2005 Vol. 22, No. 6
2005, 22(6): 1-8.
Abstract:
The fundamental issues and processing principle of electrospinning and electrospray based on electrohydrodynamics in the fabrication of nanoscale materials are briefly summarized in this article. The special attention is focused on the rapid development in the nanocomposite materials such as nanocapsules, core-shell nanofibers and hollow nanotubes or nanofibers by using coaxial electrospinning and coaxial electrospray in the recent couple of years. Potential applications of these nanocomposites in drug release systems, tissue engineering scaffold, wound dressing and absorbable sutures are discussed. Some future trends are also addressed in the paper.
The fundamental issues and processing principle of electrospinning and electrospray based on electrohydrodynamics in the fabrication of nanoscale materials are briefly summarized in this article. The special attention is focused on the rapid development in the nanocomposite materials such as nanocapsules, core-shell nanofibers and hollow nanotubes or nanofibers by using coaxial electrospinning and coaxial electrospray in the recent couple of years. Potential applications of these nanocomposites in drug release systems, tissue engineering scaffold, wound dressing and absorbable sutures are discussed. Some future trends are also addressed in the paper.
2005, 22(6): 9-14.
Abstract:
The characteristic of magnetoresistance of C/C composite prepared by preform with needle-punctured carbon felt at different heat treatment temperatures (HTT) was investigated. The magnetoresistance of C/C composite at different treatment temperatures is the same at the orientation angles of 0°~180° and increases with the rise of HTT. The intensity of magnetic field H and measured temperature (MT) have no effect on the relationship between magnetoresistance and orientation. Magnetoresistance-MT curves for the studied samples are linear in the same magnetic field and at higher MT, less magnetoresistance. The magnetoresistance of samples has negative at lower HTT value and positive value at higher HTT. The magnetoresistance of the samples tends to zero in case of enough high MT. The regressing magnetoresistance-temperature curves and the slope fall with the rise of HTT, and the shape of the slope-HTT curve is similar to that of the d002-HTT curve. The magnetoresistance of C/C composite increases with increasing the intensity of magnetic field at the same MT. The curves are quadratic function when H is less than 1.2×107A/m and the curves are linear when H is higher than 1.2×107A/m. The magnetoresistance increases with the rise of HTT in the magnetic field of any intensity.
The characteristic of magnetoresistance of C/C composite prepared by preform with needle-punctured carbon felt at different heat treatment temperatures (HTT) was investigated. The magnetoresistance of C/C composite at different treatment temperatures is the same at the orientation angles of 0°~180° and increases with the rise of HTT. The intensity of magnetic field H and measured temperature (MT) have no effect on the relationship between magnetoresistance and orientation. Magnetoresistance-MT curves for the studied samples are linear in the same magnetic field and at higher MT, less magnetoresistance. The magnetoresistance of samples has negative at lower HTT value and positive value at higher HTT. The magnetoresistance of the samples tends to zero in case of enough high MT. The regressing magnetoresistance-temperature curves and the slope fall with the rise of HTT, and the shape of the slope-HTT curve is similar to that of the d002-HTT curve. The magnetoresistance of C/C composite increases with increasing the intensity of magnetic field at the same MT. The curves are quadratic function when H is less than 1.2×107A/m and the curves are linear when H is higher than 1.2×107A/m. The magnetoresistance increases with the rise of HTT in the magnetic field of any intensity.
2005, 22(6): 15-20.
Abstract:
The high temperature anti-oxidation compound gradient MoSi2/SiC coating on carbon/carbon composites was prepared by a new complex process of two-stage holding temperature burying and sealing.The suitable gradient framework of the coating is SiC transiting layer,SiC compacting layer,MoSi2/SiC double phase layer and outer layer containing mainly MoSi2 from the inner to the outer of the coating.The oxidation mass loss rate of the unsealed coating prepared for longer holding time at the high temperature stage is less.The oxidation mass loss rates of the unsealed coating at 1200℃ and 1300℃ are larger than those at 1400℃ and 1500℃ in air.The surface of the coating is sealed with Si ( OC2H5 ) 4, and the formed SiO2 in gel fills the cracks and covers the coating.Oxidated at 1500℃ in air for a given time, the specimen with unsealed coating loses the mass,and the specimen with sealed coating gains the mass.The mass gain of sealed coating is 1.28% after oxidation at 1500℃ in air for 52 hours.The sealing improves the anti-oxidation of the coating greatly.
The high temperature anti-oxidation compound gradient MoSi2/SiC coating on carbon/carbon composites was prepared by a new complex process of two-stage holding temperature burying and sealing.The suitable gradient framework of the coating is SiC transiting layer,SiC compacting layer,MoSi2/SiC double phase layer and outer layer containing mainly MoSi2 from the inner to the outer of the coating.The oxidation mass loss rate of the unsealed coating prepared for longer holding time at the high temperature stage is less.The oxidation mass loss rates of the unsealed coating at 1200℃ and 1300℃ are larger than those at 1400℃ and 1500℃ in air.The surface of the coating is sealed with Si ( OC2H5 ) 4, and the formed SiO2 in gel fills the cracks and covers the coating.Oxidated at 1500℃ in air for a given time, the specimen with unsealed coating loses the mass,and the specimen with sealed coating gains the mass.The mass gain of sealed coating is 1.28% after oxidation at 1500℃ in air for 52 hours.The sealing improves the anti-oxidation of the coating greatly.
2005, 22(6): 21-26.
