2003 Vol. 20, No. 1
2003, 20(1): 1-6.
Abstract:
The effect of hard phases grain size on Ti(C,N) and WC based cermets fracture toughness was studied based on Palmqvist indentation toughness measurements. It was revealed that, when the composition and sintering process were the same, the fracture toughness of Ti(C,N) based cermet increased with the decrease of hard phase grain size, but the fracture toughness of WC based cermet increased with the increase of WC grain size. It may be explained by the differences existing between Ti(C,N) and WC crystal structures: There are eighteen independent slip systems in the two possible ｛110｝<11 0> and ｛111｝<11 0> slip families of face centered cubic Ti(C,N) crystal, but there are only four independent slip systems in the ｛101 0｝<111 3> slip family of close-packed hexagonal WC crystal. The propagating crack can easily seek a favorably oriented cleavage plane in Ti(C,N) grains when it crosses a big Ti(C,N) grain boundary, so it can easily propagate through contiguous Ti(C,N) grains and without markedly directional change. However, a markedly directional change occurred when a propagating crack passes through a WC crystal owing to strong anisotropy slip. With the increase of WC particle size, its crack deflecting and branching effect increases, which elevates toughness by increasing the area of fracture surface.
The effect of hard phases grain size on Ti(C,N) and WC based cermets fracture toughness was studied based on Palmqvist indentation toughness measurements. It was revealed that, when the composition and sintering process were the same, the fracture toughness of Ti(C,N) based cermet increased with the decrease of hard phase grain size, but the fracture toughness of WC based cermet increased with the increase of WC grain size. It may be explained by the differences existing between Ti(C,N) and WC crystal structures: There are eighteen independent slip systems in the two possible ｛110｝<11 0> and ｛111｝<11 0> slip families of face centered cubic Ti(C,N) crystal, but there are only four independent slip systems in the ｛101 0｝<111 3> slip family of close-packed hexagonal WC crystal. The propagating crack can easily seek a favorably oriented cleavage plane in Ti(C,N) grains when it crosses a big Ti(C,N) grain boundary, so it can easily propagate through contiguous Ti(C,N) grains and without markedly directional change. However, a markedly directional change occurred when a propagating crack passes through a WC crystal owing to strong anisotropy slip. With the increase of WC particle size, its crack deflecting and branching effect increases, which elevates toughness by increasing the area of fracture surface.
2003, 20(1): 7-11.
Abstract:
Because high damping characteristics of materials are useful in the passive attenuation of noise and vibration in structures, and for the purpose of getting good mechanical properties and good damping properties simultaneously, a woodceramics/MB15 (WCMs/MB15 hereafter) composite was fabricated using the high-pressure infiltration system. Microstructural analysis as well as measurement of mechanical properties and damping behavior of WCMs/MB15 composite was made. Experimental results show that the MB15 has infiltrated most of the pores and the WCMs/MB15 composite has an obvious interpenetrating network structure. Its strengths and elastic moduli are much higher than those of unreinforced woodceramics. Damping value of the WCMs/MB15 composite improves based on that of woodceramics and increase with the testing temperature. The intrinsic damping of woodceramics and dislocation damping in the matrix are supposed to be the main contributor of the damping of WCMs/MB15 composite at room temperature while interface damping is likely to be responsible for the majority at elevated temperatures.
Because high damping characteristics of materials are useful in the passive attenuation of noise and vibration in structures, and for the purpose of getting good mechanical properties and good damping properties simultaneously, a woodceramics/MB15 (WCMs/MB15 hereafter) composite was fabricated using the high-pressure infiltration system. Microstructural analysis as well as measurement of mechanical properties and damping behavior of WCMs/MB15 composite was made. Experimental results show that the MB15 has infiltrated most of the pores and the WCMs/MB15 composite has an obvious interpenetrating network structure. Its strengths and elastic moduli are much higher than those of unreinforced woodceramics. Damping value of the WCMs/MB15 composite improves based on that of woodceramics and increase with the testing temperature. The intrinsic damping of woodceramics and dislocation damping in the matrix are supposed to be the main contributor of the damping of WCMs/MB15 composite at room temperature while interface damping is likely to be responsible for the majority at elevated temperatures.
2003, 20(1): 12-15.
