2002 Vol. 19, No. 1
INTERFACIAL EFFECTS AND PERCOLATION BEHAVIOR IN SILICA NANOPARTICLES FILLED POLYPROPYLENE COMPOSITES
2002, 19(1): 1-4.
Abstract:
The tensile strength and the area under the tensile stress-strain curve of irradiation grafted and nano-silica filled polypropylene are studied to understand the interfacial effects and the percolation behavior induced by the nanoparticles. It is found that the nanoparticle agglomerates has a microstructure consisting of nanoparticles and grafted polymer after irradiation grafting polymerization, and thus a strong interfacial interaction can be established easily between the nanoparticles and matrix. In addition, an effect of double percolation of stress volumes, which might be responsible for the improvement of the tensile properties of the nanocomposites, is discussed in detail.
The tensile strength and the area under the tensile stress-strain curve of irradiation grafted and nano-silica filled polypropylene are studied to understand the interfacial effects and the percolation behavior induced by the nanoparticles. It is found that the nanoparticle agglomerates has a microstructure consisting of nanoparticles and grafted polymer after irradiation grafting polymerization, and thus a strong interfacial interaction can be established easily between the nanoparticles and matrix. In addition, an effect of double percolation of stress volumes, which might be responsible for the improvement of the tensile properties of the nanocomposites, is discussed in detail.
2002, 19(1): 5-11.
Abstract:
The tensile properties of short PET fiber/wollastonite/silicone resin hybrid composites have been studied. It was observed that the addition of wollastonite whisker with relatively low volume fraction to PET fiber/silicone resin system would lead to a reduction in the tensile stress of the hybrid composites. But when a very high amount of wollastonite was added, for example, 38% volume fraction, tensile strength of the hybrid composite increased sharply, which was even higher than that of PET fiber/silicone resin composites with the same fiber loading. The tensile modulus was found to increase as the volume fraction of PET fiber in the hybrid composites increases, while the wollastonite loading had little effect on the tensile modulus of the hybrid composites. The change of PET fiber efficiency factor with the addition of wollastonite to PET/silicone system was presented quantitatively.
The tensile properties of short PET fiber/wollastonite/silicone resin hybrid composites have been studied. It was observed that the addition of wollastonite whisker with relatively low volume fraction to PET fiber/silicone resin system would lead to a reduction in the tensile stress of the hybrid composites. But when a very high amount of wollastonite was added, for example, 38% volume fraction, tensile strength of the hybrid composite increased sharply, which was even higher than that of PET fiber/silicone resin composites with the same fiber loading. The tensile modulus was found to increase as the volume fraction of PET fiber in the hybrid composites increases, while the wollastonite loading had little effect on the tensile modulus of the hybrid composites. The change of PET fiber efficiency factor with the addition of wollastonite to PET/silicone system was presented quantitatively.
2002, 19(1): 12-16.
Abstract:
Experimental results proved that submicrostructure existed in short carbon fiber reinforced injection-moulded polyetherether ketone (PEEK) composites. The thickness of skin and core layers could be characterized by the metallographic optical microscope. Mechanical properties of the full plate could be calculated by the rule-of-mixture approach, in which the separately determined tensile strength and elastic modulus of the skin and core layers were combined with regard to their relative contribution to the full thickness of the original sample. The great thermo-stress and anisotropic mechanical properties between the skin and core layers resulted from different fiber orientations and PEEK crystallinities. Therefore, correlation of submicrostructure and mechanical properties of skin and core layers with the processing condition and mould configurations became one of the most important work for the product design of short fiber reinforced injection-moulded plastics composites.
Experimental results proved that submicrostructure existed in short carbon fiber reinforced injection-moulded polyetherether ketone (PEEK) composites. The thickness of skin and core layers could be characterized by the metallographic optical microscope. Mechanical properties of the full plate could be calculated by the rule-of-mixture approach, in which the separately determined tensile strength and elastic modulus of the skin and core layers were combined with regard to their relative contribution to the full thickness of the original sample. The great thermo-stress and anisotropic mechanical properties between the skin and core layers resulted from different fiber orientations and PEEK crystallinities. Therefore, correlation of submicrostructure and mechanical properties of skin and core layers with the processing condition and mould configurations became one of the most important work for the product design of short fiber reinforced injection-moulded plastics composites.
