2020 Vol. 37, No. 9
2020, 37(9): 2258-2264.
doi: 10.13801/j.cnki.fhclxb.20200103.003
Abstract:
The surface of ZnS quantum dots was modified with polyacrylic acid(PAA) by situ polymerization. The resulting ZnS@PAA composite nanoparticles were characterized by XRD, TEM, FTIR, TGA and fluorescence test. XRD results indicat that the ZnS@PAA composite nanoparticles exhibite a pure cubic phase. FTIR and TGA results reveal that the ZnS nano particles are coated with PAA. TEM results reveal that PAA coated ZnS quantum dots monodisperse and spherical shape in the water phase, the size of spherical particles is estimated to be 28 nm. The fluorescence tests show that after PAA coated, the fluorescent position and intensity of ZnS@PAA composite nanoparticles do not changed significantly. The test results display that PAA coated ZnS quantum dots have more favorable dispersion stability than that of the uncoated ones in aqueous system. The ZnS@PAA composite nanoparticles with excellen oxidation resistance, fluorescence stability, water-solubility and carboxyl-functionalization could be used for biological detection and bio-imaging.
The surface of ZnS quantum dots was modified with polyacrylic acid(PAA) by situ polymerization. The resulting ZnS@PAA composite nanoparticles were characterized by XRD, TEM, FTIR, TGA and fluorescence test. XRD results indicat that the ZnS@PAA composite nanoparticles exhibite a pure cubic phase. FTIR and TGA results reveal that the ZnS nano particles are coated with PAA. TEM results reveal that PAA coated ZnS quantum dots monodisperse and spherical shape in the water phase, the size of spherical particles is estimated to be 28 nm. The fluorescence tests show that after PAA coated, the fluorescent position and intensity of ZnS@PAA composite nanoparticles do not changed significantly. The test results display that PAA coated ZnS quantum dots have more favorable dispersion stability than that of the uncoated ones in aqueous system. The ZnS@PAA composite nanoparticles with excellen oxidation resistance, fluorescence stability, water-solubility and carboxyl-functionalization could be used for biological detection and bio-imaging.
2020, 37(9): 2265-2271.
doi: 10.13801/j.cnki.fhclxb.20200323.001
Abstract:
The Co-modified CeO2 composites with high active crystal planes were synthesized by simple one step hydrothermal method. The structure of Co-modified CeO2 composites was characterized by specific surface area and porosity analyzer, TG-DSC, TEM, SEM, XRD, ultraviolet-visible spectrophotometer (UV-vis), XPS and photothermal catalytic denitration. The results show that as the amount of Co increases, the specific surface area of the Co-modified CeO2 composites increases. The exposed high active surface is (200) and (220) crystal face, while the Co-modified CeO2 composites mainly show rod-like structure; when the concentration of Co content precursor increases, CeO2 has a nanorod structure, and the Co produces in the form of Co3O4 by chemical band connection with surface oxygen. The results of thermal-photocatalytic denitration test show that the catalytic efficiency of the Co-modified CeO2 composites reaches 98% with 15% molar ratio of Co to Ce at 400℃ calcination temperature.
The Co-modified CeO2 composites with high active crystal planes were synthesized by simple one step hydrothermal method. The structure of Co-modified CeO2 composites was characterized by specific surface area and porosity analyzer, TG-DSC, TEM, SEM, XRD, ultraviolet-visible spectrophotometer (UV-vis), XPS and photothermal catalytic denitration. The results show that as the amount of Co increases, the specific surface area of the Co-modified CeO2 composites increases. The exposed high active surface is (200) and (220) crystal face, while the Co-modified CeO2 composites mainly show rod-like structure; when the concentration of Co content precursor increases, CeO2 has a nanorod structure, and the Co produces in the form of Co3O4 by chemical band connection with surface oxygen. The results of thermal-photocatalytic denitration test show that the catalytic efficiency of the Co-modified CeO2 composites reaches 98% with 15% molar ratio of Co to Ce at 400℃ calcination temperature.
2020, 37(9): 2272-2284.
doi: 10.13801/j.cnki.fhclxb.20200218.002
Abstract:
Owing to the addition of nano SiO2 can promote the hydration rate, improve the mechanical properties and interfacial transition zone (ITZ) and refine the pore structure of polymer cement-based composites, the microscopic mechanism of influence of nano SiO2 on the early properties of polymer cement-based composites was revealed by means of XRD, SEM, EDS, microhardness (MH) and mercury intrusion porosimetry (MIP) experiments. The results show that when nano SiO2 content is 2wt%, the mechanical properties of the polymer cement-based composites are the best. The compressive strength is 57.5 MPa and 67.3 MPa in 3 d and 7 d age, respectively, which is 12.7% and 13.9% higher than that of the polymer cement-based composites with polymer simply. The addition of nano SiO2 changes the hydration products and microstructure of the polymer cement-based composites. As for ITZ, the thickness of ITZ between polymer cement hardened paste and aggregate decreases, its morphology becomes denser, the calcium-silicate ratio in ITZ declines and the microhardness in ITZ increases by nano SiO2 incorporation. Since nano SiO2 can further fill finer pores of the polymer cement-based composites, there is higher proportion of gel pores and the mean pore diameter tends to be smaller so that the pore structure of the polymer cement-based composites is greatly optimized by nano SiO2 addition.
Owing to the addition of nano SiO2 can promote the hydration rate, improve the mechanical properties and interfacial transition zone (ITZ) and refine the pore structure of polymer cement-based composites, the microscopic mechanism of influence of nano SiO2 on the early properties of polymer cement-based composites was revealed by means of XRD, SEM, EDS, microhardness (MH) and mercury intrusion porosimetry (MIP) experiments. The results show that when nano SiO2 content is 2wt%, the mechanical properties of the polymer cement-based composites are the best. The compressive strength is 57.5 MPa and 67.3 MPa in 3 d and 7 d age, respectively, which is 12.7% and 13.9% higher than that of the polymer cement-based composites with polymer simply. The addition of nano SiO2 changes the hydration products and microstructure of the polymer cement-based composites. As for ITZ, the thickness of ITZ between polymer cement hardened paste and aggregate decreases, its morphology becomes denser, the calcium-silicate ratio in ITZ declines and the microhardness in ITZ increases by nano SiO2 incorporation. Since nano SiO2 can further fill finer pores of the polymer cement-based composites, there is higher proportion of gel pores and the mean pore diameter tends to be smaller so that the pore structure of the polymer cement-based composites is greatly optimized by nano SiO2 addition.
2020, 37(9): 2285-2293.
doi: 10.13801/j.cnki.fhclxb.20200219.001
Abstract:
In order to study the pore structure change characteristics of basalt fiber reinforced concrete under two sources of damage, high temperature and mechanics, nuclear magnetic resonance(NMR) and scanning electron microscopy(SEM) techniques were used to observe the T2 spectrum distribution, pore size distribution and flaw development of the basalt fiber reinforced concrete. The results show that normal concrete, short basalt fiber reinforced concrete and long basalt fiber reinforced concrete show a trend of decreasing the number of micropores and increasing the number of mesopores after high temperature. By comparison, it is found that long basalt fiber reinforced concrete has the largest number of pores in the main peak of the T2 spectrum and the largest pore size distribution. The long basalt fiber reinforced concrete was taken as an example to illustrate the change characteristics of pore structure under two kinds of damage sources. The number of pores under high temperature damage with a relaxation time of 0.1–10 ms is greater than the number of pores under mechanical damage. And the main peak of T2 spectrum shiftes to the right as the temperature increases. However, the main peak of T2 spectrum hardly changes with the increase of load, indicating that the increase in temperature can aggravate the damage more than mechanical. And the new pore diameter increases continuously under each temperature. The main peak of T2 spectrum and pore size distribution increase with temperature increasing, and decrease at first and then increase with increasing load, which indicates that the high temperature directly causes damages to the concrete, while the mechanical makes the concrete dense at first and then damage. The same conclusion is obtained by electron microscope observation.
In order to study the pore structure change characteristics of basalt fiber reinforced concrete under two sources of damage, high temperature and mechanics, nuclear magnetic resonance(NMR) and scanning electron microscopy(SEM) techniques were used to observe the T2 spectrum distribution, pore size distribution and flaw development of the basalt fiber reinforced concrete. The results show that normal concrete, short basalt fiber reinforced concrete and long basalt fiber reinforced concrete show a trend of decreasing the number of micropores and increasing the number of mesopores after high temperature. By comparison, it is found that long basalt fiber reinforced concrete has the largest number of pores in the main peak of the T2 spectrum and the largest pore size distribution. The long basalt fiber reinforced concrete was taken as an example to illustrate the change characteristics of pore structure under two kinds of damage sources. The number of pores under high temperature damage with a relaxation time of 0.1–10 ms is greater than the number of pores under mechanical damage. And the main peak of T2 spectrum shiftes to the right as the temperature increases. However, the main peak of T2 spectrum hardly changes with the increase of load, indicating that the increase in temperature can aggravate the damage more than mechanical. And the new pore diameter increases continuously under each temperature. The main peak of T2 spectrum and pore size distribution increase with temperature increasing, and decrease at first and then increase with increasing load, which indicates that the high temperature directly causes damages to the concrete, while the mechanical makes the concrete dense at first and then damage. The same conclusion is obtained by electron microscope observation.