Abstract:
The microstructure and functionality of nanocomposites were designed using mesoporous assembly. The mesoporous silica was loaded with metal nickel to obtain the nanocomposite through sol-gel method ( mixing and immersion route ) and sequent reduction treatment in hydrogen atmosphere. The nanocomposite was characterized by means of DSC, XRD, XPS, TEM, etc, indicating that the sizes of the nickel particles are dependent on the struc-ture and pore diameter of the mesoporous silica, and are affected by the reduction temperature and composition. The sizes of the nanoscale particles range from 8 to 20nm. The nanocomposites with uniform distribution were produced easily by using immersion. The surface of nickel nanoparticles oxidized because of the interlinked pore structure of silica, leading to a formation of shell structure of nanoparticles existing in the pores. The addition of rare-earth Ce increases the network strength for the host silica and restricts the aggregation and growth of the nanoparticles.
The microstructure and functionality of nanocomposites were designed using mesoporous assembly. The mesoporous silica was loaded with metal nickel to obtain the nanocomposite through sol-gel method ( mixing and immersion route ) and sequent reduction treatment in hydrogen atmosphere. The nanocomposite was characterized by means of DSC, XRD, XPS, TEM, etc, indicating that the sizes of the nickel particles are dependent on the struc-ture and pore diameter of the mesoporous silica, and are affected by the reduction temperature and composition. The sizes of the nanoscale particles range from 8 to 20nm. The nanocomposites with uniform distribution were produced easily by using immersion. The surface of nickel nanoparticles oxidized because of the interlinked pore structure of silica, leading to a formation of shell structure of nanoparticles existing in the pores. The addition of rare-earth Ce increases the network strength for the host silica and restricts the aggregation and growth of the nanoparticles.
2005, 22(6): 27-31.
Abstract:
Mesoporous silica host was obtained by using sol-gel technique, leading to a formation of Ni/SiO2 nanocomposite through the immersion of nickel nitrate solution and hydrogen reduction treatment. The optical properties of the silica mesoporous composites were investigated. With increasing the composition and reducing the treatment temperature, the nanoparticles grow and the optical absorption edges red-shift due to the surface effect of the nano-particles. The optical properties are related to the interactions between the particles and the mesoporous host and the electron transferring. The optical absorption of the mesoporous composites contained the nanosized metal particles well correlated to the absorption mode of the indirect band transistor. The optical absorption increases with the loading of rare earth Ce. After being reduced at H2 atmosphere, the absorption edge red-shifts largely with the increase of the amount of rare earth Ce.
Mesoporous silica host was obtained by using sol-gel technique, leading to a formation of Ni/SiO2 nanocomposite through the immersion of nickel nitrate solution and hydrogen reduction treatment. The optical properties of the silica mesoporous composites were investigated. With increasing the composition and reducing the treatment temperature, the nanoparticles grow and the optical absorption edges red-shift due to the surface effect of the nano-particles. The optical properties are related to the interactions between the particles and the mesoporous host and the electron transferring. The optical absorption of the mesoporous composites contained the nanosized metal particles well correlated to the absorption mode of the indirect band transistor. The optical absorption increases with the loading of rare earth Ce. After being reduced at H2 atmosphere, the absorption edge red-shifts largely with the increase of the amount of rare earth Ce.
2005, 22(6): 32-36.
Abstract:
A method was investigated for preparing bioactive n-HA (nano-hydroxyapatite) and PA66 (Polyamide 66) nano-composite as the scaffold for the hard tissue repair using integrating composite with mold and pore. SEM, XRD, IR and burning test were used to analyze the physical and chemical properties of the scaffold. The results indicate that n-HA particles disperse with nano scale in the composite; there are hydrogen bonding and ligand bonding between HA and PA; the scaffold has three-dimensional pored structure with 450μm macropores and 0.5~50μm micropores. Animal testing shows that there are good histological compatibility and high bioactivity between the porous scaffold and bone. The scaffold is a kind of excellent carriers for bone repair because it produces bone-bonding with host and implant and its different pore sizes are beneficial to the growth of bone tissue, blood vessels and osteocytes.
A method was investigated for preparing bioactive n-HA (nano-hydroxyapatite) and PA66 (Polyamide 66) nano-composite as the scaffold for the hard tissue repair using integrating composite with mold and pore. SEM, XRD, IR and burning test were used to analyze the physical and chemical properties of the scaffold. The results indicate that n-HA particles disperse with nano scale in the composite; there are hydrogen bonding and ligand bonding between HA and PA; the scaffold has three-dimensional pored structure with 450μm macropores and 0.5~50μm micropores. Animal testing shows that there are good histological compatibility and high bioactivity between the porous scaffold and bone. The scaffold is a kind of excellent carriers for bone repair because it produces bone-bonding with host and implant and its different pore sizes are beneficial to the growth of bone tissue, blood vessels and osteocytes.
2005, 22(6): 37-43.
Abstract:
The ultrasonic dilution mechanism was analyzed through studying the fabrication process of the Zn-Al alloy matrix composites by high-intensity ultrasonic dilution of XD composites.The results show that the mechanism of ultrasonic dilution of the XD composites is the result of the cooperative effects of the acoustic cavitation and high speed acoustic streaming in the Zn-Al alloy melt. The instantaneous high temperature caused by the acoustic cavitation can promote the element’s diffusion between the interface of XD composites and the Zn-Al alloy melt.The instantaneous high pressure breaks off the long rod-like TiAl3 phase protruding along the XD composite/ Zn-Al interface,and drives the gathering particles out of the net of the rod-like TiAl3 phase. On the other hand,the intensitive agitation caused by the acoustic streaming thins the interface area and makes the short rod-like TiAl3 phase and fine particles (Al2O3 and TiB2) homogeneously disperse in the Zn-Al alloy melt.On the basis of the results, the models of the element diffusion and dilution process of the XD composites into the Zn-Al alloy melt were established.
