2015 Vol. 32, No. 2
2015, 32(2): 301-316.
doi: 10.13801/j.cnki.fhclxb.20150211.002
Abstract:
Due to the superior physical and mechanical properties of carbon fiber reinforced polymer (CFRP), it has been widely applied in aviation industry. In primary load-carrying structures, the connection between CFRP and metal materials is mechanical joints usually. However, the drilling qualities are affected seriously by the anisotropy of CFRP. Drilling technology of CFRP/metal stacks has become a difficult problem in aircraft assembly process for the different properties of CFRP and metals. First, the chip formation mechanism, drilling force and drilling heat in drilling processes of CFRP and its stacks were explained. Second, the causes and influential factors of typical machining damage during drilling processes, such as burr and spalling, delamination defects and hole surface defects were analyzed. Then, the research status of optimization designs of materials and geometries of CFRP drilling tools were introduced. Various advanced process technologies of CFRP and its stacks, such as helical milling hole, varying parameter drilling, "grinding instead of drilling" and vibration assisted drilling, and simulation researches of drilling processes were reviewed. Finally, in order to realize the precise and efficient drilling processes of CFRP and its stacks, taking the unique advantages of brazed tools and ultrasonic vibration technologies, an ultrasonic vibration processing conception by brazed diamond tool with abrasive ordered arrangement was proposed.
Due to the superior physical and mechanical properties of carbon fiber reinforced polymer (CFRP), it has been widely applied in aviation industry. In primary load-carrying structures, the connection between CFRP and metal materials is mechanical joints usually. However, the drilling qualities are affected seriously by the anisotropy of CFRP. Drilling technology of CFRP/metal stacks has become a difficult problem in aircraft assembly process for the different properties of CFRP and metals. First, the chip formation mechanism, drilling force and drilling heat in drilling processes of CFRP and its stacks were explained. Second, the causes and influential factors of typical machining damage during drilling processes, such as burr and spalling, delamination defects and hole surface defects were analyzed. Then, the research status of optimization designs of materials and geometries of CFRP drilling tools were introduced. Various advanced process technologies of CFRP and its stacks, such as helical milling hole, varying parameter drilling, "grinding instead of drilling" and vibration assisted drilling, and simulation researches of drilling processes were reviewed. Finally, in order to realize the precise and efficient drilling processes of CFRP and its stacks, taking the unique advantages of brazed tools and ultrasonic vibration technologies, an ultrasonic vibration processing conception by brazed diamond tool with abrasive ordered arrangement was proposed.
2015, 32(2): 317-322.
doi: 10.13801/j.cnki.fhclxb.20150122.001
Abstract:
Extensive application of composites is one of distinguished characteristics of the new generation of large civil aircraft. The development of composites in large civil aircraft was summarized. The quantity proportions of composites in aircraft reached from 4% (1980 s) to currently 50%, and composites were wildly used in primary structures and complex curved surface structures. Boeing 787 and Airbus A350 were taken as examples to illustrate the applications of composites in Boeing and Airbus companies. The usage of composites not only results in the reducing of structure quality, the improvement of the usage life of aircraft and the reducing of maintenance costs, but also benefits to the increase of the air pressure and humidity in cabin, which improves the economy, comfort, environmental-friendliness of civil aircraft. It has become a major trend in the world civil aircraft industry that composites will wildly instead of metal and non-metallic materials, and pose a challenge for self-developed large civil aircraft in China. Therefore, some suggestions about applying composites when developing large civil aircraft in China were proposed.
Extensive application of composites is one of distinguished characteristics of the new generation of large civil aircraft. The development of composites in large civil aircraft was summarized. The quantity proportions of composites in aircraft reached from 4% (1980 s) to currently 50%, and composites were wildly used in primary structures and complex curved surface structures. Boeing 787 and Airbus A350 were taken as examples to illustrate the applications of composites in Boeing and Airbus companies. The usage of composites not only results in the reducing of structure quality, the improvement of the usage life of aircraft and the reducing of maintenance costs, but also benefits to the increase of the air pressure and humidity in cabin, which improves the economy, comfort, environmental-friendliness of civil aircraft. It has become a major trend in the world civil aircraft industry that composites will wildly instead of metal and non-metallic materials, and pose a challenge for self-developed large civil aircraft in China. Therefore, some suggestions about applying composites when developing large civil aircraft in China were proposed.
2015, 32(2): 323-331.
doi: 10.13801/j.cnki.fhclxb.20150105.003
Abstract:
In order to obtain the vibration parameters of composite wing structure that are difficult to measure in high-temperature environments beyond 1 000 ℃ in thermal modal test, high-temperature transient heating test system and vibration test system were combined to establish a thermal/vibration joint test system that was able to perform research on the thermal modal of high-temperature-resistant composite wing structure subjected to high temperature up to 1 100℃ for hypersonic flight vehicles. A self-developed extension configuration of high-temperature-resistant ceramic pole was used to transfer the vibration signals of the composite wing structure to non high-temperature zone. Ordinary acceleration sensors were applied to identify the vibration signals of the composite wing structure in high-temperature environments for hypersonic flight vehicles. Test data were analyzed by using a time-frequency joint analysis technique, and then the key vibration characteristic parameters of composite wing structure (e.g. the modal frequency and modal vibration shape) in a thermal/vibration coupled environment up to 1 100 ℃ were obtained. The research results can provide an important basis for the dynamic performance analysis and safety design of composite wing structure in high-temperature environments for hypersonic flight vehicles.
In order to obtain the vibration parameters of composite wing structure that are difficult to measure in high-temperature environments beyond 1 000 ℃ in thermal modal test, high-temperature transient heating test system and vibration test system were combined to establish a thermal/vibration joint test system that was able to perform research on the thermal modal of high-temperature-resistant composite wing structure subjected to high temperature up to 1 100℃ for hypersonic flight vehicles. A self-developed extension configuration of high-temperature-resistant ceramic pole was used to transfer the vibration signals of the composite wing structure to non high-temperature zone. Ordinary acceleration sensors were applied to identify the vibration signals of the composite wing structure in high-temperature environments for hypersonic flight vehicles. Test data were analyzed by using a time-frequency joint analysis technique, and then the key vibration characteristic parameters of composite wing structure (e.g. the modal frequency and modal vibration shape) in a thermal/vibration coupled environment up to 1 100 ℃ were obtained. The research results can provide an important basis for the dynamic performance analysis and safety design of composite wing structure in high-temperature environments for hypersonic flight vehicles.
Effect of adding method of carbon nanotube on interlaminar property of carbon fiber/epoxy composites
2015, 32(2): 332-340.
doi: 10.13801/j.cnki.fhclxb.20140722.001
Abstract:
The carbon fiber/epoxy prepregs modified by carbon nanotube (CNTs) were prepared by two methods, including directly dispersing CNTs in resin and spraying CNTs on surface of the prepregs. Mode I and mode II interlaminar fracture toughness as well as interlaminar shear strength of CNTs-carbon fiber/epoxy composite laminates fabricated by the two different prepregs were evaluated. The viscosity, curing reaction and glass transition temperature of resin were investigated to analyze the influences of CNTs content on resin properties. The length and morphology of CNTs in the two different methods were also compared. The modification effects and reaction law of adding CNTs methods on the interlaminar fracture toughness and interlaminar shear strength were discussed. The results show that the introduction of CNTs in resin causes an increase of resin viscosity and the reduction of curing reaction degree. These two methods have no significant effect on length and morphology of CNTs. For mode I, II interlaminar fracture toughness and interlaminar shear strength of CNTs-carbon fiber/epoxy composite, the improving degree from directly dispersing CNTs in resin is smaller than that from spraying CNTs on surface of carbon fiber/epoxy prepregs. The latter method has high utilization efficiency of CNTs. Moreover, high content of CNTs causes a decline of the toughening effect, resulting from CNTs aggregation and the effect of CNTs on resin curing reaction.
The carbon fiber/epoxy prepregs modified by carbon nanotube (CNTs) were prepared by two methods, including directly dispersing CNTs in resin and spraying CNTs on surface of the prepregs. Mode I and mode II interlaminar fracture toughness as well as interlaminar shear strength of CNTs-carbon fiber/epoxy composite laminates fabricated by the two different prepregs were evaluated. The viscosity, curing reaction and glass transition temperature of resin were investigated to analyze the influences of CNTs content on resin properties. The length and morphology of CNTs in the two different methods were also compared. The modification effects and reaction law of adding CNTs methods on the interlaminar fracture toughness and interlaminar shear strength were discussed. The results show that the introduction of CNTs in resin causes an increase of resin viscosity and the reduction of curing reaction degree. These two methods have no significant effect on length and morphology of CNTs. For mode I, II interlaminar fracture toughness and interlaminar shear strength of CNTs-carbon fiber/epoxy composite, the improving degree from directly dispersing CNTs in resin is smaller than that from spraying CNTs on surface of carbon fiber/epoxy prepregs. The latter method has high utilization efficiency of CNTs. Moreover, high content of CNTs causes a decline of the toughening effect, resulting from CNTs aggregation and the effect of CNTs on resin curing reaction.
2015, 32(2): 341-346.
doi: 10.13801/j.cnki.fhclxb.20140617.002
Abstract:
In order to improve the cycle performance of lithium sulphur battery, chemical precipitation was adopted to prepare FeS immobilized mesoporous carbon (MC) composites FeS/MC. S immobilized MC composites S/MC and S-FeS immobilized composites S-FeS/MC were prepared by hot mixing. The SEM photographs show that holes on the surface of MC are filled by FeS; N2 adsorption-desorption isotherms indicate that after the immobilization of FeS, the specific area of MC decreases greatly, while the average diameter of holes increases. XRD patterns show that when the content of immobilized FeS reaches 20wt%, Fe3S4 phase appears. Electrochemical test results show that although FeS immobilized in MC shows no electrochemical activity, it has catalytic effect in the redox process of polysulfides, thus enhances the reversibility of cathode. The retention rate of 2nd specific discharge capacity of S-FeS/MC is higher than that of S/MC, and shows the lighter "shuttle effect". 2nd specific discharge capacity of S-FeS/MC is 1 108.8 mA·h/g, and the capacity retention rate after 50 cycles is 43.7%, which is higher than the capacity retention of S/MC, and shows superior cycle performance.
