2022 Vol. 39, No. 8
2022, 39(8): 3663-3673.
doi: 10.13801/j.cnki.fhclxb.20210909.002
Abstract:
Three kinds of needled fiber preforms reinforced phenolic aerogel composites (NF/PA) were prepared using lightweight needled preforms of glass fibers, carbon fibers and quartz fibers as reinforcements, respectively. The resultant fiber-dependent mechanical properties and fracture behavior were studied systematically. It is found that the NF/PA has a low density of ~0.45 g/cm3 and good insulation with room-temperature thermal conductivity as low as 0.046-0.067 W/(m·K). The phenolic aerogel has typical 3D porous structure with the overlapped and interconnected phenolic aerogel nanoparticles filling in fiber preforms, which has excellent interface structure with fiber. The NF/PA have obvious plastic deformation in the process of tension and compression. Furthermore, this work analyze the energy absorption of NF/PA during the crack propagate, and conclude that the type of fiber significantly affects the interface characteristics and thereby the fracture and failure mechanisms of composites. The interfacial bonding strength of carbon fiber is less than the ultimate shear stress of phenolic aerogel, and thereafter fibers are initially deboned with phenolic nanoparticles during the fracture process, responding to a “slip interface” feature. On the other hand, the bonding strengths of glass fiber and quartz fiber are both greater than the limit of shear stress of phenolic aerogel. Therefore, the phenolic aerogel is destroyed initially during the fracture process, which manifests as a “sticky interface” feature. Compared with glass fiber and quartz fiber, the carbon fiber shows more toughening and reinforcing effect on NF/PA.
Three kinds of needled fiber preforms reinforced phenolic aerogel composites (NF/PA) were prepared using lightweight needled preforms of glass fibers, carbon fibers and quartz fibers as reinforcements, respectively. The resultant fiber-dependent mechanical properties and fracture behavior were studied systematically. It is found that the NF/PA has a low density of ~0.45 g/cm3 and good insulation with room-temperature thermal conductivity as low as 0.046-0.067 W/(m·K). The phenolic aerogel has typical 3D porous structure with the overlapped and interconnected phenolic aerogel nanoparticles filling in fiber preforms, which has excellent interface structure with fiber. The NF/PA have obvious plastic deformation in the process of tension and compression. Furthermore, this work analyze the energy absorption of NF/PA during the crack propagate, and conclude that the type of fiber significantly affects the interface characteristics and thereby the fracture and failure mechanisms of composites. The interfacial bonding strength of carbon fiber is less than the ultimate shear stress of phenolic aerogel, and thereafter fibers are initially deboned with phenolic nanoparticles during the fracture process, responding to a “slip interface” feature. On the other hand, the bonding strengths of glass fiber and quartz fiber are both greater than the limit of shear stress of phenolic aerogel. Therefore, the phenolic aerogel is destroyed initially during the fracture process, which manifests as a “sticky interface” feature. Compared with glass fiber and quartz fiber, the carbon fiber shows more toughening and reinforcing effect on NF/PA.
2022, 39(8): 3674-3683.
doi: 10.13801/j.cnki.fhclxb.20211025.003
Abstract:
Carbon fiber/epoxy composites had been widely used in aerospace, rail transit, automobile and other fields because of their high specific strength, specific modulus and good fatigue resistance. However, as one of the main structural forms of carbon fiber/epoxy composites, the laminate structure had the weakest interlayer performance due to the lack of fiber in the thickness direction, which was prone to delamination failure and affects the bearing performance of the structure. Short fiber intercalation toughening was an effective means to improve the interlaminar properties of carbon fiber/epoxy composites. In recent years, scholars at home and abroad had carried out a lot of relevant research work, but there was still a lack of systematic research on short fiber intercalation toughening. In this work, carbon fiber, flax fiber and Kevlar fiber were selected as intercalated short fibers. The effects of short fiber types, intercalation layer density and fiber length on the interlaminar toughening effect of carbon fiber/epoxy composites were systematically analyzed and discussed. The results show that for different short fiber intercalations, the interlaminar fracture toughness of composites increases first and then decreases with the increase of short fiber length and intercalation layer density. On this basis, the toughening mechanisms of different kinds of fibers are revealed. Fiber bridging, change of crack propagation path, multi-layer failure and longitudinal tearing of fibers are helpful to improve the interlaminar fracture toughness of composites. The research results lay a foundation for the structural design of short fiber intercalated toughened composites.
Carbon fiber/epoxy composites had been widely used in aerospace, rail transit, automobile and other fields because of their high specific strength, specific modulus and good fatigue resistance. However, as one of the main structural forms of carbon fiber/epoxy composites, the laminate structure had the weakest interlayer performance due to the lack of fiber in the thickness direction, which was prone to delamination failure and affects the bearing performance of the structure. Short fiber intercalation toughening was an effective means to improve the interlaminar properties of carbon fiber/epoxy composites. In recent years, scholars at home and abroad had carried out a lot of relevant research work, but there was still a lack of systematic research on short fiber intercalation toughening. In this work, carbon fiber, flax fiber and Kevlar fiber were selected as intercalated short fibers. The effects of short fiber types, intercalation layer density and fiber length on the interlaminar toughening effect of carbon fiber/epoxy composites were systematically analyzed and discussed. The results show that for different short fiber intercalations, the interlaminar fracture toughness of composites increases first and then decreases with the increase of short fiber length and intercalation layer density. On this basis, the toughening mechanisms of different kinds of fibers are revealed. Fiber bridging, change of crack propagation path, multi-layer failure and longitudinal tearing of fibers are helpful to improve the interlaminar fracture toughness of composites. The research results lay a foundation for the structural design of short fiber intercalated toughened composites.
2022, 39(8): 3684-3694.
doi: 10.13801/j.cnki.fhclxb.20210928.004
Abstract:
In order to explore the effect of molding parameters on the structure and properties of carbon fiber reinforced poly(ether ketone ketone) composites (CF/PEKK), CF/PEKK composite laminates were prepared by vacuum molding in this paper. The effects of molding temperature and pressure on the interface structure between resin and fiber, the condensed structure of PEKK and the mechanical properties of the composites were discussed systematically. The microstructure and the failure modes of the composites was analyzed by scanning electron microscope. The crystal structure of PEKK in the composites was observed by X-ray diffraction. The relationship between interfacial damping and molding process of the composites was studied by dynamic mechanical analysis. The results show that under the molding temperature of 365℃ and molding pressure of 5.0-6.0 MPa, the comprehensive mechanical properties of CF/PEKK composites are the best, in which the tensile strength is 965 MPa, the bending strength is 849 MPa, and the inter-laminar shear strength is 59 MPa. The fracture failure modes of the composites are mainly zigzag cracking and resin breakage.
In order to explore the effect of molding parameters on the structure and properties of carbon fiber reinforced poly(ether ketone ketone) composites (CF/PEKK), CF/PEKK composite laminates were prepared by vacuum molding in this paper. The effects of molding temperature and pressure on the interface structure between resin and fiber, the condensed structure of PEKK and the mechanical properties of the composites were discussed systematically. The microstructure and the failure modes of the composites was analyzed by scanning electron microscope. The crystal structure of PEKK in the composites was observed by X-ray diffraction. The relationship between interfacial damping and molding process of the composites was studied by dynamic mechanical analysis. The results show that under the molding temperature of 365℃ and molding pressure of 5.0-6.0 MPa, the comprehensive mechanical properties of CF/PEKK composites are the best, in which the tensile strength is 965 MPa, the bending strength is 849 MPa, and the inter-laminar shear strength is 59 MPa. The fracture failure modes of the composites are mainly zigzag cracking and resin breakage.
2022, 39(8): 3695-3702.
doi: 10.13801/j.cnki.fhclxb.20211110.001
Abstract:
Adding phosphorus to the epoxy resin system could effectively improve its liquid oxygen compatibility. Anyway, the research about mechanical properties of such epoxy resin system containing phosphorus was absent. Since the cured phosphorus-containing epoxy resin system had a complex and amorphous interlaced network structure, and there were many interrelated factors affecting its mechanical properties, it was difficult to demonstrate the microscopic fracture behavior by experiments. In the present paper, based on molecular dynamics (MD) research, the curing and cross-linking process of epoxy resin containing phosphorus (synthesized from 10-(2, 5-dihydroxyphenyl)-10-hydro-9-oxa-10-phosphaphenanthrene-10-oxide (ODOPB) and epichlorohydrin and 4, 4'-diaminodiphenylmethane (DDM) was simulated. The thermodynamic parameters and microscopic failure beha-vior of the resin system were calculated, and the micromechanical response mechanism under the fracture process was revealed. And the results were compared with another phosphorus containing epoxy resin system (ODOPB modified epoxy) with 2wt% phosphorus content. The analysis results provide a reference for the design and performance optimization of high-performance epoxy composites with extreme environment resistance.
Adding phosphorus to the epoxy resin system could effectively improve its liquid oxygen compatibility. Anyway, the research about mechanical properties of such epoxy resin system containing phosphorus was absent. Since the cured phosphorus-containing epoxy resin system had a complex and amorphous interlaced network structure, and there were many interrelated factors affecting its mechanical properties, it was difficult to demonstrate the microscopic fracture behavior by experiments. In the present paper, based on molecular dynamics (MD) research, the curing and cross-linking process of epoxy resin containing phosphorus (synthesized from 10-(2, 5-dihydroxyphenyl)-10-hydro-9-oxa-10-phosphaphenanthrene-10-oxide (ODOPB) and epichlorohydrin and 4, 4'-diaminodiphenylmethane (DDM) was simulated. The thermodynamic parameters and microscopic failure beha-vior of the resin system were calculated, and the micromechanical response mechanism under the fracture process was revealed. And the results were compared with another phosphorus containing epoxy resin system (ODOPB modified epoxy) with 2wt% phosphorus content. The analysis results provide a reference for the design and performance optimization of high-performance epoxy composites with extreme environment resistance.
2022, 39(8): 3703-3711.
doi: 10.13801/j.cnki.fhclxb.20210913.004
Abstract:
In order to enhance the compression strength of three-dimensional woven spacer composites and improve its compression energy absorption, inspired by the design concept of multi-layer sandwich structure, three-dimensional woven double spacer composites with pile height of (6+6) mm and (4+8) mm were designed and fabricated. The flatwise compression and edgewise compression properties and failure modes of the double spacer composites were investigated by comparing with the single spacer composites with the pile height of 12 mm. The results show that the flatwise compressive strength, edgewise compression strength and energy absorption of the two double spacer composites are improved significantly compared with that of single spacer composites. Among them, the flatwise compression strength (11.5 MPa) and specific energy absorption value (6983.7 J/kg) of the double spacer composites with pile height of (6+6) mm are increased by 57.5% and 152.4%, respectively. In addition, the flatwise compression failure mode of the double spacer composites is the fractures of the pile yarns layer by layer, and the edgewise compression failure mode is crack propagation of panel, which show greater energy absorption characteristic. The design of double spacer structure not only enhances the flatwise compression and edgewise compression properties of three-dimensional woven spacer composites, but also optimizes its failure modes, which improves the safety of spacer composites in practical application, and provides a new idea for the structural design of spacer composites with higher pile height or multilayer.
In order to enhance the compression strength of three-dimensional woven spacer composites and improve its compression energy absorption, inspired by the design concept of multi-layer sandwich structure, three-dimensional woven double spacer composites with pile height of (6+6) mm and (4+8) mm were designed and fabricated. The flatwise compression and edgewise compression properties and failure modes of the double spacer composites were investigated by comparing with the single spacer composites with the pile height of 12 mm. The results show that the flatwise compressive strength, edgewise compression strength and energy absorption of the two double spacer composites are improved significantly compared with that of single spacer composites. Among them, the flatwise compression strength (11.5 MPa) and specific energy absorption value (6983.7 J/kg) of the double spacer composites with pile height of (6+6) mm are increased by 57.5% and 152.4%, respectively. In addition, the flatwise compression failure mode of the double spacer composites is the fractures of the pile yarns layer by layer, and the edgewise compression failure mode is crack propagation of panel, which show greater energy absorption characteristic. The design of double spacer structure not only enhances the flatwise compression and edgewise compression properties of three-dimensional woven spacer composites, but also optimizes its failure modes, which improves the safety of spacer composites in practical application, and provides a new idea for the structural design of spacer composites with higher pile height or multilayer.
2022, 39(8): 3712-3722.
doi: 10.13801/j.cnki.fhclxb.20210918.001
Abstract:
In order to improve the surface wettability of high modulus carbon fibers (HMCF) and enhance the interfacial properties of their composites, a few-layer Ti3C2Tx-MXene aqueous dispersion with a size of 100-500 nm was mixed with an aqueous epoxy emulsion to prepare an Ti3C2Tx-MXene modified sizing agent for HMCF by mechanical blending method. The continuous sizing technology was used to construct a characteristic coating rich in Ti3C2Tx-MXene on the surface of HMCF in order to improve the interface bonding of HMCF/epoxy resin (EP) composites. The surface morphology, surface chemical state and surface wettability of HMCF were characterized by SEM, XPS and dynamic contact angle test, and the interface bonding of HMCF/EP composites was analyzed and characterized by interlaminar shear strength (ILSS) and cross-sectional morphology tests. Finally, the interface enhancement mechanism of Ti3C2Tx-Mxene/EP sizing agent-modified HMCF/EP composites was investigated with the shear damage models of the composites. The results show that after the surface treatment with Ti3C2Tx-MXene modified sizing agent, the O/C (atomic ratio) of the HMCF surface is increased, and a certain amount of nano-scale convex micromechanical structures are introduced to improve the surface wettability of HMCF. When the solid content of the epoxy emulsion sizing agent is 0.8% and the concentration of Ti3C2Tx-MXene is 1.0 mg/mL, the ILSS of the HMCF/EP composites increases by 23.8% to 85.9 MPa.
In order to improve the surface wettability of high modulus carbon fibers (HMCF) and enhance the interfacial properties of their composites, a few-layer Ti3C2Tx-MXene aqueous dispersion with a size of 100-500 nm was mixed with an aqueous epoxy emulsion to prepare an Ti3C2Tx-MXene modified sizing agent for HMCF by mechanical blending method. The continuous sizing technology was used to construct a characteristic coating rich in Ti3C2Tx-MXene on the surface of HMCF in order to improve the interface bonding of HMCF/epoxy resin (EP) composites. The surface morphology, surface chemical state and surface wettability of HMCF were characterized by SEM, XPS and dynamic contact angle test, and the interface bonding of HMCF/EP composites was analyzed and characterized by interlaminar shear strength (ILSS) and cross-sectional morphology tests. Finally, the interface enhancement mechanism of Ti3C2Tx-Mxene/EP sizing agent-modified HMCF/EP composites was investigated with the shear damage models of the composites. The results show that after the surface treatment with Ti3C2Tx-MXene modified sizing agent, the O/C (atomic ratio) of the HMCF surface is increased, and a certain amount of nano-scale convex micromechanical structures are introduced to improve the surface wettability of HMCF. When the solid content of the epoxy emulsion sizing agent is 0.8% and the concentration of Ti3C2Tx-MXene is 1.0 mg/mL, the ILSS of the HMCF/EP composites increases by 23.8% to 85.9 MPa.
