved by 50.5 %.
In this paper, the modification of plasma treatment on PBO (poly(p-phenylene benzobisoxazole)) fiber surface was studied. AFM and XPS were used to analyze the influences of treating time on the morphology and surface compositions of PBO fiber respectively. The changes of fiber surface wettability and surface groups were determined by dynamic wettability test equipment and IR spectrum. The interfacial shear strength (IFSS) between fibers and resin was measured by the microbond test. The broken composites were analyzed by SEM. The results show that the wettability of the fiber surface after plasma treatment is improved and that many hydroxy groups are introduced to benzene rings on the fiber surface. Under the optimum parameters of 170 W and 10 min,the IFSS is improved by 64.7 %. The surface rough degree and oxygen content are the greatest. The ratio of oxygen to carbon is improved by 50.5 %.
2003, 20(3): 108-112.
Abstract:
The effects of different surface treatments of glass fiber on the sliding wear behaviors of PTFE composites were investigated under dry friction conditions. The worn surfaces were analyzed using a scanning electron microscope (SEM). The results show that the friction coefficients and the temperatures of the frictional surface of the polytetrafluoroethylene (PTFE) composites filled with treated glass fiber, under dry friction conditions, are lower than those of the PTFE composite filled with untreated glass fiber, and wear-reducing properties of the PTFE composites with treated glass fiber are better than those of PTFE composite with untreated glass fiber. The PTFE composite, filled with glass fiber treated with rare earths, shows the lowest friction coefficient and temperature of the frictional surface as well as the best wear-reducing properties among the researched composites. The PTFE composite untreated and the PTFE composite treated with the coupling agent are characterized by severe adhesion and transfer. The wear mechanism of the PTFE composite treated with coupling agent and rare earths is characterized by remarkable abrasive wear. The wear of the PTFE composite treated with rare earths is characterized by adhesion, transfer and slight abrasive wear.
The effects of different surface treatments of glass fiber on the sliding wear behaviors of PTFE composites were investigated under dry friction conditions. The worn surfaces were analyzed using a scanning electron microscope (SEM). The results show that the friction coefficients and the temperatures of the frictional surface of the polytetrafluoroethylene (PTFE) composites filled with treated glass fiber, under dry friction conditions, are lower than those of the PTFE composite filled with untreated glass fiber, and wear-reducing properties of the PTFE composites with treated glass fiber are better than those of PTFE composite with untreated glass fiber. The PTFE composite, filled with glass fiber treated with rare earths, shows the lowest friction coefficient and temperature of the frictional surface as well as the best wear-reducing properties among the researched composites. The PTFE composite untreated and the PTFE composite treated with the coupling agent are characterized by severe adhesion and transfer. The wear mechanism of the PTFE composite treated with coupling agent and rare earths is characterized by remarkable abrasive wear. The wear of the PTFE composite treated with rare earths is characterized by adhesion, transfer and slight abrasive wear.
2003, 20(3): 113-117.
Abstract:
The local distributions of the carbon structure and their changes with HTT of two kinds of C/C composites were analyzed and characterized by using laser Raman microspectroscopy. The reinforcement of the two composites is laminated carbon felt, and the matrix of the two composites consists exclusively of RL (Rough Layer) or SL (Smooth Layer) pyrolytic carbon respectively. Experimental results show the carbon crystal structure and structural change with HTT are different: not only between different elements in composite but also between different locations in the same element. The pyrolytic carbon in the carbon cloth layer with higher volume content of CF has a higher graphitization degree than the pyrolytic carbon in the mat layer. The graphitization degrees of the locations near the interface between CF and pyrolytic carbon in pyrolitic carbon or CF increase with HTT more rapidly than those far away from the interface. RL pyrolytic carbon is more graphitizable than SL pyrolytic carbon. The results indicate that it is possible to adjust and control the local distribution of carbon structure of C/C composites by means of laser Raman microspectroscopy.
The local distributions of the carbon structure and their changes with HTT of two kinds of C/C composites were analyzed and characterized by using laser Raman microspectroscopy. The reinforcement of the two composites is laminated carbon felt, and the matrix of the two composites consists exclusively of RL (Rough Layer) or SL (Smooth Layer) pyrolytic carbon respectively. Experimental results show the carbon crystal structure and structural change with HTT are different: not only between different elements in composite but also between different locations in the same element. The pyrolytic carbon in the carbon cloth layer with higher volume content of CF has a higher graphitization degree than the pyrolytic carbon in the mat layer. The graphitization degrees of the locations near the interface between CF and pyrolytic carbon in pyrolitic carbon or CF increase with HTT more rapidly than those far away from the interface. RL pyrolytic carbon is more graphitizable than SL pyrolytic carbon. The results indicate that it is possible to adjust and control the local distribution of carbon structure of C/C composites by means of laser Raman microspectroscopy.
2003, 20(3): 118-121.
