2001 Vol. 18, No. 1
2001, 18(1): 1-6.
Abstract:
The composite thin-walled beams are widely used in industry because of their good mechanical properties. In this paper, the research work for the composite thin-walled beams about nonlinear beam theory and analysis of the beam cross-section characteristics are surveyed. Dealing with warping displacement,the composite thin-walled work can be divided into six classes: (1) free warping model;(2) one-order warping theory; (3) high-order warping theory;(4) axial warping distribution model; (5) eigen-warping model; (6) the other models. With respect to the mechanical characteristics of the composite thin-walled beams, the recent progresses including the authors' work which considers the laminate warping effect for composite thin-walled beams are introduced.
The composite thin-walled beams are widely used in industry because of their good mechanical properties. In this paper, the research work for the composite thin-walled beams about nonlinear beam theory and analysis of the beam cross-section characteristics are surveyed. Dealing with warping displacement,the composite thin-walled work can be divided into six classes: (1) free warping model;(2) one-order warping theory; (3) high-order warping theory;(4) axial warping distribution model; (5) eigen-warping model; (6) the other models. With respect to the mechanical characteristics of the composite thin-walled beams, the recent progresses including the authors' work which considers the laminate warping effect for composite thin-walled beams are introduced.
2001, 18(1): 7-11.
Abstract:
The importance, advantages and application prospects of the composites used for strengthening and repairing constructions are described. Based on analyzing the related references and the authors' recent research work, the key technologies in this field are summarized, in which the reinforcement and resin matrix techniques are introduced in detail. The properties of several types of fiber sheet materials are presented, and the requirements in both processing and properties of those resin matrixes are proposed. Finally, the adhesive mechanism of the interface between composite and concrete is analyzed. In consideration of domestic situation, some researches which are necessary to carry out in this field are suggested.
The importance, advantages and application prospects of the composites used for strengthening and repairing constructions are described. Based on analyzing the related references and the authors' recent research work, the key technologies in this field are summarized, in which the reinforcement and resin matrix techniques are introduced in detail. The properties of several types of fiber sheet materials are presented, and the requirements in both processing and properties of those resin matrixes are proposed. Finally, the adhesive mechanism of the interface between composite and concrete is analyzed. In consideration of domestic situation, some researches which are necessary to carry out in this field are suggested.
2001, 18(1): 12-15.
Abstract:
A series of new resin systems were prepared by using diamines and N-phenol maleimide to modify BMI resin. The effect of nanometer sized TiO2 on reactivity and thermal properties of modified BMI resins was determined by gel characteristics, FT-IR and thermal analysis technology. The results show that the modified BMI resins have a low melting point (70~90℃) and better solubility, and are soluble in acetone. The nanometer sized TiO2 could decrease the curing temperature by 45~105℃ and increase the thermal stability of the cured resins as well.
A series of new resin systems were prepared by using diamines and N-phenol maleimide to modify BMI resin. The effect of nanometer sized TiO2 on reactivity and thermal properties of modified BMI resins was determined by gel characteristics, FT-IR and thermal analysis technology. The results show that the modified BMI resins have a low melting point (70~90℃) and better solubility, and are soluble in acetone. The nanometer sized TiO2 could decrease the curing temperature by 45~105℃ and increase the thermal stability of the cured resins as well.
2001, 18(1): 16-19.
Abstract:
In this paper, the rheological behavior of epoxy resin (EPON862) for resin transfer molding (RTM) was studied with DSC analysis and viscosity experiments. A rheological model based on dual-Arrhenius equation was established and used to simulate rheological behavior of the resin. The estimated viscosity of the model was in good agreement with that of the experiments. The processing window of the resin system can be well determined for the process based on the developed model. It is shown that the optimum processing temperature of the EPON862 resin for RTM process is 50℃, at which the resin can keep the viscosity less than 300 cP for 50 min. The rheological model is important for processing simulation and quality control of RTM processing for high performance composites.
In this paper, the rheological behavior of epoxy resin (EPON862) for resin transfer molding (RTM) was studied with DSC analysis and viscosity experiments. A rheological model based on dual-Arrhenius equation was established and used to simulate rheological behavior of the resin. The estimated viscosity of the model was in good agreement with that of the experiments. The processing window of the resin system can be well determined for the process based on the developed model. It is shown that the optimum processing temperature of the EPON862 resin for RTM process is 50℃, at which the resin can keep the viscosity less than 300 cP for 50 min. The rheological model is important for processing simulation and quality control of RTM processing for high performance composites.
