2017 Vol. 34, No. 10
2017, 34(10): 2121-2133.
doi: 10.13801/j.cnki.fhclxb.20170829.006
Abstract:
A research progress review of design, manufacture and analysis of variable-stiffness composite structures is provided in this paper. There are some special issues in variable-stiffness composite structures compared with traditional ones. First, the concept of variable-stiffness structure and the mechanism of Automated Fiber Placement (AFP) technology were introduced. Second, the definition of tow path was described and the key points to be considered during design and manufacture were summarized. Third, the modeling and analysis methods for variable-stiffness composite structures were curtly described. The current research situation of the mechanical properties of variable-stiffness composite structures was presented from the aspects of optimization method, stiffness and buckling, failure, and vibration. At last, the research work in the area was summarized and the future prospects of this field were proposed.
A research progress review of design, manufacture and analysis of variable-stiffness composite structures is provided in this paper. There are some special issues in variable-stiffness composite structures compared with traditional ones. First, the concept of variable-stiffness structure and the mechanism of Automated Fiber Placement (AFP) technology were introduced. Second, the definition of tow path was described and the key points to be considered during design and manufacture were summarized. Third, the modeling and analysis methods for variable-stiffness composite structures were curtly described. The current research situation of the mechanical properties of variable-stiffness composite structures was presented from the aspects of optimization method, stiffness and buckling, failure, and vibration. At last, the research work in the area was summarized and the future prospects of this field were proposed.
2017, 34(10): 2134-2140.
doi: 10.13801/j.cnki.fhclxb.20161222.001
Abstract:
In order to investigate the modification effects of organic magadiite on nylon 6(PA6), firstly, the organic magadiite (Org-Maga) was formed from magadiite (Maga), which was intercalated by the hexadecyl triphenyl phosphonium bromide selected as the intercalation agent through ion-exchange method. Org-Maga/PA6 composites were prepared through melt intercalation method. The structure and morphologies of the materials were characterized by XRD, SEM and TEM. Mechanical properties and crystallization property of the composites were investigated by mechanical property tests and DSC. The results show that the intercalation agent can intercalate the space of the Maga, the basal spacing of the Maga is increased from 1.53 nm to 2.90 nm, and there are intercalated and exfoliated structures in nano Org-Maga/PA6 composites. The addition of Org-Maga can improve mechanical properties of PA6 obviously, which reach the optimal value when the mass fraction of Org-Maga is 3wt%. The phenomenon of "Melting recrystallization" (unstable polymer crystals (γ phases) recrystallized to form α phases) is formed during the melting process of the composite, and the crystallization temperature of PA6 will raise with the addition of magadiite.
In order to investigate the modification effects of organic magadiite on nylon 6(PA6), firstly, the organic magadiite (Org-Maga) was formed from magadiite (Maga), which was intercalated by the hexadecyl triphenyl phosphonium bromide selected as the intercalation agent through ion-exchange method. Org-Maga/PA6 composites were prepared through melt intercalation method. The structure and morphologies of the materials were characterized by XRD, SEM and TEM. Mechanical properties and crystallization property of the composites were investigated by mechanical property tests and DSC. The results show that the intercalation agent can intercalate the space of the Maga, the basal spacing of the Maga is increased from 1.53 nm to 2.90 nm, and there are intercalated and exfoliated structures in nano Org-Maga/PA6 composites. The addition of Org-Maga can improve mechanical properties of PA6 obviously, which reach the optimal value when the mass fraction of Org-Maga is 3wt%. The phenomenon of "Melting recrystallization" (unstable polymer crystals (γ phases) recrystallized to form α phases) is formed during the melting process of the composite, and the crystallization temperature of PA6 will raise with the addition of magadiite.
2017, 34(10): 2141-2149.
doi: 10.13801/j.cnki.fhclxb.20170117.004
Abstract:
The vinyl-terminated oligophosphate hybrid monomer (VOPP) was synthesized by step-reaction polymerization using phenyl dichlorophosphate(PDCP), ethylene glycol(EG), methanol, hydroxyethyl methylacrylate(HEMA), VOPP and styrene (St) by graft copolymerization preparation of phosphorus element of hybrid monomer grafted polystyrene copolymer (VOPP-co-St). The structural characteristics and average molecular weight of VOPP were explored by FTIR and gel permeation chromatography(GPC).The thermal stability and flame-retardant properties of the VOPP-co-St were evaluated by TGA, limit oxygen index(LOI) and microscale combustion calorimeter; The morphology and composition of the char layer were investigated by SEM and XPS. The thermal decomposition activation energy(Ea) of VOPP-co-St was calculated by Flynn-Wall-Ozawa(FWO) method. The results show that the temperature of maximum decomposition rate, residual mass and LOI of VOPP-co-St increase with the increase of VOPP content, peak heat release rate(PHRR) and total heat release(THR) reduce with the increase of VOPP content, and droplet phenomenon disappeare, while Ea increases with the increase of degradation conversion rate.
The vinyl-terminated oligophosphate hybrid monomer (VOPP) was synthesized by step-reaction polymerization using phenyl dichlorophosphate(PDCP), ethylene glycol(EG), methanol, hydroxyethyl methylacrylate(HEMA), VOPP and styrene (St) by graft copolymerization preparation of phosphorus element of hybrid monomer grafted polystyrene copolymer (VOPP-co-St). The structural characteristics and average molecular weight of VOPP were explored by FTIR and gel permeation chromatography(GPC).The thermal stability and flame-retardant properties of the VOPP-co-St were evaluated by TGA, limit oxygen index(LOI) and microscale combustion calorimeter; The morphology and composition of the char layer were investigated by SEM and XPS. The thermal decomposition activation energy(Ea) of VOPP-co-St was calculated by Flynn-Wall-Ozawa(FWO) method. The results show that the temperature of maximum decomposition rate, residual mass and LOI of VOPP-co-St increase with the increase of VOPP content, peak heat release rate(PHRR) and total heat release(THR) reduce with the increase of VOPP content, and droplet phenomenon disappeare, while Ea increases with the increase of degradation conversion rate.
2017, 34(10): 2150-2155.
doi: 10.13801/j.cnki.fhclxb.20161219.001
Abstract:
Using a novel imidazole derivative EGE-2MI as latent accelerant for dicyandiamide-epoxy resin system, the curing behavior and the storage life of the system were investigated. The kinetics of curing reaction of the resin system were studied by DSC method, and optimum curing process parameters were determined. The storage life of the dicyandiamide-epoxy resin system at room temperature was evaluated by using DSC to measure the variation of the enthalpy at different storage time in ambient environment. And mechanical properties of the moderate-temperature curing products were also tested and analyzed. The results reveal that the dicyandiamide-epoxy resin systems with 0.6%-1.8% EGE-2MI content (content of epoxy resin as 100%) can be effectively cured at 115-125℃, the curing reaction activation energy of the resin system with 1.8% EGE-2MI content is 87.23 kJ/mol. The resin system is also chemically stable at room temperature, and has a storage life for over 35 days. Al-Al shear strength of cured system can reach 21.3 MPa, and its tensile strength is over 40 MPa.
Using a novel imidazole derivative EGE-2MI as latent accelerant for dicyandiamide-epoxy resin system, the curing behavior and the storage life of the system were investigated. The kinetics of curing reaction of the resin system were studied by DSC method, and optimum curing process parameters were determined. The storage life of the dicyandiamide-epoxy resin system at room temperature was evaluated by using DSC to measure the variation of the enthalpy at different storage time in ambient environment. And mechanical properties of the moderate-temperature curing products were also tested and analyzed. The results reveal that the dicyandiamide-epoxy resin systems with 0.6%-1.8% EGE-2MI content (content of epoxy resin as 100%) can be effectively cured at 115-125℃, the curing reaction activation energy of the resin system with 1.8% EGE-2MI content is 87.23 kJ/mol. The resin system is also chemically stable at room temperature, and has a storage life for over 35 days. Al-Al shear strength of cured system can reach 21.3 MPa, and its tensile strength is over 40 MPa.