Abstract:
The TiC/Al alloy with high TiC particles content was prepared by XDTM process. The uniformization process of TiC particles in the stable zinc melt was studied and analyzed using self-made experimental equipment, and a model of the uniformization process was built. The results show that zinc diffuses into TiC/Al alloy placed in the zinc melt at temperatures below the melting point of aluminum, forming a zinc diffusing layer on the surface of the prepared TiC/Al alloy. With the increase of the concentration of zinc in the alloy, the liquidus temperature decreases, and when the temperature is equal to or below the temperature of zinc melt, the surface of the prepared TiC/Al alloy will melt and TiC particles will drop from it, then transfer into the zinc melt, and finally distribute uniformly in the zinc melt.
The TiC/Al alloy with high TiC particles content was prepared by XDTM process. The uniformization process of TiC particles in the stable zinc melt was studied and analyzed using self-made experimental equipment, and a model of the uniformization process was built. The results show that zinc diffuses into TiC/Al alloy placed in the zinc melt at temperatures below the melting point of aluminum, forming a zinc diffusing layer on the surface of the prepared TiC/Al alloy. With the increase of the concentration of zinc in the alloy, the liquidus temperature decreases, and when the temperature is equal to or below the temperature of zinc melt, the surface of the prepared TiC/Al alloy will melt and TiC particles will drop from it, then transfer into the zinc melt, and finally distribute uniformly in the zinc melt.
2003, 20(3): 122-126.
Abstract:
The polyvinylidene fluoride (PVDF) with barium titanate (BaTiO3) was prepared in melt as a dielectric composite. BaTiO3 was modified by titanate coupling agent and Ti(OBu)4 coupling agent. The dielectric properties and the interfacial interaction of the composite were examined. It is found that the dielectric constant can reach the highest value when the BaTiO3 particle is modified by coupling agent contents of 60% and the dielectric loss has a max value when the BaTiO3 particle is modified by coupling agent of about 30%. The SEM micrographs of BaTiO 3/PVDF show that the interfacial interaction between PVDF and BaTiO3, the weight fraction of BaTiO3 and the size of modified BaTiO3 are the keys to the dielectric properties of BaTiO3/PVDF dielectric composite.
The polyvinylidene fluoride (PVDF) with barium titanate (BaTiO3) was prepared in melt as a dielectric composite. BaTiO3 was modified by titanate coupling agent and Ti(OBu)4 coupling agent. The dielectric properties and the interfacial interaction of the composite were examined. It is found that the dielectric constant can reach the highest value when the BaTiO3 particle is modified by coupling agent contents of 60% and the dielectric loss has a max value when the BaTiO3 particle is modified by coupling agent of about 30%. The SEM micrographs of BaTiO 3/PVDF show that the interfacial interaction between PVDF and BaTiO3, the weight fraction of BaTiO3 and the size of modified BaTiO3 are the keys to the dielectric properties of BaTiO3/PVDF dielectric composite.
2003, 20(3): 127-131.
Abstract:
The superplastic mechanical behavior and deformation mechanism of the beta-SiC whisker reinforced 2024 aluminum composite, fabricated by low-pressure infiltration and hot-rolling after extrusion with a low extrusion ratio of 10∶1, were investigated by using elevated tensile tests, transmission electron microscopy, X-ray diffractometer, differential scanning calorimeter and the conventional theory of superplastic deformation mechanism for fine grain metals. The results show that the composite has a fine grain size of about 1 μm, and exhibits a maximum tensile elongation of 370 % in the initial strain rate of 3.3×10-3s-1 at 788 K. A small incipient melting peak on DSC curve of the composite appears and corresponds to the peritectic reaction of Al+CuAl2+Cu4Mg5Si4Al x→Liquid+Mg2Si at 785 K. The superplastic deformation mechanism of the composite is grain boundary (interface) sliding controlled by grain boundary diffusion of the aluminum atom and an appropriate amount of liquid phase.
The superplastic mechanical behavior and deformation mechanism of the beta-SiC whisker reinforced 2024 aluminum composite, fabricated by low-pressure infiltration and hot-rolling after extrusion with a low extrusion ratio of 10∶1, were investigated by using elevated tensile tests, transmission electron microscopy, X-ray diffractometer, differential scanning calorimeter and the conventional theory of superplastic deformation mechanism for fine grain metals. The results show that the composite has a fine grain size of about 1 μm, and exhibits a maximum tensile elongation of 370 % in the initial strain rate of 3.3×10-3s-1 at 788 K. A small incipient melting peak on DSC curve of the composite appears and corresponds to the peritectic reaction of Al+CuAl2+Cu4Mg5Si4Al x→Liquid+Mg2Si at 785 K. The superplastic deformation mechanism of the composite is grain boundary (interface) sliding controlled by grain boundary diffusion of the aluminum atom and an appropriate amount of liquid phase.
