2020 Vol. 37, No. 4
Properties of multi-walled carbon nanotubes-acrylate block copolymers/epoxy resin ternary composites
2020, 37(4): 741-748.
doi: 10.13801/j.cnki.fhclxb.20190617.001
Abstract:
The multi-walled carbon nanotubes(MWCNTs)-acrylate block copolymers(ACRBC)/epoxy resin(EP) (MWCNTs-ACRBC/EP) ternary composites were prepared. The acid-treated MWCNTs properties were characterized by FTIR, XPS and SEM. The curing process characteristic temperatures of MWCNTs-ACRBC/EP composites were investigated by non-isothermal DSC analysis. The thermal performance of MWCNTs-ACRBC/EP composites were investigated by DMA analysis. The mechanical properties of MWCNTs-ACRBC/EP composites were investigated by electronic tension machine. The results show that the functional groups emerge on the surface of MWCNTs successfully. The curing process of MWCNTs-ACRBC/EP composites is 150℃×1 h+180℃×3 h. The glass transition temperature(Tg) of MWCNTs-ACRBC/EP composites is 197.5℃, which increases by 13.3%. The mechanical properties of MWCNTs-ACRBC/EP composites are improved, the flexural strength of MWCNTs-ACRBC/EP composites is 144 MPa, the flexural modulus of MWCNTs-ACRBC/EP composites is 3662 MPa, and the impact strength of MWCNTs-ACRBC/EP composites is 19.5 kJ/m2.
The multi-walled carbon nanotubes(MWCNTs)-acrylate block copolymers(ACRBC)/epoxy resin(EP) (MWCNTs-ACRBC/EP) ternary composites were prepared. The acid-treated MWCNTs properties were characterized by FTIR, XPS and SEM. The curing process characteristic temperatures of MWCNTs-ACRBC/EP composites were investigated by non-isothermal DSC analysis. The thermal performance of MWCNTs-ACRBC/EP composites were investigated by DMA analysis. The mechanical properties of MWCNTs-ACRBC/EP composites were investigated by electronic tension machine. The results show that the functional groups emerge on the surface of MWCNTs successfully. The curing process of MWCNTs-ACRBC/EP composites is 150℃×1 h+180℃×3 h. The glass transition temperature(Tg) of MWCNTs-ACRBC/EP composites is 197.5℃, which increases by 13.3%. The mechanical properties of MWCNTs-ACRBC/EP composites are improved, the flexural strength of MWCNTs-ACRBC/EP composites is 144 MPa, the flexural modulus of MWCNTs-ACRBC/EP composites is 3662 MPa, and the impact strength of MWCNTs-ACRBC/EP composites is 19.5 kJ/m2.
2020, 37(4): 749-757.
doi: 10.13801/j.cnki.fhclxb.20190619.001
Abstract:
The bisphenol A epoxy resin (E51) and bisphenol A cyanate (BCE) were used as the raw materials to study the co-curing reaction kinetics mechanism. At the same time, E51-BCE was used as the matrix resin, and Al2O3 obtained with Sol-Gel method as reinforcement to prepare the Al2O3/E51-BCE composites. The solidification process and curing kinetics of the system were determined by non-isothermal DSC, and the apparent activation energy of the system are 66.13 kJ/mol and 69.46 kJ/mol according to the Kissinger and Ozawa equation, respectively. Infrared spectroscopy was used to track the reaction route of the system at the initial curing temperature of 160℃ and 180℃. The results reveal that E51 reacts directly with BCE when the curing temperature starts at 160℃. The BCE's reactivity will be improved when the curing temperature is 180℃, BCE is mainly consumed in the self-polymerization reaction, and the formation rate of the triazine ring is accelerated. A little part of BCE directly reacts with E51 to form an oxazoline structure. The FTIR and TEM results of Al2O3 show that the structure of Al2O3 is a short fiber-like crystal with a little amount of hydroxyl groups on its surface. The SEM patterns of the Al2O3/E51-BCE composites indicate that Al2O3 presents as disperse phase in matrix, the interface between Al2O3 and matrix is fuzzy and the failure cracks are irregularity, thus it is typical ductile fracture. 3wt% Al2O3 is uniformly dispersed in matrix, and the impact strength and bending modulus of Al2O3/E51-BCE composites is 24.2 kJ/m2 and 2.54 GPa, respectively, which are increased by 53.65% and 22.12% compared with E51-BCE matrix resin. The mechanical properties of Al2O3/E51-BCE composites are improved obviously.
The bisphenol A epoxy resin (E51) and bisphenol A cyanate (BCE) were used as the raw materials to study the co-curing reaction kinetics mechanism. At the same time, E51-BCE was used as the matrix resin, and Al2O3 obtained with Sol-Gel method as reinforcement to prepare the Al2O3/E51-BCE composites. The solidification process and curing kinetics of the system were determined by non-isothermal DSC, and the apparent activation energy of the system are 66.13 kJ/mol and 69.46 kJ/mol according to the Kissinger and Ozawa equation, respectively. Infrared spectroscopy was used to track the reaction route of the system at the initial curing temperature of 160℃ and 180℃. The results reveal that E51 reacts directly with BCE when the curing temperature starts at 160℃. The BCE's reactivity will be improved when the curing temperature is 180℃, BCE is mainly consumed in the self-polymerization reaction, and the formation rate of the triazine ring is accelerated. A little part of BCE directly reacts with E51 to form an oxazoline structure. The FTIR and TEM results of Al2O3 show that the structure of Al2O3 is a short fiber-like crystal with a little amount of hydroxyl groups on its surface. The SEM patterns of the Al2O3/E51-BCE composites indicate that Al2O3 presents as disperse phase in matrix, the interface between Al2O3 and matrix is fuzzy and the failure cracks are irregularity, thus it is typical ductile fracture. 3wt% Al2O3 is uniformly dispersed in matrix, and the impact strength and bending modulus of Al2O3/E51-BCE composites is 24.2 kJ/m2 and 2.54 GPa, respectively, which are increased by 53.65% and 22.12% compared with E51-BCE matrix resin. The mechanical properties of Al2O3/E51-BCE composites are improved obviously.
2020, 37(4): 758-766.
doi: 10.13801/j.cnki.fhclxb.20190731.002
Abstract:
ZnFe2O4-TiO2/reduced graphene oxide(rGO) composites were synthesized from TiO2(P25), Fe(NO3)3·9H2O, Zn(NO3)2·6H2O and graphene oxide (GO) by one-step solvent thermal method. The properties and structures of ZnFe2O4-TiO2/rGO composites were characterized by UV-Vis, Raman spectra, XRD, SEM and EDS. The photocatalytic degradation performance of ZnFe2O4-TiO2/rGO composites prepared with different amount of GO were investigated. GO is reduced to rGO in the solvent thermal reaction process. The addition of ZnFe2O4 and rGO broadens the visible light wavelengths absorbed by ZnFe2O4-TiO2/rGO composites. ZnFe2O4-TiO2/rGO composites have magnetic performance, which is convenient for separation and recycling. ZnFe2O4-TiO2/rGO composites show the best photocatalytic degradation of methylene blue(MB) when the mass fraction of GO is 5wt%, and the degradation rate reaches 99.1% after 60 min under simulated solar irradiation. According to the scavenger experiments, the possible MB degradation mechanism is mainly contributed to the generation of active species induced by·OH and·O2-. The photo-generated electrons(e+) in conduction band(CB) of TiO2 migrate to valence band(VB) of ZnFe2O4, and form a Z-scheme photocatalytic system. The photocatalyst stability test shows that ZnFe2O4-TiO2/rGO composites have excellent stability and can be used as a photocatalyst for the degradation of organic dyes under sunlight.