The ultrasonic dilution mechanism was analyzed through studying the fabrication process of the Zn-Al alloy matrix composites by high-intensity ultrasonic dilution of XD composites.The results show that the mechanism of ultrasonic dilution of the XD composites is the result of the cooperative effects of the acoustic cavitation and high speed acoustic streaming in the Zn-Al alloy melt. The instantaneous high temperature caused by the acoustic cavitation can promote the element’s diffusion between the interface of XD composites and the Zn-Al alloy melt.The instantaneous high pressure breaks off the long rod-like TiAl3 phase protruding along the XD composite/ Zn-Al interface,and drives the gathering particles out of the net of the rod-like TiAl3 phase. On the other hand,the intensitive agitation caused by the acoustic streaming thins the interface area and makes the short rod-like TiAl3 phase and fine particles (Al2O3 and TiB2) homogeneously disperse in the Zn-Al alloy melt.On the basis of the results, the models of the element diffusion and dilution process of the XD composites into the Zn-Al alloy melt were established.
2005, 22(6): 44-48.
Abstract:
A new kind of large-displacement piezoelectric ceramics for actuators composed of reduced and un-reduced layers was prepared from PZT by chemical reduction. The distribution of stress inside the composite structure was researched and the chemical reduction conditions were explored. The actuating properties of reduced PZT were studied. It is found that the optimal ratio of reduced layer thickness for the composite structure is 0.3. The reduced composite PZT has lower resonance frequency and 3 times larger displacement than that of the traditional PZT. The re-oxide phases are found in the reduced layer of the composite PZT, showing that the reduction procedure needs to be improved.
A new kind of large-displacement piezoelectric ceramics for actuators composed of reduced and un-reduced layers was prepared from PZT by chemical reduction. The distribution of stress inside the composite structure was researched and the chemical reduction conditions were explored. The actuating properties of reduced PZT were studied. It is found that the optimal ratio of reduced layer thickness for the composite structure is 0.3. The reduced composite PZT has lower resonance frequency and 3 times larger displacement than that of the traditional PZT. The re-oxide phases are found in the reduced layer of the composite PZT, showing that the reduction procedure needs to be improved.
2005, 22(6): 49-53.
Abstract:
Compositionally graded Pb (Zr, Ti) O3 thin films were prepared on platinum-coated silicon substrates by Sol-Gel method and rapid heat-treatment. The composition depth profile of a typical up-graded film was determined by using a combination of Auger electron spectroscopy and Ar ion etching. The results confirm that the processing method produces graded composition change. XRD analysis shows that the graded thin films possess a tetragonal and rhombohedral composite structure. The curves of C-T and tgδ-T for the down-graded Pb (Zr<em>xTi1-x)O3 thin films show an F-F phase transition temperature, two Curie temperatures and the frequency dispersion phenomenon. The hysteresis loops of the graded thin films show fine ferroelectric properties. The pyroelectric coefficients of the graded thin films gradually increase with temperature, and are higher than that of every unit thin film.
Compositionally graded Pb (Zr, Ti) O3 thin films were prepared on platinum-coated silicon substrates by Sol-Gel method and rapid heat-treatment. The composition depth profile of a typical up-graded film was determined by using a combination of Auger electron spectroscopy and Ar ion etching. The results confirm that the processing method produces graded composition change. XRD analysis shows that the graded thin films possess a tetragonal and rhombohedral composite structure. The curves of C-T and tgδ-T for the down-graded Pb (Zr<em>xTi1-x)O3 thin films show an F-F phase transition temperature, two Curie temperatures and the frequency dispersion phenomenon. The hysteresis loops of the graded thin films show fine ferroelectric properties. The pyroelectric coefficients of the graded thin films gradually increase with temperature, and are higher than that of every unit thin film.
2005, 22(6): 54-58.
Abstract:
The carbon nanotubes (CNTs) were treated with acids to improve their performance. The plating layers such as Ni, Cu and Ni-Cu formed on the CNTs surface by chemical plating process were investigated. The results of TG, XRD and SEM reveal that the plated metal particle layer can grow in situ and form the nano-sized, uniform and linked stable layer on the surface of CNTs. The crystal structures and distribution states are different among those of Ni, Cu and compound metal plating layer. According to the results from the four-probe and wave-guide method, the conductivity of the plating compound material is 17.3S/cm, and the shielding effectiveness value of the material is about 71 dB, which reaches an excellent level.
The carbon nanotubes (CNTs) were treated with acids to improve their performance. The plating layers such as Ni, Cu and Ni-Cu formed on the CNTs surface by chemical plating process were investigated. The results of TG, XRD and SEM reveal that the plated metal particle layer can grow in situ and form the nano-sized, uniform and linked stable layer on the surface of CNTs. The crystal structures and distribution states are different among those of Ni, Cu and compound metal plating layer. According to the results from the four-probe and wave-guide method, the conductivity of the plating compound material is 17.3S/cm, and the shielding effectiveness value of the material is about 71 dB, which reaches an excellent level.
2005, 22(6): 59-65.
Abstract:
The spherical VC particles reinforced Fe-C-Cr-V alloy matrix composites were prepared by in-situ reaction casting. The microstructure and phase structure of the composites were observed with the metallurgical microscope, scanning electronic microscope and X-ray energy spectrum analyser. The results show that VC particles in Fe-C-Cr-V alloy containing 7% V are formed obviously above 1680℃. The almost perfect spherical VC particles are obtained at about 1750℃. The spherical phenomenon is not obvious if the holding time is too short. The long holding time would cause coarsening of VC particles. The VC particles could disperse homogeneously in 5 minutes of the holding time. The rare earth or nodulizer can be both useful to promote spheroidizing of VC particles. The formation mechanism of spherical carbonized composites in the alloy system was investigated.