2017, 34(10): 2156-2163.
doi: 10.13801/j.cnki.fhclxb.20161220.001
Abstract:
A silane hybrid sol was synthesized by a certain percentage of methyl triethoxysilane (MTES), tetraethyl orthosilicate (TEOS), p-toluenesulfonic acid (PTSA), γ-aminopropyl triethoxysilane (APS) and absolute ethanol via a sol-gel process. An aqueous solution of polyether waterborne polyurethane (WPU) and silane hybrid sol were mixed in a certain proportion to prepare the aqueous sizing agent for carbon fiber. The effects of different ratio for average particle size and stability of the sizing agent were investigated.The results show that the average particle diameter of sizing emulsions is 99.94 nm when the aqueous polyurethane concentration is 0.02 g/mL. And sizing possess narrow particle size distribution and good stability. Adopting dip-coating method to treat carbon fiber surface with the prepared sizing agent, the monofilament tensile strength of the sized carbon fiber increases by 4.45% than the commercial carbon fibers, and increases by 11.04% than unsized carbon fiber; The interfacial shear strength of treated carbon fiber/epoxy resin composites increases by 13.74%.
A silane hybrid sol was synthesized by a certain percentage of methyl triethoxysilane (MTES), tetraethyl orthosilicate (TEOS), p-toluenesulfonic acid (PTSA), γ-aminopropyl triethoxysilane (APS) and absolute ethanol via a sol-gel process. An aqueous solution of polyether waterborne polyurethane (WPU) and silane hybrid sol were mixed in a certain proportion to prepare the aqueous sizing agent for carbon fiber. The effects of different ratio for average particle size and stability of the sizing agent were investigated.The results show that the average particle diameter of sizing emulsions is 99.94 nm when the aqueous polyurethane concentration is 0.02 g/mL. And sizing possess narrow particle size distribution and good stability. Adopting dip-coating method to treat carbon fiber surface with the prepared sizing agent, the monofilament tensile strength of the sized carbon fiber increases by 4.45% than the commercial carbon fibers, and increases by 11.04% than unsized carbon fiber; The interfacial shear strength of treated carbon fiber/epoxy resin composites increases by 13.74%.
2017, 34(10): 2164-2170.
doi: 10.13801/j.cnki.fhclxb.20161227.001
Abstract:
The oxidized carbon fibers (OCF1 and OCF2) were prepared via surface oxidation treatment in H2O2 and concentrated HNO3, and then modified by silane coupling agent γ-methacryloxypropyltrimethoxysilane(KH-570), to obtain the KH-570 grafting modified carbon fibers(KCF), which were applied to the unsaturated polyester self-healing composites. Effects of different modification agents and modification methods on the properties of carbon fiber/unsaturated polyester composites were compared. The effect of surface modification of carbon fiber, the structure and the performance of carbon fiber/unsaturated polyester composites were characterized by FTIR, XPS and SEM. The mechanical properties of composites were measured by universal tensile testing machine, izod impact device and shore durometer. The results show that the activity of the carbon fiber's surface functional group content and roughness increases because of the oxidation and grafting reaction, thereby improving the compatibility between carbon fiber and unsaturated resin matrix. The integrated mechanical properties of OCF1/UP composites are better than OCF2/UP composites'. In the three composites, the mechanical properties and the self-healing efficiency of KCF/UP composites are best with self-healing efficiency of 67.03%.
The oxidized carbon fibers (OCF1 and OCF2) were prepared via surface oxidation treatment in H2O2 and concentrated HNO3, and then modified by silane coupling agent γ-methacryloxypropyltrimethoxysilane(KH-570), to obtain the KH-570 grafting modified carbon fibers(KCF), which were applied to the unsaturated polyester self-healing composites. Effects of different modification agents and modification methods on the properties of carbon fiber/unsaturated polyester composites were compared. The effect of surface modification of carbon fiber, the structure and the performance of carbon fiber/unsaturated polyester composites were characterized by FTIR, XPS and SEM. The mechanical properties of composites were measured by universal tensile testing machine, izod impact device and shore durometer. The results show that the activity of the carbon fiber's surface functional group content and roughness increases because of the oxidation and grafting reaction, thereby improving the compatibility between carbon fiber and unsaturated resin matrix. The integrated mechanical properties of OCF1/UP composites are better than OCF2/UP composites'. In the three composites, the mechanical properties and the self-healing efficiency of KCF/UP composites are best with self-healing efficiency of 67.03%.
2017, 34(10): 2171-2181.
doi: 10.13801/j.cnki.fhclxb.20170105.004
Abstract:
High friction composite materials were prepared by dry-hot molding process. The effects of proportion of mass ration of cashew oil modified phenolic resin to nitrile rubber, and the high performance filler (Main components are graphite powder, Al2O3、MoS2 and Fe powder) on the tribological performances of high friction composite materials were studied, respectively. The friction and wear behaviors of the composites were evaluated using a ring-on-block test rig. The worn surfaces and wear debris of high friction composites were analyzed by means of Laser Scanning Confocal Microscopy, SEM and EDS. The results show that the heat resistance and the adhesion are improved with the increasing of mass ratio of CPR to NR, which ensures good friction and wear properties. When the high performance filler content is low, a large number of wear surface and continuous real contact plateaus are formed on the wear surface, and the wear mechanisms are abrasive wear and adhesive wear. When the filler content is higher, the real contact plateaus decreases, severe surface spalling occures and more cracks are formed on the surface, and the wear mechanisms are abrasive wear and fatigue wear. With the increase of high performance filler, the friction surface elemental distribution changes from uniformly distributed to local enrichment, and the size of the abrasive grain gets bigger.
High friction composite materials were prepared by dry-hot molding process. The effects of proportion of mass ration of cashew oil modified phenolic resin to nitrile rubber, and the high performance filler (Main components are graphite powder, Al2O3、MoS2 and Fe powder) on the tribological performances of high friction composite materials were studied, respectively. The friction and wear behaviors of the composites were evaluated using a ring-on-block test rig. The worn surfaces and wear debris of high friction composites were analyzed by means of Laser Scanning Confocal Microscopy, SEM and EDS. The results show that the heat resistance and the adhesion are improved with the increasing of mass ratio of CPR to NR, which ensures good friction and wear properties. When the high performance filler content is low, a large number of wear surface and continuous real contact plateaus are formed on the wear surface, and the wear mechanisms are abrasive wear and adhesive wear. When the filler content is higher, the real contact plateaus decreases, severe surface spalling occures and more cracks are formed on the surface, and the wear mechanisms are abrasive wear and fatigue wear. With the increase of high performance filler, the friction surface elemental distribution changes from uniformly distributed to local enrichment, and the size of the abrasive grain gets bigger.
2017, 34(10): 2182-2186.
doi: 10.13801/j.cnki.fhclxb.20170117.003
Abstract:
The method of improving the surface roughness of Al powders by acid etching Al powders was used to obviously reduce the glossiness of Al-popyurethane(PU) composite coatings under the premise of not obviously raising the infrared emissivity of the coatings. The effects of acid etching time of Al powders on the microstructure, glossiness, infrared emissivity and mechanical properties of the Al-PU composite coatings were systematically studied. The results show that acid etching of Al powders can significantly reduce the glossiness of the coatings. Acid etching 10 min can make the coating's glossiness decrease from 20.1 to 13.0, but it has no obviously effect on microstructure of the coatings. And the effect on the emissivity of the coatings is very limited. Acid etching 50 min only can make the coating's emissivity increase from 0.208 to 0.254, still has a lower emissivity. Acid etching 20 min can make the coatings have lower glossiness and emissivity which are 12.8 and 0.228, respectively. The mechanical properties of the coatings are not sensitive to acid etching of Al powders, the hardness, adhesion strength and impact strength of the coatings before and after the treatment can reach 3 H, 1 grade, and 50 kg·cm, respectively.
The method of improving the surface roughness of Al powders by acid etching Al powders was used to obviously reduce the glossiness of Al-popyurethane(PU) composite coatings under the premise of not obviously raising the infrared emissivity of the coatings. The effects of acid etching time of Al powders on the microstructure, glossiness, infrared emissivity and mechanical properties of the Al-PU composite coatings were systematically studied. The results show that acid etching of Al powders can significantly reduce the glossiness of the coatings. Acid etching 10 min can make the coating's glossiness decrease from 20.1 to 13.0, but it has no obviously effect on microstructure of the coatings. And the effect on the emissivity of the coatings is very limited. Acid etching 50 min only can make the coating's emissivity increase from 0.208 to 0.254, still has a lower emissivity. Acid etching 20 min can make the coatings have lower glossiness and emissivity which are 12.8 and 0.228, respectively. The mechanical properties of the coatings are not sensitive to acid etching of Al powders, the hardness, adhesion strength and impact strength of the coatings before and after the treatment can reach 3 H, 1 grade, and 50 kg·cm, respectively.