2001, 18(1): 20-24.
Abstract:
A low-frequency multi-mode ultrasonic Lamb wave method suitable for characterizing thickness, density and elastic stiffness tensors of the ultra-thin uni-direction fiber-reinforced composite layer is presented. The "ultra-thin" there means that the thickness of the plate is only a fraction of the ultrasound wavelength. The dispersion properties of the low frequency Lamb wave propagating along and parallel to the fiber direction are derived, which is the basis of the characterization method. In conjunction with the method of least squares, the secant algorithm is used to estimate the parameters of the ultra-thin fiber-reinforced composite layer. The reasons for evaluation error of the parameters and the sensitivity of all methods for different parameters are analyzed. Using the ultrasound coupler and a pair of broadband longitudinal wave transducers with 2 MHz center frequency, one can successfully estimate the parameters of the ultra-thin GF/PSF composite layer by combination with employing the leaky guided wave frequency-domain analysis method.
A low-frequency multi-mode ultrasonic Lamb wave method suitable for characterizing thickness, density and elastic stiffness tensors of the ultra-thin uni-direction fiber-reinforced composite layer is presented. The "ultra-thin" there means that the thickness of the plate is only a fraction of the ultrasound wavelength. The dispersion properties of the low frequency Lamb wave propagating along and parallel to the fiber direction are derived, which is the basis of the characterization method. In conjunction with the method of least squares, the secant algorithm is used to estimate the parameters of the ultra-thin fiber-reinforced composite layer. The reasons for evaluation error of the parameters and the sensitivity of all methods for different parameters are analyzed. Using the ultrasound coupler and a pair of broadband longitudinal wave transducers with 2 MHz center frequency, one can successfully estimate the parameters of the ultra-thin GF/PSF composite layer by combination with employing the leaky guided wave frequency-domain analysis method.
2001, 18(1): 25-29.
Abstract:
In the hot water of 40℃, 60℃, 80℃ and 100℃, the hot water aging of Bayer-PC, Japan-PC and Korea-PC was investigated. The number of samples is 9 in the aging time of 0~200 h. The law of water absorption in the process of hot water aging and the effects of different hot water aging conditions on the surface fracture appearances of PCs were studied. The hot water aging mechanism of PCs was discussed. The results show: (1) with increasing of time and temperature, the moisture content increases and goes a equilibrium value; (2) the number of microcavities increases progressively with the time and temperature; (3) because of the hydrolysis of PCs, the theoretical values of equilibrium moisture Mm and diffusivity Dx are higher than the experimental values.
In the hot water of 40℃, 60℃, 80℃ and 100℃, the hot water aging of Bayer-PC, Japan-PC and Korea-PC was investigated. The number of samples is 9 in the aging time of 0~200 h. The law of water absorption in the process of hot water aging and the effects of different hot water aging conditions on the surface fracture appearances of PCs were studied. The hot water aging mechanism of PCs was discussed. The results show: (1) with increasing of time and temperature, the moisture content increases and goes a equilibrium value; (2) the number of microcavities increases progressively with the time and temperature; (3) because of the hydrolysis of PCs, the theoretical values of equilibrium moisture Mm and diffusivity Dx are higher than the experimental values.
2001, 18(1): 30-33.
Abstract:
The permeability of fibrous reinforcement is the important parameter for studying and simulating RTM process. In this paper, the unidirectional glass fabric was used to determine the permeability of different kinds of layers under constant injection pressure. During the experiment, the long axis and the short axis of the ellipse, which was formed by the resin flowing in the fabric, were recorded, and the Darcy's law was used to calculate the permeability. The effect of layers on permeability was studied. The results indicate that the orientation of layers influences the value and principal direction of permeability, and it can be determined by the superposition of the ellipse of each single layer.
The permeability of fibrous reinforcement is the important parameter for studying and simulating RTM process. In this paper, the unidirectional glass fabric was used to determine the permeability of different kinds of layers under constant injection pressure. During the experiment, the long axis and the short axis of the ellipse, which was formed by the resin flowing in the fabric, were recorded, and the Darcy's law was used to calculate the permeability. The effect of layers on permeability was studied. The results indicate that the orientation of layers influences the value and principal direction of permeability, and it can be determined by the superposition of the ellipse of each single layer.
