2017 Vol. 34, No. 8
2017, 34(8): 1625-1635.
doi: 10.13801/j.cnki.fhclxb.20170523.002
Abstract:
Particulate reinforced titanium matrix composites are one kind of important structural materials, which have a broad application prospect in the aerospace, space technology and military equipment and other high-tech fields. But the characteristics for the material such as high deformation resistance and high strength make it hard to achieve the further processing with high accuracy and quality. In this paper, the current status and progress of traditional processing technologies and special processing technologies for particulate reinforced titanium matrix composites were reviewed, which focused on the processing mechanism and performance in the traditional hot working, hydrogen processing, superplastic processing and laser manufacturing. After that, the paper presented future perspectives in processing technology for the material.
Particulate reinforced titanium matrix composites are one kind of important structural materials, which have a broad application prospect in the aerospace, space technology and military equipment and other high-tech fields. But the characteristics for the material such as high deformation resistance and high strength make it hard to achieve the further processing with high accuracy and quality. In this paper, the current status and progress of traditional processing technologies and special processing technologies for particulate reinforced titanium matrix composites were reviewed, which focused on the processing mechanism and performance in the traditional hot working, hydrogen processing, superplastic processing and laser manufacturing. After that, the paper presented future perspectives in processing technology for the material.
2017, 34(8): 1636-1644.
doi: 10.13801/j.cnki.fhclxb.20161123.002
Abstract:
The microcellular foamed wood flour/polypropylene composites were prepared by a microcellular batch foaming process using talc as the nucleating agent and supercritical CO2 fluid as foaming agent. The crystallization behavior and microcellular structure of impact fractured of microcellular foamed composite were investigated by differential scanning calorimeter (DSC), X-ray diffractometer (XRD) and scanning electron microscopy (SEM). The results indicate that talc increases the crystallization rate and temperature of microcellular foamed wood flour/polypropylene composites and induces imperfect α crystal. The addition of talc improves the melt viscosity of the polymer matrix. The talc also decreases the size of the cellular, inhibit the formation of big cellular, cellular coalescence and collapse. The cellular density of wood flour/polypropylene composites can be up to 1.0×109/cm3, the average radius is 16.4 μm, and the expansion ratio can reach 18, the apparent density is 0.055 g/cm3.
The microcellular foamed wood flour/polypropylene composites were prepared by a microcellular batch foaming process using talc as the nucleating agent and supercritical CO2 fluid as foaming agent. The crystallization behavior and microcellular structure of impact fractured of microcellular foamed composite were investigated by differential scanning calorimeter (DSC), X-ray diffractometer (XRD) and scanning electron microscopy (SEM). The results indicate that talc increases the crystallization rate and temperature of microcellular foamed wood flour/polypropylene composites and induces imperfect α crystal. The addition of talc improves the melt viscosity of the polymer matrix. The talc also decreases the size of the cellular, inhibit the formation of big cellular, cellular coalescence and collapse. The cellular density of wood flour/polypropylene composites can be up to 1.0×109/cm3, the average radius is 16.4 μm, and the expansion ratio can reach 18, the apparent density is 0.055 g/cm3.
2017, 34(8): 1645-1652.
doi: 10.13801/j.cnki.fhclxb.20161216.001
Abstract:
Maleic anhydride grafted ethylene-vinyl acetate copolymer (EVA-g-MAH) was used to toughen the calcium sulfate whiskers (CaSO4W)/nylon6 (PA6) composites. The CaSO4W/PA6 and CaSO4W-(EVA-g-MAH)/PA6 composites were prepared using by a twin screw extruder, and analyzed by means of SEM, DSC, XRD and mechanical testing. The results indicate that addition of small amounts of CaSO4W can increase the rate of crystallization, however, higher CaSO4W contents lead to a decreased rate of crystalization and promotion of forming γ-crystals of PA6. Adding 10% (mass fraction) CaSO4W increases both the stiffness and toughness of PA6. Adding 30% CaSO4W can further improve the stiffness but significantly decreases the fracture toughness of PA6. With 2.5% and 5% mass fraction of EVA-g-MAH, the impact strength of 30%CaSO4W-(EVA-g-MAH)/PA6 increases by 25.0% and 76.7%, respectively, thus imparting the higher toughness to the 30%CaSO4W/PA6. The improvement of impact strength of the composites mainly results from energy-absorption process, effective stress transfering, the increasing in interfacial adhesion between CaSO4W and PA6 in the presence of EVA-g-MAH as well as good miscibility of EVA-g-MAH/PA6 blend system.
Maleic anhydride grafted ethylene-vinyl acetate copolymer (EVA-g-MAH) was used to toughen the calcium sulfate whiskers (CaSO4W)/nylon6 (PA6) composites. The CaSO4W/PA6 and CaSO4W-(EVA-g-MAH)/PA6 composites were prepared using by a twin screw extruder, and analyzed by means of SEM, DSC, XRD and mechanical testing. The results indicate that addition of small amounts of CaSO4W can increase the rate of crystallization, however, higher CaSO4W contents lead to a decreased rate of crystalization and promotion of forming γ-crystals of PA6. Adding 10% (mass fraction) CaSO4W increases both the stiffness and toughness of PA6. Adding 30% CaSO4W can further improve the stiffness but significantly decreases the fracture toughness of PA6. With 2.5% and 5% mass fraction of EVA-g-MAH, the impact strength of 30%CaSO4W-(EVA-g-MAH)/PA6 increases by 25.0% and 76.7%, respectively, thus imparting the higher toughness to the 30%CaSO4W/PA6. The improvement of impact strength of the composites mainly results from energy-absorption process, effective stress transfering, the increasing in interfacial adhesion between CaSO4W and PA6 in the presence of EVA-g-MAH as well as good miscibility of EVA-g-MAH/PA6 blend system.
2017, 34(8): 1653-1659.
doi: 10.13801/j.cnki.fhclxb.20161124.006
Abstract:
The dispersion of nanographite (CNPs) in aqueous solution was first modified by sodium dodecyl sulfate (SDS) in order to prepare uniformly distributed CNPs on the surface of functioned graphene nanoribbons (EGNRs). Afterwards, the EGNRs75%-CNPs/EVA composite films were prepared by solution coating method on a coating machine. The morphology and properties of EGNRs75%-CNPs/EVA composite films were investigated by FTIR, XRD, XPS, FE-SEM, TEM, oxygen transmission rate and high resistance meter. The results show that the conductive network of EGNRs75%-CNPs can be observed after being loaded with CNPs, which is beneficial to the dispersion of EGNRs75%-CNPs in EVA matrix. When the mass fraction of EGNRs75%-CNPs is 1%, compared with that of the pure EVA, the oxygen transmission rate of EGNRs75%-CNPs/EVA composite films is reduced by 67.6%, thus the barrier property has improved deeply. EGNRs75%-CNPs/EVA composite films' conductivity has been improved by 8 orders of magnitude as EGNRs75%-CNPs mass fraction is 0.8% because of the formation of 3D conductive network, which exhibit the excellent room temperature conductivity.
The dispersion of nanographite (CNPs) in aqueous solution was first modified by sodium dodecyl sulfate (SDS) in order to prepare uniformly distributed CNPs on the surface of functioned graphene nanoribbons (EGNRs). Afterwards, the EGNRs75%-CNPs/EVA composite films were prepared by solution coating method on a coating machine. The morphology and properties of EGNRs75%-CNPs/EVA composite films were investigated by FTIR, XRD, XPS, FE-SEM, TEM, oxygen transmission rate and high resistance meter. The results show that the conductive network of EGNRs75%-CNPs can be observed after being loaded with CNPs, which is beneficial to the dispersion of EGNRs75%-CNPs in EVA matrix. When the mass fraction of EGNRs75%-CNPs is 1%, compared with that of the pure EVA, the oxygen transmission rate of EGNRs75%-CNPs/EVA composite films is reduced by 67.6%, thus the barrier property has improved deeply. EGNRs75%-CNPs/EVA composite films' conductivity has been improved by 8 orders of magnitude as EGNRs75%-CNPs mass fraction is 0.8% because of the formation of 3D conductive network, which exhibit the excellent room temperature conductivity.
