2013 Vol. 30, No. 2
2013, 30(2): 1-9.
Abstract:
The system of manufacturing technology of advanced polymer matrix composites in China, including the melting prepared prepreg, autoclave, and resin transfer molding process (RTM) forming techniques, has been established during the development in the past three decades. The advanced composites have been widely applied in the aeronautic manufacturing filed. The recent development progress in autoclave, RTM and automated fiber placement techniques for polymer matrix composites are introduced in this paper. The advanced polymer matrix composite manufacturing progress simulation and optimization technique are then presented. The future development directions of composite manufacture research are discussed.
The system of manufacturing technology of advanced polymer matrix composites in China, including the melting prepared prepreg, autoclave, and resin transfer molding process (RTM) forming techniques, has been established during the development in the past three decades. The advanced composites have been widely applied in the aeronautic manufacturing filed. The recent development progress in autoclave, RTM and automated fiber placement techniques for polymer matrix composites are introduced in this paper. The advanced polymer matrix composite manufacturing progress simulation and optimization technique are then presented. The future development directions of composite manufacture research are discussed.
2013, 30(2): 10-17.
Abstract:
Polyetherimide (PEI) nano-fibrous membranes with multi-walled carbon nanotubes (MWCNTs)were prepared by electrospinning. The morphology of nano-fibrous membranes was studied by SEM and TEM. The impact and tensile properties of epoxy toughed by nano-fibrous membranes were investigated. The result shows that the toughness of epoxy is improved with the loading of PEI nano-fibrous membranes with MWCNTs. The result of G IC test shows that interlaminar fracture toughness of the carbon fiber/epoxy composites toughed by PEI nano-fibrous membranes containing 3% mass fraction active MWCNTs (a-MWCNTs) can be highly enhanced.
Polyetherimide (PEI) nano-fibrous membranes with multi-walled carbon nanotubes (MWCNTs)were prepared by electrospinning. The morphology of nano-fibrous membranes was studied by SEM and TEM. The impact and tensile properties of epoxy toughed by nano-fibrous membranes were investigated. The result shows that the toughness of epoxy is improved with the loading of PEI nano-fibrous membranes with MWCNTs. The result of G IC test shows that interlaminar fracture toughness of the carbon fiber/epoxy composites toughed by PEI nano-fibrous membranes containing 3% mass fraction active MWCNTs (a-MWCNTs) can be highly enhanced.
2013, 30(2): 18-23.
Abstract:
By means of in situ emulsion copolymerization, core-shell silica hybrid particles with poly(MMA-co-BA) shells were fabricated, which were subsequently compounded with isotactic polypropylene (PP) in the molten state to prepare SiO2/PP composites. The non-isothermal crystallization kinetics of SiO2/PP composites was investigated by DSC. The results show that the addition of silica hybrid particles has an obvious nucleating effect on the crystallization of PP, increasing crystallization temperature and crystallization rate. On the contrary, the activation energies of SiO2/PP are higher than that of the pure PP. The kinetics of non-isothermal crystallization of SiO2/PP can be indicated by Mo equation. It shows that silica hybrid particles decrease the cooling rates of PP needed to reach relative crystallinities in a unite time.
By means of in situ emulsion copolymerization, core-shell silica hybrid particles with poly(MMA-co-BA) shells were fabricated, which were subsequently compounded with isotactic polypropylene (PP) in the molten state to prepare SiO2/PP composites. The non-isothermal crystallization kinetics of SiO2/PP composites was investigated by DSC. The results show that the addition of silica hybrid particles has an obvious nucleating effect on the crystallization of PP, increasing crystallization temperature and crystallization rate. On the contrary, the activation energies of SiO2/PP are higher than that of the pure PP. The kinetics of non-isothermal crystallization of SiO2/PP can be indicated by Mo equation. It shows that silica hybrid particles decrease the cooling rates of PP needed to reach relative crystallinities in a unite time.
2013, 30(2): 24-30.
Abstract:
In this study, an air-coupled ultrasonic nondestructive evaluation (NDE) method was used to measure the resin flow of a partially impregnated prepreg through thickness of fibers layer. The partially impregnated prepregs were put into a vacuum bag, and then assembled on the C-scan sweep mechanism. Vacuum was applied to the specimens and ultrasonic images at various times were obtained by using the air-coupled ultrsound evaluation instrument. Therefore, flow variation of resin penetrating into fibrous webs was monitored in situ by the ultrasonic images. As well, the permeability of the carbon fiber webs was calculated from Darcy’s law. To evaluate the validity of the used NDE method, metallographic specimens corresponding to each C-scan sample were prepared and observed, and the yielded microphotographs demonstrated the rationality of the NDE method. Results show that the proposed air-coupled ultrasonic evaluation method is an effective way for in situ monitoring resin flow through thickness of fibers layers.
In this study, an air-coupled ultrasonic nondestructive evaluation (NDE) method was used to measure the resin flow of a partially impregnated prepreg through thickness of fibers layer. The partially impregnated prepregs were put into a vacuum bag, and then assembled on the C-scan sweep mechanism. Vacuum was applied to the specimens and ultrasonic images at various times were obtained by using the air-coupled ultrsound evaluation instrument. Therefore, flow variation of resin penetrating into fibrous webs was monitored in situ by the ultrasonic images. As well, the permeability of the carbon fiber webs was calculated from Darcy’s law. To evaluate the validity of the used NDE method, metallographic specimens corresponding to each C-scan sample were prepared and observed, and the yielded microphotographs demonstrated the rationality of the NDE method. Results show that the proposed air-coupled ultrasonic evaluation method is an effective way for in situ monitoring resin flow through thickness of fibers layers.
2013, 30(2): 31-36.
Abstract:
The hollow glass microspheres were sieved to have different particle sizes, and the syntactic foams by blending hollow glass microspheres with epoxy resin were prepared. The compressive mechanical properties of the syntactic foams were studied by quasi-static compressive tests. In addition, the microscopicstructure was observed by SEM. By using the random spatial dispersing method, model of syntactic foams filled with particles having varied particle size were built. And finite element method was utilized to analyze the behavior of the matrix and particles under 1 kPa pressure. The result shows that as the particle diameter of hollow glass microspheres increases from 30 μm to 120 μm, the compressive strength of syntactic foam does not have significant change. With finite element analysis, it is found that hollow glass microspheres are the main energy loader. The value of von-Mises stress located on the hollow microspheres is higher than that of stress located on the matrix. The maximum stress is located on the inner surface of hollow glass microspheres, and it could also infer that microspheres are fully squeezed before crack from inside out with the SEM observation.
The hollow glass microspheres were sieved to have different particle sizes, and the syntactic foams by blending hollow glass microspheres with epoxy resin were prepared. The compressive mechanical properties of the syntactic foams were studied by quasi-static compressive tests. In addition, the microscopicstructure was observed by SEM. By using the random spatial dispersing method, model of syntactic foams filled with particles having varied particle size were built. And finite element method was utilized to analyze the behavior of the matrix and particles under 1 kPa pressure. The result shows that as the particle diameter of hollow glass microspheres increases from 30 μm to 120 μm, the compressive strength of syntactic foam does not have significant change. With finite element analysis, it is found that hollow glass microspheres are the main energy loader. The value of von-Mises stress located on the hollow microspheres is higher than that of stress located on the matrix. The maximum stress is located on the inner surface of hollow glass microspheres, and it could also infer that microspheres are fully squeezed before crack from inside out with the SEM observation.
2013, 30(2): 37-43.
Abstract:
Pentasulfid bis(2, 2, 4-trimethyl) pentyl (RC2540)-melamine-formaldehyde resin microcapsules was synthesized by in-situ polymerization method with sulfureted fatty additive RC2540 as core materials and melamine-formaldehyde resin (MF resin) as shell materials. FTIR, thermo-gravimetric analysis and SEM measurements were used to characterize these microcapsules. The friction and wear properties of RC2540-MF resin microcapsules were investigated with four-ball testing machine using polyethyleneglycol as base fluid. The experimental results reveal that the friction coefficient can be as low as 0.04 under the lubrication of the base oil with 3% mass fraction of RC2540-MF resin microcapsules in 314 N load, the wear diameter under 314 N load(with 5% mass fraction of RC2540-MF resin microcapsules) is 0.54 mm, the experimental load can be increased to 1000 N above. The effect of RC2540-MF resin microcapsules in reducing friction and wear may be attributed to the physical and chemical adsorption on the friction surface, and to the tribochemical reaction film by active sulfides released from broken RC2540-MF resin microcapsules, leading to anti-friction, good extreme pressure and anti-wear property.
