2010 Vol. 27, No. 6
2010, 27(6): 1-8.
Abstract:
The effect of ex-situ method on the mechanical properties and toughness of the RTMable carbon fiber (G827)／polyimide(PI-9731)composites was studied. The results show that the interlaminar shear strength of G827／PI-9731 composites toughened by the ex-situ methods with powder and film increases from 97.9MPa to 108MPa and 110MPa, respectively, when the thermoplastic PI mass fraction is 15% at room temperature. However, the interlaminar shear strength changes slightly at high temperature (288℃).The mode Ⅰ fracture toughness of G827／PI-9731 composites toughened with powder method is improved from 310J/m2 to 410J/m2. The Mode Ⅱ fracture toughness is improved from 590J/m2 to 939J/m2. However the mode Ⅰ fracture toughness of G827／PI-9731 composites toughened with film method increases to 459J/m2. The mode Ⅱ fracture toughness is improved to 1100J/m2. By SEM analysis, it is found that the toughness improvement results from the introduction of thermoplastic PI and the formation of the TP/TS phase inversion structure in the interlaminar regions, in which the PI-9731 particles wrapped by thermoplastic PI will be orientated and deformed in the process of crack extension.
The effect of ex-situ method on the mechanical properties and toughness of the RTMable carbon fiber (G827)／polyimide(PI-9731)composites was studied. The results show that the interlaminar shear strength of G827／PI-9731 composites toughened by the ex-situ methods with powder and film increases from 97.9MPa to 108MPa and 110MPa, respectively, when the thermoplastic PI mass fraction is 15% at room temperature. However, the interlaminar shear strength changes slightly at high temperature (288℃).The mode Ⅰ fracture toughness of G827／PI-9731 composites toughened with powder method is improved from 310J/m2 to 410J/m2. The Mode Ⅱ fracture toughness is improved from 590J/m2 to 939J/m2. However the mode Ⅰ fracture toughness of G827／PI-9731 composites toughened with film method increases to 459J/m2. The mode Ⅱ fracture toughness is improved to 1100J/m2. By SEM analysis, it is found that the toughness improvement results from the introduction of thermoplastic PI and the formation of the TP/TS phase inversion structure in the interlaminar regions, in which the PI-9731 particles wrapped by thermoplastic PI will be orientated and deformed in the process of crack extension.
2010, 27(6): 9-15.
Abstract:
The amide carbon nanotubes (Amid-CNT)/polyacrylonitrile (PAN) composite solution was synthesized by solution polymerization. The Amid-CNT/PAN composite fibers were prepared by wet spinning methods. The effects of Amid-CNT on the structure of PAN fiber were characterized by Fourier transform infrared spectrum, Raman spectrum, different scanning calorimetry, thermogravimetric analysis and scanning electron microscopy. The results show that the Amid-CNT and PAN macromolecules form the strong interfacial interactions. The Amid-CNTs in the Amid-CNT/PAN composite fibers are highly orientated in the processing of the formation, which increase the orientation of nitrile groups in the fiber from 1.61 to 2.30. The initiation temperature of the exothermic reaction for the composite fibers shifts from 212.30℃ to 206.01℃ in the air atmosphere compared with the PAN fiber, and the total evolve heat decreases from 3054 J/g to 2346 J/g. The initiation temperature of loss weight for the Amid---CNT/PAN composite fibers decreases by 3.7℃ compared with PAN fiber, and the residual mass for the composite fibers improves by 13.5% compared with PAN fiber at 700℃. The structures from SEM images show that the Amid---CNT/PAN composite fibers have more fibrillations than the PAN fiber.
The amide carbon nanotubes (Amid-CNT)/polyacrylonitrile (PAN) composite solution was synthesized by solution polymerization. The Amid-CNT/PAN composite fibers were prepared by wet spinning methods. The effects of Amid-CNT on the structure of PAN fiber were characterized by Fourier transform infrared spectrum, Raman spectrum, different scanning calorimetry, thermogravimetric analysis and scanning electron microscopy. The results show that the Amid-CNT and PAN macromolecules form the strong interfacial interactions. The Amid-CNTs in the Amid-CNT/PAN composite fibers are highly orientated in the processing of the formation, which increase the orientation of nitrile groups in the fiber from 1.61 to 2.30. The initiation temperature of the exothermic reaction for the composite fibers shifts from 212.30℃ to 206.01℃ in the air atmosphere compared with the PAN fiber, and the total evolve heat decreases from 3054 J/g to 2346 J/g. The initiation temperature of loss weight for the Amid---CNT/PAN composite fibers decreases by 3.7℃ compared with PAN fiber, and the residual mass for the composite fibers improves by 13.5% compared with PAN fiber at 700℃. The structures from SEM images show that the Amid---CNT/PAN composite fibers have more fibrillations than the PAN fiber.
2010, 27(6): 16-20.
Abstract:
The hygrothermal properties of high-temperature curing epoxy 5228A resin and carbon fiber/ epoxy 5228A resin composite laminate were investigated under three different hygrothermal conditions, i.e. boiling water, water immersion and relative humidity 85% at 70℃. The effects of hygrothermal condition on the interlaminar shear strength of the carbon fiber/epoxy resin composite laminates were studied. The hygrothermal aging mechanism was analyzed based on the moisture absorption, physical and chemical properties, the mechanical properties property of epoxy resin and moisture stress. The results show that the degradation degree of the interlaminar shear strength mainly depends on the moisture content, and the degradation degrees under different hygrothermal conditions are almost identical at the same water absorption content. The chemical change and interface micro-cracks have not been found in the composite laminate under the three hygrothermal conditions. The resin plasticization with water absorption and moisture stress due to different moisture expansion between fiber and resin is the main reasons for the degradation of the composites laminate.
The hygrothermal properties of high-temperature curing epoxy 5228A resin and carbon fiber/ epoxy 5228A resin composite laminate were investigated under three different hygrothermal conditions, i.e. boiling water, water immersion and relative humidity 85% at 70℃. The effects of hygrothermal condition on the interlaminar shear strength of the carbon fiber/epoxy resin composite laminates were studied. The hygrothermal aging mechanism was analyzed based on the moisture absorption, physical and chemical properties, the mechanical properties property of epoxy resin and moisture stress. The results show that the degradation degree of the interlaminar shear strength mainly depends on the moisture content, and the degradation degrees under different hygrothermal conditions are almost identical at the same water absorption content. The chemical change and interface micro-cracks have not been found in the composite laminate under the three hygrothermal conditions. The resin plasticization with water absorption and moisture stress due to different moisture expansion between fiber and resin is the main reasons for the degradation of the composites laminate.
2010, 27(6): 21-25.
Abstract:
The composite of Sm-doped TiO2 nanoparticles loaded onto carbon nanofibers (SmTiO2/CNFs ) was prepared by electrospinning technique and thermal processes. The samples were characterized by SEM, EDX, TEM, FTIR and XRD.The effect of Sm-doping on the photocatalytic activity of the SmTiO2/CNFs composite was investigated by the photocatalytic degradation of methyl orange aqueous solution under UV irradiation.The results show that the CNFs are loaded with about 20% mass fraction of Sm---doped anatase TiO2 nanoparticles. In comparison with the undoped sample (TiO2/CNFs), the photocatalytic activity of the SmTiO2/CNFs increases by about 37%.
The composite of Sm-doped TiO2 nanoparticles loaded onto carbon nanofibers (SmTiO2/CNFs ) was prepared by electrospinning technique and thermal processes. The samples were characterized by SEM, EDX, TEM, FTIR and XRD.The effect of Sm-doping on the photocatalytic activity of the SmTiO2/CNFs composite was investigated by the photocatalytic degradation of methyl orange aqueous solution under UV irradiation.The results show that the CNFs are loaded with about 20% mass fraction of Sm---doped anatase TiO2 nanoparticles. In comparison with the undoped sample (TiO2/CNFs), the photocatalytic activity of the SmTiO2/CNFs increases by about 37%.