2017, 34(8): 1660-1666.
doi: 10.13801/j.cnki.fhclxb.20170517.001
Abstract:
The ZrO2/PVDF-PAN composite membranes based as poly(vinylidene fluoride) (PVDF) and polyacrylonitrile(PAN) with different ZrO2 contents were prepared by electrospinning. The morphology and specific surface area were characterized by SEM and BET, respectively. The results show that the morphologies of the composite membranes depend on the ZrO2 content. With the increasing of ZrO2 content, the surface of fibers becomes unsmooth and the specific surface area and liquid absorption rate increase, and they reach the maximum when the ZrO2 content is 0.4% of the mass of PVDF and PAN. To study the effect of ZrO2 content on electrochemical performance of composite membranes, super-capacitors were fabricated with the composite membrane as separators. Test results of cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) show that composite membrane with 0.4wt% ZrO2 possesses excellent electrochemical performance, in which the specific capacitance value and ionic conductivity reach 126.0 F/g and 9.31×10-3 S/cm, respectively.
The ZrO2/PVDF-PAN composite membranes based as poly(vinylidene fluoride) (PVDF) and polyacrylonitrile(PAN) with different ZrO2 contents were prepared by electrospinning. The morphology and specific surface area were characterized by SEM and BET, respectively. The results show that the morphologies of the composite membranes depend on the ZrO2 content. With the increasing of ZrO2 content, the surface of fibers becomes unsmooth and the specific surface area and liquid absorption rate increase, and they reach the maximum when the ZrO2 content is 0.4% of the mass of PVDF and PAN. To study the effect of ZrO2 content on electrochemical performance of composite membranes, super-capacitors were fabricated with the composite membrane as separators. Test results of cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) show that composite membrane with 0.4wt% ZrO2 possesses excellent electrochemical performance, in which the specific capacitance value and ionic conductivity reach 126.0 F/g and 9.31×10-3 S/cm, respectively.
2017, 34(8): 1667-1673.
doi: 10.13801/j.cnki.fhclxb.20161124.002
Abstract:
ZnMgAl layered double hydroxides(LDHs), modified-LDHs and Sb2O3-LDHs were prepared via rapid nucleation/crystallization method, and modification by sodium oleate and high-speed ball-milling process, respectively, and then were characterized by XRD, FTIR, FESEM and TG etc. The flame retardant and mechanical properties of soft polyvinyl chloride(PVC) matrix composites with 6% mass ratio of Sb2O3-LDHs were investigated. The results show that all the composites can meet the requirement of V-0 grade in UL-94 test and the LOI value reach to 33.4%; the mechanical properties of modified-LDHs/soft PVC and Sb2O3-LDHs/soft PVC composites can be improved in certain extent. The FESEM images of the carbon residue after combustion show that a dense protective coal layer forms on the surface of composites after combustion to achieve flame retardant effect when adding modified-LDHs or (Sb2O3)10-LDHs. FESEM images of materials' cross-section show that the modified-LDHs is dispersed uniformly in the soft PVC, and exhibit well compatibility with soft PVC, enabling strengthen and toughen the composites. The elongation at break and tensile strength of Sb2O3-LDHs/soft PVC composites are better than that of the soft PVC, but decline gradually with the increasing of mass fraction of Sb2O3-LDHs owing to the interface difference between Sb2O3 and the polymer matrix.
ZnMgAl layered double hydroxides(LDHs), modified-LDHs and Sb2O3-LDHs were prepared via rapid nucleation/crystallization method, and modification by sodium oleate and high-speed ball-milling process, respectively, and then were characterized by XRD, FTIR, FESEM and TG etc. The flame retardant and mechanical properties of soft polyvinyl chloride(PVC) matrix composites with 6% mass ratio of Sb2O3-LDHs were investigated. The results show that all the composites can meet the requirement of V-0 grade in UL-94 test and the LOI value reach to 33.4%; the mechanical properties of modified-LDHs/soft PVC and Sb2O3-LDHs/soft PVC composites can be improved in certain extent. The FESEM images of the carbon residue after combustion show that a dense protective coal layer forms on the surface of composites after combustion to achieve flame retardant effect when adding modified-LDHs or (Sb2O3)10-LDHs. FESEM images of materials' cross-section show that the modified-LDHs is dispersed uniformly in the soft PVC, and exhibit well compatibility with soft PVC, enabling strengthen and toughen the composites. The elongation at break and tensile strength of Sb2O3-LDHs/soft PVC composites are better than that of the soft PVC, but decline gradually with the increasing of mass fraction of Sb2O3-LDHs owing to the interface difference between Sb2O3 and the polymer matrix.
2017, 34(8): 1674-1682.
doi: 10.13801/j.cnki.fhclxb.20161109.001
Abstract:
Combustion characteristics of epoxy resin matrix of T300 carbon fiber/epoxy composite and T300 carbon fiber/epoxy composite-foam laminate(there are a layer of T300 carbon fiber/epoxy composite in the upper and lower parts and a layer of 4 mm thick H60 Divinycell foam core material in the middle part) were experimentally investigated under different fire conditions using cone calorimeter. The change law of the combustion characteristic parameters of the ignition time, heat release rate, total smoke release quantity and CO generation rate were analyzed. The morphology images of T300 carbon fiber/epoxy composite before and after combustion, and the carbon layer morphology image of epoxy resin matrix and T300 carbon fiber/epoxy composite after combustion were observed by SEM. The influence of carbon fiber on pyrolysis and combustion of carbon fiber/epoxy composite was analyzed. The results show that the mean ignition time is shortened, the peak and first 300 s average of heat release rate are increased, the peak time is in advanced, and the residual percentage after burning is decreased with the increase in radiation heat flux. The ignition time, heat release and peak time of heat release rates of T300 carbon fiber/epoxy composite are delayed because of the inhibiting effect of the carbon fiber on pyrolysis and combustion of epoxy resin matrix. The ignition time, peak time of heat release rates and CO release time of T300 carbon fiber/epoxy composite-foam laminate are in advanced due to the low ignite of the foam core material.There ware obvious stratification phenomenon on T300 epoxy resin/carbon fiber composite and T300 carbon fiber/epoxy composite-foam laminate after burning, which results in the mechanical properties lose and the overall structure being destroyed. Carbon fiber has the inhibition effects on the pyrolysis and combustion of composites and the inhibition of the droplet, splashing and a lot of smoke generation in the combustion process.
Combustion characteristics of epoxy resin matrix of T300 carbon fiber/epoxy composite and T300 carbon fiber/epoxy composite-foam laminate(there are a layer of T300 carbon fiber/epoxy composite in the upper and lower parts and a layer of 4 mm thick H60 Divinycell foam core material in the middle part) were experimentally investigated under different fire conditions using cone calorimeter. The change law of the combustion characteristic parameters of the ignition time, heat release rate, total smoke release quantity and CO generation rate were analyzed. The morphology images of T300 carbon fiber/epoxy composite before and after combustion, and the carbon layer morphology image of epoxy resin matrix and T300 carbon fiber/epoxy composite after combustion were observed by SEM. The influence of carbon fiber on pyrolysis and combustion of carbon fiber/epoxy composite was analyzed. The results show that the mean ignition time is shortened, the peak and first 300 s average of heat release rate are increased, the peak time is in advanced, and the residual percentage after burning is decreased with the increase in radiation heat flux. The ignition time, heat release and peak time of heat release rates of T300 carbon fiber/epoxy composite are delayed because of the inhibiting effect of the carbon fiber on pyrolysis and combustion of epoxy resin matrix. The ignition time, peak time of heat release rates and CO release time of T300 carbon fiber/epoxy composite-foam laminate are in advanced due to the low ignite of the foam core material.There ware obvious stratification phenomenon on T300 epoxy resin/carbon fiber composite and T300 carbon fiber/epoxy composite-foam laminate after burning, which results in the mechanical properties lose and the overall structure being destroyed. Carbon fiber has the inhibition effects on the pyrolysis and combustion of composites and the inhibition of the droplet, splashing and a lot of smoke generation in the combustion process.
