2004 Vol. 21, No. 1
2004, 21(1): 1-6.
Abstract:
BaFe12O19/SiO2-B2O3-K2O microcrystallite glass ceramics were prepared by citrate sol-gel process. The dielectric constan tand permeability dispersion were investigated in 100MHz ～ 6. 0 GH zrange. It was discovered that the synthesis temperature of BaFe12O19/SiO2-B2O3-K2O microcrystallite glass ceramics is about 850℃ and the condition such as Ba/Fe had a close effect on the syn thesis of BaFe12O19/SiO2-B2O3-K2O. It also showed that the dielectric exhib it salmo stnovariation with measuring frequency increasing. The real part of permeability decreases as the measuring frequency increasing.
BaFe12O19/SiO2-B2O3-K2O microcrystallite glass ceramics were prepared by citrate sol-gel process. The dielectric constan tand permeability dispersion were investigated in 100MHz ～ 6. 0 GH zrange. It was discovered that the synthesis temperature of BaFe12O19/SiO2-B2O3-K2O microcrystallite glass ceramics is about 850℃ and the condition such as Ba/Fe had a close effect on the syn thesis of BaFe12O19/SiO2-B2O3-K2O. It also showed that the dielectric exhib it salmo stnovariation with measuring frequency increasing. The real part of permeability decreases as the measuring frequency increasing.
2004, 21(1): 7-11.
Abstract:
A PAN-based precursor carbon fiber (carbonized at 1300℃) was impregnated with different borides and heat-treated at 2500℃ under nitrogen atmosphere. The mechanical properties of the resulting graphite fibers have been measured and their microstructure investigated by X-ray diffraction (XRD) and scanning tunneling microscope (STM). It is shown that boron-doping improves the tensile modulus and strength of the fibers. This can be explained by the STM observations, which show smoother surface with fewer defects and improved crystallite orientation along the fiber axes for the boron-treated samples. The result of XRD shows that the boron-doping treatment increased the crystallite size.
A PAN-based precursor carbon fiber (carbonized at 1300℃) was impregnated with different borides and heat-treated at 2500℃ under nitrogen atmosphere. The mechanical properties of the resulting graphite fibers have been measured and their microstructure investigated by X-ray diffraction (XRD) and scanning tunneling microscope (STM). It is shown that boron-doping improves the tensile modulus and strength of the fibers. This can be explained by the STM observations, which show smoother surface with fewer defects and improved crystallite orientation along the fiber axes for the boron-treated samples. The result of XRD shows that the boron-doping treatment increased the crystallite size.
2004, 21(1): 12-16.
Abstract:
By using FeSO4·7H2O, NiSO4·6H2O and ZnSO4·7H2O as raw materials, with a coprecipitation method, the basic carbonate precursor containing very fine crystalline grain is first synthesized and then nanocrystalline (Ni,Zn)Fe2O4 composite particles followed by sintering for one hour can be obtained. The microstructure was measured by using XRD and TEM. And then, the infrared absorption and gas-sensitization of the samples have been investigated. The results show that the diameter of the nano-particles is about 50nm at 800℃.
By using FeSO4·7H2O, NiSO4·6H2O and ZnSO4·7H2O as raw materials, with a coprecipitation method, the basic carbonate precursor containing very fine crystalline grain is first synthesized and then nanocrystalline (Ni,Zn)Fe2O4 composite particles followed by sintering for one hour can be obtained. The microstructure was measured by using XRD and TEM. And then, the infrared absorption and gas-sensitization of the samples have been investigated. The results show that the diameter of the nano-particles is about 50nm at 800℃.
STUDY ON PREPARATION AND PROPERTIES OF NANOPOROUS SILICA/ALUMINA PILLARED MONTMORILLONITE COMPOSITES
2004, 21(1): 17-22.
Abstract:
The nanoporous silica/alumina pillared montmorillonite composites were synthesized by direct hydrolysis of inorganic aluminum and silicon precursor in the gallery of layered hosts through an intragallery-templated method. Powder X-ray diffraction, TG, FT-IR and N2 adsorption-desorption isotherms were used to characterize the synthetic Si/Al-clay composite, which was here designated SA-PMH. The results reveal that the SA-PMH exhibits basal spacing of 3.45 nm, a large BET specific area of 502.0 m2/g , an average pore size 2.0 nm and a high thermal stability up to 750 ℃. In comparison to the silica-PMH, little change in textural porosity and thermal stability was observed, but the SA-PMH has more surface acidity and medium-strong acid sites, as confirmed by the temperature-programmed desorption of ammonia and acid-catalyzed reactivity of catechol alkylation with tert-butyl alcohol.