2002, 19(1): 17-21.
Abstract:
A mathematical model of heat transfer in part was established to simulate thermal behavior of GMT parts during compression molding, coupled with non-isothermal crystallization kinetics of polypropylene. A finite-element method was used to solve the model. The distribution of internal temperature and crystallinity of GMT parts were calculated, based on the non-isothermal crystallization model. The effects of mold temperature and the part thickness on cooling and crystallization processes were considered. The simulated results agreed well with experimental data. The proper mold temperature should be about 80 ℃, and the mean crystallinity of the resin should be controlled in the range of 0.51~0.55.
A mathematical model of heat transfer in part was established to simulate thermal behavior of GMT parts during compression molding, coupled with non-isothermal crystallization kinetics of polypropylene. A finite-element method was used to solve the model. The distribution of internal temperature and crystallinity of GMT parts were calculated, based on the non-isothermal crystallization model. The effects of mold temperature and the part thickness on cooling and crystallization processes were considered. The simulated results agreed well with experimental data. The proper mold temperature should be about 80 ℃, and the mean crystallinity of the resin should be controlled in the range of 0.51~0.55.
2002, 19(1): 22-27.
Abstract:
Bonding of Al-Pb alloy strips and hot dipped Al or Al-2%Si steel sheets was carried out by using hot rolling. The effects of addition of 2%Si to the bath, dipping time, thickness of the intermetallic layers and fraction of blank interfaces on bonding strength are investigated. In all cases, two different kinds of interfaces are produced; hot dip aluminized steel sheets and Al-Pb alloy strips are bonded through a mechanism of the blank and block interface bonding. The total bonding strength mainly depends on that of blank interface and the fraction of blank interfaces, and there is a linear relationship between the bonding strength and fraction of blank interfaces. The effect of Si on the total bonding strength represents the fact that though it has little effect on the bonding strength of block interface, it enormously increases the bonding strength of blank interface so that the total bonding strength grows much higher evidently. Under the given experimental conditions, it increases the bonding strength of blank interfaces six times as high as that of block interfaces for hot dipped Al-2Si specimens in contrast with four times as high as that for hot dipped Al specimens.
Bonding of Al-Pb alloy strips and hot dipped Al or Al-2%Si steel sheets was carried out by using hot rolling. The effects of addition of 2%Si to the bath, dipping time, thickness of the intermetallic layers and fraction of blank interfaces on bonding strength are investigated. In all cases, two different kinds of interfaces are produced; hot dip aluminized steel sheets and Al-Pb alloy strips are bonded through a mechanism of the blank and block interface bonding. The total bonding strength mainly depends on that of blank interface and the fraction of blank interfaces, and there is a linear relationship between the bonding strength and fraction of blank interfaces. The effect of Si on the total bonding strength represents the fact that though it has little effect on the bonding strength of block interface, it enormously increases the bonding strength of blank interface so that the total bonding strength grows much higher evidently. Under the given experimental conditions, it increases the bonding strength of blank interfaces six times as high as that of block interfaces for hot dipped Al-2Si specimens in contrast with four times as high as that for hot dipped Al specimens.
2002, 19(1): 28-31.
Abstract:
Al2O3, Al3Ti/Al in situ aluminum matrix composite material was prepared by means of XD(exothermic dispersion)synthesis technique. Its kinetic mechanism was also discussed. The results showed that the Al-TiO2system can react in a very short time. The reaction was propagated in combustion wave. It was also shown that aluminum initially reacted with TiO2 to form Al2O3 and reduced Ti. The Al2O3 and Al3Ti took the shape of equal axial particle and block respectively. A certain heating rate and content of aluminum are needed, if thermal explosion occurs commonly in the Al-TiO2 system. The bulk shrinkage will be higher with lower heating rate, higher aluminum content and lower green density.
Al2O3, Al3Ti/Al in situ aluminum matrix composite material was prepared by means of XD(exothermic dispersion)synthesis technique. Its kinetic mechanism was also discussed. The results showed that the Al-TiO2system can react in a very short time. The reaction was propagated in combustion wave. It was also shown that aluminum initially reacted with TiO2 to form Al2O3 and reduced Ti. The Al2O3 and Al3Ti took the shape of equal axial particle and block respectively. A certain heating rate and content of aluminum are needed, if thermal explosion occurs commonly in the Al-TiO2 system. The bulk shrinkage will be higher with lower heating rate, higher aluminum content and lower green density.
