1997 Vol. 14, No. 3
1997, 14(3): 1-8.
Abstract:
The developing procedure and research state of in-situ toughened Si3N4 are summarized in detail. The main contents are discussed and some problems and trend in this field are proposed.
The developing procedure and research state of in-situ toughened Si3N4 are summarized in detail. The main contents are discussed and some problems and trend in this field are proposed.
1997, 14(3): 9-14.
Abstract:
This article studied the relation of the incubation necessary for the directed oxidation of the molten Al-Mg-Si alloy at high temperature in the air with the content of Mg and Si in the parent alloyby the TG experiments. It was proved that the directed oxidation of Al-Mg-Si alloy is consistent with Arrhenius formula. The relation of the nominal activation energy of the bulk oxidation of the aluminum melt with the Mg and Si content of the parent alloy was studied also.
This article studied the relation of the incubation necessary for the directed oxidation of the molten Al-Mg-Si alloy at high temperature in the air with the content of Mg and Si in the parent alloyby the TG experiments. It was proved that the directed oxidation of Al-Mg-Si alloy is consistent with Arrhenius formula. The relation of the nominal activation energy of the bulk oxidation of the aluminum melt with the Mg and Si content of the parent alloy was studied also.
1997, 14(3): 15-19.
Abstract:
The flow stresses of several aluminium alloys and SiCW reinforced composites during tensile deformation have been studied. It shows that the strengthening effect of the composites relates to the strength of the matrix alloys; the rule of mixture (ROM) is not applicable for the prediction of the tensile strength of these composites; the yield stresses of those composites with higher strength matrix alloys are lower than those of the matrix alloys, and the work hardening ability of the composites is much higher than that of the matrix alloys. Some possible reasons of these results are discussed in this paper.
The flow stresses of several aluminium alloys and SiCW reinforced composites during tensile deformation have been studied. It shows that the strengthening effect of the composites relates to the strength of the matrix alloys; the rule of mixture (ROM) is not applicable for the prediction of the tensile strength of these composites; the yield stresses of those composites with higher strength matrix alloys are lower than those of the matrix alloys, and the work hardening ability of the composites is much higher than that of the matrix alloys. Some possible reasons of these results are discussed in this paper.
1997, 14(3): 20-24.
Abstract:
The interfaces and microstructures of SiCP and short carbon fiber hybrid reinforced ZA27 composites have been observed through Transmission Electron Microscope and it was found that discontinuous interfacial precipitated products of rich-copper ZnAl phase were formed at a part of areas among SiCP and short carbon fiber and ZA27 alloy matrix. The part of interfaces between carbon fiber and ZA27 alloy matrix had a layer of carbon because of the incomplete degum of carbonfibers. Besides, the reinforcements in microareas mainly aggregated at the end of solidification position of ZA27 alloy and showed nonuniform distribution.
The interfaces and microstructures of SiCP and short carbon fiber hybrid reinforced ZA27 composites have been observed through Transmission Electron Microscope and it was found that discontinuous interfacial precipitated products of rich-copper ZnAl phase were formed at a part of areas among SiCP and short carbon fiber and ZA27 alloy matrix. The part of interfaces between carbon fiber and ZA27 alloy matrix had a layer of carbon because of the incomplete degum of carbonfibers. Besides, the reinforcements in microareas mainly aggregated at the end of solidification position of ZA27 alloy and showed nonuniform distribution.
1997, 14(3): 25-31.
Abstract:
The solidification processing of metal matrix composites has a strong influence on their mechanical properties. In the present work, the effects of solidification cooling rate on the solidification microstructure, microsegregation and mechanical properties of CF/Al-4.5Cu metal matrix composites were investigated experimentally. The results showed that during the solidification processing of squeeze casting CF/Al-4.5Cu composites, α-Al phase nucleated first in the interstice regions of CF, but eutectic θ-Al2Cu phase nucleated and grew on the surface of CF. As the solidification cooling rate decreased, crystallized quantity of θ-Al2Cu phase also decreased; its shape was changed from large block-like to particle-like; meantime, the microsegregation of Cuelement also decreased, but the bent strength of the composites increased. Besides, because the fiber-metal interface was strongly bonded in the CF/Al-4.5Cu composites, the fracture surface of the composites showed the characters of brittle fracture, and no fiber pull-out was observed in any of these composites.
