1998 Vol. 15, No. 3
1998, 15(3): 1-6.
Abstract:
The application feasibility of intermetallic MoSi2 as high temperature structural materials in terms of the intrinsic characteristics of this compound was briefly analyzed, and the present condition and prospects on several important MoSi2 matrix composites were overviewed.
The application feasibility of intermetallic MoSi2 as high temperature structural materials in terms of the intrinsic characteristics of this compound was briefly analyzed, and the present condition and prospects on several important MoSi2 matrix composites were overviewed.
1998, 15(3): 7-11.
Abstract:
In situ surface composites of hypereutectic Al-Si alloy, which possess the microstructures of accumulated primary silicon in outer layer or accumulated primary silicon in outer and inner layers and no primary silicon in the rest layer, have been achieved using preheated metal mould centrifugal casting. The formation process of the composites has been analyzed, and the structure, hardness and wear ability of the composites have been also investigated.
In situ surface composites of hypereutectic Al-Si alloy, which possess the microstructures of accumulated primary silicon in outer layer or accumulated primary silicon in outer and inner layers and no primary silicon in the rest layer, have been achieved using preheated metal mould centrifugal casting. The formation process of the composites has been analyzed, and the structure, hardness and wear ability of the composites have been also investigated.
1998, 15(3): 12-16.
Abstract:
Several types of metal matrix composites — Al/ceramic, Zn 22%Al/ceramic (2μ average size of ceramic particles), Al/Pb(lead droplets<25μ) and Al/FeAl3 were prepared in high intensity ultrasonic field, with dispersed second phases distributed homogeneously in metal matrix. Based on the effects of cavitation and acoustic streaming caused by ultrasound propagating in melt, the mechanisms for the preparation of the above composites were discussed. The experimental results showed that such a technique is widely applicable in the fabrication of metal matrix composites.
Several types of metal matrix composites — Al/ceramic, Zn 22%Al/ceramic (2μ average size of ceramic particles), Al/Pb(lead droplets<25μ) and Al/FeAl3 were prepared in high intensity ultrasonic field, with dispersed second phases distributed homogeneously in metal matrix. Based on the effects of cavitation and acoustic streaming caused by ultrasound propagating in melt, the mechanisms for the preparation of the above composites were discussed. The experimental results showed that such a technique is widely applicable in the fabrication of metal matrix composites.
1998, 15(3): 17-20.
Abstract:
The tensile strength of squeeze casting ZA22/Al2O3 short fiber composites at elevated temperature was measured with autograph AG 10TA universal testing machines made in Japan. The experimental results were analyzed by means of the rule of mixture (ROM) model modified by Friend. The results show that the tensile strength of ZA22 alloy and ZA22/Al2O3 short fiber composites decreases with the increasing temperature, but the decreasing rate of the tensile strength of ZA22 alloy is larger than that of ZA22/Al2O3 short fiber composites. There is a critical temperature T crit for any composites with a fiber volume fraction. The tensile strength of the composites is higher than that of matrix if the temperature is above T crit . The more the fiber volume fraction is, the lower the critical temperature T crit . T crit of the composites with 15% and 20% fiber volume fraction are 123℃ and 87℃, respectively. There is a critical fiber volume fraction V crit under a temperature. The tensile strength of the composites is higher than that of matrix if V f is above V crit . The higher the temperature, the lower the critical fiber volume fraction. For ZA22/Al2O3 short fiber composites, the value of the empirical parameter C * in Friend model decreases with the increasing temperature.
The tensile strength of squeeze casting ZA22/Al2O3 short fiber composites at elevated temperature was measured with autograph AG 10TA universal testing machines made in Japan. The experimental results were analyzed by means of the rule of mixture (ROM) model modified by Friend. The results show that the tensile strength of ZA22 alloy and ZA22/Al2O3 short fiber composites decreases with the increasing temperature, but the decreasing rate of the tensile strength of ZA22 alloy is larger than that of ZA22/Al2O3 short fiber composites. There is a critical temperature T crit for any composites with a fiber volume fraction. The tensile strength of the composites is higher than that of matrix if the temperature is above T crit . The more the fiber volume fraction is, the lower the critical temperature T crit . T crit of the composites with 15% and 20% fiber volume fraction are 123℃ and 87℃, respectively. There is a critical fiber volume fraction V crit under a temperature. The tensile strength of the composites is higher than that of matrix if V f is above V crit . The higher the temperature, the lower the critical fiber volume fraction. For ZA22/Al2O3 short fiber composites, the value of the empirical parameter C * in Friend model decreases with the increasing temperature.