The nanoporous silica/alumina pillared montmorillonite composites were synthesized by direct hydrolysis of inorganic aluminum and silicon precursor in the gallery of layered hosts through an intragallery-templated method. Powder X-ray diffraction, TG, FT-IR and N2 adsorption-desorption isotherms were used to characterize the synthetic Si/Al-clay composite, which was here designated SA-PMH. The results reveal that the SA-PMH exhibits basal spacing of 3.45 nm, a large BET specific area of 502.0 m2/g , an average pore size 2.0 nm and a high thermal stability up to 750 ℃. In comparison to the silica-PMH, little change in textural porosity and thermal stability was observed, but the SA-PMH has more surface acidity and medium-strong acid sites, as confirmed by the temperature-programmed desorption of ammonia and acid-catalyzed reactivity of catechol alkylation with tert-butyl alcohol.
2004, 21(1): 23-27.
Abstract:
A new inorganic and organic composite membrane with above 60% inorganic materials was developed in this paper. The composite membrane possessed good sulfuric acid resistance because part of inorganic materials crosslinked in drying. After being dried at 80℃ for 30min, the membrane could restore its original weight in moisture air, and the chemically combined water in the membrane dissolved until to 120℃,therefore the membrane showed excellent proton conductivity even in dry air with relative humidity below 40%. The conductivity was 1.14×10-2 S/cm at room temperature and increased to 2.81×10-2S/cm at 60℃. Without any humidification, the power density of this composite membrane was twice that of Nafion117 at room temperature.
A new inorganic and organic composite membrane with above 60% inorganic materials was developed in this paper. The composite membrane possessed good sulfuric acid resistance because part of inorganic materials crosslinked in drying. After being dried at 80℃ for 30min, the membrane could restore its original weight in moisture air, and the chemically combined water in the membrane dissolved until to 120℃,therefore the membrane showed excellent proton conductivity even in dry air with relative humidity below 40%. The conductivity was 1.14×10-2 S/cm at room temperature and increased to 2.81×10-2S/cm at 60℃. Without any humidification, the power density of this composite membrane was twice that of Nafion117 at room temperature.
2004, 21(1): 28-32.
Abstract:
Alumina platelets and powders coated with 3 wt% CaO-SiO2 glass and yttria-stabilized zirconia (3Y-TZP) powders were used as starting materials. The compacts were prepared in atmospheric pressure at various temperatures by templated grain growth. The mechanical properties of the composites were investigated. The results show that the composites sintered at proper temperature have high strength (800~900 MPa) and toughness (11.8~15.2MPa·m1/2). The microstructure of the composites was observed using SEM. The possible mechanism could be attributed to the enhancement of phase transformation from tetragonal to monoclinic during fracture and crack-deflection and bridging produced by the platelike Al2O3 grains. The variability in strength was quantified using conventional two-parameter Weibull statistics. The results show that the composite containing higher platelet-alumina has a high Weibull modulus.
Alumina platelets and powders coated with 3 wt% CaO-SiO2 glass and yttria-stabilized zirconia (3Y-TZP) powders were used as starting materials. The compacts were prepared in atmospheric pressure at various temperatures by templated grain growth. The mechanical properties of the composites were investigated. The results show that the composites sintered at proper temperature have high strength (800~900 MPa) and toughness (11.8~15.2MPa·m1/2). The microstructure of the composites was observed using SEM. The possible mechanism could be attributed to the enhancement of phase transformation from tetragonal to monoclinic during fracture and crack-deflection and bridging produced by the platelike Al2O3 grains. The variability in strength was quantified using conventional two-parameter Weibull statistics. The results show that the composite containing higher platelet-alumina has a high Weibull modulus.
2004, 21(1): 33-37.
Abstract:
Fibre reinforcement plastic (FRP) has the drawbacks of poor ductility and brittle failure mode, which are impediments for substituting it for steel bar in reinforced concrete materials. These shortcomings can be overcome through material design and geometric hybrid.This paper presents a new concept of geometric hybrid which uses steel as the core with ±45°angle laminations of glass fibre impregnated with epoxy around the core. It is demonstrated that the law of mixtures can be applied to the prediction for the stress-strain behavior of the hybrid rebars.