In order to improve the cycle performance of lithium sulphur battery, chemical precipitation was adopted to prepare FeS immobilized mesoporous carbon (MC) composites FeS/MC. S immobilized MC composites S/MC and S-FeS immobilized composites S-FeS/MC were prepared by hot mixing. The SEM photographs show that holes on the surface of MC are filled by FeS; N2 adsorption-desorption isotherms indicate that after the immobilization of FeS, the specific area of MC decreases greatly, while the average diameter of holes increases. XRD patterns show that when the content of immobilized FeS reaches 20wt%, Fe3S4 phase appears. Electrochemical test results show that although FeS immobilized in MC shows no electrochemical activity, it has catalytic effect in the redox process of polysulfides, thus enhances the reversibility of cathode. The retention rate of 2nd specific discharge capacity of S-FeS/MC is higher than that of S/MC, and shows the lighter "shuttle effect". 2nd specific discharge capacity of S-FeS/MC is 1 108.8 mA·h/g, and the capacity retention rate after 50 cycles is 43.7%, which is higher than the capacity retention of S/MC, and shows superior cycle performance.
2015, 32(2): 347-354.
doi: 10.13801/j.cnki.fhclxb.20140509.001
Abstract:
The wood flour-starch/poly (lactic acid)(PLA) composites were prepared by melt extrusion method with poplar wood flour, corn starch and PLA as raw material, glycerol as compatibilizer. The effect of wood flour contents on interfacial compatibility, thermal properties, mechanical properties, rheological properties and water absorption rate of composites were studied. The results show that with the increasing of wood flour contents, the interfacial compatibility between PLA and wood flour decreases, the thermal stability of wood flour-starch/PLA composites reduces, storage modulus, loss modulus and complex viscosity gradually increase. With the increasing of wood flour contents, the tensile strength and bending strength of wood flour-starch/PLA composites first increase then decrease, and reach the best values at 40.65 MPa and 60.91 MPa with 18wt% wood flour content. With the increasing of wood flour contents, the elongation at break of composites reduces gradually from 9.64% to 5.97%, and the water absorption rate increases observably from 5.38% to 13.43%.
The wood flour-starch/poly (lactic acid)(PLA) composites were prepared by melt extrusion method with poplar wood flour, corn starch and PLA as raw material, glycerol as compatibilizer. The effect of wood flour contents on interfacial compatibility, thermal properties, mechanical properties, rheological properties and water absorption rate of composites were studied. The results show that with the increasing of wood flour contents, the interfacial compatibility between PLA and wood flour decreases, the thermal stability of wood flour-starch/PLA composites reduces, storage modulus, loss modulus and complex viscosity gradually increase. With the increasing of wood flour contents, the tensile strength and bending strength of wood flour-starch/PLA composites first increase then decrease, and reach the best values at 40.65 MPa and 60.91 MPa with 18wt% wood flour content. With the increasing of wood flour contents, the elongation at break of composites reduces gradually from 9.64% to 5.97%, and the water absorption rate increases observably from 5.38% to 13.43%.
2015, 32(2): 355-364.
doi: 10.13801/j.cnki.fhclxb.20140605.002
Abstract:
Aiming at the shape precision control after the molding of large scale CFRP parts, which is one of the key technical problems, a modified shear-layer deformation simulation method was proposed based on the deformation prediction by shear-layer method. The modified method only needed a little test data, and the thickness of shear-layer could be determined by calculating the curvature of strain curve, then the warp deformation of CFRP parts could be predicted more exactly. A shape precision control method for large scale CFRP parts was developed based on the deformation simulating method above. This method could reduce the deformation of final parts by repeatedly compensating the deformation acquired by simulation to the initial mould surface. The comparison with the experimental data proved that the method above could effectively improve the accuracy and reduce the deformation of molding parts.
Aiming at the shape precision control after the molding of large scale CFRP parts, which is one of the key technical problems, a modified shear-layer deformation simulation method was proposed based on the deformation prediction by shear-layer method. The modified method only needed a little test data, and the thickness of shear-layer could be determined by calculating the curvature of strain curve, then the warp deformation of CFRP parts could be predicted more exactly. A shape precision control method for large scale CFRP parts was developed based on the deformation simulating method above. This method could reduce the deformation of final parts by repeatedly compensating the deformation acquired by simulation to the initial mould surface. The comparison with the experimental data proved that the method above could effectively improve the accuracy and reduce the deformation of molding parts.
2015, 32(2): 365-369.
doi: 10.13801/j.cnki.fhclxb.20140624.001
Abstract:
In order to improve the heat insulation performance of polycarbonate (PC) and maintain the high transparency at the same time, a series of silane coupling agent KH-570 modified nano antimony doped tin oxide (ATO)/PC composites were prepared by sol-gel method with infrared blocking agent of nano ATO. The particle size distribution and dispersion of nano ATO in PC matrix were investigated by laser particle size distribution analyzer and SEM. Meanwhile, tensile testing machine, spectrophotometer and insulation effect simulator were used to determine the mechanical properties, transmission properties and heat insulation performances of composites. The results show that silane modified nano ATO disperses in PC matrix uniformly. The tensile strength and impact strength maintain at 60.0 MPa and 16.0 kJ·m-2 or more, respectively. With the mass fraction of nano ATO increasing, the performances of infrared blocking and heat insulation enhance. When the content of nano ATO is 0.5wt%, the visible light transmittance of nano ATO/PC composites is over 80%, and the temperature difference between inside and outside of insulation effect simulator is up to 3.9 ℃.
In order to improve the heat insulation performance of polycarbonate (PC) and maintain the high transparency at the same time, a series of silane coupling agent KH-570 modified nano antimony doped tin oxide (ATO)/PC composites were prepared by sol-gel method with infrared blocking agent of nano ATO. The particle size distribution and dispersion of nano ATO in PC matrix were investigated by laser particle size distribution analyzer and SEM. Meanwhile, tensile testing machine, spectrophotometer and insulation effect simulator were used to determine the mechanical properties, transmission properties and heat insulation performances of composites. The results show that silane modified nano ATO disperses in PC matrix uniformly. The tensile strength and impact strength maintain at 60.0 MPa and 16.0 kJ·m-2 or more, respectively. With the mass fraction of nano ATO increasing, the performances of infrared blocking and heat insulation enhance. When the content of nano ATO is 0.5wt%, the visible light transmittance of nano ATO/PC composites is over 80%, and the temperature difference between inside and outside of insulation effect simulator is up to 3.9 ℃.
Influence of feed speed on surface morphology of CFRP with different fiber directions during milling
2015, 32(2): 370-377.
doi: 10.13801/j.cnki.fhclxb.20140603.002
Abstract:
Down milling processing test was conducted on carbon fiber reinforced plastics (CFRP) of four fiber directions (0°, 45°, 90°, 135°) by using a diamond coated cemented carbide tool. The effects of fiber direction and feed per rotation on processing surface quality were analyzed through comparing milling force and processing surface morphology. The results show that the main cutting force increases with the increase of feed per rotation. The maximal main cutting force is obtained with 0° fiber direction, while the main cutting force reaches its minimum value with 90° fiber direction. With the increase of feed per rotation, more broken resin and fiber could be left on surface of the workpiece with 0° fiber direction, while the adhesion of soften resin could be lightened on surface of the workpiece with 135° fiber direction. There are many shallow voids on surface of workpiece with 90° fiber direction, delamination of top and bottom laminate layers are observed at the same time. The finished surface of the workpiece with 45° fiber direction shows groove or wave-like surface morphology.
Down milling processing test was conducted on carbon fiber reinforced plastics (CFRP) of four fiber directions (0°, 45°, 90°, 135°) by using a diamond coated cemented carbide tool. The effects of fiber direction and feed per rotation on processing surface quality were analyzed through comparing milling force and processing surface morphology. The results show that the main cutting force increases with the increase of feed per rotation. The maximal main cutting force is obtained with 0° fiber direction, while the main cutting force reaches its minimum value with 90° fiber direction. With the increase of feed per rotation, more broken resin and fiber could be left on surface of the workpiece with 0° fiber direction, while the adhesion of soften resin could be lightened on surface of the workpiece with 135° fiber direction. There are many shallow voids on surface of workpiece with 90° fiber direction, delamination of top and bottom laminate layers are observed at the same time. The finished surface of the workpiece with 45° fiber direction shows groove or wave-like surface morphology.
2015, 32(2): 378-384.
doi: 10.13801/j.cnki.fhclxb.20140505.001
Abstract:
The electrospinning technique was used to produce nanoclay/polylactide (PLA) composite nanofibers, and the composite nanofibers were collected into non-woven films. SEM and TEM were used to investigate micromorphology and structure of fiber. XRD and TGA were used to investigate the crystallization and thermal properties, the relationship between the tensile mechanical properties of the composite nanofiber membranes and the contents of the nanoclay was revealed. The results reveal that the fineness and uniformity of the prepared nanoclay/PLA composite nanofibers are improved by 10wt% of PLA, 1wt% of nanoclay, solvent of CHCl3 and DMF(3:1, volume ratio). The inclusion of nanoclay in PLA is confirmed by XRD test results. TGA and mechanical test results show that the thermal stability and mechanical properties of nanoclay/PLA composite nanofibers are markedly improved than those of pure PLA. The initial temperature of heat decomposition increases by 60 ℃ by 1wt% of nanoclay, and tensile strength, elongation at break and elastic modulus increase by 111.3%, 74.9% and 20.0%, respectively.
The electrospinning technique was used to produce nanoclay/polylactide (PLA) composite nanofibers, and the composite nanofibers were collected into non-woven films. SEM and TEM were used to investigate micromorphology and structure of fiber. XRD and TGA were used to investigate the crystallization and thermal properties, the relationship between the tensile mechanical properties of the composite nanofiber membranes and the contents of the nanoclay was revealed. The results reveal that the fineness and uniformity of the prepared nanoclay/PLA composite nanofibers are improved by 10wt% of PLA, 1wt% of nanoclay, solvent of CHCl3 and DMF(3:1, volume ratio). The inclusion of nanoclay in PLA is confirmed by XRD test results. TGA and mechanical test results show that the thermal stability and mechanical properties of nanoclay/PLA composite nanofibers are markedly improved than those of pure PLA. The initial temperature of heat decomposition increases by 60 ℃ by 1wt% of nanoclay, and tensile strength, elongation at break and elastic modulus increase by 111.3%, 74.9% and 20.0%, respectively.