2017, 34(8): 1683-1692.
doi: 10.13801/j.cnki.fhclxb.20161123.003
Abstract:
NO3- and Mo7O246- intercalated ZnMgAl ternary layered double hydroxide (NO3-ZnMgAl LDHs, Mo-ZnMgAl LDHs) was prepared by the hydrothermal method and ion exchange, respectively. The flame retardancy and smoke suppression of polyurethane elastomer (PUE) composites were studied by adding two ternary LDHs with different proportions. Both the cone calorimeter combustion and smoke density tests show that the peak heat release rate (PHRR) and maximum smoke density (Ds, max) of the pure PUE are 920 kW/m2 and 452, respectively. When the mass fraction of NO3-ZnMgAl LDHs is up to 7wt%, the PHRR and Ds, max are 377 kW/m2 and 216, respectively. With the same loading of Mo-ZnMgAl LDHs, the PHRR and Ds, max are 343 kW/m2 and 190, respectively. Both ternary LDHs possess notable flame retardancy and smoke suppression effects on PUE composites. LDHs/PUE composites have better flame retardancy and smoke suppression with Mo-ZnMgAl LDHs. TGA measurement confirms that the addition of two ternary LDHs can both promote the charring formation of LDHs/PUE composites and improve the char residue rate. LRS and XPS confirm that they could improve the graphitization degree of the char residue which can in turn enhance the thermal oxidation resistance of the char layer. Furthermore, the Mo-ZnMgAl LDHs can raise the char residue and graphitization degree and strengthen the thermal oxidation resistance, which could effectively protect the substrate material from heat radiation, and consequently oxygen could be isolated, meanwhile, the volatilization of combustible gas could be restrained.
NO3- and Mo7O246- intercalated ZnMgAl ternary layered double hydroxide (NO3-ZnMgAl LDHs, Mo-ZnMgAl LDHs) was prepared by the hydrothermal method and ion exchange, respectively. The flame retardancy and smoke suppression of polyurethane elastomer (PUE) composites were studied by adding two ternary LDHs with different proportions. Both the cone calorimeter combustion and smoke density tests show that the peak heat release rate (PHRR) and maximum smoke density (Ds, max) of the pure PUE are 920 kW/m2 and 452, respectively. When the mass fraction of NO3-ZnMgAl LDHs is up to 7wt%, the PHRR and Ds, max are 377 kW/m2 and 216, respectively. With the same loading of Mo-ZnMgAl LDHs, the PHRR and Ds, max are 343 kW/m2 and 190, respectively. Both ternary LDHs possess notable flame retardancy and smoke suppression effects on PUE composites. LDHs/PUE composites have better flame retardancy and smoke suppression with Mo-ZnMgAl LDHs. TGA measurement confirms that the addition of two ternary LDHs can both promote the charring formation of LDHs/PUE composites and improve the char residue rate. LRS and XPS confirm that they could improve the graphitization degree of the char residue which can in turn enhance the thermal oxidation resistance of the char layer. Furthermore, the Mo-ZnMgAl LDHs can raise the char residue and graphitization degree and strengthen the thermal oxidation resistance, which could effectively protect the substrate material from heat radiation, and consequently oxygen could be isolated, meanwhile, the volatilization of combustible gas could be restrained.
2017, 34(8): 1693-1703.
doi: 10.13801/j.cnki.fhclxb.20161103.001
Abstract:
In order to improve the micro-cracks resistance of carbon fiber reinforced epoxy (CF/EP) at cryogenic temperature (77 K), Fe3O4 modified O-MWCNTs (Fe3O4-O-MWCNTs) with good paramagnetic properties were prepared by co-precipitation method. The effects of the addtions of aligned Fe3O4-O-MWCNTs on the properties of epoxy (EP) and CF/EP composites at 77 K were studied. The results show that the aligned Fe3O4-O-MWCNTs can effectively improve the mechanical properties of EP matrix at 77 K and reduce the coefficient of thermal expansion (α) of EP matrix. It can also obviously improve the micro-crack resistance of CF/EP composites at 77 K. Comparing to the neat EP, α of aligned Fe3O4-O-MWCNTs modified EP composite decreases by 41.6%. Comparing to CF/EP composite, the micro-crack density of aligned Fe3O4-O-MWCNTs modified CF/EP composite at 77 K decreases by 56.2%.
In order to improve the micro-cracks resistance of carbon fiber reinforced epoxy (CF/EP) at cryogenic temperature (77 K), Fe3O4 modified O-MWCNTs (Fe3O4-O-MWCNTs) with good paramagnetic properties were prepared by co-precipitation method. The effects of the addtions of aligned Fe3O4-O-MWCNTs on the properties of epoxy (EP) and CF/EP composites at 77 K were studied. The results show that the aligned Fe3O4-O-MWCNTs can effectively improve the mechanical properties of EP matrix at 77 K and reduce the coefficient of thermal expansion (α) of EP matrix. It can also obviously improve the micro-crack resistance of CF/EP composites at 77 K. Comparing to the neat EP, α of aligned Fe3O4-O-MWCNTs modified EP composite decreases by 41.6%. Comparing to CF/EP composite, the micro-crack density of aligned Fe3O4-O-MWCNTs modified CF/EP composite at 77 K decreases by 56.2%.
2017, 34(8): 1704-1711.
doi: 10.13801/j.cnki.fhclxb.20161115.002
Abstract:
In this study, the self-made hybrid aramid papers were prepared with domestic para-aramid chopped fibers, meta-aramid chopped fibers and meta-aramid fibrids. The inter-binding features between the fibers and fibrids and crystalline properties of self-made hybrid aramid paper and Nomex T410(0.13 mm)paper were observed by SEM and XRD. The heat resistance properties of papers were also examined by TGA. The mechanical and dielectic properties were studied by comparison with the self-aramid hybrid paper and Nomex T410 paper, and correspondingly the hybrid effects of different chopped fibers on aramid paper were clarified. The results show that the paper properties of tensile strength, tearing index, crystallinity and heat resistance of the self-made hybrid aramid papers increase dramatically with the content increasing of para-aramid chopped fibers in sheets, however, the dielectric strength of papers increases at the beginning of chopped fibers hybriding and then decreases. When the hybriding ratio is 2:2, a favorable inter-bond features between the chopped fibers and fibrids is alike that of Nomex T410 paper, and mechanical and dielectic properties are close to that of Nomex T410 paper. The tensile index of self-made aramid paper is 130.4 N·m·g-1, better than that of the Nomex T410 paper which is 111.1 N·m·g-1 in machine direction and 56.2 N·m·g-1 in cross direction. The tear index is 32.6 mN·m2·g-1 which is between the machine direction(37.6 mN·m2·g-1) and cross direction(23.6 mN·m2·g-1) of Nomex T410 paper. The maximum value 26.5 kV·m-1 was gained at the hybriding ratio of 2:2, which was very close to 27.0 kV·m-1 of Nomex T410 paper. The degrees of crystallinity of the two papers were 34.84% and 15.71%, respectively. The initial decomposition temperatures are 430.6℃ and 435.1℃, and their mass loss at 780℃ are 42.8% and 39.1%, respectively, which indicates that aramid papers have stable heat resistance properties.
In this study, the self-made hybrid aramid papers were prepared with domestic para-aramid chopped fibers, meta-aramid chopped fibers and meta-aramid fibrids. The inter-binding features between the fibers and fibrids and crystalline properties of self-made hybrid aramid paper and Nomex T410(0.13 mm)paper were observed by SEM and XRD. The heat resistance properties of papers were also examined by TGA. The mechanical and dielectic properties were studied by comparison with the self-aramid hybrid paper and Nomex T410 paper, and correspondingly the hybrid effects of different chopped fibers on aramid paper were clarified. The results show that the paper properties of tensile strength, tearing index, crystallinity and heat resistance of the self-made hybrid aramid papers increase dramatically with the content increasing of para-aramid chopped fibers in sheets, however, the dielectric strength of papers increases at the beginning of chopped fibers hybriding and then decreases. When the hybriding ratio is 2:2, a favorable inter-bond features between the chopped fibers and fibrids is alike that of Nomex T410 paper, and mechanical and dielectic properties are close to that of Nomex T410 paper. The tensile index of self-made aramid paper is 130.4 N·m·g-1, better than that of the Nomex T410 paper which is 111.1 N·m·g-1 in machine direction and 56.2 N·m·g-1 in cross direction. The tear index is 32.6 mN·m2·g-1 which is between the machine direction(37.6 mN·m2·g-1) and cross direction(23.6 mN·m2·g-1) of Nomex T410 paper. The maximum value 26.5 kV·m-1 was gained at the hybriding ratio of 2:2, which was very close to 27.0 kV·m-1 of Nomex T410 paper. The degrees of crystallinity of the two papers were 34.84% and 15.71%, respectively. The initial decomposition temperatures are 430.6℃ and 435.1℃, and their mass loss at 780℃ are 42.8% and 39.1%, respectively, which indicates that aramid papers have stable heat resistance properties.
