2011 Vol. 28, No. 4
2011, 28(4): 1-6.
Abstract:
The cure reaction kinetics of E-51 epoxy resin and 4,4’-diaminodiphenylsulfone(DDS) system was investigated by the isothermal DSC method, and isothermal curing kinetics parameters at 170, 180, 190, 200 ℃ were obtained through fitting between the experimental data and the curing model. According to the values of coefficient of determination (R2) of the fitted data, a suitable curing reaction kinetic model was determined. The reaction process shows to be dominated by different mechanism at different stages of the E-51/DDS system curing process, when the cure degree is less than 40%, the curing system is Kamal autocatalytic reaction model; when the cure degree is more than 40%, the curing system is nth order reation model, with an initial autocatalytic reaction shifting into an nth order reaction as the reaction proceeding.
The cure reaction kinetics of E-51 epoxy resin and 4,4’-diaminodiphenylsulfone(DDS) system was investigated by the isothermal DSC method, and isothermal curing kinetics parameters at 170, 180, 190, 200 ℃ were obtained through fitting between the experimental data and the curing model. According to the values of coefficient of determination (R2) of the fitted data, a suitable curing reaction kinetic model was determined. The reaction process shows to be dominated by different mechanism at different stages of the E-51/DDS system curing process, when the cure degree is less than 40%, the curing system is Kamal autocatalytic reaction model; when the cure degree is more than 40%, the curing system is nth order reation model, with an initial autocatalytic reaction shifting into an nth order reaction as the reaction proceeding.
2011, 28(4): 7-11.
Abstract:
Carbon fiber-polytetrafluoroethylene/polyamide 6 (CF-PTFE/PA6) composites were prepared using ultrafine PTFE powder as a friction-reducing function filler, and CF as a reinforcement. The CF-PTFE/PA6 composites were irradiated by 60Co-γ rays. The mechanical and tribological properties of the composites were studied, and the impact fracture surface morphology of the composites was observed by SEM. The results show that CF-PTFE/PA6 composites with mass fraction of 8% PTFE and 13% CF not only exhibited better mechanical strength and tribological properties, but also possessed higher bending strength, tensile strength and impact strength, which increased by 9.9%, 7.9% and 11.7%, respectively, after optimum adsorbed dose of 120 kGy.
Carbon fiber-polytetrafluoroethylene/polyamide 6 (CF-PTFE/PA6) composites were prepared using ultrafine PTFE powder as a friction-reducing function filler, and CF as a reinforcement. The CF-PTFE/PA6 composites were irradiated by 60Co-γ rays. The mechanical and tribological properties of the composites were studied, and the impact fracture surface morphology of the composites was observed by SEM. The results show that CF-PTFE/PA6 composites with mass fraction of 8% PTFE and 13% CF not only exhibited better mechanical strength and tribological properties, but also possessed higher bending strength, tensile strength and impact strength, which increased by 9.9%, 7.9% and 11.7%, respectively, after optimum adsorbed dose of 120 kGy.
2011, 28(4): 12-16.
Abstract:
The multilayer films constructed from Dawson-type iron(Ⅲ)-monosubstituted tungstophosphate and a generation-4 poly(amidoamine) dendrimer(PAMAM) were prepared on the ITO electrode by the layer-by-layer self- assembly method and characterized by XPS, UV-Vis, CV and AFM. It was shown that P2W17Fe and PAMAM were gradually and uniformly incorporated into the films. Three couples of redox waves were observed in the cyclic voltammetry of the title multilayer films at acidic condition. The title multilayer films are stable and exhibit good electrocatalytic activity on the reduction of NO-2and BrO-3.
The multilayer films constructed from Dawson-type iron(Ⅲ)-monosubstituted tungstophosphate and a generation-4 poly(amidoamine) dendrimer(PAMAM) were prepared on the ITO electrode by the layer-by-layer self- assembly method and characterized by XPS, UV-Vis, CV and AFM. It was shown that P2W17Fe and PAMAM were gradually and uniformly incorporated into the films. Three couples of redox waves were observed in the cyclic voltammetry of the title multilayer films at acidic condition. The title multilayer films are stable and exhibit good electrocatalytic activity on the reduction of NO-2and BrO-3.
2011, 28(4): 17-22.
Abstract:
By using single fiber fragmentation test(SFFT) based on WND (Wagner-Nairn-Detassis) energy model, the effects of temperature from ambient temperature to 130 ℃ on the interface fracture energy of two different kinds of sizing carbon fibers/ high temperature cured epoxy resin were investigated, and the effects of the sizing of carbon fibers on the heat resistance of the interphase was studied. Comparing with the short beam shear test, the relationship between micro and macro interfacial properties was analyzed. The results indicate that the interfacial fracture energy of the carbon fiber/epoxy resin decreases at the beginning and then almost unchanges from ambient temperature to 130 ℃. The interface fracture energy of the desized fibers and the effect of temperature are different from the case of the sized fibers, indicating that the sizing plays an important role on the heat resistance of interface. The interlaminar shear strength of the studied carbon fiber/epoxy laminates decreases linearly with increasing temperature, not according with the variation of the interface fracture energy. This is mainly attributed to the differences in the test principles of the two methods and the different damage locations of the interface.
By using single fiber fragmentation test(SFFT) based on WND (Wagner-Nairn-Detassis) energy model, the effects of temperature from ambient temperature to 130 ℃ on the interface fracture energy of two different kinds of sizing carbon fibers/ high temperature cured epoxy resin were investigated, and the effects of the sizing of carbon fibers on the heat resistance of the interphase was studied. Comparing with the short beam shear test, the relationship between micro and macro interfacial properties was analyzed. The results indicate that the interfacial fracture energy of the carbon fiber/epoxy resin decreases at the beginning and then almost unchanges from ambient temperature to 130 ℃. The interface fracture energy of the desized fibers and the effect of temperature are different from the case of the sized fibers, indicating that the sizing plays an important role on the heat resistance of interface. The interlaminar shear strength of the studied carbon fiber/epoxy laminates decreases linearly with increasing temperature, not according with the variation of the interface fracture energy. This is mainly attributed to the differences in the test principles of the two methods and the different damage locations of the interface.
2011, 28(4): 23-28.
Abstract:
Contact angle between epoxy and different kinds of carbon fibers was investigated first. Work of adhesion at different temperatures was studied by means of Young-Dupre method and Wu method. The influence of resin curing on wetting and adhesive interaction of fibers and resin was then analyzed. The results show that the wetability between T300, CCF, T700 fibers and AG80 resin is improved by increasing the temperature. Comparing with the sized fibers, polar component of surface energy of the desized fibers is lower, and wetting and adhesive interaction with epoxy AG80 resin is worse. Before the chemical reaction of epoxy system starts, wetting between AG80/DDS system and T700 fiber is better than AG80 pure resin and T700 fiber, but work of adhesion is lower. And wetting and adhesive interaction between AG80/DDS, E51/DDS system and T700 fiber are improved as curing time expands at 110 ℃.
Contact angle between epoxy and different kinds of carbon fibers was investigated first. Work of adhesion at different temperatures was studied by means of Young-Dupre method and Wu method. The influence of resin curing on wetting and adhesive interaction of fibers and resin was then analyzed. The results show that the wetability between T300, CCF, T700 fibers and AG80 resin is improved by increasing the temperature. Comparing with the sized fibers, polar component of surface energy of the desized fibers is lower, and wetting and adhesive interaction with epoxy AG80 resin is worse. Before the chemical reaction of epoxy system starts, wetting between AG80/DDS system and T700 fiber is better than AG80 pure resin and T700 fiber, but work of adhesion is lower. And wetting and adhesive interaction between AG80/DDS, E51/DDS system and T700 fiber are improved as curing time expands at 110 ℃.