2010, 27(6): 26-31.
Abstract:
A hindered phenol/nitrile---butadiene rubber (NBR) composite was successfully prepared by mixing tetrakis (methylene-3-(3-5-ditert-butyl-4-hydroxy phenyl) propionyloxy) methane (AO-60) into NBR．The microstructure of the AO-60/NBR composite was characterized by DSC, SEM and DMA, and its dynamic mechanical properties were studied. The results show that the dispersion of AO-60 is different in the various NBR matrix. Hindered phenol AO-60 forms a fine dispersion in the matrix of the NBR with the acrylonitrile mass fraction of 35% (N230S). A strong intermolecular interaction is formed between the AO---60 and NBR. Compared with the neat NBR matrix, the value of Tg and tanδ for the composites increases gradually with increasing the AO-60 amount. Moreover, AO-60/N230S composites have a high performance as a damping material.
A hindered phenol/nitrile---butadiene rubber (NBR) composite was successfully prepared by mixing tetrakis (methylene-3-(3-5-ditert-butyl-4-hydroxy phenyl) propionyloxy) methane (AO-60) into NBR．The microstructure of the AO-60/NBR composite was characterized by DSC, SEM and DMA, and its dynamic mechanical properties were studied. The results show that the dispersion of AO-60 is different in the various NBR matrix. Hindered phenol AO-60 forms a fine dispersion in the matrix of the NBR with the acrylonitrile mass fraction of 35% (N230S). A strong intermolecular interaction is formed between the AO---60 and NBR. Compared with the neat NBR matrix, the value of Tg and tanδ for the composites increases gradually with increasing the AO-60 amount. Moreover, AO-60/N230S composites have a high performance as a damping material.
2010, 27(6): 32-37.
Abstract:
The effect of void content on the static interlaminar shear strength and interlaminar shear fatigue properties of carbon fiber reinforced epoxy ［(±45)/04/(0, 90)/02］Scomposite laminates was studied. The laminates with void volume fraction 0.4% ~ 6.6% were prepared by applying different autoclave pressure. The void content and microstructure characteristics of voids were studied using optical image analysis. The results show that the fraction of large voids(S>7.85×10-3mm2) and mean void content increase with the decreasing autoclave pressure. Each 1% increase in void content with the void volume fraction in the range 0.4% ~ 4.6% induces a 2.4% reduction in interlaminar shear strength. The interlaminar shear fatigue life decreases with the increasing void content. The effect of voids on fatigue is more significant than on static failure. Large voids promote the initiation and propagation of cracks.
The effect of void content on the static interlaminar shear strength and interlaminar shear fatigue properties of carbon fiber reinforced epoxy ［(±45)/04/(0, 90)/02］Scomposite laminates was studied. The laminates with void volume fraction 0.4% ~ 6.6% were prepared by applying different autoclave pressure. The void content and microstructure characteristics of voids were studied using optical image analysis. The results show that the fraction of large voids(S>7.85×10-3mm2) and mean void content increase with the decreasing autoclave pressure. Each 1% increase in void content with the void volume fraction in the range 0.4% ~ 4.6% induces a 2.4% reduction in interlaminar shear strength. The interlaminar shear fatigue life decreases with the increasing void content. The effect of voids on fatigue is more significant than on static failure. Large voids promote the initiation and propagation of cracks.
2010, 27(6): 38-44.
Abstract:
To improve the corrosion resistance, (MWCNTs-OH)-containing organic-inorganic coatings were prepared on the aeronautic aluminum alloy substrates via the sol-gel process in which tetraethoxysilane (TEOS), KH-550 and some hydroxylated multi-walled carbon nanotubes (MWCNTs-OH) were used as precursors. HAc was added as catalyst in the sol-gel process to control the limited hydrolysis. Sols were coated on the surface of aluminum alloy substrates by dip-coating technique and the composite coatings were obtained through necessary heat treatment afterwards. The results of electrochemical analysis show that the composite coatings with nanotubes can effectively improve the corrosion resistance of aluminium alloy substrates in 3.5wt% NaCl solution. When the content of MWCNTs-OH is 0.04wt% and the heat treatment temperature is 130℃, the corrosion current density for coated sample is about 3.056×10-8A/cm2, which is 3 order lower than that for bared sample (7.216×10-5A/cm2). The SEM morphology of the coatings also reveals that the introduction of MWCNTs-OH to coatings is beneficial to prevent from the coating cracking.
To improve the corrosion resistance, (MWCNTs-OH)-containing organic-inorganic coatings were prepared on the aeronautic aluminum alloy substrates via the sol-gel process in which tetraethoxysilane (TEOS), KH-550 and some hydroxylated multi-walled carbon nanotubes (MWCNTs-OH) were used as precursors. HAc was added as catalyst in the sol-gel process to control the limited hydrolysis. Sols were coated on the surface of aluminum alloy substrates by dip-coating technique and the composite coatings were obtained through necessary heat treatment afterwards. The results of electrochemical analysis show that the composite coatings with nanotubes can effectively improve the corrosion resistance of aluminium alloy substrates in 3.5wt% NaCl solution. When the content of MWCNTs-OH is 0.04wt% and the heat treatment temperature is 130℃, the corrosion current density for coated sample is about 3.056×10-8A/cm2, which is 3 order lower than that for bared sample (7.216×10-5A/cm2). The SEM morphology of the coatings also reveals that the introduction of MWCNTs-OH to coatings is beneficial to prevent from the coating cracking.
2010, 27(6): 45-52.
Abstract:
A novel phosphorus-nitrogen quaternary ammonium salts (PAHAC) was synthesized with phoshorus oxychloride and neopentyl glycol as main raw materials. PAHAC was characterized by FTIR, 1H-NMR and HRMS. Montmorillonite (MMT) modified with PAHAC (PAHACMMT) was prepared by ion-exchanging of Na+-montmorillonite (Na-MMT) and PAHAC. FTIR and XRD indicate that PAHAC is intercalated with Na-MMT and the layer spacing and the decomposition temperature of MMT modified with 20wt% PAHAC (20%PAHACMMT) is 1.87nm and 310℃, respectively. The results of TEM show that the intercalated-exploitated nanocomposite of 20%PAHACMMT/LDPE is formed by melting intercalation blending LDPE with 20%PAHACMMT. The flame retardancy of phosphorus-nitrogenmontmorillonite/LDPE nanocomposites was investigated by cone calorimeter test. The results show that the flame retardancy properties of phosphorus-nitrogen-montmorillonite/LDPE nanocomposites are good. In comparison with LDPE, the peak heat release rates (PHRR) and the total heat release (THR) of 20%PAHACMMT(7%)/LDPE reduce by 21% and 9.5%, respectively. The results of SEM show that the compact and dense char is formed for 20%PAHACMMT/LDPE nanocomposite after combustion, which can inhibit burning effectively.
