2004 Vol. 21, No. 2
2004, 21(2): 1-7.
Abstract:
A review of studies on the mechanical properties and microscopic geometric models of three dimensional braided composites is given in this paper. The emphasis is placed on the recent developments of mechanical properties of three dimensional braided composites and author' s works in this field, in which the experimental and theoretical investigations into three dimensional braided composites are included. In theoretical investigations, elastic strain energy method, fiber inclination model, three cells model and finite element model etc. are introduced. Some future investigating trends are also presented.
A review of studies on the mechanical properties and microscopic geometric models of three dimensional braided composites is given in this paper. The emphasis is placed on the recent developments of mechanical properties of three dimensional braided composites and author' s works in this field, in which the experimental and theoretical investigations into three dimensional braided composites are included. In theoretical investigations, elastic strain energy method, fiber inclination model, three cells model and finite element model etc. are introduced. Some future investigating trends are also presented.
2004, 21(2): 8-13.
Abstract:
The metal matrix composite coating that Al2O3 particles incorporate into Co-Ni alloy was prepared by the electrodeposition technique from sulfamate electrolyte. It illustrates from the examined results of SEM, AFM and XRD that surface morphology and microstructure of Co-Ni-Al2O3 coatings appear to be mainly influenced by variations in cobalt content. The codeposition of Al2O3 particles in Co-Ni alloys cannot change the phase structure of solid solution, only affects the growth and orientation of crystal planes and mostly increases the d value of lattice. The high-temperature properties of the Co-Ni-Al2O3 coatings, including hardness, wear resistance, oxidation resistance, coefficients of thermal expansion and thermal conductivity at high temperature were also investigated. The results show that Co-Ni-Al2O3 composite coatings have good performance of wear resistance and oxidation resistance at the high temperature. Furthermore, the composite coatings with high-cobalt content show lower coefficients of thermal expansion and higher thermal conductivity than coatings with low-cobalt content do.
The metal matrix composite coating that Al2O3 particles incorporate into Co-Ni alloy was prepared by the electrodeposition technique from sulfamate electrolyte. It illustrates from the examined results of SEM, AFM and XRD that surface morphology and microstructure of Co-Ni-Al2O3 coatings appear to be mainly influenced by variations in cobalt content. The codeposition of Al2O3 particles in Co-Ni alloys cannot change the phase structure of solid solution, only affects the growth and orientation of crystal planes and mostly increases the d value of lattice. The high-temperature properties of the Co-Ni-Al2O3 coatings, including hardness, wear resistance, oxidation resistance, coefficients of thermal expansion and thermal conductivity at high temperature were also investigated. The results show that Co-Ni-Al2O3 composite coatings have good performance of wear resistance and oxidation resistance at the high temperature. Furthermore, the composite coatings with high-cobalt content show lower coefficients of thermal expansion and higher thermal conductivity than coatings with low-cobalt content do.
2004, 21(2): 14-21.
Abstract:
The secondary-working characters of in situ TiCP/Fe composites (heat treatment, welding, machining) are studied and a lot of basic works for using in industrialization producing are done. The results showed that casting stress could be eliminated, microstructures improved, properties raised, and it is improper to change the TiC particle by heat treatment. The TiC particle is not changed in the course of welding and there are not cracks in the weld seam. The weld-ability of the composites is better. The cutting force of TiC/Fe composites is enlarged and its temperature is increased due to the formation of TiC particles. The effect of TiC on the working surface is only a little. The machining quality of the composites is similar to that of 45# steel.
The secondary-working characters of in situ TiCP/Fe composites (heat treatment, welding, machining) are studied and a lot of basic works for using in industrialization producing are done. The results showed that casting stress could be eliminated, microstructures improved, properties raised, and it is improper to change the TiC particle by heat treatment. The TiC particle is not changed in the course of welding and there are not cracks in the weld seam. The weld-ability of the composites is better. The cutting force of TiC/Fe composites is enlarged and its temperature is increased due to the formation of TiC particles. The effect of TiC on the working surface is only a little. The machining quality of the composites is similar to that of 45# steel.
2004, 21(2): 22-26.
Abstract:
This paper has investigated the effect of substrate temperature on the residual stress and microstructure of Ag-MgF2 cermet films prepared by vapor deposition. X-ray diffraction (XRD) technique was employed to study the microstructure of the films. The results show that the average stress over a φ20.4 mm round area is the least and the residual stress of the films appears to be tensile stress between 300℃ and 400℃. Crystal lattice constants of Ag and MgF2 both approach the bulk values. The residual stress of the films can be decreased by altering the substrate temperature.
This paper has investigated the effect of substrate temperature on the residual stress and microstructure of Ag-MgF2 cermet films prepared by vapor deposition. X-ray diffraction (XRD) technique was employed to study the microstructure of the films. The results show that the average stress over a φ20.4 mm round area is the least and the residual stress of the films appears to be tensile stress between 300℃ and 400℃. Crystal lattice constants of Ag and MgF2 both approach the bulk values. The residual stress of the films can be decreased by altering the substrate temperature.