2011, 28(4): 29-33.
Abstract:
A homogeneous and heterogeneous reaction mathematical model of multi-field coupling was developed according to the characteristics of thermal gradient chemical vapor infiltration (CVI) fabricating C/C composites, using 2D carbon felt as the preform, natural gas as the carbon source gas, the furnace pressure of 100 kPa. The time evolution of the preform density was obtained by calculation, the effects of deposition temperatures and gas flow rates on the densification process were analyzed, and the reasonable range of deposition temperature and gas flow rate were obtained. After the preform being infiltrated for 100 h, the overall and radial-direction densities of the preform from simulation agree well with those from experiment. The model is validated to reliable and the simulation has capability of forecasting the process.
A homogeneous and heterogeneous reaction mathematical model of multi-field coupling was developed according to the characteristics of thermal gradient chemical vapor infiltration (CVI) fabricating C/C composites, using 2D carbon felt as the preform, natural gas as the carbon source gas, the furnace pressure of 100 kPa. The time evolution of the preform density was obtained by calculation, the effects of deposition temperatures and gas flow rates on the densification process were analyzed, and the reasonable range of deposition temperature and gas flow rate were obtained. After the preform being infiltrated for 100 h, the overall and radial-direction densities of the preform from simulation agree well with those from experiment. The model is validated to reliable and the simulation has capability of forecasting the process.
2011, 28(4): 34-39.
Abstract:
The glass fiber (GF) was corroded in the diluted acid solution for different times, and subsequently the GF/isotactic polypropylene (iPP) composites were prepared. The effects of the acid corroded GF on the interfacial morphology of GF/iPP composites were studied via the polarized optical microscope. The result show that the GF corroded for 4 h exhibits the nucleation ability to form novel banded nuclei in the early stage of the crystallization, and the β-transcrystallinity can be developed from these nuclei finally. In addition, the isothermal crystallization at 142 ℃ of this composite shows that GF corroded by acid for 4 h has nucleating duality towards matrix, viz., it has both β nucleation ability and α nucleation ability.
The glass fiber (GF) was corroded in the diluted acid solution for different times, and subsequently the GF/isotactic polypropylene (iPP) composites were prepared. The effects of the acid corroded GF on the interfacial morphology of GF/iPP composites were studied via the polarized optical microscope. The result show that the GF corroded for 4 h exhibits the nucleation ability to form novel banded nuclei in the early stage of the crystallization, and the β-transcrystallinity can be developed from these nuclei finally. In addition, the isothermal crystallization at 142 ℃ of this composite shows that GF corroded by acid for 4 h has nucleating duality towards matrix, viz., it has both β nucleation ability and α nucleation ability.
2011, 28(4): 40-45.
Abstract:
Graphite oxide was modified by KH-550, the modified graphite oxide was reduced to form functionalized graphene (FG) dispersing consistently in the acetone/water (mass ratio is 9∶1) solution by ultrasonic treatment before drying. The FG dispersion was intensively mixed for a certain time by ultrasonic treatment to disperse the nano-FG in α, ω-dihydroxy polydimethylsiloxane matrix and obtained an uniform and stable nano-FG/room temperature vulcanized(RTV) silicone rubber composite after curing. FTIR, TEM, SEM, XRD, and DSC analysis show that KH-550 bonds to the surface of FG sheet to make its layers wrinkled, folding and partially exfoliated, and broaden its layer spacing to 3.46 . FG exfoliates into transparent or semi-transparent layers after ultrasonic treatment. The uniform and wrinkled cross-section morphology of nano-FG/RTV silicone rubber composite, which is different from that of pure silicone rubber, shows that there is no micro-phase separation between the two parts. Compared with the pure silicone rubber, the Tg, Tm and crystallinity of all the nano-FG/RTV silicone rubber composites are improved. Mechanical property tests show that nano-FG reinforces silicone rubber a lot. The tensile strength and the elongation at break of composite with 0.5 wt% nano-FG are 0.43 MPa and 265%, respectively. The tensile strength more than doubles and the elongation at break increases 52% compared with that of pure silicone rubber.
Graphite oxide was modified by KH-550, the modified graphite oxide was reduced to form functionalized graphene (FG) dispersing consistently in the acetone/water (mass ratio is 9∶1) solution by ultrasonic treatment before drying. The FG dispersion was intensively mixed for a certain time by ultrasonic treatment to disperse the nano-FG in α, ω-dihydroxy polydimethylsiloxane matrix and obtained an uniform and stable nano-FG/room temperature vulcanized(RTV) silicone rubber composite after curing. FTIR, TEM, SEM, XRD, and DSC analysis show that KH-550 bonds to the surface of FG sheet to make its layers wrinkled, folding and partially exfoliated, and broaden its layer spacing to 3.46 . FG exfoliates into transparent or semi-transparent layers after ultrasonic treatment. The uniform and wrinkled cross-section morphology of nano-FG/RTV silicone rubber composite, which is different from that of pure silicone rubber, shows that there is no micro-phase separation between the two parts. Compared with the pure silicone rubber, the Tg, Tm and crystallinity of all the nano-FG/RTV silicone rubber composites are improved. Mechanical property tests show that nano-FG reinforces silicone rubber a lot. The tensile strength and the elongation at break of composite with 0.5 wt% nano-FG are 0.43 MPa and 265%, respectively. The tensile strength more than doubles and the elongation at break increases 52% compared with that of pure silicone rubber.
2011, 28(4): 46-51.
Abstract:
With methyl vinyl silicone as the base rubber, filled with carbon coated aluminum(C-Al) nanoparticles, the heat dissipation composites were prepared by using the method of mechanical blending. The SEM was employed to analyze the dispersion of C-Al nanoparticles disperse in silicone rubber which showed that the nanoparticles uniform distribution in silicone rubber. The effect of C-Al nanoparticles on thermal conductivity and coefficient of thermal expansion (CTE) of the silicone rubber were investigated, and it was found that thermal conductivity of the composite increases with increasing the C-Al nanoparticles content, the thermal conductivity begins to decrease when the C-Al volume fraction reaches 50%. The optimum filling amount of C-Al nanoparticles is 50%. The CTE decreases with the loading increasing. TGA shows that the addition of C-Al nanoparticles increases the thermal stability of the silicone rubber.
With methyl vinyl silicone as the base rubber, filled with carbon coated aluminum(C-Al) nanoparticles, the heat dissipation composites were prepared by using the method of mechanical blending. The SEM was employed to analyze the dispersion of C-Al nanoparticles disperse in silicone rubber which showed that the nanoparticles uniform distribution in silicone rubber. The effect of C-Al nanoparticles on thermal conductivity and coefficient of thermal expansion (CTE) of the silicone rubber were investigated, and it was found that thermal conductivity of the composite increases with increasing the C-Al nanoparticles content, the thermal conductivity begins to decrease when the C-Al volume fraction reaches 50%. The optimum filling amount of C-Al nanoparticles is 50%. The CTE decreases with the loading increasing. TGA shows that the addition of C-Al nanoparticles increases the thermal stability of the silicone rubber.
2011, 28(4): 52-57.
