2014 Vol. 31, No. 3
2014, 31(3): 533-540.
Abstract:
Based on the three-dimensional multi-physical field governing equation of the composites, the thermal and mechanical responses, such as temperature field, displacement field, pore pressure and resin residual ratio of the silica/phenolic composites during volume ablation process were studied by finite element method. The calculation results reveal that the predicted temperature field and displacement field are in good agreement with the experimental results. It is found that the peak value of pore pressure in the solid material appears at the initial thermal decomposition region, while the peak value of elastic stress is in the original material near thermal decomposition layer.
Based on the three-dimensional multi-physical field governing equation of the composites, the thermal and mechanical responses, such as temperature field, displacement field, pore pressure and resin residual ratio of the silica/phenolic composites during volume ablation process were studied by finite element method. The calculation results reveal that the predicted temperature field and displacement field are in good agreement with the experimental results. It is found that the peak value of pore pressure in the solid material appears at the initial thermal decomposition region, while the peak value of elastic stress is in the original material near thermal decomposition layer.
2014, 31(3): 541-549.
Abstract:
To improve the mechanical properties and thermal insulation properties of glazed hollow bead/cement foamed thermal insulation composite, the modified physical foam was added in foamed thermal insulation composite to reduce the density and thermal conductivity of the composite, and modified fibers were adopted to reinforce the performance of foamed thermal insulation composite. The mechanical properties and water resistance of fiber reinforced foamed thermal insulation composite were studied, and the internal micro-morphology of samples was observed by SEM. The improving mechanism of modified foam and modified fibers on foamed thermal insulation composite were explored. The results show that, mixing foam decreases the density and thermal conductivity of foamed thermal insulation composite significantly, when the content of foam is 1.05 mL/g, the density and the thermal conductivity of samples are 186 kg/m3 and 0.056 W/(m·K) respectively. The modified foam can effectively improve the strength and softening coefficient of foamed thermal insulation composite, compared with samples mixed with latex powder, the flexural strength, compressive strength and softening coefficient of samples mixed with modified foam increase by 21.05%, 21.43% and 13.56% respectively. Modified fibers can significantly improve the strength and softening coefficient of samples, the flexural strength, compressive strength and softening coefficient of samples mixed with modified fibers increase by 25.93%, 13.51% and 8.33% respectively than the samples mixed with unmodified fibers.
To improve the mechanical properties and thermal insulation properties of glazed hollow bead/cement foamed thermal insulation composite, the modified physical foam was added in foamed thermal insulation composite to reduce the density and thermal conductivity of the composite, and modified fibers were adopted to reinforce the performance of foamed thermal insulation composite. The mechanical properties and water resistance of fiber reinforced foamed thermal insulation composite were studied, and the internal micro-morphology of samples was observed by SEM. The improving mechanism of modified foam and modified fibers on foamed thermal insulation composite were explored. The results show that, mixing foam decreases the density and thermal conductivity of foamed thermal insulation composite significantly, when the content of foam is 1.05 mL/g, the density and the thermal conductivity of samples are 186 kg/m3 and 0.056 W/(m·K) respectively. The modified foam can effectively improve the strength and softening coefficient of foamed thermal insulation composite, compared with samples mixed with latex powder, the flexural strength, compressive strength and softening coefficient of samples mixed with modified foam increase by 21.05%, 21.43% and 13.56% respectively. Modified fibers can significantly improve the strength and softening coefficient of samples, the flexural strength, compressive strength and softening coefficient of samples mixed with modified fibers increase by 25.93%, 13.51% and 8.33% respectively than the samples mixed with unmodified fibers.
2014, 31(3): 550-555.
Abstract:
In order to study variation of the thermal conductivity of the diamond/Cu composite prepared by high pressure infiltration at low temperature zone, the diamond/Cu composites with different diamond particle sizes (100 μm, 250 μm and 400 μm) were separately prepared by high pressure infiltration (HPF) method, the scanning calorimetry was used to analyze and evaluate the thermal conductivity of the diamond/Cu composites at low temperature, and SEM was used to analyze the microstructure of the composites. The results show that the thermal resistance of diamond particles in the heat transfer of grain boundary is far less than that in the interfacial heat transfer, for part of the diamond in the diamond/Cu composites prepared by high pressure infiltration becomes involved in polycrystalline reaction. The inner deformation and crushing of diamond particles result in more defects under high pressure infiltration condition, and the heat transfer with phonons as the main heat carrier at low temperatures of 100-150 K is sensitive to such defects as crack and clearance. Therefore, the thermal conductivity of diamond/Cu composites prepared by high pressure infiltration method is lower than that of the composites prepared by common pressure infiltration (PF) method at low temperature.
In order to study variation of the thermal conductivity of the diamond/Cu composite prepared by high pressure infiltration at low temperature zone, the diamond/Cu composites with different diamond particle sizes (100 μm, 250 μm and 400 μm) were separately prepared by high pressure infiltration (HPF) method, the scanning calorimetry was used to analyze and evaluate the thermal conductivity of the diamond/Cu composites at low temperature, and SEM was used to analyze the microstructure of the composites. The results show that the thermal resistance of diamond particles in the heat transfer of grain boundary is far less than that in the interfacial heat transfer, for part of the diamond in the diamond/Cu composites prepared by high pressure infiltration becomes involved in polycrystalline reaction. The inner deformation and crushing of diamond particles result in more defects under high pressure infiltration condition, and the heat transfer with phonons as the main heat carrier at low temperatures of 100-150 K is sensitive to such defects as crack and clearance. Therefore, the thermal conductivity of diamond/Cu composites prepared by high pressure infiltration method is lower than that of the composites prepared by common pressure infiltration (PF) method at low temperature.
2014, 31(3): 556-562.
Abstract:
TiB2-TiC-Fe2Ti composites were prepared by plasma heating synthesis with Ti, B4C and Fe powders as the raw materials. The phase constitution, microstructure, micro-hardness and fracture morphology of TiB2-TiC-Fe2Ti were investigated. The experimental results show that the reaction products are composed of TiB2, TiC, Fe2Ti and a small amount of Fe3C. The TiB2, TiC and Fe2Ti phases distribute homogeneously and present in different shapes, in which TiB2 phases are in hexagonal or rectangular shapes and TiC in spherical ones, while Fe2Ti phases existing in the gaps between TiC and TiB2 phases promote the combination of phases. As the heating rate and the cooling rate of plasma beam are fast, the time of the grain growth would decrease and the fine structures can be obtained. With the increasing current, the heat will be higher to promote the growing of TiB2and TiC, which would bond to each other tightly.
TiB2-TiC-Fe2Ti composites were prepared by plasma heating synthesis with Ti, B4C and Fe powders as the raw materials. The phase constitution, microstructure, micro-hardness and fracture morphology of TiB2-TiC-Fe2Ti were investigated. The experimental results show that the reaction products are composed of TiB2, TiC, Fe2Ti and a small amount of Fe3C. The TiB2, TiC and Fe2Ti phases distribute homogeneously and present in different shapes, in which TiB2 phases are in hexagonal or rectangular shapes and TiC in spherical ones, while Fe2Ti phases existing in the gaps between TiC and TiB2 phases promote the combination of phases. As the heating rate and the cooling rate of plasma beam are fast, the time of the grain growth would decrease and the fine structures can be obtained. With the increasing current, the heat will be higher to promote the growing of TiB2and TiC, which would bond to each other tightly.
2014, 31(3): 563-568.
Abstract:
In order to investigate the relationship between dielectric properties of quartz fiber/polyimide (KH308) composites and fiber volume fraction of composites, frequency, temperature and water absorption, four kinds of quartz fiber reinforced KH308 composites with different fiber volume fractions were prepared by hot pressing technology. Dielectric constant and dielectric loss of these composites were characterized by high Q resonance cavity method in different conditions. The results show that dielectric constant of quartz fiber/KH308 composites increases with increasing fiber content, and the dielectric loss basically does not vary with fiber content. At 7-18 GHz, dielectric constant and dielectric loss of the composites do not vary with frequency. The dielectric constant increases with temperature slowly, while the dielectric loss decreases with increasing temperature at 25-300℃. Dielectric constant and dielectric loss of the composites increase with water content. Fiber/KH308 composites with low dielectric constant (ε<4) and low dielectric loss (tanδ<0.1), can satisfy the requirements of dielectric properties of the missile radome wave-transparent materials.
In order to investigate the relationship between dielectric properties of quartz fiber/polyimide (KH308) composites and fiber volume fraction of composites, frequency, temperature and water absorption, four kinds of quartz fiber reinforced KH308 composites with different fiber volume fractions were prepared by hot pressing technology. Dielectric constant and dielectric loss of these composites were characterized by high Q resonance cavity method in different conditions. The results show that dielectric constant of quartz fiber/KH308 composites increases with increasing fiber content, and the dielectric loss basically does not vary with fiber content. At 7-18 GHz, dielectric constant and dielectric loss of the composites do not vary with frequency. The dielectric constant increases with temperature slowly, while the dielectric loss decreases with increasing temperature at 25-300℃. Dielectric constant and dielectric loss of the composites increase with water content. Fiber/KH308 composites with low dielectric constant (ε<4) and low dielectric loss (tanδ<0.1), can satisfy the requirements of dielectric properties of the missile radome wave-transparent materials.
2014, 31(3): 569-577.
Abstract:
The modified nano hydroxyapatite (HA)/polylactic acid(PLA)-poly (butylenes adipate-co-terephthalate)(PBAT) blends were prepared by melting co-extrusion. The crystallinity, rheological behavior, mechanical impact properties and surface structure of the modified nano HA/PLA-PBAT were studied respectively with differential scanning calorimetry (DSC), rheometer, material testing machine and scanning electron microscope (SEM). The DSC results show that the glass transition temperature of HA/PLA-PBAT blends rise first and decline finally as the modified nano HA content increases. The cold crystallization temperature decreases gradually and it reduces by 13℃. The crystallization ability of HA/PLA-PBAT is improved by increasing the crystallinity from 24.33% to 33.47%. The viscosity of HA /PLA-PBAT blends which is a non-Newtonian decrease when the shear rate rises. When the mass ratio of the modified nano HA increases, the storage modulus and the loss modulus of HA/PLA-PBAT blends gradually decrease; the yield strength, the notched impact strength and the tensile strength increase first then decrease, reaching the mass ratio of modified nano HA that is added to 2%(80/20/2). The SEM results show that a little modified nano HA could be dispersed evenly in the blends, and it could enhance the toughness of the blend system significantly.