2004, 21(2): 27-33.
Abstract:
The CN<em>x/TiN multilayer composite coatings were deposited onto stainless steel substrates by combination of DC reaction magnetron sputtering deposition with multi-arc plating. The CN<em>x/TiN multilayer composite coatings are analyzed using X-ray electron energy spectrum (XPS) and transmission electron diffraction (TED). The liquid impact erosion resistance of stainless steel, high-Cr iron, cobalt-base alloys and CN<em>x/TiN multilayer composite coatings were researched by using a homemade high-pressure liquid impact erosion tester. Finally, the failure mechanism of CN<em>x/TiN multilayer composite coatings was studied. The results showed that the multilayer film, with high hardness, strong adhesion and excellent thermal shock resistance, is a good liquid impact erosion resistance coating used in the last stage blade of steam turbines.
The CN<em>x/TiN multilayer composite coatings were deposited onto stainless steel substrates by combination of DC reaction magnetron sputtering deposition with multi-arc plating. The CN<em>x/TiN multilayer composite coatings are analyzed using X-ray electron energy spectrum (XPS) and transmission electron diffraction (TED). The liquid impact erosion resistance of stainless steel, high-Cr iron, cobalt-base alloys and CN<em>x/TiN multilayer composite coatings were researched by using a homemade high-pressure liquid impact erosion tester. Finally, the failure mechanism of CN<em>x/TiN multilayer composite coatings was studied. The results showed that the multilayer film, with high hardness, strong adhesion and excellent thermal shock resistance, is a good liquid impact erosion resistance coating used in the last stage blade of steam turbines.
2004, 21(2): 34-39.
Abstract:
A novel technique by using graphite immersed by K2CO3 solution to cover with the surface of molten alloy and setting porous ceramics in advance to transport atmosphere, is realized to in situ oxygenize molten alloy from its surface into its interior. The attractive features of the new technology in comparison with conventional growth technology are densified reaction resultant, smooth macro-surface around samples, and samples of front without rugged cellular stacking on them. It is found by microstructure observation, X-radial diffraction analysis(XRD) and by electron probe X-ray microanalysis(EPMA) that oxides grow in the form of columnar crystal consisting of clumps or grains of micron oxides in whichα-alumina is the main and silica a little, with continuous ingredient variation between two phases and clumps or grains, showing a tendency ofα-alumina wrapping silica without distinct surfaces between them, and having the strong character of directional growth; and alloy phases mainly distribute in the interface of columnar crystal corps.
A novel technique by using graphite immersed by K2CO3 solution to cover with the surface of molten alloy and setting porous ceramics in advance to transport atmosphere, is realized to in situ oxygenize molten alloy from its surface into its interior. The attractive features of the new technology in comparison with conventional growth technology are densified reaction resultant, smooth macro-surface around samples, and samples of front without rugged cellular stacking on them. It is found by microstructure observation, X-radial diffraction analysis(XRD) and by electron probe X-ray microanalysis(EPMA) that oxides grow in the form of columnar crystal consisting of clumps or grains of micron oxides in whichα-alumina is the main and silica a little, with continuous ingredient variation between two phases and clumps or grains, showing a tendency ofα-alumina wrapping silica without distinct surfaces between them, and having the strong character of directional growth; and alloy phases mainly distribute in the interface of columnar crystal corps.
2004, 21(2): 40-44.
Abstract:
The present paper deals with a primary study on the dispersion behavior of Al2O3 /NiAl slurries. The experiments are shown as follows: the zeta potential of both Al2O3 and NiAlparticles reaches the highest point in a slurry with respect to pH> 10. 6. For Al2O3 slurries with a solid content higher than 40 vol% , the optimum pH range is 11～12; the optimum dispersant contents of 40 vol% , 50 vol% and 60 vol% slurries are 0. 6 wt% , 2. 8 wt% and 8. 0 wt% respectively.For NiAl slurries with a solid content less than 30 vol% , the optimum pH range is 9～11; the optimum dispersant content is 0. 5 wt% . The slurry with 50 vol% ( Al2O3 / NiAl-20) exhibits excellent dispersion behavior under the best dispersing conditions.
The present paper deals with a primary study on the dispersion behavior of Al2O3 /NiAl slurries. The experiments are shown as follows: the zeta potential of both Al2O3 and NiAlparticles reaches the highest point in a slurry with respect to pH> 10. 6. For Al2O3 slurries with a solid content higher than 40 vol% , the optimum pH range is 11～12; the optimum dispersant contents of 40 vol% , 50 vol% and 60 vol% slurries are 0. 6 wt% , 2. 8 wt% and 8. 0 wt% respectively.For NiAl slurries with a solid content less than 30 vol% , the optimum pH range is 9～11; the optimum dispersant content is 0. 5 wt% . The slurry with 50 vol% ( Al2O3 / NiAl-20) exhibits excellent dispersion behavior under the best dispersing conditions.
2004, 21(2): 45-49.
