2012 Vol. 29, No. 5
2012, (5): 1-5.
Abstract:
Polyaniline (PANI)/RuO2 composite electrodes were prepared by coating thermal decomposition and electrochemistry polymerization procedures. RuO2 film was synthesized by coating thermal decomposition method at 260℃ for 3 h, and PANI particles were deposited on RuO2 films and dried at 80℃ for 12 h. The formation of the amorphous phase of PANI/RuO2 composite was studied by XRD. Morphologic variations of the composite electrodes were established by SEM. Electrochemical performances of the composite electrodes were measured by cyclic voltammetry (CV) and galvanostatic charge-discharge. The results show that when the deposition time of PANI is 25 min, the maximum capacitance and the specific capacitance of PANI/RuO2 composite electrode is 9.72 F and 452 F·g-1 respectively. Charge-discharge curves of the composite electrodes illustrate low potential drops, internal resistances and good charge-discharge properties. Approximately 11% loss of capacitance is observed after 1000 CV cycles.
Polyaniline (PANI)/RuO2 composite electrodes were prepared by coating thermal decomposition and electrochemistry polymerization procedures. RuO2 film was synthesized by coating thermal decomposition method at 260℃ for 3 h, and PANI particles were deposited on RuO2 films and dried at 80℃ for 12 h. The formation of the amorphous phase of PANI/RuO2 composite was studied by XRD. Morphologic variations of the composite electrodes were established by SEM. Electrochemical performances of the composite electrodes were measured by cyclic voltammetry (CV) and galvanostatic charge-discharge. The results show that when the deposition time of PANI is 25 min, the maximum capacitance and the specific capacitance of PANI/RuO2 composite electrode is 9.72 F and 452 F·g-1 respectively. Charge-discharge curves of the composite electrodes illustrate low potential drops, internal resistances and good charge-discharge properties. Approximately 11% loss of capacitance is observed after 1000 CV cycles.
2012, (5): 6-10,23.
Abstract:
Carbon black (CB) was modified with hydroxyl silicone oil to improve the compatibility between CB and silicone rubber (SR), which resulted in diminishing the thermal interfacial resistance between CB and silicone rubber, for preparing CB/SR composites with high thermal conductivity. The compatibility between CB and SR, as well as the thermal conductivity of the CB/SR composites was investigated. The results show that the surface modified CB has a better compatibility with silicone rubber compared with the origin CB. When the loading of the modified CB was 36.59%, the thermal conductivity of the modified CB/SR composites can be as high as 0.591 W?(m稫)-1, 38.7% higher than that of the origin CB/SR composites with the same loading.
Carbon black (CB) was modified with hydroxyl silicone oil to improve the compatibility between CB and silicone rubber (SR), which resulted in diminishing the thermal interfacial resistance between CB and silicone rubber, for preparing CB/SR composites with high thermal conductivity. The compatibility between CB and SR, as well as the thermal conductivity of the CB/SR composites was investigated. The results show that the surface modified CB has a better compatibility with silicone rubber compared with the origin CB. When the loading of the modified CB was 36.59%, the thermal conductivity of the modified CB/SR composites can be as high as 0.591 W?(m稫)-1, 38.7% higher than that of the origin CB/SR composites with the same loading.
2012, (5): 11-17.
Abstract:
Epoxy resin enhanced with low content carbon nanotubes(CNTs) dispersed by ultrasonic disruption and ultrasonic agitation was prepared, and the influences of CNTs on the curing behavior, rheological property and mechanical properties of epoxy resin were studied. The CNTs-glass fiber/epoxy resin laminates filled with 0.01% mass fraction of CNTs were fabricated using vacuum assisted resin infusion molding (VARIM). The effects of CNTs with the two dispersing methods on the mechanical properties of composite laminates and the enhancing mechanism of CNTs were investigated. The results show that the ultrasonic disruption can shorten the CNTs and improve their dispersion state in the resin. Compared with the CNTs dispersed by the ultrasonic agitation, the influences of the CNTs dispersed by the ultrasonic disruption on the increasing viscosity and curing reaction of epoxy resin are more obvious. The flexural property, interlaminar shear strength of the laminates and the bonding strength between the resin and the glass fiber are improved using double VARIM, while the CNTs enhancing effects are not significant using single VARIM. This outcome demonstrates that due to the filter effect of fibers, low content of CNTs can increase the properties of composite laminates molded using VARIM with suitable infusion molding and dispersing method of CNTs.
Epoxy resin enhanced with low content carbon nanotubes(CNTs) dispersed by ultrasonic disruption and ultrasonic agitation was prepared, and the influences of CNTs on the curing behavior, rheological property and mechanical properties of epoxy resin were studied. The CNTs-glass fiber/epoxy resin laminates filled with 0.01% mass fraction of CNTs were fabricated using vacuum assisted resin infusion molding (VARIM). The effects of CNTs with the two dispersing methods on the mechanical properties of composite laminates and the enhancing mechanism of CNTs were investigated. The results show that the ultrasonic disruption can shorten the CNTs and improve their dispersion state in the resin. Compared with the CNTs dispersed by the ultrasonic agitation, the influences of the CNTs dispersed by the ultrasonic disruption on the increasing viscosity and curing reaction of epoxy resin are more obvious. The flexural property, interlaminar shear strength of the laminates and the bonding strength between the resin and the glass fiber are improved using double VARIM, while the CNTs enhancing effects are not significant using single VARIM. This outcome demonstrates that due to the filter effect of fibers, low content of CNTs can increase the properties of composite laminates molded using VARIM with suitable infusion molding and dispersing method of CNTs.
2012, (5): 18-23.
Abstract:
3D spacer grille fabric composites were developed in this paper. Its mechanical characteristics under flatwise compressive and shear loads were analyzed, and the effects of pile distance, pile height and foam on the mechanical properties were investigated. The results indicate that the flatwise compressive and shear properties of 3D spacer grille fabric composites decrease with the pile distance increasing. After filling the foam, synergy effects between the piles increase with the increace of pile distance. The failure modes of heavy-thickness spacer fabric composites are pile instability under flatwise compression, and fractured at the joint of pile and facesheet under shear load.
3D spacer grille fabric composites were developed in this paper. Its mechanical characteristics under flatwise compressive and shear loads were analyzed, and the effects of pile distance, pile height and foam on the mechanical properties were investigated. The results indicate that the flatwise compressive and shear properties of 3D spacer grille fabric composites decrease with the pile distance increasing. After filling the foam, synergy effects between the piles increase with the increace of pile distance. The failure modes of heavy-thickness spacer fabric composites are pile instability under flatwise compression, and fractured at the joint of pile and facesheet under shear load.
2012, (5): 24-31.
Abstract:
Sulfonated graphene mono-molecular film was synthesized and doped into perfluorosulfonic acid solution to prepare around 200 μm thick hybrid membranes with varying mass ratios. Those processes were monitored and demonstrated by attenuated total reflectance Fourier transform infrared spectroscopy. The physical performances related to electromechanical properties were detected. To make ion exchange polymer-metal composites, two Pt nano sheets were sandwiched on both sides of the resultant membranes, which was observed by SEM. Inputted the sinusoidal wave with a low frequency for fabricating electro-active actuator, detections of force and displacement sensors were taken. The results show that the flexibilities, ionic exchange capacities, and water contents of hybrid membranes increase in a degree. The Pt nano particles are relatively fine and uniform, the electrodes planes are relatively flat, and the bonding between electrode and hybrid membrane is firm. The hybrid membrane has a high electrostrictive strain, and the maximum displacement is 2.38 times higher than that of the pure perfluorosulfonic acid membrane under same conditions.
Sulfonated graphene mono-molecular film was synthesized and doped into perfluorosulfonic acid solution to prepare around 200 μm thick hybrid membranes with varying mass ratios. Those processes were monitored and demonstrated by attenuated total reflectance Fourier transform infrared spectroscopy. The physical performances related to electromechanical properties were detected. To make ion exchange polymer-metal composites, two Pt nano sheets were sandwiched on both sides of the resultant membranes, which was observed by SEM. Inputted the sinusoidal wave with a low frequency for fabricating electro-active actuator, detections of force and displacement sensors were taken. The results show that the flexibilities, ionic exchange capacities, and water contents of hybrid membranes increase in a degree. The Pt nano particles are relatively fine and uniform, the electrodes planes are relatively flat, and the bonding between electrode and hybrid membrane is firm. The hybrid membrane has a high electrostrictive strain, and the maximum displacement is 2.38 times higher than that of the pure perfluorosulfonic acid membrane under same conditions.