2017, 34(10): 2187-2193.
doi: 10.13801/j.cnki.fhclxb.20161220.003
Abstract:
To solve the environmental pollution and resources waste in recovery process of waste printed circuit boards powders(WPCBP) and achieve its high-reutilization in polymer matrix, WPCBP was incorporated in unsaturated polyester resin(UPE) together with halloysite nanotubes(HNTs) to prepare WPCBP-HNTs/UPE novel eco-friendly composites. SEM and TEM were used to characterize the structure and morphology of WPCBP and HNTs and their dispersity and interfacial interaction. Then the thermal stability and flame retardancy of WPCBP-HNTs/UPE composites were systematically investigated by TGA, cone calorimeter test (CCT) and limit oxygen index (LOI). It has been confirmed that WPCBP and HNTs can markedly enhance the thermal stability and fire retrardancy of UPE, and HNTs give a more positive contribution than WPCBP. The residue of UPE and WPCBP-HNTs/UPE composites were analyzed by SEM and EDS to investigate the flame retardancy mechanism. The mechanical performance and thermal deformation property of WPCBP-HNTs/UPE composites were studied.
To solve the environmental pollution and resources waste in recovery process of waste printed circuit boards powders(WPCBP) and achieve its high-reutilization in polymer matrix, WPCBP was incorporated in unsaturated polyester resin(UPE) together with halloysite nanotubes(HNTs) to prepare WPCBP-HNTs/UPE novel eco-friendly composites. SEM and TEM were used to characterize the structure and morphology of WPCBP and HNTs and their dispersity and interfacial interaction. Then the thermal stability and flame retardancy of WPCBP-HNTs/UPE composites were systematically investigated by TGA, cone calorimeter test (CCT) and limit oxygen index (LOI). It has been confirmed that WPCBP and HNTs can markedly enhance the thermal stability and fire retrardancy of UPE, and HNTs give a more positive contribution than WPCBP. The residue of UPE and WPCBP-HNTs/UPE composites were analyzed by SEM and EDS to investigate the flame retardancy mechanism. The mechanical performance and thermal deformation property of WPCBP-HNTs/UPE composites were studied.
2017, 34(10): 2194-2204.
doi: 10.13801/j.cnki.fhclxb.20170104.002
Abstract:
Composite adhesive-bonded repairs are efficient and cost-effective means of the technology of composite repairs. Analytical model for double lap joints of composite laminates was established and the model contained the details of stepped end. Maximum strain criterion was adopted for predicting failure load by composite laminates. Maximum shear strain criterion and damage area criterion were applied by adhesive to predict failure load. The residual function was defined to represent the distance of the ultimate load between analytical results and test results for composite double lap joints. Both ultimate load and equivalent stiffness of analytical model were verified by tests. Compared to the experimental data, analytical results show the following points:Ultimate load of double lap joints of composite laminates almost grows monotonously with the increase of lap length. Analytical equivalent stiffness has a better agreement with the test results, and its maximum error is less than 15%. The residual value of ultimate load on damage area criterion reaches a minimum value to 4.30% when the damage characteristic length is 4%. The residual value of ultimate load on maximum shear strain criterion is 6.41%. With the increasing of lap length, the ultimate load upon analytical results indicates three stages:swift growth, slow growth and scarce growth. Considering the structural weight and other factors, lap length should choose from 15 mm to 35 mm.
Composite adhesive-bonded repairs are efficient and cost-effective means of the technology of composite repairs. Analytical model for double lap joints of composite laminates was established and the model contained the details of stepped end. Maximum strain criterion was adopted for predicting failure load by composite laminates. Maximum shear strain criterion and damage area criterion were applied by adhesive to predict failure load. The residual function was defined to represent the distance of the ultimate load between analytical results and test results for composite double lap joints. Both ultimate load and equivalent stiffness of analytical model were verified by tests. Compared to the experimental data, analytical results show the following points:Ultimate load of double lap joints of composite laminates almost grows monotonously with the increase of lap length. Analytical equivalent stiffness has a better agreement with the test results, and its maximum error is less than 15%. The residual value of ultimate load on damage area criterion reaches a minimum value to 4.30% when the damage characteristic length is 4%. The residual value of ultimate load on maximum shear strain criterion is 6.41%. With the increasing of lap length, the ultimate load upon analytical results indicates three stages:swift growth, slow growth and scarce growth. Considering the structural weight and other factors, lap length should choose from 15 mm to 35 mm.
2017, 34(10): 2205-2210.
doi: 10.13801/j.cnki.fhclxb.20170302.008
Abstract:
Based on the assumption that the characteristic parameters of spring and dashpot of viscoelastic element are a function of time, double-variable parameter Maxwell models were established. Their relaxation functions were obtained by resolving the variable parameter constitutive relation. The relation between the relaxation function and the empirical KWW function was discussed, and a new empirical model for stress relaxation was proposed. The parameter determination method was established by the principle of the least square. The long term stress relaxation test of glass-fiber reinforced plastic (GFRP) composites was carried out, and the proposed model was verified through the experimental data. The research results show that the proposed model curve and experimental curve approximately coincide with each other, and the correlation coefficient reaches 96% or more. It shows that the model is suitable to describe the viscoelastic relaxation properties of GFRP composites.
Based on the assumption that the characteristic parameters of spring and dashpot of viscoelastic element are a function of time, double-variable parameter Maxwell models were established. Their relaxation functions were obtained by resolving the variable parameter constitutive relation. The relation between the relaxation function and the empirical KWW function was discussed, and a new empirical model for stress relaxation was proposed. The parameter determination method was established by the principle of the least square. The long term stress relaxation test of glass-fiber reinforced plastic (GFRP) composites was carried out, and the proposed model was verified through the experimental data. The research results show that the proposed model curve and experimental curve approximately coincide with each other, and the correlation coefficient reaches 96% or more. It shows that the model is suitable to describe the viscoelastic relaxation properties of GFRP composites.
2017, 34(10): 2211-2219.
doi: 10.13801/j.cnki.fhclxb.20170122.002
Abstract:
In order to obtain the bearing capacity of laminated tube with variable cross section, an approach based on energy method was presented. A calculation method based on 3D beam theory was adopted. The equivalent engineering elastic coefficients of the uniform cross-section part and the variable cross section part were obtained by this method. After considering the influence of shear deformation and the influence of the variable cross section on the deflection curve, the analytical formula of the overall stability bearing capacity of laminated tube was derived based on the energy method. The NASA laminated tube with variable cross section was taken as an example to conduct theoretical calculation and finite element numerical simulation. The modified and unmodified theoretical calculations were compared with finite element result. The result considering the above two factors is mostly close to the finite element result. The influence of shear deformation on the calculation of bearing capacity can be more than 10%, and the influence of deflection curve is about 1% thus can be neglected. The bearing capacity, volume and bearing efficiency of laminated tube were analyzed with two parameters of taper length and taper angle. It is found that the variation of cross section has much more influence on bending deformation energy than on shear deformation energy, and this section form can improve bearing efficiency of laminated tube. Besides, under certain taper length, there exists the optimal taper angle corresponding to the maximum bearing efficiency.
In order to obtain the bearing capacity of laminated tube with variable cross section, an approach based on energy method was presented. A calculation method based on 3D beam theory was adopted. The equivalent engineering elastic coefficients of the uniform cross-section part and the variable cross section part were obtained by this method. After considering the influence of shear deformation and the influence of the variable cross section on the deflection curve, the analytical formula of the overall stability bearing capacity of laminated tube was derived based on the energy method. The NASA laminated tube with variable cross section was taken as an example to conduct theoretical calculation and finite element numerical simulation. The modified and unmodified theoretical calculations were compared with finite element result. The result considering the above two factors is mostly close to the finite element result. The influence of shear deformation on the calculation of bearing capacity can be more than 10%, and the influence of deflection curve is about 1% thus can be neglected. The bearing capacity, volume and bearing efficiency of laminated tube were analyzed with two parameters of taper length and taper angle. It is found that the variation of cross section has much more influence on bending deformation energy than on shear deformation energy, and this section form can improve bearing efficiency of laminated tube. Besides, under certain taper length, there exists the optimal taper angle corresponding to the maximum bearing efficiency.