Abstract:
The (AlN,TiN)-Al2O3 composites were fabricated by reaction sintering (Al,Ti)-Al2O3 powder mixtures with nitrogen at 750~800℃ and sintering 1420~1550℃ in nitrogen. The effect of powder contents and sintering process on mechanical properties, phases composites and microstructures of composites was researched by some methods such as XRD and SEM. The experimental results show that the formation of AlN and TiN aids to compact composites and increases their mechanical properties. Reaction sintering 20wt%(Al,Ti)-Al2O3 powder with nitrogen in 1520℃, 30MPa, holding 30min, could receive (AlN,TiN)-Al2O3 composites, which possess hardness HRA up to 94.1, bending strength 687MPa, and fracture toughness 6.5MPa·m-1/2.
The (AlN,TiN)-Al2O3 composites were fabricated by reaction sintering (Al,Ti)-Al2O3 powder mixtures with nitrogen at 750~800℃ and sintering 1420~1550℃ in nitrogen. The effect of powder contents and sintering process on mechanical properties, phases composites and microstructures of composites was researched by some methods such as XRD and SEM. The experimental results show that the formation of AlN and TiN aids to compact composites and increases their mechanical properties. Reaction sintering 20wt%(Al,Ti)-Al2O3 powder with nitrogen in 1520℃, 30MPa, holding 30min, could receive (AlN,TiN)-Al2O3 composites, which possess hardness HRA up to 94.1, bending strength 687MPa, and fracture toughness 6.5MPa·m-1/2.
2003, 20(1): 16-21.
Abstract:
The mechanism of chemical reaction and microstructure formation process of B2O3-TiO2-Mg-C system were investigated in this paper. The results showed that TiB2-TiC ceramic powder could be obtained by SHS from B2O3-TiO2-Mg-C system. The results of analysis of different thermal analysis (DTA) and X-ray diffraction (XRD) showed the following thermal processes of B2O3-TiO2-Mg-C system: B2O3 was reduced to B and TiO2 was reduced to Ti. Metal Mg was melted at 650℃. At 680 ℃ the reaction between B and Ti nearly finished and the formation of TiC from the reaction of Ti and C began. TiO2 was reduced to element Ti step by step through the following way: TiO2→TiO→Ti. TiB2-TiC composite powder with particle size of 45 percent under 1μm and 87 percent under 3μm was obtained after MgO, the unwanted phase, was removed by leaching in hydrochloric acid. Results of SEM micrographs of TiB2-TiC ceramic multiphase powder showed that the particle size is much smaller than that of single phase TiB2 or TiC produced by the same methods. The mole ratio of Ti and C in TiC was 1∶0.7483.
The mechanism of chemical reaction and microstructure formation process of B2O3-TiO2-Mg-C system were investigated in this paper. The results showed that TiB2-TiC ceramic powder could be obtained by SHS from B2O3-TiO2-Mg-C system. The results of analysis of different thermal analysis (DTA) and X-ray diffraction (XRD) showed the following thermal processes of B2O3-TiO2-Mg-C system: B2O3 was reduced to B and TiO2 was reduced to Ti. Metal Mg was melted at 650℃. At 680 ℃ the reaction between B and Ti nearly finished and the formation of TiC from the reaction of Ti and C began. TiO2 was reduced to element Ti step by step through the following way: TiO2→TiO→Ti. TiB2-TiC composite powder with particle size of 45 percent under 1μm and 87 percent under 3μm was obtained after MgO, the unwanted phase, was removed by leaching in hydrochloric acid. Results of SEM micrographs of TiB2-TiC ceramic multiphase powder showed that the particle size is much smaller than that of single phase TiB2 or TiC produced by the same methods. The mole ratio of Ti and C in TiC was 1∶0.7483.
2003, 20(1): 22-26.
Abstract:
By hot-pressing method, TiB2-TiC multiphase ceramics were fabricated from TiB2-TiC composites powders under the following sintering conditions: sintering temperature: 1700℃ and 1800℃, pressure: 30MPa, sintering time: 60min. The relative density, the hardness and fracture toughness of TiB2-TiC multiphase ceramic at room temperature were 99.8%, 93.2HRA and 5.53MPa·m1/2 respectively. The residual porosities and dislocation in sintered ceramics went against the performance. The microstructure of TiB2-TiC multiphase ceramics from composite powders had smaller and more symmetrical grains than the TiB2-TiC ceramics sintered from the mixtures of TiB2 and TiC powders. The elements of B, C and Ti at the interface of TiB2 and TiC were distributed gradually. There were no impurities at the interface and the bonds between phases were strong, which probably has relation to the higher properties of TiB 2-TiC multiphase ceramics. The growth of TiB2 in different crystal directions was different in TiB2-TiC multiphase ceramics.