Fibre reinforcement plastic (FRP) has the drawbacks of poor ductility and brittle failure mode, which are impediments for substituting it for steel bar in reinforced concrete materials. These shortcomings can be overcome through material design and geometric hybrid.This paper presents a new concept of geometric hybrid which uses steel as the core with ±45°angle laminations of glass fibre impregnated with epoxy around the core. It is demonstrated that the law of mixtures can be applied to the prediction for the stress-strain behavior of the hybrid rebars.
2004, 21(1): 38-44.
Abstract:
Surface treatment effects were compared with alkali, water, softening agent and silane coupling agent and its constitutions of basalt fiber (B.F.) were determined. On the basis of these researches, ecomaterials were prepared by means of basalt fiber and plant fiber. The results showed that the basalt fibers were dispersed symmetrically in the plant fiber and excellent characteristics of the basalt fiber and the plant fiber were exerted adequately, respectively. The configuration of the composite was described in terms of the random coil model and scanning electro microscopy (SEM). The effect factors of beating degree, content of basalt fiber and adhesive, etc were discussed. As-prepared composite was of repeatable utilization, high ratio performance and price, no second pollution. As a result, the composite harmonized with environment and accorded with requirement of environmentally benign materials.
Surface treatment effects were compared with alkali, water, softening agent and silane coupling agent and its constitutions of basalt fiber (B.F.) were determined. On the basis of these researches, ecomaterials were prepared by means of basalt fiber and plant fiber. The results showed that the basalt fibers were dispersed symmetrically in the plant fiber and excellent characteristics of the basalt fiber and the plant fiber were exerted adequately, respectively. The configuration of the composite was described in terms of the random coil model and scanning electro microscopy (SEM). The effect factors of beating degree, content of basalt fiber and adhesive, etc were discussed. As-prepared composite was of repeatable utilization, high ratio performance and price, no second pollution. As a result, the composite harmonized with environment and accorded with requirement of environmentally benign materials.
OPTICAL FIBER PRESSURE TESTING TECHNOLOGY USED IN CURE MOLDING PROCESS FOR POLYMER MATRIX COMPOSITES
2004, 21(1): 45-50.
Abstract:
According to the cure molding process of polymer matrix composite, an optical fiber sensor system was established for testing the pressure change in the normal direction of prepreg layers, and the applicability of this system was also evaluated. As a result of experimentation, this sort of optical fiber sensor can be used in the environment where the measuring temperature is under 120℃ and measuring pressure between 0.005~0.5 MPa, steadily and repeatedly. The effect of flex density, the measuring temperature and micro bend rebound of the fiber optical sensor during the mould forming process are given. The fit equation is performed with varying loading and a comparison of numerical results with known experimental data confirms the approximate validity of the fit equation.
According to the cure molding process of polymer matrix composite, an optical fiber sensor system was established for testing the pressure change in the normal direction of prepreg layers, and the applicability of this system was also evaluated. As a result of experimentation, this sort of optical fiber sensor can be used in the environment where the measuring temperature is under 120℃ and measuring pressure between 0.005~0.5 MPa, steadily and repeatedly. The effect of flex density, the measuring temperature and micro bend rebound of the fiber optical sensor during the mould forming process are given. The fit equation is performed with varying loading and a comparison of numerical results with known experimental data confirms the approximate validity of the fit equation.
2004, 21(1): 51-55.
Abstract:
Diamond particles,with average particle sizes of 12μm, 25μm and 50μm, were mixed with WC-10wt%Co in a 20% volume fraction and densified by using SPS method. Before mixing, the diamond was coated by nanometer sized SiC layer against oxidation and graphitization. The relative density of all composites reached 98%. The Vickers hardness did not differ so much from the matrix hardness of WC-10 wt%Co by the dispersing diamond. However, the indentation toughness remarkably increased to 17.8MPa·m1/2 with 50 μm diamond dispersion. Crack deflection and block were clearly detected around diamond particles. The variation of diamond particle size did not affect the mechanical properties of the composite too much.
Diamond particles,with average particle sizes of 12μm, 25μm and 50μm, were mixed with WC-10wt%Co in a 20% volume fraction and densified by using SPS method. Before mixing, the diamond was coated by nanometer sized SiC layer against oxidation and graphitization. The relative density of all composites reached 98%. The Vickers hardness did not differ so much from the matrix hardness of WC-10 wt%Co by the dispersing diamond. However, the indentation toughness remarkably increased to 17.8MPa·m1/2 with 50 μm diamond dispersion. Crack deflection and block were clearly detected around diamond particles. The variation of diamond particle size did not affect the mechanical properties of the composite too much.