The modified nano hydroxyapatite (HA)/polylactic acid(PLA)-poly (butylenes adipate-co-terephthalate)(PBAT) blends were prepared by melting co-extrusion. The crystallinity, rheological behavior, mechanical impact properties and surface structure of the modified nano HA/PLA-PBAT were studied respectively with differential scanning calorimetry (DSC), rheometer, material testing machine and scanning electron microscope (SEM). The DSC results show that the glass transition temperature of HA/PLA-PBAT blends rise first and decline finally as the modified nano HA content increases. The cold crystallization temperature decreases gradually and it reduces by 13℃. The crystallization ability of HA/PLA-PBAT is improved by increasing the crystallinity from 24.33% to 33.47%. The viscosity of HA /PLA-PBAT blends which is a non-Newtonian decrease when the shear rate rises. When the mass ratio of the modified nano HA increases, the storage modulus and the loss modulus of HA/PLA-PBAT blends gradually decrease; the yield strength, the notched impact strength and the tensile strength increase first then decrease, reaching the mass ratio of modified nano HA that is added to 2%(80/20/2). The SEM results show that a little modified nano HA could be dispersed evenly in the blends, and it could enhance the toughness of the blend system significantly.
2014, 31(3): 578-583.
Abstract:
Methyl methacrylate (MMA) was grafted onto bamboo flour (BF) surface via the method of atom transfer radical polymerization with activators generated by electron transfer (AGET ATRP). The effects on the rheological behavior of BF/polyethylene terephthalate glycol (PETG) composite before and after being grafted by BF were investigated using haake minilab Ⅱ rheometer and rotate rheometer. The capillary rheometer results show that BF/PETG composites display pseudo plastic fluid, and all specimens exhibit shear thinning behavior. Strain scanning results show that compared to that without modification, the stain range of the linear visco-elastic zone of BF/PETG composites with graft modification of BF becomes wider; The frequency scan results indicate that graft modification of BF can accelerate the dispersion of BF into PETG matrix.
Methyl methacrylate (MMA) was grafted onto bamboo flour (BF) surface via the method of atom transfer radical polymerization with activators generated by electron transfer (AGET ATRP). The effects on the rheological behavior of BF/polyethylene terephthalate glycol (PETG) composite before and after being grafted by BF were investigated using haake minilab Ⅱ rheometer and rotate rheometer. The capillary rheometer results show that BF/PETG composites display pseudo plastic fluid, and all specimens exhibit shear thinning behavior. Strain scanning results show that compared to that without modification, the stain range of the linear visco-elastic zone of BF/PETG composites with graft modification of BF becomes wider; The frequency scan results indicate that graft modification of BF can accelerate the dispersion of BF into PETG matrix.
2014, 31(3): 584-590.
Abstract:
In order to investigate the mechanisms of matrix damage and sub-surface damage in carbon fiber reinforced resin matrix composite, cutting process simulation model was developed based on macroscopic anisotropy. Hashin-Damage failure model was adopted. Through defining ultimate stresses of fiber tension cracking and fiber compression buckling, ultimate stresses of matrix longitudinal tensile and shear damage, a dynamic physics simulation model of composite was established. The reasonability was validated by comparison cutting force between simulation results and experimental data of cutting force. By analyzing cracking and crushing phenomenon of matrix at 0° and 90° fiber orientation, it shows that the matrix cracking orientation substantially parallel to the fiber orientation, and matrix crushing mainly happened around the cutting tool tip when steady state condition is reached. The influence of fiber orientation on sub-surface damage was studied. It shows that the cracking of sub-surface damage value increases with the increase of fiber orientation angle.
In order to investigate the mechanisms of matrix damage and sub-surface damage in carbon fiber reinforced resin matrix composite, cutting process simulation model was developed based on macroscopic anisotropy. Hashin-Damage failure model was adopted. Through defining ultimate stresses of fiber tension cracking and fiber compression buckling, ultimate stresses of matrix longitudinal tensile and shear damage, a dynamic physics simulation model of composite was established. The reasonability was validated by comparison cutting force between simulation results and experimental data of cutting force. By analyzing cracking and crushing phenomenon of matrix at 0° and 90° fiber orientation, it shows that the matrix cracking orientation substantially parallel to the fiber orientation, and matrix crushing mainly happened around the cutting tool tip when steady state condition is reached. The influence of fiber orientation on sub-surface damage was studied. It shows that the cracking of sub-surface damage value increases with the increase of fiber orientation angle.
2014, 31(3): 591-596.
Abstract:
Effect of block copolymer of styrene and butadiene (SBS), maleic anhydride grafted SBS (MAH-SBS) and nano-CaCO3 on PC-ABS blends properties were studied, and the micro structure was observed by SEM. It is found that when PC:ABS=1:1, the comprehensive properties of PC-ABS is the best; only 4wt% nano-CaCO3 is added, the tensile strength of nano-CaCO3/PC-ABS is increased obviously but the impact strength is increased slightly. It is invalid when SBS is used alone. If MAH-SBS is used alone, the impact strength of MAH-SBS/PC-ABS is increased but the tensile strength is decreased seriously. The mixture of MAH-SBS and nano-CaCO3 have a synergistic effect, the impact strength is increased from 80 kJ/m2 to about 108 kJ/m2 and the tensile strength is improved from 57.0 MPa to about 61.5 MPa.
Effect of block copolymer of styrene and butadiene (SBS), maleic anhydride grafted SBS (MAH-SBS) and nano-CaCO3 on PC-ABS blends properties were studied, and the micro structure was observed by SEM. It is found that when PC:ABS=1:1, the comprehensive properties of PC-ABS is the best; only 4wt% nano-CaCO3 is added, the tensile strength of nano-CaCO3/PC-ABS is increased obviously but the impact strength is increased slightly. It is invalid when SBS is used alone. If MAH-SBS is used alone, the impact strength of MAH-SBS/PC-ABS is increased but the tensile strength is decreased seriously. The mixture of MAH-SBS and nano-CaCO3 have a synergistic effect, the impact strength is increased from 80 kJ/m2 to about 108 kJ/m2 and the tensile strength is improved from 57.0 MPa to about 61.5 MPa.
2014, 31(3): 597-603.
Abstract:
MMT-MDI was obtained by diphenylmethane-4,4'-diisocyanate (MDI) reacted with hydroxyl groups of the acidulated montmorillonite (MMT) surface, then caprolactam (CPL) was brought in to intercalate into the MMT-MDI layers and block on the excess isocyanate end groups, thereby the MMT-MDI-CPL was produced. Next, utilizing prepolymer solution intercalation method, the MMT-MDI layers and the MMT-MDI-CPL could be respectively intercalated by polyamic acid (PAA) in the solvent of dimethylacetamide (DMAC) to prepare the exfoliated nano-MMT/polyimide (PI) composite. Finally, the modified MMT and nano-MMT/PI composite were characterized by inductively coupled plasma optical emission spectrometry (ICP-OES), FTIR, TG, XRD and SEM. The results show that, MDI has been grafted on the hydroxyl groups of MMT surface. The interlayer spacing of MMT is expanded gradually by the modification of MDI, the intercalation and the block of CPL on MMT-MDI. And the XRD and SEM of nano-MMT/PI composite show that MMT in the PI matrix is fully exfoliated.
MMT-MDI was obtained by diphenylmethane-4,4'-diisocyanate (MDI) reacted with hydroxyl groups of the acidulated montmorillonite (MMT) surface, then caprolactam (CPL) was brought in to intercalate into the MMT-MDI layers and block on the excess isocyanate end groups, thereby the MMT-MDI-CPL was produced. Next, utilizing prepolymer solution intercalation method, the MMT-MDI layers and the MMT-MDI-CPL could be respectively intercalated by polyamic acid (PAA) in the solvent of dimethylacetamide (DMAC) to prepare the exfoliated nano-MMT/polyimide (PI) composite. Finally, the modified MMT and nano-MMT/PI composite were characterized by inductively coupled plasma optical emission spectrometry (ICP-OES), FTIR, TG, XRD and SEM. The results show that, MDI has been grafted on the hydroxyl groups of MMT surface. The interlayer spacing of MMT is expanded gradually by the modification of MDI, the intercalation and the block of CPL on MMT-MDI. And the XRD and SEM of nano-MMT/PI composite show that MMT in the PI matrix is fully exfoliated.
2014, 31(3): 604-609.
Abstract:
The morphologies and properties of nano-montmorillonite (MMT)/hydrogenated acrylonitrile butadiene rubber (HNBR) composites fabricated via supercritical carbon dioxide (scCO2) technology and single-handed melt mixing respectively were compared, and the effects of scCO2 processing was examined. The effect of scCO2 processing condition on the dispersion of MMT particles was also investigated. The results of XRD and TEM reveal the effectiveness of scCO2 method in the HNBR composites. ScCO2 processing facilitates the intercalation of rubber molecules into MMT galleries and the interlayer distance reaches 3.93 nm. Meanwhile, the MMT platelets are homogeneously dispersed in the matrices, and the degree of stripping is high. The temperature and pressure of scCO2 processing almost have no effect on MMT dispersion. Compared with original HNBR, the tensile strength of composite obviously improves from 14.4 MPa to 16.3 MPa (melt mixing method) and 19.6 MPa (scCO2 method) respectively, and elongation at break increases slightly. The composite obtained via scCO2 method possesses higher mechanical performances, and it can also maintain good mechanical performances before or after immersed in corrosive medium.
The morphologies and properties of nano-montmorillonite (MMT)/hydrogenated acrylonitrile butadiene rubber (HNBR) composites fabricated via supercritical carbon dioxide (scCO2) technology and single-handed melt mixing respectively were compared, and the effects of scCO2 processing was examined. The effect of scCO2 processing condition on the dispersion of MMT particles was also investigated. The results of XRD and TEM reveal the effectiveness of scCO2 method in the HNBR composites. ScCO2 processing facilitates the intercalation of rubber molecules into MMT galleries and the interlayer distance reaches 3.93 nm. Meanwhile, the MMT platelets are homogeneously dispersed in the matrices, and the degree of stripping is high. The temperature and pressure of scCO2 processing almost have no effect on MMT dispersion. Compared with original HNBR, the tensile strength of composite obviously improves from 14.4 MPa to 16.3 MPa (melt mixing method) and 19.6 MPa (scCO2 method) respectively, and elongation at break increases slightly. The composite obtained via scCO2 method possesses higher mechanical performances, and it can also maintain good mechanical performances before or after immersed in corrosive medium.
