1998 Vol. 15, No. 2
1998, 15(2): 1-5.
Abstract:
The interfacial bonding and the elastic deformation of SiCP/1100Al and SiCP/7075Al composites were compared. The results indicate that the elastic moduli of the two kinds of composites are highly different due to the difference of those interfacial bonding, load transfer that occurs through interface between the matrix and the reinforcement is the important strengthening mechanism during the elastic deformation of the composites, and the strengthening effect of the mechanism depends on the interfacial bonding between the matrix and the reinforcement.
The interfacial bonding and the elastic deformation of SiCP/1100Al and SiCP/7075Al composites were compared. The results indicate that the elastic moduli of the two kinds of composites are highly different due to the difference of those interfacial bonding, load transfer that occurs through interface between the matrix and the reinforcement is the important strengthening mechanism during the elastic deformation of the composites, and the strengthening effect of the mechanism depends on the interfacial bonding between the matrix and the reinforcement.
1998, 15(2): 6-11.
Abstract:
In this paper, the linear expansion coefficient and thermal cycling curve of three kinds of high volume fraction SiCP /Al matrix composites fabricated by vacuum assisted gas pressure infiltration casting were tested at 0～400℃ temperature interval. The results show that the linear expansion coefficient of composites is about half the value of its matrix. The composites' thermal cycling curve is obviously different from that of its matrix. Thermal cycling curves of three composites are also different from each other. It is explained by the theory of plastic strain in matrix. It was found that closing characteristic of thermal cycling curve for composite can be optimized by changing its matrix.
In this paper, the linear expansion coefficient and thermal cycling curve of three kinds of high volume fraction SiCP /Al matrix composites fabricated by vacuum assisted gas pressure infiltration casting were tested at 0～400℃ temperature interval. The results show that the linear expansion coefficient of composites is about half the value of its matrix. The composites' thermal cycling curve is obviously different from that of its matrix. Thermal cycling curves of three composites are also different from each other. It is explained by the theory of plastic strain in matrix. It was found that closing characteristic of thermal cycling curve for composite can be optimized by changing its matrix.
1998, 15(2): 12-17.
Abstract:
The relations between infiltration depth of metal liquid to the capillary between particles and processing parameter have been derived by mathematic analysis for the vacuum infiltration process,i.e. H=R2(Ρ1+2σcosθ/R)τη The heat resistant steel based composites containing WC, Ni coated Al2O3, Al2O3 particles have been gained with vacuum infiltration process, and the particles in matrix are well distributed. The effects of the wetting of metal liquid with particles and the sizes of particles on infiltration depth have been confirmed by experiments.
The relations between infiltration depth of metal liquid to the capillary between particles and processing parameter have been derived by mathematic analysis for the vacuum infiltration process,i.e. H=R2(Ρ1+2σcosθ/R)τη The heat resistant steel based composites containing WC, Ni coated Al2O3, Al2O3 particles have been gained with vacuum infiltration process, and the particles in matrix are well distributed. The effects of the wetting of metal liquid with particles and the sizes of particles on infiltration depth have been confirmed by experiments.
1998, 15(2): 18-22.
Abstract:
This paper deals with the thermodynamics and kinetics of the reaction of B2O3 with Mg-Li alloy for the production of MgO particulates reinforced Mg-Li composites, which were examined with DTA and water quenching. It can be seen that the reaction of B2O3 with Mg-Li alloy could take place at the usual melting temperature of Mg-Li alloys and the reaction rate is quick. Fine, spherical and dispersed MgO particulates were formed by reactive synthesis process, and the presence of MgO was verified by XRD data. The mechanism of reaction is also discussed.
This paper deals with the thermodynamics and kinetics of the reaction of B2O3 with Mg-Li alloy for the production of MgO particulates reinforced Mg-Li composites, which were examined with DTA and water quenching. It can be seen that the reaction of B2O3 with Mg-Li alloy could take place at the usual melting temperature of Mg-Li alloys and the reaction rate is quick. Fine, spherical and dispersed MgO particulates were formed by reactive synthesis process, and the presence of MgO was verified by XRD data. The mechanism of reaction is also discussed.
