2021 Vol. 38, No. 3
2021, 38(3): 641-667.
doi: 10.13801/j.cnki.fhclxb.20201208.002
Abstract:
Nacre is a biological composite which is made of natural aragonite platelets and organic matrix. These platelets are embedded in the continuous matrix in a parallel and staggered pattern, forming a highly ordered hierarchical structure. The mechanical properties of nacre are far superior to those of the components. Therefore, it has received wide attention of researchers in the fields of mechanics, materials science and biology. First of all, this paper introduced the microstructure, the basic deformation mechanism and mechanical properties of nacre. The research progress of biomimetic nacre-like composites was then reviewed from three perspectives including the theoretical analysis, numerical simulation and experimental preparation. The emphasis was focused on the underlying strengthening and toughening mechanism during the deformation process, and the relationship between its structure and properties was also analyzed. Finally, the latest development direction of nacreous composites is proposed.
Nacre is a biological composite which is made of natural aragonite platelets and organic matrix. These platelets are embedded in the continuous matrix in a parallel and staggered pattern, forming a highly ordered hierarchical structure. The mechanical properties of nacre are far superior to those of the components. Therefore, it has received wide attention of researchers in the fields of mechanics, materials science and biology. First of all, this paper introduced the microstructure, the basic deformation mechanism and mechanical properties of nacre. The research progress of biomimetic nacre-like composites was then reviewed from three perspectives including the theoretical analysis, numerical simulation and experimental preparation. The emphasis was focused on the underlying strengthening and toughening mechanism during the deformation process, and the relationship between its structure and properties was also analyzed. Finally, the latest development direction of nacreous composites is proposed.
2021, 38(3): 668-679.
doi: 10.13801/j.cnki.fhclxb.20201022.001
Abstract:
Ultra-high temperature oxide ceramics present high strength, hardness, and outstanding oxidation and corrosion resistance at elevated temperatures, which are ideal high temperature structural materials for long period service under the high temperature oxidizing environment. Laser additive manufacturing (LAM) technology has become the most promising near-net-shaping technology for fabricating large and complex parts due to its unique advantages of high efficiency, rapid flexible manufacturing, and free-form net shaping without molds. In this paper, the technology principles, the process characteristics, and the research progresses have been overviewed for three representative LAM technologies: the selective laser sintering, the selective laser melting, and the laser engineered net shaping for the manufacturing of the ultra-high temperature oxide ceramics. The defect control methods during the LAM processes for oxide ceramics have also been investigated in detail. Finally, the development trends and the breakthrough points have been prospected for the LAM ultra-high temperature oxide ceramics.
Ultra-high temperature oxide ceramics present high strength, hardness, and outstanding oxidation and corrosion resistance at elevated temperatures, which are ideal high temperature structural materials for long period service under the high temperature oxidizing environment. Laser additive manufacturing (LAM) technology has become the most promising near-net-shaping technology for fabricating large and complex parts due to its unique advantages of high efficiency, rapid flexible manufacturing, and free-form net shaping without molds. In this paper, the technology principles, the process characteristics, and the research progresses have been overviewed for three representative LAM technologies: the selective laser sintering, the selective laser melting, and the laser engineered net shaping for the manufacturing of the ultra-high temperature oxide ceramics. The defect control methods during the LAM processes for oxide ceramics have also been investigated in detail. Finally, the development trends and the breakthrough points have been prospected for the LAM ultra-high temperature oxide ceramics.
2021, 38(3): 680-697.
doi: 10.13801/j.cnki.fhclxb.20201126.002
Abstract:
Solid-state electrochemical devices are considered as one of the most promising candidates for next generation chemical energy devices because of their flexibility, safety and high energy density. Solid electrolyte is a key material to achieve the goal. Graphene based polymer composite electrolyte derived from the traditional polymer electrolyte represents a new-type solid electrolyte consisting of both graphene nano-fillers and polymer matrix. In recent years, the inorganic/organic hybrid electrolytes have proved to possess high ionic conductivity, good processing ability and excellent interfacial properties, so that they received extensive attentions for working as electrolyte materials in solid-state electrochemical devices. In this review, the up-to-date research progresses in the field of graphene based polymer composite electrolytes are systematically discussed with particular emphasis on the structural design, performance mechanism and application in various electrochemical energy storage devices.
Solid-state electrochemical devices are considered as one of the most promising candidates for next generation chemical energy devices because of their flexibility, safety and high energy density. Solid electrolyte is a key material to achieve the goal. Graphene based polymer composite electrolyte derived from the traditional polymer electrolyte represents a new-type solid electrolyte consisting of both graphene nano-fillers and polymer matrix. In recent years, the inorganic/organic hybrid electrolytes have proved to possess high ionic conductivity, good processing ability and excellent interfacial properties, so that they received extensive attentions for working as electrolyte materials in solid-state electrochemical devices. In this review, the up-to-date research progresses in the field of graphene based polymer composite electrolytes are systematically discussed with particular emphasis on the structural design, performance mechanism and application in various electrochemical energy storage devices.
2021, 38(3): 698-711.
doi: 10.13801/j.cnki.fhclxb.20201224.002
Abstract:
Shape memory polymer (SMP) is a kind of smart materials that can maintain a temporary shape and recover its initial configuration under external stimuli. Its advantages of high shape fixation rate, high shape recovery rate, adjustable transition temperature, high deformation ability and light weight makes it suitable to design and fabricate deformable structures. However, its application is restricted by limited response modes and poor bearing capacity. These problems can be effectively solved by adding functional particles or enhanced fibers to the polymer matrix to obtain shape memory polymer composites (SMPC). This article first introduces the shape memory mechanism of SMP and gives its actuation methods. Then, fiber microbuckling behavior of unidirectional fiber reinforced SMPC is discussed. Finally, applications of deformable structures in aerospace are presented.
Shape memory polymer (SMP) is a kind of smart materials that can maintain a temporary shape and recover its initial configuration under external stimuli. Its advantages of high shape fixation rate, high shape recovery rate, adjustable transition temperature, high deformation ability and light weight makes it suitable to design and fabricate deformable structures. However, its application is restricted by limited response modes and poor bearing capacity. These problems can be effectively solved by adding functional particles or enhanced fibers to the polymer matrix to obtain shape memory polymer composites (SMPC). This article first introduces the shape memory mechanism of SMP and gives its actuation methods. Then, fiber microbuckling behavior of unidirectional fiber reinforced SMPC is discussed. Finally, applications of deformable structures in aerospace are presented.
2021, 38(3): 712-721.
doi: 10.13801/j.cnki.fhclxb.20201106.003
Abstract:
In recent years, photocatalytic technology has been widely used in sewage treatment, CO2 reduction, hydrogen production and other fields. Among photocatalytic materials, TiO2 is widely used due to its advantages of high chemical stability, wide sources and low price. However, wide band gap and high electron and hole compound efficiency greatly limit the photocatalytic performance of TiO2. Quantum dots (QDs), a kind of nano-scale particles affected by quantum constraint effect, show the advantages of easy carrier regulation and abundant surface sites. Therefore, different methods have been used by researchers to compound TiO2 with QDs for the enhancement of photocatalytic performance of TiO2, and then a series of QDs/TiO2 composite photocatalytic materials with excellent photocatalytic performance are obtained. This review mainly introduces the research progress of QDs/TiO2 composite photocatalytic materials. Firstly, the preparation methods of QDs/TiO2 composite photocatalytic materials were described, and the enhancement mechanism of TiO2 photocatalytic performance by QDs was analyzed. Then, The application of QDs/TiO2 composite photocatalytic materials in the degradation of organic pollutants, hydrogen production and CO2 reduction were summarized. Finally, the major issues in the current research of QDs/TiO2 composite photocatalytic materials and the future research prospects were discussed.
In recent years, photocatalytic technology has been widely used in sewage treatment, CO2 reduction, hydrogen production and other fields. Among photocatalytic materials, TiO2 is widely used due to its advantages of high chemical stability, wide sources and low price. However, wide band gap and high electron and hole compound efficiency greatly limit the photocatalytic performance of TiO2. Quantum dots (QDs), a kind of nano-scale particles affected by quantum constraint effect, show the advantages of easy carrier regulation and abundant surface sites. Therefore, different methods have been used by researchers to compound TiO2 with QDs for the enhancement of photocatalytic performance of TiO2, and then a series of QDs/TiO2 composite photocatalytic materials with excellent photocatalytic performance are obtained. This review mainly introduces the research progress of QDs/TiO2 composite photocatalytic materials. Firstly, the preparation methods of QDs/TiO2 composite photocatalytic materials were described, and the enhancement mechanism of TiO2 photocatalytic performance by QDs was analyzed. Then, The application of QDs/TiO2 composite photocatalytic materials in the degradation of organic pollutants, hydrogen production and CO2 reduction were summarized. Finally, the major issues in the current research of QDs/TiO2 composite photocatalytic materials and the future research prospects were discussed.