2012, (5): 32-40.
Abstract:
A series of Mg(OH)2 with different degradation states (t-MH) were obtained by pyrolyzing Mg(OH)2 (Magnesium hydroxide, MH) at various temperatures for different time. MH/PS and t-MH/PS composites were prepared by melt-compounding MH and t-MH as halogen-free flame retardants and PS as matrix. The influence of thermal treatment of MH on combustion behavior of t-MH/PS composites was investigated in detail. Based on the experimental results, a model of the flame retardant mechanism of MH/PS composites was proposed. It is indicated that MH gradually decomposes and changes into MgO with the rise of thermal treatment temperature and the elongation of thermal treatment time. Under identical conditions, the flame retardancy of t-MH/PS composite decreases noticeably than that of its MH/PS counterpart, but it is still much better than that of pure PS. In addition, the MgO produced by decomposition of MH can promote charring of PS. It is believed that the flame retardant mechanism of MH/PS composites derives from the synergistic effect of the following factors: (1) the cooling effect from endothermal degradation of MH; (2) the gas phase diluting effect of water vapor from degradation of MH; (3) the solid phase obstructing and shielding effect of MgO from degradation of MH; (4) the fire-proof effect from charring of PS induced by MgO.
A series of Mg(OH)2 with different degradation states (t-MH) were obtained by pyrolyzing Mg(OH)2 (Magnesium hydroxide, MH) at various temperatures for different time. MH/PS and t-MH/PS composites were prepared by melt-compounding MH and t-MH as halogen-free flame retardants and PS as matrix. The influence of thermal treatment of MH on combustion behavior of t-MH/PS composites was investigated in detail. Based on the experimental results, a model of the flame retardant mechanism of MH/PS composites was proposed. It is indicated that MH gradually decomposes and changes into MgO with the rise of thermal treatment temperature and the elongation of thermal treatment time. Under identical conditions, the flame retardancy of t-MH/PS composite decreases noticeably than that of its MH/PS counterpart, but it is still much better than that of pure PS. In addition, the MgO produced by decomposition of MH can promote charring of PS. It is believed that the flame retardant mechanism of MH/PS composites derives from the synergistic effect of the following factors: (1) the cooling effect from endothermal degradation of MH; (2) the gas phase diluting effect of water vapor from degradation of MH; (3) the solid phase obstructing and shielding effect of MgO from degradation of MH; (4) the fire-proof effect from charring of PS induced by MgO.
2012, (5): 41-46.
Abstract:
Polypyrrole was coated onto pure LiFePO4 particles to form polypyrrole/lithium iron phosphate(PPy/LiFePO4) composite material by chemical oxidative polymerization, with ferric trichloride(FeCl3) as oxidant, benzene sulfonic acid sodium salt as dopant. The molecular structure and morphology of PPy/LiFePO4 were characterized by FTIR, XRD and SEM. The electrochemical performances of composite were measured by electrochemical workstation and charge-discharge test system. It is found that the battery with PPy/LiFePO4 composite as cathode shows better charge-discharge performance. The discharge capacity of PPy/LiFePO4 composite is 163 mAh穏-1, which is higher than that of LiFePO4, when the mass fraction of PPy is 17.0% and the current is 0.1 mA.The discharge specific capacity of composite is still 94.9% of initial capacity after 50 cycles. Compared with pure LiFePO4, the coating of proper amount of PPy can improve the electronic conductivity of LiFePO4. As the effective utilization of LiFePO4 increases, both the specific capacity and cycle performance of PPy/LiFePO4 composite improves.
Polypyrrole was coated onto pure LiFePO4 particles to form polypyrrole/lithium iron phosphate(PPy/LiFePO4) composite material by chemical oxidative polymerization, with ferric trichloride(FeCl3) as oxidant, benzene sulfonic acid sodium salt as dopant. The molecular structure and morphology of PPy/LiFePO4 were characterized by FTIR, XRD and SEM. The electrochemical performances of composite were measured by electrochemical workstation and charge-discharge test system. It is found that the battery with PPy/LiFePO4 composite as cathode shows better charge-discharge performance. The discharge capacity of PPy/LiFePO4 composite is 163 mAh穏-1, which is higher than that of LiFePO4, when the mass fraction of PPy is 17.0% and the current is 0.1 mA.The discharge specific capacity of composite is still 94.9% of initial capacity after 50 cycles. Compared with pure LiFePO4, the coating of proper amount of PPy can improve the electronic conductivity of LiFePO4. As the effective utilization of LiFePO4 increases, both the specific capacity and cycle performance of PPy/LiFePO4 composite improves.
2012, (5): 47-52.
Abstract:
The tribological behaviours between 25% mass fraction of glass fibers reinforced polyamide 66 composite(25%GF/PA66) and Al2O3 ceramic were studied under dry sliding and water lubricating friction condition. The microstructure, micrograph and chemical nature change of the worn surface of 25%GF/PA66 samples were examined using laser optical microscopy, scanning electron microscopy, Fourier transfom infrared spectrometer and X-ray photoelectron spectroscope. The results reveal that the friction coefficients under the water lubricated condition are lower than those of under the dry sliding condition, but the wear volume loss under water lubricating is significantly higher than that of under dry sliding for 25%GF/PA66 composite. Under water lubricated condition, continuous mechanical microcut and the increasing of the temperature induce the deformation of 25%GF/PA66 samples and the hydrolization of the amide groups, which leads the breaking of C—C link and high wear volume loss. The thermal softening temperature of 105.9℃ is estimated based on the generally thermal conductivity model of extended surface.
The tribological behaviours between 25% mass fraction of glass fibers reinforced polyamide 66 composite(25%GF/PA66) and Al2O3 ceramic were studied under dry sliding and water lubricating friction condition. The microstructure, micrograph and chemical nature change of the worn surface of 25%GF/PA66 samples were examined using laser optical microscopy, scanning electron microscopy, Fourier transfom infrared spectrometer and X-ray photoelectron spectroscope. The results reveal that the friction coefficients under the water lubricated condition are lower than those of under the dry sliding condition, but the wear volume loss under water lubricating is significantly higher than that of under dry sliding for 25%GF/PA66 composite. Under water lubricated condition, continuous mechanical microcut and the increasing of the temperature induce the deformation of 25%GF/PA66 samples and the hydrolization of the amide groups, which leads the breaking of C—C link and high wear volume loss. The thermal softening temperature of 105.9℃ is estimated based on the generally thermal conductivity model of extended surface.
2012, (5): 53-60.
Abstract:
The multi-walled carbon nanotubes (MWCNTs) were functionalized to produce oxidized MWCNTs (MWCNTs-COOH) and epoxidized MWCNTs (MWCNTs-Epon828). Three types of Graphene-MWCNTs/EP composites were prepared by adding the graphene sheets and different types of MWCNTs into the epoxy resin (EP), respectively. By means of tensile test and thermal gravimetric analysis, the synergetic effects of graphene and MWCNTs, the effects of their content and the methods of MWCNT functionalization on the mechanical and thermal properties of the composites were studied. The results indicate that the synergetic reinforcement of the graphene and MWCNTs has a better performance than that of sole MWCNTs. Even with 0.1% mass fraction of the graphene and MWCNTs, the tensile strength of Graphene-MWCNTs-Epon828/EP composite approaches the ultimate value: The tensile strength, elastic modulus, and the elongation at break have been increased by 35%, 65% and 34%, compared with the pure EP, respectively. The thermal stability of all the Graphene-MWCNTs/EP composites are improved with the addition of graphene and MWCNTs.
The multi-walled carbon nanotubes (MWCNTs) were functionalized to produce oxidized MWCNTs (MWCNTs-COOH) and epoxidized MWCNTs (MWCNTs-Epon828). Three types of Graphene-MWCNTs/EP composites were prepared by adding the graphene sheets and different types of MWCNTs into the epoxy resin (EP), respectively. By means of tensile test and thermal gravimetric analysis, the synergetic effects of graphene and MWCNTs, the effects of their content and the methods of MWCNT functionalization on the mechanical and thermal properties of the composites were studied. The results indicate that the synergetic reinforcement of the graphene and MWCNTs has a better performance than that of sole MWCNTs. Even with 0.1% mass fraction of the graphene and MWCNTs, the tensile strength of Graphene-MWCNTs-Epon828/EP composite approaches the ultimate value: The tensile strength, elastic modulus, and the elongation at break have been increased by 35%, 65% and 34%, compared with the pure EP, respectively. The thermal stability of all the Graphene-MWCNTs/EP composites are improved with the addition of graphene and MWCNTs.