2017, 34(8): 1712-1720.
doi: 10.13801/j.cnki.fhclxb.20161116.001
Abstract:
The effect of initial defect size on the mechanical behavior and failure pattern of CFRP (Carbon Fiber Reinforced Polymer)-confined concrete columns was investigated through theoretical analysis, numerical simulation and experiment validation. Qualitative theoretical analysis was firstly explored to study the effect of initial defect size on the integrity of FRP-confined concrete from macro to micro perspective. Numerical analysis and experimental investigation were then carried out and compared to investigate the failure mechanism of FRP-confined concrete column with initial defects under axial compression force and eccentric compression force. The variation of defect criticality was investigated by varying the layer number of CFRP and cross-section size of concrete columns. The effect of initial defect size on the failure mechanism of CFRP-confined concrete columns was finally demonstrated.
The effect of initial defect size on the mechanical behavior and failure pattern of CFRP (Carbon Fiber Reinforced Polymer)-confined concrete columns was investigated through theoretical analysis, numerical simulation and experiment validation. Qualitative theoretical analysis was firstly explored to study the effect of initial defect size on the integrity of FRP-confined concrete from macro to micro perspective. Numerical analysis and experimental investigation were then carried out and compared to investigate the failure mechanism of FRP-confined concrete column with initial defects under axial compression force and eccentric compression force. The variation of defect criticality was investigated by varying the layer number of CFRP and cross-section size of concrete columns. The effect of initial defect size on the failure mechanism of CFRP-confined concrete columns was finally demonstrated.
2017, 34(8): 1721-1728.
doi: 10.13801/j.cnki.fhclxb.20161124.003
Abstract:
A CFRP drilling testing platform was set up to discuss step drill structural parameters and drilling process parameters under composite drilling axial force and delamination factor influence based on the VMC850B vertical machining centers and UltraPAC ultrasonic C-scan. The result shows that drill process parameters have significant influence on the first section of the drilling thrust and step drill structural parameters have significant influence on the second section of the drilling thrust. The value of delamination factor is connection with the first section of the drilling thrust and the second section of the drilling thrust. When d/D >0.5, the size of delamination factor is mainly connection with the first section of the drilling thrust. When the first paragraph diameter and the second point angle are 2.8 mm and 95°, spindle speed and feed speed are 7000 r/min and 2.5 mm/s, the delamination can be reduced.
A CFRP drilling testing platform was set up to discuss step drill structural parameters and drilling process parameters under composite drilling axial force and delamination factor influence based on the VMC850B vertical machining centers and UltraPAC ultrasonic C-scan. The result shows that drill process parameters have significant influence on the first section of the drilling thrust and step drill structural parameters have significant influence on the second section of the drilling thrust. The value of delamination factor is connection with the first section of the drilling thrust and the second section of the drilling thrust. When d/D >0.5, the size of delamination factor is mainly connection with the first section of the drilling thrust. When the first paragraph diameter and the second point angle are 2.8 mm and 95°, spindle speed and feed speed are 7000 r/min and 2.5 mm/s, the delamination can be reduced.
2017, 34(8): 1729-1735.
doi: 10.13801/j.cnki.fhclxb.20161205.004
Abstract:
Based on quadratic Bezier curve, research on buckling property of laminates produced by fiber variable angle placement was studied. Firstly, a segmental quadratic Bezier curve fitting method was proposed by extending the original quadratic Bezier curve theory to redefine the reference path of fiber variable angle placement and determine the parameterized expression of the laminates laid according to variable angle. Secondly, taking the laminates laid by variable angle of[0± < 20(β)65>]2s and[90± < 20(β)65>]2s as examples, the buckling properties were analyzed through FEM method. And the comparison analysis with the buckling property of the laminates laid by constant angle was conducted. Finally, the influences of termination angles α and connecting point parameter β on the buckling property were studied. The results show that the linear buckling load of these two kinds of variable stiffness laminates first increases then decreases as β increases. And it is also found that the buckling load of first order increases gradually when the termination angle is larger than the initial angle, which indicates that increasing the placement angle is beneficial to improving the buckling load of the laminates.
Based on quadratic Bezier curve, research on buckling property of laminates produced by fiber variable angle placement was studied. Firstly, a segmental quadratic Bezier curve fitting method was proposed by extending the original quadratic Bezier curve theory to redefine the reference path of fiber variable angle placement and determine the parameterized expression of the laminates laid according to variable angle. Secondly, taking the laminates laid by variable angle of[0± < 20(β)65>]2s and[90± < 20(β)65>]2s as examples, the buckling properties were analyzed through FEM method. And the comparison analysis with the buckling property of the laminates laid by constant angle was conducted. Finally, the influences of termination angles α and connecting point parameter β on the buckling property were studied. The results show that the linear buckling load of these two kinds of variable stiffness laminates first increases then decreases as β increases. And it is also found that the buckling load of first order increases gradually when the termination angle is larger than the initial angle, which indicates that increasing the placement angle is beneficial to improving the buckling load of the laminates.
2017, 34(8): 1736-1744.
doi: 10.13801/j.cnki.fhclxb.20161115.008
Abstract:
According to the characteristics of VARTM, the mathematical models of resin flow and preform deformation during the mold filling process were built. A mold filling simulation algorithm based on mixed grid approach was proposed. In this approach, the geometry model of the mould cavity was meshed by 2D or 3D grid, and then a 1D affiliate element was added on each surface element of the vacuum bag to absorb or extrude some resin in real time cased by the vacuum bag deformation, so the mixed grid simulation model was established, During the simulation, resin flow and preform deformation were solved separately, then they were coupled using the above-mentioned mixed grid simulation model, the unity of simulation precision and velocity was achieved. A mold filling experimental platform for VARTM was built and a 1D mold filling experiment was implemented, according to the comparison between simulation and experiment results, the validity of the algorithm was verified. At last, the feasibility of the above-mentioned algorithm on 3D complex structure and sequential injection strategy was validated by 3D simulation example.
According to the characteristics of VARTM, the mathematical models of resin flow and preform deformation during the mold filling process were built. A mold filling simulation algorithm based on mixed grid approach was proposed. In this approach, the geometry model of the mould cavity was meshed by 2D or 3D grid, and then a 1D affiliate element was added on each surface element of the vacuum bag to absorb or extrude some resin in real time cased by the vacuum bag deformation, so the mixed grid simulation model was established, During the simulation, resin flow and preform deformation were solved separately, then they were coupled using the above-mentioned mixed grid simulation model, the unity of simulation precision and velocity was achieved. A mold filling experimental platform for VARTM was built and a 1D mold filling experiment was implemented, according to the comparison between simulation and experiment results, the validity of the algorithm was verified. At last, the feasibility of the above-mentioned algorithm on 3D complex structure and sequential injection strategy was validated by 3D simulation example.
2017, 34(8): 1745-1753.
doi: 10.13801/j.cnki.fhclxb.20161124.005
Abstract:
A computation model for critical buckling load of composite thin tube was presented. Based on the plane hypothesis and small deformation assumption, a simplified method was presented for equivalent bending stiffness of composite beam. According to the geometrical symmetry and force symmetry of tube under axial compression, the local buckling of tube was transformed into the problem of the bending deformation of the axial and circumferential strips. On the basis of the stability theory of shell, the computation model for the stability of longitudinal strip on elastic foundation was established, and the analytical formula for the buckling bearing capacity of the composite tube was obtained. Compared with the engineering calculation formula, they are similar in form and the correction factor can be obtained directly from the model, rather than from experience. Axial compression test of three kinds of laminated composite tubes was conducted, and the experimental results are consistent with the theoretical prediction. Comparing the experimental data in literature with the theoretical calculation results, the deviation meets the requirements of engineering accuracy, which verifies the correctness of the model.