Abstract:
The variation of electromagnetic parameters of the polymer magnet/ TiO2( i. e. OPM/TiO2 ) composite compactwave materials was studied in VHF and microwave frequency band at 100 MHz to 1800MHz. The results show that the OPM/ TiO2 modified by acrylic acid has a higher dielectric constant as well as lower dielectric loss and magnetic loss. The magnetic conductivity ( u′) and dielectric constant (X′) were remarkably raised for OPM/ TiO2 irradiated by cobalt-60 radiation, but its magnetic loss and dielectric loss have not changed basically. Thus, the OPM/TiO2 , as a good compactwave material, is of great value both in theory and in practice for the VHF and microwave communication, space science, computer and so on.
The variation of electromagnetic parameters of the polymer magnet/ TiO2( i. e. OPM/TiO2 ) composite compactwave materials was studied in VHF and microwave frequency band at 100 MHz to 1800MHz. The results show that the OPM/ TiO2 modified by acrylic acid has a higher dielectric constant as well as lower dielectric loss and magnetic loss. The magnetic conductivity ( u′) and dielectric constant (X′) were remarkably raised for OPM/ TiO2 irradiated by cobalt-60 radiation, but its magnetic loss and dielectric loss have not changed basically. Thus, the OPM/TiO2 , as a good compactwave material, is of great value both in theory and in practice for the VHF and microwave communication, space science, computer and so on.
STUDY ON PREPARATION THERMOSETTING PHENOLIC RESIN MODIFIED WITH SILICONE AND ITS ADHESIVE PROPERTIES
2004, 21(2): 50-54.
Abstract:
Thermosetting phenolic resin modified with silicone is directly synthesized with polyphenylmenthylsiloxane, phenol and formaldehyde. The synthetic method is much simpler than others. The curing condition, heat-resistant and adhesive property of phenolic resin modified with silicone are studied with IR, DSC, TGA, shear strength and peel strength. It is proved that the thermosetting phenolic resin modified with silicone is good at heat-resistance,toughness,shear strength and dissolution property,which can be used as heat-resistant adhesive and matrix resin in airplane and aerospace industry.
Thermosetting phenolic resin modified with silicone is directly synthesized with polyphenylmenthylsiloxane, phenol and formaldehyde. The synthetic method is much simpler than others. The curing condition, heat-resistant and adhesive property of phenolic resin modified with silicone are studied with IR, DSC, TGA, shear strength and peel strength. It is proved that the thermosetting phenolic resin modified with silicone is good at heat-resistance,toughness,shear strength and dissolution property,which can be used as heat-resistant adhesive and matrix resin in airplane and aerospace industry.
2004, 21(2): 55-59.
Abstract:
Sodium filled skutterudite NaFe4P12 whiskers and nanowires were prepared by a hydrothermal synthesis method. Skutterudite-polyaniline thermoelectric composite was prepared by in situ compounding using an emulsion polymerization method. The nanowires and whiskers as well as the composites were characterized by infrared spectra UV/VIs spectra and X-ray diffraction. Transmission electron microscope observation on the composite was carried out to investigate the morphology and growth mechanism of polyaniline on the surface of the skutterudite wires. Polyaniline can be compounded on the surface of the wires. In some samples, polyaniline grows as a brush structure on the surface of the NaFe4P12 whisker.
Sodium filled skutterudite NaFe4P12 whiskers and nanowires were prepared by a hydrothermal synthesis method. Skutterudite-polyaniline thermoelectric composite was prepared by in situ compounding using an emulsion polymerization method. The nanowires and whiskers as well as the composites were characterized by infrared spectra UV/VIs spectra and X-ray diffraction. Transmission electron microscope observation on the composite was carried out to investigate the morphology and growth mechanism of polyaniline on the surface of the skutterudite wires. Polyaniline can be compounded on the surface of the wires. In some samples, polyaniline grows as a brush structure on the surface of the NaFe4P12 whisker.
2004, 21(2): 60-64.
Abstract:
The fatigue damage accumulation of laminated steel-cord reinforced rubber composite under T-T loading is studied in this paper. The results indicate that the increase in the maximum strain exhibits a three-stage tendency in the process of fatigue. The macroscopic fatigue damage initiates from the ends of steel cords in the form of a cylindrical crack. Damage propagates along with the increase of crack numbers, the cord/matrix debonding and the growth of interply cracks. By using dynamic creep as the parameter, a linear dynamic creep fatigue damage accumulation model is established. This model can be used in the two-step loading condition to estimate the residual fatigue life of the specimen.
The fatigue damage accumulation of laminated steel-cord reinforced rubber composite under T-T loading is studied in this paper. The results indicate that the increase in the maximum strain exhibits a three-stage tendency in the process of fatigue. The macroscopic fatigue damage initiates from the ends of steel cords in the form of a cylindrical crack. Damage propagates along with the increase of crack numbers, the cord/matrix debonding and the growth of interply cracks. By using dynamic creep as the parameter, a linear dynamic creep fatigue damage accumulation model is established. This model can be used in the two-step loading condition to estimate the residual fatigue life of the specimen.
2004, 21(2): 65-69.