2014, 31(3): 610-616.
Abstract:
The flake graphite/polypropylene (PP) and flake graphite/nylon66 (PA66) thermal conductive composites were prepared by twin screw extrusion and injection molding to study the effect of the flake graphite orientation on the thermal conductivity especially thermal conductivity in different directions of flake graphite/PP and flake graphite/PA66 composites. The results were analyzed by SEM and ultrasonic test. The results show that the smaller particle size is, the higher planar orientation degree is, which makes the difference between the planar and vertical thermal conductivity of the composites bigger. The excessive shear of twin screw extruder can destroy lamella structure of flake graphite, influence the formation of the heat conducting network and reduce the thermal conductivity, but improve the uniformity of heat conducting in different directions of the composites. The moderate shear can open the lamellar structure of flake graphite and improve the thermal conductivity of the composites, the injection molding influences the anisotropy of heat conducting of composites at a large degree.
The flake graphite/polypropylene (PP) and flake graphite/nylon66 (PA66) thermal conductive composites were prepared by twin screw extrusion and injection molding to study the effect of the flake graphite orientation on the thermal conductivity especially thermal conductivity in different directions of flake graphite/PP and flake graphite/PA66 composites. The results were analyzed by SEM and ultrasonic test. The results show that the smaller particle size is, the higher planar orientation degree is, which makes the difference between the planar and vertical thermal conductivity of the composites bigger. The excessive shear of twin screw extruder can destroy lamella structure of flake graphite, influence the formation of the heat conducting network and reduce the thermal conductivity, but improve the uniformity of heat conducting in different directions of the composites. The moderate shear can open the lamellar structure of flake graphite and improve the thermal conductivity of the composites, the injection molding influences the anisotropy of heat conducting of composites at a large degree.
2014, 31(3): 617-627.
Abstract:
Nano-Al2O3/epoxy, phenolphthalein polyaryletherketone (PAEK)/epoxy and nano-Al2O3/PAEK/epoxy composites were prepared by mechanical mixing process. The tensile modulus, tensile strength, fracture toughness and thermal stability of the composites were comparatively studied. The results indicate that both nano-Al2O3 and PAEK are homogeneously dispersed in the epoxy martix. In the case of nano-Al2O3/epoxy composites, with the increase of nano-Al2O3 content, the tensile modulus increases monotonously, and the tensile strength increases first then decreases. In the case of PAEK/epoxy composites, the tensile modulus decreases slightly, and the tensile strength does not change significantly. In the case of nano-Al2O3/PAEK/epoxy ternary composites, the tensile modulus and the tensile strength show non-monotonous changes. Both nano-Al2O3 and PAEK can toughen the epoxy more or less. The toughening effect of the ternary composites is more obvious, and the combination of nano-Al2O3 and PAEK exhibits synergistic toughening effect. The high content nano-Al2O3 lowers the initial decomposition temperature of epoxy, while the other fillers improve the thermal stability of epoxy slightly. The glass transition temperature of the epoxy resin is found to be depressed with the fillers.
Nano-Al2O3/epoxy, phenolphthalein polyaryletherketone (PAEK)/epoxy and nano-Al2O3/PAEK/epoxy composites were prepared by mechanical mixing process. The tensile modulus, tensile strength, fracture toughness and thermal stability of the composites were comparatively studied. The results indicate that both nano-Al2O3 and PAEK are homogeneously dispersed in the epoxy martix. In the case of nano-Al2O3/epoxy composites, with the increase of nano-Al2O3 content, the tensile modulus increases monotonously, and the tensile strength increases first then decreases. In the case of PAEK/epoxy composites, the tensile modulus decreases slightly, and the tensile strength does not change significantly. In the case of nano-Al2O3/PAEK/epoxy ternary composites, the tensile modulus and the tensile strength show non-monotonous changes. Both nano-Al2O3 and PAEK can toughen the epoxy more or less. The toughening effect of the ternary composites is more obvious, and the combination of nano-Al2O3 and PAEK exhibits synergistic toughening effect. The high content nano-Al2O3 lowers the initial decomposition temperature of epoxy, while the other fillers improve the thermal stability of epoxy slightly. The glass transition temperature of the epoxy resin is found to be depressed with the fillers.
2014, 31(3): 628-634.
Abstract:
Nanomaterials of Manganese dioxide (MnO2) has been widely researched as the supercapacitors. To improve its charge-discharge performance, the polythiophene/nano MnO2 (PTh/MnO2) composite was synthesized by the method of the in-situ chemical oxidation polymerization to modify the properties of MnO2 in the present work. A series of PTh/MnO2 composites were obtained by changing the component of polythiophene in the composites. Fourier transform infrared spectroscopy(FIIR), X-ray diffractometer(XRD), field emission scanning electron microscope (FE-SEM) and transmission electron microscopy(TEM) were used to characterize the chemical property, crystal structure, and surface morphology in detail. Afterward, the charge-discharge performances of the sealed button batteries were measured using CT001A battery test system, in which PTh/MnO2 composite was used as the negative electrode. The results show that the morphologies of MnO2 and polythiophene in the different PTh/MnO2 composites are various. MnO2 is uniformly distributed in PTh/MnO2 composite when the component of polythiophene is 8 wt%~10 wt%. When the component of polythiophene is pretty high, however, the morphology of MnO2 is affected substantially. Its original nanotubes almost disappear. The charge-discharge property of the buttery is also affected by the ratios of polythiophene in the PTh/MnO2 composites. When the component of polythiophene is 20 wt% after 20 cycles, the capacity of the buttery is highest and reaches to 700 mAh/g. It is higher than that of the buttery in which nano MnO2 was used as the negative electrode. It demonstrates that the presence of polythiophene in PTh/MnO2 could enhance the charge-discharge property of MnO2. The present work could supply the experimental base for the research on the applications of PTh/MnO2 composite as the negative buttery.
Nanomaterials of Manganese dioxide (MnO2) has been widely researched as the supercapacitors. To improve its charge-discharge performance, the polythiophene/nano MnO2 (PTh/MnO2) composite was synthesized by the method of the in-situ chemical oxidation polymerization to modify the properties of MnO2 in the present work. A series of PTh/MnO2 composites were obtained by changing the component of polythiophene in the composites. Fourier transform infrared spectroscopy(FIIR), X-ray diffractometer(XRD), field emission scanning electron microscope (FE-SEM) and transmission electron microscopy(TEM) were used to characterize the chemical property, crystal structure, and surface morphology in detail. Afterward, the charge-discharge performances of the sealed button batteries were measured using CT001A battery test system, in which PTh/MnO2 composite was used as the negative electrode. The results show that the morphologies of MnO2 and polythiophene in the different PTh/MnO2 composites are various. MnO2 is uniformly distributed in PTh/MnO2 composite when the component of polythiophene is 8 wt%~10 wt%. When the component of polythiophene is pretty high, however, the morphology of MnO2 is affected substantially. Its original nanotubes almost disappear. The charge-discharge property of the buttery is also affected by the ratios of polythiophene in the PTh/MnO2 composites. When the component of polythiophene is 20 wt% after 20 cycles, the capacity of the buttery is highest and reaches to 700 mAh/g. It is higher than that of the buttery in which nano MnO2 was used as the negative electrode. It demonstrates that the presence of polythiophene in PTh/MnO2 could enhance the charge-discharge property of MnO2. The present work could supply the experimental base for the research on the applications of PTh/MnO2 composite as the negative buttery.
2014, 31(3): 635-643.
Abstract:
Silica aerogel is hopeful used as thermal insulation material in thermal protection system due to its extremely low thermal conductivity and low density. However, the weakness in mechanical properties has limited its application. By adding ceramic fibers, the strength and toughness of silica aerogel are improved obviously without sacrificing much of its thermal conductivities. Basic mechanical experiments including tension, compression and shear tests were carried out at room temperature for ceramic fiber reinforced silica aerogel composites. The compression tests along in-plane direction of the composite fiber layer at 300℃, 600℃ and 900℃ were also conducted, the microstructure of the samples tested at elevated temperature was analyzed by using SEM. The experimental results reveal that the mechanical properties of the ceramic fiber reinforced silica aerogel composites are transverse isotropic. Both the elastic modulus and the ultimate strength of in-plane samples are about over 28 times higher than those of the out-of-plane samples. The composites show asymmetric elastic modulus for tension and compression. The ratios of tensile modulus to corresponding compression modulus along each direction are 1.60, 1.83 and 0.56 for X, Y and Z directions, respectively. The composite keeps shrinking along thickness direction as temperature increases; the largest shrinkage can be 10.8% at 900℃. The compression properties of the composite layer along in-plane direction at elevated temperature get enhanced with increasing temperature.
Silica aerogel is hopeful used as thermal insulation material in thermal protection system due to its extremely low thermal conductivity and low density. However, the weakness in mechanical properties has limited its application. By adding ceramic fibers, the strength and toughness of silica aerogel are improved obviously without sacrificing much of its thermal conductivities. Basic mechanical experiments including tension, compression and shear tests were carried out at room temperature for ceramic fiber reinforced silica aerogel composites. The compression tests along in-plane direction of the composite fiber layer at 300℃, 600℃ and 900℃ were also conducted, the microstructure of the samples tested at elevated temperature was analyzed by using SEM. The experimental results reveal that the mechanical properties of the ceramic fiber reinforced silica aerogel composites are transverse isotropic. Both the elastic modulus and the ultimate strength of in-plane samples are about over 28 times higher than those of the out-of-plane samples. The composites show asymmetric elastic modulus for tension and compression. The ratios of tensile modulus to corresponding compression modulus along each direction are 1.60, 1.83 and 0.56 for X, Y and Z directions, respectively. The composite keeps shrinking along thickness direction as temperature increases; the largest shrinkage can be 10.8% at 900℃. The compression properties of the composite layer along in-plane direction at elevated temperature get enhanced with increasing temperature.