A computation model for critical buckling load of composite thin tube was presented. Based on the plane hypothesis and small deformation assumption, a simplified method was presented for equivalent bending stiffness of composite beam. According to the geometrical symmetry and force symmetry of tube under axial compression, the local buckling of tube was transformed into the problem of the bending deformation of the axial and circumferential strips. On the basis of the stability theory of shell, the computation model for the stability of longitudinal strip on elastic foundation was established, and the analytical formula for the buckling bearing capacity of the composite tube was obtained. Compared with the engineering calculation formula, they are similar in form and the correction factor can be obtained directly from the model, rather than from experience. Axial compression test of three kinds of laminated composite tubes was conducted, and the experimental results are consistent with the theoretical prediction. Comparing the experimental data in literature with the theoretical calculation results, the deviation meets the requirements of engineering accuracy, which verifies the correctness of the model.
2017, 34(8): 1754-1763.
doi: 10.13801/j.cnki.fhclxb.20161115.004
Abstract:
Response of carbon fiber composites under longitudinal compression were researched using the tool of compressive test and finite element simulation. The progressive damage during the loading process was detected with high speed camera and the final failure mode was observed by optical microscope. Based on fiber initial misalignment and matrix Drucker-Prager plastic constitutive model, finite element models were established using ABAQUS to analyze the results of different fiber initial misalignment models including shear mode and extensional mode. Results show that elastic and plastic deformations are both found during the longitudinal compression. Discrete two-dimensional fiber-matrix finite element model can efficiently simulate the process of compression, which corresponds to the test results. Compressive strength of composites depends on the fiber initial misalignment and shear yielding of plastic matrix. And it increases with the decreasing of fiber initial misalignment amplitude, increasing of fiber initial misalignment wavelength, as well as the increasing of fiber volume fraction.
Response of carbon fiber composites under longitudinal compression were researched using the tool of compressive test and finite element simulation. The progressive damage during the loading process was detected with high speed camera and the final failure mode was observed by optical microscope. Based on fiber initial misalignment and matrix Drucker-Prager plastic constitutive model, finite element models were established using ABAQUS to analyze the results of different fiber initial misalignment models including shear mode and extensional mode. Results show that elastic and plastic deformations are both found during the longitudinal compression. Discrete two-dimensional fiber-matrix finite element model can efficiently simulate the process of compression, which corresponds to the test results. Compressive strength of composites depends on the fiber initial misalignment and shear yielding of plastic matrix. And it increases with the decreasing of fiber initial misalignment amplitude, increasing of fiber initial misalignment wavelength, as well as the increasing of fiber volume fraction.
2017, 34(8): 1764-1771.
doi: 10.13801/j.cnki.fhclxb.20161130.002
Abstract:
The new energy absorption structure element of filament wound composite sandwich cylinder has been put forward and designed. In order to investigate the damage formation, extension and evolvement law of the element, the numerical analysis model was built by ABAQUS and the experiments were conducted under quasi-static compression loading. Comprehensive analysis of numerical simulation and experimental results show that the quasi-static compression process can be divived into three stages, including the initial elastic compression stage, the progressive damage stage and the structural damage stage. The plastic damage deformation and shear failure of solid buoyant core occur under compression load. Then steady energy absorption process is terminated by the tensile breaking of hoop fibers owing to transverse expansion effect of solid buoyant core. The results show that the energy absorption efficiency of this element is much higher than that of the traditional composite culindrical shell structure.
The new energy absorption structure element of filament wound composite sandwich cylinder has been put forward and designed. In order to investigate the damage formation, extension and evolvement law of the element, the numerical analysis model was built by ABAQUS and the experiments were conducted under quasi-static compression loading. Comprehensive analysis of numerical simulation and experimental results show that the quasi-static compression process can be divived into three stages, including the initial elastic compression stage, the progressive damage stage and the structural damage stage. The plastic damage deformation and shear failure of solid buoyant core occur under compression load. Then steady energy absorption process is terminated by the tensile breaking of hoop fibers owing to transverse expansion effect of solid buoyant core. The results show that the energy absorption efficiency of this element is much higher than that of the traditional composite culindrical shell structure.
2017, 34(8): 1772-1779.
doi: 10.13801/j.cnki.fhclxb.20161115.007
Abstract:
This paper studied the mechanical behavior and load bearing capability of composite L-type frame specimen under tension loadings through experiments and FEM analysis, which can be used to predict the mechanical response of a typical composite cabin. The results show that delamination and matrix damage are the main failure modes of composite L-type frame under tension loading, and the discrepancy of load bearing capabilities basis on simulation analysis and test is acceptable, which is only 10.1%. Future research shows that better mechanical properties can be obtained by sticking metallic gaskets around the bolted holes. The results can be used as theory reference for composite L-type frame structure designing.
This paper studied the mechanical behavior and load bearing capability of composite L-type frame specimen under tension loadings through experiments and FEM analysis, which can be used to predict the mechanical response of a typical composite cabin. The results show that delamination and matrix damage are the main failure modes of composite L-type frame under tension loading, and the discrepancy of load bearing capabilities basis on simulation analysis and test is acceptable, which is only 10.1%. Future research shows that better mechanical properties can be obtained by sticking metallic gaskets around the bolted holes. The results can be used as theory reference for composite L-type frame structure designing.
2017, 34(8): 1780-1787.
doi: 10.13801/j.cnki.fhclxb.20161018.005
Abstract:
To improve the crashworthiness of aircraft, the impact dynamic characteristics of 2D triaxial braided composite fuselage frame were investigated. Based on continuum damage mechanics, a finite element model of the fuselage frame under impact load was developed where irreversible thermodynamic theory combined with Weibull distribution and Hashin failure criterion were utilized to establish the damage growth law and determine damage threshold function, respectively. Shear stress was coupled with normal stress and the damage modes in both longitudinal and transverse direction of the material were considered independently in the iteration procedure. On this basis, the effects of varying material parameters on the impact dynamic performances of the frame were analyzed, and the transient response characteristics and energy absorption behaviors were compared further. Numerical results show that the finite element model is able to deal with this nonlinear transient dynamical problem accurately. The deviation between the simulation and the test on peak load is 1.5%, while absorbed energy is 4.7%. Besides, the longitudinal material parameters such as Young's modulus and compression strength have a significant influence on the dynamic response of the fuselage frame.
To improve the crashworthiness of aircraft, the impact dynamic characteristics of 2D triaxial braided composite fuselage frame were investigated. Based on continuum damage mechanics, a finite element model of the fuselage frame under impact load was developed where irreversible thermodynamic theory combined with Weibull distribution and Hashin failure criterion were utilized to establish the damage growth law and determine damage threshold function, respectively. Shear stress was coupled with normal stress and the damage modes in both longitudinal and transverse direction of the material were considered independently in the iteration procedure. On this basis, the effects of varying material parameters on the impact dynamic performances of the frame were analyzed, and the transient response characteristics and energy absorption behaviors were compared further. Numerical results show that the finite element model is able to deal with this nonlinear transient dynamical problem accurately. The deviation between the simulation and the test on peak load is 1.5%, while absorbed energy is 4.7%. Besides, the longitudinal material parameters such as Young's modulus and compression strength have a significant influence on the dynamic response of the fuselage frame.
2017, 34(8): 1788-1793.
doi: 10.13801/j.cnki.fhclxb.20161115.006
Abstract:
The in-situ TiB2/ZL205A composites were prepared by the method of mixed salt reaction in aluminum alloy melt. The phases, morphology and distribution of TiB2 particles and the fluidity of the fabricated composites were studied. The results show that the main phases of the TiB2/ZL205A composites are α-Al, Al2Cu and TiB2. The TiB2 particles with an average size of 500 nm and the shape of polygon or ovoid distribute mostly along the grains boundary and a few in the grains. The two relationships, that is the fluidity and casting temperature and the fluidity and mass fraction of Ti2B particles, can all be described by the exponential damping model. When the casting temperature raises from 710℃ to 750℃, the fluidity of 7wt%TiB2/ZL205A composites increases by 30.4%. When the casting temperature increases above 750℃, the increasing rate of the 7wt%TiB2/ZL205A composites fluidity is decreased with the increasing of casting temperature. Compared with the matrix alloy, the fluidity of 3wt%TiB2/ZL205A composites decreases by 21.8%, and the fluidity of 7wt%TiB2/ZL205A composites decreases by 36.4%.