2021, 38(3): 722-731.
doi: 10.13801/j.cnki.fhclxb.20200806.003
Abstract:
To improve the thermal conductivity of epoxy (EP) with a lower thermally conductive filler content, graphene nanoplates/(polyetherketone cardo-EP) (GNP/(PEK-C-EP)) composites were prepared by the solution method. The selective distribution of GNP was predicted by calculation based on contact angle measurements, and the effects of GNP and PEK-C contents on the microstructures and thermal conductivities of GNP/(PEK-C-EP) composites were investigated by SEM and laser flash method. The results show that double percolation structures are formed in GNP/(PEK-C-EP) composites as the content of PEK-C reaches 20wt%, where GNPs are selectively distributed in PEK-C to build continuous heat conduction paths. For GNP/EP composites, it reaches the highest thermal conductivity of 0.375 W(m·K)−1 at 1wt% GNP. While for GNP/(PEK-C-EP) composites, the content of 0.5wt% GNP reaches highest thermal conductivity of 0.371 W(m·K)−1, which is 48% higher than that of GNP/EP composites at 0.5wt% GNP content and basically the same as that of GNP/EP composites at 1wt% GNP. It indicates that the filler content of GNP/(PEK-C-EP) composites is reduced by 50% owing to the double percolation effect. In addition, the glass transition temperatures, thermal stability and coefficients of thermal expansion of pure EP and GNP/(PEK-C-EP) composites were compared. The results show that the GNP/(PEK-C-EP) composites are superior to pure EP in thermal properties.
To improve the thermal conductivity of epoxy (EP) with a lower thermally conductive filler content, graphene nanoplates/(polyetherketone cardo-EP) (GNP/(PEK-C-EP)) composites were prepared by the solution method. The selective distribution of GNP was predicted by calculation based on contact angle measurements, and the effects of GNP and PEK-C contents on the microstructures and thermal conductivities of GNP/(PEK-C-EP) composites were investigated by SEM and laser flash method. The results show that double percolation structures are formed in GNP/(PEK-C-EP) composites as the content of PEK-C reaches 20wt%, where GNPs are selectively distributed in PEK-C to build continuous heat conduction paths. For GNP/EP composites, it reaches the highest thermal conductivity of 0.375 W(m·K)−1 at 1wt% GNP. While for GNP/(PEK-C-EP) composites, the content of 0.5wt% GNP reaches highest thermal conductivity of 0.371 W(m·K)−1, which is 48% higher than that of GNP/EP composites at 0.5wt% GNP content and basically the same as that of GNP/EP composites at 1wt% GNP. It indicates that the filler content of GNP/(PEK-C-EP) composites is reduced by 50% owing to the double percolation effect. In addition, the glass transition temperatures, thermal stability and coefficients of thermal expansion of pure EP and GNP/(PEK-C-EP) composites were compared. The results show that the GNP/(PEK-C-EP) composites are superior to pure EP in thermal properties.
2021, 38(3): 732-740.
doi: 10.13801/j.cnki.fhclxb.20201030.004
Abstract:
Phthalonitrile resin is a new type of high performance thermosetting resin with excellent mechanical properties and high temperature resistance. In this paper, thermal plastic polyimide (PI) particles were used to improve the mechanical properties of the composites. It shows that the glass transition temperature of the composite decreases with the addition of PI. The introduction of PI can significantly improve the toughness of the composite. The interlaminar shear strength of the composite modified by 10wt% PI is increased by 41.2%, and the mode I interlaminar fracture toughness of the composite modified by 15wt% PI is increased by 156.3%. The presence of particles can be clearly observed between layers of composites. When the mass fraction of PI is further increased, particles will agglomerate, leading to the decrease of interlaminar shear strength of composite materials. In addition, the shear strength of PI toughened phthalic resin composite at 380℃ is similar to that of the unmodified composite, and the PI particle content at this temperature is no longer the main factor affecting the toughness of composites.
Phthalonitrile resin is a new type of high performance thermosetting resin with excellent mechanical properties and high temperature resistance. In this paper, thermal plastic polyimide (PI) particles were used to improve the mechanical properties of the composites. It shows that the glass transition temperature of the composite decreases with the addition of PI. The introduction of PI can significantly improve the toughness of the composite. The interlaminar shear strength of the composite modified by 10wt% PI is increased by 41.2%, and the mode I interlaminar fracture toughness of the composite modified by 15wt% PI is increased by 156.3%. The presence of particles can be clearly observed between layers of composites. When the mass fraction of PI is further increased, particles will agglomerate, leading to the decrease of interlaminar shear strength of composite materials. In addition, the shear strength of PI toughened phthalic resin composite at 380℃ is similar to that of the unmodified composite, and the PI particle content at this temperature is no longer the main factor affecting the toughness of composites.
2021, 38(3): 741-748.
doi: 10.13801/j.cnki.fhclxb.20200814.001
Abstract:
The polyacrylonitrile/polyvinylidene fluoride (PAN/PVDF) nanocomposite fiber membranes were prepared by the coaxial electrospinning technology using PVDF as the core layer and PAN as the skin layer. Structure optimization of PAN/PVDF nanocomposite fiber membrane was carried out by adding three different nanoparticles of nano-silica powder, fumed silica and silica sol to the PAN/PVDF nanocomposite fiber membrane and changing the extrusion speed of the skin-core layer solution. Meanwhile, its pore structure parameters, surface morphology, hydrophilicity and mechanical properties were studied by BET, SEM, water contact angle, fiber strength meter and so on. The results show that the conductivity of the solution after adding silica sol to the solution reaches 32.90 μL/cm, the PAN/PVDF nanocomposite fiber membrane has the best mechanical properties, and the longitudinal breaking strength reaches 13.02 MPa. The quality factor of mask cloth containing silica sol reaches 0.0236, which is much larger than the quality factor of pure polypropylene (PP) non-woven, which is 0.0127, and the filterability is significantly increased.
The polyacrylonitrile/polyvinylidene fluoride (PAN/PVDF) nanocomposite fiber membranes were prepared by the coaxial electrospinning technology using PVDF as the core layer and PAN as the skin layer. Structure optimization of PAN/PVDF nanocomposite fiber membrane was carried out by adding three different nanoparticles of nano-silica powder, fumed silica and silica sol to the PAN/PVDF nanocomposite fiber membrane and changing the extrusion speed of the skin-core layer solution. Meanwhile, its pore structure parameters, surface morphology, hydrophilicity and mechanical properties were studied by BET, SEM, water contact angle, fiber strength meter and so on. The results show that the conductivity of the solution after adding silica sol to the solution reaches 32.90 μL/cm, the PAN/PVDF nanocomposite fiber membrane has the best mechanical properties, and the longitudinal breaking strength reaches 13.02 MPa. The quality factor of mask cloth containing silica sol reaches 0.0236, which is much larger than the quality factor of pure polypropylene (PP) non-woven, which is 0.0127, and the filterability is significantly increased.
2021, 38(3): 749-760.
doi: 10.13801/j.cnki.fhclxb.20201028.001
Abstract:
The surface modification of nano-lamellar hydroxyapatite (LHAp) was carried out with silane coupling agent (SC) and stearic acid (SA), separately. The unmodified and two modified nano-platelet hydroxyapatite (np-HAp) reinforced polylactic acid (PLA) (np-HAp/PLA, SC-np-HAp/PLA, and SA-np-HAp/PLA) composites were prepared by extrusion process. The microstructure, mechanical properties, thermal stability, crystallinity, and wettability of the three composites were compared. XRD, FTIR, XPS, SEM, TGA, DSC, mechanical property test, and contact angle test were conducted to characterize the physiochemical properties of the composites. The results show that there is phase separation at the interface of np-HAp or SA-np-HAp and PLA, and the interface of SC-np-HAp/PLA composite demonstrates strong interface adhesion. Compared with np-HAp/PLA composite, the compressive yield strength and tensile strength of SC-np-HAp/PLA composite increase by 9.4% and 6.6%, respectively, while SA-np-HAp/PLA composite exhibites reductions. Further, compared with np-HAp/PLA composite, the initial decomposition temperature of SC-np-HAp/PLA and SA-np-HAp/PLA composites increases by 7.4% and 5.6%, respectively, and crystallinity of the former increases by 6.7%, while the latter decreases by 3.5%. Compared with np-HAp/PLA and SA-np-HAp/PLA composites, the SC-np-HAp/PLA composite has a significantly lower water contact angle. These results indicate that the SC-modified np-HAp has better interface compatibility with PLA matrix, which will provide a new criterion for the preparation of high-performance bone implant composites.