2020, 37(9): 2294-2302.
doi: 10.13801/j.cnki.fhclxb.20200111.002
Abstract:
In order to investigate the effects of freeze-thaw cycles on the interface bonding performance of carbon fiber reinforced polymer composite(CFRP)-sintered clay brick, a single-sided shear test was conducted on the test specimens after different times of freeze-thaw cycles by simulating the natural freeze-thaw environment. The test results show that under the action of freeze-thaw cycles, the bond performance of the CFRP-sintered clay brick has been obviously degraded. Therefore, as the number of freeze-thaw cycles increases, the interface bearing capacity and shear stress continuously decrease. The distribution of the interface shear stress under different freeze-thaw times is similar, and they all show that the shear stress gradually passes from the loading end to the free end, while the effective transfer length doesn’t change significantly. Based on the existing interface theory, the interface bond-slip model considering the freeze-thaw cycles was proposed according to the experiment. Through contrast analysis, the model can well reflect the degradation law of the interface bond performance under the action of freeze-thaw cycles.
In order to investigate the effects of freeze-thaw cycles on the interface bonding performance of carbon fiber reinforced polymer composite(CFRP)-sintered clay brick, a single-sided shear test was conducted on the test specimens after different times of freeze-thaw cycles by simulating the natural freeze-thaw environment. The test results show that under the action of freeze-thaw cycles, the bond performance of the CFRP-sintered clay brick has been obviously degraded. Therefore, as the number of freeze-thaw cycles increases, the interface bearing capacity and shear stress continuously decrease. The distribution of the interface shear stress under different freeze-thaw times is similar, and they all show that the shear stress gradually passes from the loading end to the free end, while the effective transfer length doesn’t change significantly. Based on the existing interface theory, the interface bond-slip model considering the freeze-thaw cycles was proposed according to the experiment. Through contrast analysis, the model can well reflect the degradation law of the interface bond performance under the action of freeze-thaw cycles.
2020, 37(9): 2303-2313.
doi: 10.13801/j.cnki.fhclxb.20191213.002
Abstract:
In order to study the effect of different macro fibers (including macro polypropylene fiber, macro steel fiber and hybrid fiber of polypropylene fiber and steel fiber) on the flexural toughness and crack surface topography of concrete, three-point bending test was conducted on notched beams in accordance with RILEM TC 162-TDF[10 ]. The laser scanning equipment was utilized to measure the information of crack surface topography. The four roughness parameters (roughness number (RN), fractal dimension (D), standard deviation of height distribution (σz) and crack tortuosity (τ)) were calculated according to the information of crack surface topography and the correlation between four crack roughness parameters and flexural toughness parameters were then analyzed and compared. The results show that with the increasing of fiber content, the flexural toughness and crack surface roughness increase. Compared to polypropylene fiber and steel fiber, the hybrid fiber illustrates the positive synergistic effect on the flexural toughness and crack surface roughness of concrete. Compared to ractal dimension D, standard deviation of height distribution σz and crack tortuosity τ, the correlation between RN and flexural toughness of fiber reinforced concrete beam is the most satisfactory. Meanwhile, the relationship between roughness number RN and flexural toughness parameters follows the exponential function, which can be applied to quickly estimate crack surface roughness by the bending test of fiber reinforced concrete.
In order to study the effect of different macro fibers (including macro polypropylene fiber, macro steel fiber and hybrid fiber of polypropylene fiber and steel fiber) on the flexural toughness and crack surface topography of concrete, three-point bending test was conducted on notched beams in accordance with RILEM TC 162-TDF[
2020, 37(9): 2314-2323.
doi: 10.13801/j.cnki.fhclxb.20191213.001
Abstract:
In order to study the effects of macro fibers on the crack permeability evolution of concrete under loading, the splitting test was adopted to generate cracks on the concrete specimens. The crack permeability of different crack widths was measured in real time using the vacuum permeability test. The laser scanning equipment was adopted for the measurement of information and the reconstruction of the topography of crack surface. The effects of macro steel fiber, macro polypropylene fiber and hybrid fiber(including macro polypropylene fiber and macro steel fiber) on the crack permeability of concrete and the topography of crack surface were analyzed and compared. The results show that the macro fibers increase the crack surface roughness of concrete and indirectly decrease the crack permeability of concrete. With the increasing of fiber content, the crack permeability decreases. Compared to mono fiber reinforcement, the crack surface of hybrid fiber reinforced concrete is rough and the crack permeability of hybrid fiber reinforced concrete is small. With the increase of crack width, the crack permeability is closer to the value predicted by the Poiseuille flow model. Compared to modified factor ξ of Poiseuille flow model, parameter α of permeability is suitable for quantifying the effect of macro fibers on the crack permeability of concrete.
In order to study the effects of macro fibers on the crack permeability evolution of concrete under loading, the splitting test was adopted to generate cracks on the concrete specimens. The crack permeability of different crack widths was measured in real time using the vacuum permeability test. The laser scanning equipment was adopted for the measurement of information and the reconstruction of the topography of crack surface. The effects of macro steel fiber, macro polypropylene fiber and hybrid fiber(including macro polypropylene fiber and macro steel fiber) on the crack permeability of concrete and the topography of crack surface were analyzed and compared. The results show that the macro fibers increase the crack surface roughness of concrete and indirectly decrease the crack permeability of concrete. With the increasing of fiber content, the crack permeability decreases. Compared to mono fiber reinforcement, the crack surface of hybrid fiber reinforced concrete is rough and the crack permeability of hybrid fiber reinforced concrete is small. With the increase of crack width, the crack permeability is closer to the value predicted by the Poiseuille flow model. Compared to modified factor ξ of Poiseuille flow model, parameter α of permeability is suitable for quantifying the effect of macro fibers on the crack permeability of concrete.
2020, 37(9): 2324-2335.
doi: 10.13801/j.cnki.fhclxb.20200212.002
Abstract:
Fixed tensile, tensile and shear tests were carried out on styrene-acrylic emulsion-based cement composite specimens with six different cement-powder ratios to measure the elastic recovery rate, tensile and shear mechanical performance indicators, deformation performance indicators, energy consumption performance indicators and load displacement of the specimens, thereby the effects of cement-powder ratio on the fixed tensile bonding performance, tensile mechanical properties, shear mechanical properties and failure forms of the specimens were studied. And the microscopic mechanism of cement-powder ratio influencing on the mechanical properties and failure forms of the composite was analyzed based on the results of FE-SEM test and Mercury Intrusion Porosimeter(MIP) test. The results show that increasing the cement-powder ratio appropriately can improve the microstructure and optimize the pore structure of the composite. In addition, it can also improve the compactness and significantly enhance the mechanical properties of the composite. With the increase of the cement-powder ratio, the fixed tensile and bonding performance of the specimens gradually decreases, the tensile and shear mechanical performance are continuously improved, and the tensile and shear deformation performance and energy consumption performance of the specimens firstly increase and then decrease. When the cement-powder ratio is between 30% and 35%, the tensile and shear mechanical properties of the specimens are the best. When the cement-powder ratio is 45%, the tensile and shear deformation performance and energy consumption performance of the specimens are worse than the specimens with the cement-powder ratio of 20%. As the cement-powder ratio increases, the load displacement that the specimens can withstand gradually increases firstly and decreases, and the failure form of the specimens gradually changes from “cohesive failure” to “bond failure”.