The in-situ TiB2/ZL205A composites were prepared by the method of mixed salt reaction in aluminum alloy melt. The phases, morphology and distribution of TiB2 particles and the fluidity of the fabricated composites were studied. The results show that the main phases of the TiB2/ZL205A composites are α-Al, Al2Cu and TiB2. The TiB2 particles with an average size of 500 nm and the shape of polygon or ovoid distribute mostly along the grains boundary and a few in the grains. The two relationships, that is the fluidity and casting temperature and the fluidity and mass fraction of Ti2B particles, can all be described by the exponential damping model. When the casting temperature raises from 710℃ to 750℃, the fluidity of 7wt%TiB2/ZL205A composites increases by 30.4%. When the casting temperature increases above 750℃, the increasing rate of the 7wt%TiB2/ZL205A composites fluidity is decreased with the increasing of casting temperature. Compared with the matrix alloy, the fluidity of 3wt%TiB2/ZL205A composites decreases by 21.8%, and the fluidity of 7wt%TiB2/ZL205A composites decreases by 36.4%.
2017, 34(8): 1794-1800.
doi: 10.13801/j.cnki.fhclxb.20161115.003
Abstract:
The coherent interface of Mg and SiC was established by analyzing their crystal structures. Interatomic pair potentials for SiC/Mg interfaces were inversed by Chen-Möbius lattice inversion method and analytical expre-ssions for Si-Mg and C-Mg pair potentials as a function of the SiC/Mg interfacial adhesive energy have been derived, respectively. On this basis, ab initio calculations of the adhesive energy for the SiC/Mg interface were carried out. Thus, the Si-Mg and C-Mg pair potentials were obtained by the inversion formula. In addition, a self-consistent check was conducted to validate the inversion process. Meanwhile, six other SiC/Mg interface models were built to validate the transferability of the inversed pair potentials by comparing adhesive energies predicted by the ab initio method with those calculated by the inversion method. The results show that the original ab initio adhesive energies can be precisely reproduced by the inversed potentials, indicating that the inversion method is self-consistent and the obtained potentials are of good transferability for some other interface models. The inversion formula deduced in this paper is also suitable for other interfaces similar to SiC/Mg interface structures.
The coherent interface of Mg and SiC was established by analyzing their crystal structures. Interatomic pair potentials for SiC/Mg interfaces were inversed by Chen-Möbius lattice inversion method and analytical expre-ssions for Si-Mg and C-Mg pair potentials as a function of the SiC/Mg interfacial adhesive energy have been derived, respectively. On this basis, ab initio calculations of the adhesive energy for the SiC/Mg interface were carried out. Thus, the Si-Mg and C-Mg pair potentials were obtained by the inversion formula. In addition, a self-consistent check was conducted to validate the inversion process. Meanwhile, six other SiC/Mg interface models were built to validate the transferability of the inversed pair potentials by comparing adhesive energies predicted by the ab initio method with those calculated by the inversion method. The results show that the original ab initio adhesive energies can be precisely reproduced by the inversed potentials, indicating that the inversion method is self-consistent and the obtained potentials are of good transferability for some other interface models. The inversion formula deduced in this paper is also suitable for other interfaces similar to SiC/Mg interface structures.
2017, 34(8): 1801-1809.
doi: 10.13801/j.cnki.fhclxb.20161104.002
Abstract:
The reflection and transmission properties of acoustic wave in the trilaminar plate-like adhesive structure with a linear viscous adhesive layer and the upper and lower substrates were the same kind of material were studied when longitudinal wave vertical incident. Based on the quasi-static model (QSM) of the adhesive interface and the constitutive equation of the isotropic linear viscous body, the expressions of the longitudinal wave reflection and transmission coefficients with the coefficient of viscosity and bulk modulus were derived. Firstly, the QSM and the exact solutions of the longitudinal wave were compared with each other to explain the applicable conditions of the QSM. Secondly, the effects of relative quality of interface on acoustic wave reflection and transmission coefficients were considered, by taking and not taking the fore-mentioned factor into consideration, under the condition of different interface contact forms (perfect connection and viscous weak bonding). Then, the influence of parameters changes of viscous adhesive layer on the reflection and transmission properties of the longitudinal wave was analyzed. Finally, the method of identifying the interface form in smaller frequency-thickness product range which was less than 0.1 MHz-mm was briefly interpreted. The results show that the QSM is suitable for the detection of smaller frequency-thickness product. Whether the relative mass of the interface is considered has little effect on the reflection and transmission characteristics of the longitudinal wave. The interface forms could be effectively identified by using the method of reflection or transmission coefficient of longitudinal wave combined with QSM at specific frequency-thickness product. The research results could provide a theoretical reference for the detection of the adhesive structure by longitudinal wave vertical incident.
The reflection and transmission properties of acoustic wave in the trilaminar plate-like adhesive structure with a linear viscous adhesive layer and the upper and lower substrates were the same kind of material were studied when longitudinal wave vertical incident. Based on the quasi-static model (QSM) of the adhesive interface and the constitutive equation of the isotropic linear viscous body, the expressions of the longitudinal wave reflection and transmission coefficients with the coefficient of viscosity and bulk modulus were derived. Firstly, the QSM and the exact solutions of the longitudinal wave were compared with each other to explain the applicable conditions of the QSM. Secondly, the effects of relative quality of interface on acoustic wave reflection and transmission coefficients were considered, by taking and not taking the fore-mentioned factor into consideration, under the condition of different interface contact forms (perfect connection and viscous weak bonding). Then, the influence of parameters changes of viscous adhesive layer on the reflection and transmission properties of the longitudinal wave was analyzed. Finally, the method of identifying the interface form in smaller frequency-thickness product range which was less than 0.1 MHz-mm was briefly interpreted. The results show that the QSM is suitable for the detection of smaller frequency-thickness product. Whether the relative mass of the interface is considered has little effect on the reflection and transmission characteristics of the longitudinal wave. The interface forms could be effectively identified by using the method of reflection or transmission coefficient of longitudinal wave combined with QSM at specific frequency-thickness product. The research results could provide a theoretical reference for the detection of the adhesive structure by longitudinal wave vertical incident.
2017, 34(8): 1810-1816.
doi: 10.13801/j.cnki.fhclxb.20161116.002
Abstract:
A three-dimensional (3-D) finite element model of the actual structure of closed-cell aluminum foam was reconstructed based on X-ray computed tomography. The mechanical response and deformation mechanism of aluminum foam under quasi-static uniaxial compression were investigated through numerical simulations and experiments, especially the deformation mode of the foam in plateau stage and densification stage. The results show that at the beginning of plateau stage, the deformation band occurs and the dominant deformation mode of cell edges and cell walls is plastic bending. During plateau stage, the deformation mode switches to plastic wrinkling and buckling. As densification stage starts, the cells within deformation band are seriously collapsed, and are ‘biconcave disks’. The numerical simulations are consistent with experimental measurements. Thus, the model is validated, providing a basis for further investigation on the influence of corresponding physical factors (e.g. relative density and loading speed, et al) and deformation mechanism on the energy absorption capability of closed-cell aluminum foam.
A three-dimensional (3-D) finite element model of the actual structure of closed-cell aluminum foam was reconstructed based on X-ray computed tomography. The mechanical response and deformation mechanism of aluminum foam under quasi-static uniaxial compression were investigated through numerical simulations and experiments, especially the deformation mode of the foam in plateau stage and densification stage. The results show that at the beginning of plateau stage, the deformation band occurs and the dominant deformation mode of cell edges and cell walls is plastic bending. During plateau stage, the deformation mode switches to plastic wrinkling and buckling. As densification stage starts, the cells within deformation band are seriously collapsed, and are ‘biconcave disks’. The numerical simulations are consistent with experimental measurements. Thus, the model is validated, providing a basis for further investigation on the influence of corresponding physical factors (e.g. relative density and loading speed, et al) and deformation mechanism on the energy absorption capability of closed-cell aluminum foam.