2017, 34(10): 2220-2231.
doi: 10.13801/j.cnki.fhclxb.20170106.001
Abstract:
To study the influence of temperature, stress level and other factors on the compressive strength of FRP (Reinforced Plastic Fiber) rebars in alkali and salt solution, FRP rebars were placed in 60℃ and 25℃ of alkali and salt solution, respectively. The compressive stress levels of FRP rebars at 60℃ were 0%, 20% and 40%, exposed for 10 d, 21 d and 42 d, and the stress levels of FRP rebars at 25℃ were 0%, exposed for 36 d, 64 d and 100 d. By observing the surface topography, the surface erosion degree of FRP rebars increases with time. Under the same conditions, the surface erosion degree of FRP rebars in alkali solution is greater than that in salt solution. Compressive strength tests of FRP rebars after erosion show that the increase of temperature and stress accelerate the degradation of FRP rebars. After 42 d of exposure of alkali solution, compressive strength of glass fiber reinforced polymer(GFRP), basalt fiber reinforced polymer(BFRP) and carbon fiber reinforced polymer(CFRP) rebars at 0% stress are decreased by 31.8%, 43.6% and 51.5%, while the compressive strength at 40% stress level are decreased by 44.2%, 54.8% and 57.1%. After 42 d of exposure of salt solution, compressive strength of GFRP, BFRP and CFRP at 0% stress are decreased by 22.2%, 31.8% and 18.1%, while the compressive strength at 40% stress level are decreased by 29.0%, 37.2% and 23.5%. Based on Fick's law, a compressive strength prediction model of FRP rebars was proposed, which considers stress level, temperature and time and can be used to predict the degradation of FRP rebars under actual conditions.
To study the influence of temperature, stress level and other factors on the compressive strength of FRP (Reinforced Plastic Fiber) rebars in alkali and salt solution, FRP rebars were placed in 60℃ and 25℃ of alkali and salt solution, respectively. The compressive stress levels of FRP rebars at 60℃ were 0%, 20% and 40%, exposed for 10 d, 21 d and 42 d, and the stress levels of FRP rebars at 25℃ were 0%, exposed for 36 d, 64 d and 100 d. By observing the surface topography, the surface erosion degree of FRP rebars increases with time. Under the same conditions, the surface erosion degree of FRP rebars in alkali solution is greater than that in salt solution. Compressive strength tests of FRP rebars after erosion show that the increase of temperature and stress accelerate the degradation of FRP rebars. After 42 d of exposure of alkali solution, compressive strength of glass fiber reinforced polymer(GFRP), basalt fiber reinforced polymer(BFRP) and carbon fiber reinforced polymer(CFRP) rebars at 0% stress are decreased by 31.8%, 43.6% and 51.5%, while the compressive strength at 40% stress level are decreased by 44.2%, 54.8% and 57.1%. After 42 d of exposure of salt solution, compressive strength of GFRP, BFRP and CFRP at 0% stress are decreased by 22.2%, 31.8% and 18.1%, while the compressive strength at 40% stress level are decreased by 29.0%, 37.2% and 23.5%. Based on Fick's law, a compressive strength prediction model of FRP rebars was proposed, which considers stress level, temperature and time and can be used to predict the degradation of FRP rebars under actual conditions.
2017, 34(10): 2232-2239.
doi: 10.13801/j.cnki.fhclxb.20170119.001
Abstract:
A three-dimensional finite element model of the adhesively bonding composite repair structure for cracked aluminum alloy plate was established, and the stress intensity factors around the crack tips were calculated based on the displacement extrapolation method. The run of different uniaxial tension test simulations based on experimental design methods allows us to analyze the effect of different repair parameters on stress intensity factor(SIF), such as the patch length, path thickness and adhesive elastic modulus. The most effective parameter and an optimization of repair operation were achieved by analyzing the SIF using quadratic equation. The finite element results were subjected to the uniaxial tension test. The results show that the patch length is the most effective parameter when the above three factors act at the same times, the failure strength of the repaired plate is increased by 12.1% compared with that of the unrepaired plate, restoring to 90.5% of that of unrepaired plate without cracks.
A three-dimensional finite element model of the adhesively bonding composite repair structure for cracked aluminum alloy plate was established, and the stress intensity factors around the crack tips were calculated based on the displacement extrapolation method. The run of different uniaxial tension test simulations based on experimental design methods allows us to analyze the effect of different repair parameters on stress intensity factor(SIF), such as the patch length, path thickness and adhesive elastic modulus. The most effective parameter and an optimization of repair operation were achieved by analyzing the SIF using quadratic equation. The finite element results were subjected to the uniaxial tension test. The results show that the patch length is the most effective parameter when the above three factors act at the same times, the failure strength of the repaired plate is increased by 12.1% compared with that of the unrepaired plate, restoring to 90.5% of that of unrepaired plate without cracks.
2017, 34(10): 2240-2245.
doi: 10.13801/j.cnki.fhclxb.20170531.004
Abstract:
Glass Fiber Reinforced Plastic (GFRP) is used as spare materials for the supporting flange of the BES III beam pipe in the Beijing Electron Positron Collimator(BEPCII) because of its excellent electrical insulating performance and mechanical properties. However, during the BEPC II operation, the beam pipe suffers a significant amount of γ and neutron irradiation. When GFRP is exposed to γ irradiation, the material will become damaged, and its mechanical properties will vary. The tennsion-tension fatigue properties of GFRP laminated sheets before and after 20 kGy, 100 kGy, 200 kGy γ irradiation were studied. The results show that the effect of γ irradiation on the fatigue life in the low-cycle fatigue range is obvious, but it has little impact on the high cycle fatigue range. Based on the hypothesis of fatigue proposed by Hwang and Han, a two parameter fatigue life model was establishied. The microstructure of GFRP laminated sheets before and after γ irradiation were observed by SEM. The images show the glass fiber doesn't change obviously, but the epoxy degrades to pieces after irradiation. FTIR spectra indicate that the degradation reaction predominates over the crosslinking reaction of epoxy after γ irradiation.
Glass Fiber Reinforced Plastic (GFRP) is used as spare materials for the supporting flange of the BES III beam pipe in the Beijing Electron Positron Collimator(BEPCII) because of its excellent electrical insulating performance and mechanical properties. However, during the BEPC II operation, the beam pipe suffers a significant amount of γ and neutron irradiation. When GFRP is exposed to γ irradiation, the material will become damaged, and its mechanical properties will vary. The tennsion-tension fatigue properties of GFRP laminated sheets before and after 20 kGy, 100 kGy, 200 kGy γ irradiation were studied. The results show that the effect of γ irradiation on the fatigue life in the low-cycle fatigue range is obvious, but it has little impact on the high cycle fatigue range. Based on the hypothesis of fatigue proposed by Hwang and Han, a two parameter fatigue life model was establishied. The microstructure of GFRP laminated sheets before and after γ irradiation were observed by SEM. The images show the glass fiber doesn't change obviously, but the epoxy degrades to pieces after irradiation. FTIR spectra indicate that the degradation reaction predominates over the crosslinking reaction of epoxy after γ irradiation.
2017, 34(10): 2246-2253.
doi: 10.13801/j.cnki.fhclxb.20170307.002
Abstract:
The drilling test was carried out with ultrafine cemented carbide drills to machine aramid fiber reinforce polymer composites (AFRP), and the drilling performance of the ultrafine cemented carbides drills was compared with that of conventional cemented carbides drills at the same conditions. The test results show that drilling force increases with the feed speed and decreases with the spindle speed, the drilling force of the ultrafine cemented carbides drill decreases by 40.6% compared with conventional cemented carbide drills. Drilling temperature decreases with the feed speed and increases with the spindle speed, and the drilling temperature is reduced by 47-85℃. The burr and thermal damage produced by the ultrafine cemented carbide drills are less than that of produced by the conventional cemented carbide drills, the chisel edge and the major cutting edge of the conventional cemented carbide drills exhibits tipping, and the flank faces appear severe abrasive wear after a long drilling. The wear rate of the ultrafine cemented carbide drill is relatively lower due to high hardness and resistance of the drill material, which is suitable for high efficiency and low damage in machining AFRP composites.
The drilling test was carried out with ultrafine cemented carbide drills to machine aramid fiber reinforce polymer composites (AFRP), and the drilling performance of the ultrafine cemented carbides drills was compared with that of conventional cemented carbides drills at the same conditions. The test results show that drilling force increases with the feed speed and decreases with the spindle speed, the drilling force of the ultrafine cemented carbides drill decreases by 40.6% compared with conventional cemented carbide drills. Drilling temperature decreases with the feed speed and increases with the spindle speed, and the drilling temperature is reduced by 47-85℃. The burr and thermal damage produced by the ultrafine cemented carbide drills are less than that of produced by the conventional cemented carbide drills, the chisel edge and the major cutting edge of the conventional cemented carbide drills exhibits tipping, and the flank faces appear severe abrasive wear after a long drilling. The wear rate of the ultrafine cemented carbide drill is relatively lower due to high hardness and resistance of the drill material, which is suitable for high efficiency and low damage in machining AFRP composites.