2004, 21(1): 56-60.
Abstract:
Because of the special properties of Al2O3 and heat-resistant steel at high temperature, the composite of Al2O3 particle reinforced heat-resistant matrix would possess good wear-resistance at the situation of high temperature and abrasive. After getting the coating on 154~200 μm Al2O3 particles by CVD method, the composites are made by the vacuum infiltration process, the particle volume fractions are changed from 18% to 52% through adding the heat-resistant steel particles into Al2O3 particles, and then the wear-resistances of the composites at high temperature have been investigated. The results show that the wear-resistant properties of all composites are better than those of heat-resistant steel, and the best composite is the one in which the coated-Ni Al2O3 particle volume fraction is 39%, whose wear resistance is 3.27 times that of heat-resistant steel at the situation of 900℃ and abrasive wear. Then the wear mechanism of particle composites and the effects of particle volume fraction on wear are analyzed by SEM.
Because of the special properties of Al2O3 and heat-resistant steel at high temperature, the composite of Al2O3 particle reinforced heat-resistant matrix would possess good wear-resistance at the situation of high temperature and abrasive. After getting the coating on 154~200 μm Al2O3 particles by CVD method, the composites are made by the vacuum infiltration process, the particle volume fractions are changed from 18% to 52% through adding the heat-resistant steel particles into Al2O3 particles, and then the wear-resistances of the composites at high temperature have been investigated. The results show that the wear-resistant properties of all composites are better than those of heat-resistant steel, and the best composite is the one in which the coated-Ni Al2O3 particle volume fraction is 39%, whose wear resistance is 3.27 times that of heat-resistant steel at the situation of 900℃ and abrasive wear. Then the wear mechanism of particle composites and the effects of particle volume fraction on wear are analyzed by SEM.
2004, 21(1): 61-67.
Abstract:
2024 aluminum matrix composite reinforced by SiC particles with 45% volume fraction and 1 μm diameter was successfully fabricated by a squeeze-exhaust casting method. The effect of dislocations on the aging behaviors of SiCP/2024Al composite was investigated. The results showed that the high-density dislocations in the composite cause the annihilation of quenched-in vacancies, so the GP zone formation is suppressed to some extent. However, the high-density dislocations decrease the thermal diffusion activation energy for the other precipitate formation and accelerate the nucleation of precipitates. Moreover, the high-density dislocations can supply the pathway for pipe diffusion of solute and accelerate the growth of precipitates. So the aging behavior of composite is accelerated and the aging peak of composite appears earlier than that of 2024Al alloy. The high-density dislocations, as preferential nucleation sites for precipitates, bring about the tiny and dense precipitates in the composite.
2024 aluminum matrix composite reinforced by SiC particles with 45% volume fraction and 1 μm diameter was successfully fabricated by a squeeze-exhaust casting method. The effect of dislocations on the aging behaviors of SiCP/2024Al composite was investigated. The results showed that the high-density dislocations in the composite cause the annihilation of quenched-in vacancies, so the GP zone formation is suppressed to some extent. However, the high-density dislocations decrease the thermal diffusion activation energy for the other precipitate formation and accelerate the nucleation of precipitates. Moreover, the high-density dislocations can supply the pathway for pipe diffusion of solute and accelerate the growth of precipitates. So the aging behavior of composite is accelerated and the aging peak of composite appears earlier than that of 2024Al alloy. The high-density dislocations, as preferential nucleation sites for precipitates, bring about the tiny and dense precipitates in the composite.
2004, 21(1): 68-72.
Abstract:
Based on the Double Cantilever Beam (DCB) testing method, an experimental and analytical investigation was conducted on the modeⅠinterlaminar toughness and fracture behavior of woven fabric reinforced laminates. DCB tests were completed at both room temperature (R T) and liquid nitrogen temperature (77K) to evaluate the influence of temperature and specimen size on the interlaminar fracture toughness. The broken areas were examined by scanning microscope to analyze and identify the fracture characteristics.
Based on the Double Cantilever Beam (DCB) testing method, an experimental and analytical investigation was conducted on the modeⅠinterlaminar toughness and fracture behavior of woven fabric reinforced laminates. DCB tests were completed at both room temperature (R T) and liquid nitrogen temperature (77K) to evaluate the influence of temperature and specimen size on the interlaminar fracture toughness. The broken areas were examined by scanning microscope to analyze and identify the fracture characteristics.
