2004 Vol. 21, No. 3
2004, 21(3): 1-5.
Abstract:
Residual strain and residual stress formed in cure process are two key factors that affect the quality of composite products, and both of them correlate closely with the process induced strain of pre-preg. In this paper,the fiber Bragg grating (FBG) sensors were calibrated and embedded in pre-preg to in-situ monitor the strain and temperature evolution of laminates during the cure process. Based on the strain measured with the FBG sensors, the macro residual strain of the cross-ply laminate was studied. The results show that both of unidirectional and cross-ply laminates will shrink in the course of cure. There is a negative residual strain in the longitudinal direction and a positive residual strain in the transverse direction of any ply of a cross-ply laminate. The FBG sensor can be used as a new tool to monitor the cure process and analyze the residual stress of composites, and makes it possible to monitor composite structures from manufacture stage to service stage continuously.
Residual strain and residual stress formed in cure process are two key factors that affect the quality of composite products, and both of them correlate closely with the process induced strain of pre-preg. In this paper,the fiber Bragg grating (FBG) sensors were calibrated and embedded in pre-preg to in-situ monitor the strain and temperature evolution of laminates during the cure process. Based on the strain measured with the FBG sensors, the macro residual strain of the cross-ply laminate was studied. The results show that both of unidirectional and cross-ply laminates will shrink in the course of cure. There is a negative residual strain in the longitudinal direction and a positive residual strain in the transverse direction of any ply of a cross-ply laminate. The FBG sensor can be used as a new tool to monitor the cure process and analyze the residual stress of composites, and makes it possible to monitor composite structures from manufacture stage to service stage continuously.
2004, 21(3): 6-10.
Abstract:
The resin flow in RTM process for thick section parts was investigated. A program HEXCV for three dimensional resin flow process was developed based on the hexahedral element with the finite element/control volume method (FE/CVM). The accuracy and the reliability of the HEXCV program were confirmed, compared with the analytical solutions. Numerical examples show that the HEXCV program can provide an effective reference for the process design.
The resin flow in RTM process for thick section parts was investigated. A program HEXCV for three dimensional resin flow process was developed based on the hexahedral element with the finite element/control volume method (FE/CVM). The accuracy and the reliability of the HEXCV program were confirmed, compared with the analytical solutions. Numerical examples show that the HEXCV program can provide an effective reference for the process design.
2004, 21(3): 11-16.
Abstract:
Two types of gel were made using Barium Titanate particles dispersed in gelatin containing water in the absence/presence of the applied DC electric field. The microstructures of the particles in the two types of gel were observed by a microscopical method. The compression moduli of the gels were measured as a function of weight percent Barium Titanate in the gels and applied electric field strength for curing and measuring. Consequently, it is shown that the particles were aligned in the gel by the applied DC electric field, the compression modulus of the gel could be increased by pre-aligning the particles in the gel and the applied DC electric field for curing and measuring, and the response to the applied electric field could be increased by the aligned particles. The mechanical behavior of the gels can be controlled by the electric field strength.
Two types of gel were made using Barium Titanate particles dispersed in gelatin containing water in the absence/presence of the applied DC electric field. The microstructures of the particles in the two types of gel were observed by a microscopical method. The compression moduli of the gels were measured as a function of weight percent Barium Titanate in the gels and applied electric field strength for curing and measuring. Consequently, it is shown that the particles were aligned in the gel by the applied DC electric field, the compression modulus of the gel could be increased by pre-aligning the particles in the gel and the applied DC electric field for curing and measuring, and the response to the applied electric field could be increased by the aligned particles. The mechanical behavior of the gels can be controlled by the electric field strength.
2004, 21(3): 17-21.
Abstract:
The linear heating apparatus formed by resistance wire was designed to investigate the formation of the microstructures of the cured epoxy resin. The network of the gel states was analyzed by means of SEM. And 3D Temperature Testing Instrument was employed to survey the temperature distributions in the curing epoxy resin system heated by resistance wire. The results show that the microstructures of the cured resin, heated by linear resistance wire, exhibit the formation of the gel state of the cured resin heated homogeneously. It indicates that the temperatures of the curing resin are greatly affected by the content of the curing agent. These are of great value in understanding the effects of microstructure development and temperature distribution on the composites manufacturing process.
The linear heating apparatus formed by resistance wire was designed to investigate the formation of the microstructures of the cured epoxy resin. The network of the gel states was analyzed by means of SEM. And 3D Temperature Testing Instrument was employed to survey the temperature distributions in the curing epoxy resin system heated by resistance wire. The results show that the microstructures of the cured resin, heated by linear resistance wire, exhibit the formation of the gel state of the cured resin heated homogeneously. It indicates that the temperatures of the curing resin are greatly affected by the content of the curing agent. These are of great value in understanding the effects of microstructure development and temperature distribution on the composites manufacturing process.
2004, 21(3): 22-27.
Abstract:
The electrochemical characterization, the chemical components and morphology of PAN-based carbon fibers treated by electrochemical oxidation in aqueous ammonium bicarbonate were analyzed using cyclic voltammetry, XPS and AFM. The results indicate that the electrolyzing reaction of water and the electrochemical oxide reaction of electro active materials are the main reactions taking place on the fiber surface in aqueous ammonium bicarbonate. The contents of every functional groups contained oxygen are changed during the treatment process. Amide functional groups are introduced on the fiber surface by the reactions of NH＋4 and the active functional groups. The morphology of the fiber surface is more and more rough with the treatment time extending under the coupling action of oxidizing erosion and gas etching.