2002, 19(1): 32-36.
Abstract:
A novel rapidly solidified Cr3Si / Cr2Ni3Si composite coating is fabricated on the substrate of a 0.20 % C low carbon steel by laser cladding using Cr-Si-Ni elemental powder blends. The laser clad coating has a homogeneous microstructure consisting of Cr3Si primary dendrites uniformly distributed in the Cr2Ni3Si complex silicide matrix and is metallurgically bonded to the substrate. The laser clad Cr3Si reinforced Cr2Ni3Si silicide matrix composite coating has good wear resistance under dry sliding wear test condition and pin-on-disk abrasive wear test condition.
A novel rapidly solidified Cr3Si / Cr2Ni3Si composite coating is fabricated on the substrate of a 0.20 % C low carbon steel by laser cladding using Cr-Si-Ni elemental powder blends. The laser clad coating has a homogeneous microstructure consisting of Cr3Si primary dendrites uniformly distributed in the Cr2Ni3Si complex silicide matrix and is metallurgically bonded to the substrate. The laser clad Cr3Si reinforced Cr2Ni3Si silicide matrix composite coating has good wear resistance under dry sliding wear test condition and pin-on-disk abrasive wear test condition.
2002, 19(1): 37-40.
Abstract:
The microstructure of the stainless steel layer in the composite pipe prepared by centrifugal-thermit process was investigated. The thermal stress distribution in the composite pipe during cooling of the fabrication process was analyzed by means of the finite-element method. It demonstrated that the high thermal stress and the brittleness of the steel layer, caused by nonmetal inclusions and the precipitating phases, were responsible for the cracking of the stainless steel layer. During cooling, the thermal stress was high and would beyond the tensile strength of the stainless steel layer to cause cracks if it was not to be relaxed by the plastic deformation. Increasing the plasticity and reducing the thermal stress of the stainless steel layer, the cracking could be avoided.
The microstructure of the stainless steel layer in the composite pipe prepared by centrifugal-thermit process was investigated. The thermal stress distribution in the composite pipe during cooling of the fabrication process was analyzed by means of the finite-element method. It demonstrated that the high thermal stress and the brittleness of the steel layer, caused by nonmetal inclusions and the precipitating phases, were responsible for the cracking of the stainless steel layer. During cooling, the thermal stress was high and would beyond the tensile strength of the stainless steel layer to cause cracks if it was not to be relaxed by the plastic deformation. Increasing the plasticity and reducing the thermal stress of the stainless steel layer, the cracking could be avoided.
2002, 19(1): 41-45.
Abstract:
For the first time, the study on QTi3.5-3.5graphite composite was conducted using a semi-solid processing method. The relationship between distribution of graphite particles in the ingot and solid fraction of mushy was gotten, and the condition of acquiring QTi3.5-3.5graphite composite with evenly-distributing graphite particles was determined. The results showed that the rising-gathering of graphite particles reduced gradually with the increasing of solid fraction. When solid fraction was larger than 40 %, the rising-gathering of graphite particles could be removed, and QTi3.5-3.5graphite composite with evenly-distributing graphite particles could be gotten.
For the first time, the study on QTi3.5-3.5graphite composite was conducted using a semi-solid processing method. The relationship between distribution of graphite particles in the ingot and solid fraction of mushy was gotten, and the condition of acquiring QTi3.5-3.5graphite composite with evenly-distributing graphite particles was determined. The results showed that the rising-gathering of graphite particles reduced gradually with the increasing of solid fraction. When solid fraction was larger than 40 %, the rising-gathering of graphite particles could be removed, and QTi3.5-3.5graphite composite with evenly-distributing graphite particles could be gotten.
2002, 19(1): 46-49.
Abstract:
Nonhomogeneous diffusion thought to eliminate the embrittlement of steel-Al-20Sn interface was presented and realized by conducting steel-mushy Al-20Sn rolling casting bonding. The interfacial structure changed and the interfacial embrittlement was eliminated. The results showed that under the condition of 500℃ steel plate preheat temperature and 10mm/s rolling casting speed, when solid fraction was 34.3%, the interface was made up with the right Fe-Al compound and solid solution alternatively, and because of the elimination of interfacial embrittlement, the maximum interfacial shear strength was 69.9MPa.