The spherical VC particles reinforced Fe-C-Cr-V alloy matrix composites were prepared by in-situ reaction casting. The microstructure and phase structure of the composites were observed with the metallurgical microscope, scanning electronic microscope and X-ray energy spectrum analyser. The results show that VC particles in Fe-C-Cr-V alloy containing 7% V are formed obviously above 1680℃. The almost perfect spherical VC particles are obtained at about 1750℃. The spherical phenomenon is not obvious if the holding time is too short. The long holding time would cause coarsening of VC particles. The VC particles could disperse homogeneously in 5 minutes of the holding time. The rare earth or nodulizer can be both useful to promote spheroidizing of VC particles. The formation mechanism of spherical carbonized composites in the alloy system was investigated.
2005, 22(6): 66-71.
Abstract:
The micro and macro tribology characters of sintered YBa2Cu3O7 ( YBCO)in the air were investigated by using ball on disc tester and atomic force microscope(AFM), and a comparison with Cu based solid lubricant composite was prepared. The results indicate that excessive amount of solid lubricant will lead to decrease friction coefficient and increase wear rate for solid lubricant composite. The specimen 4060Cu containing 40%WS2 exhibits the lowest friction and relatively lower wear rate under the condition of different loads ( P), speeds ( v) and pv values. The friction coefficient of the YBCO specimen is similar to that of 4060Cu, but the wear rate is greatly lower than that. The results of XRD and TEM show that CuO distributes in the YBCO’s out layer and the binder with the body is not strong enough, so they can slip easily under shear stress with a low friction coefficient. In YBCO sample, Y2O3 nano particles distribute in the substance dispersedly, which strengthens the matrix and decreases the wear rate greatly. Due to the finer and more disperse Y2O3 particles of the specimen prepared by powder melting process, YBCO2 displays better wear-resistance.
The micro and macro tribology characters of sintered YBa2Cu3O7 ( YBCO)in the air were investigated by using ball on disc tester and atomic force microscope(AFM), and a comparison with Cu based solid lubricant composite was prepared. The results indicate that excessive amount of solid lubricant will lead to decrease friction coefficient and increase wear rate for solid lubricant composite. The specimen 4060Cu containing 40%WS2 exhibits the lowest friction and relatively lower wear rate under the condition of different loads ( P), speeds ( v) and pv values. The friction coefficient of the YBCO specimen is similar to that of 4060Cu, but the wear rate is greatly lower than that. The results of XRD and TEM show that CuO distributes in the YBCO’s out layer and the binder with the body is not strong enough, so they can slip easily under shear stress with a low friction coefficient. In YBCO sample, Y2O3 nano particles distribute in the substance dispersedly, which strengthens the matrix and decreases the wear rate greatly. Due to the finer and more disperse Y2O3 particles of the specimen prepared by powder melting process, YBCO2 displays better wear-resistance.
2005, 22(6): 72-79.
Abstract:
The effect of a catalytic curing agent with different contents on viscosity of a bisphenol-A resin was studied.Based on analyzing the curing characteristics of the resin system and the isothermal viscosity curves, an engineering viscosity model was developed. The model could be used effectively to predict the viscosity change of the epoxy system during a cure process, and could be used to indicate the regularity of viscosity change which is influenced by the content of the catalytic curing agent. The work is a basic study for processing simulation and process parameters prediction of composite manufacturing.
The effect of a catalytic curing agent with different contents on viscosity of a bisphenol-A resin was studied.Based on analyzing the curing characteristics of the resin system and the isothermal viscosity curves, an engineering viscosity model was developed. The model could be used effectively to predict the viscosity change of the epoxy system during a cure process, and could be used to indicate the regularity of viscosity change which is influenced by the content of the catalytic curing agent. The work is a basic study for processing simulation and process parameters prediction of composite manufacturing.
2005, 22(6): 80-84.
Abstract:
The Fe3O4/polyaniline composite nanoparticles with diameters of 30~50nm were prepared. The Fe3O4 nanoparticles with diameters of 10~30nm were encapsulated with polyaniline (PANI) by in-situ polymerization. The inductive heating property of Fe3O4 nanoparticles and Fe3O4/polyaniline composite nanoparticles in an alternating current magnetic field was investigated. The potential of the two kinds of nanoparticles was evaluated for the localized hyperthermia treatment of cancers.The saturation magnetization Ms and coercivity Hc of Fe3O4 nanoparticles are 50.05emu/g and 137 Oe respectively, the Fe3O4/polyaniline composite nanoparticles, 26.34emu/g and 0 Oe. Exposed in the alternating current magnetic field for 30 min, the temperatures of physiological salt water suspension containing Fe3O4 nanoparticles or Fe3O4/polyaniline composite nanoparticles are 63.6℃ and 52.4℃ respectively. These two kinds of nanoparticles would be useful as good thermoseeds for the localized hyperthermia treatment of cancers.
The Fe3O4/polyaniline composite nanoparticles with diameters of 30~50nm were prepared. The Fe3O4 nanoparticles with diameters of 10~30nm were encapsulated with polyaniline (PANI) by in-situ polymerization. The inductive heating property of Fe3O4 nanoparticles and Fe3O4/polyaniline composite nanoparticles in an alternating current magnetic field was investigated. The potential of the two kinds of nanoparticles was evaluated for the localized hyperthermia treatment of cancers.The saturation magnetization Ms and coercivity Hc of Fe3O4 nanoparticles are 50.05emu/g and 137 Oe respectively, the Fe3O4/polyaniline composite nanoparticles, 26.34emu/g and 0 Oe. Exposed in the alternating current magnetic field for 30 min, the temperatures of physiological salt water suspension containing Fe3O4 nanoparticles or Fe3O4/polyaniline composite nanoparticles are 63.6℃ and 52.4℃ respectively. These two kinds of nanoparticles would be useful as good thermoseeds for the localized hyperthermia treatment of cancers.
2005, 22(6): 85-90.