1998, 15(3): 21-26.
Abstract:
In the present study, to overcome the shortcomings of particulate reinforced composites such as low strength, high brittleness and poor machinability, fine and near sphere particulates were used as reinforcement of LD2 Al alloy matrix composites, with their average size of only about 0.15μm. The tensile properties of as cast and extruded Al2O3 P/LD2 composites at room and elevated temperatures were measured. The microstructures of the composites were observed. The results showed that when the sizes of reinforcements were within submicron scale, no dislocation caused by mismatch of CTE was found in the matrix and the strengthening mechanism was changed. In the range of volume fraction of 30%?40%, the tensile strength and elongation of the composites were about 640?760MPa and 8.6?2% respectively, and the strengthening rate was 212%. Superior strength ductility and machinable property of the Al2O3 P/LD2 composites were obtained.
In the present study, to overcome the shortcomings of particulate reinforced composites such as low strength, high brittleness and poor machinability, fine and near sphere particulates were used as reinforcement of LD2 Al alloy matrix composites, with their average size of only about 0.15μm. The tensile properties of as cast and extruded Al2O3 P/LD2 composites at room and elevated temperatures were measured. The microstructures of the composites were observed. The results showed that when the sizes of reinforcements were within submicron scale, no dislocation caused by mismatch of CTE was found in the matrix and the strengthening mechanism was changed. In the range of volume fraction of 30%?40%, the tensile strength and elongation of the composites were about 640?760MPa and 8.6?2% respectively, and the strengthening rate was 212%. Superior strength ductility and machinable property of the Al2O3 P/LD2 composites were obtained.
1998, 15(3): 27-31.
Abstract:
In the present study, the fracture behavior of Al2O3 P/6061 Al alloy composites and the relationship between fracture process and mechanical properties were studied by SEM dynamic tensile stage. The fracture process of the composites was depicted quantitatively, and the toughness of the composites was discussed.
In the present study, the fracture behavior of Al2O3 P/6061 Al alloy composites and the relationship between fracture process and mechanical properties were studied by SEM dynamic tensile stage. The fracture process of the composites was depicted quantitatively, and the toughness of the composites was discussed.
1998, 15(3): 32-37.
Abstract:
A new type polar zinc electrode was fabricated by composition method. The scanning photos in the paper show it is three dimensional framework and ideal netted structure. Through experiments, the electrodes porosity was measured. The results show that the porosity is higher than 80% and almost every pore is open. The pores structure was described and quantitatively analyzed by porosity. At last, the polar zinc electrodes capacity and polarization curves were measured, investigated and compared with the general polar zinc electrode in battery.
A new type polar zinc electrode was fabricated by composition method. The scanning photos in the paper show it is three dimensional framework and ideal netted structure. Through experiments, the electrodes porosity was measured. The results show that the porosity is higher than 80% and almost every pore is open. The pores structure was described and quantitatively analyzed by porosity. At last, the polar zinc electrodes capacity and polarization curves were measured, investigated and compared with the general polar zinc electrode in battery.
1998, 15(3): 38-43.
Abstract:
The sliding wear behaviour of Al2O3/Al composite prepared by Lanxide process was investigated in this paper. It is shown that micro porosities which are disadvantageous to the mechanical property of the composite can provide a better lubrication due to their oil contained and oil supplied effects. According to the SEM observation and energy dispersive X ray analyses, the influence of metal phases and porosities upon the composite sliding wear property was discovered, which leads to an initial discussion of the sliding wear mechanism of Lanxide Al2O3/Al composites.
The sliding wear behaviour of Al2O3/Al composite prepared by Lanxide process was investigated in this paper. It is shown that micro porosities which are disadvantageous to the mechanical property of the composite can provide a better lubrication due to their oil contained and oil supplied effects. According to the SEM observation and energy dispersive X ray analyses, the influence of metal phases and porosities upon the composite sliding wear property was discovered, which leads to an initial discussion of the sliding wear mechanism of Lanxide Al2O3/Al composites.
1998, 15(3): 44-48.
Abstract:
A kind of Cu base composite reinforced by 0.1μm Al2O3 particulates was prepared by hot pressing and sintering process. The microstructures and properties were studied before and after the composite was rolled. The results show that the Al2O3 particulates distribution is uniform, and the particulates also refine the grain size. As a result, the composite has better soft resistance and wear resistance than those of Cu and Cu alloy. With increase in super Al2O3 the density and electric conductivity of the composite decrease, but hardness and strength increase. The conductivity of the present studied composite is similar to that of American SCM product.