2015, 32(2): 385-394.
doi: 10.13801/j.cnki.fhclxb.20141021.006
Abstract:
The lignocellulose/nano-montmorillonite (LNC/nano-MMT) composites prepared were taken as the adsorbent to research the adsorption and desorption properties of Cu (II) from copper-contained wastewater, which were synthesized by the chemical intercalation process of LNC and nano-MMT. The affecting parameters on the Cu (II) adsorption capacity by changing initial concentration of Cu (II) ion, solution pH value, adsorption temperature and adsorption time were studied in detail. The results show that the equilibrium adsorption capacity could be reached 322.56 mg·g-1 under the optimal condition, 0.03 mol·L-1 initial concentration of Cu (II) ion, 4.9 of the solution pH value, 50 ℃ of the adsorption temperature and 60 min of the adsorption time. The pseudo-second-order kinetic model could well describe the whole adsorption process, and the isotherm adsorption equilibrium is conformed to the Langmuir model. HNO3 was used to perform desorption and regeneration experiments of LNC/nano-MMT composites. The results show that HNO3 concentration 0.1 mol·L-1, desorption temperature 40 ℃ and desorption time 30 min treated by ultrasonic wave, the satisfactory effect of desorption capacity is 283.15 mg·g-1. The adsorption mechanism of LNC/nano-MMT was discussed in combination with the results of XRD, SEM and FTIR. The adsorption/desorption experiment displays that the adsorption capacity of LNC/nano-MMT is ideal for four cycles, so LNC/nano-MMT is confirmed as a high efficient adsorbent for recycling.
The lignocellulose/nano-montmorillonite (LNC/nano-MMT) composites prepared were taken as the adsorbent to research the adsorption and desorption properties of Cu (II) from copper-contained wastewater, which were synthesized by the chemical intercalation process of LNC and nano-MMT. The affecting parameters on the Cu (II) adsorption capacity by changing initial concentration of Cu (II) ion, solution pH value, adsorption temperature and adsorption time were studied in detail. The results show that the equilibrium adsorption capacity could be reached 322.56 mg·g-1 under the optimal condition, 0.03 mol·L-1 initial concentration of Cu (II) ion, 4.9 of the solution pH value, 50 ℃ of the adsorption temperature and 60 min of the adsorption time. The pseudo-second-order kinetic model could well describe the whole adsorption process, and the isotherm adsorption equilibrium is conformed to the Langmuir model. HNO3 was used to perform desorption and regeneration experiments of LNC/nano-MMT composites. The results show that HNO3 concentration 0.1 mol·L-1, desorption temperature 40 ℃ and desorption time 30 min treated by ultrasonic wave, the satisfactory effect of desorption capacity is 283.15 mg·g-1. The adsorption mechanism of LNC/nano-MMT was discussed in combination with the results of XRD, SEM and FTIR. The adsorption/desorption experiment displays that the adsorption capacity of LNC/nano-MMT is ideal for four cycles, so LNC/nano-MMT is confirmed as a high efficient adsorbent for recycling.
2015, 32(2): 395-402.
doi: 10.13801/j.cnki.fhclxb.20140627.002
Abstract:
The out-of-plane/in-plane impact compression response characteristics of 3-D braided basalt filament fiber reinforced epoxy composites under the temperature field of 23, 60, 90, 120, 150, 210 ℃ and different strain-rates (1 300-1 600, 1 600-2 000, 2 000-2 300 s-1) were investigated. The results indicate that the stress-strain curve movement characteristics of out-of-plane/in-plane impact compression depend on whether the test temperatures are above or below the Tg of epoxy. Even though under the same test condition (temperature and gas pressure), there is still great difference between stress-strain curves of out-plane impact compression and in-plane impact compression. Temperature and strain rate have influence on compression modulus, peak stress, failure strain and specific energy absorption at different levels. The failure modes, affected by temperature and strain rate, differ in out-plane compression and in-plane compression.
The out-of-plane/in-plane impact compression response characteristics of 3-D braided basalt filament fiber reinforced epoxy composites under the temperature field of 23, 60, 90, 120, 150, 210 ℃ and different strain-rates (1 300-1 600, 1 600-2 000, 2 000-2 300 s-1) were investigated. The results indicate that the stress-strain curve movement characteristics of out-of-plane/in-plane impact compression depend on whether the test temperatures are above or below the Tg of epoxy. Even though under the same test condition (temperature and gas pressure), there is still great difference between stress-strain curves of out-plane impact compression and in-plane impact compression. Temperature and strain rate have influence on compression modulus, peak stress, failure strain and specific energy absorption at different levels. The failure modes, affected by temperature and strain rate, differ in out-plane compression and in-plane compression.
2015, 32(2): 403-408.
doi: 10.13801/j.cnki.fhclxb.20140521.002
Abstract:
With the main raw meterials of self-made double methoxybenzoic acid anion pillared hydrotalcite (MgAl-HTlcs) and caprolactam(CL), nano MgAl-HTlcs/nylon 6 composites were prepared by reactive extrusion, and the effect of MgAl-HTlcs content on microstructure and properties of the composites were investigated. TEM photographs show that MgAl-HTlcs disperse uniformly in composites as nanoscale and there are part exfoliated hydrotalcite in composite with MgAl-HTlcs of 1.0wt%(mass fraction of MgAl-HTlcs, CL total quality). UV-Vis spectra show that, compared with pure nylon 6, the MgAl-HTlcs/nylon 6 composites can strongly absorb the ultraviolet rays whose wavelength is between 320-380 nm. XRD and DSC results show that a small amount of MgAl-HTlcs plays a good role in heterogeneous nucleation of nylon 6, and improves its crystallization temperature and crystallinity. Thermogravimetric analysis shows the exists of part exfoliated MgAl-HTlcs, which improves the thermal stability of composites obviously.
With the main raw meterials of self-made double methoxybenzoic acid anion pillared hydrotalcite (MgAl-HTlcs) and caprolactam(CL), nano MgAl-HTlcs/nylon 6 composites were prepared by reactive extrusion, and the effect of MgAl-HTlcs content on microstructure and properties of the composites were investigated. TEM photographs show that MgAl-HTlcs disperse uniformly in composites as nanoscale and there are part exfoliated hydrotalcite in composite with MgAl-HTlcs of 1.0wt%(mass fraction of MgAl-HTlcs, CL total quality). UV-Vis spectra show that, compared with pure nylon 6, the MgAl-HTlcs/nylon 6 composites can strongly absorb the ultraviolet rays whose wavelength is between 320-380 nm. XRD and DSC results show that a small amount of MgAl-HTlcs plays a good role in heterogeneous nucleation of nylon 6, and improves its crystallization temperature and crystallinity. Thermogravimetric analysis shows the exists of part exfoliated MgAl-HTlcs, which improves the thermal stability of composites obviously.
2015, 32(2): 409-419.
doi: 10.13801/j.cnki.fhclxb.20140611.003
Abstract:
Aiming at the problem of low interfacial adhesion strength between ultra-high molecular weight polyethylene (UHMWPE) fiber and matrix, ultrasonic treatment and chromic acid solution oxidation compound process were used to perform surface modifications of UHMWPE fiber, and the modified fiber was added into natural rubber (NR) to prepare short-cut UHMWPE fiber/NR composites. The results show that the compound modification process could effectively increase the roughness and oxygen-containing group contents on surface of fibers, and the optimum modification conditions are: the chromic acid etching solution is prepared by mixing potassium dichromate, distilled water, and sulfuric acid with 7:12:150 mass ratio, and put the chromic acid solution which is filled with a certain quality UHMWPE fiber into ultrasonic cleaning instrument to oxidize for 5 min at 35 ℃, and the ultrasonic frequency is 100 kHz. Then, the as-prepared fibers were added into NR with mass ratio ranging from 0 to 6:100. Compared with the pure NR samples, with the increase of short fiber content, the tensile strength of composites decreases, mostly by 50%, the hardness increases, mostly by 96%, the tear strength first increases then decreases, and reaches mostly by 49% with mass ratio 5:100 between UHMWPE fibers and NR.
Aiming at the problem of low interfacial adhesion strength between ultra-high molecular weight polyethylene (UHMWPE) fiber and matrix, ultrasonic treatment and chromic acid solution oxidation compound process were used to perform surface modifications of UHMWPE fiber, and the modified fiber was added into natural rubber (NR) to prepare short-cut UHMWPE fiber/NR composites. The results show that the compound modification process could effectively increase the roughness and oxygen-containing group contents on surface of fibers, and the optimum modification conditions are: the chromic acid etching solution is prepared by mixing potassium dichromate, distilled water, and sulfuric acid with 7:12:150 mass ratio, and put the chromic acid solution which is filled with a certain quality UHMWPE fiber into ultrasonic cleaning instrument to oxidize for 5 min at 35 ℃, and the ultrasonic frequency is 100 kHz. Then, the as-prepared fibers were added into NR with mass ratio ranging from 0 to 6:100. Compared with the pure NR samples, with the increase of short fiber content, the tensile strength of composites decreases, mostly by 50%, the hardness increases, mostly by 96%, the tear strength first increases then decreases, and reaches mostly by 49% with mass ratio 5:100 between UHMWPE fibers and NR.
2015, 32(2): 420-426.
doi: 10.13801/j.cnki.fhclxb.20140617.001
Abstract:
With the purpose to improve the interface bonding force of carbon fibers (CFs) reinforced thermoplastic resin of poly(ether sulfone) (PES), a kind of new CFs type sizing agent called sulfonated poly(ether sulfone) (SPES) was prepared by PES sulfonated modification. The effect of SPES sizing agent and its mass fraction on interfacial properties of CFs/PES composites were studied. The results show that after sizing of SPES, the fiber fuzz amount decreases, the friction resistance is impoved, and it can also infer the chemical reaction between the group of —SO3H on the SPES sample with trace reactive functional groups on surface of CFs groups from FTIR and XPS. SPES sizing agent plays a bridge role in the interface of CFs/PES composites and creates a better bonding between them. Interlaminar shear strength (ILSS) of CFs/PES composites improves most significantly than unsizing CFs/PES composites, increased by 24% when the concentration of sizing agent is 1wt%. The SEM photographs confirm a more closely combination between CFs and PES at this concentration. Dynamic mechanical thermal analysis (DMTA) also proves that the concentration of 1wt% SPES sizing agent improves the glass transition temperature of CFs/PES composites most significantly.