2004, 21(1): 73-77.
Abstract:
In this paper, according to the analysis of the ablative mechanism of thermal protective materials under elevated temperature, the ablation-phase transformation properties and the thermomechanical behavior of the component materials are investigated by Eshelby equivalent inclusion method. Through the hypothesis of the statistical uniform distribution of the phases consisting of solid products of thermodestruction at high temperatures and pores in the materials, the interaction among different phases by complicated internal physico-chemical processes in a matrix and fibers is considered. The exact relationship between the micro-structure and the macro-behavior for composites reinforced with unidirectional continuous fibres is expressed, and the numerical solution is also given. With the help of the model, the following high-temperature phenomena have been described: degradation of elastic moduli of the composite in the reinforcing direction in heating, and dependence of heat properties of the composite not only on temperature but also on duration of heating. Comparison of the theoretical and experimental results for typical ablative materials showed that the model allows one to forecast the thermomechanical characteristics of the composites according to the properties of their matrices and fibers with sufficient accuracy. It will be helpful for the analysis of the composite materials high-temperate structure.
In this paper, according to the analysis of the ablative mechanism of thermal protective materials under elevated temperature, the ablation-phase transformation properties and the thermomechanical behavior of the component materials are investigated by Eshelby equivalent inclusion method. Through the hypothesis of the statistical uniform distribution of the phases consisting of solid products of thermodestruction at high temperatures and pores in the materials, the interaction among different phases by complicated internal physico-chemical processes in a matrix and fibers is considered. The exact relationship between the micro-structure and the macro-behavior for composites reinforced with unidirectional continuous fibres is expressed, and the numerical solution is also given. With the help of the model, the following high-temperature phenomena have been described: degradation of elastic moduli of the composite in the reinforcing direction in heating, and dependence of heat properties of the composite not only on temperature but also on duration of heating. Comparison of the theoretical and experimental results for typical ablative materials showed that the model allows one to forecast the thermomechanical characteristics of the composites according to the properties of their matrices and fibers with sufficient accuracy. It will be helpful for the analysis of the composite materials high-temperate structure.
2004, 21(1): 78-83.
Abstract:
The cure kinetic model of typical BMI resin was studied, and the typical BMI resin has been obtained by copolymerization of bis (4-maleimido-phenyl)methat and o,o-diallylbisphenol-A. At present, a majority of the modified BMI resin is prepared based on the typical BMI resin. The kinetics of the cure reaction for a system of typical BMI was monitored by differential scanning calorimetry(DSC) and carried out by constant heating and isothermal methods. The cure kinetic model and kinetic parameters based on the autocatalytic and nth reaction equation were established and were applied to the processing of data by least-squares and Kissinger methods. The estimated cure of the model was in good agreement with that of the experiments. The results indicated that the curing reaction processing can be divided into two stages following different mechanics, with the autocatalytic reaction model transformation into the nth reaction model. The model is important for processing simulation and quality control of processing for high performance composites.
The cure kinetic model of typical BMI resin was studied, and the typical BMI resin has been obtained by copolymerization of bis (4-maleimido-phenyl)methat and o,o-diallylbisphenol-A. At present, a majority of the modified BMI resin is prepared based on the typical BMI resin. The kinetics of the cure reaction for a system of typical BMI was monitored by differential scanning calorimetry(DSC) and carried out by constant heating and isothermal methods. The cure kinetic model and kinetic parameters based on the autocatalytic and nth reaction equation were established and were applied to the processing of data by least-squares and Kissinger methods. The estimated cure of the model was in good agreement with that of the experiments. The results indicated that the curing reaction processing can be divided into two stages following different mechanics, with the autocatalytic reaction model transformation into the nth reaction model. The model is important for processing simulation and quality control of processing for high performance composites.
2004, 21(1): 84-89.
Abstract:
Functionally graded materials (FGMs) have been developed for the needs of the aeronautic and astronautic fields. Due to the reasons of technology, working conditions and some other factors, lots of cracks easily appear in FGMs. Therefore, it is very significant to study the crack problems of FGMs with arbitrarily oriented cracks. In this paper, the FGM with an arbitrarily oriented crack is considered. With the use of integration transform, the displacement form can be obtained. By using auxiliary functions and relative conditions, the present problem is transformed into solving a group of singular integral equations which can be solved numerically by Lobatto-Chebyshev method. Numerical results are obtained to illustrate the variations of the stress intensity factors (SIFs) with the parameters such as nonhomogeneity factor, crack direction and load conditions.