Pentasulfid bis(2, 2, 4-trimethyl) pentyl (RC2540)-melamine-formaldehyde resin microcapsules was synthesized by in-situ polymerization method with sulfureted fatty additive RC2540 as core materials and melamine-formaldehyde resin (MF resin) as shell materials. FTIR, thermo-gravimetric analysis and SEM measurements were used to characterize these microcapsules. The friction and wear properties of RC2540-MF resin microcapsules were investigated with four-ball testing machine using polyethyleneglycol as base fluid. The experimental results reveal that the friction coefficient can be as low as 0.04 under the lubrication of the base oil with 3% mass fraction of RC2540-MF resin microcapsules in 314 N load, the wear diameter under 314 N load(with 5% mass fraction of RC2540-MF resin microcapsules) is 0.54 mm, the experimental load can be increased to 1000 N above. The effect of RC2540-MF resin microcapsules in reducing friction and wear may be attributed to the physical and chemical adsorption on the friction surface, and to the tribochemical reaction film by active sulfides released from broken RC2540-MF resin microcapsules, leading to anti-friction, good extreme pressure and anti-wear property.
2013, 30(2): 44-49.
Abstract:
Carbon fibers were plated with the electroless nickel plating method, the micro-morphology of nickel-plated carbon fibers, the microstructure and composition of coatings were studied with SEM, EDX, XRD. The conductivities of nickel-plated carbon fibers were tested with broadband resistance voltage instrument. The nickel-plated carbon fibers/epoxy resin conductive composites with volume percentage of 2.5%, 5%, 7.5%, 10% were made by mixing method, the shielding effectiveness of these composites was tested by shielding enclosure method. Results show that after nickel plating, a lay of uniform nickel coating is formed on the surface of carbon fibers. The quality fraction of nickel in the coatings is about 94%. The resistances of nickel plated carbon fibers are only 1/54 of original carbon fibers. The shielding effectiveness of the nickel coated carbon fibers/epoxy resin composites is higher than that of original carbon fibers. The shielding effectiveness of the composites increases with the increasing of nickel-plated carbon fibers content. On low frequency(~kHz), the shielding effectiveness of the composites depends on material intrinsic parameters, and the shielding effectiveness is almost independent on the nickel-plated carbon fibers content. While on high and intermediate frequency(~MHz, ~GHz), the shielding effectiveness is related with resistivity of the nickel coated carbon fibers/epoxy resin composites.
Carbon fibers were plated with the electroless nickel plating method, the micro-morphology of nickel-plated carbon fibers, the microstructure and composition of coatings were studied with SEM, EDX, XRD. The conductivities of nickel-plated carbon fibers were tested with broadband resistance voltage instrument. The nickel-plated carbon fibers/epoxy resin conductive composites with volume percentage of 2.5%, 5%, 7.5%, 10% were made by mixing method, the shielding effectiveness of these composites was tested by shielding enclosure method. Results show that after nickel plating, a lay of uniform nickel coating is formed on the surface of carbon fibers. The quality fraction of nickel in the coatings is about 94%. The resistances of nickel plated carbon fibers are only 1/54 of original carbon fibers. The shielding effectiveness of the nickel coated carbon fibers/epoxy resin composites is higher than that of original carbon fibers. The shielding effectiveness of the composites increases with the increasing of nickel-plated carbon fibers content. On low frequency(~kHz), the shielding effectiveness of the composites depends on material intrinsic parameters, and the shielding effectiveness is almost independent on the nickel-plated carbon fibers content. While on high and intermediate frequency(~MHz, ~GHz), the shielding effectiveness is related with resistivity of the nickel coated carbon fibers/epoxy resin composites.
2013, 30(2): 50-55.
Abstract:
A new carbon fiber precursors was prepared by liquefied wood in phenol. The liquefied wood was modified to spinning solution by adding hexamethylenetetramine, melt-spinning then cured in combined solution of hydrochloric acid and formaldehyde to obtain precursors. The pore structure, microcrystalline structure and thermal stability of liquefied wood carbon fiber precursors were studied. The results show that the adsorption isotherm of N2 for as-spun fibers and precursors belongs to type Ⅱ , the specific surface area of as-spun fibers is 0.517 m2·g-1, and precursors is 0.142 m2·g-1. Wood powder form Chinese fir has typical diffraction peaks of cellulose Ⅰ . The typical diffraction peaks of cellulose Ⅰ in as-spun fibers and precursors disappear, at the same time a new diffraction peak around 18.8° emerges, suggesting that new crystalline structure of as-spun fibers and precursors has formed. The typical diffraction peaks around 18.8° for precursors polymer strengthen, so crystallinity increases. Interestingly, the mass loss of as-spun fibers is 88.3%, and precursors is 60%, simultaneously the apparent activation energy increases from 31.31 kJ·mol-1 of as-spun fibers to 39.18 kJ·mol-1 of precursors, the thermal stability of precursors improves.
A new carbon fiber precursors was prepared by liquefied wood in phenol. The liquefied wood was modified to spinning solution by adding hexamethylenetetramine, melt-spinning then cured in combined solution of hydrochloric acid and formaldehyde to obtain precursors. The pore structure, microcrystalline structure and thermal stability of liquefied wood carbon fiber precursors were studied. The results show that the adsorption isotherm of N2 for as-spun fibers and precursors belongs to type Ⅱ , the specific surface area of as-spun fibers is 0.517 m2·g-1, and precursors is 0.142 m2·g-1. Wood powder form Chinese fir has typical diffraction peaks of cellulose Ⅰ . The typical diffraction peaks of cellulose Ⅰ in as-spun fibers and precursors disappear, at the same time a new diffraction peak around 18.8° emerges, suggesting that new crystalline structure of as-spun fibers and precursors has formed. The typical diffraction peaks around 18.8° for precursors polymer strengthen, so crystallinity increases. Interestingly, the mass loss of as-spun fibers is 88.3%, and precursors is 60%, simultaneously the apparent activation energy increases from 31.31 kJ·mol-1 of as-spun fibers to 39.18 kJ·mol-1 of precursors, the thermal stability of precursors improves.
2013, 30(2): 56-62.
Abstract:
Nanometer copper sulfide/polydicyclopentadiene (nano-CuS/PDCPD) composites were successfully prepared by the reaction injecting molding, using tungsten complex as the main catalyst, diethyl aluminium chloride (Et2AlCl) as the cocatalyst, and surface modified CuS nanopowders as the additive. The structure, dispersion of the fillers, worn surface, mechanical properties and friction and wear performance of the as-obtained CuS nanopowders and nano-CuS/PDCPD composities were characterized and tested by many technologies, such as FTIR, SEM, TEM, 3D morphology meter, and high-temperature atmosphere friction/wear tester. The results indicate that the mechanical property and friction and wear performance of nano-CuS/PDCPD composities are significantly enhanced compared to that of pristine PDCPD when surface modified CuS nanopowders are used in low addition range, and the comprehensive properties achieve their optimum with CuS mass fraction of 1%.The most increased values of impact strength, tensile strength, and bending strength are 13.2%, 22.0% and 13.8%, respectively. The wear mass and friction coefficient decrease 31% and 36%, respectively. The well interface compatibility between the particle/matrix interfaces plays an important role for the improved mechanical and tribological properties of nano-CuS/PDCPD composities in low CuS loadings.
Nanometer copper sulfide/polydicyclopentadiene (nano-CuS/PDCPD) composites were successfully prepared by the reaction injecting molding, using tungsten complex as the main catalyst, diethyl aluminium chloride (Et2AlCl) as the cocatalyst, and surface modified CuS nanopowders as the additive. The structure, dispersion of the fillers, worn surface, mechanical properties and friction and wear performance of the as-obtained CuS nanopowders and nano-CuS/PDCPD composities were characterized and tested by many technologies, such as FTIR, SEM, TEM, 3D morphology meter, and high-temperature atmosphere friction/wear tester. The results indicate that the mechanical property and friction and wear performance of nano-CuS/PDCPD composities are significantly enhanced compared to that of pristine PDCPD when surface modified CuS nanopowders are used in low addition range, and the comprehensive properties achieve their optimum with CuS mass fraction of 1%.The most increased values of impact strength, tensile strength, and bending strength are 13.2%, 22.0% and 13.8%, respectively. The wear mass and friction coefficient decrease 31% and 36%, respectively. The well interface compatibility between the particle/matrix interfaces plays an important role for the improved mechanical and tribological properties of nano-CuS/PDCPD composities in low CuS loadings.
2013, 30(2): 63-69.