1998, 15(2): 23-26.
Abstract:
A new kind of composite with the matrix of pure magnesium was fabricated and its mechanical properties and damping capacity were studied in this paper. It was found that the strength of the magnesium matrix composite was improved largely compared with that of pure magnesium, however, its damping capacity dependent on strain amplitude was decreased due to the addition of the reinforcements. It was also proved that the effective damping mechanism in the magnesium matrix composite was G L dislocation damping model, the same way as that in the pure magnesium metal.
A new kind of composite with the matrix of pure magnesium was fabricated and its mechanical properties and damping capacity were studied in this paper. It was found that the strength of the magnesium matrix composite was improved largely compared with that of pure magnesium, however, its damping capacity dependent on strain amplitude was decreased due to the addition of the reinforcements. It was also proved that the effective damping mechanism in the magnesium matrix composite was G L dislocation damping model, the same way as that in the pure magnesium metal.
1998, 15(2): 27-30.
Abstract:
Some MgAl2O4 reaction layers were discovered on the interface of SiCP/α-Al in SiCP/ZA22 composites with STEM analyses and TEM observations, and the formation conditions were discussed. The results showed that the chemical reaction could take place spontaneously in thermodynamics within the range of temperature in which the composites was fabricated, the thickness of the reaction layer grew according to S=A t and the amount mainly depended on Mg content in the matrix as well as the thickness of SiO2 on the surface of SiCParticles.
Some MgAl2O4 reaction layers were discovered on the interface of SiCP/α-Al in SiCP/ZA22 composites with STEM analyses and TEM observations, and the formation conditions were discussed. The results showed that the chemical reaction could take place spontaneously in thermodynamics within the range of temperature in which the composites was fabricated, the thickness of the reaction layer grew according to S=A t and the amount mainly depended on Mg content in the matrix as well as the thickness of SiO2 on the surface of SiCParticles.
1998, 15(2): 31-35.
Abstract:
In this paper, Al2O3/ bronze composite has been prepared via powder metallurgy using conventional technology and equipment. The influence of various sizes and content of Al2O3 particles on properties of the composite has been investigated at different sintering temperatures. The technology of chemcial plating has been adopted to pretreat Al2O3 particles. The results show that composites fabricated by pressing and sintering two times have fine microstructure, uniformly distributing particles, and better properties than popularly used 6-6-3 bronze bearing material. Chemical plating on Al2O3 particles can further improve general properties of the composite.
In this paper, Al2O3/ bronze composite has been prepared via powder metallurgy using conventional technology and equipment. The influence of various sizes and content of Al2O3 particles on properties of the composite has been investigated at different sintering temperatures. The technology of chemcial plating has been adopted to pretreat Al2O3 particles. The results show that composites fabricated by pressing and sintering two times have fine microstructure, uniformly distributing particles, and better properties than popularly used 6-6-3 bronze bearing material. Chemical plating on Al2O3 particles can further improve general properties of the composite.
1998, 15(2): 36-41.
Abstract:
The thermal shock fatigue character of cermets has been studied and the formative mechanism of crack discussed in detail. The results have shown that the incubation period of crack nucleation decreases and the propagation rate of crack increases with increasing the cyclic temperature. The propagation rate of crack also decreases with increasing the binder content of cermets. The crack formation of thermal shock fatigue is related to the nucleation, growth and join of microvoid. The SEM has also denoted that there are some fatigue striae on the fracture surfaces.
The thermal shock fatigue character of cermets has been studied and the formative mechanism of crack discussed in detail. The results have shown that the incubation period of crack nucleation decreases and the propagation rate of crack increases with increasing the cyclic temperature. The propagation rate of crack also decreases with increasing the binder content of cermets. The crack formation of thermal shock fatigue is related to the nucleation, growth and join of microvoid. The SEM has also denoted that there are some fatigue striae on the fracture surfaces.
1998, 15(2): 42-47.