Abstract:
Ni/silicone rubber composites with nickel powders of different particle sizes were prepared at a filler/ silicone rubber mass ratio of 2.4∶1.0. The piezoresistivity and the dielectric properties of the composite samples at room temperature were measured. The mechanism of electric conduction is discussed together with the SEM images of the samples. The results show that piezoresistivity of Ni/silicone rubber composite is enhanced by reducing the filler particle size: at low pressures, the pressure derivative of resistivity, of samples prepared with Ni powders of particle size 74, 48 and 18 μm is 1.73×104、2.59×104 and 3.71×10 4 Ω·m/kPa respectively. The sharp drop in resistivity shifts to the low pressure end as the filler particle size decreases, suggesting that the percolation threshold of Ni/silicone rubber composites decreases with reduced filler particle size. AC conductivity, dielectric constant and dielectric loss of Ni/silicone rubber composites all increase with the decrease of particle size: the conductivity of the sample with filler particle diameter 18 μm reaches about 10-2 S·m-1, which is five orders of magnitude greater than that of the sample with filler particle diameter 74 μm(about 10-7 S·m-1), and the corresponding dielectric constant is also increased from about 102 to about 103. Elasticity, piezoresistivity, and electronic transport properties of the composite can be adjusted by changing the filler particle size.
Ni/silicone rubber composites with nickel powders of different particle sizes were prepared at a filler/ silicone rubber mass ratio of 2.4∶1.0. The piezoresistivity and the dielectric properties of the composite samples at room temperature were measured. The mechanism of electric conduction is discussed together with the SEM images of the samples. The results show that piezoresistivity of Ni/silicone rubber composite is enhanced by reducing the filler particle size: at low pressures, the pressure derivative of resistivity, of samples prepared with Ni powders of particle size 74, 48 and 18 μm is 1.73×104、2.59×104 and 3.71×10 4 Ω·m/kPa respectively. The sharp drop in resistivity shifts to the low pressure end as the filler particle size decreases, suggesting that the percolation threshold of Ni/silicone rubber composites decreases with reduced filler particle size. AC conductivity, dielectric constant and dielectric loss of Ni/silicone rubber composites all increase with the decrease of particle size: the conductivity of the sample with filler particle diameter 18 μm reaches about 10-2 S·m-1, which is five orders of magnitude greater than that of the sample with filler particle diameter 74 μm(about 10-7 S·m-1), and the corresponding dielectric constant is also increased from about 102 to about 103. Elasticity, piezoresistivity, and electronic transport properties of the composite can be adjusted by changing the filler particle size.
2011, 28(4): 58-62.
Abstract:
The non-isothermal degradation behaviors of calcium sulfate whisker (CSW)/fluororubber(FPM) composites in nitrogen were investigated compared with those of anhydrous calcium sulfate(ACS)/(FPM) composites by TG and DTG. The kinetic parameters were evaluated by differential method and integral method. The results show that the apparent activation energy E of CSW/FPM composites calculated by differential method is 203.33 kJ·mol-1, higher than that of ACS/FPM composites(174.74 kJ·mol-1) and the results suggest that CSW/FPM composites have better thermal stability. The thermal decomposition reaction orders are of the order of 1. The thermal decomposition apparent activation energy E increases with increasing mass loss.
The non-isothermal degradation behaviors of calcium sulfate whisker (CSW)/fluororubber(FPM) composites in nitrogen were investigated compared with those of anhydrous calcium sulfate(ACS)/(FPM) composites by TG and DTG. The kinetic parameters were evaluated by differential method and integral method. The results show that the apparent activation energy E of CSW/FPM composites calculated by differential method is 203.33 kJ·mol-1, higher than that of ACS/FPM composites(174.74 kJ·mol-1) and the results suggest that CSW/FPM composites have better thermal stability. The thermal decomposition reaction orders are of the order of 1. The thermal decomposition apparent activation energy E increases with increasing mass loss.
2011, 28(4): 63-69.
Abstract:
The microcapsules were synthesized by in-situ polymerization technology respectively with urea-formaldehyde resin (UF) or melamine-urea-formaldehyde co-condensed resin (MUF) as shell materials and epoxy resin (E-51) as core materials. A series of epoxy composite specimen were prepared using the microcapsules in order to study the effects of the microcapsules. Tensile and bending properties of the composite specimen were tested by universal tensile machine, and the fracture surface of composite materials was observed. The results show that the tensile strength and flexural strength of epoxy resin decrease with the increases of microcapsule amount. The elongation at break and fracture bending strain increase when the mass fraction of microcapsules is less than 2%, while decreases when the mass fraction of microcapsules is more than 2%. The microcapsules have a significant toughening effect on the epoxy resin. The rougher microcapsule surface and the smaller particle size are, the more ductile the composite is. The microcapsules likely rupture in the crack propagation and the microcapsules likely strip in the crack terminal zone.
The microcapsules were synthesized by in-situ polymerization technology respectively with urea-formaldehyde resin (UF) or melamine-urea-formaldehyde co-condensed resin (MUF) as shell materials and epoxy resin (E-51) as core materials. A series of epoxy composite specimen were prepared using the microcapsules in order to study the effects of the microcapsules. Tensile and bending properties of the composite specimen were tested by universal tensile machine, and the fracture surface of composite materials was observed. The results show that the tensile strength and flexural strength of epoxy resin decrease with the increases of microcapsule amount. The elongation at break and fracture bending strain increase when the mass fraction of microcapsules is less than 2%, while decreases when the mass fraction of microcapsules is more than 2%. The microcapsules have a significant toughening effect on the epoxy resin. The rougher microcapsule surface and the smaller particle size are, the more ductile the composite is. The microcapsules likely rupture in the crack propagation and the microcapsules likely strip in the crack terminal zone.
2011, 28(4): 70-76.
Abstract:
To study the influence of modified graphene(MGN/HDPE ) composite on crystal behavior of high density polyethylene, graphene (GN) and MGN were prepared by chemical oxidation-reduction, followed by the preparation of GN/HDPE and MGN/HDPE composites with melt blending method. The structures of GN and MGN were characterized by FTIR, the crystallization of composites were analyzed by DSC. The non-isothermal crystallization kinetics of samples were extensively studied by Mo's equation. The results show that stearic acid has been successfully grafted onto the GN, and MGN displays restraining the crystallization of HDPE much more strongly than GN.
To study the influence of modified graphene(MGN/HDPE ) composite on crystal behavior of high density polyethylene, graphene (GN) and MGN were prepared by chemical oxidation-reduction, followed by the preparation of GN/HDPE and MGN/HDPE composites with melt blending method. The structures of GN and MGN were characterized by FTIR, the crystallization of composites were analyzed by DSC. The non-isothermal crystallization kinetics of samples were extensively studied by Mo's equation. The results show that stearic acid has been successfully grafted onto the GN, and MGN displays restraining the crystallization of HDPE much more strongly than GN.
2011, 28(4): 77-82.
Abstract:
To solve the security problem of high-speed train in the high wind environment, the structure of anti-wind corridor was used to withstand wind and sand for the railway. Glass fiber/unsaturated polyester composites were selected as the structure materials because of their the high specific strength, stiffness and corrosion resistance. The tensile and bending properties of composites under different sand erosion conditions were measured to study the influence rules of different sand erosion conditions on the composites. The results show that with the increasing of sandblasting angle, the erosion effect is unobvious. The effect is magnified with the higher wind speed and exposure time and the erosion effect shows linear variation.
To solve the security problem of high-speed train in the high wind environment, the structure of anti-wind corridor was used to withstand wind and sand for the railway. Glass fiber/unsaturated polyester composites were selected as the structure materials because of their the high specific strength, stiffness and corrosion resistance. The tensile and bending properties of composites under different sand erosion conditions were measured to study the influence rules of different sand erosion conditions on the composites. The results show that with the increasing of sandblasting angle, the erosion effect is unobvious. The effect is magnified with the higher wind speed and exposure time and the erosion effect shows linear variation.