ZnFe2O4-TiO2/reduced graphene oxide(rGO) composites were synthesized from TiO2(P25), Fe(NO3)3·9H2O, Zn(NO3)2·6H2O and graphene oxide (GO) by one-step solvent thermal method. The properties and structures of ZnFe2O4-TiO2/rGO composites were characterized by UV-Vis, Raman spectra, XRD, SEM and EDS. The photocatalytic degradation performance of ZnFe2O4-TiO2/rGO composites prepared with different amount of GO were investigated. GO is reduced to rGO in the solvent thermal reaction process. The addition of ZnFe2O4 and rGO broadens the visible light wavelengths absorbed by ZnFe2O4-TiO2/rGO composites. ZnFe2O4-TiO2/rGO composites have magnetic performance, which is convenient for separation and recycling. ZnFe2O4-TiO2/rGO composites show the best photocatalytic degradation of methylene blue(MB) when the mass fraction of GO is 5wt%, and the degradation rate reaches 99.1% after 60 min under simulated solar irradiation. According to the scavenger experiments, the possible MB degradation mechanism is mainly contributed to the generation of active species induced by·OH and·O2-. The photo-generated electrons(e+) in conduction band(CB) of TiO2 migrate to valence band(VB) of ZnFe2O4, and form a Z-scheme photocatalytic system. The photocatalyst stability test shows that ZnFe2O4-TiO2/rGO composites have excellent stability and can be used as a photocatalyst for the degradation of organic dyes under sunlight.
2020, 37(4): 767-774.
doi: 10.13801/j.cnki.fhclxb.20190730.002
Abstract:
The 2.5D quartz fiber reinforced boron phenolic resin ceramizable composite was prepared by prepreg molding process. TG test, muffle furnace static ablation test, mechanical test, oxygen-acetylene test, field emission scanning electron microscope and other methods were used to analyze the thermal properties, mechanical properties and ablation resistance of 2.5D quartz fiber reinforced boron phenolic resin ceramizable composites. The test results show that the ceramic filler has a significant improvement on the thermal stability of the composites, and the temperature at the first stage of weight loss and the residual carbon ratio are significantly increased. After the muffle furnace pyrolysis, the 2D structure sample has many defects and damage between layers, and the bending strength is 14-20 MPa, the 2.5D structure sample maintains a good overall structure after pyrolysis, and the bending strength is 16-24 MPa. After the ablation of the 2.5D structure sample by the oxyacetylene ablation test, the mass ablation rate is 0.0413 g/s and the line ablation rate is 0.032 mm/s. After 60 s of ablation, the mass ablation rate is 0.0218 g/s, and the line ablation rate is 0.023 mm/s. The test results are better than the 2D structure samples. Through SEM and EDS analysis, the 2.5D structure samples have excellent thermal stress delamination resistance, and the fiber surface structure has stability to multiphase ceramics, which are the main reasons for low ablation rate of the composite.
The 2.5D quartz fiber reinforced boron phenolic resin ceramizable composite was prepared by prepreg molding process. TG test, muffle furnace static ablation test, mechanical test, oxygen-acetylene test, field emission scanning electron microscope and other methods were used to analyze the thermal properties, mechanical properties and ablation resistance of 2.5D quartz fiber reinforced boron phenolic resin ceramizable composites. The test results show that the ceramic filler has a significant improvement on the thermal stability of the composites, and the temperature at the first stage of weight loss and the residual carbon ratio are significantly increased. After the muffle furnace pyrolysis, the 2D structure sample has many defects and damage between layers, and the bending strength is 14-20 MPa, the 2.5D structure sample maintains a good overall structure after pyrolysis, and the bending strength is 16-24 MPa. After the ablation of the 2.5D structure sample by the oxyacetylene ablation test, the mass ablation rate is 0.0413 g/s and the line ablation rate is 0.032 mm/s. After 60 s of ablation, the mass ablation rate is 0.0218 g/s, and the line ablation rate is 0.023 mm/s. The test results are better than the 2D structure samples. Through SEM and EDS analysis, the 2.5D structure samples have excellent thermal stress delamination resistance, and the fiber surface structure has stability to multiphase ceramics, which are the main reasons for low ablation rate of the composite.
2020, 37(4): 775-785.
doi: 10.13801/j.cnki.fhclxb.20190627.001
Abstract:
In order to study the effect of corner radius on axial compressive performance of large scale steel reinforced concrete rectangular short columns confined by carbon fiber reinforced polymer(CFRP) composite, the static axial compression experiment were conducted on one contrast specimen and five strengthened specimens. The results indicate that with the increasing corner radius, both the strength and ductility of the confined columns increase, the descending portion of the load-displacement curve after the peak load point gradually turns to ascending portion; the circumferential strain of CFRP composite sheets also gets higher working value and more uniform distribution. Through numerical analysis, it was seen that with the corner radius increasing, the area of the effectively confined concrete zone on the cross-section increases, the axial compressive stress distribution of concrete tends to be uniform, and the stress in the core area surrounded by steel increases significantly. Then the different confined concrete areas in cross-section were divided, and the core area surrounded by steel was set as the high-strength confined concrete zone. The superposition formulation of the axial bearing capacity of steel reinforced concrete rectangular short columns confined by CFRP composite was proposed. The calculation results show that increasing the corner radius significantly reduces the cross-sectional area of the large-size steel reinforced concrete rectangular columns, but improves the axial compression bearing capacity.
In order to study the effect of corner radius on axial compressive performance of large scale steel reinforced concrete rectangular short columns confined by carbon fiber reinforced polymer(CFRP) composite, the static axial compression experiment were conducted on one contrast specimen and five strengthened specimens. The results indicate that with the increasing corner radius, both the strength and ductility of the confined columns increase, the descending portion of the load-displacement curve after the peak load point gradually turns to ascending portion; the circumferential strain of CFRP composite sheets also gets higher working value and more uniform distribution. Through numerical analysis, it was seen that with the corner radius increasing, the area of the effectively confined concrete zone on the cross-section increases, the axial compressive stress distribution of concrete tends to be uniform, and the stress in the core area surrounded by steel increases significantly. Then the different confined concrete areas in cross-section were divided, and the core area surrounded by steel was set as the high-strength confined concrete zone. The superposition formulation of the axial bearing capacity of steel reinforced concrete rectangular short columns confined by CFRP composite was proposed. The calculation results show that increasing the corner radius significantly reduces the cross-sectional area of the large-size steel reinforced concrete rectangular columns, but improves the axial compression bearing capacity.
2020, 37(4): 786-793.
doi: 10.13801/j.cnki.fhclxb.20190614.001
Abstract:
In order to improve the electrochemical properties of graphene/polyimide (rGO/PI) composite yarn electrode, polyaniline (PANI) particles were deposited on the surface of rGO/PI composite yarn by electrochemical polymerization, and the effect of deposition time on the morphology and weight gain of PANI-rGO/PI composite conductive yarn was studied. As a result, PANI is deposited uniformly on the surface of the rGO/PI composite yarn, and the deposition amount increases with the deposition time increasing. The electrochemical behavior of PANI-rGO/PI composite conductive yarns was studied by cyclic voltammetry (CV) and galvanostatic discharge-charge method (GCD). The results show that the PANI deposition time has a great influence on CV and GCD characterastics. When the deposition time of PANI is 900s, the CV characteristics and GCD performance of the electrode of PANI-rGO/PI composite yarn are optimal, with a specific capacitance of 81.22 Fcm-3, while the electrode of rGO/PI yarn is only 16.4 Fcm-3. The PANI-rGO/PI composite conductive yarns with optimal process were assembled into a fiber-shaped supercapacitor, the electrochemical properties of the fiber-shaped supercapacitor were studied through the electrochemical impedance spectroscopy (EIS), CV and GCD. The results show that the volume specific capacitance of the device can reach 41.73 Fcm-3, and the device shows an excellent long-life performance up to 3000 times with a retention of~85%. The PANI-rGO/PI fiber-shaped supercapacitors can be readily connected in serial to power LED.