2001, 18(1): 34-37.
Abstract:
The moisture diffusion behavior of several types of domestic polymer matrix composites was systematically studied and their basic moisture diffusion parameters, such as the equilibrium moisture content Mm, the constants a and b in the relationship between Mm and relative humidity φ, the moisture diffusion coefficient in the direction of laminate thickness Dx, the constants ΔE(the active energy of moisture diffusion)and D0 in the relationship of Dx and temperature T, were obtained.
The moisture diffusion behavior of several types of domestic polymer matrix composites was systematically studied and their basic moisture diffusion parameters, such as the equilibrium moisture content Mm, the constants a and b in the relationship between Mm and relative humidity φ, the moisture diffusion coefficient in the direction of laminate thickness Dx, the constants ΔE(the active energy of moisture diffusion)and D0 in the relationship of Dx and temperature T, were obtained.
2001, 18(1): 38-41.
Abstract:
Based on the modification of bismaleimide by allyl compound, a new type of high performance resin film which is suitable for resin film infusion (RFI) process is synthesized by employing poly(ethersulfone)(PES).The film is stable at room temperature and shows good properties of toughness and inadhesiveness. The main properties of the cured resin are 535 MPa for flexural strength, 16.7 MPa for impact strength, and 236 ℃ for HDT. It can be seen that flexural strength and impaet strength are much better than X4502 which is reported in Refs.[8], and HDT is a little less than that in Refs.[8].Comparitions were also reported for composite samples of same resin and fibre systems which were processed using the wet lay-up with autoclave consolidation and RFI. The result shows that the matrix dominated property(i.e. ILLS) is higher for the RFI samples due to the reduced void content and improved wetting, and the fibre dominated properties are similar due to the similar volume fraction. The glass fibre cloth composite manufactured by RFI has execellent synthetical performance.
Based on the modification of bismaleimide by allyl compound, a new type of high performance resin film which is suitable for resin film infusion (RFI) process is synthesized by employing poly(ethersulfone)(PES).The film is stable at room temperature and shows good properties of toughness and inadhesiveness. The main properties of the cured resin are 535 MPa for flexural strength, 16.7 MPa for impact strength, and 236 ℃ for HDT. It can be seen that flexural strength and impaet strength are much better than X4502 which is reported in Refs.[8], and HDT is a little less than that in Refs.[8].Comparitions were also reported for composite samples of same resin and fibre systems which were processed using the wet lay-up with autoclave consolidation and RFI. The result shows that the matrix dominated property(i.e. ILLS) is higher for the RFI samples due to the reduced void content and improved wetting, and the fibre dominated properties are similar due to the similar volume fraction. The glass fibre cloth composite manufactured by RFI has execellent synthetical performance.
2001, 18(1): 42-45.
Abstract:
Trilobal polycarbosilane(PCS) fibers were prepared by melt spinning PCS precursor through Y-shaped spinneret. Then, after curing in air and heat treatment under N2 atmosphere, trilobal silicon carbide fibers were manufactured. The effect of spinning temperature and velocity on the fibers degree of profile was analyzed. Preparation conditions such as curing, heat-treatment and microwave-absorbing properties were also studied. Compared with circular SiC fibers, the fiber exhibits higher mechanical properties and microwave-absorbing properties. The structural radar absorbing materials, composed of the fibers with resin, exhibit a reflection attenuation amount of 10~20 dB in the range of 8~18 GHz.
Trilobal polycarbosilane(PCS) fibers were prepared by melt spinning PCS precursor through Y-shaped spinneret. Then, after curing in air and heat treatment under N2 atmosphere, trilobal silicon carbide fibers were manufactured. The effect of spinning temperature and velocity on the fibers degree of profile was analyzed. Preparation conditions such as curing, heat-treatment and microwave-absorbing properties were also studied. Compared with circular SiC fibers, the fiber exhibits higher mechanical properties and microwave-absorbing properties. The structural radar absorbing materials, composed of the fibers with resin, exhibit a reflection attenuation amount of 10~20 dB in the range of 8~18 GHz.
2001, 18(1): 46-49.