A kind of Cu base composite reinforced by 0.1μm Al2O3 particulates was prepared by hot pressing and sintering process. The microstructures and properties were studied before and after the composite was rolled. The results show that the Al2O3 particulates distribution is uniform, and the particulates also refine the grain size. As a result, the composite has better soft resistance and wear resistance than those of Cu and Cu alloy. With increase in super Al2O3 the density and electric conductivity of the composite decrease, but hardness and strength increase. The conductivity of the present studied composite is similar to that of American SCM product.
1998, 15(3): 49-53.
Abstract:
In this paper properties of HDPE fiber/resin matrix super hybrid composites(PESHCM) were studied. Because of applying the functional tailor technique to conduct hybrid design, the PESHCM possessed good mechanical properties, high corrosion resistance, abrasion resistance and so on. By SEM, reasons of the abrasion resistance of the composites were discussed.
In this paper properties of HDPE fiber/resin matrix super hybrid composites(PESHCM) were studied. Because of applying the functional tailor technique to conduct hybrid design, the PESHCM possessed good mechanical properties, high corrosion resistance, abrasion resistance and so on. By SEM, reasons of the abrasion resistance of the composites were discussed.
1998, 15(3): 54-61.
Abstract:
In this paper, the influences of interfacial adhesion and glass fiber content and cooling rate of the specimen melts in injection molding process on the matrix crystal structure and mechanical properties of GF/HDPE composites were investigated by using SEM, SALS, DSC, material universal testing machine, etc. The results show that the produced interfacial stress from the shrinkage of specimen melts in injection molding process can strain induce the forming of the extended chain crystals in the matrix and obviously improves the mechanical properties of the composites.
In this paper, the influences of interfacial adhesion and glass fiber content and cooling rate of the specimen melts in injection molding process on the matrix crystal structure and mechanical properties of GF/HDPE composites were investigated by using SEM, SALS, DSC, material universal testing machine, etc. The results show that the produced interfacial stress from the shrinkage of specimen melts in injection molding process can strain induce the forming of the extended chain crystals in the matrix and obviously improves the mechanical properties of the composites.
1998, 15(3): 62-65.
Abstract:
Delamination of multi directional carbon fiber reinforced plastics caused by drilling was investigated via a scanning acoustic microscope (SAM). A 3-D delamination model was established based on the analyses of experimental results and the mechanism of the delamination formation was studied in detail.
Delamination of multi directional carbon fiber reinforced plastics caused by drilling was investigated via a scanning acoustic microscope (SAM). A 3-D delamination model was established based on the analyses of experimental results and the mechanism of the delamination formation was studied in detail.
1998, 15(3): 66-70.
Abstract:
A Model of conductive structure of unidirectional carbon fiber reinforced polymers (CFRP) is studied. The conductive structure of CFRP can be characterized by the contact number of neighbouring carbon fibers per unit section and the distance of two neighbouring contact points. The measurements of the variation of the electrical resistivity due to dimension of specimen show satisfactory agreement between the theoretical calculations and the experimental determinations
A Model of conductive structure of unidirectional carbon fiber reinforced polymers (CFRP) is studied. The conductive structure of CFRP can be characterized by the contact number of neighbouring carbon fibers per unit section and the distance of two neighbouring contact points. The measurements of the variation of the electrical resistivity due to dimension of specimen show satisfactory agreement between the theoretical calculations and the experimental determinations
1998, 15(3): 71-72.
Abstract:
In this paper the coupling agents such as silicone KH-550 and titanate NDZ-101 were used in the composite prepared from thermotropic liquid crystalline copolyester (PET/60PHB) and aluminum nitride(AlN) powder. The effect of the amount of coupling agents used on tensile strength, thermal conductivity and electrical properties was studied.
In this paper the coupling agents such as silicone KH-550 and titanate NDZ-101 were used in the composite prepared from thermotropic liquid crystalline copolyester (PET/60PHB) and aluminum nitride(AlN) powder. The effect of the amount of coupling agents used on tensile strength, thermal conductivity and electrical properties was studied.
1998, 15(3): 73-80.
Abstract:
Electrical conductivity of carbon fiber reinforced cement composite was measured. The conductivity of the specimens increased by several orders of magnitude while the volume fraction of fibers reached a higher value than the critic concentration. The microstructure associated with electrical percolation phenomena was observed. The influence of fiber volume fraction and fiber length on electrical conductivity and the changing of electrical conductivity under different loading levels were also discussed. The percolation threshold decreases under loading. The relative changing of electrical conductivity both under single loading and under cyclic loading may sensor the stress in elastic, nonelastic, and fracture regions with sensitive response. The results provide an important guide for the manufacture of conductive and intrinsically smart carbon fiber reinforced composites.