Nonhomogeneous diffusion thought to eliminate the embrittlement of steel-Al-20Sn interface was presented and realized by conducting steel-mushy Al-20Sn rolling casting bonding. The interfacial structure changed and the interfacial embrittlement was eliminated. The results showed that under the condition of 500℃ steel plate preheat temperature and 10mm/s rolling casting speed, when solid fraction was 34.3%, the interface was made up with the right Fe-Al compound and solid solution alternatively, and because of the elimination of interfacial embrittlement, the maximum interfacial shear strength was 69.9MPa.
2002, 19(1): 50-53.
Abstract:
It was found that the experimental result for electric conductivity of TiB2-BN multiphase ceramics is consistent with the percolation model. The critical percent content of TiB2 is 22.9% when the raw material granularity scale is related to this paper. The critical percent content will change with grain sizes, then results in the change in electric resistivity. The ratios of grain sizes of TiB2 to BN after SPS sintering are in accord with those of the raw materials.
It was found that the experimental result for electric conductivity of TiB2-BN multiphase ceramics is consistent with the percolation model. The critical percent content of TiB2 is 22.9% when the raw material granularity scale is related to this paper. The critical percent content will change with grain sizes, then results in the change in electric resistivity. The ratios of grain sizes of TiB2 to BN after SPS sintering are in accord with those of the raw materials.
2002, 19(1): 54-58.
Abstract:
In situ reinforcement of ceramic matrix can be achieved by the elongated grains or platelets in situ formed in matrix during sintering through the mechanisms of crack bridging, crack deflection, elongated grain/platelet pullout, etc. In this work, in situ Al2O3 platelet/Ce-TZP composites and in situ SrO·6Al2O3 rod-like grain/Ce-TZP composites were prepared by adding AlOOH together with the mineralizer of TiO2 or the reactant of SrCO3 to Ce-TZP matrix. The microstructure of the composites was observed by SEM, and the density and mechanical properties of the composites were measured. The results indicated that TiO2 markedly promoted the anisotropic grain growth of Al2O3 and SrCO3 reacted with Al2O3, forming Al2O3 platelets and anisotropic SrO·6Al2O3 rod-like grains respectively. The in situ Al2O3 platelets and SrO·6Al2O3 rod-like grains were well-distributed in the matrix with a larger aspect ratio. Sintering temperature obviously affected the grain size and the content of Al2O3 platelet and SrO·6Al2O3 rod-like grain. The mechanical properties of the composites were improved by in situ introduction of Al2O3 platelets and SrO·6Al2O3 rod-like grains.
In situ reinforcement of ceramic matrix can be achieved by the elongated grains or platelets in situ formed in matrix during sintering through the mechanisms of crack bridging, crack deflection, elongated grain/platelet pullout, etc. In this work, in situ Al2O3 platelet/Ce-TZP composites and in situ SrO·6Al2O3 rod-like grain/Ce-TZP composites were prepared by adding AlOOH together with the mineralizer of TiO2 or the reactant of SrCO3 to Ce-TZP matrix. The microstructure of the composites was observed by SEM, and the density and mechanical properties of the composites were measured. The results indicated that TiO2 markedly promoted the anisotropic grain growth of Al2O3 and SrCO3 reacted with Al2O3, forming Al2O3 platelets and anisotropic SrO·6Al2O3 rod-like grains respectively. The in situ Al2O3 platelets and SrO·6Al2O3 rod-like grains were well-distributed in the matrix with a larger aspect ratio. Sintering temperature obviously affected the grain size and the content of Al2O3 platelet and SrO·6Al2O3 rod-like grain. The mechanical properties of the composites were improved by in situ introduction of Al2O3 platelets and SrO·6Al2O3 rod-like grains.
2002, 19(1): 59-63.