2014, 31(3): 644-652.
Abstract:
A dispersion system of graphene oxides (GO) nanosheets was prepared by oxidization and ultrasonic treatment. The toughening effect and mechanism of GO nanosheets on cement matrix composites were investigated. GO nanosheets structure was characterized by EDS, FTIR, XRD, SEM and AFM. The results indicate that the oxygen content of GO is 32.3wt%, the thickness of GO nanosheets is about 6 nm and there are many hydroxyl, carboxyl and sulfonic groups on the GO surface. The results of SEM images and mechanical strength indicate that GO can prompt the formation of flower-like hydration crystals and increase the tensile, flexural and compressive strength of the corresponding mortar 65.5%, 60.7%, 38.9% compared with the control samples, respectively, when GO dosage is 0.03wt%. The templating regulation mechanism of GO nanosheets on cement hydration crystals is proposed and the formation of the flower-like hydration crystals is revealed.
A dispersion system of graphene oxides (GO) nanosheets was prepared by oxidization and ultrasonic treatment. The toughening effect and mechanism of GO nanosheets on cement matrix composites were investigated. GO nanosheets structure was characterized by EDS, FTIR, XRD, SEM and AFM. The results indicate that the oxygen content of GO is 32.3wt%, the thickness of GO nanosheets is about 6 nm and there are many hydroxyl, carboxyl and sulfonic groups on the GO surface. The results of SEM images and mechanical strength indicate that GO can prompt the formation of flower-like hydration crystals and increase the tensile, flexural and compressive strength of the corresponding mortar 65.5%, 60.7%, 38.9% compared with the control samples, respectively, when GO dosage is 0.03wt%. The templating regulation mechanism of GO nanosheets on cement hydration crystals is proposed and the formation of the flower-like hydration crystals is revealed.
2014, 31(3): 653-660.
Abstract:
Through the computational and experimental analysis on the modal of C/SiC ceramic matrix composite bolted fastenings, the modal parameters and vibration response characteristics were determined. The influence of tightening torque on the vibration performance of bolted fastenings was researched by sine-sweep vibration of the C/SiC ceramic matrix composite bolted fastenings. The influence of liquid polyborosilazanes (L-PBSZ) on the looseness-proof performances of C/SiC ceramic matrix composite bolted fastenings was measured. The results indicate that the first and the third natural frequency of the calculating modal are consistent with that of the experimental modal, so the finite element analysis method can be used for the vibration response characteristics analysis of C/SiC ceramic matrix composite bolted fastenings. The spectrum signal difference curves of sine-sweep vibration can be used to determine whether fasteners come loose or not. The ceramic fillers is observed between the screw pairs of L-PBSZ modified C/SiC ceramic matrix composite bolted fastenings by SEM, and the effective friction coefficient and the effective friction area increase with the nut and the screw, so the loose exit resistance of nut increases, and the looseness-proof performances of C/SiC ceramic matrix composite bolted fastenings are improved.
Through the computational and experimental analysis on the modal of C/SiC ceramic matrix composite bolted fastenings, the modal parameters and vibration response characteristics were determined. The influence of tightening torque on the vibration performance of bolted fastenings was researched by sine-sweep vibration of the C/SiC ceramic matrix composite bolted fastenings. The influence of liquid polyborosilazanes (L-PBSZ) on the looseness-proof performances of C/SiC ceramic matrix composite bolted fastenings was measured. The results indicate that the first and the third natural frequency of the calculating modal are consistent with that of the experimental modal, so the finite element analysis method can be used for the vibration response characteristics analysis of C/SiC ceramic matrix composite bolted fastenings. The spectrum signal difference curves of sine-sweep vibration can be used to determine whether fasteners come loose or not. The ceramic fillers is observed between the screw pairs of L-PBSZ modified C/SiC ceramic matrix composite bolted fastenings by SEM, and the effective friction coefficient and the effective friction area increase with the nut and the screw, so the loose exit resistance of nut increases, and the looseness-proof performances of C/SiC ceramic matrix composite bolted fastenings are improved.
2014, 31(3): 661-668.
Abstract:
One kind of multi-scale fiber reinforced cementitious composite (MSFRCC), which contains steel fiber, polyvinyl alcohol (PVA) fiber and calcium carbonate whisker, was designed from the perspective of multi-scale structure and fracture process of cementitious materials. Mechanical properties of MSFRCC, such as compressive strength, flexural strength, flexural toughness, multiple cracking patterns and fracture process, were studied. The result indicates that both the strength and toughness are improved. Hardening behavior and multiple cracking patterns are achieved under flexural loading. Multi-scale cracking resistance of multi-scale fiber is confirmed by the results of SEM and fracture test. The result shows that the toughness of cementitious composite can be significantly improved through the multi-scale combination design of fibers. The steel fiber and PVA fiber can be replaced appropriately by relative cheap calcium carbonate whisker through the multi-scale design of fibers.
One kind of multi-scale fiber reinforced cementitious composite (MSFRCC), which contains steel fiber, polyvinyl alcohol (PVA) fiber and calcium carbonate whisker, was designed from the perspective of multi-scale structure and fracture process of cementitious materials. Mechanical properties of MSFRCC, such as compressive strength, flexural strength, flexural toughness, multiple cracking patterns and fracture process, were studied. The result indicates that both the strength and toughness are improved. Hardening behavior and multiple cracking patterns are achieved under flexural loading. Multi-scale cracking resistance of multi-scale fiber is confirmed by the results of SEM and fracture test. The result shows that the toughness of cementitious composite can be significantly improved through the multi-scale combination design of fibers. The steel fiber and PVA fiber can be replaced appropriately by relative cheap calcium carbonate whisker through the multi-scale design of fibers.
2014, 31(3): 669-675.
Abstract:
In order to improve the fracture toughness, reliability and the ability of resisting damage of the ceramic materials, appropriate multiple toughening mechanisms were introduced in alumina matrix ceramic materials. Phase transformation toughening can consume some energy, reduce the concentration of stress at the crack tip and prevent or delay the crack growth rate. When the distribution of reinforced phase is reasonable and the relative density is high, there are crack deflection and bridging forms in the crack propagation, which can weaken the crack extension power, and improve the fracture toughness of the material. The crack propagation was discussed based on extended finite element (X-FEM) method, which provides a new way for the analysis of the multiple toughening mechanisms of ceramic matrix composites.
In order to improve the fracture toughness, reliability and the ability of resisting damage of the ceramic materials, appropriate multiple toughening mechanisms were introduced in alumina matrix ceramic materials. Phase transformation toughening can consume some energy, reduce the concentration of stress at the crack tip and prevent or delay the crack growth rate. When the distribution of reinforced phase is reasonable and the relative density is high, there are crack deflection and bridging forms in the crack propagation, which can weaken the crack extension power, and improve the fracture toughness of the material. The crack propagation was discussed based on extended finite element (X-FEM) method, which provides a new way for the analysis of the multiple toughening mechanisms of ceramic matrix composites.
2014, 31(3): 676-682.
Abstract:
In order to study the tensile damage behavior and the mechanical properties under low frequency cyclic loading of domestic 2D-SiC/SiC composites, their tensile loading/unloading behavior was investigated through experiments and a micromechanical approach. The stress-strain relationship of unidirectional continuous fiber reinforced ceramic matrix composites during loading, unloading and reloading was obtained by constructing a micromechanical model. The relationship between the number of matrix cracks and stress, and failure criterion of composites were obtained according to a fracture statistical method. Through stress changing, the model was applied to domestic 2D woven SiC/SiC composites. For monotonically tensile specimen, matrix Weibull modulus and interfacial shear resistance were gotten by using the orthogonal experiment and the least square method. Fiber Weibull modulus was obtained by making the failure strength of the predicted curve in good agreement with the experimental curve. The tensile loading/unloading stress-strain curve of 2D-SiC/SiC composites obtained with these parameters is in good agreement with the experimental result. The matrix cracking process associated with monotonic tension of 2D-SiC/SiC composites was also produced using Matlab. The results reveal that the matrix cracks are well-distributed when composites failure. The number of matrix cracks is monotone increasing with the raising stress, but it does not appear a platform, which is noted that matrix cracks have not been saturated when composites failure.
In order to study the tensile damage behavior and the mechanical properties under low frequency cyclic loading of domestic 2D-SiC/SiC composites, their tensile loading/unloading behavior was investigated through experiments and a micromechanical approach. The stress-strain relationship of unidirectional continuous fiber reinforced ceramic matrix composites during loading, unloading and reloading was obtained by constructing a micromechanical model. The relationship between the number of matrix cracks and stress, and failure criterion of composites were obtained according to a fracture statistical method. Through stress changing, the model was applied to domestic 2D woven SiC/SiC composites. For monotonically tensile specimen, matrix Weibull modulus and interfacial shear resistance were gotten by using the orthogonal experiment and the least square method. Fiber Weibull modulus was obtained by making the failure strength of the predicted curve in good agreement with the experimental curve. The tensile loading/unloading stress-strain curve of 2D-SiC/SiC composites obtained with these parameters is in good agreement with the experimental result. The matrix cracking process associated with monotonic tension of 2D-SiC/SiC composites was also produced using Matlab. The results reveal that the matrix cracks are well-distributed when composites failure. The number of matrix cracks is monotone increasing with the raising stress, but it does not appear a platform, which is noted that matrix cracks have not been saturated when composites failure.
2014, 31(3): 683-691.
Abstract:
The dry friction and wear properties of high chromium iron and its composites reinforced with 3D-meshy Al2O3 ceramic were investigated on an optimal schwinggung reibungund verschleiss (SRV) testing machine. The friction coefficients and wear rates of high chromium iron and Al2O3 ceramic/high chromium iron composites were measured under various friction frequencies and loads. The worn surface morphologies of the alloy and its composites were observed with SEM and the effect of the 3D-meshy Al2O3 ceramic on the wear mechanisms of composites was discussed accordingly. As the results, the Al2O3 ceramic/high chromium iron composites with good interfacial bonding between ceramic and metal matrix have stable friction coefficients and much better wear-resistance than the high chromium iron with increasing friction frequency and load. It is supposed that the continuous 3D interconnected ceramic/high chromium iron networks and good interfacial bonding provide the metal matrix composites with a capability of load transfer, the 3D-meshy Al2O3 ceramic is able to support the load applied onto the sliding surface and to protect the metal matrix;the wear mechanism involves both oxidative wear and abrassive wear.