2022, 39(8): 3723-3732.
doi: 10.13801/j.cnki.fhclxb.20210928.001
Abstract:
Basalt fiber (BF) was modified by silane coupling agent and nano-SiO2 particles-silane coupling agent, respectively. And the basalt fiber/epoxy (BF/EP) composites were prepared by winding process. The tensile properties of BF and the flexural properties of BF/EP composites were tested by universal material testing machine. The morphologies of BF surface and BF/EP composites flexural fracture were observed by FESEM. The long-term (2544 h) creep behaviors of BF/EP composites were tested by self-made three-point flexural creep test device. The short-term (6000 s) creep behaviors of BF/EP composites were tested by universal material testing machine at different stress levels. And the effect of fiber surface modification on the mechanical properties was analyzed. The results show that, with the introduction of nano-SiO2 particles into BF sizing agent, the tensile properties of the fiber and the flexural properties of BF/EP are effectively improved. FESEM morphologies show that the synergistic modification of BF improves the bonding performance between the fiber and the resin. The creep compliance and its growth rate decrease significantly in the long-term creep tests with low stress for 2544 h and in the short-term creep tests with various stress levels for 6000 s. The stress threshold of linear creep of materials can be obtained from the coincidence curves of short-term creep tests at 20%, 30%, 40% and 50% stress levels. The Hooke-Kelvin-Kelvin (HKK) model can effectively describe the long-term creep performance of BF/EP composites at low stress level, so as to carry out the long-term prediction of its creep performance.
Basalt fiber (BF) was modified by silane coupling agent and nano-SiO2 particles-silane coupling agent, respectively. And the basalt fiber/epoxy (BF/EP) composites were prepared by winding process. The tensile properties of BF and the flexural properties of BF/EP composites were tested by universal material testing machine. The morphologies of BF surface and BF/EP composites flexural fracture were observed by FESEM. The long-term (2544 h) creep behaviors of BF/EP composites were tested by self-made three-point flexural creep test device. The short-term (6000 s) creep behaviors of BF/EP composites were tested by universal material testing machine at different stress levels. And the effect of fiber surface modification on the mechanical properties was analyzed. The results show that, with the introduction of nano-SiO2 particles into BF sizing agent, the tensile properties of the fiber and the flexural properties of BF/EP are effectively improved. FESEM morphologies show that the synergistic modification of BF improves the bonding performance between the fiber and the resin. The creep compliance and its growth rate decrease significantly in the long-term creep tests with low stress for 2544 h and in the short-term creep tests with various stress levels for 6000 s. The stress threshold of linear creep of materials can be obtained from the coincidence curves of short-term creep tests at 20%, 30%, 40% and 50% stress levels. The Hooke-Kelvin-Kelvin (HKK) model can effectively describe the long-term creep performance of BF/EP composites at low stress level, so as to carry out the long-term prediction of its creep performance.
2022, 39(8): 3733-3746.
doi: 10.13801/j.cnki.fhclxb.20220302.002
Abstract:
Conjugated microporous polymers (CMPs) have attracted extensive attention due to their stable pore structure, various synthesis methods and applications in gas adsorption and dye adsorption in wastewater treatment. Based on the Sonogashira coupling reaction, two fluorine-doped porous polymers (synthetic route of ferrocene (Fc)-1,3,5-trifluoro-2,4,6-triethynylbenzene (FAB)-CMP, Fc-5,10,15,20-tetrakis(2-fluoro-4-ethynylphenyl) porphyrin (TFPP)-CMP) were designed and synthesized by using FAB and TFPP as the center construction units, 1,1'-dibromoferrocene (Fc(Br)2) as a linking unit. The chemical structure, thermal stability, elemental composition and particle morphology of CMPs were investigated in detail. The results show that the fluorine-doped porous polymer is successfully synthesised by the Sonogashira coupling reaction, and the product exhibits good thermal stabi-lity and stable porosity. The BET specific surface areas of Fc-FAB-CMP and Fc-TFPP-CMP are 302.89 m2/g and 125.2 m2/g, respectively. Moreover, the introduction of ferrocene and fluorine can be the adsorption site of cationic dye methyl violet (MV), the highest adsorption value of Fc-FAB-CMP for MV reaches 318 mg/g.
Conjugated microporous polymers (CMPs) have attracted extensive attention due to their stable pore structure, various synthesis methods and applications in gas adsorption and dye adsorption in wastewater treatment. Based on the Sonogashira coupling reaction, two fluorine-doped porous polymers (synthetic route of ferrocene (Fc)-1,3,5-trifluoro-2,4,6-triethynylbenzene (FAB)-CMP, Fc-5,10,15,20-tetrakis(2-fluoro-4-ethynylphenyl) porphyrin (TFPP)-CMP) were designed and synthesized by using FAB and TFPP as the center construction units, 1,1'-dibromoferrocene (Fc(Br)2) as a linking unit. The chemical structure, thermal stability, elemental composition and particle morphology of CMPs were investigated in detail. The results show that the fluorine-doped porous polymer is successfully synthesised by the Sonogashira coupling reaction, and the product exhibits good thermal stabi-lity and stable porosity. The BET specific surface areas of Fc-FAB-CMP and Fc-TFPP-CMP are 302.89 m2/g and 125.2 m2/g, respectively. Moreover, the introduction of ferrocene and fluorine can be the adsorption site of cationic dye methyl violet (MV), the highest adsorption value of Fc-FAB-CMP for MV reaches 318 mg/g.
2022, 39(8): 3747-3756.
doi: 10.13801/j.cnki.fhclxb.20211008.003
Abstract:
Highly thermally-conductive polymer-based composites have important application value in the field of electronic equipment. Based on the “intrinsic-filled” synergistic effect, the liquid crystal epoxy functionalized SiC nanowires (SiCNWs-LCE)/liquid crystal epoxy composites with low filling amount and high thermal conductivity were prepared by the liquid phase blending method, using the synthesized intrinsic thermally-conductive liquid crystal epoxy as matrix and SiCNWs-LCE as highly thermally-conductive fillers. The chemical structures, crystallization behaviors of the liquid crystal epoxy and microstructures, chemical structures and thermal stability of the functionalized SiCNWs were analyzed. The influences of SiCNWs-LCE content on the thermal conductivity and thermal stability of the SiCNWs-LCE/liquid crystal epoxy composites were investigated in detail. The results show that the SiCNWs functionalized by silane coupling agent and liquid crystal epoxy have good dispersibility. The “intrinsic-filled” synergistic effect endows the SiCNWs-LCE/liquid crystal epoxy composite with excellent thermal conduc-tive properties. The thermal conductivity of SiCNWs-LCE/liquid crystal epoxy composites increases with the SiCNWs-LCE content. Compared with the pure liquid crystal epoxy resin, the SiCNWs-LCE/liquid crystal epoxy composites exhibit an increased thermal conductivity from 0.33 W/(m·K) to 0.72 W/(m·K) with an improvement of 118%.
Highly thermally-conductive polymer-based composites have important application value in the field of electronic equipment. Based on the “intrinsic-filled” synergistic effect, the liquid crystal epoxy functionalized SiC nanowires (SiCNWs-LCE)/liquid crystal epoxy composites with low filling amount and high thermal conductivity were prepared by the liquid phase blending method, using the synthesized intrinsic thermally-conductive liquid crystal epoxy as matrix and SiCNWs-LCE as highly thermally-conductive fillers. The chemical structures, crystallization behaviors of the liquid crystal epoxy and microstructures, chemical structures and thermal stability of the functionalized SiCNWs were analyzed. The influences of SiCNWs-LCE content on the thermal conductivity and thermal stability of the SiCNWs-LCE/liquid crystal epoxy composites were investigated in detail. The results show that the SiCNWs functionalized by silane coupling agent and liquid crystal epoxy have good dispersibility. The “intrinsic-filled” synergistic effect endows the SiCNWs-LCE/liquid crystal epoxy composite with excellent thermal conduc-tive properties. The thermal conductivity of SiCNWs-LCE/liquid crystal epoxy composites increases with the SiCNWs-LCE content. Compared with the pure liquid crystal epoxy resin, the SiCNWs-LCE/liquid crystal epoxy composites exhibit an increased thermal conductivity from 0.33 W/(m·K) to 0.72 W/(m·K) with an improvement of 118%.
2022, 39(8): 3757-3766.
doi: 10.13801/j.cnki.fhclxb.20210913.002
Abstract:
In order to explore the ways and mechanisms to improve the thermophysical properties of paraffin-based phase change materials, Cu nano-surface-amorphous n-octadecane composite system and Cu nano-surface-graphene/n-octadecane composite system were established by introducing Cu nano-surface. And molecular dynamics simulation method was used to simulate and analyze the two composite systems. The results show that the microscopic mechanism of adding metal nanoparticles to the system to improve the thermophysical properties of phase change materials lies in not only its very high thermal conductivity, but also the interaction between the metal nano surface and the alkane molecule promoting the alkane molecule on the nano-surface directional crystallization. Graphene, as a high thermal conductivity carbon nanomaterial with excellent performance, can further promote the oriented crystallization of alkane molecules in the composite system, thereby improving the thermal conductivity of the composite phase change material in the entire system.
In order to explore the ways and mechanisms to improve the thermophysical properties of paraffin-based phase change materials, Cu nano-surface-amorphous n-octadecane composite system and Cu nano-surface-graphene/n-octadecane composite system were established by introducing Cu nano-surface. And molecular dynamics simulation method was used to simulate and analyze the two composite systems. The results show that the microscopic mechanism of adding metal nanoparticles to the system to improve the thermophysical properties of phase change materials lies in not only its very high thermal conductivity, but also the interaction between the metal nano surface and the alkane molecule promoting the alkane molecule on the nano-surface directional crystallization. Graphene, as a high thermal conductivity carbon nanomaterial with excellent performance, can further promote the oriented crystallization of alkane molecules in the composite system, thereby improving the thermal conductivity of the composite phase change material in the entire system.
2022, 39(8): 3767-3775.
doi: 10.13801/j.cnki.fhclxb.20210909.004
Abstract:
To improve the compression strength after impact of epoxy-based composites, polyethersulfone (PES) ultrafine-fiber non-woven fabric was fabricated from polyethersulfone-Nylon 6 (PES-PA6) blended fibers using solution-stripping method, which is more suitable for batch preparation. Then the obtained non-woven fabric was applied in the interlaminar toughing of carbon fiber reinforced epoxy resin-based composites. Interlaminar fracture toughness under mode I (GIC), interlaminar fracture toughness under mode II (GIIC), compressive strength after impact (CAI) and interlaminar fracture micro-morphology of composites were tested to research the influence of the non-woven fabric on the interlaminar toughness of composites and the corresponding mechanism of interla-minar toughing. The result indicates that after epoxy resin-based composites are interlaminate-toughened with the non-woven fabric, the GIC value is raised to 312 J/m2 from 289 J/m2 and GIIC value is improved to 3649 J/m2 from 1391 J/m2. Also, the post-impact damage area of tested specimens is reduced from 1050 mm2 to 204 mm2 after toughing treatment, and the corresponding post-impact compressive strength is increased from 228 MPa to 307 MPa.
To improve the compression strength after impact of epoxy-based composites, polyethersulfone (PES) ultrafine-fiber non-woven fabric was fabricated from polyethersulfone-Nylon 6 (PES-PA6) blended fibers using solution-stripping method, which is more suitable for batch preparation. Then the obtained non-woven fabric was applied in the interlaminar toughing of carbon fiber reinforced epoxy resin-based composites. Interlaminar fracture toughness under mode I (GIC), interlaminar fracture toughness under mode II (GIIC), compressive strength after impact (CAI) and interlaminar fracture micro-morphology of composites were tested to research the influence of the non-woven fabric on the interlaminar toughness of composites and the corresponding mechanism of interla-minar toughing. The result indicates that after epoxy resin-based composites are interlaminate-toughened with the non-woven fabric, the GIC value is raised to 312 J/m2 from 289 J/m2 and GIIC value is improved to 3649 J/m2 from 1391 J/m2. Also, the post-impact damage area of tested specimens is reduced from 1050 mm2 to 204 mm2 after toughing treatment, and the corresponding post-impact compressive strength is increased from 228 MPa to 307 MPa.
2022, 39(8): 3776-3785.
doi: 10.13801/j.cnki.fhclxb.20210913.005
Abstract:
Mask was an important epidemic prevention barrier to prevent virus from entering human body through respiratory system and mucous membrane. The disposable mask had some problems, such as rapid decline of filtration efficiency with electrostatic attenuation, large respiratory resistance, short service life and so on. Electrospun nanofiber membrane was compounded with melt blown cloth to reduce the dependence of particle filtration on static electricity and realize long-term filtration. Polyvinylidene fluoride (PVDF) nanofiber membrane was prepared by electrospinning with N, N-dimethylformamide (DMF) as solvent. Then it was coated with polypropylene (PP) melt blown base cloth to prepare PVDF/PP nano/micron structure composite fiber membrane. The effect of electrospinning process parameters on the aerosol filtration performance of composite fiber membrane was experimentally studied. The ternary quadratic polynomial model was established to optimize the spinning process and predict the fiber membrane resistance. At the same time, the back propagation (BP) neural network model was constructed to predict the fiber membrane resistance. The results show that the effects of voltage, receiving distance, injection speed, spinning solution concentration and fiber membrane surface density on the filtration efficiency and filtration resistance are consistent. When the concentration of spinning solution is 15wt% and the area density is 3 g/m2, the optimized spinning process parameters are voltage of 30 kV, receiving distance of 16.8 cm and injection speed of 1.6 mL/h. The filtration resistance predicted by polynomial model is 76.79 Pa, the relative error is 9.23%, and the error coefficient of variation (CV) value is 59%. The filtration resistance predicted by BP neural network is 81.25 Pa, the relative error is 1.99%, and the error CV value is 48%. The experiments show that the ternary quadratic model and BP neural network have high prediction accuracy.
Mask was an important epidemic prevention barrier to prevent virus from entering human body through respiratory system and mucous membrane. The disposable mask had some problems, such as rapid decline of filtration efficiency with electrostatic attenuation, large respiratory resistance, short service life and so on. Electrospun nanofiber membrane was compounded with melt blown cloth to reduce the dependence of particle filtration on static electricity and realize long-term filtration. Polyvinylidene fluoride (PVDF) nanofiber membrane was prepared by electrospinning with N, N-dimethylformamide (DMF) as solvent. Then it was coated with polypropylene (PP) melt blown base cloth to prepare PVDF/PP nano/micron structure composite fiber membrane. The effect of electrospinning process parameters on the aerosol filtration performance of composite fiber membrane was experimentally studied. The ternary quadratic polynomial model was established to optimize the spinning process and predict the fiber membrane resistance. At the same time, the back propagation (BP) neural network model was constructed to predict the fiber membrane resistance. The results show that the effects of voltage, receiving distance, injection speed, spinning solution concentration and fiber membrane surface density on the filtration efficiency and filtration resistance are consistent. When the concentration of spinning solution is 15wt% and the area density is 3 g/m2, the optimized spinning process parameters are voltage of 30 kV, receiving distance of 16.8 cm and injection speed of 1.6 mL/h. The filtration resistance predicted by polynomial model is 76.79 Pa, the relative error is 9.23%, and the error coefficient of variation (CV) value is 59%. The filtration resistance predicted by BP neural network is 81.25 Pa, the relative error is 1.99%, and the error CV value is 48%. The experiments show that the ternary quadratic model and BP neural network have high prediction accuracy.
2022, 39(8): 3786-3793.
doi: 10.13801/j.cnki.fhclxb.20210909.007
Abstract:
In order to solve the fire problem of carbon fiber reinforced polymer (CFRP) cable, a fire retardant mea-sure of CFRP cable was developed. The high temperature tensile test of CFRP tendons used for bridge cables was carried out, and the fire retardant effect of fire retardant coating, asbestos, ceramic fiber cloth was compared. The results show that the residual strength of the tendons at high temperature decreases linearly with the increase of temperature. After heating at 210℃ for 3 h, the minimum residual strength of the tendons is 2245.8 MPa, which is 26.13% lower than the original strength. After high temperature heating and then cooling, the strength of the tendons can be reversibly restored to a certain extent, and the residual strength can reach more than 2800 MPa, but it has a slight downward trend compared with the original strength, and the higher the heating temperature, the lower the residual strength. The fire retardant coating has a good effect by comparing. After 2 h of burning, the maximum temperature of inner surface of polyethylene (PE) sheath is 206℃. The thicker the fire retardant coating is, the longer the protection time will be. The maximum temperature of the inner surface of PE sheath is 245℃ when the cable strand with 2 mm thickness fire retardant coating is burned for 6 h. The PE sheath is not damaged, but only softened. The results show that the fire retardant coating can effectively protect the CFRP cable. The CFRP tendons can still bear the load within 2 h after fire, and the residual strength is more than 2245 MPa.