The surface modification of nano-lamellar hydroxyapatite (LHAp) was carried out with silane coupling agent (SC) and stearic acid (SA), separately. The unmodified and two modified nano-platelet hydroxyapatite (np-HAp) reinforced polylactic acid (PLA) (np-HAp/PLA, SC-np-HAp/PLA, and SA-np-HAp/PLA) composites were prepared by extrusion process. The microstructure, mechanical properties, thermal stability, crystallinity, and wettability of the three composites were compared. XRD, FTIR, XPS, SEM, TGA, DSC, mechanical property test, and contact angle test were conducted to characterize the physiochemical properties of the composites. The results show that there is phase separation at the interface of np-HAp or SA-np-HAp and PLA, and the interface of SC-np-HAp/PLA composite demonstrates strong interface adhesion. Compared with np-HAp/PLA composite, the compressive yield strength and tensile strength of SC-np-HAp/PLA composite increase by 9.4% and 6.6%, respectively, while SA-np-HAp/PLA composite exhibites reductions. Further, compared with np-HAp/PLA composite, the initial decomposition temperature of SC-np-HAp/PLA and SA-np-HAp/PLA composites increases by 7.4% and 5.6%, respectively, and crystallinity of the former increases by 6.7%, while the latter decreases by 3.5%. Compared with np-HAp/PLA and SA-np-HAp/PLA composites, the SC-np-HAp/PLA composite has a significantly lower water contact angle. These results indicate that the SC-modified np-HAp has better interface compatibility with PLA matrix, which will provide a new criterion for the preparation of high-performance bone implant composites.
2021, 38(3): 761-769.
doi: 10.13801/j.cnki.fhclxb.20200617.002
Abstract:
Functional photochromic wood-plastic composites (PWPC) have great application potential in interior decoration and other fields. However, the lifespan of PWPC is usually short. In this paper, antioxidant 1010 and light stabilizer 770 were introduced into PWPC to improve the mechanical properties and photofatigue-resist of composites. The wood flour/polylactic acid (WF/PLA) based photochromic composites were prepared via melt blending and printed by fusion deposition technology (FDM). The mechanical properties, interfacial compatibility, thermal stability, and photofatigue-resist of WF/PLA composite were then characterized. The results show that when antioxidant 1010 is added alone, compared with WF/PLA composite, the tensile, flexural and impact strength of composite increased by 42.58%, 23.25% and 6.52%, respectively. However, adding light stabilizer 770 alone, the tensile and flexural strength increase while the impact strength decreases. When antioxidant 1010 and light stabilizer 770 are added to WF/PLA composite at mass ratio of 1∶1, the tensile strength of composite increased by 1.8% under the synergistic effect of these two additives, the bending and impact strength decreased by 9.3% and 22.1%, respectively. Compared with other combinational systems, the decrease in mechanical properties is the lowest. In addition, WF/PLA composite with mass ratio antioxidant 1010 to light stabilizer 770 of 1∶1 has better thermal degradation properties and photofatigue-resist than WF/PLA composite. The temperature at mass loss of 5% is 219.84℃. On the 10th day of aging, the surface color difference ΔE of WF/PLA composite increased from 5.3 to 6.7, increase of 26.7%.
Functional photochromic wood-plastic composites (PWPC) have great application potential in interior decoration and other fields. However, the lifespan of PWPC is usually short. In this paper, antioxidant 1010 and light stabilizer 770 were introduced into PWPC to improve the mechanical properties and photofatigue-resist of composites. The wood flour/polylactic acid (WF/PLA) based photochromic composites were prepared via melt blending and printed by fusion deposition technology (FDM). The mechanical properties, interfacial compatibility, thermal stability, and photofatigue-resist of WF/PLA composite were then characterized. The results show that when antioxidant 1010 is added alone, compared with WF/PLA composite, the tensile, flexural and impact strength of composite increased by 42.58%, 23.25% and 6.52%, respectively. However, adding light stabilizer 770 alone, the tensile and flexural strength increase while the impact strength decreases. When antioxidant 1010 and light stabilizer 770 are added to WF/PLA composite at mass ratio of 1∶1, the tensile strength of composite increased by 1.8% under the synergistic effect of these two additives, the bending and impact strength decreased by 9.3% and 22.1%, respectively. Compared with other combinational systems, the decrease in mechanical properties is the lowest. In addition, WF/PLA composite with mass ratio antioxidant 1010 to light stabilizer 770 of 1∶1 has better thermal degradation properties and photofatigue-resist than WF/PLA composite. The temperature at mass loss of 5% is 219.84℃. On the 10th day of aging, the surface color difference ΔE of WF/PLA composite increased from 5.3 to 6.7, increase of 26.7%.
2021, 38(3): 770-779.
doi: 10.13801/j.cnki.fhclxb.20200622.001
Abstract:
The crystallization, conductivity, tensile properties, and response behavior of multiwall carbon nanotubes-polyurethane/polypropylene (MWCNTs-TPU/PP) composites were prepared by solution -melting method and systematically investigated. The introduction of MWCNTs can improve the conductivity and crystallization properties of the MWCNTs-TPU/PP composites, in which the mass fraction of conductive percolation value is about 1.9wt% and the onset crystallization temperature is increased from 117.5℃ to 131.2℃. Through the combination of resistance meter and temperature control device, the construction and destruction process of conductive network under different thermal treatment temperatures were characterized online. With the increase of thermal treatment temperature from 110℃ to 175℃, the conductivity and crystallinity were improved. The introduction of TPU can significantly reduce the reaction time of MWCNTs-TPU/PP composites to temperature from about 10 min to about 3 min, and the temperature response behavior has been significantly improved. The analysis of tensile data shows that the increase of MWCNTs content can improve the tensile strength and elongation at break of the MWCNTs-TPU/PP composites. When the addition amount of MWCNTs is 2.5wt%, the tensile strength of the MWCNTs-TPU/PP composites increases from ~35 MPa to ~47 MPa. The strain-resistance data shows that the introduction of TPU can improve the returnability of the strain and the stability of the conductive network structure in the process of cyclic tension.
The crystallization, conductivity, tensile properties, and response behavior of multiwall carbon nanotubes-polyurethane/polypropylene (MWCNTs-TPU/PP) composites were prepared by solution -melting method and systematically investigated. The introduction of MWCNTs can improve the conductivity and crystallization properties of the MWCNTs-TPU/PP composites, in which the mass fraction of conductive percolation value is about 1.9wt% and the onset crystallization temperature is increased from 117.5℃ to 131.2℃. Through the combination of resistance meter and temperature control device, the construction and destruction process of conductive network under different thermal treatment temperatures were characterized online. With the increase of thermal treatment temperature from 110℃ to 175℃, the conductivity and crystallinity were improved. The introduction of TPU can significantly reduce the reaction time of MWCNTs-TPU/PP composites to temperature from about 10 min to about 3 min, and the temperature response behavior has been significantly improved. The analysis of tensile data shows that the increase of MWCNTs content can improve the tensile strength and elongation at break of the MWCNTs-TPU/PP composites. When the addition amount of MWCNTs is 2.5wt%, the tensile strength of the MWCNTs-TPU/PP composites increases from ~35 MPa to ~47 MPa. The strain-resistance data shows that the introduction of TPU can improve the returnability of the strain and the stability of the conductive network structure in the process of cyclic tension.
2021, 38(3): 780-787.
doi: 10.13801/j.cnki.fhclxb.20200713.004
Abstract:
The conductive anisotropic polymer composites (ACPC) have important applications like field emission devices and electronic sensors. Conventional ACPC are difficult to obtain large conductive anisotropy coefficients and present limited mechanical properties. In this paper, novel technology integrated carbon fiber (CF) spread, surface modification with stacking thermoplastic film was used to prepare CF reinforced polyetheretherketone (CF/PEEK) composite unidirectional tape with thicknesses of 0.04 mm and 0.1 mm. CF/PEEK composite unidirectional woven cloth was prepared with PEEK fiber was used as a binder weft, and CF/PEEK composite unidirectional laminate was prepared by thermoforming process. The in-plane and the thickness directional resistivities of unidirectional laminate were measured by digital multimeter and in-plane electron mobility was tested by Hall effect system. The fiber arrangement within in-planes along the fiber direction and the thickness direction of CF/PEEK composite unidirectional laminate were observed with an ultra-depth microscope. The results show that the in-plane (fiber direction to transverse direction) conductivity ratio of ultra-thin CF/PEEK composite unidirectional laminate reaches to 377, while conductive ratio in the transverse direction to the thickness direction is close to 1, indicating that thin CF/PEEK composite unidirectional laminate presents transverse isotropic electric performance. The results of electron migration also indicate in-plane huge anisotropic conductivity. The results are important for CF/PEEK composite to be used in field emission devices and electronic sensors.