Abstract:
By the analysis of the tribological properties and the forming and stability of friction transfer films of PTFE composites modified by micro and nano metal particles respectively, the different forming and stability mechanisms of polymer friction transfer films are posted in the paper. The experiments and analysis indicate that filler particles have a great effect on improving anti-wear of composites, but also have a defect or shortage in improving the overall properties of PTFE composites purely modified by micro particles or nano particles.
By the analysis of the tribological properties and the forming and stability of friction transfer films of PTFE composites modified by micro and nano metal particles respectively, the different forming and stability mechanisms of polymer friction transfer films are posted in the paper. The experiments and analysis indicate that filler particles have a great effect on improving anti-wear of composites, but also have a defect or shortage in improving the overall properties of PTFE composites purely modified by micro particles or nano particles.
2004, 21(2): 70-75.
Abstract:
The interaction mechanism between silane coupling agent and nano silicon dioxide in the process of in-situ preparation of nano silicon dioxide composite material was studied by sol-gel method. The effects of silane coupling agent dosages on the mechanism and the application performance of the nano silicon dioxide composite material in epoxy varnish were also investigated. The mechanism of preparing nano silicon dioxide composite material is that the organic group of silane coupling agent substitutes the physisorption water and silicon alcoholic group on the surface of the nano silicon dioxide and forms nano composite material with good dispersibility. When the dosage of silane coupling agent is suitable, the composite material exhibits a good application performance in epoxy varnish as well as reinforcing and toughening properties of nano materials. The preparation technology has a good application prospect.
The interaction mechanism between silane coupling agent and nano silicon dioxide in the process of in-situ preparation of nano silicon dioxide composite material was studied by sol-gel method. The effects of silane coupling agent dosages on the mechanism and the application performance of the nano silicon dioxide composite material in epoxy varnish were also investigated. The mechanism of preparing nano silicon dioxide composite material is that the organic group of silane coupling agent substitutes the physisorption water and silicon alcoholic group on the surface of the nano silicon dioxide and forms nano composite material with good dispersibility. When the dosage of silane coupling agent is suitable, the composite material exhibits a good application performance in epoxy varnish as well as reinforcing and toughening properties of nano materials. The preparation technology has a good application prospect.
2004, 21(2): 76-80.
Abstract:
In this work, Brinson's one-dimensional constitutive relation and the refined kinetic relations for phase transformation of shape memory alloy (SMA) are used to write UMAT subroutine, so that SMA becomes one member of the material library of ABAQUS. Firstly, the stress-strain relation at various temperatures, the temperature-stress relation under constrained condition and the stress-strain relation under cyclic loading of a SMA bar are calculated to verify the UMAT code. Then the thermoviscoelastic property of the beam matrix is introduced into UTRS subroutine. The bending of the SMA reinforced epoxy resin beam under lateral load is simulated by FEM code of ABAQUS and the results coincide well with experiment.
In this work, Brinson's one-dimensional constitutive relation and the refined kinetic relations for phase transformation of shape memory alloy (SMA) are used to write UMAT subroutine, so that SMA becomes one member of the material library of ABAQUS. Firstly, the stress-strain relation at various temperatures, the temperature-stress relation under constrained condition and the stress-strain relation under cyclic loading of a SMA bar are calculated to verify the UMAT code. Then the thermoviscoelastic property of the beam matrix is introduced into UTRS subroutine. The bending of the SMA reinforced epoxy resin beam under lateral load is simulated by FEM code of ABAQUS and the results coincide well with experiment.
2004, 21(2): 81-86.
Abstract:
With mixed-mode flexure (MMF) specimens, the mixed-mode interlaminar fracture toughness of composite laminate was investigated experimentally, mainly focused on the hygrothermal effect on the strain energy release rates. It was found that: the co-function of heat and moisture caused plasticity near the tip of delamination. The critical energy release rates were calculated with two expressions (for mode Ⅰ and mode Ⅱ components, respectively) based on the beam theory. Scatter graphs of GⅠ versus GⅡ, the mode Ⅰ and mode Ⅱ components of critical energy release rates in different hygrothermal conditions, were given. The result showed that at room temperature, the hygroscopic absorption had little effect on the interlaminar fracture toughness, while at higher temperature conditions, the toughness increased as the hygroscopic degree increased. For dry laminates, the fracture toughness showed no distinct difference as the temperature increased, and for highly moisture absorpted specimens, the toughness was improved markedly. The fractograph was examined for further understanding of the mechanism.
With mixed-mode flexure (MMF) specimens, the mixed-mode interlaminar fracture toughness of composite laminate was investigated experimentally, mainly focused on the hygrothermal effect on the strain energy release rates. It was found that: the co-function of heat and moisture caused plasticity near the tip of delamination. The critical energy release rates were calculated with two expressions (for mode Ⅰ and mode Ⅱ components, respectively) based on the beam theory. Scatter graphs of GⅠ versus GⅡ, the mode Ⅰ and mode Ⅱ components of critical energy release rates in different hygrothermal conditions, were given. The result showed that at room temperature, the hygroscopic absorption had little effect on the interlaminar fracture toughness, while at higher temperature conditions, the toughness increased as the hygroscopic degree increased. For dry laminates, the fracture toughness showed no distinct difference as the temperature increased, and for highly moisture absorpted specimens, the toughness was improved markedly. The fractograph was examined for further understanding of the mechanism.