The dry friction and wear properties of high chromium iron and its composites reinforced with 3D-meshy Al2O3 ceramic were investigated on an optimal schwinggung reibungund verschleiss (SRV) testing machine. The friction coefficients and wear rates of high chromium iron and Al2O3 ceramic/high chromium iron composites were measured under various friction frequencies and loads. The worn surface morphologies of the alloy and its composites were observed with SEM and the effect of the 3D-meshy Al2O3 ceramic on the wear mechanisms of composites was discussed accordingly. As the results, the Al2O3 ceramic/high chromium iron composites with good interfacial bonding between ceramic and metal matrix have stable friction coefficients and much better wear-resistance than the high chromium iron with increasing friction frequency and load. It is supposed that the continuous 3D interconnected ceramic/high chromium iron networks and good interfacial bonding provide the metal matrix composites with a capability of load transfer, the 3D-meshy Al2O3 ceramic is able to support the load applied onto the sliding surface and to protect the metal matrix;the wear mechanism involves both oxidative wear and abrassive wear.
2014, 31(3): 692-698.
Abstract:
When ultrasonic propagates in porous composites, the interaction between ultrasonic scattering waves near voids and the scattering attenuation mechanism have not been clarified. Aiming at these problems, utilizing the finite difference time domain method, the ultrasonic propagation in carbon fiber reinforced plastic (CFRP) with the porosity of 7.47% was numerically calculated. The ultrasonic scattering attenuation coefficients of both 2D real morphology voids and spherical voids with different size ranges in CFRP laminates were studied contrastively. The results show that, for the small voids with the horizontal size m≤λ/8 and the median voids with λ/8s of the spherical voids is generally less than that of real morphology voids. When the horizontal size of voids is m<2λ/3, the large size voids and slender voids could enhance ultrasonic scattering attenuation on the whole.
When ultrasonic propagates in porous composites, the interaction between ultrasonic scattering waves near voids and the scattering attenuation mechanism have not been clarified. Aiming at these problems, utilizing the finite difference time domain method, the ultrasonic propagation in carbon fiber reinforced plastic (CFRP) with the porosity of 7.47% was numerically calculated. The ultrasonic scattering attenuation coefficients of both 2D real morphology voids and spherical voids with different size ranges in CFRP laminates were studied contrastively. The results show that, for the small voids with the horizontal size m≤λ/8 and the median voids with λ/8
2014, 31(3): 699-706.
Abstract:
Based on the global sensitivity analysis for structures with uncertainties, the effects of uncertainties of input variables on the variance of output response of composite structures and failure probability were investigated. Considering the uncertainties of mechanial properties of material, ply orientation angles, ply thickness and applied loads, the uncertain propagations of inputs on output responses displacement and strength ratio were analyzed using the global sensitivity analysis supported by the variance-based method and the method based on failure probability. The numerical example of the composite I-beam validates the effectiveness of sorting results, which are useful for the stable optimization design of composite structures in engineering.
Based on the global sensitivity analysis for structures with uncertainties, the effects of uncertainties of input variables on the variance of output response of composite structures and failure probability were investigated. Considering the uncertainties of mechanial properties of material, ply orientation angles, ply thickness and applied loads, the uncertain propagations of inputs on output responses displacement and strength ratio were analyzed using the global sensitivity analysis supported by the variance-based method and the method based on failure probability. The numerical example of the composite I-beam validates the effectiveness of sorting results, which are useful for the stable optimization design of composite structures in engineering.
2014, 31(3): 707-714.
Abstract:
In order to provide the theory and operation parameter windows for the modulated thermal wave imaging of composite materials, the rules of modulated thermography for delamination in composite materials were studied using computer simulation based on the finite element method. The relations of phase difference versus modulation frequency and defect depth were analyzed. The prediction of the best modulation frequency, half-amplitude frequency band and blind frequency were presented. The evaluation method of the defect depth by using the blind frequency was verified, and a new approach of defect depth evaluation by using the best modulation frequency was presented. The results show that both of the best modulation frequency and the blind frequency are approximately an inverse proportion function of the defect depth squared. The maximum phase difference and the width of the half-amplitude frequency band decrease when the defect depth increases. The defect depth can be estimated from the blind frequency or the best modulation frequency, and the estimated errors are about 9% and 11% respectively within the defect depth range of 1-4 mm.
In order to provide the theory and operation parameter windows for the modulated thermal wave imaging of composite materials, the rules of modulated thermography for delamination in composite materials were studied using computer simulation based on the finite element method. The relations of phase difference versus modulation frequency and defect depth were analyzed. The prediction of the best modulation frequency, half-amplitude frequency band and blind frequency were presented. The evaluation method of the defect depth by using the blind frequency was verified, and a new approach of defect depth evaluation by using the best modulation frequency was presented. The results show that both of the best modulation frequency and the blind frequency are approximately an inverse proportion function of the defect depth squared. The maximum phase difference and the width of the half-amplitude frequency band decrease when the defect depth increases. The defect depth can be estimated from the blind frequency or the best modulation frequency, and the estimated errors are about 9% and 11% respectively within the defect depth range of 1-4 mm.
2014, 31(3): 715-724.
Abstract:
A progressive damage finite element model was established for the analysis of stitched composite laminate under low velocity impact. The stitching threads were described as spatial truss elements in the model, and three-dimensional solid elements were used to simulate the stitched laminates. Strain-based Hashin failure criteria coupled with corresponding stiffness degradation technologies was used to predict the type and evolution of intralaminar damage modes. Cohesive elements were adopted in interlaminar zones to simulate the initiation and evolution of delamination through stress-based failure criteria and facture-mechanics-based criterion of strain energy release rate. The reasonability of the model was validated by the comparison between numerical simulation results and experimental data on T800 carbon fiber reinforced epoxy resin composites (T800/5228) laminate. Finally the damage law of the stitched laminates at different impact energies was discussed in detail. The results show that the evolution of delamination is restrained effectively by the stitching threads, and the distribution of fiber and matrix damage on the thickness of the stitched laminates is similar to the unstitched laminates at the same impact energy, in which the damage area of stitched laminates is less than that of the unstitched laminates.
A progressive damage finite element model was established for the analysis of stitched composite laminate under low velocity impact. The stitching threads were described as spatial truss elements in the model, and three-dimensional solid elements were used to simulate the stitched laminates. Strain-based Hashin failure criteria coupled with corresponding stiffness degradation technologies was used to predict the type and evolution of intralaminar damage modes. Cohesive elements were adopted in interlaminar zones to simulate the initiation and evolution of delamination through stress-based failure criteria and facture-mechanics-based criterion of strain energy release rate. The reasonability of the model was validated by the comparison between numerical simulation results and experimental data on T800 carbon fiber reinforced epoxy resin composites (T800/5228) laminate. Finally the damage law of the stitched laminates at different impact energies was discussed in detail. The results show that the evolution of delamination is restrained effectively by the stitching threads, and the distribution of fiber and matrix damage on the thickness of the stitched laminates is similar to the unstitched laminates at the same impact energy, in which the damage area of stitched laminates is less than that of the unstitched laminates.
2014, 31(3): 725-732.
Abstract:
The dual-scale flow and the air entrapment in the preform which cause the meso and micro bubbles formation during liquid composite molding (LCM) process were analyzed. On the basis of volume of fluid (VOF) method, the mathematical model of the resin air two-phase flow in a unit cell was established, and the porous medium resistance and capillary force source term in the model were determined. The numerical simulation method of the above-mentioned mathematical model was implemented based on the UDF function of Fluent software, and the dual-scale flow and bubble formation of the plain woven unit cell was simulated. According to the simulation results on the Rovcloth 2454 fabric, capillary number has a critical role in the bubble formation, the critical capillary Cac, at which the micro and meso bubble content is minimal, is exist. When the Ca is lower than Cac, meso bubbles are formed. At Ca higher than Cac, the micro bubbles are favored easily. The results were compared with the experimental data, and the feasibility of the simulation method was verified.
The dual-scale flow and the air entrapment in the preform which cause the meso and micro bubbles formation during liquid composite molding (LCM) process were analyzed. On the basis of volume of fluid (VOF) method, the mathematical model of the resin air two-phase flow in a unit cell was established, and the porous medium resistance and capillary force source term in the model were determined. The numerical simulation method of the above-mentioned mathematical model was implemented based on the UDF function of Fluent software, and the dual-scale flow and bubble formation of the plain woven unit cell was simulated. According to the simulation results on the Rovcloth 2454 fabric, capillary number has a critical role in the bubble formation, the critical capillary Cac, at which the micro and meso bubble content is minimal, is exist. When the Ca is lower than Cac, meso bubbles are formed. At Ca higher than Cac, the micro bubbles are favored easily. The results were compared with the experimental data, and the feasibility of the simulation method was verified.
2014, 31(3): 733-740.
Abstract:
In order to investigate the low velocity impact performance of fiber metal laminates (FML) using the finite element numerical simulation method, a modified continuum damage mechanics (CDM) model was established and the numerical simulation of low velocity drop weight impact test on FML was conducted, the numerical simulation results were compared with the experimental results. The drop weight tests were performed with impact energies of 5.11 J and 10.33 J, respectively. The impact load, displacement and energy history for each test were obtained, thus the dynamic response and the damage pattern of FML were studied. Based on a continuum damage mechanics (CDM) model, the plastic deformation and compression stiffness attenuation of S2-glass/epoxy composite were supplemented as well as fiber tensile failure property, thus a new CDM model was established. The new CDM model was used to describe the constitutive and damage model of the S2-glass/epoxy composite in the FML, and was coded in user material subroutine (VUMAT). The numerical simulation of FML under drop weight impact test was then conducted through ABAQUS/Explicit solver. The results show that the main damage patterns on the rear surface of FML are bulging and cracking when impacted by low energy, and the peak displacement increases with increasing impact energy, while peak impact load increases with increasing impact energy before perforation. The dynamic response of FML is predicted well using finite element analysis when the S2-glass/epoxy composite layers are described by the modified CDM model. It is also found that the fiber tensile failure of the second composite layer is more serious than the first layer's through the finite element numerical simulation results.