Abstract:
The effect of the content of nano particle and micro particle on mechanical properties of various level dispersing phase reinforced ceramic composites was investigated. The result has revealed that the improvement of strength and toughness is related with the content of two kinds of particles and their relative ratio. The length of critical crack of multiphase ceramics is also characterized by optimal analyzed method based on the theory of fracture mechanism derived by Griffith. The predicted microcrack length becomes short with the content of nano particles ranging from 3vol% to 12vol%. Furthermore, it is enlarged with increase of the content of micro particles. The phenomenon of different optimal volume fraction of particles between the composition of maximum strength (7.9vol%, 7.9vol%) and that of toughness(9.7vol%, 9.7vol%) may be attributed to the stronger sensibility of strength to internal defects than that of toughness to these defects formed in the process of preparation.
The effect of the content of nano particle and micro particle on mechanical properties of various level dispersing phase reinforced ceramic composites was investigated. The result has revealed that the improvement of strength and toughness is related with the content of two kinds of particles and their relative ratio. The length of critical crack of multiphase ceramics is also characterized by optimal analyzed method based on the theory of fracture mechanism derived by Griffith. The predicted microcrack length becomes short with the content of nano particles ranging from 3vol% to 12vol%. Furthermore, it is enlarged with increase of the content of micro particles. The phenomenon of different optimal volume fraction of particles between the composition of maximum strength (7.9vol%, 7.9vol%) and that of toughness(9.7vol%, 9.7vol%) may be attributed to the stronger sensibility of strength to internal defects than that of toughness to these defects formed in the process of preparation.
1998, 15(2): 48-52.
Abstract:
The batch sintering process and resultant mechanical properties of Ce-Y-ZTA composite were studied using rectangular multimode microwave oven with a power supply of 5kW, 2.45GHz. The experimental results show that a fast ceramic sintering with high stability and repetition could be realized through suitable control of heating profile and improving of hybrid heating structure. Density of sintered specimens reached 99% the theoretical value. The microwave sintering process only cost two hours, and final sintering temperature had a decrease of 50 ℃ to 100℃ compared with conventional sintering. Finer grain size and more homogeneous microstructure could be observed, for microwave processing. Also higher flexural strength (from 600 MPa to 670MPa) and fracture toughness were obtained.
The batch sintering process and resultant mechanical properties of Ce-Y-ZTA composite were studied using rectangular multimode microwave oven with a power supply of 5kW, 2.45GHz. The experimental results show that a fast ceramic sintering with high stability and repetition could be realized through suitable control of heating profile and improving of hybrid heating structure. Density of sintered specimens reached 99% the theoretical value. The microwave sintering process only cost two hours, and final sintering temperature had a decrease of 50 ℃ to 100℃ compared with conventional sintering. Finer grain size and more homogeneous microstructure could be observed, for microwave processing. Also higher flexural strength (from 600 MPa to 670MPa) and fracture toughness were obtained.
1998, 15(2): 53-56.
Abstract:
The substrate architecture of carbon/carbon composites has an effect on both properties and cost of products. In this paper, four kinds of substrate architectures, that is, 1K carbon cloth, 3K carbon cloth, 1K carbon cloth+carbon paper, 1K carbon cloth+carbon felt, were selected. The compositing technology was by the improved CVD methods. The influence of substrate architectures on the properties and microstructure of the manufactured carbon/carbon composite was studied. The results show that the samples made by the four kinds of architectures all have an obvious pseudoplastic fracture behaviour and the macroscopic appearance of bending fracture fractography shows as a “Z” shape. The sample manufactured by 1K carbon cloth has the highest flexural strength, and that by 3K carbon cloth has a lowest value. The strength of other two kinds of samples is between the two.
The substrate architecture of carbon/carbon composites has an effect on both properties and cost of products. In this paper, four kinds of substrate architectures, that is, 1K carbon cloth, 3K carbon cloth, 1K carbon cloth+carbon paper, 1K carbon cloth+carbon felt, were selected. The compositing technology was by the improved CVD methods. The influence of substrate architectures on the properties and microstructure of the manufactured carbon/carbon composite was studied. The results show that the samples made by the four kinds of architectures all have an obvious pseudoplastic fracture behaviour and the macroscopic appearance of bending fracture fractography shows as a “Z” shape. The sample manufactured by 1K carbon cloth has the highest flexural strength, and that by 3K carbon cloth has a lowest value. The strength of other two kinds of samples is between the two.