The electrochemical characterization, the chemical components and morphology of PAN-based carbon fibers treated by electrochemical oxidation in aqueous ammonium bicarbonate were analyzed using cyclic voltammetry, XPS and AFM. The results indicate that the electrolyzing reaction of water and the electrochemical oxide reaction of electro active materials are the main reactions taking place on the fiber surface in aqueous ammonium bicarbonate. The contents of every functional groups contained oxygen are changed during the treatment process. Amide functional groups are introduced on the fiber surface by the reactions of NH＋4 and the active functional groups. The morphology of the fiber surface is more and more rough with the treatment time extending under the coupling action of oxidizing erosion and gas etching.
2004, 21(3): 28-32.
Abstract:
The effects of electrochemical treatment of carbon fibers in different aqueous phosphate were investigated. The Latin square experiment was used to optimize the treatment parameters. The chemical components, morphology and specific area of fibers surface were characterized by using XPS, AFM and BET technique.The results indicate that the specific current density and the electrolyte concentration are the significant factors in fiber surface treatment in (NH4)2HPO4 and NH4H2PO4 solutions, respectively. The effect of modification is very outstanding in (NH4)2HPO4 solution because the oxidation and corrosion are moderate, and the ILSS of its composite is increased to 79.8 MPa. Whereas the effect of modification is difficult to control in NH4H2PO4 solution due to the drastic oxidation and corrosion, the tensile strength of the bulk fiber is damaged greatly and the ILSS of its composites is increased only to 70.8 MPa.
The effects of electrochemical treatment of carbon fibers in different aqueous phosphate were investigated. The Latin square experiment was used to optimize the treatment parameters. The chemical components, morphology and specific area of fibers surface were characterized by using XPS, AFM and BET technique.The results indicate that the specific current density and the electrolyte concentration are the significant factors in fiber surface treatment in (NH4)2HPO4 and NH4H2PO4 solutions, respectively. The effect of modification is very outstanding in (NH4)2HPO4 solution because the oxidation and corrosion are moderate, and the ILSS of its composite is increased to 79.8 MPa. Whereas the effect of modification is difficult to control in NH4H2PO4 solution due to the drastic oxidation and corrosion, the tensile strength of the bulk fiber is damaged greatly and the ILSS of its composites is increased only to 70.8 MPa.
2004, 21(3): 33-37.
Abstract:
The heat-resistant silicone resin was filled with Co3O4 nanometer particles to prepare composites to absorb the heat radiation, which was coated on the heat flow transducer. To improve the interfacial properties between Co3O4 particles and the matrix resin and to prevent the nano-particles aggregating, the surfaces of Co3O4 particles were treated by grafting BMA on them. The grafting characteristics and graft ratio were investigated using infrared (IR) and thermogravimetric analysis (TGA). The effects of the surface treatment of Co3O4 particles on the interfacial, endothermal and thermal properties of the composites were analyzed using TEM, the calibrating test of the heat flow transducer, TGA and differential thermogravimetric analysis (DTG). It is found that the surface treatment of Co3O4 particles improves their dispersibility in silicone resin, and the response rate of the transducer is also improved greatly. The untreated Co3O4 particles deteriorate the thermal properties of the silicone resin. However, after surface treating of Co3O4 particles, its thermal properties are improved.
The heat-resistant silicone resin was filled with Co3O4 nanometer particles to prepare composites to absorb the heat radiation, which was coated on the heat flow transducer. To improve the interfacial properties between Co3O4 particles and the matrix resin and to prevent the nano-particles aggregating, the surfaces of Co3O4 particles were treated by grafting BMA on them. The grafting characteristics and graft ratio were investigated using infrared (IR) and thermogravimetric analysis (TGA). The effects of the surface treatment of Co3O4 particles on the interfacial, endothermal and thermal properties of the composites were analyzed using TEM, the calibrating test of the heat flow transducer, TGA and differential thermogravimetric analysis (DTG). It is found that the surface treatment of Co3O4 particles improves their dispersibility in silicone resin, and the response rate of the transducer is also improved greatly. The untreated Co3O4 particles deteriorate the thermal properties of the silicone resin. However, after surface treating of Co3O4 particles, its thermal properties are improved.
2004, 21(3): 38-43.
Abstract:
The composite materials of PANI/CNT were prepared by the in-situ polymerization. Transmitting electronic microscopy (TEM), ultraviolet visible spectrum (UV-VIS), Fourier transfer infrared spectrum (FTIR), thermal gravimetry analysis (TGA) and differential scanning calorimetry (DSC) were used to investigate the structures and properties of the composites. The results indicate that aniline (ANI) is preferentially polymerized on the surface of CNT to form a layer of polyaniline (PANI) on the CNT surface and the thickness of the layer increases with increasing ANI content in the reactants. An even PANI layer is built in case of lower ANI content in the reactants while an uneven layer with a few PANI particles adhered is built in higher ANI content. There is no chemical interaction between PANI and CNT. The PANI/CNT composites exhibit higher conductivity and excellent thermal properties and the thermal properties depend also on the loadings of PANI in the composites.