2011, 28(4): 83-88.
Abstract:
To mimic the components and structure of the natural bone, chitosan (CS) and hydroxyapatite (HA) were selected as the macromolecule and the source of the calcium phosphate, respectively. The raw materials were dissolved in an acid solvent to form homogeneous solution, and then underwent sol-gel phase transition and aging procedure to prepare nano-HA/CS porous composite scaffolds in situ. The effects of aging time and pH value on the composition, micromorphology and compressive strength of the HA/CS composites were studied. The results show that the compressive strength and modulus of the scaffolds decrease obviously with the increase of the pH value, and the compressive strength is higher than pure CS scaffolds when the pH is 10 and 11. XRD results indicate that the transition of phosphorus calcium to HA can be impelled with the aging treatment, and the growth of HA crystallites orients along the c- axis in the crystal structure. SEM results reveal that the scaffolds possess inter-connected porous structure, and the rod-like or grainy nano-hydroxyapatite crystal particles disperse uniformly in the scaffolds, which formed homogeneous dense organic/inorganic composites. This kind of fast and deep mineralization method for preparation of bone scaffold provides a new way of thinking.
To mimic the components and structure of the natural bone, chitosan (CS) and hydroxyapatite (HA) were selected as the macromolecule and the source of the calcium phosphate, respectively. The raw materials were dissolved in an acid solvent to form homogeneous solution, and then underwent sol-gel phase transition and aging procedure to prepare nano-HA/CS porous composite scaffolds in situ. The effects of aging time and pH value on the composition, micromorphology and compressive strength of the HA/CS composites were studied. The results show that the compressive strength and modulus of the scaffolds decrease obviously with the increase of the pH value, and the compressive strength is higher than pure CS scaffolds when the pH is 10 and 11. XRD results indicate that the transition of phosphorus calcium to HA can be impelled with the aging treatment, and the growth of HA crystallites orients along the c- axis in the crystal structure. SEM results reveal that the scaffolds possess inter-connected porous structure, and the rod-like or grainy nano-hydroxyapatite crystal particles disperse uniformly in the scaffolds, which formed homogeneous dense organic/inorganic composites. This kind of fast and deep mineralization method for preparation of bone scaffold provides a new way of thinking.
2011, 28(4): 89-93.
Abstract:
A bombyx mori silk fibroin-RGD fusion protein was used to modify the porous hydroxyapatite/silk fibroin(HA/SF) composite scaffolds by soaking the scaffolds into the protein solution with different concentrations. The osteoblasts, MG-63 and MC3T3-E1 were seeded onto the silk-RGD modified HA/SF composite scaffolds in order to evaluate the cell adhesion, proliferation and differentiation on scaffolds. The results show that the cell adhesion property in the silk-RGD modified scaffolds is higher than that in the control (i.e., unmodified scaffolds), and depended on the concentration of silk-RGD. After being cultured for 7 d in vitro, the proliferation rates of MG-63 and MC3T3-E1 cells increase by 21% and 50%, respectively, compared with the control. For MC3T3-E1 cells, the alkaline phosphatase (ALP) activity data show an improvement of cell differentiation on the scaffolds after the silk-RGD modification, but no significant difference is found for the MG-63 cells.
A bombyx mori silk fibroin-RGD fusion protein was used to modify the porous hydroxyapatite/silk fibroin(HA/SF) composite scaffolds by soaking the scaffolds into the protein solution with different concentrations. The osteoblasts, MG-63 and MC3T3-E1 were seeded onto the silk-RGD modified HA/SF composite scaffolds in order to evaluate the cell adhesion, proliferation and differentiation on scaffolds. The results show that the cell adhesion property in the silk-RGD modified scaffolds is higher than that in the control (i.e., unmodified scaffolds), and depended on the concentration of silk-RGD. After being cultured for 7 d in vitro, the proliferation rates of MG-63 and MC3T3-E1 cells increase by 21% and 50%, respectively, compared with the control. For MC3T3-E1 cells, the alkaline phosphatase (ALP) activity data show an improvement of cell differentiation on the scaffolds after the silk-RGD modification, but no significant difference is found for the MG-63 cells.
2011, 28(4): 94-98.
Abstract:
The biodegradable composite films were prepared from corn stalks cellulose microcrystal(CSCMC) as the filler and poly(lactic acid)(PLA) as the polymeric matrix. The crystallinity, the tensile properties and the thermal properties of the composite flim were tested. The results show that the tensile properties and the thermal properties of the CSCMC/PLA composite were improved by the addition of corn stalks cellulose microcrystal. When the mass fraction of CSCMC is 10%, the initial decomposition temperature increases by 34.38 ℃, the tensile strength increases by 58.3% and the elongation at break increases by 31.1% compared to that of the pure PLA.
The biodegradable composite films were prepared from corn stalks cellulose microcrystal(CSCMC) as the filler and poly(lactic acid)(PLA) as the polymeric matrix. The crystallinity, the tensile properties and the thermal properties of the composite flim were tested. The results show that the tensile properties and the thermal properties of the CSCMC/PLA composite were improved by the addition of corn stalks cellulose microcrystal. When the mass fraction of CSCMC is 10%, the initial decomposition temperature increases by 34.38 ℃, the tensile strength increases by 58.3% and the elongation at break increases by 31.1% compared to that of the pure PLA.
2011, 28(4): 99-106.
Abstract:
The basalt fiber(BF)was treated using three coupling agents(KH550, KH560 and KH570),and the comparisons were taken with BF without any treatment. XPS results show that silicon on the surfaces of BF reacts with the silicon on the three coupling agents to form Si—O—Si bonds, and the order of amount is KH550>KH570>KH560. The results from the bending performance and interlaminar shear strength(ILSS)as well as the SEM observations of different BF/EP before and after water bathing show that the treatments of BF with coupling agents can improve the interface bonding properties of BF/EP with the order of KH550>KH560>KH570. SEM observations show that BF and epoxy combined tightly after the treatment by coupling agents, and the interface do not debond when specimen was damaged. The main damage occurs in the matrix, which shows the mechanical properties of the interface are better than that of matrix. The mechanical properties of different BF/EP decline after water bathing, and water resistance is poor. The interface of fiber and matrix debonds, and some fibers are pulled out from the matrix and holes were left in the matrix. The failure mode is a brittle fracture.
The basalt fiber(BF)was treated using three coupling agents(KH550, KH560 and KH570),and the comparisons were taken with BF without any treatment. XPS results show that silicon on the surfaces of BF reacts with the silicon on the three coupling agents to form Si—O—Si bonds, and the order of amount is KH550>KH570>KH560. The results from the bending performance and interlaminar shear strength(ILSS)as well as the SEM observations of different BF/EP before and after water bathing show that the treatments of BF with coupling agents can improve the interface bonding properties of BF/EP with the order of KH550>KH560>KH570. SEM observations show that BF and epoxy combined tightly after the treatment by coupling agents, and the interface do not debond when specimen was damaged. The main damage occurs in the matrix, which shows the mechanical properties of the interface are better than that of matrix. The mechanical properties of different BF/EP decline after water bathing, and water resistance is poor. The interface of fiber and matrix debonds, and some fibers are pulled out from the matrix and holes were left in the matrix. The failure mode is a brittle fracture.
2011, 28(4): 107-111.