In order to improve the electrochemical properties of graphene/polyimide (rGO/PI) composite yarn electrode, polyaniline (PANI) particles were deposited on the surface of rGO/PI composite yarn by electrochemical polymerization, and the effect of deposition time on the morphology and weight gain of PANI-rGO/PI composite conductive yarn was studied. As a result, PANI is deposited uniformly on the surface of the rGO/PI composite yarn, and the deposition amount increases with the deposition time increasing. The electrochemical behavior of PANI-rGO/PI composite conductive yarns was studied by cyclic voltammetry (CV) and galvanostatic discharge-charge method (GCD). The results show that the PANI deposition time has a great influence on CV and GCD characterastics. When the deposition time of PANI is 900s, the CV characteristics and GCD performance of the electrode of PANI-rGO/PI composite yarn are optimal, with a specific capacitance of 81.22 Fcm-3, while the electrode of rGO/PI yarn is only 16.4 Fcm-3. The PANI-rGO/PI composite conductive yarns with optimal process were assembled into a fiber-shaped supercapacitor, the electrochemical properties of the fiber-shaped supercapacitor were studied through the electrochemical impedance spectroscopy (EIS), CV and GCD. The results show that the volume specific capacitance of the device can reach 41.73 Fcm-3, and the device shows an excellent long-life performance up to 3000 times with a retention of~85%. The PANI-rGO/PI fiber-shaped supercapacitors can be readily connected in serial to power LED.
2020, 37(4): 794-799.
doi: 10.13801/j.cnki.fhclxb.20190716.001
Abstract:
Epicatechin (EC) was used as a non-covalent modifier to treat BN. The effects of BN@EC with different mass fraction of EC on the properties of BN@EC/epoxy resin (EP) composites were investigated. BN, BN@EC and BN@EC/EP composites were characterized by FTIR, XRD, SEM, TG, et al. The results show that EC successfully modifies BN and doesn't affect the crystal structure of BN during the modification process; the dispersibility of BN modified by EC in the resin matrix is improved; the SEM test results show that the degree of agglomeration of BN particles modified by EC is lower than that of the unmodified BN particles. The dispersion of BN@EC in the matrix is better; the stability of the modified BN@EC in water is improved; when the EC mass fraction is 10wt%, the thermal conductivity of BN@EC/EP composite is best, which reaches 1.27 Wm-1K-1, which is 106% higher than the thermal conductivity of BN/EP(0.62 Wm-1K-1). Finally, the effects of the addition of EC on the thermal stability and hardness of the composites were analyzed. The results show that the addition of EC will slightly improve the thermal stability of the composites.
Epicatechin (EC) was used as a non-covalent modifier to treat BN. The effects of BN@EC with different mass fraction of EC on the properties of BN@EC/epoxy resin (EP) composites were investigated. BN, BN@EC and BN@EC/EP composites were characterized by FTIR, XRD, SEM, TG, et al. The results show that EC successfully modifies BN and doesn't affect the crystal structure of BN during the modification process; the dispersibility of BN modified by EC in the resin matrix is improved; the SEM test results show that the degree of agglomeration of BN particles modified by EC is lower than that of the unmodified BN particles. The dispersion of BN@EC in the matrix is better; the stability of the modified BN@EC in water is improved; when the EC mass fraction is 10wt%, the thermal conductivity of BN@EC/EP composite is best, which reaches 1.27 Wm-1K-1, which is 106% higher than the thermal conductivity of BN/EP(0.62 Wm-1K-1). Finally, the effects of the addition of EC on the thermal stability and hardness of the composites were analyzed. The results show that the addition of EC will slightly improve the thermal stability of the composites.
2020, 37(4): 800-807.
doi: 10.13801/j.cnki.fhclxb.20190628.001
Abstract:
The self-developed carbon fiber wide-spreading equipment was used to pre-dip 12K carbon fiber(CF) into wide CF/epoxy(EP) prepreg with 0.02 mm and 0.10 mm thickness, and the unidirectional laminate of 1 mm thickness was fabricated by molding process. The integrated system including universal testing machine, acoustic emission device and high-speed camera was used to test the tensile strength, the damage inside the sample during loading and the macroscopic morphology of the sample during fracture failure. The tensile fracture morphology was observed by SEM. The super-depth microscope and metallographic microscope were used to observe the arrangement of CF in CF/EP composite prepreg and unidirectional laminate to characterize the influence of CF and EP distribution on the tensile properties of CF/EP composites during thinning. The results show that the CF is more uniform in the thin CF/EP composite prepreg, and the scale of the inter-layer resin enrichment zone in the CF/EP composite unidirectional laminate is much smaller than the laminate made of thick CF/EP composite prepreg. The tensile strength of CF/EP composites sample is increased by 15%. The delamination and splitting phenomenon of the laminate made of thin CF/EP composite prepreg is reduced in the macroscopic fracture morphology, and the clustering property is enhanced. No penetration cracks across the cross section are found in the micro fracture morphology of laminate made of thin CF/EP composite prepreg.
The self-developed carbon fiber wide-spreading equipment was used to pre-dip 12K carbon fiber(CF) into wide CF/epoxy(EP) prepreg with 0.02 mm and 0.10 mm thickness, and the unidirectional laminate of 1 mm thickness was fabricated by molding process. The integrated system including universal testing machine, acoustic emission device and high-speed camera was used to test the tensile strength, the damage inside the sample during loading and the macroscopic morphology of the sample during fracture failure. The tensile fracture morphology was observed by SEM. The super-depth microscope and metallographic microscope were used to observe the arrangement of CF in CF/EP composite prepreg and unidirectional laminate to characterize the influence of CF and EP distribution on the tensile properties of CF/EP composites during thinning. The results show that the CF is more uniform in the thin CF/EP composite prepreg, and the scale of the inter-layer resin enrichment zone in the CF/EP composite unidirectional laminate is much smaller than the laminate made of thick CF/EP composite prepreg. The tensile strength of CF/EP composites sample is increased by 15%. The delamination and splitting phenomenon of the laminate made of thin CF/EP composite prepreg is reduced in the macroscopic fracture morphology, and the clustering property is enhanced. No penetration cracks across the cross section are found in the micro fracture morphology of laminate made of thin CF/EP composite prepreg.
2020, 37(4): 808-815.
doi: 10.13801/j.cnki.fhclxb.20190819.001
Abstract:
In order to investigate the repair effect of carbon fiber reinforced epoxy resin composite on the ring-corroded N80Q steel pipe, the mechanical properties of the repaired steel were studied by numerical analysis and full-scale blasting test. The effects of axial length, depth and repair layer thickness on the repairing effect were analyzed. The results show that the carbon fiber/epoxy composite has a remarkable effect on repairing the N80Q steel pipe and the bursting pressure value of the 6 mm deep defect pipe is raised by 0.985 times after repaired by the carbon fiber/epoxy composite; the axial length of the defect has little effect on the strength of the N80Q steel pipe after repaired by the carbon fiber/epoxy, and as the axial length of the defect increases, the pipe burst pressure value only gets reduced by 3.5%; the depth of the defect has an obvious effect on the strength of the N80Q steel pipe after repair:Compared with the non-defective pipe, the burst pressure value of the 6 mm deep defect pipeline is reduced by 9.9%, and the burst pressure of the 7 mm deep defect pipe is reduced by 20.6%.
In order to investigate the repair effect of carbon fiber reinforced epoxy resin composite on the ring-corroded N80Q steel pipe, the mechanical properties of the repaired steel were studied by numerical analysis and full-scale blasting test. The effects of axial length, depth and repair layer thickness on the repairing effect were analyzed. The results show that the carbon fiber/epoxy composite has a remarkable effect on repairing the N80Q steel pipe and the bursting pressure value of the 6 mm deep defect pipe is raised by 0.985 times after repaired by the carbon fiber/epoxy composite; the axial length of the defect has little effect on the strength of the N80Q steel pipe after repaired by the carbon fiber/epoxy, and as the axial length of the defect increases, the pipe burst pressure value only gets reduced by 3.5%; the depth of the defect has an obvious effect on the strength of the N80Q steel pipe after repair:Compared with the non-defective pipe, the burst pressure value of the 6 mm deep defect pipeline is reduced by 9.9%, and the burst pressure of the 7 mm deep defect pipe is reduced by 20.6%.