Abstract:
This paper is mainly about the study on the processing and mechanical performance of glass-fiber composite springs. The processing parameters of cylindroid spiral springs were confirmed on the basis of a large number of experiments. Influence of processing technology and structure parameters of the composite spring on bending resilience, bending restoration rate and tensile property was also tested and analysed.The experimental results indicate that bending mechanical performance of the composite spring is directly associated with the inside diameter of the spring, and the diameter, twist and number of fiber bundles. The bending restoration rate of the composite spring is under the influence of bending time and restoration time. The processing and structure parameters can be regulated according to specific conditions.
This paper is mainly about the study on the processing and mechanical performance of glass-fiber composite springs. The processing parameters of cylindroid spiral springs were confirmed on the basis of a large number of experiments. Influence of processing technology and structure parameters of the composite spring on bending resilience, bending restoration rate and tensile property was also tested and analysed.The experimental results indicate that bending mechanical performance of the composite spring is directly associated with the inside diameter of the spring, and the diameter, twist and number of fiber bundles. The bending restoration rate of the composite spring is under the influence of bending time and restoration time. The processing and structure parameters can be regulated according to specific conditions.
2001, 18(1): 50-54.
Abstract:
In this paper, CF was treated by the surface continuous grafting technology of cold plasma. The changes of characteristic groups and surface feature of CF surface were analysed by means of XPS. The interlayer shear strength, tensile strength and impact strength of CF/PMR-15 were measured, and the influence of surface grafting on the interface strength and toughness of CF/PMR-15 was studied.
In this paper, CF was treated by the surface continuous grafting technology of cold plasma. The changes of characteristic groups and surface feature of CF surface were analysed by means of XPS. The interlayer shear strength, tensile strength and impact strength of CF/PMR-15 were measured, and the influence of surface grafting on the interface strength and toughness of CF/PMR-15 was studied.
2001, 18(1): 55-57.
Abstract:
In the course of making polystyrene-barium titanate composites, due to diffusion, etc, there exist interfaces between the scattered grains and the host medium. The dielectric properties of the interfaces are different from the dielectric properties of polystyrene and barium titanate. Considering the interfaces between polystyrene and barium titanate, a new "complex model" of dielectric constant of two-phase composites is built up. Starting from the average polarization theory and Maxwell-Garnett theory, the effective dielectric constant of two-phase random composites with an interface is presented. When the volume fraction of the scatter grain is smaller than 20%, the theoretical results on dielectric properties of polystyrene-barium titanate composites with interface are in good agreement with experimental data.
In the course of making polystyrene-barium titanate composites, due to diffusion, etc, there exist interfaces between the scattered grains and the host medium. The dielectric properties of the interfaces are different from the dielectric properties of polystyrene and barium titanate. Considering the interfaces between polystyrene and barium titanate, a new "complex model" of dielectric constant of two-phase composites is built up. Starting from the average polarization theory and Maxwell-Garnett theory, the effective dielectric constant of two-phase random composites with an interface is presented. When the volume fraction of the scatter grain is smaller than 20%, the theoretical results on dielectric properties of polystyrene-barium titanate composites with interface are in good agreement with experimental data.
2001, 18(1): 58-61.
Abstract:
In order to obtain better mechanical properties, fine particles in several micron or submicron diameter were used as reinforcement to reduce stress concentration usually induced by larger particles. Zn-22%Al matrix composites with alumina particulate reinforcement were fabricated by high intensity ultrasonic treatment. The diameters of particulates were different and the minimum one was 0.5 micron. Comparing the height changes of composites before and after remelt which have been degassed with semisolid compression, the relation between apparent viscosity and reinforcement diameter was obtained. Experiment results show that there is no interface reaction product involved in the apparent viscosity change. The smaller the particulate, the bigger the viscous force. That is the dominating reason for the composite melt apparent viscosity increment. And the gas introduced with particulate is another reason.
In order to obtain better mechanical properties, fine particles in several micron or submicron diameter were used as reinforcement to reduce stress concentration usually induced by larger particles. Zn-22%Al matrix composites with alumina particulate reinforcement were fabricated by high intensity ultrasonic treatment. The diameters of particulates were different and the minimum one was 0.5 micron. Comparing the height changes of composites before and after remelt which have been degassed with semisolid compression, the relation between apparent viscosity and reinforcement diameter was obtained. Experiment results show that there is no interface reaction product involved in the apparent viscosity change. The smaller the particulate, the bigger the viscous force. That is the dominating reason for the composite melt apparent viscosity increment. And the gas introduced with particulate is another reason.
2001, 18(1): 62-66.