By hot-pressing method, TiB2-TiC multiphase ceramics were fabricated from TiB2-TiC composites powders under the following sintering conditions: sintering temperature: 1700℃ and 1800℃, pressure: 30MPa, sintering time: 60min. The relative density, the hardness and fracture toughness of TiB2-TiC multiphase ceramic at room temperature were 99.8%, 93.2HRA and 5.53MPa·m1/2 respectively. The residual porosities and dislocation in sintered ceramics went against the performance. The microstructure of TiB2-TiC multiphase ceramics from composite powders had smaller and more symmetrical grains than the TiB2-TiC ceramics sintered from the mixtures of TiB2 and TiC powders. The elements of B, C and Ti at the interface of TiB2 and TiC were distributed gradually. There were no impurities at the interface and the bonds between phases were strong, which probably has relation to the higher properties of TiB 2-TiC multiphase ceramics. The growth of TiB2 in different crystal directions was different in TiB2-TiC multiphase ceramics.
2003, 20(1): 27-32.
Abstract:
Application of active filler aluminium (Al) in preparation of Jilin carbon fiber (JC) and M40JB fiber reinforced ceramic matrix composites (FRCMCs) by polymer-infiltration-pyrolysis (PIP) was investigated, respectively. The results showed that, after 7 cycles of polymer infiltration-pyrolysis, the flexural strength of the as-fabricated composites reinforced by JC was higher than that of those reinforced by M40JB when active filler was not added. Therefore, JC was more suitable for the reinforcement of FRCMCs than M40JB by PIP process. The flexural strength of the composites with active filler Al decreased drastically for the harmful interphase produced by the reaction between Al and carbon fiber, which was accordingly degenerated badly. The image analysis showed that the reaction layer between M40JB and Al was about 0.94μm. Suitable surface treatment of the carbon fiber such as coating was necessary to prevent the fiber from reacting.
Application of active filler aluminium (Al) in preparation of Jilin carbon fiber (JC) and M40JB fiber reinforced ceramic matrix composites (FRCMCs) by polymer-infiltration-pyrolysis (PIP) was investigated, respectively. The results showed that, after 7 cycles of polymer infiltration-pyrolysis, the flexural strength of the as-fabricated composites reinforced by JC was higher than that of those reinforced by M40JB when active filler was not added. Therefore, JC was more suitable for the reinforcement of FRCMCs than M40JB by PIP process. The flexural strength of the composites with active filler Al decreased drastically for the harmful interphase produced by the reaction between Al and carbon fiber, which was accordingly degenerated badly. The image analysis showed that the reaction layer between M40JB and Al was about 0.94μm. Suitable surface treatment of the carbon fiber such as coating was necessary to prevent the fiber from reacting.
2003, 20(1): 33-37.
Abstract:
The microstructure and mechanical properties of nano TiN modified TiC based cermets(nano modified cermets) have been discussed. Results reveal that the microstructure still consists of a ceramic phase and a metal phase, and the coarse ceramic phase in the microstructure exhibits a core/shell structure, i.e. the coarse ceramic phase generally consists of a Ti(C,N) core surrounded by a shell ("SS" phase). TEM observations show that nano TiN grains are generally distributed at the interfaces of two phases or three phases. The microstructure of nano modified cermets becomes finer with increasing the amount of nano TiN addition, and the fining effect can be related to the distribution of nano TiN at the interfaces of TiC/TiC and the inhibition of the growth of TiC grains. Bending tests show that the bending strength will reach a maximum value when the amount of nano TiN reaches 8wt%. Fracture photograph shows that intergranular fracture is the main failure mode.
The microstructure and mechanical properties of nano TiN modified TiC based cermets(nano modified cermets) have been discussed. Results reveal that the microstructure still consists of a ceramic phase and a metal phase, and the coarse ceramic phase in the microstructure exhibits a core/shell structure, i.e. the coarse ceramic phase generally consists of a Ti(C,N) core surrounded by a shell ("SS" phase). TEM observations show that nano TiN grains are generally distributed at the interfaces of two phases or three phases. The microstructure of nano modified cermets becomes finer with increasing the amount of nano TiN addition, and the fining effect can be related to the distribution of nano TiN at the interfaces of TiC/TiC and the inhibition of the growth of TiC grains. Bending tests show that the bending strength will reach a maximum value when the amount of nano TiN reaches 8wt%. Fracture photograph shows that intergranular fracture is the main failure mode.