The solidification processing of metal matrix composites has a strong influence on their mechanical properties. In the present work, the effects of solidification cooling rate on the solidification microstructure, microsegregation and mechanical properties of CF/Al-4.5Cu metal matrix composites were investigated experimentally. The results showed that during the solidification processing of squeeze casting CF/Al-4.5Cu composites, α-Al phase nucleated first in the interstice regions of CF, but eutectic θ-Al2Cu phase nucleated and grew on the surface of CF. As the solidification cooling rate decreased, crystallized quantity of θ-Al2Cu phase also decreased; its shape was changed from large block-like to particle-like; meantime, the microsegregation of Cuelement also decreased, but the bent strength of the composites increased. Besides, because the fiber-metal interface was strongly bonded in the CF/Al-4.5Cu composites, the fracture surface of the composites showed the characters of brittle fracture, and no fiber pull-out was observed in any of these composites.
1997, 14(3): 32-36.
Abstract:
The low energy friction and wear properties of carbon/carbon(C/C) composites uses for aircraft brakes were studied,curves of relationship between the moment of brake force and brake velocity were analyzed, and the essential caase was discussed of why C/C composites possess a maximum friction coefficient when energy is changed. The results show that the maximum friction coefficient is decreased as the specific pressure is increased. The friction surface of C/C composites is rougher in low energy condition. The wear rate is about twice as large as in normal energy conditions.
The low energy friction and wear properties of carbon/carbon(C/C) composites uses for aircraft brakes were studied,curves of relationship between the moment of brake force and brake velocity were analyzed, and the essential caase was discussed of why C/C composites possess a maximum friction coefficient when energy is changed. The results show that the maximum friction coefficient is decreased as the specific pressure is increased. The friction surface of C/C composites is rougher in low energy condition. The wear rate is about twice as large as in normal energy conditions.
1997, 14(3): 37-40.
Abstract:
The processing of composite with MoSi2 type coating has been studied, and the results of the oxidation resistant performance are given. It has been shown that the weightloss percent of MoSi2 coating is less-than 0.57% and its weight loss ratio is steadily 2.43×10-5g/m2·s after 242 hours of oxidizing at 1500℃.
The processing of composite with MoSi2 type coating has been studied, and the results of the oxidation resistant performance are given. It has been shown that the weightloss percent of MoSi2 coating is less-than 0.57% and its weight loss ratio is steadily 2.43×10-5g/m2·s after 242 hours of oxidizing at 1500℃.
1997, 14(3): 41-44.
Abstract:
The attenuation ability in the range 1～1000 MHz of composite consisting of PZT and Ni-Zn ferrite was studied. It was found out that PZT is a kind of material that is both ferroelectric and ferrom agnetic, so its attenuation ability is good. The at tenuation ability of composite consisting of PZT and Ni-Zn ferrite is greater than that of Ni-Zn ferrite in the range below 100 MHz, which is not to be found in the range of 100～1000 MHz.
The attenuation ability in the range 1～1000 MHz of composite consisting of PZT and Ni-Zn ferrite was studied. It was found out that PZT is a kind of material that is both ferroelectric and ferrom agnetic, so its attenuation ability is good. The at tenuation ability of composite consisting of PZT and Ni-Zn ferrite is greater than that of Ni-Zn ferrite in the range below 100 MHz, which is not to be found in the range of 100～1000 MHz.
1997, 14(3): 45-48.