Fixed tensile, tensile and shear tests were carried out on styrene-acrylic emulsion-based cement composite specimens with six different cement-powder ratios to measure the elastic recovery rate, tensile and shear mechanical performance indicators, deformation performance indicators, energy consumption performance indicators and load displacement of the specimens, thereby the effects of cement-powder ratio on the fixed tensile bonding performance, tensile mechanical properties, shear mechanical properties and failure forms of the specimens were studied. And the microscopic mechanism of cement-powder ratio influencing on the mechanical properties and failure forms of the composite was analyzed based on the results of FE-SEM test and Mercury Intrusion Porosimeter(MIP) test. The results show that increasing the cement-powder ratio appropriately can improve the microstructure and optimize the pore structure of the composite. In addition, it can also improve the compactness and significantly enhance the mechanical properties of the composite. With the increase of the cement-powder ratio, the fixed tensile and bonding performance of the specimens gradually decreases, the tensile and shear mechanical performance are continuously improved, and the tensile and shear deformation performance and energy consumption performance of the specimens firstly increase and then decrease. When the cement-powder ratio is between 30% and 35%, the tensile and shear mechanical properties of the specimens are the best. When the cement-powder ratio is 45%, the tensile and shear deformation performance and energy consumption performance of the specimens are worse than the specimens with the cement-powder ratio of 20%. As the cement-powder ratio increases, the load displacement that the specimens can withstand gradually increases firstly and decreases, and the failure form of the specimens gradually changes from “cohesive failure” to “bond failure”.
2020, 37(9): 2336-2347.
doi: 10.13801/j.cnki.fhclxb.20200201.001
Abstract:
The cube compressive test, axial compressive test and splitting tensile test were conducted on 270 polypropylene-steel fiber/concrete test blocks with polypropylene fiber content (volume fraction) of 0vol%, 0.1vol%, 0.2vol%, 0.3vol%, 0.4vol%, 0.5vol% and steel fiber content (volume fraction) of 0vol%, 0.5vol%, 1vol%, 1.5vol% and 2vol% respectively. Based on the mechanical theory of polypropylene-steel fiber/concrete composites, the strength prediction model was established considering the fiber orientation coefficient, effective length coefficient and interfacial bond coefficient. The mechanism was also analyzed. Six polypropylene-steel fiber/concrete columns were made from polypropylene fiber with a content of 0vol%, 0.1vol%, 0.3vol% and steel fiber with a content of 0vol%, 1.5vol% to perform large eccentric compression test. On the basis of strength prediction model, the bearing capacity of polypropylene-steel fiber/concrete was calculated. The results show that steel fiber can improve the compressive strength, axial compressive strength and splitting tensile strength of polypropylene-steel fiber/concrete. Polypropylene fiber can improve the splitting tensile strength of polypropylene-steel fiber/concrete, but can’t improve the compressive strength. The ultimate bearing capacity of concrete columns can be effectively increased by adding polypropylene-steel fibers.
The cube compressive test, axial compressive test and splitting tensile test were conducted on 270 polypropylene-steel fiber/concrete test blocks with polypropylene fiber content (volume fraction) of 0vol%, 0.1vol%, 0.2vol%, 0.3vol%, 0.4vol%, 0.5vol% and steel fiber content (volume fraction) of 0vol%, 0.5vol%, 1vol%, 1.5vol% and 2vol% respectively. Based on the mechanical theory of polypropylene-steel fiber/concrete composites, the strength prediction model was established considering the fiber orientation coefficient, effective length coefficient and interfacial bond coefficient. The mechanism was also analyzed. Six polypropylene-steel fiber/concrete columns were made from polypropylene fiber with a content of 0vol%, 0.1vol%, 0.3vol% and steel fiber with a content of 0vol%, 1.5vol% to perform large eccentric compression test. On the basis of strength prediction model, the bearing capacity of polypropylene-steel fiber/concrete was calculated. The results show that steel fiber can improve the compressive strength, axial compressive strength and splitting tensile strength of polypropylene-steel fiber/concrete. Polypropylene fiber can improve the splitting tensile strength of polypropylene-steel fiber/concrete, but can’t improve the compressive strength. The ultimate bearing capacity of concrete columns can be effectively increased by adding polypropylene-steel fibers.
2020, 37(9): 2348-2357.
doi: 10.13801/j.cnki.fhclxb.20200212.003
Abstract:
In order to investigate the flexural behaviors and the calculation method of the flexural capacity of steel fiber reinforced concrete(SF/concrete) beams with hybrid glass fiber reinforced polymer composites(GFRP) and steel bars, the proposed formula of the boundary reinforcement ration and the flexural capacity of hybrid reinforced SF/concrete beams were derived on the basis of considering the tensile strength of concrete in the tension zone. Based on this, three kinds of SF/concrete beams with different reinforcement methods were designed and fabricated, and the influence of the hybrid reinforcement ration and the area ratio of GFRP bars to steel bars(Af/As) on the failure modes and the flexural capacity of test beams were mainly discussed. At the same time, the variation characteristics of the flexural behaviors of the hybrid reinforced concrete beams under different concrete strengths were compared and analyzed by relying on relevant test data. The results of the test and the comparative analysis show that the cross section of the hybrid reinforced SF/concrete beams still conform to the flat section assumption. The flexural capacity and the mid-span deflection of the hybrid reinforced SF/concrete beams under the same reinforcement form increase with the increase of the area ratio of GFRP bars to steel bars Af/As. The flexural capacity of the concrete beams with single-layer reinforcement is larger than that of the double-layer reinforcement. Reasonably increasing the concrete strength can further improve the flexural capacity of the hybrid reinforced concrete beams while fully satisfying the tensile effect of GFRP bars. The reliability of the failure modes of the hybrid reinforced concrete beams predicted by the theory of boundary reinforcement ration is higher. The predicted values of the proposed calculation formula of the flexural capacity are in good agreement with the experimentally measured values, and it has good applicability.
In order to investigate the flexural behaviors and the calculation method of the flexural capacity of steel fiber reinforced concrete(SF/concrete) beams with hybrid glass fiber reinforced polymer composites(GFRP) and steel bars, the proposed formula of the boundary reinforcement ration and the flexural capacity of hybrid reinforced SF/concrete beams were derived on the basis of considering the tensile strength of concrete in the tension zone. Based on this, three kinds of SF/concrete beams with different reinforcement methods were designed and fabricated, and the influence of the hybrid reinforcement ration and the area ratio of GFRP bars to steel bars(Af/As) on the failure modes and the flexural capacity of test beams were mainly discussed. At the same time, the variation characteristics of the flexural behaviors of the hybrid reinforced concrete beams under different concrete strengths were compared and analyzed by relying on relevant test data. The results of the test and the comparative analysis show that the cross section of the hybrid reinforced SF/concrete beams still conform to the flat section assumption. The flexural capacity and the mid-span deflection of the hybrid reinforced SF/concrete beams under the same reinforcement form increase with the increase of the area ratio of GFRP bars to steel bars Af/As. The flexural capacity of the concrete beams with single-layer reinforcement is larger than that of the double-layer reinforcement. Reasonably increasing the concrete strength can further improve the flexural capacity of the hybrid reinforced concrete beams while fully satisfying the tensile effect of GFRP bars. The reliability of the failure modes of the hybrid reinforced concrete beams predicted by the theory of boundary reinforcement ration is higher. The predicted values of the proposed calculation formula of the flexural capacity are in good agreement with the experimentally measured values, and it has good applicability.
2020, 37(9): 2358-2366.
doi: 10.13801/j.cnki.fhclxb.20191223.002
Abstract:
The compressive strength of fiber reinforced polymer(FRP) confined concrete is an important parameter in the design of FRP strengthen concrete structure. Most existing compressive strength models of FRP-confined concrete column were obtained by regression analysis of experimental data, and only few models were established based on theoretical derivation method. Therefore, it is necessary to expand the compressive strength model, which is established based on theoretical derivation. In this paper, the existing models of compressive strength of FRP-confined concrete columns were summarized and evaluated with a large number of published experimental data. Then based on the Griffith failure criterion, a unified model that could predict the compressive strength of both FRP-confined undamaged and damaged concrete was proposed and evaluated. The evaluation results show that the new compressive strength model can accurately predict the compressive strength of FRP-confined undamaged and damaged concrete.
The compressive strength of fiber reinforced polymer(FRP) confined concrete is an important parameter in the design of FRP strengthen concrete structure. Most existing compressive strength models of FRP-confined concrete column were obtained by regression analysis of experimental data, and only few models were established based on theoretical derivation method. Therefore, it is necessary to expand the compressive strength model, which is established based on theoretical derivation. In this paper, the existing models of compressive strength of FRP-confined concrete columns were summarized and evaluated with a large number of published experimental data. Then based on the Griffith failure criterion, a unified model that could predict the compressive strength of both FRP-confined undamaged and damaged concrete was proposed and evaluated. The evaluation results show that the new compressive strength model can accurately predict the compressive strength of FRP-confined undamaged and damaged concrete.