Abstract:
The effects of ultraviolet A (UVA) irradiation on properties of carbon fiber (CF) reinforced epoxy resin composites were discussed. UVA irradiance from the sunlight indoor and fluorescent lamp was investigated. After UVA exposure at the irradiance of 200 μW·cm-2, the changes of mechanical properties and surface properties of CF reinforced epoxy resin composites by XPS, contact angle, nano-indentation, and atomic force microscope (AFM) were studied. The results show that UVA irradiance from the sunlight reaches the maximum value at 14: 00 on the clear days in spring and summer and the maximum value is 375 μW·cm-2 at the window and sharply decreases to 30 μW·cm-2 at 1 m far from the window. To the fluorescent lamp of 40 W, UVA irradiance is 87.3 μW·cm-2 at the lamp and 5.4 μW·cm-2 at 1 m far from the lamp. After UVA exposure of 45 days, there are no obvious changes on the interlaminar shear strength (ILSS), bending strength and tensile strength. CF reinforced epoxy resin composites have an oxidation on exposed surface and show increasing surface hardness and roughness.
The effects of ultraviolet A (UVA) irradiation on properties of carbon fiber (CF) reinforced epoxy resin composites were discussed. UVA irradiance from the sunlight indoor and fluorescent lamp was investigated. After UVA exposure at the irradiance of 200 μW·cm-2, the changes of mechanical properties and surface properties of CF reinforced epoxy resin composites by XPS, contact angle, nano-indentation, and atomic force microscope (AFM) were studied. The results show that UVA irradiance from the sunlight reaches the maximum value at 14: 00 on the clear days in spring and summer and the maximum value is 375 μW·cm-2 at the window and sharply decreases to 30 μW·cm-2 at 1 m far from the window. To the fluorescent lamp of 40 W, UVA irradiance is 87.3 μW·cm-2 at the lamp and 5.4 μW·cm-2 at 1 m far from the lamp. After UVA exposure of 45 days, there are no obvious changes on the interlaminar shear strength (ILSS), bending strength and tensile strength. CF reinforced epoxy resin composites have an oxidation on exposed surface and show increasing surface hardness and roughness.
2013, 30(2): 70-74.
Abstract:
With silicon resin as the base matrix materials, filled with multilayer graphite, the thermal conductive multilayer graphite/silicon resin composites were prepared by using the method of rotating-mixer. The effect of filler on the thermal conductivity, coefficient of thermal expansion (CTE) and the thermal stability of the composites were investigated. Results show that the multilayer graphite in silicon resin has good dispersibility. The thermal conductivity of the composites increases with the increasing content of multilayer graphite, and it reaches 2.26 W?(m稫)-1 when the mass fraction of the filler is 45%, and it begins to decrease when the mass fraction of the filler higher than 45%. CTE decreases as the filler loading increasing. The thermal stability of the silicone resin can be effectively improved through adding multilayer graphite. With the same filler loading, multilayer graphite filled silicone resin possesses higher thermal conductivity compared to SiC and AlN filled silicone resin. It proves that the flake graphite with big radius-thickness ratio can be more likely to form thermal network and improve the thermal contact.
With silicon resin as the base matrix materials, filled with multilayer graphite, the thermal conductive multilayer graphite/silicon resin composites were prepared by using the method of rotating-mixer. The effect of filler on the thermal conductivity, coefficient of thermal expansion (CTE) and the thermal stability of the composites were investigated. Results show that the multilayer graphite in silicon resin has good dispersibility. The thermal conductivity of the composites increases with the increasing content of multilayer graphite, and it reaches 2.26 W?(m稫)-1 when the mass fraction of the filler is 45%, and it begins to decrease when the mass fraction of the filler higher than 45%. CTE decreases as the filler loading increasing. The thermal stability of the silicone resin can be effectively improved through adding multilayer graphite. With the same filler loading, multilayer graphite filled silicone resin possesses higher thermal conductivity compared to SiC and AlN filled silicone resin. It proves that the flake graphite with big radius-thickness ratio can be more likely to form thermal network and improve the thermal contact.
2013, 30(2): 75-82.
Abstract:
Nano attapulgite/poly(lactic acid) (ATT/PLA) composites were prepared by melting blend with 1%, 3% and 5% mass fraction of attapulgite respectively. Effects of attapulgite on the crystallization and thermal stability properties of PLA were studied in this paper. Results show that the ATT has good compatibility with PLA when its content is less than 3%, but ATT forms in bundles when the content is more than 5%. FTIR results show there are strong interaction between ATT and PLA matrix. ATT has the function of nucleating agent and leads to accelerate the crystalline rate of PLA. In addition, the cold crystallization peaks of various nano ATT/PLA composites shift from 114.4 ℃ to 103 ℃. The crystallization rate of nano ATT/PLA composites is faster than that of the neat PLA, which indicates that ATT is one of the efficient nucleating agent for PLA. ATT can accelerate the crystalline rate of PLA and decrease the size of the spherulite with the increasing of the ATT content loading. The thermal decomposition temperature of nano ATT/PLA composites is about 11 ℃ higher than that of the neat PLA, when the ATT content is 3%. The reason is due to the forming of higher density network between PLA and ATT, which suppresses the degradation of PLA.
Nano attapulgite/poly(lactic acid) (ATT/PLA) composites were prepared by melting blend with 1%, 3% and 5% mass fraction of attapulgite respectively. Effects of attapulgite on the crystallization and thermal stability properties of PLA were studied in this paper. Results show that the ATT has good compatibility with PLA when its content is less than 3%, but ATT forms in bundles when the content is more than 5%. FTIR results show there are strong interaction between ATT and PLA matrix. ATT has the function of nucleating agent and leads to accelerate the crystalline rate of PLA. In addition, the cold crystallization peaks of various nano ATT/PLA composites shift from 114.4 ℃ to 103 ℃. The crystallization rate of nano ATT/PLA composites is faster than that of the neat PLA, which indicates that ATT is one of the efficient nucleating agent for PLA. ATT can accelerate the crystalline rate of PLA and decrease the size of the spherulite with the increasing of the ATT content loading. The thermal decomposition temperature of nano ATT/PLA composites is about 11 ℃ higher than that of the neat PLA, when the ATT content is 3%. The reason is due to the forming of higher density network between PLA and ATT, which suppresses the degradation of PLA.
2013, 30(2): 83-88.
Abstract:
The regenerated silk fibroin(SF) was modified by Genipin cross-linking, and then was made into cross-linked nanofibrous membranes via electrospinning. The structure and properties of nanofibers were characterized and tested by use of FE-SEM, FTIR, XRD, TGA and tensile tester. The results show that the degree of cross-linking, average diameter of nanofibers and standard deviation increase with the increasing of Genipin mass ratio. And the crystal structure of SF nanofibers is not influenced by Genipin cross-linking, but thermal properties are improved. Under room temperature, the mechanical properties of SF nanofibrous membranes are enhanced with the increasing of Genipin mass ratio from 2% to 15%. And the mechanical property is better when the Genipin mass ratio is 10%, the tensile strength and breaking strain are 19.6 MPa and 5.9% respectively. The tensile strength and breaking strain of SF nanofibrous membranes first increase and then decrease with the rising of tensile temperature from 40 ℃ to 200 ℃, the mechanical property is better at 80 ℃, the tensile strength and breaking strain are 41.6 MPa and 8.6% respectively.
The regenerated silk fibroin(SF) was modified by Genipin cross-linking, and then was made into cross-linked nanofibrous membranes via electrospinning. The structure and properties of nanofibers were characterized and tested by use of FE-SEM, FTIR, XRD, TGA and tensile tester. The results show that the degree of cross-linking, average diameter of nanofibers and standard deviation increase with the increasing of Genipin mass ratio. And the crystal structure of SF nanofibers is not influenced by Genipin cross-linking, but thermal properties are improved. Under room temperature, the mechanical properties of SF nanofibrous membranes are enhanced with the increasing of Genipin mass ratio from 2% to 15%. And the mechanical property is better when the Genipin mass ratio is 10%, the tensile strength and breaking strain are 19.6 MPa and 5.9% respectively. The tensile strength and breaking strain of SF nanofibrous membranes first increase and then decrease with the rising of tensile temperature from 40 ℃ to 200 ℃, the mechanical property is better at 80 ℃, the tensile strength and breaking strain are 41.6 MPa and 8.6% respectively.
2013, 30(2): 89-93.