In order to solve the fire problem of carbon fiber reinforced polymer (CFRP) cable, a fire retardant mea-sure of CFRP cable was developed. The high temperature tensile test of CFRP tendons used for bridge cables was carried out, and the fire retardant effect of fire retardant coating, asbestos, ceramic fiber cloth was compared. The results show that the residual strength of the tendons at high temperature decreases linearly with the increase of temperature. After heating at 210℃ for 3 h, the minimum residual strength of the tendons is 2245.8 MPa, which is 26.13% lower than the original strength. After high temperature heating and then cooling, the strength of the tendons can be reversibly restored to a certain extent, and the residual strength can reach more than 2800 MPa, but it has a slight downward trend compared with the original strength, and the higher the heating temperature, the lower the residual strength. The fire retardant coating has a good effect by comparing. After 2 h of burning, the maximum temperature of inner surface of polyethylene (PE) sheath is 206℃. The thicker the fire retardant coating is, the longer the protection time will be. The maximum temperature of the inner surface of PE sheath is 245℃ when the cable strand with 2 mm thickness fire retardant coating is burned for 6 h. The PE sheath is not damaged, but only softened. The results show that the fire retardant coating can effectively protect the CFRP cable. The CFRP tendons can still bear the load within 2 h after fire, and the residual strength is more than 2245 MPa.
2022, 39(8): 3794-3803.
doi: 10.13801/j.cnki.fhclxb.20211103.002
Abstract:
According to the thermogravimetric curve diagram of porous nickel foam in air, different oxidation heat treatment temperatures were employed for high temperature treatment, and the effect of the oxidation heat treatment temperature on the microstructure and electromagnetic microwaves of porous nickel foam was studied by TG-DSC, XRD, SEM, and vector network analyzer to explore the possibility of the application of porous nickel foam in electromagnetic pollution environment. The results show that when the oxidation heat treatment temperature exceeds 600℃, the surface of the porous nickel foam skeleton has obvious changes. When the oxidation heat treatment is 900℃, the surface forms a flaky structure, and when the oxidation heat treatment temperature reaches 1200℃, the surface becomes molten. The phase analysis indicates that with the increase of the oxidation heat treatment, the nickel oxide is formed on the surface of the porous nickel foam network. The electromagnetic absorption performances in the X-band are tested, and the porous nickel foam obtained by the oxidation heat treatment at 900℃ owns the most excellent microwave absorption performance, the reflection loss of which reaches the minimum value of −19.66 dB at 10.88 GHz, indicating that a certain oxidation heat treatment could effectively improve the microwave absorbing properties of the porous nickel foam.
According to the thermogravimetric curve diagram of porous nickel foam in air, different oxidation heat treatment temperatures were employed for high temperature treatment, and the effect of the oxidation heat treatment temperature on the microstructure and electromagnetic microwaves of porous nickel foam was studied by TG-DSC, XRD, SEM, and vector network analyzer to explore the possibility of the application of porous nickel foam in electromagnetic pollution environment. The results show that when the oxidation heat treatment temperature exceeds 600℃, the surface of the porous nickel foam skeleton has obvious changes. When the oxidation heat treatment is 900℃, the surface forms a flaky structure, and when the oxidation heat treatment temperature reaches 1200℃, the surface becomes molten. The phase analysis indicates that with the increase of the oxidation heat treatment, the nickel oxide is formed on the surface of the porous nickel foam network. The electromagnetic absorption performances in the X-band are tested, and the porous nickel foam obtained by the oxidation heat treatment at 900℃ owns the most excellent microwave absorption performance, the reflection loss of which reaches the minimum value of −19.66 dB at 10.88 GHz, indicating that a certain oxidation heat treatment could effectively improve the microwave absorbing properties of the porous nickel foam.
2022, 39(8): 3804-3814.
doi: 10.13801/j.cnki.fhclxb.20211008.002
Abstract:
With the rapid development of science and technology, a variety of wearable intelligent electronic devices rised. These electronic devices put forward higher requirements for the performance of chemical power supply, such as safe, efficient and flexible electrochemical energy storage devices. At present, a lot of research was devoted to flexible energy storage devices to meet the energy supply needs of various wearable intelligent electro-nic devices. By adjusting the deposition time of methanol phase method, cobalt based metal organic framework (Co-MOF) and nickel cobalt double hydroxide (NiCo DH) with high specific surface and high porosity were cleverly combined on nickel fabric (NF) to prepare high-performance flexible composite electrode. The electrode has a high specific capacity of 22.6 μA·h·cm−2 (323 mA·h·g−1), excellent cycle performance (the capacity retention rate is 56% after 2000 times of charge and discharge) and good rate performance (the current increases by 50 times, and the capacity retention rate is 60%), and the electrode has excellent flexibility. After many bends, the electrical perfor-mance of the electrode almost does not change greatly, which can meet all kinds of deformation of clothing. Therefore, this research improves a new idea for the energy supply of wearable electronic devices, and has broad prospects in the field of intelligent wearable.
With the rapid development of science and technology, a variety of wearable intelligent electronic devices rised. These electronic devices put forward higher requirements for the performance of chemical power supply, such as safe, efficient and flexible electrochemical energy storage devices. At present, a lot of research was devoted to flexible energy storage devices to meet the energy supply needs of various wearable intelligent electro-nic devices. By adjusting the deposition time of methanol phase method, cobalt based metal organic framework (Co-MOF) and nickel cobalt double hydroxide (NiCo DH) with high specific surface and high porosity were cleverly combined on nickel fabric (NF) to prepare high-performance flexible composite electrode. The electrode has a high specific capacity of 22.6 μA·h·cm−2 (323 mA·h·g−1), excellent cycle performance (the capacity retention rate is 56% after 2000 times of charge and discharge) and good rate performance (the current increases by 50 times, and the capacity retention rate is 60%), and the electrode has excellent flexibility. After many bends, the electrical perfor-mance of the electrode almost does not change greatly, which can meet all kinds of deformation of clothing. Therefore, this research improves a new idea for the energy supply of wearable electronic devices, and has broad prospects in the field of intelligent wearable.
2022, 39(8): 3815-3827.
doi: 10.13801/j.cnki.fhclxb.20210916.001
Abstract:
In order to obtain the composites with high dielectric properties, polyvinylidene fluoride (PVDF) was used as matrix, graphene oxide modified by ionic liquid as filler (GO-IL) and GO-IL/PVDF binary dielectric compo-sites with different GO-IL contents were first prepared by solution blending method. And then, hydroxylated barium titanate (BT-OH)-GO-IL/PVDF ternary composites with different proportions were prepared by solution blending. The effects of GO-IL and BT-OH contents on the thermal, mechanical and electrical properties of the compo-sites were investigated by FTIR, FESEM, XRD, tensile, electrical and DSC tests. FTIR test shows that IL is successfully grafted on GO, and the addition of GO-IL promotes β-crystal formation of PVDF. DSC and XRD characterizations further improve that the addition of GO-IL promotes the growth of β-crystal. The crystallinity reaches 35.3% and 36.9% when the fillers are 2wt%GO and 2wt%GO-IL, respectively. Electrical test shows that GO-IL is easier to form local conductive networks in PVDF matrix, promoting the electronic displacement polarization and improving the dielectric constant of the composites. For GO-IL/PVDF composite, when the content of GO-IL filler is 2wt%, the dielectric constant of the composite reaches 24.28, which is 2.6 times of the pure PVDF. However, when the filler content reaches 8wt%, the dielectric constant of the composite reaches 78.46, and the dielectric loss also increases sharply, reaching 2.25. The resistance of the composite is 1-2 orders lower than that of the pure PVDF. When the content of GO-IL is 2wt% and the content of BT-OH filler is 20wt%, the composite shows the best comprehensive properties, the dielectric constant is 40.32 and the dielectric loss is 0.38.
In order to obtain the composites with high dielectric properties, polyvinylidene fluoride (PVDF) was used as matrix, graphene oxide modified by ionic liquid as filler (GO-IL) and GO-IL/PVDF binary dielectric compo-sites with different GO-IL contents were first prepared by solution blending method. And then, hydroxylated barium titanate (BT-OH)-GO-IL/PVDF ternary composites with different proportions were prepared by solution blending. The effects of GO-IL and BT-OH contents on the thermal, mechanical and electrical properties of the compo-sites were investigated by FTIR, FESEM, XRD, tensile, electrical and DSC tests. FTIR test shows that IL is successfully grafted on GO, and the addition of GO-IL promotes β-crystal formation of PVDF. DSC and XRD characterizations further improve that the addition of GO-IL promotes the growth of β-crystal. The crystallinity reaches 35.3% and 36.9% when the fillers are 2wt%GO and 2wt%GO-IL, respectively. Electrical test shows that GO-IL is easier to form local conductive networks in PVDF matrix, promoting the electronic displacement polarization and improving the dielectric constant of the composites. For GO-IL/PVDF composite, when the content of GO-IL filler is 2wt%, the dielectric constant of the composite reaches 24.28, which is 2.6 times of the pure PVDF. However, when the filler content reaches 8wt%, the dielectric constant of the composite reaches 78.46, and the dielectric loss also increases sharply, reaching 2.25. The resistance of the composite is 1-2 orders lower than that of the pure PVDF. When the content of GO-IL is 2wt% and the content of BT-OH filler is 20wt%, the composite shows the best comprehensive properties, the dielectric constant is 40.32 and the dielectric loss is 0.38.
2022, 39(8): 3828-3844.
doi: 10.13801/j.cnki.fhclxb.20211027.003
Abstract:
Vanadium dioxide (VO2) is a typical thermochromic material that can be used for smart windows, which can effectively reduce the building energy consumption. However, the issues of the yellow brown color and instabi-lity of VO2 based smart glass restrict its wide application. Herein, a series of VO2 based three-layer fluorescent composite films has been reported. The composite films consist of VO2@SiO2 based thermochromic layer, fluorescent brightener layer and organic polymer layer. The VO2@SiO2 layer can control the sunlight intake with the change of external temperature, regulating the indoor temperature, with the core-shell structure improving the stability of the film. The fluorescent brightener layer absorbs ultraviolet irradiation and emit blue fluorescence, thus improving the color of VO2 coating. As the top layer, the organic polymer layer can effectively protect the lower layers and increase the stability of the whole composite film. Compared with the pure VO2 films, these composite films not only maintain high visible light transmittance and solar modulation ability, but also reversibly change color from yellow-brown to blue under sunlight. Meanwhile, the stability and the UV blocking property are also significantly improved. The properties of this type of composite films are beneficial to the promotion and application of VO2-based smart windows.
Vanadium dioxide (VO2) is a typical thermochromic material that can be used for smart windows, which can effectively reduce the building energy consumption. However, the issues of the yellow brown color and instabi-lity of VO2 based smart glass restrict its wide application. Herein, a series of VO2 based three-layer fluorescent composite films has been reported. The composite films consist of VO2@SiO2 based thermochromic layer, fluorescent brightener layer and organic polymer layer. The VO2@SiO2 layer can control the sunlight intake with the change of external temperature, regulating the indoor temperature, with the core-shell structure improving the stability of the film. The fluorescent brightener layer absorbs ultraviolet irradiation and emit blue fluorescence, thus improving the color of VO2 coating. As the top layer, the organic polymer layer can effectively protect the lower layers and increase the stability of the whole composite film. Compared with the pure VO2 films, these composite films not only maintain high visible light transmittance and solar modulation ability, but also reversibly change color from yellow-brown to blue under sunlight. Meanwhile, the stability and the UV blocking property are also significantly improved. The properties of this type of composite films are beneficial to the promotion and application of VO2-based smart windows.
2022, 39(8): 3845-3851.
doi: 10.13801/j.cnki.fhclxb.20210917.002
Abstract:
In order to reduce the recombination rate of graphite phase carbon nitride (g-C3N4) photocatalyst′s electron and holes, the Bi2MoS2O4/g-C3N4 heterojunction was successfully prepared by the impregnation method. The absorption edge of the modified catalyst is red-shifted from 470 nm to 490 nm as measured by ultraviolet-visible diffuse reflectance spectroscopy. The effects of loading ratio, catalyst dosage and pH on the visible light degradation rate of Rhodamine B were discussed. When the mass ratio of Bi2MoS2O4 to g-C3N4 is 18wt% and the catalyst dosage is 0.36 g/L, the catalyst can completely degrade Rhodamine B within 15 min. Free radical capture experiments and energy band analysis results show that the system has formed a type II electron transfer mechanism, the main active species is •O2−.
In order to reduce the recombination rate of graphite phase carbon nitride (g-C3N4) photocatalyst′s electron and holes, the Bi2MoS2O4/g-C3N4 heterojunction was successfully prepared by the impregnation method. The absorption edge of the modified catalyst is red-shifted from 470 nm to 490 nm as measured by ultraviolet-visible diffuse reflectance spectroscopy. The effects of loading ratio, catalyst dosage and pH on the visible light degradation rate of Rhodamine B were discussed. When the mass ratio of Bi2MoS2O4 to g-C3N4 is 18wt% and the catalyst dosage is 0.36 g/L, the catalyst can completely degrade Rhodamine B within 15 min. Free radical capture experiments and energy band analysis results show that the system has formed a type II electron transfer mechanism, the main active species is •O2−.
2022, 39(8): 3852-3862.
doi: 10.13801/j.cnki.fhclxb.20211028.004
Abstract:
Visible-light responsive two-dimensional composite semiconductor materials are significant in the field of photocatalysis. Construction of stable and effective heterojunctions to promote interface charge transport is the key in the research of two-dimensional composite materials. In this work, a face-to-face stacked 2D-2D SnO2/C3N4 composite semiconductor was synthesized by calcining carbon nitride (C3N4) nanosheets and SnO2 nanosheets. The main structure of C3N4 and SnO2 well stably retained and a stable heterojunction at the interface of them was formed. Photocatalytic test results of water splitting for hydrogen (H2) evolution and active oxygen (O2) for hydrogen peroxide (H2O2) generation show that under visible light irradiation, the composite sample of SnO2/C3N4-5% while the content of SnO2 is 5wt% shows much enhanced H2 evolution activity (54.9 µmol·h−1), which is about 2.1 times as that of C3N4 nanoseets. And the H2O2 generation activity of SnO2/C3N4-5% is 78.9 µmol·L−1·h−1, which is about 11.9 times that of C3N4 nanosheets. The structural characterization and electrochemical tests show that the establishment of heterojunction facilitate the rapid transfer of photogenerated electrons from C3N4 to SnO2, inhi-bite the recombination rate of excited electrons-holes, and greatly improve the photocatalytic reduction perfor-mance.
Visible-light responsive two-dimensional composite semiconductor materials are significant in the field of photocatalysis. Construction of stable and effective heterojunctions to promote interface charge transport is the key in the research of two-dimensional composite materials. In this work, a face-to-face stacked 2D-2D SnO2/C3N4 composite semiconductor was synthesized by calcining carbon nitride (C3N4) nanosheets and SnO2 nanosheets. The main structure of C3N4 and SnO2 well stably retained and a stable heterojunction at the interface of them was formed. Photocatalytic test results of water splitting for hydrogen (H2) evolution and active oxygen (O2) for hydrogen peroxide (H2O2) generation show that under visible light irradiation, the composite sample of SnO2/C3N4-5% while the content of SnO2 is 5wt% shows much enhanced H2 evolution activity (54.9 µmol·h−1), which is about 2.1 times as that of C3N4 nanoseets. And the H2O2 generation activity of SnO2/C3N4-5% is 78.9 µmol·L−1·h−1, which is about 11.9 times that of C3N4 nanosheets. The structural characterization and electrochemical tests show that the establishment of heterojunction facilitate the rapid transfer of photogenerated electrons from C3N4 to SnO2, inhi-bite the recombination rate of excited electrons-holes, and greatly improve the photocatalytic reduction perfor-mance.