The composite materials of PANI/CNT were prepared by the in-situ polymerization. Transmitting electronic microscopy (TEM), ultraviolet visible spectrum (UV-VIS), Fourier transfer infrared spectrum (FTIR), thermal gravimetry analysis (TGA) and differential scanning calorimetry (DSC) were used to investigate the structures and properties of the composites. The results indicate that aniline (ANI) is preferentially polymerized on the surface of CNT to form a layer of polyaniline (PANI) on the CNT surface and the thickness of the layer increases with increasing ANI content in the reactants. An even PANI layer is built in case of lower ANI content in the reactants while an uneven layer with a few PANI particles adhered is built in higher ANI content. There is no chemical interaction between PANI and CNT. The PANI/CNT composites exhibit higher conductivity and excellent thermal properties and the thermal properties depend also on the loadings of PANI in the composites.
2004, 21(3): 44-48.
Abstract:
Stress oxidation and stress corrosion of an SiC-C/SiC composite under low frequency tensile-tensile cycle stress in multi-atmospheres at 1000℃, 1200℃ and 1300℃ were studied. The atmospheres include dry oxygen, water vapor, wet oxygen and Na2SO4 vapor mixed gas.The stress corrosion kinetic of the composite at 1300℃ was discussed by comparing the differences of lives when the specimens were exposed at different temperatures and in different atmospheres under the same cycle stress. It was found that oxygen is the major factor decreasing the life of the SiC-C/SiC composite under low frequency cycle stress at 1300℃. And the oxidation kinetic is controlled by the reaction between carbon fibers and oxygen under low frequency cycle stress between 1000℃ and 1300℃. The life prediction equation of SiC-C/SiC composites under cycle stress is suggested and validated well by experimental results.
Stress oxidation and stress corrosion of an SiC-C/SiC composite under low frequency tensile-tensile cycle stress in multi-atmospheres at 1000℃, 1200℃ and 1300℃ were studied. The atmospheres include dry oxygen, water vapor, wet oxygen and Na2SO4 vapor mixed gas.The stress corrosion kinetic of the composite at 1300℃ was discussed by comparing the differences of lives when the specimens were exposed at different temperatures and in different atmospheres under the same cycle stress. It was found that oxygen is the major factor decreasing the life of the SiC-C/SiC composite under low frequency cycle stress at 1300℃. And the oxidation kinetic is controlled by the reaction between carbon fibers and oxygen under low frequency cycle stress between 1000℃ and 1300℃. The life prediction equation of SiC-C/SiC composites under cycle stress is suggested and validated well by experimental results.
2004, 21(3): 49-53.
Abstract:
Preparation and mechanical and thermoelectric properties were studied for SiC-B4C composite films. The results show that thermal plasma PVD with SiC and B4C ultrafine powders as starting materials is a suitable method for the high-rate preparation of SiC-B4C composite films.The good qualified SiC-B4C composite films with a layer-by-layer structure were deposited at a maximum deposition rate of 356 nm/s. The micro Vickers hardness of the deposited films increases with the increasing of B4C content, and the maximum hardness of 35 GPa is obtained. The electrical resistivity and Seebeck coefficient decrease with the increasing of B4C content, and the maximum power factor at 973 K reaches 640 μWm-1K-2 which is 21 times that of sintered SiC.
Preparation and mechanical and thermoelectric properties were studied for SiC-B4C composite films. The results show that thermal plasma PVD with SiC and B4C ultrafine powders as starting materials is a suitable method for the high-rate preparation of SiC-B4C composite films.The good qualified SiC-B4C composite films with a layer-by-layer structure were deposited at a maximum deposition rate of 356 nm/s. The micro Vickers hardness of the deposited films increases with the increasing of B4C content, and the maximum hardness of 35 GPa is obtained. The electrical resistivity and Seebeck coefficient decrease with the increasing of B4C content, and the maximum power factor at 973 K reaches 640 μWm-1K-2 which is 21 times that of sintered SiC.
2004, 21(3): 54-58.
Abstract:
The carbon nanotubes were prepared by catalytic decomposition of benzene using floating transition method at 1100~1200℃. Benzene was used as carbon source and ferrocene as catalyst with thiophene. The carbon nanotubes are straight with diameter 20~50 nm, internal diameter 10~30 nm and length 50~1000 μm.The Ni-P and Ni-N alloy coatings on the carbon nanotubes were deposited by electroless deposition technique.The magnetic property of Ni-P and Ni-N alloy coated carbon nanotubes and the microwave absorbing property of their composites at 2~18 GHz were investigated. Compared with the carbon nanotube/epoxy resin composites, the absorbing peak of the Ni-P alloy coated carbon nanotube/epoxy resin composites moves to the higher frequency. The absorbing peaks of the epoxy resin matrix composites containing Ni-P and Ni-N alloy coated carbon nanotubes after heat-treatment move to lower frequency. The coercive forces for the Ni-P alloy coated carbon nanotubes, Ni-P and Ni-N alloy coated carbon nanotubes after heat-treatment are 304.34 Oe, 81.65 Oe, 183.85 Oe respectively. It is found that the microwave absorbing peaks of the three different composites move to the high frequency with the increase of the coercive force. The carbon nanotubes or Ni alloy coated carbon nanotubes are used as dipoles to absorb the microwave.