Abstract:
SiC particle reinforced molybdenum disilicide(MoSi2) matrix composite has been fabricated by wet mixing and hot press sintering successfully.The microstructure and mechanical properties of the composite were determined. The experimental results showed that SiCP/MoSi2 composite has a phase constituent with about 20 vol% SiC and less Mo5Si3 in MoSi2 matrix.Compared with unreinforced MoSi2, the flexural strength of SiCP/MoSi2 composite is increased by 33% and the fracture toughness by 52% at room temperature. Compressive yield strength of SiCP/MoSi2 composite is increased by 44% at 1200℃ and by 53% at 1400℃. SiCP/MoSi2 composite has been improved in its hardness and elastic modulus.The wear resistance of SiCP/MoSi2 on Al2O3 and SiC grind wheel is very excellent. An additional SiC particle into MoSi2 matrix has reflected improvements in toughness at room temperature and strength at high temperature.
SiC particle reinforced molybdenum disilicide(MoSi2) matrix composite has been fabricated by wet mixing and hot press sintering successfully.The microstructure and mechanical properties of the composite were determined. The experimental results showed that SiCP/MoSi2 composite has a phase constituent with about 20 vol% SiC and less Mo5Si3 in MoSi2 matrix.Compared with unreinforced MoSi2, the flexural strength of SiCP/MoSi2 composite is increased by 33% and the fracture toughness by 52% at room temperature. Compressive yield strength of SiCP/MoSi2 composite is increased by 44% at 1200℃ and by 53% at 1400℃. SiCP/MoSi2 composite has been improved in its hardness and elastic modulus.The wear resistance of SiCP/MoSi2 on Al2O3 and SiC grind wheel is very excellent. An additional SiC particle into MoSi2 matrix has reflected improvements in toughness at room temperature and strength at high temperature.
2002, 19(1): 64-68.
Abstract:
The electrorheological(ER) behavior of the water-free suspensions made of modified titania(TiO2) doped with rare earth(RE), synthesized by means of Sol-gel technique, in polydimetyl-silicone oil has been investigated under a DC field. In particular, the temperature dependence of the induced shear stress of ER suspensions has been studied carefully. In the results, it can be found that pure titania based ER fluids have almost no ER effects, but modified titania based ER fluids have a strong ER effect. The strong ER effect can be kept in the range from 10 ℃ to 100 ℃ in modified titania based ER fluids, the induced shear stress increases with temperature and reaches the maximum at 80℃. But the induced shear stress of pure titania based ER fluids reaches the maximum at 40 ℃, and then declines quickly. In addition, the remarkable characteristic is that the induced shear stress has a dependence on RE/Ti mole ratio and reaches a higher ER effect when RE/Ti mole ratio is about 0.07~0.11 at different temperatures. This can be explained by the dependence of dielectric properties of ER fluids on RE/Ti mole ratio.
The electrorheological(ER) behavior of the water-free suspensions made of modified titania(TiO2) doped with rare earth(RE), synthesized by means of Sol-gel technique, in polydimetyl-silicone oil has been investigated under a DC field. In particular, the temperature dependence of the induced shear stress of ER suspensions has been studied carefully. In the results, it can be found that pure titania based ER fluids have almost no ER effects, but modified titania based ER fluids have a strong ER effect. The strong ER effect can be kept in the range from 10 ℃ to 100 ℃ in modified titania based ER fluids, the induced shear stress increases with temperature and reaches the maximum at 80℃. But the induced shear stress of pure titania based ER fluids reaches the maximum at 40 ℃, and then declines quickly. In addition, the remarkable characteristic is that the induced shear stress has a dependence on RE/Ti mole ratio and reaches a higher ER effect when RE/Ti mole ratio is about 0.07~0.11 at different temperatures. This can be explained by the dependence of dielectric properties of ER fluids on RE/Ti mole ratio.
2002, 19(1): 69-73.
Abstract:
By introducing two displacement functions and two stress functions, two independent state equations are constructed based on the three-dimensional piezoelasticity equations for transverse isotropy. The original differential equations are thus decoupled with the order reduced that will facilitate obtaining solutions of various problems. For the simply supported rectangular plate subjected to bi-axial uniform pressures, two relations between the state variables at the top and bottom surfaces are established. In particular, it is found that there exist two independent classes of stabilities. The first class corresponds to the purely in-plane stability and the second to the general flexural stability. Numerical examples are finally presented and the effects of some parameters are discussed.