Abstract:
The SiCP/Al composite brake disc designed for the front brake of SANTANA cars was prepared by semi-solid stirring melting and liquid forging. The tensile properties and microstructures of the disc materials were examined, and the tribological-wear performances of the disc were tested on the SCHENCK brake testing system made in Germany. The results show that the tensile properties of the composites are superior to those of the conventional disc material, grey cast iron; and that under different braking conditions, the friction coefficients of the composite disc against the conventional brake pad are within the range specified by the standard of VOLKSWAGEN company and with small fluctuations. It is also found that the brake disc made of the composite has such advantages as light weight, high wear resistance, low braking noise and low braking temperature rises, smooth operating, etc. Hence, it is hopeful to substitute the composite disc for the traditional cast iron disc to increase reliability and to prolong the survice life of the car brake, to lighten the weight of the hanging system, and thus, to decrease gas expenditure of cars.
The SiCP/Al composite brake disc designed for the front brake of SANTANA cars was prepared by semi-solid stirring melting and liquid forging. The tensile properties and microstructures of the disc materials were examined, and the tribological-wear performances of the disc were tested on the SCHENCK brake testing system made in Germany. The results show that the tensile properties of the composites are superior to those of the conventional disc material, grey cast iron; and that under different braking conditions, the friction coefficients of the composite disc against the conventional brake pad are within the range specified by the standard of VOLKSWAGEN company and with small fluctuations. It is also found that the brake disc made of the composite has such advantages as light weight, high wear resistance, low braking noise and low braking temperature rises, smooth operating, etc. Hence, it is hopeful to substitute the composite disc for the traditional cast iron disc to increase reliability and to prolong the survice life of the car brake, to lighten the weight of the hanging system, and thus, to decrease gas expenditure of cars.
2001, 18(1): 67-70.
Abstract:
In order to recover aluminum from aluminum matrix composites,the appropriate compound salt was prepared and the removal behavior of reinforcing materials from particle reinforced aluminum matrix composites was investigated experimentally by using molten salt process. The recovery of aluminum was measured by microscopic test and X-ray diffraction(XRD).The results indicate that the reinforcing materials can be eliminated from aluminum matrix composites by some molten salts,and the recovery ratio is about 85%.
In order to recover aluminum from aluminum matrix composites,the appropriate compound salt was prepared and the removal behavior of reinforcing materials from particle reinforced aluminum matrix composites was investigated experimentally by using molten salt process. The recovery of aluminum was measured by microscopic test and X-ray diffraction(XRD).The results indicate that the reinforcing materials can be eliminated from aluminum matrix composites by some molten salts,and the recovery ratio is about 85%.
2001, 18(1): 71-75.
Abstract:
In this paper, mechanical properties of TiC-Ni cermets were investigated, which were produced by new technique——self-propagating high-temperature combustion synthesis combined with forced compaction. The results showed that HRA hardness and bending strength reached the maximum values when Ni content was 20 wt%, and a fracture toughness maximum was obtained when Ni content was 30 wt%. At room temperature, the fracture of TiC-Ni cermets is characterized as brittle fracture. At high temperature, bending strength of TiC-Ni cermets decreased with temperature increasing and plastic distortion took place beyond 1000℃. The strength of TiC-Ni cermets is close to that of the materials with similar composition prepared by traditional powder metallurgy process.
In this paper, mechanical properties of TiC-Ni cermets were investigated, which were produced by new technique——self-propagating high-temperature combustion synthesis combined with forced compaction. The results showed that HRA hardness and bending strength reached the maximum values when Ni content was 20 wt%, and a fracture toughness maximum was obtained when Ni content was 30 wt%. At room temperature, the fracture of TiC-Ni cermets is characterized as brittle fracture. At high temperature, bending strength of TiC-Ni cermets decreased with temperature increasing and plastic distortion took place beyond 1000℃. The strength of TiC-Ni cermets is close to that of the materials with similar composition prepared by traditional powder metallurgy process.
2001, 18(1): 76-78.
Abstract:
Eutectic Al-Si composite in situ was fabricated under the condition of direct magnetic field. Eutectic segregate happened,which formed the enrichment layer of silicon in the cylindrical sample surface, and the thickness of the segregation layer grows with the increase of the magnetic induction intensity. Effect mechanism of the direct magnetic field on the microstructures' formation disciplinarian of composite in situ has been discussed.