Abstract:
An atom force microscopy in force modulation mode was adopted to study the cross-section surface of unidirectional carbon fiber/polyarylacetylene (CF/PAA) composites, and the shape, distribution and relative stiffness of various phases were obtained. The probability histogram of surface relative stiffness, obtained by the statistical analysis of the relative stiffness image, was used to compare and study the interphase characters of the composites modified by different methods. The results show that obvious interphase can not be seen in untreated composites, and the structure of the interphase area becomes more complex after oxidation treatment due to the change of stiffness. More perfect interphase can be obtained and a transitional area with moderate modulus can be established between fiber and matrix after the treatment of CF by a combined method of oxidation and coating, so that the mecha-nical properties of the interface are improved obviously.
An atom force microscopy in force modulation mode was adopted to study the cross-section surface of unidirectional carbon fiber/polyarylacetylene (CF/PAA) composites, and the shape, distribution and relative stiffness of various phases were obtained. The probability histogram of surface relative stiffness, obtained by the statistical analysis of the relative stiffness image, was used to compare and study the interphase characters of the composites modified by different methods. The results show that obvious interphase can not be seen in untreated composites, and the structure of the interphase area becomes more complex after oxidation treatment due to the change of stiffness. More perfect interphase can be obtained and a transitional area with moderate modulus can be established between fiber and matrix after the treatment of CF by a combined method of oxidation and coating, so that the mecha-nical properties of the interface are improved obviously.
2005, 22(6): 91-97.
Abstract:
An adaptive implicit algorithm was proposed for RTM mold filling simulation. The proposed implicit algorithm was based on the update of the interface in order to track the flow front.The governing equations of the filled nodes were solved to obtain the pressure distribution, and filling fractions of the front nodes were checked to determine if any node is needed to be added to the filled nodes or be removed from the filled nodes. Based on the criterion that the resin moves forward only one element-size distance at each time step, the Recursive Least Square (RLS) adaptive method was employed dynamically to update the time step. The half-filled time of control volumes was estimated by the pressures in order to construct the flow fronts at any given time. The case studies demonstrate that the adaptive implicit algorithm improves the performance and flexibility of the implicit algorithm. The computational time complexity of 2.5D is reduced to 2 order of the node number.
An adaptive implicit algorithm was proposed for RTM mold filling simulation. The proposed implicit algorithm was based on the update of the interface in order to track the flow front.The governing equations of the filled nodes were solved to obtain the pressure distribution, and filling fractions of the front nodes were checked to determine if any node is needed to be added to the filled nodes or be removed from the filled nodes. Based on the criterion that the resin moves forward only one element-size distance at each time step, the Recursive Least Square (RLS) adaptive method was employed dynamically to update the time step. The half-filled time of control volumes was estimated by the pressures in order to construct the flow fronts at any given time. The case studies demonstrate that the adaptive implicit algorithm improves the performance and flexibility of the implicit algorithm. The computational time complexity of 2.5D is reduced to 2 order of the node number.
2005, 22(6): 98-102.
Abstract:
Based on uni-axial tensile testing experiments of PES/PVC membrane materials, tensile performances of the samples were analyzed in seven in-plane directions including 0°, 15°, 30°, 45°, 60°, 75° and 90°. It is disco-vered that the stress-strain behaviors of the samples can correctly represent the elastic properties of the membrane material after three cycles of tensile loading and unloading. The results show that the elastic performance of the materials can be described by the constitutive relations of the orthotropic materials. In order to predict the tensile strength of the membrane materials under the conditions of complicated stress, the rupture mechanisms of the materials and the corresponding strength criterion were discussed. The analytical results indicate that Tsai-Hill criterion is applicable under the pure tensile or pure shear mode. However, it is less suitable under the tensile-shear mixture mode.
Based on uni-axial tensile testing experiments of PES/PVC membrane materials, tensile performances of the samples were analyzed in seven in-plane directions including 0°, 15°, 30°, 45°, 60°, 75° and 90°. It is disco-vered that the stress-strain behaviors of the samples can correctly represent the elastic properties of the membrane material after three cycles of tensile loading and unloading. The results show that the elastic performance of the materials can be described by the constitutive relations of the orthotropic materials. In order to predict the tensile strength of the membrane materials under the conditions of complicated stress, the rupture mechanisms of the materials and the corresponding strength criterion were discussed. The analytical results indicate that Tsai-Hill criterion is applicable under the pure tensile or pure shear mode. However, it is less suitable under the tensile-shear mixture mode.
2005, 22(6): 103-107.
Abstract:
The morphology of pores in carbon fiber reinforced plastics(CFRP) was statistically studied using microscopy and image analysis. The results show that pores tend to occur at the interfaces between the adjacent laminae and elongate along the interfaces. Both the area and the length of the pores increase if the pores content rises. It is also observed that the aspect ratios (width to length of a pore) of pores tend to be larger when the pores content decreases, and the pores are rounder and distribute more sporadically.
The morphology of pores in carbon fiber reinforced plastics(CFRP) was statistically studied using microscopy and image analysis. The results show that pores tend to occur at the interfaces between the adjacent laminae and elongate along the interfaces. Both the area and the length of the pores increase if the pores content rises. It is also observed that the aspect ratios (width to length of a pore) of pores tend to be larger when the pores content decreases, and the pores are rounder and distribute more sporadically.
2005, 22(6): 108-113.
Abstract:
An Epoxy/Brominated Epoxy/Cyanate Ester co-curing system was studied for liquid oxygen compatible matrix resins, and a kind of imidazole 2E4MZ was introduced to the co-curing system. The gel times of the co-curing system at different temperatures indicate that 2E4MZ could effectively accelarate the co-curing reactions no matter whether epoxy or cyanate ester was excessive, which were confirmed by the FT-IR results. The FT-IR results also show that the cured resin structures are improved by 2E4MZ with more co-curing structures such as oxazoline and oxazolidinone. The thermal analysis, flash point and oxygen index results indicate that the cured resin modified by 2E4MZ have better anti-oxidation and flame retardant properties. The liquid oxygen impact test results approve that the cured resin modified by 2E4MZ have better compatibility with liquid oxygen. This kind of modification is an easy and cheap way for epoxy systems to get better compatibility with liquid oxygen.