The carbon nanotubes were prepared by catalytic decomposition of benzene using floating transition method at 1100~1200℃. Benzene was used as carbon source and ferrocene as catalyst with thiophene. The carbon nanotubes are straight with diameter 20~50 nm, internal diameter 10~30 nm and length 50~1000 μm.The Ni-P and Ni-N alloy coatings on the carbon nanotubes were deposited by electroless deposition technique.The magnetic property of Ni-P and Ni-N alloy coated carbon nanotubes and the microwave absorbing property of their composites at 2~18 GHz were investigated. Compared with the carbon nanotube/epoxy resin composites, the absorbing peak of the Ni-P alloy coated carbon nanotube/epoxy resin composites moves to the higher frequency. The absorbing peaks of the epoxy resin matrix composites containing Ni-P and Ni-N alloy coated carbon nanotubes after heat-treatment move to lower frequency. The coercive forces for the Ni-P alloy coated carbon nanotubes, Ni-P and Ni-N alloy coated carbon nanotubes after heat-treatment are 304.34 Oe, 81.65 Oe, 183.85 Oe respectively. It is found that the microwave absorbing peaks of the three different composites move to the high frequency with the increase of the coercive force. The carbon nanotubes or Ni alloy coated carbon nanotubes are used as dipoles to absorb the microwave.
2004, 21(3): 59-62.
Abstract:
Effects of different Al contents(12.3%~25.4%,atomic fraction) on combustion synthesis of Ti3AlC2 powders were studied by using Ti,Al,C and TiC powders as raw materials in the Ti-Al-C system when the molar ratio of Ti/C was equal to 3∶2.The formation mechanism of Ti3AlC2 was investigated for different Al contents in the raw materials.The experiment results show that the phase formation of combustion synthesized Ti3AlC2 is affected greatly by the Al content in the raw materials.The amount of Ti3AlC2 in combustion products firstly increases with increasing Al content(12.3%~19.4%), and then decreases with continuously increasing amount of Al(20.6%~25.4%).
Effects of different Al contents(12.3%~25.4%,atomic fraction) on combustion synthesis of Ti3AlC2 powders were studied by using Ti,Al,C and TiC powders as raw materials in the Ti-Al-C system when the molar ratio of Ti/C was equal to 3∶2.The formation mechanism of Ti3AlC2 was investigated for different Al contents in the raw materials.The experiment results show that the phase formation of combustion synthesized Ti3AlC2 is affected greatly by the Al content in the raw materials.The amount of Ti3AlC2 in combustion products firstly increases with increasing Al content(12.3%~19.4%), and then decreases with continuously increasing amount of Al(20.6%~25.4%).
2004, 21(3): 63-68.
Abstract:
The Al2O3-Al2Cu3 multiphase coating was produced on an iron substrate by means of SHS reactive flame spraying with Al and CuO as main reactants ignited by the oxyacetylene flame. The morphology of the particles that were quenched and gathered up at different flying distances was observed.The constituent and microstructure of the coating were analyzed.The essential procedure of SHS spraying was summarized with regard to the special conditions of SHS chemical energy between Al and CuO and the physical and geometrical features of aggregated particles. It is concluded that the aggregated particles, acting as solo reactive units respectively, form into coating after going through four successive stages——pregnant reaction, flight combustion, collision, structure transformation and solidification. On the basis of this essential procedure, the reactive mechanism, structure transformation, solidifying behavior, microstructure and dominant factors in each stage were discussed in detail.
The Al2O3-Al2Cu3 multiphase coating was produced on an iron substrate by means of SHS reactive flame spraying with Al and CuO as main reactants ignited by the oxyacetylene flame. The morphology of the particles that were quenched and gathered up at different flying distances was observed.The constituent and microstructure of the coating were analyzed.The essential procedure of SHS spraying was summarized with regard to the special conditions of SHS chemical energy between Al and CuO and the physical and geometrical features of aggregated particles. It is concluded that the aggregated particles, acting as solo reactive units respectively, form into coating after going through four successive stages——pregnant reaction, flight combustion, collision, structure transformation and solidification. On the basis of this essential procedure, the reactive mechanism, structure transformation, solidifying behavior, microstructure and dominant factors in each stage were discussed in detail.
2004, 21(3): 69-72.
Abstract:
By use of compression modeling/sintering technique, a series of PST-PT/PVDF composites of different constitutions were prepared using a self-made model. SEM results show that the PST-PT ceramic particles dispersed equally in polymer. Dielectric properties of composites containing PST-PT dispersed in PVDF matrix having 0-3 connectivity were measured.The results indicate that the dielectric constant was strongly influenced by the relative proportions of the two constituents, temperature and frequency. The dielectric constant in the ferroelectric phase of PST-PT plays an important role in controlling the effective dielectric constant of the PST-PT/PVDF composites, especially for the composite containing 9%(mass fraction) PST-PT. Different from other samples, it is remarkable that the addition of 9% PST-PT to PVDF results in the appearance of a large peak of dielectric constant near 60℃.
By use of compression modeling/sintering technique, a series of PST-PT/PVDF composites of different constitutions were prepared using a self-made model. SEM results show that the PST-PT ceramic particles dispersed equally in polymer. Dielectric properties of composites containing PST-PT dispersed in PVDF matrix having 0-3 connectivity were measured.The results indicate that the dielectric constant was strongly influenced by the relative proportions of the two constituents, temperature and frequency. The dielectric constant in the ferroelectric phase of PST-PT plays an important role in controlling the effective dielectric constant of the PST-PT/PVDF composites, especially for the composite containing 9%(mass fraction) PST-PT. Different from other samples, it is remarkable that the addition of 9% PST-PT to PVDF results in the appearance of a large peak of dielectric constant near 60℃.
2004, 21(3): 73-78.