2012, (5): 61-68.
Abstract:
Polyaniline-coated conducting polyester and cotton cospinning textile (PANI/CPCCT) was prepared via an in-situ polymerization in the presence of sodium p-perfluorous nonenoxybenzene sulfonate (OBS) as the dopant, FeCl3 as the oxidant and the polyester and cotton cospinning textile (PCCT) with lots of micro/nano-sized gaps on the surface as the substrate. The effect of pH value on the PANI/CPCCT was investigated. It is found that the prepared PANI/CPCCT presents super-hydrophobic function with the biggest water conduct angle of 162?, it also takes on good conductivity and hydrophobicity in alkaline condition. The color and wettability of the PANI/CPCCT present pH-responsive function: its color can reversibly change from dark green to blue green, dark blue, and brown in turn when the pH increases from 1 to 14, and its wettability is reversibly varied from super-hydrophobic to super-hydrophilic induced by a doping and de-doping process of PANI as well. The washing test shows that PANI/CPCCT has a good washability, and its property can be recovered again by being dipped in strong acid solution. All of these superior properties make that the as-prepared PANI/CPCCT can obtain practical utility in acid-controlled wettability switching, self-cleaning textile, acidity detection and other applications.
Polyaniline-coated conducting polyester and cotton cospinning textile (PANI/CPCCT) was prepared via an in-situ polymerization in the presence of sodium p-perfluorous nonenoxybenzene sulfonate (OBS) as the dopant, FeCl3 as the oxidant and the polyester and cotton cospinning textile (PCCT) with lots of micro/nano-sized gaps on the surface as the substrate. The effect of pH value on the PANI/CPCCT was investigated. It is found that the prepared PANI/CPCCT presents super-hydrophobic function with the biggest water conduct angle of 162?, it also takes on good conductivity and hydrophobicity in alkaline condition. The color and wettability of the PANI/CPCCT present pH-responsive function: its color can reversibly change from dark green to blue green, dark blue, and brown in turn when the pH increases from 1 to 14, and its wettability is reversibly varied from super-hydrophobic to super-hydrophilic induced by a doping and de-doping process of PANI as well. The washing test shows that PANI/CPCCT has a good washability, and its property can be recovered again by being dipped in strong acid solution. All of these superior properties make that the as-prepared PANI/CPCCT can obtain practical utility in acid-controlled wettability switching, self-cleaning textile, acidity detection and other applications.
2012, (5): 69-75.
Abstract:
Glass fiber reinforced composites with different amounts of voids were prepared by applying different curing pressures (0.1~0.6 MPa). Ultrasonic C-scan and ablation density method were adopted to measure the attenuation coefficient and the average porosity. The distribution, shape and size of the voids were characterized by metallographic microscopic analysis. The effects of void content on the tensile, bending and interlaminar shear properties and the attenuation coefficient were investigated and discussed, and the critical value of void content and attenuation coefficient were also obtained. The results show that, with the decreasing of curing pressure, the voids content of specimen increases from 0.976% to 5.268%, the tensile strength, flexural strength and interlaminar shear strength decrease, the ultrasonic attenuation coefficient increases from 1.460 dB穖m-1 to 2.150 dB穖m-1, and the critical attenuation coefficient is about 1.5 dB穖m-1.
Glass fiber reinforced composites with different amounts of voids were prepared by applying different curing pressures (0.1~0.6 MPa). Ultrasonic C-scan and ablation density method were adopted to measure the attenuation coefficient and the average porosity. The distribution, shape and size of the voids were characterized by metallographic microscopic analysis. The effects of void content on the tensile, bending and interlaminar shear properties and the attenuation coefficient were investigated and discussed, and the critical value of void content and attenuation coefficient were also obtained. The results show that, with the decreasing of curing pressure, the voids content of specimen increases from 0.976% to 5.268%, the tensile strength, flexural strength and interlaminar shear strength decrease, the ultrasonic attenuation coefficient increases from 1.460 dB穖m-1 to 2.150 dB穖m-1, and the critical attenuation coefficient is about 1.5 dB穖m-1.
2012, (5): 76-82.
Abstract:
CaO-MgO-Al2O3-SiO2 (CMAS in short) deposits are often generated on the surface of in-service aircraft engine blades. In this paper, the thermal cycling behavior and associated failure mechanism of EB-PVD zirconia-based thermal barrier coatings (TBCs) with CMAS deposits were investigated. The results show that the thermal cycling life of TBCs with CMAS deposits at 1200℃ is less than 100 cycles, whereas the life of TBCs without CMAS is more than 500 cycles. CMAS deposits accelerate the spallation failure of TBCs. After 210 thermal cycles at 1200℃, about 8 μm interaction layer is formed between CMAS and zirconia ceramic layer, which is mainly due to the inward diffusion of Ca2+ from the CMAS deposits. A large number of transverse cracks are generated in the ceramic layer of TBCs with CMAS deposits. The failure of TBCs occurs mainly by chipping spallation of the ceramic layer.
CaO-MgO-Al2O3-SiO2 (CMAS in short) deposits are often generated on the surface of in-service aircraft engine blades. In this paper, the thermal cycling behavior and associated failure mechanism of EB-PVD zirconia-based thermal barrier coatings (TBCs) with CMAS deposits were investigated. The results show that the thermal cycling life of TBCs with CMAS deposits at 1200℃ is less than 100 cycles, whereas the life of TBCs without CMAS is more than 500 cycles. CMAS deposits accelerate the spallation failure of TBCs. After 210 thermal cycles at 1200℃, about 8 μm interaction layer is formed between CMAS and zirconia ceramic layer, which is mainly due to the inward diffusion of Ca2+ from the CMAS deposits. A large number of transverse cracks are generated in the ceramic layer of TBCs with CMAS deposits. The failure of TBCs occurs mainly by chipping spallation of the ceramic layer.
2012, (5): 83-87.
Abstract:
Al-doped ZnO (AZO) transparent conducting films were successfully prepared on glass substrates by radio-frequency (RF) magnetron sputtering. In order to reduce the resistivity of the thin films, the AZO film was hydrogenated with the addition of H2 in the sputtering atmosphere. The effects of hydrogen ratio in the sputtering ambient and substrate temperature on the effectiveness of hydrogen incorporation in Al-doped ZnO films were investigated. The results show that hydrogen treatment can effectively reduce the resistivity of AZO thin films at low temperatures. At the low substrate temperature of 100℃, the high-quality AZO thin films with the lowest resistivity of 6.0×10-4 Ω·cm can be obtained by adjusting the H2 ratio in sputtering ambient. The resistivity of AZO thin film with hydrogen incorporation is less than 1/3 compared with that of thin film without hydrogen incorporation under the same condition. Moreover, the improvement of hydrogen treatment on electrical properties is gradually weakened with the substrate temperature increasing.
Al-doped ZnO (AZO) transparent conducting films were successfully prepared on glass substrates by radio-frequency (RF) magnetron sputtering. In order to reduce the resistivity of the thin films, the AZO film was hydrogenated with the addition of H2 in the sputtering atmosphere. The effects of hydrogen ratio in the sputtering ambient and substrate temperature on the effectiveness of hydrogen incorporation in Al-doped ZnO films were investigated. The results show that hydrogen treatment can effectively reduce the resistivity of AZO thin films at low temperatures. At the low substrate temperature of 100℃, the high-quality AZO thin films with the lowest resistivity of 6.0×10-4 Ω·cm can be obtained by adjusting the H2 ratio in sputtering ambient. The resistivity of AZO thin film with hydrogen incorporation is less than 1/3 compared with that of thin film without hydrogen incorporation under the same condition. Moreover, the improvement of hydrogen treatment on electrical properties is gradually weakened with the substrate temperature increasing.
2012, (5): 88-93.
Abstract:
The 316 stainless steel/MCrAlY porous metal composites were prepared by laser sintering. The microstructures of the laser sintered samples were characterized by SEM and contourgraph. The mechanism of the pore formation by the polystyrene hollow was researched. Meanwhile, the mechanical properties and high temperature oxidation resistance were tested. The results show that the diameter of pores in the sample is about 20 μm with a mean porosity of 61% and good connectivity. The porous are orderly arranged, and a good connection between the pore wall is obtained using polystyrene hollow by laser sintering. Additionally, the porous composites has a good compressive strength of 4.78 MPa; the mass gain of porous composite oxidation is only 3.49 mg/cm2 in 50 h at 900℃.