Abstract:
The foamed recycled corrugated paperboard fiber/low density polyethylene(LDPE) composites were prepared by blending co-rotating extruder with recycled paper fiber and LDPE as the main materials, the compatilizer, lubricant, foaming agent as the additives. The processing rheology properties of above mentioned composites were investigated with industrial melt flow indexer by taking the concentration of recycled paper fiber, compatilizer, lubricant and foaming agent into consideration. And SEM was used to observe the influence of different melt index on cell morphology of foamed composites.The results show that: the melt flow index (MFI) of the composites declines with the increase of the recycled paper fiber concentration; The adding of MAH-g-PE enhances the interaction between the two main phases and the MFI of the composites drops after a ascension with the peak point of about 15%; PE wax performs the best lubricant effect herein and the MFI of the composites increases linearly with the loading of the PE wax; The AC foaming agent promotes the reduction of the MFI of the foamed composites, and the wall slipping effect occurs at the AC concentration beyond 5%; With the increase of MFI, the size of cell increases. When the MFI is 1.5, the size of cell is uniform and medium.
The foamed recycled corrugated paperboard fiber/low density polyethylene(LDPE) composites were prepared by blending co-rotating extruder with recycled paper fiber and LDPE as the main materials, the compatilizer, lubricant, foaming agent as the additives. The processing rheology properties of above mentioned composites were investigated with industrial melt flow indexer by taking the concentration of recycled paper fiber, compatilizer, lubricant and foaming agent into consideration. And SEM was used to observe the influence of different melt index on cell morphology of foamed composites.The results show that: the melt flow index (MFI) of the composites declines with the increase of the recycled paper fiber concentration; The adding of MAH-g-PE enhances the interaction between the two main phases and the MFI of the composites drops after a ascension with the peak point of about 15%; PE wax performs the best lubricant effect herein and the MFI of the composites increases linearly with the loading of the PE wax; The AC foaming agent promotes the reduction of the MFI of the foamed composites, and the wall slipping effect occurs at the AC concentration beyond 5%; With the increase of MFI, the size of cell increases. When the MFI is 1.5, the size of cell is uniform and medium.
2013, 30(2): 94-98.
Abstract:
The graphite-polyvinylchloride(PVC) compounding powders were successfully prepared by solid state shear compounding technology (S3C) at ambient temperature, and then the graphite-PVC/PVC nanocomposites were processed by moulding. The structure and antistatic performance of graphite-PVC compounding powder and nanocomposites prepared through S3C based on pan-milling were investigated by XRD, SEM, TEM and electrical resistivity tests. The results show that the conductivity properties of graphite/PVC nanocomposites prepared through S3C based on pan-milling 20 cycles at ambient temperature are remarkably improved. The surface resistivity of graphite-PVC/PVC nanocomposites with 2% mass fraction of graphite is 4.6×107 Ω·cm. The surface resistivity of graphite-PVC/PVC nanocomposites with 10% mass fraction of graphite reaches lowest as 4.1×104 Ω·cm. The strip flake of graphite particles with thickness less than 20 nm and the aspect ratio of 10 times disperses homogeneously in the PVC matrix.
The graphite-polyvinylchloride(PVC) compounding powders were successfully prepared by solid state shear compounding technology (S3C) at ambient temperature, and then the graphite-PVC/PVC nanocomposites were processed by moulding. The structure and antistatic performance of graphite-PVC compounding powder and nanocomposites prepared through S3C based on pan-milling were investigated by XRD, SEM, TEM and electrical resistivity tests. The results show that the conductivity properties of graphite/PVC nanocomposites prepared through S3C based on pan-milling 20 cycles at ambient temperature are remarkably improved. The surface resistivity of graphite-PVC/PVC nanocomposites with 2% mass fraction of graphite is 4.6×107 Ω·cm. The surface resistivity of graphite-PVC/PVC nanocomposites with 10% mass fraction of graphite reaches lowest as 4.1×104 Ω·cm. The strip flake of graphite particles with thickness less than 20 nm and the aspect ratio of 10 times disperses homogeneously in the PVC matrix.
2013, 30(2): 99-104.
Abstract:
TiO2 nanorod arrays film was prepared on FTO by a simple hydrothermal synthesizing method. The formation of CdS quantum dots (QDs) sensitized TiO2 nanorods was carried out by sequential chemical bath deposition (S-CBD) technique. The morphologies, phase structure, and optical absorption properties of the as-prepared materials were characterized by field emission scanning electron microscope (FESEM), X-ray diffraction (XRD) and UV-vis spectrometer. The results indicate that the length of TiO2 nanorods array is up to 2.9 μm and the diameters of CdS quantum dots range from 5 nm to 9 nm. With the increase of the sedimentary layers, the thickness of the CdS QDs increases, accompanied by the red shift of the absorption edge. By analyzing the photocurrent-voltage characteristics from I-V curve, it can be found that the photocurrent and photoelectric conversion efficiency both increase first and then decrease. A photocurrent of 2.49 mA·cm-2, an open circuit photovoltage of 1.10 V, and a conversion efficiency of 1.91% are obtained under an illumination of 100 mW/cm2, when the CdS QDs deposites on TiO2 nanorod arrays film for about 7 cycles.
TiO2 nanorod arrays film was prepared on FTO by a simple hydrothermal synthesizing method. The formation of CdS quantum dots (QDs) sensitized TiO2 nanorods was carried out by sequential chemical bath deposition (S-CBD) technique. The morphologies, phase structure, and optical absorption properties of the as-prepared materials were characterized by field emission scanning electron microscope (FESEM), X-ray diffraction (XRD) and UV-vis spectrometer. The results indicate that the length of TiO2 nanorods array is up to 2.9 μm and the diameters of CdS quantum dots range from 5 nm to 9 nm. With the increase of the sedimentary layers, the thickness of the CdS QDs increases, accompanied by the red shift of the absorption edge. By analyzing the photocurrent-voltage characteristics from I-V curve, it can be found that the photocurrent and photoelectric conversion efficiency both increase first and then decrease. A photocurrent of 2.49 mA·cm-2, an open circuit photovoltage of 1.10 V, and a conversion efficiency of 1.91% are obtained under an illumination of 100 mW/cm2, when the CdS QDs deposites on TiO2 nanorod arrays film for about 7 cycles.
2013, 30(2): 105-110.
Abstract:
Orowan strengthening, thermal mismatch strengthening and Hall-Petch strengthening are known as the main strengthening mechanisms of nano particle reinforced magnesium matrix composites. However, the distribution of the particles in the matrix has an important influence on the enhancement effect and determines the dominant mechanism. In this paper the existed strengthening models were modified. The influence of three types of nanoparticle distribution,intragranular, grain boundary and intragranular-boundary distribution, on the yield strength of the nano SiC particle reinforced AZ91D composites was analyzed based on the modified models. The calculated results were compared with the experimental results. The results show that the composite has the best strengthening effect when the particles are completely distributed within the grain and the dominant mechanism will be Orowan strengthening; the composite shows the least strengthening effect while the particles are fully distributed along the grain boundary and the main mechanism will be Hall-Petch strengthening; the multi strengthening mechanisms will work when the particles are distributed both in the grain and on the grain boundary, in which case the strengthening effects will be weakened as the proportion of the fraction of the particle inside the grain to that on the grain boundary decreases.
Orowan strengthening, thermal mismatch strengthening and Hall-Petch strengthening are known as the main strengthening mechanisms of nano particle reinforced magnesium matrix composites. However, the distribution of the particles in the matrix has an important influence on the enhancement effect and determines the dominant mechanism. In this paper the existed strengthening models were modified. The influence of three types of nanoparticle distribution,intragranular, grain boundary and intragranular-boundary distribution, on the yield strength of the nano SiC particle reinforced AZ91D composites was analyzed based on the modified models. The calculated results were compared with the experimental results. The results show that the composite has the best strengthening effect when the particles are completely distributed within the grain and the dominant mechanism will be Orowan strengthening; the composite shows the least strengthening effect while the particles are fully distributed along the grain boundary and the main mechanism will be Hall-Petch strengthening; the multi strengthening mechanisms will work when the particles are distributed both in the grain and on the grain boundary, in which case the strengthening effects will be weakened as the proportion of the fraction of the particle inside the grain to that on the grain boundary decreases.
2013, 30(2): 111-117.
Abstract:
50%SiP/Al-Cu and 70%SiP/Al-Cu composites were prepared by hot isostatic pressing(HIP) method using pure elemental powders. The microstructure evolution and dissolution of Al2Cu were studied. The properties of as-hot isostatic pressed composites before and after heat treatment were also investigated. The results show that the prepared SiP/Al-Cu composites are fully dense. The silicon particles well distribute in Al matrix and still keep the original size. The presence of Al2Cu, Si and Al is identified in the as-hot isostatic pressed composites. The Al2Cu phase is formed in the boundaries of the Cu and Al particles. After solution treatment, Al2Cu phase dissolves into the 70%SiP/Al-Cu composites, however, some Al2Cu phase does not dissolve into the matrix of 50%SiP/Al-Cu composites completely. After the peak-aged treatment, the bending strength of 50%SiP/Al-Cu and 70%SiP/Al-Cu composites as-peak-aged is 548 MPa and 404 MPa, which is increased by 38.81% and 13.51% compared with that of as-hot isostatic pressed, the three points bending of the composites can be improved remarkably.