2022, 39(8): 3863-3870.
doi: 10.13801/j.cnki.fhclxb.20211028.003
Abstract:
The molecular structure and performance of polypyrrole is very different due to the difference of its synthesis methods. Utilizing a metal-organic framework (MOF) named copper pyromellitic (Cu-BTC) with three-dimensipnal (3D) mesoporous channels as the host material, the radical polymerization of pyrrole (Py) was conducted in the pores by iodine oxidation method to obtain the composite material polypyrrole@Cu-BTC (PPy@Cu-BTC). XRD, SEM, FTIR, TG and N2 adsorption-desorption isotherm were used to characterize the prepared Cu-BTC, Py@Cu-BTC and PPy@Cu-BTC, showing the successful synthesis of polymerization in the pores. During the polymerization, the structure and morphology of Cu-BTC keep stable. Based on the charge transfer of host-guest complexation and π-π interaction, the PPy@Cu-BTC composite is a semiconductor material and has a conductivity of 10−4 S/cm which is at least four orders of magnitude higher than the conductivity of the template Cu-BTC and the as-prepared solid polypyrrole. N2 adsorption measurement indicated that the as-synthesized PPy separated from PPy@Cu-BTC composite is porous, which has excellent absorption ability of CO2 with a maximum absorption value of 16 cm3/g and twice as much as the absorption ability of the as-synthesized solid PPy.
The molecular structure and performance of polypyrrole is very different due to the difference of its synthesis methods. Utilizing a metal-organic framework (MOF) named copper pyromellitic (Cu-BTC) with three-dimensipnal (3D) mesoporous channels as the host material, the radical polymerization of pyrrole (Py) was conducted in the pores by iodine oxidation method to obtain the composite material polypyrrole@Cu-BTC (PPy@Cu-BTC). XRD, SEM, FTIR, TG and N2 adsorption-desorption isotherm were used to characterize the prepared Cu-BTC, Py@Cu-BTC and PPy@Cu-BTC, showing the successful synthesis of polymerization in the pores. During the polymerization, the structure and morphology of Cu-BTC keep stable. Based on the charge transfer of host-guest complexation and π-π interaction, the PPy@Cu-BTC composite is a semiconductor material and has a conductivity of 10−4 S/cm which is at least four orders of magnitude higher than the conductivity of the template Cu-BTC and the as-prepared solid polypyrrole. N2 adsorption measurement indicated that the as-synthesized PPy separated from PPy@Cu-BTC composite is porous, which has excellent absorption ability of CO2 with a maximum absorption value of 16 cm3/g and twice as much as the absorption ability of the as-synthesized solid PPy.
2022, 39(8): 3871-3881.
doi: 10.13801/j.cnki.fhclxb.20210910.002
Abstract:
In order to solve the problem of antimony(III) pollution in water environment, Fe-Mn layered double hydroxides (Fe-Mn LDH) were prepared by ultrasonic co-precipitation method, and the effects of initial pH, dosage, coexisting ions, adsorption time and temperature on the removal of antimony(III) from wastewater by Fe-Mn LDH were studied. The crystal structure, morphology and adsorption mechanism were characterized and analyzed by SEM, EDS, XRD, XPS and FTIR. The results show that the suitable conditions for antimony(III) removal are pH of 5, dosage of 0.4 g/L and adsorption time of 150 min under 45℃. Under these conditions, the maximum adsorption capacity is 77.39 mg/g. The adsorption process conforms to the pseudo-second-order kinetic model, and the Freundich isotherm model can well describe the adsorption behavior of antimony(III). The adsorption mechanisms of antimony(III) mainly include ion exchange, coordination complex and electrostatic interaction. The removal efficiency of antimony(III) is found to be over 83.03% by four adsorption-desorption experiments. This study indicates that Fe-Mn LDH has the potential to treat and repair wastewater containing antimony(III).
In order to solve the problem of antimony(III) pollution in water environment, Fe-Mn layered double hydroxides (Fe-Mn LDH) were prepared by ultrasonic co-precipitation method, and the effects of initial pH, dosage, coexisting ions, adsorption time and temperature on the removal of antimony(III) from wastewater by Fe-Mn LDH were studied. The crystal structure, morphology and adsorption mechanism were characterized and analyzed by SEM, EDS, XRD, XPS and FTIR. The results show that the suitable conditions for antimony(III) removal are pH of 5, dosage of 0.4 g/L and adsorption time of 150 min under 45℃. Under these conditions, the maximum adsorption capacity is 77.39 mg/g. The adsorption process conforms to the pseudo-second-order kinetic model, and the Freundich isotherm model can well describe the adsorption behavior of antimony(III). The adsorption mechanisms of antimony(III) mainly include ion exchange, coordination complex and electrostatic interaction. The removal efficiency of antimony(III) is found to be over 83.03% by four adsorption-desorption experiments. This study indicates that Fe-Mn LDH has the potential to treat and repair wastewater containing antimony(III).
2022, 39(8): 3882-3890.
doi: 10.13801/j.cnki.fhclxb.20210923.002
Abstract:
The hydrogen evolution reaction (HER) has broader research prospects than traditional hydrogen production methods, but because of its slow kinetics, low-cost and high-efficiency electrocatalysts have become parti-cularly important in HER. NbS2@MoS2 with the morphology of nanoflowers and nanosheets was prepared by one-step molten salt electrolysis. Using XRD, SEM, TEM, XPS, SAED and other methods to characterize the physical and chemical properties of the electrocatalysts. The results show that the NbS2@MoS2 nanoflower catalyst exhibits a polycrystalline state with a thin and film flower-like structure, and the Nb elements are uniformly distributed on the surface of MoS2. The HER performance is verified by electrochemical tests. The test results show that the nanoflower structure shows excellent electrocatalytic performance in HER. In a 1 mol/L KOH solution, the overpotential is 292.9 mV at a current density of 10.0 mA·cm−2, and the Tafel slope is 107.0 mV·dec−1, the charge transfer impe-dance is 31.0 Ω, and the electrochemically active surface area is 13.7 mF·cm−2. And after 20 h of catalysis, it can still maintain good electrocatalytic activity. Nb deposition forms defects on the surface of MoS2, and at the same time forms NbS2 on the surface, which provides more active sites and improves water splitting performance. High-temperature molten salt electrocrystallization provides a new method for the synthesis of catalytic materials.
The hydrogen evolution reaction (HER) has broader research prospects than traditional hydrogen production methods, but because of its slow kinetics, low-cost and high-efficiency electrocatalysts have become parti-cularly important in HER. NbS2@MoS2 with the morphology of nanoflowers and nanosheets was prepared by one-step molten salt electrolysis. Using XRD, SEM, TEM, XPS, SAED and other methods to characterize the physical and chemical properties of the electrocatalysts. The results show that the NbS2@MoS2 nanoflower catalyst exhibits a polycrystalline state with a thin and film flower-like structure, and the Nb elements are uniformly distributed on the surface of MoS2. The HER performance is verified by electrochemical tests. The test results show that the nanoflower structure shows excellent electrocatalytic performance in HER. In a 1 mol/L KOH solution, the overpotential is 292.9 mV at a current density of 10.0 mA·cm−2, and the Tafel slope is 107.0 mV·dec−1, the charge transfer impe-dance is 31.0 Ω, and the electrochemically active surface area is 13.7 mF·cm−2. And after 20 h of catalysis, it can still maintain good electrocatalytic activity. Nb deposition forms defects on the surface of MoS2, and at the same time forms NbS2 on the surface, which provides more active sites and improves water splitting performance. High-temperature molten salt electrocrystallization provides a new method for the synthesis of catalytic materials.
2022, 39(8): 3891-3897.
doi: 10.13801/j.cnki.fhclxb.20210927.002
Abstract:
As a new antibacterial method, photocatalysis has attracted extensive attention. The development of high-efficiency visible light catalyst is one of the hot research directions. In this work, graphene quantum dots (GQDs) were synthesized by a green-chemical method. GQDs/Ce-2MI was obtained via one-pot precipitation method at room temperature using GQDs, cerium nitrate and 2-methylimidazole (2MI) as raw materials. Different ratios of GQDs/Ce-2MI samples were obtained by controlling the initial amount of GQDs solution. Through photoelectrochemical test, it is found that 25vol%GQDs/Ce-2MI displayed high photocurrent response performance. Furthermore, using 2MI as fixed organic ligand, M-2MI with different central metal ions (Mn+: Co2+, Fe2+, Fe3+) were synthesized and compared. Under visible light irradiation, the antibacterial properties of different catalysts were investigated using Escherichia coli (E. coli) as target strain. The results indicate that GQDs/Ce-2MI displays the optimal antibacterial performance. After 60 min of visible light irradiation, more than 99% sterilization effect can be achieved. Using the optimized GQDs/Ce-2MI as photocatalyst, the effects of light source wavelength and different bacterial species were studied. The results indicate that GQDs/Ce-2MI has good antibacterial ability in a wide spectrum range and universal antibacterial effect toward Staphylococcus aureus (S. aureus). Through the quencher experiments, it can be speculated that the main active species for the inactivation of E. coli are holes (h+) and hydroxyl radicals (•OH).
As a new antibacterial method, photocatalysis has attracted extensive attention. The development of high-efficiency visible light catalyst is one of the hot research directions. In this work, graphene quantum dots (GQDs) were synthesized by a green-chemical method. GQDs/Ce-2MI was obtained via one-pot precipitation method at room temperature using GQDs, cerium nitrate and 2-methylimidazole (2MI) as raw materials. Different ratios of GQDs/Ce-2MI samples were obtained by controlling the initial amount of GQDs solution. Through photoelectrochemical test, it is found that 25vol%GQDs/Ce-2MI displayed high photocurrent response performance. Furthermore, using 2MI as fixed organic ligand, M-2MI with different central metal ions (Mn+: Co2+, Fe2+, Fe3+) were synthesized and compared. Under visible light irradiation, the antibacterial properties of different catalysts were investigated using Escherichia coli (E. coli) as target strain. The results indicate that GQDs/Ce-2MI displays the optimal antibacterial performance. After 60 min of visible light irradiation, more than 99% sterilization effect can be achieved. Using the optimized GQDs/Ce-2MI as photocatalyst, the effects of light source wavelength and different bacterial species were studied. The results indicate that GQDs/Ce-2MI has good antibacterial ability in a wide spectrum range and universal antibacterial effect toward Staphylococcus aureus (S. aureus). Through the quencher experiments, it can be speculated that the main active species for the inactivation of E. coli are holes (h+) and hydroxyl radicals (•OH).
2022, 39(8): 3898-3905.
doi: 10.13801/j.cnki.fhclxb.20220120.006
Abstract:
Supercapacitors have been attracted tremendous attention due to their high power density and long cycle life, etc. The electrode material is the main factor affecting electrochemical properties. Graphene/manganese dioxide composites (RGO/MnO2) were prepared using one pot hydrothermal method with graphene oxide (GO) as carbon source, as well as H2O2 and KMnO4 as MnO2 precursors. It was found that sphere-like MnO2 distributes on the graphene sheets by the microstructure tests. The energy storage mechanism of the composite was discussed. It displays that the reaction is the surface dominant process. The surface capacitance accounts for 86.2% of the total capacitance at 5 mV·s−1, While it can account for 97.3% at 200 mV·s−1. In order to assemble a device with high energy density, this work fabricated an asymmetric supercapacitor (ASC, RGO/MnO2//RGO) using the RGO/MnO2 as the positive electrode and RGO as the negative electrode, respectively, which exhibits high energy density (72.8 W·h·kg−1 at 100 W·kg−1).
Supercapacitors have been attracted tremendous attention due to their high power density and long cycle life, etc. The electrode material is the main factor affecting electrochemical properties. Graphene/manganese dioxide composites (RGO/MnO2) were prepared using one pot hydrothermal method with graphene oxide (GO) as carbon source, as well as H2O2 and KMnO4 as MnO2 precursors. It was found that sphere-like MnO2 distributes on the graphene sheets by the microstructure tests. The energy storage mechanism of the composite was discussed. It displays that the reaction is the surface dominant process. The surface capacitance accounts for 86.2% of the total capacitance at 5 mV·s−1, While it can account for 97.3% at 200 mV·s−1. In order to assemble a device with high energy density, this work fabricated an asymmetric supercapacitor (ASC, RGO/MnO2//RGO) using the RGO/MnO2 as the positive electrode and RGO as the negative electrode, respectively, which exhibits high energy density (72.8 W·h·kg−1 at 100 W·kg−1).
2022, 39(8): 3906-3914.
doi: 10.13801/j.cnki.fhclxb.20210930.002
Abstract:
This work aims to use carbon nanotubes with high aspect ratio, high specific surface area and high conductivity in the field of supercapacitors and improve the contact resistance between them and metal electrodes. Carbon nanotubes were doped with transition metal palladium by electroless deposition method and transition metal nickel by metal organic frameworks. Palladium and nickel doped carbon nanotubes/polyvinyl alcohol composites were used to modify glassy carbon electrodes and carbon cloth, respectively, and the modified carbon cloth was used as electrode material to assemble supercapacitors. Then the modified glassy carbon electrodes and supercapacitors were tested by cyclic voltammetry and alternating-current impedance. The results show that the values of specific capacitance of Pd-doped and Ni-doped carbon nanotubes modified glassy carbon electrodes are 9.89 F/g and 5.99 F/g, respectively. And the values of specific capacitance of supercapacitors assembled using carbon cloth modified with Pd-doped and Ni-doped carbon nanotubes are 175.77 mF/g and 61.92 mF/g, respectively. It can be seen that the effect of Pd doping on reducing the internal resistance and improving the electrochemical perfor-mance of carbon nanotubes modified glassy carbon electrode and supercapacitor is better than that of Ni doping, which serves as a reference for the application of doped carbon nanotubes in supercapacitors and other energy storage devices.
This work aims to use carbon nanotubes with high aspect ratio, high specific surface area and high conductivity in the field of supercapacitors and improve the contact resistance between them and metal electrodes. Carbon nanotubes were doped with transition metal palladium by electroless deposition method and transition metal nickel by metal organic frameworks. Palladium and nickel doped carbon nanotubes/polyvinyl alcohol composites were used to modify glassy carbon electrodes and carbon cloth, respectively, and the modified carbon cloth was used as electrode material to assemble supercapacitors. Then the modified glassy carbon electrodes and supercapacitors were tested by cyclic voltammetry and alternating-current impedance. The results show that the values of specific capacitance of Pd-doped and Ni-doped carbon nanotubes modified glassy carbon electrodes are 9.89 F/g and 5.99 F/g, respectively. And the values of specific capacitance of supercapacitors assembled using carbon cloth modified with Pd-doped and Ni-doped carbon nanotubes are 175.77 mF/g and 61.92 mF/g, respectively. It can be seen that the effect of Pd doping on reducing the internal resistance and improving the electrochemical perfor-mance of carbon nanotubes modified glassy carbon electrode and supercapacitor is better than that of Ni doping, which serves as a reference for the application of doped carbon nanotubes in supercapacitors and other energy storage devices.