A novel phosphorus-nitrogen quaternary ammonium salts (PAHAC) was synthesized with phoshorus oxychloride and neopentyl glycol as main raw materials. PAHAC was characterized by FTIR, 1H-NMR and HRMS. Montmorillonite (MMT) modified with PAHAC (PAHACMMT) was prepared by ion-exchanging of Na+-montmorillonite (Na-MMT) and PAHAC. FTIR and XRD indicate that PAHAC is intercalated with Na-MMT and the layer spacing and the decomposition temperature of MMT modified with 20wt% PAHAC (20%PAHACMMT) is 1.87nm and 310℃, respectively. The results of TEM show that the intercalated-exploitated nanocomposite of 20%PAHACMMT/LDPE is formed by melting intercalation blending LDPE with 20%PAHACMMT. The flame retardancy of phosphorus-nitrogenmontmorillonite/LDPE nanocomposites was investigated by cone calorimeter test. The results show that the flame retardancy properties of phosphorus-nitrogen-montmorillonite/LDPE nanocomposites are good. In comparison with LDPE, the peak heat release rates (PHRR) and the total heat release (THR) of 20%PAHACMMT(7%)/LDPE reduce by 21% and 9.5%, respectively. The results of SEM show that the compact and dense char is formed for 20%PAHACMMT/LDPE nanocomposite after combustion, which can inhibit burning effectively.
2010, 27(6): 53-57.
Abstract:
A serises of composites consisting of Ethylene-Vinyl Acetate copolymer (EVA), Acrylic Rubber(AR) and mica were prepared by melting blend. The results from dynamic mechanical analysis show that a new tanδ peak is observed at 5℃ when EVA is blended with AR. The addition of MPDI(4-methyl-pheno reaction products with dicyclopentadiene and isobutylene) in EVAAR (80/20) blend results in the shift of the tanδ peak to higher temperature and the enhancement of the value of tanδ. When mica is added in EVAARMPDI blends, both tanδ peak and the loss modulus E″ shift to a higher temperature region. With increasing mica content, tanδ peak intensity in high temperature range increases, and loss modulus E″ is enhanced greatly. The value of E″ peak changes from 79MPa to 280MPa with the content of mica from 0wt% to 58.8wt%. The analysis results of FTIR and SEM prove the increase of the dynamic mechanical properties of mica-EVA-AR-MPDI composites.
A serises of composites consisting of Ethylene-Vinyl Acetate copolymer (EVA), Acrylic Rubber(AR) and mica were prepared by melting blend. The results from dynamic mechanical analysis show that a new tanδ peak is observed at 5℃ when EVA is blended with AR. The addition of MPDI(4-methyl-pheno reaction products with dicyclopentadiene and isobutylene) in EVAAR (80/20) blend results in the shift of the tanδ peak to higher temperature and the enhancement of the value of tanδ. When mica is added in EVAARMPDI blends, both tanδ peak and the loss modulus E″ shift to a higher temperature region. With increasing mica content, tanδ peak intensity in high temperature range increases, and loss modulus E″ is enhanced greatly. The value of E″ peak changes from 79MPa to 280MPa with the content of mica from 0wt% to 58.8wt%. The analysis results of FTIR and SEM prove the increase of the dynamic mechanical properties of mica-EVA-AR-MPDI composites.
2010, 27(6): 58-63.
Abstract:
The tensile properties of three-dimension and five-direction braided/epoxy resin composites and laminated resin composites at temperature of room、 80℃, 150℃ and 180℃ were studied. The effect rules of different temperature on the tensile property of these composites were discussed. The reasons for the variations of tensile property of these composites at different temperature were also analyzed. The tensile strength of three-dimension and five-direction braided composites at 80℃ and 150℃ keeps the same level with that at room temperature. At 180℃, the tensile strength of three-dimension and five-direction braided composites decreases by 15.37% compared with that at room temperature. At 80℃、 150℃ and 180℃, the tensile strength of laminated composite decreases by 3.45%, 13.3% and 34.42%, respectively compared with that at room temperature. The significant decrease for the tensile strength of laminated composites at high temperature is due to the delamination of the laminated composites since the resin damaged, which shows that structures of reinforcements have significant influences on tensile property of resin composites at high temperature.
The tensile properties of three-dimension and five-direction braided/epoxy resin composites and laminated resin composites at temperature of room、 80℃, 150℃ and 180℃ were studied. The effect rules of different temperature on the tensile property of these composites were discussed. The reasons for the variations of tensile property of these composites at different temperature were also analyzed. The tensile strength of three-dimension and five-direction braided composites at 80℃ and 150℃ keeps the same level with that at room temperature. At 180℃, the tensile strength of three-dimension and five-direction braided composites decreases by 15.37% compared with that at room temperature. At 80℃、 150℃ and 180℃, the tensile strength of laminated composite decreases by 3.45%, 13.3% and 34.42%, respectively compared with that at room temperature. The significant decrease for the tensile strength of laminated composites at high temperature is due to the delamination of the laminated composites since the resin damaged, which shows that structures of reinforcements have significant influences on tensile property of resin composites at high temperature.
2010, 27(6): 64-69.
Abstract:
Microstructural changes of C/C composites after braking test were studied by TEM, RMS, SEM and so on. Microstructural model of worn surface layer was established. Temperature fields of specimens with asperities were simulated by Finite Element Method (FEM). The results show that a friction layer with several microns forms on the matrix firstly, and then a friction film covers on the friction layer unequally. TEM and SAED indicate that most fields of the friction film are middle textured, and the texture degree increases with approach to the worn surface. The outmost surface is highly graphitized, and this result is verified by RMS. The highest temperature of asperities is much higher than that of worn plane, which is one of the main factors of stress graphitization on worn surface.
Microstructural changes of C/C composites after braking test were studied by TEM, RMS, SEM and so on. Microstructural model of worn surface layer was established. Temperature fields of specimens with asperities were simulated by Finite Element Method (FEM). The results show that a friction layer with several microns forms on the matrix firstly, and then a friction film covers on the friction layer unequally. TEM and SAED indicate that most fields of the friction film are middle textured, and the texture degree increases with approach to the worn surface. The outmost surface is highly graphitized, and this result is verified by RMS. The highest temperature of asperities is much higher than that of worn plane, which is one of the main factors of stress graphitization on worn surface.
2010, 27(6): 70-75.
Abstract:
Organ montmorillonite (OMMT1)/polypropylene (PP) nanocomposites were prepared by the melt intercalation method. After thermal-oxidative aging for 0 ~ 12d at the temperature of 100℃, 110℃ and 120℃, the thermal property, thermal stability, the attenuation of tensile strength and kinetics were studied. The results of TG, DSC and FTIR show that, compared with PP, the thermal decomposition temperature of OMMT1/PP increases by 37℃, the crystallinity increases from 51% to 71%, and there is stronger interaction between nano-OMMT lamellar and PP.So CO vibration absorption peaks of OMMT1/PP weaken significantly in FTIR spectra and surface cracks slightly during thermal-oxidative aging. After aging at 100~120℃, strength retention of OMMT1/PP is much superior to pure polypropylene material (8~22 times), and its tensile strength was 54% after 12 d aging at 110℃. The first-order kinetics equation of OMMT1/PP thermal-oxidative aging was established with tensile strength as parameter, its activation energy was 52.3kJ/mol (1.7 times of PP). The higher the activation energy values and excellent resistance to thermal-oxidative aging of OMMT1/PP can be contributed to the mechanical protection of exfoliated nano-MMT lamella, physical barrier effect to PP and the chemical interaction between MMT and PP.
Organ montmorillonite (OMMT1)/polypropylene (PP) nanocomposites were prepared by the melt intercalation method. After thermal-oxidative aging for 0 ~ 12d at the temperature of 100℃, 110℃ and 120℃, the thermal property, thermal stability, the attenuation of tensile strength and kinetics were studied. The results of TG, DSC and FTIR show that, compared with PP, the thermal decomposition temperature of OMMT1/PP increases by 37℃, the crystallinity increases from 51% to 71%, and there is stronger interaction between nano-OMMT lamellar and PP.So CO vibration absorption peaks of OMMT1/PP weaken significantly in FTIR spectra and surface cracks slightly during thermal-oxidative aging. After aging at 100~120℃, strength retention of OMMT1/PP is much superior to pure polypropylene material (8~22 times), and its tensile strength was 54% after 12 d aging at 110℃. The first-order kinetics equation of OMMT1/PP thermal-oxidative aging was established with tensile strength as parameter, its activation energy was 52.3kJ/mol (1.7 times of PP). The higher the activation energy values and excellent resistance to thermal-oxidative aging of OMMT1/PP can be contributed to the mechanical protection of exfoliated nano-MMT lamella, physical barrier effect to PP and the chemical interaction between MMT and PP.