Abstract:
The 0-3 sulphoaluminate cement-based piezoelectric composites were fabricated by compressing technique.The effects of contents of PZT and poling conditions on piezoelectric properties of the composites were discussed.The results show that the piezoelectric properties of composites are improved by increasing the poling field E and poling time t.For the 0-3 sulphoaluminate cement-based piezoelectric composites,the optimum poling field E and poling time t are 4.0 kV/mm and 45 min respectively.The piezoelectric constant d33, g33 and the electromechanical coupling coefficient K</em>P,Kt of the composites increase rapidly with the increasing of PZT contents. When the content of PZT reaches 85%, KP and Kt are 28.54% and 28.19% respectively.
The 0-3 sulphoaluminate cement-based piezoelectric composites were fabricated by compressing technique.The effects of contents of PZT and poling conditions on piezoelectric properties of the composites were discussed.The results show that the piezoelectric properties of composites are improved by increasing the poling field E and poling time t.For the 0-3 sulphoaluminate cement-based piezoelectric composites,the optimum poling field E and poling time t are 4.0 kV/mm and 45 min respectively.The piezoelectric constant d33, g33 and the electromechanical coupling coefficient K</em>P,Kt of the composites increase rapidly with the increasing of PZT contents. When the content of PZT reaches 85%, KP and Kt are 28.54% and 28.19% respectively.
2004, 21(3): 79-83.
Abstract:
The tensile tests were made for the FRP wrapped rebar with glass fiber layers and a steel core. The results show that there is a good bilinear character in the mechanic behavior coming from such a new kind of rebar. The test result coincides with the theoretical prediction. It is the basement for the design and application of FRP rebar in concrete engineering.
The tensile tests were made for the FRP wrapped rebar with glass fiber layers and a steel core. The results show that there is a good bilinear character in the mechanic behavior coming from such a new kind of rebar. The test result coincides with the theoretical prediction. It is the basement for the design and application of FRP rebar in concrete engineering.
2004, 21(3): 84-90.
Abstract:
Compared to laminated composites, three-dimensional braided composites have higher inter-laminated shear strength and fracture toughness. The impact damage tolerance of a 3-D braided composite is higher than that of the laminated composite. The 3-D braided composite was perforated by a steel core projectile. The strike velocities and residual velocities of the projectile were measured, and the failure mode of the composite under ballistic impact was also investigated. All of the works on analysis and calculation of ballistic penetration of the 3-D braided composite so far were based on continuum assumption. It is still difficult to model the 3-D braided composite under ballistic impact from actual microstructure now. A fiber inclination model for the 3-D structural reinforced composite is employed to decompose it at quasi-microstructure hierarchy. The ballistic penetration property of one of the inclined laminae is calculated with FEM code. The residual velocity of the projectile that perforated the entire 3-D braided composite is obtained from the loss of kinetic energy of the projectile. From the simulation of ballistic penetration process and comparison between numerical results and experimental results, it proves that the analysis scheme of quasi-microstructure hierarchy in this paper is valid and reasonable.
Compared to laminated composites, three-dimensional braided composites have higher inter-laminated shear strength and fracture toughness. The impact damage tolerance of a 3-D braided composite is higher than that of the laminated composite. The 3-D braided composite was perforated by a steel core projectile. The strike velocities and residual velocities of the projectile were measured, and the failure mode of the composite under ballistic impact was also investigated. All of the works on analysis and calculation of ballistic penetration of the 3-D braided composite so far were based on continuum assumption. It is still difficult to model the 3-D braided composite under ballistic impact from actual microstructure now. A fiber inclination model for the 3-D structural reinforced composite is employed to decompose it at quasi-microstructure hierarchy. The ballistic penetration property of one of the inclined laminae is calculated with FEM code. The residual velocity of the projectile that perforated the entire 3-D braided composite is obtained from the loss of kinetic energy of the projectile. From the simulation of ballistic penetration process and comparison between numerical results and experimental results, it proves that the analysis scheme of quasi-microstructure hierarchy in this paper is valid and reasonable.
2004, 21(3): 91-95.
Abstract:
A 40 vol%SiCP/LD2 composite was fabricated by squeeze casting, and the effect of high volume fraction SiC particulates on aging characteristics at different aging temperatures was studied.The results show that the rengthening effect due to the addition of particles plays the leading role and aging strengthening is not the major strengthening mechanism for the high volume fraction SiCP/LD2 composite. With the increasing of temperature the precipitation processes become accelerated, and the time to reach the peak hardness is shortened. Comparatively, at low aging temperature the peak hardness of composite is the highest and the aging process is more accelerated than that of LD2 alloy. The formation of G.P. region is severely suppressed and the thermal diffusion activation energy of β' phase is decreased due to the addition of SiC particles, which causes the precipitation of β' phase easier and the precipitation temperature range wider than that of LD2 alloy.
A 40 vol%SiCP/LD2 composite was fabricated by squeeze casting, and the effect of high volume fraction SiC particulates on aging characteristics at different aging temperatures was studied.The results show that the rengthening effect due to the addition of particles plays the leading role and aging strengthening is not the major strengthening mechanism for the high volume fraction SiCP/LD2 composite. With the increasing of temperature the precipitation processes become accelerated, and the time to reach the peak hardness is shortened. Comparatively, at low aging temperature the peak hardness of composite is the highest and the aging process is more accelerated than that of LD2 alloy. The formation of G.P. region is severely suppressed and the thermal diffusion activation energy of β' phase is decreased due to the addition of SiC particles, which causes the precipitation of β' phase easier and the precipitation temperature range wider than that of LD2 alloy.