2017, 34(10): 2254-2262.
doi: 10.13801/j.cnki.fhclxb.20170106.002
Abstract:
According to the autoclave forming process of thermoset resin composites, a three-dimensional model which uses the generalized Maxwell viscoelastic constitutive model was established to calculate the residual stress and curing deformation. Thermo-chemical behavior, thermal expansion and contraction behavior, viscoelastic behavior and anisotropy were fully considered in the model. According to the comparison with experiment data in reference, the model established is proved to have relative superior reliability. The curing process of C-shaped composite structure was numerical simulated and compared with experimental data, and the results show high precision of the numerical model in predicting the curing deformation.
According to the autoclave forming process of thermoset resin composites, a three-dimensional model which uses the generalized Maxwell viscoelastic constitutive model was established to calculate the residual stress and curing deformation. Thermo-chemical behavior, thermal expansion and contraction behavior, viscoelastic behavior and anisotropy were fully considered in the model. According to the comparison with experiment data in reference, the model established is proved to have relative superior reliability. The curing process of C-shaped composite structure was numerical simulated and compared with experimental data, and the results show high precision of the numerical model in predicting the curing deformation.
2017, 34(10): 2263-2270.
doi: 10.13801/j.cnki.fhclxb.20170222.007
Abstract:
Failure modes and its influence factors under external load of CFRP lattice sandwich structure containing hole were investigated by experiment and finite element method. Failure modes were revealed firstly by experiment. Then a progressive damage failure model was established. Based on this model, influences of hole shape, opening rate and hole position on bending strength of CFRP lattice sandwich structure were discussed. The results show that when the panel is thicker, the main failure modes of the lattice sandwich structure containing hole are panel wrinkling and node debonding. The numerical result matches the experiment well with the error of the ultimate load of 9.1%. When the opening rate φ is less than 1.3%, the bending bearing capacity of CFRP lattice sandwich structure is uncorrelated with hole shape. When φ is from 1.3% to 8.5%, the bending bearing capacity of sandwich structure containing a rounded hole is larger. In other cases, the bending bearing capacity of sandwich structure containing a quadrate hole is larger. The holes located at the geometric center or near edges of the CFRP lattice sandwich structure have greater influence on the bending bearing capacity.
Failure modes and its influence factors under external load of CFRP lattice sandwich structure containing hole were investigated by experiment and finite element method. Failure modes were revealed firstly by experiment. Then a progressive damage failure model was established. Based on this model, influences of hole shape, opening rate and hole position on bending strength of CFRP lattice sandwich structure were discussed. The results show that when the panel is thicker, the main failure modes of the lattice sandwich structure containing hole are panel wrinkling and node debonding. The numerical result matches the experiment well with the error of the ultimate load of 9.1%. When the opening rate φ is less than 1.3%, the bending bearing capacity of CFRP lattice sandwich structure is uncorrelated with hole shape. When φ is from 1.3% to 8.5%, the bending bearing capacity of sandwich structure containing a rounded hole is larger. In other cases, the bending bearing capacity of sandwich structure containing a quadrate hole is larger. The holes located at the geometric center or near edges of the CFRP lattice sandwich structure have greater influence on the bending bearing capacity.
2017, 34(10): 2271-2278.
doi: 10.13801/j.cnki.fhclxb.20170105.003
Abstract:
Amidoxime-functionalized SiO2/polyvinyl alcohol(SiO2/PVA) nanofiber adsorbent was prepared by electrospinning technique. The composite SiO2/PVA nanofibers was analyzed by SEM, FTIR, DSC and TGA.The nanofiber adsorbent was also evaluated for mental ions adsorption capacity.The results indicate that the highest adsorption occurs at pH=6 and the adsorption capacity can be 143.7 mg/g and 125.1 mg/g for Cu2+ and Ni2+, respectively. The composite SiO2/PVA nanofibers can remove almost 90% aforementioned ions from aqueous solutions within 50 min. The kinetic data were analyzed by the pseudo-first-order and pseudo-second-order kinetic model, the kinetic process is found to fit the pseudo-second-order equation and the adsorption isotherm data fit well the Langmuir isothermal model. Furthermore, HNO3 is found to be effective in regenerating the adsorbent and 53% of the metal ions are removal from the aqueous even in the fourth regeneration/reuse cycle, which imply that the nanofibers can be suitable for water treatment as adsorbent.
Amidoxime-functionalized SiO2/polyvinyl alcohol(SiO2/PVA) nanofiber adsorbent was prepared by electrospinning technique. The composite SiO2/PVA nanofibers was analyzed by SEM, FTIR, DSC and TGA.The nanofiber adsorbent was also evaluated for mental ions adsorption capacity.The results indicate that the highest adsorption occurs at pH=6 and the adsorption capacity can be 143.7 mg/g and 125.1 mg/g for Cu2+ and Ni2+, respectively. The composite SiO2/PVA nanofibers can remove almost 90% aforementioned ions from aqueous solutions within 50 min. The kinetic data were analyzed by the pseudo-first-order and pseudo-second-order kinetic model, the kinetic process is found to fit the pseudo-second-order equation and the adsorption isotherm data fit well the Langmuir isothermal model. Furthermore, HNO3 is found to be effective in regenerating the adsorbent and 53% of the metal ions are removal from the aqueous even in the fourth regeneration/reuse cycle, which imply that the nanofibers can be suitable for water treatment as adsorbent.
2017, 34(10): 2279-2287.
doi: 10.13801/j.cnki.fhclxb.20161220.004
Abstract:
Ti2AlC-TiB2 reinforced TiAl matrix composites were synthesized by vacuum arc melting using Ti, Al and B4C powders as the raw materials. The effects of Ti2AlC-TiB2 contents on the phases, microstructures and mechanical properties of Ti2AlC-TiB2/TiAl composites were analyzed. The results show that Ti2AlC-TiB2/TiAl composites are mainly composed of TiAl, Ti3Al, TiB2 and Ti2AlC phases, among which TiAl and Ti3Al present a kind of lamellar structure and constitute the matrix. With the increasing of B4C contents in the raw materials, the amount of synthesized Ti2AlC and TiB2 particles increases, and TiAl grains are refined greatly. In addition, TiB2and Ti2AlC particles distribute along the grain boundaries or in the grains.And Ti2AlC particles are in lamellar or lath-like shapes with an average particle size of about 5-15 μm. The morphology of the TiB2is related toits content. When the contents of Ti2AlC-TiB2 ceramic phase are less than 20wt%, TiB2 particles are in a needle-rod shapes with a size of 0.5-5 μm. With the content increases to 30wt%, TiB2 particles grow into blocky faceted particles from 5-20 μm. The Ti2AlC is considered to be synthesized from a peritectic reaction between TiC and Ti-Al melt. The average hardness, ductility and the compressive strength of Ti2AlC-TiB2/TiAl composites increase obviously, with the formation and increase of Ti2AlC-TiB2. The mechanical properties of composites with 10wt% ceramic phases show the highest compression strength of 1591 MPa, and its fracture strain is 14% higher than that of pure TiAl alloy. The reinforcing mechanisms of the Ti2AlC and TiB2 include crack deflection, pinning and pull-out, which is benefit for the strengthening and ductility of Ti2AlC-TiB2/TiAl composites.
Ti2AlC-TiB2 reinforced TiAl matrix composites were synthesized by vacuum arc melting using Ti, Al and B4C powders as the raw materials. The effects of Ti2AlC-TiB2 contents on the phases, microstructures and mechanical properties of Ti2AlC-TiB2/TiAl composites were analyzed. The results show that Ti2AlC-TiB2/TiAl composites are mainly composed of TiAl, Ti3Al, TiB2 and Ti2AlC phases, among which TiAl and Ti3Al present a kind of lamellar structure and constitute the matrix. With the increasing of B4C contents in the raw materials, the amount of synthesized Ti2AlC and TiB2 particles increases, and TiAl grains are refined greatly. In addition, TiB2and Ti2AlC particles distribute along the grain boundaries or in the grains.And Ti2AlC particles are in lamellar or lath-like shapes with an average particle size of about 5-15 μm. The morphology of the TiB2is related toits content. When the contents of Ti2AlC-TiB2 ceramic phase are less than 20wt%, TiB2 particles are in a needle-rod shapes with a size of 0.5-5 μm. With the content increases to 30wt%, TiB2 particles grow into blocky faceted particles from 5-20 μm. The Ti2AlC is considered to be synthesized from a peritectic reaction between TiC and Ti-Al melt. The average hardness, ductility and the compressive strength of Ti2AlC-TiB2/TiAl composites increase obviously, with the formation and increase of Ti2AlC-TiB2. The mechanical properties of composites with 10wt% ceramic phases show the highest compression strength of 1591 MPa, and its fracture strain is 14% higher than that of pure TiAl alloy. The reinforcing mechanisms of the Ti2AlC and TiB2 include crack deflection, pinning and pull-out, which is benefit for the strengthening and ductility of Ti2AlC-TiB2/TiAl composites.