By introducing two displacement functions and two stress functions, two independent state equations are constructed based on the three-dimensional piezoelasticity equations for transverse isotropy. The original differential equations are thus decoupled with the order reduced that will facilitate obtaining solutions of various problems. For the simply supported rectangular plate subjected to bi-axial uniform pressures, two relations between the state variables at the top and bottom surfaces are established. In particular, it is found that there exist two independent classes of stabilities. The first class corresponds to the purely in-plane stability and the second to the general flexural stability. Numerical examples are finally presented and the effects of some parameters are discussed.
2002, 19(1): 74-79.
Abstract:
Composite laminated cylindrical shell is a common load-carrying structure. Delaminations may arise from its fabrication, transport and service, which will influence the load-carrying capacity of the cylindrical shell. So, it is necessary to model it correctly to investigate the load-carrying capacity of the delaminated cylindrical shell. In this paper, first, an axial-compressive cylinder shell including arbitrary delaminations in longitudinal and thickness and spanning the entire circumference was divided into multiple sublaminated shells whose axial and circumferential displacements were simulated with a cubic function of the thickness coordinate and a trigonometric series of circumferential coordinate. Then, the variational principle was applied to obtain the governing equations and determining conditions. Finally, the governing equations and determining conditions were described as state-space forms and state-space scheme was used to solve the problem.
Composite laminated cylindrical shell is a common load-carrying structure. Delaminations may arise from its fabrication, transport and service, which will influence the load-carrying capacity of the cylindrical shell. So, it is necessary to model it correctly to investigate the load-carrying capacity of the delaminated cylindrical shell. In this paper, first, an axial-compressive cylinder shell including arbitrary delaminations in longitudinal and thickness and spanning the entire circumference was divided into multiple sublaminated shells whose axial and circumferential displacements were simulated with a cubic function of the thickness coordinate and a trigonometric series of circumferential coordinate. Then, the variational principle was applied to obtain the governing equations and determining conditions. Finally, the governing equations and determining conditions were described as state-space forms and state-space scheme was used to solve the problem.
2002, 19(1): 80-84.
Abstract:
Delaminations may reduce the buckling load of the laminated structure greatly. In this paper, various examples were analyzed by using the model in part I. First, by comparing with the results of the classical theory and first-order shear-deformation theory, the model was validated and the usable range of each theory was pointed out. Three different buckling modes of delaminated shell were considered. The influence of different ratios of radius to thickness, boundary condition and length, depth and position of the delamination on the buckling load was analyzed. Finally, the buckling analysis of delaminated orthotropic shell and the influences of ply orientation of the material on the buckling load of a delaminated shell were given.
Delaminations may reduce the buckling load of the laminated structure greatly. In this paper, various examples were analyzed by using the model in part I. First, by comparing with the results of the classical theory and first-order shear-deformation theory, the model was validated and the usable range of each theory was pointed out. Three different buckling modes of delaminated shell were considered. The influence of different ratios of radius to thickness, boundary condition and length, depth and position of the delamination on the buckling load was analyzed. Finally, the buckling analysis of delaminated orthotropic shell and the influences of ply orientation of the material on the buckling load of a delaminated shell were given.
2002, 19(1): 85-89.
Abstract:
The plastic limit loads of composite materials and structures are analyzed in both the macroscopic and microscopic scales. Based on the concept of a representative volume element reflecting the microstructures of the composites, the strength parameters of the composites can be calculated. By means of the homogenization technique of micromechanics method and the finite element method, the yield surface of a composite can be determined. Then an upper bound of the plastic limit load of a composite structure can be calculated by solving a nonlinear mathematical programming problem.
The plastic limit loads of composite materials and structures are analyzed in both the macroscopic and microscopic scales. Based on the concept of a representative volume element reflecting the microstructures of the composites, the strength parameters of the composites can be calculated. By means of the homogenization technique of micromechanics method and the finite element method, the yield surface of a composite can be determined. Then an upper bound of the plastic limit load of a composite structure can be calculated by solving a nonlinear mathematical programming problem.
2002, 19(1): 90-94.