In order to investigate the low velocity impact performance of fiber metal laminates (FML) using the finite element numerical simulation method, a modified continuum damage mechanics (CDM) model was established and the numerical simulation of low velocity drop weight impact test on FML was conducted, the numerical simulation results were compared with the experimental results. The drop weight tests were performed with impact energies of 5.11 J and 10.33 J, respectively. The impact load, displacement and energy history for each test were obtained, thus the dynamic response and the damage pattern of FML were studied. Based on a continuum damage mechanics (CDM) model, the plastic deformation and compression stiffness attenuation of S2-glass/epoxy composite were supplemented as well as fiber tensile failure property, thus a new CDM model was established. The new CDM model was used to describe the constitutive and damage model of the S2-glass/epoxy composite in the FML, and was coded in user material subroutine (VUMAT). The numerical simulation of FML under drop weight impact test was then conducted through ABAQUS/Explicit solver. The results show that the main damage patterns on the rear surface of FML are bulging and cracking when impacted by low energy, and the peak displacement increases with increasing impact energy, while peak impact load increases with increasing impact energy before perforation. The dynamic response of FML is predicted well using finite element analysis when the S2-glass/epoxy composite layers are described by the modified CDM model. It is also found that the fiber tensile failure of the second composite layer is more serious than the first layer's through the finite element numerical simulation results.
2014, 31(3): 741-748.
Abstract:
To analyze the influence of side boundary condition on the compression stability performance of composite stiffened panel, finite element software was adopted firstly for modeling and numerically simulating of composite stiffened panel under axial compression to obtain the buckling load and buckling pattern of the panel with unloaded edges simply-supported or unsupported. Then, load carrying capacity of the panel was estimated by engineering calculation method. According to the calculation results, axial compression tests on composite stiffened panels were conducted to analyze the influence of side boundary condition on the buckling pattern, buckling load and post-buckling failure process of the specimen. Test results show that, side boundary condition affects the buckling pattern as well as failure pattern of the stiffened panel. For specimens with unloaded edges supported, the overall deformation after the buckling is slight and the main failure pattern is the compression fracture of stiffeners. For specimens with unloaded edges unsupported, debonding and bending fracture of stiffeners caused by overall deformation after buckling are the main failure patterns, and the debonding of stiffeners decreases the carrying capacity of the structure obviously. Finite element calculation results accord with the test results well, which validate the rationality of the finite element model. It is of preferable accuracy to estimate the carrying capacity of stiffened panels with unloaded edges simply-supported by engineering calculation method.
To analyze the influence of side boundary condition on the compression stability performance of composite stiffened panel, finite element software was adopted firstly for modeling and numerically simulating of composite stiffened panel under axial compression to obtain the buckling load and buckling pattern of the panel with unloaded edges simply-supported or unsupported. Then, load carrying capacity of the panel was estimated by engineering calculation method. According to the calculation results, axial compression tests on composite stiffened panels were conducted to analyze the influence of side boundary condition on the buckling pattern, buckling load and post-buckling failure process of the specimen. Test results show that, side boundary condition affects the buckling pattern as well as failure pattern of the stiffened panel. For specimens with unloaded edges supported, the overall deformation after the buckling is slight and the main failure pattern is the compression fracture of stiffeners. For specimens with unloaded edges unsupported, debonding and bending fracture of stiffeners caused by overall deformation after buckling are the main failure patterns, and the debonding of stiffeners decreases the carrying capacity of the structure obviously. Finite element calculation results accord with the test results well, which validate the rationality of the finite element model. It is of preferable accuracy to estimate the carrying capacity of stiffened panels with unloaded edges simply-supported by engineering calculation method.
2014, 31(3): 749-758.
Abstract:
In order to research the effects of debond size on buckling and post-buckling behaviors of composite stiffened panel, composite stiffened panel containing different debond defects were experimentally investigated. The results show that load carrying capacity of the specimens with 30 mm or 50 mm defect is almost equal to the intact panel, but the presence of 80 mm defect leads to an obvious reduction in the load carrying capacity at the post-buckling stage. By utilizing the ultrasonic scans, the damage propagation behavior was monitored. The results show that when the compression load reaches 85.3% of the failure load, signs of the expansion occur at the diagonal position located in the prefabricated defect. Shadow moiré interferometry method was applied, which shows the formation process of the buckling modes of composite stiffened panel with two half-waves and three half-waves. The monitoring results of buckling modes also reveal that the buckling mode of the stiffened panels transforms frow two half-waves to three half-waves as the debond size increases.Based on the experimental results, a finite element (FE) model was established by ABAQUS to study the numerical simulation of buckling and post-buckling behaviors of composite stiffened panels. The buckling analysis was employed to obtain the buckling load and deflection mode, and the buckling waveform was then defined on the structure as geometric imperfection to process post-buckling calculation. The numerical results agree well with the experimental results, which show the effectiveness of the FE model in the prediction of the buckling and post-buckling performances of the composite stiffened panels.
In order to research the effects of debond size on buckling and post-buckling behaviors of composite stiffened panel, composite stiffened panel containing different debond defects were experimentally investigated. The results show that load carrying capacity of the specimens with 30 mm or 50 mm defect is almost equal to the intact panel, but the presence of 80 mm defect leads to an obvious reduction in the load carrying capacity at the post-buckling stage. By utilizing the ultrasonic scans, the damage propagation behavior was monitored. The results show that when the compression load reaches 85.3% of the failure load, signs of the expansion occur at the diagonal position located in the prefabricated defect. Shadow moiré interferometry method was applied, which shows the formation process of the buckling modes of composite stiffened panel with two half-waves and three half-waves. The monitoring results of buckling modes also reveal that the buckling mode of the stiffened panels transforms frow two half-waves to three half-waves as the debond size increases.Based on the experimental results, a finite element (FE) model was established by ABAQUS to study the numerical simulation of buckling and post-buckling behaviors of composite stiffened panels. The buckling analysis was employed to obtain the buckling load and deflection mode, and the buckling waveform was then defined on the structure as geometric imperfection to process post-buckling calculation. The numerical results agree well with the experimental results, which show the effectiveness of the FE model in the prediction of the buckling and post-buckling performances of the composite stiffened panels.
2014, 31(3): 759-764.
Abstract:
Thin wall C/C-SiC components were fabricated by "chemical vapor infiltration + precursor impregnation pyrolysis" (CVI+PIP) combined methods. The effects of intermediate heat-treated C/C porous preform on the density, deformation and mechanical properties of C/C-SiC components were investigated. The results show that the intermediate heat treatment of the C/C porous preform results in carbon with open porosity, which is favorable for SiC infiltration, leading to the preparation of a C/C-SiC component with high density. The interlaminar shear properties are not influenced observably by intermediate heat treatment, while the in-plane tensile strength and integral bearing performance are affected. The thin wall C/C-SiC components deform on the inside and outside diameter and height orientation by intermediate heat treatment. The in-plane tensile strength and integral bearing performance of the components with proper interfacial strength increase obviously after heat treatment at appropriate temperature (1600-1800℃), and the higher temperature treatment (2100-2300℃) reduces the strength of carbon fiber and reduces the tensile strength and integral bearing performance of C/C-SiC components evidently.
Thin wall C/C-SiC components were fabricated by "chemical vapor infiltration + precursor impregnation pyrolysis" (CVI+PIP) combined methods. The effects of intermediate heat-treated C/C porous preform on the density, deformation and mechanical properties of C/C-SiC components were investigated. The results show that the intermediate heat treatment of the C/C porous preform results in carbon with open porosity, which is favorable for SiC infiltration, leading to the preparation of a C/C-SiC component with high density. The interlaminar shear properties are not influenced observably by intermediate heat treatment, while the in-plane tensile strength and integral bearing performance are affected. The thin wall C/C-SiC components deform on the inside and outside diameter and height orientation by intermediate heat treatment. The in-plane tensile strength and integral bearing performance of the components with proper interfacial strength increase obviously after heat treatment at appropriate temperature (1600-1800℃), and the higher temperature treatment (2100-2300℃) reduces the strength of carbon fiber and reduces the tensile strength and integral bearing performance of C/C-SiC components evidently.
2014, 31(3): 765-771.
Abstract:
A post-buckling failure evaluation method of integrated composite stiffened panels is required for improving the structure design of composite stiffened panels effectively in the aircraft structure design under uniaxial compression. Finite element models were built using commercial finite element software ABAQUS for the study of the failure evaluation method of integrated composite stiffened panels under uniaxial compression at the post-buckling stage, which was also called "global-local" analysis technique. The study of post-buckling failure for a single-stiffener panel shows that "global-local" analysis technique can provide the displacement and load at the initial point of debonding, and the failure load can also be predicted accurately. The "global-local" analysis technique therefore is demonstrated to be an efficient method for rapid evaluation on post-buckling failure of stiffened panels under uniaxial compression, and is significant for improving efficiency of structure design and lightening aircraft's structure weight.
A post-buckling failure evaluation method of integrated composite stiffened panels is required for improving the structure design of composite stiffened panels effectively in the aircraft structure design under uniaxial compression. Finite element models were built using commercial finite element software ABAQUS for the study of the failure evaluation method of integrated composite stiffened panels under uniaxial compression at the post-buckling stage, which was also called "global-local" analysis technique. The study of post-buckling failure for a single-stiffener panel shows that "global-local" analysis technique can provide the displacement and load at the initial point of debonding, and the failure load can also be predicted accurately. The "global-local" analysis technique therefore is demonstrated to be an efficient method for rapid evaluation on post-buckling failure of stiffened panels under uniaxial compression, and is significant for improving efficiency of structure design and lightening aircraft's structure weight.
2014, 31(3): 772-780.
Abstract:
A stress analysis model involving geometric nonlinearity and boundary conditions was developed to characterize adhesive stress distribution of adhesively bonded composite repair structures. The bending moment and the transverse deflection under tensile load were calculated. The bending moment at the ends of the overlap was required as boundary conditions of the differential equations governing the adhesive stresses. The solutions for induced adhesive peel stresses and shear stress were obtained, and the displacement along the mid-plane of the cracked plate was calculated. The finite element analysis was conducted to validate the present closed-form solutions. The numerical results indicate that the analytical solutions and their simplifications correlate very well with the nonlinear finite element computations. The present mathematical techniques and analysis approaches are critical to the successful design, analysis and implementation of bonded repairs.