2004, 21(2): 87-91.
Abstract:
A program SHELLCV was composed based on 3D shell element by the finite element /control volume method. SHELLCV can simulate the process of mould-filling in RTM for the 3D complex shape thin parts and predict the resin flow front advancement and the distribution of pressure field at any instant in time. Comparing with the analytical solutions validated the accuracy and the reliability of SHELLCV program. Numerical examples show SHELLCV program can provide the effective references for the process design such as inlets and outlet arrangement and the pressure of the mold.
A program SHELLCV was composed based on 3D shell element by the finite element /control volume method. SHELLCV can simulate the process of mould-filling in RTM for the 3D complex shape thin parts and predict the resin flow front advancement and the distribution of pressure field at any instant in time. Comparing with the analytical solutions validated the accuracy and the reliability of SHELLCV program. Numerical examples show SHELLCV program can provide the effective references for the process design such as inlets and outlet arrangement and the pressure of the mold.
2004, 21(2): 92-98.
Abstract:
The differences between the finite element/control volume method(FE／CVM) and the algorithm of flow analysis network(FAN) technology were analyzed. The results show that the two algorithms based on the triangular grid are uniform and the flow analysis network technology can construct more accurate schemes to calculate the flow rate through the control volume surface in comparison with the conventional finite element/control volume method. Numerical examples show that the accuracy predicted by the flow analysis network technology is several times higher than that predicted by the conventional finite element/control volume method.
The differences between the finite element/control volume method(FE／CVM) and the algorithm of flow analysis network(FAN) technology were analyzed. The results show that the two algorithms based on the triangular grid are uniform and the flow analysis network technology can construct more accurate schemes to calculate the flow rate through the control volume surface in comparison with the conventional finite element/control volume method. Numerical examples show that the accuracy predicted by the flow analysis network technology is several times higher than that predicted by the conventional finite element/control volume method.
2004, 21(2): 99-104.
Abstract:
The nylon composites were prepared with the polyamide 1010 reinforced by shorten PAN carbon fibers. The tensile strength and surface hardness were measured for the carbon reinforced nylon composites in different CF contents. It was found in this study that the carbon fibers reinforcements enhanced the tensile strength and hardness, and reduced the friction coefficients and wear rates of the nylon composites compared with the neat nylon materials. The maximum tensile strength in value of 82 MPa was obtained when the carbon fibers were filled in 20 vol%. The linear relation between hardness and tensile strength of the carbon fibers reinforced nylon composites was presented after making regression of the experimental data. The test results in this paper showed that the oxidized treatment on carbon fiber surface greatly improved the felting property of carbon fibers in nylon substrates. Therefore, the tensile strength of the oxidized carbon fiber reinforced nylon composites was about 10% higher than that filled with the untreated carbon fibers. The experiments of the wear of nylon composites against carbon steel revealed that the composite's friction coefficients and wear rates were closely in relation to the tensile strength and hardness. When the tensile strength or hardness increased, the friction coefficients and wear rates decreased. The mathematical analysis stated that the friction coefficients and wear rates were inversely proportional to the tensile strength of the nylon composites. However, they had a second order polynomial equation to the hardness. The friction coefficients and wear rates changed with the carbon fiber contents in a decay exponent curve.
The nylon composites were prepared with the polyamide 1010 reinforced by shorten PAN carbon fibers. The tensile strength and surface hardness were measured for the carbon reinforced nylon composites in different CF contents. It was found in this study that the carbon fibers reinforcements enhanced the tensile strength and hardness, and reduced the friction coefficients and wear rates of the nylon composites compared with the neat nylon materials. The maximum tensile strength in value of 82 MPa was obtained when the carbon fibers were filled in 20 vol%. The linear relation between hardness and tensile strength of the carbon fibers reinforced nylon composites was presented after making regression of the experimental data. The test results in this paper showed that the oxidized treatment on carbon fiber surface greatly improved the felting property of carbon fibers in nylon substrates. Therefore, the tensile strength of the oxidized carbon fiber reinforced nylon composites was about 10% higher than that filled with the untreated carbon fibers. The experiments of the wear of nylon composites against carbon steel revealed that the composite's friction coefficients and wear rates were closely in relation to the tensile strength and hardness. When the tensile strength or hardness increased, the friction coefficients and wear rates decreased. The mathematical analysis stated that the friction coefficients and wear rates were inversely proportional to the tensile strength of the nylon composites. However, they had a second order polynomial equation to the hardness. The friction coefficients and wear rates changed with the carbon fiber contents in a decay exponent curve.
2004, 21(2): 105-110.