2020, 37(4): 816-823.
doi: 10.13801/j.cnki.fhclxb.20190617.004
Abstract:
In order to improve the vibration suppression characteristics of sandwich structure, the research on the vibration control method of sandwich structure based on active temperature control variable damping technology was carried out. Based on the high damping property of the polymerized polymer in the glass transition zone, a technical approach to temperature control of the sandwich polymer material and increase its loss factor to improve the structural damping was proposed. According to this technical approach, a temperature-controlled sandwich beam with a polyurethane-modified epoxy material as the core material and a heating film in the middle was designed. The experimental study on the vibration response of sandwich beams under different control temperatures was carried out and the influence of temperature on the bending stiffness of sandwich beams was discussed. The experimental results show that the vibration response of the sandwich beam can be reduced by 8.85 dB compared with the normal temperature when the temperature of the sandwich beam is controlled near the left side of glass transition temperature(Tg). It is proved that the proposed active temperature-controlled variable damping technology has good vibration suppression effect.
In order to improve the vibration suppression characteristics of sandwich structure, the research on the vibration control method of sandwich structure based on active temperature control variable damping technology was carried out. Based on the high damping property of the polymerized polymer in the glass transition zone, a technical approach to temperature control of the sandwich polymer material and increase its loss factor to improve the structural damping was proposed. According to this technical approach, a temperature-controlled sandwich beam with a polyurethane-modified epoxy material as the core material and a heating film in the middle was designed. The experimental study on the vibration response of sandwich beams under different control temperatures was carried out and the influence of temperature on the bending stiffness of sandwich beams was discussed. The experimental results show that the vibration response of the sandwich beam can be reduced by 8.85 dB compared with the normal temperature when the temperature of the sandwich beam is controlled near the left side of glass transition temperature(Tg). It is proved that the proposed active temperature-controlled variable damping technology has good vibration suppression effect.
2020, 37(4): 824-836.
doi: 10.13801/j.cnki.fhclxb.20190628.002
Abstract:
Preload relaxation is one of the main causes affecting the durability of bolted composite joints. This paper focuses on the interaction between material creep and contact creep of rough surface which induces the preload relaxation. The content includes:A creep constitutive model of composites based on the elastic-viscoplastic theory was established and extended to the elastic-viscoplastic contact problem with time-dependent combined with the fractal contact theory of rough surface. The comparison between numerical results and experimental results shows that the calculation error decreases from 2.87%-4.37% to 0.04%-0.5% when considering the rough surface contact effect, whose accuracy is significantly improved. The discussion results of the surface fractal parameters D and G show that the rougher the contact surface is, the easier the preload will be to relax, which will be of guiding significance to improve the surface contact properties by controlling surface topography parameters.
Preload relaxation is one of the main causes affecting the durability of bolted composite joints. This paper focuses on the interaction between material creep and contact creep of rough surface which induces the preload relaxation. The content includes:A creep constitutive model of composites based on the elastic-viscoplastic theory was established and extended to the elastic-viscoplastic contact problem with time-dependent combined with the fractal contact theory of rough surface. The comparison between numerical results and experimental results shows that the calculation error decreases from 2.87%-4.37% to 0.04%-0.5% when considering the rough surface contact effect, whose accuracy is significantly improved. The discussion results of the surface fractal parameters D and G show that the rougher the contact surface is, the easier the preload will be to relax, which will be of guiding significance to improve the surface contact properties by controlling surface topography parameters.
2020, 37(4): 837-844.
doi: 10.13801/j.cnki.fhclxb.20190617.003
Abstract:
The failure behavior of the single fiber column is complicated during the pull-out process in the stitched foam sandwich composites, so the carrying capacity of the structure can be unpredictable. The stitched foam sandwich composites were manufactured by the vacuum assisted resin injection (VARI) process. The interlaminar tension test (ITT) was employed to investigate the fracture process of the meso-specimen containing a single fiber column in the stitched foam sandwich composites. The effects of different fracture phenomena on the pulling friction process of the fiber column were discussed, and the fracture modes of the resin sufficient specimens were analyzed. The influences of the thread thickness on the key parameters such as force, displacement and energy absorption were studied. The influence of the resin deficiency caused by manufacture process on the performance of the stitched foam sandwich composite was analyzed. The results show that the energy absorption, key displacement parameters and maximum load of the stitched foam sandwich composite present an upward trend with the increase of the stitched thread thickness. However, the failure modes of the stitched foam sandwich composite also have a certain influence on the trend, which leads to the fluctuation of the trend. The energy absorption and maximum load of the resin deficient specimen are decreased due to the existence of defects.
The failure behavior of the single fiber column is complicated during the pull-out process in the stitched foam sandwich composites, so the carrying capacity of the structure can be unpredictable. The stitched foam sandwich composites were manufactured by the vacuum assisted resin injection (VARI) process. The interlaminar tension test (ITT) was employed to investigate the fracture process of the meso-specimen containing a single fiber column in the stitched foam sandwich composites. The effects of different fracture phenomena on the pulling friction process of the fiber column were discussed, and the fracture modes of the resin sufficient specimens were analyzed. The influences of the thread thickness on the key parameters such as force, displacement and energy absorption were studied. The influence of the resin deficiency caused by manufacture process on the performance of the stitched foam sandwich composite was analyzed. The results show that the energy absorption, key displacement parameters and maximum load of the stitched foam sandwich composite present an upward trend with the increase of the stitched thread thickness. However, the failure modes of the stitched foam sandwich composite also have a certain influence on the trend, which leads to the fluctuation of the trend. The energy absorption and maximum load of the resin deficient specimen are decreased due to the existence of defects.
2020, 37(4): 845-858.
doi: 10.13801/j.cnki.fhclxb.20190628.003
Abstract:
The fiber reinforced polymer composite grid structure has the characteristics of high specific stiffness, high specific strength, high damage tolerance, and automatic forming, and has broad application prospects in aerospace structures. The stacking, bridge, bending and cutting of the fibers at the intersection of the grid structure severely affect the final performance of the structure. Aiming at the inherent defects at the intersection of the fiber reinforced polymer composite grid structure, this paper summarizes the advantages and disadvantages of filament winding, fiber placement, 3D rotary braiding, interlocked and vacuum assisted resin transfer molding process in forming grid structure. At the same time, the relationship between the grid structure design and forming process is discussed. Finally, the main problems in the current grid structure research are analyzed, and the future development direction is prospected.
The fiber reinforced polymer composite grid structure has the characteristics of high specific stiffness, high specific strength, high damage tolerance, and automatic forming, and has broad application prospects in aerospace structures. The stacking, bridge, bending and cutting of the fibers at the intersection of the grid structure severely affect the final performance of the structure. Aiming at the inherent defects at the intersection of the fiber reinforced polymer composite grid structure, this paper summarizes the advantages and disadvantages of filament winding, fiber placement, 3D rotary braiding, interlocked and vacuum assisted resin transfer molding process in forming grid structure. At the same time, the relationship between the grid structure design and forming process is discussed. Finally, the main problems in the current grid structure research are analyzed, and the future development direction is prospected.
2020, 37(4): 859-868.
doi: 10.13801/j.cnki.fhclxb.20190619.002
Abstract:
In order to study the aging failure behavior of interlaminar mechanical properties of carbon fiber reinforced polymer (CFRP) composite in high temperature environment, the interlaminar tensile and shear tests of CFRP composite were designed. Aging tests were carried out for 0 (unaged), 120 h, 240 h, 360 h, 480 h, 600 h and 720 h at high temperature (80℃). The variations of interlaminar failure strength, failure stiffness and failure mode of CFRP composite with aging time were analyzed. Secondary stress criterion response surface with high temperature aging was obtained. A prediction model of interlaminar mechanical properties of CFRP composite was established, and a degradation model based on aging attenuation coefficient was obtained, which was verified by CFRP composite interlayer simulation model. The results show that with the increase of aging time at high temperature, the interlaminar tensile strength and shear strength are degraded to a certain extent. It is easier to peel off carbon fibers during interlaminar tension, and local resin peeling occurs during interlaminar shear. The interlaminar delamination between fibers is more obvious. The interfacial bonding force between resin and fibers decreases significantly due to high temperature aging. According to the secondary stress criterion of CFRP composite interlaminar mechanical properties aging with high temperature, the cohesion model parameters after different aging time were calculated. The interlaminar strength of CFRP composite under high temperature aging condition was predicted. It is found that the error rate of simulation and experiment is less than 10%, which shows the accuracy of CFRP composite interlaminar failure prediction model.