A stress analysis model involving geometric nonlinearity and boundary conditions was developed to characterize adhesive stress distribution of adhesively bonded composite repair structures. The bending moment and the transverse deflection under tensile load were calculated. The bending moment at the ends of the overlap was required as boundary conditions of the differential equations governing the adhesive stresses. The solutions for induced adhesive peel stresses and shear stress were obtained, and the displacement along the mid-plane of the cracked plate was calculated. The finite element analysis was conducted to validate the present closed-form solutions. The numerical results indicate that the analytical solutions and their simplifications correlate very well with the nonlinear finite element computations. The present mathematical techniques and analysis approaches are critical to the successful design, analysis and implementation of bonded repairs.
2014, 31(3): 781-787.
Abstract:
The compression properties of composite cylindrical shell under axial compression load were tested, and the failure load and the load-strain curves for composite cylindrical shell of test points were collected. The results show that the damage form of the cylindrical shell is buckling failure. A relative finite element model was established and the buckling behaviors of composite cylindrical shell were analyzed by ANSYS software. The results obtained by simulation and experiment were consistent with each other, which validate the effective model. Based on the finite element model, the influences of opening size and fiber ply angle on buckling load of the cylindrical shell with rectangular opening were analyzed. A composite cover was installed to reinforce the structure, and the strength of the reinforced cylindrical shell meets the design requirement.
The compression properties of composite cylindrical shell under axial compression load were tested, and the failure load and the load-strain curves for composite cylindrical shell of test points were collected. The results show that the damage form of the cylindrical shell is buckling failure. A relative finite element model was established and the buckling behaviors of composite cylindrical shell were analyzed by ANSYS software. The results obtained by simulation and experiment were consistent with each other, which validate the effective model. Based on the finite element model, the influences of opening size and fiber ply angle on buckling load of the cylindrical shell with rectangular opening were analyzed. A composite cover was installed to reinforce the structure, and the strength of the reinforced cylindrical shell meets the design requirement.
2014, 31(3): 788-796.
Abstract:
By adopting the hypothesis of rectangle section shape for warp, hexagon section shape for weft, and broken lines for the simplified orientation of warp, a unit-cell geometric model for 2.5D woven composites was developed. A progressive strength prediction model was developed based on the new model, which adopted Hashin and Mises failure criterions to identify failure of the yarns and matrix separately, and established different stiffness degradation method for different failure mode. A parametric progressive damage analysis program was developed by finite element analysis(FEA) software, which can predict the tensile strength, as well as the progressive damage behavior of bend-joint structure of 2.5D woven composite with different woven parameters, both in warp and weft directions. Compared with tensile experimental data, the strength errors are within 10% in both directions. The predicted failure modes agree well with the test results.
By adopting the hypothesis of rectangle section shape for warp, hexagon section shape for weft, and broken lines for the simplified orientation of warp, a unit-cell geometric model for 2.5D woven composites was developed. A progressive strength prediction model was developed based on the new model, which adopted Hashin and Mises failure criterions to identify failure of the yarns and matrix separately, and established different stiffness degradation method for different failure mode. A parametric progressive damage analysis program was developed by finite element analysis(FEA) software, which can predict the tensile strength, as well as the progressive damage behavior of bend-joint structure of 2.5D woven composite with different woven parameters, both in warp and weft directions. Compared with tensile experimental data, the strength errors are within 10% in both directions. The predicted failure modes agree well with the test results.
2014, 31(3): 797-802.
Abstract:
In order to better understand the fatigue behavior of 3D orthogonal woven composites (3DOWC) and improve the fatigue resistance behavior of material, the bending fatigue property under low cycle load was studied, which combined quasi-static three-point bending test and the cyclic bending test under 60% stress levels of 3DOWC with the ABAQUS finite element software that construct whole-scale 3D solid model. The distribution of stress, fatigue damage shape of the 3DOWC were obtained. It is found that the warp yarn is the most important load bearing part, the stress concentration area is in the middle of loading area, and damage occurs mainly in warp yarn that closes to Z-yarns channels.Triangle damage area is formed up and down gradually in the middle of loading area with increasing cycle load. This study may give guidance for future design and optimization of composites.
In order to better understand the fatigue behavior of 3D orthogonal woven composites (3DOWC) and improve the fatigue resistance behavior of material, the bending fatigue property under low cycle load was studied, which combined quasi-static three-point bending test and the cyclic bending test under 60% stress levels of 3DOWC with the ABAQUS finite element software that construct whole-scale 3D solid model. The distribution of stress, fatigue damage shape of the 3DOWC were obtained. It is found that the warp yarn is the most important load bearing part, the stress concentration area is in the middle of loading area, and damage occurs mainly in warp yarn that closes to Z-yarns channels.Triangle damage area is formed up and down gradually in the middle of loading area with increasing cycle load. This study may give guidance for future design and optimization of composites.
2014, 31(3): 803-808.
Abstract:
Experimental study was conducted to investigate the failure mode and strength behavior of composite flush-repair laminates with blind damage under shear load, and the results were then compared with those from the experiments on virgin laminates without any damage. Experimental results show that composite flush-repair laminates can recover well under shear load, and the repaired laminates have the same post-buckling load-carrying capability as the virgin laminates. Furthermore, a finite element analysis (FEA) model of composite flush-repair laminates under shear load was proposed. In this model, 3D Hashin failure criteria was adopted to identify the damages of laminates on both patch and covering layers, and zero-thickness cohesive elements were used between layers to simulate inter-laminar damage. The failure modes obtained from the model conform to the experimental results. Though the failure loads obtained from theoretical simulation do not exactly match with those from experiment, the 15% maximum deviation can still meet the demand of engineering application, due to the complexity of the design and process of flush-repair. Therefore, the proposed FEA model is able to anticipate the failure mode and failure load of composite flush-repair laminates under shear load.
Experimental study was conducted to investigate the failure mode and strength behavior of composite flush-repair laminates with blind damage under shear load, and the results were then compared with those from the experiments on virgin laminates without any damage. Experimental results show that composite flush-repair laminates can recover well under shear load, and the repaired laminates have the same post-buckling load-carrying capability as the virgin laminates. Furthermore, a finite element analysis (FEA) model of composite flush-repair laminates under shear load was proposed. In this model, 3D Hashin failure criteria was adopted to identify the damages of laminates on both patch and covering layers, and zero-thickness cohesive elements were used between layers to simulate inter-laminar damage. The failure modes obtained from the model conform to the experimental results. Though the failure loads obtained from theoretical simulation do not exactly match with those from experiment, the 15% maximum deviation can still meet the demand of engineering application, due to the complexity of the design and process of flush-repair. Therefore, the proposed FEA model is able to anticipate the failure mode and failure load of composite flush-repair laminates under shear load.
2014, 31(3): 809-817.
Abstract:
Composite profiles produced by industrial pultrusion process have consistent cross-section shape (such as square, Ⅰ-shaped, grooved, etc), stable performance and continuous length. The technique of joint connection is difficult. The experimental and theoretical analysis of mechanical bolted joints were carried out. The effects of parameters such as aperture, end distance and wall thickness on bearing capacity of bolted joints were researched. The enhancement technology of unidirectional fiber profiles bolted hole wall by metal gasket around the neck was proposed. Then the design formula of joint connection for pultruded composites was fitted. The results show that when the failure mode of pultruded composite square profiles is local crush of joint on tube, the relationship between the ultimate bearing capacity and the product of pore size and thickness (d·t) is linear. Meanwhile, the failure modes of joints are related with the ratio of end distance to pore diameter. Under the mode of crushing rupture, when the thickness of the joint plate is constant, the increment of the ultimate bearing capacity decreases with increasing pore diameter. The ultimate bearing capacity of bolted joints can be significantly enhanced by 63% using metal gasket reinforced technology.
Composite profiles produced by industrial pultrusion process have consistent cross-section shape (such as square, Ⅰ-shaped, grooved, etc), stable performance and continuous length. The technique of joint connection is difficult. The experimental and theoretical analysis of mechanical bolted joints were carried out. The effects of parameters such as aperture, end distance and wall thickness on bearing capacity of bolted joints were researched. The enhancement technology of unidirectional fiber profiles bolted hole wall by metal gasket around the neck was proposed. Then the design formula of joint connection for pultruded composites was fitted. The results show that when the failure mode of pultruded composite square profiles is local crush of joint on tube, the relationship between the ultimate bearing capacity and the product of pore size and thickness (d·t) is linear. Meanwhile, the failure modes of joints are related with the ratio of end distance to pore diameter. Under the mode of crushing rupture, when the thickness of the joint plate is constant, the increment of the ultimate bearing capacity decreases with increasing pore diameter. The ultimate bearing capacity of bolted joints can be significantly enhanced by 63% using metal gasket reinforced technology.
2014, 31(3): 818-823.
Abstract:
In order to monitor the damage of integrated composite structures, an energy damage index method was proposed by using Lamb wave and Hilbert transform. First, the envelope of the time signal was picked up according to Hilbert transform of Lamb wave. Then the wavepacket which had the maximum amplitude was selected and the ratio of the wavepacket energy change for damage to the wavepacket energy of baseline was defined as damage index. This index method did not need to select the special Lamb wave mode and was helpful to overcome the problems of signal analysis with frequency dispersion, multi-mode and mode conversion of Lamb wave in composite structures. Finally this index method was tested by monitoring the damage evolvement of composite T-joint. The results show that this method can be applied to the damage monitoring of composite T-joint, when the energy damage index (EDI) value reaches to 0.62, the composite T-joint certainly has been damaged.
In order to monitor the damage of integrated composite structures, an energy damage index method was proposed by using Lamb wave and Hilbert transform. First, the envelope of the time signal was picked up according to Hilbert transform of Lamb wave. Then the wavepacket which had the maximum amplitude was selected and the ratio of the wavepacket energy change for damage to the wavepacket energy of baseline was defined as damage index. This index method did not need to select the special Lamb wave mode and was helpful to overcome the problems of signal analysis with frequency dispersion, multi-mode and mode conversion of Lamb wave in composite structures. Finally this index method was tested by monitoring the damage evolvement of composite T-joint. The results show that this method can be applied to the damage monitoring of composite T-joint, when the energy damage index (EDI) value reaches to 0.62, the composite T-joint certainly has been damaged.