The 316 stainless steel/MCrAlY porous metal composites were prepared by laser sintering. The microstructures of the laser sintered samples were characterized by SEM and contourgraph. The mechanism of the pore formation by the polystyrene hollow was researched. Meanwhile, the mechanical properties and high temperature oxidation resistance were tested. The results show that the diameter of pores in the sample is about 20 μm with a mean porosity of 61% and good connectivity. The porous are orderly arranged, and a good connection between the pore wall is obtained using polystyrene hollow by laser sintering. Additionally, the porous composites has a good compressive strength of 4.78 MPa; the mass gain of porous composite oxidation is only 3.49 mg/cm2 in 50 h at 900℃.
2012, (5): 94-98.
Abstract:
Iron group metals (Ni, Co, Fe)-doped R2O-B2O3-Al2O3-SiO2 vitrified bond were produced by special powder metallurgy technique. The effect of iron group metals (Ni, Co, Fe) on the refractoriness, fluidity, oxidation, interface and bending strength in the system of R2O-B2O3-Al2O3-SiO2 vitrified bond was studied. The results show that it has little effect on the refractoriness of the vitrified bond with the addition of Ni, but the refractoriness increases with the addition of Co and significantly decreases less than the addition of 20%Fe. When sintering at 750℃ in air, the added metal powders are partly oxidized and the degree of the oxidation is Fe>Co>Ni. The bending strength of vitrified bond increases with different degree by adding metal powders. When the mass fraction of Co is 25%, the bending strength of vitrified bond reaches the maximum value of 75.42 MPa. The close degree for the added metal powders with vitrified bond is Co>Ni>Fe.
Iron group metals (Ni, Co, Fe)-doped R2O-B2O3-Al2O3-SiO2 vitrified bond were produced by special powder metallurgy technique. The effect of iron group metals (Ni, Co, Fe) on the refractoriness, fluidity, oxidation, interface and bending strength in the system of R2O-B2O3-Al2O3-SiO2 vitrified bond was studied. The results show that it has little effect on the refractoriness of the vitrified bond with the addition of Ni, but the refractoriness increases with the addition of Co and significantly decreases less than the addition of 20%Fe. When sintering at 750℃ in air, the added metal powders are partly oxidized and the degree of the oxidation is Fe>Co>Ni. The bending strength of vitrified bond increases with different degree by adding metal powders. When the mass fraction of Co is 25%, the bending strength of vitrified bond reaches the maximum value of 75.42 MPa. The close degree for the added metal powders with vitrified bond is Co>Ni>Fe.
2012, (5): 99-105.
Abstract:
In order to identify suitable pack compositions for co-depositing Cr, Si and Y to form diffusion coatings on Nb-base in situ composites by the pack cementation process, thermochemical calculation was taken to analysis the vapour pressure of halide species generated in a series of pack powder mixtures activated by NH4Cl or CrCl3·6H2O at high temperatures. The Cr-Si-Y co-depositing coating layers on the Nb-base in situ composites were prepared according to the analysis. The microstructure, phase constituents and compositional distribution in the coatings were studied. The results show that by means of carefully controlling the composition of the packs activated by NH4Cl, co-deposition of Si-Cr-Y on Nb-Si in situ composites can be achieved at the appropriate temperature. It is demonstrated that the co-depositing coating can be formed at 1350℃ with the pack power mixtures composed of 12Cr-6Si-0.75Y2O3-5NH4Cl-76.25Al2O3(mass fraction). The coatings obtained have a multiple layer structure, consisting of an outer layer, an inner layer and a diffusion zone at the boundary between the coating and the substrate. It is suggested that the coating is formed via a sequential deposition mechanism through inward diffusion of Cr, Y and Si. The coatings are mainly composed of Cr2(Nb,Ti), (Nb,Ti)5Si3 and HfSi2, and the microstructure of the coatings can be refined by addition of Y2O3 in the pack mixtures.
In order to identify suitable pack compositions for co-depositing Cr, Si and Y to form diffusion coatings on Nb-base in situ composites by the pack cementation process, thermochemical calculation was taken to analysis the vapour pressure of halide species generated in a series of pack powder mixtures activated by NH4Cl or CrCl3·6H2O at high temperatures. The Cr-Si-Y co-depositing coating layers on the Nb-base in situ composites were prepared according to the analysis. The microstructure, phase constituents and compositional distribution in the coatings were studied. The results show that by means of carefully controlling the composition of the packs activated by NH4Cl, co-deposition of Si-Cr-Y on Nb-Si in situ composites can be achieved at the appropriate temperature. It is demonstrated that the co-depositing coating can be formed at 1350℃ with the pack power mixtures composed of 12Cr-6Si-0.75Y2O3-5NH4Cl-76.25Al2O3(mass fraction). The coatings obtained have a multiple layer structure, consisting of an outer layer, an inner layer and a diffusion zone at the boundary between the coating and the substrate. It is suggested that the coating is formed via a sequential deposition mechanism through inward diffusion of Cr, Y and Si. The coatings are mainly composed of Cr2(Nb,Ti), (Nb,Ti)5Si3 and HfSi2, and the microstructure of the coatings can be refined by addition of Y2O3 in the pack mixtures.
2012, (5): 106-112.
Abstract:
Palygorskite-based porous ceramsite (PC) was prepared by calcination with palygorskite, sawdust and sodium silicate. Effect of the mass ratio of reaction materials and clacination technique on the properties of ceramsite was investigated. Furthermore, in various tests for the ceramsite, compressive strength was the principal factor to determine the mechanical properties of ceramsite. To choose the most suitable product, porosity, calcination temperature and time were introduced as factors in orthogonal experiment design to determine the preparation of PC. XRD and SEM were used for the characterization of porous ceramic characteristics. The results show that a promising combination of palygorskite clay, sawdust, and sodium silicate would ensure PC conforming to the state industrial standards of water treatment, when the mass ratio is 10:2:1, the calcinations temperature is 700℃ and the calcinations time is 3 h. The uniform and interconnected pores in PC are suitable for the microbial growth.
Palygorskite-based porous ceramsite (PC) was prepared by calcination with palygorskite, sawdust and sodium silicate. Effect of the mass ratio of reaction materials and clacination technique on the properties of ceramsite was investigated. Furthermore, in various tests for the ceramsite, compressive strength was the principal factor to determine the mechanical properties of ceramsite. To choose the most suitable product, porosity, calcination temperature and time were introduced as factors in orthogonal experiment design to determine the preparation of PC. XRD and SEM were used for the characterization of porous ceramic characteristics. The results show that a promising combination of palygorskite clay, sawdust, and sodium silicate would ensure PC conforming to the state industrial standards of water treatment, when the mass ratio is 10:2:1, the calcinations temperature is 700℃ and the calcinations time is 3 h. The uniform and interconnected pores in PC are suitable for the microbial growth.
2012, (5): 113-120.
Abstract:
By changing the mole ratio of Ti, C and B in primary reaction system, TiC-TiB2 composite ceramic with different TiB2 mole content were prepared by combustion synthesis in high-gravity field. The microstructure of composites was characterized by FESEM. The influence of the TiB2 composition on the mechanical properties of composite ceramic was studied. The results indicate that the matrix of TiC-TiB2 composite ceramics transforms from TiC grains to TiB2 platelets with increasing TiB2 mole content, moreover, the fine-grained microstructures and even ultrafine-grained microstructures are achieved in TiC-50 %TiB2, while volume fraction of α-Al2O3 inclusions in the ceramic also reaches the lowest value. The relative density, Vickers hardness and flexural strength of ceramics simultaneously reach the maximum values as the mole content of TiB2 is 50% in the ceramic, whereas the maximum fracture toughness is achieved in TiC-66.7%TiB2. FESEM fracture morphologies of the ceramics show that intercrystalline fracture is enhanced while transgranular fracture is weakened inversely with increasing mole content of TiB2 to 66.7%. FESEM crack propagation paths of TiC-TiB2 composite ceramics show that the highest flexural strength is achieved in TiC-50%TiB2 composite ceramic due to both the achievement of solidified fine-grained and ultrafine-grained microstructures and the presence of intensive toughening mechanisms of crack deflection, frictionally crack-bridging and pull-out by a large number of fine TiB2 platelets.