2022, 39(8): 3915-3921.
doi: 10.13801/j.cnki.fhclxb.20211018.005
Abstract:
To study the photocatalytic and antibacterial properties of modified TiO2 on the surface of polypropylene (PP), silver pyrosilicate-titanium dioxide (Ag6Si2O7-TiO2) photocatalyst material was prepared by in-situ deposition, and it was loaded on the surface of PP nonwovens material which pretreat by silane coupling agent through impregnation method. The crystal structure, surface morphology and chemical composition were characterized by SEM, XRD, XPS, UV-vis and photoluminescence spectroscopy (PL). The results show that Ag6Si2O7-TiO2/PP composite photocatalytic material is successfully prepared, in which the mass fraction of Ag6Si2O7 is 1wt% and the concentration of loaded PP nonwovens is 2 g/L. In order to characterize the photocatalytic degradation of dyes by Ag6Si2O7-TiO2/PP, the methyl orange solution are used as degradation substance, Ag6Si2O7-TiO2/PP is treated under xenon lamp light with 300 W for 120 min, and the degradation rate reach 95.6%. In order to characterize the antibacterial properties of Ag6Si2O7-TiO2/PP, the antibacterial effects of Ag6Si2O7-TiO2/PP on Staphylococcus aureus and Escherichia coli under visible light and no light are contrasted. The results show that the bacteriosta-tic rates of Ag6Si2O7-TiO2/PP against both bacteria under visible light are more than 99.99%.
To study the photocatalytic and antibacterial properties of modified TiO2 on the surface of polypropylene (PP), silver pyrosilicate-titanium dioxide (Ag6Si2O7-TiO2) photocatalyst material was prepared by in-situ deposition, and it was loaded on the surface of PP nonwovens material which pretreat by silane coupling agent through impregnation method. The crystal structure, surface morphology and chemical composition were characterized by SEM, XRD, XPS, UV-vis and photoluminescence spectroscopy (PL). The results show that Ag6Si2O7-TiO2/PP composite photocatalytic material is successfully prepared, in which the mass fraction of Ag6Si2O7 is 1wt% and the concentration of loaded PP nonwovens is 2 g/L. In order to characterize the photocatalytic degradation of dyes by Ag6Si2O7-TiO2/PP, the methyl orange solution are used as degradation substance, Ag6Si2O7-TiO2/PP is treated under xenon lamp light with 300 W for 120 min, and the degradation rate reach 95.6%. In order to characterize the antibacterial properties of Ag6Si2O7-TiO2/PP, the antibacterial effects of Ag6Si2O7-TiO2/PP on Staphylococcus aureus and Escherichia coli under visible light and no light are contrasted. The results show that the bacteriosta-tic rates of Ag6Si2O7-TiO2/PP against both bacteria under visible light are more than 99.99%.
2022, 39(8): 3922-3928.
doi: 10.13801/j.cnki.fhclxb.20210903.002
Abstract:
Due to the presence of large band gap TiO2, photogenerated carriers disadvantage low rate of separation, which limits the photoelectrochemical cathodic protection. To solve this problem, TiO2 nanoarrays were prepared by hydrothermal method, and then SrTiO3/TiO2 composite films were prepared by ultrasonic spray pyrolysis. XRD, SEM, UV-visible diffuse reflectance spectrum (UV-Vis DRS), fluorescence spectra (PL) were used to characterize the phase structure, microscopic morphology, and light absorption properties of the samples. Finally, using 304 stainless steel (304 SS) as the protected substrate, the photoelectrochemical cathodic protection performance of the SrTiO3/TiO2 composite film was investigated. The results show that the SrTiO3/TiO2 composite film prepared by the ultrasonic spray pyrolysis method has a light absorption range of light below 415 nm, which enters the visible light region. The SrTiO3/TiO2 composite film has better light absorption than the TiO2 nanoarray. The separation rate of photogenerated electron-hole pairs is increased, and the mobility of photogenerated electrons is improved. In 3.5wt%NaCl solution, the SrTiO3/TiO2 composite film makes the corrosion potential of 304 stainless steel negatively shift to −0.45 V, and the negative shift is nearly 270 mV. While the TiO2 nanoarray can only move 210 mV negatively, and the performance is improved by 28.5%. The performance of the SrTiO3/TiO2 composite film is stable after four open and closed light cycle tests.
Due to the presence of large band gap TiO2, photogenerated carriers disadvantage low rate of separation, which limits the photoelectrochemical cathodic protection. To solve this problem, TiO2 nanoarrays were prepared by hydrothermal method, and then SrTiO3/TiO2 composite films were prepared by ultrasonic spray pyrolysis. XRD, SEM, UV-visible diffuse reflectance spectrum (UV-Vis DRS), fluorescence spectra (PL) were used to characterize the phase structure, microscopic morphology, and light absorption properties of the samples. Finally, using 304 stainless steel (304 SS) as the protected substrate, the photoelectrochemical cathodic protection performance of the SrTiO3/TiO2 composite film was investigated. The results show that the SrTiO3/TiO2 composite film prepared by the ultrasonic spray pyrolysis method has a light absorption range of light below 415 nm, which enters the visible light region. The SrTiO3/TiO2 composite film has better light absorption than the TiO2 nanoarray. The separation rate of photogenerated electron-hole pairs is increased, and the mobility of photogenerated electrons is improved. In 3.5wt%NaCl solution, the SrTiO3/TiO2 composite film makes the corrosion potential of 304 stainless steel negatively shift to −0.45 V, and the negative shift is nearly 270 mV. While the TiO2 nanoarray can only move 210 mV negatively, and the performance is improved by 28.5%. The performance of the SrTiO3/TiO2 composite film is stable after four open and closed light cycle tests.
2022, 39(8): 3929-3939.
doi: 10.13801/j.cnki.fhclxb.20210911.002
Abstract:
To study the shear performance of seawater sea-sand engineered cementitious composites (SSE) beams, SSE material was developed. The shear tests of basalt fiber reinforced polymer (BFRP) bars reinforced SSE (BFRP/SSE) beams were carried out, and the effects of shear span ratio and stirrup ratio on the shear performance of BFRP/SSE beams were analyzed. The experimental results show that the maximum tensile strain capacity of SSE is 8.3%, and average crack width is about 0.2 mm. When BFRP/SSE beams fail in shear, no spalling failure occurs. The crack width of BFRP/SSE beams at serviceability limit state is less than 0.3 mm, which meets the requirements of relevant code. In the case of few stirrups and no stirrups, the shear capacity of beams prepared by SSE is increased by 59.32%-99.25% and 6.37%-73.68%, and stiffness also increases. Minimum stirrup ratio may not be required in the structural design of BFRP/SSE beams. Through finite element software, the influence of mechanical properties of SSE on the shear capacity of BFRP/SSE beams without web reinforcement was analyzed. The results of finite element analysis show that with increasing the compressive strength of SSE, the shear capacity increases obviously. With the increase of tensile strength of SSE, the shear capacity increases slowly. The tensile strain capacity of SSE has little effect on the shear capacity. This study can be used as a valuable reference for the applications of SSE beams in civil engineering.
To study the shear performance of seawater sea-sand engineered cementitious composites (SSE) beams, SSE material was developed. The shear tests of basalt fiber reinforced polymer (BFRP) bars reinforced SSE (BFRP/SSE) beams were carried out, and the effects of shear span ratio and stirrup ratio on the shear performance of BFRP/SSE beams were analyzed. The experimental results show that the maximum tensile strain capacity of SSE is 8.3%, and average crack width is about 0.2 mm. When BFRP/SSE beams fail in shear, no spalling failure occurs. The crack width of BFRP/SSE beams at serviceability limit state is less than 0.3 mm, which meets the requirements of relevant code. In the case of few stirrups and no stirrups, the shear capacity of beams prepared by SSE is increased by 59.32%-99.25% and 6.37%-73.68%, and stiffness also increases. Minimum stirrup ratio may not be required in the structural design of BFRP/SSE beams. Through finite element software, the influence of mechanical properties of SSE on the shear capacity of BFRP/SSE beams without web reinforcement was analyzed. The results of finite element analysis show that with increasing the compressive strength of SSE, the shear capacity increases obviously. With the increase of tensile strength of SSE, the shear capacity increases slowly. The tensile strain capacity of SSE has little effect on the shear capacity. This study can be used as a valuable reference for the applications of SSE beams in civil engineering.
2022, 39(8): 3940-3949.
doi: 10.13801/j.cnki.fhclxb.20210902.003
Abstract:
In order to improve the performance of coal mine filling slurry before and after solidification, sodium sulfate and polycarboxylic acid water reducing agent were used to prepare a composite admixture, and the effect on the working performance and mechanical properties of the filling slurry before and after solidification was explored through indoor macroscopic experiments. Its influence mechanism was analyzed in combination with indoor microscopic experiments. Experiments show that the cement consumption of 0.5wt% sodium sulfate and 0.2wt% polycarboxylic acid water-reducing agent mixed filling slurry can be reduced by 2%, the slump can be increased by 4.1 cm, the initial and final setting time can be shortened by 20 min, and the water reduction rate can be increased by 7.7%, the 3rd day and 28th day uniaxial compressive strength can increase up to 22% and 42%. The analysis shows that the early strength mechanism of sodium sulfate, the electrostatic repulsion and steric hindrance of polycarboxylic acid water-reducing agent, and the mutual promotion of the two are the main reasons that affect the working performance of the filling slurry before curing. The needle-like product ettringite and the white fibrous substance calcium silicate hydrate are the main substances that affect the mechanical properties of the filling paste after solidification, and the formation of the two improves the uniaxial compressive strength of the filling paste.
In order to improve the performance of coal mine filling slurry before and after solidification, sodium sulfate and polycarboxylic acid water reducing agent were used to prepare a composite admixture, and the effect on the working performance and mechanical properties of the filling slurry before and after solidification was explored through indoor macroscopic experiments. Its influence mechanism was analyzed in combination with indoor microscopic experiments. Experiments show that the cement consumption of 0.5wt% sodium sulfate and 0.2wt% polycarboxylic acid water-reducing agent mixed filling slurry can be reduced by 2%, the slump can be increased by 4.1 cm, the initial and final setting time can be shortened by 20 min, and the water reduction rate can be increased by 7.7%, the 3rd day and 28th day uniaxial compressive strength can increase up to 22% and 42%. The analysis shows that the early strength mechanism of sodium sulfate, the electrostatic repulsion and steric hindrance of polycarboxylic acid water-reducing agent, and the mutual promotion of the two are the main reasons that affect the working performance of the filling slurry before curing. The needle-like product ettringite and the white fibrous substance calcium silicate hydrate are the main substances that affect the mechanical properties of the filling paste after solidification, and the formation of the two improves the uniaxial compressive strength of the filling paste.
2022, 39(8): 3950-3964.
doi: 10.13801/j.cnki.fhclxb.20210927.004
Abstract:
Since fiber reinforced polymer (FRP) has excellent corrosion resistance, it can be used to replace ordi-nary steel bars to solve the problem of steel corrosion. Because of the abundant coral and seawater resources in China, using coral instead of traditional sand aggregate is one of the effective methods to solve the problem of scarcity of traditional materials in island construction. Bonding property between FRP bars and coral aggregate seawater concrete is one of the important factors to determine whether FRP reinforced coral aggregate seawater concrete structure can be applied in practical engineering like ordinary reinforced concrete structure. At present, there is little research on the interfacial bonding property of FRP reinforced coral aggregate seawater concrete structure, especially in theory. Therefore, the rationality of the simplified bilinear model will be verified by experiments and numerical simulation. Based on the experiments and numerical simulation, the expressions of interfacial bonding stress and relative slip of FRP reinforced coral aggregate seawater concrete will be derived, and then the distribution maps of interfacial bonding stress and relative slip will be plotted. The theoretical solution obtained by the expression will be compared with the experimental and numerical simulation solution. The results show that the theoretical solution obtained by theoretical calculation is in good agreement with the experimental results. The increase of FRP bar diameter and bonding length will lead to more non-uniform distribution of interfacial bonding stress and relative slip. The change of coral aggregate concrete strength has little effect on the distribution of interfacial bonding stress and relative slip. The interfacial bond stress and relative slip distribution of glass fiber reinforced polymer (GFRP) and basalt fiber reinforced polymer (BFRP) reinforced coral aggregate seawater concrete are similar, and are more uniform than that of carbon fiber reinforced polymer (CFRP) coral aggregate concrete.
Since fiber reinforced polymer (FRP) has excellent corrosion resistance, it can be used to replace ordi-nary steel bars to solve the problem of steel corrosion. Because of the abundant coral and seawater resources in China, using coral instead of traditional sand aggregate is one of the effective methods to solve the problem of scarcity of traditional materials in island construction. Bonding property between FRP bars and coral aggregate seawater concrete is one of the important factors to determine whether FRP reinforced coral aggregate seawater concrete structure can be applied in practical engineering like ordinary reinforced concrete structure. At present, there is little research on the interfacial bonding property of FRP reinforced coral aggregate seawater concrete structure, especially in theory. Therefore, the rationality of the simplified bilinear model will be verified by experiments and numerical simulation. Based on the experiments and numerical simulation, the expressions of interfacial bonding stress and relative slip of FRP reinforced coral aggregate seawater concrete will be derived, and then the distribution maps of interfacial bonding stress and relative slip will be plotted. The theoretical solution obtained by the expression will be compared with the experimental and numerical simulation solution. The results show that the theoretical solution obtained by theoretical calculation is in good agreement with the experimental results. The increase of FRP bar diameter and bonding length will lead to more non-uniform distribution of interfacial bonding stress and relative slip. The change of coral aggregate concrete strength has little effect on the distribution of interfacial bonding stress and relative slip. The interfacial bond stress and relative slip distribution of glass fiber reinforced polymer (GFRP) and basalt fiber reinforced polymer (BFRP) reinforced coral aggregate seawater concrete are similar, and are more uniform than that of carbon fiber reinforced polymer (CFRP) coral aggregate concrete.
2022, 39(8): 3965-3981.
doi: 10.13801/j.cnki.fhclxb.20211117.002
Abstract:
Composite sandwich structure has higher specific strength, specific stiffness, excellent corrosion resistance, good fatigue resistance and simple molding process, etc. Composite sandwich specimens were produced with face sheets and lattice webs which were made from glass fiber reinforced polymer (GFRP) and core made from polyurethane (PU) foam. The vertical lattice webs were transformed into double-layered orthogonal lattice webs, double-layered dislocation lattice webs and triple-layered dislocation lattice webs. Quasi-static compression experiment was performed on specimens to compare their failure modes and performance of energy absorption. The results show that the triple-layered dislocation lattice webs have ideal load-displacement curves. After changing the spatial position of the lattice webs, the elastic decline is extended, and the bearing capacity of the specimen is improved. Compared with the vertical lattice webs, the energy absorption value of the triple-layered dislocation lattice webs increases by 91.9%. The equivalent cross model was assumed to calculate the equivalent elastic compression stiffness of the double-layered orthogonal lattice webs, and the elastic stiffness of the double-layered orthogonal lattice webs is greatly affected by the lattice compression modulus. Numerical simulations using ANSYS/LS-DYNA were conducted on composite panels. By comparing the material properties and failure modes obtained from the experimental investigations, the accuracy of the numerical simulation could be well predicted, and the energy absorption of the GFRP webs and foam was compared and analyzed by numerical simulation.
Composite sandwich structure has higher specific strength, specific stiffness, excellent corrosion resistance, good fatigue resistance and simple molding process, etc. Composite sandwich specimens were produced with face sheets and lattice webs which were made from glass fiber reinforced polymer (GFRP) and core made from polyurethane (PU) foam. The vertical lattice webs were transformed into double-layered orthogonal lattice webs, double-layered dislocation lattice webs and triple-layered dislocation lattice webs. Quasi-static compression experiment was performed on specimens to compare their failure modes and performance of energy absorption. The results show that the triple-layered dislocation lattice webs have ideal load-displacement curves. After changing the spatial position of the lattice webs, the elastic decline is extended, and the bearing capacity of the specimen is improved. Compared with the vertical lattice webs, the energy absorption value of the triple-layered dislocation lattice webs increases by 91.9%. The equivalent cross model was assumed to calculate the equivalent elastic compression stiffness of the double-layered orthogonal lattice webs, and the elastic stiffness of the double-layered orthogonal lattice webs is greatly affected by the lattice compression modulus. Numerical simulations using ANSYS/LS-DYNA were conducted on composite panels. By comparing the material properties and failure modes obtained from the experimental investigations, the accuracy of the numerical simulation could be well predicted, and the energy absorption of the GFRP webs and foam was compared and analyzed by numerical simulation.