2010, 27(6): 76-81.
Abstract:
The tensile strength, solidification microstructure and interface in Al2O3f/M124F composites made by squeeze casting technique were investigated and analyzed. The results indicate that the compact structure and uniform distribution of the fibers can be achieved by squeeze casting, the tensile strength are significantly improved, and α-Al dendrite and Si phase in matrix structure are obviously refined. The analysis show that the addition of fibers have double enhancement.The intervention of high tensile-strength ceramic fiber reinforces the matrix material. The short alumina fibers retard the growth of α-Al dendrite and serve as the propitious sites for the heterogenous nucleation of Si phase during solidification, thus refining matrix microstructure and improving the mechanical properties of the composite furthermore.Interfacial products of MgAl2O4 are not observed between fiber and matrix.
The tensile strength, solidification microstructure and interface in Al2O3f/M124F composites made by squeeze casting technique were investigated and analyzed. The results indicate that the compact structure and uniform distribution of the fibers can be achieved by squeeze casting, the tensile strength are significantly improved, and α-Al dendrite and Si phase in matrix structure are obviously refined. The analysis show that the addition of fibers have double enhancement.The intervention of high tensile-strength ceramic fiber reinforces the matrix material. The short alumina fibers retard the growth of α-Al dendrite and serve as the propitious sites for the heterogenous nucleation of Si phase during solidification, thus refining matrix microstructure and improving the mechanical properties of the composite furthermore.Interfacial products of MgAl2O4 are not observed between fiber and matrix.
2010, 27(6): 82-87.
Abstract:
The various damage mechanisms in 3D C/SiC composites were identified using acoustic emission (AE) signal parameters, and the Felicity effect was studied with tensile loading---unloading procedure. The effect of damage characterization on tensile behavior was investigated. As a result, the Kaiser effect is almost absent and the Felicity ratio decreases with the increase of the stress level and drops when the relative stress ratio is above 65%. The key factor of high performance of 3D C/SiC composite is not the amount of all AE hits but the time and quantity of major signals with higher energy and amplitude.The lower damage quantity is necessary to improv tensile strength of the composite during smaller deformation stage (strain<0.15%). The fiber cluster failure dispersion on bigger deformation stage is benificial to the enhancement of the tensile strength.
The various damage mechanisms in 3D C/SiC composites were identified using acoustic emission (AE) signal parameters, and the Felicity effect was studied with tensile loading---unloading procedure. The effect of damage characterization on tensile behavior was investigated. As a result, the Kaiser effect is almost absent and the Felicity ratio decreases with the increase of the stress level and drops when the relative stress ratio is above 65%. The key factor of high performance of 3D C/SiC composite is not the amount of all AE hits but the time and quantity of major signals with higher energy and amplitude.The lower damage quantity is necessary to improv tensile strength of the composite during smaller deformation stage (strain<0.15%). The fiber cluster failure dispersion on bigger deformation stage is benificial to the enhancement of the tensile strength.
2010, 27(6): 88-93.
Abstract:
The carbon fiber laminated boards impacted at low velocity were tested and analyzed using infrared thermal wave testing. The relationship between the damage area and impact energy was discussed. The experimental results was consistent with the literature. It is found that infrared thermal wave testing can not only detect the size of impact damage but the expansion of internal damage which revolves round the impact point along the fiber direction. The same laminated boards were tested by ultrasound C-scan. For carbon fiber laminated boards after low velocity impact, infrared thermal wave testing is a rapid, effective and reliable non-destructive evaluation method compared with the ultrasound C-scan.
The carbon fiber laminated boards impacted at low velocity were tested and analyzed using infrared thermal wave testing. The relationship between the damage area and impact energy was discussed. The experimental results was consistent with the literature. It is found that infrared thermal wave testing can not only detect the size of impact damage but the expansion of internal damage which revolves round the impact point along the fiber direction. The same laminated boards were tested by ultrasound C-scan. For carbon fiber laminated boards after low velocity impact, infrared thermal wave testing is a rapid, effective and reliable non-destructive evaluation method compared with the ultrasound C-scan.
2010, 27(6): 94-99.
Abstract:
Corn straw fibers were used as the reinforcement for desulfurization gypsum, through the experimental research on mechanical properties, the effects of different dosages of the corn straw fibers on the mechanical properties of the composite were studied. The results indicate that when the dosage of the corn straw fibers is 5%, compared with the blank sample, the samples flexural strength and compressive strength are enhanced by 92.31% and 7.14% respectively. The corn straw fibers were modified with alkaline treatment and chemical coating treatment using polyacrylamide and acrylic, through the experimental research on mechanical properties and observation on morphology using scanning electron microscopy, the effects of surface modification on the mechanical properties of the composite were studied. The results indicate that the interfacial bonding between the maize straw fibers and desulfurization gypsum is improved, and the mechanical properties of composite is increased. The research shows that the acrylic chemical coating method could enhance the strength of the composite. Compared with the unmodified corn straw fibre/desulfurization gypsum, the flexural strength increases by 55.71% and the compressive strength increases by 22.99%.
Corn straw fibers were used as the reinforcement for desulfurization gypsum, through the experimental research on mechanical properties, the effects of different dosages of the corn straw fibers on the mechanical properties of the composite were studied. The results indicate that when the dosage of the corn straw fibers is 5%, compared with the blank sample, the samples flexural strength and compressive strength are enhanced by 92.31% and 7.14% respectively. The corn straw fibers were modified with alkaline treatment and chemical coating treatment using polyacrylamide and acrylic, through the experimental research on mechanical properties and observation on morphology using scanning electron microscopy, the effects of surface modification on the mechanical properties of the composite were studied. The results indicate that the interfacial bonding between the maize straw fibers and desulfurization gypsum is improved, and the mechanical properties of composite is increased. The research shows that the acrylic chemical coating method could enhance the strength of the composite. Compared with the unmodified corn straw fibre/desulfurization gypsum, the flexural strength increases by 55.71% and the compressive strength increases by 22.99%.
2010, 27(6): 100-105.
Abstract:
The chitosan(CS)/poly(ε-caprolactone)(PCL)poly (lactide) (PLA) scaffolds were prepared by phase separation method with the glacial acetic acid as the co-solvent for polymers, NaOH solvent as the quenching bath and chitosan(CS) as the additives. The effect of mass ratio on the structure, morphology, porosity, mechanical and degradation properties of the scaffolds was studied. The results show that there is a stronger interaction between CS and matrix. CS is beneficial for forming 3D interconnected micro-pore structure. The existent of CS can decrease the melting point of each component in the matrix. The pore size and microstructure morphology change with the mass ratio of PCL to PLA varied. The porosity reaches above 90% when the ratio of PCL∶PLA is 2∶4 and 3∶3, and decreases dramatically when further increasing the ratio of PCL. The compression test indicates that the elastic modulus of prepared scaffolds is between 0.8~8.0MPa. Degradation analysis indicates that when the ratio of PCL∶PLA is 3∶3, the mass loss reaches a maximum of 5.94% after 4 weeks. These results indicate that the fabricated scaffolds have a potential application for cartilage bone tissue engineering. The expectation 3D porous scaffolds with designable properties such as degradation speed, mechanical strength can be achieved through changing the ratio of PCL∶PLA by precipitation method.