Abstract:
The CeO2/γ-Al2O3 composite powder has been studied. The experimental results showed that the CeO2 can disperse spontaneously onto the surface of γ-Al2O3 to for mamonolayer, and the CeO2/γ-Al2O3 monolayer dispersion composite powder could be prepared by impregnating γ-Al2O3 in a cerium salt's solution and followed by drying and calcining the impregnated samples. The monolayer dispersion threshold of composite powder changed by the cerium salts solution, which should be 0.042g/g (γ-Al2O3) for the composite powder prepared from Ce(NO3)3 solution and 0.10g/g (γ-Al2O3) for that prepared from Ce (Ac) solution.
The CeO2/γ-Al2O3 composite powder has been studied. The experimental results showed that the CeO2 can disperse spontaneously onto the surface of γ-Al2O3 to for mamonolayer, and the CeO2/γ-Al2O3 monolayer dispersion composite powder could be prepared by impregnating γ-Al2O3 in a cerium salt's solution and followed by drying and calcining the impregnated samples. The monolayer dispersion threshold of composite powder changed by the cerium salts solution, which should be 0.042g/g (γ-Al2O3) for the composite powder prepared from Ce(NO3)3 solution and 0.10g/g (γ-Al2O3) for that prepared from Ce (Ac) solution.
1997, 14(3): 49-53.
Abstract:
Thickening mechanism and curing behavior of a novel phenolic SMC were discussed. The results show that the influence of water in phenolic resin, thickening agent, filler and silane coupling agent on the initial stage viscosity of phenolic resin paste is very obvious. It is found that use of calcium hydroxide as a thickening agent causes rapid hardening of phenolic SMC. Use of magnesium oxide alone as a thickening agent results in a slow hardening rate. Similarly, when talc alone is used as the filler, the viscosity of the phenolic resin paste increases rapidly ; when clay alone is used as the filler, the viscosity of the mixture increases slowly. But excellent viscosity control is achieved when a mixture of calcium hydroxide magnesium oxide, talc and clay is used. It has been discovered that the silane coupling agent cat alyzes the hardening and curing of phenolic SMC, which is proved by DSC data and gel time data. These research results provide the theoretical basis for producing a good quality of phenolic SMC.
Thickening mechanism and curing behavior of a novel phenolic SMC were discussed. The results show that the influence of water in phenolic resin, thickening agent, filler and silane coupling agent on the initial stage viscosity of phenolic resin paste is very obvious. It is found that use of calcium hydroxide as a thickening agent causes rapid hardening of phenolic SMC. Use of magnesium oxide alone as a thickening agent results in a slow hardening rate. Similarly, when talc alone is used as the filler, the viscosity of the phenolic resin paste increases rapidly ; when clay alone is used as the filler, the viscosity of the mixture increases slowly. But excellent viscosity control is achieved when a mixture of calcium hydroxide magnesium oxide, talc and clay is used. It has been discovered that the silane coupling agent cat alyzes the hardening and curing of phenolic SMC, which is proved by DSC data and gel time data. These research results provide the theoretical basis for producing a good quality of phenolic SMC.
1997, 14(3): 54-60.
Abstract:
A device for the chemical treatment of fiber surface was designed and installed, with which UHM PE fibers were treated continuously. Unidirectional composites of treated UHMPE fiber/epoxy resin were manufactured. The short beam shear strength of the composites was measured in order to evaluate the effect of fiber treatment. The compressive, flexural and impact properties were also tested and the results show that this type of composites is extremely tough though its stiffnesses and streng ths are lower than those of carbon fiber reinforced composites. The main failure modes of this material include debonding and delamination, fiber buckling and bending, instead of fiber breaking usually observed in carbon or glass fiber reinforced composites.
A device for the chemical treatment of fiber surface was designed and installed, with which UHM PE fibers were treated continuously. Unidirectional composites of treated UHMPE fiber/epoxy resin were manufactured. The short beam shear strength of the composites was measured in order to evaluate the effect of fiber treatment. The compressive, flexural and impact properties were also tested and the results show that this type of composites is extremely tough though its stiffnesses and streng ths are lower than those of carbon fiber reinforced composites. The main failure modes of this material include debonding and delamination, fiber buckling and bending, instead of fiber breaking usually observed in carbon or glass fiber reinforced composites.