2004, 21(3): 96-101.
Abstract:
An analytical model was developed using the first-order laminated anisotropic plate theory to determine the stress and strain distributions within a composite pipe joint under combined torsional and tensile loading. Taking advantage of the axisymmetric nature of torsional and tensile loads about the pipe central axis, the equilibrium equations for the three-components joint system consisting of coupling, adhesive and pipe were set up based on the displacement relation. The adhesive peel stress and shear stress were calculated using the models for 54° and 26° filament-wound pipes, and good correlations were found when comparing these results with those from finite element models.
An analytical model was developed using the first-order laminated anisotropic plate theory to determine the stress and strain distributions within a composite pipe joint under combined torsional and tensile loading. Taking advantage of the axisymmetric nature of torsional and tensile loads about the pipe central axis, the equilibrium equations for the three-components joint system consisting of coupling, adhesive and pipe were set up based on the displacement relation. The adhesive peel stress and shear stress were calculated using the models for 54° and 26° filament-wound pipes, and good correlations were found when comparing these results with those from finite element models.
2004, 21(3): 102-109.
Abstract:
The relations between the interface models and the interphase model are studied for particle-reinforced composites . The imperfect interface condition which is equivalent to the effect of a thin interphase for a spherical particle is derived in terms of interface displacement and traction jumps, as is the linear spring interface condition which is equivalent to the effect of a thin interphase. According to the equivalent condition between the linear spring interface and the thin interphase with arbitrary elastic properties, the exact expressions of the spring constants are obtained.The numerical results show that by comparison with the exact solutions of the thin interphase model, high accuracy of the solutions in terms of the imperfect interface and linear spring interface is demonstrated at low modulus ratios of the interphase and the matrix. For the linear spring model, the possible normal interpenetration at the interface is discussed. The conditions for ensuring no interpenetration are established.
The relations between the interface models and the interphase model are studied for particle-reinforced composites . The imperfect interface condition which is equivalent to the effect of a thin interphase for a spherical particle is derived in terms of interface displacement and traction jumps, as is the linear spring interface condition which is equivalent to the effect of a thin interphase. According to the equivalent condition between the linear spring interface and the thin interphase with arbitrary elastic properties, the exact expressions of the spring constants are obtained.The numerical results show that by comparison with the exact solutions of the thin interphase model, high accuracy of the solutions in terms of the imperfect interface and linear spring interface is demonstrated at low modulus ratios of the interphase and the matrix. For the linear spring model, the possible normal interpenetration at the interface is discussed. The conditions for ensuring no interpenetration are established.
2004, 21(3): 110-114.
Abstract:
For three-dimensionally braided C/SiC composites,the tensile and compress experiments were carried out to get main mechanical characters, damage development and failure mechanisms under tensile and compress loads. The elastic properties and failure characters under two kinds of loads were compared and some experimental conclusions were deduced. It can be concluded from the stress-strain curves of the test that the damage development in three-dimensionally braided C/SiC composite specimens is continuous. The test results also reveal that the tensile modulus is less than the compress modulus and the tensile stress is greater than the compress stress. The acoustic emission data can reveal the damage development in C/SiC specimens.
For three-dimensionally braided C/SiC composites,the tensile and compress experiments were carried out to get main mechanical characters, damage development and failure mechanisms under tensile and compress loads. The elastic properties and failure characters under two kinds of loads were compared and some experimental conclusions were deduced. It can be concluded from the stress-strain curves of the test that the damage development in three-dimensionally braided C/SiC composite specimens is continuous. The test results also reveal that the tensile modulus is less than the compress modulus and the tensile stress is greater than the compress stress. The acoustic emission data can reveal the damage development in C/SiC specimens.
2004, 21(3): 115-119.
Abstract:
The dynamic response behavior and loaded capability were investigated for the delaminated composite plates considering the failure process. A formula of element stiffness and mass matrices for the composite laminates was deduced by using the first-order shear deformation theory combined with the selecting numerical integration scheme. A damping model was constituted on the basis of Rayleigh damping model. A delaminated constrained model and a virtual interface element were also developed for avoiding the overlap and penetration phenomenon between the upper and lower sub-laminates at the delamination region. The failure analysis method for the delaminated plates under dynamic loading was established by Tsai's failure criterion and corresponding 0.44 reduced stiffness role, and the dynamic equation was solved by the Newmark direct integral method. By some numerical examples, the effects of the frequency of dynamic load, delamination location, and reduction of structure stiffness during the failure process upon the dynamic behavior and loaded capability of the delaminated composite laminates were discussed. The method and conclusions would be useful for composite structure designers.
The dynamic response behavior and loaded capability were investigated for the delaminated composite plates considering the failure process. A formula of element stiffness and mass matrices for the composite laminates was deduced by using the first-order shear deformation theory combined with the selecting numerical integration scheme. A damping model was constituted on the basis of Rayleigh damping model. A delaminated constrained model and a virtual interface element were also developed for avoiding the overlap and penetration phenomenon between the upper and lower sub-laminates at the delamination region. The failure analysis method for the delaminated plates under dynamic loading was established by Tsai's failure criterion and corresponding 0.44 reduced stiffness role, and the dynamic equation was solved by the Newmark direct integral method. By some numerical examples, the effects of the frequency of dynamic load, delamination location, and reduction of structure stiffness during the failure process upon the dynamic behavior and loaded capability of the delaminated composite laminates were discussed. The method and conclusions would be useful for composite structure designers.