50%SiP/Al-Cu and 70%SiP/Al-Cu composites were prepared by hot isostatic pressing(HIP) method using pure elemental powders. The microstructure evolution and dissolution of Al2Cu were studied. The properties of as-hot isostatic pressed composites before and after heat treatment were also investigated. The results show that the prepared SiP/Al-Cu composites are fully dense. The silicon particles well distribute in Al matrix and still keep the original size. The presence of Al2Cu, Si and Al is identified in the as-hot isostatic pressed composites. The Al2Cu phase is formed in the boundaries of the Cu and Al particles. After solution treatment, Al2Cu phase dissolves into the 70%SiP/Al-Cu composites, however, some Al2Cu phase does not dissolve into the matrix of 50%SiP/Al-Cu composites completely. After the peak-aged treatment, the bending strength of 50%SiP/Al-Cu and 70%SiP/Al-Cu composites as-peak-aged is 548 MPa and 404 MPa, which is increased by 38.81% and 13.51% compared with that of as-hot isostatic pressed, the three points bending of the composites can be improved remarkably.
2013, 30(2): 118-123.
Abstract:
In this paper, for the recycle of rape straw waste, a new technique had been adopted to prepare palygorskite clay modified woodceramics from rape straw. The composites were prepared through mixing, hotly pressing, and sintering, using rape straw and palygorskite clay as raw materials and phenolresin as adhesive. The obtained composites were characterized with different methods. The results show that the preparation of composites with rape straw, palygorskite clay and phenolresin by the proposed process is feasible. The selection of raw materials, quality ratios and sintering temperature have much effect on the technique and the properties of composites. The mechanics performance of the composites is good, when the mass ratio of rape straw to palygorskite clay is 1∶2. Also for these composites, the carbon yield is the highest at 600~700 ℃ sintering temperature, the increase of the bending strength is the best at 600~800 ℃, and the electrical conductivity is improved at 800 ℃.
In this paper, for the recycle of rape straw waste, a new technique had been adopted to prepare palygorskite clay modified woodceramics from rape straw. The composites were prepared through mixing, hotly pressing, and sintering, using rape straw and palygorskite clay as raw materials and phenolresin as adhesive. The obtained composites were characterized with different methods. The results show that the preparation of composites with rape straw, palygorskite clay and phenolresin by the proposed process is feasible. The selection of raw materials, quality ratios and sintering temperature have much effect on the technique and the properties of composites. The mechanics performance of the composites is good, when the mass ratio of rape straw to palygorskite clay is 1∶2. Also for these composites, the carbon yield is the highest at 600~700 ℃ sintering temperature, the increase of the bending strength is the best at 600~800 ℃, and the electrical conductivity is improved at 800 ℃.
2013, 30(2): 124-131.
Abstract:
The nano-copper/paraffin composites were prepared by high energy ball milling. The microstructure, phase and thermophysical properties such as phase change temperature and latent heat enthalpy were characterized by means of TEM, SEM, XRD and DSC, and the impact of nano-copper particles on the thermal expansion, thermal sensitivity and thermal stability was also investigated. The results show that paraffin enwraps copper particles to form near-spherical composite particles with a mean size of 100 nm, which improves the antioxidant ability of nano-copper particles effectively. Those nano-composite particles tend to agglomerate to form micron-sized clumps of particles. Nano-copper particles do not exert noticeable effect on the phase change temperature, but the latent heat enthalpy of the nano-copper/paraffin composites decreases linearly with an increase of copper content. The thermal sensitivity of the composites improves effectively with the increasing of the copper content, while the thermal expansion decreases with the loading increasing. It is clear that the composites containing 60% mass fraction of copper is a desirable material for microactuator, with short heating time, a small decrease in volume expansibility and excellent thermal stability after being heated for many times.
The nano-copper/paraffin composites were prepared by high energy ball milling. The microstructure, phase and thermophysical properties such as phase change temperature and latent heat enthalpy were characterized by means of TEM, SEM, XRD and DSC, and the impact of nano-copper particles on the thermal expansion, thermal sensitivity and thermal stability was also investigated. The results show that paraffin enwraps copper particles to form near-spherical composite particles with a mean size of 100 nm, which improves the antioxidant ability of nano-copper particles effectively. Those nano-composite particles tend to agglomerate to form micron-sized clumps of particles. Nano-copper particles do not exert noticeable effect on the phase change temperature, but the latent heat enthalpy of the nano-copper/paraffin composites decreases linearly with an increase of copper content. The thermal sensitivity of the composites improves effectively with the increasing of the copper content, while the thermal expansion decreases with the loading increasing. It is clear that the composites containing 60% mass fraction of copper is a desirable material for microactuator, with short heating time, a small decrease in volume expansibility and excellent thermal stability after being heated for many times.
2013, 30(2): 132-136.
Abstract:
When the mass fraction of the tungsten concentrate powder is 1%, changing the atom fraction of Al with 50%, 60%, 70%, 80%, Fe-Al alloy was prepared by laser ignition induced SHS. By means of the XRD, SEM, hardness test and abrasion test, the effect of the content of Al on the microstructure and macroscopic properties of the sintering alloy was studied. The results show that through the sintering process, the self-propagating combustion synthesis of the blank is achieved. The product phases of the sintering alloy are AlFe, AlFe3, WO3, AlCrFe2 and with the increase of the content of Al, the Al-rich phases are formed.The structures of the sintering alloy appear small crackle, which grow up with the increase of the content of Al. When the atom fraction of the aluminum is 60%, the micro hardness of the sintering alloy is the biggest, which is HK1053,and the relative wear rate of the sintering alloy is the lowest, which is 0.04 mg穖m-2.
When the mass fraction of the tungsten concentrate powder is 1%, changing the atom fraction of Al with 50%, 60%, 70%, 80%, Fe-Al alloy was prepared by laser ignition induced SHS. By means of the XRD, SEM, hardness test and abrasion test, the effect of the content of Al on the microstructure and macroscopic properties of the sintering alloy was studied. The results show that through the sintering process, the self-propagating combustion synthesis of the blank is achieved. The product phases of the sintering alloy are AlFe, AlFe3, WO3, AlCrFe2 and with the increase of the content of Al, the Al-rich phases are formed.The structures of the sintering alloy appear small crackle, which grow up with the increase of the content of Al. When the atom fraction of the aluminum is 60%, the micro hardness of the sintering alloy is the biggest, which is HK1053,and the relative wear rate of the sintering alloy is the lowest, which is 0.04 mg穖m-2.
2013, 30(2): 137-143.
Abstract:
Based on the interphase model, the three-layer built-in model was established to describe the multi-inclusion composites with imperfect interface. Firstly, the formulations for predicting effective elastic properties of multi-inclusion composites were presented. Then, by separating the three-layer built-in model into two solving systems, the micromechanical approximation model was obtained. Secondly, the basic formulations of fast multipole boundary element method were developed according to the interphase model. Finally, these two methods were compared with each other to verify the correctness and effectiveness, and the effect of imperfect interface on the macromechanical behavior of composites was further investigated. It has been shown that the micromechanical approximation method is quite easy to perform and suitable to fast predict the effective elastic properties of composites with imperfect interface, while the numerical algorithm is able to fast and directly observe the stress distribution in the composites under the influence of the interface imperfection. Based on the analysis, it can be also observed that a stiff inclusion surrounded by a weak interphase (with thicker thickness and lower elastic modulus) behaves as a soft inclusion, and the matrix will take on more stress with the increase of the thickness of interphase, which will easily result in the failure occurred at the interphase.
Based on the interphase model, the three-layer built-in model was established to describe the multi-inclusion composites with imperfect interface. Firstly, the formulations for predicting effective elastic properties of multi-inclusion composites were presented. Then, by separating the three-layer built-in model into two solving systems, the micromechanical approximation model was obtained. Secondly, the basic formulations of fast multipole boundary element method were developed according to the interphase model. Finally, these two methods were compared with each other to verify the correctness and effectiveness, and the effect of imperfect interface on the macromechanical behavior of composites was further investigated. It has been shown that the micromechanical approximation method is quite easy to perform and suitable to fast predict the effective elastic properties of composites with imperfect interface, while the numerical algorithm is able to fast and directly observe the stress distribution in the composites under the influence of the interface imperfection. Based on the analysis, it can be also observed that a stiff inclusion surrounded by a weak interphase (with thicker thickness and lower elastic modulus) behaves as a soft inclusion, and the matrix will take on more stress with the increase of the thickness of interphase, which will easily result in the failure occurred at the interphase.