Abstract:
The theoretical analysis and experimental verification about the elastic properties of Plain Weave Fabric Composites (PWFC) is discussed in this article.Representative Volume Element (RVE) method is used to predict the elastic properties according to those of raw materials of PWFC. RVE method belongs to micromechanics, in which an element that can represent the properties of the whole material is selected and studied, thus the contribution of fiber, resin, interface can be analyzed respectively. The simplest unit cell of PWFC is taken out as RVE in this research. A mathematics model based on RVE is set up and the yarn shape in the composites is regarded as sinusoidal. The relationship between micro structure and macro properties is analyzed. A predictor program is made for predicting quickly. The predictor software programmed with Visual Basic has some convenient features. With considering all factors of the yarn geometric shape, the fiber volume content and the hollow rate, the theoretically elastic data of PWFC can be predicted. Compared experiments are done by using lay-out and RTM process to make samples. The relatively small error between the experimental result and predicted data proves the feasibility of the mathematics model and predictor method.
The theoretical analysis and experimental verification about the elastic properties of Plain Weave Fabric Composites (PWFC) is discussed in this article.Representative Volume Element (RVE) method is used to predict the elastic properties according to those of raw materials of PWFC. RVE method belongs to micromechanics, in which an element that can represent the properties of the whole material is selected and studied, thus the contribution of fiber, resin, interface can be analyzed respectively. The simplest unit cell of PWFC is taken out as RVE in this research. A mathematics model based on RVE is set up and the yarn shape in the composites is regarded as sinusoidal. The relationship between micro structure and macro properties is analyzed. A predictor program is made for predicting quickly. The predictor software programmed with Visual Basic has some convenient features. With considering all factors of the yarn geometric shape, the fiber volume content and the hollow rate, the theoretically elastic data of PWFC can be predicted. Compared experiments are done by using lay-out and RTM process to make samples. The relatively small error between the experimental result and predicted data proves the feasibility of the mathematics model and predictor method.
2002, 19(1): 95-100.
Abstract:
A model for determining the effective elastic constants of stitched lamina is established, in which the effects of stitching parameters on elastic constants of stitched lamina are analyzed by considering the nonuniform distribution and in-plan waviness of fibers induced by stitching. The results show that, when the stitching direction is perpendicular to the fiber direction, the longitudinal modulus decreases but transverse modulus and shear modulus increase gradually with decreasing row spacing or increasing stitch thread radius.
A model for determining the effective elastic constants of stitched lamina is established, in which the effects of stitching parameters on elastic constants of stitched lamina are analyzed by considering the nonuniform distribution and in-plan waviness of fibers induced by stitching. The results show that, when the stitching direction is perpendicular to the fiber direction, the longitudinal modulus decreases but transverse modulus and shear modulus increase gradually with decreasing row spacing or increasing stitch thread radius.
2002, 19(1): 101-106.
Abstract:
Based on the model for determining the effective elastic constants of stitched lamina, the constitutive relation of stitched laminates is presented and the effects of stitching parameters on stiffness are investigated. In order to validate the analytical results, the tensile stiffness and the compressive stiffness of stitched laminates are also studied experimentally, and good agreement was found between analytical and experimental results.
Based on the model for determining the effective elastic constants of stitched lamina, the constitutive relation of stitched laminates is presented and the effects of stitching parameters on stiffness are investigated. In order to validate the analytical results, the tensile stiffness and the compressive stiffness of stitched laminates are also studied experimentally, and good agreement was found between analytical and experimental results.
2002, 19(1): 107-112.
Abstract:
The characteristics of porous sound absorbing material have great effects on the behavior of a pneumatic silencer. Measurements of the centerline mean velocity, total pressure, and distribution of turbulent intensity were made to investigate the flowfield generated by compressible air passing through the porous material (polyvinyl formal) with different thickness. The details of the flowfield are different from those of the free jet of a convergent nozzle. The airflow from the porous material includes common micro-jet flow, combining and spreading flow. The effects of the porous sound absorbing material on the noise attenuation include two aspects one is the total pressure is decreased, and the other is the outer flowfield such as its axial velocity profile and distribution of turbulent intensity is changed due to a great deal of micro-jet flow interaction.