Electrical conductivity of carbon fiber reinforced cement composite was measured. The conductivity of the specimens increased by several orders of magnitude while the volume fraction of fibers reached a higher value than the critic concentration. The microstructure associated with electrical percolation phenomena was observed. The influence of fiber volume fraction and fiber length on electrical conductivity and the changing of electrical conductivity under different loading levels were also discussed. The percolation threshold decreases under loading. The relative changing of electrical conductivity both under single loading and under cyclic loading may sensor the stress in elastic, nonelastic, and fracture regions with sensitive response. The results provide an important guide for the manufacture of conductive and intrinsically smart carbon fiber reinforced composites.
1998, 15(3): 81-85.
Abstract:
This paper mainly investigates the mechanical and dielectric properties of short fibred brucite reinforced HDPE/EPDM system and the flame resistance of short fibred brucite, the mechanical, dielectric and flame resistance of short fibred brucite filled HDPE/EPDM composite are compared with common non halogen flame retardant filled systems. The micro structure of this system has also been analyzed by means of dynamic mechanical spectrum and SEM. The results show that short fibred brucite has good reinforcement on the HDPE/EPDM system apart from its flame resistance.
This paper mainly investigates the mechanical and dielectric properties of short fibred brucite reinforced HDPE/EPDM system and the flame resistance of short fibred brucite, the mechanical, dielectric and flame resistance of short fibred brucite filled HDPE/EPDM composite are compared with common non halogen flame retardant filled systems. The micro structure of this system has also been analyzed by means of dynamic mechanical spectrum and SEM. The results show that short fibred brucite has good reinforcement on the HDPE/EPDM system apart from its flame resistance.
1998, 15(3): 86-91.
Abstract:
The development of the mathematic model of critical aspect ratio of short fiber composites was briefly introduced. Based on the characters of structure stress of short fiber/rubber composites and Cox shear lag, a new model of critical aspect ratio used for short fiber/rubber composites has been founded and then discussed in detail. The results showed that the new model can better suit the characters of short fiber/rubber composite; compared to other models, the new model can reflect totally the relations between the structures of the short fiber composite and its critical aspect ratio.
The development of the mathematic model of critical aspect ratio of short fiber composites was briefly introduced. Based on the characters of structure stress of short fiber/rubber composites and Cox shear lag, a new model of critical aspect ratio used for short fiber/rubber composites has been founded and then discussed in detail. The results showed that the new model can better suit the characters of short fiber/rubber composite; compared to other models, the new model can reflect totally the relations between the structures of the short fiber composite and its critical aspect ratio.
1998, 15(3): 92-98.
Abstract:
This work is concerned with the development of bamboo fiber and coconut husk fiber reinforced cement composite materials. Some samples are made with the addition of latex cement modifier. The strength, toughness and cracking resistance of these composites are all notably improved when compared with neat cement. The effects of fiber weight fraction, latex and water content on tensile, flexural and impact properties of these natural fiber reinforced composites are investigated. The microstructural failure mechanisms are also discussed.
This work is concerned with the development of bamboo fiber and coconut husk fiber reinforced cement composite materials. Some samples are made with the addition of latex cement modifier. The strength, toughness and cracking resistance of these composites are all notably improved when compared with neat cement. The effects of fiber weight fraction, latex and water content on tensile, flexural and impact properties of these natural fiber reinforced composites are investigated. The microstructural failure mechanisms are also discussed.
1998, 15(3): 99-102.
Abstract:
Two kinds of new anti buckling supports for the specimens of smooth composite laminates and the notched composite laminates are designed. The compression compression fatigue tests of smooth composite laminate and notched composite laminate are briefly given. Furthermore their damage mechanism is analyzed and discussed. And then a “transition” concept of fatigue damage of composites is presented.
Two kinds of new anti buckling supports for the specimens of smooth composite laminates and the notched composite laminates are designed. The compression compression fatigue tests of smooth composite laminate and notched composite laminate are briefly given. Furthermore their damage mechanism is analyzed and discussed. And then a “transition” concept of fatigue damage of composites is presented.
THERMAL EXPANSION COEFFICIENTS OF THREEDIMENSIONALBRAIDED COMPOSITES WITH PENNYSHAPED MICROCRACKS
1998, 15(3): 103-107.
Abstract:
The Eshelby-Mori-Tanaka theory combined with modified Stiffness Averaging Method is used for considering the interaction of fibers and microcracks and predicting the effective thermal expansion coefficients of three dimensional braided composite with penny shaped cracks. The effects of microcrack density on the thermal mechanical behavior of the material are also studied. The developed method provides theoretical basis for material designers and manufacturers to improve the material behavior.