2004, 21(3): 120-124.
Abstract:
A mathematical model of cold symmetrical sandwich rolling was established by applying the upper bound method.The deformation mode was calculated for the sandwich with soft cladding during cold rolling. The relative calculating results were presented graphically. It is shown that there exist three possible deformation modes, namely proportional deformation, interface splitting, and unsteady deformation, depending on the process parameters. Larger reduction, stronger interface bonding, smaller relative base-metal strength and rolled thickness increase the proportional deformation zone and decrease the interface splitting zone. The unsteady deformation zone exists only when the relative base-metal strength and thickness are large enough.
A mathematical model of cold symmetrical sandwich rolling was established by applying the upper bound method.The deformation mode was calculated for the sandwich with soft cladding during cold rolling. The relative calculating results were presented graphically. It is shown that there exist three possible deformation modes, namely proportional deformation, interface splitting, and unsteady deformation, depending on the process parameters. Larger reduction, stronger interface bonding, smaller relative base-metal strength and rolled thickness increase the proportional deformation zone and decrease the interface splitting zone. The unsteady deformation zone exists only when the relative base-metal strength and thickness are large enough.
2004, 21(3): 125-130.
Abstract:
This paper presents an initial value solution of static equilibrium differential equations of the thin-walled composite laminated box beams considering both shear lag and shear deformation, which is used to establish the related element stiffness matrix and equivalent nodal forces vector. The analysis of the thin-walled composite laminated box beams is admitted into the program system of the matrix-displacement method.The present procedure can be used to analyze effectively the mechanical behaviors of some complex composite structures, such as continuous laminated box girders or laminated box beams with varying cross section, etc.
This paper presents an initial value solution of static equilibrium differential equations of the thin-walled composite laminated box beams considering both shear lag and shear deformation, which is used to establish the related element stiffness matrix and equivalent nodal forces vector. The analysis of the thin-walled composite laminated box beams is admitted into the program system of the matrix-displacement method.The present procedure can be used to analyze effectively the mechanical behaviors of some complex composite structures, such as continuous laminated box girders or laminated box beams with varying cross section, etc.
2004, 21(3): 131-136.
Abstract:
The absorption characteristics and the changes of the static mechanical properties and dynamic mechanical thermal properties of the pultruded carbon fiber/vinylester (CF/VE) composite, which is used for sucker rods in oil field, were studied during distilled water immersion at 95℃. The surface and fracture morphologies of the as-received and immersed composites were observed by using SEM. The results show that the composite obeys the second Fick's law in terms of absorption behavior, having an equilibrium moisture content of 1.046% and a diffusivity of 2.233×10-6 mm2/s. The decrease in the properties of the composite is very relative to the increase in its moisture content. After being immersed for 1176 hours, the composite has a reservation of interlaminar shear strength (ILSS) and flexural strength of 54% and 49%. The results of dynamic mechanical thermal analysis (DMTA) and SEM show that hygrothermal environment causes the swell and plasticization of the matrix, interfacial debonding and resultant microstructure changes of the matrix and interface. No chemical aging was found.
The absorption characteristics and the changes of the static mechanical properties and dynamic mechanical thermal properties of the pultruded carbon fiber/vinylester (CF/VE) composite, which is used for sucker rods in oil field, were studied during distilled water immersion at 95℃. The surface and fracture morphologies of the as-received and immersed composites were observed by using SEM. The results show that the composite obeys the second Fick's law in terms of absorption behavior, having an equilibrium moisture content of 1.046% and a diffusivity of 2.233×10-6 mm2/s. The decrease in the properties of the composite is very relative to the increase in its moisture content. After being immersed for 1176 hours, the composite has a reservation of interlaminar shear strength (ILSS) and flexural strength of 54% and 49%. The results of dynamic mechanical thermal analysis (DMTA) and SEM show that hygrothermal environment causes the swell and plasticization of the matrix, interfacial debonding and resultant microstructure changes of the matrix and interface. No chemical aging was found.
2004, 21(3): 137-141.
Abstract:
The electrical conductivity and its specific resistance varying with compressive stress of cement based composite materials (CBCM),reinforced by carbon fiber, black lead and steel fiber, were studied. The changing mechanism of specific resistance of CBCM,mixed with electric admixtures, was also researched. The results show that the precondition of CBCM possessing the piezoresistive effect is its electric net reaching the vadose zone. Moreover, due to the carbon fiber possessing a character of high slenderness ratio and low density, only a small content of it is enough to make CBCM enter the vadose zone and possess the piezoresistive effect.
The electrical conductivity and its specific resistance varying with compressive stress of cement based composite materials (CBCM),reinforced by carbon fiber, black lead and steel fiber, were studied. The changing mechanism of specific resistance of CBCM,mixed with electric admixtures, was also researched. The results show that the precondition of CBCM possessing the piezoresistive effect is its electric net reaching the vadose zone. Moreover, due to the carbon fiber possessing a character of high slenderness ratio and low density, only a small content of it is enough to make CBCM enter the vadose zone and possess the piezoresistive effect.
2004, 21(3): 142-145.
Abstract:
The PZT/PVDF piezoelectric composite was fabricated with solution-mixing method. The PZT piezoelectric powders prepared by hydrothermal synthesis method possess many fine properties. The appropriate solvent, used to mix the polymer and the ceramic powders, was selected by comparing the adsorption of PVDF on the ceramic powders. The dried composite powders were pressed into shape for poling and properties measurement. The experimental results show that the powders synthesized by hydrothermal method can improve the dispersing level and the piezoelectric and dielectric properties.