In order to study the aging failure behavior of interlaminar mechanical properties of carbon fiber reinforced polymer (CFRP) composite in high temperature environment, the interlaminar tensile and shear tests of CFRP composite were designed. Aging tests were carried out for 0 (unaged), 120 h, 240 h, 360 h, 480 h, 600 h and 720 h at high temperature (80℃). The variations of interlaminar failure strength, failure stiffness and failure mode of CFRP composite with aging time were analyzed. Secondary stress criterion response surface with high temperature aging was obtained. A prediction model of interlaminar mechanical properties of CFRP composite was established, and a degradation model based on aging attenuation coefficient was obtained, which was verified by CFRP composite interlayer simulation model. The results show that with the increase of aging time at high temperature, the interlaminar tensile strength and shear strength are degraded to a certain extent. It is easier to peel off carbon fibers during interlaminar tension, and local resin peeling occurs during interlaminar shear. The interlaminar delamination between fibers is more obvious. The interfacial bonding force between resin and fibers decreases significantly due to high temperature aging. According to the secondary stress criterion of CFRP composite interlaminar mechanical properties aging with high temperature, the cohesion model parameters after different aging time were calculated. The interlaminar strength of CFRP composite under high temperature aging condition was predicted. It is found that the error rate of simulation and experiment is less than 10%, which shows the accuracy of CFRP composite interlaminar failure prediction model.
2020, 37(4): 869-876.
doi: 10.13801/j.cnki.fhclxb.20190617.002
Abstract:
Mold-filling simulation of unsaturated flows in liquid composite molding(LCM) is important for optimizing process parameters quickly and cost-effectively in the virtual space. A dual-scale computational model for simulating unsaturated flow of dual-scale fiber mat under isothermal conditions was presented. The macro-micro flow control equations were solved by introducing the sink function, and the influence of capillary pressure in microscopic immersion was considered. The numerical simulation of unsaturated flow was realized in the finite element/control volume algorithm. The 2-dimensional radial filling experiment was carried out on the triaxial stitched fiber mat. The experimental results were compared with the numerical simulation predictions and the results show that the method can accurately simulate the unsaturated flow in the dual-scale fiber mat. Based on this calculation model, the effects of fluid viscosity, injection flow rate and the tow porosity on the unsaturated filling process were discussed. The results show that different fluid viscosity, injection flow rate and tow porosity have different effects on the length of unsaturated region, the inlet-pressure history and the filling time during filling process. The research results can provide guidance for reasonably prediction of filling process and the inlet-pressure history.
Mold-filling simulation of unsaturated flows in liquid composite molding(LCM) is important for optimizing process parameters quickly and cost-effectively in the virtual space. A dual-scale computational model for simulating unsaturated flow of dual-scale fiber mat under isothermal conditions was presented. The macro-micro flow control equations were solved by introducing the sink function, and the influence of capillary pressure in microscopic immersion was considered. The numerical simulation of unsaturated flow was realized in the finite element/control volume algorithm. The 2-dimensional radial filling experiment was carried out on the triaxial stitched fiber mat. The experimental results were compared with the numerical simulation predictions and the results show that the method can accurately simulate the unsaturated flow in the dual-scale fiber mat. Based on this calculation model, the effects of fluid viscosity, injection flow rate and the tow porosity on the unsaturated filling process were discussed. The results show that different fluid viscosity, injection flow rate and tow porosity have different effects on the length of unsaturated region, the inlet-pressure history and the filling time during filling process. The research results can provide guidance for reasonably prediction of filling process and the inlet-pressure history.
2020, 37(4): 877-885.
doi: 10.13801/j.cnki.fhclxb.20190620.001
Abstract:
The presence of pores in composites results in a decrease of material properties, therefore, it is critical to the detection of material pores. Carbon fiber (CF) cloth/epoxy resin laminated plates with different number of layers and different porosities were prepared by using different amounts of isopropanol(IPA). The ultrasonic attenuation coefficient of the test piece was calculated by pulse reflection method. The distribution, shape and size of the pore were characterized by metallographic microscopic analysis. The porosity of the test piece was obtained by analyzing the metallographic micrograph by MATLAB. The effects of porosity on the sound velocity, sound impedance and ultrasonic attenuation coefficient of the CF/epoxy resin laminated plates were discussed, and the fitting formulas of porosity, material layer number and ultrasonic attenuation were given based on the experimental data of porosity and ultrasonic attenuation of four samples with different layers. The results show that as the amount of IPA increases, the porosity of the laminate (2 mm) increases from 1.09% to 4.16%, the sound velocity and acoustic impedance of the material decrease, and the ultrasonic attenuation coefficient increases from 2.51 dB/mm to 5.34 dB/mm. When the porosity is 1%, the thickness increases from 2 mm (8 layers) to 5 mm (20 layers), and the attenuation coefficient increases by 0.54 dB/mm.
The presence of pores in composites results in a decrease of material properties, therefore, it is critical to the detection of material pores. Carbon fiber (CF) cloth/epoxy resin laminated plates with different number of layers and different porosities were prepared by using different amounts of isopropanol(IPA). The ultrasonic attenuation coefficient of the test piece was calculated by pulse reflection method. The distribution, shape and size of the pore were characterized by metallographic microscopic analysis. The porosity of the test piece was obtained by analyzing the metallographic micrograph by MATLAB. The effects of porosity on the sound velocity, sound impedance and ultrasonic attenuation coefficient of the CF/epoxy resin laminated plates were discussed, and the fitting formulas of porosity, material layer number and ultrasonic attenuation were given based on the experimental data of porosity and ultrasonic attenuation of four samples with different layers. The results show that as the amount of IPA increases, the porosity of the laminate (2 mm) increases from 1.09% to 4.16%, the sound velocity and acoustic impedance of the material decrease, and the ultrasonic attenuation coefficient increases from 2.51 dB/mm to 5.34 dB/mm. When the porosity is 1%, the thickness increases from 2 mm (8 layers) to 5 mm (20 layers), and the attenuation coefficient increases by 0.54 dB/mm.
2020, 37(4): 886-895.
doi: 10.13801/j.cnki.fhclxb.20190628.004
Abstract:
Lamb wave has been extensively used in nondestructive testing of composites due to its wide detection range and high sensitivity to defects. However, strong noise environment makes it difficult to extract effective signals, which affects the accuracy of damage location determination. To solve this problem, a damage location imaging method based on box-counting dimension and Lamb wave tomography technology in strong noise background was proposed. Firstly, the propagation characteristics of Lamb wave before and after damage of composite plate were analyzed by simulation. Circular sensor arrays were uniformly arranged on the carbon fiber reinforced polymer(CFRP) composite plate to simulate the real damage by changing the strain field of the structure with bonded mass blocks. Secondly, each sensor in turn acted as an exciter to generate Lamb wave. Other sensors collected the response signal without damage, and used wavelet transform to denoise the signal. Different levels of white noise were added to the denoised signal to realize noise interference. Finally, the damage factor was determined by calculating the difference of non-destructive signal by box-counting dimension, and the damage location imaging was realized by probability imaging algorithm. The experimental results show that the maximum and average errors of single-damage and multi-damage imaging locations are 11.18 mm and 6.88 mm respectively in strong noise environment. This method does not need signal denoising technology, and avoids the extraction process of complex reflection signals when multi-damage occurs. It has great potential in damage location and identification of composites under strong noise.