By changing the mole ratio of Ti, C and B in primary reaction system, TiC-TiB2 composite ceramic with different TiB2 mole content were prepared by combustion synthesis in high-gravity field. The microstructure of composites was characterized by FESEM. The influence of the TiB2 composition on the mechanical properties of composite ceramic was studied. The results indicate that the matrix of TiC-TiB2 composite ceramics transforms from TiC grains to TiB2 platelets with increasing TiB2 mole content, moreover, the fine-grained microstructures and even ultrafine-grained microstructures are achieved in TiC-50 %TiB2, while volume fraction of α-Al2O3 inclusions in the ceramic also reaches the lowest value. The relative density, Vickers hardness and flexural strength of ceramics simultaneously reach the maximum values as the mole content of TiB2 is 50% in the ceramic, whereas the maximum fracture toughness is achieved in TiC-66.7%TiB2. FESEM fracture morphologies of the ceramics show that intercrystalline fracture is enhanced while transgranular fracture is weakened inversely with increasing mole content of TiB2 to 66.7%. FESEM crack propagation paths of TiC-TiB2 composite ceramics show that the highest flexural strength is achieved in TiC-50%TiB2 composite ceramic due to both the achievement of solidified fine-grained and ultrafine-grained microstructures and the presence of intensive toughening mechanisms of crack deflection, frictionally crack-bridging and pull-out by a large number of fine TiB2 platelets.
2012, (5): 121-126.
Abstract:
The magnetic solid acid catalyst(S2O82-/ZrO2-SrFe12O19) was prepared by strontium ferrites(SrFe12O19) particle carrying with solid acid, which exhibited excellent magnetic properties as a magnetic matrix. The surface properties and catalytic performance of the magnetic catalyst were analyzed by means of XRD, nitrogen adsorption-desorption (BET), vibrating sample magnetometer (VSM), FTIR. The results show that the introduction of SrFe12O19 can increase thermal stability of the metastable tetragonal type t-ZrO2. The saturated magnetization (Ms) is about 30.0 emu穏-1, and the coercive force is greater than 3900 G, which is good for the magnetic separation and reuse. The specific surface area of solid acid is 16.0 m2穏-1 and the average pore size is 8.16 nm, certifying that the solid acid catalyst is a mesoporous magnetic material. The test for transesterification by tallow oil with methanol as probe reaction shows that the solid acid becomes an effective catalyst in a relatively short time.
The magnetic solid acid catalyst(S2O82-/ZrO2-SrFe12O19) was prepared by strontium ferrites(SrFe12O19) particle carrying with solid acid, which exhibited excellent magnetic properties as a magnetic matrix. The surface properties and catalytic performance of the magnetic catalyst were analyzed by means of XRD, nitrogen adsorption-desorption (BET), vibrating sample magnetometer (VSM), FTIR. The results show that the introduction of SrFe12O19 can increase thermal stability of the metastable tetragonal type t-ZrO2. The saturated magnetization (Ms) is about 30.0 emu穏-1, and the coercive force is greater than 3900 G, which is good for the magnetic separation and reuse. The specific surface area of solid acid is 16.0 m2穏-1 and the average pore size is 8.16 nm, certifying that the solid acid catalyst is a mesoporous magnetic material. The test for transesterification by tallow oil with methanol as probe reaction shows that the solid acid becomes an effective catalyst in a relatively short time.
2012, (5): 127-133.
Abstract:
Deterioration of carbonized fly ash concrete (FAC), concrete with high volume mineral admixture (HVMAC), and high performance hybrid fibers reinforced expansive concrete (HPHFREC) exposed to 5% magnesium sulfate solution was investigated. Two corrosion regimes were employed: natural immersion and dry-wet cycle. Experiment results show that carbonation changes the chemical component of concrete surface and reduces the resistance of concrete to magnesium sulfate attack, though carbonation compacts the concrete surface to some extent. The dry-wet cycles accelerate the diffusion of magnesium sulfate and develop the micro-crack of concrete. Under combined action of carbonation and magnesium sulfate, HVMAC gets the best resistance to sulfate attack and is applicable to the atrocious environment, but FAC which has been broken up is not applicable to the concrete engineering in such environment. Under combined action of carbonation, dry-wet cycle, and magnesium sulfate, HPHFREC2, of which the reinforced effect of the fibers is obviously well, shows the better resistance of concrete to sulfate attack.
Deterioration of carbonized fly ash concrete (FAC), concrete with high volume mineral admixture (HVMAC), and high performance hybrid fibers reinforced expansive concrete (HPHFREC) exposed to 5% magnesium sulfate solution was investigated. Two corrosion regimes were employed: natural immersion and dry-wet cycle. Experiment results show that carbonation changes the chemical component of concrete surface and reduces the resistance of concrete to magnesium sulfate attack, though carbonation compacts the concrete surface to some extent. The dry-wet cycles accelerate the diffusion of magnesium sulfate and develop the micro-crack of concrete. Under combined action of carbonation and magnesium sulfate, HVMAC gets the best resistance to sulfate attack and is applicable to the atrocious environment, but FAC which has been broken up is not applicable to the concrete engineering in such environment. Under combined action of carbonation, dry-wet cycle, and magnesium sulfate, HPHFREC2, of which the reinforced effect of the fibers is obviously well, shows the better resistance of concrete to sulfate attack.
2012, (5): 134-139.
Abstract:
To describe geometric behavior of an orthogonal fabric sheet draped over a sphere theoretically, a new method to determine the net position on the sphere with fishnet model was present by using coordinate transformation, and in-plane shear deformation of the fabrics and bending curvatures of tows were derived. Node positions in symmetric planes and node position in other region under local coordinate system were determined with constant arc length condition. The net coordinate on the sphere in global coordinate was obtained by coordinate transformation method, and in-plane shear deformation of the fabrics and bending curvatures of tows in two directions were calculated with the deformed net. The numeric examples show that draping deformation is related to neither net size, nor sphere radius when net size is far smaller than that of sphere radius. The distributions of shear deformation and bending deformation are only dependent on two spherical coordinates of the deformed nets.
To describe geometric behavior of an orthogonal fabric sheet draped over a sphere theoretically, a new method to determine the net position on the sphere with fishnet model was present by using coordinate transformation, and in-plane shear deformation of the fabrics and bending curvatures of tows were derived. Node positions in symmetric planes and node position in other region under local coordinate system were determined with constant arc length condition. The net coordinate on the sphere in global coordinate was obtained by coordinate transformation method, and in-plane shear deformation of the fabrics and bending curvatures of tows in two directions were calculated with the deformed net. The numeric examples show that draping deformation is related to neither net size, nor sphere radius when net size is far smaller than that of sphere radius. The distributions of shear deformation and bending deformation are only dependent on two spherical coordinates of the deformed nets.
2012, (5): 140-145.
Abstract:
A random microstructure cell model was developed to predict the effective transverse thermal conductivity of unidirectional fiber reinforced composites. The minimization of the model that can well characterize the macroscopic effective properties was investigated, and the influence mechanism of microstructures on macroscopic effective thermal conduction properties was discussed. It is shown that convergence and computational efficiency are much improved by prescribing the periodic boundary conditions for the model together with replacing the result by a large model with the average of the results by several appropriate small models. The maximum relative variation of effective thermal conductivities is only 0.6% with the model scale ranging from 10?10 to 30?30. Different fiber distributions lead to different lengths of heat flux path with a high thermal resistance, and then result in different effective thermal conductivities. For a random fiber distribution, fibers segregate in a microscopic level. When the fiber thermal conductivity is much larger than that of the matrix, portions of the fibers come into contact and form some local "heat flow channels", which result in a higher effective thermal conductivity. At a certain fiber volume fraction, the effective thermal conductivity increases dramatically because some of the local "heat flow channels" connect and form channels across the entire composite. A comparison with experimental data demonstrates the necessity of the study on microstructural randomness and the practical value of the present work.