The PZT/PVDF piezoelectric composite was fabricated with solution-mixing method. The PZT piezoelectric powders prepared by hydrothermal synthesis method possess many fine properties. The appropriate solvent, used to mix the polymer and the ceramic powders, was selected by comparing the adsorption of PVDF on the ceramic powders. The dried composite powders were pressed into shape for poling and properties measurement. The experimental results show that the powders synthesized by hydrothermal method can improve the dispersing level and the piezoelectric and dielectric properties.
2004, 21(3): 151-156.
Abstract:
This paper proposes a novel extruding technique for preparing polymeric gradient material. A columnar PP/ABS gradient material was prepared by use of this method. The composition, morphological structure and mechanical properties of the PP/ABS gradient material along the radial direction were investigated by using DSC, TEM and tensile tests. The results indicate that the content of PP gradually decreases while ABS gradually increases with increasing radius. The TEM photographs show that the morphology also evolves with the varying in the content ratio of two polymers. A phase inversion phenomenon was recognized in this gradient material. Experimental facts show that the polymeric gradient material can be prepared successfully by using this specific extruding technique.
This paper proposes a novel extruding technique for preparing polymeric gradient material. A columnar PP/ABS gradient material was prepared by use of this method. The composition, morphological structure and mechanical properties of the PP/ABS gradient material along the radial direction were investigated by using DSC, TEM and tensile tests. The results indicate that the content of PP gradually decreases while ABS gradually increases with increasing radius. The TEM photographs show that the morphology also evolves with the varying in the content ratio of two polymers. A phase inversion phenomenon was recognized in this gradient material. Experimental facts show that the polymeric gradient material can be prepared successfully by using this specific extruding technique.
2004, 21(3): 157-161.
Abstract:
The tensile deformation and fracture behavior of Cu-0.54%Al2O3 dispersion strengthened copper alloy were examined. The results show that σ</em>0.2, σ</em>b, δ and σ0.2/σb of Cu-0.54%Al2O3 composite reach 250 MPa, 340 MPa, 24% and 74% respectively after hot-extruded in the extrusion ratio of 30∶1. The strength decreases gradually with the increase of annealing temperature, while σ0.2/σb remains high value. Its strain hardening exponent n is 0.256, which is obviously lower than that of pure copper.The Al2O3 nanoparticles with the average size of 18 nm and mean interparticle spacing of 100 nm distribute uniformly in the copper matrix,and improve the strength of the copper matrix and prevent the matrix from recrystallizing during annealing at elevated temperature and lower the strain hardening exponent n. The fracture of the as-extruded composite on a macroscopic scale is cup and cone morphology and features with the toughness failure on the microscopic scale.
The tensile deformation and fracture behavior of Cu-0.54%Al2O3 dispersion strengthened copper alloy were examined. The results show that σ</em>0.2, σ</em>b, δ and σ0.2/σb of Cu-0.54%Al2O3 composite reach 250 MPa, 340 MPa, 24% and 74% respectively after hot-extruded in the extrusion ratio of 30∶1. The strength decreases gradually with the increase of annealing temperature, while σ0.2/σb remains high value. Its strain hardening exponent n is 0.256, which is obviously lower than that of pure copper.The Al2O3 nanoparticles with the average size of 18 nm and mean interparticle spacing of 100 nm distribute uniformly in the copper matrix,and improve the strength of the copper matrix and prevent the matrix from recrystallizing during annealing at elevated temperature and lower the strain hardening exponent n. The fracture of the as-extruded composite on a macroscopic scale is cup and cone morphology and features with the toughness failure on the microscopic scale.
2004, 21(3): 162-166.
Abstract:
The effects of the heat absorbed during decomposition of some flame retardant fillers on the heat release rate measurement were studied using the cone calorimeter. It was found that the endothermic effect of the filler decomposition will affect the heat release rate measured by the cone calorimeter especially at higher levels of loading. Without appropriate corrections, the heat release rate measured by the cone calorimeter would be overestimated for high endothermic materials. Some typical materials were studied quantitatively, including alumina trihydrate and magnesium hydroxide. For alumina trihydrate and magnesium hydroxide, at the loading level of 80% in polymers, high overestimation could be produced, depending on the individual polymer used. A simple correction procedure is proposed to correct the heat release rate measurement using the cone calorimeter by modifying the effective heat of combustion using pyrolysis enthalpy. The corrected results and the comparison with the experimental values measured by the cone calorimeter are presented in the paper.
The effects of the heat absorbed during decomposition of some flame retardant fillers on the heat release rate measurement were studied using the cone calorimeter. It was found that the endothermic effect of the filler decomposition will affect the heat release rate measured by the cone calorimeter especially at higher levels of loading. Without appropriate corrections, the heat release rate measured by the cone calorimeter would be overestimated for high endothermic materials. Some typical materials were studied quantitatively, including alumina trihydrate and magnesium hydroxide. For alumina trihydrate and magnesium hydroxide, at the loading level of 80% in polymers, high overestimation could be produced, depending on the individual polymer used. A simple correction procedure is proposed to correct the heat release rate measurement using the cone calorimeter by modifying the effective heat of combustion using pyrolysis enthalpy. The corrected results and the comparison with the experimental values measured by the cone calorimeter are presented in the paper.