2014, 31(3): 824-829.
Abstract:
In order to overcome the drawback of phase separation in the process of phase change and improve the thermal cycling performances of sodium acetate trihydrate (CH3COONa·3H2O), new phase change materials composed of CH3COONa·3H2O, n-Eicosane and expanded graphite (EG) were prepared by a simple blending method. The structure and thermal properties of as-prepared samples were characterized by XRD, SEM and DSC techniques. The result indicates that the thermal cycling performance of n-Eisosane-EG/CH3COONa·3H2O is improved by the coated effect of n-Eicosane and confinement effect of EG.
In order to overcome the drawback of phase separation in the process of phase change and improve the thermal cycling performances of sodium acetate trihydrate (CH3COONa·3H2O), new phase change materials composed of CH3COONa·3H2O, n-Eicosane and expanded graphite (EG) were prepared by a simple blending method. The structure and thermal properties of as-prepared samples were characterized by XRD, SEM and DSC techniques. The result indicates that the thermal cycling performance of n-Eisosane-EG/CH3COONa·3H2O is improved by the coated effect of n-Eicosane and confinement effect of EG.
2014, 31(3): 830-834.
Abstract:
The Ti(C1-xNx) powder was synthesized by utilization of tetrabutyl titanate (Ti(OC4H9)4) and nano carbon black (C) as raw materials, with their theory mass ratio of 9.4:1. Tetrabutyl titanate and carbon black with their mass ratio of m(Ti(OC4H9)4):m(C)=9:1, were mixed to prepare the sintering precursor through sol-gel process. Ultrafine Ti(C1-xNx) powder was obtained after calcination at various temperatures and N2 atmospheres for 1 h with the help of high temperature carbon thermal reductive reaction. The results show that, with increasing temperature, x values of Ti(C1-xNx) gradually reduce and range from 0.19 to 0.72. The content of total carbon(Ct) in the products increases from 14.23wt% to 18.66wt%, the contents of free carbon (Cf) and oxygen (Co) all remain below 0.5wt%. In addition, the particle sizes also show a trend of increase, in the range of 220 nm to 275 nm.
The Ti(C1-xNx) powder was synthesized by utilization of tetrabutyl titanate (Ti(OC4H9)4) and nano carbon black (C) as raw materials, with their theory mass ratio of 9.4:1. Tetrabutyl titanate and carbon black with their mass ratio of m(Ti(OC4H9)4):m(C)=9:1, were mixed to prepare the sintering precursor through sol-gel process. Ultrafine Ti(C1-xNx) powder was obtained after calcination at various temperatures and N2 atmospheres for 1 h with the help of high temperature carbon thermal reductive reaction. The results show that, with increasing temperature, x values of Ti(C1-xNx) gradually reduce and range from 0.19 to 0.72. The content of total carbon(Ct) in the products increases from 14.23wt% to 18.66wt%, the contents of free carbon (Cf) and oxygen (Co) all remain below 0.5wt%. In addition, the particle sizes also show a trend of increase, in the range of 220 nm to 275 nm.
2014, 31(3): 835-844.
Abstract:
With the widely application of composite materials in aircraft structures, the structural health monitoring imaging method has become a hot topic in composite structural health monitoring technology research, which is based on the piezoelectric sensors (PZTs) array and Lamb wave. However, the composites' anisotropic makes it difficult to achieve accurate monitoring, which depends on the signal propagation velocity, such as delay-accumulation, phased array and so on. In this paper, the spatial filter damage imaging and location method were studied, which isn't dependent on the signal propagation velocity. The feature of spatial-wavenumber domain was used in this method when Lamb propagation in structures. After setting the space weight function, the PZTs array would be formed a spatial-wavenumber filter with the bandwidth is [kmin, kmax], which can filter a specific space range of Lamb wave and imagine the damage angle. And then, the damage angle images from each of the multi-dimensional PZTs array were integrated, that would give the damage coordinate image. In result, the damage imaging and localization was accomplished without wave velocity. This method was verified on carbon fiber laminates. The verification shows that the method presented is able to locate the composite structures' damage, and the error of localization is less than 1 cm.
With the widely application of composite materials in aircraft structures, the structural health monitoring imaging method has become a hot topic in composite structural health monitoring technology research, which is based on the piezoelectric sensors (PZTs) array and Lamb wave. However, the composites' anisotropic makes it difficult to achieve accurate monitoring, which depends on the signal propagation velocity, such as delay-accumulation, phased array and so on. In this paper, the spatial filter damage imaging and location method were studied, which isn't dependent on the signal propagation velocity. The feature of spatial-wavenumber domain was used in this method when Lamb propagation in structures. After setting the space weight function, the PZTs array would be formed a spatial-wavenumber filter with the bandwidth is [kmin, kmax], which can filter a specific space range of Lamb wave and imagine the damage angle. And then, the damage angle images from each of the multi-dimensional PZTs array were integrated, that would give the damage coordinate image. In result, the damage imaging and localization was accomplished without wave velocity. This method was verified on carbon fiber laminates. The verification shows that the method presented is able to locate the composite structures' damage, and the error of localization is less than 1 cm.
2014, 31(3): 845-850.
Abstract:
The mesoporous η-Al2O3(PEG600)and η-Al2O3(PEG2000)fibers were synthesized by hydrothermal method, using polyethylene glycol (PEG)of different polymerization degree (PEG600 and PEG2000)as the templates, respectively. The prepared samples were characterized by XRD, TEM and N2 adsorption, and the effect of polymerization degree of PEG on the properties of the mesoporous η-Al2O3 fibers was investigated. The absorption property of mesoporous η-Al2O3 fibers toward methylene blue was studied by static equilibrium adsorption experiments. The results show that both of the two templates can be used to synthesize the mesoporous η-Al2O3 fibers. It is found that the polymerization degree of PEG has great effect on mesoporous structure, surface area, pore volume and pore diameter. The surface area and pore volume of η-Al2O3(PEG600)are 189.899 m2·g-1 and 0.329 cm3·g-1, which are 1.4 times and 1.2 times of that of η-Al2O3(PEG2000), respectively. And the average pore diameter of η-Al2O3(PEG600) is also bigger than η-Al2O3(PEG2000). The adsorption mechanism of the two kinds of mesoporous η-Al2O3 fibers is multi molecular layer adsorption. According to the calculation of BET multi molecular layer adsorption equations, the equilibrium adsorption capacities of η-Al2O3(PEG600)and η-Al2O3(PEG2000)towards methylene blue are 256.391 3 mg·g-1 and 204.045 9 mg·g-1, respectively.
The mesoporous η-Al2O3(PEG600)and η-Al2O3(PEG2000)fibers were synthesized by hydrothermal method, using polyethylene glycol (PEG)of different polymerization degree (PEG600 and PEG2000)as the templates, respectively. The prepared samples were characterized by XRD, TEM and N2 adsorption, and the effect of polymerization degree of PEG on the properties of the mesoporous η-Al2O3 fibers was investigated. The absorption property of mesoporous η-Al2O3 fibers toward methylene blue was studied by static equilibrium adsorption experiments. The results show that both of the two templates can be used to synthesize the mesoporous η-Al2O3 fibers. It is found that the polymerization degree of PEG has great effect on mesoporous structure, surface area, pore volume and pore diameter. The surface area and pore volume of η-Al2O3(PEG600)are 189.899 m2·g-1 and 0.329 cm3·g-1, which are 1.4 times and 1.2 times of that of η-Al2O3(PEG2000), respectively. And the average pore diameter of η-Al2O3(PEG600) is also bigger than η-Al2O3(PEG2000). The adsorption mechanism of the two kinds of mesoporous η-Al2O3 fibers is multi molecular layer adsorption. According to the calculation of BET multi molecular layer adsorption equations, the equilibrium adsorption capacities of η-Al2O3(PEG600)and η-Al2O3(PEG2000)towards methylene blue are 256.391 3 mg·g-1 and 204.045 9 mg·g-1, respectively.
2014, 31(3): 851-858.
Abstract:
In order to study the capability of the main insulation materials of the ocean energy generators under salt spray and humidity thermal ageing condition, the test for the resin-rich molding (RRM) tong-ma epoxy glass fiber power mica (TEGM) insulation materials was carried out under the simulated ocean climatic condition. The water absorption rate of the resin-rich molding insulation materials was measured under different ageing cycles. The surface morphology change before and after the ageing test was analyzed based on the observed results of the sample through the scanning electron microscope (SEM). The frequency dielectric characteristics of the TEGM insulation materials were measured by the broadband dielectric spectrometer at different ageing cycles and different measuring temperatures. The relationships of the microstructure variety and the macroscopic dielectric property were analyzed by the dielectric polarization theory. The results show that the water absorption rate of the TEGM insulation materials sample appears three stages, namely fast absorption stage, slow absorption stage and saturation absorption stage. The relative dielectric constant and loss factor show the rising tendency with the increasing ageing time, and the frequency domain spectroscopy (FDS) curve can reflect the insulation ageing state directly in the low frequency range. Through the curve fitting of measured data, it can be seen that there are the quadratic equation relationships between the dielectric parameters and the water absorption for the aging insulation materials in the low frequency range.
In order to study the capability of the main insulation materials of the ocean energy generators under salt spray and humidity thermal ageing condition, the test for the resin-rich molding (RRM) tong-ma epoxy glass fiber power mica (TEGM) insulation materials was carried out under the simulated ocean climatic condition. The water absorption rate of the resin-rich molding insulation materials was measured under different ageing cycles. The surface morphology change before and after the ageing test was analyzed based on the observed results of the sample through the scanning electron microscope (SEM). The frequency dielectric characteristics of the TEGM insulation materials were measured by the broadband dielectric spectrometer at different ageing cycles and different measuring temperatures. The relationships of the microstructure variety and the macroscopic dielectric property were analyzed by the dielectric polarization theory. The results show that the water absorption rate of the TEGM insulation materials sample appears three stages, namely fast absorption stage, slow absorption stage and saturation absorption stage. The relative dielectric constant and loss factor show the rising tendency with the increasing ageing time, and the frequency domain spectroscopy (FDS) curve can reflect the insulation ageing state directly in the low frequency range. Through the curve fitting of measured data, it can be seen that there are the quadratic equation relationships between the dielectric parameters and the water absorption for the aging insulation materials in the low frequency range.