The conductive anisotropic polymer composites (ACPC) have important applications like field emission devices and electronic sensors. Conventional ACPC are difficult to obtain large conductive anisotropy coefficients and present limited mechanical properties. In this paper, novel technology integrated carbon fiber (CF) spread, surface modification with stacking thermoplastic film was used to prepare CF reinforced polyetheretherketone (CF/PEEK) composite unidirectional tape with thicknesses of 0.04 mm and 0.1 mm. CF/PEEK composite unidirectional woven cloth was prepared with PEEK fiber was used as a binder weft, and CF/PEEK composite unidirectional laminate was prepared by thermoforming process. The in-plane and the thickness directional resistivities of unidirectional laminate were measured by digital multimeter and in-plane electron mobility was tested by Hall effect system. The fiber arrangement within in-planes along the fiber direction and the thickness direction of CF/PEEK composite unidirectional laminate were observed with an ultra-depth microscope. The results show that the in-plane (fiber direction to transverse direction) conductivity ratio of ultra-thin CF/PEEK composite unidirectional laminate reaches to 377, while conductive ratio in the transverse direction to the thickness direction is close to 1, indicating that thin CF/PEEK composite unidirectional laminate presents transverse isotropic electric performance. The results of electron migration also indicate in-plane huge anisotropic conductivity. The results are important for CF/PEEK composite to be used in field emission devices and electronic sensors.
2021, 38(3): 788-796.
doi: 10.13801/j.cnki.fhclxb.20200619.002
Abstract:
The interlaminar-toughening T300 carbon fiber/epoxy (CF/EP) composites with agglomerate microcapsules were prepared using hot-compaction laminating technology. The toughening effect was evaluated through mode Ⅰ interlaminar fracture tests conducted on double cantilever beam (DCB) CF/EP composites. The interlaminar properties of virgin and toughened CF/EP composites were evaluated by ultrasonic guided wave technology. The microstructures of interlaminar fracture surfaces of CF/EP composites were observed by SEM to reveal the toughening mechanism of microcapsules and explain the ultrasonic guided wave detection results. The results indicate that the microcapsules are distributed in the interlamination matrix resin in the form of agglomeration, which effectively improve the interlaminar fracture toughness of CF/EP composites. The filling of microcapsules changes the characteristics of the interlaminar matrix of the CF/EP composites, which increases attenuation of the propagating guided waves and causes the response signal peak to decrease. Meanwhile, the agglomerate microcapsules change the vibration response of the CF/EP composites to the excitation of the five-peak wave with a center frequency of 125 kHz, resulting in the amplitude of the center frequency in the signal spectrum being lower than that of the virgin CF/EP composites.
The interlaminar-toughening T300 carbon fiber/epoxy (CF/EP) composites with agglomerate microcapsules were prepared using hot-compaction laminating technology. The toughening effect was evaluated through mode Ⅰ interlaminar fracture tests conducted on double cantilever beam (DCB) CF/EP composites. The interlaminar properties of virgin and toughened CF/EP composites were evaluated by ultrasonic guided wave technology. The microstructures of interlaminar fracture surfaces of CF/EP composites were observed by SEM to reveal the toughening mechanism of microcapsules and explain the ultrasonic guided wave detection results. The results indicate that the microcapsules are distributed in the interlamination matrix resin in the form of agglomeration, which effectively improve the interlaminar fracture toughness of CF/EP composites. The filling of microcapsules changes the characteristics of the interlaminar matrix of the CF/EP composites, which increases attenuation of the propagating guided waves and causes the response signal peak to decrease. Meanwhile, the agglomerate microcapsules change the vibration response of the CF/EP composites to the excitation of the five-peak wave with a center frequency of 125 kHz, resulting in the amplitude of the center frequency in the signal spectrum being lower than that of the virgin CF/EP composites.
2021, 38(3): 797-808.
doi: 10.13801/j.cnki.fhclxb.20200717.002
Abstract:
The mechanical properties of the carbon fiber reinforced epoxy composite pyramid lattice sandwich prosthetic foot structure under vertical load were studied. Three kinds of prosthetic feet with different relative densities were prepared and subjected to vertical load compression test. The results show that the relative density has a significant effect on the mechanical properties of the structure. The load-displacement curve is nonlinear. The peak load and stiffness values increase with the increase of the relative density. The three failure modes of relative density are node failure and panel wrinkling. Curves and structures have a certain energy absorption capacity. The theoretical strength prediction model of the pyramid lattice sandwich prosthetic foot structure was established, and the deflection response of the structure under the vertical load was given. Four failure modes and critical failure loads were obtained. Comparing the peak load, failure mode and deflection of theoretical calculation and experiment, a good consistency is obtained. The effect of the structural parameters of the prosthetic foot (thickness of the panel, angle of the rod and diameter of the rod) on the failure mode and the critical load of the failure were given, and the structural failure mechanism diagram was drawn.
The mechanical properties of the carbon fiber reinforced epoxy composite pyramid lattice sandwich prosthetic foot structure under vertical load were studied. Three kinds of prosthetic feet with different relative densities were prepared and subjected to vertical load compression test. The results show that the relative density has a significant effect on the mechanical properties of the structure. The load-displacement curve is nonlinear. The peak load and stiffness values increase with the increase of the relative density. The three failure modes of relative density are node failure and panel wrinkling. Curves and structures have a certain energy absorption capacity. The theoretical strength prediction model of the pyramid lattice sandwich prosthetic foot structure was established, and the deflection response of the structure under the vertical load was given. Four failure modes and critical failure loads were obtained. Comparing the peak load, failure mode and deflection of theoretical calculation and experiment, a good consistency is obtained. The effect of the structural parameters of the prosthetic foot (thickness of the panel, angle of the rod and diameter of the rod) on the failure mode and the critical load of the failure were given, and the structural failure mechanism diagram was drawn.
2021, 38(3): 809-815.
doi: 10.13801/j.cnki.fhclxb.20201030.003
Abstract:
Based on resin transfer molding (RTM) process, a composite wing was fabricated. Aiming at the dry spot defect of the wing, PAM-RTM software was used to analyze the formation of dry spot. Because of the high volume fraction of fibers in the junction area of upper and lower wings and leading edges, the resin permeability in this area was lower than that in other areas, thus the envelope phenomenon appeared and the dry spot was formed. Two kinds of improved injection ways were designed to reduce the dry spot area. By comparison, it is found that the dry spot area produced by the front line injection method is significantly smaller, but the injection time increases. The resin viscosity can be reduced by increasing the injection temperature, thus the filling time is reduced. At the same time, the injection time can be further reduced by controlling the opening and closing of the outlet.
Based on resin transfer molding (RTM) process, a composite wing was fabricated. Aiming at the dry spot defect of the wing, PAM-RTM software was used to analyze the formation of dry spot. Because of the high volume fraction of fibers in the junction area of upper and lower wings and leading edges, the resin permeability in this area was lower than that in other areas, thus the envelope phenomenon appeared and the dry spot was formed. Two kinds of improved injection ways were designed to reduce the dry spot area. By comparison, it is found that the dry spot area produced by the front line injection method is significantly smaller, but the injection time increases. The resin viscosity can be reduced by increasing the injection temperature, thus the filling time is reduced. At the same time, the injection time can be further reduced by controlling the opening and closing of the outlet.
2021, 38(3): 816-823.
doi: 10.13801/j.cnki.fhclxb.20200623.001
Abstract:
The Ag@Fe3O4 composites with nano core-shell structure were successfully prepared by a one-pot method. The resulting Ag@Fe3O4 composites were characterized by TEM, XRD, UV-vis DRS and vibrating sample magnetometry (VSM). The catalytic performance and mechanism of Ag@Fe3O4 composites were investigated by photometrically monitoring the reduction of methyl orange in the presence of excess of NaBH4. Furthermore, the antibacterial of Ag@Fe3O4 composites against Staphylococcus aureus (S.aureus) and Escherichia coli (E.coli) was studied by the paper diffusion experiment using Ag and Fe3O4 as the references. The results indicate that over 98% of methyl orange is catalytically degraded within 10 min. This superior catalytic activity may be resulted from transferring electron to N=N bond by Ag, thereby causing N=N fracture and generating sodium 4-aminobenzenesulfonate and p-diaminobenzene. Antibacterial experiment shows that Ag@Fe3O4 composites more excellent bacteriostatic activity than Ag and is more sensitive to E.coli than to S.aureus. The main reason can be ascribed to the fact that phospholipid bilayer in cell wall of E.coli is thinner than that of S.aureus.
The Ag@Fe3O4 composites with nano core-shell structure were successfully prepared by a one-pot method. The resulting Ag@Fe3O4 composites were characterized by TEM, XRD, UV-vis DRS and vibrating sample magnetometry (VSM). The catalytic performance and mechanism of Ag@Fe3O4 composites were investigated by photometrically monitoring the reduction of methyl orange in the presence of excess of NaBH4. Furthermore, the antibacterial of Ag@Fe3O4 composites against Staphylococcus aureus (S.aureus) and Escherichia coli (E.coli) was studied by the paper diffusion experiment using Ag and Fe3O4 as the references. The results indicate that over 98% of methyl orange is catalytically degraded within 10 min. This superior catalytic activity may be resulted from transferring electron to N=N bond by Ag, thereby causing N=N fracture and generating sodium 4-aminobenzenesulfonate and p-diaminobenzene. Antibacterial experiment shows that Ag@Fe3O4 composites more excellent bacteriostatic activity than Ag and is more sensitive to E.coli than to S.aureus. The main reason can be ascribed to the fact that phospholipid bilayer in cell wall of E.coli is thinner than that of S.aureus.