Eutectic Al-Si composite in situ was fabricated under the condition of direct magnetic field. Eutectic segregate happened,which formed the enrichment layer of silicon in the cylindrical sample surface, and the thickness of the segregation layer grows with the increase of the magnetic induction intensity. Effect mechanism of the direct magnetic field on the microstructures' formation disciplinarian of composite in situ has been discussed.
2001, 18(1): 79-82.
Abstract:
The uniform, transparent anatase Sn-doped TiO2 composite thin films deposited on glass substrates were prepared by sol-gel processing. Sn-doped TiO2 films were composed of TiO2 sphere particles in size of 50~100 nm. The thickness of TiO2 films prepared by 1 cycle (from dipping to teat-treatment at 500℃,1 h) is 0.09 μm or so. Anatase TiO2 films show some orientation effect in (101) peak. XPS results have showed that besides Ti, O and Sn elements in films there are a certain amount of residual carbon from the starting organometallic components and a small amount of Na and Ca elements diffused from the glass substrates. Photo-catalytic degradation of Methyl orange aqueous solution has indicated that the sol-gel derived Sn-doped TiO2 films show good photo-catalytic activity, and its apparent degradation rate constant k is larger than that of un-doped TiO2 films. These results are explained on the basis of the principle of charge separation in an SnO2/TiO2 composite semiconductor system.
The uniform, transparent anatase Sn-doped TiO2 composite thin films deposited on glass substrates were prepared by sol-gel processing. Sn-doped TiO2 films were composed of TiO2 sphere particles in size of 50~100 nm. The thickness of TiO2 films prepared by 1 cycle (from dipping to teat-treatment at 500℃,1 h) is 0.09 μm or so. Anatase TiO2 films show some orientation effect in (101) peak. XPS results have showed that besides Ti, O and Sn elements in films there are a certain amount of residual carbon from the starting organometallic components and a small amount of Na and Ca elements diffused from the glass substrates. Photo-catalytic degradation of Methyl orange aqueous solution has indicated that the sol-gel derived Sn-doped TiO2 films show good photo-catalytic activity, and its apparent degradation rate constant k is larger than that of un-doped TiO2 films. These results are explained on the basis of the principle of charge separation in an SnO2/TiO2 composite semiconductor system.
2001, 18(1): 83-88.
Abstract:
SiO2-AlN composites were prepared by hot-pressing process. Mechanical properties of SiO2 matrix can be greatly improved after incorporating AlN particles. Flexural strength and fracture toughness of SiO2-AlN composites with 30 vol% AlN particles sintered at 1400℃ reached 200 MPa and 2.96 MPa·m1/2 respectively. XRD analysis indicated that no chemical reaction occurred between SiO 2 matrix and AlN particles suggesting that SiO2 matrix had excellent chemical compatibility with AlN particles. Microstructure of the as-sintered composites was investigated with SEM and TEM analysis. The relationship among the phase composition and microstructure and mechanical properties was discussed.
SiO2-AlN composites were prepared by hot-pressing process. Mechanical properties of SiO2 matrix can be greatly improved after incorporating AlN particles. Flexural strength and fracture toughness of SiO2-AlN composites with 30 vol% AlN particles sintered at 1400℃ reached 200 MPa and 2.96 MPa·m1/2 respectively. XRD analysis indicated that no chemical reaction occurred between SiO 2 matrix and AlN particles suggesting that SiO2 matrix had excellent chemical compatibility with AlN particles. Microstructure of the as-sintered composites was investigated with SEM and TEM analysis. The relationship among the phase composition and microstructure and mechanical properties was discussed.
2001, 18(1): 89-92.
Abstract:
Compared with high pure graphite, the internal friction characteristics of pyrolytic carbon matrix carbon-carbon composites were studied in the present work. According to experimental results, two internal friction mechanisms are proposed: thermoelastic and static hysteresis mechanisms. The effects of interface between carbon fibers and carbon matrix play important roles on the internal friction characters of carbon-carbon composites, which leads to some unique internal friction phenomena in carbon-carbon composites.
Compared with high pure graphite, the internal friction characteristics of pyrolytic carbon matrix carbon-carbon composites were studied in the present work. According to experimental results, two internal friction mechanisms are proposed: thermoelastic and static hysteresis mechanisms. The effects of interface between carbon fibers and carbon matrix play important roles on the internal friction characters of carbon-carbon composites, which leads to some unique internal friction phenomena in carbon-carbon composites.