1997, 14(3): 61-66.
Abstract:
The cure temperature of bismaleimide (BMI) resins is known to be higher than 200℃, although their heat resistance and many other properties are excellent. The authors previous study[1] has shown that initiator is very effective in lowering the cure temperature of BMI resins, but its cured resin is brittle. This paper tried to use diamine extender and diallyl bisphenol A comonomer to increase to ughness of modified resin. An optimum resin form ulation cured at 150℃ was obtained using a computer-aided quadratic regression orthogonal combination design method. The resin casts have been detected to have the properties of middle toughness and excellent heat resistance, and composites to have good mechanical properties. This work has laid a good foundation for manufacturing composite tools and structures.
The cure temperature of bismaleimide (BMI) resins is known to be higher than 200℃, although their heat resistance and many other properties are excellent. The authors previous study[1] has shown that initiator is very effective in lowering the cure temperature of BMI resins, but its cured resin is brittle. This paper tried to use diamine extender and diallyl bisphenol A comonomer to increase to ughness of modified resin. An optimum resin form ulation cured at 150℃ was obtained using a computer-aided quadratic regression orthogonal combination design method. The resin casts have been detected to have the properties of middle toughness and excellent heat resistance, and composites to have good mechanical properties. This work has laid a good foundation for manufacturing composite tools and structures.
1997, 14(3): 67-71.
Abstract:
Influence of temperature and boiling time on the dielectrical property of glass fiber (before and after the glass fiber is treated with five kinds of coupling agents)/epoxy resin matrix composite interface was studied. The results show that there is a strong effect of temperature and boiling time on the dielectrical property of glass fiber/epoxy matrix composite int erface, and that its improvement range depends on the polarization intensity of the interface.
Influence of temperature and boiling time on the dielectrical property of glass fiber (before and after the glass fiber is treated with five kinds of coupling agents)/epoxy resin matrix composite interface was studied. The results show that there is a strong effect of temperature and boiling time on the dielectrical property of glass fiber/epoxy matrix composite int erface, and that its improvement range depends on the polarization intensity of the interface.
1997, 14(3): 72-76.
Abstract:
The influences of adding addition agent, such as slag and cement, on the microstructure and properties of gypsum composites were investigated by means of SEM analyses. The results show that treating the surface of plant fiber with styrene-acrylic acid latex can improve effectively the fiber-matrix interface binding state of plant fiber gypsum composites, and a remarkable increase in its mechanical properties can be obtained.
The influences of adding addition agent, such as slag and cement, on the microstructure and properties of gypsum composites were investigated by means of SEM analyses. The results show that treating the surface of plant fiber with styrene-acrylic acid latex can improve effectively the fiber-matrix interface binding state of plant fiber gypsum composites, and a remarkable increase in its mechanical properties can be obtained.
1997, 14(3): 77-80.
Abstract:
The electrical conductivity of particle-filled polymer composite was analyzed by applying classical evaluation formulas and series-parallel circuit. It is pointed out that these models have their own range of application. Particular regulations of conductivity change of composite material with filler concentration, which were obtained from practical measurements, are explained by using the conduction current due to inter facial charge accumulation proposed by the authors.
The electrical conductivity of particle-filled polymer composite was analyzed by applying classical evaluation formulas and series-parallel circuit. It is pointed out that these models have their own range of application. Particular regulations of conductivity change of composite material with filler concentration, which were obtained from practical measurements, are explained by using the conduction current due to inter facial charge accumulation proposed by the authors.
1997, 14(3): 81-86.
Abstract:
The three-dimensional finite element method (FEM) was combined with me-somechanics to determine the local and average stress-strain fields of fibrous composites. Computations for the circle and non-circle fiber-reinforced composites were performed to examine the effects of micro structures on the effective properties. The results indicate that the axial Yang's modulus is insensitive to the microstructures while the fiber distributions or fiber arrays as well as fiber shapes significantly affect the transverse effective properties of the composites.