2013, 30(2): 144-151.
Abstract:
Experimental study on tensile behavior of scarfing repaired laminates with half-depth damage was conducted in the paper. Distinct differences were observed on ultimate strength and failure mode of specimens with different scarf ratio. A finite element model was developed to simulate the tensile behavior of repaired specimens. The calculated results are in good agreement with test results. The numerical results indicate that the scarf ratio is the most important design parameter of repaired specimen. Ultimate tensile strength, failure mode and interface layer damage between repaired and unrepaired sub laminates can be influenced dramatically by scarf ratio. Conclusions of the investigation provide insight into scarfing repair design method on laminates with half-depth damage.
Experimental study on tensile behavior of scarfing repaired laminates with half-depth damage was conducted in the paper. Distinct differences were observed on ultimate strength and failure mode of specimens with different scarf ratio. A finite element model was developed to simulate the tensile behavior of repaired specimens. The calculated results are in good agreement with test results. The numerical results indicate that the scarf ratio is the most important design parameter of repaired specimen. Ultimate tensile strength, failure mode and interface layer damage between repaired and unrepaired sub laminates can be influenced dramatically by scarf ratio. Conclusions of the investigation provide insight into scarfing repair design method on laminates with half-depth damage.
2013, 30(2): 152-158.
Abstract:
A new composite multiscale failure criteria based on mechanical failure mode was proposed, failure modes of fiber and matrix were characterized at the meso level, in which the fiber failure was divided into tension failure and compression failure, as well as the matrix failure was divided into dilatation failure and distortion failure. Corresponding failure criteria and damage evolution method were established. By means of square and hexagon representative volume element (RVE) models, mechanical stress amplification factors and thermal stress amplification factors which relate macro stresses and meso stresses were calculated. IM7/5250-4 composite tensile experiments were taken as an example to verify the failure model. Simulation results fit well with experiment results, which shows that the multiscale failure criteria is able to precisely forecast the failure of composite laminates.
A new composite multiscale failure criteria based on mechanical failure mode was proposed, failure modes of fiber and matrix were characterized at the meso level, in which the fiber failure was divided into tension failure and compression failure, as well as the matrix failure was divided into dilatation failure and distortion failure. Corresponding failure criteria and damage evolution method were established. By means of square and hexagon representative volume element (RVE) models, mechanical stress amplification factors and thermal stress amplification factors which relate macro stresses and meso stresses were calculated. IM7/5250-4 composite tensile experiments were taken as an example to verify the failure model. Simulation results fit well with experiment results, which shows that the multiscale failure criteria is able to precisely forecast the failure of composite laminates.
2013, 30(2): 159-164.
Abstract:
The end strengthened thick tubes with different aspect ratio and laminate samples made of carbon fiber reinforced plastic (CFRP) composite were prepared. Quasi-static and axial impact compression experiments in the range of 7.67~12.01 m穝-1 were carried out. The effects of aspect ratio, impact velocity, and the end-strengthening on the axial compressive strength and failure model of CFRP tubes were studied. In-plane compression tests with different strain rates were conducted on the laminate samples. Numerical simulations were performed by using ANSYS/LS-DYNA on the response of CFRP tube subjected to the dynamic impacting by drop weight. The results indicate that the progressive failure mode from the end is prevented, and the axial compressive strength is also enhanced effectively by end-strengthening of the CFRP tube. In addition, the compressive strength displays a marked strain rate strengthening effect for CFRP tubes and laminate samples. Numerical results are in good correlation with experimental results.
The end strengthened thick tubes with different aspect ratio and laminate samples made of carbon fiber reinforced plastic (CFRP) composite were prepared. Quasi-static and axial impact compression experiments in the range of 7.67~12.01 m穝-1 were carried out. The effects of aspect ratio, impact velocity, and the end-strengthening on the axial compressive strength and failure model of CFRP tubes were studied. In-plane compression tests with different strain rates were conducted on the laminate samples. Numerical simulations were performed by using ANSYS/LS-DYNA on the response of CFRP tube subjected to the dynamic impacting by drop weight. The results indicate that the progressive failure mode from the end is prevented, and the axial compressive strength is also enhanced effectively by end-strengthening of the CFRP tube. In addition, the compressive strength displays a marked strain rate strengthening effect for CFRP tubes and laminate samples. Numerical results are in good correlation with experimental results.
2013, 30(2): 165-172.
Abstract:
Research on damage characteristics of composite grid structures for unmanned aircraft wing under low velocity impact was presented in this paper. The composite grid structures were modeled in finite element analysis software ABAQUS. Then simulation analysis, in which the model was subjected to low velocity impact with the assumption of no penetration, was carried out by employing Hashin-Rotem strain failure criteria and Camanho Parameter degradation mode under different conditions, such as different grid shapes, different impact locations, different impact energies, et al. Simulation results show that the damage characteristics vary greatly with different impact locations, such as damage types, damage areas, damage propagation directions, et al. It also proves that grid structures have significantly resistance performances to damage propagation and failures.
Research on damage characteristics of composite grid structures for unmanned aircraft wing under low velocity impact was presented in this paper. The composite grid structures were modeled in finite element analysis software ABAQUS. Then simulation analysis, in which the model was subjected to low velocity impact with the assumption of no penetration, was carried out by employing Hashin-Rotem strain failure criteria and Camanho Parameter degradation mode under different conditions, such as different grid shapes, different impact locations, different impact energies, et al. Simulation results show that the damage characteristics vary greatly with different impact locations, such as damage types, damage areas, damage propagation directions, et al. It also proves that grid structures have significantly resistance performances to damage propagation and failures.
2013, 30(2): 173-182.
Abstract:
A new statistical second-order two-scale (SSOTS) method was presented for predicting the performances of conduction-radiation coupled heat transfer of porous materials with random distribution of pores. The statistical second-order two-scale formulation for the Rosseland problem of porous materials was discussed, and a statistical prediction algorithm for maximum heat flux density was brought forward. Besides, the validity of the proposed method by comparison with theoretical methods with simple numerical models was verified. Finally, macroscopic thermal properties for the porous ceramic materials with varying probability distribution models including volume fraction and spatial distribution model of pores were shown. The results show that the effective thermal conductivity parameters decrease and maximum heat flux density increases with the pores volume fraction increasing. What is more, the radiation is an important factor for heat transfer at a high temperature. It is also shown that the SSOTS method is valid to predict the performances of conduction-radiation coupled heat transfer of porous materials with random distribution of pores.
A new statistical second-order two-scale (SSOTS) method was presented for predicting the performances of conduction-radiation coupled heat transfer of porous materials with random distribution of pores. The statistical second-order two-scale formulation for the Rosseland problem of porous materials was discussed, and a statistical prediction algorithm for maximum heat flux density was brought forward. Besides, the validity of the proposed method by comparison with theoretical methods with simple numerical models was verified. Finally, macroscopic thermal properties for the porous ceramic materials with varying probability distribution models including volume fraction and spatial distribution model of pores were shown. The results show that the effective thermal conductivity parameters decrease and maximum heat flux density increases with the pores volume fraction increasing. What is more, the radiation is an important factor for heat transfer at a high temperature. It is also shown that the SSOTS method is valid to predict the performances of conduction-radiation coupled heat transfer of porous materials with random distribution of pores.
2013, 30(2): 183-188.
Abstract:
The mechanical properties of amorphous Fe73.5Cu1Nb3Si13.5B9 alloy powders/silicone rubber piezomagnetic composite film were investigated by the nanoindentation technique. The mechanical responses (hardness and modulus) of the piezomagnetic composite film were obtained by changing the loading rates, peak load and holding time. And the effect of these experimental parameters on nanoindentation measurement was discussed. The reasonable experimental parameters were determined and the creep stress exponent equating was acquired by indentation creep experiments. The feasibility analysis was performed to evaluate the creep behavior of amorphous Fe73.5Cu1Nb3Si13.5B9 alloy powders/silicone rubber piezomagnetic composites film by using nanoindentation technology. The results show that the modulus and hardness of the thin film respond more sensitively to the loading rates than do to the peak load. The experimental result is hardly affected by the holding time.