Abstract:
The permeability of preform is an important material processing parameter. To build a model of estimating permeability is significant for understanding the wetting mechanism of fiber to resin, forecasting the permeability and optimizing the process and material parameters accurately. In this paper, a statistical model of preform's longitudinal permeability is built based on the analysis on the microstructure of the preform used in the LCM composites processing method. Research is done into the influence of the unidirectional preform's microstructure and its parameters on its longitudinal permeability, and it is verified in experiments finally.
The permeability of preform is an important material processing parameter. To build a model of estimating permeability is significant for understanding the wetting mechanism of fiber to resin, forecasting the permeability and optimizing the process and material parameters accurately. In this paper, a statistical model of preform's longitudinal permeability is built based on the analysis on the microstructure of the preform used in the LCM composites processing method. Research is done into the influence of the unidirectional preform's microstructure and its parameters on its longitudinal permeability, and it is verified in experiments finally.
2004, 21(2): 111-116.
Abstract:
Lamb wave propagation through fiber-reinforced composites has become a subject of intensive study due to its application to nondestructive evaluation. The anisotropic multilayered media are now usually studied by the transfer matrix formalism. Though this formalism is very convenient, it leads to numerical instabilities at high frequency-thickness products. The method developed in this paper using the global matrix is an improved version of Nayfeh's matrix method. The program using the global matrix has preferable stability, which can effectively create dispersion curves for Lamb wave propagation in anisotropic multilayered composites. Characteristics of Lamb wave propagation in fiber-reinforced composites are influenced by many factors and one of them is the number of layers. The calculated dispersion curves for different layered structures are presented together with plots of the through-thickness particle stress component amplitudes for two fundamental modes a0 and s0. These numerical examples provide a powerful tool for nondestructive evaluation of anisotropic layered plates.
Lamb wave propagation through fiber-reinforced composites has become a subject of intensive study due to its application to nondestructive evaluation. The anisotropic multilayered media are now usually studied by the transfer matrix formalism. Though this formalism is very convenient, it leads to numerical instabilities at high frequency-thickness products. The method developed in this paper using the global matrix is an improved version of Nayfeh's matrix method. The program using the global matrix has preferable stability, which can effectively create dispersion curves for Lamb wave propagation in anisotropic multilayered composites. Characteristics of Lamb wave propagation in fiber-reinforced composites are influenced by many factors and one of them is the number of layers. The calculated dispersion curves for different layered structures are presented together with plots of the through-thickness particle stress component amplitudes for two fundamental modes a0 and s0. These numerical examples provide a powerful tool for nondestructive evaluation of anisotropic layered plates.
2004, 21(2): 117-122.
Abstract:
After the consolidation of the composite ring in tension winding, the mandrel is drawn out, and then a hollow ring is formed. The process is called unload of inner hole. Based on the analyses of a pressfit of multi-ring and tension winding of a composite flywheel, the simplified analyses of multi-ring pressfit of the composite flywheel is advanced, which adopts the influence of winding tension and unload of composite ring. Then the formula of stress and deformation is proposed. The result showed that the fields of stress and deformation changed evidently when the composite ring unloaded from the mandrel. The method of combination of the two ways can availably increase the radial compressive stress and smooth the hoop stress. The real interference caused by the unload of the rings had increased much relative to the initial appointed interference, which should be paid enough attention to.
After the consolidation of the composite ring in tension winding, the mandrel is drawn out, and then a hollow ring is formed. The process is called unload of inner hole. Based on the analyses of a pressfit of multi-ring and tension winding of a composite flywheel, the simplified analyses of multi-ring pressfit of the composite flywheel is advanced, which adopts the influence of winding tension and unload of composite ring. Then the formula of stress and deformation is proposed. The result showed that the fields of stress and deformation changed evidently when the composite ring unloaded from the mandrel. The method of combination of the two ways can availably increase the radial compressive stress and smooth the hoop stress. The real interference caused by the unload of the rings had increased much relative to the initial appointed interference, which should be paid enough attention to.
2004, 21(2): 123-127.
Abstract:
One of the aims in the design of 3D fabric parameters is to meet the requirement of fiber volume fraction (FVF). By analyzing the unit cell of 3D orthogonal woven fabric, the sizes of warp, fill and binder yarn cross-sections were calculated and the relationships of FVF with the fabric parameters were established. The results could be used to theoretically calculate warp, fill and binder yarns', as well as the fabric's, FVF. A piece of glass fiber orthogonal woven fabric with 6 layer warp yarns and 5 layer fill yarns was manufactured to test the FVF and the calculated values were compared with the tested ones. The reasons that caused the difference between the theoretical values and the experimental values were analyzed. The factors, such as the ratio of warp thickness to fill thickness (Texw/Texf), the ratio of fill yarn density to warp yarn density (dW/dF) and the binder thickness, all of which affect FVF, were discussed. It was found that along with the increase of Texw/Texf or the decrease of dW/dF, the FVF of warp and fabric would increase, but the FVF in the fill direction would decrease, and the thicker the binder yarn, the smaller would be the warp, fill and fabric's fiber volume fractions.