With the purpose to improve the interface bonding force of carbon fibers (CFs) reinforced thermoplastic resin of poly(ether sulfone) (PES), a kind of new CFs type sizing agent called sulfonated poly(ether sulfone) (SPES) was prepared by PES sulfonated modification. The effect of SPES sizing agent and its mass fraction on interfacial properties of CFs/PES composites were studied. The results show that after sizing of SPES, the fiber fuzz amount decreases, the friction resistance is impoved, and it can also infer the chemical reaction between the group of —SO3H on the SPES sample with trace reactive functional groups on surface of CFs groups from FTIR and XPS. SPES sizing agent plays a bridge role in the interface of CFs/PES composites and creates a better bonding between them. Interlaminar shear strength (ILSS) of CFs/PES composites improves most significantly than unsizing CFs/PES composites, increased by 24% when the concentration of sizing agent is 1wt%. The SEM photographs confirm a more closely combination between CFs and PES at this concentration. Dynamic mechanical thermal analysis (DMTA) also proves that the concentration of 1wt% SPES sizing agent improves the glass transition temperature of CFs/PES composites most significantly.
2015, 32(2): 427-434.
doi: 10.13801/j.cnki.fhclxb.20140723.001
Abstract:
Nano copper decorated multi-walled carbon nanotubes(Cu-MWCNTs)/paraffin composites were synthesized by thermal decomposition of copper(II) formate-carbon nanotubes composite precursor in paraffin using oleylamine as dispersing agent. The phase structure, morphology and phase transition behavior were investigated by means of XRD, TEM and DSC. The thermal sensitivity, thermal expansion, thermal stability and their influencing factors of Cu-MWCNTs/paraffin composites were also studied. The results show that copper nanoparticles of 2-35 nm in size are attached to MWCNTs surface. The phase change temperature and latent heat of Cu-MWCNTs/paraffin composites significantly decrease as compared to that of the paraffin. It is clear that the Cu-MWCNTs/paraffin composites containing 0.2wt% of Cu-MWCNTs are desirable materials for microactuator, with short heating time, small decrease in volume expansibility and excellent thermal stability after being heated for many times.
Nano copper decorated multi-walled carbon nanotubes(Cu-MWCNTs)/paraffin composites were synthesized by thermal decomposition of copper(II) formate-carbon nanotubes composite precursor in paraffin using oleylamine as dispersing agent. The phase structure, morphology and phase transition behavior were investigated by means of XRD, TEM and DSC. The thermal sensitivity, thermal expansion, thermal stability and their influencing factors of Cu-MWCNTs/paraffin composites were also studied. The results show that copper nanoparticles of 2-35 nm in size are attached to MWCNTs surface. The phase change temperature and latent heat of Cu-MWCNTs/paraffin composites significantly decrease as compared to that of the paraffin. It is clear that the Cu-MWCNTs/paraffin composites containing 0.2wt% of Cu-MWCNTs are desirable materials for microactuator, with short heating time, small decrease in volume expansibility and excellent thermal stability after being heated for many times.
2015, 32(2): 435-443.
doi: 10.13801/j.cnki.fhclxb.201502.004
Abstract:
The glass fiber woven fabric-carbon fiber woven fabric/poly(cyclic butylene terephthalate) (GF-CF/PCBT) interlaminated hybrid composite laminates were prepared by vacuum bag assisted hot-press processing from the cyclic butylene terephthalate (CBT) prepregs. Double cantilever beam (DCB) and three-point end notched flexure (3ENF) tests were adopted to estimate the interlaminar performance of the obtained continuous fiber reinforced PCBT composite laminates. Meanwhile, the response of hybrid fiber reinforced PCBT laminates under low-velocity impact was mainly investigated by the tests and Abaqus/Explicit finite element simulation, respectively. The test results show that, despite the excellent interlaminate performance of CF/PCBT composite laminates, CF/PCBT composite laminates are penetrated under the impact energy of 114.3 J due to the brittleness of CF. As a comparison, the GF-CF/PCBT interlaminated hybrid laminates form merely dent on surface. Compared with pure CF reinforced PCBT composite laminates, the impact strength of GF-CF/PCBT interlaminated hybrid laminates with the layer form [CF/GF/CF]25 enhances significantly by 2 times. Simulation results show that stress area in CF is larger than that in GF in the resulted stress nephogram.
The glass fiber woven fabric-carbon fiber woven fabric/poly(cyclic butylene terephthalate) (GF-CF/PCBT) interlaminated hybrid composite laminates were prepared by vacuum bag assisted hot-press processing from the cyclic butylene terephthalate (CBT) prepregs. Double cantilever beam (DCB) and three-point end notched flexure (3ENF) tests were adopted to estimate the interlaminar performance of the obtained continuous fiber reinforced PCBT composite laminates. Meanwhile, the response of hybrid fiber reinforced PCBT laminates under low-velocity impact was mainly investigated by the tests and Abaqus/Explicit finite element simulation, respectively. The test results show that, despite the excellent interlaminate performance of CF/PCBT composite laminates, CF/PCBT composite laminates are penetrated under the impact energy of 114.3 J due to the brittleness of CF. As a comparison, the GF-CF/PCBT interlaminated hybrid laminates form merely dent on surface. Compared with pure CF reinforced PCBT composite laminates, the impact strength of GF-CF/PCBT interlaminated hybrid laminates with the layer form [CF/GF/CF]25 enhances significantly by 2 times. Simulation results show that stress area in CF is larger than that in GF in the resulted stress nephogram.
2015, 32(2): 444-450.
doi: 10.13801/j.cnki.fhclxb.201502.003
Abstract:
The surface of ramie fabrics was modified by using four sorts of methods including alkali treatment, silane coupling agent treatment, alkali+silane coupling agent treatment, alkali+flame retardant+silane coupling agent treatment. Then ramie fabrics reinforced thermosetting polylactic acid (PLA) composites were prepared by means of compression molding technology. The effects of the four surface modification methods on flexural properties of ramie fabrics/PLA composites were studied. SEM was used to describe the interface bonding condition between ramie fiber and PLA matrix. The results reveal that after treating ramie fabrics using the four surface modification methods, the flexural properties of ramie fabrics/PLA composites all increase, especially, the increase of flexural strength and modulus is the most with alkali+silane coupling agent treatment, and increases 59.5%, 51.9%, respectively. Alkali+flame retardant+silane coupling agent treatment improves the flexural strength and modulus by 38.0%, 66.8%, and the burn length is 8.25 cm when the ignition time of ramie fabrics/PLA composites is 60 s, which reaches the demand of American standard DOT/FAA/AR-00/12. The results of SEM show that a better interface adhesion occurs between fiber and resin in ramie fabrics/PLA composites after modification treatment.
The surface of ramie fabrics was modified by using four sorts of methods including alkali treatment, silane coupling agent treatment, alkali+silane coupling agent treatment, alkali+flame retardant+silane coupling agent treatment. Then ramie fabrics reinforced thermosetting polylactic acid (PLA) composites were prepared by means of compression molding technology. The effects of the four surface modification methods on flexural properties of ramie fabrics/PLA composites were studied. SEM was used to describe the interface bonding condition between ramie fiber and PLA matrix. The results reveal that after treating ramie fabrics using the four surface modification methods, the flexural properties of ramie fabrics/PLA composites all increase, especially, the increase of flexural strength and modulus is the most with alkali+silane coupling agent treatment, and increases 59.5%, 51.9%, respectively. Alkali+flame retardant+silane coupling agent treatment improves the flexural strength and modulus by 38.0%, 66.8%, and the burn length is 8.25 cm when the ignition time of ramie fabrics/PLA composites is 60 s, which reaches the demand of American standard DOT/FAA/AR-00/12. The results of SEM show that a better interface adhesion occurs between fiber and resin in ramie fabrics/PLA composites after modification treatment.
2015, 32(2): 451-457.
doi: 10.13801/j.cnki.fhclxb.201502.001
Abstract:
The surface of ceramic friction component was copper plated chemically to improve the combination situation between ceramic phase and matrix of the copper-based powder metallurgy friction materials, thus the friction and wear properties of the materials were improved. Cu-plated Al2O3 particles and non-Cu-plated Al2O3 particles were adopted respectively, friction and wear specimens of Al2O3-Fe-Sn-C/Cu were fabricated by mixing, pressing and pressure sintering with copper powder, iron powder and so on. The microstructures, mechanical properties, friction and wear properties of friction materials were measured and analyzed. Results show that the copper-plating of friction components makes the combination between hard particles and copper matrix tight. The Brinell hardness of friction material is improved by 12%, the elastic modulus is improved by about 7%, the friction coefficient is increased by 5%-10%, and the linear wear loss is reduced by 20%-50%. In addition, Al2O3 particles plated with copper on the surface are difficult to fall off, and the friction coefficient stability is increased by 13%-23%. Therefore, the overall performance of the materials can be improved by copper-plating on the surface of friction component.
The surface of ceramic friction component was copper plated chemically to improve the combination situation between ceramic phase and matrix of the copper-based powder metallurgy friction materials, thus the friction and wear properties of the materials were improved. Cu-plated Al2O3 particles and non-Cu-plated Al2O3 particles were adopted respectively, friction and wear specimens of Al2O3-Fe-Sn-C/Cu were fabricated by mixing, pressing and pressure sintering with copper powder, iron powder and so on. The microstructures, mechanical properties, friction and wear properties of friction materials were measured and analyzed. Results show that the copper-plating of friction components makes the combination between hard particles and copper matrix tight. The Brinell hardness of friction material is improved by 12%, the elastic modulus is improved by about 7%, the friction coefficient is increased by 5%-10%, and the linear wear loss is reduced by 20%-50%. In addition, Al2O3 particles plated with copper on the surface are difficult to fall off, and the friction coefficient stability is increased by 13%-23%. Therefore, the overall performance of the materials can be improved by copper-plating on the surface of friction component.