2020, 37(9): 2077-2093.
doi: 10.13801/j.cnki.fhclxb.20200423.002
Abstract:
Incorporating functional fillers into the cement-based material can enable them to obtain the thermoelectric effect of converting thermal energy into electrical energy, which can be used in energy harvesting, concrete structure health monitoring and intelligent transportation system. This paper summarizes the thermoelectric effect mechanism, functional fillers, fabrication process and engineering application of thermoelectric cement-based composites (TECC). Particularly, this paper mainly focuses on the enhancement effect and mechanism of different functional fillers on the thermoelectric effect of TECC, as well as the effect of dispersion degree of functional filler, moisture, fatigue load, temperature cycle and other factors on the thermoelectric effect of TECC. This review points out the new research direction of TECC in theory and application, which will guide the experimental design and performance improvement of the thermoelectric effect of cement-based composites.
Incorporating functional fillers into the cement-based material can enable them to obtain the thermoelectric effect of converting thermal energy into electrical energy, which can be used in energy harvesting, concrete structure health monitoring and intelligent transportation system. This paper summarizes the thermoelectric effect mechanism, functional fillers, fabrication process and engineering application of thermoelectric cement-based composites (TECC). Particularly, this paper mainly focuses on the enhancement effect and mechanism of different functional fillers on the thermoelectric effect of TECC, as well as the effect of dispersion degree of functional filler, moisture, fatigue load, temperature cycle and other factors on the thermoelectric effect of TECC. This review points out the new research direction of TECC in theory and application, which will guide the experimental design and performance improvement of the thermoelectric effect of cement-based composites.
2020, 37(9): 2094-2104.
doi: 10.13801/j.cnki.fhclxb.20200115.002
Abstract:
The hollow glass microspheres(HGM) were used as additives to prepare a series of HGM/rigid polyurethane foam(RPUF) composites by one-step water-blown method. SEM, TG, limiting oxygen index(LOI) and horizontal combustion were applied to investigate the cell structure, char layer morphology, thermal stability and flame retardancy of the HGM/RPUF composites. The universal material testing machine was applied to study the compressive strength and compressive elastic modulus of the HGM/RPUF composites. Thermogravimetric analysis-Fourier transform infrared spectrophotometer(TG-FTIR) was applied to investigate the gaseous phase products of the HGM/RPUF composites. The results show that the HGM work as nucleating agent, which can reduce the pore diameter of the HGM/RPUF composites. In combustion, the HGM particles migrate to the surface of the char layer, promoting the formation of the compact char layer. When 5.4wt% of HGM were added, the compressive strength and compressive elastic modulus of the HGM/RPUF composites are increased to 0.14 MPa and 4.53 MPa, respectively, which are increased by 37.30% and 67.16% compared with those of the RPUF. At the same time, it is found that the HGM can significantly inhibit the release of toxic CO in combustion process, enhancing the fire safety of the HGM/RPUF composites.
The hollow glass microspheres(HGM) were used as additives to prepare a series of HGM/rigid polyurethane foam(RPUF) composites by one-step water-blown method. SEM, TG, limiting oxygen index(LOI) and horizontal combustion were applied to investigate the cell structure, char layer morphology, thermal stability and flame retardancy of the HGM/RPUF composites. The universal material testing machine was applied to study the compressive strength and compressive elastic modulus of the HGM/RPUF composites. Thermogravimetric analysis-Fourier transform infrared spectrophotometer(TG-FTIR) was applied to investigate the gaseous phase products of the HGM/RPUF composites. The results show that the HGM work as nucleating agent, which can reduce the pore diameter of the HGM/RPUF composites. In combustion, the HGM particles migrate to the surface of the char layer, promoting the formation of the compact char layer. When 5.4wt% of HGM were added, the compressive strength and compressive elastic modulus of the HGM/RPUF composites are increased to 0.14 MPa and 4.53 MPa, respectively, which are increased by 37.30% and 67.16% compared with those of the RPUF. At the same time, it is found that the HGM can significantly inhibit the release of toxic CO in combustion process, enhancing the fire safety of the HGM/RPUF composites.
2020, 37(9): 2105-2116.
doi: 10.13801/j.cnki.fhclxb.20200210.002
Abstract:
Using nanocellulose(CNF), carboxylated carbon nanotubes(CNTs—COOH), pencil graphite(PGr) and polypyrrole(PPy) as raw materials, the CNF-CNTs—COOH-PGr/PPy flexible electrode composite with graphite layer structure was prepared by vacuum filtration, coating, oxidative polymerization and based on the principle of hydrogen bonding interface interaction. The results show that the CNF-CNTs—COOH-PGr/PPy flexible electrode composite does not break when it is flatted, folded and stretched, and exhibits strong mechanical properties, and its tensile strength reaches 28.90 MPa. The porous structure of hydrophilic CNF and CNTs—COOH enhances the diffusion path of ions and electrons. The addition of PGr effectively improves the conductive path of CNF-CNTs—COOH-PGr/PPy flexible electrode composite and gives it excellent conductive properties. The conductivity of CNF-CNTs—COOH-PGr/PPy flexible electrode composite obtained after the oxidative polymerization reaches 5.403 S·cm−1. In the 1 mol·L−1 H2SO4 solution, the CNF-CNTs—COOH-PGr/PPy flexible electrode composite has a high specific capacitance of 521 F·g−1 at the current density of 0.5 A·g−1. And its capacitance retention rate is as high as 68% after 1 500 charge and discharge cycles. Based on the excellent mechanical properties, the electrochemical properties and electrical conductivity of the flexible electrodes, the CNF-CNTs—COOH-PGr/PPy flexible electrode composite has the basis characteristics for becoming the electrode material for flexible energy storage devices.
Using nanocellulose(CNF), carboxylated carbon nanotubes(CNTs—COOH), pencil graphite(PGr) and polypyrrole(PPy) as raw materials, the CNF-CNTs—COOH-PGr/PPy flexible electrode composite with graphite layer structure was prepared by vacuum filtration, coating, oxidative polymerization and based on the principle of hydrogen bonding interface interaction. The results show that the CNF-CNTs—COOH-PGr/PPy flexible electrode composite does not break when it is flatted, folded and stretched, and exhibits strong mechanical properties, and its tensile strength reaches 28.90 MPa. The porous structure of hydrophilic CNF and CNTs—COOH enhances the diffusion path of ions and electrons. The addition of PGr effectively improves the conductive path of CNF-CNTs—COOH-PGr/PPy flexible electrode composite and gives it excellent conductive properties. The conductivity of CNF-CNTs—COOH-PGr/PPy flexible electrode composite obtained after the oxidative polymerization reaches 5.403 S·cm−1. In the 1 mol·L−1 H2SO4 solution, the CNF-CNTs—COOH-PGr/PPy flexible electrode composite has a high specific capacitance of 521 F·g−1 at the current density of 0.5 A·g−1. And its capacitance retention rate is as high as 68% after 1 500 charge and discharge cycles. Based on the excellent mechanical properties, the electrochemical properties and electrical conductivity of the flexible electrodes, the CNF-CNTs—COOH-PGr/PPy flexible electrode composite has the basis characteristics for becoming the electrode material for flexible energy storage devices.
2020, 37(9): 2117-2124.
doi: 10.13801/j.cnki.fhclxb.20200115.001
Abstract:
In order to improve the toughness of resin transfer molding(RTM) composites, combining the “ex-situ” composite toughening technology and RTM processing, a novel thermoplastic phosphorus-containing polyaryletherketone(PAEK-P) was used to toughen the carbon fiber/bismaleimide resin(CF/BMI) composites. The rheological properties, phase separation behavior of the PAEK-P-BMI resin and the effect of PAEK-P upon the toughness of the CF/BMI composites were investigated. The results show that the PAEK-P resin has high heat resistance at the glass transition temperature of 268.8℃ for its rigid structure. The gel time and viscosity increase inflection point time of the PAEK-P-BMI composite resin are little affected by the PAEK-P content because of its poor solubility in BMI resin. The PAEK-P-BMI composite resin shows no phase separation at 110℃/300 min. However, the phase separation structure is formed in the late high temperature curing process, and the phase separation morphology is maintained in the cured CF/PAEK-P-BMI composites. Compared with CF/BMI composites, the CF/PAEK-P-BMI composites have a 69% reduction in damage area after impact, a 16.6% increase in compressive strength after impact, and a 34.4% reduction in impact pit depth.
In order to improve the toughness of resin transfer molding(RTM) composites, combining the “ex-situ” composite toughening technology and RTM processing, a novel thermoplastic phosphorus-containing polyaryletherketone(PAEK-P) was used to toughen the carbon fiber/bismaleimide resin(CF/BMI) composites. The rheological properties, phase separation behavior of the PAEK-P-BMI resin and the effect of PAEK-P upon the toughness of the CF/BMI composites were investigated. The results show that the PAEK-P resin has high heat resistance at the glass transition temperature of 268.8℃ for its rigid structure. The gel time and viscosity increase inflection point time of the PAEK-P-BMI composite resin are little affected by the PAEK-P content because of its poor solubility in BMI resin. The PAEK-P-BMI composite resin shows no phase separation at 110℃/300 min. However, the phase separation structure is formed in the late high temperature curing process, and the phase separation morphology is maintained in the cured CF/PAEK-P-BMI composites. Compared with CF/BMI composites, the CF/PAEK-P-BMI composites have a 69% reduction in damage area after impact, a 16.6% increase in compressive strength after impact, and a 34.4% reduction in impact pit depth.