2022, 39(8): 3982-3993.
doi: 10.13801/j.cnki.fhclxb.20210909.012
Abstract:
In order to better directly apply the undisturbed seawater sea-sand coral concrete to marine engineering, this paper performed a monotonous study on 12 carbon fiber reinforced plastics (CFRP)-steel composite tube filled circular seawater sea-sand coral concrete columns and 2 pure steel tube confined seawater sea-sand coral concrete columns. In the axial compression test, the main research parameters are the diameter-thickness ratio of the steel tube and the number of CFRP layers. The test has obtained the axial stress-strain relationship curve of the specimen. The results show that the specimen is in the form of shear failure with obvious shear slip line at the end of the column under axial pressure. The constraint effect of CFRP has no obvious effect on the initial section stiffness of the specimen, but has a significant effect on the stiffness of the specimen in the linear strengthening stage. With the increase of the number of CFRP layers, the ultimate stress and strain of the specimens are significantly increased. With the decrease of the diameter-thickness ratio of the steel tube, the mechanical properties of the specimens increase correspondingly. Combined with the test data, the existing FRP steel composite pipe confined concrete strength calculation model was evaluated.
In order to better directly apply the undisturbed seawater sea-sand coral concrete to marine engineering, this paper performed a monotonous study on 12 carbon fiber reinforced plastics (CFRP)-steel composite tube filled circular seawater sea-sand coral concrete columns and 2 pure steel tube confined seawater sea-sand coral concrete columns. In the axial compression test, the main research parameters are the diameter-thickness ratio of the steel tube and the number of CFRP layers. The test has obtained the axial stress-strain relationship curve of the specimen. The results show that the specimen is in the form of shear failure with obvious shear slip line at the end of the column under axial pressure. The constraint effect of CFRP has no obvious effect on the initial section stiffness of the specimen, but has a significant effect on the stiffness of the specimen in the linear strengthening stage. With the increase of the number of CFRP layers, the ultimate stress and strain of the specimens are significantly increased. With the decrease of the diameter-thickness ratio of the steel tube, the mechanical properties of the specimens increase correspondingly. Combined with the test data, the existing FRP steel composite pipe confined concrete strength calculation model was evaluated.
Axial compression behavior of high-strength recycled concrete filled steel tubular composite columns
2022, 39(8): 3994-4004.
doi: 10.13801/j.cnki.fhclxb.20210902.002
Abstract:
To study the difference of the axial compressive performance of recycled concrete composite columns and ordinary concrete composite columns, the experiments of two high-strength ordinary concrete-filled steel tube reinforced concrete columns (CFSTRCC) and three high-strength recycled CFSTRCC were conducted under axial loading. The concrete type, cross-sectional shape of the steel tube and whether the cross-shaped tie bars were set or not in the square steel tube were chosen to be the main parameters. The experimental results show that the damage development process and failure modes of recycled concrete specimens are similar to those of normal concrete specimens. The bearing capacity and energy dissipation capacity of recycled concrete specimens are higher than those of the ordinary concrete specimens. However, it has serious spalling of concrete and poor ductility. When the set cross-shaped tie bars were installed in the square steel tube, the ductility has been significantly improved, and the bearing capacity and energy consumption have also been significantly increased due to the tie bar enhancing the restraint of the square steel tube to the core concrete. Meanwhile, the peak load corresponds to a larger peak strain, so the materials are more fully utilized. Under the condition of the steel tube equal cross-sectional area and close material strength, CFSTRCC with circular steel tube has higher bearing capacity, better deformation ability and stronger energy dissipation capacity than CFSTRCC with square steel tube. According to the relevant domestic and foreign regulations, the ultimate bearing capacity of 26 recycled CFSTRCC from this paper and other references were calculated. The results show that the calculation results for the axial compression bearing capacity of CFSTRCC are in well agreement with the experiment results.
To study the difference of the axial compressive performance of recycled concrete composite columns and ordinary concrete composite columns, the experiments of two high-strength ordinary concrete-filled steel tube reinforced concrete columns (CFSTRCC) and three high-strength recycled CFSTRCC were conducted under axial loading. The concrete type, cross-sectional shape of the steel tube and whether the cross-shaped tie bars were set or not in the square steel tube were chosen to be the main parameters. The experimental results show that the damage development process and failure modes of recycled concrete specimens are similar to those of normal concrete specimens. The bearing capacity and energy dissipation capacity of recycled concrete specimens are higher than those of the ordinary concrete specimens. However, it has serious spalling of concrete and poor ductility. When the set cross-shaped tie bars were installed in the square steel tube, the ductility has been significantly improved, and the bearing capacity and energy consumption have also been significantly increased due to the tie bar enhancing the restraint of the square steel tube to the core concrete. Meanwhile, the peak load corresponds to a larger peak strain, so the materials are more fully utilized. Under the condition of the steel tube equal cross-sectional area and close material strength, CFSTRCC with circular steel tube has higher bearing capacity, better deformation ability and stronger energy dissipation capacity than CFSTRCC with square steel tube. According to the relevant domestic and foreign regulations, the ultimate bearing capacity of 26 recycled CFSTRCC from this paper and other references were calculated. The results show that the calculation results for the axial compression bearing capacity of CFSTRCC are in well agreement with the experiment results.
2022, 39(8): 4005-4016.
doi: 10.13801/j.cnki.fhclxb.20210903.006
Abstract:
In order to study the mechanical properties of steel fiber recycled aggregate concrete (SFRAC) under triaxial compression, 168 cylinder specimens were tested by considering the parameters of the lateral confining pressure, the replacement rate of recycled coarse aggregate and the volume fraction of steel fiber. The failure pattern of the specimens was observed in the test. The stress-strain curve, peak stress, peak strain and elastic modulus were obtained. Based on the test data, the influence of different parameters on the mechanical performance was analyzed. The results show that under triaxial compression, the specimens are destroyed by oblique splitting. With the increase of confining pressure, the peak of stress-strain curve increases, while the descending section becomes slower, the peak stress, peak strain and elastic modulus of SFRAC all increase significantly. Steel fiber increases the residual strength of the specimen under uniaxial compression and makes the descending section of the stress-strain curve slow down. With the increase of the replacement rate of recycled coarse aggregate, the peak stress and elastic modulus decrease and the peak strain increases. Under triaxial compression, the steel fiber has little effect on the peak stress of SFRAC, and when the volume fraction of steel fiber is 1vol%, the improvement effect on the deformation performance of SFRAC is optimal. Finally, the formulas for calculating the peak stress, peak strain and elastic modulus of SFRAC under triaxial compression are put forward.
In order to study the mechanical properties of steel fiber recycled aggregate concrete (SFRAC) under triaxial compression, 168 cylinder specimens were tested by considering the parameters of the lateral confining pressure, the replacement rate of recycled coarse aggregate and the volume fraction of steel fiber. The failure pattern of the specimens was observed in the test. The stress-strain curve, peak stress, peak strain and elastic modulus were obtained. Based on the test data, the influence of different parameters on the mechanical performance was analyzed. The results show that under triaxial compression, the specimens are destroyed by oblique splitting. With the increase of confining pressure, the peak of stress-strain curve increases, while the descending section becomes slower, the peak stress, peak strain and elastic modulus of SFRAC all increase significantly. Steel fiber increases the residual strength of the specimen under uniaxial compression and makes the descending section of the stress-strain curve slow down. With the increase of the replacement rate of recycled coarse aggregate, the peak stress and elastic modulus decrease and the peak strain increases. Under triaxial compression, the steel fiber has little effect on the peak stress of SFRAC, and when the volume fraction of steel fiber is 1vol%, the improvement effect on the deformation performance of SFRAC is optimal. Finally, the formulas for calculating the peak stress, peak strain and elastic modulus of SFRAC under triaxial compression are put forward.
2022, 39(8): 4017-4027.
doi: 10.13801/j.cnki.fhclxb.20210924.001
Abstract:
In order to investigate the crack resistance of prestressed carbon fiber reinforced polymer (CFRP) reinforced steel concrete eccentrically tensioned members, eleven specimens were fabricated with different parameters such as eccentricity, level of prestress, type of prestressed tendons and vertical tension were tested under low cyclic reversed loading. The results show that the crack resistance and crack control ability of prestressed steel reinforced concrete (SRC) biased tensioning members are significantly improved compared with the ordinary SRC biased tensioning members, and the cracking load is increased by about 1.5 times. The crack resistance of prestressed SRC biased tensioning members is positively related to the prestress level, and negatively related to the eccentricity. The type of prestressed tendons has little effect on the cracking load. In addition, the 7 mm diameter prestressed CFRP tendons are stronger than the 15 mm diameter prestressed fine rolled threaded rods in controlling the number of cracks in the members, and the crack resistance of the specimens can be improved by increasing the vertical tensile force appropriately. According to the existing theory and test results, the calculation formula of cracking load is derived, and the calculated results are in good agreement with the test values.
In order to investigate the crack resistance of prestressed carbon fiber reinforced polymer (CFRP) reinforced steel concrete eccentrically tensioned members, eleven specimens were fabricated with different parameters such as eccentricity, level of prestress, type of prestressed tendons and vertical tension were tested under low cyclic reversed loading. The results show that the crack resistance and crack control ability of prestressed steel reinforced concrete (SRC) biased tensioning members are significantly improved compared with the ordinary SRC biased tensioning members, and the cracking load is increased by about 1.5 times. The crack resistance of prestressed SRC biased tensioning members is positively related to the prestress level, and negatively related to the eccentricity. The type of prestressed tendons has little effect on the cracking load. In addition, the 7 mm diameter prestressed CFRP tendons are stronger than the 15 mm diameter prestressed fine rolled threaded rods in controlling the number of cracks in the members, and the crack resistance of the specimens can be improved by increasing the vertical tensile force appropriately. According to the existing theory and test results, the calculation formula of cracking load is derived, and the calculated results are in good agreement with the test values.
2022, 39(8): 4028-4036.
doi: 10.13801/j.cnki.fhclxb.20210928.005
Abstract:
To fabricate high performance energy storage devices with low cost, this work proposed a facile method to prepare biomass-based hierarchical activated carbon-polyaniline composites (HAC-PANI) via an in-situ chemi-cal polymerization method, and their applications in supercapacitors (SCs) and zinc-ion hybrid supercapacitors (ZHSCs) were investigated. The results show that hierarchical porous structure and high specific area of HAC provide growth sites for PANI and effectively reduce the agglomeration of PANI and meanwhile promote the transport of electrolyte ions, and degrease the charge transfer resistance. When the mass ratio of HAC to aniline monomer (An) is 1∶2, uniform PANI nanoparticles were observed growing on HAC, and the resulting composite (HAC-2PANI) electrode exhibits the optimum performance. Under the three-electrode system, the mass specific capacitance of HAC-2PANI reaches as high as 415.6 F·g−1(@1 A·g−1). The HAC-2PANI based all-solid supercapacitor (s-HAC-PANI-SC) displays a specific capacitance of 217.4 F·g−1(@1 A·g−1), an energy density of 26.5 W·h·kg−1 and a power density of 1875.0 W·kg−1. The zinc-ion hybrid supercapacitor (HAC-PANI-ZHSC) constructed with HAC-2PANI as the cathode and Zn foil as the anode exhibits a high specific capacity of 91.8 mA·h·g−1(@0.2 A·g−1), a remarkable energy density of 64.3 W·h·kg−1, and a power density of 140.0 W·kg−1, indicating promising potentials of biomass-based carbon composites for high performance and low cost electrochemical energy storage devices.
To fabricate high performance energy storage devices with low cost, this work proposed a facile method to prepare biomass-based hierarchical activated carbon-polyaniline composites (HAC-PANI) via an in-situ chemi-cal polymerization method, and their applications in supercapacitors (SCs) and zinc-ion hybrid supercapacitors (ZHSCs) were investigated. The results show that hierarchical porous structure and high specific area of HAC provide growth sites for PANI and effectively reduce the agglomeration of PANI and meanwhile promote the transport of electrolyte ions, and degrease the charge transfer resistance. When the mass ratio of HAC to aniline monomer (An) is 1∶2, uniform PANI nanoparticles were observed growing on HAC, and the resulting composite (HAC-2PANI) electrode exhibits the optimum performance. Under the three-electrode system, the mass specific capacitance of HAC-2PANI reaches as high as 415.6 F·g−1(@1 A·g−1). The HAC-2PANI based all-solid supercapacitor (s-HAC-PANI-SC) displays a specific capacitance of 217.4 F·g−1(@1 A·g−1), an energy density of 26.5 W·h·kg−1 and a power density of 1875.0 W·kg−1. The zinc-ion hybrid supercapacitor (HAC-PANI-ZHSC) constructed with HAC-2PANI as the cathode and Zn foil as the anode exhibits a high specific capacity of 91.8 mA·h·g−1(@0.2 A·g−1), a remarkable energy density of 64.3 W·h·kg−1, and a power density of 140.0 W·kg−1, indicating promising potentials of biomass-based carbon composites for high performance and low cost electrochemical energy storage devices.
2022, 39(8): 4037-4048.
doi: 10.13801/j.cnki.fhclxb.20211012.002
Abstract:
The nano photocatalyst in powder form had some problems in the process of catalytic degradation of pollutants, such as easy agglomeration of particles, difficult separation resulted in secondary pollution. A kind of polyurethane-silk fibroin supported BiOBr@CdS (BiOBr@CdS/PU-SF) nanocomposite films were prepared by blending-wet phase transformation in situ synthesis method. The XRD, FTIR, SEM, XPS, UV-Vis diffuse reflectance spectra (UV-Vis DRS) and photoluminescence spectra (PL) were used to characterize the crystal structure, micromorphology, surface element valence and optical properties. The results show that the semiconductor nanocompo-sites are formed between BiOBr and CdS in the BiOBr@CdS/PU-SF composite film, which not only improve the visible light absorption capacity of a single semiconductor, but also effectively inhibit the recombination of photogenerated carriers. The photocatalytic activity was evaluated by degradation of antibiotic wastewater (Tetracycline hydrochloride (TC) as model pollutant) under visible light irradiation. Among them, a 1:1 molar ratio of Bi and Cd for (1:1)BiOBr@CdS/PU-SF composite film shows the highest removal rate of TC (70.3%), which is the 1.33 times and 2.45 times of BiOBr/PU-SF and CdS/PU-SF composite films, respectively. The pseudo-first-order kinetic constants of TC degradation are 1.63 and 3.58 times of BiOBr/PU-SF and CdS/PU-SF composite films, respectively. Moreover, the composite film can be separated and recovered without centrifugation and filtration, and it can still maintain more than 80% of the original degradation rate after recycling for five times.
The nano photocatalyst in powder form had some problems in the process of catalytic degradation of pollutants, such as easy agglomeration of particles, difficult separation resulted in secondary pollution. A kind of polyurethane-silk fibroin supported BiOBr@CdS (BiOBr@CdS/PU-SF) nanocomposite films were prepared by blending-wet phase transformation in situ synthesis method. The XRD, FTIR, SEM, XPS, UV-Vis diffuse reflectance spectra (UV-Vis DRS) and photoluminescence spectra (PL) were used to characterize the crystal structure, micromorphology, surface element valence and optical properties. The results show that the semiconductor nanocompo-sites are formed between BiOBr and CdS in the BiOBr@CdS/PU-SF composite film, which not only improve the visible light absorption capacity of a single semiconductor, but also effectively inhibit the recombination of photogenerated carriers. The photocatalytic activity was evaluated by degradation of antibiotic wastewater (Tetracycline hydrochloride (TC) as model pollutant) under visible light irradiation. Among them, a 1:1 molar ratio of Bi and Cd for (1:1)BiOBr@CdS/PU-SF composite film shows the highest removal rate of TC (70.3%), which is the 1.33 times and 2.45 times of BiOBr/PU-SF and CdS/PU-SF composite films, respectively. The pseudo-first-order kinetic constants of TC degradation are 1.63 and 3.58 times of BiOBr/PU-SF and CdS/PU-SF composite films, respectively. Moreover, the composite film can be separated and recovered without centrifugation and filtration, and it can still maintain more than 80% of the original degradation rate after recycling for five times.