Functionally graded materials (FGMs) have been developed for the needs of the aeronautic and astronautic fields. Due to the reasons of technology, working conditions and some other factors, lots of cracks easily appear in FGMs. Therefore, it is very significant to study the crack problems of FGMs with arbitrarily oriented cracks. In this paper, the FGM with an arbitrarily oriented crack is considered. With the use of integration transform, the displacement form can be obtained. By using auxiliary functions and relative conditions, the present problem is transformed into solving a group of singular integral equations which can be solved numerically by Lobatto-Chebyshev method. Numerical results are obtained to illustrate the variations of the stress intensity factors (SIFs) with the parameters such as nonhomogeneity factor, crack direction and load conditions.
2004, 21(1): 90-94.
Abstract:
This paper presents the results of an experimental study conducted on the mechanical property of the two-step rectangle 3D braided composites. The tests include tensile in the axis, flexure and compression in the axis. Thus, the reliable mechanical property data are obtained. On the basis of the character of the microstructure, this paper relates the influence of microstructural variables such as the kinds and sizes of braider yarns, the linear density ratios of axial to braider yarn and the pitch lengths on the mechanical properties of these composites from a macroscopical view. It shows that the axial yarns dominate the tension and compression properties in the axial direction. The strength and modulus of tension and compression in the axial direction increase with the pitch length and size of braider increasing.
This paper presents the results of an experimental study conducted on the mechanical property of the two-step rectangle 3D braided composites. The tests include tensile in the axis, flexure and compression in the axis. Thus, the reliable mechanical property data are obtained. On the basis of the character of the microstructure, this paper relates the influence of microstructural variables such as the kinds and sizes of braider yarns, the linear density ratios of axial to braider yarn and the pitch lengths on the mechanical properties of these composites from a macroscopical view. It shows that the axial yarns dominate the tension and compression properties in the axial direction. The strength and modulus of tension and compression in the axial direction increase with the pitch length and size of braider increasing.
2004, 21(1): 95-99.
Abstract:
Using the principle of superposition, the transverse loading state of a laminated beam with a delamination is divided into symmetric and antisymmetric states. The problem of the delamination can be reduced to the analysis about the additional displacements and stresses which are caused by the additional shear loading. Then a simple mechanical model about the delamination is established. Finally, the analytical solutions of displacement and stress are established by the theory of engineering beam. Using the energy release rate method, one can get the stress intensity factor of the delamination.
Using the principle of superposition, the transverse loading state of a laminated beam with a delamination is divided into symmetric and antisymmetric states. The problem of the delamination can be reduced to the analysis about the additional displacements and stresses which are caused by the additional shear loading. Then a simple mechanical model about the delamination is established. Finally, the analytical solutions of displacement and stress are established by the theory of engineering beam. Using the energy release rate method, one can get the stress intensity factor of the delamination.
2004, 21(1): 100-108.
Abstract:
Using the principle of superposition, a laminate with a dissymmetric delamination under transverse loading is divided into symmetric and antisymmetric states, then the delamination problem comes down to analyze additional displacements and stresses under additional loading. According to it, a simple mechanical model can be established which only includes the delamination area. Then infinitesimal slices can be cut parallel to the boundary in the delamination area, the slices can be reduced to laminated beams with a delamination, and their displacements can be expressed by the analytical solutions of additional displacements of the beam. Based on the displacements of slices, one can get the additional displacement modes of the delamination area, which satisfy the boundary conditions. Finally a closed form solution of additional displacement is obtained by the principle of minimum potential energy, then the stress field and the energy release rate are analyzed.
Using the principle of superposition, a laminate with a dissymmetric delamination under transverse loading is divided into symmetric and antisymmetric states, then the delamination problem comes down to analyze additional displacements and stresses under additional loading. According to it, a simple mechanical model can be established which only includes the delamination area. Then infinitesimal slices can be cut parallel to the boundary in the delamination area, the slices can be reduced to laminated beams with a delamination, and their displacements can be expressed by the analytical solutions of additional displacements of the beam. Based on the displacements of slices, one can get the additional displacement modes of the delamination area, which satisfy the boundary conditions. Finally a closed form solution of additional displacement is obtained by the principle of minimum potential energy, then the stress field and the energy release rate are analyzed.