The Eshelby-Mori-Tanaka theory combined with modified Stiffness Averaging Method is used for considering the interaction of fibers and microcracks and predicting the effective thermal expansion coefficients of three dimensional braided composite with penny shaped cracks. The effects of microcrack density on the thermal mechanical behavior of the material are also studied. The developed method provides theoretical basis for material designers and manufacturers to improve the material behavior.
1998, 15(3): 108-112.
Abstract:
Based on the Eshelby's inclusion theory an analytical model is proposed to analyze the influence of a free surface on stress distribution for a particle reinforced material. The perturbed zone for the residual stress and the formation of the surface crack in the presence of a free surface are also discussed in detail.
Based on the Eshelby's inclusion theory an analytical model is proposed to analyze the influence of a free surface on stress distribution for a particle reinforced material. The perturbed zone for the residual stress and the formation of the surface crack in the presence of a free surface are also discussed in detail.
1998, 15(3): 113-118.
Abstract:
By means of the principle of superposition, the stress state of a composite laminate with inner delamination is decomposed and the problem of delamination can be reduced to the analysis of an additional stress state of the original laminate subjected to additional shear load along the delamination surfaces. The trigonometric series is applied to describe the displacement mode satisfying the boundary conditions and the principle of minimum potential energy is used to determine the unknown coefficients of the above series. The convergency tests are carried out. From the computational results, it can be shown that all of the displacement components are convergent and the deflection converges more rapidly.
By means of the principle of superposition, the stress state of a composite laminate with inner delamination is decomposed and the problem of delamination can be reduced to the analysis of an additional stress state of the original laminate subjected to additional shear load along the delamination surfaces. The trigonometric series is applied to describe the displacement mode satisfying the boundary conditions and the principle of minimum potential energy is used to determine the unknown coefficients of the above series. The convergency tests are carried out. From the computational results, it can be shown that all of the displacement components are convergent and the deflection converges more rapidly.
1998, 15(3): 119-123.
Abstract:
The inverse problem in Calculus of Variations for piezoelectric media was studied. Several kinds of variational principles and generalized variational principles of the media were established systematically by using the VI method introduced in Ref.. The results can be used in numerical analysis of the problem.
The inverse problem in Calculus of Variations for piezoelectric media was studied. Several kinds of variational principles and generalized variational principles of the media were established systematically by using the VI method introduced in Ref.. The results can be used in numerical analysis of the problem.
1998, 15(3): 124-128.
Abstract:
Low velocity impact tests are introduced into honeycomb core sandwich specimens with different energy levels. Some methods are used to study the damage of the panels after impact thoroughly: X ray, deply, microscopic examination of sections, and visual inspection. The role of the cloth on the panel surfaces is discussed. The relationship between visual damage, facesheet damage, damage of honeycomb core, and impact energy levels is also analyzed.
Low velocity impact tests are introduced into honeycomb core sandwich specimens with different energy levels. Some methods are used to study the damage of the panels after impact thoroughly: X ray, deply, microscopic examination of sections, and visual inspection. The role of the cloth on the panel surfaces is discussed. The relationship between visual damage, facesheet damage, damage of honeycomb core, and impact energy levels is also analyzed.
1998, 15(3): 129-134.
Abstract:
The behavior of the cast (wt 8%) SiCP/6061 Al composite material under impact tensile loading was reported in this paper. The tests were conducted in two environmental temperatures and three loading rates. The results showed that the broken strain of the material decreased with raising the loading rate and environmental temperature. The modulus increased when the loading rate and environmental temperature increased. The stress strain curve presented a brittle character.
The behavior of the cast (wt 8%) SiCP/6061 Al composite material under impact tensile loading was reported in this paper. The tests were conducted in two environmental temperatures and three loading rates. The results showed that the broken strain of the material decreased with raising the loading rate and environmental temperature. The modulus increased when the loading rate and environmental temperature increased. The stress strain curve presented a brittle character.
1998, 15(3): 135-141.
Abstract:
A theoretical analysis of composite interphase model composed of three phase coaxial cylinders is developed and the work done by Theocaris et al is improved in this paper. The elastic properties of interphase layer are described with an exponential law of variation. The results presented in this paper agree well with those given in the literature.
A theoretical analysis of composite interphase model composed of three phase coaxial cylinders is developed and the work done by Theocaris et al is improved in this paper. The elastic properties of interphase layer are described with an exponential law of variation. The results presented in this paper agree well with those given in the literature.