The characteristics of porous sound absorbing material have great effects on the behavior of a pneumatic silencer. Measurements of the centerline mean velocity, total pressure, and distribution of turbulent intensity were made to investigate the flowfield generated by compressible air passing through the porous material (polyvinyl formal) with different thickness. The details of the flowfield are different from those of the free jet of a convergent nozzle. The airflow from the porous material includes common micro-jet flow, combining and spreading flow. The effects of the porous sound absorbing material on the noise attenuation include two aspects one is the total pressure is decreased, and the other is the outer flowfield such as its axial velocity profile and distribution of turbulent intensity is changed due to a great deal of micro-jet flow interaction.
2002, 19(1): 113-116.
Abstract:
The use of advanced carbon-fiber composite on a flywheel rotor results in not only the increase of energy density by increasing the rotating speed when the outer diameter and mass are fixed, but also solution of the fracture problem of the flywheel rotor. The calculation on the stress distribution is conducted in the present paper according to the working situation of the flywheel. These provide the basis for proper design of composite flywheels.
The use of advanced carbon-fiber composite on a flywheel rotor results in not only the increase of energy density by increasing the rotating speed when the outer diameter and mass are fixed, but also solution of the fracture problem of the flywheel rotor. The calculation on the stress distribution is conducted in the present paper according to the working situation of the flywheel. These provide the basis for proper design of composite flywheels.
2002, 19(1): 117-121.
Abstract:
Synthesis and mechanical properties of epoxy/clay nanocomposites are studied in this paper. It is found that the affinity between the organoclay and epoxy resin is very good and the organoclay is easy to be intercalated by epoxy resin with or without solvent. By direct or solution mixing, a stable and homogeneous epoxy/clay intercalated hybrid can be obtained in which the basal spacing of clay increases to about 3.7nm. Using two different kinds of organoclay, both exfoliated and intercalated epoxy/clay nanocomposites are achieved. In the former case, the clay exfoliates completely and there is no trace of X-ray diffraction peaks while in the latter case the clay retains its previous structure and strong X-ray diffraction peaks remain. Mechanical properties test results show that the exfoliated nanocomposite performs better than the intercalated nanocomposite of the same compound. But even in the exfoliated nanocomposites the mechanical properties of epoxy resin are not improved magnificently as in the cases of thermal plastic.
Synthesis and mechanical properties of epoxy/clay nanocomposites are studied in this paper. It is found that the affinity between the organoclay and epoxy resin is very good and the organoclay is easy to be intercalated by epoxy resin with or without solvent. By direct or solution mixing, a stable and homogeneous epoxy/clay intercalated hybrid can be obtained in which the basal spacing of clay increases to about 3.7nm. Using two different kinds of organoclay, both exfoliated and intercalated epoxy/clay nanocomposites are achieved. In the former case, the clay exfoliates completely and there is no trace of X-ray diffraction peaks while in the latter case the clay retains its previous structure and strong X-ray diffraction peaks remain. Mechanical properties test results show that the exfoliated nanocomposite performs better than the intercalated nanocomposite of the same compound. But even in the exfoliated nanocomposites the mechanical properties of epoxy resin are not improved magnificently as in the cases of thermal plastic.
2002, 19(1): 122-125.
Abstract:
Monitoring damage and repairing crack are the important problems in composite materials. The method of self-diagnose and self-repair composite structures using a hollow-center optical fiber filled adhesive is a good technique. Based on this thought, the mechanism investigation and analysis of light transmission in the hollow-center optical fiber are made in detail. The measure method and experimental research of self-diagnose for the rupture location in composite materials are also put forward. In this paper, the performance of the hollow-center optical fiber is explained first. The theory of light transmission attenuation by snipping the optical fiber is used in self-diagnose of the rupture location. Finally, a Y coupler is given to measure the rupture location and a general experimental system for self-diagnose and self-repair is given as an example.
Monitoring damage and repairing crack are the important problems in composite materials. The method of self-diagnose and self-repair composite structures using a hollow-center optical fiber filled adhesive is a good technique. Based on this thought, the mechanism investigation and analysis of light transmission in the hollow-center optical fiber are made in detail. The measure method and experimental research of self-diagnose for the rupture location in composite materials are also put forward. In this paper, the performance of the hollow-center optical fiber is explained first. The theory of light transmission attenuation by snipping the optical fiber is used in self-diagnose of the rupture location. Finally, a Y coupler is given to measure the rupture location and a general experimental system for self-diagnose and self-repair is given as an example.