The chitosan(CS)/poly(ε-caprolactone)(PCL)poly (lactide) (PLA) scaffolds were prepared by phase separation method with the glacial acetic acid as the co-solvent for polymers, NaOH solvent as the quenching bath and chitosan(CS) as the additives. The effect of mass ratio on the structure, morphology, porosity, mechanical and degradation properties of the scaffolds was studied. The results show that there is a stronger interaction between CS and matrix. CS is beneficial for forming 3D interconnected micro-pore structure. The existent of CS can decrease the melting point of each component in the matrix. The pore size and microstructure morphology change with the mass ratio of PCL to PLA varied. The porosity reaches above 90% when the ratio of PCL∶PLA is 2∶4 and 3∶3, and decreases dramatically when further increasing the ratio of PCL. The compression test indicates that the elastic modulus of prepared scaffolds is between 0.8~8.0MPa. Degradation analysis indicates that when the ratio of PCL∶PLA is 3∶3, the mass loss reaches a maximum of 5.94% after 4 weeks. These results indicate that the fabricated scaffolds have a potential application for cartilage bone tissue engineering. The expectation 3D porous scaffolds with designable properties such as degradation speed, mechanical strength can be achieved through changing the ratio of PCL∶PLA by precipitation method.
2010, 27(6): 106-112.
Abstract:
Thermal wave imaging (TWI) technology was used to examine the density change of the 3D carbon fiber needled preform with density gradient, tracking the transmissibility of the internal defect before and after the chemical vapor infiltration (CVI) silicon carbide (SiC) process of the preform. The reliability of the results was validated by X-ray radiography and industrial computed tomography (CT). The results show that the cavities in the preform are filled well after the CVI process, in which, however, some new cavities or holes generated from SiC matrix. It indicates that the cavity defects transmissibility can be detected and tracked by TWI technology successfully and the density gradient of the 3D needled perform changes reversely after the CVI SiC process.
Thermal wave imaging (TWI) technology was used to examine the density change of the 3D carbon fiber needled preform with density gradient, tracking the transmissibility of the internal defect before and after the chemical vapor infiltration (CVI) silicon carbide (SiC) process of the preform. The reliability of the results was validated by X-ray radiography and industrial computed tomography (CT). The results show that the cavities in the preform are filled well after the CVI process, in which, however, some new cavities or holes generated from SiC matrix. It indicates that the cavity defects transmissibility can be detected and tracked by TWI technology successfully and the density gradient of the 3D needled perform changes reversely after the CVI SiC process.
2010, 27(6): 113-119.
Abstract:
Ca(NO3)2, (NH4)2HPO4, acid dissolved collagen and gum Arabic were used as the raw materials to prepare collagen---hydroxyapatite/gum Arabic (ColHA/Gum A) composite in situ. The structures of the composite were investigated by XRD, SEM and FTIR. The mechanical properties, water absorption, enzyme degradation and cytotoxicity of the composite were investigated as well. The results show that the inorganic substance in the composite materials is hydroxyapatite, uniformly distributed in the ColGum A composite with relatively low crystallinity, and a new interface appeared by the interactions among them. The study on the mechanical properties, water absorption, enzyme degradation and cytotoxicity indicates a potential use in bone replacement for the new composite.
Ca(NO3)2, (NH4)2HPO4, acid dissolved collagen and gum Arabic were used as the raw materials to prepare collagen---hydroxyapatite/gum Arabic (ColHA/Gum A) composite in situ. The structures of the composite were investigated by XRD, SEM and FTIR. The mechanical properties, water absorption, enzyme degradation and cytotoxicity of the composite were investigated as well. The results show that the inorganic substance in the composite materials is hydroxyapatite, uniformly distributed in the ColGum A composite with relatively low crystallinity, and a new interface appeared by the interactions among them. The study on the mechanical properties, water absorption, enzyme degradation and cytotoxicity indicates a potential use in bone replacement for the new composite.
2010, 27(6): 120-125.
Abstract:
The impacting behavior and damage evolution of basalt fiber reinforced concrete (BFRC) with different fiber mass fraction ranging from 0%~0.60% were tested using three-point bending impact equipment and ultrasonic testing technology. The continued damage detection based on ultrasonic testing was used to reveal the damage evolution process, and the stereomicroscope was applied to observe the surface cracks. The results show that the basalt fiber has little effect on the compressive strength of BFRC, but it can significantly improve the impact toughness of BFRC. The flexural toughness of BFRC with basalt fiber of 0.36% is 2.2 times higher than that of plain concrete. The results also indicate that each specimen with various mass fraction reflects the brittle fracture behavior, but the energy absorption capacity of concrete can be effectively enhanced by basalt fibers. Contrasted with the controlled concrete, the damage variable of BFRC near destruction increases by 40%～83%. BFRC specimens show multi-cracking characteristics in the failure process, and the vice crack near the main crack is clearly observed after the final destruction.
The impacting behavior and damage evolution of basalt fiber reinforced concrete (BFRC) with different fiber mass fraction ranging from 0%~0.60% were tested using three-point bending impact equipment and ultrasonic testing technology. The continued damage detection based on ultrasonic testing was used to reveal the damage evolution process, and the stereomicroscope was applied to observe the surface cracks. The results show that the basalt fiber has little effect on the compressive strength of BFRC, but it can significantly improve the impact toughness of BFRC. The flexural toughness of BFRC with basalt fiber of 0.36% is 2.2 times higher than that of plain concrete. The results also indicate that each specimen with various mass fraction reflects the brittle fracture behavior, but the energy absorption capacity of concrete can be effectively enhanced by basalt fibers. Contrasted with the controlled concrete, the damage variable of BFRC near destruction increases by 40%～83%. BFRC specimens show multi-cracking characteristics in the failure process, and the vice crack near the main crack is clearly observed after the final destruction.
2010, 27(6): 126-129.
Abstract:
Nano Co1-xZnxFe2O4/SiO2 (0≤x≤1) composites were prepared by sol-gel method using teterathylor- thodilicate and nitrates as precursor in order to investigate the effect of Zn2+ content on the structure and magnetic properties of composites. The structure, morphology and magnetic properties of the composites were investigated by XRD, TEM, VSM and Mssbauer effect. The results show that Co1-xZnxFe2O4 grains distribute uniformly in nano Co1-xZnxFe2O4/SiO2 composites and present cubic spine structure. The unit cell of Co1-xZnxFe2O4 expands after Zn2+ substituting Co2+. With the increasing of Zn2+ content, the coercivity of the composites decreases, and the value of saturation magnetization increases firstly then decreases, while the composites transform from magnetic order state into paramagnetic state. The doping of Zn2+ has more effect on the density of s-electron around Fe3+ nucleus, less effect on structural symmetry.
Nano Co1-xZnxFe2O4/SiO2 (0≤x≤1) composites were prepared by sol-gel method using teterathylor- thodilicate and nitrates as precursor in order to investigate the effect of Zn2+ content on the structure and magnetic properties of composites. The structure, morphology and magnetic properties of the composites were investigated by XRD, TEM, VSM and Mssbauer effect. The results show that Co1-xZnxFe2O4 grains distribute uniformly in nano Co1-xZnxFe2O4/SiO2 composites and present cubic spine structure. The unit cell of Co1-xZnxFe2O4 expands after Zn2+ substituting Co2+. With the increasing of Zn2+ content, the coercivity of the composites decreases, and the value of saturation magnetization increases firstly then decreases, while the composites transform from magnetic order state into paramagnetic state. The doping of Zn2+ has more effect on the density of s-electron around Fe3+ nucleus, less effect on structural symmetry.