The mechanical properties of amorphous Fe73.5Cu1Nb3Si13.5B9 alloy powders/silicone rubber piezomagnetic composite film were investigated by the nanoindentation technique. The mechanical responses (hardness and modulus) of the piezomagnetic composite film were obtained by changing the loading rates, peak load and holding time. And the effect of these experimental parameters on nanoindentation measurement was discussed. The reasonable experimental parameters were determined and the creep stress exponent equating was acquired by indentation creep experiments. The feasibility analysis was performed to evaluate the creep behavior of amorphous Fe73.5Cu1Nb3Si13.5B9 alloy powders/silicone rubber piezomagnetic composites film by using nanoindentation technology. The results show that the modulus and hardness of the thin film respond more sensitively to the loading rates than do to the peak load. The experimental result is hardly affected by the holding time.
2013, 30(2): 189-194.
Abstract:
To improve the location precision of foreign object impact in the near-field, the multiple signal classification (MUSIC) based localization algorithm was presented for the impacts estimating. Firstly, classical far-field MUSIC algorithm was extended to near-field version using the Fresnel approximation. Then Gabor transform was applied to extract the narrow-band signal at a center frequency from the impact signal. After scanning over the whole interest direction of the structure, the signal source parameters including range and direction from the peak of spatial spectrum were obtained. The experiment on the epoxy laminates plate was established to verify the validity of the proposed method. Results show that the distance error and the direction error are less than 0.94 cm and 1?, respectively.
To improve the location precision of foreign object impact in the near-field, the multiple signal classification (MUSIC) based localization algorithm was presented for the impacts estimating. Firstly, classical far-field MUSIC algorithm was extended to near-field version using the Fresnel approximation. Then Gabor transform was applied to extract the narrow-band signal at a center frequency from the impact signal. After scanning over the whole interest direction of the structure, the signal source parameters including range and direction from the peak of spatial spectrum were obtained. The experiment on the epoxy laminates plate was established to verify the validity of the proposed method. Results show that the distance error and the direction error are less than 0.94 cm and 1?, respectively.
2013, 30(2): 195-200.
Abstract:
The permeability of three typical ramie fiber woven fabrics (plain woven, twill woven and satin woven) was studied by resin transfer molding method(RTM). The tensile and interlaminar properties of the three ramie fabrics reinforced phenolic resin composites were also investigated. It is indicated that the permeability of ramie woven fabrics is mainly influenced by the crimp of the fiber and the flow area of the fabrics. The permeability of twill woven and satin woven fabrics is preferable, compared with that of plain woven ramie fabric. Tensile properties of twill woven and satin woven ramie fabric reinforced composites are better than that of plain woven counterpart due to less fiber crimps. It is also concluded that the woven styles of ramie fabrics do not show obvious effects on the interlaminar shear properties of the composites.
The permeability of three typical ramie fiber woven fabrics (plain woven, twill woven and satin woven) was studied by resin transfer molding method(RTM). The tensile and interlaminar properties of the three ramie fabrics reinforced phenolic resin composites were also investigated. It is indicated that the permeability of ramie woven fabrics is mainly influenced by the crimp of the fiber and the flow area of the fabrics. The permeability of twill woven and satin woven fabrics is preferable, compared with that of plain woven ramie fabric. Tensile properties of twill woven and satin woven ramie fabric reinforced composites are better than that of plain woven counterpart due to less fiber crimps. It is also concluded that the woven styles of ramie fabrics do not show obvious effects on the interlaminar shear properties of the composites.
2013, 30(2): 201-205.
Abstract:
The finite element model of composite overwrapped pressure vessel (COPV) including a circular surface crack in the liner was constructed with the sub-model technique. Based on the stress analysis of the metallic liner before and after autofrettage technology, the J -integrals along the crack front under operating pressure were calculated by the domain integral method. The objective was to investigate the crack tip strength under the following two cases: whether considerd the autofrettage or not and autofrettage with different pressures. Results show that the J -integrals increase significantly after autofrettage and improve slightly due to a superior autofrettage pressure; the deeper crack would lead the J -integrals to become larger and the curve to become sharper. It could be concluded that the larger the autofrettage pressure or crack size, the more likely the crack will open. Therefore it is necessary to analyze the fracture behavior of metallic liner when determining the autofrettage pressure.
The finite element model of composite overwrapped pressure vessel (COPV) including a circular surface crack in the liner was constructed with the sub-model technique. Based on the stress analysis of the metallic liner before and after autofrettage technology, the J -integrals along the crack front under operating pressure were calculated by the domain integral method. The objective was to investigate the crack tip strength under the following two cases: whether considerd the autofrettage or not and autofrettage with different pressures. Results show that the J -integrals increase significantly after autofrettage and improve slightly due to a superior autofrettage pressure; the deeper crack would lead the J -integrals to become larger and the curve to become sharper. It could be concluded that the larger the autofrettage pressure or crack size, the more likely the crack will open. Therefore it is necessary to analyze the fracture behavior of metallic liner when determining the autofrettage pressure.
2013, 30(2): 206-212.
Abstract:
A new method is proposed to analyze the stress singularity and the electricity singularity at the piezoelectric notch tip. Based on the assumption that the displacement field at the notch tip was expanded as the power series asymptotic expansion, the governing equations on the notched structure, i.e., the stress equilibrium equations and the Maxwell equation, were turned into the characteristic equations respects to the singularity orders. The mechanic and electric boundary conditions on the notch surfaces were transformed into the combination of the singularity order and the corresponding eigen-functions. The analysis of the piezoelectric notch singularity orders was turned into calculating the eigen-values of the ordinary differential equations under corresponding boundary conditions. The interpolate matrix method was introduced to solving the established differential equations. Numerical results show that all the singularity orders at the piezoelectric notch can be evaluated in the present method. As a special case of the notch, the singularity orders of cracks can also be obtained by the present method.
A new method is proposed to analyze the stress singularity and the electricity singularity at the piezoelectric notch tip. Based on the assumption that the displacement field at the notch tip was expanded as the power series asymptotic expansion, the governing equations on the notched structure, i.e., the stress equilibrium equations and the Maxwell equation, were turned into the characteristic equations respects to the singularity orders. The mechanic and electric boundary conditions on the notch surfaces were transformed into the combination of the singularity order and the corresponding eigen-functions. The analysis of the piezoelectric notch singularity orders was turned into calculating the eigen-values of the ordinary differential equations under corresponding boundary conditions. The interpolate matrix method was introduced to solving the established differential equations. Numerical results show that all the singularity orders at the piezoelectric notch can be evaluated in the present method. As a special case of the notch, the singularity orders of cracks can also be obtained by the present method.
2013, 30(2): 213-219.
Abstract:
In this paper, according to the analysis of the thermo-chemical mechanism, the change rules of ablation properties of the C/C composites in thermo-chemical ablation, ablation surface receding and temperature field coupling were investigated by finite element method. The receding of the ablation boundary by virtual failure and rebuilding orphan mesh part was achieved, and finite element model of ablation temperature field at receding boundary conditions was established.The net heat flux flowed into the material and ablation rate were calculated by the thermo-chemical ablation theory.The phenomenon of large local heat flux on the irregular surface was corrected by programming after ablation surface receding when the heat flux was reloaded.The result shows that as the ablation time increases, the heat flux flows into composite materials will reach a dynamic balance.The ablation of the material is the results of a variety of factors and coupled calculation can truly reflect the characteristics of the ablation of the material.
In this paper, according to the analysis of the thermo-chemical mechanism, the change rules of ablation properties of the C/C composites in thermo-chemical ablation, ablation surface receding and temperature field coupling were investigated by finite element method. The receding of the ablation boundary by virtual failure and rebuilding orphan mesh part was achieved, and finite element model of ablation temperature field at receding boundary conditions was established.The net heat flux flowed into the material and ablation rate were calculated by the thermo-chemical ablation theory.The phenomenon of large local heat flux on the irregular surface was corrected by programming after ablation surface receding when the heat flux was reloaded.The result shows that as the ablation time increases, the heat flux flows into composite materials will reach a dynamic balance.The ablation of the material is the results of a variety of factors and coupled calculation can truly reflect the characteristics of the ablation of the material.
2013, 30(2): 220-225.
Abstract:
In light of the viscoelastic property of the adhesive and resin matrix of the composite patch, a series of specimens were prepared by UV curing and conventionally thermal curing methods. The effect of the resin formula on the strain rate was investigated. And the effect of the loading rate on the bonded composite repair structure was studied. Results show that the crosslinking degree of the resin is an important factor affecting the strain rate effect. The lower crosslinking degree may mean the more pronounced strain rate effect. The increase of the loading rate can enhance load-share fraction of the composite patch. However, the stress redistribution function of the composite and adhesive by deformation may be reduced. The loading rate can affect the failure modes of the bonded composite repair structure.