2020, 37(9): 2125-2136.
doi: 10.13801/j.cnki.fhclxb.20200512.001
Abstract:
The PW12O40-ZnAl layered double hydroxides(LDHs) was prepared by using [PW12O40]3− ion pillared intercalation NO3-ZnAl LDHs. The composition and structure were analyzed by XRD, FTIR, inductively coupled plasma(ICP) and SEM. The flame retardant epoxy-polyamide resin(EP-PA) were prepared by NO3-ZnAl LDHs or PW12O40-ZnAl LDHs compound with intumescent flame retardants(IFRs) containing ammonium polyphosphate, melamine, pentaerythritol. The heat and smoke release rules of different ZnAl LDHs-IFRs flame retardant EP-PA were evaluated by back temperature experiment and cone calorimetry experiment. TGA result shows that the maximum degradation rate of PW12O40-ZnAl-IFRs/(EP-PA) composite is the lowest, and the carbon residue rate is the highest, which indicate that PW12O40-ZnAl LDHs improve the oxidation resistance of PW12O40-ZnAl-IFRs/(EP-PA) composite at high temperature. The back temperature experiment results show that under the same heat radiation intensity, the back temperature of PW12O40-ZnAl-IFRs/(EP-PA) composite reaches to 200℃ and 300℃ with the longest time and the lowest rate of back temperature rise. The results show that PW12O40-ZnAl LDHs can obviously enhance the fire resistance of EP-PA. From cone calorimetry experimental data, it can be seen that PW12O40-ZnAl-IFRs makes PW12O40-ZnAl-IFRs/(EP-PA) composite have the lowest peak of heat release rate(PHRR), mean heat release rate(MHRR), mean effective heat of combustion(MEHC) and total heat release(THR). Its fire growth index (FGI) is only 14.5% of IFRs/(EP-PA) composite, and the total smoke production (TSP) is 27.6% lower than NO3-ZnAl-IFRs/(EP-PA) composite and 55.3% lower than IFRs/(EP-PA) composite. The results suggest that PW12O40-ZnAl-IFRs is more effective than NO3-ZnAl-IFRs in reducing the heat release and inhibiting the generation of flue gas.
The PW12O40-ZnAl layered double hydroxides(LDHs) was prepared by using [PW12O40]3− ion pillared intercalation NO3-ZnAl LDHs. The composition and structure were analyzed by XRD, FTIR, inductively coupled plasma(ICP) and SEM. The flame retardant epoxy-polyamide resin(EP-PA) were prepared by NO3-ZnAl LDHs or PW12O40-ZnAl LDHs compound with intumescent flame retardants(IFRs) containing ammonium polyphosphate, melamine, pentaerythritol. The heat and smoke release rules of different ZnAl LDHs-IFRs flame retardant EP-PA were evaluated by back temperature experiment and cone calorimetry experiment. TGA result shows that the maximum degradation rate of PW12O40-ZnAl-IFRs/(EP-PA) composite is the lowest, and the carbon residue rate is the highest, which indicate that PW12O40-ZnAl LDHs improve the oxidation resistance of PW12O40-ZnAl-IFRs/(EP-PA) composite at high temperature. The back temperature experiment results show that under the same heat radiation intensity, the back temperature of PW12O40-ZnAl-IFRs/(EP-PA) composite reaches to 200℃ and 300℃ with the longest time and the lowest rate of back temperature rise. The results show that PW12O40-ZnAl LDHs can obviously enhance the fire resistance of EP-PA. From cone calorimetry experimental data, it can be seen that PW12O40-ZnAl-IFRs makes PW12O40-ZnAl-IFRs/(EP-PA) composite have the lowest peak of heat release rate(PHRR), mean heat release rate(MHRR), mean effective heat of combustion(MEHC) and total heat release(THR). Its fire growth index (FGI) is only 14.5% of IFRs/(EP-PA) composite, and the total smoke production (TSP) is 27.6% lower than NO3-ZnAl-IFRs/(EP-PA) composite and 55.3% lower than IFRs/(EP-PA) composite. The results suggest that PW12O40-ZnAl-IFRs is more effective than NO3-ZnAl-IFRs in reducing the heat release and inhibiting the generation of flue gas.
2020, 37(9): 2137-2143.
doi: 10.13801/j.cnki.fhclxb.20200210.001
Abstract:
To reduce the dielectric loss(tanδ) and increase the dielectric breakdown strength(Eb) of silicon particles/poly(vinylidene fluoride)(Si/PVDF) composites, two kinds of core-shell structured Si particles, i.e., Si@SiO2 and Si@SiO2@PS were prepared by high temperature oxidation and polystyrene(PS) coating. The FTIR, XRD and TEM measurements were used to characterize the formed shell structure. The measurements results verify the existence of SiO2 and SiO2@PS shells on the surface of Si. The results show that the Si@SiO2 interlayer significantly suppresses the tanδ and reduces the leakage conductivity of the Si@SiO2/PVDF composites compared with Si/PVDF composites, and the double-shell Si@SiO2@PS/PVDF composites exhibit the lowest tanδ and the highest Eb among the three composites because the organic PS interlayer enhances the interfacial compatibility and promotes the fillers’ homogeneous dispersion in PVDF. The improvement in dielectric properties of Si@SiO2/PVDF and Si@SiO2@PS/PVDF composites can be ascribed to the facts that the insulating SiO2 and SiO2@PS shells effectively prevent the semi-conducting Si particles from direct contacting, thereby remarkably reducing the tanδ. The enhanced phase interfacial compatibility between the Si@SiO2 or Si@SiO2@PS and PVDF matrix reduces the interface defects and suppresses the local electrical field distortion, thereby improving Eb of the core-shell structured Si/PVDF composites. The prepared Si@SiO2@PS/PVDF composites with a high dielectric constant of 48 and tanδ of 0.07, Eb of 6 kV/mm, have potential applications in the field of microelectronic devices and power equipment.
To reduce the dielectric loss(tanδ) and increase the dielectric breakdown strength(Eb) of silicon particles/poly(vinylidene fluoride)(Si/PVDF) composites, two kinds of core-shell structured Si particles, i.e., Si@SiO2 and Si@SiO2@PS were prepared by high temperature oxidation and polystyrene(PS) coating. The FTIR, XRD and TEM measurements were used to characterize the formed shell structure. The measurements results verify the existence of SiO2 and SiO2@PS shells on the surface of Si. The results show that the Si@SiO2 interlayer significantly suppresses the tanδ and reduces the leakage conductivity of the Si@SiO2/PVDF composites compared with Si/PVDF composites, and the double-shell Si@SiO2@PS/PVDF composites exhibit the lowest tanδ and the highest Eb among the three composites because the organic PS interlayer enhances the interfacial compatibility and promotes the fillers’ homogeneous dispersion in PVDF. The improvement in dielectric properties of Si@SiO2/PVDF and Si@SiO2@PS/PVDF composites can be ascribed to the facts that the insulating SiO2 and SiO2@PS shells effectively prevent the semi-conducting Si particles from direct contacting, thereby remarkably reducing the tanδ. The enhanced phase interfacial compatibility between the Si@SiO2 or Si@SiO2@PS and PVDF matrix reduces the interface defects and suppresses the local electrical field distortion, thereby improving Eb of the core-shell structured Si/PVDF composites. The prepared Si@SiO2@PS/PVDF composites with a high dielectric constant of 48 and tanδ of 0.07, Eb of 6 kV/mm, have potential applications in the field of microelectronic devices and power equipment.
2020, 37(9): 2144-2151.
doi: 10.13801/j.cnki.fhclxb.20191219.002
Abstract:
Three silane coupling agents with different hydrophobic groups, namely phenyl-containing coupling agent 1(Ph-1), fluorine-containing coupling agent 2(F-2) and a glycidoxy-containing coupling agent 3(GP-3) were used to modify SiO2. The SiO2/polytetrafluoroethylene(PTFE) composite films with 35wt% SiO2 and thickness of 50 μm were prepared by air-assisted dry blending, cold-pressing, sintering and skiving techniques. The dispersion of SiO2 throughout the PTFE matrix is uniform after the modification. The effects of F-2 contents on the properties of SiO2/PTFE composite film were studied. The results show that when the content(mass ratio to SiO2) of the coupling agent is 0.3%, the pinhole defects of SiO2/PTFE composite film are rarely observed, and the tensile strength increases from 9.2 MPa to 16.2 MPa. Meanwhile, the dielectric constant decreases from 2.475 to 2.416 at 10 GHz, and the dielectric loss decreases from 2.66×10−3 to 2.01×10−3, exhibiting improved dielectric properties.