2015, 32(2): 458-464.
doi: 10.13801/j.cnki.fhclxb.20140418.001
Abstract:
Cu-Si alloy powder was prepared by induction furnace melting and water atomization process, and the Si3N4 in-situ reinforced Cu matrix composites (Si3N4/Cu) were prepared after gas mixture of N2 and H2 selective nitriding and vacuum spark plasma sintering (SPS) forming. The selective nitriding product and its crystalline structure were investigated by extraction method. Results show that nitrogen content of composite powder rises with the increase of nitriding temperature and extension of nitriding time. The nitrogen content significantly increases after nitriding for more than 60 h under 1 000 ℃. Overall diffraction peaks of Cu apparently move to the big angle, and the lattice constant decreases at the same time, which suggest that Si exsolves from Cu matrix to form Si3N4 while reacts with N. The reinforcement in Si3N4/Cu composites is mainly β-Si3N4. With nitriding temperature and time increasing, the electrical conductivity and hardness of Si3N4/Cu composites gradually increase.
Cu-Si alloy powder was prepared by induction furnace melting and water atomization process, and the Si3N4 in-situ reinforced Cu matrix composites (Si3N4/Cu) were prepared after gas mixture of N2 and H2 selective nitriding and vacuum spark plasma sintering (SPS) forming. The selective nitriding product and its crystalline structure were investigated by extraction method. Results show that nitrogen content of composite powder rises with the increase of nitriding temperature and extension of nitriding time. The nitrogen content significantly increases after nitriding for more than 60 h under 1 000 ℃. Overall diffraction peaks of Cu apparently move to the big angle, and the lattice constant decreases at the same time, which suggest that Si exsolves from Cu matrix to form Si3N4 while reacts with N. The reinforcement in Si3N4/Cu composites is mainly β-Si3N4. With nitriding temperature and time increasing, the electrical conductivity and hardness of Si3N4/Cu composites gradually increase.
2015, 32(2): 465-470.
doi: 10.13801/j.cnki.fhclxb.20140509.002
Abstract:
Aminopropyltriethoxysilane (KH550)-phenyltrimethoxysilan (Z6124) compound coupling agents with different components mixing ratios modified SiO2/polytetrafluoroethylene (PTFE) composites were prepared, and the effects of mixing ratios of KH550-Z6124 components on the dielectric properties, water absorption rate and heat conduction properties were investigated systematically. Lichtenecker model was adopted to calculate the theoretical values of dielectric constant and dielectric loss of SiO2/PTFE composites, and the theoretical values were compared with the experimental values. The research results show that when the mass ratios of KH550 and Z6124 to SiO2 are 0.3wt% and 1.7wt%, the dielectric loss of KH550-Z6124 modified SiO2/PTFE composites reduces from 1.7×10-3 (Z6124 modified SiO2/PTFE composites) to 1.0×10-3, the water absorption rate reduces from 0.082 6wt% to 0.020 3wt% and thermal conductivity increases by 66%. The SEM microstructure analysis show that KH550-Z6124 modified SiO2 particles disperse uniformly in PTFE matrix, and the interface connection is stronger. The experimental values of dielectric constant and dielectric loss of KH550-Z6124 modified SiO2/PTFE composites are more closer to the theoretical values.
Aminopropyltriethoxysilane (KH550)-phenyltrimethoxysilan (Z6124) compound coupling agents with different components mixing ratios modified SiO2/polytetrafluoroethylene (PTFE) composites were prepared, and the effects of mixing ratios of KH550-Z6124 components on the dielectric properties, water absorption rate and heat conduction properties were investigated systematically. Lichtenecker model was adopted to calculate the theoretical values of dielectric constant and dielectric loss of SiO2/PTFE composites, and the theoretical values were compared with the experimental values. The research results show that when the mass ratios of KH550 and Z6124 to SiO2 are 0.3wt% and 1.7wt%, the dielectric loss of KH550-Z6124 modified SiO2/PTFE composites reduces from 1.7×10-3 (Z6124 modified SiO2/PTFE composites) to 1.0×10-3, the water absorption rate reduces from 0.082 6wt% to 0.020 3wt% and thermal conductivity increases by 66%. The SEM microstructure analysis show that KH550-Z6124 modified SiO2 particles disperse uniformly in PTFE matrix, and the interface connection is stronger. The experimental values of dielectric constant and dielectric loss of KH550-Z6124 modified SiO2/PTFE composites are more closer to the theoretical values.
2015, 32(2): 471-476.
doi: 10.13801/j.cnki.fhclxb.20140616.002
Abstract:
Carbon nanotubes (CNTs) were introduced into carbon fiber surface and SiC matrix through electrodeposition and chemical vapor infiltration (CVI) method. Then the C/SiC composites (CNTs-C)/SiC and C/(CNTs-SiC) with CNTs deposited at different phases were obtained. The effects of CNTs deposition phases on the mechanical properties of C/SiC composites were investigated. The tensile strength and fracture mechanisms of C/SiC composites with CNTs deposited at different phases were studied. The results show that compared with C/SiC composite without the addition of CNTs, the tensile strength of (CNTs-C)/SiC composites with CNTs deposited on the surface of carbon fibers increases by 67.3%, and the work of fracture increases by 107.2%. However, the work of fracture of C/(CNTs-SiC) composites which introducing CNTs into the SiC matrix decreases, and the tensile strength only increases by 6.9%, the CNTs does not show significant strengthening and toughening effects. C/(CNTs-SiC) composites have the similar fracture morphology characteristics of traditional C/SiC composites, and both of them have the similar fracture and pullout mechanisms, mostly for carbon fiber strengthening and toughening, and CNTs does not play a significant role.
Carbon nanotubes (CNTs) were introduced into carbon fiber surface and SiC matrix through electrodeposition and chemical vapor infiltration (CVI) method. Then the C/SiC composites (CNTs-C)/SiC and C/(CNTs-SiC) with CNTs deposited at different phases were obtained. The effects of CNTs deposition phases on the mechanical properties of C/SiC composites were investigated. The tensile strength and fracture mechanisms of C/SiC composites with CNTs deposited at different phases were studied. The results show that compared with C/SiC composite without the addition of CNTs, the tensile strength of (CNTs-C)/SiC composites with CNTs deposited on the surface of carbon fibers increases by 67.3%, and the work of fracture increases by 107.2%. However, the work of fracture of C/(CNTs-SiC) composites which introducing CNTs into the SiC matrix decreases, and the tensile strength only increases by 6.9%, the CNTs does not show significant strengthening and toughening effects. C/(CNTs-SiC) composites have the similar fracture morphology characteristics of traditional C/SiC composites, and both of them have the similar fracture and pullout mechanisms, mostly for carbon fiber strengthening and toughening, and CNTs does not play a significant role.
2015, 32(2): 477-483.
doi: 10.13801/j.cnki.fhclxb.20140704.001
Abstract:
Using N-methylpolyborosilazane (PBSZ) as precursor, SiBNC fiber (SiBNCf) as reinforcement fiber, SiBNCf/SiBNC ceramic composites were fabricated by precursor polymer pyrolysis conversion and hot-press sintering method. The evolution of oxidation mechanism and kinetics of oxidation behavior of SiBNCf/SiBNC composites were investigated by non-isothermal oxidation tests under 800-1 500 ℃ for 1-3 h in air. The morphology and phase of SiBNCf/SiBNC ceramic composites before and after oxidation resistance were analyzed by means of SEM and XRD. The density, porosity and mechanical properties of composites were tested by Archimedes drainage volume method and three point bending test method. The results show that SiBNCf/SiBNC ceramic composites possess of outstanding oxidation resistance and high temperature stability. The prepared oxidation film can effectively block the entry of oxygen, and effectively fill the crack in SiBNCf/SiBNC composites and hole defect. The SiBNCf/SiBNC composites possess of high temperature self healing performance.The density of SiBNCf/SiBNC composites can be improved after oxidation, which can enhance the three point bending strength largely. As the density increase from 1.67 g/cm3 to 1.86 g/cm3, porosity decreases by 41%, bending strength inceases from 7.51 MPa to 26.54 MPa.
Using N-methylpolyborosilazane (PBSZ) as precursor, SiBNC fiber (SiBNCf) as reinforcement fiber, SiBNCf/SiBNC ceramic composites were fabricated by precursor polymer pyrolysis conversion and hot-press sintering method. The evolution of oxidation mechanism and kinetics of oxidation behavior of SiBNCf/SiBNC composites were investigated by non-isothermal oxidation tests under 800-1 500 ℃ for 1-3 h in air. The morphology and phase of SiBNCf/SiBNC ceramic composites before and after oxidation resistance were analyzed by means of SEM and XRD. The density, porosity and mechanical properties of composites were tested by Archimedes drainage volume method and three point bending test method. The results show that SiBNCf/SiBNC ceramic composites possess of outstanding oxidation resistance and high temperature stability. The prepared oxidation film can effectively block the entry of oxygen, and effectively fill the crack in SiBNCf/SiBNC composites and hole defect. The SiBNCf/SiBNC composites possess of high temperature self healing performance.The density of SiBNCf/SiBNC composites can be improved after oxidation, which can enhance the three point bending strength largely. As the density increase from 1.67 g/cm3 to 1.86 g/cm3, porosity decreases by 41%, bending strength inceases from 7.51 MPa to 26.54 MPa.
2015, 32(2): 484-490.
doi: 10.13801/j.cnki.fhclxb.20140704.002
Abstract:
Continuous fiber-reinforced nitride ceramic matrix composites are the main development direction of high-temperature wave-transparent materials, fiber is the pivotal issue which restrict the development of high-temperature wave-transparent composite materials, and SiBN ceramic fibers are a new kind of ceramic fibers which have excellent performances of high temperature resistance, wave transmission and mechanics. Polyborosilazane was used as ceramic precursor, and SiBN continuous fiber was used as reinforcement, SiBN fiber reinforced SiBN ceramic matrix composites were prepared by precursor infiltration-pyrolysis method. The thermal expansion properties, mechanical properties, fracture modes and microstructures of SiBN fiber reinforced SiBN ceramic matrix composites were investigated, and the preparation of new high-temperature wave-transparent ceramic matrix composites by precursor infiltration-pyrolysis was explored. The results show that the SiBN fiber reinforced SiBN ceramic matrix composites exhibits distinct brittle fracture characteristic, the bending strength and tensile strength of the composites are 88.52 MPa and 6.6 MPa respectively, which means the mechanical properties of the fiber still needs to be improved.