2021, 38(3): 824-831.
doi: 10.13801/j.cnki.fhclxb.20200713.002
Abstract:
The effect of discontinuous interfacial phase Al4C3 on the interface bonding of SiC/Al composites was discussed by using the first-principle approach based on density functional theory and experimental method, in comparison, the interface without new phase was also investigated. The results show that the C atom adsorbed on the surface of Al(111) is the most stable at the bridge position, and the adsorption energy of C atoms decreases gradually with the increase of C coverage. The formation of a discontinuous Al4C3 product leads to the interface changing from SiC/Al to (SiC+Al4C3)/Al, and their corresponding work of interfacial adhesion increases from 0.851 J/m2 to 1.231 J/m2, which is attributed to the fact that covalent bonds or ionic bonds are formed between C atoms with Al atoms when C atoms are adsorbed on the surface of Al, and covalent bonds between C atoms with Si atoms. In addition, the calculated adhesions of SiC/Al, (SiC+Al4C3)/Al system by first-principles are in good agreement with these of experiment, which has high reference value.
The effect of discontinuous interfacial phase Al4C3 on the interface bonding of SiC/Al composites was discussed by using the first-principle approach based on density functional theory and experimental method, in comparison, the interface without new phase was also investigated. The results show that the C atom adsorbed on the surface of Al(111) is the most stable at the bridge position, and the adsorption energy of C atoms decreases gradually with the increase of C coverage. The formation of a discontinuous Al4C3 product leads to the interface changing from SiC/Al to (SiC+Al4C3)/Al, and their corresponding work of interfacial adhesion increases from 0.851 J/m2 to 1.231 J/m2, which is attributed to the fact that covalent bonds or ionic bonds are formed between C atoms with Al atoms when C atoms are adsorbed on the surface of Al, and covalent bonds between C atoms with Si atoms. In addition, the calculated adhesions of SiC/Al, (SiC+Al4C3)/Al system by first-principles are in good agreement with these of experiment, which has high reference value.
2021, 38(3): 832-842.
doi: 10.13801/j.cnki.fhclxb.20200703.002
Abstract:
The BiOBr/graphene (BiOBr/RGO) hydrogel composites were prepared via hydrothermal method in this study. The composition and morphology of materials were characterized by XRD and SEM. Photocatalytic properties of the BiOBr/RGO hydrogel composites on sodium n-butyl xanthate were systematically investigated, respectively. The results show that three dimensional macroscopical BiOBr/RGO hydrogel composites are successfully prepared, which is beneficial to recycling. When initial concentration of 50 mL sodium n-butyl xanthate is 25 mg·L−1, degradation time is 85 min, and the dosage of photocatalyst is 10 mg. The degradation efficiency of the BiOBr/RGO hydrogel composite (mass fraction of BiOBr is 92wt%) for sodium n-butyl xanthate can reach 96.69%, and that of BiOBr is merely 44.84%. In all, the introduction of RGO can improve the photocatalytic performance of BiOBr, and macro material is favorable for recycling.
The BiOBr/graphene (BiOBr/RGO) hydrogel composites were prepared via hydrothermal method in this study. The composition and morphology of materials were characterized by XRD and SEM. Photocatalytic properties of the BiOBr/RGO hydrogel composites on sodium n-butyl xanthate were systematically investigated, respectively. The results show that three dimensional macroscopical BiOBr/RGO hydrogel composites are successfully prepared, which is beneficial to recycling. When initial concentration of 50 mL sodium n-butyl xanthate is 25 mg·L−1, degradation time is 85 min, and the dosage of photocatalyst is 10 mg. The degradation efficiency of the BiOBr/RGO hydrogel composite (mass fraction of BiOBr is 92wt%) for sodium n-butyl xanthate can reach 96.69%, and that of BiOBr is merely 44.84%. In all, the introduction of RGO can improve the photocatalytic performance of BiOBr, and macro material is favorable for recycling.
Preparation and properties of modified soy protein-bacterial cellulose composites for air filtration
2021, 38(3): 843-853.
doi: 10.13801/j.cnki.fhclxb.20200727.001
Abstract:
Environmentally-friendly air filtration composite materials were prepared to filter polluted air using soybean protein and bacterial cellulose (BC) as raw materials. 7S and 11S with high solubility were firstly obtained through purification and separation of soy protein by adopting Nagano. Thereafter, soy protein isolate (SPI), 7S and 11S were treated with acrylic acid to unfold the polypeptide chains. Finally, modified soy protein-BC (MSPI-BC, M7S-BC and M11S-BC) composites were prepared by adding soy protein treated with acrylic acid to BC. Besides, the morphology, air filtration efficiency, adsorption capacity and air penetration of the modified soy protein-BC composites were evaluated. The results show that MSPI unevenly distributes in BC, aggregating on the surface of BC fibers. While M7S and M11S uniformly cover on the surface of BC fibers, without aggregation. The air filtration efficiency of MSPI-BC, M7S-BC and M11S-BC composites for particulate pollutants is 73.07%±0.02%, 82.13%±0.01% and 85.44%±0.02%, respectively. Moreover, M7S-BC and M11S-BC composites adsorb more particulate pollutants than MSPI-BC composite. The prepared modified soy protein-BC composites in this study own stable structure and high air filtration efficiency, and they are environmentally-friendly, thus being potential to be used in the field of air filtration.
Environmentally-friendly air filtration composite materials were prepared to filter polluted air using soybean protein and bacterial cellulose (BC) as raw materials. 7S and 11S with high solubility were firstly obtained through purification and separation of soy protein by adopting Nagano. Thereafter, soy protein isolate (SPI), 7S and 11S were treated with acrylic acid to unfold the polypeptide chains. Finally, modified soy protein-BC (MSPI-BC, M7S-BC and M11S-BC) composites were prepared by adding soy protein treated with acrylic acid to BC. Besides, the morphology, air filtration efficiency, adsorption capacity and air penetration of the modified soy protein-BC composites were evaluated. The results show that MSPI unevenly distributes in BC, aggregating on the surface of BC fibers. While M7S and M11S uniformly cover on the surface of BC fibers, without aggregation. The air filtration efficiency of MSPI-BC, M7S-BC and M11S-BC composites for particulate pollutants is 73.07%±0.02%, 82.13%±0.01% and 85.44%±0.02%, respectively. Moreover, M7S-BC and M11S-BC composites adsorb more particulate pollutants than MSPI-BC composite. The prepared modified soy protein-BC composites in this study own stable structure and high air filtration efficiency, and they are environmentally-friendly, thus being potential to be used in the field of air filtration.
2021, 38(3): 854-862.
doi: 10.13801/j.cnki.fhclxb.20200709.001
Abstract:
The perfluorodecyltrimethoxysilane (PFDMS)-n-decanoic acid (DA)-TiO2 solution was prepared by a simple sol-gel method, and immersed to obtain the PFDMS-DA-TiO2 superamphiphobic sponge. Under the induction of ammonia gas with a mass fraction of 25wt%–28wt%, the surface wettability of the PFDMS-DA-TiO2 sponge is switched from superamphiphobic to superhydrophilic and superoleophobic in air. The surface of the PFDMS-DA-TiO2 sponge before and after modification was characterized by FTIR and SEM, and its chemical composition and surface morphology were analyzed. The effect of the volume ratio of DA on the reversible switching effect of the PFDMS-DA-TiO2 superhydrophilic sponge surface infiltration was studied, and its salt tolerance, friction resistance and oil-water separation performance were tested. The results show that the optimal volume ratio of DA is 5.8%. At this time, the oil-water separation efficiency and flux can reach 99.6% and 4775 L/(m2·h), respectively. After the PFDMS-DA-TiO2 superhydrophilic sponge was subjected to an abrasion test and immersed in 3.5wt% NaCl solution for 12 h, they all exhibit excellent superamphiphobic performance and sponges show high abrasion resistance and salt tolerance. After 20 times of reversibly switching of surface wettability between superamphiphobic and superhydrophobic-superhydrophilic in air induced by ammonia, the two wetting properties can still maintain their own stability, which can be used to effectively separate oil-water mixtures in practical industries.