An Epoxy/Brominated Epoxy/Cyanate Ester co-curing system was studied for liquid oxygen compatible matrix resins, and a kind of imidazole 2E4MZ was introduced to the co-curing system. The gel times of the co-curing system at different temperatures indicate that 2E4MZ could effectively accelarate the co-curing reactions no matter whether epoxy or cyanate ester was excessive, which were confirmed by the FT-IR results. The FT-IR results also show that the cured resin structures are improved by 2E4MZ with more co-curing structures such as oxazoline and oxazolidinone. The thermal analysis, flash point and oxygen index results indicate that the cured resin modified by 2E4MZ have better anti-oxidation and flame retardant properties. The liquid oxygen impact test results approve that the cured resin modified by 2E4MZ have better compatibility with liquid oxygen. This kind of modification is an easy and cheap way for epoxy systems to get better compatibility with liquid oxygen.
2005, 22(6): 114-119.
Abstract:
Carbon fiber reinforced sulphoaluminate cement was fabricated by pressing technology; its smart pro-perties were studied. The phases and relationship between pore diameter and pore volume were analyzed by XRD test and Poremaster analyzer. The influences of different carbon fiber contents on the smart properties of CFRS under monotone stress and cycle stress were studied. The results of pore structure analysis and XRD analysis indicate that the structure is dense, the hydration of sulphoaluminate cement is not completed and the pore diameter is mostly smaller than 0.9 μ m. The monotoning stress test indicates that the fractional changes in capacity of CFRS containing 0.3% and 0.5% carbon fiber are linear to the stress, and having smarter properties; the cycle stress test indicates that the fractional change in capacity of CFRS containing 0.7% carbon fiber is corresponding to the cycle stress change, and the CFRS containing 0.7% carbon fiber has smarter properties.
Carbon fiber reinforced sulphoaluminate cement was fabricated by pressing technology; its smart pro-perties were studied. The phases and relationship between pore diameter and pore volume were analyzed by XRD test and Poremaster analyzer. The influences of different carbon fiber contents on the smart properties of CFRS under monotone stress and cycle stress were studied. The results of pore structure analysis and XRD analysis indicate that the structure is dense, the hydration of sulphoaluminate cement is not completed and the pore diameter is mostly smaller than 0.9 μ m. The monotoning stress test indicates that the fractional changes in capacity of CFRS containing 0.3% and 0.5% carbon fiber are linear to the stress, and having smarter properties; the cycle stress test indicates that the fractional change in capacity of CFRS containing 0.7% carbon fiber is corresponding to the cycle stress change, and the CFRS containing 0.7% carbon fiber has smarter properties.
2005, 22(6): 120-124.
Abstract:
To develop the design and computational theory for GFWRP reinforced concrete structure, GFWRP reinforced concrete column specimens were designed and fabricated with different tube diameters, thicknesses and winding angles. The axial compression testing of the specimen was conducted, and its experimental results were analyzed based on the regression method. The equations describing the development of Poisson’s ratio and corresponding axial strain of GFWRP-concrete columns at the critical point and failure point were obtained. The equation to predict Poisson’s ratio development in the whole axial compression process was presented. So the peak Poisson’s ratio and corresponding axial strain of any GFWRP-concrete column can be forecasted in terms of the properties of its constituent materials, which can be used to predict the practical structural resistance and deformation capacity of the GFWRP-concrete column. According to the experimental and theoretical results, the Poisson’s ratio developments between GFWRP-concrete and traditional steel-concrete columns are quite different. The effect of the fiber winding angle of GFWRP tubes on the Poisson’s ratio of the combined structure under axial compression was analyzed. It reveals nearly inverse Poisson’s ratio dependences on the fiber winding angle. The results provide the theoretical basis for setting up the rational GFWRP-concrete structure standards.
To develop the design and computational theory for GFWRP reinforced concrete structure, GFWRP reinforced concrete column specimens were designed and fabricated with different tube diameters, thicknesses and winding angles. The axial compression testing of the specimen was conducted, and its experimental results were analyzed based on the regression method. The equations describing the development of Poisson’s ratio and corresponding axial strain of GFWRP-concrete columns at the critical point and failure point were obtained. The equation to predict Poisson’s ratio development in the whole axial compression process was presented. So the peak Poisson’s ratio and corresponding axial strain of any GFWRP-concrete column can be forecasted in terms of the properties of its constituent materials, which can be used to predict the practical structural resistance and deformation capacity of the GFWRP-concrete column. According to the experimental and theoretical results, the Poisson’s ratio developments between GFWRP-concrete and traditional steel-concrete columns are quite different. The effect of the fiber winding angle of GFWRP tubes on the Poisson’s ratio of the combined structure under axial compression was analyzed. It reveals nearly inverse Poisson’s ratio dependences on the fiber winding angle. The results provide the theoretical basis for setting up the rational GFWRP-concrete structure standards.
2005, 22(6): 125-129.
Abstract:
A 3D dynamic finite element method with stitching threads is described by the space bar element and combined with experiment work to study the damages of the stitched composites induced by the low-velocity impact in this paper. Impact induced contact forces by modified Hertz contact law are obtained, the dynamic equations are solved with NewMark direct integral scheme, and strain and stress during impact are obtained. A modified delamination criterion considering fibre failure is proposed based on that of Chang and Hou, and the method to analyse the impact induced failure area is developed. Impact tests on the stitched and unstitched composite laminates with the same ply sequence are performed. Good agreement is found between experiment and finite element computing results, and the results indicate that stitching greatly reduces the extent of the impact damage area at the same impact energy level.