1998, 15(2): 57-61.
Abstract:
PP and PA6 were extruded with a single screw extruder. PA6 could form microfibrils in PP matrix. When the blends were compression molded at the temperature between the melting temperature of PP and that of PA6, these fibrils could be maintained in the matrix. The existence of PA6 microfibrils improved the impact strength but the tensile strength of the composites decreased.
PP and PA6 were extruded with a single screw extruder. PA6 could form microfibrils in PP matrix. When the blends were compression molded at the temperature between the melting temperature of PP and that of PA6, these fibrils could be maintained in the matrix. The existence of PA6 microfibrils improved the impact strength but the tensile strength of the composites decreased.
1998, 15(2): 62-67.
Abstract:
It was employed that changing the processing temperature, screw speed and draw rate in order to study how PP/PA6 in situ fibrillation composite was affected by the processing conditions. The morphology and mechanical properties of the composites, which were processed under different conditions, were investigated in the present study. It was found that at the higher screw speed, the higher draw rate and the lower processing temperature the PA6 fibrils were finer and the mechanical properties of PP/PA6 composites were better.
It was employed that changing the processing temperature, screw speed and draw rate in order to study how PP/PA6 in situ fibrillation composite was affected by the processing conditions. The morphology and mechanical properties of the composites, which were processed under different conditions, were investigated in the present study. It was found that at the higher screw speed, the higher draw rate and the lower processing temperature the PA6 fibrils were finer and the mechanical properties of PP/PA6 composites were better.
1998, 15(2): 68-73.
Abstract:
A modified bismaleimide resin has been obtained by copolymerization of bis(4 maleimido phenyl)methant and o,o ' diallylbisphenol A with suitable catalyzer. This paper deals with the solubility, curing kinetic and mechanism of the resin system, as well as mechanical, electrical, and thermal stability properties of the cured resin matrix and unidirectional glass fiber composites.
A modified bismaleimide resin has been obtained by copolymerization of bis(4 maleimido phenyl)methant and o,o ' diallylbisphenol A with suitable catalyzer. This paper deals with the solubility, curing kinetic and mechanism of the resin system, as well as mechanical, electrical, and thermal stability properties of the cured resin matrix and unidirectional glass fiber composites.
1998, 15(2): 74-81.
Abstract:
In this paper the relationships between the ballistic energy absorption of aramid fiber, UHMWPE fiber, glass fiber, carbon fiber reinforced composites and areal density, projectile velocity, molding pressure, resin matrix content were investigated and analyzed through lots of ballistic testings. The ballistic resistance of different fiber composites under different conditions was revealed. The study results would be a very valuable reference to the optimal design of ballistic composites and lightweight composite armor.
In this paper the relationships between the ballistic energy absorption of aramid fiber, UHMWPE fiber, glass fiber, carbon fiber reinforced composites and areal density, projectile velocity, molding pressure, resin matrix content were investigated and analyzed through lots of ballistic testings. The ballistic resistance of different fiber composites under different conditions was revealed. The study results would be a very valuable reference to the optimal design of ballistic composites and lightweight composite armor.
1998, 15(2): 82-86.
Abstract:
Computer aided regression orthogonal design was used to optimize formulation of easy processable bismaleimide (BMI) resin systems. The resin system with optimized formulation had fine all round properties and met the needs of the most part processing technology including RTM technology.
Computer aided regression orthogonal design was used to optimize formulation of easy processable bismaleimide (BMI) resin systems. The resin system with optimized formulation had fine all round properties and met the needs of the most part processing technology including RTM technology.
1998, 15(2): 87-92.
Abstract:
Poly(butylene terephthalate)(PBT) showed low impact strength values. Whereas the addition of thermoplastic polyamide elastomers(TPAE) and compatibilizers alloys showed high impact strength values. Polarization optical microscope(POM) and scanning electron microscope(SEM) observations of the fracture surfaces and deformed regions beneath the fracture surfaces revealed that the fracture process of PBT was brittle which was originated from plastic constraint at the notch tip. The fracture of alloys was also caused by plastic constraint at the notch tip. However, the plastic deformation zone at the notch tip was composed of many voids and partially elongated fibrils, and this absorbed impact energy. The plastic deformation was enhanced by the transition of the stress state from plane strain to plane stress. The final fracture occurred from the notch tip connecting voids in the plastic deformation zone.