2001, 18(1): 93-96.
Abstract:
Concerning the existing methods (empty element technique and embedded process zone method used for releasing nodal forces) applied to the numerical simulation of damage and cracking in materials, a new method of modeling is proposed for releasing the internal nodal forces of the empty elements. It provides a way to release the residual stresses which are not specified by the previous empty element technique, but without resort to using redundant overlap nodes as that in the embedded process zone method. Previous computation examples have demonstrated that this method has the advantages of simple modeling and convenient implementation.
Concerning the existing methods (empty element technique and embedded process zone method used for releasing nodal forces) applied to the numerical simulation of damage and cracking in materials, a new method of modeling is proposed for releasing the internal nodal forces of the empty elements. It provides a way to release the residual stresses which are not specified by the previous empty element technique, but without resort to using redundant overlap nodes as that in the embedded process zone method. Previous computation examples have demonstrated that this method has the advantages of simple modeling and convenient implementation.
2001, 18(1): 97-100.
Abstract:
The Eshelby equivalent inclusion method is used to study the viscoelastic problem of polymeric composite materials. The creep constitutive relations of particulate reinforced composites are investigated by Laplace transformation and the corresponding principle. The variation of the moduli of materials with time and inclusion volume fraction is given, and the theoretical prediction coincides with experimental results.
The Eshelby equivalent inclusion method is used to study the viscoelastic problem of polymeric composite materials. The creep constitutive relations of particulate reinforced composites are investigated by Laplace transformation and the corresponding principle. The variation of the moduli of materials with time and inclusion volume fraction is given, and the theoretical prediction coincides with experimental results.
2001, 18(1): 101-104.
Abstract:
A study on the structure and property of uneven hot-resistant functionally gradient materials was introduced in this paper.The macro- and meso-scopic mechanical model was established by analyzing ceramic-metals FGM structure. Based on this analytical model,a three-dimensional constitutive relation reflecting its macro-properties was derived.
A study on the structure and property of uneven hot-resistant functionally gradient materials was introduced in this paper.The macro- and meso-scopic mechanical model was established by analyzing ceramic-metals FGM structure. Based on this analytical model,a three-dimensional constitutive relation reflecting its macro-properties was derived.
2001, 18(1): 105-108.
Abstract:
These series works are concentrated on finding the general solutions in smart materials and structures. In order to find the solutions of a piezoelectric cantilever beam under different kinds of load conditions, the semi-inverse method is used. As the first part of all, the present paper deals with a piezoelectric cantilever beam subjected to a couple of forces. Some important parameters of the electro-mechanical fields are obtained and discussed. Several distribution curves such as stress and electric potential for material PZT (i.e. Pb(Ti0.48Zr0.52)O3) are given. It should be pointed out that the material is functionally gradient in density.
These series works are concentrated on finding the general solutions in smart materials and structures. In order to find the solutions of a piezoelectric cantilever beam under different kinds of load conditions, the semi-inverse method is used. As the first part of all, the present paper deals with a piezoelectric cantilever beam subjected to a couple of forces. Some important parameters of the electro-mechanical fields are obtained and discussed. Several distribution curves such as stress and electric potential for material PZT (i.e. Pb(Ti0.48Zr0.52)O3) are given. It should be pointed out that the material is functionally gradient in density.
2001, 18(1): 109-111.
Abstract:
As the second part of these series works, the present paper deals with the piezoelectric cantilever beam under tension by use of the semi-inverse method. The piezoelectric cantilever beam is considered under three different cases: without body force, with constant body force and with gradient body force. The general solutions of the electro-mechanical fields in the smart beam are obtained and discussed.
As the second part of these series works, the present paper deals with the piezoelectric cantilever beam under tension by use of the semi-inverse method. The piezoelectric cantilever beam is considered under three different cases: without body force, with constant body force and with gradient body force. The general solutions of the electro-mechanical fields in the smart beam are obtained and discussed.
2001, 18(1): 112-114.
Abstract:
As the third part of these series works, the present paper deals with a piezoelectric cantilever beam subjected to a transverse concentrated force at the free end. The general solutions of the electro-mechanical fields in the smart beam are obtained and discussed by use of the semi-inverse method. In order to get a solution clearly and comparably, a piezoelectric cantilever beam is considered under three different cases: without body force, with constant body force and with gradient body force.