Lamb wave has been extensively used in nondestructive testing of composites due to its wide detection range and high sensitivity to defects. However, strong noise environment makes it difficult to extract effective signals, which affects the accuracy of damage location determination. To solve this problem, a damage location imaging method based on box-counting dimension and Lamb wave tomography technology in strong noise background was proposed. Firstly, the propagation characteristics of Lamb wave before and after damage of composite plate were analyzed by simulation. Circular sensor arrays were uniformly arranged on the carbon fiber reinforced polymer(CFRP) composite plate to simulate the real damage by changing the strain field of the structure with bonded mass blocks. Secondly, each sensor in turn acted as an exciter to generate Lamb wave. Other sensors collected the response signal without damage, and used wavelet transform to denoise the signal. Different levels of white noise were added to the denoised signal to realize noise interference. Finally, the damage factor was determined by calculating the difference of non-destructive signal by box-counting dimension, and the damage location imaging was realized by probability imaging algorithm. The experimental results show that the maximum and average errors of single-damage and multi-damage imaging locations are 11.18 mm and 6.88 mm respectively in strong noise environment. This method does not need signal denoising technology, and avoids the extraction process of complex reflection signals when multi-damage occurs. It has great potential in damage location and identification of composites under strong noise.
2020, 37(4): 896-906.
doi: 10.13801/j.cnki.fhclxb.20190618.002
Abstract:
The anchoring effect of the glass fiber reinforced polymer (GFRP) composite anchors and the concrete floor of the building is related to the safety and stability of the entire structure. In order to deeply explore the anchoring mechanism between GFRP anchors and concrete, the GFRP composite anti-floating anchors of different anchoring forms were tested by the self-designed full-scale anchor pull-pull test device to determine the ultimate pull-up bearing capacity of the bolt and the relative slip between the rod and the concrete. The test results show that the anchoring efficiency of the external anchorage section of GFRP composite anti-floating anchors anchored by new stress-distributed anchor is above 80%, and the relative slippage of concrete is larger than that of bare-strand direct anchoring specimens, confirming the new stress-distributed anchors can effectively improve the anchoring effect of the external anchorage section of GFRP composite anti-floating anchors. In addition, it was proposed to introduce the material reference coefficient based on the hyperbolic model, and the influence of GFRP composite anchor diameter and external anchor length on the bond-slip constitutive relationship between the anchor rod and the concrete was comprehensively considered in order to establish a new type of GFRP composite anchor and concrete bond-slip curve. The model prediction results are consistent with the test results, and the rationality and accuracy of the model are verified.
The anchoring effect of the glass fiber reinforced polymer (GFRP) composite anchors and the concrete floor of the building is related to the safety and stability of the entire structure. In order to deeply explore the anchoring mechanism between GFRP anchors and concrete, the GFRP composite anti-floating anchors of different anchoring forms were tested by the self-designed full-scale anchor pull-pull test device to determine the ultimate pull-up bearing capacity of the bolt and the relative slip between the rod and the concrete. The test results show that the anchoring efficiency of the external anchorage section of GFRP composite anti-floating anchors anchored by new stress-distributed anchor is above 80%, and the relative slippage of concrete is larger than that of bare-strand direct anchoring specimens, confirming the new stress-distributed anchors can effectively improve the anchoring effect of the external anchorage section of GFRP composite anti-floating anchors. In addition, it was proposed to introduce the material reference coefficient based on the hyperbolic model, and the influence of GFRP composite anchor diameter and external anchor length on the bond-slip constitutive relationship between the anchor rod and the concrete was comprehensively considered in order to establish a new type of GFRP composite anchor and concrete bond-slip curve. The model prediction results are consistent with the test results, and the rationality and accuracy of the model are verified.
2020, 37(4): 907-918.
doi: 10.13801/j.cnki.fhclxb.20190726.001
Abstract:
According to the microstructure of the continuous graphite fiber reinforced aluminium matrix (CF/Al) composites, the micromechanical finite element model was established based on the representative volume element (RVE) with different fibre arrangements. The progressive damage and fracture behaviors of the CF/Al composites under axial tensile condition were investigated by quasi-static tensile testing and numerical simulation method. The results show that the axial tensile modulus and strength calculated by the micromechanical model with the diagonal quadrilateral fiber arrangement agree well with the experimental results, while the fracture strain is underestimated. At the first tensile stage, the interface damage initiates and accumulates. With the increase of strain, the interface damage induces the local interfacial debonding and matrix alloy failure at the middle stage. At the last stage, the occurrence of fiber failure leads to the eventual fracture of the composites, which results in a fracture surface with coexistence of matrix tearing and fiber pull out. According to the micromechanical calculation results, the influence of interfacial strength and stiffness on the axial tensile behavior is inapparent in the case of insufficient fiber strength, while the axial mechanical properties of the composite are primarily determined by the in-situ fiber ultimate strength.
According to the microstructure of the continuous graphite fiber reinforced aluminium matrix (CF/Al) composites, the micromechanical finite element model was established based on the representative volume element (RVE) with different fibre arrangements. The progressive damage and fracture behaviors of the CF/Al composites under axial tensile condition were investigated by quasi-static tensile testing and numerical simulation method. The results show that the axial tensile modulus and strength calculated by the micromechanical model with the diagonal quadrilateral fiber arrangement agree well with the experimental results, while the fracture strain is underestimated. At the first tensile stage, the interface damage initiates and accumulates. With the increase of strain, the interface damage induces the local interfacial debonding and matrix alloy failure at the middle stage. At the last stage, the occurrence of fiber failure leads to the eventual fracture of the composites, which results in a fracture surface with coexistence of matrix tearing and fiber pull out. According to the micromechanical calculation results, the influence of interfacial strength and stiffness on the axial tensile behavior is inapparent in the case of insufficient fiber strength, while the axial mechanical properties of the composite are primarily determined by the in-situ fiber ultimate strength.
2020, 37(4): 919-926.
doi: 10.13801/j.cnki.fhclxb.20190730.001
Abstract:
The mesoporous silica (mSiO2) microspheres were grafted with the Sm-doped CeO2 nanoparticles via a facile and efficient co-precipitation approach. The uniform non-rigid mSiO2@Ce1-xSmxO2(x=0, 0.23) composite particles with a well-defined core-shell structure were obtained. The resulting samples were characterized in terms of powder XRD, SEM, HRTEM, STEM-EDX Mapping, Raman, and N2 adsorption-desorption measurements. The effects of Sm doping on the polishing performance of mSiO2@Ce1-xSmxO2(x=0, 0.23) composite abrasives were evaluated using AFM and three-dimensional noncontact interferometric microscope. The ultra-precision and high-efficiency polishing mechanisms of the Sm-doped abrasives were also discussed. The polishing results show that the Sm doping contributes to 36% increment of the removal rate which is 84 nm/min compared to the undoped composites. The Sm-doped abrasives achieve an atomic-scale surface finish, and the average roughness and root-mean-square roughness of the polished SiO2 films are 1.4 and 0.17 nm, respectively.
The mesoporous silica (mSiO2) microspheres were grafted with the Sm-doped CeO2 nanoparticles via a facile and efficient co-precipitation approach. The uniform non-rigid mSiO2@Ce1-xSmxO2(x=0, 0.23) composite particles with a well-defined core-shell structure were obtained. The resulting samples were characterized in terms of powder XRD, SEM, HRTEM, STEM-EDX Mapping, Raman, and N2 adsorption-desorption measurements. The effects of Sm doping on the polishing performance of mSiO2@Ce1-xSmxO2(x=0, 0.23) composite abrasives were evaluated using AFM and three-dimensional noncontact interferometric microscope. The ultra-precision and high-efficiency polishing mechanisms of the Sm-doped abrasives were also discussed. The polishing results show that the Sm doping contributes to 36% increment of the removal rate which is 84 nm/min compared to the undoped composites. The Sm-doped abrasives achieve an atomic-scale surface finish, and the average roughness and root-mean-square roughness of the polished SiO2 films are 1.4 and 0.17 nm, respectively.