2017, 34(10): 2288-2295.
doi: 10.13801/j.cnki.fhclxb.20170302.007
Abstract:
The WC particles reinforced Fe matrix composites were fabricated by spark plasma sintering (SPS) with the WC particle mass friction of approximately 40%. The influence of sintering temperature on the density, micro-structure and mechanical properties of friction and wear properties of the WC/Fe composites were investigated. The phases of WC/Fe composites under different sintering temperatures were analyzed by XRD and SEM. The worn surface morphologeies of the two kinds of samples were observed by SEM and the wear mechanisms of samples were determined. The specific wear rates of the WC/Fe composites and matensitic wear-resistant steel were measured on a pin-disc tester (the counter face was a grade~80 μm Al2O3 abrasive paper). As the results, the complete densified WC/Fe composites can be obtained under 1080℃ and a homogenous distribution of WC particles within the Fe matrix with good interfacial bonding is obtained. The hardness and wear resistance of the WC/Fe composites increase gradually with the composites fully densification. The wear resistant performance of WC/Fe composites is far better than that of matensitic wear-resistant steel. The main wear mechanism of the matensitic wear-resistant steel is plough wear, and that of WC/Fe composites is oxidation wear and abrasive wear. Under low load condition, oxide film rupture is caused by particles break away from the substrate and lead to the worn surface; Under high load condition, brittle WC ceramics accelerate oxidation film broken, which lead to speed up the loss of WC/Fe composites.
The WC particles reinforced Fe matrix composites were fabricated by spark plasma sintering (SPS) with the WC particle mass friction of approximately 40%. The influence of sintering temperature on the density, micro-structure and mechanical properties of friction and wear properties of the WC/Fe composites were investigated. The phases of WC/Fe composites under different sintering temperatures were analyzed by XRD and SEM. The worn surface morphologeies of the two kinds of samples were observed by SEM and the wear mechanisms of samples were determined. The specific wear rates of the WC/Fe composites and matensitic wear-resistant steel were measured on a pin-disc tester (the counter face was a grade~80 μm Al2O3 abrasive paper). As the results, the complete densified WC/Fe composites can be obtained under 1080℃ and a homogenous distribution of WC particles within the Fe matrix with good interfacial bonding is obtained. The hardness and wear resistance of the WC/Fe composites increase gradually with the composites fully densification. The wear resistant performance of WC/Fe composites is far better than that of matensitic wear-resistant steel. The main wear mechanism of the matensitic wear-resistant steel is plough wear, and that of WC/Fe composites is oxidation wear and abrasive wear. Under low load condition, oxide film rupture is caused by particles break away from the substrate and lead to the worn surface; Under high load condition, brittle WC ceramics accelerate oxidation film broken, which lead to speed up the loss of WC/Fe composites.
2017, 34(10): 2296-2303.
doi: 10.13801/j.cnki.fhclxb.20161129.002
Abstract:
Homogeneous carbon nanotubes (CNTs)-graphene (GR) dispersion was used as the precursor solution, and the 3.0wt% of 1788-polyving alcohol (PVA) solution as organic binder to fabricate the lightweight, smooth and good mechanical cutting performance CNTs-GR aerogel by freeze drying technique. Microstructures and mechanical properties were characterized by TEM, SEM, compression testing machine and the specific surface area measuring instrument. Results suggest that when the mass fraction of CNTs-GR hybrid solution is 3% and the mass ratio of CNTs and GR is 5:3, hierarchical dimension of pores are presented, and the pores distribution is the most uniform in the aerogel. The contraction distortion of the sample can be prevented effectively by using the PVA as a binder. The mass of the solid object is minus a linear correlation with the density of the sample, matching the function relational expression of y=-0.125 x +106.26. And the specific surface area of aerogel is 138.77 m2/g, mesoporous account for the majority of the aerogel, the average pore diameter is 46.6 nm according to the N2 adsorption-desorption test and the porosity can reach 97%. The samples appear three distinct stages of plastic deformation during the compressive testing and reply to the prototype at last.
Homogeneous carbon nanotubes (CNTs)-graphene (GR) dispersion was used as the precursor solution, and the 3.0wt% of 1788-polyving alcohol (PVA) solution as organic binder to fabricate the lightweight, smooth and good mechanical cutting performance CNTs-GR aerogel by freeze drying technique. Microstructures and mechanical properties were characterized by TEM, SEM, compression testing machine and the specific surface area measuring instrument. Results suggest that when the mass fraction of CNTs-GR hybrid solution is 3% and the mass ratio of CNTs and GR is 5:3, hierarchical dimension of pores are presented, and the pores distribution is the most uniform in the aerogel. The contraction distortion of the sample can be prevented effectively by using the PVA as a binder. The mass of the solid object is minus a linear correlation with the density of the sample, matching the function relational expression of y=-0.125 x +106.26. And the specific surface area of aerogel is 138.77 m2/g, mesoporous account for the majority of the aerogel, the average pore diameter is 46.6 nm according to the N2 adsorption-desorption test and the porosity can reach 97%. The samples appear three distinct stages of plastic deformation during the compressive testing and reply to the prototype at last.
2017, 34(10): 2304-2311.
doi: 10.13801/j.cnki.fhclxb.20170222.004
Abstract:
The activated carbon fiber(ACF)was modified firstly by soaked method, then nano Ag particles-loaded ACF (ACF-nano AgP)was obtained by hydrothermal synthesis method with sugar as the reducer and torpent. Then ACF-nano AgP was used for the study of sterilization for drinking water. The Surface properties, Zeta potential, EDS and XRD tests show that the different amount and morphology of nano AgP is loaded on the different modified ACF. The modified ACF by soaking with KMnO4(0.4 mol L-1), NH3·H2O(3 mol L-1) and HNO3(65%-85%) respectively for 24 h show a relatively better nano AgP loading behavior. These three kinds of modified ACF-nano AgP present good antimicrobial performance for both Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli). And 100% of sterilizing rate for drinking water presents by using ACF-nano AgP modified with HNO3 within 2 h. When ACF-nano AgP modified by HNO3 and NH3·H2O as the electrode, more than 97% of sterilizing rate for drinking water is achieved only in 10 min. With the reutilization of ACF-nano AgP, microbial residues adhere to the surface of electrode porosity gradually, resulting in a reduction of sterilization efficiency. A small amount of leaked Ag can be completely recovered to the ACF-nano AgP by everse the connection of the battery power terminals. This method can effectively restrain the loss of nano AgP to prevent the potential toxicity and ensure the safety of the drinking water.
The activated carbon fiber(ACF)was modified firstly by soaked method, then nano Ag particles-loaded ACF (ACF-nano AgP)was obtained by hydrothermal synthesis method with sugar as the reducer and torpent. Then ACF-nano AgP was used for the study of sterilization for drinking water. The Surface properties, Zeta potential, EDS and XRD tests show that the different amount and morphology of nano AgP is loaded on the different modified ACF. The modified ACF by soaking with KMnO4(0.4 mol L-1), NH3·H2O(3 mol L-1) and HNO3(65%-85%) respectively for 24 h show a relatively better nano AgP loading behavior. These three kinds of modified ACF-nano AgP present good antimicrobial performance for both Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli). And 100% of sterilizing rate for drinking water presents by using ACF-nano AgP modified with HNO3 within 2 h. When ACF-nano AgP modified by HNO3 and NH3·H2O as the electrode, more than 97% of sterilizing rate for drinking water is achieved only in 10 min. With the reutilization of ACF-nano AgP, microbial residues adhere to the surface of electrode porosity gradually, resulting in a reduction of sterilization efficiency. A small amount of leaked Ag can be completely recovered to the ACF-nano AgP by everse the connection of the battery power terminals. This method can effectively restrain the loss of nano AgP to prevent the potential toxicity and ensure the safety of the drinking water.