Continuous fiber-reinforced nitride ceramic matrix composites are the main development direction of high-temperature wave-transparent materials, fiber is the pivotal issue which restrict the development of high-temperature wave-transparent composite materials, and SiBN ceramic fibers are a new kind of ceramic fibers which have excellent performances of high temperature resistance, wave transmission and mechanics. Polyborosilazane was used as ceramic precursor, and SiBN continuous fiber was used as reinforcement, SiBN fiber reinforced SiBN ceramic matrix composites were prepared by precursor infiltration-pyrolysis method. The thermal expansion properties, mechanical properties, fracture modes and microstructures of SiBN fiber reinforced SiBN ceramic matrix composites were investigated, and the preparation of new high-temperature wave-transparent ceramic matrix composites by precursor infiltration-pyrolysis was explored. The results show that the SiBN fiber reinforced SiBN ceramic matrix composites exhibits distinct brittle fracture characteristic, the bending strength and tensile strength of the composites are 88.52 MPa and 6.6 MPa respectively, which means the mechanical properties of the fiber still needs to be improved.
2015, 32(2): 491-500.
doi: 10.13801/j.cnki.fhclxb.20140616.004
Abstract:
The compressional properties of composite single-stiffened panel specimens with rib were investigated through tests and finite element methods. Specimens with and without connector between stringer and rib were investigated. Test and numerical results reflect that specimens with connector between stringer and rib have higher rigidity, higher critical buckling loads, smaller deformation quantities in the post-buckling loading progress and smaller ultimate failure loads than specimen without connector. The ultimate failure mode of the specimen is always the interfacial debonding between stringer and panel, which reflects that the connector between stringer and rib has no effects on the final failure mode of the stiffened panel specimen. In the designing of composite airfoil structure, effects of connector between stringer and rib on the initial critical buckling load, post-buckling deformation and carrying capacity of the structure should be considered.
The compressional properties of composite single-stiffened panel specimens with rib were investigated through tests and finite element methods. Specimens with and without connector between stringer and rib were investigated. Test and numerical results reflect that specimens with connector between stringer and rib have higher rigidity, higher critical buckling loads, smaller deformation quantities in the post-buckling loading progress and smaller ultimate failure loads than specimen without connector. The ultimate failure mode of the specimen is always the interfacial debonding between stringer and panel, which reflects that the connector between stringer and rib has no effects on the final failure mode of the stiffened panel specimen. In the designing of composite airfoil structure, effects of connector between stringer and rib on the initial critical buckling load, post-buckling deformation and carrying capacity of the structure should be considered.
2015, 32(2): 501-507.
doi: 10.13801/j.cnki.fhclxb.20140627.003
Abstract:
To solve the problem of the lack of effective all-composite truss torsional stiffness characterization method except for experiment, based on the homogenization concept and according to the principle of equal single cell shear stiffness, the all-composite truss was equivalent to closed thin-walled beam to deduce their equivalent torsional stiffness firstly. Then the displacement conversion method was proposed and the torsional angles of truss were measured, and an experimental investigation on all-composite truss torsional stiffness was conducted. The fine joint models were embedded into truss model of beam elements to simulate and analyze the all-composite truss torsional stiffness finally. The results show that equivalent and simulative results agree with experimental values basically, which indicates that the equivalent analysis method can predict all-composite truss torsional stiffness effectively, and the truss simulation model has certain engineering practicability. Moreover, the experimental scheme is reliable, and the proposed displacement conversion method can solve the problem of larger relative errors of small angle measurement.
To solve the problem of the lack of effective all-composite truss torsional stiffness characterization method except for experiment, based on the homogenization concept and according to the principle of equal single cell shear stiffness, the all-composite truss was equivalent to closed thin-walled beam to deduce their equivalent torsional stiffness firstly. Then the displacement conversion method was proposed and the torsional angles of truss were measured, and an experimental investigation on all-composite truss torsional stiffness was conducted. The fine joint models were embedded into truss model of beam elements to simulate and analyze the all-composite truss torsional stiffness finally. The results show that equivalent and simulative results agree with experimental values basically, which indicates that the equivalent analysis method can predict all-composite truss torsional stiffness effectively, and the truss simulation model has certain engineering practicability. Moreover, the experimental scheme is reliable, and the proposed displacement conversion method can solve the problem of larger relative errors of small angle measurement.
2015, 32(2): 508-514.
doi: 10.13801/j.cnki.fhclxb.20140603.001
Abstract:
In order to investigate the anti-tearing behaviors of envelop thin films with initial cracks, Kevlar fabric reinforced envelope thin films used in stratospheric airships with prefabricated initial crack (PIC) were chosen and the plane stress analysis method of elastic-plastic fracture mechanics was adopted. Considering the effects of slipping friction between warp and weft, the tearing strength and deformation modes of film crack tips were analyzed. Physical model of crack tip tearing and arithmetical tensile deformation computational model based on friction effects were established. The stress distribution of stress concentration area among crack tip was obtained. In order to verify the rationality of the computational model above, specimens with PIC length of 10, 20, 30 and 40 mm were tested to obtain the tearing strength, respectively. Results show that when PIC width ratio does not exceed 0.50, the deviation between calculated values of models and testing values is lower than 4.12%. Compared with the improved stress intensity factor theory, the computational model established above is more accurate, which provides an effective approach for the tearing strength design of stratospheric airship envelope.
In order to investigate the anti-tearing behaviors of envelop thin films with initial cracks, Kevlar fabric reinforced envelope thin films used in stratospheric airships with prefabricated initial crack (PIC) were chosen and the plane stress analysis method of elastic-plastic fracture mechanics was adopted. Considering the effects of slipping friction between warp and weft, the tearing strength and deformation modes of film crack tips were analyzed. Physical model of crack tip tearing and arithmetical tensile deformation computational model based on friction effects were established. The stress distribution of stress concentration area among crack tip was obtained. In order to verify the rationality of the computational model above, specimens with PIC length of 10, 20, 30 and 40 mm were tested to obtain the tearing strength, respectively. Results show that when PIC width ratio does not exceed 0.50, the deviation between calculated values of models and testing values is lower than 4.12%. Compared with the improved stress intensity factor theory, the computational model established above is more accurate, which provides an effective approach for the tearing strength design of stratospheric airship envelope.
2015, 32(2): 515-525.
doi: 10.13801/j.cnki.fhclxb.20140627.005
Abstract:
The properties of 3D six-directional braided composite bolted joint structure were investigated by the test and numerical simulation. First, the joint strength of bolted joint structure with different lateral restraint was tested by tensile test. The test results show that the second bend phenomenon of the single-lap joint structure is obvious, there is a certain relationship between joint strength and lateral restraint. The joint strength can be effectively improved by using the gasket. The increase of tightening torque of bolted has little effect on joint strength. The failure modes of joint structure include bearing failure and tensile failure. The dominant failure mode is bearing failure when the aperture is small. Then based on the failure mode which was found in test, the analytical model was established basing on the point stress criteria, and the tightening torque was applied to the bolted joints by using temperature rising method. The reliability analysis model can be verified by comparing the numerical results with the test results. Finally, the verified analytical model was used to analyze the second bend phenomenon of single-lap bolted joint structures. The effects of lateral restraint area, tightening torque of bolted joints and the plate thickness on mechanical properties of single-lap bolted joint structures were obtained. The results indicate the joint strength first increases and then decreases with the increase of lateral restraint stress.
The properties of 3D six-directional braided composite bolted joint structure were investigated by the test and numerical simulation. First, the joint strength of bolted joint structure with different lateral restraint was tested by tensile test. The test results show that the second bend phenomenon of the single-lap joint structure is obvious, there is a certain relationship between joint strength and lateral restraint. The joint strength can be effectively improved by using the gasket. The increase of tightening torque of bolted has little effect on joint strength. The failure modes of joint structure include bearing failure and tensile failure. The dominant failure mode is bearing failure when the aperture is small. Then based on the failure mode which was found in test, the analytical model was established basing on the point stress criteria, and the tightening torque was applied to the bolted joints by using temperature rising method. The reliability analysis model can be verified by comparing the numerical results with the test results. Finally, the verified analytical model was used to analyze the second bend phenomenon of single-lap bolted joint structures. The effects of lateral restraint area, tightening torque of bolted joints and the plate thickness on mechanical properties of single-lap bolted joint structures were obtained. The results indicate the joint strength first increases and then decreases with the increase of lateral restraint stress.
2015, 32(2): 526-533.
doi: 10.13801/j.cnki.fhclxb.20140718.002
Abstract:
Modified semi-analytical method (MAM) was created by applying the concept of differential and rule of composite ply stiffness distribution, which can be used to predict adhesive stress for scarf joints in composite structure. Firstly, validation of MAM was studied through the models of different ply angles and number of plies with finite element method (FEM) 2D plane strain. Then, the load carrying capacity of the composite scarf joints was predicted with average shear stress method, FEM and MAM. At last, MAM was used for analyzing engineering applications which concerned scarf joints with dissimilar modulus of adherends and variation of adhesive thickness. The comparison of results of these methods with the test values demonstrates that MAM is appropriate for designing scarf joints in composite structures, and the peak value of adhesive stress can be obtained with MAM and stress distribution is in accord with FEM calculation.
Modified semi-analytical method (MAM) was created by applying the concept of differential and rule of composite ply stiffness distribution, which can be used to predict adhesive stress for scarf joints in composite structure. Firstly, validation of MAM was studied through the models of different ply angles and number of plies with finite element method (FEM) 2D plane strain. Then, the load carrying capacity of the composite scarf joints was predicted with average shear stress method, FEM and MAM. At last, MAM was used for analyzing engineering applications which concerned scarf joints with dissimilar modulus of adherends and variation of adhesive thickness. The comparison of results of these methods with the test values demonstrates that MAM is appropriate for designing scarf joints in composite structures, and the peak value of adhesive stress can be obtained with MAM and stress distribution is in accord with FEM calculation.