2004, 21(1): 109-113.
Abstract:
A dynamic meso-scale model for non-straight steel fiber is proposed on the work of Chanvillard G. The model is time-dependent and related to the impact loading through the interfacial shearing stress along the embedded part of the steel fiber. Thus, properly setting the thresholds, a dynamic model of the fiber's debonding and pullout process considering the evolution of meso-damage is eventually constructed. The rate sensitivity of the reinforcing effect of the steel fibers can be demonstrated in this model. The model prediction fits the experimental data of Chanvillard G for non-straight steel fiber under static condition well.
A dynamic meso-scale model for non-straight steel fiber is proposed on the work of Chanvillard G. The model is time-dependent and related to the impact loading through the interfacial shearing stress along the embedded part of the steel fiber. Thus, properly setting the thresholds, a dynamic model of the fiber's debonding and pullout process considering the evolution of meso-damage is eventually constructed. The rate sensitivity of the reinforcing effect of the steel fibers can be demonstrated in this model. The model prediction fits the experimental data of Chanvillard G for non-straight steel fiber under static condition well.
2004, 21(1): 114-118.
Abstract:
Epoxy resin-montmorillonite nanocomposite, which is cured by methyl tetra-hydrogen anhydride, is prepared, in which montmorillonite is modified by polyhydroxyl long-chain alkyl quaternary ammonium salts. The microstructure and properties are characterized by means of TEM, SEM, TGA and DMA. The results of TEM show that epoxy resin-organic montmorillonite nanocomposite, with nanometer scale layered montmorillonite, has been formed. Epoxy resin with 3 wt% organic montmorillonite is toughened and strengthened, the resistance to impact of composite is improved by 87.8 %, and the tensile strength of composites is enhanced by 20.9 %. Additionally, the nanometer scale layered montmorillonite in epoxy matrix ameliorates thermal stability and dynamic mechanics properties. With 5 wt% organic montmorillonite, the heat distortion temperature increases by 8.7℃, and the thermal decomposition temperature also increases by 14.7℃. And when the temperature is less than Tg, the storage modulus of composites is heightened by 42.86%; when the temperature is greater than Tg, the storage modulus of composites is heightened by 229.8%. And the Tg is also improved by 14.7℃.
Epoxy resin-montmorillonite nanocomposite, which is cured by methyl tetra-hydrogen anhydride, is prepared, in which montmorillonite is modified by polyhydroxyl long-chain alkyl quaternary ammonium salts. The microstructure and properties are characterized by means of TEM, SEM, TGA and DMA. The results of TEM show that epoxy resin-organic montmorillonite nanocomposite, with nanometer scale layered montmorillonite, has been formed. Epoxy resin with 3 wt% organic montmorillonite is toughened and strengthened, the resistance to impact of composite is improved by 87.8 %, and the tensile strength of composites is enhanced by 20.9 %. Additionally, the nanometer scale layered montmorillonite in epoxy matrix ameliorates thermal stability and dynamic mechanics properties. With 5 wt% organic montmorillonite, the heat distortion temperature increases by 8.7℃, and the thermal decomposition temperature also increases by 14.7℃. And when the temperature is less than Tg, the storage modulus of composites is heightened by 42.86%; when the temperature is greater than Tg, the storage modulus of composites is heightened by 229.8%. And the Tg is also improved by 14.7℃.
2004, 21(1): 119-123.
Abstract:
In this paper,the effect of the processing and composition on the mechanical properties of the PVC/elastomer/nano-CaCO3 ternary-phase composites was investigated in detail.Customarily, CPE or ACR as impact modifier and nano-CaCO3 was directly added to PVC. However, in this study, the master batch prepared by dispersing the nano-CaCO3 in CPE, as a novel modifier, was processed with PVC. Improved dispersion of nano-filler in the matrix (observed by SEM ) and good cooperation effect of nano-CaCO3 and CPE on the toughness were obtained during the processing, as the results showed. Improvement of mechanical properties of the blend system was preferred,when the proportion of CPE to nano-CaCO3 in the master batch is 1∶2.