The three-dimensional finite element method (FEM) was combined with me-somechanics to determine the local and average stress-strain fields of fibrous composites. Computations for the circle and non-circle fiber-reinforced composites were performed to examine the effects of micro structures on the effective properties. The results indicate that the axial Yang's modulus is insensitive to the microstructures while the fiber distributions or fiber arrays as well as fiber shapes significantly affect the transverse effective properties of the composites.
1997, 14(3): 87-90.
Abstract:
Based on the third-order zigzag displacement model, a bending theory for laminated composite plates in an initially stressed state is derived by use of the principle of virtual work. Numerical example shows high precision of the present results.
Based on the third-order zigzag displacement model, a bending theory for laminated composite plates in an initially stressed state is derived by use of the principle of virtual work. Numerical example shows high precision of the present results.
1997, 14(3): 91-98.
Abstract:
The permittivity of a composite with embedded conducting particles exhibits a large enhancement above the value by the Clausius-Mossotti and other dipole approximation. Recently a few people have developed an effective cluster model for the law, in which the effect on the shape of the conducting particles was described by using a factor u0. The insulator was treated only as a matrix. This paper is aimed to treat the metal and the insulator on an equal footing and improve the model as in paper [2]. Finally a comparison was made with our permittivity measurement of the composites LDPE with embedded Cu and Al powders and the electron micrograph of the samples was examined, which shows that the theory is in excellent agreement with the experiments.
The permittivity of a composite with embedded conducting particles exhibits a large enhancement above the value by the Clausius-Mossotti and other dipole approximation. Recently a few people have developed an effective cluster model for the law, in which the effect on the shape of the conducting particles was described by using a factor u0. The insulator was treated only as a matrix. This paper is aimed to treat the metal and the insulator on an equal footing and improve the model as in paper [2]. Finally a comparison was made with our permittivity measurement of the composites LDPE with embedded Cu and Al powders and the electron micrograph of the samples was examined, which shows that the theory is in excellent agreement with the experiments.
1997, 14(3): 99-106.
Abstract:
Void content non-destructive evaluation oriented, an ultrasonic attenuation model of carbon fibre reinforced plastics with voids is presented. A relationship formula between the ultrasonic at tenuation, the main parameters of the material and the voids contained is also given. The model and the formula give support to a new method for non-dest uctive evaluation of void content of carbon-fibre reinforced plastics in our next paper. As a partial result, a sub-model of ultrasonic attenuation of fibre within plastics is established. The relationship between the ultrasonic at tenuation and content and the radius of fibre is accordingly derived out and presented. Another partial result gives a sub-madel of at tenuation due to the socalled distributed voids, in which it is considered that the content of voids is relative to their sizes (e. g. radius of voids) and the property is different in different void sizes. So the statistics property of the distribution of the sizes of the voids is int roduced into the single radius based model.
Void content non-destructive evaluation oriented, an ultrasonic attenuation model of carbon fibre reinforced plastics with voids is presented. A relationship formula between the ultrasonic at tenuation, the main parameters of the material and the voids contained is also given. The model and the formula give support to a new method for non-dest uctive evaluation of void content of carbon-fibre reinforced plastics in our next paper. As a partial result, a sub-model of ultrasonic attenuation of fibre within plastics is established. The relationship between the ultrasonic at tenuation and content and the radius of fibre is accordingly derived out and presented. Another partial result gives a sub-madel of at tenuation due to the socalled distributed voids, in which it is considered that the content of voids is relative to their sizes (e. g. radius of voids) and the property is different in different void sizes. So the statistics property of the distribution of the sizes of the voids is int roduced into the single radius based model.
1997, 14(3): 107-114.