2015, 32(2): 534-541.
doi: 10.13801/j.cnki.fhclxb.20140616.003
Abstract:
New negative Poisson's ratio crush box (NPRC) structure of vehicle front frame was presented. By studying the failure mode and plateau stress in plateau stage of cell, the mechanical properties of failure were discussed. It can be concluded that the NPRC structure shows better energy absorption capability than usual cellular structure with enhanced equivalent elastic modulus and plateau stress under in-plane loading. With mechanical analytical model of NPRC cell in plateau stage, the critical stress equations of elastic buckling and plastic collapse were developed, the conclusion that plastic collapse is the main failure mode of the structure is also presented. The parametric finite element model of NPRC cell by Matlab software was used to study the relationship between geometric parameters and plateau stress, which indicates that the plateau stress of cell is inversely proportional to length ratio and cell angle and in proportion to thickness ratio. And in-plane axial quasi static compressive experiment using 3×3 NPRC sample was carried out to verify finite element analysis results. The results conclude that the NPRC sample has equivalent negative Poisson's ratio (-11.97). The NPRC sample appears densification of cell and peak value of plateau stress increases with the increase of strain, which provides theoretical significance for improving energy absorption performance.
New negative Poisson's ratio crush box (NPRC) structure of vehicle front frame was presented. By studying the failure mode and plateau stress in plateau stage of cell, the mechanical properties of failure were discussed. It can be concluded that the NPRC structure shows better energy absorption capability than usual cellular structure with enhanced equivalent elastic modulus and plateau stress under in-plane loading. With mechanical analytical model of NPRC cell in plateau stage, the critical stress equations of elastic buckling and plastic collapse were developed, the conclusion that plastic collapse is the main failure mode of the structure is also presented. The parametric finite element model of NPRC cell by Matlab software was used to study the relationship between geometric parameters and plateau stress, which indicates that the plateau stress of cell is inversely proportional to length ratio and cell angle and in proportion to thickness ratio. And in-plane axial quasi static compressive experiment using 3×3 NPRC sample was carried out to verify finite element analysis results. The results conclude that the NPRC sample has equivalent negative Poisson's ratio (-11.97). The NPRC sample appears densification of cell and peak value of plateau stress increases with the increase of strain, which provides theoretical significance for improving energy absorption performance.
2015, 32(2): 542-548.
doi: 10.13801/j.cnki.fhclxb.20140718.003
Abstract:
Filled-hole form and virtual interlaminar boundary method were proposed to solve interlaminar stress to study interlaminar stress distribution law of composite laminates connector with bolts, and three-dimensional finite element model was established for analyzing the filled-hole laminate with bolt clamping under in-plane compression load. The results show that interlaminar stress concentration of laminates occurs not only at the hole edge, but also in the vicinity of bolt head edge, and the greater bolt-clamping force, the more serious interlaminar stress concentration near the bolt head edge. A reasonable bolt-clamping force can improve the stress state of hole edge, and enhance the ability to resist delamination of hole edge, but can not change the interlaminar shear stress concentration state near the bolt head edge. Therefore, to improve the safety of composite structures, the interlaminar shear stress concentration problems near the bolt head edge should be considered in the laminate mechanical joint interlaminar strength design of hole edge with bolt clamping.
Filled-hole form and virtual interlaminar boundary method were proposed to solve interlaminar stress to study interlaminar stress distribution law of composite laminates connector with bolts, and three-dimensional finite element model was established for analyzing the filled-hole laminate with bolt clamping under in-plane compression load. The results show that interlaminar stress concentration of laminates occurs not only at the hole edge, but also in the vicinity of bolt head edge, and the greater bolt-clamping force, the more serious interlaminar stress concentration near the bolt head edge. A reasonable bolt-clamping force can improve the stress state of hole edge, and enhance the ability to resist delamination of hole edge, but can not change the interlaminar shear stress concentration state near the bolt head edge. Therefore, to improve the safety of composite structures, the interlaminar shear stress concentration problems near the bolt head edge should be considered in the laminate mechanical joint interlaminar strength design of hole edge with bolt clamping.
2015, 32(2): 549-556.
doi: 10.13801/j.cnki.fhclxb.20140725.005
Abstract:
A new method for the stress determination of short concrete columns under axial load by using cement-based piezoelectric ceramic sensors was proposed. The piezoelectric sensors were embedded into the core area of concrete rectangular short columns. Axial dynamic fatigue load of short concrete columns before and after the confine of fiber reinforced polymer was determinated. The numerical model between output signals of sensors and core area stress of short concrete concretes was established, and the calculated theoretical stress values were contrasted with the stress values derived by model. The results show that the stress values derived by model tallies with the calculated theoretical stress values basically. Then the feasibility of this new method, which the stress of short concrete columns under dynamic load effect is measured by piezoelectric sensors, is verified.
A new method for the stress determination of short concrete columns under axial load by using cement-based piezoelectric ceramic sensors was proposed. The piezoelectric sensors were embedded into the core area of concrete rectangular short columns. Axial dynamic fatigue load of short concrete columns before and after the confine of fiber reinforced polymer was determinated. The numerical model between output signals of sensors and core area stress of short concrete concretes was established, and the calculated theoretical stress values were contrasted with the stress values derived by model. The results show that the stress values derived by model tallies with the calculated theoretical stress values basically. Then the feasibility of this new method, which the stress of short concrete columns under dynamic load effect is measured by piezoelectric sensors, is verified.
2015, 32(2): 557-564.
doi: 10.13801/j.cnki.fhclxb.20140722.003
Abstract:
The impact properties of ultra-high molecular weight polyethylene (UHMWPE) fiber/epoxy weft plain knitted composites by vacuum assisted resin transfer molding (VARTM) process were investigated by considering impact energy and absorbtion energy profile diagram and the related contact force–deflection curves. The composites consisting of 4, 6, 8 layers weft plain knitted structure were subjected to different impact energies (10-55 J). The damage modes and damage processes of fabrics under varied impact energies were also discussed. Results show that the maximum contact force is observed in 8 layers weft plain knitted structure, followed by 6 layers weft plain knitted structure, and the minimum contact force is observed in 4 layers weft plain knitted structure; the impact deflection of three knitted composites is increased by increasing the impact energy; the effective damage modes for penetration are matrix cracking and fiber splitting, matrix and fiber breakage is the effective damage mode in the case of perforation.
The impact properties of ultra-high molecular weight polyethylene (UHMWPE) fiber/epoxy weft plain knitted composites by vacuum assisted resin transfer molding (VARTM) process were investigated by considering impact energy and absorbtion energy profile diagram and the related contact force–deflection curves. The composites consisting of 4, 6, 8 layers weft plain knitted structure were subjected to different impact energies (10-55 J). The damage modes and damage processes of fabrics under varied impact energies were also discussed. Results show that the maximum contact force is observed in 8 layers weft plain knitted structure, followed by 6 layers weft plain knitted structure, and the minimum contact force is observed in 4 layers weft plain knitted structure; the impact deflection of three knitted composites is increased by increasing the impact energy; the effective damage modes for penetration are matrix cracking and fiber splitting, matrix and fiber breakage is the effective damage mode in the case of perforation.
2015, 32(2): 565-570.
doi: 10.13801/j.cnki.fhclxb.20140722.002
Abstract:
Finite element model of composite wing on unmanned aerial vehicle of a particular type was established based on large-scale commercial software MSC.Patran. Three typical damages including skin delamination, debond between skin, beam and rib and crack on the beam were simulated in the wing. The effects of location and size of damage on vibration performance of wing were analyzed through comparing with the natural vibration frequency of undamaged wing. The results show that the three typical damages cannot induce the change of vibration modals of each order generally, but affect the vibration frequencies of each order. The effects on vibration frequencies of each order are not only concerned with the damage location, but also with the damage degree of major load-carrying structures. When skin delamination or crack on the beam appears in the root segment of the wing, the influence on the vibration frequency of wing is most obvious.
Finite element model of composite wing on unmanned aerial vehicle of a particular type was established based on large-scale commercial software MSC.Patran. Three typical damages including skin delamination, debond between skin, beam and rib and crack on the beam were simulated in the wing. The effects of location and size of damage on vibration performance of wing were analyzed through comparing with the natural vibration frequency of undamaged wing. The results show that the three typical damages cannot induce the change of vibration modals of each order generally, but affect the vibration frequencies of each order. The effects on vibration frequencies of each order are not only concerned with the damage location, but also with the damage degree of major load-carrying structures. When skin delamination or crack on the beam appears in the root segment of the wing, the influence on the vibration frequency of wing is most obvious.
2015, 32(2): 571-578.
doi: 10.13801/j.cnki.fhclxb.201502.002
Abstract:
Two-dimensional plane strain models were used to analyze the failure of Z-pin reinforced T-joint specimens. The cohesive zone model was used to simulate the interface failure, and the reinforcement effect of Z-pin was simulated by the inserting of nonlinear springs into the upper and lower interfaces of delamination. The mechanical properties (bridging law) of nonlinear spring were obtained by micromechanical approach. The numerical results agree well with the testing values. Based on the verified finite element method, the effects of the diameter, density and inserting angle et al of Z-pin on the pull-off carrying capacity of T-joints were studied. Results show that Z-pin reinforcement can effectively improve the pull-off carrying capacity of T-joints and delay the decrease of the load after peak loading significantly compared to the T-joints before Z-pin reinforcement. The pull-off carrying capacity of T-joint increases as the diameter and density of Z-pin increase and decreases as the inserting angle of Z-pin increases. In the angle range investigated, the pull-off carrying capacity of T-joints reaches the best when the inserting angle is 60°. The effect of diameter and density of Z-pin on pull-off carrying capacity is much more significant than that of inserting angle.
Two-dimensional plane strain models were used to analyze the failure of Z-pin reinforced T-joint specimens. The cohesive zone model was used to simulate the interface failure, and the reinforcement effect of Z-pin was simulated by the inserting of nonlinear springs into the upper and lower interfaces of delamination. The mechanical properties (bridging law) of nonlinear spring were obtained by micromechanical approach. The numerical results agree well with the testing values. Based on the verified finite element method, the effects of the diameter, density and inserting angle et al of Z-pin on the pull-off carrying capacity of T-joints were studied. Results show that Z-pin reinforcement can effectively improve the pull-off carrying capacity of T-joints and delay the decrease of the load after peak loading significantly compared to the T-joints before Z-pin reinforcement. The pull-off carrying capacity of T-joint increases as the diameter and density of Z-pin increase and decreases as the inserting angle of Z-pin increases. In the angle range investigated, the pull-off carrying capacity of T-joints reaches the best when the inserting angle is 60°. The effect of diameter and density of Z-pin on pull-off carrying capacity is much more significant than that of inserting angle.