Abstract:
Three different C/SiC composites were fabricated by polymer infiltration and pyrolysis(PIP), slurry infiltration(SI) combined with PIP and chemical vapor infiltration(CVI). ZrC coatings were prepared by chemical vapor deposition(CVD) on C/SiC to form C/SiC-ZrC composites. The oxidation behaviors of the C/SiC-ZrC composites were investigated in a CH4 combustion gas environment. The results indicate that the surfaces of the C/SiC-ZrC composites fabricated by PIP and SI+PIP are severely oxidized with mass loss higher than 12% after oxidation at 1800 ℃ for 30 min. The C/SiC-ZrC composites fabricated by CVI exhibit the best oxidation resistance with a mass loss of 6.9%.
Three different C/SiC composites were fabricated by polymer infiltration and pyrolysis(PIP), slurry infiltration(SI) combined with PIP and chemical vapor infiltration(CVI). ZrC coatings were prepared by chemical vapor deposition(CVD) on C/SiC to form C/SiC-ZrC composites. The oxidation behaviors of the C/SiC-ZrC composites were investigated in a CH4 combustion gas environment. The results indicate that the surfaces of the C/SiC-ZrC composites fabricated by PIP and SI+PIP are severely oxidized with mass loss higher than 12% after oxidation at 1800 ℃ for 30 min. The C/SiC-ZrC composites fabricated by CVI exhibit the best oxidation resistance with a mass loss of 6.9%.
2011, 28(4): 112-116.
Abstract:
The Fe-filled single-walled carbon nanotubes (SWCNTs) were fabricated by a DC arc discharge method. After purification process and then doped the very substance into the nanocrystalline M-type barium hexaferrite (BaFe12O19), which was synthesized by a sol-gel auto-combustion method. The electromagnetic parameters of the samples were tested using coaxial method, and microwave absorption properties of SWCNTs/BaFe12O19 composite with different doping ratios were investigated. The results indicate that the magnetic loss of composite SWCNTs/BaFe12O19 is mainly attributed to the natural resonance and exchange resonance. When doping 2% mass fraction of SWCNTs, the maximum reflection loss of composite can reach 24.85 dB and the frequency band width of above 10 dB is 6.30 GHz, which is a wide microwave absorption frequency band.
The Fe-filled single-walled carbon nanotubes (SWCNTs) were fabricated by a DC arc discharge method. After purification process and then doped the very substance into the nanocrystalline M-type barium hexaferrite (BaFe12O19), which was synthesized by a sol-gel auto-combustion method. The electromagnetic parameters of the samples were tested using coaxial method, and microwave absorption properties of SWCNTs/BaFe12O19 composite with different doping ratios were investigated. The results indicate that the magnetic loss of composite SWCNTs/BaFe12O19 is mainly attributed to the natural resonance and exchange resonance. When doping 2% mass fraction of SWCNTs, the maximum reflection loss of composite can reach 24.85 dB and the frequency band width of above 10 dB is 6.30 GHz, which is a wide microwave absorption frequency band.
2011, 28(4): 117-123.
Abstract:
Nb-16Si-22Ti-6Hf(-2Cr-2Al) alloys were prepared using vacuum induction melting in Y2O3 crucible, and the heat treatment was conducted at 1500 ℃ for 100 h. The constituent phases analysis show that the ingots are composed of the phases of Nb solid solution(NbSS)、Nb3Si、β-Nb5Si3 and γ-Nb5Si3 . The cooling rate, alloying elements and heat treatment have effects on the microstructures of the ingots. The lower the cooling rate is, the coarser the microstructures at the top of the ingots are. The addition of Cr and Al promotes the eutectoid reaction, resulting in the much more homogenous and finer of the microstructures. While the heat treatment promotes the eutectoid reaction of Nb3Si→Nb5Si3+NbSS, leading to the decrease in the dimension and the volume fraction of Nb3Si, and the smooth of the boundary. Furthermore, the NbSS dendrites coarsen slightly, and the lamellar-like eutectic structures change into irregular island-like during the heat treatment.
Nb-16Si-22Ti-6Hf(-2Cr-2Al) alloys were prepared using vacuum induction melting in Y2O3 crucible, and the heat treatment was conducted at 1500 ℃ for 100 h. The constituent phases analysis show that the ingots are composed of the phases of Nb solid solution(NbSS)、Nb3Si、β-Nb5Si3 and γ-Nb5Si3 . The cooling rate, alloying elements and heat treatment have effects on the microstructures of the ingots. The lower the cooling rate is, the coarser the microstructures at the top of the ingots are. The addition of Cr and Al promotes the eutectoid reaction, resulting in the much more homogenous and finer of the microstructures. While the heat treatment promotes the eutectoid reaction of Nb3Si→Nb5Si3+NbSS, leading to the decrease in the dimension and the volume fraction of Nb3Si, and the smooth of the boundary. Furthermore, the NbSS dendrites coarsen slightly, and the lamellar-like eutectic structures change into irregular island-like during the heat treatment.
2011, 28(4): 124-129.
Abstract:
An oxide dispersion strengthened(ODS) ferritic steel with nominal composition of Fe-12Cr-2.5W-0.25Ti-0.2V-0.4Y2O3 (0.4Y2O3/12Cr, mass fraction, %) was produced by using ethylene diamine tetraacetic acid(EDTA) complex method to add Y2O3 particles to an argon atomized steel powder, followed by hot isostatic pressing, forging and heat treatment. The formation process and behavior of oxides in the composite powder, the 0.4Y2O3/12Cr steels in hot isostatic pressing and under forged conditions were characterized by using SEM, FE-SEM and XRD. The results show that the oxides formation mechanisms of 0.4 Y2O3/12Cr steel by EDTA complex method are complex thermal decomposition mechanism, interfacial reaction mechanism, and reprecipitation mechanism. The fine and uniform oxide dispersoids distributtion in the ferrite matrix could be obtained by choosing appropriate parameters and mechanical dispersing effect.
An oxide dispersion strengthened(ODS) ferritic steel with nominal composition of Fe-12Cr-2.5W-0.25Ti-0.2V-0.4Y2O3 (0.4Y2O3/12Cr, mass fraction, %) was produced by using ethylene diamine tetraacetic acid(EDTA) complex method to add Y2O3 particles to an argon atomized steel powder, followed by hot isostatic pressing, forging and heat treatment. The formation process and behavior of oxides in the composite powder, the 0.4Y2O3/12Cr steels in hot isostatic pressing and under forged conditions were characterized by using SEM, FE-SEM and XRD. The results show that the oxides formation mechanisms of 0.4 Y2O3/12Cr steel by EDTA complex method are complex thermal decomposition mechanism, interfacial reaction mechanism, and reprecipitation mechanism. The fine and uniform oxide dispersoids distributtion in the ferrite matrix could be obtained by choosing appropriate parameters and mechanical dispersing effect.
2011, 28(4): 130-135.
Abstract:
Al2O3/Al composites of different volume fractions were produced by using reciprocating extrusion technology with pure Al powder and Al2O3 particle. Then the damping capacity of the composites was measured. Relationship of damping behavior and strain amplitude or frequency, and the contribution of different content of reinforced particles to damping capacity were investigated. The result shows that the Al2O3 particles homogeneously distributed in Al matrix, and the Al2O3P/Al composite prepared by reciprocating extrusion has an excellent damping capacity. The damping property improves with increase of the particles content. At low strain amplitude, the main damping mechanism of Al2O3P/Al composites is dislocation damping, whereas at high strain amplitude, interface-sliding damping becomes the main damping mechanism.