Poly(butylene terephthalate)(PBT) showed low impact strength values. Whereas the addition of thermoplastic polyamide elastomers(TPAE) and compatibilizers alloys showed high impact strength values. Polarization optical microscope(POM) and scanning electron microscope(SEM) observations of the fracture surfaces and deformed regions beneath the fracture surfaces revealed that the fracture process of PBT was brittle which was originated from plastic constraint at the notch tip. The fracture of alloys was also caused by plastic constraint at the notch tip. However, the plastic deformation zone at the notch tip was composed of many voids and partially elongated fibrils, and this absorbed impact energy. The plastic deformation was enhanced by the transition of the stress state from plane strain to plane stress. The final fracture occurred from the notch tip connecting voids in the plastic deformation zone.
1998, 15(2): 93-97.
Abstract:
The hole drilling method is presented to measure residual stresses in orthotropic materials. Based on the analytical solution to stress field around a hole in a stressed orthotropic infinite width plate, a set of equations was derived to calculate the relieved strain matrix. An example was given to assess the validity of these equations.
The hole drilling method is presented to measure residual stresses in orthotropic materials. Based on the analytical solution to stress field around a hole in a stressed orthotropic infinite width plate, a set of equations was derived to calculate the relieved strain matrix. An example was given to assess the validity of these equations.
1998, 15(2): 98-101.
Abstract:
The damping function of the sandwich outer ring of rolling bearings was studied according to polymer composite material delayed strain response to stress under the rolling bearing vibration. This paper also presents the results of noise test to this kind of rolling bearings. The conclusion is obtained that this kind of structure has good vibration absorption and noise abatement. This study will furnish the theoretical basis for design and application in engineering.
The damping function of the sandwich outer ring of rolling bearings was studied according to polymer composite material delayed strain response to stress under the rolling bearing vibration. This paper also presents the results of noise test to this kind of rolling bearings. The conclusion is obtained that this kind of structure has good vibration absorption and noise abatement. This study will furnish the theoretical basis for design and application in engineering.
1998, 15(2): 102-107.
Abstract:
The governing equations of laminate faced sandwich cylindrical shallow shells based on the first order shear theory with large deflection are high order partial differential equations. Four dependent functions are involved. They are the deflection w, the rotations of the normal to the undeformed median surface Φx, Φy and the force function F. In the present paper these dependent functions are expressed as generalized double Fourier series with beam eigenfunctions as general terms. These series are chosen so that various boundary conditions are satisfied. By substituting these expressions into the high order partial differential governing equations, they become a set of algebraic equations. Here is developed a universal and effective method to solve the problems on the shear theory of laminated or sandwich thin walled structures with large deflection.
The governing equations of laminate faced sandwich cylindrical shallow shells based on the first order shear theory with large deflection are high order partial differential equations. Four dependent functions are involved. They are the deflection w, the rotations of the normal to the undeformed median surface Φx, Φy and the force function F. In the present paper these dependent functions are expressed as generalized double Fourier series with beam eigenfunctions as general terms. These series are chosen so that various boundary conditions are satisfied. By substituting these expressions into the high order partial differential governing equations, they become a set of algebraic equations. Here is developed a universal and effective method to solve the problems on the shear theory of laminated or sandwich thin walled structures with large deflection.
1998, 15(2): 108-112.
Abstract:
The natural frequencies of a radial tire at a given pressure were determined in terms of the material and structure of the radial tire. With respect to viscoelsticity of rubber, the radial tire was modeled as a ring on elastic tire's body and viscoelastic tread. A natural frequency equation was created on the basis of this model. Experimental values of resonant frequencies at a given pressure are in agreement with the predicted values well.
The natural frequencies of a radial tire at a given pressure were determined in terms of the material and structure of the radial tire. With respect to viscoelsticity of rubber, the radial tire was modeled as a ring on elastic tire's body and viscoelastic tread. A natural frequency equation was created on the basis of this model. Experimental values of resonant frequencies at a given pressure are in agreement with the predicted values well.