A 3D dynamic finite element method with stitching threads is described by the space bar element and combined with experiment work to study the damages of the stitched composites induced by the low-velocity impact in this paper. Impact induced contact forces by modified Hertz contact law are obtained, the dynamic equations are solved with NewMark direct integral scheme, and strain and stress during impact are obtained. A modified delamination criterion considering fibre failure is proposed based on that of Chang and Hou, and the method to analyse the impact induced failure area is developed. Impact tests on the stitched and unstitched composite laminates with the same ply sequence are performed. Good agreement is found between experiment and finite element computing results, and the results indicate that stitching greatly reduces the extent of the impact damage area at the same impact energy level.
2005, 22(6): 130-134.
Abstract:
Three-dimensional solutions for free vibration of the magneto-electric-elastic multilayered rectangular plates were investigated. Based on the three-dimension elastic theory and piezoelectric-piezomagnetic theory, the dynamics equation of the laminate with magnetoelectric effect was deduced. The solution for simply-supported panel was obtained by employing the power series method. The effect of the plate as a sensor and as an actuator on the vibration frequency was analysed. The calculating result for the piezoelectric mono-player is compatible with that in the previous paper. The influence of the thickness and the sequence of layers on the vibration frequency was discussed. When the volume fraction of the middle layer increases from 25% to 75%, the frequency varies gently.
Three-dimensional solutions for free vibration of the magneto-electric-elastic multilayered rectangular plates were investigated. Based on the three-dimension elastic theory and piezoelectric-piezomagnetic theory, the dynamics equation of the laminate with magnetoelectric effect was deduced. The solution for simply-supported panel was obtained by employing the power series method. The effect of the plate as a sensor and as an actuator on the vibration frequency was analysed. The calculating result for the piezoelectric mono-player is compatible with that in the previous paper. The influence of the thickness and the sequence of layers on the vibration frequency was discussed. When the volume fraction of the middle layer increases from 25% to 75%, the frequency varies gently.
2005, 22(6): 135-138.
Abstract:
The mechanical properties of the stitched laminates were compared with those of the unstitched laminates, considering changes in thickness due to stitching. Experimental investigation was conducted to understand the effect of stitching on tensile strength, compression strength, open-hole tensile strength, open-hole compression strength and failure mechanisms. The results show that the change in thickness due to stitching affects the volume fractions of in-plane fibers, which is important to assessing the mechanical properties of the stitched laminates.
The mechanical properties of the stitched laminates were compared with those of the unstitched laminates, considering changes in thickness due to stitching. Experimental investigation was conducted to understand the effect of stitching on tensile strength, compression strength, open-hole tensile strength, open-hole compression strength and failure mechanisms. The results show that the change in thickness due to stitching affects the volume fractions of in-plane fibers, which is important to assessing the mechanical properties of the stitched laminates.
2005, 22(6): 139-143.
Abstract:
A homogenization method based on the perturbation theory is presented to deduce the mathematical expression of the micro-stress. The FEM method was used to simulate the micro-stress of three-dimensional braided composites. The proper criteria of strength were used to judge the failure of each element under the loading of the limited tensile stress. A kind of micro failure criterion of strength can be concluded. The calculation results of stress obtained by this method agree quite well with some conclusions of the tensile experiment.
A homogenization method based on the perturbation theory is presented to deduce the mathematical expression of the micro-stress. The FEM method was used to simulate the micro-stress of three-dimensional braided composites. The proper criteria of strength were used to judge the failure of each element under the loading of the limited tensile stress. A kind of micro failure criterion of strength can be concluded. The calculation results of stress obtained by this method agree quite well with some conclusions of the tensile experiment.
2005, 22(6): 144-149.
Abstract:
The main mechanical properties of the 3D 6-directional braided composites were obtained by tensile, compressive, in-plane shear, and compressive after impact experiments. The bar specimens with two types of holes, mechanical circular hole or braided circular hole, were used for tensile and compressive tests. The damage modes and failure mechanism of the material under tensile, compressive and shearing loads were experimentally studied. The influence of the two types of holes (mechanical hole and braided hole) on the tensile and compressive mechanical properties was analyzed. The effect of impact on the compressive mechanical properties was also studied. The pre-sent work establishes a foundation for the predictions of stiffness and strength of the 3D 6-directional braided composites.
The main mechanical properties of the 3D 6-directional braided composites were obtained by tensile, compressive, in-plane shear, and compressive after impact experiments. The bar specimens with two types of holes, mechanical circular hole or braided circular hole, were used for tensile and compressive tests. The damage modes and failure mechanism of the material under tensile, compressive and shearing loads were experimentally studied. The influence of the two types of holes (mechanical hole and braided hole) on the tensile and compressive mechanical properties was analyzed. The effect of impact on the compressive mechanical properties was also studied. The pre-sent work establishes a foundation for the predictions of stiffness and strength of the 3D 6-directional braided composites.
2005, 22(6): 150-155.
Abstract:
Based on the dynamic finite element method in conjunction of neural networks,a strategy for detecting delamination of composite laminates was proposed.To establish the data-base for neural networks,a nonlinear dynamic finite element method,developed by the authors,was used to calculate the values of natural frequencies and mode damping of the delaminated composite plates,while a back propagation ( BP) neural network was employed for training and testing the network.The typical simulating results show that the high order mode damping is better than frequencies as an input parameter for detecting delamination damage,because the former is more sensitive to the extent of delamination.The present strategy is an effective and low cost method for detecting delamination of the composite laminates.
Based on the dynamic finite element method in conjunction of neural networks,a strategy for detecting delamination of composite laminates was proposed.To establish the data-base for neural networks,a nonlinear dynamic finite element method,developed by the authors,was used to calculate the values of natural frequencies and mode damping of the delaminated composite plates,while a back propagation ( BP) neural network was employed for training and testing the network.The typical simulating results show that the high order mode damping is better than frequencies as an input parameter for detecting delamination damage,because the former is more sensitive to the extent of delamination.The present strategy is an effective and low cost method for detecting delamination of the composite laminates.