Three silane coupling agents with different hydrophobic groups, namely phenyl-containing coupling agent 1(Ph-1), fluorine-containing coupling agent 2(F-2) and a glycidoxy-containing coupling agent 3(GP-3) were used to modify SiO2. The SiO2/polytetrafluoroethylene(PTFE) composite films with 35wt% SiO2 and thickness of 50 μm were prepared by air-assisted dry blending, cold-pressing, sintering and skiving techniques. The dispersion of SiO2 throughout the PTFE matrix is uniform after the modification. The effects of F-2 contents on the properties of SiO2/PTFE composite film were studied. The results show that when the content(mass ratio to SiO2) of the coupling agent is 0.3%, the pinhole defects of SiO2/PTFE composite film are rarely observed, and the tensile strength increases from 9.2 MPa to 16.2 MPa. Meanwhile, the dielectric constant decreases from 2.475 to 2.416 at 10 GHz, and the dielectric loss decreases from 2.66×10−3 to 2.01×10−3, exhibiting improved dielectric properties.
2020, 37(9): 2152-2162.
doi: 10.13801/j.cnki.fhclxb.20200429.002
Abstract:
The carbon fiber/polyimide composite rudder was designed. And the PAM-RTM software was used to simulate the resin flow of the rudder during the injection process. The forming die was designed according to the simulation results. The high-temperature resistant carbon fiber/polyimide composite rudder was fabricated via resin transfer molding (RTM) process accordingly and the mechanical properties under bending load were investigated to compare with the 3D finite element analysis (FEA) results. The experimental results show that the carbon fiber/polyimide composite rudder maintains the structural integrity under 150% of the service load. The maximum strain of the metal skeleton is 2 408×10–6, and the maximum strain of the carbon fiber/polyimide composite skin is 2 371×10–6. The FEA results reveal that the maximum stress of the metal skeleton appears at the arc transitional region of the rudder shaft root, while the maximum stress of the carbon fiber/polyimide composite skin emerges in the resin junctional area of the gasket outer arc. The initial damage of the carbon fiber/polyimide composite rudder is the transverse tensile failure of the skin unidirectional tape.
The carbon fiber/polyimide composite rudder was designed. And the PAM-RTM software was used to simulate the resin flow of the rudder during the injection process. The forming die was designed according to the simulation results. The high-temperature resistant carbon fiber/polyimide composite rudder was fabricated via resin transfer molding (RTM) process accordingly and the mechanical properties under bending load were investigated to compare with the 3D finite element analysis (FEA) results. The experimental results show that the carbon fiber/polyimide composite rudder maintains the structural integrity under 150% of the service load. The maximum strain of the metal skeleton is 2 408×10–6, and the maximum strain of the carbon fiber/polyimide composite skin is 2 371×10–6. The FEA results reveal that the maximum stress of the metal skeleton appears at the arc transitional region of the rudder shaft root, while the maximum stress of the carbon fiber/polyimide composite skin emerges in the resin junctional area of the gasket outer arc. The initial damage of the carbon fiber/polyimide composite rudder is the transverse tensile failure of the skin unidirectional tape.
2020, 37(9): 2163-2172.
doi: 10.13801/j.cnki.fhclxb.20200102.001
Abstract:
The axial tensile failure mechanism of carbon fiber/epoxy composite winding joint was studied by means of experiment and simulation. Based on ABAQUS, the continuum damage model and cohesive zone model were used to simulate each part and interface of the carbon fiber/epoxy composite winding joint, respectively. The progressive damage model of the carbon fiber/epoxy composite was established by writing user-defined material subroutine(UMAT). As a result, the stress distribution and load-displacement curve of the carbon fiber/epoxy composite winding joint were obtained and the failure mechanism of the structure was determined by comparison with the experimental results. The results show that the calculated damage position and failure modes of the carbon fiber/epoxy composite winding joint agree well with the experimental results, and the difference between the calculated value and test value of the failure load is small, which proves the validity of the simulation analysis method. By comparing the failure modes, it is found that under tensile load, the loop plies are the main bearing component, and the curved end of which is the position where the stress is concentrated. The fiber fracture starts from here and gradually spreads outward until the loop plies fracture, which leads to the structural damage.
The axial tensile failure mechanism of carbon fiber/epoxy composite winding joint was studied by means of experiment and simulation. Based on ABAQUS, the continuum damage model and cohesive zone model were used to simulate each part and interface of the carbon fiber/epoxy composite winding joint, respectively. The progressive damage model of the carbon fiber/epoxy composite was established by writing user-defined material subroutine(UMAT). As a result, the stress distribution and load-displacement curve of the carbon fiber/epoxy composite winding joint were obtained and the failure mechanism of the structure was determined by comparison with the experimental results. The results show that the calculated damage position and failure modes of the carbon fiber/epoxy composite winding joint agree well with the experimental results, and the difference between the calculated value and test value of the failure load is small, which proves the validity of the simulation analysis method. By comparing the failure modes, it is found that under tensile load, the loop plies are the main bearing component, and the curved end of which is the position where the stress is concentrated. The fiber fracture starts from here and gradually spreads outward until the loop plies fracture, which leads to the structural damage.
2020, 37(9): 2173-2182.
doi: 10.13801/j.cnki.fhclxb.20200122.001
Abstract:
The interfacial strain of wood fiber/high density polyethylene(WF/HDPE) composites was studied. Digital image correlation(DIC) was used to investigate the effects of WF mass fraction (10wt%–40wt%) and modified ammonium polyphosphate(mAPP) flame retardant mass fraction (10wt%–25wt%) on the strain distribution and transmission evolution of WF/HDPE composites. The mechanical properties and interfacial bonding of WF/HDPE composites were analyzed by mechanical tests and SEM, respectively. With WF mass fraction rising from 10wt% to 30wt%, the strain transfers stably and uniformly from both ends to the axial center of the WF/HDPE composite. When the WF amount reaches 30wt%, the high strain transfers within 1/2 region of WF/HDPE composite and its tensile strength and impact strength are 21.5 MPa and 10.22 kJ/m2, respectively. However, when WF mass fraction is 40wt%, the stress concentration occurs at tensile bearing end of the WF/HDPE composite, and prevents uniform transmission of strain in WF/HDPE composites. mAPP exacerbates debonding and impedes mechanical meshing between WF and HDPE. As WF mass fraction increases from 10wt% to 25wt%, several scattered high strain regions appear and the full-field strain transfers irregularly. When the WF mass fraction reaches 25wt%, the strain distribution of WF/HDPE composite becomes polarized, resulting in a decrease of the tensile strength and impact strength to 15.5 MPa and 5.49 kJ/m2, respectively.
The interfacial strain of wood fiber/high density polyethylene(WF/HDPE) composites was studied. Digital image correlation(DIC) was used to investigate the effects of WF mass fraction (10wt%–40wt%) and modified ammonium polyphosphate(mAPP) flame retardant mass fraction (10wt%–25wt%) on the strain distribution and transmission evolution of WF/HDPE composites. The mechanical properties and interfacial bonding of WF/HDPE composites were analyzed by mechanical tests and SEM, respectively. With WF mass fraction rising from 10wt% to 30wt%, the strain transfers stably and uniformly from both ends to the axial center of the WF/HDPE composite. When the WF amount reaches 30wt%, the high strain transfers within 1/2 region of WF/HDPE composite and its tensile strength and impact strength are 21.5 MPa and 10.22 kJ/m2, respectively. However, when WF mass fraction is 40wt%, the stress concentration occurs at tensile bearing end of the WF/HDPE composite, and prevents uniform transmission of strain in WF/HDPE composites. mAPP exacerbates debonding and impedes mechanical meshing between WF and HDPE. As WF mass fraction increases from 10wt% to 25wt%, several scattered high strain regions appear and the full-field strain transfers irregularly. When the WF mass fraction reaches 25wt%, the strain distribution of WF/HDPE composite becomes polarized, resulting in a decrease of the tensile strength and impact strength to 15.5 MPa and 5.49 kJ/m2, respectively.