2017, 34(8): 1817-1824.
doi: 10.13801/j.cnki.fhclxb.20161130.001
Abstract:
The honeycomb core of cells was modeled as a layer of orthotropic material whose physical and the mechanical properties were determined by using the corrected Gibson's formula. Based on the Reddy Third-order shear plate theory, a preliminary study was conducted for the natural frequency of the super elliptical honeycomb panels with simply supported boundary conditions. Comparing the FEM results with experimental data of concrete calculated examples, it shows the method mentioned in this article has great calculation precision. The effects of panel width, thickness and structure parameters of core layer cell on the natural frequency of super elliptical honeycomb panels with simply supported boundary conditions were investigated. And plotted corresponding graphs will guide the further research and engineering application of super elliptical honeycomb panels.
The honeycomb core of cells was modeled as a layer of orthotropic material whose physical and the mechanical properties were determined by using the corrected Gibson's formula. Based on the Reddy Third-order shear plate theory, a preliminary study was conducted for the natural frequency of the super elliptical honeycomb panels with simply supported boundary conditions. Comparing the FEM results with experimental data of concrete calculated examples, it shows the method mentioned in this article has great calculation precision. The effects of panel width, thickness and structure parameters of core layer cell on the natural frequency of super elliptical honeycomb panels with simply supported boundary conditions were investigated. And plotted corresponding graphs will guide the further research and engineering application of super elliptical honeycomb panels.
2017, 34(8): 1825-1832.
doi: 10.13801/j.cnki.fhclxb.20161107.001
Abstract:
The flow behavior and microstructure evolution of Al2O3/Cu composites, which conducted at deformation temperature of 300-900℃ and strain rate of 0.01-10 s-1, were investigated by using Gleeble-1500 thermal simulator and TEM analysis. A constitutive equation of the peak value yield stress-deformation temperature-strain stress was also defined based on the Zener-Hollomn parameter and Arrhenius equation. The results show that the stress-strain curve of the composites is a typical softening mechanism of dynamic recrystallization type, and the curve consists of work hardening, dynamic softening and stabilization stage. The peak value of stress decreases with the increase of deformation temperature or the decrease of strain rate. In addition, the material parameters of the composites are obtained as follows:the structure factor ln A of 15.2391, the stress level parameter α of 0.020788 mm2/N, the stress exponent n of 5.933035, and the deformation activation energy Q of 2.1697×105 kJ/mol. With increasing of deformation temperature, the dislocation density in the matrix is gradually decreased, and an obviously recrystallization feature appears. However, in the case of isothermal compression, the dislocation density is increased at first, and then decreased, with increasing of strain rates. According to the microstructure evolution and hot processing maps, the optimum processing condition for good hot workability of Al2O3/Cu composites can be summed up as:temperature range 500-850℃ and strain rate range below 0.1 s-1.
The flow behavior and microstructure evolution of Al2O3/Cu composites, which conducted at deformation temperature of 300-900℃ and strain rate of 0.01-10 s-1, were investigated by using Gleeble-1500 thermal simulator and TEM analysis. A constitutive equation of the peak value yield stress-deformation temperature-strain stress was also defined based on the Zener-Hollomn parameter and Arrhenius equation. The results show that the stress-strain curve of the composites is a typical softening mechanism of dynamic recrystallization type, and the curve consists of work hardening, dynamic softening and stabilization stage. The peak value of stress decreases with the increase of deformation temperature or the decrease of strain rate. In addition, the material parameters of the composites are obtained as follows:the structure factor ln A of 15.2391, the stress level parameter α of 0.020788 mm2/N, the stress exponent n of 5.933035, and the deformation activation energy Q of 2.1697×105 kJ/mol. With increasing of deformation temperature, the dislocation density in the matrix is gradually decreased, and an obviously recrystallization feature appears. However, in the case of isothermal compression, the dislocation density is increased at first, and then decreased, with increasing of strain rates. According to the microstructure evolution and hot processing maps, the optimum processing condition for good hot workability of Al2O3/Cu composites can be summed up as:temperature range 500-850℃ and strain rate range below 0.1 s-1.
2017, 34(8): 1833-1838.
doi: 10.13801/j.cnki.fhclxb.20161116.003
Abstract:
The W fiber Wf/Zr-based metallic glass composites with different fiber volume fraction VF were prepared by infiltration and rapid solidification. The VF were 47%, 66%, 77% and 86%, respectively. The effect of VF on the quasi-static compression mechanical properties and deformation behavior of the Wf/Zr-based metallic glass composites was researched in detail. The results show that the yield strength of the Wf/Zr-based metallic glass composites increases with increase of the VF. The plastic strain firstly increases and then decreases with increase of the VF. The plastic strain is the largest when the VF is 66%. The change of the plastic strain in the Wf/Zr-based metallic glass composites mainly depends on the interaction between matrix and Wf. With increase of strain, the quantity and density of the shear bands in the matrix increase, and the main shear band deflects towards the direction more than 45°. The stress state in the end and middle of the Wf/Zr-based metallic glass composites sample is different during compression because of the influence of the pressure head, which results in the direction of the shear bands difference in different areas of the sample. The failure modes of the Wf/Zr-based metallic glass composites change from shear fracture to longitudinal splitting with the increase of the VF. The fracture behavior the Wf/Zr-based metallic glass composites complies with the Mohr-Coulomb criterion.
The W fiber Wf/Zr-based metallic glass composites with different fiber volume fraction VF were prepared by infiltration and rapid solidification. The VF were 47%, 66%, 77% and 86%, respectively. The effect of VF on the quasi-static compression mechanical properties and deformation behavior of the Wf/Zr-based metallic glass composites was researched in detail. The results show that the yield strength of the Wf/Zr-based metallic glass composites increases with increase of the VF. The plastic strain firstly increases and then decreases with increase of the VF. The plastic strain is the largest when the VF is 66%. The change of the plastic strain in the Wf/Zr-based metallic glass composites mainly depends on the interaction between matrix and Wf. With increase of strain, the quantity and density of the shear bands in the matrix increase, and the main shear band deflects towards the direction more than 45°. The stress state in the end and middle of the Wf/Zr-based metallic glass composites sample is different during compression because of the influence of the pressure head, which results in the direction of the shear bands difference in different areas of the sample. The failure modes of the Wf/Zr-based metallic glass composites change from shear fracture to longitudinal splitting with the increase of the VF. The fracture behavior the Wf/Zr-based metallic glass composites complies with the Mohr-Coulomb criterion.
2017, 34(8): 1839-1846.
doi: 10.13801/j.cnki.fhclxb.20161008.002
Abstract:
The Dynamic Shear Rheometer (DSR) and Atomic Force Microscope (AFM) were utilized to test matrix asphalt and rubber-modified asphalt before and after freeze-thaw cycles. The dynamic viscoelastic parameters and its microstructure had been compared and analyzed under different salt concentrations and cycle times, and three major indexes of two kinds of asphalt had also been tested before and after freeze-thaw cycles. The results show that storage modulus and rutting factor of matrix asphalt increase, and fatigue factor decreases, but rubber-modified asphalt has no significant change after freeze-thaw cycles, while freeze-thaw cycle increases the high temperature elastic property, but it decreases anti-fatigue ability of matrix asphalt greatly, and makes little influence on high temperature rheological properties of rubber-modified asphalt. AFM observations show that matrix asphalt appears "bee structures", which becomes bigger and longer after freeze-thaw cycles, but rubber-modified asphalt has no significant change, so rubber-modified asphalt used as pavement material has more advantage in north cold region.
The Dynamic Shear Rheometer (DSR) and Atomic Force Microscope (AFM) were utilized to test matrix asphalt and rubber-modified asphalt before and after freeze-thaw cycles. The dynamic viscoelastic parameters and its microstructure had been compared and analyzed under different salt concentrations and cycle times, and three major indexes of two kinds of asphalt had also been tested before and after freeze-thaw cycles. The results show that storage modulus and rutting factor of matrix asphalt increase, and fatigue factor decreases, but rubber-modified asphalt has no significant change after freeze-thaw cycles, while freeze-thaw cycle increases the high temperature elastic property, but it decreases anti-fatigue ability of matrix asphalt greatly, and makes little influence on high temperature rheological properties of rubber-modified asphalt. AFM observations show that matrix asphalt appears "bee structures", which becomes bigger and longer after freeze-thaw cycles, but rubber-modified asphalt has no significant change, so rubber-modified asphalt used as pavement material has more advantage in north cold region.