2003, 20(1): 38-44.
Abstract:
The transient response of delaminated composite laminate under low-velocity is discussed in the present paper. At first, the Mindlin plate finite element is used to describe the movement and deformation of composite laminates with a circular delamination, in which large deformation is considered. Secondly, an improved Hertzian indentation law is used to calculate the contact force between the laminates and the rigid ball. To deal with the contact problem between delamination, we use an improved Lagrange multiplier method which was posed previously by the author. To explore delamination growth mechanism, we present a numerical method based on the Mindlin plate model to calculate the strain energy release rate at the front of a delamination. Finally, the influence of initial impact velocity, delamination area and delamination location is discussed. And the results of numerical examples provide a great deal of information for people to understand the delamination growth mechanism and its influence on the impact response of delaminated composite laminates.
The transient response of delaminated composite laminate under low-velocity is discussed in the present paper. At first, the Mindlin plate finite element is used to describe the movement and deformation of composite laminates with a circular delamination, in which large deformation is considered. Secondly, an improved Hertzian indentation law is used to calculate the contact force between the laminates and the rigid ball. To deal with the contact problem between delamination, we use an improved Lagrange multiplier method which was posed previously by the author. To explore delamination growth mechanism, we present a numerical method based on the Mindlin plate model to calculate the strain energy release rate at the front of a delamination. Finally, the influence of initial impact velocity, delamination area and delamination location is discussed. And the results of numerical examples provide a great deal of information for people to understand the delamination growth mechanism and its influence on the impact response of delaminated composite laminates.
2003, 20(1): 45-50.
Abstract:
A piece-wise Ritz direct method for the analysis of laminated shell structure is developed in order to obtain a precise and effective solution to laminated shell problems. The semi-analytic solution is constructed by the Ritz procedure in two distinct steps. Firstly, the laminated shell structure under consideration is divided into patches and represented by parametric surfaces which are connected on common boundaries of C° continuity. The trial functions of the Ritz procedure with parametric surface characteristics are constructed for the total energy functional and governing equations thereafter. Numerical examples are given and it is shown through comparisons that the present method is fairly accurate and adequate.
A piece-wise Ritz direct method for the analysis of laminated shell structure is developed in order to obtain a precise and effective solution to laminated shell problems. The semi-analytic solution is constructed by the Ritz procedure in two distinct steps. Firstly, the laminated shell structure under consideration is divided into patches and represented by parametric surfaces which are connected on common boundaries of C° continuity. The trial functions of the Ritz procedure with parametric surface characteristics are constructed for the total energy functional and governing equations thereafter. Numerical examples are given and it is shown through comparisons that the present method is fairly accurate and adequate.
2003, 20(1): 51-54.
Abstract:
A thermoelastic model of functionally gradient material plates is developed. In order to deal conveniently with the through-thickness variation of its material properties, a functionally gradient material plate is divided to a number of layers through its thickness like a composite laminate,each layer being treated as an isotropic one. When the number of layers involved is big enough, the material properties of each layer may be assumed as constants. A temperature zigzag hypothesis through the thickness and a displacement field hypothesis including transverse shear deformation are introduced to ensure the accuracy of the present model. The continuities of temperature, displacements and stresses between layers are ensured exactly. A transverse deformation function developed for the analysis of laminated composites is adopted in the present model to improve its accuracy. The present model is proved to be highly accurate and the existing analytical methods are examined in the numerical examples. The choice of the number of layers is also discussed.
A thermoelastic model of functionally gradient material plates is developed. In order to deal conveniently with the through-thickness variation of its material properties, a functionally gradient material plate is divided to a number of layers through its thickness like a composite laminate,each layer being treated as an isotropic one. When the number of layers involved is big enough, the material properties of each layer may be assumed as constants. A temperature zigzag hypothesis through the thickness and a displacement field hypothesis including transverse shear deformation are introduced to ensure the accuracy of the present model. The continuities of temperature, displacements and stresses between layers are ensured exactly. A transverse deformation function developed for the analysis of laminated composites is adopted in the present model to improve its accuracy. The present model is proved to be highly accurate and the existing analytical methods are examined in the numerical examples. The choice of the number of layers is also discussed.
2003, 20(1): 55-59.
Abstract:
The effect of diffusion controlled interfacial sliding on the transverse shear deformation of fibrous composites is studied. The matrix and fiber are assumed elastic, and the sliding rate is proportional to the shear stress on the interface. As an auxiliary problem, the special case of a single fiber embedded into an infinite matrix is considered firstly, and the time dependent stress in the composite at any time is given. The overall response of the composite is then analysed by Mori-Tanaka method. Numerical results reveal that the transverse shear modulus of the composite decreases significantly with the occurrence of interfacial sliding.