One of the aims in the design of 3D fabric parameters is to meet the requirement of fiber volume fraction (FVF). By analyzing the unit cell of 3D orthogonal woven fabric, the sizes of warp, fill and binder yarn cross-sections were calculated and the relationships of FVF with the fabric parameters were established. The results could be used to theoretically calculate warp, fill and binder yarns', as well as the fabric's, FVF. A piece of glass fiber orthogonal woven fabric with 6 layer warp yarns and 5 layer fill yarns was manufactured to test the FVF and the calculated values were compared with the tested ones. The reasons that caused the difference between the theoretical values and the experimental values were analyzed. The factors, such as the ratio of warp thickness to fill thickness (Texw/Texf), the ratio of fill yarn density to warp yarn density (dW/dF) and the binder thickness, all of which affect FVF, were discussed. It was found that along with the increase of Texw/Texf or the decrease of dW/dF, the FVF of warp and fabric would increase, but the FVF in the fill direction would decrease, and the thicker the binder yarn, the smaller would be the warp, fill and fabric's fiber volume fractions.
2004, 21(2): 128-133.
Abstract:
A cross model of 3-D braided composites is presented based on elastic theory. The model is simple and programmed easily. Modulus is calculated easily, but certain error exists in results. The author summarizes the factors which affect the elastic modulus of 3-D braided composites and the cross model of the composites is modified twice firstly. The reasons and results of the model modified are different. Firstly, the traditional global-cell model of unilateral composites is modified. Based on this, the model is modified secondly considering the fiber curve radian of fabric structures. And fiber's curve radian is simulated by sinusoid. Using the cross model modified and MATLAB software, the composites modulus and stress on a fiber section at tensile load are calculated. The predicted results of the modulus based on the cross model modified twice are in good agreement with experiments results. The 3-D braided composites mechanism of fracture is interpreted by stress results.
A cross model of 3-D braided composites is presented based on elastic theory. The model is simple and programmed easily. Modulus is calculated easily, but certain error exists in results. The author summarizes the factors which affect the elastic modulus of 3-D braided composites and the cross model of the composites is modified twice firstly. The reasons and results of the model modified are different. Firstly, the traditional global-cell model of unilateral composites is modified. Based on this, the model is modified secondly considering the fiber curve radian of fabric structures. And fiber's curve radian is simulated by sinusoid. Using the cross model modified and MATLAB software, the composites modulus and stress on a fiber section at tensile load are calculated. The predicted results of the modulus based on the cross model modified twice are in good agreement with experiments results. The 3-D braided composites mechanism of fracture is interpreted by stress results.
2004, 21(2): 134-141.
Abstract:
On the basis of structural analysis for the three-dimensional four-step(1×1) braided composites, further improvement was made on the three-cell model which includes interior,surface and corner cells. The modified model realizes the geometric continuity of the fibers in the space, and also really simulates the moving orientation of fibers in the braided preforms. Based on this model, we predicted the elastic properties of three-dimensional and four-directional braided composites with the method of stiffness averaging. Comparison of the calculating results with the available experimental data shows the applicability of the present model.
On the basis of structural analysis for the three-dimensional four-step(1×1) braided composites, further improvement was made on the three-cell model which includes interior,surface and corner cells. The modified model realizes the geometric continuity of the fibers in the space, and also really simulates the moving orientation of fibers in the braided preforms. Based on this model, we predicted the elastic properties of three-dimensional and four-directional braided composites with the method of stiffness averaging. Comparison of the calculating results with the available experimental data shows the applicability of the present model.
2004, 21(2): 142-146.
Abstract:
A smart structure embedded with SMA and PZT as united actuators is solved by finite element method. Piezoelectric patch and shape memory alloy slim are bonded to its surface or embedded within the laminate. The applied voltage of PZT and the temperature of SMA are given for any plate shapes using optimization algorithms, with the difference between the desired and actual shapes as the objective function, and the constraint of the applied voltage and temperature is considered. The comparison among the effects of different control methods is given.
A smart structure embedded with SMA and PZT as united actuators is solved by finite element method. Piezoelectric patch and shape memory alloy slim are bonded to its surface or embedded within the laminate. The applied voltage of PZT and the temperature of SMA are given for any plate shapes using optimization algorithms, with the difference between the desired and actual shapes as the objective function, and the constraint of the applied voltage and temperature is considered. The comparison among the effects of different control methods is given.
2004, 21(2): 147-152.
Abstract:
The in vitro bioactivities of PA6 and nano-HA/PA6 were studied in SBF(simulated body fluid). The results show that PA6 was not bioactive in SBF, and Ca-P compound is slowly deposited on the surface of PA6, but it was not HA. Nano-HA/PA6 composite was chemically active in SBF, and dissolution and deposition of Ca, P ions happened during the culture in SBF. The Ca-P precipitate on the surface of HA/PA6 composite surface was carbonated-apatite. Its weight lost by about 2 % every week. This kind of composite could be one of the best potential bioactive materials for load-bearing bones, substitution or as bioengineering material.