The perfluorodecyltrimethoxysilane (PFDMS)-n-decanoic acid (DA)-TiO2 solution was prepared by a simple sol-gel method, and immersed to obtain the PFDMS-DA-TiO2 superamphiphobic sponge. Under the induction of ammonia gas with a mass fraction of 25wt%–28wt%, the surface wettability of the PFDMS-DA-TiO2 sponge is switched from superamphiphobic to superhydrophilic and superoleophobic in air. The surface of the PFDMS-DA-TiO2 sponge before and after modification was characterized by FTIR and SEM, and its chemical composition and surface morphology were analyzed. The effect of the volume ratio of DA on the reversible switching effect of the PFDMS-DA-TiO2 superhydrophilic sponge surface infiltration was studied, and its salt tolerance, friction resistance and oil-water separation performance were tested. The results show that the optimal volume ratio of DA is 5.8%. At this time, the oil-water separation efficiency and flux can reach 99.6% and 4775 L/(m2·h), respectively. After the PFDMS-DA-TiO2 superhydrophilic sponge was subjected to an abrasion test and immersed in 3.5wt% NaCl solution for 12 h, they all exhibit excellent superamphiphobic performance and sponges show high abrasion resistance and salt tolerance. After 20 times of reversibly switching of surface wettability between superamphiphobic and superhydrophobic-superhydrophilic in air induced by ammonia, the two wetting properties can still maintain their own stability, which can be used to effectively separate oil-water mixtures in practical industries.
2021, 38(3): 863-870.
doi: 10.13801/j.cnki.fhclxb.20200826.003
Abstract:
The Sn-based materials have been a focus as promising high-capacity electrode materials of lithium-ion battery. However, its poor cycling performance has severely restricted the large-scale practical applications. The Sn quantum dot/graphene (SnQds/rGO) composite electrode material was synthesized by chemical reduction method, using graphene oxide as the carrier. The Sn quantum dots with <10 nm were uniformly loaded on the surface of graphene. The experimental results show that the SnQds/rGO composite with Sn mass fraction of 90wt% has good comprehensive electrochemical performance. The first discharge capacity and Coulomb efficiency of the SnQds/rGO composite are 939 mAh/g and 66.6%, respectively. It’s discapacity can reach 621 mAh/g after 200 cycles and the capacity retention rate is 66.1%. The structure stability of SnQds/rGO composite is improve, meanwhile its impedance reduce, owing to the commposite of small size Sn quantum dots and graphenethe. As a result, the cycle performance and rate performance of the SnQds/rGO composite have been significantly improved. However, the initial Coulomb efficiency of SnQds/rGO composite decreases.
The Sn-based materials have been a focus as promising high-capacity electrode materials of lithium-ion battery. However, its poor cycling performance has severely restricted the large-scale practical applications. The Sn quantum dot/graphene (SnQds/rGO) composite electrode material was synthesized by chemical reduction method, using graphene oxide as the carrier. The Sn quantum dots with <10 nm were uniformly loaded on the surface of graphene. The experimental results show that the SnQds/rGO composite with Sn mass fraction of 90wt% has good comprehensive electrochemical performance. The first discharge capacity and Coulomb efficiency of the SnQds/rGO composite are 939 mAh/g and 66.6%, respectively. It’s discapacity can reach 621 mAh/g after 200 cycles and the capacity retention rate is 66.1%. The structure stability of SnQds/rGO composite is improve, meanwhile its impedance reduce, owing to the commposite of small size Sn quantum dots and graphenethe. As a result, the cycle performance and rate performance of the SnQds/rGO composite have been significantly improved. However, the initial Coulomb efficiency of SnQds/rGO composite decreases.
2021, 38(3): 871-878.
doi: 10.13801/j.cnki.fhclxb.20200921.002
Abstract:
The transition metal sulfide is an extremely high capacity anode material for lithium ion batteries. In this paper, a new kind of hollow out nanosheets lithium battery anode material with self-supporting CuS/SnS2 lithium battery anode material was designed and prepared. The conductive carbon cloth was used as the substrate to grow and clad CuS/SnS2 hollow out nanosheets. It has high specific capacity, good cycling performance and excellent electrochemical performance. The effects of different Cu/Sn contents on electrochemical properties were investigated. The specific capacity of CuS/SnS2 anode material is 1480 mAh·g−1 at 99.5% coulomb efficiency after 50 cycles under the current density of 0.2 A·g−1. After 200 cycles at the large current density of 2 A·g−1, the specific capacity remains at 697 mAh·g−1, and the coulomb efficiency is stable at 99.8%.
The transition metal sulfide is an extremely high capacity anode material for lithium ion batteries. In this paper, a new kind of hollow out nanosheets lithium battery anode material with self-supporting CuS/SnS2 lithium battery anode material was designed and prepared. The conductive carbon cloth was used as the substrate to grow and clad CuS/SnS2 hollow out nanosheets. It has high specific capacity, good cycling performance and excellent electrochemical performance. The effects of different Cu/Sn contents on electrochemical properties were investigated. The specific capacity of CuS/SnS2 anode material is 1480 mAh·g−1 at 99.5% coulomb efficiency after 50 cycles under the current density of 0.2 A·g−1. After 200 cycles at the large current density of 2 A·g−1, the specific capacity remains at 697 mAh·g−1, and the coulomb efficiency is stable at 99.8%.
2021, 38(3): 879-890.
doi: 10.13801/j.cnki.fhclxb.20200713.001
Abstract:
For the requirement of mold bag concrete to achieve high frost resistance under large flowability, the effects of air content, antifoaming agent and viscosity enhancing agent on the workability and frost resistance of concrete were studied by orthogonal test. The test results show that the air and antifoaming agent contents are significant factors that affect the relative dynamic elastic modulus and the air content of mold bag concrete is significantly greater than antifoaming agent content; the viscosity enhancing agent increases the relative dynamic elastic modulus to a lesser extent. The compounding of antifoaming agent and viscosity enhancing agent can achieve the effects of synergistically improving the workability, pore structure and frost resistance of mold bag concrete. When the air content is 5vol%–6vol%, the compounding of 0.15wt% antifoaming agent and 0.03wt% viscosity enhancing agent can reduce the air content loss rate and the slump flow loss rate by 64.28% and 55.04%, respectively. The number of harmful large bubbles is eliminated by 81.38%. The number of air bubbles is increased by 14.89%,. The spacing factor is decreased by 11.54%. The specific surface area is increased by 20.49%. The relative dynamic elastic modulus is increased by 11.97%. Both the spacing factor and the specific area have a good correlation with the relative dynamic elastic modulus. The frost resistance grade of the mold bag concrete with spacing factor not more than 361 μm and specific surface area not less than 16.13 mm−1 can reach F300. The test results are regressed, and the prediction models of the frost resistence of the mold bag concrete are obtained.
For the requirement of mold bag concrete to achieve high frost resistance under large flowability, the effects of air content, antifoaming agent and viscosity enhancing agent on the workability and frost resistance of concrete were studied by orthogonal test. The test results show that the air and antifoaming agent contents are significant factors that affect the relative dynamic elastic modulus and the air content of mold bag concrete is significantly greater than antifoaming agent content; the viscosity enhancing agent increases the relative dynamic elastic modulus to a lesser extent. The compounding of antifoaming agent and viscosity enhancing agent can achieve the effects of synergistically improving the workability, pore structure and frost resistance of mold bag concrete. When the air content is 5vol%–6vol%, the compounding of 0.15wt% antifoaming agent and 0.03wt% viscosity enhancing agent can reduce the air content loss rate and the slump flow loss rate by 64.28% and 55.04%, respectively. The number of harmful large bubbles is eliminated by 81.38%. The number of air bubbles is increased by 14.89%,. The spacing factor is decreased by 11.54%. The specific surface area is increased by 20.49%. The relative dynamic elastic modulus is increased by 11.97%. Both the spacing factor and the specific area have a good correlation with the relative dynamic elastic modulus. The frost resistance grade of the mold bag concrete with spacing factor not more than 361 μm and specific surface area not less than 16.13 mm−1 can reach F300. The test results are regressed, and the prediction models of the frost resistence of the mold bag concrete are obtained.
2021, 38(3): 891-901.
doi: 10.13801/j.cnki.fhclxb.20200723.006
Abstract:
According to the characteristics of the sand environment in the middle and west regions of Inner Mongolia, the erosion resistance of polypropylene (PP) fiber/cement composites with different PP fiber contents in the sand environment was studied by using the simulated wind sand environment erosion experimental system. The micro-morphology of PP fiber/cement composites after erosion was observed by using SEM, and the erosion mechanism was explored. The results show that the erosion rates of the PP fiber/cement composites with different PP fiber contents are as follows: Cement mortar PP fiber/cement composite with mass ratio of PP fiber to cementitious is 1.5% PP fiber/cement composite with mass ratio of PP fiber to cementitious is 0.5%. Within a certain erosion time range, the evolution characteristics of erosion damage have changed significantly. The erosion rates of PP fiber/cement composites with different fiber contents increase with the erosion angle, and different peaks appear when the erosion angle is 90°, which accords with the characteristics of brittle materials. By analyzing the surface contact stress in erosion process and combined with the micro morphology after erosion, it is pointed out that the appropriate amount of PP fiber will improve the compactness and toughness of the PP fiber/cement composites. However, the addition of excessive PP fiber will cause uneven dispersion and reduce the compactness and erosion resistance of the mortar. The PP fiber/cement composites with excellent erosion resistance can be produced by matching the content of PP fiber reasonably.