The effect of diffusion controlled interfacial sliding on the transverse shear deformation of fibrous composites is studied. The matrix and fiber are assumed elastic, and the sliding rate is proportional to the shear stress on the interface. As an auxiliary problem, the special case of a single fiber embedded into an infinite matrix is considered firstly, and the time dependent stress in the composite at any time is given. The overall response of the composite is then analysed by Mori-Tanaka method. Numerical results reveal that the transverse shear modulus of the composite decreases significantly with the occurrence of interfacial sliding.
2003, 20(1): 60-66.
Abstract:
This paper takes the study of the numerical model and the corresponding algorithm for multi-scale elastic-plastic analysis of composite materials. Main work is focused on the problem of unit cell analysis. A numerical technique with approximation to establish the eigen-strain matrices and the corresponding consistent algorithm are proposed to be easily implemented in the computer program. A numerical example for analysis of a composite material composed of two different materials is computed. Numerical results demonstrate the validity and efficiency of the theoretical work presented in this paper. Finally, some further works are discussed.
This paper takes the study of the numerical model and the corresponding algorithm for multi-scale elastic-plastic analysis of composite materials. Main work is focused on the problem of unit cell analysis. A numerical technique with approximation to establish the eigen-strain matrices and the corresponding consistent algorithm are proposed to be easily implemented in the computer program. A numerical example for analysis of a composite material composed of two different materials is computed. Numerical results demonstrate the validity and efficiency of the theoretical work presented in this paper. Finally, some further works are discussed.
2003, 20(1): 67-73.
Abstract:
Tire curing heat transfer is treated as an axisymmetric heat transfer problem. By using Galerkin's method, the finite element formulation of the axisymmetric heat transfer problem is carried out for composite materials from the heat transfer differential equations expressed by heat fluid density. The rubber curing dynamics model and real tire curing temperature history are further combined with the finite element formulation to develop a finite element analysis software for numerical simulation of the tire curing process. Finite element analysis of a tire curing process shows that numerical simulation results given by the software are correct in tendency.
Tire curing heat transfer is treated as an axisymmetric heat transfer problem. By using Galerkin's method, the finite element formulation of the axisymmetric heat transfer problem is carried out for composite materials from the heat transfer differential equations expressed by heat fluid density. The rubber curing dynamics model and real tire curing temperature history are further combined with the finite element formulation to develop a finite element analysis software for numerical simulation of the tire curing process. Finite element analysis of a tire curing process shows that numerical simulation results given by the software are correct in tendency.
2003, 20(1): 74-78.
Abstract:
Bromize epoxy (BEP), which is always used as the resin matrix of copper clad laminate (CCL), has faced the challenge to prepare the high performance CCL for the deficiencies such as not-enough thermal resistance, poorer dielectric properties at higher frequencies, inferior size stability at higher temperatures and lower toughness and so on. The authors prepared high-performance CCL by introducing poly (2,6-dimethyl-1, 4-phenylene ether)(PPO or PPE) as the modification resin to solve the problem mentioned above. For solutions of PPO and BEP, the upper critical solution temperature (UCST) cloud point curves intersect the glass transition-composition lines at a PPO content of 60 wt%~70 wt%. Cure behavior and miscibility have been studied in blends of PPO with BEP and dicyandiamide (DICY) hardener, EMI-2, 4imidazole as accelerator by gel tests and FTIR. The reasonable process of half-curing are settled down by considering the influence of the process on the properties of the half-cured sheet and CCL. The results show that PPO/BEP form a uniform system or glue with some certain solvents; the properties of the CCL prepared using the PPO/BEP are much better than those of the conventional CCL (FR-4), especially the dielectric properties, thermal stability, flexural strength and water resistance.