2017, 34(8): 1847-1852.
doi: 10.13801/j.cnki.fhclxb.20161124.001
Abstract:
BiOCl/coal gangue precursor was prepared by using sonochemical method with the raw materials of modified coal gangue, Bi(NO3)·5H2O and NH4Cl. Bi2S3-BiOCl/coal gangue composite photocatalysts were in-situ synthesized through an anion exchange reaction between BiOCl/coal gangue precursor and thioacetamide (TAA). The crystal structure and morphology of Bi2S3-BiOCl/coal gangue composite photocatalysts were investigated by XRD and SEM. The photocatalytic activity of the as-prepared sample was evaluated by degradation of methyl orange under visible light. The results show that the Bi2S3-BiOCl/coal gangue composite photocatalysts exhibit an pronounced photocatalytic activity. The high photocatalytic activity could be mainly attributed to the formation of the heterostructures between Bi2S3 and BiOCl, which effectively separate the photoinduced electron-hole pairs and suppress their recombination.
BiOCl/coal gangue precursor was prepared by using sonochemical method with the raw materials of modified coal gangue, Bi(NO3)·5H2O and NH4Cl. Bi2S3-BiOCl/coal gangue composite photocatalysts were in-situ synthesized through an anion exchange reaction between BiOCl/coal gangue precursor and thioacetamide (TAA). The crystal structure and morphology of Bi2S3-BiOCl/coal gangue composite photocatalysts were investigated by XRD and SEM. The photocatalytic activity of the as-prepared sample was evaluated by degradation of methyl orange under visible light. The results show that the Bi2S3-BiOCl/coal gangue composite photocatalysts exhibit an pronounced photocatalytic activity. The high photocatalytic activity could be mainly attributed to the formation of the heterostructures between Bi2S3 and BiOCl, which effectively separate the photoinduced electron-hole pairs and suppress their recombination.
2017, 34(8): 1853-1861.
doi: 10.13801/j.cnki.fhclxb.20161202.002
Abstract:
Splitting test and water permeability test were conducted. The effect of steel fiber, macro polypropylene fiber and micro polypropylene fiber were evaluated on crack relaxation ratio, splitting test toughness and permeability coefficients of cracked concrete. The results show that the addition of steel fiber and macro polypropylene fiber restrains crack propagation and improves toughness of concrete. They aid in converting the brittle failure of concrete into ductile failure. The crack relaxation increased with the use of steel fiber and macro polypropylene fiber. The permeability coefficients also decrease. The crack relaxation and impermeability increase with the increasing of steel fiber dosage. The permeability of concrete decreases by 87%, with steel fiber content increasing from 25 kg/m3 to 55 kg/m3. The hybrid use of steel fiber and macro polypropylene fiber shows significant positive hybrid effect. When unloading at crack width of 150 μm, the permeability of concrete reinforced by 25 kg/m3 steel fiber and 4 kg/m3 macro polypropylene fiber decreases by 60%, compared to that reinforced by 35 kg/m3 steel fiber. Micro polypropylene fiber has little effect on crack relaxation and permeability of cracked concrete.
Splitting test and water permeability test were conducted. The effect of steel fiber, macro polypropylene fiber and micro polypropylene fiber were evaluated on crack relaxation ratio, splitting test toughness and permeability coefficients of cracked concrete. The results show that the addition of steel fiber and macro polypropylene fiber restrains crack propagation and improves toughness of concrete. They aid in converting the brittle failure of concrete into ductile failure. The crack relaxation increased with the use of steel fiber and macro polypropylene fiber. The permeability coefficients also decrease. The crack relaxation and impermeability increase with the increasing of steel fiber dosage. The permeability of concrete decreases by 87%, with steel fiber content increasing from 25 kg/m3 to 55 kg/m3. The hybrid use of steel fiber and macro polypropylene fiber shows significant positive hybrid effect. When unloading at crack width of 150 μm, the permeability of concrete reinforced by 25 kg/m3 steel fiber and 4 kg/m3 macro polypropylene fiber decreases by 60%, compared to that reinforced by 35 kg/m3 steel fiber. Micro polypropylene fiber has little effect on crack relaxation and permeability of cracked concrete.
2017, 34(8): 1862-1869.
doi: 10.13801/j.cnki.fhclxb.20161124.004
Abstract:
The three-point bending tests on notched beams with different steel fibre volume fractions and different specimen sizes were conducted. The resistances to crack initiation of randomly distributed steel fibre reinforced cementitious composite (SFRC) and aligned steel fibre reinforced cementitious composite (ASFRC) were studied. Based on the load-crack mouth opening displacement curves, the influence of steel fibres on fracture properties of cementitious composites was disscussed, and the initial fracture toughness was determined by sudden reduction of linearly related coefficient. The results show that the initial fracture toughness of ASFRC is significantly greater than that of SFRC. The initial fracture toughness increases with the steel fibre volume fraction, and the increasing tendency of ASFRC tends to be stable when the steel fibre volume fraction is higher than 0.9%. The initial fracture toughnesses of SFRC and ASFRC all increase with the specimen sizes varying from 40 mm to 100 mm, and the increasing tendency is slower in ASFRC. In addition, the enhancement of ASFRC to initial fracture toughness was explained by taking into account the fact that the inclusion embedded at the crack tip of composite would change the crack tip stress intensity factor.
The three-point bending tests on notched beams with different steel fibre volume fractions and different specimen sizes were conducted. The resistances to crack initiation of randomly distributed steel fibre reinforced cementitious composite (SFRC) and aligned steel fibre reinforced cementitious composite (ASFRC) were studied. Based on the load-crack mouth opening displacement curves, the influence of steel fibres on fracture properties of cementitious composites was disscussed, and the initial fracture toughness was determined by sudden reduction of linearly related coefficient. The results show that the initial fracture toughness of ASFRC is significantly greater than that of SFRC. The initial fracture toughness increases with the steel fibre volume fraction, and the increasing tendency of ASFRC tends to be stable when the steel fibre volume fraction is higher than 0.9%. The initial fracture toughnesses of SFRC and ASFRC all increase with the specimen sizes varying from 40 mm to 100 mm, and the increasing tendency is slower in ASFRC. In addition, the enhancement of ASFRC to initial fracture toughness was explained by taking into account the fact that the inclusion embedded at the crack tip of composite would change the crack tip stress intensity factor.
2017, 34(8): 1870-1877.
doi: 10.13801/j.cnki.fhclxb.20161207.001
Abstract:
Specimens of sandwich plate with viscoelastic core for 3-points bending test appear delay debonding at interface after unloading. Theoretical and experimental approaches for sandwich plate with steel faceplates and polyurethane elastomer core were utilized here to study this phenomenon. Double Cantilever Beam(DCB) and Single Cantilever Beam(SLB) tests were conducted here to obtain strain energy release rate (SERR) between face plates and core. And the expression of critical SERR was deduced on condition of unchanged crack tip opening angle. Furthermore, critical crack length for two types of sandwich plate with different core was calculated. The results show that despite of some limitations, crack tip opening angle can illustrate the propagation of interface crack and reveal the characteristic of delay debonding of sandwich plate with polyurethane core and steel faceplate.
Specimens of sandwich plate with viscoelastic core for 3-points bending test appear delay debonding at interface after unloading. Theoretical and experimental approaches for sandwich plate with steel faceplates and polyurethane elastomer core were utilized here to study this phenomenon. Double Cantilever Beam(DCB) and Single Cantilever Beam(SLB) tests were conducted here to obtain strain energy release rate (SERR) between face plates and core. And the expression of critical SERR was deduced on condition of unchanged crack tip opening angle. Furthermore, critical crack length for two types of sandwich plate with different core was calculated. The results show that despite of some limitations, crack tip opening angle can illustrate the propagation of interface crack and reveal the characteristic of delay debonding of sandwich plate with polyurethane core and steel faceplate.