2010, 27(6): 130-134.
Abstract:
The magnetron sputtering was employed to sputter Al on the hollow glass microspheres. The electromagnetic characteristic of the composites consisting of Al-coated hollow glass microspheresFeCo powders was studied in the frequency range of 2~18GHz. The microwave absorbing property (R) of the composite was theoretically calculated. It has been found that the ε′,μ′and μ″ of the composites decreased with increasing the volume fraction of the Al-coated hollow glass microspheres, while ε″ has no significant change, when the overall volume fraction of Al-coated hollow glass microspheres and FeCo powders was fixed. The calculated peak value of R was moved to high frequency. The material with Al-coated hollow glass microspheres and FeCo powders volume ratio of 2∶1 and thickness of 2mm achieves the maximum absorbing value of -29.69dB, and the surface density is only 3.71kg/m2, and the bandwidth (with respect to -10dB absorption) is 2.4 GHz. Thus through changing the volume ratio of Al-coated hollow glass microspheres and FeCo powders, the electromagnetic parameter of the composite could be adjusted and the microwave absorbing property of the materials could be improved.
The magnetron sputtering was employed to sputter Al on the hollow glass microspheres. The electromagnetic characteristic of the composites consisting of Al-coated hollow glass microspheresFeCo powders was studied in the frequency range of 2~18GHz. The microwave absorbing property (R) of the composite was theoretically calculated. It has been found that the ε′,μ′and μ″ of the composites decreased with increasing the volume fraction of the Al-coated hollow glass microspheres, while ε″ has no significant change, when the overall volume fraction of Al-coated hollow glass microspheres and FeCo powders was fixed. The calculated peak value of R was moved to high frequency. The material with Al-coated hollow glass microspheres and FeCo powders volume ratio of 2∶1 and thickness of 2mm achieves the maximum absorbing value of -29.69dB, and the surface density is only 3.71kg/m2, and the bandwidth (with respect to -10dB absorption) is 2.4 GHz. Thus through changing the volume ratio of Al-coated hollow glass microspheres and FeCo powders, the electromagnetic parameter of the composite could be adjusted and the microwave absorbing property of the materials could be improved.
2010, 27(6): 135-140.
Abstract:
Constant stress tensile creep tests were conducted on the 25vol% Al2O3SiO2 short fiber/AZ91D composite and the unreinforced AZ91D matrix alloy at 473K and 573K under the applied stresses of 30~100MPa. The true stress exponent, the true creep activation energy, the threshold stress and the creep constitutive equation of the composite were calulated according to the curves of strain and strain rate. Microstructural investigations by TEM reveal that the threshold stress of the composite results from the pinning effect of MgO particles and Mg17Al12 precipitation on the fiber surface on the movable dislocations during creep exposure. Short fibers have a great function in load bearing and load transfer, and result in the enhancement of the creep resistance of the composite.
Constant stress tensile creep tests were conducted on the 25vol% Al2O3SiO2 short fiber/AZ91D composite and the unreinforced AZ91D matrix alloy at 473K and 573K under the applied stresses of 30~100MPa. The true stress exponent, the true creep activation energy, the threshold stress and the creep constitutive equation of the composite were calulated according to the curves of strain and strain rate. Microstructural investigations by TEM reveal that the threshold stress of the composite results from the pinning effect of MgO particles and Mg17Al12 precipitation on the fiber surface on the movable dislocations during creep exposure. Short fibers have a great function in load bearing and load transfer, and result in the enhancement of the creep resistance of the composite.
2010, 27(6): 141-145.
Abstract:
The carboxymethyl cellulose（CMC）Fe3O4 nano composite particles were prepared in the CMC solution by a modified oxidation deposition method. The properties, structure, and size of the products were characterized by IR, ZP (zeta potential), VSM (vibrating sample magnetometer), XRD and TEM. The results show that CMCFe3O4 which dispersed homogeneously in water is inverse spinel structure and the average particle size is 40nm. Carboxymethyl cellulose molecules are chemically adsorbed on the surface of Fe3O4nano-particles.The zeta potential of CMCFe3O4 is lower than common Fe3O4 under the same pH and its saturation magnetization is 36.74emu·g-1. Filtration coefficient of CMCFe3O4 in the soil is approximately 0.03 cm-1, and 72% of CMCFe3O4 suspension could penetrate through the soil column (10cm) under gravity in the soil column tests.
The carboxymethyl cellulose（CMC）Fe3O4 nano composite particles were prepared in the CMC solution by a modified oxidation deposition method. The properties, structure, and size of the products were characterized by IR, ZP (zeta potential), VSM (vibrating sample magnetometer), XRD and TEM. The results show that CMCFe3O4 which dispersed homogeneously in water is inverse spinel structure and the average particle size is 40nm. Carboxymethyl cellulose molecules are chemically adsorbed on the surface of Fe3O4nano-particles.The zeta potential of CMCFe3O4 is lower than common Fe3O4 under the same pH and its saturation magnetization is 36.74emu·g-1. Filtration coefficient of CMCFe3O4 in the soil is approximately 0.03 cm-1, and 72% of CMCFe3O4 suspension could penetrate through the soil column (10cm) under gravity in the soil column tests.
2010, 27(6): 146-151.
Abstract:
In order to prepare conductive functionally gradient material (CFGM), a series of Cu/acrylouitrile butadiene styrene copolymer （ABS） composites with different Cu content were prefabricated by use of HAAKE torque rheometer. The Cu/ABS conductive functionally gradient materials were prepared successfully by laminate molding through changing the content of the Cu filler of each layer. The structure and performane of the materials were investigated. The experimental results indicate that the performance of the materials changes gradually along the thickness direction based on the content of Cu, which shows great difference from the homogeneous composites. Conductivity test shows that the percolation phenomenon takes place in the CFGM and the corresponding volume resistivity changes from 1016Ω·cm of one side to 105Ω·cm of another side. Bending tests indicate that the ABS rich side shows better bending strength, which is 6% lower than neat ABS only; and that the filler rich side show good bending modulus, which is 20% higher than neat ABS. The experimental facts demonstrate that CFGM can effectively match the mechanical performance with conductive performance of the conductive composites.
In order to prepare conductive functionally gradient material (CFGM), a series of Cu/acrylouitrile butadiene styrene copolymer （ABS） composites with different Cu content were prefabricated by use of HAAKE torque rheometer. The Cu/ABS conductive functionally gradient materials were prepared successfully by laminate molding through changing the content of the Cu filler of each layer. The structure and performane of the materials were investigated. The experimental results indicate that the performance of the materials changes gradually along the thickness direction based on the content of Cu, which shows great difference from the homogeneous composites. Conductivity test shows that the percolation phenomenon takes place in the CFGM and the corresponding volume resistivity changes from 1016Ω·cm of one side to 105Ω·cm of another side. Bending tests indicate that the ABS rich side shows better bending strength, which is 6% lower than neat ABS only; and that the filler rich side show good bending modulus, which is 20% higher than neat ABS. The experimental facts demonstrate that CFGM can effectively match the mechanical performance with conductive performance of the conductive composites.
2010, 27(6): 152-157.
Abstract:
This paper presents finite element(FE) model study on reinforcing in through-thickness direction of composite T-joint with z-pin based experiment of z-pin bridging law. Function of z-pin contain two aspects, i. e. z-direction and x-direction resistance of composite delamination. In the model, z-direction and x-direction resistance based z-pin are modeled by z-direction and x-direction nonlinear-spring that link a pair nodes.So, the curves of force-displacement gained by experiments of mode Ⅰand mode Ⅱ z-pin bridging laws were endued to all nonlinear-springs to simulate z-pinned composite T-joint interlaminar performance. The effects of different z-pin spacing and span on the force of pulling off were examined. The results show that the displacement and the maximal force of pulling out is greatly dependent on span and z-pin spacing, respectively.