As the third part of these series works, the present paper deals with a piezoelectric cantilever beam subjected to a transverse concentrated force at the free end. The general solutions of the electro-mechanical fields in the smart beam are obtained and discussed by use of the semi-inverse method. In order to get a solution clearly and comparably, a piezoelectric cantilever beam is considered under three different cases: without body force, with constant body force and with gradient body force.
2001, 18(1): 115-119.
Abstract:
Compressive failure tests were carried out on composite laminates and stitched laminates after low velocity impact to study compressive failure mechanisms of laminates after low velocity impact. Methods of X-ray, C-scan, deply, etc were used to measure and to record the internal and external damage of the laminates. The implications of this study were that sub-laminate buckling and the delamination expending were the important factors causing large reductions in strength while CFRP laminates were compressed after low velocity impact if the interface properties were not very fine. And the buckling area expended mainly in the direction perpendicular to the compressive load. For quasi-isotropic composite laminates, the orientation of the ply in buckled sub-laminate next to parent medium was generally 90°. There was no direct relation between residual compressive strength and impact damage area.
Compressive failure tests were carried out on composite laminates and stitched laminates after low velocity impact to study compressive failure mechanisms of laminates after low velocity impact. Methods of X-ray, C-scan, deply, etc were used to measure and to record the internal and external damage of the laminates. The implications of this study were that sub-laminate buckling and the delamination expending were the important factors causing large reductions in strength while CFRP laminates were compressed after low velocity impact if the interface properties were not very fine. And the buckling area expended mainly in the direction perpendicular to the compressive load. For quasi-isotropic composite laminates, the orientation of the ply in buckled sub-laminate next to parent medium was generally 90°. There was no direct relation between residual compressive strength and impact damage area.
2001, 18(1): 120-127.
Abstract:
In this paper, the mechanical behaviors of 2124, Al-5Cu, Al-Li and 6061 alloys reinforced by silicon carbide particulate, together with the silicon carbide whisker reinforced 6061 Al alloy, were studied under quasi-static and impact loading conditions, by using the Split Hopkinson Tension / Compressure Bars and Instron universal testing machine. The effect of the strain rate on the UTS, hardening modulus, and failure strain was investigated. At the same time, the SEM observations of dynamic fracture surfaces of various MMC materials showed some distinguished failure characteristics, which determined the sensitivity of the strain rate of failure strain and the asymmetry of tension and pressure of MMC materials. Some new characteristics of asymmetry of mechanical behaviors of MMC materials under tension and compression loadings were also presented and explained in details in this paper, which can be considered as flags, to some degree, to determine the controlling mechanism of damage and failure of metal matrix composites under impact loading. The development of new constitutive laws about MMC materials under impact loadings should benefit from these experiment results and theoretical analysis.
In this paper, the mechanical behaviors of 2124, Al-5Cu, Al-Li and 6061 alloys reinforced by silicon carbide particulate, together with the silicon carbide whisker reinforced 6061 Al alloy, were studied under quasi-static and impact loading conditions, by using the Split Hopkinson Tension / Compressure Bars and Instron universal testing machine. The effect of the strain rate on the UTS, hardening modulus, and failure strain was investigated. At the same time, the SEM observations of dynamic fracture surfaces of various MMC materials showed some distinguished failure characteristics, which determined the sensitivity of the strain rate of failure strain and the asymmetry of tension and pressure of MMC materials. Some new characteristics of asymmetry of mechanical behaviors of MMC materials under tension and compression loadings were also presented and explained in details in this paper, which can be considered as flags, to some degree, to determine the controlling mechanism of damage and failure of metal matrix composites under impact loading. The development of new constitutive laws about MMC materials under impact loadings should benefit from these experiment results and theoretical analysis.
2001, 18(1): 128-130.
Abstract:
The behavior of the digital shearing speckle fringe formation was discussed systematically with the theory of statistical optics. Quantitative NDT of bimaterial interface defects was achieved by using the phase-shifting shearing speckle interferometry system with non-contact, high accuracy, full-field and real-time.
The behavior of the digital shearing speckle fringe formation was discussed systematically with the theory of statistical optics. Quantitative NDT of bimaterial interface defects was achieved by using the phase-shifting shearing speckle interferometry system with non-contact, high accuracy, full-field and real-time.