2017, 34(10): 2312-2320.
doi: 10.13801/j.cnki.fhclxb.20170420.001
Abstract:
Cellulose nanofibers loaded with carbon nanotubes (CNF-CNT complexes) were well-dispersed in PVA-borax solution to form electrically conductive composite CNF-CNT/PVA-B hydrogel with a three-dimensional network structure, aiming to enhance the viscoelasticity, stiffness and conductivity of hydrogels. The results show that the micro-scale honeycomb cellular structure exists in CNF-CNT/PVA-B hydrogel. The CNF-CNT complexes form network and enhance viscoelasticity, stiffness and conductivity of hydrogels. When the CNT content is 0.5wt% in CNF-CNT/PVA-B hydrogel, the compressive strength and elastic modulus are 24 kPa and 53 kPa, the maximum and high-frequency plateau of shear modulus are 7 028 Pa and 6 945 Pa, and the conductivity is 0.8×10-1 S·cm-1, respectively.
Cellulose nanofibers loaded with carbon nanotubes (CNF-CNT complexes) were well-dispersed in PVA-borax solution to form electrically conductive composite CNF-CNT/PVA-B hydrogel with a three-dimensional network structure, aiming to enhance the viscoelasticity, stiffness and conductivity of hydrogels. The results show that the micro-scale honeycomb cellular structure exists in CNF-CNT/PVA-B hydrogel. The CNF-CNT complexes form network and enhance viscoelasticity, stiffness and conductivity of hydrogels. When the CNT content is 0.5wt% in CNF-CNT/PVA-B hydrogel, the compressive strength and elastic modulus are 24 kPa and 53 kPa, the maximum and high-frequency plateau of shear modulus are 7 028 Pa and 6 945 Pa, and the conductivity is 0.8×10-1 S·cm-1, respectively.
2017, 34(10): 2321-2329.
doi: 10.13801/j.cnki.fhclxb.20170105.002
Abstract:
Based on Halpin-Tsai formula, direction factor was brought in for establishment of elastic modulus prediction model of fiber reinforced pneumatic wheel. By ANSYS simulation, rules of stress and strain of pneumatic wheel with different volume ratios of fiber were given. It is proved out that aramid fiber reinforced method can overcome defect of inner rubber deformation in contact process. By mixed refining method, pneumatic wheels reinforced by aramid fiber were achieved. Multi-dimension nets distribution of aramid fiber reinforced polymer (AFRP)were observed in micro-view. Elastic modulus prediction model was confirmed by traction experiments. After that, well-distributed aramid fiber pneumatic wheel machining experiments were carried out. The results show that aramid fiber reinforced method can improve surface roughness efficiently in pneumatic wheel machining process and decrease scratch damages of surface.
Based on Halpin-Tsai formula, direction factor was brought in for establishment of elastic modulus prediction model of fiber reinforced pneumatic wheel. By ANSYS simulation, rules of stress and strain of pneumatic wheel with different volume ratios of fiber were given. It is proved out that aramid fiber reinforced method can overcome defect of inner rubber deformation in contact process. By mixed refining method, pneumatic wheels reinforced by aramid fiber were achieved. Multi-dimension nets distribution of aramid fiber reinforced polymer (AFRP)were observed in micro-view. Elastic modulus prediction model was confirmed by traction experiments. After that, well-distributed aramid fiber pneumatic wheel machining experiments were carried out. The results show that aramid fiber reinforced method can improve surface roughness efficiently in pneumatic wheel machining process and decrease scratch damages of surface.
2017, 34(10): 2330-2336.
doi: 10.13801/j.cnki.fhclxb.20170112.009
Abstract:
Polyphosphoric acid (PPA) is a newly modifier with advantages of low prices and simple process, which has a good application prospect.For study the modification mechanism of PPA modified asphalt, the 0.5%、1%、1.5%、2%(mass ratio of PPA to asphalt) PPA modified asphalt were prepared. Three main indexes test shows that penetration index decreases and softening point increases, moreover ductility decreases as mixing amount of PPA increases, indicating improvement of high-temperature property and a little bit weakness of low-temperature property when asphalt is modified by PPA. The content of asphaltene is increased with the decrease of the content of colloid and the content of aromatics and saturation stay around same test by SARA. The FTIR spectrogram of PPA modified asphalt shows that the whole curve changes and a new absorption peak appears compared with pure asphalt, which reveals the modification mechanism of PPA modified asphalt is chemical modification. Topography images and phase images of PPA modified asphalt were obtained by atomic force microscopy(AFM), which shows that compared with pure asphalt, the area of para-phase is smaller, while the area of peri-phase is larger moreover, and the valley of catana-phase become wider, which means the content of asphaltene increasing and weakening of low temperature anti-cracking performance.
Polyphosphoric acid (PPA) is a newly modifier with advantages of low prices and simple process, which has a good application prospect.For study the modification mechanism of PPA modified asphalt, the 0.5%、1%、1.5%、2%(mass ratio of PPA to asphalt) PPA modified asphalt were prepared. Three main indexes test shows that penetration index decreases and softening point increases, moreover ductility decreases as mixing amount of PPA increases, indicating improvement of high-temperature property and a little bit weakness of low-temperature property when asphalt is modified by PPA. The content of asphaltene is increased with the decrease of the content of colloid and the content of aromatics and saturation stay around same test by SARA. The FTIR spectrogram of PPA modified asphalt shows that the whole curve changes and a new absorption peak appears compared with pure asphalt, which reveals the modification mechanism of PPA modified asphalt is chemical modification. Topography images and phase images of PPA modified asphalt were obtained by atomic force microscopy(AFM), which shows that compared with pure asphalt, the area of para-phase is smaller, while the area of peri-phase is larger moreover, and the valley of catana-phase become wider, which means the content of asphaltene increasing and weakening of low temperature anti-cracking performance.
2017, 34(10): 2337-2343.
doi: 10.13801/j.cnki.fhclxb.20170222.001
Abstract:
Three kinds of thick-wall needled C/C composites, namely IR-C/C, IP-C/C, P-C/C respectively, were prepared by means of chemical vapor infiltration(CVI)and resin impregnation/carbonization(PIC), CVI and pitch impregnation/high pressure carbonization (HPIC), HPIC.The thermodynamic property and density uniformity were studied. The results indicated that, axial tensile strength of IP-C/C is 24.7 MPa, axial compressive strength of IR-C/C reaches to 200 MPa, while axial tensile strength of P-C/C is merely 7.4 MPa, which is 53% less than IR-C/C, and 70% less than IP-C/C. Material prepared by compound technology has lower thermal expansion coefficient, while the thermal expansion coefficient at 1000℃ of P-C/C is 3.566×10-6℃-1, which is 2.5 times than IP-C/C. IP-C/C and P-C/C are both prepared by high pressure carbonization, their densities are higher, density distribution are uniform, which make it own higher thermal conductivity coefficient.The density drop is 14.5% within the IR-C/C, and showing high-low-high distribution across the wall.The needled C/C composites, made by the technology of CVI+HPIC, has the excellent comprehensive performance and uniform distribution across the wall, all of these make it suitable for preparing the thick-wall composites.
Three kinds of thick-wall needled C/C composites, namely IR-C/C, IP-C/C, P-C/C respectively, were prepared by means of chemical vapor infiltration(CVI)and resin impregnation/carbonization(PIC), CVI and pitch impregnation/high pressure carbonization (HPIC), HPIC.The thermodynamic property and density uniformity were studied. The results indicated that, axial tensile strength of IP-C/C is 24.7 MPa, axial compressive strength of IR-C/C reaches to 200 MPa, while axial tensile strength of P-C/C is merely 7.4 MPa, which is 53% less than IR-C/C, and 70% less than IP-C/C. Material prepared by compound technology has lower thermal expansion coefficient, while the thermal expansion coefficient at 1000℃ of P-C/C is 3.566×10-6℃-1, which is 2.5 times than IP-C/C. IP-C/C and P-C/C are both prepared by high pressure carbonization, their densities are higher, density distribution are uniform, which make it own higher thermal conductivity coefficient.The density drop is 14.5% within the IR-C/C, and showing high-low-high distribution across the wall.The needled C/C composites, made by the technology of CVI+HPIC, has the excellent comprehensive performance and uniform distribution across the wall, all of these make it suitable for preparing the thick-wall composites.