Al2O3/Al composites of different volume fractions were produced by using reciprocating extrusion technology with pure Al powder and Al2O3 particle. Then the damping capacity of the composites was measured. Relationship of damping behavior and strain amplitude or frequency, and the contribution of different content of reinforced particles to damping capacity were investigated. The result shows that the Al2O3 particles homogeneously distributed in Al matrix, and the Al2O3P/Al composite prepared by reciprocating extrusion has an excellent damping capacity. The damping property improves with increase of the particles content. At low strain amplitude, the main damping mechanism of Al2O3P/Al composites is dislocation damping, whereas at high strain amplitude, interface-sliding damping becomes the main damping mechanism.
2011, 28(4): 136-141.
Abstract:
The microstructure of Al2O3/Mo composite was analyzed and the wear behavior was tested. The analysis results of wear data and wear morphology show that the amount of density first increases and then decreases gradually, but hardness increased with the increasing of the volumn fraction of Al2O3. There is some degree of reduction on the wear produced by the process of cutting, plowing. When the Al2O3 volume fraction is 3%, the specific wear rate of composites increases gradually with the particle size decreases. However, at higher Al2O3 volume fraction (5%, 10%, 15%), the specific wear rate first increases and then decreases with the increasing of abrasive grain diameter. The wear loss increases with the increase of the load, while there is no influence on the order. On the same load, the wear loss shows a declining trend with the continuous increase of Al2O3 content, but the speed is slower.
The microstructure of Al2O3/Mo composite was analyzed and the wear behavior was tested. The analysis results of wear data and wear morphology show that the amount of density first increases and then decreases gradually, but hardness increased with the increasing of the volumn fraction of Al2O3. There is some degree of reduction on the wear produced by the process of cutting, plowing. When the Al2O3 volume fraction is 3%, the specific wear rate of composites increases gradually with the particle size decreases. However, at higher Al2O3 volume fraction (5%, 10%, 15%), the specific wear rate first increases and then decreases with the increasing of abrasive grain diameter. The wear loss increases with the increase of the load, while there is no influence on the order. On the same load, the wear loss shows a declining trend with the continuous increase of Al2O3 content, but the speed is slower.
2011, 28(4): 142-148.
Abstract:
The phase composition, microstructure, micro-hardness and brittleness of gas nitriding layer and laser quenching-nitriding layer have been studied. The results show that the content of ε-Fe3N in bright layer of laser quenching-nitriding layer increases from 14.74% to 69.45%, while the content of crisp and hard ξ-Fe2N drops from 79.95% to 25.03%. The curve of nitrogen concentration in nitriding layer decreases gently with the decrease of the nitrogen content in the surface layer. The total diffusion flux of nitrogen and the thickness of nitriding layer increase. After laser quenching-nitriding, the crystal grain is tiny with cementite distributing in strip lower bainite. The number of high hardness Cr2N particles enchances, which obviously improves the micro-hardness of bright layer. Brittle fracture critical pressure of nitriding layer increases from 3 N of gas nitriding layer to 6 N of laser quenching-nitriding layer.
The phase composition, microstructure, micro-hardness and brittleness of gas nitriding layer and laser quenching-nitriding layer have been studied. The results show that the content of ε-Fe3N in bright layer of laser quenching-nitriding layer increases from 14.74% to 69.45%, while the content of crisp and hard ξ-Fe2N drops from 79.95% to 25.03%. The curve of nitrogen concentration in nitriding layer decreases gently with the decrease of the nitrogen content in the surface layer. The total diffusion flux of nitrogen and the thickness of nitriding layer increase. After laser quenching-nitriding, the crystal grain is tiny with cementite distributing in strip lower bainite. The number of high hardness Cr2N particles enchances, which obviously improves the micro-hardness of bright layer. Brittle fracture critical pressure of nitriding layer increases from 3 N of gas nitriding layer to 6 N of laser quenching-nitriding layer.
2011, 28(4): 149-155.
Abstract:
The MnO2/CMSs composite was obtained by coating MnO2 onto the surface of carbon microspheres (CMSs), which were prepared by chemical vapor deposition and oxidized by a mixture of 0.1 mol/L KMnO4 and 0.1 mol/L HNO3. And then MnO2/CMSs composite was washed by H2C2O4 to obtain oxidized-CMSs. The morphology and structure of all samples were characterized by FESEM, TEM, XRD and so on. The dispersion of MnO2/CMSs in water and ethanol was also investigated. The electrochemical property of the composite was measured by cyclic voltammetry. The results show that the MnO2/CMSs composite with appropriate capacitance performance in neutral solution was synthesized using in-situ coating technique in KMnO4 and HNO3 solution, the loading of MnO2 in the composite was about 60%, and the oxidized-CMSs with oxygen-containing functional groups on their surface have good dispersion in water and ethanol.
The MnO2/CMSs composite was obtained by coating MnO2 onto the surface of carbon microspheres (CMSs), which were prepared by chemical vapor deposition and oxidized by a mixture of 0.1 mol/L KMnO4 and 0.1 mol/L HNO3. And then MnO2/CMSs composite was washed by H2C2O4 to obtain oxidized-CMSs. The morphology and structure of all samples were characterized by FESEM, TEM, XRD and so on. The dispersion of MnO2/CMSs in water and ethanol was also investigated. The electrochemical property of the composite was measured by cyclic voltammetry. The results show that the MnO2/CMSs composite with appropriate capacitance performance in neutral solution was synthesized using in-situ coating technique in KMnO4 and HNO3 solution, the loading of MnO2 in the composite was about 60%, and the oxidized-CMSs with oxygen-containing functional groups on their surface have good dispersion in water and ethanol.
2011, 28(4): 156-161.
Abstract:
Nylon6 nanofibers containing TiO2 nanoparticles and Ag or Cu-doped composite nanoribbons were synthesized by a facile combination of a mixed electrospinning technique. By means of SEM, TEM and FTIR, the nanofibers were subsequently characterized. The antibacterial performance of the nonwoven mats was also measured. The results show that the morphology of the electrospun fibers is improved by dopping of Ag +, while the Cu2 + does in the opposite way. The photocatalytic antibacterial efficiency of the Nylon6-TiO2 fibers shows fine performance, while Nylon6-TiO2 membrane, doped by the Cu2 + and (or) Ag +, displays good antibacterial one without the catalytic effect.
Nylon6 nanofibers containing TiO2 nanoparticles and Ag or Cu-doped composite nanoribbons were synthesized by a facile combination of a mixed electrospinning technique. By means of SEM, TEM and FTIR, the nanofibers were subsequently characterized. The antibacterial performance of the nonwoven mats was also measured. The results show that the morphology of the electrospun fibers is improved by dopping of Ag +, while the Cu2 + does in the opposite way. The photocatalytic antibacterial efficiency of the Nylon6-TiO2 fibers shows fine performance, while Nylon6-TiO2 membrane, doped by the Cu2 + and (or) Ag +, displays good antibacterial one without the catalytic effect.
2011, 28(4): 162-166.
Abstract:
Zeolite was synthesized on the surface and interior pores of expanded graphite (EG) by hydrothermal method and a new EG/Na-X zeolite composite was prepared. The effect of SiO2/Al2O3 molar ratio on the types of zeolite was investigated. Microstructures of the composite were characterized using XRD, FE-SEM, FTIR and N2 adsorption-desorption techniques. The static desiccator method was used for adsorption capacity measurement. The results indicate that the types of zeolite are dependent on SiO2/Al2O3 molar ratio. With the increase of SiO2/Al2O3 molar ratio, types of zeolite transform from Na-A to Na-X gradually and transform completely when the SiO2/Al2O3 molar ratio is 7.9. Adsorption datas show that static adsorption capacity of the composite for benzene gas can reach 340 mg/g at the temperature of 25 ℃.