2020, 37(4): 927-934.
doi: 10.13801/j.cnki.fhclxb.20190529.003
Abstract:
In order to solve the problem that the silica sol shell is easy to crack during handling and dewaxing, Polyamide 66(PA66) fibers were mixed into sand material as reinforcing material at room temperature and pore former to prepare composite shell with different PA66 fiber contents. The effects of PA66 fiber content on the flexural strength, permeability and porosity of the composite shell were investigated. The mechanism of PA66 fiber affecting the properties of silica sol shell was analyzed. The research shows that the mixing of PA66 fiber significantly improves the flexural strength and porosity of the composite shell at room temperature. With the increase of PA66 fiber content, the flexural strength and permeability of the composite shell increase at room temperature, and the flexural strength increases first and then decreases after baking. When the mass fraction of PA66 fiber is 0.75wt%, the flexural strength after roasting of the composite shell is 7.94 MPa, which is not much different from that of the composite shell without PA66 fiber. But its normal temperature flexural strength reaches 4.80 MPa, which is 32.21% higher than that of the composite shell without PA66 fiber. The permeability and porosity also increase to 4.2 and 22.77%, which are 90.91% and 13.35% higher than that of without PA66 fiber respectively.
In order to solve the problem that the silica sol shell is easy to crack during handling and dewaxing, Polyamide 66(PA66) fibers were mixed into sand material as reinforcing material at room temperature and pore former to prepare composite shell with different PA66 fiber contents. The effects of PA66 fiber content on the flexural strength, permeability and porosity of the composite shell were investigated. The mechanism of PA66 fiber affecting the properties of silica sol shell was analyzed. The research shows that the mixing of PA66 fiber significantly improves the flexural strength and porosity of the composite shell at room temperature. With the increase of PA66 fiber content, the flexural strength and permeability of the composite shell increase at room temperature, and the flexural strength increases first and then decreases after baking. When the mass fraction of PA66 fiber is 0.75wt%, the flexural strength after roasting of the composite shell is 7.94 MPa, which is not much different from that of the composite shell without PA66 fiber. But its normal temperature flexural strength reaches 4.80 MPa, which is 32.21% higher than that of the composite shell without PA66 fiber. The permeability and porosity also increase to 4.2 and 22.77%, which are 90.91% and 13.35% higher than that of without PA66 fiber respectively.
2020, 37(4): 935-943.
doi: 10.13801/j.cnki.fhclxb.20190909.001
Abstract:
A semi-analytical method to investigate the free vibration characteristics of moderately thick functionally graded material(FGM)spherical torus structures with general boundary conditions was proposed. The theoretical formulas were derived by applying the first-order shear deformation theory, in which the displacement admissible functions were expressed by Improved Fourier Series to eliminate the discontinuity of the boundary. The general boundary conditions of the functionally graded spherical torus structure were simulated by different spring parameters. The natural frequencies of functionally graded spherical torus were obtained by Ritz method. The data in this paper were compared with those obtained by finite element method, experiment and literatures based on convergence analysis, and the influences of correlation parameter were studied. The results show that the proposed method has advantages of good convergence and high accuracy. The frequency parameter of functionally graded spherical torus structures increases with the increase of thickness and shear correction factors.
A semi-analytical method to investigate the free vibration characteristics of moderately thick functionally graded material(FGM)spherical torus structures with general boundary conditions was proposed. The theoretical formulas were derived by applying the first-order shear deformation theory, in which the displacement admissible functions were expressed by Improved Fourier Series to eliminate the discontinuity of the boundary. The general boundary conditions of the functionally graded spherical torus structure were simulated by different spring parameters. The natural frequencies of functionally graded spherical torus were obtained by Ritz method. The data in this paper were compared with those obtained by finite element method, experiment and literatures based on convergence analysis, and the influences of correlation parameter were studied. The results show that the proposed method has advantages of good convergence and high accuracy. The frequency parameter of functionally graded spherical torus structures increases with the increase of thickness and shear correction factors.
2020, 37(4): 944-951.
doi: 10.13801/j.cnki.fhclxb.20190828.001
Abstract:
With the magnetized hot braised slag or unmagnetized hot braised slag, electric furnace slag and wind quenching slag as the research object, ethylene glycol, triethanolamine and absolute ethyl alcohol were used to prepare steel slag grinding aid. The steel slag ultrafine powders were obtained by mixing steel slag grinding aid and steel slag. The steel slag ultrafine powder/rubber composites were prepared by the steel slag ultrafine powder, carbon black N220, accelerant, sulfur, ZnO, stearic acid and the natural rubber. The influences of types of the steel slag and amount of steel slag grinding aid on the mechanical properties and flame retardant properties of the steel slag ultrafine powder/rubber composites were studied. The chemical composition, mineral composition, particle size distribution and composition structure were tested by XRF, XRD, LPSA and FTIR, respectively. The results show that the steel slag ultrafine powder/rubber composites prepared with electric furnace slag have good mechanical properties, the steel slag ultrafine powder/rubber composites prepared with electric furnace slag magnetized hot braised slag or unmagnetized hot braised slag have good flame retardant properties. The particle size of the steel slag ultrafine powder is reduced and the particle size distribution uniformity of the steel slag ultrafine powder is improved by steel slag grinding aid. With the increase of the amount of steel slag grinding aid, the particle size distribution uniformity of the steel slag ultrafine powder is improved, the mechanical properties of the steel slag ultrafine powder/rubber composites are improved and the flame retardant properties are reduced.
With the magnetized hot braised slag or unmagnetized hot braised slag, electric furnace slag and wind quenching slag as the research object, ethylene glycol, triethanolamine and absolute ethyl alcohol were used to prepare steel slag grinding aid. The steel slag ultrafine powders were obtained by mixing steel slag grinding aid and steel slag. The steel slag ultrafine powder/rubber composites were prepared by the steel slag ultrafine powder, carbon black N220, accelerant, sulfur, ZnO, stearic acid and the natural rubber. The influences of types of the steel slag and amount of steel slag grinding aid on the mechanical properties and flame retardant properties of the steel slag ultrafine powder/rubber composites were studied. The chemical composition, mineral composition, particle size distribution and composition structure were tested by XRF, XRD, LPSA and FTIR, respectively. The results show that the steel slag ultrafine powder/rubber composites prepared with electric furnace slag have good mechanical properties, the steel slag ultrafine powder/rubber composites prepared with electric furnace slag magnetized hot braised slag or unmagnetized hot braised slag have good flame retardant properties. The particle size of the steel slag ultrafine powder is reduced and the particle size distribution uniformity of the steel slag ultrafine powder is improved by steel slag grinding aid. With the increase of the amount of steel slag grinding aid, the particle size distribution uniformity of the steel slag ultrafine powder is improved, the mechanical properties of the steel slag ultrafine powder/rubber composites are improved and the flame retardant properties are reduced.
2020, 37(4): 952-961.
doi: 10.13801/j.cnki.fhclxb.20190730.004
Abstract:
The effect of multi-wall carbon nanotubes (MWCNTs) on the nanomechanical properties of cementitious materials with sand was investigated by nanoindentation technique. The original mechanical values of the indentation modulus (M) and indentation hardness (H) under 50 GPa and 4.0 GPa were statistically analyzed. The experimental frequency plot and fitted Gaussian probability density functions (PDF) were got by deconvolution technique. The quantitative computation of the volume fraction of the low density C-S-H gel(LD C-S-H) and the high density C-S-H gel(HD C-S-H) was performed. In addition to LD C-S-H, HD C-S-H and calcium hydroxide (CH), a spurious phase is found in the hydration products. With the addition of MWCNTs, the volume fraction of LD C-S-H decreases and the volume fraction of HD C-S-H increases, the modulus of C-S-H is improved. But the volume fractions of each phase calculated from the testing results of modulus and indentation hardness are different. MWCNTs induce the formation of HD C-S-H as nanocrystals, which reveals the mechanism of how MWCNTs enhance the properties of cementitious materials.
The effect of multi-wall carbon nanotubes (MWCNTs) on the nanomechanical properties of cementitious materials with sand was investigated by nanoindentation technique. The original mechanical values of the indentation modulus (M) and indentation hardness (H) under 50 GPa and 4.0 GPa were statistically analyzed. The experimental frequency plot and fitted Gaussian probability density functions (PDF) were got by deconvolution technique. The quantitative computation of the volume fraction of the low density C-S-H gel(LD C-S-H) and the high density C-S-H gel(HD C-S-H) was performed. In addition to LD C-S-H, HD C-S-H and calcium hydroxide (CH), a spurious phase is found in the hydration products. With the addition of MWCNTs, the volume fraction of LD C-S-H decreases and the volume fraction of HD C-S-H increases, the modulus of C-S-H is improved. But the volume fractions of each phase calculated from the testing results of modulus and indentation hardness are different. MWCNTs induce the formation of HD C-S-H as nanocrystals, which reveals the mechanism of how MWCNTs enhance the properties of cementitious materials.