2015, 32(2): 579-585.
doi: 10.13801/j.cnki.fhclxb.20140702.004
Abstract:
First, the expressions of axial force and bending moment for the rotating composite beams were deduced based on the constitutive relations of composites under hygrothermal environment. The influences of temperature and humidity on axial force and bending moment were analyzed. Then, the d'Alembert principle was employed to establish the lead-lag vibration governing equation for the rotating composite beams. The temperature and humidity effects on the stiffness of rotating composite beams were investigated after solving the equation by Galerkin method. Finally, the effects of hygrothermal environment on lead-lag vibration dynamic characteristics of rotating composite beams were analyzed by numerical simulation. The results show that hygrothermal environment affects lead-lag vibration frequency and modal of rotating composites beams conspicuously. Lead-lag vibration frequency decreases when the hygrothermal environment exacerbates. The effect of thermal expansion on lead-lag vibration frequency is more obvious than that of material properties variations. The combined effect of hygrothermal environment and rotating result in the obvious locational excursion of modal nodes.
First, the expressions of axial force and bending moment for the rotating composite beams were deduced based on the constitutive relations of composites under hygrothermal environment. The influences of temperature and humidity on axial force and bending moment were analyzed. Then, the d'Alembert principle was employed to establish the lead-lag vibration governing equation for the rotating composite beams. The temperature and humidity effects on the stiffness of rotating composite beams were investigated after solving the equation by Galerkin method. Finally, the effects of hygrothermal environment on lead-lag vibration dynamic characteristics of rotating composite beams were analyzed by numerical simulation. The results show that hygrothermal environment affects lead-lag vibration frequency and modal of rotating composites beams conspicuously. Lead-lag vibration frequency decreases when the hygrothermal environment exacerbates. The effect of thermal expansion on lead-lag vibration frequency is more obvious than that of material properties variations. The combined effect of hygrothermal environment and rotating result in the obvious locational excursion of modal nodes.
2015, 32(2): 586-593.
doi: 10.13801/j.cnki.fhclxb.20140604.004
Abstract:
The nylon nonwoven fabric (Polyamide Nonwoven Fabric, PNF) was selected as structural toughening layer to investigate its effect on the permeability of fiber preforms during resin transfer molding (RTM) process. Results show that under unsaturated radial flow pattern, the permeability of the interlaminar toughened preform along the direction of fiber (5.2×10-12 m2) is lower than that of the untoughened preform (7.1×10-12 m2). On the contrary, the permeability of the toughened preform perpendicular to the fiber direction (2.3×10-12 m2) is higher than that of the untoughened preform (1.6×10-12 m2). Moreover, the unidirectional saturated flow permeability of interlaminar toughened preform is 2.6×10-12 m2, which is much lower than that of untoughened preform (1.9×10-11 m2), decreased by an order of magnitude. The z -directional saturated permeability also dramatically decreases from 1.3×10-13 m2 (untoughened preform) to 2.5×10-14 m2, decreased by an order of magnitude. The interlaminar morphology analysis results reveal that the decrease of the permeability of preform mainly results from the inhibition of rapid flow of resin, introduced by PNF as structural layers and the increment of interlaminar fiber contents rising from 55.3vol% to 63.7vol%.
The nylon nonwoven fabric (Polyamide Nonwoven Fabric, PNF) was selected as structural toughening layer to investigate its effect on the permeability of fiber preforms during resin transfer molding (RTM) process. Results show that under unsaturated radial flow pattern, the permeability of the interlaminar toughened preform along the direction of fiber (5.2×10-12 m2) is lower than that of the untoughened preform (7.1×10-12 m2). On the contrary, the permeability of the toughened preform perpendicular to the fiber direction (2.3×10-12 m2) is higher than that of the untoughened preform (1.6×10-12 m2). Moreover, the unidirectional saturated flow permeability of interlaminar toughened preform is 2.6×10-12 m2, which is much lower than that of untoughened preform (1.9×10-11 m2), decreased by an order of magnitude. The z -directional saturated permeability also dramatically decreases from 1.3×10-13 m2 (untoughened preform) to 2.5×10-14 m2, decreased by an order of magnitude. The interlaminar morphology analysis results reveal that the decrease of the permeability of preform mainly results from the inhibition of rapid flow of resin, introduced by PNF as structural layers and the increment of interlaminar fiber contents rising from 55.3vol% to 63.7vol%.
2015, 32(2): 594-600.
doi: 10.13801/j.cnki.fhclxb.20140529.001
Abstract:
Bamboo-wood composites with different filling content of Ca and Mg natural mineral powder were prepared, and the thermal pyrolysis performances and pyrolysis kinetics of bamboo-wood composites filled with Ca and Mg natural mineral powder were investigated by thermal gravity (TG) analysis, pyrolysis-gas chromatography-mass spectrometry (PY-GC/MS), Li Chung-Hsiung integral method and Malek method. Then the pyrolysis model of bamboo-wood composites filled with Ca and Mg natural mineral powder was built. The results show that when the pyrolysis of natural mineral powder occurs, the heat around will be adsorbed. Then the pyrolysis of bamboo-wood composites is inhibited by the products of natural mineral powder pyrolysis, such as free radicals inhibitor as well as CaO and MgO which are difficult to pyrolysis. The contents of CO, CO2 and single benzodiazepines aromatic compounds in pyrolysis products decrease compared with those of unfilled bamboo-wood composites, while the content of aliphatic compounds increases. The pyrolysis reaction model of unfilled bamboo-wood composites is random nucleation, each particle has one nuclear, while the pyrolysis reaction model of bamboo-wood composites filled with Ca and Mg natural mineral powder is phase boundary reaction and spherical symmetry.
Bamboo-wood composites with different filling content of Ca and Mg natural mineral powder were prepared, and the thermal pyrolysis performances and pyrolysis kinetics of bamboo-wood composites filled with Ca and Mg natural mineral powder were investigated by thermal gravity (TG) analysis, pyrolysis-gas chromatography-mass spectrometry (PY-GC/MS), Li Chung-Hsiung integral method and Malek method. Then the pyrolysis model of bamboo-wood composites filled with Ca and Mg natural mineral powder was built. The results show that when the pyrolysis of natural mineral powder occurs, the heat around will be adsorbed. Then the pyrolysis of bamboo-wood composites is inhibited by the products of natural mineral powder pyrolysis, such as free radicals inhibitor as well as CaO and MgO which are difficult to pyrolysis. The contents of CO, CO2 and single benzodiazepines aromatic compounds in pyrolysis products decrease compared with those of unfilled bamboo-wood composites, while the content of aliphatic compounds increases. The pyrolysis reaction model of unfilled bamboo-wood composites is random nucleation, each particle has one nuclear, while the pyrolysis reaction model of bamboo-wood composites filled with Ca and Mg natural mineral powder is phase boundary reaction and spherical symmetry.
2015, 32(2): 601-607.
doi: 10.13801/j.cnki.fhclxb.20140616.001
Abstract:
By constructing new conformal mapping and using complex variable function method, anti-plane problem of isotropic piezoelectroelastic solids containing regular triangle hole with smooth vertices which emanates edge crack was studied. Under the assumption that the surfaces of the crack and hole were electrically permeable and electrically impermeable, respectively, and their surfaces are free traction, combined with Cauchy integral and complex variable function method, the expressions of the field intensity factors and the energy release rates near crack tip were obtained. The numerical examples were conducted to show the influences of the geometrical parameters of crack and applied mechanical loads on energy release rate and mechanical strain energy release rate under different boundary conditions. The results show that, under the electrically permeable and impermeable boundaries, the increases of the length of crack and the size of triangle hole lead to the increase of the energy release rate. The mechanical loads always promote crack growth. Under the electrically impermeable boundary the electric displacements may promote or retard the crack growth, but the electric displacements have no effect on the crack growth under the electrically permeable boundary.
By constructing new conformal mapping and using complex variable function method, anti-plane problem of isotropic piezoelectroelastic solids containing regular triangle hole with smooth vertices which emanates edge crack was studied. Under the assumption that the surfaces of the crack and hole were electrically permeable and electrically impermeable, respectively, and their surfaces are free traction, combined with Cauchy integral and complex variable function method, the expressions of the field intensity factors and the energy release rates near crack tip were obtained. The numerical examples were conducted to show the influences of the geometrical parameters of crack and applied mechanical loads on energy release rate and mechanical strain energy release rate under different boundary conditions. The results show that, under the electrically permeable and impermeable boundaries, the increases of the length of crack and the size of triangle hole lead to the increase of the energy release rate. The mechanical loads always promote crack growth. Under the electrically impermeable boundary the electric displacements may promote or retard the crack growth, but the electric displacements have no effect on the crack growth under the electrically permeable boundary.
2015, 32(2): 608-615.
doi: 10.13801/j.cnki.fhclxb.20140627.001
Abstract:
The carbon fiber/bismaleimide (T300/QY8911) embedded co-cured composite damping structure (ECCDS) specimens were manufactured by pressed-film process and brush coating process. The moisture absorption properties of T300/QY8911 composite damping structure specimens were studied, and the relationship between moisture absorption rate and the thickness of damping layer was obtained. The interlayer bonding properties of moisture absorption treated composites made by the two processes above were investigated, and the relationship between the thickness of damping layer and the maximum interlamination shear stress was analyzed. Results show that the ECCDS with perforated viscous-elastic damping layer can increase the interlaminar bonding properties after moisture absorption treatment, and provide a foundation for the theoretical design and application research of ECCDS.
The carbon fiber/bismaleimide (T300/QY8911) embedded co-cured composite damping structure (ECCDS) specimens were manufactured by pressed-film process and brush coating process. The moisture absorption properties of T300/QY8911 composite damping structure specimens were studied, and the relationship between moisture absorption rate and the thickness of damping layer was obtained. The interlayer bonding properties of moisture absorption treated composites made by the two processes above were investigated, and the relationship between the thickness of damping layer and the maximum interlamination shear stress was analyzed. Results show that the ECCDS with perforated viscous-elastic damping layer can increase the interlaminar bonding properties after moisture absorption treatment, and provide a foundation for the theoretical design and application research of ECCDS.