Zeolite was synthesized on the surface and interior pores of expanded graphite (EG) by hydrothermal method and a new EG/Na-X zeolite composite was prepared. The effect of SiO2/Al2O3 molar ratio on the types of zeolite was investigated. Microstructures of the composite were characterized using XRD, FE-SEM, FTIR and N2 adsorption-desorption techniques. The static desiccator method was used for adsorption capacity measurement. The results indicate that the types of zeolite are dependent on SiO2/Al2O3 molar ratio. With the increase of SiO2/Al2O3 molar ratio, types of zeolite transform from Na-A to Na-X gradually and transform completely when the SiO2/Al2O3 molar ratio is 7.9. Adsorption datas show that static adsorption capacity of the composite for benzene gas can reach 340 mg/g at the temperature of 25 ℃.
2011, 28(4): 167-170.
Abstract:
In order to study the relationship between the composite structure and sound insulation property of integrated hollow core sandwich composites, the glass fabric/epoxy resin composites with different heights, panel thicknesses and core structures were fabricated. The experiments for sound insulation property were carried out in a reverberation-anechoic chambers measuring system. The results show that the structure of glass fabric has an obvious influence on the sound insulation property of integrated hollow core sandwich composites. The sound properties of the composites increase gradually with the increase in height. The panel thickness has a greater impact on the sound insulation properties of the composites, and the effect of core structure is relatively weak. The sound insulation property of the composites with 8 shaped core structure is slightly higher than that of the composites with 88 shaped and X shaped core structure.
In order to study the relationship between the composite structure and sound insulation property of integrated hollow core sandwich composites, the glass fabric/epoxy resin composites with different heights, panel thicknesses and core structures were fabricated. The experiments for sound insulation property were carried out in a reverberation-anechoic chambers measuring system. The results show that the structure of glass fabric has an obvious influence on the sound insulation property of integrated hollow core sandwich composites. The sound properties of the composites increase gradually with the increase in height. The panel thickness has a greater impact on the sound insulation properties of the composites, and the effect of core structure is relatively weak. The sound insulation property of the composites with 8 shaped core structure is slightly higher than that of the composites with 88 shaped and X shaped core structure.
2011, 28(4): 171-179.
Abstract:
Four-point bending tests were performed on ultrahigh toughness cementitious composite(UHTCC)specimens for the purpose of understanding the influence of specimens’ thickness on its flexural behavior. The further explanation on this influence was made through theoretical dimension analysis. In the evaluation of toughness property, a new parameter, defined as energy dissipation per unit volume of plastic hinge region was proposed. The experimental results show that, the nominal flexural strength-flexural strain curves and crack width evolution curves of different thickness specimens are almost identical. Mid-span deflection decreases in an inversely proportional manner with the increase in specimen’s thickness. The ratio of neutral axis depth to specimens’ thickness at ultimate failure nearly keeps a constant value(about 0.88). Toughness index calculated based on ASTM C 1609 standard rises as the specimens’ thickness increases, whereas new proposed toughness index Tv is independent of specimens’ thickness. Therefore, for ultrahigh toughness cementitious composite exhibiting tensile strain-hardening characteristic, flexural strength, toughness capacity and crack width have no size effect. With these findings, standard specimen dimension, i.e., 100 mm×100 mm×400 mm specified for traditional FRC, is suggested for the flexural test of ultrahigh toughness cementitious composite.
Four-point bending tests were performed on ultrahigh toughness cementitious composite(UHTCC)specimens for the purpose of understanding the influence of specimens’ thickness on its flexural behavior. The further explanation on this influence was made through theoretical dimension analysis. In the evaluation of toughness property, a new parameter, defined as energy dissipation per unit volume of plastic hinge region was proposed. The experimental results show that, the nominal flexural strength-flexural strain curves and crack width evolution curves of different thickness specimens are almost identical. Mid-span deflection decreases in an inversely proportional manner with the increase in specimen’s thickness. The ratio of neutral axis depth to specimens’ thickness at ultimate failure nearly keeps a constant value(about 0.88). Toughness index calculated based on ASTM C 1609 standard rises as the specimens’ thickness increases, whereas new proposed toughness index Tv is independent of specimens’ thickness. Therefore, for ultrahigh toughness cementitious composite exhibiting tensile strain-hardening characteristic, flexural strength, toughness capacity and crack width have no size effect. With these findings, standard specimen dimension, i.e., 100 mm×100 mm×400 mm specified for traditional FRC, is suggested for the flexural test of ultrahigh toughness cementitious composite.
2011, 28(4): 180-184.
Abstract:
A concurrent topology optimization method for dynamic designs associating materials and structures with periodical microstructures of different sizes was presented and related numerical experiments were carried out. In the method, the optimization object was to maximize the structure fundamental frequency, rational approximation of material properties (RAMP) was adopted to ensure clear topologies in both macro and micro scales, and design variables for macro structure and microstructures were defined separately and integrated into one system by using the super-element technique. Based on the numerical experiments, the effects of representative volume element (RVE) sizes and materials ratios of both the macro-scale and the micro-scale on structural topology were investigated, and the results indicate that the proposed method is effective and can be used as an innovative dynamic design one for lightweight structures.
A concurrent topology optimization method for dynamic designs associating materials and structures with periodical microstructures of different sizes was presented and related numerical experiments were carried out. In the method, the optimization object was to maximize the structure fundamental frequency, rational approximation of material properties (RAMP) was adopted to ensure clear topologies in both macro and micro scales, and design variables for macro structure and microstructures were defined separately and integrated into one system by using the super-element technique. Based on the numerical experiments, the effects of representative volume element (RVE) sizes and materials ratios of both the macro-scale and the micro-scale on structural topology were investigated, and the results indicate that the proposed method is effective and can be used as an innovative dynamic design one for lightweight structures.
2011, 28(4): 185-195.
Abstract:
Thermal behavior and heat transfer characteristics of a composite sandwich structures with lattice cores under loading with a constant temperature field were simulated by computational fluid dynamics FLUENT software during forced convection with auxiliary fluid. The distribution and characteristics of flow field, such as the fields of pressure, velocity and temperature, were analyzed. The influence of structural morphology on the inner end-wall and heat transfer patterns in a unit cell was described in details. Three dimensionless parameters Reynolds number, Nusselt number and pressure drop coefficient, scaling by the characteristic length of unit cell were used to characterize and assess the heat transfer performance of structure. Furthermore, by introducing concepts of the minimum permeability, maximum permeability and horizontal permeability of temperature, the heat transfer performance of structure was visually characterized. The analytic results indicate that heat transfer performance of this lattice-cores sandwich structure can be evidently improved in the case of forced convection, and therefore reveal the structure is more suitable for the mulitifunctionalities of lightweight structure achievement in the future.
Thermal behavior and heat transfer characteristics of a composite sandwich structures with lattice cores under loading with a constant temperature field were simulated by computational fluid dynamics FLUENT software during forced convection with auxiliary fluid. The distribution and characteristics of flow field, such as the fields of pressure, velocity and temperature, were analyzed. The influence of structural morphology on the inner end-wall and heat transfer patterns in a unit cell was described in details. Three dimensionless parameters Reynolds number, Nusselt number and pressure drop coefficient, scaling by the characteristic length of unit cell were used to characterize and assess the heat transfer performance of structure. Furthermore, by introducing concepts of the minimum permeability, maximum permeability and horizontal permeability of temperature, the heat transfer performance of structure was visually characterized. The analytic results indicate that heat transfer performance of this lattice-cores sandwich structure can be evidently improved in the case of forced convection, and therefore reveal the structure is more suitable for the mulitifunctionalities of lightweight structure achievement in the future.
2011, 28(4): 196-201.