1998, 15(2): 113-118.
Abstract:
The main objective of this paper is to investigate a new measurement method to identify plate rigidities of a circular orthotropic disk using vibration data. The method consists of three parts: (1) a correct finite element model; (2) a set of reliable experimental data; (3) a fast and robust estimation method.
The main objective of this paper is to investigate a new measurement method to identify plate rigidities of a circular orthotropic disk using vibration data. The method consists of three parts: (1) a correct finite element model; (2) a set of reliable experimental data; (3) a fast and robust estimation method.
1998, 15(2): 119-124.
Abstract:
A combined micro and macro model is developed for predicting the elastic moduli of fiber reinforced composites, that is, a microscopic single fiber/matrix cylindrical element with co-focal elliptical cross sections is embedded in an infinite composite which is regarded as a homogeneous medium. The axial shear modulus has been derived in closed form by using the conformal mapping approach integrated with the Laurent expansion. The present model removes the weakness of the classical model and gives theoretical values in good agreement with experimental results.
A combined micro and macro model is developed for predicting the elastic moduli of fiber reinforced composites, that is, a microscopic single fiber/matrix cylindrical element with co-focal elliptical cross sections is embedded in an infinite composite which is regarded as a homogeneous medium. The axial shear modulus has been derived in closed form by using the conformal mapping approach integrated with the Laurent expansion. The present model removes the weakness of the classical model and gives theoretical values in good agreement with experimental results.
1998, 15(2): 125-129.
Abstract:
To increase the whole strength and stiffness of the composite wing and to lower the manufacturing cost, the main component of the wing is employed with stitched technique. Intercostal is made from web and flanges, and is tailored from a whole knitted stitched laminate plate. Intercostal horizontal and vertical flanges are stitched on the skin and stringer blade respectfully; stringer flanges are stitched on the skin; then they can be integrated into structure by RTM. Direction of applied tension is on the intercostal web. There is shear stress between intercostal horizontal flanges and skin, causing slip delamination. There is tension stress between intercostal vertical flange and stringer blade, causing tensile delamination. Using a mixed 2D/3D FE model to the analysis gives the interface stress distribution among the intercostal, skin and stringer blade; the correctness of the analysis and calculation is also proved by test.
To increase the whole strength and stiffness of the composite wing and to lower the manufacturing cost, the main component of the wing is employed with stitched technique. Intercostal is made from web and flanges, and is tailored from a whole knitted stitched laminate plate. Intercostal horizontal and vertical flanges are stitched on the skin and stringer blade respectfully; stringer flanges are stitched on the skin; then they can be integrated into structure by RTM. Direction of applied tension is on the intercostal web. There is shear stress between intercostal horizontal flanges and skin, causing slip delamination. There is tension stress between intercostal vertical flange and stringer blade, causing tensile delamination. Using a mixed 2D/3D FE model to the analysis gives the interface stress distribution among the intercostal, skin and stringer blade; the correctness of the analysis and calculation is also proved by test.
1998, 15(2): 130-135.
Abstract:
For the first time, this paper presents the mathematical derivation of non geodesic winding on a general surface. It amends the theoretical defects of published literature and makes non-geodesic winding theoretically convincing. It also gives an algorithm to determine the outwards directed normal vector. Based on this method, criteria to evaluate the manufacturability of winding are concluded.
For the first time, this paper presents the mathematical derivation of non geodesic winding on a general surface. It amends the theoretical defects of published literature and makes non-geodesic winding theoretically convincing. It also gives an algorithm to determine the outwards directed normal vector. Based on this method, criteria to evaluate the manufacturability of winding are concluded.
1998, 15(2): 136-139.
Abstract:
A filament wound inner pressure vessel with an inner metal bladder is analysed by a theory of laminated thin shell. The solution is obtained by B spline collocation technique. The results of numerical calculation agree well with experiments.
A filament wound inner pressure vessel with an inner metal bladder is analysed by a theory of laminated thin shell. The solution is obtained by B spline collocation technique. The results of numerical calculation agree well with experiments.