2020, 37(9): 2183-2199.
doi: 10.13801/j.cnki.fhclxb.20191207.002
Abstract:
As main aviation materials, there are a lot of assembly relationships between carbon fiber/epoxy composites and aluminum in aircraft structures. However, due to limitation of the composite forming process, assembly gaps will be created between the mating surfaces in the case of manufacturing and assembly deviations. When the gap exceeds a certain size, gap-filling compensation is necessary. Based on the actual structure, the carbon fiber/epoxy composite-aluminum assembly model was abstracted, the assembly test bench was used to simulate the pre-tightening force of the bolt, and the strain gauge and 3D digital image correlation(3D-DIC) experiment were used to compare the strain on the surface under the condition of forced assembly and gap-filling compensation in older to analyze the deformation rule of the component. The interlaminar stress analysis was carried out by finite element method, and the effects of gap-filling compensation on the interlaminar stress and local damage of the carbon fiber/epoxy composite-aluminum assembly structure were studied by extracting the stress components and damage of the cohesive element. The results of experimental and simulation analysis show that with the assembly gap increasing, the strain values increase; Gap-filling compensation improves the strain state caused by the bending deformation, while the strain of the bolt head extrusion zone is also increased. In general, gap-filling compensation makes the strain distribution more uniform and reduces damage of the carbon fiber/epoxy composite, and the liquid shim effect is slightly better than the peelable shim.
As main aviation materials, there are a lot of assembly relationships between carbon fiber/epoxy composites and aluminum in aircraft structures. However, due to limitation of the composite forming process, assembly gaps will be created between the mating surfaces in the case of manufacturing and assembly deviations. When the gap exceeds a certain size, gap-filling compensation is necessary. Based on the actual structure, the carbon fiber/epoxy composite-aluminum assembly model was abstracted, the assembly test bench was used to simulate the pre-tightening force of the bolt, and the strain gauge and 3D digital image correlation(3D-DIC) experiment were used to compare the strain on the surface under the condition of forced assembly and gap-filling compensation in older to analyze the deformation rule of the component. The interlaminar stress analysis was carried out by finite element method, and the effects of gap-filling compensation on the interlaminar stress and local damage of the carbon fiber/epoxy composite-aluminum assembly structure were studied by extracting the stress components and damage of the cohesive element. The results of experimental and simulation analysis show that with the assembly gap increasing, the strain values increase; Gap-filling compensation improves the strain state caused by the bending deformation, while the strain of the bolt head extrusion zone is also increased. In general, gap-filling compensation makes the strain distribution more uniform and reduces damage of the carbon fiber/epoxy composite, and the liquid shim effect is slightly better than the peelable shim.
2020, 37(9): 2200-2206.
doi: 10.13801/j.cnki.fhclxb.20200111.001
Abstract:
Composite materials have been widely used in aircraft structures, and gradually applied to the main load-bearing structures. However, the brittle characteristic of composite materials has brought new challenges for aircraft crashworthiness design and evaluation. As the important energy-absorbing element, the composite stanchions for the cargo floor structure seriously affect the crashworthiness properties of composite fuselage. Composite stanchions can be designed to absorb much more energy through crushing failures than in a brittle global buckling mode. Based on the design requirements of the civil aircraft composite cargo floor stanchion, the trigger configuration, height, section, and section area were evaluated using quasi-static and dynamic crushing tests. The key influence factors of energy absorption characteristic properties for woven T700GC carbon fiber/epoxy composite stanchions were estimated. It provides reference for the structure design.
Composite materials have been widely used in aircraft structures, and gradually applied to the main load-bearing structures. However, the brittle characteristic of composite materials has brought new challenges for aircraft crashworthiness design and evaluation. As the important energy-absorbing element, the composite stanchions for the cargo floor structure seriously affect the crashworthiness properties of composite fuselage. Composite stanchions can be designed to absorb much more energy through crushing failures than in a brittle global buckling mode. Based on the design requirements of the civil aircraft composite cargo floor stanchion, the trigger configuration, height, section, and section area were evaluated using quasi-static and dynamic crushing tests. The key influence factors of energy absorption characteristic properties for woven T700GC carbon fiber/epoxy composite stanchions were estimated. It provides reference for the structure design.
2020, 37(9): 2207-2222.
doi: 10.13801/j.cnki.fhclxb.20200110.002
Abstract:
Based on the continuum damage mechanics, a 3D damage constitutive model which takes into account the nonlinear shear behavior of composites and material properties degradation due to damage development was proposed. The model differentiates between different failure modes, such as fiber failure mode, matrix failure mode and delamination. The damage variables corresponding to each failure mode were defined. The onsets of fiber damage, matrix damage and delamination of composite laminates were predicted using maximum stress failure criteria, Puck’s matrix failure criteria and Hou’s delamination criteria, respectively. In order to predict the angle of fracture surface in Puck’s matrix fracture failure theory, a selective parabola algorithm was proposed and coded using Matlab procedure. Compared with the Puck’s algorithm and the selective range golden section search algorithm, it shows that the selective parabola algorithm effectively reduces the number of calculations and improves the calculation efficiency and accuracy. A strain-driven explicit integration algorithm for the proposed material constitutive model was developed to update stresses and solution dependent state variables. The user-defined material subroutine VUMAT containing the numerical integration algorithm was coded and implemented in the finite element procedure Abaqus v6.14. The efficiency of the material constitutive model was demonstrated through progressive failure analyses of AS4 carbon fiber/3501-6 epoxy composite laminates, the mechanical behavior of which demonstrates significant nonlinear shear effects. The numerical results show that the proposed model is able to predict the mechanical behavior and failure strength of composites with sufficient accuracy. The proposed approach provides an efficient method for the design of composite components and structures.
Based on the continuum damage mechanics, a 3D damage constitutive model which takes into account the nonlinear shear behavior of composites and material properties degradation due to damage development was proposed. The model differentiates between different failure modes, such as fiber failure mode, matrix failure mode and delamination. The damage variables corresponding to each failure mode were defined. The onsets of fiber damage, matrix damage and delamination of composite laminates were predicted using maximum stress failure criteria, Puck’s matrix failure criteria and Hou’s delamination criteria, respectively. In order to predict the angle of fracture surface in Puck’s matrix fracture failure theory, a selective parabola algorithm was proposed and coded using Matlab procedure. Compared with the Puck’s algorithm and the selective range golden section search algorithm, it shows that the selective parabola algorithm effectively reduces the number of calculations and improves the calculation efficiency and accuracy. A strain-driven explicit integration algorithm for the proposed material constitutive model was developed to update stresses and solution dependent state variables. The user-defined material subroutine VUMAT containing the numerical integration algorithm was coded and implemented in the finite element procedure Abaqus v6.14. The efficiency of the material constitutive model was demonstrated through progressive failure analyses of AS4 carbon fiber/3501-6 epoxy composite laminates, the mechanical behavior of which demonstrates significant nonlinear shear effects. The numerical results show that the proposed model is able to predict the mechanical behavior and failure strength of composites with sufficient accuracy. The proposed approach provides an efficient method for the design of composite components and structures.
2020, 37(9): 2223-2229.
doi: 10.13801/j.cnki.fhclxb.20200220.002
Abstract:
In order to study the effect of composite volume fraction on the impact wear properties of composites in architecture composites, the zirconium oxide toughened alumina particles(ZTAP) 3D network reinforced 40Cr steel matrix composites(ZTAP/40Cr architecture composite) with different composite volume fractions(35vol%, 50vol%, 65vol%) were fabricated by squeeze casting, which were subjected to no abrasives impact wear test with an impact energy of 1.5 J after quenching at 850℃ and tempering at 460℃. The results show that when the volume fraction of the composite area is 35vol%, 50vol% and 65vol%, the wear rates of the ZTAP/40Cr architecture composites are 4.7×10−3 cm3/h, 3.4×10−3 cm3/h and 1.0×10−3 cm3/h, respectively. The wear rates of the ZTAP/40Cr composite and the 40Cr steel are 13.41×10−3 cm3/h and 79.87×10−3 cm3/h, respectively. The wear resistance of the ZTAP/40Cr architecture composite increases as the volume fraction of the composite area increases. Further analysis show that the impact wear mechanism of the ZTAP/40Cr architecture composite includes abrasive wear and adhesive wear on the surface, mainly the adhesion of the matrix and the ploughing of the entire surface, as well as the fatigue wear of the subsurface, which is a blockage of materials caused by ZTAP breakage and ZTAP/40Cr interfacial cracking during repeated impact.