2022, 39(8): 4049-4056.
doi: 10.13801/j.cnki.fhclxb.20210917.001
Abstract:
In this paper, the structure of skin dermal collagen fibers were simulated, and the sodium alginate (SA)-gelatin (GEL) composite scaffold with three topological angles of 45°, 60° and 90° were 3D printed to study the effect of topology on the performance of the hydrogel scaffold, respectively. SEM were used to characterize the microstructure of the scaffolds. The water content, porosity, mechanical properties, swelling ratio and in vitro degradation ratio of each group of scaffolds were measured. FTIR were used to test the functional groups of SA, GEL and composite hydrogel. Cell counting kit-8 (CCK-8) reagent and immunofluorescence staining were used to test the toxicity of the scaffolds to human dermal fibroblasts (HFb) and the biocompatibility of scaffolds. The results show that the topology of each group is clear. The relative position of the absorption peak in the FTIR spectrum provides the chemical structure of the scaffold material. The water content and porosity of the three groups are all greater than 80%. The compressive elastic modulus of the 45°, 60° and 90° scaffolds are (3.57±0.14) kPa, (3.18±0.31) kPa and (2.03±0.29) kPa, respectively. CCK-8 results show that the cell activity on three groups is maintained at more than 90% of control group without scaffolds. The results of microfilament and nuclear staining show that the spread of HFb on the 45° scaffold on the first day of inoculation is better than that of the other two groups, HFb proliferates significantly on the three groups of scaffolds with the increase of time, indicating that the scaffold has good cytocompatibility. This paper designs and characterizes the performance of SA-GEL scaffolds with different topologies, and provides an important foundation for the construction of subsequent tissue engineering dermis and the analysis of HFb collective migration on a three dimensional matrix.
In this paper, the structure of skin dermal collagen fibers were simulated, and the sodium alginate (SA)-gelatin (GEL) composite scaffold with three topological angles of 45°, 60° and 90° were 3D printed to study the effect of topology on the performance of the hydrogel scaffold, respectively. SEM were used to characterize the microstructure of the scaffolds. The water content, porosity, mechanical properties, swelling ratio and in vitro degradation ratio of each group of scaffolds were measured. FTIR were used to test the functional groups of SA, GEL and composite hydrogel. Cell counting kit-8 (CCK-8) reagent and immunofluorescence staining were used to test the toxicity of the scaffolds to human dermal fibroblasts (HFb) and the biocompatibility of scaffolds. The results show that the topology of each group is clear. The relative position of the absorption peak in the FTIR spectrum provides the chemical structure of the scaffold material. The water content and porosity of the three groups are all greater than 80%. The compressive elastic modulus of the 45°, 60° and 90° scaffolds are (3.57±0.14) kPa, (3.18±0.31) kPa and (2.03±0.29) kPa, respectively. CCK-8 results show that the cell activity on three groups is maintained at more than 90% of control group without scaffolds. The results of microfilament and nuclear staining show that the spread of HFb on the 45° scaffold on the first day of inoculation is better than that of the other two groups, HFb proliferates significantly on the three groups of scaffolds with the increase of time, indicating that the scaffold has good cytocompatibility. This paper designs and characterizes the performance of SA-GEL scaffolds with different topologies, and provides an important foundation for the construction of subsequent tissue engineering dermis and the analysis of HFb collective migration on a three dimensional matrix.
2022, 39(8): 4057-4064.
doi: 10.13801/j.cnki.fhclxb.20211027.001
Abstract:
In order to expand multi-function and high-value application of wood, balsa wood was used as raw material. Firstly, they were performed with chemical treatment to remove the matrix including lignin and hemicellulose, followed with drying. The acetylated balsa wood frame (AWF) was prepared by acetylation modification. Afterwards, by vacuum impregnation, polydimethylsiloxane (PDMS) elastomer was introduced into balsa wood frame (WF) and AWF respectively, in order to fabricate composite film materials (PDMS/WF and PDMS/AWF). The effects of acetylation modification on morphology, mechanical properties, chemical composition and surface hydrophilicity of composite films were systematically studied. The results show that after acetylation, the interface between balsa wood frame and PDMS is more compact, and the pores between PDMS and white wood are smaller. At the same time, the tensile strength of PDMS/AWF composite film (along the fiber growth direction, L-direction) is around 176 MPa, and the toughness is about 6.58 MJ/m3, which is nearly twice as high as that of PDMS/WF compo-site film. Furthermore, the prepared PDMS/AWF wood-based composite film was used as a flexible substrate to assemble a flexible sensor. As a result, it shows stable and repeatable changes for relative resistance values under various deformations. Altogether, it has great potential to be applied in the research fields of smart furniture, elastic substrates of smart response devices, flexible electronic components and wearable devices.
In order to expand multi-function and high-value application of wood, balsa wood was used as raw material. Firstly, they were performed with chemical treatment to remove the matrix including lignin and hemicellulose, followed with drying. The acetylated balsa wood frame (AWF) was prepared by acetylation modification. Afterwards, by vacuum impregnation, polydimethylsiloxane (PDMS) elastomer was introduced into balsa wood frame (WF) and AWF respectively, in order to fabricate composite film materials (PDMS/WF and PDMS/AWF). The effects of acetylation modification on morphology, mechanical properties, chemical composition and surface hydrophilicity of composite films were systematically studied. The results show that after acetylation, the interface between balsa wood frame and PDMS is more compact, and the pores between PDMS and white wood are smaller. At the same time, the tensile strength of PDMS/AWF composite film (along the fiber growth direction, L-direction) is around 176 MPa, and the toughness is about 6.58 MJ/m3, which is nearly twice as high as that of PDMS/WF compo-site film. Furthermore, the prepared PDMS/AWF wood-based composite film was used as a flexible substrate to assemble a flexible sensor. As a result, it shows stable and repeatable changes for relative resistance values under various deformations. Altogether, it has great potential to be applied in the research fields of smart furniture, elastic substrates of smart response devices, flexible electronic components and wearable devices.
2022, 39(8): 4065-4073.
doi: 10.13801/j.cnki.fhclxb.20210917.003
Abstract:
In order to study the effect of bamboo gradient structure on the properties of bamboo bundle fiber composites, bamboo bundle fiber (BF) as the enhanced phase, epoxy resin (EP)-methyl tetrahydrophthalic anhydride (MeTHPA) system is the matrix phase, BF/EP-MeTHPA composite was prepared by thermopress molding. By changing the BF unit: yellow side (BF-YS) and green side bundle fiber (BF-GS), the effect of natural structure on the failure of interface of BF/EP composite was studied. Based on the mechanical properties of composites, through nano and micro test means such as dynamic thermomechanical analysis (DMA), in situ SEM and FTIR, the state of BF/EP-MeTHPA, interface microregion, thermal analysis and macromechanical characterization were studied. The experimental results show that due to the high fiber content and strength in BF-GS, the enhancement effect and distribution uniformity in epoxy system is better than BF-YS. But the permeability and interface performance are lower than bamboo bundle fiber of yellow side/epoxy resin-MeTHPA (BF-YS/EP-MeTHPA). Through the observation of the bamboo structure, it is found that BF-YS remains more parenchyma cells, and the rough surface favors the infiltration and adhesion of EP, so the infiltration force of BF-YS is about 60% in the contact angle test of BF-GS. FTIR shows that MeTHPA can react with BF hydroxyl groups to generate new ester bonds, making the chemical bond between BF and EP-MeTHPA system to improve the interface stability, while the exposure of the non-crystalline area of BF-YS makes its polarity stronger (106.5 mN/m), the relative area variation of the characteristic peaks is greater than BF-GS, easier to form, and the stability will also improve.
In order to study the effect of bamboo gradient structure on the properties of bamboo bundle fiber composites, bamboo bundle fiber (BF) as the enhanced phase, epoxy resin (EP)-methyl tetrahydrophthalic anhydride (MeTHPA) system is the matrix phase, BF/EP-MeTHPA composite was prepared by thermopress molding. By changing the BF unit: yellow side (BF-YS) and green side bundle fiber (BF-GS), the effect of natural structure on the failure of interface of BF/EP composite was studied. Based on the mechanical properties of composites, through nano and micro test means such as dynamic thermomechanical analysis (DMA), in situ SEM and FTIR, the state of BF/EP-MeTHPA, interface microregion, thermal analysis and macromechanical characterization were studied. The experimental results show that due to the high fiber content and strength in BF-GS, the enhancement effect and distribution uniformity in epoxy system is better than BF-YS. But the permeability and interface performance are lower than bamboo bundle fiber of yellow side/epoxy resin-MeTHPA (BF-YS/EP-MeTHPA). Through the observation of the bamboo structure, it is found that BF-YS remains more parenchyma cells, and the rough surface favors the infiltration and adhesion of EP, so the infiltration force of BF-YS is about 60% in the contact angle test of BF-GS. FTIR shows that MeTHPA can react with BF hydroxyl groups to generate new ester bonds, making the chemical bond between BF and EP-MeTHPA system to improve the interface stability, while the exposure of the non-crystalline area of BF-YS makes its polarity stronger (106.5 mN/m), the relative area variation of the characteristic peaks is greater than BF-GS, easier to form, and the stability will also improve.
2022, 39(8): 4074-4084.
doi: 10.13801/j.cnki.fhclxb.20210916.007
Abstract:
In order to improve the microhardness and corrosion resistance of Ni-W-ZrO2 composite coating, Ni-W-ZrO2-graphene nanosheets (GNPs) composite coating was prepared on 7075 aluminum alloy by electrodeposition method, and GNPs was used to improve the surface performance of Ni-W-ZrO2 composite coating. Orthogonal experiment was used to optimize the experimental process conditions: the current density was 10 A/dm2, the stirring speed was 250 r/min, and the temperature was 60℃. Under the optimal process conditions, ZrO2 nanoparticles maintain 10 g/L, change the content of GNPs (1, 2, 3, 4 g/L), and seek the best GNPs addition amount of Ni-W-10 g/L ZrO2-GNPs composite coating. The microhardness and abrasion resistance were studied by the microhardness tester and the rotating friction tester, and the microscopic characterization was carried out by SEM, EDS, XRD and AFM. The corrosion resistance of Ni-W-ZrO2-GNPs composite coating in 3.5wt%NaCl solution was studied by electrochemical method. The results show that GNPs and ZrO2 nanoparticles are uniformly co-deposited in the nickel-tungsten coating, and the incorporation of GNPs has a significant effect on the microscopic morphology, grain size, microhardness, friction performance and corrosion resistance of the Ni-W-ZrO2 composite coating. When the amount of GNPs added is 3 g/L, the grain size of the Ni (W) matrix is the smallest, the microhardness (HV 942) is the highest, and the average friction coefficient (0.1981) is the smallest. When the amount of GNPs is 2 g/L, the corrosion resistance of Ni-W-ZrO2-GNPs composite coating (Charge transfer resistance Rct: 9532 Ω·cm2) is significantly improved compared to Ni-W-ZrO2 composite coating (Rct: 1766 Ω·cm2).
In order to improve the microhardness and corrosion resistance of Ni-W-ZrO2 composite coating, Ni-W-ZrO2-graphene nanosheets (GNPs) composite coating was prepared on 7075 aluminum alloy by electrodeposition method, and GNPs was used to improve the surface performance of Ni-W-ZrO2 composite coating. Orthogonal experiment was used to optimize the experimental process conditions: the current density was 10 A/dm2, the stirring speed was 250 r/min, and the temperature was 60℃. Under the optimal process conditions, ZrO2 nanoparticles maintain 10 g/L, change the content of GNPs (1, 2, 3, 4 g/L), and seek the best GNPs addition amount of Ni-W-10 g/L ZrO2-GNPs composite coating. The microhardness and abrasion resistance were studied by the microhardness tester and the rotating friction tester, and the microscopic characterization was carried out by SEM, EDS, XRD and AFM. The corrosion resistance of Ni-W-ZrO2-GNPs composite coating in 3.5wt%NaCl solution was studied by electrochemical method. The results show that GNPs and ZrO2 nanoparticles are uniformly co-deposited in the nickel-tungsten coating, and the incorporation of GNPs has a significant effect on the microscopic morphology, grain size, microhardness, friction performance and corrosion resistance of the Ni-W-ZrO2 composite coating. When the amount of GNPs added is 3 g/L, the grain size of the Ni (W) matrix is the smallest, the microhardness (HV 942) is the highest, and the average friction coefficient (0.1981) is the smallest. When the amount of GNPs is 2 g/L, the corrosion resistance of Ni-W-ZrO2-GNPs composite coating (Charge transfer resistance Rct: 9532 Ω·cm2) is significantly improved compared to Ni-W-ZrO2 composite coating (Rct: 1766 Ω·cm2).
2022, 39(8): 4085-4092.
doi: 10.13801/j.cnki.fhclxb.20211012.003
Abstract:
The physical properties of metamaterials with negative parameters and the negative permittivity behavior of the intrinsic properties of materials deserves further investigation, the systematic study of the influence of chemical composition on their permittivity behavior, and the investigation of the realization and regulation mecha-nism of negative permittivity behavior. The carbon fiber/alumina (CF/Al2O3) ceramic composites were prepared by hot-press sintering, and the effects of different CF content on the micromorphology and electrical properties of composites were studied. By adjusting the CF content in the composites, the negative dielectric behavior was rea-lized in the frequency range of 1 kHz-10 MHz, and the conductive mechanism changed from hopping conduction to metal-like conductivity. It is found that the increased CF forms three-dimensional interconnection network in the composites, and the negative permittivity is caused by the plasma oscillation of the internal free electrons in the CF network. With the increase of CF content, the absolute value of negative permittivity becomes larger, and the dispersion characteristics of permittivity conforms to the Drude model.
The physical properties of metamaterials with negative parameters and the negative permittivity behavior of the intrinsic properties of materials deserves further investigation, the systematic study of the influence of chemical composition on their permittivity behavior, and the investigation of the realization and regulation mecha-nism of negative permittivity behavior. The carbon fiber/alumina (CF/Al2O3) ceramic composites were prepared by hot-press sintering, and the effects of different CF content on the micromorphology and electrical properties of composites were studied. By adjusting the CF content in the composites, the negative dielectric behavior was rea-lized in the frequency range of 1 kHz-10 MHz, and the conductive mechanism changed from hopping conduction to metal-like conductivity. It is found that the increased CF forms three-dimensional interconnection network in the composites, and the negative permittivity is caused by the plasma oscillation of the internal free electrons in the CF network. With the increase of CF content, the absolute value of negative permittivity becomes larger, and the dispersion characteristics of permittivity conforms to the Drude model.
2022, 39(8): 4093-4101.
doi: 10.13801/j.cnki.fhclxb.20211018.003
Abstract:
To improve the quality of electrodeposited Ni-nano TiC composite coating, the Ni-nano TiC composite coating was prepared on the Q235 steel by electrodeposition. The effects of three different electrodeposition methods of direct current (DC), single pulse and double pulse on the microstructure and surface properties of the composite coating were compared and analyzed. The surface morphology and element distribution of the coatings were analyzed by SEM/EDS. The phase and grain size of the coatings were studied by XRD, and the hardness and corrosion behavior were tested by microhardness tester and electrochemical workstation respectively. The results show that the compactness and microhardness of the composite coating increase in turn, and the porosity, plating rate and grain size decrease in turn according to DC, single pulse and double pulse electrodeposition methods. The content of TiC in pulse deposition composite coating is obviously less than that in DC deposition coating. The microhardness of double pulse electrodeposition composite coating is HV 740.5, which is 67% higher than that of DC electrodeposition coating. Compared with DC and single pulse electrodeposited coatings, the self-corrosion current density of double pulse electrodeposited composite coatings in 3.5wt%NaCl solution decreases by an order of magnitude (5.275×10−6 A·cm−2), the self-corrosion potential shifts positively (−0.113 V), and the charge transfer resistance is the largest, showing the best corrosion resistance.