In light of the viscoelastic property of the adhesive and resin matrix of the composite patch, a series of specimens were prepared by UV curing and conventionally thermal curing methods. The effect of the resin formula on the strain rate was investigated. And the effect of the loading rate on the bonded composite repair structure was studied. Results show that the crosslinking degree of the resin is an important factor affecting the strain rate effect. The lower crosslinking degree may mean the more pronounced strain rate effect. The increase of the loading rate can enhance load-share fraction of the composite patch. However, the stress redistribution function of the composite and adhesive by deformation may be reduced. The loading rate can affect the failure modes of the bonded composite repair structure.
2013, 30(2): 226-232.
Abstract:
The materials with a set of penny-shaped cracks exhibited transversely radically isotropic. The Walpole’s base was introduced for tensorial represtation and calculation. The macroscopic stress states of the composites were defined by introducing the energy density supporting function. In order to capture the local deviatoric effects induced by a hydrostatic loading, the modified secant method based on energy approach was adopted in non-linear homogenized. Three schemes of macroscopic elastic moduli for microcracks materials were considered, i.e. dilute scheme, MT scheme and PCW scheme. It can be found from the research result that the elastic modulus ratios and the macroscopic friction coefficient tend to decrease with the increase of the crack volume fraction. The smaller the crack aspect ratio is, the larger of the difference is between the predictions by the dilute scheme, MT scheme and PCW scheme.
The materials with a set of penny-shaped cracks exhibited transversely radically isotropic. The Walpole’s base was introduced for tensorial represtation and calculation. The macroscopic stress states of the composites were defined by introducing the energy density supporting function. In order to capture the local deviatoric effects induced by a hydrostatic loading, the modified secant method based on energy approach was adopted in non-linear homogenized. Three schemes of macroscopic elastic moduli for microcracks materials were considered, i.e. dilute scheme, MT scheme and PCW scheme. It can be found from the research result that the elastic modulus ratios and the macroscopic friction coefficient tend to decrease with the increase of the crack volume fraction. The smaller the crack aspect ratio is, the larger of the difference is between the predictions by the dilute scheme, MT scheme and PCW scheme.
2013, 30(2): 233-239.
Abstract:
Co-woven-knitted (CWK) fabric and multi-layered biaxial weft knitted (MBWK) fabric were produced by different ways of inserted yarn, using high tenacity and high modulus basalt fiber filaments with different linear density as warp, weft and stitch yarns. Then the fabrics were used for preparing the basalt fiber/ethylene composites by vacuum assisted resin transfer molding process. The bending tests were carried out in 0?, 90? and 45? directions. The mechanical properties of the composites were investigated and compared by analyzing the bending stress-strain curves. The results reveal that the bending strength and the elastic modulus of the two materials in 0? and 90? directions are all better than that in 45? direction, and the curves have the characteristics of plastic fracture. The bending properties in 0? and 90? directions of the MBWK fabric reinforced composites are better than that of the CWK fabric reinforced composites. The buckling of the warp and weft yarns causes that specific modulus and strength of yarns of the MBWK fabric reinforced composites are better than that of the CWK fabric reinforced composites. The bending properties of the composites are affected by different ways of inserted yarn. Bending damage forms of the composites are similar. The results provide a reference for the application of the composites.
Co-woven-knitted (CWK) fabric and multi-layered biaxial weft knitted (MBWK) fabric were produced by different ways of inserted yarn, using high tenacity and high modulus basalt fiber filaments with different linear density as warp, weft and stitch yarns. Then the fabrics were used for preparing the basalt fiber/ethylene composites by vacuum assisted resin transfer molding process. The bending tests were carried out in 0?, 90? and 45? directions. The mechanical properties of the composites were investigated and compared by analyzing the bending stress-strain curves. The results reveal that the bending strength and the elastic modulus of the two materials in 0? and 90? directions are all better than that in 45? direction, and the curves have the characteristics of plastic fracture. The bending properties in 0? and 90? directions of the MBWK fabric reinforced composites are better than that of the CWK fabric reinforced composites. The buckling of the warp and weft yarns causes that specific modulus and strength of yarns of the MBWK fabric reinforced composites are better than that of the CWK fabric reinforced composites. The bending properties of the composites are affected by different ways of inserted yarn. Bending damage forms of the composites are similar. The results provide a reference for the application of the composites.
2013, 30(2): 240-246.
Abstract:
For the study of the damage evolution and the effect of fiber pre-broken on the mechanical properties of composites for wind turbine blades, unidirectional and loading-unloading tensile tests of unidirectional and multi-axial composite were conducted. In this experiment, real-time acoustic emission monitoring was used, and tensile mechanical properties, damage failure characteristics and the corresponding acoustic emission response characteristics were obtained. The results show that because of the presence of fiber pre-broken, the damage of matrix and interface in the defect location and the adjacent region of unidirectional composites appears obviously when the load reaches to about 30% of the failure load. As the load increases to about 60%, interlaminar shear failure between defects layer and adjacent layers are induced, leading to a sharp reduction in stiffness, the acoustic emission cumulative hits are significantly higher than that of the defect-free ones. As the load reaches to about 60% of the failure load, the obvious damage of matrix resin in fiber pre-broken region occurs in the case of multi-axial composite with fiber pre-broken. As the relative stress level increases, the Felicity ratio of multi-axial composite gradually decreases.
For the study of the damage evolution and the effect of fiber pre-broken on the mechanical properties of composites for wind turbine blades, unidirectional and loading-unloading tensile tests of unidirectional and multi-axial composite were conducted. In this experiment, real-time acoustic emission monitoring was used, and tensile mechanical properties, damage failure characteristics and the corresponding acoustic emission response characteristics were obtained. The results show that because of the presence of fiber pre-broken, the damage of matrix and interface in the defect location and the adjacent region of unidirectional composites appears obviously when the load reaches to about 30% of the failure load. As the load increases to about 60%, interlaminar shear failure between defects layer and adjacent layers are induced, leading to a sharp reduction in stiffness, the acoustic emission cumulative hits are significantly higher than that of the defect-free ones. As the load reaches to about 60% of the failure load, the obvious damage of matrix resin in fiber pre-broken region occurs in the case of multi-axial composite with fiber pre-broken. As the relative stress level increases, the Felicity ratio of multi-axial composite gradually decreases.
2013, 30(2): 247-253.
Abstract:
The body armor composites were fabricated by the mould pressing. The influences of resin type, fabric type and resin content on stab resistance of the composites were investigated. The results show that the stab resistance of Surlyn resin matrix composite is better than that of PU resin matrix composites. The stab resistance of Kevlar/Surlyn composite is better than that of UHMWPE/Surlyn composites. Kevlar/Surlyn composite with resin mass fraction of 47% has the best stab resistant performance.
The body armor composites were fabricated by the mould pressing. The influences of resin type, fabric type and resin content on stab resistance of the composites were investigated. The results show that the stab resistance of Surlyn resin matrix composite is better than that of PU resin matrix composites. The stab resistance of Kevlar/Surlyn composite is better than that of UHMWPE/Surlyn composites. Kevlar/Surlyn composite with resin mass fraction of 47% has the best stab resistant performance.
2013, 30(2): 254-259.
Abstract:
The dynamic modulus of elasticity (MOE) of wood-plastic structural planks was measured nondestructively by the longitudinal transmission, longitudinal vibration, and flexural vibration test. Three point bending test was used to measured the static MOE and maximum bending force (Fm). The maximum bending force of same wood plastic structural planks was predicted by the regression formulas between dynamic MOE and Fm, and the First-Order Second-Moment method (FOSM) was used to analyze reliability index based on measured and predicted Fm. The results indicate that there is a significant correlation between dynamic MOE and Fm. The reliabilities of the wood-plastic structural planks based on predicted Fm are slightly greater than that based on measured Fm, in which the biggest difference is 0.66%.
The dynamic modulus of elasticity (MOE) of wood-plastic structural planks was measured nondestructively by the longitudinal transmission, longitudinal vibration, and flexural vibration test. Three point bending test was used to measured the static MOE and maximum bending force (Fm). The maximum bending force of same wood plastic structural planks was predicted by the regression formulas between dynamic MOE and Fm, and the First-Order Second-Moment method (FOSM) was used to analyze reliability index based on measured and predicted Fm. The results indicate that there is a significant correlation between dynamic MOE and Fm. The reliabilities of the wood-plastic structural planks based on predicted Fm are slightly greater than that based on measured Fm, in which the biggest difference is 0.66%.