In this paper,the effect of the processing and composition on the mechanical properties of the PVC/elastomer/nano-CaCO3 ternary-phase composites was investigated in detail.Customarily, CPE or ACR as impact modifier and nano-CaCO3 was directly added to PVC. However, in this study, the master batch prepared by dispersing the nano-CaCO3 in CPE, as a novel modifier, was processed with PVC. Improved dispersion of nano-filler in the matrix (observed by SEM ) and good cooperation effect of nano-CaCO3 and CPE on the toughness were obtained during the processing, as the results showed. Improvement of mechanical properties of the blend system was preferred,when the proportion of CPE to nano-CaCO3 in the master batch is 1∶2.
2004, 21(1): 124-128.
Abstract:
The steady and dynamic rheology behaviors of UHMWPE/Kaolin composites prepared by a polymerization-filling method were investigated with capillary and parallel plate rheometer. The composites showed an unusual rheological behavior.The material could be smoothly extruded through the capillary and the addition of Kaolin particles could decrease the apparent viscosity, dynamic viscosity, complex viscosity and the moduli of the melt. The relationship between rheological behaviors and the unique structure governed by polymerization-filling was further discussed.
The steady and dynamic rheology behaviors of UHMWPE/Kaolin composites prepared by a polymerization-filling method were investigated with capillary and parallel plate rheometer. The composites showed an unusual rheological behavior.The material could be smoothly extruded through the capillary and the addition of Kaolin particles could decrease the apparent viscosity, dynamic viscosity, complex viscosity and the moduli of the melt. The relationship between rheological behaviors and the unique structure governed by polymerization-filling was further discussed.
2004, 21(1): 129-133.
Abstract:
The sensing arm of a fiber optical Mach-Zehnder Interferometer is embedded into the middle of composite beams to detect the delamination in the beams. Good results are obtained showing the delaminations can be detected easily whether the beams are simply supported or continuously supported. By pressing the beam continuously using a hammer, the output curve can be obtained from the fiber optical interferometer. One can judge if there exists delamination, and where the delamination is from the curve exactly.
The sensing arm of a fiber optical Mach-Zehnder Interferometer is embedded into the middle of composite beams to detect the delamination in the beams. Good results are obtained showing the delaminations can be detected easily whether the beams are simply supported or continuously supported. By pressing the beam continuously using a hammer, the output curve can be obtained from the fiber optical interferometer. One can judge if there exists delamination, and where the delamination is from the curve exactly.
2004, 21(1): 134-140.
Abstract:
An interphase plays a key role in composites performance, its mechanical properties vary spatially due to diffusion and chemical reaction, but most actual models assume uniform material property in the interphase region. It is assumed that the material property of an interphase follows a power law function. The coated fiber and particle with such interphase in an infinite matrix under hydrostatic and pure shear loading have been analyzed respectively; the local stresses and the average stresses in the fiber or particle and the interphase are obtained analytically. With the help of the mean field concept in micromechanics, the effective moduli of the composite with such coated fibers or particles are derived as a function of the microstructure. The computed results show that the presence of an interphase can have an important influence on the effective property and local stress distribution of the composites.
An interphase plays a key role in composites performance, its mechanical properties vary spatially due to diffusion and chemical reaction, but most actual models assume uniform material property in the interphase region. It is assumed that the material property of an interphase follows a power law function. The coated fiber and particle with such interphase in an infinite matrix under hydrostatic and pure shear loading have been analyzed respectively; the local stresses and the average stresses in the fiber or particle and the interphase are obtained analytically. With the help of the mean field concept in micromechanics, the effective moduli of the composite with such coated fibers or particles are derived as a function of the microstructure. The computed results show that the presence of an interphase can have an important influence on the effective property and local stress distribution of the composites.
2004, 21(1): 141-145.
Abstract:
Al2O3f+Cf/ZL109 short fibers reinforced hybrid composites were fabricated by squeeze casting.The effects of alumina and carbon fibres volume fraction on the drilling machinability of the hybrid composites were researched.The influences of quantity used in cutting and orientation of fiber on drilling force,tool wear and drilling precision were investigated,and the mechanism was analyzed. The conclusion can be drawn that according to the drill wear,the machinability of Al2O3f+Cf/ZL109 is inferior to that of ZL109 alloy.
Al2O3f+Cf/ZL109 short fibers reinforced hybrid composites were fabricated by squeeze casting.The effects of alumina and carbon fibres volume fraction on the drilling machinability of the hybrid composites were researched.The influences of quantity used in cutting and orientation of fiber on drilling force,tool wear and drilling precision were investigated,and the mechanism was analyzed. The conclusion can be drawn that according to the drill wear,the machinability of Al2O3f+Cf/ZL109 is inferior to that of ZL109 alloy.