According to the characteristics of the sand environment in the middle and west regions of Inner Mongolia, the erosion resistance of polypropylene (PP) fiber/cement composites with different PP fiber contents in the sand environment was studied by using the simulated wind sand environment erosion experimental system. The micro-morphology of PP fiber/cement composites after erosion was observed by using SEM, and the erosion mechanism was explored. The results show that the erosion rates of the PP fiber/cement composites with different PP fiber contents are as follows: Cement mortar PP fiber/cement composite with mass ratio of PP fiber to cementitious is 1.5% PP fiber/cement composite with mass ratio of PP fiber to cementitious is 0.5%. Within a certain erosion time range, the evolution characteristics of erosion damage have changed significantly. The erosion rates of PP fiber/cement composites with different fiber contents increase with the erosion angle, and different peaks appear when the erosion angle is 90°, which accords with the characteristics of brittle materials. By analyzing the surface contact stress in erosion process and combined with the micro morphology after erosion, it is pointed out that the appropriate amount of PP fiber will improve the compactness and toughness of the PP fiber/cement composites. However, the addition of excessive PP fiber will cause uneven dispersion and reduce the compactness and erosion resistance of the mortar. The PP fiber/cement composites with excellent erosion resistance can be produced by matching the content of PP fiber reasonably.
2021, 38(3): 902-910.
doi: 10.13801/j.cnki.fhclxb.20200616.001
Abstract:
A quasi-static punching test was conducted on polyvinyl alcohol (PVA) fiber/cementitious composite slab by using MTS testing machine. The effects of the PVA fiber content on the failure mode and bearing capacity of PVA/cementitious composite slab were studied based on the experimental results. The results show that incorporating of PVA fiber can change the failure mode of the PVA/cementitious composite slab from brittle failure to ductile failure. And both the punching capacity and the energy absorption capacity of the PVA/cementitious composite slab increase with the fiber content and more obvious rise can be observed for the energy absorption capacity. Then the dynamic punching test of PVA reinforced cementitious composite slab with 2vol% volume fraction of PVA was carried out by using Instron drop-weight impact system. The influences of the impact velocity (2.0–4.2 m/s) on the failure mode, cracking impact loading, ultimate impact loading, initial stiffness and energy absorption capacity of the PVA/cementitious composite slab were investigated. The results show that compared with the results from the quasi-static test, the ultimate loading of the PVA/cementitious composite slab increases while the energy absorption capacity decreases under the punching force. Also, a more significant increase in ultimate loading with the loading velocity can be observed, compared with that of the energy absorption capacity. A qua-linear tensile constitutive model of fiber reinforced cementitious composite was constructed based on these experimental results, and the punching mechanic behavior of the fiber reinforced cementitious composite slab was simulated by the back-calculation model based on the plastic hinge method, and the material parameters of the fiber reinforced cementitious composite were obtained. This study can provide a solid base for the punch performance design of the PVA/cementitious composite slab.
A quasi-static punching test was conducted on polyvinyl alcohol (PVA) fiber/cementitious composite slab by using MTS testing machine. The effects of the PVA fiber content on the failure mode and bearing capacity of PVA/cementitious composite slab were studied based on the experimental results. The results show that incorporating of PVA fiber can change the failure mode of the PVA/cementitious composite slab from brittle failure to ductile failure. And both the punching capacity and the energy absorption capacity of the PVA/cementitious composite slab increase with the fiber content and more obvious rise can be observed for the energy absorption capacity. Then the dynamic punching test of PVA reinforced cementitious composite slab with 2vol% volume fraction of PVA was carried out by using Instron drop-weight impact system. The influences of the impact velocity (2.0–4.2 m/s) on the failure mode, cracking impact loading, ultimate impact loading, initial stiffness and energy absorption capacity of the PVA/cementitious composite slab were investigated. The results show that compared with the results from the quasi-static test, the ultimate loading of the PVA/cementitious composite slab increases while the energy absorption capacity decreases under the punching force. Also, a more significant increase in ultimate loading with the loading velocity can be observed, compared with that of the energy absorption capacity. A qua-linear tensile constitutive model of fiber reinforced cementitious composite was constructed based on these experimental results, and the punching mechanic behavior of the fiber reinforced cementitious composite slab was simulated by the back-calculation model based on the plastic hinge method, and the material parameters of the fiber reinforced cementitious composite were obtained. This study can provide a solid base for the punch performance design of the PVA/cementitious composite slab.
2021, 38(3): 911-919.
doi: 10.13801/j.cnki.fhclxb.20200714.002
Abstract:
By using a sandwich construction that consists of aluminum alloy panels-rigid polyurethane foam, a common bulkhead was devised for cryogenic launch vehicle tanks. The common bulkhead has the characteristics of lightweight, easy to manufacture, and integrated load bearing/thermal insulation. Based on numerical simulations, thermal insulation effect, structural stability and thermal-mechanical coupling behavior of the common bulkhead were analyzed. The results show that the common bulkhead not only satisfies the thermal insulation requirements of cryogenic tanks for liquid hydrogen and oxygen, but also keeps structural stability under a differential pressure of 0.342 MPa and material safety with a pressure of 0.5 MPa. The design and analysis of this structure can provide technical support for the design of new cryogenic tanks with a common bulkhead.
By using a sandwich construction that consists of aluminum alloy panels-rigid polyurethane foam, a common bulkhead was devised for cryogenic launch vehicle tanks. The common bulkhead has the characteristics of lightweight, easy to manufacture, and integrated load bearing/thermal insulation. Based on numerical simulations, thermal insulation effect, structural stability and thermal-mechanical coupling behavior of the common bulkhead were analyzed. The results show that the common bulkhead not only satisfies the thermal insulation requirements of cryogenic tanks for liquid hydrogen and oxygen, but also keeps structural stability under a differential pressure of 0.342 MPa and material safety with a pressure of 0.5 MPa. The design and analysis of this structure can provide technical support for the design of new cryogenic tanks with a common bulkhead.
2021, 38(3): 920-931.
doi: 10.13801/j.cnki.fhclxb.20200710.001
Abstract:
In our country, there are many eccentric tension members, such as steel reinforced concrete truss transfer layer straining beam, low-rise building corner column. For these members, large-scale cracks easily appear during normal use stage. Aiming at these problems, this paper took the light, high-strength and anti-corrosion carbon fiber reinforced polymer composite (CFRP) tendons as the prestressed reinforcement, the prestressed CFRP-steel reinforced concrete structure system was designed by combining CFRP tendons with prestressed steel reinforced concrete, which can effectively restrain the crack. And on this basis, a systematic study on the crack resistance under eccentric tension was carried out. A total of eleven members were designed and fabricated with the prestress level, eccentricity, longitudinal reinforcement diameter and profile flange thickness as the main parameters, and eccentric loading was achieved through the self-developed tension-compression conversion truss system. The results indicate that the crack resistance of the prestressed CFRP tendons-steel/concrete members is greatly strengthened. Compared with the ordinary eccentric members, the cracking loads of the large tension members with prestressed CFRP tendons are increased by 64.8%–102.3%, the cracking loads of the small tension members with prestressed CFRP tendons are increased by 61.7%–117%. The crack resistance of the member is positively related to the prestress level, longitudinal reinforcement diameter and steel flange thickness, and negatively related to the eccentricity. With reference to the combined structural design specification, three positions of the neutral axis of the prestressed CFRP tendons-steel reinforced concrete members during the cracking stage are proposed, and the calculation formula of cracking load is derived. Compared with the test value, the agreement is perfect, which can provide a reference for the application of other composites in the prestressed eccentric tension system.
In our country, there are many eccentric tension members, such as steel reinforced concrete truss transfer layer straining beam, low-rise building corner column. For these members, large-scale cracks easily appear during normal use stage. Aiming at these problems, this paper took the light, high-strength and anti-corrosion carbon fiber reinforced polymer composite (CFRP) tendons as the prestressed reinforcement, the prestressed CFRP-steel reinforced concrete structure system was designed by combining CFRP tendons with prestressed steel reinforced concrete, which can effectively restrain the crack. And on this basis, a systematic study on the crack resistance under eccentric tension was carried out. A total of eleven members were designed and fabricated with the prestress level, eccentricity, longitudinal reinforcement diameter and profile flange thickness as the main parameters, and eccentric loading was achieved through the self-developed tension-compression conversion truss system. The results indicate that the crack resistance of the prestressed CFRP tendons-steel/concrete members is greatly strengthened. Compared with the ordinary eccentric members, the cracking loads of the large tension members with prestressed CFRP tendons are increased by 64.8%–102.3%, the cracking loads of the small tension members with prestressed CFRP tendons are increased by 61.7%–117%. The crack resistance of the member is positively related to the prestress level, longitudinal reinforcement diameter and steel flange thickness, and negatively related to the eccentricity. With reference to the combined structural design specification, three positions of the neutral axis of the prestressed CFRP tendons-steel reinforced concrete members during the cracking stage are proposed, and the calculation formula of cracking load is derived. Compared with the test value, the agreement is perfect, which can provide a reference for the application of other composites in the prestressed eccentric tension system.