A random microstructure cell model was developed to predict the effective transverse thermal conductivity of unidirectional fiber reinforced composites. The minimization of the model that can well characterize the macroscopic effective properties was investigated, and the influence mechanism of microstructures on macroscopic effective thermal conduction properties was discussed. It is shown that convergence and computational efficiency are much improved by prescribing the periodic boundary conditions for the model together with replacing the result by a large model with the average of the results by several appropriate small models. The maximum relative variation of effective thermal conductivities is only 0.6% with the model scale ranging from 10?10 to 30?30. Different fiber distributions lead to different lengths of heat flux path with a high thermal resistance, and then result in different effective thermal conductivities. For a random fiber distribution, fibers segregate in a microscopic level. When the fiber thermal conductivity is much larger than that of the matrix, portions of the fibers come into contact and form some local "heat flow channels", which result in a higher effective thermal conductivity. At a certain fiber volume fraction, the effective thermal conductivity increases dramatically because some of the local "heat flow channels" connect and form channels across the entire composite. A comparison with experimental data demonstrates the necessity of the study on microstructural randomness and the practical value of the present work.
2012, (5): 146-150.
Abstract:
To overcome the limitation of traditional probabilistic statistical method, two non-probabilistic methods to research the residual elastic modulus of the damaged composite with uncertainties were presented. In the non-probabilistic methods, uncertain variables were described as interval numbers or convex sets, and then the interval range of residual elastic modulus could be obtained by means of Taylor expansion and interval calculation. The main advantages of non-probabilistic methods are that the needed uncertain information is decreased; the methods are simple, easily applicable and the results are highly precise. Through two cases of a numerical example, the residual elastic modulus of damaged composite with uncertainties were calculated using the presented non-probabilistic methods. The results indicate that when the information of uncertain parameters is less, using the presented methods can obtain satisfying results for the uncertain problem.
To overcome the limitation of traditional probabilistic statistical method, two non-probabilistic methods to research the residual elastic modulus of the damaged composite with uncertainties were presented. In the non-probabilistic methods, uncertain variables were described as interval numbers or convex sets, and then the interval range of residual elastic modulus could be obtained by means of Taylor expansion and interval calculation. The main advantages of non-probabilistic methods are that the needed uncertain information is decreased; the methods are simple, easily applicable and the results are highly precise. Through two cases of a numerical example, the residual elastic modulus of damaged composite with uncertainties were calculated using the presented non-probabilistic methods. The results indicate that when the information of uncertain parameters is less, using the presented methods can obtain satisfying results for the uncertain problem.
2012, (5): 151-156.
Abstract:
A new type of zero-thickness cohesive element model is proposed to study the composite interlaminar damage, which can accurately predict the delamination propagation of mode Ⅱ problem. The model consists of constitutive relationship, damage criterion and damage evolvement. This cohesive model was implemented in the explicit integration scheme with the commercial finite element software ABAQUS using the user defined element subroutine (VUEL). The model was used to predict the delamination propagation in the end notched flexure test (ENF) of domestic carbon fiber/resin composite CCF300/5428. The result shows that this cohesive element is effective to analysis the delamination in the composite laminates.
A new type of zero-thickness cohesive element model is proposed to study the composite interlaminar damage, which can accurately predict the delamination propagation of mode Ⅱ problem. The model consists of constitutive relationship, damage criterion and damage evolvement. This cohesive model was implemented in the explicit integration scheme with the commercial finite element software ABAQUS using the user defined element subroutine (VUEL). The model was used to predict the delamination propagation in the end notched flexure test (ENF) of domestic carbon fiber/resin composite CCF300/5428. The result shows that this cohesive element is effective to analysis the delamination in the composite laminates.
2012, (5): 157-163.
Abstract:
The tests on T700/TDE85 unidirectional laminates single-lap joints (SLJ) with defect and no defect in the adhesive layer under the uniaxial tensile loading were performed. Two different types of joints were designed and analyzed. According to the experimental results, failure modes of two kinds of joints were characterized and load-displacement curves were compared. It is appeared that interfacial failure is the major failure mode and the joint strength is slightly affected by defects with the small size in the adhesive layer. For investigating failure mechanism of joints, a finite element simulation was carried out to analyze the failure behavior and the peel/shear stress fields along the adhesive layer interface for the joints. It is found that the joint strength decreases with the decreasing length of defect location from the overlap end, and effect of length of defect location from the overlap end within 2.5 mm on the joint strength is more greatly. In addition, the joint strength decreases with the increasing of defect area, and area fraction of defect along the overlap zone within 4.4% has a little influence on the joint strength. The computational results are in good agreement with the experimental results.
The tests on T700/TDE85 unidirectional laminates single-lap joints (SLJ) with defect and no defect in the adhesive layer under the uniaxial tensile loading were performed. Two different types of joints were designed and analyzed. According to the experimental results, failure modes of two kinds of joints were characterized and load-displacement curves were compared. It is appeared that interfacial failure is the major failure mode and the joint strength is slightly affected by defects with the small size in the adhesive layer. For investigating failure mechanism of joints, a finite element simulation was carried out to analyze the failure behavior and the peel/shear stress fields along the adhesive layer interface for the joints. It is found that the joint strength decreases with the decreasing length of defect location from the overlap end, and effect of length of defect location from the overlap end within 2.5 mm on the joint strength is more greatly. In addition, the joint strength decreases with the increasing of defect area, and area fraction of defect along the overlap zone within 4.4% has a little influence on the joint strength. The computational results are in good agreement with the experimental results.
2012, (5): 164-170.
Abstract:
The tightening characteristic of threaded fasteners made of C/SiC ceramic matrix composite at room temperature was investigated. Through experiment the relationship between torque and clamping force was measured during tightening and loosening process, meanwhile, the loss rate of clamping force in short or long time was recorded and the condition of wear on the thread surface was observed using microscope. In addition, the effect of material’s nonlinear tensile behavior on the tightening state was also analyzed. The results indicate that there is an approximately linear relationship between clamping force and tightening or loosening torque, and the average friction coefficients of thread and bearing surfaces are 0.52 and 0.46, respectively. As the tightening torque increasing, some wear abrasion occurs on the thread surfaces which, however, will weaken the effect of embedment process between engaged threads, and hence reduces the loss rate of clamping force and promotes its stability after assembly. After proper pre-tension treatment on the bolt in order to increase the elastic limit of the material, the anti-loosening capacity of the fastener can be improved.
The tightening characteristic of threaded fasteners made of C/SiC ceramic matrix composite at room temperature was investigated. Through experiment the relationship between torque and clamping force was measured during tightening and loosening process, meanwhile, the loss rate of clamping force in short or long time was recorded and the condition of wear on the thread surface was observed using microscope. In addition, the effect of material’s nonlinear tensile behavior on the tightening state was also analyzed. The results indicate that there is an approximately linear relationship between clamping force and tightening or loosening torque, and the average friction coefficients of thread and bearing surfaces are 0.52 and 0.46, respectively. As the tightening torque increasing, some wear abrasion occurs on the thread surfaces which, however, will weaken the effect of embedment process between engaged threads, and hence reduces the loss rate of clamping force and promotes its stability after assembly. After proper pre-tension treatment on the bolt in order to increase the elastic limit of the material, the anti-loosening capacity of the fastener can be improved.
2012, (5): 171-178.
Abstract:
Residual compressive strength and compression-compression fatigue tests of T300/QY8911 laminates with low velocity impact damage were studied. The damage characteristic of impacted laminates was measured by visual check and ultrasonic C-scan. Damage propagation in compression-compression fatigue test was measured in detail. The relationship between damage area, compressive strength after impact (CAI) and impact energy was discussed. The major damage mechanism of damaged composites under compressive or compression-compression fatigue load was also analyzed. The results show that low velocity impact damage has a great effect on the compressive strength and fatigue performance of laminates, residual compressive strength reduces by 65% when the laminates is impacted by energy of 3.75 J/mm. The damage propagation under compression-compression fatigue load can divide in two stages, on the first 60% of fatigue life, damage grows slowly; and on the rest of fatigue life, damage has a rapid growth.
Residual compressive strength and compression-compression fatigue tests of T300/QY8911 laminates with low velocity impact damage were studied. The damage characteristic of impacted laminates was measured by visual check and ultrasonic C-scan. Damage propagation in compression-compression fatigue test was measured in detail. The relationship between damage area, compressive strength after impact (CAI) and impact energy was discussed. The major damage mechanism of damaged composites under compressive or compression-compression fatigue load was also analyzed. The results show that low velocity impact damage has a great effect on the compressive strength and fatigue performance of laminates, residual compressive strength reduces by 65% when the laminates is impacted by energy of 3.75 J/mm. The damage propagation under compression-compression fatigue load can divide in two stages, on the first 60% of fatigue life, damage grows slowly; and on the rest of fatigue life, damage has a rapid growth.