Bromize epoxy (BEP), which is always used as the resin matrix of copper clad laminate (CCL), has faced the challenge to prepare the high performance CCL for the deficiencies such as not-enough thermal resistance, poorer dielectric properties at higher frequencies, inferior size stability at higher temperatures and lower toughness and so on. The authors prepared high-performance CCL by introducing poly (2,6-dimethyl-1, 4-phenylene ether)(PPO or PPE) as the modification resin to solve the problem mentioned above. For solutions of PPO and BEP, the upper critical solution temperature (UCST) cloud point curves intersect the glass transition-composition lines at a PPO content of 60 wt%~70 wt%. Cure behavior and miscibility have been studied in blends of PPO with BEP and dicyandiamide (DICY) hardener, EMI-2, 4imidazole as accelerator by gel tests and FTIR. The reasonable process of half-curing are settled down by considering the influence of the process on the properties of the half-cured sheet and CCL. The results show that PPO/BEP form a uniform system or glue with some certain solvents; the properties of the CCL prepared using the PPO/BEP are much better than those of the conventional CCL (FR-4), especially the dielectric properties, thermal stability, flexural strength and water resistance.
2003, 20(1): 79-84.
Abstract:
Surface of nano-SiO2 particles was covered with PMMA by emulsion polymerization to prevent their reunion. The structures of emulsion polymeric products of alkyl-nano-SiO2/MMA were characterized by TEM and FTIR. The results indicate that the particles of emulsion polymeric products are approximate ball in shape and that the particle consists of centered core(SiO2) and shell (PMMA) and that chemical bonds exist between the core and shell of alkylaed-nano-silica/PMMA. The toughness, process flowability and heat resistance of PC were notably raised by core-shell particles of alkylated-nano-silica/PMMA with the cooperation of a third component.Its toughening mechanism was studied with the newest theory of multi-layer crack extension.
Surface of nano-SiO2 particles was covered with PMMA by emulsion polymerization to prevent their reunion. The structures of emulsion polymeric products of alkyl-nano-SiO2/MMA were characterized by TEM and FTIR. The results indicate that the particles of emulsion polymeric products are approximate ball in shape and that the particle consists of centered core(SiO2) and shell (PMMA) and that chemical bonds exist between the core and shell of alkylaed-nano-silica/PMMA. The toughness, process flowability and heat resistance of PC were notably raised by core-shell particles of alkylated-nano-silica/PMMA with the cooperation of a third component.Its toughening mechanism was studied with the newest theory of multi-layer crack extension.
2003, 20(1): 85-90.
Abstract:
A physics model possessed of medium interlayer composite shielding structure was proposed. The contrast experiments of monolayer shielding structure and composite interlayer shielding structure were designed and carried out. The ΔSE, the abbreviation for electromagnetic shielding effectiveness increments, of composite interlayer shielding structure was measured, while it was confirmed by Ватолцн multilayer electromagnetic shielding theory formulas. The electromagnetic shielding effectiveness of the composite interlayer shielding structure materials is obviously superior to that of the monolayer shielding structure materials. The preparation of the supple electromagnetic shielding materials possessed of composite interlayer shielding structure was performed by the method of electrochemical modification. Terylene non-woven and polytetrafluoroethylene, two kinds of synthetic fibres, were selected as research objects. The results show that the composite interlayer shielding structure-modified materials on synthetic fibre can be prepared by means of selecting objects and optimizing technics of electrochemical modification, which includes selecting different metallic plating layers, adjusting the impulse electroplate parameters, plating time, temperature and pH. Within the incident frequency range from 1MHz to 1000 MHz, this kind of modified synthetic fibre can meet different demands, and the maximum SE is up to 98dB. Not only is the composite interlayer shielding structure obtained, but also synthetic fibre materials are endowed with new electromagnetic characteristics, by way of the process of metallic modification.
A physics model possessed of medium interlayer composite shielding structure was proposed. The contrast experiments of monolayer shielding structure and composite interlayer shielding structure were designed and carried out. The ΔSE, the abbreviation for electromagnetic shielding effectiveness increments, of composite interlayer shielding structure was measured, while it was confirmed by Ватолцн multilayer electromagnetic shielding theory formulas. The electromagnetic shielding effectiveness of the composite interlayer shielding structure materials is obviously superior to that of the monolayer shielding structure materials. The preparation of the supple electromagnetic shielding materials possessed of composite interlayer shielding structure was performed by the method of electrochemical modification. Terylene non-woven and polytetrafluoroethylene, two kinds of synthetic fibres, were selected as research objects. The results show that the composite interlayer shielding structure-modified materials on synthetic fibre can be prepared by means of selecting objects and optimizing technics of electrochemical modification, which includes selecting different metallic plating layers, adjusting the impulse electroplate parameters, plating time, temperature and pH. Within the incident frequency range from 1MHz to 1000 MHz, this kind of modified synthetic fibre can meet different demands, and the maximum SE is up to 98dB. Not only is the composite interlayer shielding structure obtained, but also synthetic fibre materials are endowed with new electromagnetic characteristics, by way of the process of metallic modification.