This paper presents finite element(FE) model study on reinforcing in through-thickness direction of composite T-joint with z-pin based experiment of z-pin bridging law. Function of z-pin contain two aspects, i. e. z-direction and x-direction resistance of composite delamination. In the model, z-direction and x-direction resistance based z-pin are modeled by z-direction and x-direction nonlinear-spring that link a pair nodes.So, the curves of force-displacement gained by experiments of mode Ⅰand mode Ⅱ z-pin bridging laws were endued to all nonlinear-springs to simulate z-pinned composite T-joint interlaminar performance. The effects of different z-pin spacing and span on the force of pulling off were examined. The results show that the displacement and the maximal force of pulling out is greatly dependent on span and z-pin spacing, respectively.
2010, 27(6): 158-166.
Abstract:
A strength analysis model was presented to study the buckling and post-buckling analysis of stiffened composite panels subjected to compressive loading by using the nonlinear finite element method. In the model, the debond failure of the adhesive between the skin and stiffener was considered by adding cohesive elements between the shell elements. Quads failure criteria and Hashin failure criteria were adopted to identify the occurring of damage events of the cohesive elements and the composite panels, respectively. By using a degradation constitutive model of the mechanical properties, the equilibrium paths, propagation and catastrophic failure of the structure were simulated in details. The calculated values by the model were well agreed with the measured values. Numerical results show the effectiveness of the model. Parametric studies were conducted to study the effects of geometric parameters of stiffeners, adhesive strength and stacking sequences on the buckling load and compressive strength of stiffened composite panels. The results indicate that the increased sectional moment of inertia and number of stiffeners can improve the buckling load and compressive strength. The transition from instability failure to compression failure exists when the especial number of stiffeners is obtained. Interfacial strength and fiber orientation significantly influence the compressive strength. The debonding damage is an important factor leading to the eventually failure.
A strength analysis model was presented to study the buckling and post-buckling analysis of stiffened composite panels subjected to compressive loading by using the nonlinear finite element method. In the model, the debond failure of the adhesive between the skin and stiffener was considered by adding cohesive elements between the shell elements. Quads failure criteria and Hashin failure criteria were adopted to identify the occurring of damage events of the cohesive elements and the composite panels, respectively. By using a degradation constitutive model of the mechanical properties, the equilibrium paths, propagation and catastrophic failure of the structure were simulated in details. The calculated values by the model were well agreed with the measured values. Numerical results show the effectiveness of the model. Parametric studies were conducted to study the effects of geometric parameters of stiffeners, adhesive strength and stacking sequences on the buckling load and compressive strength of stiffened composite panels. The results indicate that the increased sectional moment of inertia and number of stiffeners can improve the buckling load and compressive strength. The transition from instability failure to compression failure exists when the especial number of stiffeners is obtained. Interfacial strength and fiber orientation significantly influence the compressive strength. The debonding damage is an important factor leading to the eventually failure.
2010, 27(6): 167-171.
Abstract:
In FEM simulation programme, a shear layer was introduced to predict the deformation induced by the mold/composite interaction. And the predictions are in accordance well with the experimental measurements in the literature. A model to predict parameters of shear layers was developed. By comparing with experimental measurements, the simulation results are accurate for different processing conditions and different dimensions of composite parts.
In FEM simulation programme, a shear layer was introduced to predict the deformation induced by the mold/composite interaction. And the predictions are in accordance well with the experimental measurements in the literature. A model to predict parameters of shear layers was developed. By comparing with experimental measurements, the simulation results are accurate for different processing conditions and different dimensions of composite parts.
2010, 27(6): 172-178.
Abstract:
The vibration properties of 3D four-step rectangular cross-sectional braided composites cantilever beam with experimental verification were studied. Based on the meso-structure and unit cell model of four-directional and five-directional composites, the law of vibration characteristics influenced by material parameters (i.e. braiding angle and fiber volume fraction) was explored by the theoretical analysis. By analyzing and modifying the three-cell model, the first order natural frequency was obtained from global stiffness using the rule of mixture method, while loss factor was obtained by calculating the consumed energy by yarns with different orientations and matrix, and the whole vibration energy in a vibration cycle. Comparing the calculation results with the experimental results, the first order natural frequency increases with fiber volume fraction, but decreases with braiding angle; while loss factor increases non-linearly with braiding angle, but decreases with fiber volume fraction.
The vibration properties of 3D four-step rectangular cross-sectional braided composites cantilever beam with experimental verification were studied. Based on the meso-structure and unit cell model of four-directional and five-directional composites, the law of vibration characteristics influenced by material parameters (i.e. braiding angle and fiber volume fraction) was explored by the theoretical analysis. By analyzing and modifying the three-cell model, the first order natural frequency was obtained from global stiffness using the rule of mixture method, while loss factor was obtained by calculating the consumed energy by yarns with different orientations and matrix, and the whole vibration energy in a vibration cycle. Comparing the calculation results with the experimental results, the first order natural frequency increases with fiber volume fraction, but decreases with braiding angle; while loss factor increases non-linearly with braiding angle, but decreases with fiber volume fraction.
2010, 27(6): 179-183.
Abstract:
SiO2 aerogel insulation composites were prepared by impregnating inorganic ceramic fiber with SiO2 sols results via supercritical drying. The effect of SiO2 sol on mechanical properties of the composites was investigated. The results show the higher the ethanol (EtOH) content in sol, the lower the density of aerogel, the bigger the average pore size, the less the cross-linking between the clusters and the lower the network strength of aerogel. The inorganic ceramic fibers are dispersed within the aerogel and closely packed by aerogels, thus a well interface is formed. With increasing the EtOH/TEOS molar ratio from 2 to 20, the load transfer capability of SiO2 aerogel is weakened, therefore, the mechanical properties of the aerogel composites decrease. The tensile, bending and compressive strengths of the composites decrease from 1.9MPa, 2.7MPa, 1.73MPa (10% strain) to 0.17MPa、 0.12MPa、 0.04MPa (10% strain), respectively.
SiO2 aerogel insulation composites were prepared by impregnating inorganic ceramic fiber with SiO2 sols results via supercritical drying. The effect of SiO2 sol on mechanical properties of the composites was investigated. The results show the higher the ethanol (EtOH) content in sol, the lower the density of aerogel, the bigger the average pore size, the less the cross-linking between the clusters and the lower the network strength of aerogel. The inorganic ceramic fibers are dispersed within the aerogel and closely packed by aerogels, thus a well interface is formed. With increasing the EtOH/TEOS molar ratio from 2 to 20, the load transfer capability of SiO2 aerogel is weakened, therefore, the mechanical properties of the aerogel composites decrease. The tensile, bending and compressive strengths of the composites decrease from 1.9MPa, 2.7MPa, 1.73MPa (10% strain) to 0.17MPa、 0.12MPa、 0.04MPa (10% strain), respectively.
2010, 27(6): 184-192.
Abstract:
In order to validate the superiority of anti-plane shear closed solution to bend closed solution, two different methods were used. By means of the principle of superposition, the problem of bimetal laminate with delamination was predigested to the additional displacements of the original objects subjected to additional shear loading along the delamination surfaces. Using the mode of anti-plane shear to get the closed solution of additional displacement of transverse shear loading slice, the closed solution of additional displacements mode of the bimetal laminate with rectangular delamination was obtained by the method of state decomposition and slice composition in which the slice loaded longitudinal shear was caused by the mode of bend. The finite element model of bimetal laminate with symmetrical or asymmetrical delamination was established in ANSYS to get numerical solution. Contact element was used to simulate the asymmetric delamination surface. Finally, according to comparing closed solution with finite element solution, correctness of closed solutions and feasibility of numerical simulation model is proved, furthermore, according to taking shear into account the anti-plane shear closed solution is testified more accurate than the bend one.