2012, (5): 179-183.
Abstract:
In order to understand the fatigue characteristics of the carbon fiber yarn and the residual strength of the carbon fiber yarn after fatigue loading, an experiment program was designed and conducted under the static and fatigue loading conditions. The test data was used to establish a micromechanics analysis model for analyzing the fatigue characteristics of carbon fiber composite materials. The stress-life (S-N) curve of the carbon fiber yarn was fitted by the least squares method. A static tension experiment was conducted using carbon fiber yarn after fatigue loading to set up the expression of the residual strength model. The experimental results show that the conditional fatigue limit of the carbon fiber yarn is 80.47% of the static tension strength. Carbon fiber yarn going through a certain number of tension-tension fatigue loading cycles can increase its strength. The residual strength of the carbon fiber yarn increases firstly and then decreases with the increasing of fatigue loading cycles.
In order to understand the fatigue characteristics of the carbon fiber yarn and the residual strength of the carbon fiber yarn after fatigue loading, an experiment program was designed and conducted under the static and fatigue loading conditions. The test data was used to establish a micromechanics analysis model for analyzing the fatigue characteristics of carbon fiber composite materials. The stress-life (S-N) curve of the carbon fiber yarn was fitted by the least squares method. A static tension experiment was conducted using carbon fiber yarn after fatigue loading to set up the expression of the residual strength model. The experimental results show that the conditional fatigue limit of the carbon fiber yarn is 80.47% of the static tension strength. Carbon fiber yarn going through a certain number of tension-tension fatigue loading cycles can increase its strength. The residual strength of the carbon fiber yarn increases firstly and then decreases with the increasing of fatigue loading cycles.
2012, (5): 184-190.
Abstract:
The optimization of first natural frequency of composite laminate was carried out in FEA software under Four-Edge-Simple-Support and Four-Edge-Fixing-Support boundary conditions, while the ply angles of every single layer of the laminate were confirmed as design variables. The result indicates that fundamental frequency under two boundary conditions is improved by 4.9% and 16.2%, respectively. The failure intensity of the structure before and after optimization was also analyzed comparatively. Then, the optimization method was applied in composite grid-structure aerofoil box of pilotless aircraft with the ply angles of 24 single layers of skin and ribs confirmed as design variables, and the results indicate that the fundamental frequency is improved by 10.6%. At the same time, the load capacity of the wing after optimization is improved to some degree.
The optimization of first natural frequency of composite laminate was carried out in FEA software under Four-Edge-Simple-Support and Four-Edge-Fixing-Support boundary conditions, while the ply angles of every single layer of the laminate were confirmed as design variables. The result indicates that fundamental frequency under two boundary conditions is improved by 4.9% and 16.2%, respectively. The failure intensity of the structure before and after optimization was also analyzed comparatively. Then, the optimization method was applied in composite grid-structure aerofoil box of pilotless aircraft with the ply angles of 24 single layers of skin and ribs confirmed as design variables, and the results indicate that the fundamental frequency is improved by 10.6%. At the same time, the load capacity of the wing after optimization is improved to some degree.
2012, (5): 191-195.
Abstract:
The multi-field coupling relationship in curing process was analyzed according to the problem of process-induced deformation of the composite part prepared in autoclave. Finite element analysis model of curing process of the composite part was developed with mould effect considered. Based on the FEA model, effects of the material, thickness and form of the tool on the process-induced deformation of the part were studied. The results show that the mould has a great effect on the process-induced deformation. The CTE mismatch between the part and the mould affects spring-in angle of the part. The difference of thickness of the tool causes different spring-in angle. The deformation of the part prepared with female mould is less than that of male mould and the direction of deformation is opposite.
The multi-field coupling relationship in curing process was analyzed according to the problem of process-induced deformation of the composite part prepared in autoclave. Finite element analysis model of curing process of the composite part was developed with mould effect considered. Based on the FEA model, effects of the material, thickness and form of the tool on the process-induced deformation of the part were studied. The results show that the mould has a great effect on the process-induced deformation. The CTE mismatch between the part and the mould affects spring-in angle of the part. The difference of thickness of the tool causes different spring-in angle. The deformation of the part prepared with female mould is less than that of male mould and the direction of deformation is opposite.
2012, (5): 196-202.
Abstract:
For improving the ability of fiber reinforced plastic blades, especially for the maximal bending moment of the blade root, the theory of genetic algorithm(GA) was studied and applied in the optimization of the root laminate of composite blades. In allusion to the separate characteristic of the lamination shell design parameter, the integer code strategy suitable for the GA optimizing design of composite lamination shells was proposed. In analyzing the structural intensity of laminated shells, the fitness function of GA was established to optimize the structure intensity. Referencing a number of layup rules, under the condition of four different directions of the ply angles, the stacking sequence of the blade root was optimized. The result shows that there are many advantages in dealing with disperse problem, and the method is reliable and feasible.
For improving the ability of fiber reinforced plastic blades, especially for the maximal bending moment of the blade root, the theory of genetic algorithm(GA) was studied and applied in the optimization of the root laminate of composite blades. In allusion to the separate characteristic of the lamination shell design parameter, the integer code strategy suitable for the GA optimizing design of composite lamination shells was proposed. In analyzing the structural intensity of laminated shells, the fitness function of GA was established to optimize the structure intensity. Referencing a number of layup rules, under the condition of four different directions of the ply angles, the stacking sequence of the blade root was optimized. The result shows that there are many advantages in dealing with disperse problem, and the method is reliable and feasible.
2012, (5): 203-208.
Abstract:
Based on theories of Darcy-law, micro-element and the fiber spreading, this paper extended the pin-assisted melt impregnation theory which traditionally built for single pin, to multi pins-assisted melt impregnation, in particular for the high viscosity thermoplastic resin. The equation in terms of all of influence factors for multi pins-assisted melt impregnation was developed. The theoretical prediction calculated with assigned parameters was in accordance with the experimental data reported. The results show: pins arrangement for the fiber spreading should be in zigzag as the horizontally-arranged pins has less spread effect; as the fiber tension will raise greatly with adding the number of impregnation pins, which increases the fiber break risk, the number of impregnation pins ought to be 3~5.
Based on theories of Darcy-law, micro-element and the fiber spreading, this paper extended the pin-assisted melt impregnation theory which traditionally built for single pin, to multi pins-assisted melt impregnation, in particular for the high viscosity thermoplastic resin. The equation in terms of all of influence factors for multi pins-assisted melt impregnation was developed. The theoretical prediction calculated with assigned parameters was in accordance with the experimental data reported. The results show: pins arrangement for the fiber spreading should be in zigzag as the horizontally-arranged pins has less spread effect; as the fiber tension will raise greatly with adding the number of impregnation pins, which increases the fiber break risk, the number of impregnation pins ought to be 3~5.
2012, (5): 209-214.
Abstract:
The in situ properties of components including the epoxy matrix, the carbon fiber and the interlayer of the carbon fiber/epoxy composites were examined by the nanoindentation. The hardness, Young’s modulus and creep behavior of the components in the composites were obtained. The results show that the hardness and Young’s modulus have a gradient variation from the epoxy matrix to carbon fiber. Compared with the intrinsical value, the in situ Young’s modulus of the fiber has a decline, and the Young’s modulus of the matrix exhibits an enhancement. The in situ properties are influenced by the surface residual stress due to mechanical grinding of the specimen and the interaction of the components of the composites. Moreover, a remarkable change of creep behavior at the transition zone from the fiber to the epoxy matrix is found in the present nanoindentation tests.
The in situ properties of components including the epoxy matrix, the carbon fiber and the interlayer of the carbon fiber/epoxy composites were examined by the nanoindentation. The hardness, Young’s modulus and creep behavior of the components in the composites were obtained. The results show that the hardness and Young’s modulus have a gradient variation from the epoxy matrix to carbon fiber. Compared with the intrinsical value, the in situ Young’s modulus of the fiber has a decline, and the Young’s modulus of the matrix exhibits an enhancement. The in situ properties are influenced by the surface residual stress due to mechanical grinding of the specimen and the interaction of the components of the composites. Moreover, a remarkable change of creep behavior at the transition zone from the fiber to the epoxy matrix is found in the present nanoindentation tests.
2012, (5): 215-221.