To improve the quality of electrodeposited Ni-nano TiC composite coating, the Ni-nano TiC composite coating was prepared on the Q235 steel by electrodeposition. The effects of three different electrodeposition methods of direct current (DC), single pulse and double pulse on the microstructure and surface properties of the composite coating were compared and analyzed. The surface morphology and element distribution of the coatings were analyzed by SEM/EDS. The phase and grain size of the coatings were studied by XRD, and the hardness and corrosion behavior were tested by microhardness tester and electrochemical workstation respectively. The results show that the compactness and microhardness of the composite coating increase in turn, and the porosity, plating rate and grain size decrease in turn according to DC, single pulse and double pulse electrodeposition methods. The content of TiC in pulse deposition composite coating is obviously less than that in DC deposition coating. The microhardness of double pulse electrodeposition composite coating is HV 740.5, which is 67% higher than that of DC electrodeposition coating. Compared with DC and single pulse electrodeposited coatings, the self-corrosion current density of double pulse electrodeposited composite coatings in 3.5wt%NaCl solution decreases by an order of magnitude (5.275×10−6 A·cm−2), the self-corrosion potential shifts positively (−0.113 V), and the charge transfer resistance is the largest, showing the best corrosion resistance.
2022, 39(8): 4102-4116.
doi: 10.13801/j.cnki.fhclxb.20210913.003
Abstract:
In aircraft assembly, it is widely used to install temporary fasteners to fix the relative position between components, which is called pre-joining. This pre-joining operation can also eliminate the gap between the contact surfaces and enhance the stability of the structure. Aiming at aircraft composite panel assembly, in order to improve the pre-joining efficiency and assembly quality, an optimization method of the number and layout of temporary fasteners considering composite material damage was proposed. Combining the finite element method and genetic algorithm, this optimization method aimed at improving the elimination rate of gap between panels and frames, and reducing the number of temporary fasteners installed. In this optimization method, the number, layout and load of temporary fasteners were taken as control variables, and the damage state of the composite panel predicted by 3D Hashin criterion was taken as constraint conditions. An experimental model of pre-joining of compo-site panel was taken as an example to demonstrate that this optimization technology can avoid the damage of composite panels, and achieve a higher gap elimination rate with less temporary fasteners.
In aircraft assembly, it is widely used to install temporary fasteners to fix the relative position between components, which is called pre-joining. This pre-joining operation can also eliminate the gap between the contact surfaces and enhance the stability of the structure. Aiming at aircraft composite panel assembly, in order to improve the pre-joining efficiency and assembly quality, an optimization method of the number and layout of temporary fasteners considering composite material damage was proposed. Combining the finite element method and genetic algorithm, this optimization method aimed at improving the elimination rate of gap between panels and frames, and reducing the number of temporary fasteners installed. In this optimization method, the number, layout and load of temporary fasteners were taken as control variables, and the damage state of the composite panel predicted by 3D Hashin criterion was taken as constraint conditions. An experimental model of pre-joining of compo-site panel was taken as an example to demonstrate that this optimization technology can avoid the damage of composite panels, and achieve a higher gap elimination rate with less temporary fasteners.
2022, 39(8): 4117-4128.
doi: 10.13801/j.cnki.fhclxb.20211019.001
Abstract:
Composite materials with negative Poisson's ratio have received extensive attention in recent years due to their excellent mechanical properties. The trapezoidal and sinusoidal two-dimensional double arrow carbon fiber composite sandwich structures were fabricated by molding and autoclave process. The vibration frequency response curves of the structures were obtained by frequency sweep test with shaking table. The three-dimensional finite element model of the structure was established and compared with the experimental results to verify the accuracy of the simulation model. Based on this, the effects of cell thickness, angle, topological configuration and thickness gradient on the vibration characteristics and damping performance of the structure were systematically studied. The results show that with the increase of the thickness and angle of the core cell, the natural frequency of the structure increases, the peak value of the acceleration response decreases, and the damping performance of the structure improves. Compared with the sinusoidal structure, the trapezoidal structure usually has higher natural frequency and better damping performance. Compared with other uniform and gradient structures, the weakening structure has better damping performance.
Composite materials with negative Poisson's ratio have received extensive attention in recent years due to their excellent mechanical properties. The trapezoidal and sinusoidal two-dimensional double arrow carbon fiber composite sandwich structures were fabricated by molding and autoclave process. The vibration frequency response curves of the structures were obtained by frequency sweep test with shaking table. The three-dimensional finite element model of the structure was established and compared with the experimental results to verify the accuracy of the simulation model. Based on this, the effects of cell thickness, angle, topological configuration and thickness gradient on the vibration characteristics and damping performance of the structure were systematically studied. The results show that with the increase of the thickness and angle of the core cell, the natural frequency of the structure increases, the peak value of the acceleration response decreases, and the damping performance of the structure improves. Compared with the sinusoidal structure, the trapezoidal structure usually has higher natural frequency and better damping performance. Compared with other uniform and gradient structures, the weakening structure has better damping performance.
2022, 39(8): 4129-4138.
doi: 10.13801/j.cnki.fhclxb.20211102.001
Abstract:
The 3D meso-structures of the fiber preforms was reconstructed based on the micro-computed tomography (micro-CT) technology, two quantitative indexes were proposed to characterize the deformation of the fiber preforms' geometric structure. The influence mechanism of weft densities and thicknesses on the meso-structure of the 3D woven preform was studied. The results show that the micro-CT technology can be used to characterize the cross-section and spatial path of the yarns inside the 3D woven preform effectively. The preform samples with the weft density of 2.0 picks/cm show obvious deformation, and thus are not suitable for practical engineering application. With the increase of the weft density, the internal structure of the fiber preform tends to be stable. The internal structures of the 10 mm samples are more stable than that of the 5 mm samples, however, the cross section and path of the surface yarns still show large deformation.
The 3D meso-structures of the fiber preforms was reconstructed based on the micro-computed tomography (micro-CT) technology, two quantitative indexes were proposed to characterize the deformation of the fiber preforms' geometric structure. The influence mechanism of weft densities and thicknesses on the meso-structure of the 3D woven preform was studied. The results show that the micro-CT technology can be used to characterize the cross-section and spatial path of the yarns inside the 3D woven preform effectively. The preform samples with the weft density of 2.0 picks/cm show obvious deformation, and thus are not suitable for practical engineering application. With the increase of the weft density, the internal structure of the fiber preform tends to be stable. The internal structures of the 10 mm samples are more stable than that of the 5 mm samples, however, the cross section and path of the surface yarns still show large deformation.
2022, 39(8): 4139-4151.
doi: 10.13801/j.cnki.fhclxb.20210909.011
Abstract:
Nanosecond laser processing is widely used in the processing of fiber-reinforced composites, but it is easy to produce uncontrollable thermal damage in the laser processing of Kevlar fiber reinforced plastics (KFRP), owing to its poor high temperature resistance. During the nanosecond laser cutting of KFRP, the temperature evolution process was analyzed. According to the ablation threshold theory of laser processing, the ablation threshold and the ablation mechanism were analyzed. Based on the conservation law of energy in heat conduction, the conservation of mass and the conservation of momentum, the damage prediction models of the Kevlar fiber and the resin matrix in the heat-affected zone were established, respectively. The results show that there are significant differences in the heat-affected zone of KFRP laser machining, and the different damage zones can be distinguished by the change law of cutting temperature. The ablation threshold of the Kevlar fiber and that of the epoxy resin matrix are 0.01 J·cm−2 and 0.005 J·cm−2, respectively. The theoretical model of the kerf width, the kerf depth and the carbonization zone width is consistent with the experimental result. The heat-affected zone is significantly affected by the laser processing process parameters. Among them, the kerf width is most significantly affected by the laser power, the kerf depth and the width of the carbonization zone are most significantly affected by the scanning speed. But, the heat-affected zone is little affected by the pulse width and the repetition frequency.
Nanosecond laser processing is widely used in the processing of fiber-reinforced composites, but it is easy to produce uncontrollable thermal damage in the laser processing of Kevlar fiber reinforced plastics (KFRP), owing to its poor high temperature resistance. During the nanosecond laser cutting of KFRP, the temperature evolution process was analyzed. According to the ablation threshold theory of laser processing, the ablation threshold and the ablation mechanism were analyzed. Based on the conservation law of energy in heat conduction, the conservation of mass and the conservation of momentum, the damage prediction models of the Kevlar fiber and the resin matrix in the heat-affected zone were established, respectively. The results show that there are significant differences in the heat-affected zone of KFRP laser machining, and the different damage zones can be distinguished by the change law of cutting temperature. The ablation threshold of the Kevlar fiber and that of the epoxy resin matrix are 0.01 J·cm−2 and 0.005 J·cm−2, respectively. The theoretical model of the kerf width, the kerf depth and the carbonization zone width is consistent with the experimental result. The heat-affected zone is significantly affected by the laser processing process parameters. Among them, the kerf width is most significantly affected by the laser power, the kerf depth and the width of the carbonization zone are most significantly affected by the scanning speed. But, the heat-affected zone is little affected by the pulse width and the repetition frequency.
2022, 39(8): 4152-4163.
doi: 10.13801/j.cnki.fhclxb.20210915.002
Abstract:
The symmetry of the fiber layering and the anisotropy of the guided wave propagation of carbon fiber reinforced plastic (CFRP) plate were considered. A rapid and accurate method for locating CFRP impact damage in the isochronous circumferential trajectory method was proposed. By means of damage index and simulation calculation, the propagation velocity of guided wave around CFRP plate and the flight time of damage reflected wave were determined. According to the trigonometric function relationship between the transducer, the sensor and the damage location, the likelihood point which satisfies both the propagation velocity of guided wave in each direction and the flight time in CFRP plate was calculated. The linear fitting likelihood points formed isochronous circumferential trajectory curve spline. According to the laminated symmetry of CFRP plate, the mirrored trajectory curve spline formed a closed isochronous circumferential trajectory curve, and the damage location was realized by the intersection point of three curves. The impact damage detection experiment of CFRP plate was carried out by using a four-point rectangular array diagonally excitation method. The experimental results show that the damage index value increases significantly due to damage, and the flight time of damage reflected wave can be obtained. The number of likelihood points needed to fit the trajectory is only 155, which has a small amount of calculation. The localization error of the isochronous circumferential trajectory method is controllable, and the localization accuracy is good under the expected error, and is not beyond the damaged area.
The symmetry of the fiber layering and the anisotropy of the guided wave propagation of carbon fiber reinforced plastic (CFRP) plate were considered. A rapid and accurate method for locating CFRP impact damage in the isochronous circumferential trajectory method was proposed. By means of damage index and simulation calculation, the propagation velocity of guided wave around CFRP plate and the flight time of damage reflected wave were determined. According to the trigonometric function relationship between the transducer, the sensor and the damage location, the likelihood point which satisfies both the propagation velocity of guided wave in each direction and the flight time in CFRP plate was calculated. The linear fitting likelihood points formed isochronous circumferential trajectory curve spline. According to the laminated symmetry of CFRP plate, the mirrored trajectory curve spline formed a closed isochronous circumferential trajectory curve, and the damage location was realized by the intersection point of three curves. The impact damage detection experiment of CFRP plate was carried out by using a four-point rectangular array diagonally excitation method. The experimental results show that the damage index value increases significantly due to damage, and the flight time of damage reflected wave can be obtained. The number of likelihood points needed to fit the trajectory is only 155, which has a small amount of calculation. The localization error of the isochronous circumferential trajectory method is controllable, and the localization accuracy is good under the expected error, and is not beyond the damaged area.
2022, 39(8): 4164-4171.
doi: 10.13801/j.cnki.fhclxb.20210831.001
Abstract:
The surface and internal damage of carbon fiber reinforced polymer (CFRP) laminates under 20 J and 40 J impact loads were identified by infrared thermography. Aiming at the inaccuracy of quantitative defect extraction, a multi-scale eight-direction edge detection image segmentation algorithm was proposed by analyzing the spatial characteristics of infrared images. Firstly, the optimal image was selected according to the maximum standard deviation of the sensitive area, and the fuzzy C-means clustering algorithm was used to presegment the defect image to obtain prior information. Then a circular convolution template was constructed to perform a multi-scale eight-direction convolution operation on the infrared image. The OTSU algorithm was introduced to segment the gradient image, combined with morphological operations to obtain the defect edge map, and the connected domain of the target area was analyzed to realize the quantitative extraction of defect features. The results show that the proposed algorithm improves the detection ability of weak edges in the damaged area and ensures the integrity and connectivity of defect edges. Compared with the traditional image segmentation algorithm, the detection accuracy of the defect area, long diameter and short diameter obtained by the proposed algorithm are improved by more than 20.41%, 5.61% and 9.77%, respectively.
The surface and internal damage of carbon fiber reinforced polymer (CFRP) laminates under 20 J and 40 J impact loads were identified by infrared thermography. Aiming at the inaccuracy of quantitative defect extraction, a multi-scale eight-direction edge detection image segmentation algorithm was proposed by analyzing the spatial characteristics of infrared images. Firstly, the optimal image was selected according to the maximum standard deviation of the sensitive area, and the fuzzy C-means clustering algorithm was used to presegment the defect image to obtain prior information. Then a circular convolution template was constructed to perform a multi-scale eight-direction convolution operation on the infrared image. The OTSU algorithm was introduced to segment the gradient image, combined with morphological operations to obtain the defect edge map, and the connected domain of the target area was analyzed to realize the quantitative extraction of defect features. The results show that the proposed algorithm improves the detection ability of weak edges in the damaged area and ensures the integrity and connectivity of defect edges. Compared with the traditional image segmentation algorithm, the detection accuracy of the defect area, long diameter and short diameter obtained by the proposed algorithm are improved by more than 20.41%, 5.61% and 9.77%, respectively.
2022, 39(8): 4172-4178.
doi: 10.13801/j.cnki.fhclxb.20210915.003
Abstract:
For the analysis of free-edge effect of laminates, the out-plane stresses obtained by displacement solid finite element usually cannot guarantee the requirement of continuity between layers, and the out-plane stress values on the surface are not exactly same with the actual values, so the accuracy of numerical results of displacement finite element method is low. Based on the noncompatible generalized mixed variational principle, noncompatible generalized partial mixed element had been proposed, and had been used for the analysis of the free-edge effect of different ply laminates. By using the characteristics of the noncompatible generalized partial mixed element, which could introduce the boundary conditions of displacement and stress at the same time, solve the displacement and out of plane stress at the same time, the more accurate out-plane stress results at the free-edge are obtained with less computational cost. The numerical example shows that with sparser mesh, the noncompatible generalized partial mixed element predicts the high stress gradient of out-plane stresses near the free-edge accurately. At the same time, the accuracy of singularity is better than the literature results.
For the analysis of free-edge effect of laminates, the out-plane stresses obtained by displacement solid finite element usually cannot guarantee the requirement of continuity between layers, and the out-plane stress values on the surface are not exactly same with the actual values, so the accuracy of numerical results of displacement finite element method is low. Based on the noncompatible generalized mixed variational principle, noncompatible generalized partial mixed element had been proposed, and had been used for the analysis of the free-edge effect of different ply laminates. By using the characteristics of the noncompatible generalized partial mixed element, which could introduce the boundary conditions of displacement and stress at the same time, solve the displacement and out of plane stress at the same time, the more accurate out-plane stress results at the free-edge are obtained with less computational cost. The numerical example shows that with sparser mesh, the noncompatible generalized partial mixed element predicts the high stress gradient of out-plane stresses near the free-edge accurately. At the same time, the accuracy of singularity is better than the literature results.