2020, 37(4): 962-970.
doi: 10.13801/j.cnki.fhclxb.20190730.003
Abstract:
The heterostructure LaCO3OH/In(OH)3/In2S3 photocatalysts were synthesized by in-suit wet chemical method. The composition, structure and morphology of the prepared heterostructure LaCO3OH/In(OH)3/In2S3 photocatalysts were investigated by characterization technologies such as XRD, SEM, XPS, BET and TG. The photocatalytic activity of the heterostructure LaCO3OH/In(OH)3/In2S3 photocatalysts was evaluated by degradation of dye Rhodamine B under visible light (λ ≥ 420 nm). The results show that when the molar ratio of La/In is 15mol%, the obtained heterostructure LaCO3OH/In(OH)3/In2S3 photocatalyst holds the best photocatalytic activity. And the activity is twice as that of the In(OH)3/In2S3 photocatalyst. It is because that the obtained heterostructure LaCO3OH/In(OH)3/In2S3 photocatalyst has higher BET surface, proper energy band structure and optimal absorption capacity. Using terephthalic acid (TA) as probe molecule, the photocatalytic experiment demonstrates that hydroxyl radical is the key active species. The possible degradation mechanism was proposed.
The heterostructure LaCO3OH/In(OH)3/In2S3 photocatalysts were synthesized by in-suit wet chemical method. The composition, structure and morphology of the prepared heterostructure LaCO3OH/In(OH)3/In2S3 photocatalysts were investigated by characterization technologies such as XRD, SEM, XPS, BET and TG. The photocatalytic activity of the heterostructure LaCO3OH/In(OH)3/In2S3 photocatalysts was evaluated by degradation of dye Rhodamine B under visible light (λ ≥ 420 nm). The results show that when the molar ratio of La/In is 15mol%, the obtained heterostructure LaCO3OH/In(OH)3/In2S3 photocatalyst holds the best photocatalytic activity. And the activity is twice as that of the In(OH)3/In2S3 photocatalyst. It is because that the obtained heterostructure LaCO3OH/In(OH)3/In2S3 photocatalyst has higher BET surface, proper energy band structure and optimal absorption capacity. Using terephthalic acid (TA) as probe molecule, the photocatalytic experiment demonstrates that hydroxyl radical is the key active species. The possible degradation mechanism was proposed.
2020, 37(4): 971-977.
doi: 10.13801/j.cnki.fhclxb.20190612.001
Abstract:
CT scanning tests of cement paste with water/cement ratios of 0.3 and 0.5 from 1-40 days' age were carried out. The 3D microscopic model of cement paste was successfully reconstructed, and the morphological changes of unhydrated cement particles, hydration products and pores during this period were observed. Based on the results of CT scanning, the volume fraction of unhydrated clinkers and the hydration degree were calculated. The calculated results were compared with the commonly used TGA method, and agree well with the TGA results. CT scanning could be used as a reliable method for quantifying the hydration degree of cement.
CT scanning tests of cement paste with water/cement ratios of 0.3 and 0.5 from 1-40 days' age were carried out. The 3D microscopic model of cement paste was successfully reconstructed, and the morphological changes of unhydrated cement particles, hydration products and pores during this period were observed. Based on the results of CT scanning, the volume fraction of unhydrated clinkers and the hydration degree were calculated. The calculated results were compared with the commonly used TGA method, and agree well with the TGA results. CT scanning could be used as a reliable method for quantifying the hydration degree of cement.
2020, 37(4): 978-984.
doi: 10.13801/j.cnki.fhclxb.20190717.001
Abstract:
Si is a promising anode material for use in lithium-ion batteries. To solve the problems of rapid capacity decay and short cycle life caused by its huge volume expansion, a simple agitation and thermal reduction method to modify Si nanoparticles with polyethylene glycol-derived thin carbon (C-PEG@Si NPs) was used, and hierarchical graphene@C-PEG@Si NPs composites by bridge of graphene were prepared. A series of characterization test methods including SEM, TEM, X-ray diffraction and constant charge-discharge test were used to investigate the structure, morphology and electrochemical properties of graphene@C-PEG@Si NPs composites. The thin carbon from PEG and graphene wrapping was used to block electrolyte contact and buffer volume changes, respectively. The results show that compared to pure Si, the graphene@C-PEG@Si composites exhibit outstanding electrochemical performance with the reversible specific capacity of 1 032 mAh/g after 100 cycles at a current density of 210 mA/g, and a capacity higher than 430 mAh/g at a current density of 4 200 mA/g after 100 cycles.
Si is a promising anode material for use in lithium-ion batteries. To solve the problems of rapid capacity decay and short cycle life caused by its huge volume expansion, a simple agitation and thermal reduction method to modify Si nanoparticles with polyethylene glycol-derived thin carbon (C-PEG@Si NPs) was used, and hierarchical graphene@C-PEG@Si NPs composites by bridge of graphene were prepared. A series of characterization test methods including SEM, TEM, X-ray diffraction and constant charge-discharge test were used to investigate the structure, morphology and electrochemical properties of graphene@C-PEG@Si NPs composites. The thin carbon from PEG and graphene wrapping was used to block electrolyte contact and buffer volume changes, respectively. The results show that compared to pure Si, the graphene@C-PEG@Si composites exhibit outstanding electrochemical performance with the reversible specific capacity of 1 032 mAh/g after 100 cycles at a current density of 210 mA/g, and a capacity higher than 430 mAh/g at a current density of 4 200 mA/g after 100 cycles.
2020, 37(4): 985-996.
doi: 10.13801/j.cnki.fhclxb.20190731.001
Abstract:
In order to study the compressive properties of high ductility concrete (HDC) exposed to elevated temperature, 49 groups of cubic specimens were designed considering three factors:temperature, cooling and curing mode, and standing time. And their compressive strength was tested. The relationship among compressive strength, maximum temperature, ultrasonic velocity and rebound value of HDC was studied by ultrasonic rebound test of five groups of prism specimens. The results show that the temperature has significant impact on compressive strength, and with the increase of temperature, the compressive strength decreases; the influence of cooling mode cannot be neglected when the temperature is below 200℃ and the standing time has a great impact on the natural cooling specimens when the temperature is 400℃. Ultrasonic rebound test shows that the compressive strength of HDC is well correlated with the ultrasonic velocity and rebound value. Based on the regression analysis of test data, the strength curve of HDC exposed to elevated temperature and the formula for estimating the highest exposure temperature were established. The effect mechanism of elevated temperature on the mechanical properties of HDC was revealed by using XRD, SEM and thermogravimetric-differential thermal analysis (TG-DSC).
In order to study the compressive properties of high ductility concrete (HDC) exposed to elevated temperature, 49 groups of cubic specimens were designed considering three factors:temperature, cooling and curing mode, and standing time. And their compressive strength was tested. The relationship among compressive strength, maximum temperature, ultrasonic velocity and rebound value of HDC was studied by ultrasonic rebound test of five groups of prism specimens. The results show that the temperature has significant impact on compressive strength, and with the increase of temperature, the compressive strength decreases; the influence of cooling mode cannot be neglected when the temperature is below 200℃ and the standing time has a great impact on the natural cooling specimens when the temperature is 400℃. Ultrasonic rebound test shows that the compressive strength of HDC is well correlated with the ultrasonic velocity and rebound value. Based on the regression analysis of test data, the strength curve of HDC exposed to elevated temperature and the formula for estimating the highest exposure temperature were established. The effect mechanism of elevated temperature on the mechanical properties of HDC was revealed by using XRD, SEM and thermogravimetric-differential thermal analysis (TG-DSC).