2003, 20(1): 91-95.
Abstract:
The elongation, compression and shearing characteristics of ER fluids under external electric fields are investigated. The compressive strength of ER fluids is found to be about one order higher than shear stress, and is 2~3 times of tensile strength. The compressive modulus is proportional to the square of electric field. The relationship between tensile yield stress and shear yield stress verified the credibility of the calculation model employing a yield angle shaped between particles. From the tested strength, the yield angle is found to be between 15°~18.5°, according with other reports well and verifying the validity of the calculation through particle shift in traditional theoretical analysis.
The elongation, compression and shearing characteristics of ER fluids under external electric fields are investigated. The compressive strength of ER fluids is found to be about one order higher than shear stress, and is 2~3 times of tensile strength. The compressive modulus is proportional to the square of electric field. The relationship between tensile yield stress and shear yield stress verified the credibility of the calculation model employing a yield angle shaped between particles. From the tested strength, the yield angle is found to be between 15°~18.5°, according with other reports well and verifying the validity of the calculation through particle shift in traditional theoretical analysis.
2003, 20(1): 96-99.
Abstract:
In order to control the growth speed and volume of the composite in the DIMOX, the method of added metal or alloy is adopted with the help of pressure head, with the result that the composition of the remanent aluminum alloy metal can be adjusted and continuously contacted with the growing Al2O3/Al composite material layer obtained by directed metal oxidation growth. The effect of the additional alloy composition on the oxidation growth of Al-3Mg-10Si alloy was studied. The results show that the additional pure aluminum or aluminum alloy with low Mg and Si content can reduce Mg content of aluminum alloy melt, shorten the time of reaching Al2O3-(Al, Mg)phase zone of the alloy melt of growth forward position, promote mass transmission process, accelerate material growth, and be favorable to obtain more larger volume composite material.
In order to control the growth speed and volume of the composite in the DIMOX, the method of added metal or alloy is adopted with the help of pressure head, with the result that the composition of the remanent aluminum alloy metal can be adjusted and continuously contacted with the growing Al2O3/Al composite material layer obtained by directed metal oxidation growth. The effect of the additional alloy composition on the oxidation growth of Al-3Mg-10Si alloy was studied. The results show that the additional pure aluminum or aluminum alloy with low Mg and Si content can reduce Mg content of aluminum alloy melt, shorten the time of reaching Al2O3-(Al, Mg)phase zone of the alloy melt of growth forward position, promote mass transmission process, accelerate material growth, and be favorable to obtain more larger volume composite material.
2003, 20(1): 100-105.
Abstract:
Short mullite fiber reinforced Al-4.5Cu composite and its monolithic alloy were produced by squeeze casting. The effect of the retained deformation made afterice-water quench with 0%,12.5%,25% or 34.4% and/or that of the fibers fabricated well with the matrix on the age-precipitation behaviour of the testing materials have been investigated by means of hardness measurement (HB),differential scanning calorimetry (DSC) and transmission electron microscope (TEM),respectively. The results indicate that the retained deformation considerably accelerates the ageing response of Al-4.5Cu alloy and the effect of precipitation acceleration is further promoted with increasing the deformation degree. Short mullite fibers also accelerate the ageing response of Al-4.5Cu alloy. Moreover,the age-precipitation progress of the testing composite is further accelerated when there exist both of the fiber and the deformation. The GP zone formation is, however,suppressed due to the introduction of retained deformation and/or short mullite fibers.
Short mullite fiber reinforced Al-4.5Cu composite and its monolithic alloy were produced by squeeze casting. The effect of the retained deformation made afterice-water quench with 0%,12.5%,25% or 34.4% and/or that of the fibers fabricated well with the matrix on the age-precipitation behaviour of the testing materials have been investigated by means of hardness measurement (HB),differential scanning calorimetry (DSC) and transmission electron microscope (TEM),respectively. The results indicate that the retained deformation considerably accelerates the ageing response of Al-4.5Cu alloy and the effect of precipitation acceleration is further promoted with increasing the deformation degree. Short mullite fibers also accelerate the ageing response of Al-4.5Cu alloy. Moreover,the age-precipitation progress of the testing composite is further accelerated when there exist both of the fiber and the deformation. The GP zone formation is, however,suppressed due to the introduction of retained deformation and/or short mullite fibers.
2003, 20(1): 106-110.