2021, 38(3): 932-943.
doi: 10.13801/j.cnki.fhclxb.20200623.003
Abstract:
The tension stiffening effect is the premise of accurate evaluation of the deformation and crack width of fiber reinforced polymer composite (FRP) bar/concrete members. An analytical method for determining the deformation of FRP bar/concrete tension member was proposed. A simplified four-linear model based on the modified Eligehausen model (modified BPE model) was presented. The distribution of stress, displacement of FRP bars and concrete and the distribution of bond force, slip between bars and concrete were established. By combining with the cracking criterion of concrete, an algorithm for the deformation of FRP reinforced tensive ties at different loading stages was proposed. After verification by comparing with experimental data in the literature, the effects of different parameters on the tension stiffening were analyzed. Parametric analysis results indicate that concrete strength and reinforcement ratio of FRP bars have a minor impact on the tension stiffening effect. However, the elastic modulus of FRP bars dominates the tension stiffening behavior of FRP reinforced concrete tensile elements.
The tension stiffening effect is the premise of accurate evaluation of the deformation and crack width of fiber reinforced polymer composite (FRP) bar/concrete members. An analytical method for determining the deformation of FRP bar/concrete tension member was proposed. A simplified four-linear model based on the modified Eligehausen model (modified BPE model) was presented. The distribution of stress, displacement of FRP bars and concrete and the distribution of bond force, slip between bars and concrete were established. By combining with the cracking criterion of concrete, an algorithm for the deformation of FRP reinforced tensive ties at different loading stages was proposed. After verification by comparing with experimental data in the literature, the effects of different parameters on the tension stiffening were analyzed. Parametric analysis results indicate that concrete strength and reinforcement ratio of FRP bars have a minor impact on the tension stiffening effect. However, the elastic modulus of FRP bars dominates the tension stiffening behavior of FRP reinforced concrete tensile elements.
2021, 38(3): 944-952.
doi: 10.13801/j.cnki.fhclxb.20200615.002
Abstract:
In order to study the compressive creep performance of bamboo scrimber, creep tests were carried out on twelve bamboo scrimber specimens. By analyzing the creep growth rate and the parameters in Burgers model, the variation law of compression creep was obtained. The results show that the creep deformation of bamboo scrimber, subjected to compressive loads effect, develops stably and the bamboo scrimber is not destructed under the bearing capacity when the stress level is low. When the stress level is large (reaching 60% of the ultimate load), it will directly lead to the buckling failure of bamboo scrimber, and the creep deformation will show an unstable increase. The growth rate of the compressive creep strain of the bamboo scrimber gradually increases with the increase of time, its growth rate shows a decelerating state and the growth rate also increases as the stress ratio goes up. Based on the results, the variation law of elastic deformation, viscoelastic deformation and viscous deformation in the compression creep test were given. The parameters of Burgers model with different load levels were determined, and the variation law of parameters with stress level was derived. Based on above, a prediction model that takes into consideration the stress level for compressive creep of bamboo scrimber is proposed, and the results are consistent with the test curves.
In order to study the compressive creep performance of bamboo scrimber, creep tests were carried out on twelve bamboo scrimber specimens. By analyzing the creep growth rate and the parameters in Burgers model, the variation law of compression creep was obtained. The results show that the creep deformation of bamboo scrimber, subjected to compressive loads effect, develops stably and the bamboo scrimber is not destructed under the bearing capacity when the stress level is low. When the stress level is large (reaching 60% of the ultimate load), it will directly lead to the buckling failure of bamboo scrimber, and the creep deformation will show an unstable increase. The growth rate of the compressive creep strain of the bamboo scrimber gradually increases with the increase of time, its growth rate shows a decelerating state and the growth rate also increases as the stress ratio goes up. Based on the results, the variation law of elastic deformation, viscoelastic deformation and viscous deformation in the compression creep test were given. The parameters of Burgers model with different load levels were determined, and the variation law of parameters with stress level was derived. Based on above, a prediction model that takes into consideration the stress level for compressive creep of bamboo scrimber is proposed, and the results are consistent with the test curves.
2021, 38(3): 953-965.
doi: 10.13801/j.cnki.fhclxb.20200722.002
Abstract:
The test on uniaxial compression, split tension, freeze-thaw cycle, air-void and SEM analysis were carried out on basalt fiber-slag powder-fly ash concrete (BF-SP-FAC). The changes of damage amount, compressive strength and tensile strength of BF-SP-FAC were studied under different freeze-thaw cycles. The relationships of air-void structure parameters (air content, specific surface area, spacing factor and average chord length) with compressive strength, tensile strength of BF-SP-FAC were analyzed. The effects of the air-void structure parameters on the compressive strength, tensile strength and damage amount were investigated by grey correlation entropy analysis. The results show that under the same freezing and thawing times, compared with other fiber dosage, BF-SP-FAC mixed with basalt fiber of 0.18vol% has the best frost resistance and the highest compressive strength and tensile strength. Under the same fiber content, the compressive and tensile strength of BF-SP-FAC decrease with the increase of air content, spacing factor, and average chord length, while the damage amount increases. The compressive strength and tensile strength of BF-SP-FAC increase with the increase of specific surface area, while the damage amount decreases. The most important factor to the compressive strength and tensile strength of BF-SP-FAC is specific surface area, the main factor to the damage amount of BF-SP-FAC is the average chord length. The minimum grey entropy correlations are 0.998 and 0.993, respectively. The establishment of relationships among air-void structure parameters, strength and freeze-thaw damage can predict the strength and freeze-thaw damage of concrete.
The test on uniaxial compression, split tension, freeze-thaw cycle, air-void and SEM analysis were carried out on basalt fiber-slag powder-fly ash concrete (BF-SP-FAC). The changes of damage amount, compressive strength and tensile strength of BF-SP-FAC were studied under different freeze-thaw cycles. The relationships of air-void structure parameters (air content, specific surface area, spacing factor and average chord length) with compressive strength, tensile strength of BF-SP-FAC were analyzed. The effects of the air-void structure parameters on the compressive strength, tensile strength and damage amount were investigated by grey correlation entropy analysis. The results show that under the same freezing and thawing times, compared with other fiber dosage, BF-SP-FAC mixed with basalt fiber of 0.18vol% has the best frost resistance and the highest compressive strength and tensile strength. Under the same fiber content, the compressive and tensile strength of BF-SP-FAC decrease with the increase of air content, spacing factor, and average chord length, while the damage amount increases. The compressive strength and tensile strength of BF-SP-FAC increase with the increase of specific surface area, while the damage amount decreases. The most important factor to the compressive strength and tensile strength of BF-SP-FAC is specific surface area, the main factor to the damage amount of BF-SP-FAC is the average chord length. The minimum grey entropy correlations are 0.998 and 0.993, respectively. The establishment of relationships among air-void structure parameters, strength and freeze-thaw damage can predict the strength and freeze-thaw damage of concrete.
2021, 38(3): 966-978.
doi: 10.13801/j.cnki.fhclxb.20201210.002
Abstract:
In order to study the mechanical properties of carbon fiber reinforced polymer composite (CFRP) confined concrete columns deteriorated in sulfate environment and establish corresponding mechanical models, two types of testing conditions were considered, i.e., deterioration after confinement and confinement after deterioration. Based on the testing results, two quantitative indicators, damage ratio and residual strength ratio were introduced to represent the degree of concrete damage, and a relationship between the damage ratio and the residual strength ratio was setup. Through a regression analysis of the strength and the strain, the models for ultimate strength, ultimate strain and stress-stain relationship were given for these columns, respectively. The results show that with the corrosion time growing, the ultimate strength, ultimate strain and corrosion rate of the CFRP confined concrete are different for the both testing conditions, respectively. Before the pre-deteriorated concrete column is confined subsequently, internal damaged has occurred and will have an effect on its performance. Hence, the effect of initial damage should be considered when CFRP confined concrete columns are adopted in a corrosive environment.
In order to study the mechanical properties of carbon fiber reinforced polymer composite (CFRP) confined concrete columns deteriorated in sulfate environment and establish corresponding mechanical models, two types of testing conditions were considered, i.e., deterioration after confinement and confinement after deterioration. Based on the testing results, two quantitative indicators, damage ratio and residual strength ratio were introduced to represent the degree of concrete damage, and a relationship between the damage ratio and the residual strength ratio was setup. Through a regression analysis of the strength and the strain, the models for ultimate strength, ultimate strain and stress-stain relationship were given for these columns, respectively. The results show that with the corrosion time growing, the ultimate strength, ultimate strain and corrosion rate of the CFRP confined concrete are different for the both testing conditions, respectively. Before the pre-deteriorated concrete column is confined subsequently, internal damaged has occurred and will have an effect on its performance. Hence, the effect of initial damage should be considered when CFRP confined concrete columns are adopted in a corrosive environment.