In order to validate the superiority of anti-plane shear closed solution to bend closed solution, two different methods were used. By means of the principle of superposition, the problem of bimetal laminate with delamination was predigested to the additional displacements of the original objects subjected to additional shear loading along the delamination surfaces. Using the mode of anti-plane shear to get the closed solution of additional displacement of transverse shear loading slice, the closed solution of additional displacements mode of the bimetal laminate with rectangular delamination was obtained by the method of state decomposition and slice composition in which the slice loaded longitudinal shear was caused by the mode of bend. The finite element model of bimetal laminate with symmetrical or asymmetrical delamination was established in ANSYS to get numerical solution. Contact element was used to simulate the asymmetric delamination surface. Finally, according to comparing closed solution with finite element solution, correctness of closed solutions and feasibility of numerical simulation model is proved, furthermore, according to taking shear into account the anti-plane shear closed solution is testified more accurate than the bend one.
2010, 27(6): 193-199.
Abstract:
Axial compression test of the composites adapter skirt integrally manufactured by VARTM was designed and conducted. The relationships between the axial strain and the hoop strain with the axial compression load were tested and analyzed, and the apparent structural stiffness of the skirt was characterized. The experimental results show that under the applied loading of 625.7kN the strain of the skirt is less than 0.5% and distributions of the strain are uniform in the skirt, and the apparent structural stiffness of the integral skirt reaches 40.9GPa.
Axial compression test of the composites adapter skirt integrally manufactured by VARTM was designed and conducted. The relationships between the axial strain and the hoop strain with the axial compression load were tested and analyzed, and the apparent structural stiffness of the skirt was characterized. The experimental results show that under the applied loading of 625.7kN the strain of the skirt is less than 0.5% and distributions of the strain are uniform in the skirt, and the apparent structural stiffness of the integral skirt reaches 40.9GPa.
2010, 27(6): 200-207.
Abstract:
A 3D finite element model with cohesive was established for simulating composite laminated under transversely low velocity impact. The strain-based failure criterion of composite including fiber tensile failure, fiber compress failure, matrix crushing and matrix cracking with corresponding stiffness degradation technology, were adopted to model the in-plate damage. Cohesive elements were used for modeling the regions between two laminas. The initial and evolution of interlaminar damage was decided by a bilinear cohesive law which combines stress-based and facture-mechanics-based failure criterion. And a cohesive element initial damage strength function was introduced. A good agreement was obtained between numerical analysis and experimental results.
A 3D finite element model with cohesive was established for simulating composite laminated under transversely low velocity impact. The strain-based failure criterion of composite including fiber tensile failure, fiber compress failure, matrix crushing and matrix cracking with corresponding stiffness degradation technology, were adopted to model the in-plate damage. Cohesive elements were used for modeling the regions between two laminas. The initial and evolution of interlaminar damage was decided by a bilinear cohesive law which combines stress-based and facture-mechanics-based failure criterion. And a cohesive element initial damage strength function was introduced. A good agreement was obtained between numerical analysis and experimental results.
2010, 27(6): 208-212.
Abstract:
The residual strength of glass fiber/epoxy composites after immersion aging in water was studied. The water absorption property of resin and the tensile properties of resin, fiber and composites were tested after and before aging in water. Based on the test, the residual strength of the glass fiber/epoxy composites after water immersion aging was calculated using a bridging model. The numerical results indicate that the theoretical values calculated by the method are well fitted with the test results. The results show that the model could be used to accurately predict the progressing damage regulation and the strength under the condition of low water absorption ratio. When the main bearing layers damage are controlled by fiber, the descending of fiber tensile strength caused by water immersion directly results in the descending of the composites maximum tensile strength. The major factor on the residual strength of composites is resin harden and tensile strength decreasing caused by water immersion to the layers controlled by resin. The effect of the low water absorption ratio on the strength of the interface of fiber and resin is finite.
The residual strength of glass fiber/epoxy composites after immersion aging in water was studied. The water absorption property of resin and the tensile properties of resin, fiber and composites were tested after and before aging in water. Based on the test, the residual strength of the glass fiber/epoxy composites after water immersion aging was calculated using a bridging model. The numerical results indicate that the theoretical values calculated by the method are well fitted with the test results. The results show that the model could be used to accurately predict the progressing damage regulation and the strength under the condition of low water absorption ratio. When the main bearing layers damage are controlled by fiber, the descending of fiber tensile strength caused by water immersion directly results in the descending of the composites maximum tensile strength. The major factor on the residual strength of composites is resin harden and tensile strength decreasing caused by water immersion to the layers controlled by resin. The effect of the low water absorption ratio on the strength of the interface of fiber and resin is finite.
2010, 27(6): 213-217.
Abstract:
Nanostructured silver with different slenderness ratio was prepared by a microwave (MW) assisted method. The nano-silvers were characterized by scanning electron microscope (SEM) and X-ray diffraction (XRD). Isotropical conductive adhesive (ICA) was prepared by using the different slenderness ratio nano-silver as the conductive filler. The conductivity of the adhesive was measured by four-points method. The results indicate that the slenderness ratio of the nano-silver has important influence on it’s percolation threshold. A feasible modified threshold theory was put forward to simulate the relationship between ratio and threshold. The simulation results agree well with the experimental results.
Nanostructured silver with different slenderness ratio was prepared by a microwave (MW) assisted method. The nano-silvers were characterized by scanning electron microscope (SEM) and X-ray diffraction (XRD). Isotropical conductive adhesive (ICA) was prepared by using the different slenderness ratio nano-silver as the conductive filler. The conductivity of the adhesive was measured by four-points method. The results indicate that the slenderness ratio of the nano-silver has important influence on it’s percolation threshold. A feasible modified threshold theory was put forward to simulate the relationship between ratio and threshold. The simulation results agree well with the experimental results.
2010, 27(6): 218-224.
Abstract:
Based on the features of damaged steel plates bonded by composite patch, a three demensional mechanical modeling of elasticity was presented in this paper. The stresses and deformation of axially stretched flat double-side bonded by composite patch were investigated. The distribution of the shear stresses within the bondline and the distribution of the axial force in the steel plate and the patch were studied. The relative stiffness of the reinforced plate versus intact plate was determined. And the relative stiffness of steel plate with a elliptical cutout after versus before reinforced by bonded composite patches and versus intact plate were evaluated. The results indicate that the stiffness of the steel plate with a circular cutout reinforced by bonded composite patches increases with the increase of thickness of the composite patch, and the amount of increasing gradually mitigates. The rehabilitation efficiency can not be effectively improved depending on increasing the thinckness of the patch alone, as more than 5 layers. The present results have validated the finite element predictions and test results.
Based on the features of damaged steel plates bonded by composite patch, a three demensional mechanical modeling of elasticity was presented in this paper. The stresses and deformation of axially stretched flat double-side bonded by composite patch were investigated. The distribution of the shear stresses within the bondline and the distribution of the axial force in the steel plate and the patch were studied. The relative stiffness of the reinforced plate versus intact plate was determined. And the relative stiffness of steel plate with a elliptical cutout after versus before reinforced by bonded composite patches and versus intact plate were evaluated. The results indicate that the stiffness of the steel plate with a circular cutout reinforced by bonded composite patches increases with the increase of thickness of the composite patch, and the amount of increasing gradually mitigates. The rehabilitation efficiency can not be effectively improved depending on increasing the thinckness of the patch alone, as more than 5 layers. The present results have validated the finite element predictions and test results.