Abstract:
A new method is proposed for non-destructive evaluation (NDE) of void content of carbon-fibre reinforced plastics. The method establishes a testing model which is based on a theoretical model and calibrated by experiment. Thus the problem of the disagreement between present models and experiment results is well solved. Under reasonable simplifying conditions, the detection relationship between ultrasonic attenuation and void content established is simple for practice. The unif ying form of the relationship has general meanings and the application formula calibrated by experiment is just fit to given materials. Attention is paid in this paper both to the conformability and reliability of the method.
A new method is proposed for non-destructive evaluation (NDE) of void content of carbon-fibre reinforced plastics. The method establishes a testing model which is based on a theoretical model and calibrated by experiment. Thus the problem of the disagreement between present models and experiment results is well solved. Under reasonable simplifying conditions, the detection relationship between ultrasonic attenuation and void content established is simple for practice. The unif ying form of the relationship has general meanings and the application formula calibrated by experiment is just fit to given materials. Attention is paid in this paper both to the conformability and reliability of the method.
1997, 14(3): 115-124.
Abstract:
The irrecoverable process of energy dissipation is analyzed during the fatigue damage of the fiber-reinforced laminated composites. After thinking about the different loading sequence, a nonlinear fatigue cumulative damage rule, which is based on the effective hysteresis energy dissipation, is suggested. The present cumulative damage rule is able to correctly describe the loading order effect, about which a rigorous theoretical and experimental proof is provided.
The irrecoverable process of energy dissipation is analyzed during the fatigue damage of the fiber-reinforced laminated composites. After thinking about the different loading sequence, a nonlinear fatigue cumulative damage rule, which is based on the effective hysteresis energy dissipation, is suggested. The present cumulative damage rule is able to correctly describe the loading order effect, about which a rigorous theoretical and experimental proof is provided.
1997, 14(3): 125-129.
Abstract:
Ananalysis was given to the dynamic pulse buckling of a finite-length laminated composite cylindrical shell subjected to uniform radial impact. The buckling equations including transverse shear deformation and rotatory inertia were derived from Lagrange equation. According to numerical results generated by the fourth-order Runge-Kutt a method, the number of the most amplified mode and critical velocity were obtained. Finally, the effects of transverse shear, geometric parameter and lamination angle on the behavior of dynamic buckling of laminated cylindrical shells were discussed.
Ananalysis was given to the dynamic pulse buckling of a finite-length laminated composite cylindrical shell subjected to uniform radial impact. The buckling equations including transverse shear deformation and rotatory inertia were derived from Lagrange equation. According to numerical results generated by the fourth-order Runge-Kutt a method, the number of the most amplified mode and critical velocity were obtained. Finally, the effects of transverse shear, geometric parameter and lamination angle on the behavior of dynamic buckling of laminated cylindrical shells were discussed.
1997, 14(3): 130-135.
Abstract:
Based on continuum damage mechanics, the deformation and damage process of composite laminates impacted by projectile were studied theoretically. The basic equations for this simulation were then derived. The composites are of anisotropy and nonhomogeneity, the micro-damage induced by impact is anisotropic and results in nonlinearity of materials, and the local large-deformations of target construct geomet rical nonlinearity. The macro-damages which include cracking of matrix, fibers fracture within lamina and inter face debonded as well are treated by the nodal division for finite element analysis. The projectile made of steel is assumed to be linear elastic and its damage in the impact process is not taken into account. The theory used in this paper can simulate the process of damage and deformation of composite laminates impacted by projectile.
Based on continuum damage mechanics, the deformation and damage process of composite laminates impacted by projectile were studied theoretically. The basic equations for this simulation were then derived. The composites are of anisotropy and nonhomogeneity, the micro-damage induced by impact is anisotropic and results in nonlinearity of materials, and the local large-deformations of target construct geomet rical nonlinearity. The macro-damages which include cracking of matrix, fibers fracture within lamina and inter face debonded as well are treated by the nodal division for finite element analysis. The projectile made of steel is assumed to be linear elastic and its damage in the impact process is not taken into account. The theory used in this paper can simulate the process of damage and deformation of composite laminates impacted by projectile.