2017, 34(10): 2344-2355.
doi: 10.13801/j.cnki.fhclxb.20170112.008
Abstract:
In order to study the stability of the hybrid fiber asphalt mixture under high temperature and continuous loading, three kinds of hybrid fiber were selected according to the commonly used fiber and existing research results, and the deformation development and characteristics of internal void structure were experimentally carried out. Firstly, the accelerated loading test was carried out on the mixture of no fiber and three kinds of hybrid fiber under high temperature and continuous loading, cross sectional variation and rutting depth records of different loading times were studied; then the different hybrid fiber mixture void gradation and evolution of void morphology were studied using X-CT scanning technology and three-dimensional reconstruction function of VG software. The results indicate that under high temperature and continuous loading, cross section deformation of hybrid fiber asphalt mixture presents the "W" shape, the different fiber in the mixture plays a "reinforcement", "thickening", "absorbing oil" synergistic effect, the flow deformation of asphalt mixture can be significantly reduced, the flow deformation of the hybrid fiber Ⅲ mixture is the smallest and y=a-b·ln(x + c) can be used to predict the rutting depth of asphalt mixture with different hybrid fibers. After the accelerated loading test, the porosity of the three hybrid fiber increases by only 7%, and the fractal coefficient only decreases by less than 0.5%. Research shows that adding three kinds of hybrid fiber can not change the characteristics of void structure, and under high temperature and continuous loading, the three-dimensional shape characteristics of the internal voids of asphalt mixture can be kept well, in order to improve the anti deformation ability of asphalt mixture.
In order to study the stability of the hybrid fiber asphalt mixture under high temperature and continuous loading, three kinds of hybrid fiber were selected according to the commonly used fiber and existing research results, and the deformation development and characteristics of internal void structure were experimentally carried out. Firstly, the accelerated loading test was carried out on the mixture of no fiber and three kinds of hybrid fiber under high temperature and continuous loading, cross sectional variation and rutting depth records of different loading times were studied; then the different hybrid fiber mixture void gradation and evolution of void morphology were studied using X-CT scanning technology and three-dimensional reconstruction function of VG software. The results indicate that under high temperature and continuous loading, cross section deformation of hybrid fiber asphalt mixture presents the "W" shape, the different fiber in the mixture plays a "reinforcement", "thickening", "absorbing oil" synergistic effect, the flow deformation of asphalt mixture can be significantly reduced, the flow deformation of the hybrid fiber Ⅲ mixture is the smallest and y=a-b·ln(x + c) can be used to predict the rutting depth of asphalt mixture with different hybrid fibers. After the accelerated loading test, the porosity of the three hybrid fiber increases by only 7%, and the fractal coefficient only decreases by less than 0.5%. Research shows that adding three kinds of hybrid fiber can not change the characteristics of void structure, and under high temperature and continuous loading, the three-dimensional shape characteristics of the internal voids of asphalt mixture can be kept well, in order to improve the anti deformation ability of asphalt mixture.
2017, 34(10): 2356-2366.
doi: 10.13801/j.cnki.fhclxb.20170222.002
Abstract:
The results of experiment investigation of 24 PVC-CFRP confined reinforced steel tube concrete columns were presented. The influences of hoop spacing of CFRP strips and eccentricity on the failure mode, bearing capacity, strain and load-displacement of PVC-CFRP confined reinforced steel tube concrete column were studied. The experimental results show that small eccentric specimens take the compressive failure of concrete and PVC tube as a sign, while large eccentric specimens take the tensile yield of longitudinal reinforcement and tensile failure of PVC tube as a mark. Compared with PVC confined reinforced steel tube concrete column, the bearing capacity gradually decreases with the increasing hoop spacing of CFRP strips and eccentricity, the ductility coefficient of the small eccentric specimens is improved in different degrees, and the ductility coefficient of the large eccentric specimens remains unchanged. The development of longitudinal reinforcement and concrete strain is basically the same, the strain of CFRP strips in the compression side of the cross section is small, and the strain of the specimen section is basically in accordance with the assumption of plane section. The curves of load-deflection and moment-curvature are divided into two stages. The hoop spacing of CFRP strips and eccentricity have no effect on the first stage. The second stage is the straight line segment, and the slope of the second stage gradually decreases with the increment of the hoop spacing of CFRP strips and eccentricity.
The results of experiment investigation of 24 PVC-CFRP confined reinforced steel tube concrete columns were presented. The influences of hoop spacing of CFRP strips and eccentricity on the failure mode, bearing capacity, strain and load-displacement of PVC-CFRP confined reinforced steel tube concrete column were studied. The experimental results show that small eccentric specimens take the compressive failure of concrete and PVC tube as a sign, while large eccentric specimens take the tensile yield of longitudinal reinforcement and tensile failure of PVC tube as a mark. Compared with PVC confined reinforced steel tube concrete column, the bearing capacity gradually decreases with the increasing hoop spacing of CFRP strips and eccentricity, the ductility coefficient of the small eccentric specimens is improved in different degrees, and the ductility coefficient of the large eccentric specimens remains unchanged. The development of longitudinal reinforcement and concrete strain is basically the same, the strain of CFRP strips in the compression side of the cross section is small, and the strain of the specimen section is basically in accordance with the assumption of plane section. The curves of load-deflection and moment-curvature are divided into two stages. The hoop spacing of CFRP strips and eccentricity have no effect on the first stage. The second stage is the straight line segment, and the slope of the second stage gradually decreases with the increment of the hoop spacing of CFRP strips and eccentricity.
2017, 34(10): 2367-2374.
doi: 10.13801/j.cnki.fhclxb.20170109.001
Abstract:
Considering the reinforcement layer of basalt fiber reinforced polymer composites (BFRP) grid and mixing proportion of engineered cementitious composites(ECC), an experimental program on BFRP grid reinforced ECC with high-volume fly ash/slag powder was conducted under the uniaxial tensile loading. Based on the experimental results and the Richard-Abbot analytical model, a stress-strain model of BFRP reinforced ECC was established. The test results indicate that the ultimate tensile stress of reinforced ECC composite can get greatly improvement with the increase of basalt grid reinforcement. The ECC with slag powder has higher compressive strength and cracking strain/stress than those of ECC with fly ash in the same mixing ratio. The BFRP enhanced ECC with slag powder can get better tensile mechanical behavior. The analysis results show that the established model can effectively predict the stress-strain relationship and ultimate tensile strength of BFRP reinforced ECC.
Considering the reinforcement layer of basalt fiber reinforced polymer composites (BFRP) grid and mixing proportion of engineered cementitious composites(ECC), an experimental program on BFRP grid reinforced ECC with high-volume fly ash/slag powder was conducted under the uniaxial tensile loading. Based on the experimental results and the Richard-Abbot analytical model, a stress-strain model of BFRP reinforced ECC was established. The test results indicate that the ultimate tensile stress of reinforced ECC composite can get greatly improvement with the increase of basalt grid reinforcement. The ECC with slag powder has higher compressive strength and cracking strain/stress than those of ECC with fly ash in the same mixing ratio. The BFRP enhanced ECC with slag powder can get better tensile mechanical behavior. The analysis results show that the established model can effectively predict the stress-strain relationship and ultimate tensile strength of BFRP reinforced ECC.
2017, 34(10): 2375-2384.
doi: 10.13801/j.cnki.fhclxb.20170228.003
Abstract:
A size-dependent model for the free vibration of plane orthotropic functionally graded micro-beams was developed on the basis of a new modified couple stress theory. The model contains two material length scale parameters, which enables it to separately represent the different scale effects in two orthogonal directions. The present model can be degenerated to classical macroscopic model when the geometrical size of the beam is much larger than the material length parameter. The governing equations were derived through Hamilton's principle. A simply supported micro-beam was taken as the illustrative example and analytical solved. The influences of geometrical size and power law index on the scale effects were analyzed. Numerical results indicate that the natural frequencies of the micro-beam predicted by the present model are always greater than those predicted by the classical FG beam model, i.e. the scale effects are captured. The scale effects will be gradually weaken with the increasing of the geometrical size of the beam, and diminish when the geometrical size is much larger than the material length parameter. The scale effects reflected by higher order natural frequencies are more apparent than that reflected by lower order natural frequencies. In addition, the power law index also has a specific influence on the scale effects.
A size-dependent model for the free vibration of plane orthotropic functionally graded micro-beams was developed on the basis of a new modified couple stress theory. The model contains two material length scale parameters, which enables it to separately represent the different scale effects in two orthogonal directions. The present model can be degenerated to classical macroscopic model when the geometrical size of the beam is much larger than the material length parameter. The governing equations were derived through Hamilton's principle. A simply supported micro-beam was taken as the illustrative example and analytical solved. The influences of geometrical size and power law index on the scale effects were analyzed. Numerical results indicate that the natural frequencies of the micro-beam predicted by the present model are always greater than those predicted by the classical FG beam model, i.e. the scale effects are captured. The scale effects will be gradually weaken with the increasing of the geometrical size of the beam, and diminish when the geometrical size is much larger than the material length parameter. The scale effects reflected by higher order natural frequencies are more apparent than that reflected by lower order natural frequencies. In addition, the power law index also has a specific influence on the scale effects.