In order to study the effect of composite volume fraction on the impact wear properties of composites in architecture composites, the zirconium oxide toughened alumina particles(ZTAP) 3D network reinforced 40Cr steel matrix composites(ZTAP/40Cr architecture composite) with different composite volume fractions(35vol%, 50vol%, 65vol%) were fabricated by squeeze casting, which were subjected to no abrasives impact wear test with an impact energy of 1.5 J after quenching at 850℃ and tempering at 460℃. The results show that when the volume fraction of the composite area is 35vol%, 50vol% and 65vol%, the wear rates of the ZTAP/40Cr architecture composites are 4.7×10−3 cm3/h, 3.4×10−3 cm3/h and 1.0×10−3 cm3/h, respectively. The wear rates of the ZTAP/40Cr composite and the 40Cr steel are 13.41×10−3 cm3/h and 79.87×10−3 cm3/h, respectively. The wear resistance of the ZTAP/40Cr architecture composite increases as the volume fraction of the composite area increases. Further analysis show that the impact wear mechanism of the ZTAP/40Cr architecture composite includes abrasive wear and adhesive wear on the surface, mainly the adhesion of the matrix and the ploughing of the entire surface, as well as the fatigue wear of the subsurface, which is a blockage of materials caused by ZTAP breakage and ZTAP/40Cr interfacial cracking during repeated impact.
2020, 37(9): 2230-2239.
doi: 10.13801/j.cnki.fhclxb.20191224.001
Abstract:
To investigate the dynamic behavior and energy absorption performance of foam filled honeycomb (FFH) under impact loading, a series of meso-structure models were established by material point method (MPM). The stress-strain curves of foam meso-structure models agree well with the theoretical model and experimental data. The deformation and damage morphologies of FFH models are consistent with those of experiments. The result shows that the filled foam and honeycomb consume energy through plastic deformation and buckling separately, and the filled-foam makes a remarkable enhancement effect on the energy absorption of the honeycomb. The influences of the filled-foam density and loading strain rate were investigated. As the filled-foam density increases, the dynamic behavior of FFH turns better, the total energy absorption and that of honeycomb component increase as well. Since the filled-foam intensifies the buckling strength of the honeycomb, the honeycomb could withstand more deformation. The stress-strain curves of FFH are sensitive to the loading strain rate, which has a certain impact on the energy absorption performance, and the total energy absorptions are confined to less than 15%. The total energy absorption and those of each component are determined by the FFH structure, and not irrelevant with the loading strain rate.
To investigate the dynamic behavior and energy absorption performance of foam filled honeycomb (FFH) under impact loading, a series of meso-structure models were established by material point method (MPM). The stress-strain curves of foam meso-structure models agree well with the theoretical model and experimental data. The deformation and damage morphologies of FFH models are consistent with those of experiments. The result shows that the filled foam and honeycomb consume energy through plastic deformation and buckling separately, and the filled-foam makes a remarkable enhancement effect on the energy absorption of the honeycomb. The influences of the filled-foam density and loading strain rate were investigated. As the filled-foam density increases, the dynamic behavior of FFH turns better, the total energy absorption and that of honeycomb component increase as well. Since the filled-foam intensifies the buckling strength of the honeycomb, the honeycomb could withstand more deformation. The stress-strain curves of FFH are sensitive to the loading strain rate, which has a certain impact on the energy absorption performance, and the total energy absorptions are confined to less than 15%. The total energy absorption and those of each component are determined by the FFH structure, and not irrelevant with the loading strain rate.
2020, 37(9): 2240-2249.
doi: 10.13801/j.cnki.fhclxb.20200115.003
Abstract:
The silicon nitride fiber has excellent high temperature resistance and wave transmission capability, which is an ideal reinforcement using for high-temperature wave-transparent composites. In this paper, preparation and test methods for the dielectric properties of ceramic fibers tested by high-Q cavity method were studied and optimized for continuous ceramic fibers. The study shows that the fiber content in the dielectric test sample should be no less than 20wt%, and less fiber content tended to result in a relatively smaller value of the fiber dielectric constant. Meanwhile, the length of chopped fiber has effect on the repeatability of the fiber dielectric properties. The samples made by the chopped fiber with the length no more than 1.0 mm are of high quality and the resulted fiber dielectric data are more reliable. In terms of data processing, the applicability of three dielectric mixing models of Lichtenecker, Bruggeman and Looyenga was discussed in comparison. Finally, the permittivity of quartz fibers was calculated based on Lichtenecker dielectric constant logarithmic mixing rule, which was consistent with the reported data. It has been found that the silicon nitride fiber has a permittivity of 4.4 and a loss tangent of 0.0005 at 10 GHz, demonstrating excellent low dielectric. Furthermore, it shows that the surface sizing agent has a significant effect on the dielectric properties particularly the loss tangent of the silicon nitride fiber, which is associated with its surface polarity characteristics of the silicon nitride fiber.
The silicon nitride fiber has excellent high temperature resistance and wave transmission capability, which is an ideal reinforcement using for high-temperature wave-transparent composites. In this paper, preparation and test methods for the dielectric properties of ceramic fibers tested by high-Q cavity method were studied and optimized for continuous ceramic fibers. The study shows that the fiber content in the dielectric test sample should be no less than 20wt%, and less fiber content tended to result in a relatively smaller value of the fiber dielectric constant. Meanwhile, the length of chopped fiber has effect on the repeatability of the fiber dielectric properties. The samples made by the chopped fiber with the length no more than 1.0 mm are of high quality and the resulted fiber dielectric data are more reliable. In terms of data processing, the applicability of three dielectric mixing models of Lichtenecker, Bruggeman and Looyenga was discussed in comparison. Finally, the permittivity of quartz fibers was calculated based on Lichtenecker dielectric constant logarithmic mixing rule, which was consistent with the reported data. It has been found that the silicon nitride fiber has a permittivity of 4.4 and a loss tangent of 0.0005 at 10 GHz, demonstrating excellent low dielectric. Furthermore, it shows that the surface sizing agent has a significant effect on the dielectric properties particularly the loss tangent of the silicon nitride fiber, which is associated with its surface polarity characteristics of the silicon nitride fiber.
2020, 37(9): 2250-2257.
doi: 10.13801/j.cnki.fhclxb.20200110.003
Abstract:
The (C/C)/SiC-ZrC composites with different ZrC content were fabricated by precursor infiltration and pyrolysis (PIP) process, and effects of the ZrC content on the microstructures and anti-ablative properties of the (C/C)/SiC-ZrC composites were investigated. The results show that after oxyacetylene ablation 600 s, the surface of (C/C)/SiC composites are loose, and a rather large ablation pit appeared. Whereas the surface of (C/C)/SiC-ZrC composites are compact relatively and coverd by white oxide. Compared with (C/C)/SiC composites, ablation rate of (C/C)/SiC-ZrC composites with different ZrC content decreases. When the ZrC content is low, ZrO2-SiO2 binary eutectic systems a oxide film is formed on the surface, which can effectively prevent the infiltration of oxidation atmosphere, and also the oxide melt and volatilize continuously, which can reduce temperature of ablation surface of the (C/C)/SiC-ZrC composites. When the ZrC volume fraction rises to 12.4vol%, outer ZrO2 and inner SiO2 are formed by the oxidation of ZrC and SiC, respectively. ZrO2 is a excellent heat barrier material with low heat conduction coefficient, which can alleviate the heat diffusion of ablation area during ablation, leading the higher surface temperature of the (C/C)/SiC-ZrC composites, but two dense oxidation film can prevent the corrosion of oxidation atmosphere, resulting in a good ablation resistance of (C/C)/SiC-ZrC composites.
The (C/C)/SiC-ZrC composites with different ZrC content were fabricated by precursor infiltration and pyrolysis (PIP) process, and effects of the ZrC content on the microstructures and anti-ablative properties of the (C/C)/SiC-ZrC composites were investigated. The results show that after oxyacetylene ablation 600 s, the surface of (C/C)/SiC composites are loose, and a rather large ablation pit appeared. Whereas the surface of (C/C)/SiC-ZrC composites are compact relatively and coverd by white oxide. Compared with (C/C)/SiC composites, ablation rate of (C/C)/SiC-ZrC composites with different ZrC content decreases. When the ZrC content is low, ZrO2-SiO2 binary eutectic systems a oxide film is formed on the surface, which can effectively prevent the infiltration of oxidation atmosphere, and also the oxide melt and volatilize continuously, which can reduce temperature of ablation surface of the (C/C)/SiC-ZrC composites. When the ZrC volume fraction rises to 12.4vol%, outer ZrO2 and inner SiO2 are formed by the oxidation of ZrC and SiC, respectively. ZrO2 is a excellent heat barrier material with low heat conduction coefficient, which can alleviate the heat diffusion of ablation area during ablation, leading the higher surface temperature of the (C/C)/SiC-ZrC composites, but two dense oxidation film can prevent the corrosion of oxidation atmosphere, resulting in a good ablation resistance of (C/C)/SiC-ZrC composites.