The in vitro bioactivities of PA6 and nano-HA/PA6 were studied in SBF(simulated body fluid). The results show that PA6 was not bioactive in SBF, and Ca-P compound is slowly deposited on the surface of PA6, but it was not HA. Nano-HA/PA6 composite was chemically active in SBF, and dissolution and deposition of Ca, P ions happened during the culture in SBF. The Ca-P precipitate on the surface of HA/PA6 composite surface was carbonated-apatite. Its weight lost by about 2 % every week. This kind of composite could be one of the best potential bioactive materials for load-bearing bones, substitution or as bioengineering material.
2004, 21(2): 153-156.
Abstract:
Extensive dislocation structure was observed by TEM in the Fe3Al/Al2O3 nanocomposite. The composites were thus strengthened due to microstructure refinement through subgrain formation. The ordered strengthening mechanism of Fe3Al intermetallic further increased the mechanical properties of Fe3Al/Al2O3 composites. It was seen from TEM that lots of dislocations were produced in Al2O3 intergrains by introducing Fe3Al. The dislocations mainly existed near the interphase of Fe3Al and Al2O. TEM shows Fe3Al can breed rich dislocations in Al2O3, which were nailed by nano grains. The composites were strengthened due to microstructure refinement through subgrain formation. Superlattice dislocations observed in Fe3Al can produce orderly strengthening.
Extensive dislocation structure was observed by TEM in the Fe3Al/Al2O3 nanocomposite. The composites were thus strengthened due to microstructure refinement through subgrain formation. The ordered strengthening mechanism of Fe3Al intermetallic further increased the mechanical properties of Fe3Al/Al2O3 composites. It was seen from TEM that lots of dislocations were produced in Al2O3 intergrains by introducing Fe3Al. The dislocations mainly existed near the interphase of Fe3Al and Al2O. TEM shows Fe3Al can breed rich dislocations in Al2O3, which were nailed by nano grains. The composites were strengthened due to microstructure refinement through subgrain formation. Superlattice dislocations observed in Fe3Al can produce orderly strengthening.
2004, 21(2): 157-160.
Abstract:
Fe3O4 nanoparticles were prepared by a precipitation method. The Fe3O4 nanoparticles were dealt with ethanol to form an organic surface. Then polypyrrole composite was polymerized by the emulsion polymerization method in the presence of these Fe3O4 nanoparticles. The structural characterization by TEM, XPS, and AAS proved that the dispersion of Fe3O4 nanoparticles dealt with alcohol was better than that of naked ones. Fe3O4 nanoparticles were entrapped or encapsulated in the PPy chain. The thickness of the PPy layer was about 10 nm. The Fe3O4 / PPy composites showed electrical and ferromagnetic property( e= 7. 69 s/ cm～13. 6 s/ cm, Ms= 12. 06 emu/ g～24. 38 emu/ g, Hc= 11 Oe～41 Oe) . The environmental stability of composites was better than that of PPy.
Fe3O4 nanoparticles were prepared by a precipitation method. The Fe3O4 nanoparticles were dealt with ethanol to form an organic surface. Then polypyrrole composite was polymerized by the emulsion polymerization method in the presence of these Fe3O4 nanoparticles. The structural characterization by TEM, XPS, and AAS proved that the dispersion of Fe3O4 nanoparticles dealt with alcohol was better than that of naked ones. Fe3O4 nanoparticles were entrapped or encapsulated in the PPy chain. The thickness of the PPy layer was about 10 nm. The Fe3O4 / PPy composites showed electrical and ferromagnetic property( e= 7. 69 s/ cm～13. 6 s/ cm, Ms= 12. 06 emu/ g～24. 38 emu/ g, Hc= 11 Oe～41 Oe) . The environmental stability of composites was better than that of PPy.
2004, 21(2): 161-167.
Abstract:
In RTM, it needs pre-placing fibrous preform into the mold. It is most probable to create an edge effect, which offers injected resin paths of least resistance due to the variation of fibrous preform structure and the shape and dimension of the mold. The edge effect may drastically affect resin flow front advancement and the distribution of pressure fields. In this paper, simulations are carried out with the approach of equivalent permeability, and the resin flow front curve and pressure fields with flow channels are obtained. The studies demonstrate that on the one hand the edge effect may lead to the unwanted effect on resin flow fields to form defects——dry spot, on the other hand it may be used to enhance the mold filling process: reduction of mold and injection pressures at constant flow rate injection; shorter fill time at constant pressure injection.
In RTM, it needs pre-placing fibrous preform into the mold. It is most probable to create an edge effect, which offers injected resin paths of least resistance due to the variation of fibrous preform structure and the shape and dimension of the mold. The edge effect may drastically affect resin flow front advancement and the distribution of pressure fields. In this paper, simulations are carried out with the approach of equivalent permeability, and the resin flow front curve and pressure fields with flow channels are obtained. The studies demonstrate that on the one hand the edge effect may lead to the unwanted effect on resin flow fields to form defects——dry spot, on the other hand it may be used to enhance the mold filling process: reduction of mold and injection pressures at constant flow rate injection; shorter fill time at constant pressure injection.