Abstract:
The localized deformation of matrix plays an important role in determining the failure process of composites. In the current work, based on the finite element analysis, a proper elasto-plastic constitutive model considering the softening after yielding was introduced using the user-defined material mechanical behavior (UMAT) subroutine. Then the evolution of the localized deformation of matrix during the unidirectional tensile test of the fiber/epoxy composites was presented. The effect of the post-yield softening character of the polymer matrix on the loading transfer in the fiber/epoxy composites was studied. The results show that the stress distributions of fiber and the plastic deformation of matrix are nonuniform. The localized deformation of matrix reduces the degree of the stress concentration of the adjacent fiber. The range of the stress concentration in adjacent fiber becomes wider, while the stress concentration degree degrades, with the inter-fiber spacing increasing.
The localized deformation of matrix plays an important role in determining the failure process of composites. In the current work, based on the finite element analysis, a proper elasto-plastic constitutive model considering the softening after yielding was introduced using the user-defined material mechanical behavior (UMAT) subroutine. Then the evolution of the localized deformation of matrix during the unidirectional tensile test of the fiber/epoxy composites was presented. The effect of the post-yield softening character of the polymer matrix on the loading transfer in the fiber/epoxy composites was studied. The results show that the stress distributions of fiber and the plastic deformation of matrix are nonuniform. The localized deformation of matrix reduces the degree of the stress concentration of the adjacent fiber. The range of the stress concentration in adjacent fiber becomes wider, while the stress concentration degree degrades, with the inter-fiber spacing increasing.
2012, (5): 222-229.
Abstract:
Uniaxial tensile experiments of yarns and textile reinforced concrete (TRC) plates were carried out to study the stress-strain relationship of the epoxy resin-impregnated textile. The experimental results show that even if the carbon fiber yarn is impregnated with the epoxy resin, its tensile strength is not fully utilized. Besides some nonlinear characteristic of its stress-strain curve after the tensile stress of the yarn reaching about 80% of its ultimate strength, its stress-strain relationship is almost linear when the carbon fiber yarn is tensioned alone. Assume that only the textile bears the load after fine grained concrete cracking, and thus the stress-strain relationship of the carbon fiber yarn, which was obtained from the curves of the load-deformation with uniaxial tensile test of TRC-thin plate specimens, could be reasonably simplified as the bilinear form, and the corresponding control parameters of the textile in this study were presented. Based on the flexural calculation theory and using the tensile model of the yarn proposed in this paper, the obtained calculated values of two series of flexural members coincide well with their experimental values.
Uniaxial tensile experiments of yarns and textile reinforced concrete (TRC) plates were carried out to study the stress-strain relationship of the epoxy resin-impregnated textile. The experimental results show that even if the carbon fiber yarn is impregnated with the epoxy resin, its tensile strength is not fully utilized. Besides some nonlinear characteristic of its stress-strain curve after the tensile stress of the yarn reaching about 80% of its ultimate strength, its stress-strain relationship is almost linear when the carbon fiber yarn is tensioned alone. Assume that only the textile bears the load after fine grained concrete cracking, and thus the stress-strain relationship of the carbon fiber yarn, which was obtained from the curves of the load-deformation with uniaxial tensile test of TRC-thin plate specimens, could be reasonably simplified as the bilinear form, and the corresponding control parameters of the textile in this study were presented. Based on the flexural calculation theory and using the tensile model of the yarn proposed in this paper, the obtained calculated values of two series of flexural members coincide well with their experimental values.
2012, (5): 230-235.
Abstract:
The deep-sea environment was simulated through pressure vessels with nitrogen pressing system, and the seawater absorption data of glass fiber reinforced epoxy resin composite (GF/CYD-128) laminates under different pressures was obtained by weighing method to investigate the seawater absorption behavior of GF/CYD-128 laminates in the deep sea environment. The results show that the saturated seawater absorption of GF/CYD-128 laminates firstly decreases with the seawater pressure then increases with the increasing pressure. The saturated seawater absorption of GF/CYD-128 laminates deceases to the minimum value at the pressure of 2.5 MPa. The relationship between the saturated seawater absorption and the seawater pressure can be depicted by the quadratic polynomials. The seawater absorption behavior of GF/CYD-128 laminates at the deep-sea enviroment is non-Fick, however, it can be simulated by the Langmuir-type model. The seawater absorption behavior of GF/CYD-128 laminates under the deep-sea pressure is successfully predicted by the Langmuir-type model.
The deep-sea environment was simulated through pressure vessels with nitrogen pressing system, and the seawater absorption data of glass fiber reinforced epoxy resin composite (GF/CYD-128) laminates under different pressures was obtained by weighing method to investigate the seawater absorption behavior of GF/CYD-128 laminates in the deep sea environment. The results show that the saturated seawater absorption of GF/CYD-128 laminates firstly decreases with the seawater pressure then increases with the increasing pressure. The saturated seawater absorption of GF/CYD-128 laminates deceases to the minimum value at the pressure of 2.5 MPa. The relationship between the saturated seawater absorption and the seawater pressure can be depicted by the quadratic polynomials. The seawater absorption behavior of GF/CYD-128 laminates at the deep-sea enviroment is non-Fick, however, it can be simulated by the Langmuir-type model. The seawater absorption behavior of GF/CYD-128 laminates under the deep-sea pressure is successfully predicted by the Langmuir-type model.
2012, (5): 236-243.
Abstract:
The interfacial debonding shear strength and ultimate strength of short-cut shape memory alloy (SMA) reinforced epoxy composites were determined based on SMA single fiber pull-out test and uniaxial tensile test, respectively. An algorithm for the automatic generation of unidirectional random distribution short-cut SMA fiber/epoxy composites was developed, using Monte-Carlo method and boundary condition control equation via algorithmic processor description language (APDL). The interfacial debonding process between SMA fibers and epoxy matrix was simulated by means of exponential cohesive zone model (CZM). The results indicate that the macroscopic elastic modulus gradually reduce with the decrease of fiber slendevness ratio and the overall elastic modulus of composite are enhanced owing to the driving of SMA fiber, under the same fiber volume.
The interfacial debonding shear strength and ultimate strength of short-cut shape memory alloy (SMA) reinforced epoxy composites were determined based on SMA single fiber pull-out test and uniaxial tensile test, respectively. An algorithm for the automatic generation of unidirectional random distribution short-cut SMA fiber/epoxy composites was developed, using Monte-Carlo method and boundary condition control equation via algorithmic processor description language (APDL). The interfacial debonding process between SMA fibers and epoxy matrix was simulated by means of exponential cohesive zone model (CZM). The results indicate that the macroscopic elastic modulus gradually reduce with the decrease of fiber slendevness ratio and the overall elastic modulus of composite are enhanced owing to the driving of SMA fiber, under the same fiber volume.
2012, (5): 244-248.
Abstract:
The non-contact electric eddy current displacement sensor system was applied to real-time monitor the preform thickness change throughout the vacuum assisted resin infusion (VARI) process. The compaction behavior of the preform during the VARI process was discussed. And the effect of the post-filling time on the preform thickness and the fiber volume fraction was studied. The result indicates that the compaction behavior of the preform can be divided into three stages: the preform thickness increases rapidly when the resin is infused; the perform thickness is almost not changed during the post-filling; the preform thickness decreases rapidly and drives to a stable value after that the resin-inlet is clamped. The final part thickness varies with the post-filling time, and the variation tendency is similar to a sinusoid. The fiber volume fraction is the lowest and decreases 1.7% compared with that without post-filling, when the post-filling time is about 10 min. And the fiber volume fraction is the greatest and increases 1.6% compared with that without post-filling, when the post filling time is about 40 min.
The non-contact electric eddy current displacement sensor system was applied to real-time monitor the preform thickness change throughout the vacuum assisted resin infusion (VARI) process. The compaction behavior of the preform during the VARI process was discussed. And the effect of the post-filling time on the preform thickness and the fiber volume fraction was studied. The result indicates that the compaction behavior of the preform can be divided into three stages: the preform thickness increases rapidly when the resin is infused; the perform thickness is almost not changed during the post-filling; the preform thickness decreases rapidly and drives to a stable value after that the resin-inlet is clamped. The final part thickness varies with the post-filling time, and the variation tendency is similar to a sinusoid. The fiber volume fraction is the lowest and decreases 1.7% compared with that without post-filling, when the post-filling time is about 10 min. And the fiber volume fraction is the greatest and increases 1.6% compared with that without post-filling, when the post filling time is about 40 min.