Abstract:
The snap-through of two stable configurations of rectangular unsymmetric cross-ply composite laminate were investigated through experimental and numerical ways. The critical loads of snap-through of the two stable configurations were measured in experiments, and a non-linear finite element model of bi-stable rectangular unsymmetric cross-ply composite laminate was built. The finite element model successfully predicts the two stable configurations and further predicts their critical loads of snap-through. It shows that the predicted results agree well with the experiment results. Finite element analysis(FEA) and experiments both reveal that the characteristics of snap-through of the two stable configurations are discrepant, and the corresponding critical loads are different greatly.
The snap-through of two stable configurations of rectangular unsymmetric cross-ply composite laminate were investigated through experimental and numerical ways. The critical loads of snap-through of the two stable configurations were measured in experiments, and a non-linear finite element model of bi-stable rectangular unsymmetric cross-ply composite laminate was built. The finite element model successfully predicts the two stable configurations and further predicts their critical loads of snap-through. It shows that the predicted results agree well with the experiment results. Finite element analysis(FEA) and experiments both reveal that the characteristics of snap-through of the two stable configurations are discrepant, and the corresponding critical loads are different greatly.
2011, 28(4): 202-211.
Abstract:
A strength analysis model was presented to study the progressive damage of integral stiffened composite panels subjected to compressive loading by using the nonlinear finite element method. In the model, the debonding failure of the adhesive between the skin and stiffener was considered by adding cohesive elements between the shell elements. Quads failure criteria and Hashin’s failure criteria were adopted to identify the occurring of damage events of the cohesive elements and the composite panels, respectively. Based on ABAQUS, a material degradation rule containing continuum damage status variables was presented.The process of damage initiation, propagation and catastrophic failure of the integral stiffened composite panels was simulated in detail by the proposed model, and the initial geometric imperfection was taken into account. Axial stiffness ratio of stiffener and skin was defined and conducted to study the effects to the structure on the carrying capacity and failure modes. The results indicate that: the model can predict the damage process of integral stiffened panel effectively; under the condition the ply design is reasonable, increasing the stiffness ratio can to some extent improve the unit area bearing capacity of the cross section of stiffened composite panels.
A strength analysis model was presented to study the progressive damage of integral stiffened composite panels subjected to compressive loading by using the nonlinear finite element method. In the model, the debonding failure of the adhesive between the skin and stiffener was considered by adding cohesive elements between the shell elements. Quads failure criteria and Hashin’s failure criteria were adopted to identify the occurring of damage events of the cohesive elements and the composite panels, respectively. Based on ABAQUS, a material degradation rule containing continuum damage status variables was presented.The process of damage initiation, propagation and catastrophic failure of the integral stiffened composite panels was simulated in detail by the proposed model, and the initial geometric imperfection was taken into account. Axial stiffness ratio of stiffener and skin was defined and conducted to study the effects to the structure on the carrying capacity and failure modes. The results indicate that: the model can predict the damage process of integral stiffened panel effectively; under the condition the ply design is reasonable, increasing the stiffness ratio can to some extent improve the unit area bearing capacity of the cross section of stiffened composite panels.
2011, 28(4): 212-218.
Abstract:
In order to design energy-absorption tubes for different impact loadings, the dynamic fracture process of composite tubes under axial crash loads was simulated by nonlinear explicit finite element method. The orthotropic material constants for fiber-reinforced polymer were obtained based on the strength and stiffness theory of composites. According to the principle of orthogonal design, the nonlinear mapping relations between specific energy absorption of tubes and their geometry parameters were established, and corresponding response surfaces were constructed. With the restriction of peak acceleration in frontal vehicle collision, the structural parameters of tubes with high specific energy absorption and low peak impact force were optimized by using sequential quadratic programming algorithm. The simulation results show that the deformation modes, absorbed energy, impact force versus displacement curve as well as the peak impact load agree well with that of experiments. The obtained maximum special energy absorption is 29.231 J/g when the wall thickness, edge length and tube length of square tube are 2.1, 44 and 200 mm, respectively.
In order to design energy-absorption tubes for different impact loadings, the dynamic fracture process of composite tubes under axial crash loads was simulated by nonlinear explicit finite element method. The orthotropic material constants for fiber-reinforced polymer were obtained based on the strength and stiffness theory of composites. According to the principle of orthogonal design, the nonlinear mapping relations between specific energy absorption of tubes and their geometry parameters were established, and corresponding response surfaces were constructed. With the restriction of peak acceleration in frontal vehicle collision, the structural parameters of tubes with high specific energy absorption and low peak impact force were optimized by using sequential quadratic programming algorithm. The simulation results show that the deformation modes, absorbed energy, impact force versus displacement curve as well as the peak impact load agree well with that of experiments. The obtained maximum special energy absorption is 29.231 J/g when the wall thickness, edge length and tube length of square tube are 2.1, 44 and 200 mm, respectively.
Model of dynamic damping behaviour for a new BTG plastic alloy about temperature frequency amplitude
2011, 28(4): 219-224.
Abstract:
A mathematical model is constructed to describe the dynamic damping performance for a new type of BTG plastic alloy about the temperature-frequency-amplitude. The experimental data of dynamic damping loss factor of BTG plastic alloy were obtained through test of frequency sweep, temperature sweep and amplitude sweep in the dynamic thermal analyzer DMA242. Through the analysis of the experimental data, the amount of damping loss factor is separated 2 components, namely, the amount related only to the frequency and the amount related to both the frequency and temperature .The amount related only to the frequency is described by Kelvin model of fractional derivative and the amount related to both the frequency and temperature is described by Gaussian function. A comprehensive model considering of the temperature-frequency-amplitude is established reference to the above model plus the amplitude factor. The results show that the comprehensive model can accurately describe the experimental data.
A mathematical model is constructed to describe the dynamic damping performance for a new type of BTG plastic alloy about the temperature-frequency-amplitude. The experimental data of dynamic damping loss factor of BTG plastic alloy were obtained through test of frequency sweep, temperature sweep and amplitude sweep in the dynamic thermal analyzer DMA242. Through the analysis of the experimental data, the amount of damping loss factor is separated 2 components, namely, the amount related only to the frequency and the amount related to both the frequency and temperature .The amount related only to the frequency is described by Kelvin model of fractional derivative and the amount related to both the frequency and temperature is described by Gaussian function. A comprehensive model considering of the temperature-frequency-amplitude is established reference to the above model plus the amplitude factor. The results show that the comprehensive model can accurately describe the experimental data.
2011, 28(4): 225-230.
Abstract:
The carrying capacity was calculated using the load transfer mechanism and the bonded-bolted deformation harmony condition for the bonded-bolted hybrid composite joints, which make holes, adhere coat and install bolts. The failure load of the bonded connection portion was calculated, and the shearing strain of the adhesive layer along the bonded length was analyzed when the bonded connection portion endured its failure load, and the load of the bolted connection portion was calculated using the bonded-bolted deformation harmony condition. The carrying capacity is the sum of the two loads. The carrying capacity calculated by the method was in good agreement with the experimental data, which validate the method.
The carrying capacity was calculated using the load transfer mechanism and the bonded-bolted deformation harmony condition for the bonded-bolted hybrid composite joints, which make holes, adhere coat and install bolts. The failure load of the bonded connection portion was calculated, and the shearing strain of the adhesive layer along the bonded length was analyzed when the bonded connection portion endured its failure load, and the load of the bolted connection portion was calculated using the bonded-bolted deformation harmony condition. The carrying capacity is the sum of the two loads. The carrying capacity calculated by the method was in good agreement with the experimental data, which validate the method.