2005, 22(6): 156-164.
Abstract:
The dynamic stress intensity factor was studied about the Griffith crack between elastic and visco-elastic layers in an infinite length strip under impact load. The controlling equations expressed by the displacement of elastic and viscoelastic materials were deduced separately after using Laplace and Fourier integral transforms of the basic equations. The displacements in the Laplace domain were obtained by inverse Fourier integral transform;uniting the constitutive and geometrical equations, the analytical expressions of stress in Laplace domain were derived. By defining a dislocation density function, the Cauchy singular integral equations were given according to the boundary conditions and the problem was reduced to algebraic equations using Chebyshev orthogonal polynomial; then it can be solved with the method of collocation dots in the Laplace domain. The time response of the dynamic stress intensity factor was calculated with the numerical method and the influence of material parameters on it was analyzed. The results show that the influence of the shear relaxation parameter on mode Ⅰ dynamic stress intensity factor is bigger than on mode Ⅱ ,and the influence of the swelling relaxation parameter is opposite.
The dynamic stress intensity factor was studied about the Griffith crack between elastic and visco-elastic layers in an infinite length strip under impact load. The controlling equations expressed by the displacement of elastic and viscoelastic materials were deduced separately after using Laplace and Fourier integral transforms of the basic equations. The displacements in the Laplace domain were obtained by inverse Fourier integral transform;uniting the constitutive and geometrical equations, the analytical expressions of stress in Laplace domain were derived. By defining a dislocation density function, the Cauchy singular integral equations were given according to the boundary conditions and the problem was reduced to algebraic equations using Chebyshev orthogonal polynomial; then it can be solved with the method of collocation dots in the Laplace domain. The time response of the dynamic stress intensity factor was calculated with the numerical method and the influence of material parameters on it was analyzed. The results show that the influence of the shear relaxation parameter on mode Ⅰ dynamic stress intensity factor is bigger than on mode Ⅱ ,and the influence of the swelling relaxation parameter is opposite.
2005, 22(6): 165-171.
Abstract:
The meshless local Petrov-Galerkin ( MLPG) method is extended to solve the symmetric laminates of fiber-reinforced composite materials using the moving least-square approximation to interpolate solution variables,and the equivalent integral weak form to the governing equation of Kirchhoff’s anisotropic plates.The present method is an effective truly meshless one as it doesn’t need any meshgrids,and all integrals can be easily evaluated over regularly shaped domains and their boundaries.In the analysis,the essential boundary conditions are enforced by a penalty method.Several examples are given and compared with other methods. The result shows that the meshless local Petrov-Galerkin method has a number of advantages such as the quite good accuracy and the high rate of convergence in solving the problems of composite laminated plates.
The meshless local Petrov-Galerkin ( MLPG) method is extended to solve the symmetric laminates of fiber-reinforced composite materials using the moving least-square approximation to interpolate solution variables,and the equivalent integral weak form to the governing equation of Kirchhoff’s anisotropic plates.The present method is an effective truly meshless one as it doesn’t need any meshgrids,and all integrals can be easily evaluated over regularly shaped domains and their boundaries.In the analysis,the essential boundary conditions are enforced by a penalty method.Several examples are given and compared with other methods. The result shows that the meshless local Petrov-Galerkin method has a number of advantages such as the quite good accuracy and the high rate of convergence in solving the problems of composite laminated plates.
2005, 22(6): 172-177.
Abstract:
Based on 3-D or 2.5-D weaving technique and 3-D FEA, the experiments and numerical analyses have been fulfilled to the structure design for the composite multi-joints of the satellite antenna truss. A basement was set up to manufacture a non-metal multi-joint into reality. The tests of tension,compression and bending were carried out for the composite joints made by weaving technique. Based on the numerical analyses it is confirmed that the intensity of the composite joint reaches about 400 MPa, and the fractural location is in accordance with the experimental results. The replacement of metallic joints by composites is reasonable.
Based on 3-D or 2.5-D weaving technique and 3-D FEA, the experiments and numerical analyses have been fulfilled to the structure design for the composite multi-joints of the satellite antenna truss. A basement was set up to manufacture a non-metal multi-joint into reality. The tests of tension,compression and bending were carried out for the composite joints made by weaving technique. Based on the numerical analyses it is confirmed that the intensity of the composite joint reaches about 400 MPa, and the fractural location is in accordance with the experimental results. The replacement of metallic joints by composites is reasonable.
2005, 22(6): 178-182.
Abstract:
There is a difficult problem for composites designers to solve; that is, how to confirm the relationship between preform structural design parameters and composites thickness.Based on observing and analyzing digital images and microstructure of 3D woven composites cross-sections,the results show that the position of deciding the thickness of 3D woven composites is located at the cross-section which passes through the center of the weft thread,the cross-section of a warp thread is rectangular,and the longitudinal track of a weft thread is linear.Furthermore,thickness equations for 3D woven composites are deduced,which are expressed by preform structural design param-eters.In the end, an example is given to certify the validity of the thickness equations.The result shows that the thickness equations are correct and practical.
There is a difficult problem for composites designers to solve; that is, how to confirm the relationship between preform structural design parameters and composites thickness.Based on observing and analyzing digital images and microstructure of 3D woven composites cross-sections,the results show that the position of deciding the thickness of 3D woven composites is located at the cross-section which passes through the center of the weft thread,the cross-section of a warp thread is rectangular,and the longitudinal track of a weft thread is linear.Furthermore,thickness equations for 3D woven composites are deduced,which are expressed by preform structural design param-eters.In the end, an example is given to certify the validity of the thickness equations.The result shows that the thickness equations are correct and practical.