Abstract:
The S-N curve of strongly-bonded (Al2O3)f/Al composite wire was determined under tension-tension loading. To understand the fatigue damage mode of the composite, interrupted tests were carried out at different stresses. The fatigue fractograph and microstructures of samples were examined using SEM. The endurance limit of the composite was about 750MPa, which is much higher than about 600 MPa of the SCS-6 fiber reinforced Ti matrix composites. The composite possesses fatigue damage modes of both Ti and resin matrix composites. At high stresses, the initiation and growth of a single crack result in the failure of the composite, while at low stresses the fatigue damage mode includes fiber splitting and transverse propagation of numerous matrix cracks at beginning and single crack propagation at the final stage. The fiber splitting is a controlling mechanism of the composite and the higher endurance limit of the composite can be attributed to it.
The S-N curve of strongly-bonded (Al2O3)f/Al composite wire was determined under tension-tension loading. To understand the fatigue damage mode of the composite, interrupted tests were carried out at different stresses. The fatigue fractograph and microstructures of samples were examined using SEM. The endurance limit of the composite was about 750MPa, which is much higher than about 600 MPa of the SCS-6 fiber reinforced Ti matrix composites. The composite possesses fatigue damage modes of both Ti and resin matrix composites. At high stresses, the initiation and growth of a single crack result in the failure of the composite, while at low stresses the fatigue damage mode includes fiber splitting and transverse propagation of numerous matrix cracks at beginning and single crack propagation at the final stage. The fiber splitting is a controlling mechanism of the composite and the higher endurance limit of the composite can be attributed to it.
2003, 20(1): 111-115.
Abstract:
Temperature field and stress field in (TiB2+Fe)/Fe layered materials fabricated by self-propagating high-temperature synthesis plus quick pressing (SHS/QP) were analyzed. Finite element analysis shows that the temperature of Fe substrate at the interface increases and liquid Fe exists longer with the increase of the thickness of SHS layer. The peculiar point of the axial stress and shear stress is located at the peripheral area of the bonding boundary of (TiB2+Fe)/Fe two-layered sample and this peculiar point would be considered as the major reason for the exfoliation between the bonding boundaries.
Temperature field and stress field in (TiB2+Fe)/Fe layered materials fabricated by self-propagating high-temperature synthesis plus quick pressing (SHS/QP) were analyzed. Finite element analysis shows that the temperature of Fe substrate at the interface increases and liquid Fe exists longer with the increase of the thickness of SHS layer. The peculiar point of the axial stress and shear stress is located at the peripheral area of the bonding boundary of (TiB2+Fe)/Fe two-layered sample and this peculiar point would be considered as the major reason for the exfoliation between the bonding boundaries.
2003, 20(1): 116-120.
Abstract:
(TiB2+Fe)/Fe layered materials were fabricated by SHS/QP process. SEM analysis showed TiB2+Fe cermet layer in the layered material was fully dense. Interfacial bonding between TiB2+Fe cermet and Fe substrate was analyzed by EPMA, which showed the interfacial bonding of two-layered product was obtained by the dissolution and the diffusion of TiB2 in the Fe substrate and joining of Fe binder with Fe substrate. The fracture of joints took place in the TiB2+Fe cermet layer rather than at the interface.
(TiB2+Fe)/Fe layered materials were fabricated by SHS/QP process. SEM analysis showed TiB2+Fe cermet layer in the layered material was fully dense. Interfacial bonding between TiB2+Fe cermet and Fe substrate was analyzed by EPMA, which showed the interfacial bonding of two-layered product was obtained by the dissolution and the diffusion of TiB2 in the Fe substrate and joining of Fe binder with Fe substrate. The fracture of joints took place in the TiB2+Fe cermet layer rather than at the interface.
2003, 20(1): 121-124.
Abstract:
The post-buckling behavior of composite laminates subjected to thermal loads and mechanical loads at the same time is studied using geometrically nonlinear 3-D finite element analysis. The major feather of this method is that every 3-D element contains several layers of different materials and plied orientations. The gap element is used to prevent the overlap of the delamination. The strain energy release rate is studied along the delamination front. The results show that the temperature affects the delamination damage significantly.
The post-buckling behavior of composite laminates subjected to thermal loads and mechanical loads at the same time is studied using geometrically nonlinear 3-D finite element analysis. The major feather of this method is that every 3-D element contains several layers of different materials and plied orientations. The gap element is used to prevent the overlap of the delamination. The strain energy release rate is studied along the delamination front. The results show that the temperature affects the delamination damage significantly.
